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Methyl green-pyronin ( MGP ) is a classical histological staining technique using two basic (cationic) dyes for the demonstration and differentiation of DNA and RNA . Methyl green is specific for phosphate radicals in the DNA double helix staining it green-blue. Pyronin does not possess this affinity and binds to the remaining negatively charged RNA staining it red. The method is useful in identifying the distribution of Nissl substance in neuronal cell bodies. [ 1 ]
This article related to pathology is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Methyl_green-pyronin_stain |
In organic chemistry , a methyl group is an alkyl derived from methane , containing one carbon atom bonded to three hydrogen atoms, having chemical formula CH 3 (whereas normal methane has the formula CH 4 ). In formulas , the group is often abbreviated as Me . This hydrocarbon group occurs in many organic compounds . It is a very stable group in most molecules. While the methyl group is usually part of a larger molecule , bonded to the rest of the molecule by a single covalent bond ( −CH 3 ), it can be found on its own in any of three forms: methanide anion ( CH − 3 ), methylium cation ( CH + 3 ) or methyl radical ( CH • 3 ). The anion has eight valence electrons , the radical seven and the cation six. All three forms are highly reactive and rarely observed. [ 1 ]
The methylium cation ( CH + 3 ) exists in the gas phase , but is otherwise not encountered. Some compounds are considered to be sources of the CH + 3 cation, and this simplification is used pervasively in organic chemistry. For example, protonation of methanol gives an electrophilic methylating reagent that reacts by the S N 2 pathway:
Similarly, methyl iodide and methyl triflate are viewed as the equivalent of the methyl cation because they readily undergo S N 2 reactions by weak nucleophiles .
The methyl cation has been detected in interstellar space . [ 2 ] [ 3 ]
The methanide anion ( CH − 3 ) exists only in rarefied gas phase or under exotic conditions. It can be produced by electrical discharge in ketene at low pressure (less than one torr ) and its enthalpy of reaction is determined to be about 252.2 ± 3.3 kJ / mol . [ 4 ] It is a powerful superbase ; only the lithium monoxide anion ( LiO − ) and the diethynylbenzene dianions are known to be stronger. [ 5 ]
In discussing mechanisms of organic reactions, methyl lithium and related Grignard reagents are often considered to be salts of CH − 3 ; and though the model may be useful for description and analysis, it is only a useful fiction. Such reagents are generally prepared from the methyl halides :
where M is an alkali metal .
The methyl radical has the formula CH • 3 . It exists in dilute gases, but in more concentrated form it readily dimerizes to ethane . It is routinely produced by various enzymes of the radical SAM and methylcobalamin varieties. [ 6 ] [ 7 ]
The reactivity of a methyl group depends on the adjacent substituents . Methyl groups can be quite unreactive. For example, in organic compounds, the methyl group resists attack by even the strongest acids . [ citation needed ]
The oxidation of a methyl group occurs widely in nature and industry. The oxidation products derived from methyl are hydroxymethyl group −CH 2 OH , formyl group −CHO , and carboxyl group −COOH . For example, permanganate often converts a methyl group to a carboxyl ( −COOH ) group, e.g. the conversion of toluene to benzoic acid . Ultimately oxidation of methyl groups gives protons and carbon dioxide , as seen in combustion.
Demethylation (the transfer of the methyl group to another compound) is a common process, and reagents that undergo this reaction are called methylating agents. Common methylating agents are dimethyl sulfate , methyl iodide , and methyl triflate . Methanogenesis , the source of natural gas, arises via a demethylation reaction. [ 8 ] Together with ubiquitin and phosphorylation, methylation is a major biochemical process for modifying protein function. [ 9 ] The field of epigenetics focuses on the influence of methylation on gene expression. [ 10 ]
Certain methyl groups can be deprotonated. For example, the acidity of the methyl groups in acetone ( (CH 3 ) 2 CO ) is about 10 20 times more acidic than methane. The resulting carbanions are key intermediates in many reactions in organic synthesis and biosynthesis . Fatty acids are produced in this way.
When placed in benzylic or allylic positions, the strength of the C−H bond is decreased, and the reactivity of the methyl group increases. One manifestation of this enhanced reactivity is the photochemical chlorination of the methyl group in toluene to give benzyl chloride . [ 11 ]
In the special case where one hydrogen is replaced by deuterium (D) and another hydrogen by tritium (T), the methyl substituent becomes chiral . [ 12 ] Methods exist to produce optically pure methyl compounds, e.g., chiral acetic acid (deuterotritoacetic acid CHDTCO 2 H ). Through the use of chiral methyl groups, the stereochemical course of several biochemical transformations have been analyzed. [ 13 ]
A methyl group may rotate around the R−C axis. This is a free rotation only in the simplest cases like gaseous methyl chloride CH 3 Cl . In most molecules, the remainder R breaks the C ∞ symmetry of the R−C axis and creates a potential V ( φ ) that restricts the free motion of the three protons. For the model case of ethane CH 3 CH 3 , this is discussed under the name ethane barrier .
In condensed phases, neighbour molecules also contribute to the potential. Methyl group rotation can be experimentally studied using quasielastic neutron scattering . [ 14 ]
French chemists Jean-Baptiste Dumas and Eugene Peligot , after determining methanol's chemical structure, introduced " methylene " from the Greek μέθυ ( methy ) "wine" and ὕλη ( hȳlē ) "wood, patch of trees" with the intention of highlighting its origins, "alcohol made from wood (substance)". [ 15 ] [ 16 ] The term "methyl" was derived in about 1840 by back-formation from "methylene", and was then applied to describe "methyl alcohol" (which since 1892 is called " methanol ").
Methyl is the IUPAC nomenclature of organic chemistry term for an alkane (or alkyl) molecule, using the prefix "meth-" to indicate the presence of a single carbon. | https://en.wikipedia.org/wiki/Methyl_group |
Methyl hydroperoxide is the organic compound with the formula CH 3 OOH. It is a volaltile colorless liquid. In addition to being of theoretical interest as the simplest organic hydroperoxide , methyl hydroperoxide is an intermediate in the oxidation of methane . [ 1 ] When condensed or in concentrated form methyl hydroperoxide is rather explosive, unlike tertiary hydroperoxides such as tert-butylhydroperoxide . [ 2 ] Its laboratory preparation was first reported in 1929. [ 3 ] | https://en.wikipedia.org/wiki/Methyl_hydroperoxide |
Methyl isocyanate ( MIC ) is an organic compound with the molecular formula CH 3 NCO. Synonyms are isocyanatomethane and methyl carbylamine . Methyl isocyanate is an intermediate chemical in the production of carbamate pesticides and Haffmann Bromamide Degradation (such as carbaryl , carbofuran , methomyl , and aldicarb ). It has also been used in the production of rubbers and adhesives . As an extremely toxic and irritating compound, it is very hazardous to human health. MIC was the principal toxicant involved in the Bhopal gas disaster , which short-term killed 4,000–8,000 people and caused permanent injury and premature deaths to approximately 15,000-20,000. [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] It is also a very potent lachrymatory agent . [ 11 ]
Methyl isocyanate is a colorless, poisonous, lachrymatory ( tearing agent), flammable liquid. [ 12 ] It is soluble in water to 6–10 parts per 100 parts, but it also reacts with water (see Reactions below).
It has a refractive index of 1.363 with a wavelength of 589 nm at a temperature of 20 °C [ 13 ]
Methyl isocyanate is usually manufactured by the reaction of monomethylamine and phosgene . For large-scale production it is advantageous to combine these reactants at higher temperature in the gas phase. A mixture of methyl isocyanate and two moles of hydrogen chloride is formed, but N-methylcarbamoyl chloride (MCC) forms as the mixture is condensed, leaving one mole of hydrogen chloride as a gas.
