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Transition metal carbyne complex Transition metal carbyne complexes are organometallic compounds with a triple bond between carbon and the transition metal. This triple bond consists of a σ-bond and two π-bonds. The HOMO of the carbyne ligand interacts with the LUMO of the metal to create the σ-bond. The two π-bonds are formed when the two HOMO orbitals of the metal back-donate to the LUMO of the carbyne. They are also called metal alkylidynes—the carbon is a carbyne ligand. Such compounds are useful in organic synthesis of alkynes and nitriles. They have been the focus on much fundamental research. Transition metal carbyne complexes are most common for the early transition metals, especially niobium, tantalum, molybdenum, tungsten, and rhenium. They can also have low-valence metals as well as high-valence metals. The first example of a metal carbyne complex was prepared by the Fischer school by treatment of Cr(CO)(C(OMe)Ph) with boron trichloride: Many high-valent carbyne complexes have since been prepared, often by dehydrohalogenation of carbene complexes. Alternatively, amino-substituted carbyne ligands sometimes form upon protonation of electron-rich isonitrile complexes. Similarly, "O"-protonation of "μ"-CO ligands in clusters gives hydroxycarbyne complexes. Vinyl ligands have been shown to rearrange into carbyne ligands. Addition of electrophiles to vinylidene ligands also affords carbyne complexes. Some metal carbynes dimerize to give dimetallacyclobutadienes. In these complexes, the carbyne ligand serves as a bridging ligand | https://en.wikipedia.org/wiki?curid=29889269 |
Transition metal carbyne complex Many cluster-bound carbyne complexes are known, typically with CO ligands. These compounds do not feature MC triple bonds; instead the carbyne carbon is tetrahedral. Some of the best known are the tricobalt derivatives, which are prepared by treating cobalt carbonyl with haloforms: Monomeric metal carbyne complexes exhibit fairly linear M–C–R linkages according to X-ray crystallography. The M–C distances are typically shorter than the M–C bonds found in metal carbenes. The bond angle is generally between 170° and 180° Analogous to Fischer and Schrock carbenes; Fischer and Schrock carbynes are also known. Fischer carbynes usually have lower oxidation state metals and the ligands are π-accepting/electron-withdrawing ligands. Schrock carbynes on the other hand typically have higher oxidation state metals and electron-donating/anionic ligands. In a Fischer carbyne the C-carbyne exhibits electrophilic behavior while Schrock carbynes display nucleophilic reactivity on the carbyne carbon Carbyne complexes have also been characterized by many methods including infrared Spectroscopy, Raman spectroscopy. Bond lengths, bond angles and structures can be inferred from these and other analytical techniques. The first Fischer carbyne was isolated in 1973. Two years later in 1975, the first Schrock carbyne was reported. Metal carbyne complexes also exhibit a large "trans" effect, where the ligand opposite the carbyne is typically labile | https://en.wikipedia.org/wiki?curid=29889269 |
Transition metal carbyne complex Metal alkylidyne complexes have mainly been used for specialized reactions in the laboratory, the main used being alkyne metathesis. Triply-bridging carbynes are sometimes prepared by the condensation of terminal carbyne complexes with other metals. Transition metal carbyne complexes usually react with Lewis acids at the C-carbyne. This reaction generally causes them to become transition metal carbene complexes. Depending on the charge of the carbyne complex depends on how well the complex will react with a nucleophile. A cationic carbyne complex will react with a nucleophile right at the C-carbyne, while a nucleophile will not react with the C-carbyne of a transition metal carbyne complex but instead it would react with the metal. This is due to the LUMO of the complexes caused by the electron orbitals of the metal and C-carbyne. Also, the higher the energy of the d-orbitals belonging to an electron-rich metal center the higher the energy of the metal–carbon π-bonds. This improves the conditions for coupling. Some carbyne complexes react with electrophiles at C-carbyne followed by association of the anion. The net reaction gives a transition metal carbene complex: These complexes can also undergo photochemical reactions. In some carbyne complexes, coupling of the carbyne ligand to a carbonyl is observed. Protonation of the carbyne carbon and conversion of the carbyne ligand into a π-allyl. A sulfur-based main group analog of a carbyne complex has been prepared by Seppalt and coworkers | https://en.wikipedia.org/wiki?curid=29889269 |
Transition metal carbyne complex The compound, trifluoro(2,2,2-trifluoroethylidyne)-λ-sulfurane, FC–C≡SF, prepared by dehydrofluorination of FC–CH=SF or FC–CH–SF, is an unstable gas that readily undergoes dimerization to form "trans"-(CF)(SF)C=C(CF)(SF) at above –50 °C. | https://en.wikipedia.org/wiki?curid=29889269 |
Oxaziridine An oxaziridine is an organic molecule that features a three-membered heterocycle containing oxygen, nitrogen, and carbon. In their largest application, oxaziridines are intermediates in the industrial production of hydrazine. derivatives are also used as specialized reagents in organic chemistry for a variety of oxidations, including alpha hydroxylation of enolates, epoxidation and aziridination of olefins, and other heteroatom transfer reactions. Oxaziridines also serve as precursors to amides and participate in [3+2] cycloadditions with various heterocumulenes to form substituted five-membered heterocycles. Chiral oxaziridine derivatives effect asymmetric oxygen transfer to prochiral enolates as well as other substrates. Some oxaziridines also have the property of a high barrier to inversion of the nitrogen, allowing for the possibility of chirality at the nitrogen center. derivatives were first reported in the mid-1950s by Emmons and subsequently by Krimm and Horner and Jürgens. Whereas oxygen and nitrogen typically act as nucleophiles due to their high electronegativity, oxaziridines allow for electrophilic transfer of both heteroatoms. This unusual reactivity is due to the presence of the highly strained three membered ring and the relatively weak N-O bond. Nucleophiles tend to attack at the aziridine nitrogen when the nitrogen substituent is small (R= H), and at the oxygen atom when the nitrogen substituent has greater steric bulk | https://en.wikipedia.org/wiki?curid=29890027 |
Oxaziridine The unusual electronics of the oxaziridine system may be exploited to perform a number of oxygen and nitrogen transfer reactions including, but not limited to: α-hydroxylation of enolates, epoxidation of alkenes, selective oxidation of sulfides and selenides, amination of "N"-nucleophiles and "N"-acylamidation. The peroxide process for the industrial production of hydrazine through the oxidation of ammonia with hydrogen peroxide in the presence of ketones was developed in the early 1970s. Chiral camphorsulfonyloxaziridines proved useful in the syntheses of complex products, such as taxol which is marketed as a chemotherapy agent. Both the Holton Taxol total synthesis and the Wender Taxol total synthesis feature asymmetric α-hydroxylation with camphorsulfonyloxaziridine. The two main approaches to synthesis of N-H, N-alkyl, and N-aryloxaziridines are oxidation of imines with peracids (A) and amination of carbonyls (B). Additionally, oxidation of chiral imines and oxidation of imines with chiral peracids may yield enantiopure oxaziridines. Some oxaziridines have the unique property of configurationally stable nitrogen atoms at room temperature due to an inversion barrier of 100 to 130 kJ/mol. Enantiopure oxaziridines where stereochemistry is entirely due to configurationally stable nitrogen are reported. In the late 1970s and early 1980s Franklin A | https://en.wikipedia.org/wiki?curid=29890027 |
Oxaziridine Davis synthesized the first "N"-sulfonyloxaziridines, which act exclusively as oxygen transfer reagents, and are the most predominantly used class of oxaziridines today. While originally synthesized with mCPBA and the phase transfer catalyst benzyltrimethylammonium chloride, an improved synthesis using oxone as the oxidant is now most prevalent. Many N-sulfonyloxaziridines are used today, each with slightly different properties and reactivity. These reagents are summarized in the table below. With highly electron withdrawing perfluoroalkyl substituents, oxaziridines exhibit reactivity more similar to that of dioxiranes than typical oxaziridines. Notably, perfluoroalkyloxaziridines hydroxylate certain C-H bonds with high selectivity. Perfluorinated oxaziridines may be synthesized by subjecting a perfluorinated imine to perfluoromethyl fluorocarbonyl peroxide and a metal fluoride to act as an HF scavenger. Oxaziridines are intermediates in the peroxide process for the production of hydrazine. Many millions of kilograms of hydrazine are produced annually by this method that involves a step wherein ammonia is oxidized in the presence of methyl ethyl ketone to give the oxaziridine: In subsequent steps the oxaziridine is converted to the hydrazone, which is the immediate in the way to hydrazine: α-Hydroxyketones, or acyloins, are an important synthetic motifs present in many natural products | https://en.wikipedia.org/wiki?curid=29890027 |
Oxaziridine α-Hydroxyketones have been synthesized in many ways, including reduction of α-diketones, substitution of a hydroxyl for a leaving group and direct oxidation of an enolate. Oxodiperoxymolybdenum(pyridine)-(hexamethylphosphoric triamide) (MoOPH) and "N"-sulfonyloxaziridines are the most common electrophilic sources of oxygen implemented in this process. One advantage of using "N"-sulfonyloxaziridines is that higher chiral induction is almost invariably observed relative to MoOPH and other oxidants. High yield (77–91%) and "dr" (95:5 – 99:1) are reported for α-hydroxylation with the Evans' chiral auxiliary with "N"-sulfonyloxaziridine as the electrophile. Chiral induction has been demonstrated with many other chiral ketones and ketones with chiral auxiliaries, including SAMP and RAMP. Extensive work has been reported on asymmetric hydroxylation of prochiral enolates with camphorsulfonyloxaziridine derivatives, achieving moderate to high enantiomeric excess. The commonly accepted proposed transition state that justifies this stereochemical outcome involves an open transition state where the steric bulk of R determines the face of approach. The selectivity of some hydroxylations may be drastically improved in some cases with the addition of coordinating groups alpha to the oxaziridine ring as oxaziridines 3b and 3c in the table above | https://en.wikipedia.org/wiki?curid=29890027 |
Oxaziridine In these instances it is proposed that the reaction proceeds through a closed transition state where the metal oxyanion is stabilized by chelation from the sulfate and coordinating groups on the camphor skeleton. α-Hydroxylation with oxaziridines has been widely implemented in total synthesis. It is a key step in both the Holton Taxol total synthesis and the Wender Taxol total synthesis. Additionally, Forsyth implemented the transformation in his synthesis of the C3-C14 (substituted 1,7-Dioxaspiro[5.5]undec-3-ene) System of okadaic acid. Epoxidation of alkenes is a common reaction because epoxides can be derivatized in a number of useful ways. Classically, laboratory epoxidation is carried out with mCPBA or other peracids. Oxaziridines have been found to be useful for the formation of highly acid sensitive epoxides. (−)-Chaetominine was synthesized via oxaziridine epoxidation as a late stage transformation as seen below. Another transformation of high synthetic utility is asymmetric epoxidation. A number of asymmetric epoxidations exist: the Sharpless epoxidation, the Jacobsen-Katsuki epoxidation, and the Juliá-Colonna epoxidation. These methods require specific functionality in order to achieve selectivity. The Sharpless epoxidation is specific to allylic alcohols, the Jacobsen epoxidation requires "cis"-disubstituted aryl alkenes, and the Juliá epoxidation requires α-β unsaturated ketones. Chiral oxaziridines act stereospecifically on many unfunctionalized alkenes | https://en.wikipedia.org/wiki?curid=29890027 |
Oxaziridine It has even possible to effect stereospecific epoxidation catalytically in the oxaziridine chiral unit. Further investigation into these reactions may be required before levels of enantiometic excess become practical for large scale synthesis. Lusinichi et al. have investigated asymmetric epoxidation with a chiral oxaziridinium salt using oxone as the stoichiometric oxidant seen below. Perfluorinated oxaziridines are known to hydroxylate unactivated hydrocarbons with remarkable regio- and diastereospecificity. This is a highly coveted transformation, and similar reactivity and specificity is seldom rivaled, especially considering the nonmetallic nature of the oxidant. Perfluorinated oxaziridines show high selectivity toward tertiary hydrogens. Hydroxylation of primary carbons and dihydroxylation of a compound with two oxidizable sites have never been observed. Retention of stereochemistry is very high, often 95 - 98%. (retenton of stereochemistry may be further enhanced by the addition of a fluoride salt). Oxaziridines with unsubstituted or acylated nitrogens are capable of nitrogen atom transfer, although this reactivity has received considerably less attention. Amination of nucleophiles with "N"-unsubstituted oxaziridines is quite versatile in the breadth of possible nucleophiles and corresponding products | https://en.wikipedia.org/wiki?curid=29890027 |
Oxaziridine Hydrazines may be derived from the amination of secondary or tertiary amines, hydroxylamine and thiohydroxamines may be formed from their corresponding alcohols and thiols, sulfimides may be formed from thioethers and α-aminoketones may be formed by attack of corresponding enolates. The transfer of acylated amines is more difficult than that of unsubstituted amines, although, unlike amine transfer by oxaziridines, there are no alternative methods that directly transfer acylated amines. Acylamine transfer has primarily been performed using amines and hydrazines as nucleophiles. Very few transfers of acylated nitrogens to carbon nucleophiles have been successfully performed, although some do exist in the literature. Oxaziridines have been found to undergo rearrangement reactions via a radical mechanism when irradiated with UV light or in the presence of a single electron transfer reagent such as Cu. spirocylic oxaziridines undergo ring expansions to the corresponding lactam. The migrating substituent is determined by a stereoelectronic effect where the group trans to the lone pair on the nitrogen will always be the predominant migration product. In light of this effect, it is possible to take advantage of the chiral nitrogen due to high inversion barrier to direct the rearrangement. This phenomenon is demonstrated by observed selectivities in the rearrangements below | https://en.wikipedia.org/wiki?curid=29890027 |
