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In chemistry , the iodine value ( IV ; also iodine absorption value , iodine number or iodine index ) is the mass of iodine in grams that is consumed by 100 grams of a chemical substance . Iodine numbers are often used to determine the degree of unsaturation in fats , oils and waxes . In fatty acids , unsaturation occurs mainly as double bonds which are very reactive towards halogens , the iodine in this case. Thus, the higher the iodine value, the more unsaturations are present in the fat. [ 1 ] It can be seen from the table that coconut oil is very saturated, which means it is good for making soap . On the other hand, linseed oil is highly unsaturated , which makes it a drying oil , well suited for making oil paints .
The determination of iodine value is a particular example of iodometry . A solution of iodine I 2 is yellow/brown in color. When this is added to a solution to be tested, however, any chemical group (usually in this test −C=C− double bonds) that react with iodine effectively reduce the strength, or magnitude of the color (by taking I 2 out of solution). Thus the amount of iodine required to make a solution retain the characteristic yellow/brown color can effectively be used to determine the amount of iodine sensitive groups present in the solution.
The chemical reaction associated with this method of analysis involves formation of the diiodo alkane (R and R' symbolize alkyl or other organic groups):
The precursor alkene ( RCH=CHR’ ) is colorless and so is the organoiodine product ( RCHI−CHIR’ ).
In a typical procedure, the fatty acid is treated with an excess of the Hanuš or Wijs solution , which are, respectively, solutions of iodine monobromide (IBr) and iodine monochloride (ICl) in glacial acetic acid . Unreacted iodine monobromide (or monochloride) is then allowed to react with potassium iodide , converting it to iodine I 2 , whose concentration can be determined by back-titration with sodium thiosulfate ( Na 2 S 2 O 3 ) standard solution. [ 2 ] [ 3 ]
The basic principle of iodine value was originally introduced in 1884 by A. V. Hübl as “ Jodzahl ”. He used iodine alcoholic solution in presence of mercuric chloride ( HgCl 2 ) and carbon tetrachloride ( CCl 4 ) as fat solubilizer. [Note 1] The residual iodine is titrated against sodium thiosulfate solution with starch used as endpoint indicator. [ 4 ] This method is now considered as obsolete.
J. J. A. Wijs modified the Hübl method by using iodine monochloride (ICl) in glacial acetic acid, which became known as Wijs's solution , dropping the HgCl 2 reagent. [ 4 ] Alternatively, J. Hanuš used iodine monobromide (IBr), which is more stable than ICl when protected from light. Typically, fat is dissolved in chloroform [Note 2] and treated with excess ICl/IBr. Some of the halogen reacts with the double bonds in the unsaturated fat while the rest remains.
Then, saturated solution of potassium iodide (KI) is added to this mixture, which reacts with remaining free ICl/IBr to form potassium chloride (KCl) and diiodide ( I 2 ).
Afterward, the liberated I 2 is titrated against sodium thiosulfate, in presence of starch, to indirectly determine the concentration of the reacted iodine. [ 5 ]
IV (g I/ 100 g) is calculated from the formula :
The determination of IV according to Wijs is the official method currently accepted by international standards such as DIN 53241-1:1995-05, AOCS Method Cd 1-25, EN 14111 and ISO 3961:2018. One of the major limitations of is that halogens does not react stoichiometrically with conjugated double bonds (particularly abundant in some drying oils ). Therefore, Rosenmund-Kuhnhenn method makes more accurate measurement in this situation. [ 6 ]
Proposed by H. P. Kaufmann in 1935, it consists in the bromination of the double bonds using an excess of bromine and anhydrous sodium bromide dissolved in methanol . The reaction involves the formation of a bromonium intermediate as follows: [ 7 ]
Then the unused bromine is reduced to bromide with iodide ( I − ).
Now, the amount of iodine formed is determined by back-titration with sodium thiosulfate solution.
The reactions must be carried out in the dark, since the formation of bromine radicals is stimulated by light. This would lead to undesirable side reactions, and thus falsifying a result consumption of bromine. [ 8 ]
For educational purposes, Simurdiak et al. (2016) [ 3 ] suggested the use of pyridinium tribromide as bromination reagent which is more safer in chemistry class and reduces drastically the reaction time.
This method is suitable for the determination of iodine value in conjugated systems ( ASTM D1541). It has been observed that Wijs/ Hanuš method gives erratic values of IV for some sterols (i.e. cholesterol ) and other unsaturated components of insaponifible fraction. [ 9 ] The original method uses pyridine dibromide sulfate solution as halogenating agent and an incubation time of 5 min. [ 10 ]
Measurement of iodine value with the official method is time-consuming (incubation time of 30 min with Wijs solution) and uses hazardous reagents and solvents. [ 3 ] Several non-wet methods have been proposed for determining the iodine value. For example, IV of pure fatty acids and acylglycerols can be theoretically calculated as follows: [ 11 ]
Accordingly, the IVs of oleic , linoleic , and linolenic acids are respectively 90, 181, and 273. Therefore, the IV of the mixture can be approximated by the following equation : [ 12 ]
For fats and oils, the IV of the mixture can be calculated from the fatty acid composition profile as determined by gas chromatography ( AOAC Cd 1c-85; ISO 3961:2018). However this formula does not take into consideration the olefinic substances in the unsaponifiable fraction . Therefore, this method is not applicable for fish oils as they may contain appreciable amounts of squalene . [ 13 ]
IV can be also predicted from near-infrared , FTIR and Raman spectroscopy data using the ratio between the intensities of ν (C=C) and ν (CH 2 ) bands. [ 14 ] [ 15 ] High resolution proton-NMR provides also fast and reasonably accurate estimation of this parameter. [ 16 ]
Although modern analytical methods (such as GC ) provides more detailed molecular information including unsaturation degree, the iodine value still widely considered as an important quality parameter for oils and fats. Moreover, IV generally indicates oxidative stability of the fats which directly depend on unsaturation amount. Such a parameter has a direct impact on the processing, the shelf-life and the suitable applications for fat-based products. It is also of a crucial interest for lubricants and fuel industries. In biodiesel specifications, the required limit for IV is 120 g I 2 /100 g, according to standard EN 14214 . [ 17 ]
IV is extensively used to monitor the industrial processes of hydrogenation and frying . However it must be completed by additional analyses as it does not differentiate cis / trans isomers.
G. Knothe (2002) [ 12 ] criticized the use of IV as oxidative stability specification for fats esterification products. He noticed that not only the number but the position of double bonds is involved in oxidation susceptibility. For instance, linolenic acid with two bis - allylic positions (at the carbons no. 11 and 14 between the double bonds Δ9, Δ12 and Δ15) is more prone to autoxidation than linoleic acid exhibiting one bis - allylic position (at C-11 between Δ9 and Δ12). Therefore, Knothe introduced alternative indices termed allylic position and bis -allylic position equivalents (APE and BAPE), which can be calculated directly from the integration resultas of chromatographic analysis.
Iodine value helps to classify oils according to the degree of unsaturation into drying oils , having IV > 150 (i.e. linseed , tung ), semi-drying oils IV : 125 – 150 ( soybean , sunflower ) and non-drying oils with IV < 125 ( canola , olive , coconut ). The IV ranges of several common oils and fats is provided by the table below. | https://en.wikipedia.org/wiki/Iodine_value |
The iodine–starch test is a chemical reaction that is used to test for the presence of starch or for iodine . The combination of starch and iodine is intensely blue-black. [ 1 ] [ 2 ] The interaction between starch and the triiodide anion ( I − 3 ) is the basis for iodometry .
The iodine–starch test was first described in 1814 by Jean-Jacques Colin and Henri-François Gaultier de Claubry , [ 3 ] and independently by Friedrich Stromeyer the same year. [ 4 ] [ 5 ]
In 1937, Canadian-American biochemist Charles S. Hanes extensively investigated the action of amylases on starch and the changes in iodine coloration during starch degradation and proposed a spiral chain conformation for the starch molecule, suggesting that fragments with more than one complete coil of the spiral might be necessary for iodine coloration. [ 6 ]
Karl Freudenberg et al., in 1939, building upon Hanes' helical model, proposed that the helical conformation of amylose creates a hydrophobic cavity lined with CH groups, which attracts iodine molecules and leads to a shift in iodine's absorption spectrum, explaining the characteristic blue color of the complex. [ 7 ]
This model was subsequently confirmed by Robert E. Rundle and co-workers ca. 1943, who used X-ray diffraction and optical studies to provide experimental evidence for the linear arrangement of iodine molecules within the amylose helix. [ 8 ]
Research in the mid-20th century began to highlight the importance of iodide anion (as opposed to neutral molecules) in the complex formation, particularly in aqueous solutions. Studies by Mukherjee and Bhattacharyya demonstrated in 1946 that varying potassium iodide concentrations affected the ratio of I- to I2 in the complex. Thoma and French in 1960 further emphasized the necessity of iodide for complex formation in aqueous media. [ 8 ]
By the 1980s, the presence of polyiodide chains within the amylose helix became widely accepted. [ 8 ] However, the precise composition/structure of these chains, including the balance between molecular iodine and various iodide anions, continues to be debated and investigated, with a 2022 article suggesting that they might alternate. [ 9 ]
The triiodide anion instantly produces an intense blue-black colour upon contact with starch. The intensity of the colour decreases with increasing temperature and with the presence of water-miscible organic solvents such as ethanol. The test cannot be performed at very low pH due to the hydrolysis of the starch under these conditions. [ 10 ] It is thought that the iodine–iodide mixture combines with the starch to form an infinite polyiodide homopolymer . This was rationalized through single crystal X-ray crystallography and comparative Raman spectroscopy . [ 11 ]
Starch is often used in chemistry as an indicator for redox titrations where triiodide is present. [ 1 ] Starch forms a very dark blue-black complex with triiodide. However, the complex is not formed if only iodine or only iodide (I − ) is present. The colour of the starch complex is so deep, that it can be detected visually when the concentration of the iodine is as low as 20 μM at 20 °C. [ 12 ] During iodine titrations, concentrated iodine solutions must be reacted with some titrant, often thiosulfate , in order to remove most of the iodine before the starch is added. This is due to the insolubility of the starch–triiodide complex which may prevent some of the iodine reacting with the titrant. Close to the endpoint, the starch is added, and the titration process is resumed taking into account the amount of thiosulfate added before adding the starch.
The color change can be used to detect moisture or perspiration, as in the Minor test or starch–iodine test.
Starch is also useful in detecting the enzyme amylase , which breaks down starch into sugars. Many bacteria like Bacillus subtilis can produce such an enzyme to help scientists identify unknown bacterial samples -- the starch-iodine test is one of many tests needed to identify the exact bacterium. [ 13 ] The positive test for bacteria that has starch hydrolysis capabilities (able to produce amylase) is the presence of a yellow zone around a colony when iodine is added to detect starch. [ 14 ]
Although the starch-iodine test is predominantly employed in the lab, recent assessments have shown potential for clinical use, such as confirming the diagnosis of Horner's syndrome . Hospitals with limited technical accessibility can exploit this diagnostic tool since it requires resources that may be easily attainable. In order to perform the experiment, a patient's skin is first dried with 70% alcohol; with the iodine solution added, subsequently. After the skin dries completely once more, it will be dusted with a starch material. Inducing sweating conditions will cause the skin to turn dark blue. Physicians can then make a diagnosis if the test shows sweating of different intensities on the left and right side of the body. [ 15 ] | https://en.wikipedia.org/wiki/Iodine–starch_test |
Iodobenzene dichloride (PhICl 2 ) is a complex of iodobenzene with chlorine . As a reagent for organic chemistry, it is used as an oxidant and chlorinating agent .
Single-crystal X-ray crystallography has been used to determine its structure; as can be predicted by VSEPR theory , it adopts a T-shaped geometry about the central iodine atom. [ 2 ]
Iodobenzene dichloride is not stable and is not commonly available commercially. It is prepared by passing chlorine gas through a solution of iodobenzene in chloroform , from which it precipitates. [ 3 ] The same reaction has been reported at pilot plant scale (20 kg) as well. [ 4 ]
An alternate preparation involving the use of chlorine generated in situ by the action of sodium hypochlorite on hydrochloric acid has also been described. [ 5 ]
Iodobenzene dichloride is hydrolyzed by basic solutions to give iodosobenzene (PhIO) [ 6 ] and is oxidized by sodium hypochlorite to give iodoxybenzene (PhIO 2 ). [ 7 ]
In organic synthesis , iodobenzene dichloride is used as a reagent for the selective chlorination of alkenes . [ 1 ] and alkynes . [ 8 ] | https://en.wikipedia.org/wiki/Iodobenzene_dichloride |
Iodolactonization (or, more generally, halolactonization ) is an organic reaction that forms a ring (the lactone ) by the addition of an oxygen and iodine across a carbon-carbon double bond. It is an intramolecular variant of the halohydrin synthesis reaction. The reaction was first reported by M. J. Bougalt in 1904 and has since become one of the most effective ways to synthesize lactones. [ 1 ] Strengths of the reaction include the mild conditions and incorporation of the versatile iodine atom into the product.
Iodolactonization has been used in the synthesis of many natural products including those with medicinal applications such as vernolepin and vernomenin, [ 2 ] two compounds used in tumor growth inhibition, and vibralactone , a pancreatic lipase inhibitor. [ 3 ] Iodolactonization has also been used by Elias James Corey to synthesize numerous prostaglandins . [ 4 ]
Bougalt's report of iodolactonization represented the first example of a reliable lactonization that could be used in many different systems. Bromolactonization was actually developed in the twenty years prior to Bougalt’s publication of iodolactonization. [ 1 ] However, bromolactonization is much less commonly used because the simple electrophilic addition of bromine to an alkene , seen below, can compete with the bromolactonization reaction and reduce the yield of the desired lactone. [ 5 ]
Chlorolactonization methods first appeared in the 1950s [ 1 ] but are even less commonly employed than bromolactonization. The use of elemental chlorine is procedurally difficult because it is a gas at room temperature, and the electrophilic addition product can be rapidly produced as in bromolactonization. [ 6 ]
The reaction mechanism involves the formation of a positively charged halonium ion in a molecule that also contains a carboxylic acid (or other functional group that is a precursor to it). The oxygen of the carboxyl acts as a nucleophile , attacking to open the halonium ring and instead form a lactone ring. The reaction is usually performed under mildly basic conditions to increase the nucleophilicity of the carboxyl group.
The iodolactonization reaction includes a number of nuances that affect product formation including regioselectivity , ring size preference, and thermodynamic and kinetic control . In terms of regioselectivity, iodolactonization preferentially occurs at the most hindered carbon atom adjacent to the iodonium cation . This is due to the fact that the more substituted carbon is better able to maintain a partial positive charge and is thus more electrophilic and susceptible to nucleophilic attack. When multiple double bonds in a molecule are equally reactive, conformational preferences dominate. However, when one double bond is more reactive, that reactivity always dominates regardless of conformational preference. [ 7 ]
Both five- and six-membered rings could be formed in the iodolactonization shown below, but the five-membered ring is formed preferentially as predicted by Baldwin's rules for ring closure. [ 8 ] According to the rules, 5-exo-tet ring closures are favored while 6-endo-tet ring closures are disfavored. [ 9 ] The regioselectivity of each iodolactonization can be predicted and explained using Baldwin's rules.
Stereoselective iodolactonizations have been seen in literature and can be very useful in synthesizing large molecules such as the aforementioned vernopelin and vernomenin because the lactone can be formed while maintaining other stereocenters. The ring closure can even be driven by stereocenters adjacent to the carbon-carbon multiple bond as shown below. [ 7 ]
Even in systems without existing stereocenters, Bartlett and coworkers found that stereoselectivity was achievable. They were able to synthesize the cis and trans five membered lactones by adjusting reactions conditions such as temperature and reaction time. The trans product was formed under thermodynamic conditions (e.g. a long reaction time) while the cis product was formed under kinetic conditions (e.g. a relatively shorter reaction time). [ 10 ]
Iodolactonization has been used in the synthesis of many biologically important products such as the tumor growth inhibitors vernolepin and vernomenin, the pancreatic lipase inhibitor vibralactone, and prostaglandins, a lipid found in animals. The following total syntheses all use iodolactonization as a key step in obtaining the desired product.
In 1977, Samuel Danishefsky and coworkers were able to synthesize the tumor growth inhibitors dl -vernolepin and dl -vernomenin via a multistep process in which a lactonization was employed. [ 2 ] This synthesis demonstrates the use of iodolactonization to preferentially form a five-membered ring over a four- or six-membered ring, as expected from Baldwin's rules.
In 2006, Zhou and coworkers synthesized another natural product, vibralactone, in which the key step was the formation of a lactone. [ 3 ] The stereoselectivity of the iodolactonization sets a critical stereochemical configuration for the target compound.
In 1969, Corey and coworkers synthesized prostaglandin E 2 using an iodolactone intermediate. [ 4 ] Again, the stereoselectivity of the iodolactonization plays an integral role in product formation. | https://en.wikipedia.org/wiki/Iodolactonization |
Iodometry , known as iodometric titration , is a method of volumetric chemical analysis , a redox titration where the appearance or disappearance of elementary iodine indicates the end point.
Note that iodometry involves indirect titration of iodine liberated by reaction with the analyte, whereas iodimetry involves direct titration using iodine as the titrant.
Redox titration using sodium thiosulphate , Na 2 S 2 O 3 (usually) as a reducing agent is known as iodometric titration since it is used specifically to titrate iodine. The iodometric titration is a general method to determine the concentration of an oxidising agent in solution. In an iodometric titration, a starch solution is used as an indicator since it can absorb the I 2 that is released, visually indicating a positive iodine-starch test with a deep blue hue. This absorption will cause the solution to change its colour from deep blue to light yellow when titrated with standardized thiosulfate solution. This indicates the end point of the titration. Iodometry is commonly used to analyze the concentration of oxidizing agents in water samples, such as oxygen saturation in ecological studies or active chlorine in swimming pool water analysis.
To a known volume of sample, an excess but known amount of I − is added, which the oxidizing agent then oxidizes to I 2 . I 2 dissolves in the iodide-containing solution to give triiodide ions (I 3 − ), which have a dark brown color. The triiodide ion solution is then titrated against standard thiosulfate solution to give iodide again using starch indicator:
Together with reduction potential of thiosulfate: [ 1 ]
The overall reaction is thus:
For simplicity, the equations will usually be written in terms of aqueous molecular iodine rather than the triiodide ion, as the iodide ion did not participate in the reaction in terms of mole ratio analysis. The disappearance of the deep blue color is, due to the decomposition of the iodine-starch clathrate , marks the end point .
The reducing agent used does not necessarily need to be thiosulfate; stannous chloride , sulfites , sulfides , arsenic (III), and antimony (III) salts are commonly used alternatives [ 2 ] at pH above 8.
At low pH, the following reaction might occur with thiosulfate:
Some reactions involving certain reductants are reversible at certain pH, thus the pH of the sample solution should be carefully adjusted before performing the analysis. For example, the reaction:
is reversible at pH below 4.
The volatility of iodine is also a source of error for the titration, this can be effectively prevented by ensuring an excess iodide is present and cooling the titration mixture. Strong light, nitrite and copper ions catalyse the conversion of iodide to iodine, so these should be removed prior to the addition of iodide to the sample.
For prolonged titrations, it is advised to add dry ice to the titration mixture to displace air from the Erlenmeyer flask so as to prevent the aerial oxidation of iodide to iodine. Standard iodine solution is prepared from potassium iodate and potassium iodide, which are both primary standards :
Iodine in organic solvents, such as diethyl ether and carbon tetrachloride , may be titrated against sodium thiosulfate dissolved in acetone . [ clarification needed ]
Iodometry in its many variations is extremely useful in volumetric analysis . Examples include the determination of copper(II), chlorate , hydrogen peroxide , and dissolved oxygen:
Available chlorine refers to chlorine liberated by the action of dilute acids on hypochlorite . Iodometry is commonly employed to determine the active amount of hypochlorite in bleach responsible for the bleaching action. In this method, excess but known amount of iodide is added to known volume of sample, in which only the active ( electrophilic ) can oxidize iodide to iodine. The iodine content and thus the active chlorine content can be determined with iodometry. [ 3 ]
The determination of arsenic(V) compounds is the reverse of the standardization of iodine solution with sodium arsenite , where a known and excess amount of iodide is added to the sample:
For analysis of antimony (V) compounds, some tartaric acid is added to solubilize the antimony(III) product. [ 2 ]
Sulfites and hydrogensulfites reduce iodine readily in acidic medium to iodide. Thus when a diluted but excess amount of standard iodine solution is added to known volume of sample, the sulfurous acid and sulfites present reduces iodine quantitatively:
(This application is used for iodimetry titration because here iodine is directly used)
Although the sulfide content in sample can be determined straight forwardly as described for sulfites, the results are often poor and inaccurate. A better, alternative method with higher accuracy is available, which involves the addition of excess but known volume of standard sodium arsenite solution to the sample, during which arsenic trisulfide is precipitated:
The excess arsenic trioxide is then determined by titrating against standard iodine solution using starch indicator. Note that for the best results, the sulfide solution must be dilute with the sulfide concentration not greater than 0.01 M. [ 2 ]
When iodide is added to a solution of hexacyanoferrate(III) , the following equilibrium exists:
Under strongly acidic solution, the above equilibrium lies far to the right hand side, but is reversed in almost neutral solution. This makes analysis of hexacyanoferrate(III) troublesome as the iodide and thiosulfate decomposes in strongly acidic medium. To drive the reaction to completion, an excess amount of zinc salt can be added to the reaction mixture containing potassium ions, which precipitates the hexacyanoferrate(II) ion quantitatively:
The precipitation occurs in slightly acidic medium, thus avoids the problem of decomposition of iodide and thiosulfate in strongly acidic medium, and the hexacyanoferrate(III) can be determined by iodometry as usual. [ 2 ] | https://en.wikipedia.org/wiki/Iodometry |
Iodosobenzene or iodosylbenzene is an organoiodine compound with the empirical formula C 6 H 5 IO . This colourless solid compound is used as an oxo transfer reagent in research laboratories examining organic and coordination chemistry .
Iodosobenzene is prepared from iodobenzene . [ 3 ] It is prepared by first oxidizing iodobenzene by peracetic acid . Hydrolysis of resulting diacetate affords "PhIO": [ 4 ]
The structure of iodosobenzene has been verified by crystallographically . [ 5 ] Related derivatives are also oligomeric. [ 6 ] Its low solubility in most solvents and vibrational spectroscopy indicate that it is not molecular, but is polymeric, consisting of –I–O–I–O– chains. [ 7 ] The related diacetate, C 6 H 5 I(O 2 CCH 3 ) 2 , illustrates the ability of iodine(III) to adopt a T-shaped geometry without multiple bonds. [ 8 ] Theoretical studies show that the bonding between the iodine and oxygen atoms in iodosobenzene represents a single dative I-O sigma bond, confirming the absence of the double I=O bond. [ 9 ]
A monomeric derivative iodosylbenzene is known in the form of 2-(tert-butylsulfonyl)iodosylbenzene, a yellow solid. C-I-O angle is 94.78°, C-I and I-O distances are 2.128 and 1.848 Å. [ 10 ]
Iodosobenzene has no commercial uses, but in the laboratory it is employed as an "oxo-transfer reagent." It epoxidizes certain alkenes and converts some metal complexes into the corresponding oxo derivatives. Although it is an oxidant, it is also mildly nucleophilic. These oxo-transfer reactions operate by the intermediacy of adducts PhI=O→M, which release PhI. [ 11 ]
A mixture of iodosobenzene and sodium azide in acetic acid converts alkenes to vicinal diazides :. [ 12 ] [ 13 ]
This compound is explosive and should not be heated under vacuum. | https://en.wikipedia.org/wiki/Iodosobenzene |
Iodous acid is the chemical compound with the formula HIO 2 . Its salts are named iodites ; these are exceedingly unstable and have been observed but never isolated. [ 1 ] They will rapidly disproportionate to molecular iodine and iodates .
Iodous acid is part of a series of oxyacids in which iodine can assume oxidation states of −1, +1, +3, +5, or +7. A number of neutral iodine oxides are also known.
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Iodous_acid |
Ioliomics (from a portmanteau of io ns and li quids) is the study of ions in liquids (or liquid phases ) and stipulated with fundamental differences of ionic interactions . [ 1 ] Ioliomics covers a broad research area concerning structure, properties and applications of ions involved in various biological and chemical systems. The concept of this research discipline is related to other comprehensive research fields, such as genomics , proteomics , glycomics , petroleomics , etc., where the suffix -omics is used for describing the comprehensiveness of data. [ 2 ]
The nature of chemical reactions and their description is one of the most fundamental problems in chemistry . The concepts of covalent and ionic bonds which emerged in the beginning of the 20th century specify the profound differences between their electronic structures . These differences, in turn, lead to dramatically different behavior of covalent and ionic compounds both in the solution and solid phase . [ 3 ] In the solid phase, ionic compounds, e.g. salts , are prone to formation of crystal lattices ; in polar solvents , they dissociate into ions surrounded by solvate shells, thus rendering the solution highly ionic conductive . [ 4 ] In contrast to covalent bonds , ionic interactions demonstrate flexible, dynamic behavior, which allows tuning ionic compounds to obtain desired properties.
Ionic compounds interact strongly with the solvent medium; therefore, their impact on chemical and biochemical processes involving ions can be significant. Even in the case of simplest ions and solvents , the presence of the former can lead to rearrangement and restructuring of the latter. [ 5 ] It is established that ionic reactions are involved in numerous phenomena at the scales of whole galaxies or single living cells . [ 6 ] [ 7 ] To name a few, in living cells , metal ions bind to metalloenzymes and other proteins therefore modulating their activity; [ 6 ] ions are involved in the control of neuronal functioning during sleep – wakefulness cycles ; [ 8 ] anomalous activity of ion channels results in the development of various disorders, such as Parkinson's and Alzheimer's diseases, [ 9 ] etc. Thus, despite the problems associated with the studies on properties and activities of ions in various chemical and biological systems, [ 1 ] this research field is among the most urgent ones.
Of special interest are ion-abundant liquid media (such as ionic liquids , molten salts , liquid electrolytes , etc.), which represent “liquid ions” with excellent tunable properties for different applications. The systems are famous for their ability to solvent-solute self-organization phenomena and are often employed in chemistry , biochemistry and pharmaceutical research. [ 1 ] [ 10 ] One of the most important features of ion-abundant liquid media is their huge potential to be fine-tuned. Thus, one can design an ionic liquid with virtually any combination of physicochemical or biochemical properties. [ 11 ] Research in the area of “liquid ions” is a rapidly developing scientific field, and numerous data on their properties and activities have been accumulated so far. [ 1 ] [ 12 ] Currently, the concept finds applications in catalysis , electrochemistry , analytics, fuel production, biomass processing, biotechnology , biochemistry and pharmaceutics . [ 1 ] [ 11 ] [ 13 ] [ 14 ] | https://en.wikipedia.org/wiki/Ioliomics |
Ion-Beam sculpting is a two-step process to make solid-state nanopores . The term itself was coined by Golovchenko and co-workers at Harvard in the paper "Ion-beam sculpting at nanometer length scales." [ 1 ] In the process, solid-state nanopores are formed by lateral mass transport about the surface of the substrate, not simply by sputtering , which is the removal of material from the surface.
The first step in ion sculpting is to make either a through hole or a blind hole (not penetrating completely), most commonly using a focused ion beam (FIB). The holes are commonly about 100 nm in diameter, but can be made much smaller. This step may or may not be done at room temperature , with a low temperature of -120 C. Next, three common techniques can be used to 'sculpt' the hole: broad area ion exposure, TEM exposure, and FIB exposure. Holes can be closed completely, or left open at a lower limit of 1 - 10 nm .
This technique uses a broad area argon ion source beam. If the hole is blind (a blind hole is a hole that has not broken through on the backside yet) the wafer (often SiN or silicon/ silicon oxide ) is then turned upside down, and exposed with the argon beam. A detector counts the amount of ions passing through the membrane (which should be zero). The process stops when ions begin to be detected. This enables a much smaller hole to be opened than if using an FIB alone. This method of nanopore fabrication relies on the ion beam to remove (sputter) some of the material from the back of the sample, revealing part of the hole underneath.
Alternatively, if the hole has already been milled through the substrate, the argon beam is aimed at the wafer, and by lateral mass transport atoms from elsewhere on the wafer move to the edge of the hole. It is this process of solid-state nanopore fabrication that was originally termed "ion-beam sculpting". Of paramount importance in this method is the ability to utilize a feedback-controlled system to monitor nanopore fabrication in real time. A detector registers the number of ions passing through the hole as a function of time. As the hole closes from about 100 nm to its final dimension (>20 nm) the number of ions able to pass through the hole is reduced. The process is stopped when the final pore size is reached. If the current drops to zero, the hole is closed. This process of nanopore fabrication is used by the laboratories of J. Li and J. Golovchenko. As of 2006 this method was shown to be applicable with all the noble gases , not just argon. [ 2 ]
A through hole in a wafer can be closed down by a transmission electron microscope . Due to hydrocarbon buildup, the electrons stimulate hole closure. This method is very slow, taking over an hour to close a 100 nm hole; this has the advantage that the hole can be watched as it reduces, allowing good control of the hole size, but takes a long time. Citation: T.Schenkel, V.Radmilovic, E.A.Stach, S.-J.Park, A.Persaud, J.Va.Sci.Tech.B 21, 2720 (2003).
This is the easiest of the techniques, but the least useful. After a hole is milled with an FIB , the hole can be imaged as with the TEM technique. The ions stimulate movement on the wafer, and also implant themselves to help close the hole. Unlike for the other two methods, the holes closed in this technique are not smooth or accurately circular; they appear jagged under TEM photos. Also, it is much harder to control the size of the hole to the single nanometer regime. Another drawback is that while imaging the hole the ion beam is continually sputtering membrane material away. If the beam scan area is large enough, the rate of atoms moving to close the hole will be greater than the rate of sputtering, so the hole will close. If the membrane is too thin or the scan area too small, then the rate of sputtering will win, and the hole will open up.
An alternative ion beam sculpting technique has been developed using a commercially available FIB system. [ 3 ] This sculpting method [ 4 ] can fabricate symmetrically circular nanopores with smooth edge, and can also sculpt multiple nanopores of similar shape and size simultaneously. Dependent on the resolution and working condition of the instrument, this method can produce symmetrically shaped nanopores with diameters below 10 nm. | https://en.wikipedia.org/wiki/Ion-beam_sculpting |
An ion-beam shepherd ( IBS ) is a concept in which the orbit and/or attitude of a spacecraft or a generic orbiting body is modified by having a beam of quasi-neutral plasma impinging against its surface to create a force and/or a torque on the target. Ion and plasma thrusters commonly used to propel spacecraft can be employed to produce a collimated plasma/ion beam and point it towards the body.
The fact that the beam can be generated on a "shepherd" spacecraft placed in proximity of the target without physical attachment with the latter provides an interesting solution for space applications such as space debris removal, asteroid deflection and space transportation in general.
The Technical University of Madrid (UPM) is exploring this concept [ 1 ] by developing analytical and numerical control models in collaboration with the Advanced Concepts Team of the European Space Agency. The concept has also been proposed independently by JAXA and CNES .
The force and torque transmitted to the target originate from the momentum carried out by the plasma ions (typically xenon) which are accelerated to a few tens of kilometer per second by an ion or plasma thruster. The ions that reach the target surface lose their energy following nuclear collision in the substrate of the target material.
In order to keep a constant distance between the target and the shepherd spacecraft the latter must carry a secondary propulsion system (e.g. another ion or plasma thruster) compensating for the reaction force created by the targeted ion beam.
The concept has been suggested as a possible solution for active space debris removal, [ 2 ] [ 3 ] [ 4 ] [ 5 ] as well as for accurate deflection of Earth threatening asteroids. [ 6 ] Further in the future the concept could play an important role in areas such as space mobility, transportation, assembly of large orbital infrastructures and small asteroid capturing in Earth orbit.
Beam divergence angles of ion and plasma thrusters, typically greater than 10 degrees make it necessary to have the shepherd flying not more than a few target diameters away if efficient beam overlap is to be reached. Proximity formation flying guidance and control [ 7 ] as well as collision avoidance are among the most critical technological challenges of the concept. | https://en.wikipedia.org/wiki/Ion-beam_shepherd |
An ion-exchange membrane is a semi-permeable membrane that transports certain dissolved ions, while blocking other ions or neutral molecules. [ 1 ]
Ion-exchange membranes are therefore electrically conductive. They are often used in desalination and chemical recovery applications, moving ions from one solution to another with little passage of water. [ 2 ]
Important examples of ion-exchange membranes include the proton-exchange membranes , that transport H + cations , and the anion exchange membranes used in certain alkaline fuel cells to transport OH − anions .
An ion-exchange membrane is generally made of organic or inorganic polymer with charged (ionic) side groups, such as ion-exchange resins . Anion-exchange membranes contain fixed cationic groups with predominantly mobile anions; because anions are the majority species, most of the conductivity is due to anion transport. The reverse holds for cation-exchange membranes .
The so-called heterogeneous ion-exchange membranes have low cost and a thicker composition with higher resistance and a rough surface that can be subject to fouling. Homogeneous membranes are more expensive, but have a thinner composition with lower resistance and a smooth surface, less susceptible to fouling. Homogeneous membrane surfaces can be modified to alter the membrane permselectivity to protons, monovalent ions, and divalent ions. [ 3 ]
The selectivity of an ion-exchange membrane is due to Gibbs-Donnan equilibrium and not due to physically blocking or electrostatically excluding specific charged species.
The selectivity to the transport of ions of opposite charges is called its permselectivity. [ 3 ]
Ion-exchange membranes are traditionally used in electrodialysis or diffusion dialysis by means of an electrical potential or concentration gradient, respectively, to selectively transport cationic and anionic species. When applied in an electrodialysis desalination process, anion- and cation-exchange membranes are typically arranged in an alternating pattern between two electrodes (an anode and a cathode) within the electrodialysis stack. A galvanic potential is supplied as a voltage generated at the electrodes. [ 3 ]
A typical industrial electrodialysis stack consists of two chambers: a product-water chamber and a concentrate-reject chamber. During stack operation, salts are transferred from the product to the concentrate. As a result, the reject stream is concentrated up while the product stream is desalted. [ 3 ]
Exemplary applications of ion-exchange membranes utilized in electrodialysis and EDR include seawater desalination, industrial wastewater treatment of highly scaling waters, food and beverage production, and other industrial wastewaters. [ 3 ] | https://en.wikipedia.org/wiki/Ion-exchange_membrane |
An ion-exchange resin or ion-exchange polymer is a resin or polymer that acts as a medium for ion exchange , that is also known as an ionex . [ 1 ] It is an insoluble matrix (or support structure) normally in the form of small (0.25–1.43 mm radius) microbeads , usually white or yellowish, fabricated from an organic polymer substrate. The beads are typically porous (with a specific size distribution that will affect its properties), providing a large surface area on and inside them where the trapping of ions occurs along with the accompanying release of other ions, and thus the process is called ion exchange. There are multiple types of ion-exchange resin, that differ in composition if the target is an anion or a cation. Most commercial resins are made of polystyrene sulfonate , [ 2 ] followed up by polyacrylate . [ 3 ]
Ion-exchange resins are widely used in different separation , purification, and decontamination processes. The most common examples are water softening and water purification . In many cases, ion-exchange resins were introduced in such processes as a more flexible alternative to the use of natural or artificial zeolites . Also, ion-exchange resins are highly effective in the biodiesel filtration process.
Most typical ion-exchange resins are based on crosslinked polystyrene . The actual ion-exchanging sites are introduced after polymerisation. Additionally, in the case of polystyrene, crosslinking is introduced by copolymerisation of styrene and a few percent of divinylbenzene . Crosslinking decreases ion-exchange capacity of the resin and prolongs the time needed to accomplish the ion-exchange processes but improves the robustness of the resin. Particle size also influences the resin parameters; smaller particles have larger outer surface, but cause larger head loss in the column processes. [ 4 ]
Besides being made as bead-shaped materials, ion-exchange resins are also produced as membranes. These ion-exchange membranes , which are made of highly cross-linked ion-exchange resins that allow passage of ions, but not of water, are used for electrodialysis .
Four main types of ion-exchange resins differ in their functional groups :
Specialised ion-exchange resins are also known such as chelating resins ( iminodiacetic acid , thiourea -based resins, and many others).
Anion resins and cation resins are the two most common resins used in the ion-exchange process. While anion resins attract negatively charged ions, cation resins attract positively charged ions.
Formula: R-OH basic
Anion resins may be either strongly or weakly basic. Strongly basic anion resins maintain their negative charge across a wide pH range, whereas weakly basic anion resins are neutralized at higher pH levels. [ 5 ] Weakly basic resins do not maintain their charge at a high pH because they undergo deprotonation. [ 5 ] They do, however, offer excellent mechanical and chemical stability. This, combined with a high rate of ion exchange, make weakly base anion resins well suited for the organic salts.
For anion resins, regeneration typically involves treatment of the resin with a strongly basic solution, e.g. aqueous sodium hydroxide. During regeneration, the regenerant chemical is passed through the resin, and trapped negative ions are flushed out, renewing the resin exchange capacity.
Formula: R−H acidic
The cation exchange method removes the hardness of water but induces acidity in it, which is further removed in the next stage of treatment of water by passing this acidic water through an anion exchange process . [ 6 ]
Reaction:
Similar to anion resins, in cation resins the regeneration involves the use of a strongly acidic solution, e.g. aqueous hydrochloric acid. During regeneration, the regenerant chemical passes through the resin and flushes out the trapped positive ions, renewing the resin exchange capacity.
Formula: –NR 4 + OH −
Often these are styrene – divinylbenzene copolymer resins that have quaternary ammonium cations as an integral part of the resin matrix. [ 6 ]
Reaction:
Anion-exchange chromatography makes use of this principle to extract and purify materials from mixtures or solutions .
Ion exchange resins are often described according to some of the following features. [ 7 ]
The pore media of the resin particles is one of the most important parameters for the efficiency of the product. These pores make different functions depending on their sizes and are the main feature responsible for the mass transfer between phases making the whole ion exchange process possible. There are three main types of pore sizes: [ 7 ]
In this application, Ion-exchange resins are used to replace the magnesium and calcium ions found in hard water with sodium ions. When the resin is fresh, it contains sodium ions at its active sites. When in contact with a solution containing magnesium and calcium ions (but a low concentration of sodium ions), the magnesium and calcium ions preferentially migrate out of solution to the active sites on the resin, being replaced in solution by sodium ions. This process reaches equilibrium with a much lower concentration of magnesium and calcium ions in solution than was started with.
The resin can be recharged by washing it with a solution containing a high concentration of sodium ions (e.g. it has large amounts of common salt (NaCl) dissolved in it). The calcium and magnesium ions migrate from the resin, being replaced by sodium ions from the solution until a new equilibrium is reached. The salt is used to recharge an ion-exchange resin, which itself is used to soften the water.
In this application, ion-exchange resins are used to remove poisonous (e.g. copper ) and hazardous metal (e.g. lead or cadmium ) ions from solution, replacing them with more innocuous ions, such as sodium and potassium , in the process cation and anion exchange resins are used to remove dissolved ions from the water.
Few ion-exchange resins remove chlorine or organic contaminants from water – this is usually done by using an activated charcoal filter mixed in with the resin. There are some ion-exchange resins that do remove organic ions, such as MIEX (magnetic ion-exchange) resins. Domestic water purification resin is not usually recharged – the resin is discarded when it can no longer be used.
Water of highest purity is required for electronics, scientific experiments, production of superconductors, and nuclear industry, among others. Such water is produced using ion-exchange processes or combinations of membrane and ion-exchange methods.
Ion-exchange processes are used to separate and purify metals , including separating uranium from plutonium and other actinides , including thorium ; and lanthanum , neodymium , ytterbium , samarium , lutetium , from each other and the other lanthanides . There are two series of rare-earth metals , the lanthanides and the actinides. Members of each family have very similar chemical and physical properties. Ion exchange was for many years the only practical way to separate the rare earths in large quantities. This application was developed in the 1940s by Frank Spedding . Subsequently, solvent extraction has mostly supplanted use of ion-exchange resins except for the highest-purity products.
A very important case is the PUREX process (plutonium-uranium extraction process), which is used to separate the plutonium and the uranium from the spent fuel products from a nuclear reactor , and to be able to dispose of the waste products. Then, the plutonium and uranium are available for making nuclear-energy materials, such as new reactor fuel and nuclear weapons .
Ion-exchange beads are also an essential component in in-situ leach uranium mining. In-situ recovery involves the extraction of uranium-bearing water (grading as low as 0.05% U 3 O 8 ) through boreholes. The extracted uranium solution is then filtered through the resin beads. Through an ion-exchange process, the resin beads attract uranium from the solution. Uranium-loaded resins are then transported to a processing plant, where U 3 O 8 is separated from the resin beads, and yellowcake is produced. The resin beads can then be returned to the ion-exchange facility, where they are reused.
The ion-exchange process is also used to separate other sets of very similar chemical elements, such as zirconium and hafnium , which incidentally is also very important for the nuclear industry. Zirconium is practically transparent to free neutrons, used in building reactors, but hafnium is a very strong absorber of neutrons, used in reactor control rods .
Ion exchange resins are used in organic synthesis , e.g. for esterification and hydrolysis . Being high surface area and insoluble, they are suitable for vapor-phase and liquid-phase reactions. Examples can be found where basic (OH − -form) of ion exchange resins are used to neutralize of ammonium salts [ 8 ] and convert quaternary ammonium halides to hydroxides. [ 9 ] Acidic (H + -form) ion exchange resins have been used as solid acid catalysts for scission of ether protecting groups. [ 10 ] and for rearrangement reactions. [ 11 ]
Ion-exchange resins are used in the manufacture of fruit juices such as orange and cranberry juice, where they are used to remove bitter-tasting components and so improve the flavor. This allows tart or poorer-tasting fruit sources to be used for juice production.
Ion-exchange resins are used in the manufacturing of sugar from various sources. They are used to help convert one type of sugar into another type of sugar, and to decolorize and purify sugar syrups.
Ion-exchange resins are used in the manufacturing of pharmaceuticals, not only for catalyzing certain reactions, but also for isolating and purifying pharmaceutical active ingredients .
Three ion-exchange resins, sodium polystyrene sulfonate , colestipol , and cholestyramine , are used as active ingredients . Sodium polystyrene sulfonate is a strongly acidic ion-exchange resin and is used to treat hyperkalemia . Colestipol is a weakly basic ion-exchange resin and is used to treat hypercholesterolemia . Cholestyramine is a strongly basic ion-exchange resin and is also used to treat hypercholesterolemia . Colestipol and cholestyramine are known as bile acid sequestrants .
Ion-exchange resins are also used as excipients in pharmaceutical formulations such as tablets, capsules, gums, and suspensions. In these uses the ion-exchange resin can have several different functions, including taste-masking, extended release, tablet disintegration, increased bioavailability , and improving the chemical stability of the active ingredients .
Selective polymeric chelators have been proposed for maintenance therapy of some pathologies, where chronic ion accumulation occurs, such as Wilson disease (where copper accumulation occurs) [ 12 ] or hereditary hemochromatosis ( iron overload , where iron accumulation occurs) [ 13 ] [ 14 ] [ 15 ] These polymers or particles have a negligible or null systemic biological availability and they are designed to form stable complexes with Fe 2+ and Fe 3+ in the GIT and thus limiting the uptake of these ions and their long-term accumulation. Although this method has only a limited efficacy, unlike small-molecular chelators ( deferasirox , deferiprone , or deferoxamine ), such an approach may have only minor side effects in sub-chronic studies . [ 15 ] Interestingly, the simultaneous chelation of Fe 2+ and Fe 3+ increases the treatment efficacy. [ 15 ]
Anion exchange resins readily absorb CO 2 when dry and release it again when exposed to moisture. [ 16 ] This makes them one of the most promising materials for direct carbon capture from ambient air, [ 17 ] or direct air capture , since the moisture swing replaces the more energy-intensive temperature swing or pressure swing used with other sorbents. A prototype demonstrating this process has been developed by Klaus Lackner at the Center for Negative Carbon Emissions . | https://en.wikipedia.org/wiki/Ion-exchange_resin |
Ion mobility spectrometry–mass spectrometry ( IMS-MS ) is an analytical chemistry method that separates gas phase ions based on their interaction with a collision gas and their masses. In the first step, the ions are separated according to their mobility through a buffer gas on a millisecond timescale using an ion mobility spectrometer . The separated ions are then introduced into a mass analyzer in a second step where their mass-to-charge ratios can be determined on a microsecond timescale. [ 1 ] The effective separation of analytes achieved with this method makes it widely applicable in the analysis of complex samples such as in proteomics and metabolomics.
Earl W. McDaniel has been called the father of ion mobility mass spectrometry. [ 1 ] In the early 1960s, he coupled a low-field ion mobility drift cell to a sector mass spectrometer. [ 2 ]
The combination of time-of-flight mass spectrometry and ion mobility spectrometry was pioneered in 1963 at Bell Labs . In 1963 McAfee and Edelson published an IMS-TOF combination. In 1967 McKnight, McAfee and Sipler published an IMS-TOF combination. Their instrument included an orthogonal TOF. [ 3 ] In 1969 Cohen et al. filed a patent on an IMS-QMS system. The QMS at that time was an improvement compared to the TOFMS, because the TOFMS had a slow electronic data acquisition systems at that time. In 1970, Young, Edelson and Falconer published an IMS-TOF with orthogonal extraction. [ 4 ] They seem to have used the same system as McKnight et al. in 1967, incorporating slight modifications. Their work was later reproduced in the landmark book of Mason/McDaniel, which is regarded as the “bible of IMS” by those skilled in the art.
In 1996 Guevremont et al. presented a poster at the ASMS conference about IMS-TOF. In 1997 Tanner patented a quadrupole with axial fields which can be used as a drift cell for IMS separation. He also mentions the combination of these quadrupoles with an orthogonal TOFMS. In 1998 Clemmer developed an IMS-TOF combination, using a co-axial IMS-TOF setup. [ 5 ] In 1999 Clemmer developed an IMS-TOF with an orthogonal TOF system. [ 6 ] This work led to the development of an ion mobility-quadrupole-CID-TOFMS instrument by Micromass in the UK and ultimately led Micromass / Waters corporation to develop of the world's first commercial ion mobility-mass spectrometer instrument in 2006. The Synapt, as it is called, incorporates a pre ion mobility quadrupole allowing precursor ion selection prior to IMS separation further enhancing the flexibility of the ion mobility-mass spectrometry combinations. In 2013, Agilent Technologies released the first commercial drift tube ion mobility-mass spectrometer named 6560 with an 80 cm drift tube. Ion funnels are used to improve the ion transmission efficiency. The design thus greatly improved the sensitivity of ion mobility and allowed commercialization. [ 7 ]
A variation of IMS-MS is differential ion mobility spectrometry-mass spectrometry (DIMS-MS), in which gas phase ions are separated based on their ion mobility in varying strengths of electric fields. [ 8 ] This analytical method is currently being advanced by Gary Glish and the Glish Group. [ 8 ]
The IMS-MS is a combination of an ion mobility spectrometer [ 9 ] and a mass spectrometer , as discussed by Professor Claire E. Eyers and colleagues in a recent review. [ 7 ]
The first stage of the instrument is an ion source where samples are converted to gas phase ions. Many ionization methods similar to those traditionally used for mass spectrometry have been employed for IM-MS depending on the physical state of the analyte. [ 9 ] Gas phase samples are typically ionized with radioactive ionization, corona discharge ionization and photoionization techniques. Electrospray ionization is a common method for ionizing samples in solution. [ 1 ] Solid-phase analytes are ionized with matrix-assisted laser desorption ionization (MALDI) for large mass molecules or laser desorption ionization (LDI) for molecules with smaller masses.
There are different types of ion mobility spectrometers and there are different types of mass spectrometers. In principle it is possible to combine every type of the former with any type of the latter. However, in the real world, different types of ion mobility are coupled with different types of mass spectrometers to achieve reasonable sensitivity. The main types of ion mobility spectrometers that have been coupled to a mass spectrometer for IM-MS applications are discussed below.
In DTIMS, ions are drifted through a tube whose length could vary from 5 cm to 300 cm using as electric field gradient. Smaller ions travel faster through the drift tube than ions with larger collision cross section. Thus, ions are separated based on their drift time through the tube. [ 10 ] Drift tube ion mobility does not employ RF voltage which may heat ions, and it can preserve the structure of the ions. The rotationally averaged collision cross section (CCS) which is a physical property of ions reflecting the shape of the ions can be measured accurately on drift tube ion mobility. [ 11 ] The resolving power is high (CCS resolution can be higher than 100). Drift tube ion mobility is widely used for structure analysis. It is usually coupled with time-of-flight (TOF) mass spectrometer. [ 7 ]
Also known as field asymmetric-waveform ion mobility spectrometry (FAIMS) or RF-DC ion mobility spectrometry is a technique in which ions are separated by the application of a high-voltage asymmetric waveform at radio frequency (RF) combined with a static ( DC ) waveform applied between two electrodes. [ 12 ] [ 13 ] Depending on the ratio of the high-field and low-field mobility of the ion, it will migrate toward one or the other electrode . Only ions with specific mobility will pass through the device. It is well known that the high RF field distort the conformation of the ions, FAIMS thus is a separation technique without preserving the structure of the ions and the CCSs of the ions cannot be measured. [ 14 ] Because FAIMS is a mass selector (other ions are excluded), the sensitivity in the scan mode is much lower than that of the drift tube ion mobility (all the ions are analyzed). Therefore, FAIMS is usually coupled with triple quadrupole mass spectrometer which is also ion selection type instrument.
In TWIMS, ions are separated according to their mobility through a travelling wave in a gas filled cell. Both radio-frequency (RF) and direct current (DC) voltages are applied to a series of ring electrodes called a stacked ring ion guide (SRIG) to confine the ions and create a travelling wave. [ 7 ] Based on the speed and magnitude of the travelling wave, ions can be separated. Smaller ions have higher mobility through the wave due to fewer collisions with gas molecules and exit the cell faster than ions of lower mobility (larger ions). Similar to DTIMS, CCS values of ions can be calculated with TWIMS using a calibration derived with known standards. [ 15 ] A commercial example of the TWIMS-MS instrumentation is Waters Corp Synapt G2-S instrument.
The traditional IM-MS instrument uses a time‐of‐flight (TOF) mass spectrometer interfaced to an IMS. [ 1 ] The TOF-MS has many advantages including the high speed of data acquisition and good sensitivity. Since mass spectral data is acquired on a microsecond time scale, multiple mass spectra are collected for each IMS spectrum (acquired on millisecond timescale). The quadrupole mass spectrometer has also been coupled to an IMS, although at a slower scan rate. Other mass spectrometers including the ion trap, Fourier transform ion cyclotron resonance (FT-ICR), or magnetic sector mass spectrometers have also been coupled with different IMS for various applications. [ 10 ] Additionally, hybrid mass spectrometers have been interfaced to more than one ion mobility cell for tandem or IMS n –MS m applications. [ 16 ]
The IM-MS technique can be used for analyzing complex mixtures based on differing mobilities in an electric field. The gas phase ion structure can be studied using IM-MS through measurement of the CCS and comparison with CCS of standard samples or CCS calculated from molecular modelling. The signal-to-noise ratio is obviously improved because the noise can be physically separated with signal in IM-MS. In addition, isomers can be separated if their shapes are different. The peak capacity of IM-MS is much larger than MS so more compounds can be found and analyzed. This character is very critical for -omics study which requires analyzing as many compounds as possible in a single run. [ 17 ] It has been used in the detection of chemical warfare agents, detection of explosives, in proteomics for the analysis of proteins, peptides, drug-like molecules and nano particles. [ 18 ] Moreover, IM-MS can be used to monitor isomeric reaction intermediates and probe their kinetics. [ 19 ] Recently, microscale FAIMS has been integrated with electrospray ionization MS and liquid chromatography MS to rapidly separate ions in milliseconds prior to mass analysis. The use of microscale FAIMS in electrospray ionization MS and liquid chromatography MS can significantly improve peak capacity and signal-to-noise for a range of applications including proteomics, and pharmaceutical analysis. [ 20 ]
Recently, gas phase ion activation methods have been used to gain new insights into complex structures. Collision induced unfolding (CIU) is a technique in which an ion's internal energy is increased through collisions with a buffer gas prior to IM-MS analysis. Unfolding of the ion is observed through larger CCSs, and the energy at which unfolding occurs corresponds partially to noncovalent interactions within the ion. [ 21 ] This technique has been used to differentiate polyubiquitin linkages [ 21 ] and intact antibodies. [ 22 ] | https://en.wikipedia.org/wiki/Ion-mobility_spectrometry–mass_spectrometry |
An ion-neutral complex in chemistry is an aggregate of an ion with one or more neutral molecules in which at least one of the partners has a rotational degree of freedom about an axis perpendicular to the intermolecular direction [ 1 ] In chemistry, the dissociation of a molecule into two or more fragments can take place in the gas phase , provided there is sufficient internal energy for the requisite barriers to be overcome.
For many years, it was assumed that the fragments of a gas phase dissociation simply fly apart. In 1958, Allan Maccoll suggested that the decomposition of alkyl halides (RX) might take place via the intermediacy of ion pairs , [R + X − ], in which the charged fragments were no longer covalently bonded but were held together by electrostatic attraction . [ 2 ] Maccoll and coworkers subsequently examined chlorine isotope effects in the thermal decomposition of chloroethane and concluded that the data did not support that interpretation; [ 3 ] however, he had provided the germ of an idea that came to fruition two decades later in the study of decompositions of electrically charged molecules.
In the late 1970s three research groups—in England, [ 4 ] the United States, [ 5 ] and France [ 6 ] —independently provided evidence for the occurrence of ion-neutral complexes (sometimes called ion-dipole complexes or ion-molecule complexes ) in the unimolecular dissociations of positive ions under the conditions associated with mass spectrometry (i.e. as isolated species in a vacuum). The general idea is that a charged species, RY + , can give rise to dissociation fragments via a transient complex, [R + Y], in which the electrically charged partner, R + , can undergo molecular rearrangements at the same time as it rotates relative to the neutral partner, Y. Similarly, the neutral partner, Y, can also rotate relative to the charged partner, as well as having the ability to exchange Hydrogens and internal energy with it.
More recently several research groups have provided evidence that revives Maccoll's original hypothesis, but with the variation that the fragments that sojourn in the presence of one another are both electrically uncharged. [ 7 ] In other words, dissociations of a neutral molecule RX can take place in the gas phase via the intermediacy of radical pairs [R · X · ], where X · can be as small as a hydrogen atom. In the gas phase such intermediates are often called roaming radicals . [ 8 ] | https://en.wikipedia.org/wiki/Ion-neutral_complex |
Ion Barbu ( Romanian pronunciation: [iˈon ˈbarbu] , pen name of Dan Barbilian ; 18 March 1895 –11 August 1961) was a Romanian mathematician and poet. His name is associated with the Mathematics Subject Classification number 51C05, which is a major posthumous recognition reserved only to pioneers of investigations in an area of mathematical inquiry. [ 1 ] As a poet, he is known for his volume Joc secund ("Mirrored Play"), [ 2 ] in which he sought to fulfill his vision of a poetry which adhered to the same virtues that he found in mathematics. [ 3 ]
Born in Câmpulung-Muscel , Argeș County , he was the son of Constantin Barbilian and Smaranda, born Șoiculescu. He attended elementary school in Câmpulung, Dămienești , and Stâlpeni , and for secondary studies he went to the Ion Brătianu High School in Pitești , the Dinicu Golescu High School in Câmpulung, and finally the Gheorghe Lazăr High School and the Mihai Viteazul High School in Bucharest . [ 4 ] During that time, he discovered that he had a talent for mathematics, and started publishing in Gazeta Matematică [ ro ] ; it was also then that he discovered his passion for poetry.
He was a student at the University of Bucharest when World War I caused his studies to be interrupted by military service. After being sent to Botoșani in December 1916, he attended the Reserve Officers' School in Bârlad and was promoted to the rank of corporal in April 1917. Serving under the command of major Barbu Alinescu , he advanced to platoon leader by April 1918, and went into reserve as a sub-lieutenant in 1919. [ 5 ] Barbilian completed his undergraduate degree in 1921. The next year he won a doctoral grant to go to the University of Göttingen , where he studied number theory with Edmund Landau for two years. [ 6 ] : 169 However, he attended few classes, suffered from cocaine and ether addiction, and eventually abandoned his studies at Göttingen. [ 3 ] [ 7 ] [ 8 ] Returning to Bucharest, chronically ill as a result of drug intoxication, he was hospitalized for rehabilitation from August 1924 to January 1925. [ 7 ] In 1925 he began to teach mathematics at Spiru Haret High School [ ro ] , along with his German wife, Gerda, who taught German literature. [ 6 ] : 174 He then studied with Gheorghe Țițeica , completing in 1929 his Ph.D. thesis, Reprezentarea canonică a adunării funcțiilor ipereliptice (Canonical representation of the addition of hyperelliptic functions). [ 9 ] [ 10 ] [ 3 ] The thesis defense committee was presided by David Emmanuel and included Țițeica and Dimitrie Pompeiu . [ 7 ] In the spring of 1929 he bought a house at 8, Carol Davila Street, Bucharest, [ 7 ] where he would live for the rest of his life. [ 2 ] For a while, he taught at the Cantemir Vodă High School . [ 11 ] In the summer of 1937, he served as president of the commission administering the Baccalaureate at the Gheorghe Lazăr High School in Sibiu , after which he issued a scathing report to the Ministry of Education . [ 12 ]
In 1935, Barbilian published his article [ 13 ] describing metrization of a region K , the interior of a simple closed curve J . Let xy denote the Euclidean distance from x to y . Barbilian's function for the distance from a to b in K is
As Barbilian noted, this construction generates various geometries that are generalizations of the Klein projective model ; he highlighted four special cases, including the Poincaré disk model in hyperbolic geometry . [ 6 ] : 175 At the University of Missouri in 1938 Leonard Blumenthal wrote Distance Geometry. A Study of the Development of Abstract Metrics , [ 14 ] where he used the term "Barbilian spaces" for metric spaces based on Barbilian's function to obtain their metric . And in 1954 the American Mathematical Monthly published an article by Paul J. Kelly on Barbilian's method of metrizing a region bounded by a curve. [ 15 ] Barbilian claimed he did not have access to Kelly's publication, but he did read Blumenthal's review of it in Mathematical Reviews and he understood Kelly's construction. This motivated him to write in final form a series of four papers, which appeared after 1958, where the metric geometry of the spaces that today bears his name is investigated thoroughly.
He answered in 1959 with an article [ 16 ] which described "a very general procedure of metrization through which the positive functions of two points, on certain sets, can be refined to a distance." Besides Blumenthal and Kelly, articles on "Barbilian spaces" have appeared in the 1990s from Patricia Souza, while Wladimir G. Boskoff, Marian G. Ciucă and Bogdan Suceavă wrote in the 2000s about "Barbilian's metrization procedure". [ 17 ] Barbilian indicated in his paper Asupra unui principiu de metrizare that he preferred the term " Apollonian metric space", and articles from Alan F. Beardon , Frederick Gehring and Kari Hag , Peter A. Häströ, Zair Ibragimov and others use that term. According to Suceavă, [ 18 ] "Barbilian's metrization procedure is important for at least three reasons: (1) It yields a natural generalization of Poincaré and Beltrami–Klein's hyperbolic geometries; (2) It has been studied in the context of the study of Apollonian metric; (3) Provides a large class of examples of Lagrange generalized metrics irreducible to Riemann, Finsler, or Lagrange metrics."
Barbilian made a contribution to the foundations of geometry with his articles in 1940 and 1941 in Jahresbericht der Deutschen Mathematiker-Vereinigung on projective planes with coordinates from a ring . [ 19 ] [ 20 ] According to Boskoff and Suceavă, this work "inspired research in ring geometries, nowadays associated with his, Hjelmslev's and Klingenberg 's names."
A more critical stance was taken in 1995 by Ferdinand D. Velkamp:
Nevertheless, in 1989 John R. Faulkner wrote an article "Barbilian Planes" [ 22 ] that clarified terminology and advanced the study. In his introduction, he wrote:
The terms affine Barbilian plane and Barbilian domain were introduced by Werner Leissner in 1975, in two papers ("Affine Barbilian planes I and II"). [ 23 ] Referring to these papers, Dirk Keppens says that Leissner introduced this terminology "as a tribute to Barbilian, who was one of the founders of (projective) ring geometry." [ 24 ]
In 1930, Barbilian returned to full-time mathematics and joined the academic staff at the University of Bucharest . [ 6 ] : 175 In 1942, he was named professor, with some help from fellow mathematician Grigore Moisil . [ 25 ]
As a mathematician, Barbilian authored 80 research papers and studies. His last paper, written in collaboration with Nicolae Radu, appeared posthumously, in 1962, [ 26 ] and is the last in the cycle of four works where he investigates the Apollonian metric.
Barbu made his literary debut in 1918 in Alexandru Macedonski 's magazine Literatorul [ ro ] , and then started contributing to Sburătorul , where Eugen Lovinescu saw him as a "new poet". [ 2 ] His first volume of poetry, După melci ("After Snails"), was published in 1921. This was followed by his major work, Joc secund , published in 1930, to critical acclaim. The volume contains some 35 of Barbu’s total published output of around 100 poems. [ 3 ]
His poem Ut algebra poesis (As Algebra, So Poetry), written in to his fellow poet Nina Cassian (with whom he had fallen in love [ 27 ] ), alludes to his regret at having abandoned his studies at Göttingen and an appreciation of two great mathematicians: Emmy Noether , who he had met there, and Carl Friedrich Gauss , who left a lasting legacy at Göttingen. [ 3 ] [ 28 ]
Ut algebra poesis [Ninei Cassian] La anii-mi încă tineri, în târgul Göttingen, Cum Gauss, altădată, sub curba lui alee — Boltirea geometriei astrale să încheie — Încovoiam poemul spre ultimul catren. [..] Și algebrista Emmy, sordida și divina, Al cărei steag și preot abia să fiu, Se mută-m nefireasca — nespus de albă ! — Nina.
As Algebra, So Poetry [For Nina Cassian] In my young days I strolled the lanes of Göttingen - Where Gauss, beneath arched canopies of leaves, Sealed once for all the vaults of higher geometries - And curved a poem towards its last quatrain. [..] And algebraist Emmy, both common and divine, Whose priest and standard-bearer I would dare emerge, Surpasses Nina—transcendental and indescribably fair!
— translation by Sarah Glaz and JoAnne Growney [ 28 ]
According to Loveday Kempthorne and Peter Donelan, Barbu "saw mathematics and poetry as equally capable of holding the answer to understanding and reaching a transcendental ideal." [ 3 ] He is known as "one of the greatest Romanian poets of the twentieth century and perhaps the greatest of all" according to Romanian literary critic Alexandru Ciorănescu [ ro ] . [ 29 ]
Barbu was mostly apolitical, with one exception: around 1940 he became a sympathizer of the fascist movement The Iron Guard (hoping to be promoted to full professor if they came to power), dedicating a poem to one of its leaders, Corneliu Zelea Codreanu . [ 30 ] In 1940, he also wrote a poem praising Hitler . [ 31 ] [ 8 ] Suceavă attributes these moves to be opportunistic devices in a professional advancement plan and ignores Barbu’s own explanation, that he was attempting to deflect attention from the fact that he was hiding in his house his wife’s brother, a German citizen who eluded conscription by staying hidden in Romania. [ 30 ]
After the Communists came to power in the wake of World War II, his friend Alexandru Rosetti sought to convince Barbu to write poems praising the new regime. Barbu reluctantly wrote in early 1948 one poem that can be interpreted as pro-communist, namely "Bălcescu living", but he never relapsed and kept his dignified demeanor until the end. [ 31 ]
Ion Barbu died of liver failure in Bucharest in 1961. He is buried in the city's Bellu Cemetery .