The methyl isocyanate is obtained by treating the MCC with a tertiary amine , such as N , N -dimethylaniline , or with pyridine , [ 14 ] or by separating it by using distillation techniques. [ 15 ]
Methyl isocyanate is also manufactured from N -methylformamide and air. In the latter process, it is immediately consumed in a closed-loop process to make methomyl . [ 16 ] Other manufacturing methods have been reported. [ 17 ] [ 18 ]
Methyl isocyanate reacts readily with many substances that contain N-H or O-H groups. With water, it forms 1,3-dimethylurea and carbon dioxide with the evolution of heat (1358.5 joules, or 325 calories, per gram of MIC): It is relatively slow to react at below 68 °F, but will increase its rate with elevated temperatures or in the presence of acid or base. [ 19 ]
At 25 °C, in excess water, half of the MIC is consumed in 9 min.; [ 20 ] if the heat is not efficiently removed from the reacting mixture, the rate of the reaction will increase and rapidly cause the MIC to boil. Such a reaction triggered the Bhopal disaster after a large amount of water was introduced to a MIC storage tank. The consequence of the out of control exothermic process was a runaway reaction and the direct release of 42 tons of MIC to the atmosphere.
If MIC is in excess, 1,3,5-trimethylbiuret is formed along with carbon dioxide . [ 12 ] Alcohols and phenols , which contain an O-H group, react slowly with MIC, but the reaction can be catalyzed by trialkylamines or dialkyltin dicarboxylate. Oximes , hydroxylamines , and enols also react with MIC to form methylcarbamates. [ 12 ] These reactions produce the products described below ( Uses ).
Ammonia , primary, and secondary amines rapidly react with MIC to form substituted ureas . Other N-H compounds, such as amides and ureas , react much more slowly with MIC. [ 21 ]
It also reacts with itself to form a trimer or higher-molecular-weight polymers. In the presence of catalysts , MIC reacts with itself to form a solid trimer, trimethyl isocyanurate, or a higher-molecular-weight polymer:
Sodium methoxide , triethyl phosphine , ferric chloride and certain other metal compounds catalyze the formation of the MIC-trimer, while the high-molecular-weight polymer formation is catalyzed by certain trialkylamines. Since the formation of the MIC trimer is exothermic (1246 joules, or 298 calories, per gram of MIC), the reaction can lead to violent boiling of the MIC. The high-molecular-weight polymer hydrolyzes in hot water to form the trimethyl isocyanurate . Since catalytic metal salts can be formed from impurities in commercial grade MIC and steel, this product must not be stored in steel drums or tanks. [ 12 ]
Methyl isocyanate is extremely toxic . There is no known antidote . The threshold limit value set by the American Conference of Governmental Industrial Hygienists is 0.02 ppm . MIC is toxic by inhalation, ingestion and contact in quantities as low as 0.4 ppm . Exposure symptoms include coughing, chest pain, dyspnea , asthma , irritation of the eyes , nose and throat , as well as skin damage. Higher levels of exposure, over 21 ppm, can result in pulmonary or lung edema , emphysema and hemorrhages , bronchial pneumonia and death . Although the odor of methyl isocyanate cannot be detected at 5 ppm by most people, its potent lachrymal properties provide an excellent warning of its presence (at a concentration of 2–4 parts per million (ppm) subjected to eyes are irritated, while at 21 ppm, subjects could not tolerate the presence of methyl isocyanate in air). [ 11 ] The irritant effects of methyl isocyanate are mediated by the irritant and tear gas receptor TRPA1 in pain-sensing nerve endings in the eye. [ 22 ]
Proper care must be taken to store methyl isocyanate because of its ease of exothermically polymerizing (see Reactions ) and its similar sensitivity to water. Only stainless steel or glass containers may be safely used; the MIC must be stored at temperatures below 40 °C (104 °F) and preferably at 4 °C (39 °F). [ citation needed ]
The toxic effect of the compound was apparent in the 1984 Bhopal disaster , when around 42,000 kilograms (93,000 lb) of methyl isocyanate and other gases were released from the underground reservoirs of the Union Carbide India Limited (UCIL) factory, over a populated area on 3 December 1984, killing about 3,500 people immediately, 8,000 people in the first 48 hours and 15,000 more over the next several years. 200,000 people had lasting health effects from the disaster. [ 23 ] [ 24 ]
During structural fires, natural materials can contribute to releasing isocyanates including methyl isocyanate. [ 25 ]
Until recent decades, the mechanism of methyl isocyanate toxicity in humans was largely unknown or unclear. [ 26 ] [ 27 ] Methyl isocyanate and other isocyanates are electrophiles and are currently thought to cause toxicity by the alkylation of biomolecules. [ 28 ] The mechanism of methyl isocyanate was previously suspected to be the carbamylation of hemoglobin , thus interfering with its oxygen-binding capability and causing hypoxia . However, experiments showed that when rats and guinea pigs were exposed to methyl isocyanate at concentrations above the median lethal concentration ( LC 50 , the concentration sufficient to kill 50% of the tested population), only 2% of hemoglobin molecules were carbamylated, suggesting that this is probably not the mechanism of toxicity. [ 29 ] [ 30 ]
On 30 July 2015, scientists reported that upon the first touchdown of the Philae lander on comet 67/P 's surface, measurements by the COSAC and Ptolemy instruments revealed sixteen organic compounds , four of which were seen for the first time on a comet , including acetamide , acetone , methyl isocyanate and propionaldehyde . [ 32 ] [ 33 ] [ 34 ]
In 2017, two teams of astronomers using the Atacama Large Millimeter Array (ALMA) interferometer made of 66 radio telescopes in the Atacama Desert (northern Chile ) have discovered the presence of MIC around young Sun-like stars. [ 31 ]
MIC is considered a prebiotic molecule as explained by the discoverers of the ALMA findings in IRAS 16293-2422 , a multiple system of very young stars: "This family of organic molecules is involved in the synthesis of peptides and amino acids , which, in the form of proteins , are the biological basis for life as we know it". [ 31 ] | https://en.wikipedia.org/wiki/Methyl_isocyanate |
This page provides supplementary chemical data on Methyl methacrylate .
The handling of this chemical may incur notable safety precautions. It is highly recommend that you seek the Material Safety Datasheet ( MSDS ) for this chemical from a reliable source such as SIRI , and follow its directions.
e - extrapolated data | https://en.wikipedia.org/wiki/Methyl_methacrylate_(data_page) |
Methyl methanesulfonate (MMS), also known as methyl mesylate , is an alkylating agent and a carcinogen . It is also a suspected reproductive toxicant, and may also be a skin/sense organ toxicant. [ 1 ] It is used in cancer treatment. [ 2 ] Its chemical formula is C H 3 − S O 2 −O−CH 3 .
MMS methylates DNA predominantly on N7- deoxyguanosine and N3- deoxyadenosine , and to a much lesser extent also methylates at other oxygen and nitrogen atoms in DNA bases, and also methylates one of the non-carbon bound oxygen atoms of the phosphodiester linkage. Originally, this action was believed to directly cause double-stranded DNA breaks, because homologous recombination -deficient cells are particularly vulnerable to the effects of MMS. [ 3 ] However, it is now believed that MMS stalls replication forks , and cells that are homologous recombination-deficient have difficulty repairing the damaged replication forks. [ 3 ] | https://en.wikipedia.org/wiki/Methyl_methanesulfonate |
Methyl nitrate is the methyl ester of nitric acid and has the chemical formula CH 3 NO 3 . It is a colourless explosive volatile liquid.
It can be produced by the condensation of nitric acid and methanol : [ 3 ]
A newer method uses methyl iodide and silver nitrate : [ 4 ]
Methyl nitrate can be produced on a laboratory or industrial scale either through the distillation of a mixture of methanol and nitric acid, or by the nitration of methanol by a mixture of sulfuric and nitric acids. The first procedure is not preferred due to the great explosion danger presented by the methyl nitrate vapour . The second procedure is essentially identical to that of making nitroglycerin . However, the process is usually run at a slightly higher temperature and the mixture is stirred mechanically on an industrial scale instead of with compressed air.
Electrolytic production methods have been reported involving electrolyzing sodium acetate and sodium nitrate in acetic acid. [ 5 ]
Methyl nitrate is also the product of the oxidation of some organic compounds in the presence of nitrogen oxides and chlorine, namely chloroethane or di-tert-butyl ether , while also producing nitromethane. [ 6 ] Oxidation of nitromethane using nitrogen dioxide in an inert atmosphere can also yield methyl nitrate. [ 7 ]
Methyl nitrate is a sensitive explosive . When ignited it burns extremely fiercely with a gray-blue flame. Methyl nitrate is a very strong explosive with a detonation velocity of 6,300 m/s, [ 8 ] like nitroglycerin , ethylene glycol dinitrate , and other nitrate esters . The sensitivity of methyl nitrate to initiation by detonation is among the greatest known, with even a number one blasting cap , the lowest power available, producing a near full detonation of the explosive. [ citation needed ]
Despite the superior explosive properties of methyl nitrate, it has not received application as an explosive due mostly to its high volatility , which prevents it from being stored or handled safely.