Oxaziridine In the rearrangement on the left the thermodynamically unfavorable product is observed exclusively, while in the reaction on the right the product derived from the less stable radical intermediate is favored. Aubé takes advantage of this rearrangement as the key step in his synthesis of (+)-yohimbine, a natural medicine classified by the NIH as possibly effective in the treatment of erectile dysfunction and the sexual problems caused by selective serotonin reuptake inhibitors. It is also notable that oxaziridines will thermally rearrange to nitrones. Cis-trans selectivity of the resulting nitrone is poor, however, yields are good to excellent. It is thought that some oxaziridines racemize over time through a nitrone intermediate. Oxaziridines undergo cycloaddition reactions with heterocumulenes to afford a number of unique five membered heterocycles, as shown in the figure below. This reactivity is due to the strained three membered ring and weak N-O bond. | https://en.wikipedia.org/wiki?curid=29890027 |
Metal carbon dioxide complex Metal carbon dioxide complexes are coordination complexes that contain carbon dioxide ligands. Aside from the fundamental interest in the coordination chemistry of simple molecules, studies in this field are motivated by the possibility that transition metals might catalyze useful transformations of CO. This research is relevant both to organic synthesis and to the production of "solar fuels" that would avoid the use of petroleum-based fuels. Carbon dioxide binds to metals in only a few ways. The bonding mode depends on the electrophilicity and basicity of the metal centre. Most common is the η-CO coordination mode as illustrated by Aresta's complex, Ni(CO)(PCy), which was the first reported complex of CO This square-planar compound is a derivative of Ni(II) with a reduced CO ligand. In rare cases, CO binds to metals as a Lewis base through its oxygen centres, but such adducts are weak and mainly of theoretical interest. A variety of multinuclear complexes are also known often involving Lewis basic and Lewis acidic metals, e.g. metallacarboxylate salts (CH)Fe(CO)COK. In multinuclear cases (compounds containing more than one metal), more complicated and more varied coordination geometries are observed. One example is the unsymmetrical compound containing four rhenium centres, [(CO)ReCORe(CO)]. Carbon dioxide can also bind to ligands on a metal complex (vs just the metal), e.g. by converting hydroxy ligands to carbonato ligands. Transition metal carbon dioxide complexes undergo a variety of reactions | https://en.wikipedia.org/wiki?curid=29904190 |
Metal carbon dioxide complex Metallacarboxylic acids protonate at oxygen and eventually convert to metal carbonyl complexes: This reaction is relevant to the potential catalytic conversion of CO to fuels. N-heterocyclic carbene (NHC) supported Cu complexes catalyze carboxylation of organoboronic esters. The catalyst forms "in situ" from CuCl, an NHC ligand, and KOBu. Copper "tert"-butoxide can transmetallate with the organoboronic ester to generate the Cu-C bond, which intermediate can insert into CO smoothly to get the respective carboxylate. Salt metathesis with KOBu releases product and regenerates catalyst (Scheme 2). In the presence of palladium acetate under 1-30 bar of CO, simple aromatic compounds convert to aromatic carboxylic acids. A PSiP-pincer ligand (5) promotes carboxylation of allene without using pre-functionalized substrates. Catalyst regeneration, EtAl was added to do transmetallation with palladium. Catalyst is regenerated by the following β-H elimination. Apart from terminal allenes, some of internal allenes are also tolerated in this reaction, generating allyl carboxylic acid with the yield between 54% and 95%. This system was also applied to 1,3-diene, generating carboxylic acid in 1,2 addition fashion. In 2015, Iwasawa "et al." reported the germanium analogue (6) and combined CO source together with hydride source to formate salts | https://en.wikipedia.org/wiki?curid=29904190 |
Metal carbon dioxide complex Similar to Cu(I) chemistry mentioned above, Rh(I) complexes can also transmetallate with arylboronic esters to get aryl rhodium intermediates, to which CO is inserted giving carboxylic acids. Later, Iwasawa "et al". described C-H carboxylation strategy. Rh(I) undergoes oxidative addition to aryl C-H bond followed by transmetallation with alkyl aluminum species. Ar-Rh(I) regenerates by reductive elimination releasing methane. Ar-Rh(I) attacks CO then transmetallates with aryl boronic acid to release the boronic acid of product, giving final carboxylic acid by hydrolysis. Directed and non-directed versions are both achieved. Iwasawa and co-workers developed Rh(I) catalyzed carbonation reaction initiated by Rh-H insertion to vinylarenes. In order to regenerate reactive Rh-H after nucleophilic addition to CO, photocatalytic proton-coupled electron transfer approach was adopted. In this system, excess amount of diethylpropylethylamine works as sacrificial electron donor (Scheme 5). Carboxylation of benzyl halides has been reported. The reaction mechanism is proposed to involve oxidative addition of benzyl chloride to Ni(0). The Ni(II) benzyl complex is reduced to Ni(I), e.g., by zinc, which inserts CO delivering the nickel carboxylate. Reduction of the Ni(I) carboxylate to Ni(0) releases the zinc carboxylate (Scheme 6). Similarly, such carboxylation has been achieved on aryl and benzyl pivalate, alkyl halides, and allyl esters. | https://en.wikipedia.org/wiki?curid=29904190 |
C3H8O10P2 The molecular formula CHOP may refer to: | https://en.wikipedia.org/wiki?curid=29906062 |
C3H7O7P The molecular formula CHOP may refer to: | https://en.wikipedia.org/wiki?curid=29906173 |
C3H7O6P The molecular formula CHOP may refer to: | https://en.wikipedia.org/wiki?curid=29906407 |
Reaxys is a web-based tool for the retrieval of chemistry information and data from published literature, including journals and patents. The information includes chemical compounds, chemical reactions, chemical properties, related bibliographic data, substance data with synthesis planning information, as well as experimental procedures from selected journals and patents. It is licensed by Elsevier. was launched in 2009 as the successor to the CrossFire databases. It was developed to provide research chemists with access to current and historical, relevant, organic, inorganic and organometallic chemistry information, from reliable sources via an easy-to-use interface. One of the primary goals of is to provide research chemists with access to experimentally measured data – reactions, physical, chemical or pharmacological – in one universal and factual platform. Content covers organic, medicinal, synthetic, agro, fine, catalyst, inorganic and process chemistry and provides information on structures, reactions, and citations. Additional features include a synthesis planner and access to commercial availability information. There have been regular releases and enhancements to since it was first launched, including similarity searching. provides links to Scopus for all matching articles and interoperability with ScienceDirect. Access to the database is subject to an annual license agreement | https://en.wikipedia.org/wiki?curid=29914012 |
Reaxys The content covers more than 200 years of chemistry and has been abstracted from several thousands of journal titles, books and patents. Today the data is drawn from selected journals (400 titles) and chemistry patents, and the excerption process for each reaction or substance data included needs to meet three conditions: Journals covered include "Advanced Synthesis and Catalysis", "Journal of American Chemical Society", "Journal of Organometallic Chemistry", "Synlett" and "Tetrahedron". Patents in come from the International Patent Classes: | https://en.wikipedia.org/wiki?curid=29914012 |
Arc system The stands for Anoxic Respiratory Control system. It is an example of a two-component system, in that it has a sensor molecule and a response regulator. It has been determined that the regulates as many as 30 genes, with repression of the following examples: cytochrome o oxidase, cytochrome d oxidase, and various gluconeogenic enzymes, such as for the glyoxylate cycle, and fatty acid oxidation. It also induces the expression of Pyruvate formate lyase. The uses a two component regulatory system. The sensor, ArcB, is an unusual histidine kinase in that it contains three signaling domains. ArcB senses the redox state of the cell, and becomes phosphorylated. The phosphate is shuttled onto various signalling domains until it winds up on ArcA, the response regulator. The phosphorylated ArcA is then able to act as either an activator or repressor for various metabolic genes. So, when oxygen is low, then gene products that utilize oxygen will be repressed, while genes that do not require oxygen will be upregulated. | https://en.wikipedia.org/wiki?curid=29916392 |
Swelling capacity The swelling capacity of a polymer is determined by the amount of liquid material that can be absorbed by it. This test can done by two methods: In this method | https://en.wikipedia.org/wiki?curid=29920367 |
Bismuthate is an ion. Its chemical formula is BiO. It has bismuth in its +5 oxidation state. It is a very strong oxidizing agent. It reacts with hot water to make bismuth(III) oxide and oxygen. It also reacts with acids. Sodium bismuthate is the most common bismuthate. It is one of the few sodium compounds that does not dissolve in water. | https://en.wikipedia.org/wiki?curid=29927036 |
C6H14O12P2 The molecular formula CHOP may refer to: | https://en.wikipedia.org/wiki?curid=29927807 |
C6H13O10P The molecular formula CHOP (molar mass: 276.134 g/mol) may refer to: | https://en.wikipedia.org/wiki?curid=29928070 |
5-Deoxyinositol (quercitol) is a cyclitol. It can be found in wines aged in oak wood barrels. It can also be found in "Quercus" sp. (oaks) and in "Gymnema sylvestre". It is different from , a synonym of quercetin. | https://en.wikipedia.org/wiki?curid=29930851 |
Orbital overlap In chemical bonds, an orbital overlap is the concentration of orbitals on adjacent atoms in the same regions of space. can lead to bond formation. The importance of orbital overlap was emphasized by Linus Pauling to explain the molecular bond angles observed through experimentation and is the basis for the concept of orbital hybridization. Since "s" orbitals are spherical (and have no directionality) and "p" orbitals are oriented 90° to each other, a theory was needed to explain why molecules such as methane (CH) had observed bond angles of 109.5°. Pauling proposed that s and p orbitals on the carbon atom can combine to form hybrids (sp in the case of methane) which are directed toward the hydrogen atoms. The carbon hybrid orbitals have greater overlap with the hydrogen orbitals, and can therefore form stronger C–H bonds. A quantitative measure of the overlap of two atomic orbitals Ψ and Ψ on atoms A and B is their overlap integral, defined as where the integration extends over all space. The star on the first orbital wavefunction indicates the complex conjugate of the function, which in general may be complex-valued. The overlap matrix is a square matrix, used in quantum chemistry to describe the inter-relationship of a set of basis vectors of a quantum system, such as an atomic orbital basis set used in molecular electronic structure calculations. In particular, if the vectors are orthogonal to one another, the overlap matrix will be diagonal | https://en.wikipedia.org/wiki?curid=29943244 |
Orbital overlap In addition, if the basis vectors form an orthonormal set, the overlap matrix will be the identity matrix. The overlap matrix is always "n"×"n", where "n" is the number of basis functions used. It is a kind of Gramian matrix. In general, each overlap matrix element is defined as an overlap integral: where In particular, if the set is normalized (though not necessarily orthogonal) then the diagonal elements will be identically 1 and the magnitude of the off-diagonal elements less than or equal to one with equality if and only if there is linear dependence in the basis set as per the Cauchy–Schwarz inequality. Moreover, the matrix is always positive definite; that is to say, the eigenvalues are all strictly positive. "Quantum Chemistry: Fifth Edition", Ira N. Levine, 2000 | https://en.wikipedia.org/wiki?curid=29943244 |
C17H16O9 The molecular formula CHO may refer to : | https://en.wikipedia.org/wiki?curid=29946093 |
Chlorophyll fluorescence is light re-emitted by chlorophyll molecules during return from excited to non-excited states. It is used as an indicator of photosynthetic energy conversion in higher plants, algae and bacteria. Excited chlorophyll dissipates the absorbed light energy by driving photosynthesis (photochemical energy conversion), as heat in non-photochemical quenching or by emission as fluorescence radiation. As these processes are complementary processes, the analysis of chlorophyll fluorescence is an important tool in plant research with a wide spectrum of applications. Upon illumination of a dark-adapted leaf, there is a rapid rise in fluorescence from Photosystem II (PSII), followed by a slow decline. First observed by "Kautsky et al., 1960", this is called the Kautsky Effect. This variable rise in chlorophyll fluorescence rise is due to photosystem II. Fluorescence from photosystem I is not variable, but constant. The increase in fluorescence is due to PSII reaction centers being in a "closed" or chemically reduced state. Reaction centers are "closed" when unable to accept further electrons. This occurs when electron acceptors downstream of PSII have not yet passed their electrons to a subsequent electron carrier, so are unable to accept another electron. Closed reaction centres reduce the overall photochemical efficiency, and so increases the level of fluorescence. Transferring a leaf from dark into light increases the proportion of closed PSII reaction centres, so fluorescence levels increase for 1–2 seconds | https://en.wikipedia.org/wiki?curid=29946595 |
Chlorophyll fluorescence Subsequently, fluorescence decreases over a few minutes. This is due to; 1. more "photochemical quenching" in which electrons are transported away from PSII due to enzymes involved in carbon fixation; and 2. more "non-photochemical quenching" in which more energy is converted to heat. Usually the initial measurement is the minimal level of fluorescence, formula_1. This is the fluorescence in the absence of photosynthetic light. To use measurements of chlorophyll fluorescence to analyse photosynthesis, researchers must distinguish between photochemical quenching and non-photochemical quenching (heat dissipation). This is achieved by stopping photochemistry, which allows researchers to measure fluorescence in the presence of non-photochemical quenching alone. To reduce photochemical quenching to negligible levels, a high intensity, short flash of light is applied to the leaf. This transiently closes all PSII reaction centres, which prevents energy of PSII being passed to downstream electron carriers. Non-photochemical quenching will not be affected if the flash is short. During the flash, the fluorescence reaches the level reached in the absence of any photochemical quenching, known as maximum fluorescence formula_2. The efficiency of photochemical quenching (which is a proxy of the efficiency of PSII) can be estimated by comparing formula_2 to the steady yield of fluorescence in the light formula_4 and the yield of fluorescence in the absence of photosynthetic light formula_1 | https://en.wikipedia.org/wiki?curid=29946595 |