The Dan Barbilian Theoretical High School in Câmpulung , the Ion Barbu Theoretical High School in Pitești , the Ion Barbu Technological High School in Giurgiu , and a secondary school in Galați are all named after him. There are Ion Barbu streets in Alba Iulia , Hărman , Murfatlar , Sânmartin , Șelimbăr , Tâncăbești , Timișoara , Zalău , and 1 Decembrie , and Dan Barbilian streets in Câmpulung and Giurgiu. | https://en.wikipedia.org/wiki/Ion_Barbu |
In chemistry , ion association is a chemical reaction whereby ions of opposite electric charge come together in solution to form a distinct chemical entity. [ 1 ] [ 2 ] Ion associates are classified, according to the number of ions that associate with each other, as ion pairs, ion triplets, etc. Ion pairs are also classified according to the nature of the interaction as contact, solvent-shared or solvent-separated. The most important factor to determine the extent of ion association is the dielectric constant of the solvent . Ion associates have been characterized by means of vibrational spectroscopy , as introduced by Niels Bjerrum , and dielectric-loss spectroscopy . [ 3 ] [ 4 ]
Ion pairs are formed when a cation and anion , which are present in a solution of an ionizable substance, come together to form a discrete chemical species. There are three distinct types of ion pairs , depending on the extent of solvation of the two ions. For example, magnesium sulfate exists as both contact and solvent-shared ion-pairs in seawater . [ 5 ]
In the schematic representation above, the circles represent spheres. The sizes are arbitrary and not necessarily similar as illustrated. The cation is coloured red and the anion is coloured blue. The green area represents solvent molecules in a primary solvation shell ; secondary solvation is ignored. When both ions have a complete primary solvation sphere, the ion pair may be termed fully solvated (separated ion pair, SIP). When there is about one solvent molecule between cation and anion, the ion pair may be termed solvent-shared . Lastly, when the ions are in contact with each other, the ion pair is termed a contact ion pair (CIP). Even in a contact ion pair, however, the ions retain most of their solvation shell. The nature of this solvation shell is generally not known with any certainty. In aqueous solution and in other donor solvents, metal cations are surrounded by between 4 and 9 solvent molecules in the primary solvation shell , [ 6 ]
An alternative name for a solvent-shared ion pair is an outer-sphere complex . This usage is common in coordination chemistry and denotes a complex between a solvated metal cation and an anion. Similarly, a contact ion pair may be termed an inner-sphere complex . The essential difference between the three types is the closeness with which the ions approach each other: fully solvated > solvent-shared > contact. With fully solvated and solvent-shared ion pairs the interaction is primarily electrostatic, but in a contact ion pair some covalent character in the bond between cation and anion is also present.
An ion triplet may be formed from one cation and two anions or from one anion and two cations. [ 7 ] Higher aggregates, such as a tetramer (AB) 4 , may be formed.
Ternary ion associates involve the association of three species. [ 8 ] Another type, named intrusion ion pair , has also been characterized. [ 9 ]
Ions of opposite charge are naturally attracted to each other by the electrostatic force . [ 10 ] [ 11 ] This is described by Coulomb's law:
where F is the force of attraction, q 1 and q 2 are the magnitudes of the electrical charges, ε is the dielectric constant of the medium and r is the distance between the ions. For ions in solution this is an approximation because the ions exert a polarizing effect on the solvent molecules that surround them, which attenuates the electric field somewhat. Nevertheless, some general conclusions can be inferred.
The equilibrium constant K for ion-pair formation, like all equilibrium constants, is related to the standard free-energy change: [ 12 ]
where R is the gas constant and T is the temperature in kelvin s . Free energy is made up of an enthalpy term and an entropy term:
The coulombic energy released when ions associate contributes to the enthalpy term, Δ H ⊖ {\displaystyle \Delta H^{\ominus }} . In the case of contact ion pairs, the covalent interaction energy also contributes to the enthalpy, as does the energy of displacing a solvent molecule from the solvation shell of the cation or anion. The tendency to associate is opposed by the entropy term, which results from the fact that the solution containing unassociated ions is more disordered than a solution containing associates. The entropy term is similar for electrolytes of the same type, with minor differences due to solvation effects. Therefore, it is the magnitude of the enthalpy term that mostly determines the extent of ion association for a given electrolyte type. This explains the general rules given above.
Dielectric constant is the most important factor in determining the occurrence of ion association. A table of some typical values can be found under dielectric constant.
Water has a relatively high dielectric constant value of 78.7 at 298K (25 °C), so in aqueous solutions at ambient temperatures 1:1 electrolytes such as NaCl do not form ion pairs to an appreciable extent except when the solution is very concentrated. [ 13 ] 2:2 electrolytes ( q 1 = 2, q 2 = 2) form ion pairs more readily. Indeed, the solvent-shared ion pair [Mg(H 2 O) 6 ] 2+ SO 4 2− was famously discovered to be present in seawater, in equilibrium with the contact ion pair [Mg(H 2 O) 5 (SO 4 )] [ 14 ] Trivalent ions such as Al 3+ , Fe 3+ and lanthanide ions form weak complexes with monovalent anions.
The dielectric constant of water decreases with increasing temperature to about 55 at 100 °C and about 5 at the critical temperature (217.7 °C). [ 15 ] Thus ion pairing will become more significant in superheated water .
Solvents with a dielectric constant in the range, roughly, 20–40, show extensive ion-pair formation. For example, in acetonitrile both contact and solvent-shared ion pairs of Li(NCS) have been observed. [ 16 ] In methanol the 2:1 electrolyte Mg(NCS) 2 is partially dissociated into a contact ion pair, [Mg(NCS)] + and the thiocyanate ion. [ 17 ]
The dielectric constant of liquid ammonia decreases from 26 at its freezing point (−80 °C) to 17 at 20 °C (under pressure). Many simple 1:1 electrolytes form contact ion pairs at ambient temperatures. The extent of ion pairing decreases as temperature decreases. With lithium salts there is evidence to show that both inner-sphere and outer-sphere complexes exist in liquid-ammonia solutions. [ 18 ]
Of the solvents with dielectric constant of 10 or less, tetrahydrofuran (THF) is particularly relevant in this context, as it solvates cations strongly with the result that simple electrolytes have sufficient solubility to make the study of ion association possible. In this solvent ion association is the rule rather than the exception. Indeed, higher associates such as tetramers are often formed. [ 19 ] Triple cations and triple anions have also been characterized in THF solutions. [ 20 ]
Ion association is an important factor in phase-transfer catalysis , since a species such as R 4 P + Cl − is formally neutral and so can dissolve easily in a non-polar solvent of low dielectric constant. In this case it also helps that the surface of the cation is hydrophobic .
In S N 1 reactions the carbocation intermediate may form an ion pair with an anion, particularly in solvents of low dielectric constant, such as diethylether . [ 21 ] This can affect both the kinetic parameters of the reaction and the stereochemistry of the reaction products.
Vibrational spectroscopy provides the most widely used means for characterizing ion associates. Both infrared spectroscopy and Raman spectroscopy have been used. Anions containing a CN group, such as cyanide , cyanate and thiocyanide have a vibration frequency a little above 2000 cm −1 , which can be easily observed, as the spectra of most solvents (other than nitriles ) are weak in this region. The anion vibration frequency is "shifted" on formation of ion pairs and other associates, and the extent of the shift gives information about the nature of the species. Other monovalent anions that have been studied include nitrate , nitrite and azide . Ion pairs of monatomic anions, such as halide ions, cannot be studied by this technique. Standard NMR spectroscopy is not very useful, as association/dissociation reactions tend to be fast on the NMR time scale, giving time-averaged signals of the cation and/or anion. However, diffusion ordered spectroscopy (DOSY), with which the sample tube is not spinning, can be used as ion pairs diffuse more slowly than do single ions due to their greater size. [ 22 ]
Nearly the same shift of vibration frequency is observed for solvent-shared ion pairs of LiCN, Be(CN) 2 and Al(CN) 3 in liquid ammonia. The extent of this type of ion pairing decreases as the size of the cation increases. Thus, solvent-shared ion pairs are characterized by a rather small shift of vibration frequency with respect to the "free" solvated anion, and the value of the shift is not strongly dependent on the nature of the cation. The shift for contact ion pairs is, by contrast, strongly dependent on the nature of the cation and decreases linearly with the ratio of the cations charge to the squared radius: [ 18 ]
The extent of contact ion pairing can be estimated from the relative intensities of the bands due to the ion pair and free ion. It is greater with the larger cations. [ 18 ] This is counter to the trend expected if coulombic energy were the determining factor. Instead, the formation of a contact ion pair is seen to depend more on the energy needed to displace a solvent molecule from the primary solvation sphere of the cation. This energy decreases with the size of the cation, making ion pairing occur to a greater extent with the larger cations. The trend may be different in other solvents. [ 18 ]
Higher ion aggregates, sometimes triples M + X − M + , sometimes dimers of ion pairs (M + X − ) 2 , or even larger species can be identified in the Raman spectra of some liquid-ammonia solutions of Na + salts by the presence of bands that cannot be attributed to either contact- or solvent-shared ion pairs. [ 18 ]
Evidence for the existence of fully solvated ion pairs in solution is mostly indirect, as the spectroscopic properties of such ion pairs are indistinguishable from those of the individual ions. Much of the evidence is based on the interpretation of conductivity measurements. [ 23 ] [ 24 ] | https://en.wikipedia.org/wiki/Ion_association |
An ion beam is a beam of ions , a type of charged particle beam . Ion beams have many uses in electronics manufacturing (principally ion implantation ) and other industries. There are many ion beam sources , some derived from the mercury vapor thrusters developed by NASA in the 1960s. The most widely used ion beams are of singly-charged ions.
Ion current density is typically measured in mA/cm 2 , and ion energy in electronvolts (eV). The use of eV is convenient for converting between voltage and energy, especially when dealing with singly charged ion beams. [ 1 ]
Most commercial applications use two popular types of ion source, gridded and gridless, which differ in current and power characteristics and the ability to control ion trajectories. [ 1 ] In both cases electrons are needed to generate an ion beam. The most common types of electron emitter are hot filament and hollow cathode .
In a gridded ion source, DC or RF discharge are used to generate ions, which are then accelerated and decimated using grids and apertures. Here, the DC discharge current or the RF discharge power are used to control the beam current.
The ion current density j {\displaystyle j} that can be accelerated using a gridded ion source is limited by the space charge effect, which is described by Child's law : j ≈ 4 ϵ 0 9 2 e m ( Δ V ) 3 2 d 2 , {\displaystyle j\approx {\frac {4\epsilon _{0}}{9}}{\sqrt {\frac {2e}{m}}}{\frac {(\Delta V)^{\frac {3}{2}}}{d^{2}}},} where Δ V {\displaystyle \Delta V} is the voltage between the grids, d {\displaystyle d} is the distance between the grids, and m {\displaystyle m} is the ion mass.
The grids are spaced as closely as possible to increase the current density, typically d ∼ 1 m m {\displaystyle d\sim 1\ \mathrm {mm} } . The ions used have a significant impact on the maximum ion beam current, since j ∝ m − 1 / 2 {\displaystyle j\propto m^{-{1}/{2}}} . All else being equal, the maximum ion beam current with krypton is only 69% of the maximum ion current of an argon beam; with xenon the ratio drops to 55%. [ 1 ]
In a gridless ion source, ions are generated by a flow of electrons, without grids. The most common gridless ion source is the end-Hall ion source , with which the discharge current and the gas flow are used to control the beam current.
Ion beams can be used for material modification (e.g. by sputtering or ion beam etching) and for ion beam analysis .
Ion beam application, etching, or sputtering, is a technique conceptually similar to sandblasting , but using individual atoms in an ion beam to ablate a target. Reactive ion etching is an important extension that uses chemical reactivity to enhance the physical sputtering effect.
In a typical use in semiconductor manufacturing , a mask can selectively expose a layer of photoresist on a substrate made of a semiconductor material, such as a silicon dioxide or gallium arsenide wafer . The wafer is developed, and for a positive photoresist, the exposed portions are removed in a chemical process. The result is a pattern left on the surface areas of the wafer that had been masked from exposure. The wafer is then placed in a vacuum chamber , and exposed to the ion beam. The impact of the ions erodes the target, abrading away the areas not covered by the photoresist.
Focused ion beam (FIB) instruments have numerous applications for characterization of thin-film devices. Using a focused, high-brightness ion beam in a scanned raster pattern, material is removed (sputtered) in precise rectilinear patterns revealing a two-dimensional, or stratigraphic profile of a solid material. The most common application is to verify the integrity of the gate oxide layer in a CMOS transistor. A single excavation site exposes a cross section for analysis using a scanning electron microscope. Dual excavations on either side of a thin lamella bridge are utilized for preparing transmission electron microscope samples. [ 2 ]
Another common use of FIB instruments is for design verification and/or failure analysis of semiconductor devices. Design verification combines selective material removal with gas-assisted material deposition of conductive, dielectric, or insulating materials. Engineering prototype devices may be modified using the ion beam in combination with gas-assisted material deposition in order to rewire an integrated circuit's conductive pathways. The techniques are effectively used to verify the correlation between the CAD design and the actual functional prototype circuit, thereby avoiding the creation of a new mask for the purpose of testing design changes.
Ions beams are also used for analysis purposes in Materials science. For example sputtering techniques can be used for surface analysis or depth profiling by performing secondary ion mass spectrometry . It is also possible to gain information from the spectroscopy of transmitted or backscattered primary ions, e.g. depth profiles can be obtained from Rutherford backscattering (RBS) spectra. [ 2 ] In difference to secondary ion spectroscopy scattering based techniques like RBS are often less destructive to the sample.
In radiobiology a broad or focused ion beam is used to study mechanisms of inter- and intra- cellular communication, signal transduction and DNA damage and repair .
Ion beams are also used in particle therapy , most often in the treatment of cancer.
Ion beams produced by ion and plasma thrusters on board a spacecraft can be used to transmit a force to a nearby object (e.g. another spacecraft, an asteroid, etc.) that is irradiated by the beam. This innovative propulsion technique named Ion Beam Shepherd has been shown to be effective in the area of active space debris removal as well as asteroid deflection.
High-energy ion beams produced by particle accelerators are used in atomic physics , nuclear physics and particle physics .
Ion beams can theoretically be used to make a weapon, but this has not been demonstrated. Electron beam weapons were tested by the U.S. Navy in the early 20th century [ citation needed ] , but the hose instability effect prevents them from being accurate at a distance of over approximately 30 inches. | https://en.wikipedia.org/wiki/Ion_beam |
Ion beam analysis (IBA) is an important family of modern analytical techniques involving the use of MeV ion beams to probe the composition and obtain elemental depth profiles in the near-surface layer of solids. IBA is not restricted to MeV energy ranges. It can be operated at low energy (<Kev) using techniques such as FIB , and Secondary ion mass spectroscopy , as well as at higher energies (>GeV) using instruments like the LHC . All IBA methods are highly sensitive and allow the detection of elements in the sub-monolayer range. The depth resolution is typically in the range of a few
nanometers to a few ten nanometers. Atomic depth resolution can be achieved, but requires special equipment. The analyzed depth ranges from a few ten nanometers to a few ten micrometers. IBA methods are always quantitative with an accuracy of a few percent.
Channeling allows to determine the depth profile of damage in single crystals.
The quantitative evaluation of IBA methods requires the use of specialized simulation and data analysis software. SIMNRA and DataFurnace are popular programs for the analysis of RBS, ERD and NRA, while GUPIX is popular for PIXE. A review of IBA software [ 2 ] was followed by an intercomparison of several codes dedicated to RBS, ERD and NRA, organized by the International Atomic Energy Agency . [ 3 ]
IBA is an area of active research. The last major Nuclear Microbeam conference in Debrecen (Hungary) was published in NIMB 267(12–13).
Ion beam analysis works on the basis that ion-atom interactions are produced by the introduction of ions to the sample being tested. Major interactions result in the emission of products that enable information regarding the number, type, distribution and structural arrangement of atoms to be collected. To use these interactions to determine sample composition a technique must be selected along with irradiation conditions and the detection system that will best isolate the radiation of interest providing the desired sensitivity and detection limits. The basic layout of an ion beam apparatus is an accelerator which produces an ion beam that is feed through an evacuated beam-transport tube to a beam handling device. This device isolates the ion species and charge of interest which then are transported through an evacuated beam-transport tube into the target chamber. This chamber is where the refined ion beam will come into contact with the sample and thus the resulting interactions can be observed. The configuration of the ion beam apparatus can be changed and made more complex with the incorporation of additional components. The techniques for ion beam analysis are designed for specific purposes. Some techniques and ion sources are shown in table 1. Detector types and arrangements for ion beam techniques are shown in table 2.
(off-axis extraction)
Energy measurement requires
Electrostatic/magnetic analyser
Low mass resolution with ESA, QMA
High mass resolution with Sector Field Analyser
IG
Small and simple arrangement
NaI
High Resolution, Low efficiency
Poor Resolution, high efficiency
Li glass
Scintillator
Detection only
Broad resolution by unfolding
Ion beam analysis has found use in a number of variable applications, ranging from biomedical uses to studying ancient artifacts. The popularity of this technique stems from the sensitive data that can be collected without significant distortion to the system on which it is studying. The unparalleled success found in using ion beam analysis has been virtually unchallenged over the past thirty years until very recently with new developing technologies. Even then, the use of ion beam analysis has not faded, and more applications are being found that take advantage of its superior detection capabilities. In an era where older technologies can become obsolete at an instant, ion beam analysis has remained a mainstay and only appears to be growing as researchers are finding greater use for the technique.
Gold nanoparticles have been recently used as a basis for a count of atomic species, especially with studying the content of cancer cells. [ 5 ] Ion beam analysis is a great way to count the amount of atomic species per cell. Scientists have found an effective way to make accurate quantitative data available by using ion beam analysis in conjunction with elastic backscattering spectrometry (EBS). [ 5 ] The researchers of a gold nanoparticle study were able to find much greater success using ion beam analysis in comparison to other analytical techniques, such as PIXE or XRF. [ 5 ] This success is due to the fact that the EBS signal can directly measure depth information using ion beam analysis, whereas this cannot be done with the other two methods. The unique properties of ion beam analysis make great use in a new line of cancer therapy.
Ion beam analysis also has a very unique application in the use of studying archaeological artifacts, also known as archaeometry. [ 6 ] For the past three decades, this has been the much preferred method to study artifacts while preserving their content. What many have found useful in using this technique is its offering of excellent analytical performance and non-invasive character. More specifically, this technique offers unparalleled performance in terms of sensitivity and accuracy. Recently however, there have been competing sources for archaeometry purposes using X-ray based methods such as XRF. Nonetheless, the most preferred and accurate source is ion beam analysis, which is still unmatched in its analysis of light elements and chemical 3D imaging applications (i.e. artwork and archaeological artifacts). [ 6 ] [ 7 ]
A third application of ion beam analysis is in forensic studies, particularly with gunshot residue characterization. Current characterization is done based on heavy metals found in bullets, however, manufacturing changes are slowly making these analyses obsolete. The introduction of techniques such as ion beam analysis are believed to alleviate this issue. Researchers are currently studying the use of ion beam analysis in conjunction with a scanning electron microscope and an Energy Dispersive X-ray spectrometer (SEM-EDS). [ 8 ] The hope is that this setup will detect the composition of new and old chemicals that older analyses could not efficiently detect in the past. [ 8 ] The greater amount of analytical signal used and more sensitive lighting found in ion beam analysis gives great promise to the field of forensic science.
The spatially resolved detection of light elements, for example lithium, remains challenging for most techniques based on the electronic shell of the target atoms such as XRF or SEM-EDS. For lithium and lithium-ion batteries, the quantification of the lithium stoichiometry and its spatial distribution are important to understand the mechanisms behind dis-/charging and aging. Through ion beam focussing and a combination of methods, ion beam analysis offers the unique possibility for measuring the local state of charge (SoC) on the μm-scale. [ 9 ]
Ion beam-based analytical techniques represent a powerful set of tools for non-destructive, standard-less, depth-resolved and highly accurate elemental composition analysis in the depth regime from several nm up to few μm. [ 10 ] By changing type of incident ion, the geometry of experiment, particle energy, or by acquiring different products originating from ion-solid interaction, complementary information can be extracted. However, analysis is often challenged either in terms of mass resolution—when several comparably heavy elements are present in the sample—or in terms of sensitivity—when light species are present in heavy matrices. Hence, a combination of two or more ion beam-based techniques can overcome the limitations of each individual method and provide complementary information about the sample. [ 4 ] [ 5 ]
An iterative and self-consistent analysis also enhances the accuracy of the information that can be obtained from each independent measurement. [ 11 ] [ 12 ] [ 13 ]
Dating back to the 1960s the data collected via ion beam analysis has been analyzed through a multitude of computer simulation programs. Researchers who frequently use ion beam analysis in conjunction with their work require that this software be accurate and appropriate for describing the analytical process they are observing. [ 14 ] Applications of these software programs range from data analysis to theoretical simulations and modeling based on assumptions about the atomic data, mathematics and physics properties that detail the process in question. As the purpose and implementation of ion beam analysis has changed over the years, so has the software and codes used to model it. Such changes are detailed through the five classes by which the updated software are categorized. [ 15 ] [ 16 ]
Includes all programs developed in the late 1960s and early 1970s. This class of software solved specific problems in the data; niy did not provide the full potential to analyze a spectrum of a full general case. The prominent pioneering program was IBA, developed by Ziegler and Baglin in 1971. At the time, the computational models only tackled the analysis associated with the back-scattering techniques of ion beam analysis and performed calculation based on a slab analysis. A variety of other programs arose during this time, such as RBSFIT, though due to the lack of in-depth knowledge on ion beam analysis, it became increasingly hard to develop programs that accurate.
A new wave of programs sought to solve this accuracy problem in this next class of software. Developed during the 1980s, programs like SQEAKIE and BEAM EXPERT, afforded an opportunity to solve the complete general case by employing codes to perform direct analysis. This direct approach unfolds the produced spectrum with no assumptions made about the sample. Instead it calculates through separated spectrum signals and solves a set of linear equations for each layer. Problems still arise, though, and adjustments made to reduce noise in the measurements and room for uncertainty.
In a trip back to square one, this third class of programs, created in the 1990s, take a few principles from Class A in accounting for the general case, however, now through the use of indirect methods. RUMP and SENRAS, for example, use an assumed model of the sample and simulate a comparative theoretical spectra, which afforded such properties as fine structure retention and uncertainty calculations. In addition to the improvement in software analysis tools came the ability to analyze other techniques aside from back-scattering; i.e. ERDA and NRA.
Exiting the Class C era and into the early 2000s, software and simulation programs for ion beam analysis were tackling a variety of data collecting techniques and data analysis problems. Following along with the world's technological advancements, adjustments were made to enhance the programs into a state more generalized codes, spectrum evaluation, and structural determination. Programs produced like SIMNRA now account for the more complex interactions with the beam and sample; also providing a known database of scattering data.
This most recently developed class, having similar characteristics to the previous, makes use of primary principles in the Monte Carlo computational techniques. [ 17 ] This class applies molecular dynamic calculations that are able to analyze both low and high energy physical interactions taking place in the ion beam analysis. A key and popular feature that accompanies such techniques is the possibility for the computations to be incorporated in real time with the ion beam analysis experiment itself. | https://en.wikipedia.org/wiki/Ion_beam_analysis |
Ion beam mixing is the atomic intermixing and alloying that can occur at the interface separating two different materials during ion irradiation. [ 1 ] It is applied as a process for adhering two multilayers, especially a substrate and deposited surface layer. The process involves bombarding layered samples with doses of ion radiation in order to promote mixing at the interface, and generally serves as a means of preparing electrical junctions, especially between non-equilibrium or metastable alloys and intermetallic compounds. Ion implantation equipment can be used to achieve ion beam mixing.
The unique effects that stem from ion beam mixing are primarily a result of ballistic effects; that is, impinging ions have high kinetic energies that are transferred to target atoms on collision. Ion energies can be seen on the order of 1 k eV to 200 keV. When accelerated, such ion energies are sufficiently high to break intra- and especially inter-molecular bonds, and initiate relocations within an atomic lattice .
The sequence of collisions is known as a collision cascade .
During this ballistic process, energies of impinging ions displace atoms and electrons of the target material several lattice sites away, resulting in relocations there and interface mixing at the boundary layer. (Note that energies must be sufficiently high in order for the lattice rearrangements to be permanent rather than manifesting as mere vibrational responses to the impinging radiation, i.e. the kinetic energies must be above the threshold displacement energy of the material.) If energies are kept sufficiently high in these nuclear collisions, then, compared to traditional high-dose implantation processes, ballistic ion implantation produces higher intrafilm alloy concentrations at lower doses of irradiation compared to conventional implantation processes.
The degree of mixing of a film scales with the ion mass, with the intensity of any given incident ion beam, and with the duration of the impingement of the ion beam on a target. The amount of mixing is proportional to the square roots of time, mass and ion dose. [ 2 ]
At temperatures below 100 °C for most implanted materials, ion beam mixing is essentially independent of temperature but, as temperature increases beyond that point, mixing rises exponentially with temperature. This temperature-dependence is a manifestation of incident ion beams effectively imparting the target species-dependent activation energy to the barrier layer. [ 3 ]
Ballistic ion beam mixing can be classified into two basic subtypes, recoil mixing and cascade mixing, which take place simultaneously as a result of ion bombardment. In recoil mixing, atoms are relocated by single collision events. Recoil mixing is predominately seen at large angles as a result of soft collisions, with the number of atoms undergoing recoil implantation varying linearly with ion dose. Recoil implantation, however, is not the dominant process in ion beam mixing. Most relocated atoms are part of a collision cascade in which recoiled atoms initiate a series of lower energy lattice displacements, which is referred to as cascade mixing. [ 3 ] Ion beam mixing can be further enhanced by heat spike effects [ 4 ]
Ion mixing (IM) is essentially similar in result to interdiffusion, hence most models of ion mixing involve an effective diffusion coefficient that is used to characterize thickness of the reacted layer as a function of ion beam implantation over a period of time. [ 3 ]
The diffusion model does not take into account the miscibility of substrate and layer, so for immiscible or low-miscibility systems it will overestimate the degree of mixing, while for highly miscible systems the model will underestimate the degree of mixing. Thermodynamic effects are also not considered in this basic interdiffusion equation, but can be modeled by equations that consider the enthalpies of mixing and the molar fractions of the target species, and one can thereby develop a thermodynamic effective diffusion coefficient reflecting temperature effects (which become pronounced at high temperatures).
Advantages of ion beam mixing as a means of synthesis over traditional modes of implantation include the process' ability to produce materials with high solute concentrations using lower amounts of irradiation, and better control of band gap variation and diffusion between layers. [ 3 ] [ 5 ] The cost of IM is also less prohibitive than that of other modes of film preparation on substrates, such as chemical vapor deposition (CVD) and molecular beam epitaxy (MBE).
Disadvantages include the inability to completely direct and control lattice displacements initiated in the process, which can result in an undesirable degree of disorder in ion mixed samples, rendering them unsuitable for applications in which precise lattice orderings are paramount. Ion beams cannot be perfectly directed, nor the collision cascade controlled, once IM effects propagate, which can result in leaking, electron diffraction , radiation enhanced diffusion (RED), chemical migration and mismatch. [ 6 ] Additionally, all ion mixed samples must be annealed. | https://en.wikipedia.org/wiki/Ion_beam_mixing |
Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential , [ 1 ] shaping action potentials and other electrical signals by gating the flow of ions across the cell membrane , controlling the flow of ions across secretory and epithelial cells , and regulating cell volume. Ion channels are present in the membranes of all cells. [ 2 ] [ 3 ] Ion channels are one of the two classes of ionophoric proteins, the other being ion transporters . [ 4 ]
The study of ion channels often involves biophysics , electrophysiology , and pharmacology , while using techniques including voltage clamp , patch clamp , immunohistochemistry , X-ray crystallography , fluoroscopy , and RT-PCR . Their classification as molecules is referred to as channelomics .
There are two distinctive features of ion channels that differentiate them from other types of ion transporter proteins: [ 4 ]
Ion channels are located within the membrane of all excitable cells, [ 3 ] and of many intracellular organelles . They are often described as narrow, water-filled tunnels that allow only ions of a certain size and/or charge to pass through. This characteristic is called selective permeability . The archetypal channel pore is just one or two atoms wide at its narrowest point and is selective for specific species of ion, such as sodium or potassium . However, some channels may be permeable to the passage of more than one type of ion, typically sharing a common charge: positive ( cations ) or negative ( anions ). Ions often move through the segments of the channel pore in a single file nearly as quickly as the ions move through the free solution. In many ion channels, passage through the pore is governed by a "gate", which may be opened or closed in response to chemical or electrical signals, temperature, or mechanical force. [ citation needed ]
Ion channels are integral membrane proteins , typically formed as assemblies of several individual proteins. Such "multi- subunit " assemblies usually involve a circular arrangement of identical or homologous proteins closely packed around a water-filled pore through the plane of the membrane or lipid bilayer . [ 6 ] [ 7 ] For most voltage-gated ion channels , the pore-forming subunit(s) are called the α subunit, while the auxiliary subunits are denoted β, γ, and so on.
Because channels underlie the nerve impulse and because "transmitter-activated" channels mediate conduction across the synapses , channels are especially prominent components of the nervous system . Indeed, numerous toxins that organisms have evolved for shutting down the nervous systems of predators and prey (e.g., the venoms produced by spiders, scorpions, snakes, fish, bees, sea snails, and others) work by modulating ion channel conductance and/or kinetics. In addition, ion channels are key components in a wide variety of biological processes that involve rapid changes in cells, such as cardiac , skeletal , and smooth muscle contraction , epithelial transport of nutrients and ions, T-cell activation, and pancreatic beta-cell insulin release. In the search for new drugs, ion channels are a frequent target. [ 8 ] [ 9 ] [ 10 ]
There are over 300 types of ion channels just in the cells of the inner ear. [ 11 ] Ion channels may be classified by the nature of their gating , the species of ions passing through those gates, the number of gates (pores), and localization of proteins. [ 12 ]
Further heterogeneity of ion channels arises when channels with different constitutive subunits give rise to a specific kind of current. [ 13 ] Absence or mutation of one or more of the contributing types of channel subunits can result in loss of function and, potentially, underlie neurologic diseases. [ 14 ]
Ion channels may be classified by gating, i.e. what opens and closes the channels. For example, voltage-gated ion channels open or close depending on the voltage gradient across the plasma membrane, while ligand-gated ion channels open or close depending on binding of ligands to the channel. [ 15 ]
Voltage-gated ion channels open and close in response to membrane potential .
Also known as ionotropic receptors , this group of channels open in response to specific ligand molecules binding to the extracellular domain of the receptor protein. [ 16 ] Ligand binding causes a conformational change in the structure of the channel protein that ultimately leads to the opening of the channel gate and subsequent ion flux across the plasma membrane. Examples of such channels include the cation-permeable nicotinic acetylcholine receptors , ionotropic glutamate-gated receptors , acid-sensing ion channels (ASICs), [ 17 ] ATP-gated P2X receptors , and the anion-permeable γ-aminobutyric acid-gated GABA A receptor .
Ion channels activated by second messengers may also be categorized in this group, although ligands and second messengers are otherwise distinguished from each other. [ citation needed ]
This group of channels opens in response to specific lipid molecules binding to the channel's transmembrane domain typically near the inner leaflet of the plasma membrane. [ 18 ] Phosphatidylinositol 4,5-bisphosphate ( PIP 2 ) and phosphatidic acid ( PA ) are the best-characterized lipids to gate these channels. [ 19 ] [ 20 ] [ 21 ] Many of the leak potassium channels are gated by lipids including the inward-rectifier potassium channels and two pore domain potassium channels TREK-1 and TRAAK. KCNQ potassium channel family are gated by PIP 2 . [ 22 ] The voltage activated potassium channel (Kv) is regulated by PA. Its midpoint of activation shifts +50 mV upon PA hydrolysis, near resting membrane potentials. [ 23 ] This suggests Kv could be opened by lipid hydrolysis independent of voltage and may qualify this channel as dual lipid and voltage gated channel.
Gating also includes activation and inactivation by second messengers from the inside of the cell membrane – rather than from outside the cell, as in the case for ligands.
Ion channels are also classified according to their subcellular localization. The plasma membrane accounts for around 2% of the total membrane in the cell, whereas intracellular organelles contain 98% of the cell's membrane. The major intracellular compartments are endoplasmic reticulum , Golgi apparatus , and mitochondria . On the basis of localization, ion channels are classified as:
Some ion channels are classified by the duration of their response to stimuli:
Channels differ with respect to the ion they let pass (for example, Na + , K + , Cl − ), the ways in which they may be regulated, the number of subunits of which they are composed and other aspects of structure. [ 33 ] Channels belonging to the largest class, which includes the voltage-gated channels that underlie the nerve impulse, consist of four or sometimes five [ 34 ] subunits with six transmembrane helices each. On activation, these helices move about and open the pore. Two of these six helices are separated by a loop that lines the pore and is the primary determinant of ion selectivity and conductance in this channel class and some others. [ citation needed ]
The existence and mechanism for ion selectivity was first postulated in the late 1960s by Bertil Hille and Clay Armstrong . [ 35 ] [ 36 ] [ 37 ] [ 38 ] [ 39 ] The idea of the ionic selectivity for potassium channels was that the carbonyl oxygens of the protein backbones of the "selectivity filter" (named by Bertil Hille ) could efficiently replace the water molecules that normally shield potassium ions, but that sodium ions were smaller and cannot be completely dehydrated to allow such shielding, and therefore could not pass through. This mechanism was finally confirmed when the first structure of an ion channel was elucidated. A bacterial potassium channel KcsA, consisting of just the selectivity filter, "P" loop, and two transmembrane helices was used as a model to study the permeability and the selectivity of ion channels in the Mackinnon lab. The determination of the molecular structure of KcsA by Roderick MacKinnon using X-ray crystallography won a share of the 2003 Nobel Prize in Chemistry . [ 40 ]
Because of their small size and the difficulty of crystallizing integral membrane proteins for X-ray analysis, it is only very recently that scientists have been able to directly examine what channels "look like." Particularly in cases where the crystallography required removing channels from their membranes with detergent, many researchers regard images that have been obtained as tentative. An example is the long-awaited crystal structure of a voltage-gated potassium channel, which was reported in May 2003. [ 41 ] [ 42 ] One inevitable ambiguity about these structures relates to the strong evidence that channels change conformation as they operate (they open and close, for example), such that the structure in the crystal could represent any one of these operational states. Most of what researchers have deduced about channel operation so far they have established through electrophysiology , biochemistry , gene sequence comparison and mutagenesis .
Channels can have single (CLICs) to multiple transmembrane (K channels, P2X receptors, Na channels) domains which span plasma membrane to form pores. Pore can determine the selectivity of the channel. Gate can be formed either inside or outside the pore region.
Chemical substances can modulate the activity of ion channels, for example by blocking or activating them.
A variety of ion channel blockers (inorganic and organic molecules) can modulate ion channel activity and conductance.
Some commonly used blockers include:
Several compounds are known to promote the opening or activation of specific ion channels. These are classified by the channel on which they act:
There are a number of disorders which disrupt normal functioning of ion channels and have disastrous consequences for the organism. Genetic and autoimmune disorders of ion channels and their modifiers are known as channelopathies . See Category:Channelopathies for a full list.
The fundamental properties of currents mediated by ion channels were analyzed by the British biophysicists Alan Hodgkin and Andrew Huxley as part of their Nobel Prize -winning research on the action potential , published in 1952. They built on the work of other physiologists, such as Cole and Baker's research into voltage-gated membrane pores from 1941. [ 45 ] [ 46 ] The existence of ion channels was confirmed in the 1970s by Bernard Katz and Ricardo Miledi using noise analysis [ citation needed ] . It was then shown more directly with an electrical recording technique known as the " patch clamp ", which led to a Nobel Prize to Erwin Neher and Bert Sakmann , the technique's inventors. Hundreds if not thousands of researchers continue to pursue a more detailed understanding of how these proteins work. In recent years the development of automated patch clamp devices helped to increase significantly the throughput in ion channel screening.
The Nobel Prize in Chemistry for 2003 was awarded to Roderick MacKinnon for his studies on the physico-chemical properties of ion channel structure and function, including x-ray crystallographic structure studies.
Roderick MacKinnon commissioned Birth of an Idea , a 5-foot (1.5 m) tall sculpture based on the KcsA potassium channel . [ 47 ] The artwork contains a wire object representing the channel's interior with a blown glass object representing the main cavity of the channel structure.
The behavior of ion channels can be usefully modeled using mathematics and probability. Stochastic processes are mathematical models of systems and phenomena that appear to vary in a random manner. [ 48 ] A very simple example is flipping a coin; each flip has an equal chance to be heads or tails, the chances are not influenced by the outcome of past flips, and we can say that p heads = 0.5 and p tails = 0.5. [ 49 ]
A particularly relevant form of stochastic processes in the study of ion channels is Markov chains . In a Markov chain, there are multiple states, each of which has given chances to transition to different states over a particular period of time. [ 49 ] Ion channels undergo state transitions (e.g. open, closed, inactive) that behave like Markov chains. [ 50 ] Markov chain analysis can be used to make conclusions regarding the nature of a given ion channel, including the likely number of open and closed states. [ 51 ] We can also use Markov chain analysis to produce models that accurately simulate the insertion of ion channels into cell membranes. [ 52 ]
Markov chains can also be used in combination with the stochastic matrix to determine the stable distribution matrix by solving the equation PX=X, where P is the stochastic matrix and X is the stable distribution matrix. This stable distribution matrix tells us the relative frequencies of each state after a long time, which in the context of ion channels can be the frequencies of the open, closed, and inactive states for an ion channel. [ 53 ] Note that Markov chain assumptions apply, including that (1) all transition probabilities for each state sum to one, (2) the probability model applies to all possible states, and (3) that the probability of transitions are constant over time. Therefore, Markov chains have limited applicability in some situations. [ 53 ]
There are a variety of other stochastic processes that are utilized in the study of ion channels, but are too complex to relate here and can be examined more closely elsewhere. [ 54 ] | https://en.wikipedia.org/wiki/Ion_channel |
The ion channel hypothesis of Alzheimer's disease (AD), also known as the channel hypothesis or the amyloid beta ion channel hypothesis, is a more recent variant of the amyloid hypothesis of AD, which identifies amyloid beta (Aβ) as the underlying cause of neurotoxicity seen in AD. [ 1 ] While the traditional formulation of the amyloid hypothesis pinpoints insoluble, fibrillar aggregates of Aβ as the basis of disruption of calcium ion homeostasis and subsequent apoptosis in AD, [ 1 ] [ 2 ] the ion channel hypothesis in 1993 introduced the possibility of an ion-channel-forming oligomer of soluble, non-fibrillar Aβ as the cytotoxic species allowing unregulated calcium influx into neurons in AD. [ 3 ]
The ion channel hypothesis is broadly supported as an explanation for the calcium ion influx that disrupts calcium ion homeostasis and induces apoptosis in neurons . Because the extracellular deposition of Aβ fibrils in senile plaques is not sufficient to predict risk or onset of AD, and clinical trials of drugs that target the Aβ fibrillization process have largely failed, the ion channel hypothesis provides novel molecular targets for continued development of AD therapies and for better understanding of the mechanism underlying onset and progression of AD. [ 4 ]
The ion channel hypothesis was first proposed by Arispe and colleagues in 1993 upon discovery that Aβ could form unregulated cation -selective ion channels when incorporated into planar lipid bilayers . [ 3 ] Further research showed that a particular fragment of Aβ, Aβ (25-35), spontaneously inserts into planar lipid bilayers to form weakly selective ion channels [ 5 ] and that membrane insertion occurs non-specifically, irreversibly, and with a broad range of oligomer conformations. [ 6 ] Though more recent studies have found that Aβ channels can be blocked by small molecules, [ 7 ] the broad variety of Aβ ion channel conformations and chemistries make it difficult to design a channel blocker specific to Aβ without compromising other ion channels in the cell membrane. [ 4 ]
The Aβ monomer generally assumes an α-helical formation in aqueous solution , [ 8 ] but can reversibly transition between α-helix and β-sheet structures at varying polarities. [ 9 ] Atomic force microscopy captured images of Aβ channel structures that facilitated calcium uptake and subsequent neuritic degeneration. [ 10 ] Molecular dynamics simulations of Aβ in lipid bilayers suggest that Aβ adopts a β-sheet-rich structure within lipid bilayers that gradually evolves to result in a wide variety of relaxed channel conformations. [ 11 ] In particular, data support the organization of Aβ channels in β-barrels , structural formations commonly seen in transmembrane pore-forming toxins including anthrax . [ 12 ]
Aβ channels are selective for cations over anions, voltage-independent, and display a long channel lifetime, from minutes to hours. [ 13 ] They can be extremely large, up to 5 nS in size, and can insert into the cell membrane from aqueous solution. [ 14 ] Aβ channels are heterogeneous and allow flow of physiologically relevant ions such as Ca 2+ , Na + , K + , Cs + , and Li + across the cell membrane. [ 13 ]
Cytotoxicity caused by ion channel formation is commonly seen in the world of bacteria. [ 15 ] While eukaryotic cells are generally less vulnerable to channel-forming toxins because of their larger volume and stiffer, sterol -containing membranes, several eukaryotic channel-forming toxins have been seen to sidestep these obstacles by forming especially large, stable ion channels or anchoring to sterols in the cell membrane. [ 15 ] [ 16 ] Neurons are particularly vulnerable to channel-forming toxins because of their reliance on maintenance of strict Na + , K + , and Ca 2+ concentration gradients and membrane potential for proper functioning and action potential propagation. [ 15 ] Leakage caused by insertion of an ion channel such as Aβ rapidly alters intracellular ionic concentrations, resulting in energetic stress, failure of signaling, and cell death. [ 3 ] [ 15 ]
The large, poorly selective, and long-lived nature of Aβ channels allows rapid degradation of membrane potential in neurons. [ 13 ] A single Aβ channel 4 nS in size can cause Na + concentration to change as much as 10 μM/s. [ 14 ] Degradation of membrane potential in this manner also generates additional Ca 2+ influx through voltage-sensitive Ca 2+ channels in the plasma membrane. [ 13 ] Ionic leakage alone has been demonstrated to be sufficient to rapidly disrupt cellular homeostasis and induce cell necrosis . [ 16 ] [ 17 ] [ 18 ]
Aβ channels may also trigger apoptosis through insertion in mitochondrial membranes. [ 13 ] Aβ injection in rats has been shown to damage mitochondrial structure in neurons, decrease mitochondrial membrane potential, and increase intracellular Ca 2+ concentration. [ 19 ] Additionally, Aβ accumulation increases expression of genes associated with the mitochondrial permeability transition pore (MPTP), a non-selective, high conductance channel spanning the inner and outer mitochondrial membrane. [ 19 ] [ 20 ] Ca 2+ influx into mitochondria can collapse mitochondrial membrane potential, causing MPTP opening, which then induces mitochondrial swelling, further dissipation of membrane potential, generation of mitochondrial reactive oxygen species (ROS), rupture of the outer mitochondrial membrane, and release of apoptogenic factors such as cytochrome c . [ 21 ] [ 22 ]
The only treatments currently approved for AD are either cholinesterase inhibitors (such as donepezil ) or glutamate receptor antagonists (such as memantine ), which show limited efficacy in treating symptoms or halting progression of AD. [ 23 ] The slight improvement in cognitive function brought about by these drugs is only seen in patients with mild to moderate AD, and is confined to the first year of treatment, as efficacy progressively declines, completely disappearing by 2 or 3 years of treatment. Extensive research has gone into the design of potential AD treatments to reduce Aβ production or aggregation, but these therapeutics have historically failed in Phase III clinical trials. [ 24 ] [ 25 ] The ion channel hypothesis of AD provides a novel avenue for development of AD therapies that may more directly target the underlying pathophysiology of AD. [ 23 ]
Nonspecific Aβ channel blockers including tromethamine (Tris) and Zn 2+ have successfully inhibited Aβ cytotoxicity . [ 26 ] Least-energy molecular models of the Aβ channel have been used to create polypeptide segments to target the mouth of the Aβ pore, and these selective Aβ channel blockers have also been shown to inhibit Aβ cytotoxicity. [ 4 ] [ 7 ] Structural modeling of Aβ channels, however, suggests that the channels are highly polymorphic, with the ability to move and change size and shape within the lipid membrane. The broad range of conformations adopted by the Aβ channel makes design of a specific, highly effective Aβ channel blocker difficult. [ 4 ]
Indirect methods such as membrane hyperpolarization may help limit the cytotoxic depolarizing effects of Aβ channels. [ 4 ] Potassium ATP channel activation has been demonstrated to attenuate Ca 2+ influx and reduce oxidative stress in neurons, as well as to improve memory and reduce Aβ and tau pathology in a transgenic AD mouse model. [ 27 ] Similarly, drugs that block voltage-gated Ca 2+ channels have also been shown to protect neurons from Aβ toxicity. [ 28 ]
Several other classes of amyloid proteins also form ion channels, including proteins implicated in type II diabetes mellitus , prion diseases, Parkinson's disease , and Huntington's disease . [ 13 ] [ 15 ] Consistent with Aβ channels, other amyloid channels have also been reported to be large, non-selective, voltage-independent, heterogeneous, and irreversible. [ 15 ] These distinct properties set amyloid channels apart from other ion channels in neurons and facilitate unregulated ionic leakage resulting in cell depolarization, disruption of ion homeostasis, and cell death. [ 4 ] [ 15 ] Further investigation of amyloid proteins and the cytotoxic effects of amyloid channel formation is necessary for development of drug candidates that are able to selectively block amyloid channels or bind them prior to membrane insertion, an area of research that may prove highly relevant to not just AD but a wide variety of other diseases. [ 15 ] | https://en.wikipedia.org/wiki/Ion_channel_hypothesis_of_Alzheimer's_disease |
Ion chromatography (or ion-exchange chromatography ) is a form of chromatography that separates ions and ionizable polar molecules based on their affinity to the ion exchanger. [ 1 ] It works on almost any kind of charged molecule —including small inorganic anions, [ 2 ] large proteins , [ 3 ] small nucleotides , [ 4 ] and amino acids . However, ion chromatography must be done in conditions that are one pH unit away from the isoelectric point of a protein. [ 5 ]
The two types of ion chromatography are anion-exchange and cation-exchange. Cation-exchange chromatography is used when the molecule of interest is positively charged. The molecule is positively charged because the pH for chromatography is less than the pI (also known as pH(I)). [ 6 ] In this type of chromatography, the stationary phase is negatively charged and positively charged molecules are loaded to be attracted to it. Anion-exchange chromatography is when the stationary phase is positively charged and negatively charged molecules (meaning that pH for chromatography is greater than the pI) are loaded to be attracted to it. [ 7 ] It is often used in protein purification, water analysis, [ 8 ] [ 9 ] and quality control. The water-soluble and charged molecules such as proteins, amino acids, and peptides bind to moieties which are oppositely charged by forming ionic bonds to the insoluble stationary phase. [ 10 ] The equilibrated stationary phase consists of an ionizable functional group where the targeted molecules of a mixture to be separated and quantified can bind while passing through the column—a cationic stationary phase is used to separate anions and an anionic stationary phase is used to separate cations. Cation exchange chromatography is used when the desired molecules to separate are cations and anion exchange chromatography is used to separate anions. [ 11 ] The bound molecules then can be eluted and collected using an eluant which contains anions and cations by running a higher concentration of ions through the column or by changing the pH of the column.
One of the primary advantages for the use of ion chromatography is that only one interaction is involved the separation, as opposed to other separation techniques; therefore, ion chromatography may have higher matrix tolerance. Another advantage of ion exchange is the predictability of elution patterns (based on the presence of the ionizable group). [ 12 ] For example, when cation exchange chromatography is used, certain cations will elute out first and others later. A local charge balance is always maintained. However, there are also disadvantages involved when performing ion-exchange chromatography, such as constant evolution of the technique which leads to the inconsistency from column to column. [ 13 ] A major limitation to this purification technique is that it is limited to ionizable group. [ 6 ]
Ion chromatography has advanced through the accumulation of knowledge over a course of many years. Starting from 1947, Spedding and Powell used displacement ion-exchange chromatography for the separation of the rare earths. Additionally, they showed the ion-exchange separation of 14N and 15N isotopes in ammonia. At the start of the 1950s, Kraus and Nelson demonstrated the use of many analytical methods for metal ions dependent on their separation of their chloride, fluoride, nitrate or sulfate complexes by anion chromatography. Automatic in-line detection was progressively introduced from 1960 to 1980 as well as novel chromatographic methods for metal ion separations. A groundbreaking method by Small, Stevens and Bauman at Dow Chemical Co. unfolded the creation of the modern ion chromatography. Anions and cations could now be separated efficiently by a system of suppressed conductivity detection. In 1979, a method for anion chromatography with non-suppressed conductivity detection was introduced by Gjerde et al. Following it in 1980, was a similar method for cation chromatography. [ 14 ]
As a result, a period of extreme competition began within the IC market, with supporters for both suppressed and non-suppressed conductivity detection. This competition led to fast growth of new forms and the fast evolution of IC. [ 15 ] A challenge that needs to be overcome in the future development of IC is the preparation of highly efficient monolithic ion-exchange columns and overcoming this challenge would be of great importance to the development of IC. [ 16 ]
The boom of Ion exchange chromatography primarily began between 1935 and 1950 during World War II and it was through the " Manhattan project " that applications and IC were significantly extended. Ion chromatography was originally introduced by two English researchers, agricultural Sir Thompson and chemist J T Way. The works of Thompson and Way involved the action of water-soluble fertilizer salts, ammonium sulfate and potassium chloride. These salts could not easily be extracted from the ground due to the rain. They performed ion methods to treat clays with the salts, resulting in the extraction of ammonia in addition to the release of calcium. [ 17 ] [ unreliable source? ] It was in the fifties and sixties that theoretical models were developed for IC for further understanding and it was not until the seventies that continuous detectors were utilized, paving the path for the development from low-pressure to high-performance chromatography. Not until 1975 was "ion chromatography" established as a name in reference to the techniques, and was thereafter used as a name for marketing purposes. Today IC is important for investigating aqueous systems, such as drinking water. It is a popular method for analyzing anionic elements or complexes that help solve environmentally relevant problems. Likewise, it also has great uses in the semiconductor industry. [ 18 ]
Because of the abundant separating columns, elution systems, and detectors available, chromatography has developed into the main method for ion analysis. [ 19 ]
When this technique was initially developed, it was primarily used for water treatment. Since 1935, ion exchange chromatography rapidly manifested into one of the most heavily leveraged techniques, with its principles often being applied to majority of fields of chemistry, including distillation, adsorption, and filtration. [ 20 ]
Ion-exchange chromatography separates molecules based on their respective charged groups. Ion-exchange chromatography retains analyte molecules on the column based on coulombic (ionic) interactions. The ion exchange chromatography matrix consists of positively and negatively charged ions. [ 21 ] Essentially, molecules undergo electrostatic interactions with opposite charges on the stationary phase matrix. The stationary phase consists of an immobile matrix that contains charged ionizable functional groups or ligands . [ 22 ] The stationary phase surface displays ionic functional groups (R-X) that interact with analyte ions of opposite charge. To achieve electroneutrality, these immobilized charges couple with exchangeable counterions in the solution. Ionizable molecules that are to be purified, compete with these exchangeable counterions, for binding to the immobilized charges on the stationary phase. These ionizable molecules are retained or eluted based on their charge. Initially, molecules that do not bind or bind weakly to the stationary phase are first to be washed away. Altered conditions are needed for the elution of the molecules that bind to the stationary phase. The concentration of the exchangeable counterions, which competes with the molecules for binding, can be increased, or the pH can be changed to affect the ionic charge of the eluent or the solute. A change in pH affects the charge on the particular molecules and, therefore, alter their binding. When reducing the net charge of the solute's molecules, they start eluting out. This way, such adjustments can be used to release the proteins of interest. Additionally, concentration of counterions can be gradually varied to affect the retention of the ionized molecules, thus separate them. This type of elution is called gradient elution. On the other hand, step elution can be used, in which the concentration of counterions are varied in steps. [ 5 ] This type of chromatography is further subdivided into cation exchange chromatography and anion-exchange chromatography . Positively charged molecules bind to cation exchange resins, while negatively charged molecules bind to anion exchange resins. [ 23 ] The ionic compound consisting of the cationic species M+ and the anionic species B− can be retained by the stationary phase.
Cation exchange chromatography retains positively charged cations because the stationary phase displays a negatively charged functional group:
Anion exchange chromatography retains anions using positively charged functional group:
Note that the ion strength of either C+ or A− in the mobile phase can be adjusted to shift the equilibrium position, thus retention time.
The ion chromatogram shows a typical chromatogram obtained with an anion exchange column.
Before ion-exchange chromatography can be initiated, it must be equilibrated. The stationary phase must be equilibrated to certain requirements that depend on the experiment that you are working with. Once equilibrated, the charged ions in the stationary phase will be attached to its opposite charged exchangeable ions, such as Cl − or Na + . Next, a buffer should be chosen in which the desired protein can bind to. After equilibration, the column needs to be washed. The washing phase will help elute out all impurities that does not bind to the matrix while the protein of interest remains bounded. This sample buffer needs to have the same pH as the buffer used for equilibration to help bind the desired proteins. Uncharged proteins will be eluted out of the column at a similar speed of the buffer flowing through the column with no retention. Once the sample has been loaded onto to the column, and the column has been washed with the buffer to elute out all non-desired proteins, elution is carried out at specific conditions to elute the desired proteins that are bound to the matrix. Bound proteins are eluted out by utilizing a gradient of linearly increasing salt concentration. With increasing ionic strength of the buffer, the salt ions will compete with the desired proteins in order to bind to charged groups on the surface of the medium. This will cause desired proteins to be eluted out of the column. Proteins that have a low net charge will be eluted out first as the salt concentration increases causing the ionic strength to increase. Proteins with high net charge will need a higher ionic strength for them to be eluted out of the column. [ 21 ]
It is possible to perform ion exchange chromatography in bulk, on thin layers of medium such as glass or plastic plates coated with a layer of the desired stationary phase, or in chromatography columns. Thin layer chromatography or column chromatography share similarities in that they both act within the same governing principles; there is constant and frequent exchange of molecules as the mobile phase travels along the stationary phase. It is not imperative to add the sample in minute volumes as the predetermined conditions for the exchange column have been chosen so that there will be strong interaction between the mobile and stationary phases. Furthermore, the mechanism of the elution process will cause a compartmentalization of the differing molecules based on their respective chemical characteristics. This phenomenon is due to an increase in salt concentrations at or near the top of the column, thereby displacing the molecules at that position, while molecules bound lower are released at a later point when the higher salt concentration reaches that area. These principles are the reasons that ion exchange chromatography is an excellent candidate for initial chromatography steps in a complex purification procedure as it can quickly yield small volumes of target molecules regardless of a greater starting volume. [ 6 ]
Comparatively simple devices are often used to apply counterions of increasing gradient to a chromatography column. Counterions such as copper (II) are chosen most often for effectively separating peptides and amino acids through complex formation. [ 24 ]
A simple device can be used to create a salt gradient. Elution buffer is consistently being drawn from the chamber into the mixing chamber, thereby altering its buffer concentration. Generally, the buffer placed into the chamber is usually of high initial concentration, whereas the buffer placed into the stirred chamber is usually of low concentration. As the high concentration buffer from the left chamber is mixed and drawn into the column, the buffer concentration of the stirred column gradually increase. Altering the shapes of the stirred chamber, as well as of the limit buffer, allows for the production of concave, linear, or convex gradients of counterion.
A multitude of different mediums are used for the stationary phase. Among the most common immobilized charged groups used are trimethylaminoethyl (TAM), triethylaminoethyl (TEAE), diethyl-2-hydroxypropylaminoethyl (QAE), aminoethyl (AE), diethylaminoethyl (DEAE), sulpho (S), sulphomethyl (SM), sulphopropyl (SP), carboxy (C), and carboxymethyl (CM). [ 5 ]
Successful packing of the column is an important aspect of ion chromatography. Stability and efficiency of a final column depends on packing methods, solvent used, and factors that affect mechanical properties of the column. In contrast to early inefficient dry- packing methods, wet slurry packing, in which particles that are suspended in an appropriate solvent are delivered into a column under pressure, shows significant improvement. Three different approaches can be employed in performing wet slurry packing: the balanced density method (solvent's density is about that of porous silica particles), the high viscosity method (a solvent of high viscosity is used), and the low viscosity slurry method (performed with low viscosity solvents). [ 25 ]
Polystyrene is used as a medium for ion- exchange. It is made from the polymerization of styrene with the use of divinylbenzene and benzoyl peroxide. Such exchangers form hydrophobic interactions with proteins which can be irreversible. Due to this property, polystyrene ion exchangers are not suitable for protein separation. They are used on the other hand for the separation of small molecules in amino acid separation and removal of salt from water. Polystyrene ion exchangers with large pores can be used for the separation of protein but must be coated with a hydrophilic substance. [ 26 ]
Cellulose based medium can be used for the separation of large molecules as they contain large pores. Protein binding in this medium is high and has low hydrophobic character. DEAE is an anion exchange matrix that is produced from a positive side group of diethylaminoethyl bound to cellulose or Sephadex. [ 27 ]
Agarose gel based medium contain large pores as well but their substitution ability is lower in comparison to dextrans. The ability of the medium to swell in liquid is based on the cross-linking of these substances, the pH and the ion concentrations of the buffers used. [ 26 ]
Incorporation of high temperature and pressure allows a significant increase in the efficiency of ion chromatography, along with a decrease in time. Temperature has an influence of selectivity due to its effects on retention properties. The retention factor ( k = ( t R g − t M g )/( t M g − t ext )) increases with temperature for small ions, and the opposite trend is observed for larger ions. [ 28 ] [ 29 ]
Despite ion selectivity in different mediums, further research is being done to perform ion exchange chromatography through the range of 40–175 °C. [ 30 ]
An appropriate solvent can be chosen based on observations of how column particles behave in a solvent. Using an optical microscope, one can easily distinguish a desirable dispersed state of slurry from aggregated particles. [ 25 ]
A "strong" ion exchanger will not lose the charge on its matrix once the column is equilibrated and so a wide range of pH buffers can be used. "Weak" ion exchangers have a range of pH values in which they will maintain their charge. If the pH of the buffer used for a weak ion exchange column goes out of the capacity range of the matrix, the column will lose its charge distribution and the molecule of interest may be lost. [ 31 ] Despite the smaller pH range of weak ion exchangers, they are often used over strong ion exchangers due to their having greater specificity. In some experiments, the retention times of weak ion exchangers are just long enough to obtain desired data at a high specificity. [ 32 ]
Resins (often termed 'beads') of ion exchange columns may include functional groups such as weak/strong acids and weak/strong bases. There are also special columns that have resins with amphoteric functional groups that can exchange both cations and anions. [ 33 ] Some examples of functional groups of strong ion exchange resins are quaternary ammonium cation (Q), which is an anion exchanger, and sulfonic acid (S, -SO 2 OH), which is a cation exchanger. [ 34 ] These types of exchangers can maintain their charge density over a pH range of 0–14. Examples of functional groups of Weak ion exchange resins include diethylaminoethyl (DEAE, -C 2 H 4 N(C 2 H 5 ) 2 ), which is an anion exchanger, and carboxymethyl (CM, -CH 2 -COOH), [ 35 ] which is a cation exchanger. These two types of exchangers can maintain the charge density of their columns over a pH range of 5–9. [ citation needed ]
In ion chromatography, the interaction of the solute ions and the stationary phase based on their charges determines which ions will bind and to what degree. When the stationary phase features positive groups which attracts anions, it is called an anion exchanger; when there are negative groups on the stationary phase, cations are attracted and it is a cation exchanger. [ 36 ] The attraction between ions and stationary phase also depends on the resin, organic particles used as ion exchangers.
Each resin features relative selectivity which varies based on the solute ions present who will compete to bind to the resin group on the stationary phase. The selectivity coefficient, the equivalent to the equilibrium constant, is determined via a ratio of the concentrations between the resin and each ion, however, the general trend is that ion exchangers prefer binding to the ion with a higher charge, smaller hydrated radius, and higher polarizability, or the ability for the electron cloud of an ion to be disrupted by other charges. [ 37 ] Despite this selectivity, excess amounts of an ion with a lower selectivity introduced to the column would cause the lesser ion to bind more to the stationary phase as the selectivity coefficient allows fluctuations in the binding reaction that takes place during ion exchange chromatography.
Following table shows the commonly used ion exchangers [ 38 ]
A sample is introduced, either manually or with an autosampler , into a sample loop of known volume. A buffered aqueous solution known as the mobile phase carries the sample from the loop onto a column that contains some form of stationary phase material. This is typically a resin or gel matrix consisting of agarose or cellulose beads with covalently bonded charged functional groups. Equilibration of the stationary phase is needed in order to obtain the desired charge of the column. If the column is not properly equilibrated the desired molecule may not bind strongly to the column. The target analytes (anions or cations) are retained on the stationary phase but can be eluted by increasing the concentration of a similarly charged species that displaces the analyte ions from the stationary phase. For example, in cation exchange chromatography, the positively charged analyte can be displaced by adding positively charged sodium ions. The analytes of interest must then be detected by some means, typically by conductivity or UV/visible light absorbance.
Control an IC system usually requires a chromatography data system (CDS). In addition to IC systems, some of these CDSs can also control gas chromatography (GC) and HPLC.
A type of ion exchange chromatography, membrane exchange [ 39 ] [ 40 ] is a relatively new method of purification designed to overcome limitations of using columns packed with beads. Membrane Chromatographic [ 41 ] [ 42 ] devices are cheap to mass-produce and disposable unlike other chromatography devices that require maintenance and time to revalidate. There are three types of membrane absorbers that are typically used when separating substances. The three types are flat sheet, hollow fibre, and radial flow. The most common absorber and best suited for membrane chromatography is multiple flat sheets because it has more absorbent volume. It can be used to overcome mass transfer limitations [ 43 ] and pressure drop, [ 44 ] making it especially advantageous for isolating and purifying viruses, plasmid DNA, and other large macromolecules. The column is packed with microporous membranes with internal pores which contain adsorptive moieties that can bind the target protein. Adsorptive membranes are available in a variety of geometries and chemistry which allows them to be used for purification and also fractionation, concentration, and clarification in an efficiency that is 10 fold that of using beads. [ 45 ] Membranes can be prepared through isolation of the membrane itself, where membranes are cut into squares and immobilized. A more recent method involved the use of live cells that are attached to a support membrane and are used for identification and clarification of signaling molecules. [ 46 ]
Ion exchange chromatography can be used to separate proteins because they contain charged functional groups. The ions of interest (in this case charged proteins) are exchanged for another ions (usually H + ) on a charged solid support. The solutes are most commonly in a liquid phase, which tends to be water. Take for example proteins in water, which would be a liquid phase that is passed through a column. The column is commonly known as the solid phase since it is filled with porous synthetic particles that are of a particular charge. These porous particles are also referred to as beads, may be aminated (containing amino groups) or have metal ions in order to have a charge. The column can be prepared using porous polymers, for macromolecules of a mass of over 100 000 Da, the optimum size of the porous particle is about 1 μm 2 . This is because slow diffusion of the solutes within the pores does not restrict the separation quality. [ 47 ] The beads containing positively charged groups, which attract the negatively charged proteins, are commonly referred to as anion exchange resins. The amino acids that have negatively charged side chains at pH 7 (pH of water) are glutamate and aspartate. The beads that are negatively charged are called cation exchange resins, as positively charged proteins will be attracted. The amino acids that have positively charged side chains at pH 7 are lysine, histidine and arginine. [ 48 ]
The isoelectric point is the pH at which a compound - in this case a protein - has no net charge. A protein's isoelectric point or PI can be determined using the pKa of the side chains, if the amino (positive chain) is able to cancel out the carboxyl (negative) chain, the protein would be at its PI. Using buffers instead of water for proteins that do not have a charge at pH 7 is a good idea as it enables the manipulation of pH to alter ionic interactions between the proteins and the beads. [ 49 ] Weakly acidic or basic side chains are able to have a charge if the pH is high or low enough respectively. Separation can be achieved based on the natural isoelectric point of the protein. Alternatively a peptide tag can be genetically added to the protein to give the protein an isoelectric point away from most natural proteins (e.g., 6 arginines for binding to a cation-exchange resin or 6 glutamates for binding to an anion-exchange resin such as DEAE-Sepharose).
Elution by increasing ionic strength of the mobile phase is more subtle. It works because ions from the mobile phase interact with the immobilized ions on the stationary phase, thus "shielding" the stationary phase from the protein, and letting the protein elute.
Elution from ion-exchange columns can be sensitive to changes of a single charge- chromatofocusing . Ion-exchange chromatography is also useful in the isolation of specific multimeric protein assemblies, allowing purification of specific complexes according to both the number and the position of charged peptide tags. [ 50 ] [ 51 ]
In ion exchange chromatography, the Gibbs–Donnan effect is observed when the pH of the applied buffer and the ion exchanger differ, even up to one pH unit. For example, in anion-exchange columns, the ion exchangers repeal protons so the pH of the buffer near the column differs is higher than the rest of the solvent. [ 52 ] As a result, an experimenter has to be careful that the protein(s) of interest is stable and properly charged in the "actual" pH.
This effect comes as a result of two similarly charged particles, one from the resin and one from the solution, failing to distribute properly between the two sides; there is a selective uptake of one ion over another. [ 53 ] [ 54 ] For example, in a sulphonated polystyrene resin, a cation exchange resin, the chlorine ion of a hydrochloric acid buffer should equilibrate into the resin. However, since the concentration of the sulphonic acid in the resin is high, the hydrogen of HCl has no tendency to enter the column. This, combined with the need of electroneutrality, leads to a minimum amount of hydrogen and chlorine entering the resin. [ 54 ]
A use of ion chromatography can be seen in argentation chromatography . [ citation needed ] Usually, silver and compounds containing acetylenic and ethylenic bonds have very weak interactions. This phenomenon has been widely tested on olefin compounds. The ion complexes the olefins make with silver ions are weak and made based on the overlapping of pi, sigma, and d orbitals and available electrons therefore cause no real changes in the double bond. This behavior was manipulated to separate lipids, mainly fatty acids from mixtures in to fractions with differing number of double bonds using silver ions. The ion resins were impregnated with silver ions, which were then exposed to various acids (silicic acid) to elute fatty acids of different characteristics.