As well as being an explosive, methyl nitrate is toxic and causes headaches when inhaled.
Methyl nitrate has not received much attention as an explosive, but as a mixture containing 25% methanol it was used as rocket fuel and volumetric explosive under the name Myrol in Nazi Germany during World War II . This mixture would evaporate at a constant rate and so its composition would not change over time. It presents a slight explosive danger (it is somewhat difficult to detonate) and does not detonate easily via shock. [ 9 ] [ 10 ]
According to A. Stettbacher, the substance was used as a combustible during the Reichstag fire in 1933. [ 11 ] Gartz shows in a recent work that only methyl nitrate with its production and explosion potential can represent the famous and mysterious "shooting water" from the German Feuerwerkbuch ("fireworks book") of about 1420 [ 12 ] (the oldest technical text in German language , handwritten in Dresden and later printed in Augsburg ). [ 13 ]
An extract of the text from the 1420 Feuerwerkbuch is as follows (written in Early New High German ):
"Wildu mit wasser schyessen // daß du kein pulfer prauch // est vnd sterker und waiter // mit schewst dann als du daß aller // pest pulfer hast das yemann gehab // en mag und ye gemacht wurd so ny // salpeter und distillier den mit wasser // vnd nym oleo benedicto dazu auch … // … vnd zunt sie an mit sinnen das du davon kommen magst … //
…mit disem wasser schewst du dreytousent schrit weit … // … es ist gar köstlich…"
Translated:
"Do you want to shoot with water // so that you don't need powder // and stronger and further // you shoot than the very // best powder somebody might have had ever // and was made ever // so take salpetre and distill it with water // and also take oleo benedicto (the oil of Benedicus) // and ignite it with the intention that you may get off ... with this water you will shoot threethousand foot // it is so delicious"
The structure of methyl nitrate has been studied experimentally in the gas phase (combined gas-electron diffraction and microwave spectroscopy , GED/MW) and in the crystalline state ( X-ray diffraction , XRD) (see Table 1). [ 4 ]
In the solid state there are weak interactions between the O and N atoms of different molecules (see figure). | https://en.wikipedia.org/wiki/Methyl_nitrate |
Methyl nitrite is an organic compound with the chemical formula CH 3 ONO . It is a gas, and is the simplest alkyl nitrite .
At room temperature, methyl nitrite exists as a mixture of cis and trans conformers . The cis conformer is 3.13 kJ mol −1 , more stable than the trans form, with an energy barrier to rotation of 45.3 kJ mol −1 . [ 3 ] The cis and trans structure have also been determined by microwave spectroscopy (see external links).
Methyl nitrite can be prepared by the reaction of silver nitrite with iodomethane : Silver nitrite (AgNO 2 ) exists in solution as the silver ion , Ag + and the nitrite ion, NO 2 − . One of the lone pairs on an oxygen from nitrite ion attacks the methyl group (−CH 3 ), releasing the iodide ion into solution. [ 4 ] Unlike silver nitrite, silver iodide is highly insoluble in water and thus forms a solid. [ 5 ] Note that nitrogen is a better nucleophile than oxygen and most nitrites would react via an S N 2 -like mechanism and the major product would be nitromethane . For example, sodium and potassium nitrite reacting with iodomethane would produce mostly nitromethane, with methyl nitrite as the minor product. However, the presence of the silver ion in solution has a stabilizing effect on the formation of carbocation intermediates , increasing the percent yield of methyl nitrite. In either case, some nitromethane and methyl nitrite are both formed. [ 4 ]
The figure shows the two gas-phase structures of methyl nitrite, as determined by IR and microwave spectroscopy.
Methyl nitrite free of nitromethane can be made by reacting iodomethane with nitrogen dioxide :
Methyl nitrite is a precursor and intermediate, e.g. during production of phenylpropanolamine . [ 6 ]
Methyl nitrite is also present in aged cigarette smoke. Here it is presumably formed from nitrogen dioxide (itself formed by oxidation of nitric oxide ) and methanol . [ 7 ]
As one product of the combustion of unleaded petrol in air, methyl nitrite has been proposed as a cause of the decline of insects , and hence that of songbirds in Europe . [ 8 ]
Methyl nitrite is a toxic asphyxiating gas, a potent cyanotic agent. Exposure may result in methemoglobinemia . [ 6 ]
Methyl nitrite is an oxidizing agent and a heat-sensitive explosive; its sensitivity increases in presence of metal oxides. With inorganic bases it forms explosive salts. It forms explosive mixtures with air. It is used as a rocket propellant , a monopropellant . [ 9 ] It explodes more violently than ethyl nitrite. Lower alkyl nitrites may decompose and burst the container even when stored under refrigeration. [ 10 ] | https://en.wikipedia.org/wiki/Methyl_nitrite |
Methyl orange is a pH indicator frequently used in titration because of its clear and distinct color variance at different pH values. Methyl orange shows red color in acidic medium and yellow color in basic medium. Because it changes color at the p K a of a mid strength acid, it is usually used in titration of strong acids in weak bases that reach the equivalence point at a pH of 3.1-4.4. [ 4 ] Unlike a universal indicator , methyl orange does not have a full spectrum of color change, but it has a sharp end point. In a solution becoming less acidic, methyl orange changes from red to orange and, finally, to yellow—with the reverse process occurring in a solution of increasing acidity.
In a solution that decreases in acidity, methyl orange moves from the color red to orange and finally to yellow with the opposite occurring for a solution increasing in acidity. This color change from yellow to red occurs because the protons in the acidic solution react with the N=N bond of the molecule, protonating one of them and changing the visible light absorption of the molecule to reflect more red light than orange/yellow.
In an acid, it is reddish and in alkali, it is yellow. Methyl orange has a p K a of 3.47 in water at 25 °C (77 °F). [ 5 ]
Modified (or screened) methyl orange, an indicator consisting of a solution of methyl orange and xylene cyanol , changes from grey-violet to green as the solution becomes more basic.
Methyl orange has mutagenic properties. [ 2 ] When methyl orange is put under oxidative stress , one of the double-bonded nitrogen atoms that connects the aromatic rings gets radicalized and can further break down into reactive oxygen species or anilines , which are carcinogenic and can mutate DNA. [ 6 ] Various bacteria and enzymes can also cause this breakdown to occur.
Methyl orange is an azobenzene derivative that can be formed from dimethylaniline and sulfanilic acid , first through a diazonium salt formation with the sulfanilic acid, followed by a nucleophilic attack from the dimethylaniline and rearomatization . [ 7 ]
The absorption of methyl orange on the UV-vis spectrum is between 350-550 nm, with its peak at 464 nm. This is in the green-purple visible light range and explains why methyl orange is, in fact, orange. [ 8 ] | https://en.wikipedia.org/wiki/Methyl_orange |
Methyl phenyldiazoacetate is the organic compound with the formula C 6 H 5 C(N 2 )CO 2 Me. It is a diazo derivative of methyl phenylacetate . Colloquially referred to as "phenyldiazoacetate", it is generated and used in situ after isolation as a yellow oil.
Methyl phenyldiazoacetate and many related derivatives are precursors to donor-acceptor carbenes , which can be used for cyclopropanation or to insert into C-H bonds of organic substrates. These reactions are catalyzed by dirhodium tetraacetate or related chiral complexes. [ 1 ] Methyl phenyldiazoacetate is prepared by treating methyl phenylacetate with p-acetamidobenzenesulfonyl azide in the presence of base. [ 2 ] [ 3 ] | https://en.wikipedia.org/wiki/Methyl_phenyldiazoacetate |
Methyl radical is an organic compound with the chemical formula CH • 3 (also written as [CH 3 ] • ). It is a metastable colourless gas, which is mainly produced in situ as a precursor to other hydrocarbons in the petroleum cracking industry. It can act as either a strong oxidant or a strong reductant , and is quite corrosive to metals.