Chlorophyll fluorescence The efficiency of non-photochemical quenching is altered by various internal and external factors. Alterations in heat dissipation mean changes in formula_2. Heat dissipation cannot be totally stopped, so the yield of chlorophyll fluorescence in the absence of non-photochemical quenching cannot be measured. Therefore, researchers use a dark-adapted point (formula_7) with which to compare estimations of non-photochemical quenching. formula_1: Minimal fluorescence (arbitrary units). Fluorescence level of dark-adapted sample when all reaction centers of the photosystem II are open. formula_2: Maximal fluorescence (arbitrary units). Fluorescence level of dark-adapted sample when a high intensity pulse has been applied. All reaction centers of the photosystem II are closed. formula_10: Minimal fluorescence (arbitrary units). Fluorescence level of light-adapted sample when all reaction centers of the photosystem II are open; it is lowered with respect to formula_1 by non-photochemical quenching. formula_12: Maximal fluorescence (arbitrary units). Fluorescence level of light-adapted sample when a high intensity pulse has been applied. All reaction centers of the photosystem II are closed. formula_13: Steady-state terminal fluorescence (arbitrary units). A steady-state fluorescence level decreased (= quenched) by photochemical and non-photochemical processes. formula_14: Half rise time from formula_1 to formula_2. formula_17 is variable fluorescence. Calculated as formula_17 = formula_2 - formula_1 | https://en.wikipedia.org/wiki?curid=29946595 |
Chlorophyll fluorescence formula_21 is the ratio of variable fluorescence to maximal fluorescence. Calculated as formula_22. This is a measure of the maximum efficiency of PSII (the efficiency if all PSII centres were open). formula_21 can be used to estimate the potential efficiency of PSII by taking dark-adapted measurements. formula_24 measures the efficiency of Photosystem II. Calculated as formula_25 = <math>,\frac | https://en.wikipedia.org/wiki?curid=29946595 |
European Coatings Journal The is an English-language trade magazine for the coatings industry. It is published by Vincentz Network. It was established in 1986. According to the Informationsgemeinschaft zur Feststellung der Verbreitung von Werbeträgern, it reached about 33.000 readers per issue in 2010. The "European Coatings Journal" is an official partner of the Conseil Européen de l'Industrie des Peintures, des Encres d'Imprimerie et des Couleurs d'Arts, the European coatings association. Topics from research and development as well as topics from coatings production and raw materials are dealt with in extensive articles. There is always one main topic (e.g. powder coating, additives or water based coatings). The articles are written by external professionals and revised by the editorial team. Next to professional articles which compose the main part of the journal, there are some permanent sections: The "European Coatings Journal" publishes preliminary reports and news reports about subject specific fairs and congresses (e.g. FATIPEC-Congress, European Coatings Show). Market studies of various key markets are published at irregular intervals. The "EC Directory" is a buyer's guide for the coatings industry. It includes company profiles and an overview of the most important organizations and institutes. List of magazines in Germany | https://en.wikipedia.org/wiki?curid=29947591 |
Phase telescope A phase telescope or Bertrand lens is an optical device used in aligning the various optical components of a light microscope. In particular it allows observation of the back focal plane of the objective lens and its conjugated focal planes. The phase telescope/Bertrand lens is inserted into the microscope in place of an eyepiece to move the intermediate image plane to a point where it can be observed. Phase telescopes are primarily used for aligning the optical components required for Köhler illumination and phase contrast microscopy. For Köhler illumination the light source and condenser diaphragm should appear in focus at the back focal plane of the objective lens. For phase contrast microscopy the phase ring (at the back focal plane of the objective) and the annulus (at the back focal plane of the condenser lens) should appear in focus and in alignment. Bertrand lenses find use in creating interference figures and assisting in aligning a microscope to generate interference figures. The name "Bertrand lens" commemorates French mineralogist Emile Bertrand (1844-1909), for whom the mineral Bertrandite is also named. | https://en.wikipedia.org/wiki?curid=29949355 |
Nesmeyanov Institute of Organoelement Compounds The A.N. of Russian Academy of Sciences (INEOS RAS) () was founded in 1954 by a prominent scientist, the President of the USSR Academy of Sciences, academician A. N. Nesmeyanov (1899–1980), who was a "father" of the modern chemistry of organoelement and organometallic compounds. He headed the Institute for 26 years. Major directions of research of the Institute are the following: Laboratories of Organoelement Profile, Laboratories of Polymer Profile, and Laboratories of Physical Profile. The successors of A.N. Nesmeyanov as directors of the Institute were the Members of the Academy of Sciences of USSR and afterwards the Members of the Russian Academy of Sciences: At present INEOS RAS is a large research centre having ~660 employees with 564 scientific researchers of various levels. 77 Professors, holding Doctor of Science (Dr. Sci.) degree, and 248 researchers having PhD degree are actively working at INEOS RAS. INEOS RAS is an internationally recognized research establishment, where the chemistry of organoelement and macromolecular compounds is developed. Its reputation as a scientific centre in chemistry is very high both in Russia and abroad. Many outstanding scientists who initiated new directions in organic and organoelement chemistry, polymer chemistry, physical chemistry, and physics, such as K.A. Andrianov, I.L. Knunyants, V.V. Korshak, I.V. Obreimov, M.E. Vol’pin, M.I. Kabachnik, O.A. Reutov, D.N. Kursanov, Yu.T. Struchkov, R.Kh. Freydlina, A.I .Kitaigorodsky, T.A. Mastryukova, M.Yu | https://en.wikipedia.org/wiki?curid=29949856 |
Nesmeyanov Institute of Organoelement Compounds Antipin and many others have been fruitfully working at INEOS RAS. For recent years the scientific activities of the Institute have been supported by ~20 international grants (7th European Commission program, Swiss National Science Foundation (SNCF), Deutsche Forschungsgemeinschaft (DFG), etc.), 50-60 grants from the Russian Foundation for Basic Research (RFBR), more than 50 grants from the Presidium of the RAS and Department of Chemistry and Material Sciences of the RAS. INEOS is also incorporated in six Federal Scientific and Technical Programmes. Six young scientists received personal Grants from the President of Russian Federation for Government support of Young Russian Scientists and four scientists received the grants from Foundation for Russian Science Support. One of the important part of the INEOS RAS activity aimed at the future is the training of young specialists of high qualification. In 2003, a scientific educational centre “INEOS Department” was founded within the framework of the RAS Presidium Programme “Support for Young Scientists” and according to the resolution of the INEOS RAS Scientific Council. The goal of the Centre is to train a new generation of young highly educated specialists of wide profile who know modern research methods, on the basis of the priority scientific line performed at INEOS RAS. The results of scientific research carried out at the Institute since 2008 have been summarized in more than 1500 scientific papers and 16 monographs | https://en.wikipedia.org/wiki?curid=29949856 |
Nesmeyanov Institute of Organoelement Compounds For the past five years, mutually beneficial contracts have been signed with numerous universities, institutes and industrial centres in Russia and abroad. Outstanding foreign scientists and representatives of science-oriented companies are frequent visitors to INEOS RAS. The Institute participates in several joint projects with foreign institutions and companies directed to research collaboration and commercialization of “know-how” and new synthesized products. Within the recent years INEOS RAS participated in organization of more than 20 conferences, symposia, and seminars. The list of most important international meetings includes the following international conferences: INEOS RAS includes 34 laboratories and 11 research teams: Division of Organoelement compounds Division of Macromolecular compounds Laboratories of Physical Research Methods and Computing Chemistry Awards and prizes in last years 2003 year 2004 year 2005 year 2006 year 2007 year 2008 year 2009 year 2010 year 2013 year 2016 year Historical background At the INEOS's earliest stages it was implied that synthetic work in organoelement and macromolecular chemistry should be combined with the necessity of relevant theoretical and physical investigations, and therefore many laboratories at INEOS are carrying out their research at the junction of several branches in chemistry and physics. This determines “the points of growth” which lead to progress in modern science and technology as A.N. Nesmeyanov used to say | https://en.wikipedia.org/wiki?curid=29949856 |
Nesmeyanov Institute of Organoelement Compounds Apart from traditional, scientific disciplines (to which the organoelement chemistry itself belongs too), valuable experience accumulated during these years has given rise to a series of new scientific fields which are characterized by a unique combination of organic, organoelement, coordination, physical chemistry, and chemistry of the macromolecular and natural biologically active compounds. Thus, new branches in chemistry have appeared at the junction of organic, organometallic and coordination chemistry, namely the chemistry of the organic derivatives of the transition metals, p-complexes and clusters, asymmetric catalysis etc. The unique properties of these new compounds made it possible to develop new organometallic catalysts, to study an activation of small molecules, including molecular nitrogen, hydrocarbons, etc. Combination of organic and organoelement chemistry with the experimental and theoretical methods of physical chemistry promoted the development of relevant studies in reactivity, structural chemistry, catalysis and molecular dynamics of organoelement compounds. The interaction between organophosphorus chemistry, biochemistry, pharmacology, and toxicology made it possible to unlock the secrets of the mechanisms responsible for the action of organophosphorus compounds upon biological structures and living organisms. Significant progress has been also achieved in the field of new tumor-selective anticancer preparations and physiologically active organofluorine compounds | https://en.wikipedia.org/wiki?curid=29949856 |
Nesmeyanov Institute of Organoelement Compounds The works at the junction of the organic and inorganic chemistry, studies of the processes of polymer formation as well as structure—property relations, brought about the chemistry of polymers with organoelement and inorganic molecular chains and opened the routes to novel classes of linear and network polymers. New materials with valuable thermal, catalytic, sorptional and electro-physical properties, engineering plastics, thermostable composites and adhesives, membranes and polymers for electronics and medicine have been made up on the basis of these polymers. | https://en.wikipedia.org/wiki?curid=29949856 |
Chemistry: A Volatile History is a 2010 BBC documentary on the history of chemistry presented by Jim Al-Khalili. It was nominated for the 2010 British Academy Television Awards in the category Specialist Factual. Only in the last 200 years have we known what an element is – a substance that cannot be broken down further by chemical reaction. The Ancient Greeks, with no way of breaking open substances, could only base their ideas of the elements on what they could see: Earth, Fire, Water and Air. In the 16th century alchemists were busy trying to turn base metals like lead, into gold. It was the Swiss alchemist and surgeon Paracelsus who first challenged the Ancient Greek idea of four elements. In 1526 Paracelsus was in Basel, when the famous printer Frobenius was told he would have to have his leg amputated in a life-saving operation. Instead of accepting the received wisdom, he called upon Paracelsus who cured him in the unconventional way of using his alchemical knowledge. This established him as a radical thinker, giving weight to his ideas, principal amongst which was the idea that the world was actually made of three elements: the tria prima comprising salt, sulphur and mercury. Paracelsus did not succeed in convincing the establishment – instead he managed to enrage them by burning their established medical texts, and eventually had to flee Switzerland for Germany. It was, however, the alchemical pursuit for gold that led to the first breakthrough in the hunt for new elements | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History In 1669 Hennig Brand was looking for a way of extracting gold from the human body, and struck upon the idea of using urine, thinking that urine might contain some part of the ‘life force’ vital to sustaining human life. To get rid of the unimportant parts, primarily water, Brand boiled the urine for several days until he was left with a thick paste. Finally, fragments of a substance emerged which burned brighter than any Medieval candle available at the time, but which left the vessel it burnt in cold: Brand named this new substance icy noctiluca – ‘cold night light’. Soon after its discovery, icy noctiluca toured the Royal Houses of Europe and in 1677 it came before the Royal Society in London, then under the chairmanship of Charles II, where one of its members decided to investigate. In his book "New Experiments and Observations Made Upon the Icy Noctiluca" Robert Boyle describes an experiment in which sulphur and phosphorus powders are mixed causing them to burn fiercely. This discovery was the basis for the invention of the match. Phosphorus, as icy noctiluca is now known, is used in everything from match heads to toothpaste and ultimately in the Second World War bombs which destroyed the very city in which Brand discovered it – Hamburg. Whilst Brand never discovered gold, his accidental discovery of the element now known as phosphorus gave rise to the idea that elements could