Detection limits as low as 1 μM can be obtained for alkali metal ions. [ 55 ] It may be used for measurement of HbA1c , porphyrin and with water purification . Ion Exchange Resins(IER) have been widely used especially in medicines due to its high capacity and the uncomplicated system of the separation process. One of the synthetic uses is to use Ion Exchange Resins for kidney dialysis. This method is used to separate the blood elements by using the cellulose membraned artificial kidney. [ 56 ]
Another clinical application of ion chromatography is in the rapid anion exchange chromatography technique used to separate creatine kinase (CK) isoenzymes from human serum and tissue sourced in autopsy material (mostly CK rich tissues were used such as cardiac muscle and brain). [ citation needed ] These isoenzymes include MM, MB, and BB, which all carry out the same function given different amino acid sequences. The functions of these isoenzymes are to convert creatine, using ATP, into phosphocreatine expelling ADP. Mini columns were filled with DEAE-Sephadex A-50 and further eluted with tris- buffer sodium chloride at various concentrations (each concentration was chosen advantageously to manipulate elution). Human tissue extract was inserted in columns for separation. All fractions were analyzed to see total CK activity and it was found that each source of CK isoenzymes had characteristic isoenzymes found within. Firstly, CK- MM was eluted, then CK-MB, followed by CK-BB. Therefore, the isoenzymes found in each sample could be used to identify the source, as they were tissue specific.
Using the information from results, correlation could be made about the diagnosis of patients and the kind of CK isoenzymes found in most abundant activity. From the finding, about 35 out of 71 patients studied suffered from heart attack (myocardial infarction) also contained an abundant amount of the CK-MM and CK-MB isoenzymes. Findings further show that many other diagnosis including renal failure, cerebrovascular disease, and pulmonary disease were only found to have the CK-MM isoenzyme and no other isoenzyme. The results from this study indicate correlations between various diseases and the CK isoenzymes found which confirms previous test results using various techniques. Studies about CK-MB found in heart attack victims have expanded since this study and application of ion chromatography.
Since 1975 ion chromatography has been widely used in many branches of industry. The main beneficial advantages are reliability, very good accuracy and precision, high selectivity, high speed, high separation efficiency, and low cost of consumables. The most significant development related to ion chromatography are new sample preparation methods; improving the speed and selectivity of analytes separation; lowering of limits of detection and limits of quantification; extending the scope of applications; development of new standard methods; miniaturization and extending the scope of the analysis of a new group of substances. Allows for quantitative testing of electrolyte and proprietary additives of electroplating baths. [ 57 ] It is an advancement of qualitative hull cell testing or less accurate UV testing. Ions, catalysts, brighteners and accelerators can be measured. [ 57 ] Ion exchange chromatography has gradually become a widely known, universal technique for the detection of both anionic and cationic species. Applications for such purposes have been developed, or are under development, for a variety of fields of interest, and in particular, the pharmaceutical industry. The usage of ion exchange chromatography in pharmaceuticals has increased in recent years, and in 2006, a chapter on ion exchange chromatography was officially added to the United States Pharmacopia -National Formulary (USP-NF). Furthermore, in 2009 release of the USP-NF, the United States Pharmacopia made several analyses of ion chromatography available using two techniques: conductivity detection, as well as pulse amperometric detection. Majority of these applications are primarily used for measuring and analyzing residual limits in pharmaceuticals, including detecting the limits of oxalate, iodide, sulfate, sulfamate, phosphate, as well as various electrolytes including potassium, and sodium. In total, the 2009 edition of the USP-NF officially released twenty eight methods of detection for the analysis of active compounds, or components of active compounds, using either conductivity detection or pulse amperometric detection. [ 58 ]
There has been a growing interest in the application of IC in the analysis of pharmaceutical drugs. IC is used in different aspects of product development and quality control testing. For example, IC is used to improve stabilities and solubility properties of pharmaceutical active drugs molecules as well as used to detect systems that have higher tolerance for organic solvents. IC has been used for the determination of analytes as a part of a dissolution test. For instance, calcium dissolution tests have shown that other ions present in the medium can be well resolved among themselves and also from the calcium ion. Therefore, IC has been employed in drugs in the form of tablets and capsules in order to determine the amount of drug dissolve with time. [ 59 ] IC is also widely used for detection and quantification of excipients or inactive ingredients used in pharmaceutical formulations. Detection of sugar and sugar alcohol in such formulations through IC has been done due to these polar groups getting resolved in ion column. IC methodology also established in analysis of impurities in drug substances and products. Impurities or any components that are not part of the drug chemical entity are evaluated and they give insights about the maximum and minimum amounts of drug that should be administered in a patient per day. [ 60 ] | https://en.wikipedia.org/wiki/Ion_chromatography |
Ion cyclotron resonance is a phenomenon related to the movement of ions in a magnetic field . It is used for accelerating ions in a cyclotron , and for measuring the masses of an ionized analyte in mass spectrometry , particularly with Fourier transform ion cyclotron resonance mass spectrometers. It can also be used to follow the kinetics of chemical reactions in a dilute gas mixture, provided these involve charged species.
An ion in a static and uniform magnetic field will move in a circle due to the Lorentz force . The angular frequency of this cyclotron motion for a given magnetic field strength B is given by
where z is the number of positive or negative charges of the ion, e is the elementary charge and m is the mass of the ion. [ 1 ] An electric excitation signal having a frequency f will therefore resonate with ions having a mass-to-charge ratio m/z given by
The circular motion may be superimposed with a uniform axial motion, resulting in a helix , or with a uniform motion perpendicular to the field (e.g., in the presence of an electrical or gravitational field) resulting in a cycloid .
Ion cyclotron resonance heating (or ICRH) is a technique in which electromagnetic waves with frequencies corresponding to the ion cyclotron frequency is used to heat up a plasma . [ 2 ] The ions in the plasma absorb the electromagnetic radiation and as a result of this, increase in kinetic energy . This technique is commonly used in the heating of tokamak plasmas. [ 3 ] [ 4 ] [ 5 ] [ 6 ]
On March 8, 2013, NASA released an article according to which ion cyclotron waves were identified by its solar probe spacecraft called WIND as the main cause for the heating of the solar wind as it rises from the Sun's surface. Before this discovery, it was unclear why the solar wind particles would heat up instead of cool down, when speeding away from the Sun's surface. [ 7 ]
In fusion devices, such as tokamaks and stellarators , ICRH antennas are installed in the machine vessel to heat the plasma using radio waves with frequencies in the range of the ion cyclotron resonance.
ICRH provides localized heating of ions in fusion plasmas, which can generate a large population of energetic particles typically inaccessible with other heating methods (such as electron cyclotron resonance heating or neutral beam injection ). The confinement properties of fast ions in plasma is a major research topic in fusion plasma physics. | https://en.wikipedia.org/wiki/Ion_cyclotron_resonance |
An ion drift meter is a device used to measure the velocity of individual ions in the area of a spacecraft . This information can then be used to calculate the ion drift in the space surrounding the instrument as well as the strength of an electric field present, provided that the magnetic field strength has been determined using a magnetometer . [ 1 ] [ 2 ]
The device itself works by allowing ions to pass through an opening at the front of the instrument and measuring the currents produced by the impacts of ions in different locations on a grid at the back. The trajectories of the ions can then be determined.
Ion drift meters have been used on several spacecraft including the Dynamics Explorer , CHAMP and Ionospheric Connection Explorer . [ 3 ]
This physics -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ion_drift_meter |
Ion exchange is a reversible interchange of one species of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid. Ion exchange is used in softening or demineralizing of water, purification of chemicals, and separation of substances.
Ion exchange usually describes a process of purification of aqueous solutions using solid polymeric ion-exchange resin . More precisely, the term encompasses a large variety of processes where ions are exchanged between two electrolytes . [ 1 ] Aside from its use to purify drinking water, the technique is widely applied for purification and separation of a variety of industrially and medicinally important chemicals. Although the term usually refers to applications of synthetic (human-made) resins, it can include many other materials such as soil.
Typical ion exchangers are ion-exchange resins (functionalized porous or gel polymer), zeolites , montmorillonite , clay , and soil humus . Ion exchangers are either cation exchangers , which exchange positively charged ions ( cations ), or anion exchangers , which exchange negatively charged ions ( anions ). There are also amphoteric exchangers that are able to exchange both cations and anions simultaneously. However, the simultaneous exchange of cations and anions is often performed in mixed beds , which contain a mixture of anion- and cation-exchange resins, or passing the solution through several different ion-exchange materials.
Ion exchangers can have binding preferences for certain ions or classes of ions, depending on the physical properties and chemical structure of both the ion exchanger and ion. This can be dependent on the size, charge, or structure of the ions. Common examples of ions that can bind to ion exchangers are:
Along with absorption and adsorption , ion exchange is a form of sorption .
Ion exchange is a reversible process , and the ion exchanger can be regenerated or loaded with desirable ions by washing with an excess of these ions.
Ion exchange resins are the physical medium that facilitates ion exchange reactions. The resin is composed of cross-linked organic polymers, typically polystyrene matrix and functional groups where the ion exchange process takes place.
Used to exchange heavy metals from alkaline earth and alkali metal solutions.
Used for organic compound removal.
Ion exchange is widely used in the food and beverage industry, hydrometallurgy, metals finishing, chemical, petrochemical, pharmaceutical technology, sugar and sweetener production, ground- and potable-water treatment, nuclear, softening, industrial water treatment, semiconductor, power, and many other industries. [ citation needed ]
A typical example of application is preparation of high-purity water for power engineering , electronic and nuclear industries; i.e. polymeric or inorganic insoluble ion exchangers are widely used for water softening , water purification , [ 2 ] [ 3 ] water decontamination , etc.
Ion exchange is a method widely used in household filters to produce soft water for the benefit of laundry detergents, soaps , and water heaters. This is accomplished by exchanging divalent cations (such as calcium Ca 2+ and magnesium Mg 2+ ) with highly soluble monovalent cations (e.g., Na + or H + ) (see water softening ). Another application for ion exchange in domestic water treatment is the removal of nitrate and natural organic matter . In domestic filtration systems ion exchange is one of the alternatives for water softening in households along with reverse osmosis (RO) membranes. Compared to RO membranes, ion exchange requires repetitive regeneration when inlet water is hard (has high mineral content). [ citation needed ]
Industrial and analytical ion-exchange chromatography is another area to be mentioned.
Ion-exchange chromatography is a chromatographical method that is widely used for chemical analysis and separation of ions. For example, in biochemistry it is widely used to separate charged molecules such as proteins . An important area of the application is extraction and purification of biologically produced substances such as proteins ( amino acids ) and DNA / RNA .
Ion-exchange processes are used to separate and purify metals , including separating uranium from plutonium and the other actinides , including thorium , neptunium , and americium . This process is also used to separate the lanthanides , such as lanthanum , cerium , neodymium , praseodymium , europium , and ytterbium , from each other. The separation of neodymium and praseodymium was a particularly difficult one, and those were formerly thought to be just one element didymium – but that is an alloy of the two. [ citation needed ]
There are two series of rare-earth metals , the lanthanides and the actinides, both of whose families all have very similar chemical and physical properties. Using methods developed by Frank Spedding in the 1940s, ion-exchange processes were formerly the only practical way to separate them in large quantities, until the development of the "solvent extraction" techniques that can be scaled up enormously.
A very important case of ion-exchange is the plutonium-uranium extraction process ( PUREX ), which is used to separate the plutonium (mainly 239 Pu ) and the uranium (in that case known as reprocessed uranium ) contained in spent fuel from americium , curium , neptunium (the minor actinides ), and the fission products that come from nuclear reactors . Thus the waste products can be separated out for disposal. Next, the plutonium and uranium are available for making nuclear-energy materials, such as new reactor fuel ( MOX-fuel ) and (plutonium-based) nuclear weapons . Historically some fission products such as Strontium-90 or Caesium-137 were likewise separated for use as radionuclides employed in industry or medicine.
The ion-exchange process is also used to separate other sets of very similar chemical elements, such as zirconium and hafnium , which is also very important for the nuclear industry. Physically, zirconium is practically transparent to free neutrons, used in building nuclear reactors, but hafnium is a very strong absorber of neutrons, used in reactor control rods .
Thus, ion-exchange is used in nuclear reprocessing and the treatment of radioactive waste .
Ion-exchange resins in the form of thin membranes are also used in chloralkali process , fuel cells , and vanadium redox batteries .
Ion exchange can also be used to remove hardness from water by exchanging calcium and magnesium ions for sodium ions in an ion-exchange column. Liquid-phase (aqueous) ion-exchange desalination has been demonstrated. [ 5 ] In this technique anions and cations in salt water are exchanged for carbonate anions and calcium cations respectively using electrophoresis . Calcium and carbonate ions then react to form calcium carbonate , which then precipitates, leaving behind fresh water. The desalination occurs at ambient temperature and pressure and requires no membranes or solid ion exchangers. The theoretical energy efficiency of this method is on par with electrodialysis and reverse osmosis .
Most ion-exchange systems use columns of ion-exchange resin that are operated on a cyclic basis.
During the filtration process, water flows through the resin column until the resin is considered exhausted. That happens only when water leaving the column contains more than the maximal desired concentration of the ions being removed. Resin is then regenerated by sequentially backwashing the resin bed to remove accumulated suspended solids, flushing removed ions from the resin with a concentrated solution of replacement ions, and rinsing the flushing solution from the resin. Production of backwash, flushing, and rinsing wastewater during regeneration of ion-exchange media limits the usefulness of ion exchange for wastewater treatment . [ 6 ]
Water softeners are usually regenerated with brine containing 10% sodium chloride . [ 7 ] Aside from the soluble chloride salts of divalent cations removed from the softened water, softener regeneration wastewater contains the unused 50–70% of the sodium chloride regeneration flushing brine required to reverse ion-exchange resin equilibria. Deionizing resin regeneration with sulfuric acid and sodium hydroxide is approximately 20–40% efficient. Neutralized deionizer regeneration wastewater contains all of the removed ions plus 2.5–5 times their equivalent concentration as sodium sulfate . [ 8 ] | https://en.wikipedia.org/wiki/Ion_exchange |
In mass spectrometry , an ion funnel is a device used to focus a beam of ions using a series of stacked ring electrodes with decreasing inner diameter. A combined radio frequency and fixed electrical potential is applied to the grids. [ 1 ] [ 2 ] In electrospray ionization -mass spectrometry (ESI-MS), ions are created at atmospheric pressure, but are analyzed at subsequently lower pressures. Ions can be lost while they are shuttled from areas of higher to lower pressure due to the transmission process caused by a phenomenon called joule expansion or “free-jet expansion.” These ion clouds expand outward, which limits the amount of ions that reach the detector, so fewer ions are analyzed. The ion funnel refocuses and transmits ions efficiently from those areas of high to low pressure. [ 3 ]
The first ion funnel was created in 1997 in the Environmental Molecular Sciences Laboratory Pacific Northwest National Laboratory by the researchers in Richard D. Smith 's lab. The ion funnel was implemented to replace the ion transmission-limited skimmer for more efficient ion capture in an ESI source. [ 4 ] Many characteristics of the ion funnel are attributed to the stacked ring ion guide, however, the disks of an ion funnel vary in diameter down its long axis. There is a portion at the base of the ion funnel in which a series of cylindrical ring electrodes have decreasing diameters, which enables the ion cloud entering the ion funnel to be spatially dispersed. [ 5 ] This allows for efficient transfer of the ion cloud through the conductance limiting orifice at the exit as the ion cloud becomes focused to a much smaller radial size. The DC electric field serves to push ions through the funnel. For positive ions, the front plate of the funnel has the most positive DC voltage, and subsequent plates have gradually decreasing DC components, providing added control. RF and DC electric fields are co-applied with a pseudopotential created with alternating RF polarities on adjacent electrodes. This “pseudo-potential” radially confines ions and causes instability in ions with a lower m/z (mass to charge ratio) while ions with a higher m/z are focused to the center of the funnel. [ 6 ] The initial ion funnel design used in the Smith research lab proved inefficient for collecting ions with low m/z . Simulations suggest that decreasing the spacing between the lenses so that they are less than the diameter of the smallest ring electrode could be a plausible solution to this problem. [ 7 ] Another issue with the design is that the funnel is susceptible to noise with fast neutrals and charged droplets at many atmospheric interfaces during the initial vacuum phase. Modifications increase the efficiency and signal to noise ratio of the ion funnel.
Some of the earliest ion funnels struggled to control gas flow as the pressure in the ion vacuum chamber was not uniform due to gas dynamic effects. The pressure at the funnel's exit was estimated to be 2 to 3 times higher than the pressure from the pressure gauge. The higher pressure required greater pumping in downstream vacuum chambers to compensate for the larger injection of gas. The discrepancy between the measured pressure and the pressure at the exit of the funnel was caused by the a sizable portion of the supersonic gas jet from the injector continuing beyond the Mach disk or shock diamond at the beginning of the funnel and continuing through until the end. The most effective resolution is the us of a jet disrupter that consists of a 9 mm diameter brass disk suspended perpendicular to the gas flow in the center of the ion funnel. [ 5 ]
Ion funnels are frequently used in mass spectroscopy devices to collect ions from an ionization source. Previous devices lacking an ion funnel often lost ions during the transition from ionization source to the detector of the mass spectrometer. This loss was due to the increasing number of collisions undergone by ions with other gas molecules present in the atmosphere. The introduction of the ion funnel greatly reduced the amount of ions lost during experiments by guiding ions towards a desired destination, [ 8 ] and through modification of the number of inlets is also able to increases sensitivity of measurements taken by the mass spectrometer. Multiple inlets allow multiple electrospray emitters, reducing the flow through each individual emitter. This creates many highly efficient electrosprays at low flow rates. [ 5 ] Multiple inlets also improve sensitivity, with a linearly arranged 19 electrospray emitter coupled to 19 inlets operating at 18 Torr giving a nine-fold increase compared to a single inlet. [ 5 ]
Proton transfer reaction mass spectrometry has traditionally used drift tubes as ion traps. However, radio frequency ion funnels offer an attractive alternative, as they improve compound specific sensitivity significantly. This is due to increasing the effective reaction time and focusing the ions. The same pressure ranges are required for ion funnels and drift tubes, so the technology is not difficult to implement. Ion funnels have been shown to favor transmission of ions with high m/z. [ 9 ]
Breath analysis is a convenient and non-invasive way to detect chemicals in a bodily system such as alcohol content to determine intoxication, monitor the levels of anesthetics in the body during surgical procedures, and identify performance-enhancing substances in the system of athletes. However, conventional techniques are ineffective at low concentrations. An electrospray ionization interface assisted by an ion funnel used in a linear trap quadrupole Fourier-transform ion cyclotron resonance mass spectrometer was shown to greatly increase sensitivity with high resolution. [ 10 ] | https://en.wikipedia.org/wiki/Ion_funnel |
An Ion Gun typically is an instrument that generates a beam of heavy ions with a well defined energy distribution. The ion beam is produced from a plasma that has been confined within a volume. Ions of a particular energy are extracted, accelerated, collimated and/or focused. The ion gun is composed of an ion source , extraction grid structure and a collimation/lensing structure. The plasma can be made up of an inert or reactive gas (e.g. N + and O + ) or an easily condensable substance (e.g. C + and B + ). The plasma can be formed from molecules that contain the substance which will form the beam, in which case, these molecules must be fragmented then ionized (e.g. H and CH 4 can together be fragmented and ionized to create a beam for depositing diamond-like carbon films).
The ion current density (or similarly the ion flux), the ion energy spread, and the resolution of the ion beam are key factors in ion gun design. The ion current density is controlled by the ion source , the energy spread is determined primarily by the extraction grid, and the resolution is determined primarily by the optical column.
The ion gun is an important component in surface science in that it provides the scientist with a means to sputter etch a surface and generate an elemental or chemical depth profile. [ 1 ] Modern ion guns can produce beam energies from 10eV to more than 10keV.
A Nanocoulombmeter in combination with a Faraday cup can be used
to detect and measure the beams emitted from ion guns.
The term "ion gun" might also refer to an accelerator of any charged particle. See the following: | https://en.wikipedia.org/wiki/Ion_gun |
Ion implantation is a low-temperature process by which ions of one element are accelerated into a solid target, thereby changing the target's physical, chemical, or electrical properties. Ion implantation is used in semiconductor device fabrication and in metal finishing, as well as in materials science research. The ions can alter the elemental composition of the target (if the ions differ in composition from the target) if they stop and remain in the target. Ion implantation also causes chemical and physical changes when the ions impinge on the target at high energy. The crystal structure of the target can be damaged or even destroyed by the energetic collision cascades , and ions of sufficiently high energy (tens of MeV) can cause nuclear transmutation .
Ion implantation equipment typically consists of an ion source , where ions of the desired element are produced, an accelerator , where the ions are electrostatically accelerated to a high energy or using radiofrequency, and a target chamber, where the ions impinge on a target, which is the material to be implanted. Thus ion implantation is a special case of particle radiation . Each ion is typically a single atom or molecule, and thus the actual amount of material implanted in the target is the integral over time of the ion current. This amount is called the dose. The currents supplied by implants are typically small (micro-amperes), and thus the dose which can be implanted in a reasonable amount of time is small. Therefore, ion implantation finds application in cases where the amount of chemical change required is small.
Typical ion energies are in the range of 10 to 500 keV (1,600 to 80,000 aJ). Energies in the range 1 to 10 keV (160 to 1,600 aJ) can be used, but result in a penetration of only a few nanometers or less. Energies lower than this result in very little damage to the target, and fall under the designation ion beam deposition . Higher energies can also be used: accelerators capable of 5 MeV (800,000 aJ) are common. However, there is often great structural damage to the target, and because the depth distribution is broad ( Bragg peak ), the net composition change at any point in the target will be small.
The energy of the ions, as well as the ion species and the composition of the target determine the depth of penetration of the ions in the solid: A monoenergetic ion beam will generally have a broad depth distribution. The average penetration depth is called the range of the ions. Under typical circumstances ion ranges will be between 10 nanometers and 1 micrometer. Thus, ion implantation is especially useful in cases where the chemical or structural change is desired to be near the surface of the target. Ions gradually lose their energy as they travel through the solid, both from occasional collisions with target atoms (which cause abrupt energy transfers) and from a mild drag from overlap of electron orbitals, which is a continuous process. The loss of ion energy in the target is called stopping and can be simulated with the binary collision approximation method.
Accelerator systems for ion implantation are generally classified into medium current (ion beam currents between 10 μA and ~2 mA), high current (ion beam currents up to ~30 mA), high energy (ion energies above 200 keV and up to 10 MeV), and very high dose (efficient implant of dose greater than 10 16 ions/cm 2 ). [ 1 ] [ 2 ] [ 3 ]
All varieties of ion implantation beamline designs contain general groups of functional components (see image). The first major segment of an ion beamline includes an ion source used to generate the ion species. The source is closely coupled to biased electrodes for extraction of the ions into the beamline and most often to some means of selecting a particular ion species for transport into the main accelerator section.
The ion source is often made of materials with a high melting point such as tungsten, tungsten doped with lanthanum oxide (lanthanated tungsten), molybdenum and tantalum. Lanthanum oxide helps extend the life of the ion source. [ 4 ] Often, inside the ion source a plasma is created between two tungsten electrodes, called reflectors, using a gas often based on fluorine or hydrogen containing the ion to be implanted whether it is germanium , boron , or silicon , such as boron trifluoride, [ 5 ] boron difluoride, [ 6 ] germanium tetrafluoride or silicon tetrafluoride. [ 7 ] Arsine gas or phosphine gas can be used in the ion source to provide arsenic or phosphorus respectively for implantation. [ 8 ] The ion source also has an indirectly heated cathode. Alternatively this heated cathode can be used as one of the reflectors, eliminating the need for a dedicated one, [ 9 ] [ 10 ] [ 11 ] or a directly heated cathode is used. [ 12 ]
Oxygen-based gases (oxides) can be used to provide ions for implantation such as carbon dioxide for implanting carbon . Hydrogen or hydrogen with xenon, krypton or argon may be added to the plasma to delay the degradation of tungsten components due to the halogen cycle. [ 7 ] [ 11 ] [ 13 ] [ 14 ] The hydrogen can come from a high pressure cylinder or from a hydrogen generator that uses electrolysis. [ 15 ] Repellers at each end of the ion source continually move the atoms from one end of the ion source to the other, resembling two mirrors pointed at each other constantly reflecting light. [ 9 ]
The ions are extracted from the source by an extraction electrode outside the ion source through a slit shaped aperture in the source, [ 16 ] [ 17 ] then the ion beam then passes through an analysis magnet to select the ions that will be implanted and then passes through one or two [ 18 ] linear accelerators (linacs) [ 19 ] that accelerate the ions before they reach the wafer in a process chamber. [ 19 ] In medium current ion implanters there is also a neutral ion trap before the process chamber to remove neutral ions from the ion beam. [ 20 ]
Some dopants such as aluminum, are often not provided to the ion source as a gas but as a solid compound based on Chlorine or Iodine that is vaporized in a nearby crucible such as Aluminium iodide or Aluminium chloride or as a solid sputtering target inside the ion source made of Aluminium oxide or Aluminium nitride . [ 15 ] Implanting antimony often requires the use of a vaporizer attached to the ion source, in which antimony trifluoride, antimony trioxide, or solid antimony are vaporized in a crucible and a carrier gas is used to route the vapors to an adjacent ion source, although it can also be implanted from a gas containing fluorine such as antimony hexafluoride or vaporized from liquid antimony pentafluoride. [ 7 ] Gallium, Selenium and Indium are often implanted from solid sources such as selenium dioxide for selenium although it can also be implanted from hydrogen selenide. Crucibles often last 60–100 hours and prevent ion implanters from changing recipes or process parameters in less than 20–30 minutes. Ion sources can often last 300 hours. [ 21 ] [ 7 ]
The "mass" selection (just like in mass spectrometer ) is often accompanied by passage of the extracted ion beam through a magnetic field region with an exit path restricted by blocking apertures, or "slits", that allow only ions with a specific value of the product of mass and velocity/charge to continue down the beamline. If the target surface is larger than the ion beam diameter and a uniform distribution of implanted dose is desired over the target surface, then some combination of beam scanning and wafer motion is used. Finally, the implanted surface is coupled with some method for collecting the accumulated charge of the implanted ions so that the delivered dose can be measured in a continuous fashion and the implant process stopped at the desired dose level. [ 22 ]
Semiconductor doping with boron, phosphorus, or arsenic is a common application of ion implantation. When implanted in a semiconductor, each dopant atom can create a charge carrier in the semiconductor after annealing . Annealing is necessary after ion implantation to activate dopants and can be carried out using a tube or batch furnace, Rapid Thermal Processing, flash lamp anneal, laser anneal or other annealing techniques. A hole can be created for a p-type dopant, and an electron for an n-type dopant. This modifies the conductivity of the semiconductor in its vicinity. The technique is used, for example, for adjusting the threshold voltage of a MOSFET . Ion implantation is practical due to the high sensitivity of semiconductor devices to foreign atoms, as ion implantation does not deposit large numbers of atoms. [ 2 ] Sometimes such as during the manufacturing of SiC devices, ion implantation is carried out while heating the SiC wafer to 500 °C. [ 23 ] This is known as a hot implant and it is used to control damage to the surface of the semiconductor. [ 24 ] [ 25 ] [ 26 ] Cryogenic implants (Cryo-implants) can have the same effect. [ 27 ]
The energies used in doping often vary from 1 KeV to 3 MeV and it is not possible to build an ion implanter capable of providing ions at any energy due to physical limitations. To increase the throughput of ion implanters, efforts have been made to increase the current of the beam created by the implanter. [ 2 ] The beam can be scanned across the wafer magnetically, electrostatically, [ 28 ] mechanically or with a combination of these techniques. [ 29 ] [ 30 ] [ 31 ] A mass analyzer magnet is used to select the ions that will be implanted on the wafer. [ 32 ] Ion implantation is also used in displays containing LTPS transistors. [ 19 ]
Ion implantation was developed as a method of producing the p-n junction of photovoltaic devices in the late 1970s and early 1980s, [ 33 ] along with the use of pulsed-electron beam for rapid annealing, [ 34 ] although pulsed-electron beam for rapid annealing has not to date been used for commercial production. Ion implantation is not used in most photovoltaic silicon cells, instead, thermal diffusion doping is used. [ 35 ]
One prominent method for preparing silicon on insulator (SOI) substrates from conventional silicon substrates is the SIMOX (separation by implantation of oxygen) process, wherein a buried high dose oxygen implant is converted to silicon oxide by a high temperature annealing process.
Mesotaxy is the term for the growth of a crystallographically matching phase underneath the surface of the host crystal (compare to epitaxy , which is the growth of the matching phase on the surface of a substrate). In this process, ions are implanted at a high enough energy and dose into a material to create a layer of a second phase, and the temperature is controlled so that the crystal structure of the target is not destroyed. The crystal orientation of the layer can be engineered to match that of the target, even though the exact crystal structure and lattice constant may be very different. For example, after the implantation of nickel ions into a silicon wafer, a layer of nickel silicide can be grown in which the crystal orientation of the silicide matches that of the silicon.
Nitrogen or other ions can be implanted into a tool steel target (drill bits, for example). The structural change caused by the implantation produces a surface compression in the steel, which prevents crack propagation and thus makes the material more resistant to fracture. The chemical change can also make the tool more resistant to corrosion .
In some applications, for example prosthetic devices such as artificial joints, it is desired to have surfaces very resistant to both chemical corrosion and wear due to friction. Ion implantation is used in such cases to engineer the surfaces of such devices for more reliable performance. As in the case of tool steels, the surface modification caused by ion implantation includes both a surface compression which prevents crack propagation and an alloying of the surface to make it more chemically resistant to corrosion.
Ion implantation can be used to achieve ion beam mixing , i.e. mixing up atoms of different elements at an interface. This may be useful for achieving graded interfaces or strengthening adhesion between layers of immiscible materials.
Ion implantation may be used to induce nano-dimensional particles in oxides such as sapphire and silica . The particles may be formed as a result of precipitation of the ion implanted species, they may be formed as a result of the production of a mixed oxide species that contains both the ion-implanted element and the oxide substrate, and they may be formed as a result of a reduction of the substrate, first reported by Hunt and Hampikian. [ 36 ] [ 37 ] [ 38 ] Typical ion beam energies used to produce nanoparticles range from 50 to 150 keV, with ion fluences that range from 10 16 to 10 18 ions/cm 2 . [ 39 ] [ 40 ] [ 41 ] [ 42 ] [ 43 ] [ 44 ] [ 45 ] [ 46 ] [ 47 ] The table below summarizes some of the work that has been done in this field for a sapphire substrate. A wide variety of nanoparticles can be formed, with size ranges from 1 nm on up to 20 nm and with compositions that can contain the implanted species, combinations of the implanted ion and substrate, or that are comprised solely from the cation associated with the substrate.
Composite materials based on dielectrics such as sapphire that contain dispersed metal nanoparticles are promising materials for optoelectronics and nonlinear optics . [ 43 ]
Each individual ion produces many point defects in the target crystal on impact such as vacancies and interstitials. Vacancies are crystal lattice points unoccupied by an atom: in this case the ion collides with a target atom, resulting in transfer of a significant amount of energy to the target atom such that it leaves its crystal site. This target atom then itself becomes a projectile in the solid, and can cause successive collision events .
Interstitials result when such atoms (or the original ion itself) come to rest in the solid, but find no vacant space in the lattice to reside. These point defects can migrate and cluster with each other, resulting in dislocation loops and other defects.
Because ion implantation causes damage to the crystal structure of the target which is often unwanted, ion implantation processing is often followed by a thermal annealing. This can be referred to as damage recovery.
The amount of crystallographic damage can be enough to completely amorphize the surface of the target: i.e. it can become an amorphous solid (such a solid produced from a melt is called a glass ). In some cases, complete amorphization of a target is preferable to a highly defective crystal: An amorphized film can be regrown at a lower temperature than required to anneal a highly damaged crystal. Amorphisation of the substrate can occur as a result of the beam damage. For example, yttrium ion implantation into sapphire at an ion beam energy of 150 keV to a fluence of 5*10 16 Y + /cm 2 produces an amorphous glassy layer approximately 110 nm in thickness, measured from the outer surface. [Hunt, 1999]
Some of the collision events result in atoms being ejected ( sputtered ) from the surface, and thus ion implantation will slowly etch away a surface. The effect is only appreciable for very large doses.
If there is a crystallographic structure to the target, and especially in semiconductor substrates where the crystal structure is more open, particular crystallographic directions offer much lower stopping than other directions. The result is that the range of an ion can be much longer if the ion travels exactly along a particular direction, for example the <110> direction in silicon and other diamond cubic materials. [ 48 ] This effect is called ion channelling , and, like all the channelling effects, is highly nonlinear, with small variations from perfect orientation resulting in extreme differences in implantation depth. For this reason, most implantation is carried out a few degrees off-axis, where tiny alignment errors will have more predictable effects.
Ion channelling can be used directly in Rutherford backscattering and related techniques as an analytical method to determine the amount and depth profile of damage in crystalline thin film materials.
In fabricating wafers , toxic materials such as arsine and phosphine are often used in the ion implanter process. Other common carcinogenic , corrosive , flammable , or toxic elements include antimony , arsenic , phosphorus , and boron . Semiconductor fabrication facilities are highly automated, but residue of hazardous elements in machines can be encountered during servicing and in vacuum pump hardware.
High voltage power supplies used in ion accelerators necessary for ion implantation can pose a risk of electrical injury . In addition, high-energy atomic collisions can generate X-rays and, in some cases, other ionizing radiation and radionuclides . In addition to high voltage, particle accelerators such as radio frequency linear particle accelerators and laser wakefield plasma accelerators present other hazards. | https://en.wikipedia.org/wiki/Ion_implantation |
Ion implantation-induced nanoparticle formation is a technique for creating nanometer -sized particles for use in electronics .
Ion Implantation is a technique extensively used in the field of materials science for material modification. The effect it has on nanomaterials allows manipulation of mechanical, electronic, morphological, and optical properties. [ 1 ]
One-dimensional nano-materials are an important contributor to the creation of nano-devices such as field effect transistors , nanogenerators and solar cells . The offer the potential of high integration density, lower power consumption , higher speed and super high frequency .
The effects of ion implantation varies according to multiple variables. Collision cascade may occur during implantation and this causes of interstitials and vacancies in target materials (although these defects may be mitigated through dynamic annealing). Collision modes are nuclear collision, electron collision and charge exchange . Another process is the sputtering effect, which significantly affects the morphology and shape of nano-materials.
This nanotechnology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ion_implantation-induced_nanoparticle_formation |
Ion interaction chromatography ( ion-pair chromatography ) is a laboratory technique for separating ions with chromatography . In this technique ions are mixed with ion pairing reagents (IPR). [ 1 ] The analyte combines with its reciprocal ion in the IPR, this corresponds to retention time . Often organic salts are selected to pair with solute(s) . The formation of this pair affects the interaction of the pair with the mobile phase and the stationary phase . [ 2 ]
This article related to chromatography is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ion_interaction_chromatography |
Ion layer gas reaction (ILGAR®) is a non-vacuum, thin-film deposition technique developed and patented [ 1 ] by the group of Professor Dr. Christian-Herbert Fischer at the Helmholtz-Zentrum Berlin for materials and energy in Berlin, Germany. It is a sequential and cyclic process that enables the deposition of semiconductor thin films, mainly for (although not restricted to) photovoltaic applications, specially chalcopyrite absorber layers and buffer layers. The ILGAR technique was awarded as German High Tech Champion 2011 by the Fraunhofer Society . [ 2 ]
ILGAR is a chemical process that allows for the deposition of layers in a homogeneous, adherent and mechanically stable form without using vacuum or high temperatures. It is a sequential and cyclic process which can be automated and scaled up. It consists basically of the following steps:
These steps are repeated until the desired layer thickness is obtained.
In the case of spray-ILGAR, the spray deposition of the ionic layer is performed using similar equipment to atmospheric pressure aerosol assisted chemical vapour deposition or spray pyrolysis.
Spray pyrolysis can be regarded as a simplified version of the spray ILGAR process, where there is no reaction of the precursor layer with a reactant gas.
The cyclical nature of this process makes it similar to atomic layer deposition (ALD) , which is also used for buffer layer deposition.
The applications of the ILGAR and spray-pyrolysis techniques at the Helmholtz-Zentrum Berlin lie mainly in the field of chalcopyrite thin-film solar cells, although these techniques can be used for other applications involving substrate coating with thin films.
The following list summarizes the applications of these techniques:
The advantage of ILGAR compared to chemical bath deposition (CBD) lies in the fact that it is easier to deposit high quality precursor layers and convert them to the chalcogenide than to directly deposit chalcogenide thin films. It is also possible to grow films with graded properties or compositions by changing the precursors or the process parameters. Furthermore, ILGAR is an in-line process whereas chemical bath deposition is intrinsically a batch process . | https://en.wikipedia.org/wiki/Ion_layer_gas_reaction |
Ion plating ( IP ) is a physical vapor deposition (PVD) process that is sometimes called ion assisted deposition (IAD) or ion vapor deposition (IVD) and is a modified version of vacuum deposition . Ion plating uses concurrent or periodic bombardment of the substrate, and deposits film by atomic-sized energetic particles called ions . Bombardment prior to deposition is used to sputter clean the substrate surface. During deposition the bombardment is used to modify and control the properties of the depositing film. It is important that the bombardment be continuous between the cleaning and the deposition portions of the process to maintain an atomically clean interface. If this interface is not properly cleaned, then it can result into a weaker coating or poor adhesion.
They are many different processes to vacuum deposited coatings in which they are used for various applications such as corrosion resistance and wear on the material. [ 1 ]
In ion plating, the energy, flux and mass of the bombarding species along with the ratio of bombarding particles to depositing particles are important processing variables. The depositing material may be vaporized either by evaporation, sputtering (bias sputtering), arc vaporization or by decomposition of a chemical vapor precursor chemical vapor deposition (CVD). The energetic particles used for bombardment are usually ions of an inert or reactive gas , or, in some cases, ions of the condensing film material ("film ions"). Ion plating can be done in a plasma environment where ions for bombardment are extracted from the plasma or it may be done in a vacuum environment where ions for bombardment are formed in a separate ion gun . The latter ion plating configuration is often called Ion Beam Assisted Deposition (IBAD). By using a reactive gas or vapor in the plasma, films of compound materials can be deposited.
Ion plating is used to deposit hard coatings of compound materials on tools, adherent metal coatings, optical coatings with high densities, and conformal coatings on complex surfaces.
The ion plating process was first described in the technical literature by Donald M. Mattox of Sandia National Laboratories in 1964. [ 3 ] As described by this article, it was used initially to enhance film adhesion and improve surface coverage. [ 4 ]
This process was first used in the 1960's and was continued throughout the time by using specific cleaning techniques and film growth reactive and quasi reactive deposition techniques. Sputter cleaning has been used since the 1950's for cleaning scientific surfaces. In the 1970's, high-rate DC magnetron sputtering has shown that bombardment densified the films and helped the hardness of materials. As we further progressed, we learned in 1983 that bombardment was used as concurrent bombardment of inserted gas ions. [ 4 ] | https://en.wikipedia.org/wiki/Ion_plating |
Ion semiconductor sequencing is a method of DNA sequencing based on the detection of hydrogen ions that are released during the polymerization of DNA . This is a method of "sequencing by synthesis", during which a complementary strand is built based on the sequence of a template strand .
A microwell containing a template DNA strand to be sequenced is flooded with a single species of deoxyribonucleotide triphosphate (dNTP). If the introduced dNTP is complementary to the leading template nucleotide , it is incorporated into the growing complementary strand. This causes the release of a hydrogen ion that triggers an ion-sensitive field-effect transistor (ISFET) sensor, which indicates that a reaction has occurred. If homopolymer repeats are present in the template sequence, multiple dNTP molecules will be incorporated in a single cycle. This leads to a corresponding number of released hydrogens and a proportionally higher electronic signal.
This technology differs from other sequencing -by-synthesis technologies in that no modified nucleotides or optics are used. Ion semiconductor sequencing may also be referred to as Ion Torrent sequencing, pH-mediated sequencing, silicon sequencing, or semiconductor sequencing.
The technology was licensed from DNA Electronics Ltd, [ 1 ] [ 2 ] developed by Ion Torrent Systems Inc. and was released in February 2010. [ 3 ] Ion Torrent have marketed their machine as a rapid, compact and economical sequencer that can be utilized in a large number of laboratories as a bench top machine. [ 4 ] Roche's 454 Life Sciences is partnering with DNA Electronics on the development of a long-read, high-density semiconductor sequencing platform using this technology. [ 5 ]
In nature, the incorporation of a deoxyribonucleoside triphosphate (dNTP) into a growing DNA strand involves the formation of a covalent bond and the release of pyrophosphate and a positively charged hydrogen ion . [ 1 ] [ 3 ] [ 6 ] A dNTP will only be incorporated if it is complementary to the leading unpaired template nucleotide. Ion semiconductor sequencing exploits these facts by determining if a hydrogen ion is released upon providing a single species of dNTP to the reaction.
Microwells on a semiconductor chip that each contain many copies of one single-stranded template DNA molecule to be sequenced and DNA polymerase are sequentially flooded with unmodified A, C, G or T dNTP. [ 3 ] [ 7 ] [ 8 ] If an introduced dNTP is complementary to the next unpaired nucleotide on the template strand it is incorporated into the growing complementary strand by the DNA polymerase. [ 9 ] If the introduced dNTP is not complementary there is no incorporation and no biochemical reaction. The hydrogen ion that is released in the reaction changes the pH of the solution, which is detected by an ISFET. [ 1 ] [ 3 ] [ 7 ] The unattached dNTP molecules are washed out before the next cycle when a different dNTP species is introduced. [ 7 ]
Beneath the layer of microwells is an ion sensitive layer, below which is an ISFET ion sensor. [ 4 ] All layers are contained within a CMOS semiconductor chip, similar to that used in the electronics industry. [ 4 ] [ 10 ]
Each chip contains an array of microwells with corresponding ISFET detectors. [ 7 ] Each released hydrogen ion then triggers the ISFET ion sensor. The series of electrical pulses transmitted from the chip to a computer is translated into a DNA sequence, with no intermediate signal conversion required. [ 7 ] [ 11 ] Because nucleotide incorporation events are measured directly by electronics, the use of labeled nucleotides and optical measurements are avoided. [ 4 ] [ 10 ] Signal processing and DNA assembly can then be carried out in software.
The per base accuracy achieved on the Ion Torrent Ion semiconductor sequencer as of February 2011 was 99.6% based on 50 base reads, with 100 Mb per run. [ 12 ] The read-length as of February 2011 was 100 base pairs . [ 12 ] The accuracy for homopolymer repeats of 5 repeats in length was 98%. [ 12 ] Later releases show a read length of 400 base pairs [ 13 ] These figures have not yet been independently verified outside of the company.
The major benefits of ion semiconductor sequencing are rapid sequencing speed and low upfront and operating costs. [ 8 ] [ 11 ] This has been enabled by the avoidance of modified nucleotides and optical measurements.
Because the system records natural polymerase-mediated nucleotide incorporation events, sequencing can occur in real-time. In reality, the sequencing rate is limited by the cycling of substrate nucleotides through the system. [ 14 ] Ion Torrent Systems Inc., the developer of the technology, claims that each incorporation measurement takes 4 seconds and each run takes about one hour, during which 100-200 nucleotides are sequenced. [ 11 ] [ 15 ] If the semiconductor chips are improved (as predicted by Moore’s law ), the number of reads per chip (and therefore per run) should increase. [ 11 ]
The cost of acquiring a pH-mediated sequencer at time of launch was priced at around $50,000 USD, excluding sample preparation equipment and a server for data analysis. [ 8 ] [ 11 ] [ 15 ] The cost per run is also significantly lower than that of alternative automated sequencing methods, at roughly $1,000. [ 8 ] [ 12 ]
If homopolymer repeats of the same nucleotide (e.g. TTTTT ) are present on the template strand (strand to be sequenced) then multiple introduced nucleotides are incorporated and more hydrogen ions are released in a single cycle. This results in a greater pH change and a proportionally greater electronic signal. [ 11 ] This is a limitation of the system in that it is difficult to enumerate long repeats. This limitation is shared by other techniques that detect single nucleotide additions such as pyrosequencing . [ 16 ] Signals generated from a high repeat number are difficult to differentiate from repeats of a similar but different number; e.g. , homorepeats of length 7 are difficult to differentiate from those of length 8.
Another limitation of this system is the short read length compared to other sequencing methods such as Sanger sequencing or pyrosequencing. Longer read lengths are beneficial for de novo genome assembly . Ion Torrent semiconductor sequencers produce an average read length of approximately 400 nucleotides per read. [ 3 ] [ 8 ]
The throughput is currently lower than that of other high-throughput sequencing technologies, although the developers hope to change this by increasing the density of the chip . [ 3 ]
The developers of Ion Torrent semiconductor sequencing have marketed it as a rapid, compact and economical sequencer that can be utilized in a large number of laboratories as a bench top machine. [ 3 ] [ 4 ] The company hopes that their system will take sequencing outside of specialized centers and into the reach of hospitals and smaller laboratories. [ 17 ] A January 2011 New York Times article, "Taking DNA Sequencing to the Masses" , underlines these ambitions. [ 17 ]
Due to the ability of alternative sequencing methods to achieve a greater read length (and therefore being more suited to whole genome analysis ) this technology may be best suited to small scale applications such as microbial genome sequencing, microbial transcriptome sequencing, targeted sequencing, amplicon sequencing, or for quality testing of sequencing libraries. [ 3 ] [ 8 ] [ 18 ] | https://en.wikipedia.org/wiki/Ion_semiconductor_sequencing |
An ion source is a device that creates atomic and molecular ions . [ 1 ] Ion sources are used to form ions for mass spectrometers , optical emission spectrometers , particle accelerators , ion implanters and ion engines .
Electron ionization is widely used in mass spectrometry, particularly for organic molecules. The gas phase reaction producing electron ionization is
where M is the atom or molecule being ionized, e − {\displaystyle {\ce {e^-}}} is the electron, and M + ∙ {\displaystyle {\ce {M^{+\bullet }}}} is the resulting ion.
The electrons may be created by an arc discharge between a cathode and an anode .
An electron beam ion source (EBIS) is used in atomic physics to produce highly charged ions by bombarding atoms with a powerful electron beam . [ 2 ] [ 3 ] Its principle of operation is shared by the electron beam ion trap .
Electron capture ionization (ECI) is the ionization of a gas phase atom or molecule by attachment of an electron to create an ion of the form A −• . The reaction is
where the M over the arrow denotes that to conserve energy and momentum a third body is required (the molecularity of the reaction is three).
Electron capture can be used in conjunction with chemical ionization . [ 4 ]
An electron capture detector is used in some gas chromatography systems. [ 5 ]
Chemical ionization (CI) is a lower energy process than electron ionization because it involves ion/molecule reactions rather than electron removal. [ 6 ] The lower energy yields less fragmentation , and usually a simpler spectrum . A typical CI spectrum has an easily identifiable molecular ion. [ 7 ]
In a CI experiment, ions are produced through the collision of the analyte with ions of a reagent gas in the ion source. Some common reagent gases include: methane , ammonia , and isobutane . Inside the ion source, the reagent gas is present in large excess compared to the analyte. Electrons entering the source will preferentially ionize the reagent gas. The resultant collisions with other reagent gas molecules will create an ionization plasma . Positive and negative ions of the analyte are formed by reactions with this plasma. For example, protonation occurs by
Charge-exchange ionization (also known as charge-transfer ionization) is a gas phase reaction between an ion and an atom or molecule in which the charge of the ion is transferred to the neutral species. [ 8 ]
Chemi-ionization is the formation of an ion through the reaction of a gas phase atom or molecule with an atom or molecule in an excited state . [ 9 ] [ 10 ] Chemi-ionization can be represented by
where G is the excited state species (indicated by the superscripted asterisk), and M is the species that is ionized by the loss of an electron to form the radical cation (indicated by the superscripted "plus-dot").
Associative ionization is a gas phase reaction in which two atoms or molecules interact to form a single product ion. [ 11 ] [ 12 ] [ 13 ] One or both of the interacting species may have excess internal energy .
For example,
where species A with excess internal energy (indicated by the asterisk) interacts with B to form the ion AB + .
Penning ionization is a form of chemi-ionization involving reactions between neutral atoms or molecules. [ 14 ] [ 15 ] The process is named after the Dutch physicist Frans Michel Penning who first reported it in 1927. [ 16 ] Penning ionization involves a reaction between a gas-phase excited-state atom or molecule G * and a target molecule M resulting in the formation of a radical molecular cation M +. , an electron e − , and a neutral gas molecule G: [ 17 ]
Penning ionization occurs when the target molecule has an ionization potential lower than the internal energy of the excited-state atom or molecule.
Associative Penning ionization can proceed via
Surface Penning ionization (also known as Auger deexcitation) refers to the interaction of the excited-state gas with a bulk surface S, resulting in the release of an electron according to
Ion-attachment ionization is similar to chemical ionization in which a cation is attached to the analyte molecule in a reactive collision:
Where M is the analyte molecule, X + is the cation and A is a non-reacting collision partner. [ 18 ]
In a radioactive ion source, a small piece of radioactive material, for instance 63 Ni or 241 Am , is used to ionize a gas. [ citation needed ] This is used in ionization smoke detectors and ion mobility spectrometers .
These ion sources use a plasma source or electric discharge to create ions.
Ions can be created in an inductively coupled plasma, which is a plasma source in which the energy is supplied by electrical currents which are produced by electromagnetic induction , that is, by time-varying magnetic fields . [ 19 ]
Microwave induced plasma ion sources are capable of exciting electrodeless gas discharges to create ions for trace element mass spectrometry. [ 20 ] [ 21 ] A microwave plasma has high frequency electromagnetic radiation in the GHz range. It is capable of exciting electrodeless gas discharges . If applied in surface-wave-sustained mode , they are especially well suited to generate large-area plasmas of high plasma density. If they are both in surface-wave and resonator mode , they can exhibit a high degree of spatial localization. This allows to spatially separate the location of plasma generations from the location of surface processing. Such a separation (together with an appropriate gas-flow scheme) may help reduce the negative effect, that particles released from a processed substrate may have on the plasma chemistry of the gas phase .
The ECR ion source makes use of the electron cyclotron resonance to ionize a plasma. Microwaves are injected into a volume at the frequency corresponding to the electron cyclotron resonance, defined by the magnetic field applied to a region inside the volume. The volume contains a low pressure gas.
Ions can be created in an electric glow discharge. A glow discharge is a plasma formed by the passage of electric current through a low-pressure gas. It is created by applying a voltage between two metal electrodes in an evacuated chamber containing gas. When the voltage exceeds a certain value, called the striking voltage , the gas forms a plasma.
A duoplasmatron is a type of glow discharge ion source that consists of a hot cathode or cold cathode that produces a plasma that is used to ionize a gas. [ 1 ] [ 22 ] THey can produce positive or negative ions. [ 23 ] They are used for secondary ion mass spectrometry, ion beam etching, and high-energy physics. [ 24 ] [ 25 ] [ 26 ]
In a flowing plasma afterglow, ions are formed in a flow of inert gas, typically helium or argon . [ 27 ] [ 28 ] [ 29 ] Reagents are added downstream to create ion products and study reaction rates. Flowing-afterglow mass spectrometry is used for trace gas analysis for organic compounds. [ 30 ] [ 31 ]
Electric spark ionization is used to produce gas phase ions from a solid sample. When incorporated with a mass spectrometer the complete instrument is referred to as a spark ionization mass spectrometer or as a spark source mass spectrometer (SSMS). [ 32 ]
A closed drift ion source uses a radial magnetic field in an annular cavity in order to confine electrons for ionizing a gas. They are used for ion implantation and for space propulsion ( Hall-effect thrusters ).
Photoionization is the ionization process in which an ion is formed from the interaction of a photon with an atom or molecule. [ 33 ]
In multi-photon ionization (MPI), several photons of energy below the ionization threshold may actually combine their energies to ionize an atom.
Resonance-enhanced multiphoton ionization (REMPI) is a form of MPI in which one or more of the photons accesses a bound-bound transition that is resonant in the atom or molecule being ionized.
Atmospheric pressure photoionization (APPI) uses a source of photons, usually a vacuum UV (VUV) lamp, to ionize the analyte with single photon ionization process. Analogous to other atmospheric pressure ion sources, a spray of solvent is heated to relatively high temperatures (above 400 degrees Celsius) and sprayed with high flow rates of nitrogen for desolvation. The resulting aerosol is subjected to UV radiation to create ions. Atmospheric-pressure laser ionization uses UV laser light sources to ionize the analyte via MPI.
Field desorption refers to an ion source in which a high-potential electric field is applied to an emitter with a sharp surface, such as a razor blade, or more commonly, a filament from which tiny "whiskers" have formed. [ 34 ] This results in a very high electric field which can result in ionization of gaseous molecules of the analyte. Mass spectra produced by FI have little or no fragmentation. They are dominated by molecular radical cations M +. and less often, protonated molecules [M + H] +
Particle bombardment with atoms is called fast atom bombardment (FAB) and bombardment with atomic or molecular ions is called secondary ion mass spectrometry (SIMS). [ 35 ] Fission fragment ionization uses ionic or neutral atoms formed as a result of the nuclear fission of a suitable nuclide , for example the Californium isotope 252 Cf.
In FAB the analytes is mixed with a non-volatile chemical protection environment called a matrix and is bombarded under vacuum with a high energy (4000 to 10,000 electron volts ) beam of atoms. [ 36 ] The atoms are typically from an inert gas such as argon or xenon . Common matrices include glycerol , thioglycerol , 3-nitrobenzyl alcohol (3-NBA), 18-crown-6 ether, 2-nitrophenyloctyl ether , sulfolane , diethanolamine , and triethanolamine . This technique is similar to secondary ion mass spectrometry and plasma desorption mass spectrometry.
Secondary ion mass spectrometry (SIMS) is used to analyze the composition of solid surfaces and thin films by sputtering the surface of the specimen with a focused primary ion beam and collecting and analyzing ejected secondary ions. The mass/charge ratios of these secondary ions are measured with a mass spectrometer to determine the elemental, isotopic, or molecular composition of the surface to a depth of 1 to 2 nm.
In a liquid metal ion source (LMIS), a metal (typically gallium ) is heated to the liquid state and provided at the end of a capillary or a needle. Then a Taylor cone is formed under the application of a strong electric field. As the cone's tip get sharper, the electric field becomes stronger, until ions are produced by field evaporation. These ion sources are particularly used in ion implantation or in focused ion beam instruments.
Plasma desorption ionization mass spectrometry (PDMS), also called fission fragment ionization, is a mass spectrometry technique in which ionization of material in a solid sample is accomplished by bombarding it with ionic or neutral atoms formed as a result of the nuclear fission of a suitable nuclide , typically the californium isotope 252 Cf. [ 37 ] [ 38 ]
Matrix-assisted laser desorption/ionization (MALDI) is a soft ionization technique. The sample is mixed with a matrix material. Upon receiving a laser pulse, the matrix absorbs the laser energy and it is thought that primarily the matrix is desorbed and ionized (by addition of a proton) by this event. The analyte molecules are also desorbed. The matrix is then thought to transfer proton to the analyte molecules (e.g., protein molecules), thus charging the analyte.
Surface-assisted laser desorption/ionization (SALDI) is a soft laser desorption technique used for analyzing biomolecules by mass spectrometry . [ 39 ] [ 40 ] In its first embodiment, it used graphite matrix. [ 39 ] At present, laser desorption/ionization methods using other inorganic matrices, such as nanomaterials , are often regarded as SALDI variants. A related method named "ambient SALDI" - which is a combination of conventional SALDI with ambient mass spectrometry incorporating the DART ion source - has also been demonstrated. [ 41 ]
Surface-enhanced laser desorption/ionization (SELDI) is a variant of MALDI that is used for the analysis of protein mixtures that uses a target modified to achieve biochemical affinity with the analyte compound. [ 42 ]
Desorption ionization on silicon (DIOS) refers to laser desorption/ionization of a sample deposited on a porous silicon surface. [ 43 ]
A laser vaporization cluster source produces ions using a combination of laser desorption ionization and supersonic expansion. [ 44 ] The Smalley source (or Smalley cluster source ) [ 45 ] was developed by Richard Smalley at Rice University in the 1980s and was central to the discovery of fullerenes in 1985. [ 46 ] [ 47 ]
In aerosol mass spectrometry with time-of-flight analysis, micrometer sized solid aerosol particles extracted from the atmosphere are simultaneously desorbed and ionized by a precisely timed laser pulse as they pass through the center of a time-of-flight ion extractor. [ 48 ] [ 49 ]
Spray ionization methods involve the formation of aerosol particles from a liquid solution and the formation of bare ions after solvent evaporation. [ 50 ]
Solvent-assisted ionization (SAI) is a method in which charged droplets are produced by introducing a solution containing analyte into a heated inlet tube of an atmospheric pressure ionization mass spectrometer. Just as in Electrospray Ionization (ESI), desolvation of the charged droplets produces multiply charged analyte ions. Volatile and nonvolatile compounds are analyzed by SAI, and high voltage is not required to achieve sensitivity comparable to ESI. [ 51 ] Application of a voltage to the solution entering the hot inlet through a zero dead volume fitting connected to fused silica tubing produces ESI-like mass spectra, but with higher sensitivity. [ 52 ] The inlet tube to the mass spectrometer becomes the ion source.
Matrix-Assisted Ionization (MAI) is similar to MALDI in sample preparation, but a laser is not required to convert analyte molecules included in a matrix compound into gas-phase ions. In MAI, analyte ions have charge states similar to electrospray ionization but obtained from a solid matrix rather than a solvent. No voltage or laser is required, but a laser can be used to obtain spatial resolution for imaging. Matrix-analyte samples are ionized in the vacuum of a mass spectrometer and can be inserted into the vacuum through an atmospheric pressure inlet. Less volatile matrices such as 2,5-dihydroxybenzoic acid require a hot inlet tube to produce analyte ions by MAI, but more volatile matrices such as 3-nitrobenzonitrile require no heat, voltage, or laser. Simply introducing the matrix-analyte sample to the inlet aperture of an atmospheric pressure ionization mass spectrometer produces abundant ions. Compounds at least as large as bovine serum albumin [66 kDa] can be ionized with this method. [ 53 ] In this method, the inlet to the mass spectrometer can be considered the ion source.
Atmospheric-pressure chemical ionization uses a solvent spray at atmospheric pressure. [ 54 ] A spray of solvent is heated to relatively high temperatures (above 400 degrees Celsius), sprayed with high flow rates of nitrogen and the entire aerosol cloud is subjected to a corona discharge that creates ions with the evaporated solvent acting as the chemical ionization reagent gas. APCI is not as "soft" (low fragmentation) an ionization technique as ESI. [ 55 ] Note that atmospheric pressure ionization (API) should not be used as a synonym for APCI. [ 56 ]
Thermospray ionization is a form of atmospheric pressure ionization in mass spectrometry . It transfers ions from the liquid phase to the gas phase for analysis. It is particularly useful in liquid chromatography-mass spectrometry . [ 57 ]
In electrospray ionization, a liquid is pushed through a very small, charged and usually metal, capillary . [ 58 ] This liquid contains the substance to be studied, the analyte , dissolved in a large amount of solvent , which is usually much more volatile than the analyte. Volatile acids, bases or buffers are often added to this solution as well. The analyte exists as an ion in solution either in its anion or cation form. Because like charges repel, the liquid pushes itself out of the capillary and forms an aerosol, a mist of small droplets about 10 μm across. The aerosol is at least partially produced by a process involving the formation of a Taylor cone and a jet from the tip of this cone. An uncharged carrier gas such as nitrogen is sometimes used to help nebulize the liquid and to help evaporate the neutral solvent in the droplets. As the solvent evaporates, the analyte molecules are forced closer together, repel each other and break up the droplets. This process is called Coulombic fission because it is driven by repulsive Coulombic forces between charged molecules. The process repeats until the analyte is free of solvent and is a bare ion. The ions observed are created by the addition of a proton (a hydrogen ion) and denoted [M + H] + , or of another cation such as sodium ion, [M + Na] + , or the removal of a proton, [M − H] − . Multiply charged ions such as [M + 2H] 2+ are often observed. For macromolecules , there can be many charge states, occurring with different frequencies; the charge can be as great as [M + 25H] 25+ , for example. [ citation needed ]
Probe electrospray ionization (PESI) is a modified version of electrospray, where the capillary for sample solution transferring is replaced by a sharp-tipped solid needle with periodic motion. [ 59 ]
Contactless atmospheric pressure ionization is a technique used for analysis of liquid and solid samples by mass spectrometry. [ 60 ] Contactless API can be operated without an additional electric power supply (supplying voltage to the source emitter), gas supply, or syringe pump . Thus, the technique provides a facile means for analyzing chemical compounds by mass spectrometry at atmospheric pressure.
Sonic spray ionization is method for creating ions from a liquid solution, for example, a mixture of methanol and water. [ 61 ] A pneumatic nebulizer is used to turn the solution into a supersonic spray of small droplets. Ions are formed when the solvent evaporates and the statistically unbalanced charge distribution on the droplets leads to a net charge and complete desolvation results in the formation of ions. Sonic spray ionization is used to analyze small organic molecules and drugs and can analyze large molecules when an electric field is applied to the capillary to help increase the charge density and generate multiple charged ions of proteins. [ 62 ]
Sonic spray ionization has been coupled with high performance liquid chromatography for the analysis of drugs. [ 63 ] [ 64 ] Oligonucleotides have been studied with this method. [ 65 ] [ 66 ] SSI has been used in a manner similar to desorption electrospray ionization [ 67 ] for ambient ionization and has been coupled with thin-layer chromatography in this manner. [ 68 ]
Ultrasonication-assisted spray ionization (UASI) is similar to the above techniques but uses an ultrasonic transducer to achieve atomization of the material and generate ions. [ 69 ] [ 70 ]
Thermal ionization (also known as surface ionization, or contact ionization) involves spraying vaporized, neutral atoms onto a hot surface, from which the atoms re-evaporate in ionic form. To generate positive ions, the atomic species should have a low ionization energy , and the surface should have a high work function . This technique is most suitable for alkali atoms (Li, Na, K, Rb, Cs) which have low ionization energies and are easily evaporated. [ 71 ]
To generate negative ions, the atomic species should have a high electron affinity , and the surface should have a low work function. This second approach is most suited for halogen atoms Cl, Br, I, At. [ 72 ]
In ambient ionization, ions are formed outside the mass spectrometer without sample preparation or separation. [ 73 ] [ 74 ] [ 75 ] Ions can be formed by extraction into charged electrospray droplets, thermally desorbed and ionized by chemical ionization , or laser desorbed or ablated and post-ionized before they enter the mass spectrometer.
Solid-liquid extraction based ambient ionization uses a charged spray to create a liquid film on the sample surface. [ 74 ] [ 76 ] Molecules on the surface are extracted into the solvent. The action of the primary droplets hitting the surface produces secondary droplets that are the source of ions for the mass spectrometer. Desorption electrospray ionization (DESI) creates charged droplets that are directed at a solid sample a few millimeters to a few centimeters away. The charged droplets pick up the sample through interaction with the surface and then form highly charged ions that can be sampled into a mass spectrometer. [ 77 ]
Plasma-based ambient ionization is based on an electrical discharge in a flowing gas that produces metastable atoms and molecules and reactive ions. Heat is often used to assist in the desorption of volatile species from the sample. Ions are formed by chemical ionization in the gas phase. A direct analysis in real time (DART) source operates by exposing the sample to a dry gas stream (typically helium or nitrogen) that contains long-lived electronically or vibronically excited neutral atoms or molecules (or "metastables" ). Excited states are typically formed in the DART source by creating a glow discharge in a chamber through which the gas flows. A similar method called atmospheric solids analysis probe (ASAP) uses the heated gas from ESI or APCI probes to vaporize sample placed on a melting point tube inserted into an ESI/APCI source. [ 78 ] Ionization is by APCI.
Laser-based ambient ionization is a two-step process in which a pulsed laser is used to desorb or ablate material from a sample and the plume of material interacts with an electrospray or plasma to create ions. Electrospray-assisted laser desorption/ionization (ELDI) uses a 337 nm UV laser [ 79 ] or 3 μm infrared laser [ 80 ] to desorb material into an electrospray source. Matrix-assisted laser desorption electrospray ionization (MALDESI) [ 81 ] is an atmospheric pressure ionization source for generation of multiply charged ions. An ultraviolet or infrared laser is directed onto a solid or liquid sample containing the analyte of interest and matrix desorbing neutral analyte molecules that are ionized by interaction with electrosprayed solvent droplets generating multiply charged ions. Laser ablation electrospray ionization (LAESI) is an ambient ionization method for mass spectrometry that combines laser ablation from a mid-infrared (mid-IR) laser with a secondary electrospray ionization (ESI) process.