Its first ionization potential (yielding the methenium ion, CH + 3 ) is 9.837 ± 0.005 eV . [ 2 ]
The carbon centre in methyl can bond with electron-donating molecules by reacting:
Because of the capture of the nucleophile (R • ), methyl has oxidising character. Methyl is a strong oxidant with organic chemicals. However, it is equally a strong reductant with chemicals such as water. It does not form aqueous solutions, as it reduces water to produce methanol and elemental hydrogen:
The molecular geometry of the methyl radical is trigonal planar (bond angles are 120°), although the energy cost of distortion to a pyramidal geometry is small. All other electron-neutral, non-conjugated alkyl radicals are pyramidalized to some extent, though with very small inversion barriers. For instance, the t -butyl radical has a bond angle of 118° with a 0.7 kcal/mol (2.9 kJ/mol) barrier to pyramidal inversion . On the other hand, substitution of hydrogen atoms by more electronegative substituents leads to radicals with a strongly pyramidal geometry (112°), such as the trifluoromethyl radical, CF • 3 , with a much more substantial inversion barrier of around 25 kcal/mol (100 kJ/mol). [ 3 ]
Methyl undergoes the typical chemical reactions of a radical. Below approximately 1,100 °C (1,400 K), it rapidly dimerises to form ethane . Upon treatment with an alcohol, it converts to methane and either an alkoxy or hydroxyalkyl. Reduction of methyl gives methane. When heated above, at most, 1,400 °C (1,700 K), methyl decomposes to produce methylidyne and elemental hydrogen, or to produce methylene and atomic hydrogen:
Methyl is very corrosive to metals, forming methylated metal compounds:
Some radical SAM enzymes generate methyl radicals by reduction of S-adenosylmethionine. [ 4 ]
It can be produced by the ultraviolet photodissociation of acetone vapour at 193 nm: [ 5 ]
It is also produced by the ultraviolet dissociation of halomethanes :
It can also be produced by the reaction of methane with the hydroxyl radical :
This process begins the major removal mechanism of methane from the atmosphere. The reaction occurs in the troposphere or stratosphere . In addition to being the largest known sink for atmospheric methane, this reaction is one of the most important sources of water vapor in the upper atmosphere.
This reaction in the troposphere gives a methane lifetime of 9.6 years. Two more minor sinks are soil sinks (160 year lifetime) and stratospheric loss by reaction with • OH, • Cl and • O 1 D in the stratosphere (120 year lifetime), giving a net lifetime of 8.4 years. [ 6 ]
Methyl radicals can also be obtained by pyrolysis of azomethane , CH 3 N=NCH 3 , in a low-pressure system.
Methyl was discovered in interstellar medium in 2000 by a team led by Helmut Feuchtgruber who detected it using the Infrared Space Observatory . It was first detected in molecular clouds toward the centre of the Milky Way. [ 7 ] | https://en.wikipedia.org/wiki/Methyl_radical |
Methyl red (2-( N , N -dimethyl-4-aminophenyl) azobenzenecarboxylic acid), also called C.I. Acid Red 2 , is an indicator dye that turns red in acidic solutions. It is an azo dye , and is a dark red crystalline powder. Methyl red is a pH indicator ; it is red in pH under 4.4, yellow in pH over 6.2, and orange in between, with a p K a of 5.1. [ 2 ] Murexide and methyl red are investigated as promising enhancers of sonochemical destruction of chlorinated hydrocarbon pollutants . Methyl red is classed by the IARC in group 3 - unclassified as to carcinogenic potential in humans.
As an azo dye, methyl red may be prepared by diazotization of anthranilic acid , followed by reaction with dimethylaniline : [ 3 ]
The color of methyl red is pH dependent, because protonation causes it to adopt a hydrazone / quinone structure.
Methyl Red has a special use in histopathology for showing acidic nature of tissue and presence of organisms with acidic natured cell walls.
Methyl Red is detectably fluorescent in 1:1 water:methanol (pH 7.0), with an emission maximum at 375 nm ( UVA ) upon excitation with 310 nm light ( UVB ). [ 4 ]
In microbiology , methyl red is used in the methyl red test (MR test), used to identify bacteria producing stable acids by mechanisms of mixed acid fermentation of glucose ( cf. Voges–Proskauer test).
The MR test, the "M" portion of the four IMViC tests, is used to identify enteric bacteria based on their pattern of glucose metabolism. All enterics initially produce pyruvic acid from glucose metabolism. Some enterics subsequently use the mixed acid pathway to metabolize pyruvic acid to other acids, such as lactic , acetic , and formic acids. These bacteria are called methyl-red positive and include Escherichia coli and Proteus vulgaris . Other enterics subsequently use the butylene glycol pathway to metabolize pyruvic acid to neutral end products. These bacteria are called methyl-red-negative and include Serratia marcescens and Enterobacter aerogenes .
A tube filled with a glucose phosphate broth is inoculated with a sterile transfer loop. The tube is incubated at 35 °C (95 °F) for 2–5 days. After incubation, 2.5 ml of the medium are transferred to another tube. Five drops of the pH indicator methyl red is added to this tube. The tube is gently rolled between the palms to disperse the methyl red.
Enterics that subsequently metabolize pyruvic acid to other acids lower the pH of the medium to 4.2. At this pH, methyl red turns red, a positive test. Enterics that subsequently metabolize pyruvic acid to neutral end products lower the pH of the medium to only 6.0. At this pH, methyl red is yellow, a negative test. | https://en.wikipedia.org/wiki/Methyl_red |
Methyl tert -butyl ether ( MTBE ), also known as tert -butyl methyl ether , is an organic compound with a structural formula (CH 3 ) 3 COCH 3 . MTBE is a volatile, flammable, and colorless liquid that is sparingly soluble in water. [ 1 ] Primarily used as a fuel additive, MTBE is blended into gasoline to increase its octane rating and knock resistance , and reduce unwanted emissions . [ 2 ] [ 3 ]
MTBE is manufactured via the chemical reaction of methanol and isobutylene . Methanol is primarily derived from natural gas , [ 4 ] where steam reforming converts the various light hydrocarbons in natural gas (primarily methane) into carbon monoxide and hydrogen. [ 5 ] The resulting gases then further react in the presence of a catalyst to form methanol. [ 6 ] Isobutylene can be produced through a variety of methods. n -butane can be isomerized into isobutane which can be dehydrogenated to isobutylene. [ 7 ] In the Halcon process, t -Butyl hydroperoxide derived from isobutane oxygenation is treated with propylene to produce propylene oxide and t -butanol . The t -butanol can be dehydrated to isobutylene.
MTBE production across the globe has been steady because of its positive impact on engine performance. [ 8 ] The global demand has been mainly driven by growing Asian markets. [ 9 ] Chinese capacity grew from ~18 million metric tons in 2017 [ 10 ] to ~22 millions in 2023, with actual production standing at ~16 millions in the same year. [ 11 ]
Under pressure from the bioethanol lobby, [ 8 ] production of MTBE in the U.S. peaked in 1999 at 260,000 barrels per day [ 12 ] before dropping down due to environmental and health concerns to about 50,000 barrels per day and holding steady, [ 13 ] mostly for the export market. After the purchase of SABIC , [ 14 ] [ 15 ] oil giant Saudi Aramco is now considered to be the world's largest producer [ 16 ] with an estimated production capacity of 2.37 million metric tons per year (mt/yr). [ 17 ] Worldwide production capacity of MTBE in 2018 was estimated to be 35 million metric tons. [ 18 ]
MTBE is used as a fuel component in fuel for gasoline engines. It is one of a group of chemicals commonly known as oxygenates because they raise the oxygen content of gasoline.
In the U.S. MTBE has been used in gasoline at low levels since 1979, replacing tetraethyllead (TEL) as an antiknock (octane rating) additive to prevent engine knocking . [ 19 ] Oxygenates also help gasoline burn more completely, reducing tailpipe emissions . Oxygenates also dilute or displace gasoline components such as aromatics (e.g., benzene ). Before the introduction of other oxygenates and octane enhancers, refiners chose MTBE for its blending characteristics and low cost.
Other oxygenates are available as additives for gasoline including ethanol and other ethers such as ETBE .
Ethanol has been advertised as a safe alternative by agricultural and other interest groups in the U.S. and Europe. In 2003, California was the first U.S. state to start replacing MTBE with ethanol.
An alternative to ethanol is ETBE, which is manufactured from ethanol and isobutene. Its performance as an additive is similar to MTBE, but due to the higher price of ethanol compared to methanol, it is more expensive.