be hidden inside other substances | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History More than a decade earlier in 1661, a year after the Royal Society opened, Boyle deposited "The Sceptical Chymist" in its vaults. This book is usually regarded as the turning point that signaled the transition from alchemy to chemistry. "The Sceptical Chymist" was innovative in several ways: it was not written in Latin, as had been the tradition for alchemist books, but in English; it dispensed with the old chemical symbols for various elements, using English names instead; and most crucially it was actually published, as opposed to kept secret. Boyle was willing to share his discoveries to allow others to build on his work and further the scientific understanding of the elements. He wanted to put alchemy on a more scientific footing – ditching the metaphysical baggage it had brought with it from the previous century. Unfortunately, this new age of chemical enlightenment was fraught with blind alleys. In 1667 the German scientist Johann Becker proposed that fire was caused by an ethereal, odourless, tasteless, colourless, weightless entity called phlogiston. The idea was that phlogiston causes things to burn, reducing them to their pure form. For example, burning wood releases phlogiston, leaving the pure form of wood – ash, therefore wood is composed of ash (pure wood) and phlogiston. Phlogiston was accepted as scientific truth, paralysing the scientific community's ability to discover more, true elements. One scientist even claimed to have isolated phlogiston | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History A major shareholder in the Bank of England with royal connections, Henry Cavendish was a painfully shy character, who made the vital chemical contribution of discovering the first elemental gas. He added some zinc to spirit of salt (hydrochloric acid) and collected the evanescence given off as bubbles. The gas he collected was tasteless, odourless and colourless, and moreover it produced a squeaky pop in the presence of a flame – this led Cavendish to name the gas inflammable air, which he believed to be one and the same as phlogiston. Cavendish, though he did not realise it, made an important observation about burning phlogiston in air; a dewy liquid was formed on the inside of the glassware: water. This should have had enormous repercussions for the whole scientific community in the 1700s, who still believed water to be an elemental substance. Yet, if water could be "made" by burning inflammable air, then water is "not" an element, but a compound. However, it simply did not occur to Cavendish that water was a compound – instead he assumed that the airs contained a form of water, which phlogiston modified into liquid, elemental water. Phlogiston had given the Ancient Greek idea of water as an element a brief reprieve, but the Greek system was now under heavy scrutiny as the Royal Society commissioned its members to investigate the invisible airs | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History By the mid-1700s there were three known ‘airs’: It was this last air which caught the attention of Joseph Priestley, a Unitarian minister whose favourite pastime was the investigation of airs – specifically, fixed air, given off by the fermentation process in breweries. Priestley's passion for science led to an invitation to Bowood House, to tutor the children of Lord Shelburne. This was an excellent opportunity, given that Priestley did not have the money of earlier chemists like Boyle and Cavendish, and would still be free to pursue his own research. In 1774 Priestley performed a hugely important experiment: he heated mercuric calc and collected the gas given off. He discovered that this gas was able to relight the embers of a previously lit wooden splint. He concluded that the splint was introducing phlogiston to the gas, only after which could it burn, therefore the gas must be ‘without phlogiston’ – this led Priestley to name it dephlogisticated air. In October 1775 Priestley accompanied Lord Shelburne on a trip to Paris where they were invited to dine with the preeminent scientists of the time. It is here that Priestley met the French scientist Antoine Lavoisier. Priestley told Lavoisier all the details of his experiments upon the production of dephlogisticated air. Unlike Priestley, Lavoisier had one of the best equipped laboratories in Europe and now turned his attention to the highly accurate measurement of the masses of substances before and after they were heated | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History Lavoisier weighted a sample of tin, then reweighed after he had heated it and found it had increased in mass. This was an unexpected result given that the tin was thought to have released phlogiston during the burning process. Lavoisier was struck with a ground-breaking thought – maybe the tin had absorbed something from the air, making it heavier, but if so, what? To investigate this further, Lavoisier reran Priestley's experiment in reverse – he heated some mercury in a sealed container until it turned into mercuric calc and measured the amount of air absorbed. He then heated the mercuric calc and measured the amount of air released and discovered the quantities were the same. Lavoisier realised that something was absorbed from the air when mercury was heated to make mercuric calc, and that same gas was released when the mercuric calc was heated. Lavoisier concluded that this gas was unrelated to phlogiston, but was in fact a brand new element, which he named oxygen. Lavoisier had successfully dispensed with the need for the theory of phlogiston and recognised Priestley's ‘dephlogisticated air’ as the element oxygen. Despite the fact it was Priestley's original work that laid the foundations for his discovery, Lavoisier claimed he had discovered oxygen; Priestley, after all, had failed to recognise it as a new element. Lavoisier went on to give science its first definition of an element: a substance that cannot be decomposed by existing chemical means | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History He also set about drawing up a list of all the elements – now 33 elements replaced the ancient four. His list was grouped into four categories: gases, non-metals, metals and earths. On top of this, Lavoisier created a classification system for the ever-increasing array of chemicals being discovered. As mentioned, ‘dephlogisticated air’ became oxygen, ‘inflammable air’ became hydrogen, but the nomenclature of compounds was also put on a more logical footing as ‘oil of vitriol’ became sulphuric acid, ‘philosophical wool’ became zinc oxide and ‘astringent mars saffron’ became iron oxide. Unfortunately, whilst Lavoisier had rid the world of the phlogiston paradigm, he introduced two new erroneous elements now known to be pure energy: lumière and calorique; light and heat. In revenge for his sympathies with the revolutionaries in France, Priestley's home in England was targeted by arsonists in 1791, luckily he escaped thanks to a tip-off, but decided to flee to America. Lavoisier's contributions to science were cut short in 1794 by the revolutionaries, who arrested him on grounds of being an enemy of the French people, and had him guillotined. In 1807, the Professor of Chemistry at the Royal Institution in London was the Cornishman Humphry Davy. He was investigating crystalline salts of potash because he was unconvinced potash was an element, but by the end of the previous century, Lavoisier had been unable to break it down further | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History Since then however, the first electric battery had recently been invented (rows of metal plates and cardboard soaked in saltwater). Although scientists were aware that the production of a continuous electric current was due to some property of the metals, Davy believed that a chemical reaction was taking place. If that was true, then maybe the reverse was also true: an electric current could cause a chemical reaction. Davy heated the potash until it was liquid, then introduced two electrodes and passed a current through the molten potash. A lilac flame was observed, the result of successfully breaking down potash into its constituent elements – one of which, was the previously never before seen element potassium. Davy went on to add six new elements to Lavoisier's list, as well as confirming that substances like chlorine and iodine were also elements. By the time of his death in 1829 the idea of the elements was firmly established, 55 separate elements had been discovered, and the world had a new science: Chemistry. At the beginning of the 19th century only 55 of the 92 naturally occurring elements had been discovered. Scientists had no idea how many more they might find, or indeed if there were an infinite number of elements. They also sought to answer a fundamental question, namely: is there a pattern to the elements? Scientists had recently discovered that when elements combine to form compounds, they always do so in the same proportions, by weight | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History John Dalton thought that for this to happen, each element had to be made of its own unique building blocks, which he called atoms. Dalton suggested that everything in the universe was made of atoms, and that there are as many kinds of atoms as there are elements, each one with its own signature weight. Based on these ideas, working completely alone, Dalton attempted to impose some order on the elements by drawing up a list, where each element was represented by an alchemical-looking symbol, ordered by atomic weight. Although Dalton did not get all his atomic weights correct, he was pointing science in the right direction. Sadly, in the early 1800s few scientists accepted the idea that elements had different weights. The Swedish scientist Jöns Jacob Berzelius was one of the few scientists who strongly believed in the idea of atomic weights, and thought that knowing as much as possible about their weights was vitally important. When he heard of Dalton's theory, he set about the gargantuan task of measuring the atomic weight of every single known element – without any proof that Dalton's atoms actually existed. This was even more challenging than it first seems once you consider the fact that very little of the chemical glassware necessary for such precise measurements had been invented. Berzelius had to manufacture much of it himself. Berzelius’ experiences with glass-blowing had an additional bonus, in 1824 he discovered that one of the constituents of glass was a new element – silicon | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History Having already discovered three other elements prior to silicon: thorium, cerium and selenium, Berzelius spent the next ten years obsessively measuring more than two thousand chemical compounds in pursuit of accurate atomic weights for the elements. Eventually Berzelius had remarkably accurate atomic weights for 45 elements; his value for chlorine was accurate to within 0.2% of the value we know today. However, by the time Berzelius had produced his results, other scientists were now measuring atomic weights – and getting conflicting results. In fact, scientists were looking for all sorts of patterns throughout the elements. One such pattern hunter was German chemist Johann Döbereiner. He believed the key to understanding the elements lay not with their atomic weights but with their chemical properties. He noticed that one could often single out three elements that exhibited similar properties, such as the alkali metals, which he called triads. The problem was that Döbereiner's triads only worked for a few of the elements and got scientists no further than atomic weights. In 1848 a huge fire destroyed the factory of the widow Maria Mendeleeva. Facing destitution she decided to embark on the 1,300 mile journey from Western Siberia to St Petersburg – walking a significant portion of the route – so her son Dmitri Mendeleev could continue his education in the capital of the Russian Empire | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History At the time the scientific community was grappling with the problem of how to bring order to the 63 elements that were now known. Mendeleev was still a student when he attended the world's first international chemistry congress – convened to settle the confusion surrounding atomic weights. Sicilian chemist Stanislao Cannizzaro was still convinced that atomic weights held the key to the order of the elements and had found a new way of measuring them. Cannizzaro knew that equal volumes of gases contain equal numbers of particles, therefore instead of working with solids and liquids and all the unreliability that entails, he proposed measuring the densities of gases to measure the weights of individual gaseous atoms. Whereas Berzelius’ results had failed to convince anyone, Cannizzaro's method set an agreed standard for measuring atomic weights accurately. Chemists soon found that even with accurate atomic weights, the elements still seemed unordered, but then, a solitary English chemist made a curious discovery. In 1863 John Newlands noticed that when ordered by weight, every eighth element seemed to share similar properties, such as carbon and silicon in the sequence: carbon, nitrogen, oxygen, fluorine, sodium, magnesium and silicon. He called this a Law of Octaves. Three years later, in 1866, he presented his ideas to the Chemical Society, unfortunately for Newlands, the musical analogy was not well received – the audience suggesting he might as well have ordered the elements alphabetically | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History Today, Newlands’ Octaves are known as the Law of Periodicity, and Mendeleev was thinking along the same lines. By 1869 Mendeleev had been trying to find an order for the elements for a decade. One day he struck upon the idea of making up a pack of cards with the elements’ names on and began playing a game he called ‘chemical solitaire’. He began laying out the cards, over and over, just to see if he could form a pattern where everything fitted together. To date, chemists had tried to group elements in one of two ways: Mendeleev's genius was to combine those two methods together. However, the odds were stacked against him – little more than half the known elements had been discovered: he was playing with an incomplete deck of cards. He stayed up for three days and nights then, finally, on 17 February 1869, he fell asleep and dreamt of all 63 known elements laid out in a grand table. Mendeleev's table reveals the relationship between all the elements in their order: Notice carbon and silicon are in Group IV and the volatile gases fluorine, chlorine and bromine are in Group VII. Mendeleev was sufficiently confident in the layout of his table that he was willing to leave gaps for unknown elements to make the pattern fit – believing other elements would later be discovered that filled the gaps. So, for Mendeleev to be vindicated, the gaps needed to be filled, and luckily, in 1859, new instrumentation had