In a mass spectrometer a sample is ionized in an ion source and the resulting ions are separated by their mass-to-charge ratio. The ions are detected and the results are displayed as spectra of the relative abundance of detected ions as a function of the mass-to-charge ratio. The atoms or molecules in the sample can be identified by correlating known masses to the identified masses or through a characteristic fragmentation pattern.
In particle accelerators an ion source creates a particle beam at the beginning of the machine, the source . The technology to create ion sources for particle accelerators depends strongly on the type of particle that needs to be generated: electrons , protons , H − ion or a Heavy ions .
Electrons are generated with an electron gun , of which there are many varieties.
Protons are generated with a plasma -based device, like a duoplasmatron or a magnetron .
H − ions are generated with a magnetron or a Penning source. A magnetron consists of a central cylindrical cathode surrounded by an anode. The discharge voltage is typically greater than 150 V and the current drain is around 40 A. A magnetic field of about 0.2 tesla is parallel to the cathode axis. Hydrogen gas is introduced by a pulsed gas valve. Caesium is often used to lower the work function of the cathode, enhancing the amount of ions that are produced. Large caesiated sources are also used for plasma heating in nuclear fusion devices.
For a Penning source , a strong magnetic field parallel to the electric field of the sheath guides electrons and ions on cyclotron spirals from cathode to cathode. Fast H-minus ions are generated at the cathodes as in the magnetron. They are slowed down due to the charge exchange reaction as they migrate to the plasma aperture. This makes for a beam of ions that is colder than the ions obtained from a magnetron.
Heavy ions can be generated with an electron cyclotron resonance ion source. The use of electron cyclotron resonance (ECR) ion sources for the production of intense beams of highly charged ions has immensely grown over the last decade. ECR ion sources are used as injectors into linear accelerators, Van-de-Graaff generators or cyclotrons in nuclear and elementary particle physics. In atomic and surface physics ECR ion sources deliver intense beams of highly charged ions for collision experiments or for the investigation of surfaces. For the highest charge states, however, Electron beam ion sources (EBIS) are needed. They can generate even bare ions of mid-heavy elements. The Electron beam ion trap (EBIT), based on the same principle, can produce up to bare uranium ions and can be used as an ion source as well.
Heavy ions can also be generated with an ion gun which typically uses the thermionic emission of electrons to ionize a substance in its gaseous state. Such instruments are typically used for surface analysis.
Gas flows through the ion source between the anode and the cathode. A positive voltage is applied to the anode. This voltage, combined with the high magnetic field between the tips of the internal and external cathodes allow a plasma to start. Ions from the plasma are repelled by the anode's electric field. This creates an ion beam. [ 83 ] | https://en.wikipedia.org/wiki/Ion_source |
Ion suppression in LC-MS and LC-MS/MS refers to reduced detector response, or signal:noise as a manifested effect of competition for ionisation efficiency in the ionisation source , between the analyte(s) of interest and other endogenous or exogenous (e.g. plasticisers extracted from plastic tubes, [ 1 ] mobile phase additives) species which have not been removed from the sample matrix during sample preparation . Ion suppression is not strictly a problem unless interfering compounds elute at the same time as the analyte of interest. In cases where ion suppressing species do co-elute with an analyte, the effects on the important analytical parameters including precision, accuracy and limit of detection (analytical sensitivity) can be extensive, severely limiting the validity of an assay's results. [ 2 ]
Since its inception as a tool of analytical chemistry , LC-MS/MS spread rapidly and indeed continues to do so in (amongst others) bioanalytical fields. One of the advantages of the technique is its selectivity for many analytes of interest. However, this high selectivity could lead to a misconception that it is always possible to simplify or (on occasion) almost completely remove the necessity for extensive sample preparation . However, during and after uptake by bioanalytical laboratories worldwide, it became apparent that there were inherent problems with detection of relatively small analyte concentrations in the complex sample matrices associated with biological fluids (e.g. blood and urine). [ 3 ]
Put simply, ion suppression describes the adverse effect on detector response due to reduced ionisation efficiency for analyte(s) of interest, resulting from the presence of species in the sample matrix which compete for ionisation, or inhibit efficient ionisation in other ways. Use of MS/MS as a means of detection may give the impression that there are no interfering species present, since no chromatographic impurities are detected. However, species which are not isobaric may still have an adverse effect on the sensitivity, accuracy and precision of the assay owing to suppression of the ionisation of the analyte of interest. [ 4 ]
Although the precise chemical and physical factors involved in ion suppression are not fully understood, it has been proposed that basicity, high concentration, mass and more intuitively, co-elution with the analyte of interest are factors which should not be ignored. [ 5 ]
The most common atmospheric pressure ionisation techniques used in LC-MS/MS are electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). APCI is less prone to pronounced ion suppression than ESI, [ 6 ] an inherent property of the respective ionisation mechanisms.
In APCI, the sole source of ion suppression can be attributed to the change of colligative properties in the solute during evaporization (King et al, J. Am. Soc. Mass Spectrom 2000, 11, 942-950).
ESI has a more complex ionisation mechanism, relying heavily on droplet charge excess and as such there are many more factors to consider when exploring the cause of ion suppression. It has been widely observed that for many analytes, at high concentrations, ESI exhibits a loss of detector response linearity , perhaps due to reduced charge excess caused by analyte saturation at the droplet surface, inhibiting subsequent ejection of gas phase ions from further inside the droplet. Thus competition for space and/or charge may be considered as a source of ion suppression in ESI. Both physical and chemical properties of analytes (e.g. basicity and surface activity) determine their inherent ionisation efficiency. Biological sample matrices naturally tend to contain many endogenous species with high basicity and surface activity, hence the total concentration of these species in the sample will quickly reach levels at which ion suppression should be expected.
Another explanation of ion suppression in ESI considers the physical properties of the droplet itself rather than the species present. High concentrations of interfering components give rise to an increased surface tension and viscosity, giving a reduction in desolvation (solvent evaporation), which is known to have a marked effect of ionisation efficiency.
The third proposed theory for ion suppression in ESI relates to the presence of non-volatile species which can either cause co-precipitation of analyte in the droplet (thus preventing ionisation) or prevent the contraction of droplet size to the critical radius required for the ion evaporation and/or charge residue mechanisms to form gas phase ions efficiently.
It is worthwhile to consider that the degree of ion suppression may be dependent on the concentration of the analyte being monitored. A higher analyte/matrix ratio can give a reduced effect of ion suppression. [ 7 ]
Since it is accepted that ion suppression has the potential to affect the other analytical parameters of any assay, a prudent approach to any LC-MS method development should include an evaluation of ion-suppression. There are two accepted protocols by which this may be achieved, described as follows.
The more comprehensive approach to assessment of ion suppression is to constantly infuse an appropriate concentration into the mobile phase flow, downstream from the analytical column, using a syringe pump and a 'tee union'. A typical sample should then be injected through the HPLC inlet as per the usual analytical parameters.
Monitoring of detector response during this experiment should yield a constant signal appropriate to the concentration of infused species. Once the sample has been injected, a drop in signal intensity (or a negative response) should be observed any time a species is ionised in the ion source. This should allow the retention time of any such species under the analytical parameters of the assay to be determined. Any species causing a negative response may be considered to be contributing to ion suppression, but only if such species co- elute with the analyte of interest.
It is also important to consider that species contributing to ion suppression may be retained by the column to a much greater extent than the analyte of interest. To this end, the detector response should be monitored for several times the usual chromatographic run time to ensure that ion suppression will not affect subsequent injections.
Another approach to evaluation of ion suppression is to make a comparison between:
There are several strategies for removal and/or negation of ion suppression. These approaches may require in-depth understanding of the ionisation mechanisms involved in different ionisation sources or may be completely independent of the physical factors involved.
If the chromatographic separation can be modified to prevent coelution of suppressing species then other approaches need not be considered. The effect of chromatographic modification may be evaluated using the detector response monitoring under constant infusion approach described previously.
An effective sample preparation protocol, usually involving either liquid-liquid extraction (LLE) or solid phase extraction (SPE) and frequently derivatisation can remove ion suppressing species from the sample matrix prior to analysis. These common approaches may also remove other interferences, such as isobaric species.
Protein precipitation is another method that can be employed for small molecule analysis. Removal of all protein species from the sample matrix may be effective in some cases, although for many analytes, ion suppressing species are not of protein origin and so this technique is often used in conjunction with extraction and derivatisation.
Dilution of sample or reducing the volume of sample injected may give a reduction of ion suppression by reducing the quantity of interfering species present, although the quantity of analyte of interest will also be reduced, making this an undesirable approach for trace analysis.
Similar is the effect of reducing the mobile phase flow rate to the nanolitre-per-minute range since, in addition to resulting in improved desolvation, the smaller droplets formed are more tolerant to the presence of non-volatile species in the sample matrix.
It is not always possible to eliminate ion suppression by sample preparation and/or chromatographic resolution. In such cases it may be possible to compensate for the effects of ion suppression on accuracy and precision (although not for analytical sensitivity) by adopting complex calibration strategies.
Using matrix matched calibration standards can compensate for ion suppression. Using this technique, calibration standards are prepared in identical sample matrix to that used for analysis (e.g. plasma) by spiking a normal sample with known concentrations of analyte. This is not always possible for biological samples, since the analyte of interest is often endogenously present in a clinically significant, albeit normal, quantity. For matrix matched calibration standards to be effective in compensating for ion suppression, the sample matrix must be free of the analyte of interest. Additionally, it is important that there is little variation in test sample composition since both the test sample and the prepared calibration sample must be affected in the same way by ion suppression. Again, in complex biological samples from different individuals, or even the same individual at a different time, there may be large fluctuations in the concentrations of ion suppressing species.
The standard addition approach involves spiking the same sample extract with several known concentrations of analyte. This technique is more robust and effective than using matrix matched standards but is labor-intensive since each sample must be prepared several times to achieve a reliable calibration.
In this approach, the sample is spiked with a species ( internal standard ) which is used to normalise the response of analyte, compensating for variables at any stage of the sample preparation and analysis, including ion suppression.
It is important that the internal standard displays very similar (ideally identical) properties, with respect to detector response (i.e. ionisation), as the analyte of interest. To simplify the selection of internal standard, most laboratories use an analogous stable isotope in an isotope dilution type analysis. The stable isotope is almost guaranteed to be chemically and physically as close as possible to the analyte of interest, hence producing an almost identical detector response in addition to behaving identically during sample preparation and chromatographic resolution. To this end, the ion suppression experienced by both the analyte and the internal standard should be identical. It is important to note that an excessively high concentration of stable isotope internal standard may cause ion suppression itself, since it will co-elute with the analyte of interest. Hence, the internal standard should be added at an appropriate concentration.
APCI generally suffers less ion suppression than ESI, as discussed previously. Where possible, if ion suppression is unavoidable it may be advisable to switch from ESI to APCI. If this is not possible, it may be useful to switch the ESI ionisation mode from positive to negative. Since fewer compounds are ionisable in negative ionisation mode, it is entirely possible that the ion suppressing species may be removed from the analysis. However, it should also be considered that the analyte of interest may not be ionised effectively in negative mode either, rendering this approach useless. | https://en.wikipedia.org/wiki/Ion_suppression_in_liquid_chromatography–mass_spectrometry |
Ion tracks are damage-trails created by swift heavy ions penetrating through solids, which may be sufficiently-contiguous for chemical etching in a variety of crystalline, glassy, and/or polymeric solids. [ 1 ] [ 2 ] They are associated with cylindrical damage-regions several nanometers in diameter [ 3 ] [ 4 ] and can be studied by Rutherford backscattering spectrometry (RBS), transmission electron microscopy (TEM), small-angle neutron scattering (SANS), small-angle X-ray scattering ( SAXS ) or gas permeation . [ 5 ]
Ion track technology deals with the production and application of ion tracks in microtechnology and nanotechnology . [ 6 ] Ion tracks can be selectively etched in many insulating solids, leading to cones or cylinders, down to 8 nanometers in diameter. [ 7 ] Etched track cylinders can be used as filters , [ 8 ] [ 9 ] Coulter counter microchannels, [ 10 ] be modified with monolayers , [ 11 ] or be filled by electroplating . [ 12 ] [ 13 ]
Ion track technology has been developed to fill certain niche areas where conventional nanolithography fails, including:
The class of ion track recording materials is characterized by the following properties: [ 2 ]
Several types of swift heavy ion generators and irradiation schemes are currently used:
When a swift heavy ion penetrates through a solid, it leaves behind a trace of irregular and modified material confined to a cylinder of few nanometers in diameter. The energy transfer between the heavy projectile ion and the light target electrons occurs in binary collisions . The knocked-off primary electrons leave a charged region behind, inducing a secondary electron collision cascade involving an increasing number of electrons of decreasing energy. This electron collision cascade stops when ionization is no longer possible. The remaining energy leads to atomic excitation and vibration, producing ( heat ). Due to the large proton-to-electron mass ratio , the energy of the projectile decreases gradually and the projectile path is straight. [ 29 ] A small fraction of the transferred energy remains as an ion track in the solid. The diameter of the ion track increases with increasing radiation sensitivity of the material. Several models are used to describe ion track formation.
The thermal spike model suggests the radiation sensitivity of different materials depends on their thermal conductivity and their melting temperature.
Selective ion track etching [ 2 ] is closely related to the selective etching of grain boundaries and crystal dislocations . The etch process must be sufficiently slow to discriminate between the irradiated and the pristine material. The resulting shape depends on the type of material, the concentration of the etchant, and the temperature of the etch bath. In crystals and glasses, selective etching is due to the reduced density of the ion track. In polymers, selective etching is due to polymer fragmentation in the ion track core. The core zone is surrounded by a track halo in which cross-linking can impede track etching. After removal of the cross-linked track halo, the track radius grows linear in time. The result of selective etching is a trough, pore, or channel.
Surfactant enhanced etching is used to modify ion track shapes. [ 34 ] It is based on self-organized monolayers . [ 11 ] The monolayers are semi-permeable for the solvated ions of the etch medium and reduce surface attack. Depending on the relative concentration of the surfactant and the etch medium, barrel or cylindrical shaped ion track pores are obtained. The technique can be used to increase the aspect ratio . [ 35 ]
Repeated irradiation and processing : A two-step irradiation and etching process used to create perforated wells.
Arbitrary irradiation angles enforce an anisotropy along one specific symmetry axis.
Multiangular channels are interpenetrating networks consisting of two or more channel arrays in different directions.
1) Sensitizers increase the track etch ratio by breaking bonds or by increasing the free volume. 2) Desensitizers decrease the track etch ratio. Alternatively ion tracks can be thermally annealed. 3) Typical etch bath temperature range. Etch rates increase strongly with concentration and temperature. 4) Axial etching depends on track etch speed v t , radial etching depends on general etch speed v g . 5) Selectivity (aspect ratio, track etch ratio) = track etch speed / general etch speed = v t / v g . 6) This method requires to remove remaining metal oxide deposits by aqueous HCl solutions.
Etched ion tracks can be replicated by polymers [ 37 ] or metals . [ 12 ] [ 38 ] Replica and template can be used as composite . A replica can be separated from its template mechanically or chemically. Polymer replicas are obtained by filling the etched track with a liquid precursor of the polymer and curing it. Curing can be activated by a catalyst , by ultraviolet radiation , or by heat . Metal replicas can be obtained either by electroless deposition or by electro-deposition . For replication of through-pores, a cathode film is deposited on one side of the membrane, and the membrane is immersed in a metal salt solution. The cathode film is negatively charged with respect to the anode, which is placed on the opposite side of the membrane. The positive metal ions are pulled toward the cathode, where they catch electrons and precipitate as a compact metal film. During electro-deposition, the channels fill gradually with metal, and the lengths of the nano-wires are controlled by the deposition time. Rapid deposition leads to polycrystalline wires, while slow deposition leads to single crystalline wires. A free-standing replica is obtained by removing the template after deposition of a bearing film on the anode side of the membrane.
Interpenetrating wire networks are fabricated by electro-deposition in multi-angle, track-etched membranes. Free-standing three-dimensional networks with tunable complexity and interwire connectivity are obtained. [ 39 ]
Segmented nanowires are fabricated by alternating the polarity during electro-deposition. [ 40 ] The segment length is adjusted by the pulse duration. In this way electrical, thermal, and optical properties can be tuned.
Microtechnology : The common mechanical tools of the macroworld are being supplemented and complemented, and in some applications replaced by, particle beams . Here, beams of photons and electrons modify the solubility of radiation-sensitive polymers , so-called " resists ", while masking protects a selected area from exposure to radiation , chemical attack , and erosion by atomic impact . Typical products produced in this way are integrated circuits and microsystems . At present, the field of microtechnology is expanding toward nanotechnology . A recent branch of microfabrication is based on manipulation of individual ions .
Geology: Ion tracks are useful as they can remain unaltered for millions of years In minerals. Their density yields information about the time when the mineral solidified from its melt, and are used as geological clocks in fission track dating
Filters : Homoporous filters were among the first applications [ 8 ] of ion track technology, and are now fabricated by several companies. [ 41 ] Mica membranes with ion track pores were used by Beck and Schultz to determine the mechanism of hindered diffusion in nanopores. [ 42 ] [ 43 ]
Classifying micro- and nanoparticles : The resistance of a channel filled by an electrolyte depends on the volume of the particle passing through it. [ 10 ] This technique is applied to the counting and sizing of individual red blood cells, bacteria, and virus particles.
pH Sensor : Charged channels filled with an electrolyte have a surface conductivity , in addition to the regular volume conductivity , of the electrolyte. Ions attached to a charged surface attract a cloud of mobile counterions . Fixed and mobile ions form a double layer . For small channels, surface conductivity is responsible for most of the charge transport. For small channels, surface conductivity exceeds volume conductivity . Negative surface charges can be occupied by firmly bound protons. At low pH (high proton concentration), the wall charge is completely neutralized. Surface conductivity vanishes. Due to the dependence of surface conductivity on pH, the channel becomes a pH sensor. [ 44 ]
Current rectifying pores : Asymmetric pores are obtained by one-sided etching. The geometric asymmetry translates into a conduction asymmetry. The phenomenon is similar to an electrical valve. The pore has two characteristic conduction states, open and closed. Above a certain voltage the valve opens. Below a certain voltage the valve closes. [ 45 ] [ 46 ]
Thermo-responsive channel : Obtained by lining a channel with a thermo-responsive gel . [ 47 ]
Bio-sensor : Chemical modification of the channel wall changes its interaction with passing particles. Different wall claddings bind to specific molecules and delay their passage. In this sense, the wall recognizes the passing particle. As an example, DNA fragments are selectively bound by their complementary fragments. The attached molecules reduce the channel volume. The induced resistance change reflects the molecule's concentration. [ 48 ]
Anisotropic conduction : A platform covered with many free standing wires acts as large area field emitter. [ 49 ]
Magnetic multilayers : Nano-wires consisting of alternating magnetic/nonmagnetic layers act as magnetic sensors. As an example, cobalt/copper nanowires are obtained from an electrolyte containing both metals. At low voltage, pure copper is deposited while cobalt resists electro-deposition. At high voltage, both metals are deposited as an alloy. If the electrolyte contains predominantly cobalt, a magnetic cobalt-copper alloy is deposited with a high fraction of cobalt. The electrical conductivity of the multilayer wire depends on the applied external magnetic field. The magnetic order of the cobalt layers increases with the applied field. Without magnetic field, neighboring magnetic layers prefer the anti-parallel order. With magnetic field, the magnetic layers prefer the orientation parallel with the magnetic field. The parallel orientation corresponds to a reduced electrical resistance. The effect is used in reading heads of magnetic storage media (the "GMR effect"). [ 50 ]
Spintronics : Spin valve structure consists of two magnetic layers of different thicknesses. The thick layer has a higher magnetic stability and is used as polarizer. The thin layer acts as analyzer. Depending on its magnetization direction with respect to the polarizer (parallel or antiparallel), its conductivity is low or high, respectively. [ 51 ]
Textures : Tilted textures with a hydrophobic coating are at the same time superhydrophobic and anisotropic, [ 18 ] and show a preferred direction of transport. The effect has been demonstrated to convert vibration into translation. [ 52 ] | https://en.wikipedia.org/wiki/Ion_track |
In chemistry , ion transport number , also called the transference number , is the fraction of the total electric current carried in an electrolyte by a given ionic species i : [ 1 ]
Differences in transport number arise from differences in electrical mobility . For example, in an aqueous solution of sodium chloride , less than half of the current is carried by the positively charged sodium ions (cations) and more than half is carried by the negatively charged chloride ions (anions) because the chloride ions are able to move faster, i.e., chloride ions have higher mobility than sodium ions. The sum of the transport numbers for all of the ions in solution always equals unity:
The concept and measurement of transport number were introduced by Johann Wilhelm Hittorf in the year 1853. [ 2 ] Liquid junction potential can arise from ions in a solution having different ion transport numbers.
At zero concentration, the limiting ion transport numbers may be expressed in terms of the limiting molar conductivities of the cation ( λ 0 + {\displaystyle \lambda _{0}^{+}} ), anion ( λ 0 − {\displaystyle \lambda _{0}^{-}} ), and electrolyte ( Λ 0 {\displaystyle \Lambda _{0}} ):
and
where ν + {\displaystyle \nu ^{+}} and ν − {\displaystyle \nu ^{-}} are the numbers of cations and anions respectively per formula unit of electrolyte. [ 1 ] In practice the molar ionic conductivities are calculated from the measured ion transport numbers and the total molar conductivity. For the cation λ 0 + = t + ⋅ Λ 0 ν + {\displaystyle \lambda _{0}^{+}=t_{+}\cdot {\tfrac {\Lambda _{0}}{\nu ^{+}}}} , and similarly for the anion. In solutions, where ionic complexation or associaltion are important, two different transport/transference numbers can be defined. [ 3 ]
The practical importance of high (i.e. close to 1) transference numbers of the charge-shuttling ion (i.e. Li + in lithium-ion batteries ) is related to the fact, that in single-ion devices (such as lithium-ion batteries) electrolytes with the transfer number of the ion near 1, concentration gradients do not develop. A constant electrolyte concentration is maintained during charge-discharge cycles. In case of porous electrodes a more complete utilization of solid electroactive materials at high current densities is possible, even if the ionic conductivity of the electrolyte is reduced. [ 4 ] [ 3 ]
There are several experimental techniques for the determination of transport numbers. [ 3 ] The Hittorf method is based on measurements of ion concentration changes near the electrodes. The moving boundary method involves measuring the speed of displacement of the boundary between two solutions due to an electric current. [ 5 ]
This method was developed by German physicist Johann Wilhelm Hittorf in 1853., [ 5 ] and is based on observations of the changes in concentration of an electrolyte solution in the vicinity of the electrodes. In the Hittorf method, electrolysis is carried out in a cell with three compartments: anode , central, and cathode . Measurement of the concentration changes in the anode and cathode compartments determines the transport numbers. [ 6 ] The exact relationship depends on the nature of the reactions at the two electrodes. For the electrolysis of aqueous copper(II) sulfate ( CuSO 4 ) as an example, with Cu 2+ (aq) and SO 2− 4 (aq) ions, the cathode reaction is the reduction Cu 2+ (aq) + 2 e − → Cu(s) and the anode reaction is the corresponding oxidation of Cu to Cu 2+ . At the cathode, the passage of Q {\displaystyle Q} coulombs of electricity leads to the reduction of Q / 2 F {\displaystyle Q/2F} moles of Cu 2+ , where F {\displaystyle F} is the Faraday constant . Since the Cu 2+ ions carry a fraction t + {\displaystyle t_{+}} of the current, the quantity of Cu 2+ flowing into the cathode compartment is t + ( Q / 2 F ) {\displaystyle t_{+}(Q/2F)} moles, so there is a net decrease of Cu 2+ in the cathode compartment equal to ( 1 − t + ) ( Q / 2 F ) = t − ( Q / 2 F ) {\displaystyle (1-t_{+})(Q/2F)=t_{-}(Q/2F)} . [ 7 ] This decrease may be measured by chemical analysis in order to evaluate the transport numbers. Analysis of the anode compartment gives a second pair of values as a check, while there should be no change of concentrations in the central compartment unless diffusion of solutes has led to significant mixing during the time of the experiment and invalidated the results. [ 7 ]
This method was developed by British physicists Oliver Lodge in 1886 and William Cecil Dampier in 1893. [ 5 ] It depends on the movement of the boundary between two adjacent electrolytes under the influence of an electric field . If a colored solution is used and the interface stays reasonably sharp, the speed of the moving boundary can be measured and used to determine the ion transference numbers.
The cation of the indicator electrolyte should not move faster than the cation whose transport number is to be determined, and it should have same anion as the principle electrolyte. Besides the principal electrolyte (e.g., HCl) is kept light so that it floats on indicator electrolyte. CdCl 2 serves best because Cd 2+ is less mobile than H + and Cl − is common to both CdCl 2 and the principal electrolyte HCl.
For example, the transport numbers of hydrochloric acid (HCl(aq)) may be determined by electrolysis between a cadmium anode and an Ag-AgCl cathode. The anode reaction is Cd → Cd 2+ + 2 e − so that a cadmium chloride ( CdCl 2 ) solution is formed near the anode and moves toward the cathode during the experiment. An acid-base indicator such as bromophenol blue is added to make visible the boundary between the acidic HCl solution and the near-neutral CdCl 2 solution. [ 8 ] The boundary tends to remain sharp since the leading solution HCl has a higher conductivity that the indicator solution CdCl 2 , and therefore a lower electric field to carry the same current. If a more mobile H + ion diffuses into the CdCl 2 solution, it will rapidly be accelerated back to the boundary by the higher electric field; if a less mobile Cd 2+ ion diffuses into the HCl solution it will decelerate in the lower electric field and return to the CdCl 2 solution. Also the apparatus is constructed with the anode below the cathode, so that the denser CdCl 2 solution forms at the bottom. [ 1 ]
The cation transport number of the leading solution is then calculated as
where z + {\displaystyle z_{+}} is the cation charge, c the concentration, L the distance moved by the boundary in time Δ t , A the cross-sectional area, F the Faraday constant , and I the electric current . [ 1 ]
This quantity can be calculated from the slope of the function E T = f ( E ) {\displaystyle E_{\mathrm {T} }=f(E)} of two concentration cells , without or with ionic transport.
The EMF of transport concentration cell involves both the transport number of the cation and its activity coefficient:
where a 2 {\displaystyle a_{2}} and a 1 {\displaystyle a_{1}} are activities of HCl solutions of right and left hand electrodes, respectively, and t M {\displaystyle t_{M}} is the transport number of Cl − .
This method is based on magnetic resonance imaging of the distribution of ions comprising NMR-active nuclei (usually 1 H, 19 F, 7 Li) in an electrochemical cells upon application of electric current. [ 9 ] | https://en.wikipedia.org/wiki/Ion_transport_number |
An ion trap is a combination of electric and/or magnetic fields used to capture charged particles — known as ions — often in a system isolated from an external environment. Atomic and molecular ion traps have a number of applications in physics and chemistry such as precision mass spectrometry , improved atomic frequency standards, and quantum computing . [ 1 ] In comparison to neutral atom traps, ion traps have deeper trapping potentials (up to several electronvolts ) that do not depend on the internal electronic structure of a trapped ion. This makes ion traps more suitable for the study of light interactions with single atomic systems. The two most popular types of ion traps are the Penning trap , which forms a potential via a combination of static electric and magnetic fields, and the Paul trap which forms a potential via a combination of static and oscillating electric fields. [ 2 ]
Penning traps can be used for precise magnetic measurements in spectroscopy. Studies of quantum state manipulation most often use the Paul trap. This may lead to a trapped ion quantum computer [ 3 ] and has already been used to create the world's most accurate atomic clocks . [ 4 ] [ 5 ] Electron guns (a device emitting high-speed electrons, used in CRTs ) can use an ion trap to prevent degradation of the cathode by positive ions.
The physical principles of ion traps were first explored by F. M. Penning (1894–1953), who observed that electrons released by the cathode of an ionization vacuum gauge follow a long cycloidal path to the anode in the presence of a sufficiently strong magnetic field. [ 6 ] A scheme for confining charged particles in three dimensions without the use of magnetic fields was developed by W. Paul based on his work with quadrupole mass spectrometers .
Ion traps were used in television receivers prior to the introduction of aluminized CRT faces around 1958, to protect the phosphor screen from ions. [ 7 ] The ion trap must be delicately adjusted for maximum brightness. [ 8 ] [ 9 ]
Any charged particle, such as an ion , feels a force from an electric or magnetic field. Ion traps work by using this force to confine ions in a small, isolated volume of space so that they can be studied or manipulated. Although any static (constant in time) electromagnetic field produces a force on an ion, it is not possible to confine an ion using only a static electric field. This is a consequence of Earnshaw's theorem . However, physicists have various ways of working around this theorem by using combinations of static magnetic and electric fields (as in a Penning trap ) or by an oscillating electric field and a static electric field( Paul trap ). Ion motion and confinement in the trap is generally divided into axial and radial components, which are typically addressed separately by different fields. In both Paul and Penning traps, axial ion motion is confined by a static electric field. Paul traps use an oscillating electric field to confine the ion radially and Penning traps generate radial confinement with a static magnetic field.
A Paul trap that uses an oscillating quadrupole field to trap ions radially and a static potential to confine ions axially. The quadrupole field is realized by four parallel electrodes laying in the z {\displaystyle z} -axis positioned at the corners of a square in the x y {\displaystyle xy} -plane. Electrodes diagonally opposite each other are connected and an a.c. voltage V = V 0 cos ( Ω t ) {\displaystyle V=V_{0}\cos(\Omega t)} is applied. Using Maxwell's equations , the electric field produced by this potential is electric field E = E 0 sin ( Ω t ) {\displaystyle \mathbf {E} =\mathbf {E} _{0}\sin(\Omega t)} . Applying Newton's second law to an ion of charge e {\displaystyle e} and mass M {\displaystyle M} in this a.c. electric field, we can find the force on the ion using F = e E {\displaystyle \mathbf {F} =e\mathbf {E} } . We wind up with
Assuming that the ion has zero initial velocity, two successive integrations give the velocity and displacement as
where r 0 {\displaystyle \mathbf {r} _{0}} is a constant of integration. Thus, the ion oscillates with angular frequency Ω {\displaystyle \Omega } and amplitude proportional to the electric field strength and is confined radially.
Working specifically with a linear Paul trap, we can write more specific equations of motion. Along the z {\displaystyle z} -axis, an analysis of the radial symmetry yields a potential [ 10 ]
The constants α {\displaystyle \alpha } and β {\displaystyle \beta } are determined by boundary conditions on the electrodes and ϕ {\displaystyle \phi } satisfies Laplace's equation ∇ 2 ϕ = 0 {\displaystyle \nabla ^{2}\phi =0} . Assuming the length of the electrodes r {\displaystyle r} is much greater than their separation r 0 {\displaystyle r_{0}} , it can be shown that
Since the electric field is given by the gradient of the potential, we get that
Defining τ = Ω t / 2 {\displaystyle \tau =\Omega t/2} , the equations of motion in the x y {\displaystyle xy} -plane are a simplified form of the Mathieu equation ,
A standard configuration for a Penning trap consists of a ring electrode and two end caps. A static voltage differential between the ring and end caps confines ions along the axial direction (between end caps). However, as expected from Earnshaw's theorem , the static electric potential is not sufficient to trap an ion in all three dimensions. To provide the radial confinement, a strong axial magnetic field is applied.
For a uniform electric field E = E e ^ x {\displaystyle \mathbf {E} =E\mathbf {\hat {e}} _{x}} , the force F = e E {\displaystyle \mathbf {F} =e\mathbf {E} } accelerates a positively charged ion along the x {\displaystyle x} -axis. For a uniform magnetic field B = B e ^ z {\displaystyle \mathbf {B} =B\mathbf {\hat {e}} _{z}} , the Lorentz force causes the ion to move in circular motion with cyclotron frequency
Assuming an ion with zero initial velocity placed in a region with E = E e ^ x {\displaystyle \mathbf {E} =E\mathbf {\hat {e}} _{x}} and B = B e ^ z {\displaystyle \mathbf {B} =B\mathbf {\hat {e}} _{z}} , the equations of motion are
The resulting motion is a combination of oscillatory motion around the z {\displaystyle z} -axis with frequency ω c {\displaystyle \omega _{c}} and a drift velocity in the y {\displaystyle y} -direction. The drift velocity is perpendicular to the direction of the electric field.
For the radial electric field produced by the electrodes in a Penning trap, the drift velocity will precess around the axial direction with some frequency ω m {\displaystyle \omega _{m}} , called the magnetron frequency. An ion will also have a third characteristic frequency ω z {\displaystyle \omega _{z}} between the two end cap electrodes. The frequencies usually have widely different values with ω z ≪ ω m <≪ ω c {\displaystyle \omega _{z}\ll \omega _{m}<\ll \omega _{c}} . [ 11 ]
An ion trap mass spectrometer may incorporate a Penning trap ( Fourier-transform ion cyclotron resonance ), [ 12 ] Paul trap [ 13 ] or the Kingdon trap . [ 14 ] The Orbitrap , introduced in 2005, is based on the Kingdon trap. [ 15 ] Other types of mass spectrometers may also use a linear quadrupole ion trap as a selective mass filter.
A Penning trap stores charged particles using a strong homogeneous axial magnetic field to confine particles radially and a quadrupole electric field to confine the particles axially. [ 16 ] Penning traps are well suited for measurements of the properties of ions and stable charged subatomic particles . Precision studies of the electron magnetic moment by Dehmelt and others are an important topic in modern physics.
Penning traps can be used in quantum computation and quantum information processing [ 17 ] and are used at CERN to store antimatter. Penning traps form the basis of Fourier-transform ion cyclotron resonance mass spectrometry for determining the mass-to-charge ratio of ions . [ 18 ]
The Penning Trap was invented by Frans Michel Penning and Hans Georg Dehmelt , who built the first trap in the 1950s. [ 19 ]
A Paul trap is a type of quadrupole ion trap that uses static direct current (DC) and radio frequency (RF) oscillating electric fields to trap ions. Paul traps are commonly used as components of a mass spectrometer . The invention of the 3D quadrupole ion trap itself is attributed to Wolfgang Paul who shared the Nobel Prize in Physics in 1989 for this work. [ 20 ] [ 21 ] The trap consists of two hyperbolic metal electrodes with their foci facing each other and a hyperbolic ring electrode halfway between the other two electrodes. Ions are trapped in the space between these three electrodes by the oscillating and static electric fields.
A Kingdon trap consists of a thin central wire, an outer cylindrical electrode and isolated end cap electrodes at both ends. A static applied voltage results in a radial logarithmic potential between the electrodes. [ 14 ] In a Kingdon trap there is no potential minimum to store the ions; however, they are stored with a finite angular momentum about the central wire and the applied electric field in the device allows for the stability of the ion trajectories. [ 22 ] In 1981, Knight introduced a modified outer electrode that included an axial quadrupole term that confines the ions on the trap axis. [ 23 ] The dynamic Kingdon trap has an additional AC voltage that uses strong defocusing to permanently store charged particles. [ 24 ] The dynamic Kingdon trap does not require the trapped ions to have angular momentum with respect to the filament. An Orbitrap is a modified Kingdon trap that is used for mass spectrometry . Though the idea has been suggested and computer simulations performed [ 25 ] neither the Kingdon nor the Knight configurations were reported to produce mass spectra, as the simulations indicated mass resolving power would be problematic.
Some experimental work towards developing quantum computers use trapped ions . Units of quantum information called qubits are stored in stable electronic states of each ion, and quantum information can be processed and transferred through the collective quantized motion of the ions, interacting by the Coulomb force . Lasers are applied to induce coupling between the qubit states (for single qubit operations) or between the internal qubit states and external motional states (for entanglement between qubits). | https://en.wikipedia.org/wiki/Ion_trap |
The ion vibration current ( IVI ) and the associated ion vibration potential is an electric signal that arises when an acoustic wave propagates through a homogeneous fluid.
Historically, the IVI was the first known electroacoustic phenomenon . It was predicted by Peter Debye in 1933. [ 1 ]
When a longitudinal sound wave travels through a solvent, the associated pressure gradients push the fluid particles back and forth, and it is easy in practice to create such accelerations that measure thousands or millions of g's . If a solute molecule is more dense or less dense than the surrounding liquid, then in this accelerating environment, the molecule will move relative to the surrounding liquid. This relative motion is essentially the same phenomenon that occurs in a centrifuge , or more simply, it is essentially the same phenomenon that occurs when low-density objects float to the top of a glass of water, and high-density particles sink to the bottom (see the equivalence principle , which states that gravity is just like any other acceleration). The amount of relative motion depends on the balance between the molecule's effective mass (which includes both the mass of the molecule itself and any solvent molecules that are so tightly bound to the molecule that they follow along with the molecule's motion), its effective volume (related to buoyant force ), and the viscous drag (friction) between the molecule and the surrounding fluid.
IVI concerns the case where the particles in question are anions and cations . In general, they will have different amounts of motion relative to the fluid during the sound wave oscillations, and that discrepancy creates an alternating electric potential between various points in a sound wave .
This effect was extensively used in the 1950s and 1960s for characterizing ion solvation . These works are mostly associated with the names of Zana and Yaeger, who published a review of their studies in 1982. [ 2 ]
This effect can be studied with modern devices that employ electroacoustics for studying zeta potential, as described in the book. [ 3 ] | https://en.wikipedia.org/wiki/Ion_vibration_current |
Ionic Atmosphere is a concept employed in Debye–Hückel theory which explains the electrolytic conductivity behaviour of solutions. It can be generally defined as the area at which a charged entity is capable of attracting an entity of the opposite charge.
If an electrical potential is applied to an electrolytic solution, a positive ion will move towards the negative electrode and drag along an entourage of negative ions with it. The more concentrated the solution, the closer these negative ions are to the positive ion and thus the greater the resistance experienced by the positive ion. This influence on the speed of an ion is known as the "Asymmetry effect" because the ionic atmosphere moving around the ion is not symmetrical; the charge density behind is greater than in the front, slowing the motion of the ion. [ 1 ] The time required to form a new ionic atmosphere on the right or time required for ionic atmosphere on the left to fade away is known as time of relaxation. The asymmetrization of ionic atmosphere does not occur in the case of Debye Falkenhagen effect due to high frequency dependence of conductivity.
This is another factor which slows the motion of ions within a solution. It is the tendency of the applied potential to move the ionic atmosphere itself. This drags the solvent molecules along because of the attractive forces between ions and solvent molecules. As a result, the central ion at the centre of the ionic atmosphere is influenced to move towards the pole opposite its ionic atmosphere. This inclination retards its motion. [ 1 ]
The model of ionic atmosphere is less adequate for concentrated ionic solutions near saturation. These solutions as well as molten salts or ionic liquids have a structure similar to the crystalline lattice where water molecules are located between ions. | https://en.wikipedia.org/wiki/Ionic_atmosphere |
In chemistry , a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations ) and negatively charged ions ( anions ), [ 1 ] which results in a compound with no net electric charge (electrically neutral). The constituent ions are held together by electrostatic forces termed ionic bonds .
The component ions in a salt can be either inorganic , such as chloride (Cl − ), or organic , such as acetate ( CH 3 COO − ). Each ion can be either monatomic (termed simple ion ), such as sodium (Na + ) and chloride (Cl − ) in sodium chloride , or polyatomic , such as ammonium ( NH + 4 ) and carbonate ( CO 2− 3 ) ions in ammonium carbonate . Salts containing basic ions hydroxide (OH − ) or oxide (O 2− ) are classified as bases , such as sodium hydroxide and potassium oxide .
Individual ions within a salt usually have multiple near neighbours, so they are not considered to be part of molecules, but instead part of a continuous three-dimensional network. Salts usually form crystalline structures when solid.
Salts composed of small ions typically have high melting and boiling points , and are hard and brittle . As solids they are almost always electrically insulating , but when melted or dissolved they become highly conductive , because the ions become mobile. Some salts have large cations, large anions, or both. In terms of their properties, such species often are more similar to organic compounds.
In 1913 the structure of sodium chloride was determined by William Henry Bragg and his son William Lawrence Bragg . [ 2 ] [ 3 ] [ 4 ] This revealed that there were six equidistant nearest-neighbours for each atom, demonstrating that the constituents were not arranged in molecules or finite aggregates, but instead as a network with long-range crystalline order. [ 4 ] Many other inorganic compounds were also found to have similar structural features. [ 4 ] These compounds were soon described as being constituted of ions rather than neutral atoms , but proof of this hypothesis was not found until the mid-1920s, when X-ray reflection experiments (which detect the density of electrons), were performed. [ 4 ] [ 5 ]
Principal contributors to the development of a theoretical treatment of ionic crystal structures were Max Born , Fritz Haber , Alfred Landé , Erwin Madelung , Paul Peter Ewald , and Kazimierz Fajans . [ 6 ] Born predicted crystal energies based on the assumption of ionic constituents, which showed good correspondence to thermochemical measurements, further supporting the assumption. [ 4 ]
Many metals such as the alkali metals react directly with the electronegative halogens gases to form salts. [ 7 ] [ 8 ]
Salts form upon evaporation of their solutions . [ 9 ] Once the solution is supersaturated and the solid compound nucleates. [ 9 ] This process occurs widely in nature and is the means of formation of the evaporite minerals. [ 10 ]
Insoluble salts can be precipitated by mixing two solutions, one with the cation and one with the anion in it. Because all solutions are electrically neutral, the two solutions mixed must also contain counterions of the opposite charges. To ensure that these do not contaminate the precipitated salt, it is important to ensure they do not also precipitate. [ 11 ] If the two solutions have hydrogen ions and hydroxide ions as the counterions, they will react with one another in what is called an acid–base reaction or a neutralization reaction to form water. [ 12 ] Alternately the counterions can be chosen to ensure that even when combined into a single solution they will remain soluble as spectator ions . [ 11 ]
If the solvent is water in either the evaporation or precipitation method of formation, in many cases the ionic crystal formed also includes water of crystallization , so the product is known as a hydrate , and can have very different chemical properties compared to the anhydrous material. [ 13 ]
Molten salts will solidify on cooling to below their freezing point . [ 14 ] This is sometimes used for the solid-state synthesis of complex salts from solid reactants, which are first melted together. [ 15 ] In other cases, the solid reactants do not need to be melted, but instead can react through a solid-state reaction route . In this method, the reactants are repeatedly finely ground into a paste and then heated to a temperature where the ions in neighboring reactants can diffuse together during the time the reactant mixture remains in the oven. [ 8 ] Other synthetic routes use a solid precursor with the correct stoichiometric ratio of non-volatile ions, which is heated to drive off other species. [ 8 ]
In some reactions between highly reactive metals (usually from Group 1 or Group 2 ) and highly electronegative halogen gases, or water, the atoms can be ionized by electron transfer , [ 16 ] a process thermodynamically understood using the Born–Haber cycle . [ 17 ]
Salts are formed by salt-forming reactions
Ions in salts are primarily held together by the electrostatic forces between the charge distribution of these bodies, and in particular, the ionic bond resulting from the long-ranged Coulomb attraction between the net negative charge of the anions and net positive charge of the cations. [ 18 ] There is also a small additional attractive force from van der Waals interactions which contributes only around 1–2% of the cohesive energy for small ions. [ 19 ] When a pair of ions comes close enough for their outer electron shells (most simple ions have closed shells ) to overlap, a short-ranged repulsive force occurs, [ 20 ] due to the Pauli exclusion principle . [ 21 ] The balance between these forces leads to a potential energy well with minimum energy when the nuclei are separated by a specific equilibrium distance. [ 20 ]
If the electronic structure of the two interacting bodies is affected by the presence of one another, covalent interactions (non-ionic) also contribute to the overall energy of the compound formed. [ 22 ] Salts are rarely purely ionic, i.e. held together only by electrostatic forces. The bonds between even the most electronegative / electropositive pairs such as those in caesium fluoride exhibit a small degree of covalency . [ 23 ] [ 24 ] Conversely, covalent bonds between unlike atoms often exhibit some charge separation and can be considered to have a partial ionic character. [ 22 ] The circumstances under which a compound will have ionic or covalent character can typically be understood using Fajans' rules , which use only charges and the sizes of each ion. According to these rules, compounds with the most ionic character will have large positive ions with a low charge, bonded to a small negative ion with a high charge. [ 25 ] More generally HSAB theory can be applied, whereby the compounds with the most ionic character are those consisting of hard acids and hard bases: small, highly charged ions with a high difference in electronegativities between the anion and cation. [ 26 ] [ 27 ] This difference in electronegativities means that the charge separation, and resulting dipole moment, is maintained even when the ions are in contact (the excess electrons on the anions are not transferred or polarized to neutralize the cations). [ 28 ]
Although chemists classify idealized bond types as being ionic or covalent, the existence of additional types such as hydrogen bonds and metallic bonds , for example, has led some philosophers of science to suggest that alternative approaches to understanding bonding are required. This could be by applying quantum mechanics to calculate binding energies. [ 29 ] [ 30 ]
The lattice energy is the summation of the interaction of all sites with all other sites. For unpolarizable spherical ions, only the charges and distances are required to determine the electrostatic interaction energy. For any particular ideal crystal structure, all distances are geometrically related to the smallest internuclear distance. So for each possible crystal structure, the total electrostatic energy can be related to the electrostatic energy of unit charges at the nearest neighboring distance by a multiplicative constant called the Madelung constant [ 20 ] that can be efficiently computed using an Ewald sum . [ 31 ] When a reasonable form is assumed for the additional repulsive energy, the total lattice energy can be modelled using the Born–Landé equation , [ 32 ] the Born–Mayer equation , or in the absence of structural information, the Kapustinskii equation . [ 33 ]
Using an even simpler approximation of the ions as impenetrable hard spheres, the arrangement of anions in these systems are often related to close-packed arrangements of spheres, with the cations occupying tetrahedral or octahedral interstices . [ 34 ] [ 35 ] Depending on the stoichiometry of the salt, and the coordination (principally determined by the radius ratio ) of cations and anions, a variety of structures are commonly observed, [ 36 ] and theoretically rationalized by Pauling's rules . [ 37 ]
In some cases, the anions take on a simple cubic packing and the resulting common structures observed are:
Some ionic liquids , particularly with mixtures of anions or cations, can be cooled rapidly enough that there is not enough time for crystal nucleation to occur, so an ionic glass is formed (with no long-range order). [ 53 ]
Within any crystal, there will usually be some defects. To maintain electroneutrality of the crystals, defects that involve loss of a cation will be associated with loss of an anion, i.e. these defects come in pairs. [ 54 ] Frenkel defects consist of a cation vacancy paired with a cation interstitial and can be generated anywhere in the bulk of the crystal, [ 54 ] occurring most commonly in compounds with a low coordination number and cations that are much smaller than the anions. [ 55 ] Schottky defects consist of one vacancy of each type, and are generated at the surfaces of a crystal, [ 54 ] occurring most commonly in compounds with a high coordination number and when the anions and cations are of similar size. [ 55 ] If the cations have multiple possible oxidation states , then it is possible for cation vacancies to compensate for electron deficiencies on cation sites with higher oxidation numbers, resulting in a non-stoichiometric compound . [ 54 ] Another non-stoichiometric possibility is the formation of an F-center , a free electron occupying an anion vacancy. [ 56 ] When the compound has three or more ionic components, even more defect types are possible. [ 54 ] All of these point defects can be generated via thermal vibrations and have an equilibrium concentration. Because they are energetically costly but entropically beneficial, they occur in greater concentration at higher temperatures. Once generated, these pairs of defects can diffuse mostly independently of one another, by hopping between lattice sites. This defect mobility is the source of most transport phenomena within an ionic crystal, including diffusion and solid state ionic conductivity . [ 54 ] When vacancies collide with interstitials (Frenkel), they can recombine and annihilate one another. Similarly, vacancies are removed when they reach the surface of the crystal (Schottky). Defects in the crystal structure generally expand the lattice parameters , reducing the overall density of the crystal. [ 54 ] Defects also result in ions in distinctly different local environments, which causes them to experience a different crystal-field symmetry , especially in the case of different cations exchanging lattice sites. [ 54 ] This results in a different splitting of d-electron orbitals , so that the optical absorption (and hence colour) can change with defect concentration. [ 54 ]
Ionic compounds containing hydrogen ions (H + ) are classified as acids , and those containing electropositive cations [ 57 ] and basic anions ions hydroxide (OH − ) or oxide (O 2− ) are classified as bases . Other ionic compounds are known as salts and can be formed by acid–base reactions . [ 58 ] Salts that produce hydroxide ions when dissolved in water are called alkali salts , and salts that produce hydrogen ions when dissolved in water are called acid salts . If the compound is the result of a reaction between a strong acid and a weak base , the result is an acid salt . If it is the result of a reaction between a strong base and a weak acid , the result is a base salt . If it is the result of a reaction between a strong acid and a strong base, the result is a neutral salt. Weak acids reacted with weak bases can produce ionic compounds with both the conjugate base ion and conjugate acid ion, such as ammonium acetate .
Some ions are classed as amphoteric , being able to react with either an acid or a base. [ 59 ] This is also true of some compounds with ionic character, typically oxides or hydroxides of less-electropositive metals (so the compound also has significant covalent character), such as zinc oxide , aluminium hydroxide , aluminium oxide and lead(II) oxide . [ 60 ]
Electrostatic forces between particles are strongest when the charges are high, and the distance between the nuclei of the ions is small. In such cases, the compounds generally have very high melting and boiling points and a low vapour pressure . [ 61 ] Trends in melting points can be even better explained when the structure and ionic size ratio is taken into account. [ 62 ] Above their melting point, salts melt and become molten salts (although some salts such as aluminium chloride and iron(III) chloride show molecule-like structures in the liquid phase). [ 63 ] Inorganic compounds with simple ions typically have small ions, and thus have high melting points, so are solids at room temperature. Some substances with larger ions, however, have a melting point below or near room temperature (often defined as up to 100 °C), and are termed ionic liquids . [ 64 ] Ions in ionic liquids often have uneven charge distributions, or bulky substituents like hydrocarbon chains, which also play a role in determining the strength of the interactions and propensity to melt. [ 65 ]
Even when the local structure and bonding of an ionic solid is disrupted sufficiently to melt it, there are still strong long-range electrostatic forces of attraction holding the liquid together and preventing ions boiling to form a gas phase. [ 66 ] This means that even room temperature ionic liquids have low vapour pressures, and require substantially higher temperatures to boil. [ 66 ] Boiling points exhibit similar trends to melting points in terms of the size of ions and strength of other interactions. [ 66 ] When vapourized, the ions are still not freed of one another. For example, in the vapour phase sodium chloride exists as diatomic "molecules". [ 67 ]
Most salts are very brittle . Once they reach the limit of their strength, they cannot deform malleably , because the strict alignment of positive and negative ions must be maintained. Instead the material undergoes fracture via cleavage . [ 68 ] As the temperature is elevated (usually close to the melting point) a ductile–brittle transition occurs, and plastic flow becomes possible by the motion of dislocations . [ 68 ] [ 69 ]
The compressibility of a salt is strongly determined by its structure, and in particular the coordination number . For example, halides with the caesium chloride structure (coordination number 8) are less compressible than those with the sodium chloride structure (coordination number 6), and less again than those with a coordination number of 4. [ 70 ]
When simple salts dissolve , they dissociate into individual ions, which are solvated and dispersed throughout the resulting solution. Salts do not exist in solution. [ 71 ] In contrast, molecular compounds, which includes most organic compounds, remain intact in solution.
The solubility of salts is highest in polar solvents (such as water ) or ionic liquids , but tends to be low in nonpolar solvents (such as petrol / gasoline ). [ 72 ] This contrast is principally because the resulting ion–dipole interactions are significantly stronger than ion-induced dipole interactions, so the heat of solution is higher. When the oppositely charged ions in the solid ionic lattice are surrounded by the opposite pole of a polar molecule, the solid ions are pulled out of the lattice and into the liquid. If the solvation energy exceeds the lattice energy , the negative net enthalpy change of solution provides a thermodynamic drive to remove ions from their positions in the crystal and dissolve in the liquid. In addition, the entropy change of solution is usually positive for most solid solutes like salts, which means that their solubility increases when the temperature increases. [ 73 ] There are some unusual salts such as cerium(III) sulfate , where this entropy change is negative, due to extra order induced in the water upon solution, and the solubility decreases with temperature. [ 73 ]
The lattice energy , the cohesive forces between these ions within a solid, determines the solubility. The solubility is dependent on how well each ion interacts with the solvent, so certain patterns become apparent. For example, salts of sodium , potassium and ammonium are usually soluble in water. Notable exceptions include ammonium hexachloroplatinate and potassium cobaltinitrite . Most nitrates and many sulfates are water-soluble. Exceptions include barium sulfate , calcium sulfate (sparingly soluble), and lead(II) sulfate , where the 2+/2− pairing leads to high lattice energies. For similar reasons, most metal carbonates are not soluble in water. Some soluble carbonate salts are: sodium carbonate , potassium carbonate and ammonium carbonate .
Strong salts or strong electrolyte salts are chemical salts composed of strong electrolytes . These salts dissociate completely or almost completely in water . They are generally odorless and nonvolatile .
Strong salts start with Na__, K__, NH 4 __, or they end with __NO 3 , __ClO 4 , or __CH 3 COO. Most group 1 and 2 metals form strong salts. Strong salts are especially useful when creating conductive compounds as their constituent ions allow for greater conductivity. [ citation needed ]
Weak salts or weak electrolyte salts are composed of weak electrolytes . These salts do not dissociate well in water. They are generally more volatile than strong salts. They may be similar in odor to the acid or base they are derived from. For example, sodium acetate , CH 3 COONa, smells similar to acetic acid CH 3 COOH.
Salts are characteristically insulators . Although they contain charged atoms or clusters, these materials do not typically conduct electricity to any significant extent when the substance is solid. In order to conduct, the charged particles must be mobile rather than stationary in a crystal lattice . This is achieved to some degree at high temperatures when the defect concentration increases the ionic mobility and solid state ionic conductivity is observed. When the salts are dissolved in a liquid or are melted into a liquid , they can conduct electricity because the ions become completely mobile. For this reason, molten salts and solutions containing dissolved salts (e.g., sodium chloride in water) can be used as electrolytes . [ 75 ] This conductivity gain upon dissolving or melting is sometimes used as a defining characteristic of salts. [ 76 ]
In some unusual salts: fast-ion conductors , and ionic glasses , [ 53 ] one or more of the ionic components has a significant mobility, allowing conductivity even while the material as a whole remains solid. [ 77 ] This is often highly temperature dependent, and may be the result of either a phase change or a high defect concentration. [ 77 ] These materials are used in all solid-state supercapacitors , batteries , and fuel cells , and in various kinds of chemical sensors . [ 78 ] [ 79 ]
The colour of a salt is often different from the colour of an aqueous solution containing the constituent ions, [ 80 ] or the hydrated form of the same compound. [ 13 ]
The anions in compounds with bonds with the most ionic character tend to be colorless (with an absorption band in the ultraviolet part of the spectrum). [ 81 ] In compounds with less ionic character, their color deepens through yellow, orange, red, and black (as the absorption band shifts to longer wavelengths into the visible spectrum). [ 81 ]
The absorption band of simple cations shifts toward a shorter wavelength when they are involved in more covalent interactions. [ 81 ] This occurs during hydration of metal ions, so colorless anhydrous salts with an anion absorbing in the infrared can become colorful in solution. [ 81 ]
Salts exist in many different colors , which arise either from their constituent anions, cations or solvates . For example:
Some minerals are salts, some of which are soluble in water. [ dubious – discuss ] [ clarification needed ] Similarly, inorganic pigments tend not to be salts, because insolubility is required for fastness. Some organic dyes are salts, but they are virtually insoluble in water.
Salts can elicit all five basic tastes , e.g., salty ( sodium chloride ), sweet ( lead diacetate , which will cause lead poisoning if ingested), sour ( potassium bitartrate ), bitter ( magnesium sulfate ), and umami or savory ( monosodium glutamate ).
Salts of strong acids and strong bases (" strong salts ") are non- volatile and often odorless, whereas salts of either weak acids or weak bases (" weak salts ") may smell like the conjugate acid (e.g., acetates like acetic acid ( vinegar ) and cyanides like hydrogen cyanide ( almonds )) or the conjugate base (e.g., ammonium salts like ammonia ) of the component ions. That slow, partial decomposition is usually accelerated by the presence of water, since hydrolysis is the other half of the reversible reaction equation of formation of weak salts.
Salts have long had a wide variety of uses and applications. Many minerals are ionic. [ 82 ] Humans have processed common salt (sodium chloride) for over 8000 years, using it first as a food seasoning and preservative, and now also in manufacturing, agriculture , water conditioning, for de-icing roads, and many other uses. [ 83 ] Many salts are so widely used in society that they go by common names unrelated to their chemical identity. Examples of this include borax , calomel , milk of magnesia , muriatic acid , oil of vitriol , saltpeter , and slaked lime . [ 84 ]
Soluble salts can easily be dissolved to provide electrolyte solutions. This is a simple way to control the concentration and ionic strength . The concentration of solutes affects many colligative properties , including increasing the osmotic pressure , and causing freezing-point depression and boiling-point elevation . [ 85 ] Because the solutes are charged ions they also increase the electrical conductivity of the solution. [ 86 ] The increased ionic strength reduces the thickness of the electrical double layer around colloidal particles, and therefore the stability of emulsions and suspensions . [ 87 ]
The chemical identity of the ions added is also important in many uses. For example, fluoride containing compounds are dissolved to supply fluoride ions for water fluoridation . [ 88 ]
Solid salts have long been used as paint pigments, and are resistant to organic solvents, but are sensitive to acidity or basicity. [ 89 ] Since 1801 pyrotechnicians have described and widely used metal-containing salts as sources of colour in fireworks. [ 90 ] Under intense heat, the electrons in the metal ions or small molecules can be excited. [ 91 ] These electrons later return to lower energy states, and release light with a colour spectrum characteristic of the species present. [ 92 ] [ 93 ]
In chemical synthesis , salts are often used as precursors for high-temperature solid-state synthesis. [ 94 ]
Many metals are geologically most abundant as salts within ores . [ 95 ] To obtain the elemental materials, these ores are processed by smelting or electrolysis , in which redox reactions occur (often with a reducing agent such as carbon) such that the metal ions gain electrons to become neutral atoms. [ 96 ] [ 97 ]
According to the nomenclature recommended by IUPAC , salts are named according to their composition, not their structure. [ 98 ] In the most simple case of a binary salt with no possible ambiguity about the charges and thus the stoichiometry , the common name is written using two words. [ 99 ] The name of the cation (the unmodified element name for monatomic cations) comes first, followed by the name of the anion. [ 100 ] [ 101 ] For example, MgCl 2 is named magnesium chloride , and Na 2 SO 4 is named sodium sulfate ( SO 2− 4 , sulfate , is an example of a polyatomic ion ). To obtain the empirical formula from these names, the stoichiometry can be deduced from the charges on the ions, and the requirement of overall charge neutrality. [ 102 ]
If there are multiple different cations and/or anions, multiplicative prefixes ( di- , tri- , tetra- , ...) are often required to indicate the relative compositions, [ 103 ] and cations then anions are listed in alphabetical order. [ 104 ] For example, KMgCl 3 is named magnesium potassium trichloride to distinguish it from K 2 MgCl 4 , magnesium dipotassium tetrachloride [ 105 ] (note that in both the empirical formula and the written name, the cations appear in alphabetical order, but the order varies between them because the symbol for potassium is K). [ 106 ] When one of the ions already has a multiplicative prefix within its name, the alternate multiplicative prefixes ( bis- , tris- , tetrakis- , ...) are used. [ 107 ] For example, Ba(BrF 4 ) 2 is named barium bis(tetrafluoridobromate) . [ 108 ]
Compounds containing one or more elements which can exist in a variety of charge/ oxidation states will have a stoichiometry that depends on which oxidation states are present, to ensure overall neutrality. This can be indicated in the name by specifying either the oxidation state of the elements present, or the charge on the ions. [ 108 ] Because of the risk of ambiguity in allocating oxidation states, IUPAC prefers direct indication of the ionic charge numbers. [ 108 ] These are written as an arabic integer followed by the sign (... , 2−, 1−, 1+, 2+, ...) in parentheses directly after the name of the cation (without a space separating them). [ 108 ] For example, FeSO 4 is named iron(2+) sulfate (with the 2+ charge on the Fe 2+ ions balancing the 2− charge on the sulfate ion), whereas Fe 2 (SO 4 ) 3 is named iron(3+) sulfate (because the two iron ions in each formula unit each have a charge of 3+, to balance the 2− on each of the three sulfate ions). [ 108 ] Stock nomenclature , still in common use, writes the oxidation number in Roman numerals (... , −II, −I, 0, I, II, ...). So the examples given above would be named iron(II) sulfate and iron(III) sulfate respectively. [ 109 ] For simple ions the ionic charge and the oxidation number are identical, but for polyatomic ions they often differ. For example, the uranyl(2+) ion, UO 2+ 2 , has uranium in an oxidation state of +6, so would be called a dioxouranium(VI) ion in Stock nomenclature. [ 110 ] An even older naming system for metal cations, also still widely used, appended the suffixes -ous and -ic to the Latin root of the name, to give special names for the low and high oxidation states. [ 111 ] For example, this scheme uses "ferrous" and "ferric", for iron(II) and iron(III) respectively, [ 111 ] so the examples given above were classically named ferrous sulfate and ferric sulfate . [ citation needed ]
Common salt-forming cations include:
Common salt-forming anions (parent acids in parentheses where available) include:
Salts with varying number of hydrogen atoms replaced by cations as compared to their parent acid can be referred to as monobasic , dibasic , or tribasic , identifying that one, two, or three hydrogen atoms have been replaced; polybasic salts refer to those with more than one hydrogen atom replaced. Examples include:
Zwitterions contain an anionic and a cationic centre in the same molecule , but are not considered salts. Examples of zwitterions are amino acids , many metabolites , peptides , and proteins . [ 112 ] | https://en.wikipedia.org/wiki/Ionic_compound |
Ionic conductivity (denoted by λ ) is a measure of a substance's tendency towards ionic conduction . Ionic conduction is the movement of ions . The phenomenon is observed in solids and solutions. Ionic conduction is one mechanism of current . [ 1 ]
In most solids, ions rigidly occupy fixed positions, strongly embraced by neighboring atoms or ions. In some solids, selected ions are highly mobile allowing ionic conduction. The mobility increases with temperature. Materials exhibiting this property are used in batteries. A well-known ion conductive solid is β''-alumina ("BASE"), a form of aluminium oxide that has channels through which sodium cations can hop. When this ceramic is complexed with a mobile ion , such as Na + , it behaves as so-called fast ion conductor . BASE is used as a membrane in several types of molten salt electrochemical cell . [ 2 ]
Ionic conduction in solids has been a subject of interest since the beginning of the 19th century. Michael Faraday established in 1839 that the laws of electrolysis are also obeyed in ionic solids like lead(II) fluoride ( PbF 2 ) and silver sulfide ( Ag 2 S ). In 1921, solid silver iodide ( AgI ) was found to have had extraordinary high ionic conductivity at temperatures above 147 °C, AgI changes into a phase that has an ionic conductivity of ~ 1 –1 cm −1 . [ clarification needed ] This high temperature phase of AgI is an example of a superionic conductor . The disordered structure of this solid allows the Ag + ions to move easily. The present record holder for ionic conductivity is the related material Ag 2 [HgI 4 ] . [ 3 ] β''-alumina was developed at the Ford Motor Company in the search for a storage device for electric vehicles while developing the sodium–sulfur battery . [ 2 ]
This electrochemistry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ionic_conductivity_(solid_state) |
Ionic hydrogenation refers to hydrogenation achieved by the addition of a hydride to substrate that has been activated by an electrophile. Some ionic hydrogenations entail addition of H 2 to the substrate and some entail replacement of a heteroatom with hydride. [ 1 ] Traditionally, the method was developed for acid-induced reductions with hydrosilanes . Alternatively ionic hydrogenation can be achieved using H 2 . [ 2 ] Ionic hydrogenation is employed when the substrate can produce a stable carbonium ion . Polar double bonds are favored substrates.
Because silicon (1.90) is more electropositive than hydrogen (2.20), hydrosilanes exhibit (mild) hydridic character. Hydrosilanes can serve as hydride donors to highly electrophilic organic substrates. Many alcohols, alkyl halides, acetals, orthoesters, alkenes, aldehydes, ketones, and carboxylic acid derivatives are suitable substrates. Such reactions often require Lewis acids . Only reactive electrophiles undergo reduction, selectivity is possible in reactions of substrates with multiple reducible functional groups.