Higher quality gasoline is also an alternative, so that additives such as MTBE are unnecessary. Iso-octane itself is used. MTBE plants can be retrofitted to produce iso-octane from isobutylene. [ 20 ] [ 21 ]
MTBE is sometimes used as a solvent, [ 22 ] [ 23 ] [ 24 ] although it is used less commonly than diethyl ether. Although an ether, MTBE is a poor Lewis base and does not support formation of Grignard reagents . It is also unstable toward strong acids. It reacts dangerously with bromine . [ 25 ]
MTBE forms azeotropes with water (52.6 °C; 96.5% MTBE) [ 26 ] and methanol (51.3 °C; 68.6% MTBE). [ 27 ] The solubility of water in MTBE is reported to be 1.5 g/100g at 23 °C. [ 26 ]
In an investigational medical procedure called contact dissolution therapy, MTBE is injected directly into the gallbladder to dissolve cholesterol gallstones . Due to concerns of MTBE toxicity and potentially serious side effects in the event of solvent draining into the duodenum , and the advent of laparoscopic surgery techniques, this procedure is considered obsolete. [ 28 ] [ 29 ] [ 30 ]
MTBE is used in organic chemistry as a relatively inexpensive solvent with properties comparable to diethyl ether, but with a higher boiling point and less solubility in water. As a solvent, MTBE has one distinct advantage over most ethers - it has a much lower tendency to form explosive organic peroxides. It is widely used as a solvent in industry where, for safety and regulatory reasons, handling diethyl ether or other ethers is much more difficult and expensive. MTBE as a solvent is used in the oil refining industry as a method for dewaxing waxy petroleum fractions.
MTBE gives water an unpleasant taste, even at very low concentrations of <30 μg/L (<30ppb). [ 31 ] MTBE often is introduced into water-supply aquifers by leaking underground storage tanks (USTs) at gasoline stations or spills of gasoline. The higher water solubility and persistence of MTBE cause it to travel faster and farther than many other components of gasoline when released into an aquifer. [ 32 ]
MTBE is biodegraded by the action of bacteria. In the proper type of bioreactor , such as a fluidized bed bioreactor, MTBE may be removed rapidly and economically from water to undetectable levels. Activated carbon produced from coconut shells and optimized for MTBE adsorption may reduce MTBE to undetectable levels, [ 33 ] although this level of reduction is likely to occur only in the most ideal circumstances. There are currently no known published cases of any in-situ treatment method that has been capable of reducing contaminant concentrations to baseline (pre-development) conditions within the aquifer soil matrix.
According to the International Agency for Research on Cancer (IARC), a branch of the World Health Organization , MTBE is not classified as a human carcinogen .
The Energy Policy Act of 2005 , as approved by the U.S. House of Representatives, did not include a provision for shielding MTBE manufacturers from water contamination lawsuits. This provision was first proposed in 2003 and had been thought by some to be a priority of Tom DeLay and Rep. Joe Barton , then chairman of the Energy and Commerce Committee. [ 34 ] This bill did include a provision that gave MTBE makers, including some major oil companies , $2 billion in transition assistance while MTBE was phased out over the following nine years. [ 35 ] Due to opposition in the Senate, [ 36 ] the conference report dropped all MTBE provisions. The final bill was signed into law by President George W. Bush . [ 37 ] The lack of MTBE liability protection is resulting in a switchover to the use of ethanol as a gasoline additive.
MTBE removal from groundwater and soil contamination in the U.S. was estimated to cost from $1 billion [ 38 ] to US$30 billion , [ 39 ] including removing the compound from aquifers and municipal water supplies and replacing leaky underground oil tanks. In one case, the cost to oil companies to clean up the MTBE in wells belonging to the city of Santa Monica, California was estimated to exceed $200 million. [ 40 ] In another case, New York City estimated a $250 million cost for cleanup of a single wellfield in the borough of Queens in 2009. [ 41 ] In 2013 a jury awarded the State of New Hampshire $236 million in damages in order to treat groundwater contaminated by MTBE. [ 42 ]
Many lawsuits are still pending regarding MTBE contamination of public and private drinking water supplies.
EPA first listed MTBE in 1998 as a candidate for development of a national Maximum Contaminant Level (MCL) standard in drinking water. [ 43 ] The agency listed MTBE on its Contaminant Candidate List in 2022 but has not announced whether it will develop an MCL. [ 44 ] EPA uses toxicity data in developing MCLs for public water systems . [ 45 ]
California established a state-level MCL for MTBE, 13 micrograms per liter, in 2000. [ 46 ] | https://en.wikipedia.org/wiki/Methyl_tert-butyl_ether |
Methyl violet is a family of organic compounds that are mainly used as dyes . Depending on the number of attached methyl groups, the color of the dye can be altered. Its main use is as a purple dye for textiles and to give deep violet colors in paint and ink. It is also used as a hydration indicator for silica gel . Methyl violet 10B is also known as crystal violet (and many other names) and has medical uses. [ 1 ]
The term methyl violet encompasses three compounds that differ in the number of methyl groups attached to the amine functional group . Methyl violets are mixtures of tetramethyl (2B), pentamethyl (6B) and hexamethyl (10B) pararosanilins. [ 2 ]
They are all soluble in water , ethanol , diethylene glycol and dipropylene glycol .
Methyl violet 2B (IUPAC name: 4,4′-((4-Iminocyclohexa-2,5-dien-1-ylidene)methylene)bis( N , N -dimethylaniline) monohydrochloride) is a green powder which is soluble in water and ethanol but not in xylene. It appears yellow in solution of low pH (approximately 0.15) and changes to violet with pH increasing toward 3.2. [ 3 ]
Methyl violet 10B has six methyl groups. It is known in medicine as Gentian violet (or crystal violet or pyoctanin(e) [ 1 ] ) and is the active ingredient in a Gram stain , used to classify bacteria. It is used as a pH indicator , with a range between 0 and 1.6. The protonated form (found in acidic conditions) is yellow, turning blue-violet above pH levels of 1.6. [ 4 ]
Methyl violet 10B inhibits the growth of many Gram positive bacteria, except streptococci . [ citation needed ] When used in conjunction with nalidixic acid (which destroys gram-negative bacteria), it can be used to isolate the streptococci bacteria for the diagnosis of an infection. [ citation needed ]
Methyl violet is a mutagen and mitotic poison, therefore concerns exist regarding the ecological impact of the release of methyl violet into the environment. Methyl violet has been used in vast quantities for textile and paper dyeing, and 15% of such dyes produced worldwide are released to environment in wastewater. Numerous methods have been developed to treat methyl violet pollution. The three most prominent are chemical bleaching, biodegradation, and photodegradation .
Chemical bleaching is achieved by oxidation or reduction . Oxidation can destroy the dye completely, e.g. through the use of sodium hypochlorite (NaClO, common bleach) or hydrogen peroxide . [ 5 ] [ 6 ] Reduction of methyl violet occurs in microorganisms but can be attained chemically using sodium dithionite .
Biodegradation has been well investigated because of its relevance to sewage plants with specialized microorganisms. Two microorganisms that have been studied in depth are the white rot fungus and the bacterium Nocardia corallina . [ 7 ] [ 8 ]
Light alone does not rapidly degrade methyl violet, [ 9 ] but the process is accelerated upon the addition of large band-gap semiconductors, titanium dioxide or zinc oxide . [ 10 ] [ 11 ]
Many other methods have been developed to treat the contamination of dyes in a solution, including electrochemical degradation, [ 12 ] ion exchange, [ 13 ] laser degradation, and absorption onto various solids such as activated charcoal . | https://en.wikipedia.org/wiki/Methyl_violet |
Methyl yellow , or C.I. 11020 , is an organic compound with the formula C 6 H 5 N 2 C 6 H 4 N(CH 3 ) 2 . It is an azo dye derived from dimethylaniline . It is a yellow solid. According to X-ray crystallography , the C 14 N 3 core of the molecule is planar. [ 3 ]
It is used as a dye for plastics and may be used as a pH indicator .
In aqueous solution at low pH, methyl yellow appears red. Between pH 2.9 and 4.0, methyl yellow undergoes a transition, to become yellow above pH 4.0.