been developed for discovering elements | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History Robert Bunsen knew that when certain elements burned in the flames of his burner they each turned the flame a different colour. Copper burned green, strontium red and potassium lilac – Bunsen wondered if every element had a unique colour. Bunsen was joined in his research by Gustav Kirchhoff. Kirchhoff used the concept of the dispersion of white light by a prism in the invention of the spectroscope, a device with a prism at its centre which split the light from Bunsen's flames into distinct bands of its constituent colours – the element's spectral lines. Kirchhoff and Bunsen realised these spectral lines were unique to each element, and, using this technique they discovered two new elements, cesium and rubidium. In 1875, the Parisian chemist Paul Emile Lecoq de Boisbaudran used a spectroscope to discover a new metallic element. It was a silvery-white, soft metal with an atomic weight of 68, which he named gallium, after his native France. It also turned out to have a very low melting point, thus matching all the expected properties of the element Mendeleev expected to fill the gap he had left after zinc; indeed, this is exactly where the element was placed in the periodic table. Even though Mendeleev had left the necessary gap for gallium as well as other elements, it was becoming clear there was an entire group that was missing altogether. In 1868, the French astronomer Pierre Janssen travelled to India in time for the total solar eclipse that occurred in August of that year | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History As well as his telescope, he also went equipped with a spectroscope, to study the spectral lines of the light emitted from the sun. Normally, due to the intensity of sunlight many weaker spectral lines are not visible next to the extreme brightness of the stronger lines. Janssen hoped that he would observe more spectral lines during the eclipse when the sun's light was less intense. The eclipse allowed Janssen to observe a spectral line never seen before, which was not associated with any known element. The same spectral line was confirmed by the English astronomer Norman Lockyer, who thinking the element only existed in the sun, named it helium, after the Greek Sun God. However, it wasn’t long before another British scientist had discovered helium on Earth. By dissolving the radioactive ore cleveite in acid, William Ramsay was able to collect a gas trapped within the rock, which had an atomic weight of 4, and the same spectral lines which Lockyer had observed: helium. Prior to this, Ramsay had already isolated a new gas from the atmosphere; argon, with an atomic weight of 40. A problem now arose – Mendeleev had not left any gaps which were suitable for either of these two new elements, which led Ramsay to conclude an entire group was missing from the periodic table – only two of whose members were now known to exist, helium and argon. Ramsey successfully discovered all the other stable elements in the group which he named neon (Greek for new), krypton (Greek for hidden) and xenon (Greek for stranger) | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History All the elements of this new group had one overwhelming characteristic; their lack of reactivity. It was this particular characteristic that brought to mind a name for the new group: the noble gases. Mendeleev's periodic table had brought order to all the elements, allowing him to make predictions that future scientists tested and found to be true. By the time he died he was world-renowned in chemistry. His periodic table was set in stone in St Petersburg and an element was eventually named after him: mendelevium. The periodic table does not however tell us why some elements are highly reactive, others completely inert, why some are volatile, whilst others less so. It wasn’t until the beginning of the 20th century that an entirely different branch of science began to unravel the answers to these questions. In 1909, the physicist Ernest Rutherford proposed the structure of the atom was like that of a solar system: mostly empty space with electrons floating around a dense nucleus. Subsequently, the Danish Physicist Niels Bohr introduced the idea that electrons occupied "fixed shells" around the nucleus, which was further developed when it was suggested that each such shell could only accommodate a fixed number of electrons: 2 in the first shell; 8 in the second shell; 18 in the third shell, and so on, each shell holding an increasing number of electrons | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History The chemical behaviour of all elements is explained by the number of electrons in their outer shells: to increase the energetic stability of their electron configurations atoms have a tendency to gain or lose electrons in such a way so as to achieve a full outer shell. Sodium, with 11 electrons – one in its outer-most occupied shell, will transfer an electron in the presence of fluorine to its outer-most occupied shell, which contains seven electrons. The result is both sodium and fluorine now have a full outer shell, and Sodium Fluoride is formed. This theory explained why all elements react in the way they do and why some formed the compounds they do, while others did not. It also explained why elements had the physical properties they did, which in turn explained why the periodic table had the shape it did. However, there was one fundamental question left unanswered: how many elements were there – could there be an infinite number of elements between Hydrogen and Uranium? Early 20th century chemist Henry Moseley speculated that the answer to the number of protons lay in the nucleus. By firing a radioactive source at copper, he was able to knock electrons from their atoms, releasing a burst of energy in the form of an x-ray. When measured, the x-rays always had the same energy, unique to copper. He discovered each element released x-rays of different energies. Moseley's brilliance was to realise the x-ray energy is related to the number of protons inside the atom: the atomic number | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History Because this is the number of protons, the atomic number must be a whole number – there cannot be any fractional values. Moseley realised it was the atomic number, not the atomic weight that determines the order of the elements. What's more, because the atomic number increases in whole numbers from one element to the next there can be no extra elements between Hydrogen (atomic number 1) and Uranium (atomic number 92) – there can only be 92 elements, there is no room for any more. Moseley was just 26 when he completed this research. Aged 27 he was killed in action during the First World War – shot through the head by a sniper. Just 92 elements combine to form all the compounds on Earth. Iron, when combined with chromium, carbon and nickel makes stainless steel. Glass is made of silicon and oxygen. Since prehistoric times, people have been engaging in ‘bucket chemistry’ – adding all sorts of chemicals together, just to see what would happen. As a result, many early discoveries in chemistry were accidental. In 18th century Prussia, Heinrich Diesbach was trying to produce a synthetic red paint. He started by heating potash (potassium carbonate), with no idea that his potash had been contaminated with blood. When heated, the proteins in blood are altered, allowing them to combine with the iron in the blood, whilst the carbonate reacts with the haemoglobin to produce a solid | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History After heating the resulting solid to an ash, filtering and diluting, Diesbach added green vitriol (iron sulphate) to create a complex ion: ferric ferrocyanide. Finally, adding spirit of salt (hydrochloric acid) draws out a brilliant colour: Prussian blue. Ever since seeing fireworks as a child, another German chemist, Justus von Liebig, had become obsessed with trying to better understand the elements by creating explosive combinations. Specifically, he was interested in the explosive compound silver fulminate. In 1825 he read a paper written by Friedrich Wöhler in which he describes a compound called silver cyanate, made in equal parts of silver, carbon, nitrogen and oxygen, which he described as harmless and stable. Von Liebig immediately wrote back a furious letter condemning Wöhler as a hopeless analyst: those elements combined in equal proportions were exactly what made the explosive silver fulminate. Instead of backing down, Wöhler challenged von Liebig to make silver cyanate for himself. The results would have astounded him – the same elements that combined according to von Liebig's method, when combined according to Wöhler's method made two completely different compounds. Wöhler and von Liebig had inadvertently discovered isomerism: the same number of atoms of the same elements "combining in different ways" to make "different" compounds. In time, this would explain how just 92 elements could make the vast array of compounds we know today | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History Chemists started to realise that understanding the arrangement of atoms within compounds was crucial if they wished to design new compounds, and the first step in this direction was taken by studying carbon. In 1796 Smithson Tennant was experimenting on diamonds when he decided to burn one. Using only sunlight and a magnifying glass he managed to ignite a diamond sufficiently for it to produce a gas, which he collected and was able to identify as carbon dioxide. Having started with only diamond and oxygen, and produced a gas which contains only carbon and oxygen, Tennant had discovered that diamonds are made of carbon. Unaware of atomic theory at the time, scientists were unable to explain how carbon, already known to exist as one of the softest substances in the form of graphite, could also be the sole constituent element of the hardest known substance: diamond. Exactly 50 years later, a young Scottish chemist discovered there are no prizes in Science for coming second. In 1856 Archibald Scott Couper went to work for a French chemist, Charles-Adolphe Wurtz. Whilst in Paris he came up with the idea of links between atoms that could explain how individual atoms formed compounds. He called these links bonds | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History Somehow, Couper realised that carbon can form four bonds, thereby attaching itself with different strengths to other carbon atoms in a compound: The ability of carbon to form four bonds also means it can exist in a huge variety of chemical structures, such as long chains and even rings, making it a rarity amongst the elements. This helped to explain the abundance of carbon in all life forms, from protein and fat, to DNA and cellulose, and why carbon exists in more compounds than any other element. All that remained for Couper was to get his paper published... Friedrich Kekulé was a German scientist who spent some time studying in London. It was apparently whilst riding a London bus he struck upon the idea of atoms ‘holding hands’ to form long chains. Kekulé rushed to compose a paper formalising his ideas on an equivalent theory of chemical bonds. Meanwhile, in Paris, Wurtz had been slow to publish Couper's paper and Kekulé, whose work appeared in print first, claimed all the credit. When Couper discovered Wurtz had delayed in sending his paper to be published he flew into a rage and was promptly expelled from the laboratory by Wurtz. The crushing disappointment at having lost out on his chance of scientific recognition led him first to withdraw from Science and then to suffer a nervous breakdown. He spent years in and out of an asylum | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History However, now that scientists were beginning to understand the way carbon combines with itself and other elements, it was possible to create new compounds by design and industrial chemistry was born. Two decades after the world's first plastic – Bakelite – had been invented in 1907, Wallace Carothers successfully drew off a fibre from the interface of two liquids: hexane-1,6-diamine and decanedioyl-dichloride, which could be spun into a very fine, very strong thread. It was given the name nylon. Shockingly, only three weeks after the patent for nylon had been filed, a depressed Carothers slipped another carbon based compound into his own drink, potassium cyanide, and killed himself. Evidently, industrial chemistry wasn’t without its downsides, and one chemist was arguably responsible for single-handedly polluting the entire Earth with lead. In his capacity as an engineer with General Motors, Thomas Midgley experimented with a myriad of different compounds, which he added to petrol in an attempt to prevent engines from knocking. Eventually, he discovered one compound that worked brilliantly: tetraethyllead. By the 1970s the use of leaded petrol was ubiquitous worldwide, but research was emerging about the damage that it was doing to humans and the environment. In 1983, a Royal Commission asked the question: "Is there any part of the Earth’s surface, or any form of life that remains uncontaminated?" Today nearly all petrol is unleaded, although lead lives on in motor vehicles in their batteries | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History In 1896 the French scientist Henri Becquerel was working with uranium crystals when he found UV light made them glow. Leaving the uranium crystals on an unexposed photographic plate overnight, he returned the next morning to discover they had caused the part of the plate they were sat on to develop. Becquerel correctly reasoned the only source of energy that could have caused this was the crystals themselves. He had discovered radioactivity, and a young Polish scientist began to investigate. Marie Curie began her investigations by testing a uranium ore called pitchblende with an electrometer. She discovered it was four times more radioactive than pure uranium, and wondered if this was due to the presence of an even more radioactive element in the pitchblende. Curie began stockpiling tonnes of pitchblende, then in the most basic of workshops with primitive equipment she undertook a multitude of complex and dangerous procedures in an attempt to isolate this new element. In the event, Curie discovered two new elements, polonium named after her native Poland and radium. Whilst these were naturally occurring elements, they fuelled a scientific desire to create entirely new, artificial elements. At the beginning of the 20th century it was widely believed that atoms never change: an atom of one element stayed that way forever | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History Rutherford had already revealed the structure of an atom to consist mostly of empty space with a dense nucleus of protons at the centre, and Henry Mosley had shown that it is the number of protons that gives an atom its identity as a particular element. An atom of the element carbon has 6 protons, whilst an atom with 7 protons is one of