Upon the generation of a carbocation, rate-determining hydride transfer from the organosilane occurs to yield a reduced product. Retention of configuration at silicon has been observed in silane reductions of chiral triaryl methyl chlorides in benzene. This result suggests that the exchange of chlorine for hydrogen occurs through σ-bond metathesis. [ 3 ] Reductions in more polar solvents may involve silicenium ions. [ 4 ]
Polymeric hydrosilanes , such as polymethylhydrosiloxane (PHMS) may be employed to facilitate separation of the reduced products from silicon-containing byproducts. [ 5 ] [ 6 ]
The proton and hydride transfers are usually sequential or concerted. Usually ionic hydrogenation is shown to occur in two steps, starting with protonation.
In the case of metal-catalyzed ionic hydrogenation, the substrates and their products must not bind to metal sites, as this would interfere with H 2 activation. Ketones are the most common substrates. [ 7 ] Less common are imines and N-heterocycles. The reaction can also be performed in reverse to effect hydrogenolysis . Liquid substrates can sometimes be hydrogenated without solvent, a goal of green chemistry . [ 2 ]
The most common hydrogenating pair is an organosilane as the hydride source (e.g. triethylsilane ), and a strong oxyacid as the proton source (e.g. trifluoroacetic acid or triflic acid ). The hydride and proton source cannot combine to give H 2 , which limits the hydricity and acidity of the H − and H + sources, respectively.
Transition metal hydride complexes can be used in place of organosilanes as the hydride source. In these cases, triflic acid is a typical proton donor. Ketones such as benzophenones , and 1,1-disubstituted olefins are typical substrates. Hydrides of tungsten, chromium, osmium, and molybdenum complexes have also been reported. Tungsten dihydride complexes can hydrogenate ketones stoichiometrically with no external acids. One hydride serves as the hydride source, and the other serves as a proton source. [ 2 ]
In the case of ionic hydrogenation, a dihydride complex is regenerated by hydrogen gas following hydrogenation. Typical catalysts are tungsten or molybdenum complexes. An example of such a catalyst is CpMo(CO) 2 (PR 3 )(OCR' 2 )]+ where M = W or Mo. [ 7 ]
Transfer hydrogenation (TH) catalysts, e.g. Shvo catalyst , are related to catalysts used for ionic hydrogenation. TH catalysts however do not employ strong acids and both the H − and H + components are covalently bonded to the complex prior to transfer to the unsaturated substrates. Typically, TH catalysts are more widely employed in organic synthesis. [ 8 ] | https://en.wikipedia.org/wiki/Ionic_hydrogenation |
An ionic liquid ( IL ) is a salt in the liquid state at ambient conditions. In some contexts, the term has been restricted to salts whose melting point is below a specific temperature, such as 100 °C (212 °F). [ 1 ] While ordinary liquids such as water and gasoline are predominantly made of electrically neutral molecules , ionic liquids are largely made of ions . These substances are variously called liquid electrolytes , ionic melts , ionic fluids , fused salts , liquid salts , or ionic glasses . [ 2 ] [ 3 ] [ 4 ]
Ionic liquids have many potential applications. [ 5 ] [ 6 ] They are powerful solvents and can be used as electrolytes . Salts that are liquid at near-ambient temperature are important for electric battery applications, and have been considered as sealants due to their very low vapor pressure .
Any salt that melts without decomposing or vaporizing usually yields an ionic liquid. Sodium chloride (NaCl), for example, melts at 801 °C (1,474 °F) into a liquid that consists largely of sodium cations ( Na + ) and chloride anions ( Cl − ). Conversely, when an ionic liquid is cooled, it often forms an ionic solid —which may be either crystalline or glassy .
The ionic bond is usually stronger than the Van der Waals forces between the molecules of ordinary liquids. Because of these strong interactions, salts tend to have high lattice energies , manifested in high melting points. Some salts, especially those with organic cations, have low lattice energies and thus are liquid at or below room temperature . Examples include compounds based on the 1-ethyl-3-methylimidazolium (EMIM) cation and include: EMIM:Cl , EMIMAc (acetate anion), EMIM dicyanamide , ( C 2 H 5 )( CH 3 ) C 3 H 3 N + 2 · N(CN) − 2 , that melts at −21 °C (−6 °F); [ 7 ] and 1-butyl-3,5-dimethylpyridinium bromide which becomes a glass below −24 °C (−11 °F). [ 8 ]
Low-temperature ionic liquids can be compared to ionic solutions , liquids that contain both ions and neutral molecules, and in particular to the so-called deep eutectic solvents , mixtures of ionic and non-ionic solid substances which have much lower melting points than the pure compounds. Certain mixtures of nitrate salts can have melting points below 100 °C. [ 9 ]
The term "ionic liquid" in the general sense was used as early as 1943. [ 10 ]
The discovery date of the "first" ionic liquid is disputed, along with the identity of its discoverer. Ethanolammonium nitrate (m.p. 52–55 °C) was reported in 1888 by S. Gabriel and J. Weiner. [ 11 ] In 1911 Ray and Rakshit, during preparation of the nitrite salts of ethylamine, dimethylamine, and trimethylamine observed that the reaction between ethylamine hydrochloride and silver nitrate yielded an unstable ethylammonium nitrite ( C 2 H 5 ) NH + 3 · NO − 2 , a heavy yellow liquid which on immersion in a mixture of salt and ice could not be solidified and was probably the first report of room-temperature ionic liquid. [ 12 ] [ 13 ] Later in 1914, Paul Walden reported one of the first stable room-temperature ionic liquids ethylammonium nitrate ( C 2 H 5 ) NH + 3 · NO − 3 (m.p. 12 °C). [ 14 ] In the 1970s and 1980s, ionic liquids based on alkyl-substituted imidazolium and pyridinium cations, with halide or tetrahalogenoaluminate anions, were developed as potential electrolytes in batteries. [ 15 ] [ 16 ]
For the imidazolium halogenoaluminate salts, their physical properties—such as viscosity , melting point , and acidity —could be adjusted by changing the alkyl substituents and the imidazolium/pyridinium and halide/halogenoaluminate ratios. [ 17 ] Two major drawbacks for some applications were moisture sensitivity and acidity or basicity. In 1992, Wilkes and Zawarotko obtained ionic liquids with 'neutral' weakly coordinating anions such as hexafluorophosphate ( PF − 6 ) and tetrafluoroborate ( BF − 4 ), allowing a much wider range of applications. [ 18 ]
ILs are typically colorless viscous liquids. [ 19 ] They are often moderate to poor conductors of electricity, and rarely self-ionize. [ citation needed ] They do, however, have a very large electrochemical window , enabling electrochemical refinement of otherwise intractable ores. [ 19 ]
They exhibit low vapor pressure , which can be as low as 10 −10 Pa. [ 20 ] Many have low combustibility and are thermally stable.
The solubility properties of ILs are diverse. Saturated aliphatic compounds are generally only sparingly soluble in ionic liquids, whereas alkenes show somewhat greater solubility, and aldehydes often completely miscible. Solubility differences can be exploited in biphasic catalysis, such as hydrogenation and hydrocarbonylation processes, allowing for relatively easy separation of products and/or unreacted substrate(s). Gas solubility follows the same trend, with carbon dioxide gas showing good solubility in many ionic liquids. Carbon monoxide is less soluble in ionic liquids than in many popular organic solvents, and hydrogen is only slightly soluble (similar to the solubility in water) and may vary relatively little between the more common ionic liquids.
Many classes of chemical reactions , The miscibility of ionic liquids with water or organic solvents varies with side chain lengths on the cation and with choice of anion . They can be functionalized to act as acids , bases , or ligands , and are precursors salts in the preparation of stable carbenes . Because of their distinctive properties, ionic liquids have been investigated for many applications.
Some ionic liquids can be distilled under vacuum conditions at temperatures near 300 °C. [ 21 ] The vapor is not made up of separated ions, [ 22 ] but consists of ion pairs. [ 23 ]
ILs have a wide liquid range. Some ILs do not freeze down to very low temperatures (even −150 °C), The glass transition temperature was detected below −100 °C in the case of N-methyl-N-alkylpyrrolidinium cations fluorosulfonyl-trifluoromethanesulfonylimide (FTFSI). [ 24 ] Low-temperature ionic liquids (below 130 K ) have been proposed as the fluid base for an extremely large diameter spinning liquid-mirror telescope to be based on the Moon. [ 25 ]
Water is a common impurity in ionic liquids, as it can be absorbed from the atmosphere and influences the transport properties of RTILs, even at relatively low concentrations. [ 4 ]
Classically, ILs consist of salts of unsymmetrical, flexible organic cations with symmetrical weakly coordinating anions . Both cationic and anionic components have been widely varied. [ 4 ]
Room-temperature ionic liquids (RTILs) are dominated by salts derived from 1-methylimidazole, i.e., 1-alkyl-3-methylimidazolium. Examples include 1-ethyl-3-methyl- (EMIM), 1-butyl-3-methyl- (BMIM), 1-octyl-3 methyl (OMIM), 1-decyl-3-methyl-(DMIM), 1-dodecyl-3-methyl- (dodecylMIM). Other imidazolium cations are 1-butyl-2,3-dimethylimidazolium (BMMIM or DBMIM) and 1,3-di(N,N-dimethylaminoethyl)-2-methylimidazolium (DAMI). Other N-heterocyclic cations are derived from pyridine : 4-methyl-N-butyl-pyridinium (MBPy) and N-octylpyridinium (C8Py). Conventional quaternary ammonium cations also form ILs, e.g. tetraethylammonium (TEA) and tetrabutylammonium (TBA).
Typical anions in ionic liquids include the following: tetrafluoroborate (BF 4 ), hexafluorophosphate (PF 6 ), bis-trifluoromethanesulfonimide (NTf 2 ), trifluoromethanesulfonate (OTf), dicyanamide (N(CN) 2 ), hydrogensulfate ( HSO − 4 ), and ethyl sulfate (EtOSO 3 ). Magnetic ionic liquids can be synthesized by incorporating paramagnetic anions, illustrated by 1-butyl-3-methylimidazolium tetrachloroferrate .
Protic ionic liquids are formed via a proton transfer from an acid to a base . [ 26 ] In contrast to other ionic liquids, which generally are formed through a sequence of synthesis steps, [ 2 ] protic ionic liquids can be created more easily by simply mixing the acid and base. [ 26 ]
Phosphonium cations (R 4 P + ) are less common but offer some advantageous properties. [ 27 ] [ 28 ] [ 29 ] Some examples of phosphonium cations are trihexyl(tetradecyl)phosphonium (P 6,6,6,14 ) and tributyl(tetradecyl)phosphonium (P 4,4,4,14 ).
Polymerized ionic liquids, poly(ionic liquid)s or polymeric ionic liquids, all abbreviated as PIL is the polymeric form of ionic liquids. [ 30 ] They have half of the ionicity of ionic liquids since one ion is fixed as the polymer moiety to form a polymeric chain. PILs have a similar range of applications, comparable with those of ionic liquids but the polymer architecture provides a better chance for controlling the ionic conductivity. They have extended the applications of ionic liquids for designing smart materials or solid electrolytes. [ 31 ] [ 32 ]
Many applications have been considered, but few have been commercialized. [ 33 ] [ 34 ] ILs are used in the production of gasoline by catalyzing alkylation . [ 35 ] [ 36 ]
An IL based on tetraalkyl phosphonium iodide is a solvent for tributyltin iodide, which functions as a catalyst to rearrange the monoepoxide of butadiene . This process was commercialized as a route to 2,5-dihydrofuran , but later discontinued. [ 37 ]
ILs improve the catalytic performance of palladium nanoparticles. [ 38 ] Furthermore, ionic liquids can be used as pre-catalysts for chemical transformations. In this regard dialkylimidazoliums such as [EMIM]Ac have been used in the combination with a base to generate N-heterocyclic carbenes (NHCs). These imidazolium based NHCs are known to catalyse a number transformations such as the benzoin condensation and the OTHO reaction. [ 39 ]
Recognizing that approximately 50% of commercial pharmaceuticals are salts, ionic liquid forms of a number of pharmaceuticals have been investigated. Combining a pharmaceutically active cation with a pharmaceutically active anion leads to a Dual Active ionic liquid in which the actions of two drugs are combined. [ 40 ] [ 41 ]
ILs can extract specific compounds from plants for pharmaceutical, nutritional and cosmetic applications, such as the antimalarial drug artemisinin from the plant Artemisia annua . [ 42 ]
The dissolution of cellulose by ILs has attracted interest. [ 43 ] A patent application from 1930 showed that 1-alkylpyridinium chlorides dissolve cellulose. [ 44 ] Following in the footsteps of the lyocell process, which uses hydrated N-methylmorpholine N-oxide as a solvent for pulp and paper. The "valorization" of cellulose, i.e. its conversion to more valuable chemicals, has been achieved by the use of ionic liquids. Representative products are glucose esters, sorbitol , and alkylgycosides. [ 45 ] IL 1-butyl-3-methylimidazolium chloride dissolves freeze-dried banana pulp and with an additional 15% dimethyl sulfoxide , lends itself to carbon-13 NMR analysis. In this way the entire complex of starch , sucrose , glucose , and fructose can be monitored as a function of banana ripening. [ 46 ] [ 47 ]
Beyond cellulose, ILs have also shown potential in the dissolution, extraction, purification, processing and modification of other biopolymers such as chitin / chitosan , starch , alginate , collagen, gelatin , keratin , and fibroin . [ 48 ] [ 49 ] For example, ILs allow for the preparation of biopolymer materials in different forms (e.g. sponges, films, microparticles, nanoparticles, and aerogels) and better biopolymer chemical reactions, leading to biopolymer-based drug/gene-delivery carriers. [ 49 ] Moreover, ILs enable the synthesis of chemically modified starches with high efficiency and degrees of substitution (DS) and the development of various starch-based materials such as thermoplastic starch, composite films, solid polymer electrolytes, nanoparticles and drug carriers. [ 50 ]
The IL 1-butyl-3-methylimidazolium chloride has been investigated for the recovery of uranium and other metals from spent nuclear fuel and other sources. [ 51 ]
ILs are potential heat transfer and storage media in solar thermal energy systems. Concentrating solar thermal facilities such as parabolic troughs and solar power towers focus the sun's energy onto a receiver, which can generate temperatures of around 600 °C (1,112 °F). This heat can then generate electricity in a steam or other cycle. For buffering during cloudy periods or to enable generation overnight, energy can be stored by heating an intermediate fluid. Although nitrate salts have been the medium of choice since the early 1980s, they freeze at 220 °C (428 °F) and thus require heating to prevent solidification. Ionic liquids such as [C 4 mim][ BF 4 ] have more favorable liquid-phase temperature ranges (−75 to 459 °C) and could therefore be excellent liquid thermal storage media and heat transfer fluids. [ 52 ]
ILs can aid the recycling of synthetic goods, plastics, and metals. They offer the specificity required to separate similar compounds from each other, such as separating polymers in plastic waste streams. This has been achieved using lower temperature extraction processes than current approaches [ 53 ] and could help avoid incinerating plastics or dumping them in landfill.
ILs can replace water as the electrolyte in metal-air batteries . ILs are attractive because of their low vapor pressure. Furthermore, ILs have an electrochemical window of up to six volts [ 54 ] (versus 1.23 for water) supporting more energy-dense metals. Energy densities from 900 to 1600 watt-hours per kilogram appear possible. [ 55 ]
ILs can act as dispersing agents in paints to enhance finish, appearance, and drying properties. [ 56 ] ILs are used for dispersing nanomaterials at IOLITEC.
ILs and amines have been investigated for capturing carbon dioxide CO 2 and purifying natural gas . [ 57 ] [ 58 ] [ 59 ]
Some ionic liquids have been shown to reduce friction and wear in basic tribological testing, [ 60 ] [ 61 ] [ 62 ] [ 63 ] and their polar nature makes them candidate lubricants for tribotronic applications. While the comparatively high cost of ionic liquids currently prevents their use as neat lubricants, adding ionic liquids in concentrations as low as 0.5 wt% may significantly alter the lubricating performance of conventional base oils. Thus, the current focus of research is on using ionic liquids as additives to lubricating oils, often with the motivation to replace widely used, ecologically harmful lubricant additives . However, the claimed ecological advantage of ionic liquids has been questioned repeatedly and is yet to be demonstrated from a life-cycle perspective. [ 64 ]
Ionic liquids' low volatility effectively eliminates a major pathway for environmental release and contamination.
Ionic liquids' aquatic toxicity is as severe as or more so than many current solvents. [ 65 ] [ 66 ] [ 67 ]
Ultrasound can degrade solutions of imidazolium-based ionic liquids with hydrogen peroxide and acetic acid to relatively innocuous compounds. [ 68 ]
Despite low vapor pressure many ionic liquids are combustible . [ 69 ] [ 70 ]
When Tawny crazy ants ( Nylanderia fulva ) combat fire ants ( Solenopsis invicta ), the latter spray them with a toxic, lipophilic , alkaloid-based venom. The Tawny crazy ant then exudes its own venom, formic acid , and self-grooms with it, an action which de-toxifies the fire ant venom. The mixed venoms chemically react with one another to form an ionic liquid, the first naturally occurring IL to be described. [ 71 ] | https://en.wikipedia.org/wiki/Ionic_liquid |
The use of ionic liquids in carbon capture is a potential application of ionic liquids as absorbents for use in carbon capture and sequestration . Ionic liquids, which are salts that exist as liquids near room temperature, are polar, nonvolatile materials that have been considered for many applications. The urgency of climate change has spurred research into their use in energy-related applications such as carbon capture and storage .
Amines are the most prevalent absorbent in postcombustion carbon capture technology today. In particular, monoethanolamine (MEA) has been used in industrial scales in postcombustion carbon capture , as well as in other CO 2 separations, such as "sweetening" of natural gas. [ 1 ] However, amines are corrosive, degrade over time, and require large industrial facilities. Ionic liquids on the other hand, have low vapor pressures . This property results from their strong Coulombic attractive force. Vapor pressure remains low through the substance's thermal decomposition point (typically >300 °C). [ 2 ] In principle, this low vapor pressure simplifies their use and makes them " green " alternatives. Additionally, it reduces risk of contamination of the CO 2 gas stream and of leakage into the environment. [ 3 ]
The solubility of CO 2 in ionic liquids is governed primarily by the anion, less so by the cation. [ 4 ] The hexafluorophosphate (PF 6 – ) and tetrafluoroborate (BF 4 – ) anions have been shown to be especially amenable to CO 2 capture. [ 4 ]
Ionic liquids have been considered as solvents in a variety of liquid-liquid extraction processes, but never commercialized. [ 5 ] Beside that, ionic liquids have replaced the conventional volatile solvents in industry such as absorption of gases or extractive distillation . Additionally, ionic liquids are used as co-solutes for the generation of aqueous biphasic systems, or purification of biomolecules.
A typical CO 2 absorption process consists of a feed gas, an absorption column, a stripper column, and output streams of CO 2 -rich gas to be sequestered, and CO 2 -poor gas to be released to the atmosphere. Ionic liquids could follow a similar process to amine gas treating , where the CO 2 is regenerated in the stripper using higher temperature. However, ionic liquids can also be stripped using pressure swings or inert gases, reducing the process energy requirement. [ 3 ] A current issue with ionic liquids for carbon capture is that they have a lower working capacity than amines. Task-specific ionic liquids that employ chemisorption and physisorption are being developed in an attempt to increase the working capacity. 1-butyl-3-propylamineimidazolium tetrafluoroborate is one example of a TSIL. [ 2 ]
In 2023, a research team composed of Chuo University , Nihon University , Kanazawa University , and the Research Institute of Innovative Technology for the Earth utilized electronic state informatics to design and synthesize ionic liquids. [ 6 ] Subsequently, they conducted precise measurements of CO 2 solubility and successfully developed ionic liquids with the highest physical absorption capacity for CO 2 to date. [ 6 ]
In carbon capture an effective absorbent is one which demonstrates a high selectivity, meaning that CO 2 will preferentially dissolve in the absorbent compared to other gaseous components. In post-combustion carbon capture the most salient separation is CO 2 from N 2 , whereas in pre-combustion separation CO is primarily separated from H 2 . Other components and impurities may be present in the flue gas , such as hydrocarbons, SO 2 , or H 2 S. Before selecting the appropriate solvent to use for carbon capture it is critical to ensure that at the given process conditions and flue gas composition CO 2 maintains a much higher solubility in the solvent than the other species in the flue gas and thus has a high selectivity.
The selectivity of CO 2 in ionic liquids has been widely studied by researchers. Generally, polar molecules and molecules with an electric quadrupole moment are highly soluble in liquid ionic substances. [ 7 ] It has been found that at high process temperatures the solubility of CO 2 decreases, while the solubility of other species, such as CH 4 and H 2 , may increase with increasing temperature, thereby reducing the effectiveness of the solvent. However, the solubility of N 2 in ionic liquids is relatively low and does not increase with increasing temperature so the use of ionic liquids in post-combustion carbon capture may be appropriate due to the consistently high CO 2 /N 2 selectivity. [ 8 ] The presence of common flue gas impurities such as H 2 S severely inhibits CO 2 solubility in ionic liquids and should be carefully considered by engineers when choosing an appropriate solvent for a particular flue gas. [ 9 ]
A primary concern with the use of ionic liquids for carbon capture is their high viscosity compared with that of commercial solvents. Ionic liquids which employ chemisorption depend on a chemical reaction between solute and solvent for CO 2 separation. The rate of this reaction is dependent on the diffusivity of CO 2 in the solvent and is thus inversely proportional to viscosity. The self diffusivity of CO 2 in ionic liquids are generally to the order of 10 −10 m 2 /s, [ 10 ] approximately an order of magnitude less than similarly performing commercial solvents used on CO 2 capture. The viscosity of an ionic liquid can vary significantly according to the type of anion and cation, the alkyl chain length, and the amount of water or other impurities in the solvent. [ 11 ] [ 12 ] Because these solvents can be “designed” and these properties chosen, developing ionic liquids with lowered viscosities is a current topic of research. Supported ionic liquid phases (SILPs) are one proposed solution to this problem. [ 5 ]
As required for all separation techniques, ionic liquids exhibit selectivity towards one or more of the phases of a mixture. 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF 6 ) is a room-temperature ionic liquid that was identified early on as a viable substitute for volatile organic solvents in liquid-liquid separations. [ 13 ] Other [PF 6 ]- and [BF 4 ]- containing ionic liquids have been studied for their CO 2 absorption properties, as well as 1-ethyl-3-methylimidazolium (EMIM) and unconventional cations like trihexyl(tetradecyl) phosphonium ([P 66614 ]). [ 3 ] Selection of different anion and cation combinations in ionic liquids affects their selectivity and physical properties. Additionally, the organic cations in ionic liquids can be "tuned" by changing chain lengths or by substituting radicals. [ 5 ] Finally, ionic liquids can be mixed with other ionic liquids, water, or amines to achieve different properties in terms of absorption capacity and heat of absorption. This tunability has led some to call ionic liquids "designer solvents." [ 14 ] 1-butyl-3-propylamineimidazolium tetrafluoroborate was specifically developed for CO 2 capture; it is designed to employ chemisorption to absorb CO 2 and maintain efficiency under repeated absorption/regeneration cycles. [ 2 ] Other ionic liquids have been simulated or experimentally tested for potential use as CO 2 absorbents.
Currently, CO 2 capture uses mostly amine -based absorption technologies, which are energy intensive and solvent intensive. Volatile organic compounds alone in chemical processes represent a multibillion-dollar industry. [ 13 ] Therefore, ionic liquids offer an alternative that prove attractive should their other deficiencies be addressed.
During the capture process, the anion and cation play a crucial role in the dissolution of CO 2 . Spectroscopic results suggest a favorable interaction between the anion and CO 2 , wherein CO 2 molecules preferentially attach to the anion. Furthermore, intermolecular forces , such as hydrogen bonds , van der Waals bonds , and electrostatic attraction, contributes to the solubility of CO 2 in ionic liquids. This makes ionic liquids promising candidates for CO 2 capture because the solubility of CO 2 can be modeled accurately by the regular solubility theory (RST), which reduces operational costs in developing more sophisticated model to monitor the capture process. | https://en.wikipedia.org/wiki/Ionic_liquids_in_carbon_capture |
Similar to Pourbaix diagrams for the speciation of redox species as a function of the redox potential and the pH , ionic partition diagrams indicate in which phase an acid or a base is predominantly present in a biphasic system as a function of the Galvani potential difference between the two phases and the pH of the aqueous solution. One of the functions of these diagrams is to reveal drug transport across biological membranes. [ 1 ]
This electrochemistry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ionic_partition_diagram |
Ionic polymer–metal composites ( IPMCs ) are synthetic composite nanomaterials that display artificial muscle behavior under an applied voltage or electric field. IPMCs are composed of an ionic polymer like Nafion or Flemion whose surfaces are chemically plated or physically coated with conductors such as platinum or gold. Under an applied voltage (1–5 V for typical 10 mm × 40 mm × 0.2 mm samples), ion migration and redistribution due to the imposed voltage across a strip of IPMCs result in a bending deformation. Also, IPMCs can be ionic hydrogel which is being immersed in an electrolyte solution and connected to the electric field indirectly. [ 2 ]
If the plated electrodes are arranged in a non-symmetric configuration, the imposed voltage can induce a variety of deformations such as twisting, rolling, torsioning, turning, twirling, whirling and non-symmetric bending deformation. Alternatively, if such deformations are physically applied to an IPMC strips they generate an output voltage signal (few millivolts for typical small samples) as sensors and energy harvesters. IPMCs are a type of electroactive polymer . They work very well in a liquid environment as well as in air. They have a force density of about 40 in a cantilever configuration, meaning that they can generate a tip force of almost 40 times their own weight in a cantilever mode. IPMCs in actuation, sensing and energy harvesting have a very broad bandwidth to kilo HZ and higher. IPMCs were first introduced in 1998 by Shahinpoor, Bar-Cohen, Xue, Simpson and Smith (see references below) but the original idea of ionic polymer actuators and sensors goes back to 1992-93 by Adolf, Shahinpoor, Segalman, Witkowski, Osada, Okuzaki, Hori, Doi, Matsumoto, Hirose, Oguro, Takenaka, Asaka and Kawami as depicted below:
1-Segalman D. J., Witkowski W. R., Adolf D. B., Shahinpoor M.,"Theory and Application of Electrically Controlled Polymeric Gels", Int. Journal of Smart Material and Structures, vol. 1, pp. 95–100, (1992) 2-Shahinpoor M.,"Conceptual Design, Kinematics and Dynamics of Swimming Robotic Structures Using Ionic Polymeric Gel Muscles", Int. Journal of Smart Material and Structures, vol.1, pp. 91–94, (1992) 3-Y. Osada, H. Okuzaki and H. Hori, "A Polymer Gel with Electrically Driven Motility", Nature, vol. 355, pp. 242–244, (1992) 4-Oguro K., Kawami Y.and Takenaka H.,"Bending of an Ion-Conducting Polymer Film Electrode Composite by An Electric Stimulus at Low Voltage", Trans. J. Micro-Machine Society, vol. 5, pp. 27–30, (1992) 5-M. Doi, M. Marsumoto and Y. Hirose, "Deformation of Ionic Gels by Electric Fields", Macromolecules, vol. 25, pp. 5504–5511, (1992) 6-Oguro, K., K. Asaka, and H. Takenaka, "Polymer film actuator driven by low voltage", In Proceedings of the 4th International Symposium of Micro Machines and Human Science", Nagoya, pp. 38–40, (1993) 7-Adolf D., Shahinpoor M., Segalman D., Witkowski W.,"Electrically Controlled Polymeric Gel Actuators", US Patent Office, US Patent No. 5,250,167, Issued October 5, (1993) 8-Oguro K., Kawami Y.and Takenaka H.,"Actuator Element", US Patent Office, US Patent No. 5,268,082, Issued December 7, (1993)
These patents were followed by additional related patents:
9-Shahinpoor, M., "Spring-Loaded Ionic Polymeric Gel Linear Actuator", US Patent Office, US Patent No. 5,389,222, Issued February 14,(1995) 10-Shahinpoor, M. and Mojarrad, M., "Soft Actuators and Artificial Muscles", US Patent Office, United States Patent 6,109,852, Issued August 29,(2000) 11-Shahinpoor, M. and Mojarrad, M.,"Ionic Polymer Sensors and Actuators", US Patent Office, No. 6,475,639, Issued November 5, (2002) 12-Shahinpoor, M. and Kim, K.J.,“Method of Fabricating a Dry Electro-Active Polymeric Synthetic Muscle”, US Patent Office, Patent No. 7,276,090, Issued October 2,(2007) It should also be mentioned that Tanaka, Nishio and Sun introduced the phenomenon of ionic gel collapse in an electric field: 13-T. Tanaka, I. Nishio and S.T. Sun, "Collapse of Gells in an Electric Field", Science, vol. 218, pp. 467–469, (1982)
It should also be mentioned that Hamlen, Kent and Shafer introduced the electrochemical contraction of ionic polymer fibers:
14-R. P. Hamlen, C. E. Kent and S. N. Shafer, "Electrolytically Activated Contractile Polymer", Nature, vol. 206, no. 4989, pp. 1140–1141, (1965)
Credit should also be extended to Darwin G. Caldwell and Paul M. Taylor for early work on chemically stimulated gels as artificial muscles:
15-Darwin G. Caldwell and Paul M. Taylor,"Chemically stimulated pseudo-muscular actuation", International Journal of Engineering Science, Volume 28, Issue 8, pp. 797–808, (1990) | https://en.wikipedia.org/wiki/Ionic_polymer–metal_composites |
Ionic potential is the ratio of the electrical charge ( z ) to the radius ( r ) of an ion . [ 1 ]
Ionic potential = electrical charge ionic radius = z r {\displaystyle {\text{Ionic potential}}={\frac {\text{electrical charge}}{\text{ionic radius}}}={\frac {z}{r}}}
As such, this ratio is a measure of the charge density at the surface of the ion; usually the denser the charge, the stronger the bond formed by the ion with ions of opposite charge. [ 2 ]
The ionic potential gives an indication of how strongly, or weakly, the ion will be electrostatically attracted by ions of opposite charge; and to what extent the ion will be repelled by ions of the same charge.
Victor Moritz Goldschmidt , the father of modern geochemistry found that the behavior of an element in its environment could be predicted from its ionic potential and illustrated this with a diagram (plot of the bare ionic radius as a function of the ionic charge). [ 3 ] For instance, the solubility of dissolved iron is highly dependent on its redox state. Fe 2+ with a lower ionic potential than Fe 3+ is much more soluble because it exerts a weaker interaction force with OH − ion present in water and exhibits a less pronounced trend to hydrolysis and precipitation . Under reducing conditions Fe(II) can be present at relatively high concentration in anoxic water , similar to these encountered for other divalent species such as Ca 2+ and Mg 2+ . However, once anoxic ground water is pumped from a deep well and is discharged to the surface, it enters in contact with atmospheric oxygen. Then Fe 2+ is easily oxidized to Fe 3+ and this latter rapidly hydrolyzes and precipitates because of its lower solubility due to a higher z/r ratio.
Millot (1970) also illustrated the importance of the ionic potential of cations to explain the high, or the low, solubility of minerals and the expansive behaviour (swelling/shrinking) of clay materials . [ 4 ]
The ionic potential of the different cations ( Na + , K + , Mg 2+ and Ca 2+ ) present in the interlayer of clay minerals also contribute to explain their swelling/shrinking properties. [ 5 ] The more hydrated cations such as Na + and Mg 2+ are responsible for the swelling of smectite while the less hydrated K + and Ca 2+ cause the collapse of the interlayer. In illite , the interlayer is totally collapsed because of the presence of the poorly hydrated K + .
Ionic potential is also a measure of the polarising power of a cation .
Ionic potential could be used as a general criterion for the selection of efficient adsorbents for toxic elements . [ 6 ]
This electrochemistry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ionic_potential |
Ionic radius , r ion , is the radius of a monatomic ion in an ionic crystal structure. Although neither atoms nor ions have sharp boundaries, they are treated as if they were hard spheres with radii such that the sum of ionic radii of the cation and anion gives the distance between the ions in a crystal lattice . Ionic radii are typically given in units of either picometers (pm) or angstroms (Å), with 1 Å = 100 pm. Typical values range from 31 pm (0.3 Å) to over 200 pm (2 Å).
The concept can be extended to solvated ions in liquid solutions taking into consideration the solvation shell .
Ions may be larger or smaller than the neutral atom, depending on the ion's electric charge . When an atom loses an electron to form a cation, the other electrons are more attracted to the nucleus, and the radius of the ion gets smaller. Similarly, when an electron is added to an atom, forming an anion, the added electron increases the size of the electron cloud by interelectronic repulsion.
The ionic radius is not a fixed property of a given ion, but varies with coordination number , spin state and other parameters. Nevertheless, ionic radius values are sufficiently transferable to allow periodic trends to be recognized. As with other types of atomic radius , ionic radii increase on descending a group . Ionic size (for the same ion) also increases with increasing coordination number, and an ion in a high-spin state will be larger than the same ion in a low-spin state. In general, ionic radius decreases with increasing positive charge and increases with increasing negative charge.
An "anomalous" ionic radius in a crystal is often a sign of significant covalent character in the bonding. No bond is completely ionic, and some supposedly "ionic" compounds, especially of the transition metals , are particularly covalent in character. This is illustrated by the unit cell parameters for sodium and silver halides in the table. On the basis of the fluorides, one would say that Ag + is larger than Na + , but on the basis of the chlorides and bromides the opposite appears to be true. [ 1 ] This is because the greater covalent character of the bonds in AgCl and AgBr reduces the bond length and hence the apparent ionic radius of Ag + , an effect which is not present in the halides of the more electropositive sodium, nor in silver fluoride in which the fluoride ion is relatively unpolarizable .
The distance between two ions in an ionic crystal can be determined by X-ray crystallography , which gives the lengths of the sides of the unit cell of a crystal. For example, the length of each edge of the unit cell of sodium chloride is found to be 564.02 pm. Each edge of the unit cell of sodium chloride may be considered to have the atoms arranged as Na + ∙∙∙Cl − ∙∙∙Na + , so the edge is twice the Na-Cl separation. Therefore, the distance between the Na + and Cl − ions is half of 564.02 pm, which is 282.01 pm. However, although X-ray crystallography gives the distance between ions, it doesn't indicate where the boundary is between those ions, so it doesn't directly give ionic radii.
Landé [ 2 ] estimated ionic radii by considering crystals in which the anion and cation have a large difference in size, such as LiI. The lithium ions are so much smaller than the iodide ions that the lithium fits into holes within the crystal lattice, allowing the iodide ions to touch. That is, the distance between two neighboring iodides in the crystal is assumed to be twice the radius of the iodide ion, which was deduced to be 214 pm. This value can be used to determine other radii. For example, the inter-ionic distance in RbI is 356 pm, giving 142 pm for the ionic radius of Rb + . In this way values for the radii of 8 ions were determined.
Wasastjerna estimated ionic radii by considering the relative volumes of ions as determined from electrical polarizability as determined by measurements of refractive index . [ 3 ] These results were extended by Victor Goldschmidt . [ 4 ] Both Wasastjerna and Goldschmidt used a value of 132 pm for the O 2− ion.
Pauling used effective nuclear charge to proportion the distance between ions into anionic and a cationic radii. [ 5 ] His data gives the O 2− ion a radius of 140 pm.
A major review of crystallographic data led to the publication of revised ionic radii by Shannon. [ 6 ] Shannon gives different radii for different coordination numbers, and for high and low spin states of the ions. To be consistent with Pauling's radii, Shannon has used a value of r ion (O 2− ) = 140 pm; data using that value are referred to as "effective" ionic radii. However, Shannon also includes data based on r ion (O 2− ) = 126 pm; data using that value are referred to as "crystal" ionic radii. Shannon states that "it is felt that crystal radii correspond more closely to the physical size of ions in a solid." [ 6 ] The two sets of data are listed in the two tables below.
For many compounds, the model of ions as hard spheres does not reproduce the distance between ions, d m x {\displaystyle {d_{mx}}} , to the accuracy with which it can be measured in crystals. One approach to improving the calculated accuracy is to model ions as "soft spheres" that overlap in the crystal. Because the ions overlap, their separation in the crystal will be less than the sum of their soft-sphere radii. [ 12 ]
The relation between soft-sphere ionic radii, r m {\displaystyle {r_{m}}} and r x {\displaystyle {r_{x}}} , and d m x {\displaystyle {d_{mx}}} , is given by
where k {\displaystyle k} is an exponent that varies with the type of crystal structure. In the hard-sphere model, k {\displaystyle k} would be 1, giving d m x = r m + r x {\displaystyle {d_{mx}}={r_{m}}+{r_{x}}} .
In the soft-sphere model, k {\displaystyle k} has a value between 1 and 2.
For example, for crystals of group 1 halides with the sodium chloride structure , a value of 1.6667 gives good agreement with experiment.
Some soft-sphere ionic radii are in the table.
These radii are larger than the crystal radii given above (Li + , 90 pm; Cl − , 167 pm). Inter-ionic separations calculated with these radii give remarkably good agreement with experimental values. Some data are given in the table. Curiously, no theoretical justification for the equation containing k {\displaystyle k} has been given.
The concept of ionic radii is based on the assumption of a spherical ion shape. However, from a group-theoretical point of view the assumption is only justified for ions that reside on high-symmetry crystal lattice sites like Na and Cl in halite or Zn and S in sphalerite . A clear distinction can be made, when the point symmetry group of the respective lattice site is considered, [ 13 ] which are the cubic groups O h and T d in NaCl and ZnS. For ions on lower-symmetry sites significant deviations of their electron density from a spherical shape may occur. This holds in particular for ions on lattice sites of polar symmetry, which are the crystallographic point groups C 1 , C 1 h , C n or C nv , n = 2, 3, 4 or 6. [ 14 ] A thorough analysis of the bonding geometry was recently carried out for pyrite-type compounds, where monovalent chalcogen ions reside on C 3 lattice sites. It was found that chalcogen ions have to be modeled by ellipsoidal charge distributions with different radii along the symmetry axis and perpendicular to it. [ 15 ] | https://en.wikipedia.org/wiki/Ionic_radius |
The ionic strength of a solution is a measure of the concentration of ions in that solution. Ionic compounds , when dissolved in water, dissociate into ions. The total electrolyte concentration in solution will affect important properties such as the dissociation constant or the solubility of different salts . One of the main characteristics of a solution with dissolved ions is the ionic strength. Ionic strength can be molar (mol/L solution) or molal (mol/kg solvent) and to avoid confusion the units should be stated explicitly. [ 1 ] The concept of ionic strength was first introduced by Lewis and Randall in 1921 while describing the activity coefficients of strong electrolytes . [ 2 ]
The molar ionic strength , I , of a solution is a function of the concentration of all ions present in that solution . [ 3 ]
where one half is because we are including both cations and anions , c i is the molar concentration of ion i (M, mol/L), z i is the charge number of that ion, and the sum is taken over all ions in the solution. For a 1:1 electrolyte such as sodium chloride , where each ion is singly-charged, the ionic strength is equal to the concentration. For the electrolyte MgSO 4 , however, each ion is doubly-charged, leading to an ionic strength that is four times higher than an equivalent concentration of sodium chloride:
Generally multivalent ions contribute strongly to the ionic strength.
As a more complex example, the ionic strength of a mixed solution 0.050 M in Na 2 SO 4 and 0.020 M in KCl is:
Because in non- ideal solutions volumes are no longer strictly additive it is often preferable to work with molality b (mol/kg of H 2 O) rather than molarity c (mol/L). In that case, molal ionic strength is defined as:
in which
The ionic strength plays a central role in the Debye–Hückel theory that describes the strong deviations from ideality typically encountered in ionic solutions. [ 5 ] [ 6 ] It is also important for the theory of double layer and related electrokinetic phenomena and electroacoustic phenomena in colloids and other heterogeneous systems. That is, the Debye length , which is the inverse of the Debye parameter ( κ ), is inversely proportional to the square root of the ionic strength. Both molar and molal ionic strength have been used, often without explicit definition. Debye length is characteristic of the double layer thickness. Increasing the concentration or valence of the counterions compresses the double layer and increases the electrical potential gradient .
Media of high ionic strength are used in stability constant determination in order to minimize changes, during a titration, in the activity quotient of solutes at lower concentrations. Natural waters such as mineral water and seawater have often a non-negligible ionic strength due to the presence of dissolved salts which significantly affects their properties. | https://en.wikipedia.org/wiki/Ionic_strength |
Ionic transfer is the transfer of ions from one liquid phase to another. This is related to the phase transfer catalysts which are a special type of liquid-liquid extraction which is used in synthetic chemistry .
For instance nitrate anions can be transferred between water and nitrobenzene . One way to observe this is to use a cyclic voltammetry experiment where the liquid-liquid interface is the working electrode . This can be done by placing secondary electrodes in each phase and close to interface each phase has a reference electrode . One phase is attached to a potentiostat [ 1 ] which is set to zero volts, while the other potentiostat is driven with a triangular wave. This experiment is known as a polarised Interface between Two Immiscible Electrolyte Solutions ( ITIES ) experiment. | https://en.wikipedia.org/wiki/Ionic_transfer |
Ionium-thorium dating is a technique for determining the age of marine sediments based upon the quantities present of nearly stable thorium-232 and more radioactive thorium-230 . ( 230 Th was once known as ionium, before it was realised it was the same element as 232 Th.)
Uranium (in nature, predominantly uranium-238 ) is soluble in water. However, when it decays into thorium , the latter element is insoluble and so precipitates out to become part of the sediment. [ 1 ] Thorium-232 has a half-life of 14.5 billion years, but thorium-230 has a half-life of only 75,200 [ 2 ] years, so the ratio is useful for dating sediments up to 400,000 years old. [ 1 ] Conversely, this technique can be used to determine the rate of ocean sedimentation over time. [ 2 ]
The ionium/thorium method of dating assumes that the proportion of thorium-230 to thorium-232 is a constant during the time period that the sediment layer was formed. Likewise, both thorium-230 and thorium-232 are assumed to precipitate out in a constant ratio; no chemical process favors one form over the other. It must also be assumed that the sediment does not contain any pre-existing particles of eroded rock, known as detritus , that already contain thorium isotopes. Finally, there must not be a process that causes the thorium to shift its position within the sediment. If these assumptions are correct, this dating technique can produce accurate results. [ 1 ] [ 2 ]
This radioactivity –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ionium–thorium_dating |
Ionization or ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons , often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion . Ionization can result from the loss of an electron after collisions with subatomic particles , collisions with other atoms, molecules, electrons, positrons , [ 1 ] protons , antiprotons , [ 2 ] and ions, [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] or through the interaction with electromagnetic radiation . [ 11 ] Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs. Ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected.
Everyday examples of gas ionization occur within a fluorescent lamp or other electrical discharge lamps. It is also used in radiation detectors such as the Geiger-Müller counter or the ionization chamber . The ionization process is widely used in a variety of equipment in fundamental science (e.g., mass spectrometry ) and in medical treatment (e.g., radiation therapy ). It is also widely used for air purification , though studies have shown harmful effects of this application. [ 12 ] [ 13 ]
Negatively charged ions [ 14 ] are produced when a free electron collides with an atom and is subsequently trapped inside the electric potential barrier, releasing any excess energy. The process is known as electron capture ionization .
Positively charged ions are produced by transferring an amount of energy to a bound electron in a collision with charged particles (e.g. ions, electrons or positrons) or with photons. The threshold amount of the required energy is known as ionization energy . The study of such collisions is of fundamental importance with regard to the few-body problem , which is one of the major unsolved problems in physics. Kinematically complete experiments , [ 15 ] i.e. experiments in which the complete momentum vector of all collision fragments (the scattered projectile, the recoiling target-ion, and the ejected electron) are determined, have contributed to major advances in the theoretical understanding of the few-body problem in recent years.
Adiabatic ionization is a form of ionization in which an electron is removed from or added to an atom or molecule in its lowest energy state to form an ion in its lowest energy state. [ 16 ]
The Townsend discharge is a good example of the creation of positive ions and free electrons due to ion impact. It is a cascade reaction involving electrons in a region with a sufficiently high electric field in a gaseous medium that can be ionized, such as air . Following an original ionization event, due to such as ionizing radiation, the positive ion drifts towards the cathode , while the free electron drifts towards the anode of the device. If the electric field is strong enough, the free electron gains sufficient energy to liberate a further electron when it next collides with another molecule. The two free electrons then travel towards the anode and gain sufficient energy from the electric field to cause impact ionization when the next collisions occur; and so on. This is effectively a chain reaction of electron generation, and is dependent on the free electrons gaining sufficient energy between collisions to sustain the avalanche. [ 17 ]
Ionization efficiency is the ratio of the number of ions formed to the number of electrons or photons used. [ 18 ] [ 19 ]
The trend in the ionization energy of atoms is often used to demonstrate the periodic behavior of atoms with respect to the atomic number, as summarized by ordering atoms in Mendeleev's table . This is a valuable tool for establishing and understanding the ordering of electrons in atomic orbitals without going into the details of wave functions or the ionization process. An example is presented in the figure to the right. The periodic abrupt decrease in ionization potential after rare gas atoms, for instance, indicates the emergence of a new shell in alkali metals . In addition, the local maximums in the ionization energy plot, moving from left to right in a row, are indicative of s, p, d, and f sub-shells.
Classical physics and the Bohr model of the atom can qualitatively explain photoionization and collision-mediated ionization. In these cases, during the ionization process, the energy of the electron exceeds the energy difference of the potential barrier it is trying to pass. The classical description, however, cannot describe tunnel ionization since the process involves the passage of electron through a classically forbidden potential barrier.
The interaction of atoms and molecules with sufficiently strong laser pulses or with other charged particles leads to the ionization to singly or multiply charged ions. The ionization rate, i.e. the ionization probability in unit time, can be calculated using quantum mechanics . (There are classical methods available also, like the Classical Trajectory Monte Carlo Method (CTMC), [ 20 ] [ 21 ] but it is not overall accepted and often criticized by the community.) There are two quantum mechanical methods exist, perturbative and non-perturbative methods like time-dependent coupled-channel or time independent close coupling [ 22 ] methods where the wave function is expanded in a finite basis set. There are numerous options available e.g. B-splines, [ 23 ] generalized Sturmians [ 24 ] or Coulomb wave packets. [ 25 ] [ 26 ] Another non-perturbative method is to solve the corresponding Schrödinger equation fully numerically on a lattice. [ 27 ]
In general, the analytic solutions are not available, and the approximations required for manageable numerical calculations do not provide accurate enough results. However, when the laser intensity is sufficiently high, the detailed structure of the atom or molecule can be ignored and analytic solution for the ionization rate is possible.
Tunnel ionization is ionization due to quantum tunneling . In classical ionization, an electron must have enough energy to make it over the potential barrier, but quantum tunneling allows the electron simply to go through the potential barrier instead of going all the way over it because of the wave nature of the electron. The probability of an electron's tunneling through the barrier drops off exponentially with the width of the potential barrier. Therefore, an electron with a higher energy can make it further up the potential barrier, leaving a much thinner barrier to tunnel through and thus a greater chance to do so. In practice, tunnel ionization is observable when the atom or molecule is interacting with near-infrared strong laser pulses. This process can be understood as a process by which a bounded electron, through the absorption of more than one photon from the laser field, is ionized. This picture is generally known as multiphoton ionization (MPI).
Keldysh [ 28 ] modeled the MPI process as a transition of the electron from the ground state of the atom to the Volkov states. [ 29 ] In this model the perturbation of the ground state by the laser field is neglected and the details of atomic structure in determining the ionization probability are not taken into account. The major difficulty with Keldysh's model was its neglect of the effects of Coulomb interaction on the final state of the electron. As it is observed from figure, the Coulomb field is not very small in magnitude compared to the potential of the laser at larger distances from the nucleus. This is in contrast to the approximation made by neglecting the potential of the laser at regions near the nucleus. Perelomov et al. [ 30 ] [ 31 ] included the Coulomb interaction at larger internuclear distances. Their model (which we call the PPT model) was derived for short range potential and includes the effect of the long range Coulomb interaction through the first order correction in the quasi-classical action. Larochelle et al. [ 32 ] have compared the theoretically predicted ion versus intensity curves of rare gas atoms interacting with a Ti:Sapphire laser with experimental measurement. They have shown that the total ionization rate predicted by the PPT model fit very well the experimental ion yields for all rare gases in the intermediate regime of the Keldysh parameter.
The rate of MPI on atom with an ionization potential E i {\displaystyle E_{i}} in a linearly polarized laser with frequency ω {\displaystyle \omega } is given by
where
The coefficients f l m {\displaystyle f_{lm}} , g ( γ ) {\displaystyle g(\gamma )} and C n ∗ l ∗ {\displaystyle C_{n^{*}l^{*}}} are given by
The coefficient A m ( ω , γ ) {\displaystyle A_{m}(\omega ,\gamma )} is given by
where
The quasi-static tunneling (QST) is the ionization whose rate can be satisfactorily predicted by the ADK model, [ 33 ] i.e. the limit of the PPT model when γ {\displaystyle \gamma } approaches zero. [ 34 ] The rate of QST is given by
As compared to W P P T {\displaystyle W_{PPT}} the absence of summation over n, which represent different above threshold ionization (ATI) peaks, is remarkable.
The calculations of PPT are done in the E -gauge, meaning that the laser field is taken as electromagnetic waves. The ionization rate can also be calculated in A -gauge, which emphasizes the particle nature of light (absorbing multiple photons during ionization). This approach was adopted by Krainov model [ 35 ] based on the earlier works of Faisal [ 36 ] and Reiss. [ 37 ] The resulting rate is given by
where:
In calculating the rate of MPI of atoms only transitions to the continuum states are considered. Such an approximation is acceptable as long as there is no multiphoton resonance between the ground state and some excited states. However, in real situation of interaction with pulsed lasers, during the evolution of laser intensity, due to different Stark shift of the ground and excited states there is a possibility that some excited state go into multiphoton resonance with the ground state. Within the dressed atom picture, the ground state dressed by m {\displaystyle m} photons and the resonant state undergo an avoided crossing at the resonance intensity I r {\displaystyle I_{r}} . The minimum distance, V m {\displaystyle V_{m}} , at the avoided crossing is proportional to the generalized Rabi frequency, Γ ( t ) = Γ m I ( t ) m / 2 {\displaystyle \Gamma (t)=\Gamma _{m}I(t)^{m/2}} coupling the two states. According to Story et al., [ 38 ] the probability of remaining in the ground state, P g {\displaystyle P_{g}} , is given by
where W {\displaystyle W} is the time-dependent energy difference between the two dressed states. In interaction with a short pulse, if the dynamic resonance is reached in the rising or the falling part of the pulse, the population practically remains in the ground state and the effect of multiphoton resonances may be neglected. However, if the states go onto resonance at the peak of the pulse, where d W / d t = 0 {\displaystyle \mathrm {d} W/\mathrm {d} t=0} , then the excited state is populated. After being populated, since the ionization potential of the excited state is small, it is expected that the electron will be instantly ionized.
In 1992, de Boer and Muller [ 39 ] showed that Xe atoms subjected to short laser pulses could survive in the highly excited states 4f, 5f, and 6f. These states were believed to have been excited by the dynamic Stark shift of the levels into multiphoton resonance with the field during the rising part of the laser pulse. Subsequent evolution of the laser pulse did not completely ionize these states, leaving behind some highly excited atoms. We shall refer to this phenomenon as "population trapping".
We mention the theoretical calculation that incomplete ionization occurs whenever there is parallel resonant excitation into a common level with ionization loss. [ 40 ] We consider a state such as 6f of Xe which consists of 7 quasi-degnerate levels in the range of the laser bandwidth. These levels along with the continuum constitute a lambda system. The mechanism of the lambda type trapping is schematically presented in figure. At the rising part of the pulse (a) the excited state (with two degenerate levels 1 and 2) are not in multiphoton resonance with the ground state. The electron is ionized through multiphoton coupling with the continuum. As the intensity of the pulse is increased the excited state and the continuum are shifted in energy due to the Stark shift. At the peak of the pulse (b) the excited states go into multiphoton resonance with the ground state. As the intensity starts to decrease (c), the two state are coupled through continuum and the population is trapped in a coherent superposition of the two states. Under subsequent action of the same pulse, due to interference in the transition amplitudes of the lambda system, the field cannot ionize the population completely and a fraction of the population will be trapped in a coherent superposition of the quasi degenerate levels. According to this explanation the states with higher angular momentum – with more sublevels – would have a higher probability of trapping the population. In general the strength of the trapping will be determined by the strength of the two photon coupling between the quasi-degenerate levels via the continuum. In 1996, using a very stable laser and by minimizing the masking effects of the focal region expansion with increasing intensity, Talebpour et al. [ 41 ] observed structures on the curves of singly charged ions of Xe, Kr and Ar. These structures were attributed to electron trapping in the strong laser field. A more unambiguous demonstration of population trapping has been reported by T. Morishita and C. D. Lin . [ 42 ]
The phenomenon of non-sequential ionization (NSI) of atoms exposed to intense laser fields has been a subject of many theoretical and experimental studies since 1983. The pioneering work began with the observation of a "knee" structure on the Xe 2+ ion signal versus intensity curve by L’Huillier et al. [ 43 ] From the experimental point of view, the NS double ionization refers to processes which somehow enhance the rate of production of doubly charged ions by a huge factor at intensities below the saturation intensity of the singly charged ion. Many, on the other hand, prefer to define the NSI as a process by which two electrons are ionized nearly simultaneously. This definition implies that apart from the sequential channel A + L − > A + + L − > A + + {\displaystyle A+L->A^{+}+L->A^{++}} there is another channel A + L − > A + + {\displaystyle A+L->A^{++}} which is the main contribution to the production of doubly charged ions at lower intensities. The first observation of triple NSI in argon interacting with a 1 μm laser was reported by Augst et al. [ 44 ] Later, systematically studying the NSI of all rare gas atoms, the quadruple NSI of Xe was observed. [ 45 ] The most important conclusion of this study was the observation of the following relation between the rate of NSI to any charge state and the rate of tunnel ionization (predicted by the ADK formula) to the previous charge states;
where W A D K ( A i + ) {\displaystyle W_{ADK}\left(A^{i+}\right)} is the rate of quasi-static tunneling to i'th charge state and α n ( λ ) {\displaystyle \alpha _{n}(\lambda )} are some constants depending on the wavelength of the laser (but not on the pulse duration).
Two models have been proposed to explain the non-sequential ionization; the shake-off model and electron re-scattering model. The shake-off (SO) model, first proposed by Fittinghoff et al., [ 46 ] is adopted from the field of ionization of atoms by X rays and electron projectiles where the SO process is one of the major mechanisms responsible for the multiple ionization of atoms. The SO model describes the NSI process as a mechanism where one electron is ionized by the laser field and the departure of this electron is so rapid that the remaining electrons do not have enough time to adjust themselves to the new energy states. Therefore, there is a certain probability that, after the ionization of the first electron, a second electron is excited to states with higher energy (shake-up) or even ionized (shake-off). We should mention that, until now, there has been no quantitative calculation based on the SO model, and the model is still qualitative.
The electron rescattering model was independently developed by Kuchiev, [ 47 ] Schafer et al , [ 48 ] Corkum, [ 49 ] Becker and Faisal [ 50 ] and Faisal and Becker. [ 51 ] The principal features of the model can be understood easily from Corkum's version. Corkum's model describes the NS ionization as a process whereby an electron is tunnel ionized. The electron then interacts with the laser field where it is accelerated away from the nuclear core. If the electron has been ionized at an appropriate phase of the field, it will pass by the position of the remaining ion half a cycle later, where it can free an additional electron by electron impact. Only half of the time the electron is released with the appropriate phase and the other half it never return to the nuclear core. The maximum kinetic energy that the returning electron can have is 3.17 times the ponderomotive potential ( U p {\displaystyle U_{p}} ) of the laser. Corkum's model places a cut-off limit on the minimum intensity ( U p {\displaystyle U_{p}} is proportional to intensity) where ionization due to re-scattering can occur.
The re-scattering model in Kuchiev's version (Kuchiev's model) is quantum mechanical. The basic idea of the model is illustrated by Feynman diagrams in figure a. First both electrons are in the ground state of an atom. The lines marked a and b describe the corresponding atomic states. Then the electron a is ionized. The beginning of the ionization process is shown by the intersection with a sloped dashed line. where the MPI occurs. The propagation of the ionized electron in the laser field, during which it absorbs other photons (ATI), is shown by the full thick line. The collision of this electron with the parent atomic ion is shown by a vertical dotted line representing the Coulomb interaction between the electrons. The state marked with c describes the ion excitation to a discrete or continuum state. Figure b describes the exchange process. Kuchiev's model, contrary to Corkum's model, does not predict any threshold intensity for the occurrence of NS ionization.
Kuchiev did not include the Coulomb effects on the dynamics of the ionized electron. This resulted in the underestimation of the double ionization rate by a huge factor. Obviously, in the approach of Becker and Faisal (which is equivalent to Kuchiev's model in spirit), this drawback does not exist. In fact, their model is more exact and does not suffer from the large number of approximations made by Kuchiev. Their calculation results perfectly fit with the experimental results of Walker et al. [ 52 ] Becker and Faisal [ 53 ] have been able to fit the experimental results on the multiple NSI of rare gas atoms using their model. As a result, the electron re-scattering can be taken as the main mechanism for the occurrence of the NSI process.
The ionization of inner valence electrons are responsible for the fragmentation of polyatomic molecules in strong laser fields. According to a qualitative model [ 54 ] [ 55 ] the dissociation of the molecules occurs through a three-step mechanism:
The short pulse induced molecular fragmentation may be used as an ion source for high performance mass spectroscopy. The selectivity provided by a short pulse based source is superior to that expected when using the conventional electron ionization based sources, in particular when the identification of optical isomers is required. [ 56 ] [ 57 ]
Sources: [ 58 ] [ 59 ]
The Kramers–Henneberger(KF) frame is the non-inertial frame moving with the free electron under the influence of the harmonic laser pulse, obtained by applying a translation to the laboratory frame equal to the quiver motion of a classical electron in the laboratory frame. In other words, in the Kramers–Henneberger frame the classical electron is at rest. [ 60 ] Starting in the lab frame (velocity gauge), we may describe the electron with the Hamiltonian:
In the dipole approximation, the quiver motion of a classical electron in the laboratory frame for an arbitrary field can be obtained from the vector potential of the electromagnetic field:
where α 0 ≡ E 0 ω − 2 {\displaystyle \alpha _{0}\equiv E_{0}\omega ^{-2}} for a monochromatic plane wave.
By applying a transformation to the laboratory frame equal to the quiver motion α ( t ) {\displaystyle \mathbf {\alpha } (t)} one moves to the ‘oscillating’ or ‘Kramers–Henneberger’ frame, in which the classical electron is at rest. By a phase factor transformation for convenience one obtains the ‘space-translated’ Hamiltonian, which is unitarily equivalent to the lab-frame Hamiltonian, which contains the original potential centered on the oscillating point − α ( t ) {\displaystyle -\mathbf {\alpha } (t)} :
The utility of the KH frame lies in the fact that in this frame the laser-atom interaction can be reduced to the form of an oscillating potential energy, where the natural parameters describing the electron dynamics are ω {\displaystyle \omega } and α 0 {\displaystyle \alpha _{0}} (sometimes called the “excursion amplitude’, obtained from α ( t ) {\displaystyle \mathbf {\alpha } (t)} ).
From here one can apply Floquet theory to calculate quasi-stationary solutions of the TDSE. In high frequency Floquet theory, to lowest order in ω − 1 {\displaystyle \omega ^{-1}} the system reduces to the so-called ‘structure equation’, which has the form of a typical energy-eigenvalue Schrödinger equation containing the ‘dressed potential’ V 0 ( α 0 , r ) {\displaystyle V_{0}(\alpha _{0},\mathbf {r} )} (the cycle-average of the oscillating potential). The interpretation of the presence of V 0 {\displaystyle V_{0}} is as follows: in the oscillating frame, the nucleus has an oscillatory motion of trajectory − α ( t ) {\displaystyle -\mathbf {\alpha } (t)} and V 0 {\displaystyle V_{0}} can be seen as the potential of the smeared out nuclear charge along its trajectory.
The KH frame is thus employed in theoretical studies of strong-field ionization and atomic stabilization (a predicted phenomenon in which the ionization probability of an atom in a high-intensity, high-frequency field actually decreases for intensities above a certain threshold) in conjunction with high-frequency Floquet theory. [ 61 ]
The KF frame was successfully applied for different problems as well e.g. for higher-hamonic generation from a metal surface in a powerful laser field [ 62 ]
A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar dissociate in water (sugar is dissolved) but exist as intact neutral entities. Another subtle event is the dissociation of sodium chloride (table salt) into sodium and chlorine ions. Although it may seem as a case of ionization, in reality the ions already exist within the crystal lattice. When salt is dissociated, its constituent ions are simply surrounded by water molecules and their effects are visible (e.g. the solution becomes electrolytic ). However, no transfer or displacement of electrons occurs. | https://en.wikipedia.org/wiki/Ionization |
For each atom, the column marked 1 is the first ionization energy to ionize the neutral atom, the column marked 2 is the second ionization energy to remove a second electron from the +1 ion, the column marked 3 is the third ionization energy to remove a third electron from the +2 ion, and so on.
"use" and "WEL" give ionization energy in the unit kJ/mol ; "CRC" gives atomic ionization energy in the unit eV . [ 1 ]
As quoted at http://www.webelements.com/ from these sources: | https://en.wikipedia.org/wiki/Ionization_energies_of_the_elements_(data_page) |
In physics and chemistry , ionization energy ( IE ) is the minimum energy required to remove the most loosely bound electron of an isolated gaseous atom , positive ion , or molecule . [ 1 ] The first ionization energy is quantitatively expressed as
where X is any atom or molecule, X + is the resultant ion when the original atom was stripped of a single electron, and e − is the removed electron. [ 2 ] Ionization energy is positive for neutral atoms, meaning that the ionization is an endothermic process . Roughly speaking, the closer the outermost electrons are to the nucleus of the atom , the higher the atom's ionization energy.
In physics, ionization energy (IE) is usually expressed in electronvolts (eV) or joules (J). In chemistry, it is expressed as the energy to ionize a mole of atoms or molecules, usually as kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol). [ 3 ]
Comparison of ionization energies of atoms in the periodic table reveals two periodic trends which follow the rules of Coulombic attraction : [ 4 ]
The latter trend results from the outer electron shell being progressively farther from the nucleus, with the addition of one inner shell per row as one moves down the column.
The n th ionization energy refers to the amount of energy required to remove the most loosely bound electron from the species having a positive charge of ( n − 1). For example, the first three ionization energies are defined as follows:
The most notable influences that determine ionization energy include:
Minor influences include:
The term ionization potential is an older and obsolete term [ 6 ] for ionization energy, [ 7 ] because the oldest method of measuring ionization energy was based on ionizing a sample and accelerating the electron removed using an electrostatic potential .
The ionization energy of atoms, denoted E i , is measured [ 8 ] by finding the minimal energy of light quanta ( photons ) or electrons accelerated to a known energy that will kick out the least bound atomic electrons. The measurement is performed in the gas phase on single atoms. While only noble gases occur as monatomic gases , other gases can be split into single atoms. [ citation needed ] Also, many solid elements can be heated and vaporized into single atoms. Monatomic vapor is contained in a previously evacuated tube that has two parallel electrodes connected to a voltage source. The ionizing excitation is introduced through the walls of the tube or produced within.
When ultraviolet light is used, the wavelength is swept down the ultraviolet range. At a certain wavelength (λ) and frequency of light (ν=c/λ, where c is the speed of light), the light quanta, whose energy is proportional to the frequency, will have energy high enough to dislodge the least bound electrons. These electrons will be attracted to the positive electrode, and the positive ions remaining after the photoionization will get attracted to the negatively charged electrode. These electrons and ions will establish a current through the tube. The ionization energy will be the energy of photons hν i ( h is the Planck constant ) that caused a steep rise in the current: E i = hν i .
When high-velocity electrons are used to ionize the atoms, they are produced by an electron gun inside a similar evacuated tube. The energy of the electron beam can be controlled by the acceleration voltages. The energy of these electrons that gives rise to a sharp onset of the current of ions and freed electrons through the tube will match the ionization energy of the atoms.
Generally, the ( N +1)th ionization energy of a particular element is larger than the N th ionization energy (it may also be noted that the ionization energy of an anion is generally less than that of cations and neutral atom for the same element). When the next ionization energy involves removing an electron from the same electron shell, the increase in ionization energy is primarily due to the increased net charge of the ion from which the electron is being removed. Electrons removed from more highly charged ions experience greater forces of electrostatic attraction; thus, their removal requires more energy. In addition, when the next ionization energy involves removing an electron from a lower electron shell, the greatly decreased distance between the nucleus and the electron also increases both the electrostatic force and the distance over which that force must be overcome to remove the electron. Both of these factors further increase the ionization energy.