It is a possible carcinogen . [ 2 ] As "butter yellow", the agent had been used as a food additive in butter and margarine before its toxicity was recognized. [ 4 ]
Butter yellow was synthesized by Peter Griess in the 1860s at the Royal College of Chemistry in London. [ 5 ] The dye was used to dye butter in Germany [ 5 ] [ 6 ] and other parts of the world [ citation needed ] during the latter half of the 19th century and the beginning of the 20th before being phased out in the 1930s and 40s. It was in the 1930s that research led by Riojun Kinosita showed the link between several azo dyes and cancer, linking butter yellow to liver cancer in rats after two to three months exposure. [ 7 ] In 1939, the International Congress for Cancer Research issued a recommendation for the banning of cancer-causing food dyes (including butter yellow) from food production. [ 5 ] [ 6 ]
In 2014, dried tofu products (a.k.a. dougan 豆乾) from Taiwan were found to have been adulterated with methyl yellow, used as a coloring agent. [ 8 ]
Structurally similar compounds: | https://en.wikipedia.org/wiki/Methyl_yellow |
Methylacetylene-propadiene ( MPS ) gas is a type of fuel gas used in oxy-fuel welding and cutting torches, comprising a mixture of several gases.
An MPS gas is a mixture of two or more of propane , butane , butadiene , methylacetylene (propyne, CH 3 C≡CH) and propadiene (CH 2 =C=CH 2 ). [ 1 ] They are marketed under different names including: "MPS", "Chem-O-Lean", "Apachi Gas", "FG-2 Gas", "Flamex" and "natural gas". [ 1 ] The most commonly known type of MPS gas is the discontinued MAPP gas . [ 2 ]
As a fuel gas, it burns hotter than propylene , propane or natural gas .
This organic chemistry article is a stub . You can help Wikipedia by expanding it .
This metalworking article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Methylacetylene-propadiene_gas |
Methylaluminoxane , commonly called MAO , is a mixture of organoaluminium compounds with the approximate formula (Al(CH 3 )O) n . It is usually encountered as a solution in ( aromatic ) solvents , commonly toluene but also xylene , cumene , or mesitylene , [ 1 ] Used in large excess, it activates precatalysts for alkene polymerization. [ 2 ] [ 3 ] [ 4 ]
MAO is prepared by the incomplete hydrolysis of trimethylaluminium , as indicated by this idealized equation: [ 5 ]
After many years of study, single crystals of an active MAO were analyzed by X-ray crystallography . The molecule adopts a ruffled sheet of tetrahedral Al centers linked by triply bridging oxides. [ 4 ]
MAO is well known as catalyst activator for olefin polymerizations by homogeneous catalysis . In traditional Ziegler–Natta catalysis, supported titanium trichloride is activated by treatment with trimethylaluminium (TMA). TMA only weakly activates homogeneous precatalysts, such as zirconocene dichloride . In the mid-1970s Kaminsky discovered that metallocene dichlorides can be activated by MAO (see Kaminsky catalyst ). [ 6 ] The effect was discovered when a small amount of water was found to enhance the activity in the Ziegler–Natta system.
MAO serves multiple functions in the activation process. First it alkylates the metal-chloride pre-catalyst species giving Ti/Zr-methyl intermediates. Second, it abstracts a ligand from the methylated precatalysts, forming an electrophilic, coordinatively unsaturated catalysts that can undergo ethylene insertion. This activated catalyst is an ion pair between a cationic catalyst and an weakly basic MAO-derived anion. [ 7 ] MAO also functions as scavenger for protic impurities.
Diverse mechanisms have been proposed for the formation of MAO and many structures as well. | https://en.wikipedia.org/wiki/Methylaluminoxane |
In biochemistry , an N -methylamide (NME) is a blocking group for the C-terminus end of peptides . When the carboxyl group of the C-terminus is replaced with a methylamide, further elongation of the peptide chain is prevented. C-Terminal modified peptides are also useful for the modulation of structure-activity relationships and for modifying conformational properties of peptides. N -Methylamides can be prepared directly from solid phase resin-bound peptides. [ 1 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Methylamide |
Methylammonium formate is an ionic liquid consisting of methylammonium (CH 3 NH 3 + ) as the cation and formate (HCOO – ) as the anion . [ 1 ] This salt can be formed by the reaction between methylamine (CH 3 NH 2 ) and formic acid (HCOOH). It has characteristics of both an ammonium salt and a formate salt. It is soluble in water , [ 2 ] as well as other polar solvents .
This article about analytical chemistry is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Methylammonium_formate |
Methylammonium nitrate is an explosive chemical with the molecular formula CH 6 N 2 O 3 , alternately CH 3 NH 3 + NO 3 − . It is the salt formed by the neutralization of methylamine with nitric acid . This substance is also known as methylamine nitrate and monomethylamine nitrate, not to be confused with methyl nitramine or monomethyl nitramine.
Methylammonium nitrate was first used as an explosive ingredient by the Germans during World War II . [ 1 ] It was originally called mono-methylamine nitrate, a name that has largely stuck among chemists who formulate energetic materials.
Methylammonium nitrate is somewhat similar in explosive properties to ammonium nitrate (AN) which yields 85% of the power of nitroglycerine when the ammonium nitrate is incorporated into an explosive. The addition of the carbon-containing methyl group in methylammonium nitrate imparts better explosive properties and helps create a more favorable oxygen balance.
After World War II, methylammonium nitrate was largely ignored by explosives manufacturers, in favor of less-costly ammonium nitrate. Ammonium nitrate-fuel oil mixtures ( ANFO ) were sufficient for most large-diameter explosives uses.
Methylammonium nitrate saw a resurgence when E. I. du Pont de Nemours and Company ( DuPont ), seeking to lower the cost of its TNT-based Tovex water-gel explosives , incorporated a mixture of methylammonium nitrate with ammonium nitrate which served as a basis for DuPont's water-gels manufactured under the names "Tovex Extra" and "Pourvex Extra". Methylammonium nitrate, also known as PR-M (which stands for "Potomac River—Mono-methylamine nitrate") soon was seen as the possible path toward creating a low-cost blasting agent (water gel explosives) that might replace the explosives based on nitroglycerin (dynamites).
In late 1973, DuPont started to phase out dynamite and replace it with water-gels based on PR-M. However, PR-M proved to have unusual "mass effects". That is, if there was sufficient mass, under certain conditions, PR-M could explode without warning. On August 6, 1974, a tank car containing PR-M blew up in Wenatchee, Washington, rail yard, killing two and injuring 66 others. [ 2 ] On July 4, 1976, a PR-M storage with 60,000 pounds (approximately 27,200Kg) of PR-M detonated at DuPont's Potomac River Works at Martinsburg, WV. Though there was no loss of life, there were many injuries and a substantial loss of property. | https://en.wikipedia.org/wiki/Methylammonium_nitrate |
Methylated DNA immunoprecipitation (MeDIP or mDIP) is a large-scale ( chromosome - or genome -wide) purification technique in molecular biology that is used to enrich for methylated DNA sequences . It consists of isolating methylated DNA fragments via an antibody raised against 5-methylcytosine (5mC). This technique was first described by Weber M. et al. [ 1 ] in 2005 and has helped pave the way for viable methylome -level assessment efforts, as the purified fraction of methylated DNA can be input to high-throughput DNA detection methods such as high-resolution DNA microarrays ( MeDIP-chip ) or next-generation sequencing (MeDIP-seq). Nonetheless, understanding of the methylome remains rudimentary; its study is complicated by the fact that, like other epigenetic properties, patterns vary from cell-type to cell-type.