nitrogen. Rutherford came to the conclusion that the number of protons in a radioactive element "could" change – through a process of decay where parts of the nucleus are ejected from the atom. Rutherford named these fragments of ejected nucleus alpha particles. Rutherford realised that if an atom is losing protons, its identity is changing at the same time, since an atom's identity is governed by its proton number. Radioactive decay causes atoms of one element to transmute into atoms of a "different" element. He then sought to artificially engineer a specific transmutation. Rutherford fixed a source of alpha particles – each of which contains two protons – at one end of a cylindrical chamber. At the other end he fixed a screen. Each time an alpha particle reached the screen it produced a flash. He then introduced nitrogen into the chamber and observed additional, different flashes on the screen. Occasionally, an alpha particle would collide with a nitrogen nucleus and get absorbed by it, knocking out a proton in the process. These protons then travelled on through the chamber to the screen to produce the additional flashes | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History However, the nucleus of nitrogen – having absorbed two protons but lost only one – had gained a proton and become a nucleus of oxygen. Rutherford's work gave hope to scientists trying to create new elements, but one final discovery about the atom was necessary. In 1932 the Cambridge scientist James Chadwick discovered the neutron – electrically neutral particles which also sit inside the nucleus along with the protons. Now in Italy, Enrico Fermi – nicknamed ‘the pope’ by his colleagues for his infallibility, realised the potential of the newly discovered neutron in the search for elements heavier than uranium. Until now, scientists had been bombarding uranium with alpha particles in the hope they would enter the nucleus. Unfortunately, this was very unlikely because both alpha particles and nuclei are positively charged – the alpha particles could never overcome the electrostatic repulsion of the nucleus. Fermi reasoned that because neutrons carried no electric charge, they would have a much better chance of penetrating the nucleus of a uranium atom. So Fermi set about firing neutrons at uranium. Fermi thought that this, coupled with his knowledge of beta decay, whereby an unstable nucleus attempts stabilisation by converting one neutron to a proton and ejecting a newly formed electron, would result in an element with one extra proton than uranium: element 93. Indeed, Fermi discovered elements he did not recognise | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History He tested for elements below uranium in the periodic table: radon, actinium, polonium, as far back as lead – it was none of these. So, in 1934, the infallible Fermi declared to the world he had created elements heavier than uranium. In 1938, a team of German scientists, led by Otto Hahn, decided to investigate Fermi's bold claim. Unfortunately for Fermi, they quickly disproved his assertion; one of the elements produced was barium, which, with 56 protons, was nowhere near the 92 protons the nucleus started with when it was uranium. Hahn wrote of his confusion to his colleague Lisa Meitner who, as an Austrian Jew, had recently fled Nazi Germany for Sweden. Over Christmas 1938, Meitner considered the problem of the uranium nucleus, which she reasoned, given its relative size, must be quite unstable. She decided to model the nucleus as a drop of water, ready to divide with the impact of a single neutron. She realised the nucleus had split in half, and both Fermi and Hahn had witnessed what is now known as nuclear fission. However, in doing the calculations for such an event, Meitner was unable to make the equations balance. She calculated that the products of the fission reaction were lighter than the initial uranium, by about one fifth of a proton. Somehow, a small amount of mass had disappeared. Then slowly, the solution to this discrepancy occurred to Meitner – Einstein and "E = mc" – the missing mass had been converted to energy | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History Meitner's work was published in 1939, but as well generating interest amongst the scientific community, Meitner's revelations were also coming to the attention of governments on the verge of war. Fuelled by fears Nazi Germany was investigating nuclear weapons of its own, scientists were assembled in America to work on the Manhattan Project aimed at creating the first atomic bomb. For an explosion to occur, there must be a rapid release of energy – a slow release of energy from uranium nuclei would give a uranium fire, but no explosion. Both sides poured their effort into creating the necessary conditions for a chain reaction. In 1942 Enrico Fermi, now living in America, successfully induced a chain reaction in uranium, but processing uranium for bombs was both difficult and costly. America had just come up with a different solution to win the atomic race. Now finally, scientists’ dream of creating an element beyond the end of the periodic table was about to be realized. In California, scientists were trying to create a new element heavier than uranium using cyclotron machines. This involved using huge magnets to steer atoms round in circles faster and faster until they reached a tenth of the speed of light, whereupon they were smashed into a uranium target. Edwin McMillan and Philip H. Abelson blasted uranium with a beam of particles to create the first synthetic element, heavier than uranium – element 93, which they named neptunium | https://en.wikipedia.org/wiki?curid=29952420 |
Chemistry: A Volatile History The next synthetic element, plutonium, quickly followed in 1941, which scientists realized was readily able to undergo fission in a way capable of producing the desired chain reaction. It was soon being made into a bomb. A mere seven years after the discovery of nuclear fission, on 6 August 1945, half a gram of uranium was converted into energy when the world's first atomic bomb was dropped on Hiroshima. As Lisa Meitner's calculations suggested, this conversion released energy equivalent to 13,000 tons of TNT. A plutonium bomb was dropped on Nagasaki three days later. Using one of the world's largest particle accelerators, scientists working at the Heavy Ion Research facility in Darmstadt, Germany, have so far confirmed the existence of element 112, which they have named copernicium, after Polish astronomer Nicholas Copernicus. These physicists have become the new chemists – testing the foundations of the periodic table, and hence our understanding of the universe, in light of new discoveries. In addition to producing new elements, scientists are also attempting to discern their properties. Copernicium is found to be a volatile metal that would be liquid at room temperature if enough were ever made – exactly what Mendeleev would predict for an element that sits directly beneath liquid mercury in the periodic table. It aired in the United States under the title "Unlocking the Universe." The full series was released as a region 2 DVD set in 2015 by the Dutch company B-Motion. | https://en.wikipedia.org/wiki?curid=29952420 |
Critical illumination or Nelsonian illumination is a method of specimen illumination used for transmitted and reflected light (trans- and epi-illuminated) optical microscopy. focuses an image of a light source on to the specimen for bright illumination. generally has problems with evenness of illumination as an image of the illumination source (for example a halogen lamp filament) is visible in the resulting image. Köhler illumination has largely replaced critical illumination in modern scientific light microscopy although it requires additional optics which may not be present in less expensive and simpler light microscopes. acts to form an image of the light source on the specimen to illuminate it. This image is formed by the condenser or collector lens. This illumination is bright but not always even, as any structure in the light source (for example the filament of a light bulb) will be visible in the resulting image. Homogeneous light sources such as a flame or sunlight give more even illumination. Alternatively, a ground or opal glass diffuser can be used to homogenize the light source, but this will cause a significant amount of light to be scattered away from the sample. | https://en.wikipedia.org/wiki?curid=29953061 |
Borrowing hydrogen catalysis, also called hydrogen autotransfer, is an important catalytic concept. "Borrowing hydrogen" can be seen as an example of Green chemistry. It is based on the intermediate oxidation of an alcohol substrate to the corresponding aldehyde by the catalyst (which "borrows" hydrogen from the substrate); the intermediate aldehyde then reacts with e.g. a secondary amine in a condensation reaction to produce e.g. an imine, that is then reduced by the catalyst in the final step to yield e.g. a tertiary amine. The method is highly atom economic, because is circumvents the activation of the alcohol (which is a poor electrophile itself, see tosylation or Swern oxidation). The method is not limited to the preparation of amines, it can also be used to form Carbon–carbon bonds (C-C bonds). Alcohols can be temporarily converted into carbonyl compounds by the metal-catalysed removal of hydrogen. The carbonyl compounds are reactive in a wider range of transformations than the precursor alcohols and can react in situ to give imines, alkenes, and α-functionalised carbonyl compounds. The metal catalyst, which had borrowed the hydrogen, then returns it to the transformed carbonyl compound, leading to an overall process in which alcohols can be converted into amines, compounds containing C-C bonds and β-functionalised alcohols | https://en.wikipedia.org/wiki?curid=29953491 |
Borrowing hydrogen Microwave heating enables a Borrowing Hydrogen strategy to form C-N bonds from alcohols and amines, removes the need for solvent and reduces the reaction times, while the results are comparable with those using thermal heating. Nitroaromatics can also give this reaction, reducing nitro to amine and imine giving secondary amines. | https://en.wikipedia.org/wiki?curid=29953491 |
List of radioactive nuclides by half-life This is a list of radioactive nuclides (sometimes also called isotopes), ordered by half-life from shortest to longest, in seconds, minutes, hours, days, and years. Tellurium-128's half-life is over 160 trillion times greater than the age of the universe. | https://en.wikipedia.org/wiki?curid=29969297 |
Ultrasonic impact treatment (UIT) is a metallurgical processing technique, similar to work hardening, in which ultrasonic energy is applied to a metal object. This technique is part of the High Frequency Mechanical Impact (HFMI) processes. Other acronyms are also equivalent: Ultrasonic Needle Peening (UNP), Ultrasonic Peening (UP). can result in controlled residual compressive stress, grain refinement and grain size reduction. Low and high cycle fatigue are enhanced and have been documented to provide increases up to ten times greater than non-UIT specimens. In UIT, ultrasonic waves are produced by an electro-mechanical ultrasonic transducer, and applied to a workpiece. An acoustically tuned resonator bar is caused to vibrate by energizing it with a magnetostrictive or Piezoelectric ultrasonic transducer. The energy generated from these high frequency impulses is imparted to the treated surface through the contact of specially designed steel pins. These transfer pins are free to move axially between the resonant body and the treated surface. When the tool, made up of the ultrasonic transducer, pins and other components, comes into contact with the work piece it acoustically couples with the work piece, creating harmonic resonance. This harmonic resonance is performed at a carefully calibrated frequency, to which metals respond very favorably, resulting in compressive residual stress, stress relief and grain structure improvements | https://en.wikipedia.org/wiki?curid=29972322 |
Ultrasonic impact treatment Depending on the desired effects of treatment a combination of different frequencies and displacement amplitude is applied. Depending on the tool and the Original Equipment Manufacturer, these frequencies range between 15 and 55 kHz, with the displacement amplitude of the resonant body of between . UIT is highly controllable. Incorporating a programmable logic controller (PLC) or a Digital Ultrasonic Generator, the frequency and amplitude of UIT are easily set and maintained, thus removing a significant portion of operator dependency. UIT can also be mechanically controlled, thus providing repeatability of results from one application to the next. Examples of mechanical control employed with UIT include: With these types of controlled applications, the surface finish of the work piece is highly controllable. For many applications, UIT is most effectively employed by hand. The high portability of the UIT system enables travel to austere locations and hard to reach places. The flexibility that is facilitated by variations in the tool configuration (such as angle-peening-head) ensures that access to very tight locations is possible. UIT's effectiveness has been illustrated on the following metals, among others: UIT was originally developed in 1972 and has since been perfected by a team of Russian scientists under the leadership of Dr. Efim Statnikov | https://en.wikipedia.org/wiki?curid=29972322 |
Ultrasonic impact treatment Originally developed and utilized to enhance the fatigue and corrosion attributes of ship and submarine structures, UIT has been utilized in aerospace, mining, offshore drilling, shipbuilding, infrastructure, automotive, energy production and other industries. Different industrial solutions exist nowadays and are commercialized by a limited number of Original Equipment Manufacturers worldwide. UIT enables life extension of steel bridges. This technique has been employed in numerous US states as well as other nations. The result is a greatly reduced cost of infrastructure. UIT has been certified for this use by AASHTO. The use of UIT on draglines and other heavy equipment in the mining industry has resulted in increased production and has decreased downtime and maintenance costs. UIT is employed on drive shafts and crank shafts in a number of industries. Results show that UIT increases shaft life by over a factor of 3. The US Navy uses UIT to address cracked areas in certain aluminum decks. Without UIT, crack repairs resulted in almost immediate re-cracking. With UIT, repairs have shown to last over eight months without cracks. IIW PUBLICATIONS: | https://en.wikipedia.org/wiki?curid=29972322 |