Some values for elements of the third period are given in the following table:
Large jumps in the successive molar ionization energies occur when passing noble gas configurations. For example, as can be seen in the table above, the first two molar ionization energies of magnesium (stripping the two 3s electrons from a magnesium atom) are much smaller than the third, which requires stripping off a 2p electron from the neon configuration of Mg 2+ . That 2p electron is much closer to the nucleus than the 3s electrons removed previously.
Ionization energy is also a periodic trend within the periodic table. Moving left to right within a period , or upward within a group , the first ionization energy generally increases, [ 9 ] with exceptions such as aluminium and sulfur in the table above. As the nuclear charge of the nucleus increases across the period, the electrostatic attraction increases between electrons and protons, hence the atomic radius decreases, and the electron cloud comes closer to the nucleus [ 10 ] because the electrons, especially the outermost one, are held more tightly by the higher effective nuclear charge.
On moving downward within a given group, the electrons are held in higher-energy shells with higher principal quantum number n, further from the nucleus and therefore are more loosely bound so that the ionization energy decreases. The effective nuclear charge increases only slowly so that its effect is outweighed by the increase in n. [ 11 ]
There are exceptions to the general trend of rising ionization energies within a period. For example, the value decreases from beryllium ( 4 Be : 9.3 eV) to boron ( 5 B : 8.3 eV), and from nitrogen ( 7 N : 14.5 eV) to oxygen ( 8 O : 13.6 eV). These dips can be explained in terms of electron configurations. [ 12 ]
Boron has its last electron in a 2p orbital, which has its electron density further away from the nucleus on average than the 2s electrons in the same shell. The 2s electrons then shield the 2p electron from the nucleus to some extent, and it is easier to remove the 2p electron from boron than to remove a 2s electron from beryllium, resulting in a lower ionization energy for B. [ 2 ]
In oxygen, the last electron shares a doubly occupied p-orbital with an electron of opposing spin . The two electrons in the same orbital are closer together on average than two electrons in different orbitals, so that they shield each other from the nucleus more effectively and it is easier to remove one electron, resulting in a lower ionization energy. [ 2 ] [ 13 ]
Furthermore, after every noble gas element, the ionization energy drastically drops. This occurs because the outer electron in the alkali metals requires a much lower amount of energy to be removed from the atom than the inner shells. This also gives rise to low electronegativity values for the alkali metals. [ 14 ] [ 15 ] [ 16 ]
The trends and exceptions are summarized in the following subsections:
Ionization energy values tend to decrease on going to heavier elements within a group [ 12 ] as shielding is provided by more electrons and overall, the valence shells experience a weaker attraction from the nucleus, attributed to the larger covalent radius which increase on going down a group [ 27 ] Nonetheless, this is not always the case. As one exception, in Group 10 palladium ( 46 Pd : 8.34 eV) has a higher ionization energy than nickel ( 28 Ni : 7.64 eV), contrary to the general decrease for the elements from technetium 43 Tc to xenon 54 Xe . Such anomalies are summarized below:
The ionization energy of the hydrogen atom ( Z = 1 {\displaystyle Z=1} ) can be evaluated in the Bohr model , [ 38 ] which predicts that the atomic energy level n {\displaystyle n} has energy
R H is the Rydberg constant for the hydrogen atom. For hydrogen in the ground state Z = 1 {\displaystyle Z=1} and n = 1 {\displaystyle n=1} so that the energy of the atom before ionization is simply E = − 13.6 e V {\displaystyle E=-13.6\ \mathrm {eV} }
After ionization, the energy is zero for a motionless electron infinitely far from the proton, so that the ionization energy is
According to the more complete theory of quantum mechanics , the location of an electron is best described as a probability distribution within an electron cloud , i.e. atomic orbital . [ 39 ] [ 40 ] The energy can be calculated by integrating over this cloud. The cloud's underlying mathematical representation is the wavefunction , which is built from Slater determinants consisting of molecular spin orbitals. [ 41 ] These are related by Pauli's exclusion principle to the antisymmetrized products of the atomic or molecular orbitals .
There are two main ways in which ionization energy is calculated. In general, the computation for the N th ionization energy requires calculating the energies of Z − N + 1 {\displaystyle Z-N+1} and Z − N {\displaystyle Z-N} electron systems. Calculating these energies exactly is not possible except for the simplest systems (i.e. hydrogen and hydrogen-like elements), primarily because of difficulties in integrating the electron correlation terms. [ 42 ] Therefore, approximation methods are routinely employed, with different methods varying in complexity (computational time) and accuracy compared to empirical data. This has become a well-studied problem and is routinely done in computational chemistry . The second way of calculating ionization energies is mainly used at the lowest level of approximation, where the ionization energy is provided by Koopmans' theorem , which involves the highest occupied molecular orbital or " HOMO " and the lowest unoccupied molecular orbital or " LUMO ", and states that the ionization energy of an atom or molecule is equal to the negative value of energy of the orbital from which the electron is ejected. [ 43 ] This means that the ionization energy is equal to the negative of HOMO energy, which in a formal equation can be written as: [ 44 ]
Ionization of molecules often leads to changes in molecular geometry , and two types of (first) ionization energy are defined – adiabatic and vertical . [ 45 ]
The adiabatic ionization energy of a molecule is the minimum amount of energy required to remove an electron from a neutral molecule, i.e. the difference between the energy of the vibrational ground state of the neutral species (v" = 0 level) and that of the positive ion (v' = 0). The specific equilibrium geometry of each species does not affect this value.
Due to the possible changes in molecular geometry that may result from ionization, additional transitions may exist between the vibrational ground state of the neutral species and vibrational excited states of the positive ion. In other words, ionization is accompanied by vibrational excitation . The intensity of such transitions is explained by the Franck–Condon principle , which predicts that the most probable and intense transition corresponds to the vibrationally excited state of the positive ion that has the same geometry as the neutral molecule. This transition is referred to as the "vertical" ionization energy since it is represented by a completely vertical line on a potential energy diagram (see Figure).
For a diatomic molecule, the geometry is defined by the length of a single bond . The removal of an electron from a bonding molecular orbital weakens the bond and increases the bond length. In Figure 1, the lower potential energy curve is for the neutral molecule and the upper surface is for the positive ion. Both curves plot the potential energy as a function of bond length. The horizontal lines correspond to vibrational levels with their associated vibrational wave functions . Since the ion has a weaker bond, it will have a longer bond length. This effect is represented by shifting the minimum of the potential energy curve to the right of the neutral species. The adiabatic ionization is the diagonal transition to the vibrational ground state of the ion. Vertical ionization may involve vibrational excitation of the ionic state and therefore requires greater energy.
In many circumstances, the adiabatic ionization energy is often a more interesting physical quantity since it describes the difference in energy between the two potential energy surfaces. However, due to experimental limitations, the adiabatic ionization energy is often difficult to determine, whereas the vertical detachment energy is easily identifiable and measurable.
While the term ionization energy is largely used only for gas-phase atomic, cationic, or molecular species, there are a number of analogous quantities that consider the amount of energy required to remove an electron from other physical systems.
Electron binding energy is a generic term for the minimum energy needed to remove an electron from a particular electron shell for an atom or ion, due to these negatively charged electrons being held in place by the electrostatic pull of the positively charged nucleus. [ 46 ] For example, the electron binding energy for removing a 3p 3/2 electron from the chloride ion is the minimum amount of energy required to remove an electron from the chlorine atom when it has a charge of −1. In this particular example, the electron binding energy has the same magnitude as the electron affinity for the neutral chlorine atom. In another example, the electron binding energy refers to the minimum amount of energy required to remove an electron from the dicarboxylate dianion − O 2 C(CH 2 ) 8 CO − 2 .
The graph to the right shows the binding energy for electrons in different shells in neutral atoms. The ionization energy is the lowest binding energy for a particular atom (although these are not all shown in the graph).
Work function is the minimum amount of energy required to remove an electron from a solid surface, where the work function W for a given surface is defined by the difference [ 47 ]
where − e is the charge of an electron , ϕ is the electrostatic potential in the vacuum nearby the surface, and E F is the Fermi level ( electrochemical potential of electrons) inside the material. | https://en.wikipedia.org/wiki/Ionization_energy |
An ionization instability is any one of a category of plasma instabilities which is mediated by electron-impact ionization . In the most general sense, an ionization instability occurs from a feedback effect, when electrons produced by ionization go on to produce still more electrons through ionization in a self-reinforcing way.
Ionization instabilities have been seen in such plasma physics apparatus as glow discharges , [ 1 ] [ 2 ] Penning discharges, [ 3 ] magnetic nozzles , [ 4 ] [ 5 ] [ 6 ] and MHD generators . [ 7 ] [ 8 ] [ 9 ] Ionization instabilities may occur in magnetized or unmagnetized [ 10 ] plasma. They occur mostly when the plasma is relatively cold and only partially ionized, so that there is a lot of neutral gas mixed in with the plasma.
A glow discharge is a plasma-containing apparatus in which the plasma is formed by a large voltage placed across a rarefied gas. Glow discharges are used for electric lighting and materials processing. In a glow discharge, ionization instability takes the form of striations , [ 1 ] or bands of enhanced and suppressed light production. The distance between each striation is the distance required for an electron to gain enough energy to ionize a neutral gas particle.
A magnetic nozzle is an apparatus through which plasma flows, in which the plasma is constricted by a magnetic field. Magnetic nozzles are used in electric propulsion to enhance the thrust produced by a stream of plasma. In magnetic nozzles, ionization instability is caused by ionization downstream of the nozzle, causing electrons born there to migrate upstream, counter to the direction of flow. This causes the plasma flow rate and energy through the nozzle to oscillate. [ 4 ] [ 5 ] [ 6 ]
An MHD generator is an apparatus through which hot gas flows, in which the gas is ionized and a magnetic field is used to extract flow energy as electrical energy. MHD generators were studied mostly in the 1960s and 1970s to increase the efficiency of fossil-fueled and nuclear-fission power plants. [ 11 ] In MHD generators, the specific kind of magnetized ionization instability is called the electrothermal instability . It was discovered by Evgeny Velikhov in 1962. The added electrical resistance caused by ionization instability thwarted a research effort to lower the required temperature by heating electrons preferentially. [ 11 ] | https://en.wikipedia.org/wiki/Ionization_instability |
Ionized-air glow is the luminescent emission of characteristic blue–purple–violet light, often of a color called electric blue , by air subjected to an energy flux either directly or indirectly from solar radiation . [ 1 ]
When energy is deposited in air, the air molecules become excited. As air is composed primarily of nitrogen and oxygen , excited N 2 and O 2 molecules are produced. These can react with other molecules, forming mainly ozone and nitrogen(II) oxide . Water vapor , when present, may also play a role; its presence is characterized by the hydrogen emission lines. The reactive species present in the plasma can readily react with other chemicals present in the air or on nearby surfaces.
The excited nitrogen deexcites primarily by emission of a photon , with emission lines in ultraviolet, visible, and infrared band:
The blue light observed is produced primarily by this process. [ 2 ] The spectrum is dominated by lines of single-ionized nitrogen, with presence of neutral nitrogen lines.
The excited state of oxygen is somewhat more stable than nitrogen. While deexcitation can occur by emission of photons, the more probable mechanism at atmospheric pressure is a chemical reaction with other oxygen molecules, forming ozone: [ 2 ]
This reaction is responsible for the production of ozone in the vicinity of strongly radioactive materials and electrical discharges.
Excitation energy can be deposited in air by a number of different mechanisms:
In dry air, the color of produced light (e.g. by lightning) is dominated by the emission lines of nitrogen, yielding the spectrum with primarily blue emission lines. The lines of neutral nitrogen (NI), neutral oxygen (OI), singly ionized nitrogen (NII) and singly ionized oxygen (OII) are the most prominent features of a lightning emission spectrum. [ 14 ] Neutral nitrogen radiates primarily at one line in the red part of the spectrum. Ionized nitrogen radiates primarily as a set of lines in the blue part of the spectrum. [ 15 ]
A violet hue can occur when the spectrum contains emission lines of atomic hydrogen. This may happen when the air contains high amount of water, e.g. with lightnings in low altitudes passing through rain thunderstorms . Water vapor and small water droplets ionize and dissociate easier than large droplets, therefore have higher impact on color. [ citation needed ]
The hydrogen emission lines at 656.3 nm (the strong H-alpha line) and at 486.1 nm (H-beta) are characteristic for lightnings. [ 16 ] Rydberg atoms , generated by low-frequency lightnings, emit at red to orange color and can give the lightning a yellowish to greenish tint. ( confusing? ) [ citation needed ] Generally, the radiant species present in atmospheric plasma are N 2 , N 2 + , O 2 , NO (in dry air) and OH (in humid air). The temperature, electron density , and electron temperature of the plasma can be inferred from the distribution of rotational lines of these species. At higher temperatures, atomic emission lines of N and O, and (in presence of water) H, are present. Other molecular lines, e.g. CO and CN, mark the presence of contaminants in the air. [ 17 ]
The emission of blue light is often attributed to Cherenkov radiation . [ 9 ] [ verification needed ] Cherenkov radiation is produced by charged particles which are traveling through a dielectric substance at a speed greater than the speed of light in that medium. Despite the production of similarity-colored light and an association with high-energy particles, Cherenkov radiation is generated by a fundamentally different mechanism. [ citation needed ] | https://en.wikipedia.org/wiki/Ionized-air_glow |
In quantum mechanics , ionized impurity scattering is the scattering of charge carriers by ionization in the lattice. The most primitive models can be conceptually understood as a particle responding to unbalanced local charge that arises near a crystal impurity; similar to an electron encountering an electric field. [ 1 ] This effect is the mechanism by which doping decreases mobility.
In the current quantum mechanical picture of conductivity the ease with which electrons traverse a crystal lattice is dependent on the near perfectly regular spacing of ions in that lattice. Only when a lattice contains perfectly regular spacing can the ion-lattice interaction (scattering) lead to almost transparent behavior of the lattice. Impurity atoms in a crystal have an effect similar to thermal vibrations where conductivity has a direct relationship with temperature.
A crystal with impurities is less regular than a pure crystal, and a reduction in electron mean free paths occurs. Impure crystals have lower conductivity than pure crystals with less temperature sensitivity in that lattice. [ 2 ]
Lundstrom, Mark (2000). Fundamentals of carrier transport . Cambridge University Press 2000. pp. 58 –60. ISBN 0-521-63134-3 .
This quantum mechanics -related article is a stub . You can help Wikipedia by expanding it .
This scattering –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ionized_impurity_scattering |
Ionizing (ionising) radiation , including nuclear radiation , consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionize atoms or molecules by detaching electrons from them. [ 1 ] Some particles can travel up to 99% of the speed of light , and the electromagnetic waves are on the high-energy portion of the electromagnetic spectrum .
Gamma rays , X-rays , and the higher energy ultraviolet part of the electromagnetic spectrum are ionizing radiation; whereas the lower energy ultraviolet , visible light , infrared , microwaves , and radio waves are non-ionizing radiation . Nearly all types of laser light are non-ionizing radiation. The boundary between ionizing and non-ionizing radiation in the ultraviolet area cannot be sharply defined, as different molecules and atoms ionize at different energies . The energy of ionizing radiation starts between 10 electronvolts (eV) and 33 eV. [ citation needed ]
Ionizing subatomic particles include alpha particles , beta particles , and neutrons . These particles are created by radioactive decay , and almost all are energetic enough to ionize. There are also secondary cosmic particles produced after cosmic rays interact with Earth's atmosphere, including muons , mesons , and positrons . [ 2 ] [ 3 ] Cosmic rays may also produce radioisotopes on Earth (for example, carbon-14 ), which in turn decay and emit ionizing radiation. Cosmic rays and the decay of radioactive isotopes are the primary sources of natural ionizing radiation on Earth, contributing to background radiation . Ionizing radiation is also generated artificially by X-ray tubes , particle accelerators , and nuclear fission .
Ionizing radiation is not immediately detectable by human senses, so instruments such as Geiger counters are used to detect and measure it. However, very high energy particles can produce visible effects on both organic and inorganic matter (e.g. water lighting in Cherenkov radiation ) or humans (e.g. acute radiation syndrome ). [ 4 ]
Ionizing radiation is used in a wide variety of fields such as medicine , nuclear power , research, and industrial manufacturing, but is a health hazard if proper measures against excessive exposure are not taken. Exposure to ionizing radiation causes cell damage to living tissue and organ damage . In high acute doses, it will result in radiation burns and radiation sickness , and lower level doses over a protracted time can cause cancer . [ 5 ] [ 6 ] The International Commission on Radiological Protection (ICRP) issues guidance on ionizing radiation protection, and the effects of dose uptake on human health.
Ionizing radiation may be grouped as directly or indirectly ionizing.
Any charged particle with mass can ionize atoms directly by fundamental interaction through the Coulomb force if it has enough kinetic energy. Such particles include atomic nuclei , electrons , muons , charged pions , protons , and energetic charged nuclei stripped of their electrons. When moving at relativistic speeds (near the speed of light , c) these particles have enough kinetic energy to be ionizing, but there is considerable speed variation. For example, a typical alpha particle moves at about 5% of c, but an electron with 33 eV (just enough to ionize) moves at about 1% of c.
Two of the first types of directly ionizing radiation to be discovered are alpha particles which are helium nuclei ejected from the nucleus of an atom during radioactive decay, and energetic electrons, which are called beta particles .
Natural cosmic rays are made up primarily of relativistic protons but also include heavier atomic nuclei like helium ions and HZE ions . In the atmosphere such particles are often stopped by air molecules, and this produces short-lived charged pions, which soon decay to muons, a primary type of cosmic ray radiation that reaches the surface of the earth. Pions can also be produced in large amounts in particle accelerators .
Alpha (α) particles consist of two protons and two neutrons bound together into a particle: a helium -4 nucleus . Alpha particle emissions are generally produced in the process of alpha decay .
Alpha particles are a strongly ionizing form of radiation, but when emitted by radioactive decay they have low penetration power and can be absorbed by a few centimeters of air, or by the top layer of human skin. More powerful alpha particles from ternary fission are three times as energetic, and penetrate proportionately farther in air. The helium nuclei that form 10–12% of cosmic rays, are also usually of much higher energy than those from radioactive decay and pose shielding problems in space. However, this type of radiation is significantly absorbed by Earth's atmosphere, which is a radiation shield equivalent to about 10 meters of water. [ 7 ]
The alpha particle was named by Ernest Rutherford after the first letter in the Greek alphabet , α , when he ranked the known radioactive emissions in descending order of ionizing effect in 1899. The symbol is α or α 2+ . Because they are identical to helium nuclei, they are also called He 2+ or 4 2 He 2+ indicating helium with a +2 charge (missing its two electrons). If the ion gains electrons from its environment, the α particle can be written as a normal (electrically neutral) helium atom 4 2 He .
Beta (β) particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei , such as potassium-40 . The production of β particles is termed beta decay . There are two forms of β decay, β − and β + , which respectively give rise to the electron and the positron. [ 8 ] Beta particles are much less penetrating than gamma radiation, but more penetrating than alpha particles.
High-energy beta particles may produce X-rays known as bremsstrahlung ("braking radiation") or secondary electrons ( delta ray ) as they pass through matter. Both of these can cause an indirect ionization effect. Bremsstrahlung is of concern when shielding beta emitters, as the interaction of beta particles with some shielding materials produces bremsstrahlung. The effect is greater with material having high atomic numbers, so material with low atomic numbers is used for beta source shielding.
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron . When a low-energy positron collides with a low-energy electron, annihilation occurs, resulting in their conversion into the energy of two or more gamma ray photons (see electron–positron annihilation ). As positrons are positively charged particles they can directly ionize an atom through Coulomb interactions.
Positrons can be generated by positron emission nuclear decay (through weak interactions ), or by pair production from a sufficiently energetic photon . Positrons are common artificial sources of ionizing radiation used in medical positron emission tomography (PET) scans.
Charged nuclei are characteristic of galactic cosmic rays and solar particle events and except for alpha particles (charged helium nuclei) have no natural sources on Earth. In space, however, very high energy protons, helium nuclei, and HZE ions can be initially stopped by relatively thin layers of shielding, clothes, or skin. However, the resulting interaction will generate secondary radiation and cause cascading biological effects. If just one atom of tissue is displaced by an energetic proton, for example, the collision will cause further interactions in the body. This is called " linear energy transfer " (LET), which utilizes elastic scattering .
LET can be visualized as a billiard ball hitting another in the manner of the conservation of momentum , sending both away with the energy of the first ball divided between the two unequally. When a charged nucleus strikes a relatively slow-moving nucleus of an object in space, LET occurs and neutrons, alpha particles, low-energy protons, and other nuclei will be released by the collisions and contribute to the total absorbed dose of tissue. [ 9 ]
Indirectly ionizing radiation is electrically neutral and does not interact strongly with matter, therefore the bulk of the ionization effects are due to secondary ionization.
Even though photons are electrically neutral, they can ionize atoms indirectly through the photoelectric effect and the Compton effect . Either of those interactions cause the ejection of an electron from an atom at relativistic speeds, turning that electron into a (secondary) beta particle that will ionize other atoms. Since most of the ionized atoms are due to the secondary beta particles, photons are indirectly ionizing radiation. [ 10 ]
Radiated photons are called gamma rays if they are produced by a nuclear reaction , subatomic particle decay, or radioactive decay within the nucleus. They are called x-rays if produced outside the nucleus. The generic term "photon" is used to describe both. [ 11 ] [ 12 ] [ 13 ]
X-rays normally have a lower energy than gamma rays, and an older convention was to define the boundary as a wavelength of 10 −11 m (or a photon energy of 100 keV). [ 14 ] That threshold was driven by historic limitations of older X-ray tubes and low awareness of isomeric transitions . Modern technologies and discoveries have shown an overlap between X-ray and gamma energies. In many fields they are functionally identical, differing for terrestrial studies only in origin of the radiation. In astronomy, however, where radiation origin often cannot be reliably determined, the old energy division has been preserved, with X-rays defined as being between about 120 eV and 120 keV, and gamma rays as being of any energy above 100 to 120 keV, regardless of source. Most astronomical " gamma-rays " are known not to originate from radioactivity but, rather, result from processes like those that produce astronomical X-rays, except driven by much more energetic electrons.
Photoelectric absorption is the dominant mechanism in organic materials for photon energies below 100 keV, typical of classical X-ray tube originated X-rays . At energies beyond 100 keV, photons ionize matter increasingly through the Compton effect , and then indirectly through pair production at energies beyond 5 MeV. The accompanying interaction diagram shows two Compton scatterings happening sequentially. In every scattering event, the gamma ray transfers energy to an electron, and it continues on its path in a different direction and with reduced energy.
The lowest ionization energy of any element is 3.89 eV, for caesium . However, US Federal Communications Commission material defines ionizing radiation as that with a photon energy greater than 10 eV (equivalent to a far ultraviolet wavelength of 124 nanometers ). [ 15 ] Roughly, this corresponds to both the first ionization energy of oxygen, and the ionization energy of hydrogen, both about 14 eV. [ 16 ] In some Environmental Protection Agency references, the ionization of a typical water molecule at an energy of 33 eV is referenced [ 17 ] as the appropriate biological threshold for ionizing radiation: this value represents the so-called W-value , the colloquial name for the ICRU 's mean energy expended in a gas per ion pair formed , [ 18 ] which combines ionization energy plus the energy lost to other processes such as excitation . [ 19 ] At 38 nanometers wavelength for electromagnetic radiation , 33 eV is close to the energy at the conventional 10 nm wavelength transition between extreme ultraviolet and X-ray radiation, which occurs at about 125 eV. Thus, X-ray radiation is always ionizing, but only extreme-ultraviolet radiation can be considered ionizing under all definitions.
Neutrons have a neutral electrical charge often misunderstood as zero electrical charge and thus often do not directly cause ionization in a single step or interaction with matter. However, fast neutrons will interact with the protons in hydrogen via linear energy transfer , energy that a particle transfers to the material it is moving through. This mechanism scatters the nuclei of the materials in the target area, causing direct ionization of the hydrogen atoms. When neutrons strike the hydrogen nuclei, proton radiation (fast protons) results. These protons are themselves ionizing because they are of high energy, are charged, and interact with electrons.
Neutrons that strike other nuclei besides hydrogen, transfer less energy to the other particle if linear energy transfer does occur. But, for many nuclei struck by neutrons, inelastic scattering occurs. Whether elastic or inelastic scatter occurs is dependent on the speed of the neutron, whether fast or thermal or somewhere in between. It is also dependent on the nuclei it strikes and its neutron cross section .
In inelastic scattering, neutrons are readily absorbed in a type of nuclear reaction called neutron capture and attributes to the neutron activation of the nucleus. Neutron interactions with most types of matter in this manner usually produce radioactive nuclei. Oxygen-16 , for example, undergoes neutron activation, rapidly decays by a proton emission forming nitrogen-16 , which decays to oxygen-16. The short-lived nitrogen-16 decay emits a powerful beta ray. This process can be written as:
16 O (n,p) 16 N (fast neutron capture possible with >11 MeV neutron)
16 N → 16 O + β − (Decay t 1/2 = 7.13 s)
This high-energy β − further interacts rapidly with other nuclei, emitting high-energy γ via Bremsstrahlung
While not a favorable reaction, the 16 O (n,p) 16 N reaction is a major source of X-rays emitted from the cooling water of a pressurized water reactor and contributes enormously to the radiation generated by a water-cooled nuclear reactor while operating.
For the best shielding of neutrons, hydrocarbons that have an abundance of hydrogen are used.
In fissile materials, secondary neutrons may produce nuclear chain reactions , causing a larger amount of ionization from the daughter products of fission.
Outside the nucleus, free neutrons are unstable and have a mean lifetime of 14 minutes, 42 seconds. Free neutrons decay by emission of an electron and an electron antineutrino to become a proton, a process known as beta decay : [ 20 ]
In the adjacent diagram, a neutron collides with a proton of the target material, and then becomes a fast recoil proton that ionizes in turn. At the end of its path, the neutron is captured by a nucleus in an (n,γ)-reaction that leads to the emission of a neutron capture photon. Such photons always have enough energy to qualify as ionizing radiation.
Neutron radiation, alpha radiation, and extremely energetic gamma (> ~20 MeV) can cause nuclear transmutation and induced radioactivity . The relevant mechanisms are neutron activation , alpha absorption , and photodisintegration . A large enough number of transmutations can change macroscopic properties and cause targets to become radioactive themselves, even after the original source is removed.
Ionization of molecules can lead to radiolysis (breaking chemical bonds), and formation of highly reactive free radicals . These free radicals may then react chemically with neighbouring materials even after the original radiation has stopped (e.g. ozone cracking of polymers by ozone formed by ionization of air). Ionizing radiation can also accelerate existing chemical reactions such as polymerization and corrosion, by contributing to the activation energy required for the reaction. Optical materials deteriorate under the effect of ionizing radiation.
High-intensity ionizing radiation in air can produce a visible ionized air glow of telltale bluish-purple color. The glow can be observed, e.g., during criticality accidents , around mushroom clouds shortly after a nuclear explosion , or the inside of a damaged nuclear reactor like during the Chernobyl disaster .
Monatomic fluids, e.g. molten sodium , have no chemical bonds to break and no crystal lattice to disturb, so they are immune to the chemical effects of ionizing radiation. Simple diatomic compounds with very negative enthalpy of formation , such as hydrogen fluoride will reform rapidly and spontaneously after ionization.
The ionization of materials temporarily increases their conductivity, potentially permitting damaging current levels. This is a particular hazard in semiconductor microelectronics used in electronic equipment; subsequent currents introduce operation errors or even permanently damage the devices. Devices intended for high-radiation environments such as the nuclear industry or outer space, may be made radiation hard to resist such effects through design, material selection, and fabrication methods.
Proton radiation found in space can also cause single-event upsets in digital circuits. The electrical effects of ionizing radiation are exploited in gas-filled radiation detectors, e.g. the Geiger counter or the ion chamber .
Most adverse health effects of exposure to ionizing radiation may be grouped in two general categories:
The most common impact is stochastic radiation-induced cancer with a latent period of years or decades after exposure. For example, ionizing radiation is one cause of chronic myelogenous leukemia , [ 22 ] [ 23 ] [ 24 ] although most people with CML have not been exposed to radiation. [ 23 ] [ 24 ] The mechanism by which this occurs is well understood, but quantitative models predicting the level of risk remain controversial. [ citation needed ]
The most widely accepted model, the Linear no-threshold model (LNT), holds that the incidence of cancers due to ionizing radiation increases linearly with effective radiation dose at a rate of 5.5% per sievert . [ 25 ] If this is correct, then natural background radiation is the most hazardous source of radiation to general public health, followed by medical imaging as a close second. Other stochastic effects of ionizing radiation are teratogenesis , cognitive decline , and heart disease . [ citation needed ]
Though DNA is always susceptible to damage by ionizing radiation, the DNA molecule may also be damaged by radiation with enough energy to excite certain molecular bonds to form pyrimidine dimers . This energy may be less than ionizing, but near to it. A good example is ultraviolet spectrum energy which begins at about 3.1 eV (400 nm) at close to the same energy level which can cause sunburn to unprotected skin, as a result of photoreactions in collagen and (in the UV-B range) also damage in DNA (for example, pyrimidine dimers). Thus, the mid and lower ultraviolet electromagnetic spectrum is damaging to biological tissues as a result of electronic excitation in molecules which falls short of ionization, but produces similar non-thermal effects. To some extent, visible light and also ultraviolet A (UVA) which is closest to visible energies, have been proven to result in formation of reactive oxygen species in skin, which cause indirect damage since these are electronically excited molecules which can inflict reactive damage, although they do not cause sunburn (erythema). [ 26 ] Like ionization-damage, all these effects in skin are beyond those produced by simple thermal effects. [ citation needed ]
The table below shows radiation and dose quantities in SI and non-SI units.
Ionizing radiation has many industrial, military, and medical uses. Its usefulness must be balanced with its hazards, a compromise that has shifted over time. For example, at one time, assistants in shoe shops in the US used X-rays to check a child's shoe size , but this practice was halted when the risks of ionizing radiation were better understood. [ 27 ]
Neutron radiation is essential to the working of nuclear reactors and nuclear weapons . The penetrating power of x-ray, gamma, beta, and positron radiation is used for medical imaging , nondestructive testing , and a variety of industrial gauges. Radioactive tracers are used in medical and industrial applications, as well as biological and radiation chemistry . Alpha radiation is used in static eliminators and smoke detectors . The sterilizing effects of ionizing radiation are useful for cleaning medical instruments, food irradiation , and the sterile insect technique . Measurements of carbon-14 , is used for radiocarbon dating .
Ionizing radiation is generated through nuclear reactions, nuclear decay, by very high temperature, or via acceleration of charged particles in electromagnetic fields. Natural sources include the Sun, lightning and supernova explosions. Artificial sources include nuclear reactors, particle accelerators, and x-ray tubes .
The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) itemized types of human exposures.
The International Commission on Radiological Protection manages the International System of Radiological Protection, which sets recommended limits for dose uptake.
Background radiation comes from both natural and human-made sources.
The global average exposure of humans to ionizing radiation is about 3 mSv (0.3 rem) per year, 80% of which comes from nature. The remaining 20% results from exposure to human-made radiation sources, mainly medical imaging . Average human-made exposure is much higher in developed countries, mostly due to CT scans and nuclear medicine .
Natural background radiation comes from five primary sources: cosmic radiation, solar radiation, external terrestrial sources, radiation in the human body, and radon .
The background rate for natural radiation varies considerably with location, being as low as 1.5 mSv/a (1.5 mSv per year) in some areas and over 100 mSv/a in others. The highest level of purely natural radiation recorded on the Earth's surface is 90 μGy/h (0.8 Gy/a) on a Brazilian black beach composed of monazite . [ 28 ] The highest background radiation in an inhabited area is found in Ramsar , mainly due to naturally radioactive limestone used as a building material. Some 2000 of the most exposed residents receive an average radiation dose of 10 mGy per year, (1 rad /yr) ten times more than the ICRP recommended limit for exposure to the public from artificial sources. [ 29 ] Record levels were found in a house where the effective radiation dose due to external radiation was 135 mSv/a, (13.5 rem/yr) and the committed dose from radon was 640 mSv/a (64.0 rem/yr). [ 30 ] This unique case is over 200 times higher than the world average background radiation. Despite the high levels of background radiation that the residents of Ramsar receive there is no compelling evidence that they experience a greater health risk. The ICRP recommendations are conservative limits and may represent an over representation of the actual health risk. Generally radiation safety organization recommend the most conservative limits assuming it is best to err on the side of caution. This level of caution is appropriate but should not be used to create fear about background radiation danger. Radiation danger from background radiation may be a serious threat but is more likely a small overall risk compared to all other factors in the environment.
The Earth, and all living things on it, are constantly bombarded by radiation from outside the Solar System . This cosmic radiation consists of relativistic particles: positively charged nuclei (ions) from 1 amu protons (about 85% of it) to ~56 amu iron nuclei and even beyond. (The high-atomic number particles are called HZE ions .) The energy of this radiation can far exceed that which humans can create, even in the largest particle accelerators (see ultra-high-energy cosmic ray ). This radiation interacts in the atmosphere to create secondary radiation that rains down, including x-rays , muons , protons , antiprotons , alpha particles , pions , electrons , positrons , and neutrons .
The dose from cosmic radiation is largely from muons, neutrons, and electrons, with a dose rate that varies in different parts of the world and based largely on the geomagnetic field, altitude, and solar cycle. The cosmic-radiation dose rate on airplanes is so high that, according to the United Nations UNSCEAR 2000 Report (see links at bottom), airline flight crew workers receive more dose on average than any other worker, including those in nuclear power plants. Airline crews receive more cosmic rays if they routinely work flight routes that take them close to the North or South pole at high altitudes, where this type of radiation is maximal.
Cosmic rays also include high-energy gamma rays, which are far beyond the energies produced by solar or human sources.
Most materials on Earth contain some radioactive atoms , even if in small quantities. Most of the dose received from these sources is from gamma-ray emitters in building materials, or rocks and soil when outside. The major radionuclides of concern for terrestrial radiation are isotopes of potassium , uranium , and thorium . Each of these sources has been decreasing in activity since the formation of the Earth.
All earthly materials that are the building blocks of life contain a radioactive component. As organisms consume food, air, and water, an inventory of radioisotopes builds up within the organism (see banana equivalent dose ). Some radionuclides, like potassium-40 , emit a high-energy gamma ray that can be measured by sensitive electronic radiation measurement systems. These internal radiation sources contribute to an individual's total radiation dose from natural background radiation .
An important source of natural radiation is radon gas, which seeps continuously from bedrock but can, because of its high density, accumulate in poorly ventilated houses.
Radon-222 is a gas produced by the α-decay of radium -226. Both are a part of the natural uranium decay chain. Uranium is found in soil throughout the world in varying concentrations. Radon is the largest cause of lung cancer among non-smokers and the second-leading cause overall. [ 31 ]
There are three standard ways to limit exposure:
These can all be applied to natural and human-made sources. For human-made sources the use of Containment is a major tool in reducing dose uptake and is effectively a combination of shielding and isolation from the open environment. Radioactive materials are confined in the smallest possible space and kept out of the environment such as in a hot cell (for radiation) or glove box (for contamination). Radioactive isotopes for medical use, for example, are dispensed in closed handling facilities, usually gloveboxes, while nuclear reactors operate within closed systems with multiple barriers that keep the radioactive materials contained. Work rooms, hot cells and gloveboxes have slightly reduced air pressures to prevent escape of airborne material to the open environment.
In nuclear conflicts or civil nuclear releases civil defense measures can help reduce exposure of populations by reducing ingestion of isotopes and occupational exposure. One is the issue of potassium iodide (KI) tablets, which blocks the uptake of radioactive iodine (one of the major radioisotope products of nuclear fission ) into the human thyroid gland.
Occupationally exposed individuals are controlled within the regulatory framework of the country they work in, and in accordance with any local nuclear licence constraints. These are usually based on the recommendations of the International Commission on Radiological Protection .
The ICRP recommends limiting artificial irradiation. For occupational exposure, the limit is 50 mSv in a single year with a maximum of 100 mSv in a consecutive five-year period. [ 25 ]
The radiation exposure of these individuals is carefully monitored with the use of dosimeters and other radiological protection instruments which will measure radioactive particulate concentrations, area gamma dose readings and radioactive contamination . A legal record of dose is kept.
Examples of activities where occupational exposure is a concern include:
Some human-made radiation sources affect the body through direct radiation, known as effective dose (radiation) while others take the form of radioactive contamination and irradiate the body from within. The latter is known as committed dose .
Medical procedures, such as diagnostic X-rays , nuclear medicine , and radiation therapy are by far the most significant source of human-made radiation exposure to the general public. Some of the major radionuclides used are I-131 , Tc-99m , Co-60 , Ir-192 , and Cs-137 . The public is also exposed to radiation from consumer products, such as tobacco ( polonium -210), combustible fuels (gas, coal , etc.), televisions , luminous watches and dials ( tritium ), airport X-ray systems, smoke detectors ( americium ), electron tubes, and gas lantern mantles ( thorium ).
Of lesser magnitude, members of the public are exposed to radiation from the nuclear fuel cycle, which includes the entire sequence from processing uranium to the disposal of the spent fuel. The effects of such exposure have not been reliably measured due to the extremely low doses involved. Opponents use a cancer per dose model to assert that such activities cause several hundred cases of cancer per year, an application of the widely accepted Linear no-threshold model (LNT).
The International Commission on Radiological Protection recommends limiting artificial irradiation to the public to an average of 1 mSv (0.001 Sv) of effective dose per year, not including medical and occupational exposures. [ 25 ]
In a nuclear war , gamma rays from both the initial weapon explosion and fallout would be sources of radiation exposure.
Massive particles are a concern for astronauts outside the Earth's magnetic field who would receive solar particles from solar proton events (SPE) and galactic cosmic rays from cosmic sources. These high-energy charged nuclei are blocked by Earth's magnetic field but pose a major health concern for astronauts traveling to the Moon and to any distant location beyond Earth orbit. Highly charged HZE ions in particular are known to be extremely damaging, though protons make up the vast majority of galactic cosmic rays. Evidence indicates past SPE radiation levels that would have been lethal for unprotected astronauts. [ 35 ]
Air travel exposes people on aircraft to increased radiation from space as compared to sea level, including cosmic rays and from solar flare events. [ 36 ] [ 37 ] Software programs such as Epcard , CARI, SIEVERT, PCAIRE are attempts to simulate exposure by aircrews and passengers. [ 37 ] An example of a measured dose (not simulated dose) is 6 μSv per hour from London Heathrow to Tokyo Narita on a polar route. [ 37 ] However, dosages can vary, such as during periods of high solar activity. [ 37 ] The United States FAA requires airlines to provide flight crew with information about cosmic radiation, and an International Commission on Radiological Protection recommendation for the general public is no more than 1 mSv per year. [ 37 ] Also, many airlines do not allow pregnant flightcrew members, to comply with a European Directive. [ 37 ] The FAA has a recommended limit of 1 mSv total for a pregnancy, and no more than 0.5 mSv per month. [ 37 ] Information originally based on Fundamentals of Aerospace Medicine published in 2008. [ 37 ]
Hazardous levels of ionizing radiation are signified by the trefoil sign on a yellow background. These are usually posted at the boundary of a radiation controlled area or in any place where radiation levels are significantly above background due to human intervention.
The red ionizing radiation warning symbol (ISO 21482) was launched in 2007, and is intended for IAEA Category 1, 2 and 3 sources defined as dangerous sources capable of death or serious injury, including food irradiators, teletherapy machines for cancer treatment and industrial radiography units. The symbol is to be placed on the device housing the source, as a warning not to dismantle the device or to get any closer. It will not be visible under normal use, only if someone attempts to disassemble the device. The symbol will not be located on building access doors, transportation packages or containers. [ 38 ] | https://en.wikipedia.org/wiki/Ionizing_radiation |
Hazard symbols are universally recognized symbols designed to alert individuals to the presence of hazardous or dangerous materials, locations, or conditions. These include risks associated with electromagnetic fields , electric currents , toxic chemicals, explosive substances , and radioactive materials . Their design and use are often governed by laws and standards organizations to ensure clarity and consistency. Hazard symbols may vary in color, background, borders, or accompanying text to indicate specific dangers and levels of risk, such as toxicity classes. These symbols provide a quick, universally understandable visual warning that transcends language barriers, making them more effective than text-based warnings in many situations.
Tape with yellow and black diagonal stripes is commonly used as a generic hazard warning. This can be in the form of barricade tape , or as a self-adhesive tape for marking floor areas and the like. In some regions (for instance the UK) [ 1 ] yellow tape is buried a certain distance above buried electrical cables to warn future groundworkers of the hazard.
On roadside warning signs, an exclamation mark is often used to draw attention to a generic warning of danger, hazards, and the unexpected. In Europe and elsewhere in the world (except North America and Australia), this type of sign is used if there are no more-specific signs to denote a particular hazard. [ 2 ] [ 3 ] When used for traffic signs, it is accompanied by a supplementary sign describing the hazard, usually mounted under the exclamation mark.
This symbol has also been more widely adopted for generic use in many other contexts not associated with road traffic. It often appears on hazardous equipment, in instruction manuals to draw attention to a precaution, on tram/train blind spot warning stickers and on natural disaster (earthquake, tsunami, hurricane, volcanic eruption) preparedness posters/brochures—as an alternative when a more-specific warning symbol is not available.
The skull-and-crossbones symbol, consisting of a human skull and two bones crossed together behind the skull, is today generally used as a warning of danger of death , particularly in regard to poisonous substances.
The symbol, or some variation thereof, specifically with the bones (or swords) below the skull, was also featured on the Jolly Roger , the traditional flag of European and American seagoing pirates . It is also part of the Canadian WHMIS home symbols placed on containers to warn that the contents are poisonous.
In the United States, due to concerns that the skull-and-crossbones symbol's association with pirates might encourage children to play with toxic materials, the Mr. Yuk symbol is also used to denote poison.
This symbol has also been more widely adopted for generic use in many other contexts not associated with poisonous materials. It used for denoting number of dead victims caused by natural disasters (e.g. earthquakes) or armed conflicts on event infographics.
The international radiation symbol is a trefoil around a small central circle representing radiation from an atom. It first appeared in 1946 at the University of California, Berkeley Radiation Laboratory . [ 4 ] At the time, it was rendered as magenta , and was set on a blue background. The shade of magenta used (Martin Senour Roman Violet No. 2225) was chosen because it was expensive and less likely to be used on other signs. [ 5 ] However, a blue background for other signs started to be used extensively. Blue was typically used on information signs and the color tended to fade with weathering. This resulted in the background being changed on the radiation hazard sign. [ 6 ] The original version used in the United States is magenta against a yellow background, and it is drawn with a central circle of radius R , an internal radius of 1.5 R and an external radius of 5 R for the blades, which are separated from each other by 60°. The trefoil is black in the international version, which is also used in the United States. [ 7 ]
The symbol was adopted as a standard in the US by ANSI in 1969. [ 6 ] [ 8 ] It was first documented as an international symbol in 1963 in International Organization for Standardization (ISO) recommendation R.361. [ 9 ] In 1974, after approval by national standards bodies, the symbol became an international standard as ISO 361 Basic ionizing radiation symbol . [ 10 ] The standard specifies the shape, proportions, application and restrictions on the use of the symbol. It may be used to signify the actual or potential presence of ionizing radiation. It is not used for non-ionizing electromagnetic waves or sound waves. The standard does not specify the radiation levels at which it is to be used. [ 10 ]
The sign is commonly referred to as a radioactivity warning sign, but it is actually a warning sign of ionizing radiation . Ionizing radiation is a much broader category than radioactivity alone, as many non-radioactive sources also emit potentially dangerous levels of ionizing radiation. This includes x-ray apparatus, radiotherapy linear accelerators, and particle accelerators. Non-ionizing radiation can also reach potentially dangerous levels, but this warning sign is different from the trefoil ionizing radiation warning symbol. [ 11 ] The sign is not to be confused with the fallout shelter identification sign introduced by the Office of Civil Defense in 1961. This was originally intended to be the same as the radiation hazard symbol but was changed to a slightly different symbol because shelters are a place of safety, not of hazard. [ 6 ] [ 12 ]
On February 15, 2007, two groups—the International Atomic Energy Agency (IAEA) and the International Organization for Standardization (ISO)—jointly announced the adoption of a new ionizing radiation warning symbol to supplement the traditional trefoil symbol. The new symbol, to be used on sealed radiation sources, is aimed at alerting anyone, anywhere to the danger of being close to a strong source of ionizing radiation. [ 13 ] It depicts, on a red background, a black trefoil with waves of radiation streaming from it, along with a black skull and crossbones , and a running figure with an arrow pointing away from the scene. The radiating trefoil suggests the presence of radiation, while the red background and the skull and crossbones warn of danger. The figure running away from the scene is meant to suggest taking action to avoid the labeled material. The new symbol is not intended to be generally visible, but rather to appear on internal components of devices that house radiation sources so that if anybody attempts to disassemble such devices they will see an explicit warning not to proceed any further. [ 14 ] [ 15 ]
The biohazard symbol is used in the labeling of biological materials that carry a significant health risk, including viral and bacteriological samples, including infected dressings and used hypodermic needles (see sharps waste ). [ 16 ]
The biohazard symbol was developed in 1966 by Charles Baldwin , an environmental-health engineer working for the Dow Chemical Company on their containment products. [ 17 ]
According to Baldwin, who was assigned by Dow to its development: "We wanted something that was memorable but meaningless, so we could educate people as to what it means." In an article in Science in 1967, the symbol was presented as the new standard for all biological hazards ("biohazards"). The article explained that over 40 symbols were drawn up by Dow's artists, and all of the symbols investigated had to meet a number of criteria: "(i) striking in form in order to draw immediate attention; (ii) unique and unambiguous, in order not to be confused with symbols used for other purposes; (iii) quickly recognizable and easily recalled; (iv) easily stenciled; (v) symmetrical, in order to appear identical from all angles of approach; and (vi) acceptable to groups of varying ethnic backgrounds." The chosen scored the best on nationwide testing for uniqueness and memorability. [ 16 ]
All parts of the biohazard sign can be drawn with a compass and straightedge . The basic outline of the symbol is a plain trefoil , which is three circles overlapping each other equally like in a triple Venn diagram with the overlapping parts erased. The diameter of the overlapping part is equal to half the radius of the three circles. Then three inner circles are drawn in with 2 ⁄ 3 radius of the original circles so that it is tangent to the outside three overlapping circles. A tiny circle in center has a diameter 1 ⁄ 2 of the radius of the three inner circles, and arcs are erased at 90°, 210°, and 330°. The arcs of the inner circles and the tiny circle are connected by a line. Finally, the ring under is drawn from the distance to the perimeter of the equilateral triangle that forms between the centers of the three intersecting circles. An outer circle of the ring under is drawn and finally enclosed with the arcs from the center of the inner circles with a shorter radius from the inner circles. [ 7 ]
A chemical hazard symbol is a pictogram applied to containers and storage areas of dangerous chemical compounds to indicate the specific hazard, and thus the required precautions. There are several systems of labels, depending on the purpose, such as on the container for transportation, containers for end-use, or on a vehicle during transportation.
The United Nations has designed GHS hazard pictograms and GHS hazard statements to internationally harmonize chemical hazard warnings under the Globally Harmonized System of Classification and Labelling of Chemicals . These symbols have gradually replaced nation and region specific systems such as the European Union's Directive 67/548/EEC symbols, [ 24 ] Canada's Workplace Hazardous Materials Information System. [ 25 ] It has also been adopted in the United States for materials being sold and shipped by manufacturers, distributors and importers. [ 26 ] The USA previously did not mandate a specific system, instead allowing any system, provided it had met certain requirements. [ 27 ]
The European Union aligned its regulations with the GHS standards in 2008 with the adoption of CLP Regulation , replacing its existing Directive 67/548/EEC symbols during the mid-2010s, and requiring use of GHS symbols after 1 June 2017. [ 28 ] [ 29 ] Since 2015,
European standards are set by:
The Workplace Hazardous Materials Information System, or WHMIS, is Canada 's national workplace hazard communication standard, first introduced in 1988, and included eight chemical hazard symbols. [ 30 ] This system was brought into alignment with GHS in 2015, with a gradual phase in of GHS symbols and label designs through 15 December 2025. [ 25 ] The WHMIS system does deviate from GHS by retaining the former WHMIS symbol for Class 3, Division 3, biohazardous infectious materials , as GHS lacks a biological hazard symbol. [ 25 ]
The US-based National Fire Protection Association (NFPA) has a standard NFPA 704 using a diamond with four colored sections each with a number indicating severity 0–4 (0 for no hazard, 4 indicates a severe hazard). [ 31 ] The system was developed in the early 1960s, as a means to warn firefighters of possible dangers posed by storage tanks filled with chemicals. The red section denotes flammability. The blue section denotes health risks. Yellow represents reactivity (tendency to explode). The white section denotes special hazard information, not properly covered by the other categories, such as water reactivity, oxidizers, and asphyxiant gases. [ 31 ]
A large number of warning symbols with non-standard designs are in use around the world.
Some warning symbols have been redesigned to be more comprehensible to children, such as the Mr. Ouch (depicting an electricity danger as a snarling, spiky creature) and Mr. Yuk (a green frowny face sticking its tongue out, to represent poison) designs in the United States. | https://en.wikipedia.org/wiki/Ionizing_radiation_symbol |
Ionochromism , similar to chromic methods such as photochromism , thermochromism and other chromism phenomena, is the reversible process of changing the color of a material by absorption or emission spectra of molecules using ions . [ 1 ] Electrochromism is similar to ionochromism as it involves the use of electrons in order to change the color of materials. Both electrochromic and ionochromic materials undergo a change in color by the flow of charged particles, where electrochromic materials only involve an anionic species or negatively charged species such as electrons. An example of an ionochromic dye is a complexometric indicator . A complexometric indicator involves the presence of metal ions in order to facilitate color change and is often used in complexometric titration .
Ionochromism is the process of reacting an ionochromic material with a charged species, or a positively or negatively charged ion. Materials that have ionochromic properties exhibit reversible color change, where the absence of a stimulus such as an ionic species can result in the compound changing to its original color. [ 2 ] Various ionic color changing mechanisms that are used in chromic processes can be used in ionochromism, including:
Ionochromic materials exist in a wide range of molecules, including organic molecules , pH-sensitive dyes and indicators , and other color-changing compounds with chromophores . Some of these molecules include phthalides , fluorans , and leucotriarylmethanes. [ 2 ]
4.4
Yellow
6.2
Yellow | https://en.wikipedia.org/wiki/Ionochromism |
An ionomer ( / ˌ aɪ ˈ ɑː n ə m ər / ) ( iono- + -mer ) is a polymer composed of repeat units of both electrically neutral repeating units and ionized units covalently bonded to the polymer backbone as pendant group moieties . Usually no more than 15 mole percent are ionized. The ionized units are often carboxylic acid groups.
The classification of a polymer as an ionomer depends on the level of substitution of ionic groups as well as how the ionic groups are incorporated into the polymer structure. For example, polyelectrolytes also have ionic groups covalently bonded to the polymer backbone, but have a much higher ionic group molar substitution level (usually greater than 80%); ionenes are polymers where ionic groups are part of the actual polymer backbone. These two classes of ionic-group-containing polymers have vastly different morphological and physical properties and are therefore not considered ionomers.
Ionomers have unique physical properties including electrical conductivity and viscosity —increase in ionomer solution viscosity with increasing temperatures (see conducting polymer ). Ionomers also have unique morphological properties as the non-polar polymer backbone is energetically incompatible with the polar ionic groups. As a result, the ionic groups in most ionomers will undergo microphase separation to form ionic-rich domains.
Commercial applications for ionomers include golf ball covers, semipermeable membranes , sealing tape and thermoplastic elastomers . Common examples of ionomers include polystyrene sulfonate , Nafion and Hycar .
Ionomer : A polymer composed of ionomer molecules . [ 1 ]
Ionomer molecule : A macromolecule in which a small but significant proportion of the constitutional units have ionizable or ionic groups, or both.
Note : Some protein molecules may be classified as ionomer molecules. [ 2 ]
Usually ionomer synthesis consists of two steps – the introduction of acid groups to the polymer backbone and the neutralization of some of the acid groups by a metal cation. In very rare cases, the groups introduced are already neutralized by a metal cation. The first step (introduction of acid groups) can be done in two ways; a neutral non-ionic monomer can be copolymerized with a monomer that contains pendant acid groups or acid groups can be added to a non-ionic polymer through post-reaction modifications. For example, ethylene-methacrylic acid and sulfonated perfluorocarbon (Nafion) are synthesized through copolymerization while polystyrene sulfonate is synthesized through post-reaction modifications.
In most cases, the acid form of the copolymer is synthesized (i.e. 100% of the carboxylic acid groups are neutralized by hydrogen cations) and the ionomer is formed through subsequent neutralization by the appropriate metal cation. The identity of the neutralizing metal cation has an effect on the physical properties of the ionomer; the most commonly used metal cations (at least in academic research) are zinc, sodium, and magnesium. Neutralization or ionomerization, can also be accomplished in two ways: the acid copolymer can be melt-mixed with a basic metal or neutralization can be achieved through solution processes. The former method is preferred commercially. However, as commercial manufacturers are reluctant to share their procedures, little is known about the exact conditions of the melt-mixing neutralization process other than that hydroxides are generally used to provide the metal cation. The latter solution neutralization process is generally used in academic settings. The acid copolymer is dissolved and a basic salt with the appropriate metal cation is added to this solution. Where dissolution of the acid copolymer is difficult, simply swelling the polymer in the solvent is sufficient, though dissolving is always preferred. Because basic salts are polar and are not soluble in the non-polar solvents used to dissolve most polymers, mixed solvents (e.g. 90:10 toluene/alcohol) are often used.
Neutralization level must be determined after an ionomer is synthesized as varying the neutralization level varies the morphological and physical properties of the ionomer. One method used to do this is to examine the peak heights of infrared vibrations of the acid form. However, there may be substantial error in determining peak height, especially since small amounts of water appear in the same wavenumber range. Titration of the acid groups is another method that can be used, though this is not possible in some systems.
Surlyn is the brand name of an ionomer resin created by DuPont , a copolymer of ethylene and methacrylic acid used as a coating and packaging material. [ 3 ] DuPont neutralizes the acid with NaOH , yielding the sodium salt. [ 4 ] Crystals of ethylene-methacrylic acid ionomers exhibit dual melting behavior. [ 5 ]
Nafion | https://en.wikipedia.org/wiki/Ionomer |
Mineral processing and extraction of metals are very energy-intensive processes, which are not exempted of producing large volumes of solid residues and wastewater, which also require energy to be further treated and disposed. Moreover, as the demand for metals increases, the metallurgical industry must rely on sources of materials with lower metal contents both from a primary (e.g., mineral ores) and/or secondary (e.g., slags, tailings, municipal waste) raw materials. Consequently, mining activities and waste recycling must evolve towards the development of more selective, efficient and environmentally friendly mineral and metal processing routes.
Mineral processing operations are needed firstly to concentrate the mineral phases of interest and reject the unwanted material physical or chemically associated to a defined raw material. The process, however, demand about 30 GJ/tonne of metal, which accounts about 29% of the total energy spent on mining in the USA. [ 1 ] Meanwhile, pyrometallurgy is a significant producer of greenhouse gas emissions and harmful flue dust. Hydrometallurgy entails the consumption of large volumes of lixiviants such as H 2 SO 4 , HCl, KCN, NaCN which have poor selectivity. [ 2 ] Moreover, despite the environmental concern and the use restriction imposed by some countries, cyanidation is still considered the prime process technology to recover gold from ores. Mercury is also used by artisanal miners in less economically developed countries to concentrate gold and silver from minerals, despite its obvious toxicity. Bio-hydro-metallurgy make use of living organisms, such as bacteria and fungi, and although this method demands only the input of O 2 and CO 2 from the atmosphere, it requires low solid-to-liquid ratios and long contact times, which significantly reduces space-time yields.
Ionometallurgy makes use of non-aqueous ionic solvents such ionic liquids (ILs) and deep eutectic solvents (DESs), which allows the development of closed-loop flow sheet to effectively recover metals by, for instance, integrating the metallurgical unit operations of leaching and electrowinning. It allows to process metals at moderate temperatures in a non-aqueous environment which allows controlling metal speciation, tolerates impurities and at the same time exhibits suitable solubilities and current efficiencies. This simplify conventional processing routes and allows a substantial reduction in the size of a metal processing plant.
DESs are fluids generally composed of two or three cheap and safe components that are capable of self-association, often through hydrogen bond interactions, to form eutectic mixtures with a melting point lower than that of each individual component. DESs are generally liquid at temperatures lower than 100 °C, and they exhibit similar physico-chemical properties to traditional ILs, while being much cheaper and environmentally friendlier. Most of them are mixtures of choline chloride and a hydrogen-bond donor (e.g., urea, ethylene glycol, malonic acid) or mixtures of choline chloride with a hydrated metal salt. Other choline salts (e.g. acetate, citrate, nitrate) have a much higher costs or need to be synthesised, [ 3 ] and the DES formulated from these anions are typically much more viscous and can have higher conductivities than for choline chloride . [ 4 ] This results in lower plating rates and poorer throwing power and for this reason chloride-based DES systems are still favoured. For instance, Reline (a 1:2 mixture of choline chloride and urea) has been used to selectively recover Zn and Pb from a mixed metal oxide matrix. [ 5 ] Similarly, Ethaline (a 1: 2 mixture of choline chloride and ethylene glycol) facilitates metal dissolution in electropolishing of steels. [ 6 ] DESs have also demonstrated promising results to recover metals from complex mixtures such Cu/Zn and Ga/As, [ 7 ] and precious metals from minerals. [ 8 ] It has also been demonstrated that metals can be recovered from complex mixtures by electrocatalysis using a combination of DESs as lixiviants and an oxidising agent, [ 9 ] while metal ions can be simultaneously separated from the solution by electrowinning . [ 10 ]
Precious metals are rare, naturally occurring metallic chemical elements of high economic value. Chemically, the precious metals tend to be less reactive than most elements. They include gold and silver, but also the so-called platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum (see precious metals). Extraction of these metals from their corresponding hosting minerals would typically require pyrometallurgy (e.g., roasting), hydrometallurgy (cyanidation), or both as processing routes.
Early studies have demonstrated that gold dissolution rate in Ethaline compares very favourably to the cyanidation method, which is further enhanced by the addition of iodine as an oxidising agent. In an industrial process the iodine has the potential to be employed as an electrocatalyst, whereby it is continuously recovered in situ from the reduced iodide by electrochemical oxidation at the anode of an electrochemical cell. Dissolved metals can be selectively deposited at the cathode by adjusting the electrode potential. The method also allows better selectivity as part of the gangue (e.g., pyrite) tend to be dissolved more slowly. [ 11 ]
Sperrylite (PtAs 2 ) and moncheite (PtTe 2 ), which are typically the more abundant platinum minerals in many orthomagmatic deposits, do not react under the same conditions in Ethaline because they are disulphide (pyrite), diarsenide (sperrylite) or ditellurides (calaverite and moncheite) minerals, which are particularly resistant to iodine oxidation. The reaction mechanism by which dissolution of platinum minerals is taking place is still under investigation.
Metal sulfides (e.g., pyrite FeS 2 , arsenopyrite FeAsS, chalcopyrite CuFeS 2 ) are normally processed by chemical oxidation either in aqueous media or at high temperatures. In fact, most base metals, e.g., aluminium, chromium, must be (electro)chemically reduced at high temperatures by which the process entails a high energy demand, and sometimes large volumes of aqueous waste is generated. In aqueous media chalcopyrite, for instance, is more difficult to dissolve chemically than covellite and chalcocite due to surface effects (formation of polysulfide species, [ 12 ] [ 13 ] ). The presence of Cl − ions has been suggested to alter the morphology of any sulfide surface formed, allowing the sulfide mineral to leach more easily by preventing passivation. [ 14 ] DESs provide a high Cl − ion concentration and low water content, whilst reducing the need for either high additional salt or acid concentrations, circumventing most oxide chemistry. Thus, the electrodissolution of sulfide minerals has demonstrated promising results in DES media in absence of passivation layers, with the release into the solution of metal ions which could be recovered from solution.
During extraction of copper from copper sulfide minerals with Ethaline, chalcocite (Cu 2 S) and covellite (CuS) produce a yellow solution, indicating that [CuCl 4 ] 2− complex are formed. Meanwhile, in the solution formed from chalcopyrite, Cu 2+ and Cu + species co-exist in solution due to the generation of reducing Fe 2+ species at the cathode. The best selective recovery of copper (>97 %) from chalcopyrite can be obtained with a mixed DES of 20 wt.% ChCl-oxalic acid and 80 wt.% Ethaline. [ 15 ]
Recovery of metals from oxide matrixes is generally carried out using mineral acids. However, electrochemical dissolution of metal oxides in DES can allow to enhance the dissolution up to more than 10 000 times in pH neutral solutions. [ 16 ]
Studies have shown that ionic oxides such as ZnO tend to have high solubility in ChCl:malonic acid, ChCl:urea and Ethaline, which can resemble the solubilities in aqueous acidic solutions, e.g., HCl. Covalent oxides such as TiO 2 , however, exhibits almost no solubility. The electrochemical dissolution of metal oxides is strongly dependent on the proton activity from the HBD, i.e. capability of the protons to act as oxygen acceptors, and on the temperature. It has been reported that eutectic ionic fluids of lower pH-values, such as ChCl:oxalic acid and ChCl:lactic acid, allow a better solubility than that of higher pH (e.g., ChCl:acetic acid). [ 17 ] Hence, different solubilities can be obtained by using, for instance, different carboxylic acids as HBD. [ 18 ]
Currently, the stability of most ionic liquids under practical electrochemical conditions is unknown, and the fundamental choice of ionic fluid is still empirical as there is almost no data on metal ion thermodynamics to feed into solubility and speciation models. Also, there are no Pourbaix diagrams available, no standard redox potentials, and bare knowledge of speciation or pH-values. It must be noticed that most processes reported in the literature involving ionic fluids have a Technology Readiness Level (TRL) 3 (experimental proof-of-concept) or 4 (technology validated in the lab), which is a disadvantage for short-term implementation. However, ionometallurgy has the potential to effectively recover metals in a more selective and sustainable way, as it considers environmentally benign solvents, reduction of greenhouse gas emissions and avoidance of corrosive and harmful reagents. | https://en.wikipedia.org/wiki/Ionometallurgy |
Ionomics is the measurement of the total elemental composition of an organism to address biological problems. [ 1 ] [ 2 ] Questions within physiology , ecology , evolution , and many other fields can be investigated using ionomics, often coupled with bioinformatics, chemometrics [ 3 ] and other genetic tools. [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] Observing an organism's ionome is a powerful approach to the functional analysis of its genes and the gene networks. Information about the physiological state of an organism can also be revealed indirectly through its ionome, for example iron deficiency in a plant can be identified by looking at a number of other elements , rather than iron itself. [ 9 ] A more typical example is in a blood test, where a number of conditions involving nutrition or disease may be inferred from testing this single tissue for sodium , potassium , iron , chlorine , zinc , magnesium , calcium and copper . [ 10 ]
In practice, the total elemental composition of an organism is rarely determined. The number and type of elements measured are limited by the available instrumentation, the assumed value of the element in question, and the added cost of measuring each additional element. Also, a single tissue may be measured instead of the entire organism, as in the example given above of a blood test , or in the case of plants , the sampling of just the leaves [ 11 ] or seeds. These are simply issues of practicality. [ 9 ]
Various techniques may be fruitfully used to measure elemental composition. Among the best are Inductively-Coupled Plasma Optical Emission Spectroscopy (ICP-OES), [ 3 ] Inductively-Coupled Plasma Mass Spectrometry (ICP-MS), X-Ray Fluorescence (XRF), synchrotron-based microXRF, [ 12 ] and Neutron activation analysis (NAA). This latter technique has been applied to perform ionomics in the study of breast cancer , [ 13 ] [ 14 ] colorectal cancer [ 15 ] and brain cancer . [ 16 ] High-throughput ionomic phenotyping has created the need for data management systems to collect, organize and share the collected data with researchers worldwide. [ 17 ]
The ionomicshub (iHUB) is a collaborative international network for ionomics [10] | https://en.wikipedia.org/wiki/Ionomics |
In chemistry , an ionophore (from Greek ion and -phore ' ion carrier ' ) is a chemical species that reversibly binds ions . [ 1 ] Many ionophores are lipid-soluble entities that transport ions across the cell membrane . Ionophores catalyze ion transport across hydrophobic membranes, such as liquid polymeric membranes (carrier-based ion selective electrodes) or lipid bilayers found in the living cells or synthetic vesicles ( liposomes ). [ 1 ] Structurally, an ionophore contains a hydrophilic center and a hydrophobic portion that interacts with the membrane.