DNA methylation , referring to the reversible methylation of the 5 position of cytosine by methyltransferases , is a major epigenetic modification in multicellular organisms. [ 2 ] In mammals, this modification primarily occurs at CpG sites , which in turn tend to cluster in regions called CpG islands . [ 3 ] There is a small fraction of CpG islands that can overlap or be in close proximity to promoter regions of transcription start sites. The modification may also occur at other sites, [ 4 ] but methylation at either of these sites can repress gene expression by either interfering with the binding of transcription factors or modifying chromatin structure to a repressive state. [ 5 ]
Disease condition studies have largely fueled the effort in understanding the role of DNA methylation. Currently, the major research interest lies in investigating disease conditions such as cancer to identify regions of the DNA that has undergone extensive methylation changes. The genes contained in these regions are of functional interest as they may offer a mechanistic explanation to the underlying genetic causes of a disease. For instance, the abnormal methylation pattern of cancer cells [ 6 ] [ 7 ] [ 8 ] was initially shown to be a mechanism through which tumor suppressor -like genes are silenced, [ 9 ] although it was later observed that a much broader range of gene types are affected. [ 10 ] [ 11 ] [ 12 ]
There are two approaches to methylation analysis: typing and profiling technologies. Typing technologies are targeted towards a small number of loci across many samples, and involve the use of techniques such as PCR , restriction enzymes , and mass spectrometry . Profiling technologies such as MeDIP are targeted towards a genome - or methylome -wide level assessment of methylation; this includes restriction landmark genomic scanning (RLGS), [ 13 ] and bisulfite conversion -based methods, which rely on the treatment of DNA with bisulfite to convert unmethylated cytosine residues to uracil . [ 14 ] [ 15 ] [ 16 ] [ 17 ]
Other methods mapping and profiling the methylome have been effective but are not without their limitations that can affect resolution, level of throughput, or experimental variations. For instance, RLGS is limited by the number of restriction sites in genome that can be targets for the restriction enzyme; typically, a maximum of ~4100 landmarks can be assessed. [ 18 ] Bisulfite sequencing -based methods, despite possible single-nucleotide resolution, have a drawback: the conversion of unmethylated cytosine to uracil can be unstable. [ 19 ] In addition, when bisulfite conversion is coupled with DNA microarrays to detect bisulfite converted sites, the reduced sequence complexity of DNA is a problem. Microarrays capable of comprehensively profiling the whole-genome become difficult to design as fewer unique probes are available. [ 20 ]
The following sections outline the method of MeDIP coupled with either high-resolution array hybridization or high-throughput sequencing. Each DNA detection method will also briefly describe post-laboratory processing and analysis. Different post-processing of the raw data is required depending on the technology used to identify the methylated sequences. This is analogous to data generated using ChIP-chip and ChIP-seq .
Genomic DNA is extracted ( DNA extraction ) from the cells and purified. The purified DNA is then subjected to sonication to shear it into random fragments. This sonication process is quick, simple, and avoids restriction enzyme biases. The resulting fragments range from 300 to 1000 base pairs (bp) in length, although they are typically between 400 and 600 bp. [ 21 ] The short length of these fragments is important in obtaining adequate resolution, improving the efficiency of the downstream step in immunoprecipitation, and reducing fragment-length effects or biases. Also, the size of the fragment affects the binding of 5-methyl-cytidine (5mC) antibody because the antibody needs more than just a single 5mC for efficient binding. [ 22 ] To further improve binding affinity of the antibodies, the DNA fragments are denatured to produce single-stranded DNA. Following denaturation, the DNA is incubated with monoclonal 5mC antibodies. The classical immunoprecipitation technique is then applied: magnetic beads conjugated to anti-mouse- IgG are used to bind the anti-5mC antibodies, and unbound DNA is removed in the supernatant. To purify the DNA, proteinase K is added to digest the antibodies and release the DNA, which can be collected and prepared for DNA detection.
For more details regarding the experimental steps see. [ 1 ] [ 19 ] [ 23 ] [ 24 ]
A fraction of the input DNA obtained after the sonication step above is labeled with cyanine -5 (Cy5; red) deoxy-cytosine-triphosphate while the methylated DNA, enriched after the immunoprecipitation step, is labeled with cyanine -3 (Cy3; green). The labeled DNA samples are cohybridized on a 2-channel, high-density genomic microarray to probe for presence and relative quantities. The purpose of this comparison is to identify sequences that show significant differences in hybridization levels, thereby confirming the sequence of interest is enriched.
Array-based identification of MeDIP sequences are limited to the array design. As a result, the resolution is restricted to the probes in the array design. There are additional standard steps required in signal processing to correct for hybridization issues such as noise, as is the case with most array technologies.
See [ 23 ] [ 24 ] [ 25 ] for more details.
The MeDIP-seq approach, i.e. the coupling of MeDIP with next generation, short-read sequencing technologies such as 454 pyrosequencing or Illumina (Solexa), was first described by Down et al. in 2008. [ 20 ] The high-throughput sequencing of the methylated DNA fragments produces a large number of short reads (36-50bp [ 26 ] or 400 bp, [ 27 ] depending on the technology). The short reads are aligned to a reference genome using alignment software such as Mapping and Assembly with Quality ( Maq ), which uses a Bayesian approach, along with base and mapping qualities to model error probabilities for the alignments. [ 28 ] The reads can then be extended to represent the ~400 to 700 bp fragments from the sonication step. The coverage of these extended reads can be used to estimate the methylation level of the region. A genome browser such as Ensembl can also be used to visualize the data.
Validation of the approach to assess quality and accuracy of the data can be done with quantitative PCR . This is done by comparing a sequence from the MeDIP sample against an unmethylated control sequence. The samples are then run on a gel and the band intensities are compared. [ 19 ] The relative intensity serves as the guide for finding enrichment. The results can also be compared with MeDIP-chip results to help determine coverage needed.
Cell-free methylated DNA immunoprecipitation and high-throughput sequencing (cfMeDIP-seq) is a variation of the MeDIP-seq technique specifically adapted for profiling DNA methylation from low amounts of circulating cell-free DNA (cfDNA) or cfRNA found in bodily fluids such as plasma, urine, and cerebrospinal fluid. [ 29 ] [ 30 ]
Standard MeDIP-seq protocols typically require higher DNA input amounts (e.g., 100 ng), which can be a limitation when working with the scarce quantities of cfDNA. [ 31 ] cfMeDIP-seq addresses this challenge by employing optimized protocols that can handle significantly lower DNA input (typically 1–10 ng). [ 31 ] A key adaptation often involves the addition of " filler DNA " (e.g., bacteriophage lambda DNA or synthetic DNA) to the low-input cfDNA sample before the immunoprecipitation step. This filler DNA acts as a carrier, improving the efficiency and specificity of the antibody-mediated capture of methylated cfDNA fragments. [ 31 ] Some protocols also incorporate synthetic spike-in controls to help quantify methylation and correct for technical variations. [ 32 ]
Like standard MeDIP-seq, cfMeDIP-seq is a bisulfite-free method, which avoids the DNA degradation associated with bisulfite conversion, a process used in other methylation profiling techniques like whole-genome bisulfite sequencing (WGBS). This makes it advantageous for analyzing fragmented cfDNA. [ 29 ]
cfMeDIP-seq has emerged as a promising technique for liquid biopsy applications, particularly in cancer detection and minimal residual disease monitoring. By analyzing the methylation patterns of cfDNA, it is possible to identify tumor-specific epigenetic signatures circulating in the bloodstream, offering a non-invasive approach for early detection, prognostication, and assessment of treatment response. [ 29 ] Beyond oncology , cfMeDIP-seq is also being explored for applications in prenatal diagnostics and cardiology. [ 31 ] Bioinformatic pipelines specifically designed for cfMeDIP-seq data analysis have been developed to address the unique characteristics of cfDNA fragments and low input data. [ 33 ]
The DNA methylation level estimations can be confounded by varying densities of methylated CpG sites across the genome when observing data generated by MeDIP. This can be problematic for analyzing CpG-poor (lower density) regions. One reason for this density issue is its effect on the efficiency of immunoprecipitation. In their study, Down et al. [ 20 ] developed a tool to estimate absolute methylation levels from data generated by MeDIP by modeling the density of methylated CpG sites. This tool is called Bayesian tool for methylation analysis (Batman) . The study reports the coverage of ~90% of all CpG sites in promoters, gene-coding regions, islands, and regulatory elements where methylation levels can be estimated; this is almost 20 times better coverage than any previous methods.
Studies using MeDIP-seq or MeDIP-chip are both genome-wide approaches that have the common aim of obtaining the functional mapping of the methylome. Once regions of DNA methylation are identified, a number of bioinformatics analyses can be applied to answer certain biological questions. One obvious step is to investigate genes contained in these regions and investigate the functional significance of their repression. For example, silencing of tumour-suppressor genes in cancer can be attributed to DNA methylation. [ 34 ] By identifying mutational events leading to hypermethylation and subsequent repression of known tumour-suppressor genes, one can more specifically characterize the contributing factors to the cause of the disease. Alternatively, one can identify genes that are known to be normally methylated but, as a result of some mutation event, is no longer silenced.
Also, one can try and investigate and identify whether some epigenetic regulator has been affected such as DNA methyltransferase (DNMT); [ 21 ] in these cases, enrichment may be more limited.