Dynamic strain aging Although sometimes dynamic strain aging (DSA) is used interchangeably with the Portevin–Le Chatelier effect (or serrated yielding), dynamic strain aging refers specifically to the microscopic mechanism that induces the Portevin–Le Chatelier effect. This strengthening mechanism is related to solid-solution strengthening and has been observed in a variety of fcc and bcc substitutional and interstitial alloys, metalloids like silicon, and ordered intermetallics within specific ranges of temperature and strain rate. In materials, the motion of dislocations is a discontinuous process. When dislocation meets obstacles (like forest dislocations) they are temporarily arrested for a certain time. During this time solutes (such as interstitial particles) diffuse around the dislocations further strengthening the obstacles held on the dislocations. Eventually these dislocations will overcome these obstacles with sufficient stress and will quickly move to the next obstacle where they are stopped and the process can repeat. This process's most well-known manifestations are Lüders bands and the Portevin–Le Chatelier effect. Though the mechanism is known to affect materials without these physical observations. Although serrations in the stress–strain curve caused by the Portevin–Le Chatelier effect are the most visible effect of dynamic strain aging, other effects may be present when this effect is not seen. Often when serrated flow is not seen, dynamic strain aging is marked by a lower strain rate sensitivity | https://en.wikipedia.org/wiki?curid=29985074 |
Dynamic strain aging That becomes negative in the Portevin–Le Chatelier regime. also causes a plateau in the strength, a peak in flow stress a peak in work hardening, a peak in the Hall–Petch constant, and minimum variation of ductility with temperature. Since dynamic strain aging is a hardening phenomenon it increases the strength of the material. Two categories can be distinguished by the interaction pathway. The first class of Elements, such as carbon(C) and nitrogen(N), contribute to DSA directly by diffusing quickly enough through the lattice to the dislocations and locking them. Such effect is determined with the element’s solubility, diffusion coefficient, and the interaction energy between the elements and dislocations, i.e. the severity of dislocation locking. Elements of the second category affect DSA by altering the behavior of the first-class elements. Some substitutional solute atoms, like Mn, Mo, and Cr, stress-induced ordering of substitutional-interstitial pairs, and thus reduce the mobility of carbon and nitrogen. Some elements, for example, Ti, Zr, and Nb introduce carbides, nitrides and so on, which then shift the DSA region to higher temperature zone. At least five classes can be identified according to the stress-strain relation appearance of Serration | https://en.wikipedia.org/wiki?curid=29985074 |
Dynamic strain aging Arising from the repeated nucleation of shear bands and the continuous propagation of Lüders bands, this type consists of periodic locking serrations with abrupt increase in flow stress followed by drop of stress below the general level of the stress-strain curve. It is usually seen in the low temperature (high strain rate) part of the DS regime. Result from the nucleation of narrow shear bands, which propagate discontinuously or do not propagate due to the adjacent nucleation sites, and thus oscillate about the general level of the flow curve. It occurs at higher temperature or lower strain rates than type A. It may also be developed from type A when it comes to higher strain. Caused by dislocation unlocking, the stress drop of type C is below the general level of the flow curve. It occurs at even higher temperature and lower strain comparation to A and B type. When there is no work hardening, a plateau on the stress-strain curve is seen and therefore is also named staircase type. This type forms a mixed mode with type B. Occurring at higher strain after type A, type E is not easy to be recognized. has been shown to be linked to these specific material problems: | https://en.wikipedia.org/wiki?curid=29985074 |
Lead picrate Lead picrate, Pb(CH(NO)O), is an organic chemical compound from the group of picrates, salt of picric acid and lead with a +2 oxidation state. It is an initiating explosive, and thus highly sensitive. For demonstration purposes, it can be most easily and safely prepared "in situ". Picric acid is mixed with red lead (PbO), and then heated. It is not recommended that more than 50 mg is ever made at any one time. At around 130–160 °C, as the picric acid melts, the mixture detonates violently. | https://en.wikipedia.org/wiki?curid=29987638 |
C7H12N2O4 The molecular formula CHNO may refer to: | https://en.wikipedia.org/wiki?curid=29998984 |
C11H19N3O6 The molecular formula CHNO (molar mass: 289.285 g/mol) may refer to: | https://en.wikipedia.org/wiki?curid=29998992 |
Steven M. Weinreb (born May 10, 1941) is an American chemist and is a professor of chemistry at Pennsylvania State University in United States. Together with Steven Nahm, he developed the Weinreb ketone synthesis, which allows for mono-addition of an organometallic reagent such as a Grignard reagent or organolithium reagent to an amide. Weinreb received his PhD for work with Marshall Gates at the University of Rochester in 1967. After post-docs with Gilbert Stork and George H. Buchi, he worked at Fordham University. He joined the Pennsylvania State University in 1978, where he holds the Russell and Mildred Marker Professor of Natural Products Chemistry chair. | https://en.wikipedia.org/wiki?curid=30007715 |
Filamin Filamins are a class of proteins that hold two actin filaments at large angles. protein in mammals is made up of an actin-binding domain at its N-terminus that is followed by 24 immunoglobulin-like repeat modules of roughly 95 amino acids. There are two hinge regions; between repeats 15-16 and 23-24. gets cleaved at these hinge regions to generate smaller fragments of the protein. has two actin-binding sites with a V-linkage between them, so that it cross-links actin filaments into a network with the filaments orientated almost at right angles to one another. proteins include: Over-expression of FLNA stops the regeneration of bladder carcinoma (BC) cells, by inhibiting the cell cycle and inducing apoptosis of BC cells. FLNA has also been shown to reduce the mobility and invasion abilities of BC cells. | https://en.wikipedia.org/wiki?curid=30015453 |
Photochemistry and Photobiology is a bimonthly peer-reviewed scientific journal covering photochemistry and photobiology. It was established in 1962 and is pub lished by Wiley-Blackwell on behalf of the American Society for Photobiology. The editor-in-chief is Jean Cadet (University of Sherbrooke). The journal's name was decided in Copenhagen at the 1960 International Congress on Photobiology. The journal has been published since 1962, originally by Pergamon Press under Robert Maxwell, who personally agreed to give the journal to the American Society for Photobiology (ASP), soon after its formation in 1972, and it has been the society's official journal ever since. In 1986, the 38th Council of the ASP established a committee to investigate the proposal that the European Society for Photobiology (ESP) would share the operation of the journal with the ASP. Financial and contractual problems prevented agreement and, instead, ESP contracted with Elsevier leading to the publication of the "Journal of Photochemistry and Photobiology" in 1987. After the widespread challenge of falling journal subscription revenues, the journal was an early participant in the not-for-profit publishing initiative, BioOne. The journal is abstracted and indexed in Academic Search, Biological Abstracts, BIOSIS Previews, CAB HEALTH, CABDirect, Chemical Abstracts Service, CSA Biological Sciences Database, Current Contents/Life Sciences, GeoRef, Index Medicus/MEDLINE/PubMed, ProQuest Health & Medical Complete, Proquest Medical Library, and the Science Citation Index | https://en.wikipedia.org/wiki?curid=30025579 |
Photochemistry and Photobiology According to the "Journal Citation Reports", the journal has a 2017 impact factor of 2.214. | https://en.wikipedia.org/wiki?curid=30025579 |
Magic pipe A magic pipe is a surreptitious change to a ship's oily water separator, or other waste-handing equipment, which allows waste liquids to be discharged in contravention of maritime pollution regulations. The pipe may be improvised, aboard ship, from available hoses and pumps, to discharge untreated waste water directly into the sea. As ships are required to keep records of waste and its treatment, magic pipe cases often involve falsification of these records too. The pipe is ironically called "magic" because it bypasses the ship's oily water separator and goes right overboard. Therefore it can make untreated bilge water "magically disappear". Often the pipe can be easily disconnected and stored away into a different spot of the ship so state and regulatory officers would not be able to detect its usage. The use of magic pipes continues to this day as well as efforts to improve bilge water treatment to make the use of magic pipes unnecessary also continue. In the United States, magic pipe cases often attract large fines for shipping lines, and prison sentences for crew. Cases are often brought to light by whistle blowers, including a 2016 case involving Princess Cruises, which resulted in a record US $40 million fine. On older OWS systems bypass pipes were fitted with regulatory approval. These approved pipes are no longer fitted on newer vessels | https://en.wikipedia.org/wiki?curid=30027748 |
Magic pipe In some serious emergencies ship's crews are allowed to discharge untreated bilge water overboard, but they need to declare these emergencies in the ship's records and oil record book. Unregistered discharges violate the MARPOL 73/78 international pollution control treaty. The problem is worsened by a lack of facilities in developing countries; some port reception facilities do not allow for oily water to be discharged easily and cost effectively. Crew members, engineers, and ship owners can receive huge fines and even imprisonment if they continue to use a magic pipe to pollute the environment. Conclusively, some engineers use the magic pipe manipulation technique because of: The oily bilge waste comes from a ship’s engines and fuel systems. The waste is required to be offloaded when a ship is in port and either burned in an incinerator or taken to a waste management facility. In rare occasions, bilge water can be discharged into the ocean but only after almost all oil is separated out. | https://en.wikipedia.org/wiki?curid=30027748 |
Cocrystal Cocrystals are "solids that are crystalline single phase materials composed of two or more different molecular or ionic compounds generally in a stoichiometric ratio which are neither solvates nor simple salts." A broader definition is that cocrystals "consist of two or more components that form a unique crystalline structure having unique properties." Several subclassifications of cocrystals exist. Cocrystals can encompass many types of compounds, including hydrates, solvates and clathrates, which represent the basic principle of host–guest chemistry. Hundreds of examples of cocrystallization are the reported annually. The first reported cocrystal, quinhydrone, was studied by Friedrich Wöhler in 1844. Quinhydrone is a cocrystal of quinone and hydroquinone (known archaically as quinol). He found that this material was made up of a 1:1 molar combination of the components. Quinhydrone was analyzed by numerous groups over the next decade and several related cocrystals were made from halogenated quinones. Many cocrystals discovered in the late 1800s and early 1900s were reported in "Organische Molekulverbindungen", published by Paul Pfeiffer in 1922. This book separated the cocrystals into two categories; those made of inorganic:organic components, and those made only of organic components. The inorganic:organic cocrystals include organic molecules cocrystallized with alkali and alkaline earth salts, mineral acids, and halogens as in the case of the halogenated quinones | https://en.wikipedia.org/wiki?curid=30031679 |
Cocrystal A majority of the organic:organic cocrystals contained aromatic compounds, with a significant fraction containing di- or trinitro aromatic compounds. The existence of several cocrystals containing eucalyptol, a compound which has no aromatic groups, was an important finding which taught scientists that pi stacking is not necessary for the formation of cocrystals. Cocrystals continued to be discovered throughout the 1900s. Some were discovered by chance and others by screening techniques. Knowledge of the intermolecular interactions and their effects on crystal packing allowed for the engineering of cocrystals with desired physical and chemical properties. In the last decade there has been an enhanced interest in cocrystal research, primarily due to applications in the pharmaceutical industry. Cocrystals represent about 0.5% of the crystal structures archived in the Cambridge Structural Database (CSD). However, the study of cocrystals has a long history spanning more than 160 years. They have found use in a number of industries, including pharmaceutical, textile, paper, chemical processing, photographic, propellant, and electronic. The meaning of the term "cocrystal" is subject of disagreement. One definition states that a cocrystal is a crystalline structure composed of at least two components, where the components may be atoms, ions or molecules. This definition is sometimes extended to specify that the components be solid in their pure forms at ambient conditions | https://en.wikipedia.org/wiki?curid=30031679 |
Cocrystal However, it has been argued that this separation based on ambient phase is arbitrary. A more inclusive definition is that cocrystals "consist of two or more components that form a unique crystalline structure having unique properties." Due to variation in the use of the term, structures such as solvates and clathrates may or may not be considered cocrystals in a given situation. The difference between a crystalline salt and a cocrystal lies merely in the transfer of a proton. The transfer of protons from one component to another in a crystal is dependent on the environment. For this reason, crystalline salts and cocrystals may be thought of as two ends of a proton transfer spectrum, where the salt has completed the proton transfer at one end and an absence of proton transfer exists for cocrystals at the other end. The components interact via non-covalent interactions such as hydrogen bonding, ionic interactions, van der Waals interactions and Π-interactions. These interactions lead to a cocrystal lattice energy that is generally more stable than the crystal structures of the individual components. The intermolecular interactions and resulting crystal structures can generate physical and chemical properties that differ from the properties of the individual components. Such properties include melting point, solubility, chemical stability, and mechanical properties. Some cocrystals have been observed to exist as polymorphs, which may display different physical properties depending on the form of the crystal | https://en.wikipedia.org/wiki?curid=30031679 |