Some ionophores are synthesized by microorganisms to import ions into their cells. Synthetic ion carriers have also been prepared. Ionophores selective for cations and anions have found many applications in analysis. [ 2 ] These compounds have also shown to have various biological effects and a synergistic effect when combined with the ion they bind. [ 3 ]
Biological activities of metal ion-binding compounds can be changed in response to the increment of the metal concentration, and based on the latter compounds can be classified as "metal ionophores", " metal chelators " or "metal shuttles". [ 3 ] If the biological effect is augmented by increasing the metal concentration, it is classified as a "metal ionophore". If the biological effect is decreased or reversed by increasing the metal concentration, it is classified as a "metal chelator". If the biological effect is not affected by increasing the metal concentration, and the compound-metal complex enters the cell, it is classified as a "metal shuttle". The term ionophore (from Greek ion carrier or ion bearer ) was proposed by Berton Pressman in 1967 when he and his colleagues were investigating the antibiotic mechanisms of valinomycin and nigericin . [ 4 ]
Many ionophores are produced naturally by a variety of microbes , fungi and plants , and act as a defense against competing or pathogenic species. Multiple synthetic membrane-spanning ionophores have also been synthesized. [ 5 ] The two broad classifications of ionophores synthesized by microorganisms are:
Ionophores that transport hydrogen ions (H + , i.e. protons) across the cell membrane are called protonophores . Iron ionophores and chelating agents are collectively called siderophores .
Many synthetic ionophores are based on crown ethers , cryptands , and calixarenes . Pyrazole - pyridine and bis-pyrazole derivatives have also been synthesized. [ 9 ] These synthetic species are often macrocyclic . [ 10 ] Some synthetic agents are not macrocyclic, e.g. carbonyl cyanide- p -trifluoromethoxyphenylhydrazone . Even simple organic compounds, such as phenols , exhibit ionophoric properties. The majority of synthetic receptors used in the carrier-based anion-selective electrodes employ transition elements or metalloids as anion carriers, although simple organic urea - and thiourea -based receptors are known. [ 11 ]
Ionophores are chemical compounds that reversibly bind and transport ions through biological membranes in the absence of a protein pore. This can disrupt the membrane potential , and thus these substances could exhibit cytotoxic properties. [ 1 ] Ionophores modify the permeability of biological membranes toward certain ions to which they show affinity and selectivity. Many ionophores are lipid-soluble and transport ions across hydrophobic membranes, such as lipid bilayers found in the living cells or synthetic vesicles ( liposomes ), or liquid polymeric membranes (carrier-based ion selective electrodes). [ 1 ] Structurally, an ionophore contains a hydrophilic center and a hydrophobic portion that interacts with the membrane. Ions are bound to the hydrophilic center and form an ionophore-ion complex. The structure of the ionophore-ion complex has been verified by X-ray crystallography . [ 12 ]
Several chemical factors affect the ionophore activity. [ 13 ] The activity of an ionophore-metal complex depends on its geometric configuration and the coordinating sites and atoms which create coordination environment surrounding the metal center. This affects the selectivity and affinity towards a certain ion. Ionophores can be selective to a particular ion but may not be exclusive to it. Ionophores facilitate the transport of ions across biological membranes most commonly via passive transport , which is affected by lipophilicity of the ionophore molecule. The increase in lipophilicity of the ionophore-metal complex enhances its permeability through lipophilic membranes. The hydrophobicity and hydrophilicity of the complex also determines whether it will slow down or ease the transport of metal ions into cell compartments. The reduction potential of a metal complex influences its thermodynamic stability and affects its reactivity . The ability of an ionophore to transfer ions is also affected by the temperature.
Ionophores are widely used in cell physiology experiments and biotechnology as these compounds can effectively perturb gradients of ions across biological membranes and thus they can modulate or enhance the role of key ions in the cell. [ 14 ] Many ionophores have shown antibacterial and antifungal activities. [ 15 ] Some of them also act against insects , pests and parasites . Some ionophores have been introduced into medicinal products for dermatological and veterinary use. [ 16 ] [ 17 ] A large amount of research has been directed toward investigating novel antiviral, anti-inflammatory, anti-tumor, antioxidant and neuroprotective properties of different ionophores. [ 15 ] [ 18 ] [ 3 ]
Chloroquine is an antimalarial and antiamebic drug. [ 19 ] It is also used in the management of rheumatoid arthritis and lupus erythematosus . Pyrithione is used as an anti-dandruff agent in medicated shampoos for seborrheic dermatitis . [ 16 ] It also serves as an anti-fouling agent in paints to cover and protect surfaces against mildew and algae . [ 20 ] Clioquinol and PBT2 are 8-hydroxyquinoline derivatives. [ citation needed ] Clioquinol has antiprotozoal and topical antifungal properties, however its use as an antiprotozoal agent has widely restricted because of neurotoxic concerns. [ 21 ] Clioquinol and PBT2 are currently being studied for neurodegenerative diseases, such as Alzheimer's disease , Huntington's disease and Parkinson's disease . Gramicidin is used in throat lozenges and has been used to treat infected wounds. [ 22 ] [ 23 ] Epigallocatechin gallate is used in many dietary supplements [ 24 ] and has shown slight cholesterol-lowering effects. [ 25 ] Quercetin has a bitter flavor and is used as a food additive and in dietary supplements . [ 26 ] Hinokitiol (ß- thujaplicin ) is used in commercial products for skin, hair and oral care, insect repellents and deodorants. [ 27 ] [ 28 ] It is also used as a food additive, [ 29 ] shelf-life extending agent in food packaging , [ 30 ] and wood preservative in timber treatment. [ 31 ]
Polyene antimycotics , such as nystatin , natamycin and amphotericin B , are a subgroup of macrolides and are widely used antifungal and antileishmanial medications. These drugs act as ionophores by binding to ergosterol in the fungal cell membrane and making it leaky and permeable for K + and Na + ions, as a result contributing to fungal cell death. [ 32 ]
Carboxylic ionophores, i.e. monensin , lasalocid , salinomycin , narasin , maduramicin , semduramycin and laidlomycin, are marketed globally and widely used as anticoccidial feed additives to prevent and treat coccidiosis in poultry . [ 33 ] Some of these compounds have also been used as growth and production promoters in certain ruminants , such as cattle , and chickens, however this use has been mainly restricted because of safety issues. [ 34 ] [ 35 ]
Zinc ionophores have been shown to inhibit replication of various viruses in vitro , including coxsackievirus , [ 36 ] [ 37 ] equine arteritis virus , [ 38 ] coronavirus , [ 38 ] HCV , [ 39 ] HSV , [ 40 ] HCoV-229E , [ 41 ] HIV , [ 42 ] [ 43 ] mengovirus , [ 36 ] [ 37 ] MERS-CoV , [ 41 ] rhinovirus , [ 36 ] SARS-CoV-1 , [ 38 ] [ 41 ] Zika virus . [ 44 ] [ 45 ] | https://en.wikipedia.org/wiki/Ionophore |
Ionosilicas are defined as organosilicas containing chemically bound ionic groups. They represent a class of mesoporous organosilicas .
Mesoporous materials have been defined as porous materials with pore size ranging from 2 nm – 50 nm. Ionosilicas belong to the mesoporous organosilicas materials, but are more specifically constituted by ionic substructures.
Ionosilicas are synthesized by hydrolysis - polycondensation reactions or post synthesis grafting procedures involving ionic precursors. [ 1 ] Due to their mixed mineral-ionic nature, ionosilicas are situated at the interface of silica hybrid materials and ionic liquids . [ 2 ] Similarly to conventional functional silica based materials, two classes of ionosilicas can be distinguished, depending on the way the ionic group is anchored to the silica support and where it is located. Surface functionalized ionosilicas contain ionic groups located on the materials’ surface and can be obtained either via ‘one-pot’ co-condensation reactions [ 2 ] or post grafting procedures. [ 3 ] [ 4 ] On the other side, periodic mesoporous ionosilicas, belonging to the PMO family, are produced starting from oligo silylated ionic precursors. [ 5 ] [ 6 ] [ 7 ]
Ionosilicas are synthesized via hydrolysis-polycondensation reactions involving ionic precursors. The ionic nature of these compounds has deep influence on the mechanism of the formation of the solid. Ionosilicas with regular architectures are often formed in the presence of anionic surfactants. This behaviour displays the formation of precursor-surfactant ion pairs in the hydrolysis polycondensation mixture.
These hybrid ionosilicas display very specific and unusual surface properties such as high hydrophilicity and high water-affinity . These features can efficiently be varied both via the cation [ 8 ] and the anion, [ 9 ] resulting in an ability to fine-tune the properties of these materials.
Ionosilicas are functional materials for applications in (organo-)catalysis and separation. | https://en.wikipedia.org/wiki/Ionosilica |
The IPP or Ionospheric Pierce Point is the altitude in the ionosphere where electron density is greatest. [ 1 ]
These points can change based on factors like time of day, solar activity, and geographical location, which all influence ionospheric conditions. [ 2 ]
Most global navigation satellite systems (GNSS) are subjected to errors induced by the ionosphere. Because ionospheric delay affects the speed of microwave signals differently depending on their frequency—a characteristic known as dispersion , delays measured on two or more frequency bands can be used to measure dispersion, and this measurement can then be used to estimate the delay at each frequency.
The principal source of the dispersion comes from the total electron content (TEC) in the ionosphere, along the line of sight from the satellite to the receiver. Because it is difficult to measure the TEC along the line of sight, instead a prediction can be made using a simplified model of the ionosphere.
This model assumes that the ionosphere is a thin, uniform-density shell about the Earth, located near the mean altitude H of maximum TEC (approx. 350 km). Using geometry, a slant intersection with this shell model can be determined and a vertical TEC measurement inferred. The intersection between line of sight and this shell is called the ionospheric pierce point (IPP). The perpendicular projection onto the Earth's surface is called the subionospheric point .
This plasma physics –related article is a stub . You can help Wikipedia by expanding it .
This astrophysics -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ionospheric_pierce_point |
An ionotropic effect is the effect of a transmitter substance or hormone that activates or deactivates ionotropic receptors ( ligand-gated ion channels ). The effect can be either positive or negative, specifically a depolarization or a hyperpolarization respectively. This term is commonly confused with an inotropic effect, which refers to a change in the force of contraction (e.g. in heart muscle ) produced by transmitter substances or hormones.
This term could be used to describe the action of acetylcholine on nicotinic receptors , glutamate on NMDA receptors or GABA on GABAa receptors .
This article related to medical imaging is a stub . You can help Wikipedia by expanding it .
This neuroscience article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ionotropic_effect |
Iontophoresis is a process of transdermal drug delivery by use of a voltage gradient on the skin . [ 1 ] [ 2 ] Molecules are transported across the stratum corneum by electrophoresis and electroosmosis and the electric field can also increase the permeability of the skin. [ 3 ] [ 4 ] These phenomena, directly and indirectly, constitute active transport of matter due to an applied electric current. The transport is measured in units of chemical flux , commonly μmol/(cm 2 ×hour).
Iontophoresis has experimental, therapeutic and diagnostic applications.
Iontophoresis is useful in laboratory experiments, especially in neuropharmacology . [ 5 ] Transmitter molecules naturally pass signals between neurons . By microelectrophoretic techniques, including microiontophoresis, neurotransmitters and other chemical agents can be artificially administered very near living and naturally functioning neurons, the activity of which can be simultaneously recorded. This is used to elucidate their pharmacological properties and natural roles. [ 6 ]
Therapeutically, electromotive drug administration (EMDA) delivers a medicine or other chemical through the skin. [ 7 ] In a manner of speaking, it is an injection without a needle, and may be described as non-invasive. It is different from dermal patches , which do not rely on an electric field. It drives a charged substance, usually a medication or bioactive agent, transdermally by repulsive electromotive force, through the skin. A small electric current is applied to an iontophoretic chamber placed on the skin, containing a charged active agent and its solvent vehicle. Another chamber or a skin electrode carries the return current. One or two chambers are filled with a solution containing an active ingredient and its solvent vehicle. The positively charged chamber, called the anode , will repel a positively charged chemical species, whereas the negatively charged chamber, called the cathode , will repel a negatively charged species into the skin. [ 8 ]
It is used to treat some types of palmar-plantar hyperhidrosis . [ 9 ] In the treatment of hyperhidrosis, tap water is often the chosen solution for mild and medium forms. In very serious cases of hyperhidrosis, a solution containing glycopyrronium bromide or glycopyrrolate , a cholinergic inhibitor, can be used. [ 10 ] [ 11 ]
Iontophoresis of acetylcholine is used in research as a way to test the health of the endothelium by stimulating endothelium-dependent generation of nitric oxide and subsequent microvascular vasodilation. Acetylcholine is positively charged and is therefore placed in the anode chamber.
Pilocarpine iontophoresis is often used to stimulate sweat secretion, as part of cystic fibrosis diagnosis. [ 12 ]
Reverse iontophoresis is a technique by which molecules are removed from within the body for detection. The negative charge of the skin at buffered pH causes it to be permselective to cations such as sodium and potassium ions, allowing iontophoresis which causes electroosmosis, solvent flow towards the anode. Electroosmosis then causes electrophoresis, by which neutral molecules, including glucose, are transported across the skin. This is currently being used in such devices as the GlucoWatch , which allows for blood glucose detection across skin layers. | https://en.wikipedia.org/wiki/Iontophoresis |
iostat ( i nput/ o utput stat istics ) is a computer system monitor tool used to collect and show operating system storage input and output statistics. It is often used to identify performance issues with storage devices, including local disks , or remote disks accessed over network file systems such as NFS . It can also be used to provide information about terminal (TTY) input and output, [ 1 ] and also includes some basic CPU information.
iostat -x displays output where each line (row) gives numerical data for one device. The first column lists the device name, and subsequent columns show various statistics for that device. Columns include the average service time ( svc_t , which includes not only the time a request is in the service queue, but also the seek time and transfer time [ 2 ] ), the average busy percentage ( %b , essentially the proportion of time that the device is in use), and the percentage of time that the queue is not empty ( %w , which means the proportion of time in which requests from the device have not yet been fulfilled). [ 1 ]
It is best to run iostat specifying a time interval in seconds (for example iostat -x 30 ) in order to see the results over time. This is because otherwise, the output will reflect the values over the entire timespan since the system was last rebooted . [ 2 ]
The iostat tool is available on most Unix and Unix-like operating systems, such as FreeBSD , macOS ( com.apple.pkg.Core package), Linux ( sysstat package), and Solaris . The syntax and output of iostat often differs slightly between them. [ 3 ]
Sun Microsystems stated that high values in the wait and svc_t fields suggest a lack of overall throughput in the system, indicating that "the system is overloaded with I/O operations". Consistently high values in the kr/s , kw/s , %w and %b fields also indicate "a possible I/O bottleneck". [ 1 ]
In versions of Solaris before Solaris 7, iostat can give misleading information in the wait field on multiprocessor systems. This is because iostat can misinterpret one processor being in a state where it is waiting for I/O, as meaning that all processors in the system are having to wait. [ 2 ]
It is also advisable to disregard high values in the svc_t field for disks that have very low rates of activity (less than 5%). This is because the fsflush process can force up the average service time when synchronising data on disk with what is in memory. [ 2 ]
iostat does not display information about the individual volumes on each disk if a volume manager is used . The vxstat command can be used to show this information instead. [ 1 ] In contrast, when using Linux LVM as a volume manager, iostat does display volume information individually, because each logical volume has its own device mapper (dm) device. | https://en.wikipedia.org/wiki/Iostat |
Iota Sigma Pi ( ΙΣΠ ) is a national honor society in the United States. It was established in 1900 and specializes in the promotion of women in the sciences, especially chemistry . It also focuses on personal and professional growth for women in these fields. [ 1 ] As with all honor societies, they create professional networks [ 2 ] along with recognizing achievements of women in chemistry. [ 3 ]
Iota Sigma Pi was formed during a period when women gained little recognition for their work; therefore, women began to set up their own awards to highlight their abilities on their resumes . [ 4 ] It was created by the merger of three chemistry honor societies for women that were established in the early 20th century. [ 5 ]
Agnes Fay Morgan , department chair of the Department of Household Science and Arts at the University of California , formed Alchemi in 1900. [ 1 ] [ 6 ] [ 5 ] Alchemi spread to the University of Southern California and Stanford University . [ 5 ] In 1911, a national chemistry honor society was established at the University of Washington . A third honor society, Iota Sigma Pi, was established at the University of Nebraska in 1912. [ 5 ] The latter two societies merged as Iota Sigma Pi in 1913 and were joined by the three chapters of Alchmi in 1916. [ 5 ]
The goals of Iota Sigma Pi were to encourage women to pursue chemistry academically, to "stimulate personal accomplishment in chemical fields" and to promote the academic, business, and social lives of its members. [ 7 ] It continued to spread across the country, and eventually held meetings for the American Chemical Society . [ 4 ]
Iota Sigma Pi was a charter member of the Professional Panhellenic Association in 1925. [ 8 ] In the 1930s, there was an offer of amalgamation from the Phi Lambda Upsilon honor society for male chemists but this was refused. [ 9 ]
Iota Sigma Pi was briefly a member of the Association of College Honor Societies or ACHS, joining in February 1955 , but resigned to operate independently in 1963. In 1963, it had 19 active chapters, 8 inactive chapters, and 6,271 initiates. [ 5 ]
As of 2025, Iota Sigma Pi has chartered 47 chapters and initiated more than 11,000 members. [ 10 ] Its national headquarters is based at De Paul University in Chicago, Illinois .
Iota Sigma Pi's emblem is a hexagonal key that features a crescent a circle, and the Greek letters ΙΣΠ . [ 5 ] The society's colors are white, gold, and cedar green. [ 5 ] Its flower is the white narcissus. [ 5 ] Its publication is The Iotan, first published in 1941 . [ 5 ]
As of 2025, Iota Sigma Pi has chartered 47 chapters. [ 10 ]
The highest award from the society is the National Honorary Member which is given to female chemists who have made an exceptional and significant achievement in the field. The certificate is awarded with a prize fund of $1,500. Some of the previous winners include: Marie Sklodowska-Curie , Gerti Cori and Dorothy Hodgkin . [ 3 ] [ 11 ]
The Violet Diller Professional Excellence Award, named after a previous member (treasurer and president), is awarded for "accomplishments in academic, governmental, or industrial chemistry, in education, in administration, or a combination of these areas". The award consists of a certificate and a $1,000 prize fund. [ 3 ] This award was first awarded to Joan P. Lambros in 1984. [ 12 ]
The Agnes Fay Morgan Research Award is given to women who have achieved in the field of chemistry or biochemistry. [ 3 ] The Centennial Award for Excellence in Undergraduate Teaching is given to those who have excelled in teaching chemistry, biochemistry, or a similar subject. The nominee must spend at least 75 percent of their time teaching undergraduates to qualify for the certificate and $500 award. [ 3 ]
The Anna Louise Hoffman Award for Outstanding Achievement in Graduate Research is given to the nominee who has demonstrated outstanding chemical research. The nominee must also be a full-time graduate student to get the certification and $500 reward. [ 13 ] There are two awards for Undergraduate Excellence in Chemistry; one must go to a first-generation student. Again, the reward is a certificate and $500. [ 13 ]
As of 2025, Iota Sigma Pi has initiated more than 11,000 members. [ 10 ] | https://en.wikipedia.org/wiki/Iota_Sigma_Pi |
In formal language theory and computer science , Iota and Jot (from Greek iota ι, Hebrew yodh י, the smallest letters in those two alphabets) are languages, extremely minimalist formal systems , designed to be even simpler than other more popular alternatives, such as lambda calculus and SKI combinator calculus . Thus, they can also be considered minimalist computer programming languages , or Turing tarpits , esoteric programming languages designed to be as small as possible but still Turing-complete . Both systems use only two symbols and involve only two operations. Both were created by professor of linguistics Chris Barker in 2001. Zot (2002) is a successor to Iota that supports input and output. [ 1 ]
Note that this article uses Backus-Naur form to describe syntax.
Chris Barker's universal iota combinator ι has the very simple λf.fSK structure defined here, using denotational semantics in terms of the lambda calculus ,
From this, one can recover the usual SKI expressions , thus:
Because of its minimalism, it has influenced research concerning Chaitin's constant . [ 2 ]
Iota is the LL(1) language that prefix orders trees of the aforementioned Universal iota ι combinator leafs, consed by function application ε ,
so that for example 0011011 denotes ( ( ι ι ) ( ι ι ) ) {\displaystyle ((\iota \iota )(\iota \iota ))} , whereas 0101011 denotes ( ι ( ι ( ι ι ) ) ) {\displaystyle (\iota (\iota (\iota \iota )))} .
Jot is the regular language consisting of all sequences of 0 and 1,
The semantics is given by translation to SKI expressions.
The empty string denotes I {\displaystyle I} , w 0 {\displaystyle w0} denotes ( ( [ w ] S ) K ) {\displaystyle (([w]S)K)} ,
where [ w ] {\displaystyle [w]} is the translation of w {\displaystyle w} ,
and w 1 {\displaystyle w1} denotes ( S ( K [ w ] ) ) {\displaystyle (S(K[w]))} .
The point of the w 1 {\displaystyle w1} case is that the translation satisfies ( ( [ w 1 ] A ) B ) = ( [ w ] ( A B ) ) {\displaystyle (([w1]A)B)=([w](AB))} for arbitrary SKI terms A {\displaystyle A} and B {\displaystyle B} .
For example, [ w 11100 ] = ( ( [ w 1110 ] S ) K ) = ( ( ( ( [ w 111 ] S ) K ) S ) K ) = ( ( ( [ w 11 ] ( S K ) ) S ) K ) = ( ( [ w 1 ] ( ( S K ) S ) ) K ) = ( [ w ] ( ( ( S K ) S ) K ) ) = ( [ w ] K ) {\displaystyle [w11100]=(([w1110]S)K)=(((([w111]S)K)S)K)=((([w11](SK))S)K)=(([w1]((SK)S))K)=([w](((SK)S)K))=([w]K)} holds for arbitrary strings w {\displaystyle w} .
Similarly, [ w 11111000 ] = ( ( ( ( ( ( [ w 11111 ] S ) K ) S ) K ) S ) K ) = ( [ w ] ( ( ( ( ( S K ) S ) K ) S ) K ) ) = ( [ w ] S ) {\displaystyle [w11111000]=(((((([w11111]S)K)S)K)S)K)=([w](((((SK)S)K)S)K))=([w]S)} holds as well.
These two examples are the base cases of the translation of arbitrary SKI terms to Jot given by Barker,
making Jot a natural Gödel numbering of all algorithms .
Jot is connected to Iota by the fact that [ w 0 ] = ( ι [ w ] ) {\displaystyle [w0]=(\iota [w])} and by using the same identities on SKI terms for obtaining the basic combinators K {\displaystyle K} and S {\displaystyle S} .
The Zot and Positive Zot languages command Iota computations , from inputs to outputs by continuation-passing style , in syntax resembling Jot ,
where 1 produces the continuation λ c L . L ( λ l R . R ( λ r . c ( l r ) ) ) {\displaystyle \lambda cL.L(\lambda lR.R(\lambda r.c(lr)))} ,
and 0 produces the continuation λ c . c ι {\displaystyle \lambda c.c\iota } ,
and wi consumes the final input digit i by continuing through the continuation w . | https://en.wikipedia.org/wiki/Iota_and_Jot |
ip.access Limited is a multinational corporation that designs, manufactures, and markets small cells ( picocell and femtocell ) technologies and infrastructure equipment for GSM , GPRS , EDGE , 3G , 4G and 5G . The company was acquired by Mavenir in September 2020.
The company’s headquarters is based in Cambourne , England. The company also maintains offices in Gurgaon and Pune , India.
ip.access combines IP and cellular technologies to provide 2G , 3G and LTE coverage and for mobile networks. Using satellite backhaul , its products provide coverage to commercial passenger aircraft, [ 1 ] ships, [ 2 ] and users in remote rural areas.
The firm is a member of 3GPP , [ 3 ] CBRS Alliance, European Telecommunications Standards Institute (ETSI), [ 4 ] Having previously been an individual member of the Telecom Infra Project , following its acquisition, ip.access continues to be involved through Mavenir's membership. [ 5 ]
ip.access was founded in December 1999 [ 6 ] as a wholly owned subsidiary of TTP Group PLC [ 7 ] aimed at developing technologies that would allow multiple radio access technologies to communicate over the Internet. To accommodate its growing staff, in 2006 ip.access relocated to new offices in Cambourne Business Park, Cambridge, where it remains. [ 8 ]
In October 2000, TTP Group spun off its communications division (TTP Communications, or TTPCom) in an initial public offering on the London Stock Exchange , and ip.access joined the spin-off as a wholly owned subsidiary of the TTPCom group.
In March 2006, the company secured an £8.5 million round of funding from Intel Capital , Scottish Equity Partners, and Rothschild & Cie Banque . [ 9 ] As part of its June 2006 acquisition of TTP Communications, Motorola also gained a stake in ip.access. [ 10 ] In 2007, after signing an OEM agreement with ip.access, ADC [ 11 ] (now part of Tyco Electronics ) made a minority interest investment in the company. Followed by, both Cisco Systems [ 12 ] and Qualcomm [ 13 ] making strategic financial investments in the company in 2008.
In July 2007, the firm became a founding member of the Femto Forum, renamed Small Cell Forum in February 2012. [ 14 ] [ 15 ] ip.access was named in The Sunday Times Fast Tech Track 100 in both 2007 [ 16 ] and 2008. [ 17 ] The company was cited as the number one picocell vendor by ABI Research in 2008. [ 18 ]
In 2009, ip.access was named in the Deloitte Technology Fast 500 EMEA . [ 19 ] In April 2009, the company announced its Oyster 3G product would support femtocell standards published by 3GPP and the Broadband Forum . [ 20 ] In March 2010, the company took part in the first Plugfest , [ 21 ] organized by ETSI as part of its Plugtests [ 22 ] program, held to demonstrate the effectiveness of the 3GPP femtocell standards in supporting interoperability between femtocell access points and network equipment from different vendors.
In June 2011, the market research and analysis firm Infonetics [ 23 ] named ip.access along with its partner Cisco Systems, as the leading supplier of 3G femtocells. [ 24 ] In August 2011, ip.access [ 25 ] announced it had made more than 500,000 installations of its 3G technologies. [ 26 ] In February 2013, ip.access announced it had become the first 3G small cell provider to ship one million residential units. [ 27 ] In the same month, ip.access and iDirect completed successful interoperability testing of 3G small cells over IP Satellite. [ 28 ]
In February 2014, ip.access launched a new range of small cells called presenceCell, [ 29 ] which unlike traditional small cells, do not rely on providing indoor coverage and capacity to deliver a return on investment. Rather, the ultra-compact base stations are designed to capture anonymous user location and phone identity information from smartphones, which can be analysed and packaged as a service for a variety of businesses.
Private equity fund Zouk Capital invested in ip.access in July 2015 [ 30 ] alongside Amadeus Capital Partners.
In August 2015, ip.access was named as a partner in the European Commission -funded €8 million Horizon 2020 Project SESAME. [ 31 ] Led by Hellenic Telecommunications Organisation (OTE) the project's remit was to develop virtualised cloud-enabled, multi-operator, 5G radio access infrastructure and services. In February, 2016. ip.access launched its Viper platform to provide end-to-end connectivity and management for small cells. [ 32 ]
nanoVirt, a virtualised small cell gateway which integrates 2G, 3G and 4G small cell management and access control functions and can run on a carrier-grade Virtual Machine (VM) environment or hosted in a third-party data centre was announced in May 2016. [ 33 ] Ip.access has deployed more than 2 million small cells globally which are used by mobile operators to densify their networks to improve network coverage and/or capacity. [ 34 ] Small cells are also the foundation for private network use cases based on spectrum sharing such as CBRS in the United States .
AeroMobile and SITAONAIR use ip.access small cells combined with satellite backhaul to provide cellular coverage on commercial and private aircraft. [ 35 ] The company also supplies maritime solutions on freight vessels and cruise liners working with partners such as Pentonet, SpeedCast and Telecom26. Ip.access has also provided small cells connected over satellite as rapid deployment disaster response systems. Ip.access small cell solution have also been deployed in Africa, Asia, and Latin America to provide connectivity to rural and remote communities and reduce the digital divide.
On September 27, 2020 ip.access was acquired by Mavenir, the supplier of cloud-native network software to communication service providers. The acquisition allowed the integration of ip.access’ 2G and 3G technologies into Mavenir's existing 4G and 5G OpenRAN portfolio broadband suite and also extend its reach into the enterprise market for private wireless networks based on 3GPP technologies such as 4G/LTE and 5G.
The sale of ip.access Ltd to Mavenir was led by the ip.access management team; Richard Staveley (CEO), Nick Johnson (CTO & Founder), Neil Winrow (COO) and Laura Lawrence (CFO).
The two companies had worked together to deliver Vodafone UK's first Open RAN site at the Royal Welsh Showground in Builth Wells in August 2020.
In November 2020, Mavenir announced the establishment of an OpenRAN Centre of Innovation to be centred at the ip.access headquarters in Cambridge, UK.
The telecommunications firms AT&T [ 36 ] uses Oyster 3G as the core femtocell technology for its 3G MicroCell [ 37 ] product. Cisco Systems , [ 38 ] has jointly developed a femtocell solution with ip.access in compliance with the Broadband Forum's TR-069 [ 20 ] technical specification.
In 2002, ip.access introduced the world's first IP basestation controller for indoor GSM networks. [ 39 ] nanoGSM uses 2G picocells that leverage the standard GSM air interface, full IP-based BSC , and an OMC-R management system that delivers voice, messaging and data to both 2G and 3G handsets at an indoor range of up to 200m.
nano3G is an end-to-end femtocell system with access points for Enterprise, E-class [E8, E16 and E24] and Small Medium Business, S-class [S8], access controller and element management system, providing carrier-class coverage to commercial [ 40 ] and consumer users. [ 41 ]
Launched at the 2007 3GSM World Congress in Barcelona , Spain, [ 42 ] the Oyster 3G is ip.access' core 3G femtocell technology used by system integrators and OEM customers to integrate WCDMA femtocells into home gateways, set-top boxes, and other devices. ip.access' Oyster 3G is the core technology of AT&T's 3G MicroCell [ 43 ]
nanoLTE [E-40, E-60, E-100] is an Enterprise grade platform that brings LTE capacity both in-doors and in public spaces, while also offering the option of providing extra 3G infill and Circuit Switch Fall Back (CSFB) capacity.
Launched in 2014, the presenceCell is a new range of small cell, designed to capture precise user location data via their smart phone, which can be analysed and packaged as a service for a variety of businesses. In addition to the presenceCell, ip.access also provides the back-end processing and management system that delivers the Presence data anonymously and securely to vertical application providers. The company's Network Orchestration System serves as the infrastructure management solution and also supports the GSMA's OneAPI standard, which allows third parties to provide value-added services through web friendly message interfaces. The presenceCell was commercially deployed by Vodafone Turkey in 2015. [ 44 ] In January 2017, ip.access entered into a strategic partnership with wireless network analytics company Inovva to enhance the Presence offering.
Viper is a virtualised, in-premises enterprise 3G/4G radio access network platform launched in February 2016 that can be deployed by mobile operators or enterprises to offer indoor coverage through a “small cells as a service” (ScaaS) business model. [ 45 ] In May 2017, ip.access announced the updating of the Viper2020 Cloud Managed Small Cell platform to support 5G, first responders and neutral host networks with Presence.
The S-60, announced in February 2016, is ip.access’ first freestanding low-cost 4G/LTE access point designed for small offices and retailers.
Also launched in February 2016, the 4G Access Control Gateway provides mobile operators with a single interface between their existing core network and LTE small cells.
nanoVirt, launched in May 2016, is a software solution that integrates 2G, 3G and 4G small cell management and access control functions as virtualized components that can be deployed by mobile operators and neutral hosts on their preferred Virtual Machine server hardware or third-party data centre.
Announced in February 2019, the E62 is a multi-Radio Access Technology 3G/4G platform that is software-upgradable to 5G.
nanoCBRS is an OnGo certified solution for the deployment of private LTE networks in the 3.5 GHz band. Launched in October 2019, the solution incorporates Citizens Band Radio Devices, a suite of architectures – nanoViNE - to support use cases and nanoCBRSLab, a mobile network lab solution for testing.
Among ip.access' major customers are AT&T , [ 36 ] Batelco , Bharti Airtel , [ 46 ] Blue Ocean Wireless, [ 2 ] Bouygues Telecom , [ 47 ] Caribsat, Digicel , Globe , Jersey Telecom [ 48 ] Monaco Telecom, [ 49 ] O2 (UK) , SFR , [ 50 ] SPIE SA , [ 50 ] T-Mobile , [ 51 ] Tele2 , [ 52 ] Telefónica O2 Czech Republic , [ 53 ] Telenet , Telia Sonera , [ 54 ] T-Mobile , Vivacom [ 55 ] and Vodafone . [ 56 ]
The company's technology partners [ 57 ] include AeroMobile , [ 58 ] Africa Mobile Networks, Altobridge, [ 59 ] Blue Ocean Wireless, [ 60 ] Cisco Systems, [ 38 ] Druid Software, Intel, Pentonet, Private Mobile Networks, [ 61 ] Qualcomm , [ 62 ] Quortus, [ 63 ] Setcom, [ 63 ] and TriaGnoSys. [ 64 ]
Corporate, product, and personnel awards won by ip.access include the following: | https://en.wikipedia.org/wiki/Ip.access |
iperf , Iperf , or iPerf , is a tool for network performance measurement and tuning. It is a cross-platform tool that can produce standardized performance measurements for any network. iperf has client and server functionality, and can create data streams to measure the throughput between the two ends in one or both directions. [ 2 ] Typical iperf output contains a time-stamped report of the amount of data transferred and the throughput measured.
The data streams can be either Transmission Control Protocol (TCP) or User Datagram Protocol (UDP):
iperf is open-source software written in C , and it runs on various platforms including Linux , Unix and Windows (either natively or inside Cygwin [ 3 ] ). The availability of the source code enables the user to scrutinize the measurement methodology.
iperf is a compatible reimplementation of the ttcp program that was developed at the National Center for Supercomputing Applications at the University of Illinois by the Distributed Applications Support Team (DAST) of the National Laboratory for Applied Network Research (NLANR), [ 4 ] which was shut down on December 31, 2006, on termination of funding by the United States National Science Foundation .
iperf3 is a rewrite of iperf from scratch to create a smaller, simpler code base. iperf3 was started in 2009, with the first release in January 2014. iperf3 is not backwards compatible with iperf2. iperf3 also includes a library version which enables other programs to use the provided functionality. iperf3 is single threaded while iperf2 is multi-threaded. [ 5 ]
Officially iperf3 supports only Linux. Unofficial builds for Windows provided by Vivien Guéant. [ 6 ] A user of Neowin , BudMan, [ 7 ] provides unofficial Windows builds on his server. [ 8 ]
Most current Linux distributions have iperf3 in their native package repositories. Unix packages are available from Oracle for Solaris 11.4. | https://en.wikipedia.org/wiki/Iperf |
Iphigenia Photaki ( Greek : Ιφιγένεια Φωτάκη , pronounced [ifiˈʝeni.a foˈtaki] ; also known after marriage as Iphigenia Vourvidou-Photaki , Greek : Ιφιγένεια Βουρβίδου-Φωτάκη ; 1921–1983) was a Greek organic chemist remembered for her contributions in peptide chemical synthesis , especially in the synthesis of biologically/ enzymatically active peptides. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ]
Photaki was in 1965 the fourth woman overall to be habilitated in a scientific discipline in Greece, and the second to do so in the field of Chemistry . [ 3 ] [ 4 ] She specialised in peptide synthesis, influenced by her mentor and doctoral advisor Leonidas Zervas , a global authority on the subject. [ 1 ] [ 2 ] [ 4 ] After distinguished research in Basel, Athens, and later Cornell, Photaki eventually rose to Professor of Organic Chemistry and Head of the Laboratory of Organic Chemistry of the University of Athens . [ 2 ] [ 3 ] [ 5 ]
Photaki was born in Corinth in 1921 and finished her secondary education at the 2nd Girls' Gymnasium of Athens in 1938. [ 2 ] [ 4 ] In the same year she enrolled at the Department of Chemistry in the University of Athens, where she specialised in Organic chemistry under the mentorship of Leonidas Zervas . [ 2 ] [ 3 ] [ 4 ] Her studies were interrupted during the Axis occupation of Greece when the Laboratory of Organic Chemistry was destroyed and Zervas was imprisoned as a member of the Greek Resistance . [ 2 ] [ 3 ] Photaki was finally awarded her degree summa cum laude in 1946 and subsequently continued her postgraduate studies under Zervas, earning her PhD in 1950 with a dissertation regarding glucosamine . [ 1 ] [ 2 ] [ 3 ] [ 4 ] Concurrently, she held a paid laboratory assistant position at the university already from 1943, carrying on as a research assistant until 1953. [ 3 ] [ 4 ]
In 1953, Photaki was awarded a scholarship to conduct research in Basel after examinations by the Greek State Scholarships Foundation. [ 2 ] [ 3 ] [ 4 ] At the University of Basel she worked in the Laboratory of Organic Chemistry, at the time headed by Nobel laureate Tadeusz Reichstein . [ 2 ] [ 4 ] For the first two years of her stay (1953–1955) she was part of the Max Brenner research group, later moving as an independent scientific associate of Hans Erlenmeyer . [ 2 ] [ 4 ] Upon returning to Greece, she initially worked at the biochemical lab of the Evangelismos Hospital before being invited by Zervas to the nascent National Hellenic Research Foundation (NHRF) which he had helped found. [ 3 ] [ 4 ]
Photaki was selected in 1962 by the US Department of Health, Education and Welfare among an international pool of candidates to conduct research by the side of Nobel laureate Vincent du Vigneaud at Cornell University . [ 2 ] [ 3 ] [ 4 ] While in New York , she also delivered a short series of lectures both in Cornell and at the National Institutes of Health (NIH). [ 4 ]
Back in the University of Athens after Cornell, Photaki continued her research and was soon habilitated in 1965 following a thesis on oxytocin , building on the work she started under du Vigneaud. [ 1 ] [ 3 ] [ 4 ] [ 6 ] Despite her internationally distinguished research and sizeable recent grants from the NHRF and the United States NIH, she was not allowed to teach by the Greek military junta until 1969 and was intensively interrogated by the Cities Police Security Directorate on account of her anti-dictatorial political beliefs. [ 2 ] [ 3 ] [ 4 ]
Photaki's teaching career was purposefully hindered by the Ministry of Education until the restoration of democracy in 1974; indeed, in 1975 she was promoted to extraordinary professor, a decade after receiving her habilitation. [ 2 ] [ 3 ] [ 5 ] Shortly afterwards, in 1977, she was promoted to full professor (as Professor of Organic Chemistry) and Head of the Organic Chemistry Laboratory, both positions once held by her mentor Zervas. [ 2 ] Photaki died in 1983 at the age of 62. [ 1 ] [ 2 ]
She was reported to spend very long hours at the laboratory, occasionally from "8 in the morning till 10 in the evening". [ 2 ] [ 3 ] In her 20-year career as a member of the University of Athens faculty, she supervised (alone or jointly with other colleagues) more than 15 doctoral dissertations. [ 4 ] [ 5 ]
Although many of Photaki's important contributions were related to peptide synthesis , her scientific work touched on a large number of topics within organic synthesis . [ 1 ] [ 4 ] [ 5 ] In total she published around 50 papers in international English- or German-language chemical journals. [ 1 ] [ 4 ] [ 5 ]
Continuing and expanding the tradition of the University of Athens within the subject, starting from Zervas of Bergmann-Zervas carbobenzoxy method fame, Photaki initially worked on further refinement of suitable protecting groups for oligopeptide synthesis. [ 4 ] [ 5 ] She investigated with Zervas new types of protection such as N -protection with benzyl phosphate esters ( N -phosphamide derivatives), S -protection using trityl , benzhydryl or benzoyl groups (as part of the greater effort for the synthesis of asymmetric cysteine -containing peptides), N -protection using the o -nitrophenylsulfenyl (NPS) group discovered in their Athens laboratory, or S -protection using the p -methoxycarbobenzoxy group (a modification of the Z group ). [ 4 ] [ 5 ]
With the above methodologies she embarked on the synthesis of complex polypeptides, especially fragments of enzyme active sites and peptide hormones. [ 1 ] [ 5 ] Some notable achievements in papers Photaki co-authored include the first synthesis of the 20-membered insulin intra-chain ring or –following her research under du Vigneaud– several previously inaccessible oxytocin analogues ( e.g. 4-deamido-oxytocin) and a novel oxytocin synthesis via a different route than the du Vigneaud synthesis. [ 4 ] [ 5 ]
In later years she also examined the preparation of biologically active atypical peptides such as N ω -arginine or lanthionine -containing peptides. [ 5 ]
With her expertise on peptide synthesis, Photaki examined the biocatalytic properties and kinetics of enzyme active site analogues she prepared. [ 4 ] [ 5 ]
Another research topic she developed in the early part of her career was the chemical transformation of carbohydrates and glycosylated species, such as the stereoselective conversion of D - glucosamine to L - serinaldehyde which formed the basis of her doctoral thesis. [ 3 ] [ 4 ]
Finally, she examined some of the coordination complexes formed by histidine -containing peptides with Cu 2+ , Co 2+ , Zn 2+ and Ce 4+ , and after the antitumour properties of platinum complexes were realised, she also worked on the peptide enzymatic reactions in the presence of Pt 2+ amine complexes. [ 4 ] [ 5 ]
In 1970 Iphigenia Vourvidou-Photaki was awarded the one-off Georgios Panopoulos Prize of the Academy of Athens , presented to her for "...her research on the chemical synthesis of polypeptide hormones and investigation of enzyme active sites, which constitute an internationally notable contribution of Greek science to the modern discipline of Chemistry". [ 5 ]
During her lifetime, she was invited many times as a distinguished researcher in academic conferences related to her subject; some examples were the personal invitations she received to the 3rd European Peptide Symposium (EPS) (Basel, 1960), the 5th EPS (Oxford, 1962), 6th EPS (Athens, 1963 as organiser), 6th International Biochemistry Conference (New York, 1964), 7th EPS (Budapest, 1964), Symposium on Natural Sulfur Compounds (Copenhagen, 1966), NATO Seminar of Molecular Biology (Spetses, 1966), 8th EPS (Noordwijk, 1966), 9th EPS (Paris, 1968), 10th EPS (Abano, 1970), 11th EPS (Vienna, 1971), 3rd American Peptide Symposium (APS) (Boston, 1972), 13th EPS (Kiryat, 1974), 4th APS (New York, 1975), and the 14th EPS (Wépion, 1976) over which she presided. [ 1 ] [ 4 ] [ 5 ] | https://en.wikipedia.org/wiki/Iphigenia_Photaki |
iproute2 is a collection of userspace utilities for controlling and monitoring various aspects of networking in the Linux kernel , including routing , network interfaces, tunnels, traffic control , and network-related device drivers .
iproute2 is an open-source project released under the terms of version 2 of the GNU General Public License . Its development is closely tied to the development of networking components of the Linux kernel. As of December 2013 [update] , iproute2 is maintained by Stephen Hemminger and David Ahern. The original author, Alexey Kuznetsov, was responsible for the quality of service (QoS) implementation in the Linux kernel. [ 2 ]
iproute2 collection contains the following command-line utilities : arpd , bridge , ctstat , dcb , devlink , ip , lnstat , nstat , rdma , routef , routel , rtacct , rtmon , rtstat , ss , tc , tipc and vdpa . [ 3 ] tc is used for traffic control . iproute2 utilities communicate with the Linux kernel using the netlink protocol. Some of the iproute2 utilities are often recommended over now-obsolete net-tools utilities that provide the same functionality. [ 4 ] [ 5 ] Below is a table of obsolete utilities and their iproute2 replacements. | https://en.wikipedia.org/wiki/Iproute2 |
Ipse dixit ( Latin for "he said it himself") is an assertion without proof, or a dogmatic expression of opinion. [ 1 ] [ 2 ]
The fallacy of defending a proposition by baldly asserting that it is "just how it is" distorts the argument by opting out of it entirely: the claimant declares an issue to be intrinsic and immutable. [ 3 ]
The Latin form of the expression comes from the Roman orator and philosopher Marcus Tullius Cicero (106–43 BC) in his theological studies De Natura Deorum ( On the Nature of the Gods ) and is his translation of the Greek expression (with the identical meaning) autòs épha ( αὐτὸς ἔφα ), an argument from authority made by the disciples of Pythagoras when appealing to the pronouncements of the master rather than to reason or evidence. [ 4 ]
Before the early 17th century, scholars applied the ipse dixit term to justify their subject-matter arguments if the arguments previously had been used by the ancient Greek philosopher Aristotle (384–322 BC). [ 5 ]
In the late 18th century, Jeremy Bentham adapted the term ipse dixit into the word ipse-dixitism. [ 6 ] Bentham coined the term to apply to all non- utilitarian political arguments. [ 7 ]
In modern legal and administrative decisions, the term ipse dixit has generally been used as a criticism of arguments based solely upon the authority of an individual or organization. For example, in National Tire Dealers & Retreaders Association, Inc. v. Brinegar, 491 F.2d 31, 40 (D.C. Cir. 1974), Circuit Judge Wilkey considered that the Secretary of Transportation's "statement of the reasons for his conclusion that the requirements are practicable is not so inherently plausible that the court can accept it on the agency's mere ipse dixit. " [ 8 ]
In 1997, the Supreme Court of the United States recognized the problem of "opinion evidence which is connected to existing data only by the ipse dixit of an expert." [ 9 ] Likewise, the Supreme Court of Texas has held "a claim will not stand or fall on the mere ipse dixit of a credentialed witness." [ 10 ] "[W]hen you come across an argument that you recall the majority took issue with," U.S. Supreme Court Justice Elena Kagan advised readers of her dissent in 2023's Andy Warhol Foundation for the Visual Arts, Inc. v. Goldsmith , "go back to its response and ask yourself about the ratio of reasoning to ipse dixit ." [ 11 ]
In 1858, Abraham Lincoln said in his speech at Freeport, Illinois , at the second joint debate with Stephen A. Douglas : [ 12 ]
I pass one or two points I have because my time will very soon expire, but I must be allowed to say that Judge Douglas recurs again, as he did upon one or two other occasions, to the enormity of Lincoln,—an insignificant individual like Lincoln,— upon his ipse dixit charging a conspiracy upon a large number of members of Congress, the Supreme Court, and two Presidents, to nationalize slavery. I want to say that, in the first place, I have made no charge of any sort upon my ipse dixit . I have only arrayed the evidence tending to prove it, and presented it to the understanding of others, saying what I think it proves, but giving you the means of judging whether it proves it or not. This is precisely what I have done. I have not placed it upon my ipse dixit at all. | https://en.wikipedia.org/wiki/Ipse_dixit |
Ipso facto is a Latin phrase, directly translated as "by the fact itself", [ 1 ] which means that a specific phenomenon is a direct consequence , a resultant effect , of the action in question, instead of being brought about by a previous action. (Contrast this with the expressions "by itself" or " per se " .) It is a term of art used in philosophy , law , and science .
Aside from its technical uses, it occurs frequently in literature, particularly in scholarly addenda: e.g., "Faustus had signed his life away, and was, ipso facto , incapable of repentance" (from Christopher Marlowe , The Tragical History of Dr. Faustus ) or "These prejudices are rooted in the idea that every tramp ipso facto is a blackguard" (from George Orwell , Down and Out in Paris and London ).
Ipso facto denotes the automatic character of the loss of membership in a religious body by someone guilty of a specified action. [ 2 ] Within the canon law of the Catholic Church , the phrase latae sententiae is more commonly used than ipso facto with regard to ecclesiastical penalties such as excommunication . It indicates that the effect follows even if no verdict (in Latin, sententia ) is pronounced by an ecclesiastical superior or tribunal.
[ 1 ] [ 2 ] [ 3 ] [ 4 ] | https://en.wikipedia.org/wiki/Ipso_facto |
Ipso jure is a Latin phrase, directly translated as "by the law itself". It is used as an adverb . [ 1 ]
The phrase is used to describe legal consequences that occur by the act of the law itself. For example, if property is held in a tenancy by the entirety by a husband and wife, who then get divorced , the property is converted ipso jure (i.e. by the law itself) into another form of tenancy, usually a tenancy in common , at the very instant the marriage is dissolved. Likewise, contracts that establish partnerships sometimes provide that the partnership is ipso jure dissolved if one partner attempts to sell his or her interest in the partnership. In all of these situations, when one legally significant fact occurs, other relationships are automatically changed by the law.
This legal article about a Latin phrase is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ipso_jure |
Iqbal Hussain Qureshi ( Urdu :اقبال حسين قریشی) 27 September 1937 – 8 December 2012) SI , FPAS , [ 1 ] best known as I.H. Qureshi , was a Pakistani nuclear chemist and an Emeritus professor of chemistry at the University of Karachi . [ 2 ] Qureshi was the principal contributor of scientific understanding of various chemical elements: bismuth , cobalt , strontium , thallium , tritium , iron, rubidium , and zinc . : 1–68 [ 3 ] [ 4 ]
His career was mostly spent with the Government of Pakistan after leaving his research work at the national laboratories, and advising the government on nuclear policy issues. He pushed his influential role at the Nuclear Regulatory Authority (PNRA) and the peaceful applications of nuclear science. [ 2 ] He spent many years as an educator and research scientist at the Institute of Engineering and Applied Sciences in Nilore before taking a professorship at the Karachi University . [ 2 ]
Iqbal Hussain Qureshi was born on 27 September 1937 in Ajmer , Rajasthan in India where he received his early education. [ 2 ] Following the Partition of India in 1947, his family emigrated to Pakistan and settled in Hyderabad , Sindh , where he matriculated from a public high school. [ 2 ] He was a child prodigy , being accepted at the Sindh University in his teenage years to study chemistry. : 88–89 [ 5 ] In 1956, he graduated with a Bachelor of Science (BSc) in chemistry from the Sindh University and was noted in newspapers for his top standing in his class, winning the silver medallion with his degree. : 89 [ 5 ] He continued his studies at the Sindh University, and graduated in 1958 with a Master of Science (MSc) in chemistry with Gold medallion. : 88 [ 5 ] [ 2 ]
After earning a scholarship from the Pakistan Atomic Energy Commission (PAEC) in 1960, Qureshi went to the United States to attend the University of Michigan and graduated in 1962 with an MSc in nuclear chemistry . : 97 [ 6 ] He went to Japan for his doctoral studies, attending the University of Tokyo where in 1963 he defended his thesis, "Radiochemical separations by Amalgam exchange" , which contained fundamental work on chemical amalgam applications in radiochemistry . [ 7 ] In 1994, his biography was written and published by the University of Michigan in American Men & Women of Science: A Biographical Directory of Today's Leaders in Physical, Biological, and Related Sciences journal. : 12 [ 8 ]
In 1967, Qureshi returned to the United States and briefly worked for the US National Bureau of Standards as a postdoctoral researcher before leaving for Denmark in 1969. : 210 [ 9 ] : 96 [ 2 ] In Denmark, he received training in the areas of uranium and plutonium isotope separation , which was vital when he returned to Pakistan in 1971 with his expertise and knowledge. [ 2 ]
In 1960, Qureshi found employment with the Pakistan Atomic Energy Commission (PAEC), and was posted to the Atomic Energy Center in Lahore where his interest built in radiochemistry . : 96 [ 10 ] Upon returning to Pakistan from Denmark in 1971, he joined the Institute of Nuclear Science and Technology (the national lab) in Nilore , working at the Nuclear Chemistry Division (NCD). : 96 [ 10 ]
As early as 1972, Qureshi joined the team of scientists that began working on the equation of state of the radioactive decay element plutonium , while he established the computerized radiation detection chemical analysis laboratories at the Pakistan Institute of Nuclear Science and Technology in 1973. : 96 [ 10 ] In 1974, Qureshi and his team was instrumental at the national laboratory when he was the first to confirm the detection of radiation emissions coming from Rajasthan in India. Hence, by using neutron activation analysis , confirming Pokhran-I the first Indian nuclear test , which India later announced was indeed conducted at the Pokhran Test Range. : 96 [ 10 ] Notably, he led the team that balanced the chemical equation required for the exothermic chemical reaction in fission devices . : 57–58 [ 11 ] By 1977, he discovered the technique for balancing the nuclear Q-value and energy balance in a boosted fission weapon . [ 12 ] [ 13 ]
Eventually, Qureshi headed the Nuclear Chemistry Division (NCD) at the Institute of Nuclear Science and Technology which was responsible for the multi-stage chemical process that separated, concentrated and isolated plutonium from uranium. [ 13 ] At NCD, he also played a supervisory role in developing the Analytical Chemistry Group comprising modern and state of the art analytical chemistry laboratories such as the Analytical Chemistry Laboratory, Atomic Absorption Spectroscopy lab, Emission Spectrography lab, Chromatography lab, Electrochemical Analysis lab and radioisotope production labs. : 96 [ 10 ] The Analytical Chemistry Laboratory was later certified by the International Atomic Energy Agency (IAEA), and oversaw the successful commissioning of the PARR-III reactor that went 'phase critical' [ clarification needed ] in 1973. : 96 [ 10 ]
Qureshi engaged in research about copper-nickel alloys after introducing the lattice dynamical method to evaluate the Cu 29 / Ni 28 alloys. [ 14 ] Key and fundamental research on understanding neutron flux was carried out by Qureshi, for which he managed to secure patents from the IAEA. [ 14 ] After the conclusion of the Pakistan's clandestine atomic bomb projects , he was appointed chief technical officer at the Pakistan Atomic Energy Commission (PAEC) in 1991; though he was more eager to return to academia. [ 2 ]
Throughout his time at PAEC, Qureshi earned several scientific honors, including the Gold Medal and a Fellowship of the Pakistan Academy of Sciences in 1994. He was a recipient of the Sitara-i-Imtiaz (Star of Excellence) from the Government of Pakistan in 1992. [ 2 ] In 1997, from the Iranian Government, he received the Khwarizmi International Award for advancing and understanding the "Nuclear analytical techniques development and application in Pakistan". [ 15 ]
In 1996, Qureshi retired from PAEC as Chief Scientific Officer and was made scientist emeritus , which allowed him to continue research at PINSTECH before moving to Karachi. [ 2 ] He took up the professorship of chemistry at the Karachi University and headed the nuclear chemistry section at the H.E.J. Research Institute of Chemistry . During this time, he authored several articles and published books on nuclear chemistry. He retained his position till 2001 when he joined the Pakistan Nuclear Regulatory Authority (PNRA). [ 16 ]
At PNRA, Qureshi served as the chief scientific officer and adviser to the government on nuclear policy issues. [ 17 ] His contribution and policy efforts led to the physical security of the commercial nuclear power infrastructure in the country and helped launched the nuclear awareness campaign following the Fukushima nuclear disaster in 2011. [ 18 ] He served until 2009 when he decided to accept the professorship of chemistry at the Institute of Engineering and Applied Sciences . In December 2012 Qureshi had a sudden breathing problem and died. He is buried in Karachi , Sindh. [ 2 ]
In Pakistan's academia and nuclear society , Qureshi was well known for his interests in classical music theory and love of playing the guitar and sitar , which he played on several occasions. [ 2 ] He also had an interest in American poetry , which he often quoted among his peers while working on the bomb program, and played tennis avidly during his later life. [ 2 ] He was married twice; his first wife died in the 1980s and he later remarried. [ 2 ] He had two sons, one a neurosurgeon while the other is a computer scientist . [ 2 ] | https://en.wikipedia.org/wiki/Iqbal_Hussain_Qureshi |
Iridium tetrabromide is a binary inorganic chemical compound of iridium and bromine with the chemical formula IrBr 4 . [ 1 ] [ 2 ] [ 3 ] This is a salt of iridium metal and hydrobromic acid .
Synthesis of iridium tetrabromide can be by solution of iridium(IV) oxide in hydrobromic acid :
Iridium tetrabromide compound forms black crystals, soluble in water and alcohol. [ 4 ] [ 5 ]
Iridium tetrabromide reacts with water:
Iridium tetrabromide decomposes when heated:
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/IrBr4 |
316.60 g/mol (hydrate)
Iridium(III) chloride is the inorganic compound with the formula IrCl 3 . The anhydrous compound is relatively rare, but the related hydrate is much more commonly encountered. The anhydrous salt has two polymorphs , α and β, which are brown and red colored respectively. More commonly encountered is the hygroscopic dark green trihydrate IrCl 3 (H 2 O) 3 which is a common starting point for iridium chemistry. [ 4 ]
Iridium is separated from the other platinum group metals as crystalline ammonium hexachloroiridate , (NH 4 ) 2 [IrCl 6 ], which can be reduced to iridium metal in a stream of hydrogen . The spongy Ir thus produced reacts with chlorine at 650 °C to give iridium(III) chloride. [ 5 ]
Hydrated iridium trichloride is obtained by heating hydrated iridium(III) oxide with hydrochloric acid . [ 6 ]
Like the related rhodium compound, IrCl 3 adopts the structure seen for aluminium chloride . [ 6 ] This is the monoclinic α polymorph . [ 7 ] A rhombohedral β polymorph also exists. Both polymorphs have effectively the same anion lattice but differ in the octahedral interstices the iridium ions occupy. [ 8 ] The α polymorph converts to the β polymorph when heated to around 650 °C. [ 4 ]
The structure of the trihydrate has not been elucidated yet.
Industrially, most iridium complexes are generated from ammonium hexachloroiridate or the related chloroiridic acid (H 2 IrCl 6 ). The Cativa process , source of most of the world's acetic acid relies on such catalysts.
Hydrated iridium(III) chloride is used in the for the preparation of other iridium complexes such as Vaska's complex , trans -[IrCl(CO)(PPh 3 ) 2 ]. [ 9 ] With the presence of the chloride anion, it forms hexachloroiridate(III) , and produces hexachloroiridate(IV) in aqua regia . The trihydrate react with ammonia to form ammine complexes , such as pentaamminechloroiridium(III) chloride, formulated [IrCl(NH 3 ) 5 ]Cl 2 . It also reacts with concentrated ammonium hydroxide at 150 °C to form the fully ammoniated complex, [Ir(NH 3 ) 6 ]Cl 3 . The hydrate can also form complexes upon reaction with bipyridine , acetonitrile , and pyridine . [ 4 ]
Alkene complexes such as cyclooctadiene iridium chloride dimer [ 10 ] [ 11 ] and chlorobis(cyclooctene)iridium dimer [ 11 ] [ 10 ] can also be prepared by heating the hydrate with the appropriate alkene in water/alcohol mixtures.
The trihydrate decomposes to the anhydrous form at 200 °C, which then oxidizes in air at 763 °C to iridium(IV) oxide , which then decomposes to iridium metal at 1070 °C. However, under hydrogen , it is directly reduced at 190 °C to iridium metal: [ 2 ] [ 12 ] [ 13 ]
Iridium(III) chloride is not listed under Annex I of Directive 67/548/EEC , but is listed in the inventory of the Toxic Substances Control Act (TSCA). It is also known as a mild skin and eye-irritating agent. [ 14 ] | https://en.wikipedia.org/wiki/IrCl3 |
Iridium(IV) fluoride is a chemical compound of iridium and fluorine , with the chemical formula IrF 4 and is a dark brown solid. [ 1 ] Early reports of IrF 4 prior to 1965 are questionable and appear to describe the compound IrF 5 . [ 1 ] The solid can be prepared by reduction of IrF 5 with iridium black [ 1 ] or reduction with H 2 in aqueous HF. [ 2 ] The crystal structure of the solid is notable as it was the first example of a three-dimensional lattice structure found for a metal tetrafluoride and subsequently
RhF 4 , PdF 4 and PtF 4 have been found to have the same structure. [ 3 ] The structure has 6 coordinate, octahedral, iridium where two edges of the octahedra are shared and the two unshared fluorine atoms are cis to one another. [ 3 ] | https://en.wikipedia.org/wiki/IrF4 |
Iridium(V) fluoride , IrF 5 , is a chemical compound of iridium and fluorine . A highly reactive yellow low melting solid, it has a tetrameric structure, Ir 4 F 20 , which contains octahedrally coordinated iridium atoms. [ 1 ] This structure is shared with RuF 5 and OsF 5 . It can be prepared by the controlled decomposition of IrF 6 [ 1 ] or the reduction of IrF 6 with silicon powder or H 2 in anhydrous HF . [ 2 ] [ 3 ] | https://en.wikipedia.org/wiki/IrF5 |
Iridium hexafluoride , also iridium(VI) fluoride , (IrF 6 ) is a compound of iridium and fluorine and one of the seventeen known binary hexafluorides . It is one of only a few compounds with iridium in the oxidation state +6.
Iridium hexafluoride is made by a direct reaction of iridium metal in an excess of elemental fluorine gas at 300 °C. However, it is thermally unstable and must be frozen out of the gaseous reaction mixture to avoid dissociation.
Iridium hexafluoride is a yellow crystalline solid that melts at 44 °C and boils at 53.6 °C. [ 1 ] The solid structure measured at −140 °C is orthorhombic space group Pnma . Lattice parameters are a = 9.411 Å , b = 8.547 Å, and c = 4.952 Å. There are four formula units (in this case, discrete molecules) per unit cell , giving a density of 5.11 g·cm −3 . [ 2 ]
The IrF 6 molecule itself (the form important for the liquid or gas phase) has octahedral molecular geometry , which has point group ( O h ). The Ir–F bond length is 1.833 Å. [ 2 ]
Calculations suggest that fluorine might react with iridium hexafluoride at 39 GPa to form IrF 8 . [ 3 ] | https://en.wikipedia.org/wiki/IrF6 |
Iridium trihydride ( IrH 3 ) is a chemical compound of iridium and hydrogen that can be formed under high pressure. The crystalline form has a distorted simple cubic structure. The hydrogen atoms are on the centre of the faces of the crystal cell cube, and Iridium is at the centre. It forms at over 55 GPa . [ 1 ]
The bulk modulus of iridium trihydride is 190 GPa which is much less than that of iridium (383 GPa).
Decomposition of iridium trihydride is slow when the pressure is reduced to 6 GPa, and perhaps it can be metastable at atmospheric pressures.
A dihydride, IrH 2 , is predicted to be stable over 14 GPa. [ 2 ] | https://en.wikipedia.org/wiki/IrH3 |
Iridium(IV) oxide , IrO 2 , is the only well-characterised oxide of iridium. It is a blue-black solid. The compound adopts the TiO 2 rutile structure , featuring six coordinate iridium and three coordinate oxygen. [ 1 ]
It is used with other rare oxides in the coating of anode-electrodes for industrial electrolysis and in microelectrodes for electrophysiology research. [ 2 ]
As described by its discoverers, it can be formed by treating the green form of iridium trichloride with oxygen at high temperatures:
A hydrated form is also known. [ 3 ]
Iridium dioxide can be used as an anode electrode for industrial electrolysis and as a microelectrode for electrophysiological studies. [ 4 ]
Iridium dioxide can be used to make coated electrodes. [ 5 ]
Oxide materials are typically hard and brittle, which means it can fracture under stress without significant prior deformation. [ 6 ] Iridium oxide is also a stiff material and does not easily deform under stress. [ 7 ] Since iridium oxide’s applications focus on electrode coating and catalytic materials for electrolysis, the discussion of mechanical properties is related to these applications.
Young’s modulus is a material property that measures the stiffness of the material. By experimentally measuring Young’s modulus, people could understand how much a material will deform under a specific load, which is essential in designing structures and preventing deformations. [ 8 ] For iridium oxide films, the young’s modulus data is crucial for accurate modeling and design of electromechanical devices where the mechanical properties of the electrode material significantly affect device performance.
Therefore, researchers used the cantilever bending method to determine Young’s modulus of iridium oxide thin film. [ 7 ] First, iridium oxide was deposited onto a silicon wafer and fabricated to cantilever beams. Using an atomic force microscope (AFM), a fine tip is aligned to the free end of the beam and a tiny force is applied. The force exerted and the resulting deflection were precisely measured to calculate the stiffness and then the Young’s modulus of iridium oxide. The experimental measurement of the young’s modulus of Iridium oxide thin film is reported to be 300 ± 15 GPa. [ 7 ] Compared to metal Iridium, which has a young’s modulus of 517 GPa, [ 9 ] the oxidation of iridium lower the stiffness of the material.
Fracture and delamination are well-known problems when fabricating devices that incorporate iridium oxide film. The delamination is typically due to stresses that develop between the IrO 2 layer and its substrate during manufacturing processes.
One potential cause of delamination is lattice mismatch between iridium oxide and the substrate material. Iridium oxide has a tetragonal lattice with lattice parameters of 4.5Å and 3.15Å. [ 10 ] In contrast, popular substrates like gold and platinum have lattice constants of approximately 4.08 Å and 3.92 Å, respectively. [ 11 ] The difference in lattice parameter can lead to strain at the interface between the iridium oxide layer and the substrate, resulting in fracture and delamination of the iridium film. Iridium oxide sputtered on liquid crystal polymer could be a potential way to avoid delamination. [ 12 ]
Another cause of delamination is the incorporation of high temperature processes during fabrication, such as annealing . Annealing involves heating iridium oxide to a high temperature but under melting point (around 750-900 °C) and then cooling it, relieving internal stresses and improving the iridium oxide’s crystallinity and mechanical properties. [ 13 ] However, if the lattice parameter of the iridium oxide layer changes significantly compared to the substrate following annealing, it can result in a greater lattice mismatch, which increases the surface tension and assist the formation of long cracks (similar to mechanically stressed cracks reported by Mailley et al. [ 14 ] ). The cracks create a breakpoint where the surface strain is relieved, leading to delamination and other types of mechanical failure.
Even if the iridium oxide film remains intact under equilibrium conditions, it may still delaminate during operation. Cogan et al. reported that sputtered iridium oxide films could delaminate after several cyclic voltammetry cycles, which suggests that the film could delaminate under operational loads. [ 15 ] The team then limits the maximum potential bias to 0.9V and no visible delamination occurs. | https://en.wikipedia.org/wiki/IrO2 |
Iridium tetroxide (IrO 4 , Iridium(VIII) oxide ) is a binary compound of oxygen and iridium in oxidation state +8. [ 1 ] This compound was formed by photochemical rearrangement of [( η 1 -O 2 )IrO 2 ] in solid argon at a temperature of 6 K (−267.15 °C; −448.87 °F). At higher temperatures, the oxide is unstable. [ 2 ] The detection of the iridium tetroxide cation IrO + 4 by infrared photodissociation spectroscopy with formal oxidation state +9 has been reported, the highest currently known of any element. [ 3 ] [ 4 ] However no salts are known, as attempted production of an Ir(IX) salt such as IrO 4 SbF 6 did not result in anything. | https://en.wikipedia.org/wiki/IrO4 |
Iridium disulfide is the binary inorganic compound with the formula IrS 2 . Prepared by the direct reaction of the elements, the compound adopts the pyrite crystal structure at high pressure. [ 1 ] At normal atmospheric pressures, an orthorhombic polymorph is observed. [ 2 ] . The high- and low-pressure forms both feature octahedral Ir centers, but the S–S distances are pressure dependent. [ 3 ] Although not practical, IrS 2 is a highly active catalyst for hydrodesulfurization . [ 4 ] | https://en.wikipedia.org/wiki/IrS2 |
Ira N. Levine (February 12, 1937 – December 17, 2015) was an American author, scientist, professor and faculty member in the chemistry department at Brooklyn College . He widely acknowledged for his research in the field of microwave spectroscopy , and for several widely known textbooks in physical chemistry and quantum chemistry .
Levine was born in Brooklyn , New York. He was graduated from Erasmus Hall High School . In 1952, Levine was graduated with an honorary degree in chemistry and named as top scholastic honorary graduate in the College of Engineering and Science at Carnegie Mellon College of Engineering . [ 3 ] In 1959, he went on to graduate school in the field of physical chemistry and mathematical physics at Harvard University. [ 4 ] In 1963, he was awarded a PhD in chemistry under the guidance of Professor E. Bright Wilson by Harvard University . [ 2 ] [ 5 ] [ 1 ] He started his academic career at Brooklyn College in 1964 where he taught first-year courses in general chemistry as well as advanced courses in physical and quantum chemistry. He became a full-time professor in 1978. Levine is recognized for several textbooks he authored and for his research in physical chemistry, quantum chemistry and microwave spectroscopy. Levine textbooks include Quantum Chemistry (7th ed.), [ 6 ] Physical Chemistry (6th ed.), [ 7 ] Solutions Manual to Physical Chemistry (5th ed.), [ 8 ] and a textbook on Molecular Spectroscopy. [ 9 ] His textbooks have been translated into many languages, including Arabic, Chinese, Czech, Hungarian, Polish, and Spanish, and they have been used by many Chemistry departments in the US and elsewhere. He died on December 17, 2015. [ 10 ] [ 11 ] [ 12 ]
This biographical article about an American chemist is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Ira_N._Levine |
The Iranian Parliament Committee on Energy ( Persian : کمیسیون انرژی مجلس شورای اسلامی ), or Energy Committee is a standing committee of the Islamic Consultative Assembly of Representatives. The Parliament Committee on Energy has general Oil, gas, electricity, water and electric dams and power plants, nuclear power and renewable energy and it can recommend funding appropriations for various governmental agencies, programs, and activities, as defined by House rules. in the 11th parliament ; Fereidon Hasanvand was president, Qasem Saedi first deputy and Ahmad Moradi second deputy.
"Committee on Energy" . Majlis Research Center . Retrieved 5 June 2016 . | https://en.wikipedia.org/wiki/Iranian_Parliament_Commission_on_Energy |
Iranian Society of Mechanical Engineers (ISME) is an organization founded in 1991 by some Iranian Mechanical engineers and professors (among them: Dr. Mahdi Bahadori Nezhad , Mr. Mohammad Bagherian ) to develop and enhance Mechanical Engineering in Iranian universities and industries. It is now responsible for annual mechanical engineering conference in Iran which is held in spring.
Other activities include: Publishing technical journal and contributing with ASME . [ 1 ]
Board of Managers since 21 March 2011: | https://en.wikipedia.org/wiki/Iranian_Society_of_Mechanical_Engineers |
Saddam Hussein (1937–2006) began an extensive biological weapons (BW) program in Iraq in the early 1980s, despite having signed (but not ratified until 1991) the Biological Weapons Convention (BWC) of 1972. Details of the BW program and a chemical weapons program surfaced after the Gulf War (1990–91) during the disarmament of Iraq under the United Nations Special Commission (UNSCOM). By the end of the war, program scientists had investigated the BW potential of five bacterial strains, one fungal strain, five types of virus, and four toxins . [ 1 ] Of these, three— anthrax , botulinum and aflatoxin —had proceeded to weaponization for deployment. [ 2 ] Because of the UN disarmament program that followed the war, more is known today about the once-secret bioweapons program in Iraq than that of any other nation.
The program no longer existed when the George W. Bush administration cited it as justification for its 2003 invasion of Iraq and the subsequent Iraq War .
In the early 1980s, five German firms supplied equipment to manufacture botulin toxin and mycotoxin to Iraq. Iraq's State Establishment for Pesticide Production (SEPP) also ordered culture media and incubators from Germany's Water Engineering Trading . [ 3 ] Strains of dual-use biological material from France also helped advance Iraq's biological warfare program. [ 4 ] From the United States, the non-profit American Type Culture Collection and the U.S. Centers for Disease Control sold or sent biological samples to Iraq up until 1989, which Iraq claimed to need for medical research. These materials included anthrax , West Nile virus and botulism , as well as Brucella melitensis , and Clostridium perfringens . Some of these materials were used for Iraq's biological weapons research program, while others were used for vaccine development. [ 5 ] In delivering these materials "The CDC was abiding by World Health Organization guidelines that encouraged the free exchange of biological samples among medical researchers..." according to Thomas Monath, CDC lab director. It was a request "which we were obligated to fulfill," as described in WHO and UN treaties. [ 6 ]
Iraq's BW facilities included its main biowarfare research center at Salman Pak (just south of Baghdad ), the main bioweapons production facility at Al Hakum (the "Single-Cell Protein Production Plant") and the viral biowarfare research site at Al Manal (the "Foot and Mouth Disease Center"). [ 7 ]
The Al Hakum facility began mass production of weapons-grade anthrax in 1989, eventually producing 8,000 liters or more (the 8,000 liter figure is based on declared amounts). Iraq officially acknowledged that it had worked with several species of bacterial pathogen, including Bacillus anthracis , Clostridium botulinum and Clostridium perfringens ( gas gangrene ) and several viruses (including enterovirus 17 [human conjunctivitis ], rotavirus and camelpox ). The program also purified biological toxins, such as botulinum toxin , ricin and aflatoxin . [ 8 ] After 1995, it was learned that, in all, Iraq had produced 19,000 liters of concentrated botulinum toxin (nearly 10,000 liters filled into munitions), 8,500 liters of concentrated anthrax (6,500 liters filled into munitions) and 2,200 liters of aflatoxin (1,580 liters filled into munitions). [ 9 ] In total, the program grew a half million liters of biological agents. [ 10 ]
During UN inspections in 1998, it emerged that Hussein had prisoners tied to stakes and bombarded with anthrax and chemical weapons for experimental purposes. These experiments began in the 1980s during the Iran–Iraq War after initial experiments on sheep and camels. Dozens of prisoners are believed to have died in agony during the program. According to an article in the London Sunday Times :
In one incident, Iranian prisoners of war are said to have been tied up and killed by bacteria from a shell detonated nearby. Others were exposed to an aerosol of anthrax sprayed into a chamber while doctors watched behind a glass screen. Two British-trained scientists have been identified as leading figures in the programme. … According to Israeli military intelligence sources, 10 Iranian prisoners of war were taken to a location near Iraq's border with Saudi Arabia . They were lashed to posts and left helpless as an anthrax bomb was exploded by remote control 15 yards away. All died painfully from internal haemorrhaging. In another experiment, 15 Kurdish prisoners were tied up in a field while shells containing camel pox , a mild virus, were dropped from a light aircraft. The results were slower but the test was judged a success; the prisoners fell ill within a week. Iraqi sources say some of the cruellest research has been conducted at an underground facility near Salman Pak , southwest of Baghdad . Here, the sources say, experiments with biological and chemical agents were carried out first on dogs and cats, then on Iranian prisoners. The prisoners were secured to a bed in a purpose-built chamber, into which lethal agents, including anthrax, were sprayed from a high-velocity device mounted in the ceiling. Medical researchers viewed the results through fortified glass. Details of the experiments were known only to Saddam and an inner circle of senior government officials and Iraqi scientists educated in the West. … The facility, which is understood to have been built by German engineers in the 1980s, has been at the centre of Iraq's experiments on "human guinea pigs" for more than 10 years, according to Israeli military sources. [ 11 ]
Iraqi scientist Nassir al-Hindawi was described by United Nations inspectors as the "father of Iraq's biological weapons program". Two of the leading researchers in the program studied in Britain. Rihab al-Taha ("Dr. Germ"), educated at the University of East Anglia , was head of Iraq's military research and development institute. Another scientist received a doctorate in molecular biology from the University of Edinburgh . [ 12 ] U.S. officials alleged that a third scientist — Huda Salih Mahdi Ammash ("Mrs. Anthrax", "Chemical Sally"), who was trained at the University of Missouri — helped to rebuild Iraq's BW program in the mid-1990s after the Gulf War. Both al-Taha and Ammash were captured by U.S. forces after the 2003 invasion of Iraq, but both were released in 2005 after they were among those an American-Iraqi board found to be no longer security threats. They had no charges filed against them. [ 13 ]
During the Gulf War, US and other intelligence reports had suggested that Iraq was operating a BW program. Coalition troops trained with protective gear and stockpiled the antibiotic ciprofloxacin for use as post-exposure prophylaxis against anthrax . Approximately 150,000 US troops received the U.S. Food and Drug Administration –licensed anthrax vaccine ( BioThrax ), and 8,000 received a botulinum toxoid vaccine also approved by the FDA as an investigational new drug . Although Iraq had loaded anthrax, botulinum, and aflatoxin bio-agent into missiles and artillery shells in preparing for the war, and although these munitions were deployed to four locations in Iraq, [ 14 ] they were never used.
In August 1991, the UN carried out its first inspection of Iraq's BW capabilities in the aftermath of the Gulf War. On 2 August 1991, representatives of the Iraqi government announced to leaders of UNSCOM's "Team 7" that they had conducted research into the offensive use of B. anthracis , botulinum toxins, and Clostridium perfringens toxins. [ 15 ] Post-war inspections by UNSCOM, however, were confounded by misinformation and obfuscation. After Iraqi General Hussein Kamel al-Majid defected to Jordan in August 1995, the Iraqi government further disclosed that it had operated a robust BW program at six major sites since the 1980s. It was revealed that the Iraqi program conducted basic research on B. anthracis , rotavirus , camelpox virus , aflatoxin , botulinum toxins , mycotoxins , and an anticrop agent ( wheat cover smut ). It tested several delivery systems including aerial spray tanks and drone aircraft . The Iraqi government had weaponized 6,000 liters of B. anthracis spores and 12,000 liters of botulinum toxin in aerial bombs, rockets, and missile warheads before the outbreak of war in 1991. [ 16 ] These bio-weapons were deployed but never used. [ 17 ] [ 18 ]
After Kamel's defection, it became known that in December 1990 the Iraqis had filled 100 R-400 bombs with botulinum toxin, 50 with anthrax, and 16 with aflatoxin. In addition, 13 Al Hussein (SCUD) warheads were filled with botulinum toxin, 10 with anthrax, and 2 with aflatoxin. These weapons were deployed in January 1991 to four locations for use against Coalition forces. [ 19 ]
Why Saddam Hussein did not use these biological weapons in 1991 is unclear, but the presumption has been that he was concerned about provoking massive retaliation. Other plausible factors include the perceived ineffectiveness of the untested delivery and dispersal systems, the probable ineffectiveness of liquid slurries resulting from poor aerosolization, and the potential hazards to the Iraqi troops themselves, as they lacked the protective equipment and training available to Coalition forces. [ 20 ] [ 21 ]
Several defectors (see Khidir Hamza ) have claimed that these weapons were intended only as "weapons of last resort" in case the Coalition stormed the gates of Baghdad . Since this never happened, Saddam found their use unnecessary.
The Iraqis claimed to have destroyed their biological arsenal immediately after the 1991 war, but they did not provide confirmatory evidence. A covert military research and development program continued for another four years, with the intent of resuming agent production and weapons manufacture after the end of UN sanctions. [ 22 ] Basic infrastructure was preserved, and research on producing dried agent was conducted under the guise of biopesticide production at Al Hakum until its destruction by UNSCOM inspectors in 1996. [ 23 ] The same year, operational portions of the facilities at Salman Pak and Al Manal were also supposedly destroyed, either by the Iraqis themselves or under direct UNSCOM supervision. But UNSCOM inspectors never received full cooperation from the Hussein regime and they were finally expelled from Iraq in 1998. International concerns led to renewed inspections in 2002 under UN Security Council Resolution 1441 and these facilities were again targets for the U.S. military during the 2003 invasion of Iraq as potentially still being operational. President Bush cited the non-cooperation with inspectors as a major justification for military action .
The extent of Iraq's BW program between 1998 when UNSCOM left Iraq and the U.S. Coalition invasion in March 2003 remains unknown. Current information indicates the discovery of a clandestine network of biological laboratories operated by the Iraqi Intelligence Service ( Mukhabarat ), a prison laboratory complex possibly used for human experimentation, an Iraqi scientist's private culture collection with a strain of possible BW interest, and new research activities involving Brucella and Crimean-Congo hemorrhagic fever virus. [ 24 ] Despite diligent investigations since 2003, evidence for the existence of additional BW stockpiles in Iraq has not been documented. [ citation needed ]
In 2005, the Iraq Survey Group — an international group composed of civilian and military experts — concluded that the Iraqi military BW program had been abandoned during 1995 and 1996 because of fear that discovery of continued activity would result in severe political repercussions including the extension of UN sanctions. However, they concluded, Hussein had perpetuated ambiguity regarding a possible program as a strategic deterrent against Iran . [ 25 ] Other conclusions were that the Mukhabarat continued to investigate toxins as tools of assassination, concealed its program from UNSCOM inspectors after the 1991 war, and reportedly conducted lethal human experimentation until 1994. Small-scale covert laboratories were maintained until 2003. [ 26 ] | https://en.wikipedia.org/wiki/Iraqi_biological_weapons_program |
During the Iran–Iraq War (1980–1988), Iraq engaged in chemical warfare against Iran on multiple occasions, including more than 30 targeted attacks on Iranian civilians. Iran employed its own chemical warfare against Iraq on a few occasions during the war as well. [ 1 ] The Iraqi chemical weapons program , which had been active since the 1970s, was aimed at regulated offensive use, as evidenced in the chemical attacks against Iraqi Kurds as part of the Anfal campaign in the late 1980s. The Iraqis had also utilized chemical weapons against Iranian hospitals and medical centres. [ 2 ] According to a 2002 article in the American newspaper The Star-Ledger , 20,000 Iranian soldiers and combat medics were killed on the spot by nerve gas . As of 2002, 5,000 of the 80,000 survivors continue to seek regular medical treatment, while 1,000 are hospital inpatients. [ 3 ] [ 4 ] Though the use of chemical weapons in international armed conflict was banned under the Geneva Protocol , much of the international community remained indifferent to the attacks; Iraq's military campaign in Iran was supported by the United States and the Soviet Union , both of whom had sought to contain Iranian influence after the Islamic Revolution of 1979. [ 5 ]
After the 1973 Arab–Israeli War , Iraq decided to improve all aspects of its army . Iraqi General Ra'ad al-Hamdani stated that, in spite of careful analysis of the 1973 Arab–Israeli War, no clear progress in the Iraqi army was achieved by the Ba'ath Party . In comparison to their Israeli counterparts, the Iraqi Army was faced with a significant deficit in technological expertise. In 1979, due to Saddam Hussein 's policies as well as those of leading Ba'ath Party officials and senior military officers, the Iraqi Army underwent increasing politicization. There was a saying at the time, "better a good Ba'athist than a good soldier". During the early months of the Iran–Iraq War , Iraq attained successes because of Ba'ath Party interference and its attempts to improve the Iraqi Army, but the essential problem was that the military leaders did not have a clear strategy or operational aim for a war. [ 6 ]
Reporter Michael Dobbs of the Washington Post stated that Reagan's administration was well aware that the materials sold to Iraq would be used to manufacture chemical weapons for use in the war against Iran. He stated that Iraq's use of chemical weapons was "hardly a secret, with the Iraqi military issuing this warning in February 1984: 'The invaders should know that for every harmful insect, there is an insecticide capable of annihilating it ... and Iraq possesses this annihilation insecticide.'" According to Reagan's foreign policy , every attempt to save Iraq was necessary and legal. [ 5 ]
According to Iraqi documents, assistance in the development of chemical weapons was obtained from firms in many countries, including the United States, West Germany , the Netherlands , the United Kingdom , and France . A report stated that Dutch , Australian , Italian , French and both West and East German companies were involved in the export of raw materials to Iraqi chemical weapons factories. [ 7 ]
Chemical weapons were employed by Iraqi forces against Iranian combatants and non-combatants during the Iran–Iraq war (1980–1988). These have been classified based on chemical composition and casualty-producing effects. The best-known substances used by the Iraqi army were organophosphate neurotoxins , known as nerve agents Tabun , Sarin , and mustard gas . According to Iraqi reports, in 1981 vomiting agents were used in initial and small-scale attacks. In August 1983, chemical weapons had been employed on the Piranshahr and Haji Omaran battlefields. Next, they were used on the Panjwin battlefield, in November 1983. The Iraqi army began extensive chemical attacks in 1984, by using tons of sulfur mustard and nerve agents on the Majnoon Islands. [ 2 ]
In 1986, the Iranian forces mounted an attack on the Faw Peninsula southeast of Basra and occupied the peninsula. This attack had not been anticipated by the Iraqi military, which did not prepare for an assault on the Faw Peninsula from across the Shatt Al-Arab . The integration and cooperation between the Iranian Army and various militias allowed them to organize operations during winter 1985–1986 carefully. As a result, Iraq's oil wells were in danger. Iraqi General Hamdani called the fighting for the liberation of the peninsula another "Battle of the Somme", where both militaries suffered huge losses. The chemical attacks played an important role in Iraq's success. [ 6 ] [ 8 ] The chemical attacks took place until the last day of war, in August 1988. [ 9 ] During the eight-year Iran–Iraq War, more than 350 large-scale gas attacks were reported in the border areas. [ 2 ]
The Iraqi Army employed chemical weapons in attacks against combatants and non-combatants in border cities and villages and more than 30 attacks against Iranian civilians have been reported, as follows: [ 2 ]
There have been chemical attacks by the Iraqi army against medical centers and hospitals. [ 2 ]
In a declassified 1991 report, the CIA estimated that Iran had suffered more than 50,000 casualties from Iraq's use of several chemical weapons, [ 10 ] though current estimates are more than 100,000, as the long-term effects continue to cause damage. [ 11 ] The official CIA estimate did not include the civilian population contaminated in bordering towns or the children and relatives of veterans, many of whom have developed blood, lung and skin complications, according to the Organization for Veterans of Iran. According to a 2002 article in the Star-Ledger , 20,000 Iranian soldiers were killed on the spot by nerve gas. As of 2002, 5,000 of the 80,000 survivors continue to seek regular medical treatment, with 1,000 being hospital inpatients. [ 3 ] [ 4 ]
Because of reports implying the use of chemical weapons by the Iraqi army, a presidential directive was issued by the U.S. [ 5 ] Iran asked the UN to engage in preventing Iraq from using chemical weapon agents, but there were no strong actions by the UN or other international organizations. UN specialist teams were dispatched to Iran at the request of the Iranian Government, in March 1984, April 1985, February–March 1986, April 1987, and in March, July and August 1988. As a result, according to the field inspections, clinical examinations of casualties and laboratory analyses of samples done by the UN fact-finding team's investigations, the use by the Iraqi army of mustard gas and nerve agents against Iranians was confirmed. The Security Council ratified these reports and two statements were issued, on 13 March 1984 and 21 March 1986, condemning Iraq for those chemical attacks, but the Iraqi regime did not abide by those condemnations and continued launching chemical attacks. [ 2 ]
The Iraqi chemical weapons program was curtailed in 1991, and the group found no evidence of its work at a later date. After the invasion, Saddam's son Uday tried to find chemical weapons in Iraq and use them against coalition forces, but he failed to do so. The biological weapons program was curtailed in 1995, as it seemed to Hussein that UN inspectors were about to be able to detect it. The arsenal of biological weapons was destroyed back in 1991 and 1992. Only a few copies remained intact, which were preserved in the hope of the future. The production of nuclear weapons was also shut down in 1991. The authorities destroyed all documents related to this program, except for documentation on several projects, which the scientists saved on their own initiative. Thus, the claims of Blair and Bush about Saddam's existing WMD production programs have now been officially recognized as false. | https://en.wikipedia.org/wiki/Iraqi_chemical_attacks_against_Iran |
The Iraq–Saudi Arabia border is 811 km (504 mi) in length and runs from the tripoint with Jordan in the west to the tripoint with Kuwait in the east. [ 1 ]
The border starts on the west at the tripoint with Jordan, and consists of six straight lines broadly orientated to the south-east, eventually reaching the tripoint with Kuwait on the Wadi al-Batin .
Historically there was no clearly defined boundary in this part of the Arabian peninsula; at the start of the 20th century the Ottoman Empire controlled what is now Iraq, with areas further south consisting of loosely organised Arab groupings, occasionally forming emirates, most prominent of which was the Emirate of Nejd and Hasa ruled by the al-Saud family. [ 2 ] [ 3 ]
During the First World War an Arab Revolt , supported by Britain, succeeded in removing the Ottomans from most of the Middle East. As a result of the secret 1916 Anglo-French Sykes-Picot Agreement Britain gained control of the Ottoman Vilayets of Mosul , Baghdad and Basra , which it organised into the mandate of Iraq in 1920. [ 3 ] In the meantime Ibn Saud had managed to expand his domains considerably, eventually proclaiming the Kingdom of Saudi Arabia in 1932.
In December 1922 Percy Cox , British High Commissioner in Iraq, met with ibn Saud and signed the Uqair Protocol , which finalised Saudi Arabia's borders with both Kuwait and Iraq. [ 3 ] The border thus created differed slightly from the modern frontier, with a Saudi 'kink' in the middle-south section. It also created a Saudi–Iraqi neutral zone , immediately west of Kuwait. This border was confirmed by the Bahra Agreement in November 1925. [ 4 ]
The Saudi-Iraq neutral zone was split in 1975 and a final border treaty signed in 1981, [ 5 ] which also appears to have 'ironed out' the Saudi kink. [ 6 ] [ 7 ] The details of this treaty were not revealed until 1991 when Saudi Arabia deposited the agreements at the United Nations following the Gulf War . [ 8 ] The Gulf War seriously strained relations between the two countries; Iraq fired scud missiles into Saudi territory and also breached the Kuwait–Saudi Arabia border . [ 9 ]
In April 2006, while Iraq was experiencing a high level of sectarian violence , Saudi Arabia began to call for tenders to construct a border barrier in the form of a fence along the border in an attempt to prevent the violence in Iraq spilling over into its territory. [ 10 ] The proposed fence would run for approximately 900 kilometres (560 mi) along Saudi Arabia's isolated northern desert border with Iraq. It was part of a larger package of fence-building to secure all of the Saudi Arabia's 6,500 km (4,039 mi) of border. It would supplement the existing 7-meter-high sand berm that runs along the border, in front of which there is an 8-km stretch of no-mans-land which is regularly swept smooth so that trespassers can be tracked. [ 11 ]
The proposals were not implemented until September 2014, when the Iraqi Civil War had escalated following the rise of the Islamic State of Iraq and the Levant . ISIL's occupation of much of western Iraq had given it a substantial land border with Saudi Arabia to the south, and the barrier is intended to keep ISIL militants from entering Saudi Arabia. [ 12 ] The line consists of a multi-layered fence and ditch barrier wall. The border zone includes five layers of fencing with includes 78 monitoring watch towers, night-vision cameras, and radar cameras, eight command centres, 10 mobile surveillance vehicles, 32 rapid-response centres, and three rapid intervention squads. [ 13 ] [ 14 ] The works were completed with the assistance of Airbus , a European multinational aerospace corporation. [ 15 ] | https://en.wikipedia.org/wiki/Iraq–Saudi_Arabia_border |
The Ireland–Claisen rearrangement is a chemical reaction of an allylic ester with strong base to give an γ,δ-unsaturated carboxylic acid . [ 1 ] [ 2 ] [ 3 ]
Several reviews have been published. [ 4 ] [ 5 ] [ 6 ]
The Ireland–Claisen rearrangement is a type of Claisen rearrangement . The mechanism is therefore a concerted [3,3]-sigmatropic rearrangement which according to the Woodward–Hoffmann rules show a concerted, suprafacial , pericyclic reaction pathway. | https://en.wikipedia.org/wiki/Ireland–Claisen_rearrangement |
Iridium Communications Inc. (formerly Iridium Satellite LLC ) is a publicly traded American company headquartered in McLean, Virginia, United States . Iridium operates the Iridium satellite constellation , a system of 80 satellites: 66 are active satellites and the remaining fourteen function as in-orbit spares. [ 2 ] Iridium Satellites are used for worldwide voice and data communication from handheld satellite phones , satellite messenger communication devices and integrated transceivers, as well as for two-way satellite messaging service from supported conventional mobile phones . [ 3 ] [ 4 ] [ 5 ] The nearly polar orbit and communication between satellites via inter-satellite links provide global service availability.
The Iridium communications service was launched on November 1, 1998, formerly known as Iridium SSC. The first Iridium call was made from Vice President of the United States Al Gore to Gilbert Grosvenor , the great-grandson of Alexander Graham Bell and chairman of the National Geographic Society . [ 6 ] Motorola provided the technology and major financial backing. [ 7 ] The logo of the company represents the Big Dipper . [ 8 ] The company derives its name from the chemical element iridium , which has an atomic number of 77, equaling the initial number of satellites which were calculated to be required for global coverage. [ 9 ] However, due to optimizations of orbit trajectories, technology updates and real-world conditions, only 66 are required for global coverage. A total of 95 satellites were launched in this constellation, with 66 active and the remaining 29 satellites operating as spares. [ 10 ]
On August 13, 1999, nine months after the launch of the organization, the founding company went into Chapter 11 bankruptcy . [ 11 ] The handsets could not operate as promoted until the entire constellation of satellites was in place, requiring a massive initial capital cost of billions of dollars. [ 12 ] The cost of service dissuaded many potential users. Reception indoors was difficult and the handheld devices, when compared to terrestrial cellular mobile phones were bulkier and more expensive, both of which discouraged adoption among potential users. [ 11 ]
Mismanagement is another major factor that was cited in the original program's failure. In 1999, CNN writer David Rohde detailed how he applied for Iridium service and was sent information kits, but was never contacted by a sales representative. He encountered programming problems on Iridium's website, and a "run-around" from the company's representatives. [ 13 ] After Iridium filed bankruptcy, it cited "difficulty gaining subscribers." [ 14 ]
The initial commercial failure of Iridium had a damping effect on other proposed commercial satellite constellation projects, including Teledesic . Other schemes ( Orbcomm , ICO Global Communications , and Globalstar ) followed Iridium into bankruptcy protection, while a number of other proposed schemes were never even constructed. [ 11 ]
In August 2000, Motorola announced that the Iridium satellites would have to be deorbited. [ 15 ] Despite this, they remained in orbit and operational. [ 16 ] [ 17 ] In December 2000, the US government stepped in to save Iridium by providing US$72 million in exchange for a two-year contract. They also approved the fire sale of the company from US bankruptcy court for $25 million [ 15 ] in March 2001. This erased over $4 billion in debt. [ 18 ]
Iridium service was restarted in 2001, by the newly founded Iridium Satellite LLC, which was owned by a group of private investors. [ 12 ]
On February 10, 2009, the Iridium 33 satellite collided with a defunct Russian satellite, named Kosmos 2251 , 800 kilometres (500 mi) over Siberia . [ 19 ] Two large debris clouds were created. [ 20 ]
Iridium replaced its original constellation by sending 75 new Iridium satellites into space on SpaceX Falcon 9 rockets in a series of 8 launches. The campaign also consisted of upgrades to Iridium ground infrastructure. [ 21 ]
The Iridium NEXT launch campaign was announced in 2007. Within three years, Iridium completed financing and began work on launching new satellites. [ 22 ] In June 2010, Iridium announced a fixed-price contract with Thales Alenia Space for the design and construction of the next-generation satellites for the upgraded constellation. [ 23 ] Two weeks later, Iridium announced a $492 million contract designating the Falcon 9 as a major provider of launch services for the Iridium NEXT campaign, becoming the largest single commercial launch deal ever signed (simultaneously representing a benchmark in cost-effective satellite delivery to space). [ 24 ]
On January 14, 2017, 10 years after the campaign was first announced, the first of eight Iridium NEXT launches took place with SpaceX from Vandenberg Air Force Base in California. [ 25 ] Over the next two years, Iridium sent an additional 65 satellites into low Earth orbit to completely replace the original satellite constellation. The final Iridium NEXT launch took place on January 11, 2019, less than two years after the first launch. [ 26 ]
The Iridium NEXT network covers the entire Earth , including poles, oceans and airways, with 66 satellites, with the remaining nine acting as active backups, for a total of 75 launched. [ 3 ] Six remain on the ground as spares for a total of 81 built. [ 27 ] [ 28 ]
Iridium Satellite LLC merged with a special-purpose acquisition company (GHQ) created by the investment bank Greenhill & Co. in September 2009 to create Iridium Communications Inc. The public company trades on NASDAQ under the symbol "IRDM". The company surpassed one million subscribers in March 2018. [ 29 ] Revenue for the full year 2018 was $523.0 million with operational EBITDA of $302.0 million, a 14% increase from $265.6 million in the prior year. [ 30 ]
Iridium manages several operations centers, including Tempe, Arizona and Leesburg, Virginia , United States. [ 31 ] [ 32 ]
The system is being used by the U.S. Department of Defense . [ 33 ] [ better source needed ]
Matt Desch is the current CEO of Iridium LLC. [ 34 ]
Iridium is a founding member of the Hosted Payload Alliance (HPA), a satellite industry alliance program. Membership in the HPA is open to satellite operators, satellite manufacturers, system integrators, and other interested parties. [ 35 ]
In July 2011, the Federal Aviation Administration (FAA) issued a ruling that approves the use of Iridium for Future Air Navigation System (FANS) data links, enabling satellite data links with air-traffic control for aircraft flying in the FANS environment, including areas not served by Inmarsat (above or below 70 degrees latitude) which includes polar routes. [ 36 ]
In January 2020, the Iridium constellation was certified for use in the Global Maritime Distress and Safety System (GMDSS). The certification ended a monopoly on the provision of maritime distress services that had previously been held by Inmarsat since the system became operational in 1999. [ 37 ]
In 2023, Qualcomm and Iridium announced an agreement that was supposed to bring two-way satellite messaging service to Android smartphones. The service, called Snapdragon Satellite, should have been supported starting with devices that feature Snapdragon 8 Gen 2 chipsets, which was expected to be launched in the second half of 2023. The solution for smartphones was supposed to utilize Iridium's L Band spectrum for downlink and uplink. [ 38 ] [ 39 ]
On November 9, 2023, Iridium announced that Qualcomm had notified them about the end of their partnership due to a lack of interest in Qualcomm's and Iridium's proprietary solution by smartphone manufacturers. A Qualcomm spokesman stated "Smartphone makers have indicated a preference towards standards-based solutions for satellite-to-phone connectivity. We expect to continue to collaborate with Iridium on standards-based solutions while discontinuing efforts on the proprietary solution that was introduced earlier this year." [ 40 ] [ 41 ] [ 42 ]
In 2024, Iridium introduced Project Stardust, a 3GPP standard-based satellite-to-cellphone service focusing on messaging, emergency communications and IoT for devices like cars, smartphones, tablets and related consumer applications. The solution will be supported using a version of the NB-IoT standard for 5G non-terrestrial networks (NTN). Scheduled for launch in 2026, it won't replace the company’s proprietary solution for voice and high-speed data; instead it will co-exist with that offering on the Iridium's existing global low-earth orbit satellite network. [ 43 ] [ 44 ]
From 2015–2022, Iridium Satellite was selling navigation systems directly to its Russian subsidiary, Iridium Communications. In 2022, the Moscow-based subsidiary gave the National Guard of Russia access to the satellite constellation.
Following the 2022 Russian invasion of Ukraine , Iridium structured their operations to comply with US sanctions and stopped shipment of end-user equipment to Russia. Despite this, In 2023, Iridium Communications, via some unknown intermediaries, imported machines made by the American parent company for receiving and converting voice and images. [ 45 ]
The Iridium system requires 66 active satellites in low Earth orbit to complete its constellation and 9 spare satellites are kept in-orbit to serve in case of failure. [ 46 ] The satellites are in six polar orbital planes at a height of approximately 485 miles (780 km). [ 47 ] Satellites communicate with neighboring satellites via Ka band intersatellite links to relay communications to and from ground stations . [ 48 ] The original constellation was launched in the late 1990s before the company went through bankruptcy. In January 2017, Iridium began to launch its next-generation satellites through its $3 billion launch campaign, Iridium NEXT . The new satellites were sent into space on SpaceX Falcon 9 launch vehicles from Vandenberg AFB Space Launch Complex 4 in California over the course of eight launches between January 2017 and January 2019. [ 49 ] [ 50 ] On January 14, 2017, SpaceX launched 10 of the new Iridium satellites into orbit. [ 51 ] The second launch of Iridium NEXT satellites took place on June 25, 2017 on a SpaceX Falcon 9 rocket out of Vandenberg Space Force Base . This was the second of eight scheduled launches. [ 52 ] The third launch of 10 NEXT satellites took place on October 9, 2017. On December 22, 2017, ten additional satellites were deployed after a successful launch on a SpaceX Falcon 9 rocket . On May 22, SpaceX successfully launched an additional five Iridium NEXT satellites from Vandenberg Space Force Base . [ 53 ]
On January 11, 2019, the final ten satellites were placed in orbit by SpaceX . [ 54 ]
Iridium offers four satellite handsets: the 9555, 9575A (which is only available to US government customers), the Extreme, and the Extreme PTT. [ 55 ]
In 2014, Iridium began to offer the Iridium Go! hotspot , which can also be used as a distress beacon under certain circumstances. [ 56 ] As of September 2020, Iridium's manufacturing contractor, Beam Communications, had built 50,000 of these devices. [ 57 ]
Two pagers were made for the Iridium network – the Motorola 9501 and Kyocera SP-66K. [ 58 ] These are one-way devices that could receive messages sent in the form of SMS .
Messages are delivered to pre-selected "MDAs" which cover a certain geographic area. Three of these MDAs may be selected on a web-based portal or updated automatically if the paging service is bound to an Iridium phone. Each country has its own MDA based on its country code ; some of the larger countries are divided into several MDAs, while separate MDAs exist for sections of ocean and common aeronautic routes.
Pagers are assigned with telephone numbers in area code 480 and can also be contacted using email, SMS and the web-based interface used to send messages to Iridium phones. [ 59 ]
In 2017, Garmin announced inReach SE+ and inReach Explorer+ satellite communicators, which use Iridium satellite network for global coverage. [ 60 ] Garmin inReach mini, a satellite messenger, was announced a year later. [ 61 ] These devices can send and receive text messages with any cell phone number, email address or another inReach device, as well as to provide location sharing, navigation and direct communication options to emergency services.
ZOLEO satellite communicator uses global Iridium network when cellular or Wi-Fi coverage is unavailable. It does so by means of Bluetooth connection to provide two-way messaging to connected smartphone or tablet devices. [ 62 ]
Several other Iridium-based telephones exist, such as payphones , [ 63 ] and equipment intended for installation on ships and aircraft. The DPL handset made by NAL Research combined with a 9522 transceiver is used for some of these products. This handset provides a user interface nearly identical to that of the 9505 series phones. [ 64 ]
These can be used for data-logging applications in remote areas (as in data collection satellites ). Some types of buoys , such as those used for the tsunami warning system , use Iridium satellites to communicate with their base. The remote device is programmed to call or send short burst data (SBD) messages to the base at specified intervals, or it can be set to accept calls in order for it to offload its collected data.
The following transceivers have been released over the years:
These devices support only SBD for Internet of things (IoT) services and do not use a SIM card.
Iridium OpenPort is a broadband satellite voice and data communications system for maritime vessels. The system is used for crew calling and e-mail services on sea vessels such as merchant fleets, government and navy vessels, fishing fleets and personal yachts. [ 69 ]
Iridium operates at only 2.2 to 3.8 kbit/s , which requires very aggressive voice compression [ 70 ] and decompression algorithms . [ 71 ] (By comparison, AMR used in 3G phones requires a minimum of 4.75 kbit/s, G.729 requires 6.4 kbit/s, and iLBC requires 13.33 kbit/s.) Latency for data connections averages 1800 ms round-trip, with a mode of 1300 to 1400 ms and a minimum around 980 ms. [ 72 ] Latency is highly variable depending on the path data takes through the satellite constellation as well the need for retransmissions due to errors, which may be around 2 to 3% for mobile originated packets under good conditions.
One of the Iridium NEXT services is Iridium Certus, a globally available satellite broadband which is capable of up to 704 Kbps of bandwidth across maritime, aviation, land mobile, government, and IoT applications. Terminals for the service are provided by Cobham , Intellian Technologies and Thales . [ 73 ] [ 74 ] [ 75 ]
Iridium is providing Satellite Time & Location (STL) service. [ 76 ] It was developed by Satelles company, which was later acquired by Iridium Communications in April 2024. [ 77 ]
According to the company, it is the only LEO satellite based commercial positioning, navigation, and timing (PNT) service (as of April 2024). [ 76 ] | https://en.wikipedia.org/wiki/Iridium_Communications |
The Iridium satellite constellation provides L band voice and data information coverage to satellite phones , satellite messenger communication devices and integrated transceivers. Iridium Communications owns and operates the constellation , additionally selling equipment and access to its services. It was conceived by Bary Bertiger, Raymond J. Leopold and Ken Peterson in late 1987 (in 1988 protected by patents Motorola filed in their names) and then developed by Motorola on a fixed-price contract from July 29, 1993, to November 1, 1998, when the system became operational and commercially available.
The constellation consists of 66 active satellites in orbit, required for global coverage, and additional spare satellites to serve in case of failure. [ 3 ] Satellites are placed in low Earth orbit at a height of approximately 781 kilometres (485 mi) and inclination of 86.4°. The nearly polar orbit and communication between satellites via Ka band inter-satellite links provide global service availability (including both poles , oceans and airways), regardless of the position of ground stations and gateways.
In 1999, The New York Times quoted a wireless market analyst, regarding people having "one number that they could carry with them anywhere" as "expensive... There never was a viable market." [ 4 ]
Due to the shape of the original Iridium satellites' reflective antennas, the first generation satellites focused sunlight on a small area of the Earth surface in an incidental manner. This resulted in a phenomenon called Iridium flares , whereby the satellite momentarily appeared as one of the brightest objects in the night sky and could be seen even during daylight. [ 5 ] Newer Iridium satellites do not produce flares.
The Iridium system was designed to be accessed by small handheld phones, the size of a cell phone. While "the weight of a typical cell phone in the early 1990s was 10.5 ounces" [ 6 ] (300 grams) Advertising Age wrote in mid 1999 that "when its phone debuted, weighing 1 pound (453 grams) and costing $3,000, it was viewed as both unwieldly and expensive." [ 7 ]
An omnidirectional antenna was intended to be small enough to be mounted on the planned phone, but the low handset battery power was insufficient for contact with a satellite in geostationary orbit , 35,785 km (22,236 mi) above the Earth; the normal orbit of communications satellites , in which the satellite appears stationary in the sky. In order for a handheld phone to communicate with them, the Iridium satellites are closer to the Earth, in low Earth orbit , about 781 km (485 mi) above the surface. With an orbital period of about 100 minutes a satellite can only be in view of a phone for about 7 minutes, so the call is automatically "handed off" to another satellite when one passes beyond the local horizon. This requires a large number of satellites, carefully spaced out in polar orbits (see animated image of coverage) to ensure that at least one satellite is continually in view from every point on the Earth's surface. At least 66 satellites are required, in 6 polar orbits containing 11 satellites each, for seamless coverage.
Orbital velocity of the satellites is approximately 27,000 km/h (17,000 mph). Satellites communicate with neighboring satellites via Ka band inter-satellite links. Each satellite can have four inter-satellite links: one each to neighbors fore and aft in the same orbital plane, and one each to satellites in neighboring planes to either side. The satellites orbit from pole to same pole with an orbital period of roughly 100 minutes. [ 8 ] This design means that there is excellent satellite visibility and service coverage especially at the North and South poles. The over-the-pole orbital design produces "seams" where satellites in counter-rotating planes next to one another are traveling in opposite directions. Cross-seam inter-satellite link hand-offs would have to happen very rapidly and cope with large Doppler shifts ; therefore, Iridium supports inter-satellite links only between satellites orbiting in the same direction. The constellation of 66 active satellites has six orbital planes spaced 30° apart, with 11 satellites in each plane (not counting spares). The original concept was to have 77 satellites, which is where the name Iridium came from; the element iridium has the atomic number 77, and the satellites evoked the Bohr model image of electrons orbiting around the Earth as its nucleus. This reduced set of six planes is sufficient to cover the entire Earth surface at every moment.
The Iridium satellite constellation was conceived in the early 1990s as a way to reach high Earth latitudes with reliable satellite communication services. [ 9 ] Early calculations showed that 77 satellites would be needed, hence the name Iridium, after the metal with atomic number 77 . It turned out that just 66 were required to complete the blanket coverage of the planet with communication services. [ 9 ] [ 1 ]
The first-generation constellation was developed by Iridium SSC , and financed by Motorola . The satellites were deployed in 1997–2002. All the satellites needed to be in orbit before commercial service could begin. [ 1 ]
Iridium SSC employed a globally diverse fleet of rockets to get their 77 satellites into orbit, including launch vehicles (LVs) from the United States, Russia, and China. 60 were launched to orbit on twelve Delta II rocket carrying five satellites each; 21 on three Proton-K/DM2 rocket with seven each, two on one Rokot/Briz-KM rocket carrying two; and 12 on six Long March 2C/SD rocket carrying two each. The total setup cost for the first-generation fleet was approximately US$5 billion . [ 1 ]
The first test telephone call was made over the network in 1998, and full global coverage was complete by 2002. However, although the system met its technical requirements, it was not a success in the market. Poor reception from inside buildings, bulky and expensive handsets, and competition with the conventional cellular phone contributed to its failure. [ 10 ] Insufficient market demand existed for the product at the price points on offer from Iridium as set by its parent company Motorola. The company failed to earn revenue sufficient to service the debt associated with building out the constellation and Iridium went bankrupt , one of the largest bankruptcies in US history at the time. [ 1 ] [ 9 ]
The constellation continued operation following the bankruptcy of the original Iridium corporation. A new entity emerged to operate the satellites and developed a different product placement and pricing strategy, offering communication services to a niche market of customers who required reliable services of this type in areas of the planet not covered by traditional geosynchronous orbit communication satellite services. Users include journalists , explorers, and military units. [ 9 ]
No new satellites were launched 2002–2017 to replenish the constellation, even though the original satellites based on the LM-700A model had been projected to have a design life of only 8 years. [ 1 ]
The second-generation Iridium-NEXT satellites began to be deployed into the existing constellation in January 2017. Iridium Communications , the successor company to Iridium SSC, has ordered a total of 81 new satellites being built by Thales Alenia Space and Orbital ATK : 66 operational units, nine on-orbit spares, and six ground spares. [ 1 ]
In August 2008, Iridium selected two companies — Lockheed Martin and Thales Alenia Space — to participate in the final phase of the procurement of the next-generation satellite constellation. [ 11 ]
As of 2009 [update] , the original plan had been to begin launching new satellites in 2014. [ 12 ]
The design was complete by 2010, and Iridium stated that the existing constellation of satellites would remain operational until Iridium NEXT is fully operational, with many satellites expected to remain in service until the 2020s, while the NEXT satellites would have improved bandwidth. The new system was to be backward-compatible with the current system. In June 2010, the winner of the contract was announced as Thales Alenia Space, in a $2.1 billion deal underwritten by Compagnie Française d'Assurance pour le Commerce Extérieur . [ 11 ] Iridium additionally stated that it expected to spend about $800 million to launch the satellites and upgrade some ground facilities. [ 13 ]
SpaceX was contracted to launch all the Iridium NEXT satellites. All the Iridium NEXT launches have taken place using a Falcon 9 rocket launch from Vandenberg Space Force Base in California. Deployment of the constellation began in January 2017, with the launch of the first ten Iridium NEXT satellites. [ 14 ] Most recently, on January 11, 2019, SpaceX launched an additional ten satellites, bringing the number of upgraded satellites in orbit to 75. [ 15 ]
The satellites each contained seven Motorola/ Freescale PowerPC 603E processors running at roughly 200 MHz, [ 16 ] connected by a custom backplane network. One processor was dedicated to each cross-link antenna ("HVARC"), and two processors ("SVARC"s) were dedicated to satellite control, one being a spare. Late in the project an extra processor ("SAC") was added to perform resource management and phone call processing.
The cellular look down antenna had 48 spot beams arranged as 16 beams in three sectors. [ 17 ] The four inter-satellite cross links on each satellite operated at 10 Mbit/s. Optical links could have supported a much greater bandwidth and a more aggressive growth path, but microwave cross links were chosen because their bandwidth was more than sufficient for the desired system. Nevertheless, a parallel optical cross link option was carried through a critical design review, and ended when the microwave cross links were shown to support the size, weight and power requirements allocated within the individual satellite's budget. Iridium Satellite LLC stated that their second generation satellites would also use microwave, not optical, inter-satellite communications links. Iridium's cross-links are unique in the satellite telephone industry as other providers do not relay data between satellites; Globalstar and Inmarsat both use a transponder without cross-links.
The original design as envisioned in the 1960s was that of a completely static "dumb satellite" with a set of control messages and time-triggers for an entire orbit that would be uploaded as the satellite passed over the poles. It was found that this design did not have enough bandwidth in the space-based backhaul to upload each satellite quickly and reliably over the poles. Moreover, fixed, static scheduling would have left more than 90% of the satellite links idle at all times. Therefore, the design was scrapped in favour of a design that performed dynamic control of routing and channel selection late in the project, resulting in a one-year delay in system delivery. [ citation needed ]
Each satellite can support up to 1,100 concurrent phone calls at 2,400 bit/s [ 18 ] and weighs about 680 kilograms (1,500 lb). [ 19 ] The Iridium System presently operates within a dedicated band segment from 1,618.725 to 1,626.5 MHz and shares with Globalstar a band segment from 1,617.775 to 1,618.725 MHz. [ 20 ] These segments are part of the wider L band , adjacent to the Radio Astronomy Service (RAS) band segment from 1,610.6 to 1,613.8 MHz.
The configuration of the Satellite concept was designated as Triangular Fixed, 80 Inch Main Mission Antenna, Light-weight (TF80L). The packaging design of the spacecraft was managed by Lockheed Bus Spacecraft team; it was the first commercial satellite bus designed at the Sunnyvale Space Systems Division in California. The TF80L configuration was considered a non-conventional, innovative approach to developing a satellite design that could be assembled and tested in five days. The TF80L design configuration was also instrumental in simultaneously solving fundamental design problems involving optimization of the communications payload thermal environment and RF main mission antenna performance, while achieving the highest payload fairing packaging for each of the three main launch vehicle providers.
The first spacecraft mock-up of this design was built in the garage workshop in Santa Clara, California for the Bus PDR/CDR as a proof-of-concept model. This first prototype paved the way for the design and construction of the first engineering models. This design was the basis of the largest constellation of satellites deployed in low Earth orbit . After ten years of successful on-orbit performance, the Iridium team celebrated the equivalent of 1,000 cumulative years of on-orbit performance in 2008. One of the engineering Iridium satellite models was placed on permanent exhibit in the National Air and Space Museum in Washington, D.C.
95 of the 99 built satellites were launched between 1997 and 2002. [ clarification needed ] Four satellites were kept on the ground as spares.
The 95 satellites were launched over twenty-two missions (nine missions in 1997, ten in 1998, one in 1999 and two in 2002). One extra mission on Chang Zheng was a payload test and did not carry any actual satellites.
^ Iridium satellite number changed over time following failure and replacement.
Spare satellites are usually held in a 666 kilometres (414 mi) storage orbit. [ 3 ] These can be boosted to the correct altitude and put into service in case of a satellite failure. After the Iridium company emerged from bankruptcy the new owners decided to launch seven new spares, which would have ensured two spare satellites were available in each plane. As of 2009, not every plane had a spare satellite; however, the satellites can be moved to a different plane if required. A move can take several weeks and consumes fuel which will shorten the satellite's expected service life.
Significant orbital inclination changes are normally very fuel-intensive, but orbital perturbation analysis aids the process. The Earth's equatorial bulge causes the orbital right ascension of the ascending node (RAAN) to precess at a rate that depends mainly on the period and inclination .
A spare Iridium satellite in the lower storage orbit has a shorter period so its RAAN moves westward more quickly than the satellites in the standard orbit. Iridium simply waits until the desired RAAN (i.e., the desired orbital plane) is reached and then raises the spare satellite to the standard altitude, fixing its orbital plane with respect to the constellation. Although this saves substantial amounts of fuel, it can be a time-consuming process.
During 2016, Iridium experienced in-orbit failures which could not be corrected with in-orbit spare satellites, thus only 64 of the 66 satellites required for seamless global coverage were in operation. This caused some service interruptions until the next-generation constellation was put into service. [ 21 ]
In 2017, Iridium began launching [ 22 ] [ 23 ] [ 24 ] [ 25 ] Iridium NEXT, a second-generation worldwide network of telecommunications satellites, consisting of 66 active satellites, with another nine in-orbit spares and six on-ground spares. These satellites incorporate features such as data transmission that were not emphasized in the original design. [ 26 ] The next-generation terminals and service became commercially available in 2018. [ 27 ] One of the Iridium NEXT services is Iridium Certus, a globally available satellite broadband, which is capable of up to 704 kbit/s of bandwidth across maritime, aviation, land mobile, government, and IoT applications. [ 28 ]
The NEXT satellites incorporate a secondary payload for Aireon , [ 29 ] a space-qualified ADS-B data receiver for use by air traffic control and, via FlightAware , by airlines. [ 30 ] A tertiary payload on 58 satellites is a marine AIS ship-tracker receiver for Canadian company ExactEarth Ltd . [ 31 ]
In January 2020, the Iridium constellation was certified for use in the Global Maritime Distress and Safety System (GMDSS). The certification ended a monopoly on the provision of maritime distress services that had previously been held by Inmarsat since the system became operational in 1999. [ 32 ]
Iridium NEXT also provides data link to other satellites in space, enabling command and control of other space assets regardless of the position of ground stations and gateways. [ 26 ]
In June 2010, Iridium signed the largest commercial rocket-launch deal ever at that time, a US$492 million contract with SpaceX to launch 70 Iridium NEXT satellites on seven Falcon 9 rockets from 2015 to 2017 via SpaceX leased launch facility at Vandenberg Space Force Base . [ 33 ] The final two satellites were originally slated to be orbited by a single launch [ 34 ] of an ISC Kosmotras Dnepr . [ 35 ] Technical issues and consequential demands from Iridium's insurance delayed the launch of the first pair of Iridium NEXT satellites until April 2016. [ 36 ]
Iridium NEXT launch plans originally [ 37 ] included launch of satellites on both Ukrainian Dnepr launch vehicles and SpaceX Falcon 9 launch vehicles, with the initial satellites launching on Dnepr in April 2016; however, in February 2016, Iridium announced a change. Due to an extended slowdown in obtaining the requisite launch licenses from Russian authorities, Iridium revamped the entire launch sequence for the 75-satellite constellation. It launched and successfully deployed 10 satellites with SpaceX on January 14, 2017, delayed due to weather from January 9, 2017, [ 38 ] and the first of those new satellites took over the duties of an old satellite on March 11, 2017. [ 39 ]
At the time of the launch of the first batch, the second flight of ten satellites was planned to launch only three months later in April 2017. [ 40 ] However, in a February 15 statement, Iridium said that SpaceX pushed back the launch of its second batch of Iridium NEXT satellites from mid-April to mid-June 2017. This second launch, which occurred on June 25, 2017, delivered another ten Iridium NEXT satellites to low Earth orbit (LEO) on a SpaceX Falcon 9 rocket. A third launch, which occurred on October 9, 2017, delivered another ten satellites to LEO, as planned. The Iridium NEXT IV mission launched with ten satellites on December 23, 2017. The fifth mission, Iridium NEXT V, launched with ten satellites on March 30, 2018. The sixth launch on May 22, 2018, sent another 5 satellites into LEO. [ 41 ] The penultimate Iridium NEXT launch occurred on July 25, 2018, launching another 10 Iridium NEXT satellites. [ 42 ] The final ten NEXT satellites launched on January 11, 2019. Of the six additional spare satellites five have been launched on 20 May 2023 while the last one, Iridium 101, is still on the ground. [ 43 ]
^ Iridium satellite number could change over time following failure and replacement.
Iridium 127 had to be re-designated as Iridium 100 before launch due to a ground software issue. [ 45 ] [ 44 ]
The main patents on the Iridium system, U.S. Patents 5,410,728: "Satellite cellular telephone and data communication system" , and 5,604,920, are in the field of satellite communications, and the manufacturer generated several hundred patents protecting the technology in the system. Satellite manufacturing initiatives were also instrumental in the technical success of the system. Motorola made a key hire of the engineer who set up the automated factory for Apple 's Macintosh . He created the technology necessary to mass-produce satellites on a gimbal , taking weeks instead of months or years. At its peak during the launch campaign in 1997 and 1998, Motorola produced a new satellite every 4.3 days, with the lead-time of a single satellite being 21 days. [ 46 ] [ non-primary source needed ]
Over the years a number of Iridium satellites have ceased to work and are no longer in active service, some are partially functional and have remained in orbit whereas others have tumbled out of control or have reentered the atmosphere. [ 47 ]
Iridium 21, 27, 20, 11, 46, 71, 44, 14, 79, 69 and 85 all suffered from issues before entering operational service soon after their launch. By 2018, of these eleven, Iridium 27, 79 and 85 have decayed out of orbit; Iridium 11, 14, 20 and 21 were renamed to Iridium 911, 914, 920 and 921 respectively since replacements of the same name were launched. [ 48 ]
From 2017, several first-generation Iridium satellites have been deliberately de-orbited after being replaced by operational Iridium NEXT satellites. [ 47 ]
As of January 2023, a total of 80 previously operating satellites are now defunct or no longer exist.
At 16:56 UTC on February 10, 2009, Iridium 33 collided with the defunct Russian satellite Kosmos 2251 . [ 50 ] This accidental collision was the first hypervelocity collision between two artificial satellites in low Earth orbit . [ 51 ] [ 52 ] Iridium 33 was in active service when the accident took place. It was one of the oldest satellites in the constellation, having been launched in 1997. The satellites collided at a relative speed of roughly 35,000 km/h (22,000 miles per hour) [ 53 ] This collision created over 2000 large space debris fragments that could be hazardous to other satellites. [ 54 ]
Iridium moved one of its in-orbit spares, Iridium 91 (formerly known as Iridium 90), to replace the destroyed satellite, [ 55 ] completing the move on March 4, 2009.
Communication between satellites and handsets is done using a TDMA and FDMA based system using L-band spectrum between 1,616 and 1,626.5 MHz. [ 17 ] Iridium exclusively controls 7.775 MHz of this and shares a further 0.95 MHz. In 1999, Iridium agreed to timeshare a portion of spectrum, allowing radio astronomers to observe hydroxyl emissions. in 2010, the amount of shared spectrum was reduced from 2.625 MHz. [ 56 ] [ 57 ]
External "hockey puck" type antennas used with Iridium handheld phones, data modems and SBD terminals are usually defined as 3 dB gain, 50 ohms impedance with RHCP (right hand circular polarization ) and 1.5:1 VSWR . [ 58 ] As Iridium antennas function at frequencies very close to those of GPS , a single antenna may be utilized through a pass-through for both Iridium and GPS reception.
The type of modulation used is normally DE- QPSK , although DE- BPSK is used on the uplink (mobile to satellite) for acquisition and synchronization. [ 59 ] Each time slot is 8.28 milliseconds long and sits in a 90 milliseconds frame. Within each FDMA channel there are four TDMA time slots in each direction. [ 60 ] The TDMA frame starts off with a 20.32 milliseconds period used for simplex messaging to devices such as pagers and to alert Iridium phones of an incoming call, followed by the four upstream slots and four downstream slots. This technique is known as time-division multiplexing . Small guard periods are used between time slots. Regardless of the modulation method being used, communication between mobile units and satellites is performed at 25 kilobaud .
Channels are spaced at 41.666 kHz and each channel occupies a bandwidth of 31.5 kHz; this allows space for Doppler shifts. [ 61 ]
The Iridium system uses three different handoff types. As a satellite travels over the ground location, calls are handed to adjacent spot-beams; this occurs approximately every fifty seconds. A satellite only stays in view for seven minutes at the equator. [ 62 ] When the satellite disappears from view, an attempt is made to hand the call to another satellite. If no other satellite is in view, the connection is dropped. This may occur when the signal from either satellite is blocked by an obstacle. When successful, the inter-satellite handoff may be noticeable by a quarter-second interruption. [ 60 ]
The satellites are also able to transfer mobile units to different channels and time slots within the same spot beam.
Iridium routes phone calls through space. In addition to communicating with the satellite phones in its footprint, each satellite in the constellation also maintains contact with two to four adjacent satellites, and routes data between them, to effectively create a large mesh network . There are several ground stations which link to the network through the satellites visible to them. The space-based backhaul routes outgoing phone call packets through space to one of the ground station downlinks ("feeder links"). Iridium ground stations interconnect the satellite network with land-based fixed or wireless infrastructures worldwide to improve availability. [ 63 ] Station-to-station calls from one satellite phone to another can be routed directly through space without going through a ground station. As satellites leave the area of a ground station, the routing tables are updated and packets headed for the ground station are forwarded to the next satellite just coming into view of the ground station. Communication between satellites and ground stations is at 20 and 30 GHz. [ 64 ]
Gateways are located in
The pre-bankruptcy corporate incarnation of Iridium built eleven gateways, most of which have since been closed. [ 68 ]
In 2024, Iridium introduced Project Stardust, a 3GPP standard-based satellite-to-cellphone service focusing on messaging, emergency communications and IoT for devices like cars, smartphones, tablets and related consumer applications. The solution will be supported using a version of the NB-IoT standard for 5G non-terrestrial networks (NTN). Scheduled for launch in 2026, it won't replace the company's proprietary solution for voice and high-speed data; instead it will co-exist with that offering on the Iridium's existing global low-earth orbit satellite network. [ 69 ] [ 70 ] | https://en.wikipedia.org/wiki/Iridium_satellite_constellation |
Demidov Prize (2003)
Irina Petrovna Beletskaya ( Russian : Ири́на Петро́вна Беле́цкая ; born 10 March 1933) is a Soviet and Russian professor of chemistry at Moscow State University . She specializes in organometallic chemistry and its application to problems in organic chemistry . She is best known for her studies on aromatic reaction mechanisms, as well as work on carbanion acidity and reactivity. [ 1 ] She developed some of the first methods for carbon-carbon bond formation using palladium or nickel catalysts, and extended these reactions to work in aqueous media. She also helped to open up the chemistry of organolanthanides .
Beletskaya was born in Leningrad ( St. Petersburg , Russia) in 1933. [ 1 ] She graduated from the Department of Chemistry of Lomonosov Moscow State University in 1955 where she focused her undergraduate research on organoarsenic chemistry. [ 2 ] She obtained the Candidate of Chemistry (analogous to Ph.D.) degree in 1958. [ 3 ] For this degree she investigated electrophilic substitution reactions. More specifically, she explored the influence of ammonia on a-bromomercurophenylacetic acid reactions. [ 2 ] In 1963 she received her Dr.Sci. degree from the same institution. [ 4 ] In 1970 she became a Full Professor of Chemistry at Moscow State University , [ 5 ] where she currently serves as head of the Organoelement Chemistry Laboratory . Beletskaya was elected a corresponding member of the Academy of Science of USSR in 1974. In 1992 she became a full member (academician) of the Russian Academy of Sciences . [ 1 ] Between 1991 and 1993 she served as president of the Division of Organic Chemistry of IUPAC . [ 1 ] Until 2001 she served on the IUPAC Committee on Chemical Weapons Destruction Technology (CWDT). [ 6 ] She is editor-in chief of the Russian Journal of Organic Chemistry . [ 7 ]
Beletskaya initially researched the reaction mechanisms of organic reactions, focusing on compounds with metal-carbon bonds. [ 2 ] Her research included Grignard-like reactions and lanthanide complexes in the context of catalysts. She and Prof. O. Reutov worked on electrophilic reactions at saturated carbon. She also investigated the reaction mechanisms of organometallic compounds. She also researched carbanion reactivity, emphasizing the reactivity and structure of ion pairs. [ 3 ] Once more advanced in her career, Beltskaya focused more on transition metal catalysts and developing economically favorable catalysts. Currently, she serves as the head of the Laboratory of Organoelement Compounds within the Department of Chemistry at Moscow State University, where she has concentrated her research on carbon dioxide utilization and its utility in renewable energy and reactions with epoxides. [ 8 ]
Beletskaya is known for her foundational contributions to organometallic chemistry and as one of the first prominent female chemists. Her work helped pave the way for women in Russia to participate in the scientific community. [ 9 ] Her pioneering role in organometallic synthesis has laid an essential foundation for future organic chemists. Her work advocating for rare-earth elements in organic chemistry led to the publication of many new textbooks, changing how organic chemistry is taught everywhere. [ 8 ] The current field of organic chemists does not always see the need to include other elements in the study of organic chemistry, as it is all carbon-based. [ 2 ] Beletskaya’s work helps to expand the use of precious metals in organic reactions.
Source: [ 14 ] | https://en.wikipedia.org/wiki/Irina_Beletskaya |
The Irish Astronomical Society , the oldest astronomy club in Ireland , was founded in D'Olier Street , Dublin on 5 October 1937. [ 1 ] [ 2 ]
The society holds public stargazing events to raise interest in astronomy . Some members bring their telescopes to these events and have been nicknamed Dublin Sidewalk Astronomers . It is also one of the founding organisations of the Irish Federation of Astronomical Societies . Most members are amateur astronomers , with some professionals.
Orbit is published every two months containing articles by members and non-members. Sky-High is published annually. Both are free to members.
The Irish Astronomical Society was founded in October 1937. The core group in its formative years included Joseph MacDermott, Uinsionn S. Deiseach (Vincent Deasy), Lorcan O hUiginn, Veronica Burns , M. A. Magennis, H. A. Haughton, Muiris Mac Ionnraic, Mrs. M. Jones, William Farquharson and William R. Mackle. [ 1 ] [ 2 ] It was reorganised in 1947 to allow local centres to work under a central committee. It published the Irish Astronomical Journal every quarter from 1949 to 1959. Later, Dunsink Observatory and Armagh Observatory took over publication of the journal. [ 3 ]
By 1974, only the Dublin and Belfast centres still existed, then the Belfast one left to form the Irish Astronomical Association . The society expanded rapidly between 1988 and 1990, leading to financial strains and disagreements about the direction of the society. [ 4 ] This led to some members to leave to form Astronomy Ireland in 1990. | https://en.wikipedia.org/wiki/Irish_Astronomical_Society |
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