Cocrystal Phase diagrams determined from the "contact method" of thermal microscopy is valuable in the detection of cocrystals. The construction of these phase diagrams is made possible due to the change in melting point upon cocrystallization. Two crystalline substances are deposited on either side of a microscope slide and are sequentially melted and resolidified. This process creates thin films of each substance with a contact zone in the middle. A melting point phase diagram may be constructed by slow heating of the slide under a microscope and observation of the melting points of the various portions of the slide. For a simple binary phase diagram, if one eutectic point is observed then the substances do not form a cocrystal. If two eutectic points are observed, then the composition between these two points corresponds to the cocrystal. There are many synthetic strategies that are available to prepare cocrystals. However, it may be difficult to prepare single cocrystals for X-ray diffraction, as it has been known to take up to 6 months to prepare these materials. Cocrystals are typically generated through slow evaporation of solutions of the two components. This approach has been successful with molecules of complementary hydrogen bonding properties, in which case cocrystallization is likely to be thermodynamically favored. Many other methods exist in order to produce cocrystals. Crystallizing with a molar excess of one cocrystal former may produce a cocrystal by a decrease in solubility of that one component | https://en.wikipedia.org/wiki?curid=30031679 |
Cocrystal Another method to synthesize cocrystals is to conduct the crystallization in a slurry. As with any crystallization, solvent considerations are important. Changing the solvent will change the intermolecular interactions and possibly lead to cocrystal formation. Also, by changing the solvent, phase considerations may be utilized. The role of a solvent in nucleation of cocrystals remains poorly understood but critical in order to obtain a cocrystal from solution. Cooling molten mixture of cocrystal formers often affords cocrystals. Seeding can be useful. Another approach that exploits phase change is sublimation which often forms hydrates. Grinding, both neat and liquid-assisted, is employed to produce cocrystal, e.g., using a mortar and pestle, using a ball mill, or using a vibratory mill. In liquid-assisted grinding, or kneading, a small or substoichiometric amount of liquid (solvent) is added to the grinding mixture. This method was developed in order to increase the rate of cocrystal formation, but has advantages over neat grinding such as increased yield, ability to control polymorph production, better product crystallinity, and applies to a significantly larger scope of cocrystal formers. and nucleation through seeding. Supercritical fluids (SCFs) serve as a medium for growing cocrystals. Crystal growth is achieved due to unique properties of SCFs by using different supercritical fluid properties: supercritical CO2 solvent power, anti-solvent effect and its atomization enhancement | https://en.wikipedia.org/wiki?curid=30031679 |
Cocrystal Using intermediate phases to synthesize solid-state compounds is also employed. The use of a hydrate or an amorphous phase as an intermediate during synthesis in a solid-state route has proven successful in forming a cocrystal. Also, the use of a metastable polymorphic form of one cocrystal former can be employed. In this method, the metastable form acts as an unstable intermediate on the nucleation pathway to a cocrystal. As always, a clear connection between pairwise components of the cocrystal is needed in addition to the thermodynamic requirements in order to form these compounds. Importantly, the phase that is obtained is independent of the synthetic methodology used. It may seem facile to synthesize these materials, but on the contrary the synthesis is far from routine. Cocrystals may be characterized in a wide variety of ways. Powder X-Ray diffraction proves to be the most commonly used method in order to characterize cocrystals. It is easily seen that a unique compound is formed and if it could possibly be a cocrystal or not owing to each compound having its own distinct powder diffractogram. Single-crystal X-ray diffraction may prove difficult on some cocrystals, especially those formed through grinding, as this method more often than not provides powders. However, these forms may be formed often through other methodologies in order to afford single crystals | https://en.wikipedia.org/wiki?curid=30031679 |
Cocrystal Aside from common spectroscopic methods such as FT-IR and Raman spectroscopy, solid state NMR spectroscopy allows differentiation of chiral and racemic cocrystals of similar structure. Other physical methods of characterization may be employed. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) are two commonly used methods in order to determine melting points, phase transitions, and enthalpic factors which can be compared to each individual cocrystal former. engineering is relevant to production of energetic materials, pharmaceuticals, and other compounds. Of these, the most widely studied and used application is in drug development and more specifically, the formation, design, and implementation of active pharmaceutical ingredients (API). Changing the structure and composition of the API can greatly influence the bioavailability of a drug. The engineering of cocrystals takes advantage of the specific properties of each component to make the most favorable conditions for solubility that could ultimately enhance the bioavailability of the drug. The principal idea is to develop superior physico-chemical properties of the API while holding the properties of the drug molecule itself constant. structures have also become a staple for drug discovery. Structure-based virtual screening methods, such as docking, makes use of cocrystal structures of known proteins or receptors to elucidate new ligand-receptor binding conformations | https://en.wikipedia.org/wiki?curid=30031679 |
Cocrystal engineering has become of such great importance in the field of pharmaceuticals that a particular subdivision of multicomponent cocrystals has been given the term pharmaceutical cocrystals to refer to a solid cocrystal former component and a molecular or ionic API (active pharmaceutical ingredient). However, other classifications also exist when one or more of the components are not in solid form under ambient conditions. For example, if one component is a liquid under ambient conditions, the cocrystal might actually be deemed a cocrystal solvate as discussed previously. The physical states of the individual components under ambient conditions is the only source of division among these classifications. The classification naming scheme of the cocrystals might seem to be of little importance to the cocrystal itself, but in the categorization lies significant information regarding the physical properties, such as solubility and melting point, and the stability of APIs. The objective for pharmaceutical cocrystals is to have properties that differ from that expected of the pure APIs without making and/or breaking covalent bonds. Among the earliest pharmaceutical cocrystals reported are of sulfonamides. The area of pharmaceutical cocrystals has thus increased on the basis of interactions between APIs and cocrystal formers | https://en.wikipedia.org/wiki?curid=30031679 |
Cocrystal Most commonly, APIs have hydrogen-bonding capability at their exterior which makes them more susceptible to polymorphism, especially in the case of cocrystal solvates which can be known to have different polymorphic forms. Such a case is in the drug sulfathiazole, a common oral and topical antimicrobial, which has over a hundred different solvates. It is thus important in the field of pharmaceuticals to screen for every polymorphic form of a cocrystal before it is considered as a realistic improvement to the existing API. Pharmaceutical cocrystal formation can also be driven by multiple functional groups on the API, which introduces the possibility of binary, ternary, and higher ordered cocrystal forms. Nevertheless, the cocrystal former is used to optimize the properties of the API but can also be used solely in the isolation and/or purification of the API, such as a separating enantiomers from each other, as well and removed preceding the production of the drug. It is with reasoning that the physical properties of pharmaceutical cocrystals could then ultimately change with varying amounts and concentrations of the individual components. One of the most important properties to change with varying the concentrations of the components is solubility. It has been shown that if the stability of the components is less than the cocrystal formed between them, then the solubility of the cocrystal will be lower than the pure combination of the individual constituents | https://en.wikipedia.org/wiki?curid=30031679 |
Cocrystal If the solubility of the cocrystal is lower, this means that there exists a driving force for the cocrystallization to occur. Even more important for pharmaceutical applications is the ability to alter the stability to hydration and bioavailability of the API with cocrystal formation, which has huge implications on drug development. The cocrystal can increase or decrease such properties as melting point and stability to relative humidity compared to the pure API and therefore, must be studied on a case to case basis for their utilization in improving a pharmaceutical on the market. A screening procedure has been developed to help determine the formation of cocrystals from two components and the ability to improve the properties of the pure API. First, the solubilities of the individual compounds are determined. Secondly, the cocrystallization of the two components is evaluated. Finally, phase diagram screening and powder X-ray diffraction (PXRD) are further investigated to optimize conditions for cocrystallization of the components. This procedure is still done to discover cocrystals of pharmaceutical interest including simple APIs, such as carbamazepine (CBZ), a common treatment for epilepsy, trigeminal neuralgia, and bipolar disorder. CBZ has only one primary functional group involved in hydrogen bonding, which simplifies the possibilities of cocrystal formation that can greatly improve its low dissolution bioavailability | https://en.wikipedia.org/wiki?curid=30031679 |
Cocrystal Another example of an API being studied would be that of Piracetam, or (2-oxo-1-pyrrolidinyl)acetamide, which is used to stimulate the central nervous system and thus, enhance learning and memory. Four polymorphs of Piracetam exist that involve hydrogen bonding of the carbonyl and primary amide. It is these same hydrogen bonding functional groups that interact with and enhance the cocrystallization of Piracetam with gentisic acid, a non-steroidal anti-inflammatory drug (NSAID), and with p-hydroxybenzoic acid, an isomer of the aspirin precursor salicylic acid. No matter what the API is that is being researched, it is quite evident of the wide applicability and possibility for constant improvement in the realm of drug development, thus making it clear that the driving force of cocrystallization continues to consist of attempting to improve on the physical properties in which the existing cocrystals are lacking. On August 16, 2016, the US food and drug administration (FDA) published a draft guidance Regulatory Classification of Pharmaceutical Co-Crystals. In this guide, the FDA suggests treating co-crystals as polymorphs, as long as proof is presented to rule out the existence of ionic bonds. Two explosives HMX and CL-20 cocrystallized in a ratio 1:2 to form a hybrid explosive. This explosive had the same low sensitivity of HMX and nearly the same explosive power of CL-20 | https://en.wikipedia.org/wiki?curid=30031679 |
Cocrystal Physically mixing explosives creates a mixture that has the same sensitivity as the most sensitive component, which cocrystallisation overcomes. | https://en.wikipedia.org/wiki?curid=30031679 |
Separator (electricity) A separator is a permeable membrane placed between a battery's anode and cathode. The main function of a separator is to keep the two electrodes apart to prevent electrical short circuits while also allowing the transport of ionic charge carriers that are needed to close the circuit during the passage of current in an electrochemical cell. Separators are critical components in liquid electrolyte batteries. A separator generally consists of a polymeric membrane forming a microporous layer. It must be chemically and electrochemically stable with regard to the electrolyte and electrode materials and mechanically strong enough to withstand the high tension during battery construction. They are important to batteries because their structure and properties considerably affect the battery performance, including the batteries energy and power densities, cycle life, and safety. Unlike many forms of technology, polymer separators were not developed specifically for batteries. They were instead spin-offs of existing technologies, which is why most are not optimized for the systems they are used in. Even though this may seem unfavorable, most polymer separators can be mass-produced at a low cost, because they are based on existing forms of technologies. Yoshino and co-workers at Asahi Kasei first developed them for a prototype of secondary lithium-ion batteries (LIBs) in 1983. Initially, lithium cobalt oxide was used as the cathode and polyacetylene as the anode | https://en.wikipedia.org/wiki?curid=30038658 |
Separator (electricity) Later in 1985, it was found that using lithium cobalt oxide as the cathode and graphite as the anode produced an excellent secondary battery with enhanced stability, employing the frontier electron theory of Kenichi Fukui. This enabled the development of portable devices, such as cell phones and laptops. However, before lithium ion batteries could be mass-produced, safety concerns needed to be addressed such as overheating and over potential. One key to ensuring safety was the separator between the cathode and anode. Yoshino developed a microporous polyethylene membrane separator with a “fuse” function. In the case of abnormal heat generation within the battery cell, the separator provides a shutdown mechanism. The micropores close by melting and the ionic flow terminates. In 2004, a novel electroactive polymer separator with the function of overcharge protection was first proposed by Denton and coauthors. This kind of separator reversibly switches between insulating and conducting states. Changes in charge potential drive the switch. More recently, separators primarily provide charge transport and electrode separation. Materials include nonwoven fibers (cotton, nylon, polyesters, glass), polymer films (polyethylene, polypropylene, poly (tetrafluoroethylene), polyvinyl chloride), ceramic and naturally occurring substances (rubber, asbestos, wood). Some separators employ polymeric materials with pores of less than 20 Å, generally too small for batteries. Both dry and wet processes are used for fabrication | https://en.wikipedia.org/wiki?curid=30038658 |
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