Gene-set analysis (for example using tools like DAVID and GoSeq) has been shown to be severely biased when applied to high-throughput methylation data (e.g. MeDIP-seq and MeDIP-ChIP); it has been suggested that this can be corrected using sample label permutations or using a statistical model to control for differences in the numberes of CpG probes / CpG sites that target each gene. [ 35 ]
Limitations to take note when using MeDIP are typical experimental factors. This includes the quality and cross-reactivity of 5mC antibodies used in the procedure. Furthermore, DNA detection methods (i.e. array hybridization and high-throughput sequencing) typically involve well established limitations. Particularly for array-based procedures, as mentioned above, sequences being analyzed are limited to the specific array design used.
Most typical limitations to high-throughput, next generation sequencing apply. The problem of alignment accuracy to repetitive regions in the genome will result in less accurate analysis of methylation in those regions. Also, as was mentioned above, short reads (e.g. 36-50bp from an Illumina Genome Analyzer ) represent a part of a sheared fragment when aligned to the genome; therefore, the exact methylation site can fall anywhere within a window that is a function of the fragment size. [ 19 ] In this respect, bisulfite sequencing has much higher resolution (down to a single CpG site; single nucleotide level). However, this level of resolution may not be required for most applications, as the methylation status of CpG sites within < 1000 bp has been shown to be significantly correlated. [ 20 ] | https://en.wikipedia.org/wiki/Methylated_DNA_immunoprecipitation |
Methylation , in the chemical sciences , is the addition of a methyl group on a substrate , or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation , with a methyl group replacing a hydrogen atom. These terms are commonly used in chemistry , biochemistry , soil science , and biology .
In biological systems , methylation is catalyzed by enzymes ; such methylation can be involved in modification of heavy metals , regulation of gene expression , regulation of protein function , and RNA processing . In vitro methylation of tissue samples is also a way to reduce some histological staining artifacts . The reverse of methylation is demethylation .
In biological systems, methylation is accomplished by enzymes. Methylation can modify heavy metals and can regulate gene expression, RNA processing, and protein function. It is a key process underlying epigenetics . Sources of methyl groups include S-methylmethionine, methyl folate, methyl B12. [ 1 ]
Methanogenesis , the process that generates methane from CO 2 , involves a series of methylation reactions. These reactions are caused by a set of enzymes harbored by a family of anaerobic microbes. [ 2 ]
In reverse methanogenesis, methane is the methylating agent. [ 3 ]
A wide variety of phenols undergo O-methylation to give anisole derivatives. This process, catalyzed by such enzymes as caffeoyl-CoA O-methyltransferase , is a key reaction in the biosynthesis of lignols , percursors to lignin , a major structural component of plants.
Plants produce flavonoids and isoflavones with methylations on hydroxyl groups, i.e. methoxy bonds . This 5-O-methylation affects the flavonoid's water solubility. Examples are 5-O-methylgenistein , 5-O-methylmyricetin , and 5-O-methylquercetin (azaleatin).
Along with ubiquitination and phosphorylation , methylation is a major biochemical process for modifying protein function. The most prevalent protein methylations affect arginine and lysine residue of specific histones. Otherwise histidine, glutamate, asparagine, cysteine are susceptible to methylation. Some of these products include S -methylcysteine , two isomers of N -methylhistidine, and two isomers of N -methylarginine. [ 4 ]
Methionine synthase regenerates methionine (Met) from homocysteine (Hcy). The overall reaction transforms 5-methyltetrahydrofolate (N 5 -MeTHF) into tetrahydrofolate (THF) while transferring a methyl group to Hcy to form Met. Methionine Syntheses can be cobalamin-dependent and cobalamin-independent: Plants have both, animals depend on the methylcobalamin-dependent form.
In methylcobalamin-dependent forms of the enzyme, the reaction proceeds by two steps in a ping-pong reaction. The enzyme is initially primed into a reactive state by the transfer of a methyl group from N 5 -MeTHF to Co(I) in enzyme-bound cobalamin ((Cob), also known as vitamine B12)) ,
, forming methyl-cobalamin(Me-Cob) that now contains Me-Co(III) and activating the enzyme. Then, a Hcy that has coordinated to an enzyme-bound zinc to form a reactive thiolate reacts with the Me-Cob. The activated methyl group is transferred from Me-Cob to the Hcy thiolate, which regenerates Co(I) in Cob, and Met is released from the enzyme. [ 5 ]
Biomethylation is the pathway for converting some heavy elements into more mobile or more lethal derivatives that can enter the food chain . The biomethylation of arsenic compounds starts with the formation of methanearsonates . Thus, trivalent inorganic arsenic compounds are methylated to give methanearsonate. S-adenosylmethionine is the methyl donor. The methanearsonates are the precursors to dimethylarsonates, again by the cycle of reduction (to methylarsonous acid) followed by a second methylation. [ 6 ] Related pathways are found in the microbial methylation of mercury to methylmercury .
DNA methylation is the conversion of the cytosine to 5-methylcytosine . The formation of Me-CpG is catalyzed by the enzyme DNA methyltransferase . In vertebrates, DNA methylation typically occurs at CpG sites (cytosine-phosphate-guanine sites—that is, sites where a cytosine is directly followed by a guanine in the DNA sequence). In mammals, DNA methylation is common in body cells, [ 7 ] and methylation of CpG sites seems to be the default. [ 8 ] [ 9 ] Human DNA has about 80–90% of CpG sites methylated, but there are certain areas, known as CpG islands , that are CG-rich (high cytosine and guanine content, made up of about 65% CG residues ), wherein none is methylated. These are associated with the promoters of 56% of mammalian genes, including all ubiquitously expressed genes . One to two percent of the human genome are CpG clusters, and there is an inverse relationship between CpG methylation and transcriptional activity. Methylation contributing to epigenetic inheritance can occur through either DNA methylation or protein methylation. Improper methylations of human genes can lead to disease development, [ 10 ] [ 11 ] including cancer. [ 12 ] [ 13 ]
In honey bees , DNA methylation is associated with alternative splicing and gene regulation based on functional genomic research published in 2013. [ 14 ] In addition, DNA methylation is associated with expression changes in immune genes when honey bees were under lethal viral infection. [ 15 ] Several review papers have been published on the topics of DNA methylation in social insects. [ 16 ] [ 17 ]
RNA methylation occurs in different RNA species viz. tRNA , rRNA , mRNA , tmRNA , snRNA , snoRNA , miRNA , and viral RNA. Different catalytic strategies are employed for RNA methylation by a variety of RNA-methyltransferases. RNA methylation is thought to have existed before DNA methylation in the early forms of life evolving on earth. [ 18 ]
N6-methyladenosine (m6A) is the most common and abundant methylation modification in RNA molecules (mRNA) present in eukaryotes. 5-methylcytosine (5-mC) also commonly occurs in various RNA molecules. Recent data strongly suggest that m6A and 5-mC RNA methylation affects the regulation of various biological processes such as RNA stability and mRNA translation, [ 19 ] and that abnormal RNA methylation contributes to etiology of human diseases. [ 20 ]
In social insects such as honey bees, RNA methylation is studied as a possible epigenetic mechanism underlying aggression via reciprocal crosses. [ 21 ]
Protein methylation typically takes place on arginine or lysine amino acid residues in the protein sequence. [ 22 ] Arginine can be methylated once (monomethylated arginine) or twice, with either both methyl groups on one terminal nitrogen ( asymmetric dimethylarginine ) or one on both nitrogens (symmetric dimethylarginine), by protein arginine methyltransferases (PRMTs). Lysine can be methylated once, twice, or three times by lysine methyltransferases . Protein methylation has been most studied in the histones . The transfer of methyl groups from S-adenosyl methionine to histones is catalyzed by enzymes known as histone methyltransferases . Histones that are methylated on certain residues can act epigenetically to repress or activate gene expression. [ 23 ] [ 24 ] Protein methylation is one type of post-translational modification .
Methyl metabolism is very ancient and can be found in all organisms on earth, from bacteria to humans, indicating the importance of methyl metabolism for physiology. [ 25 ] Indeed, pharmacological inhibition of global methylation in species ranging from human, mouse, fish, fly, roundworm, plant, algae, and cyanobacteria causes the same effects on their biological rhythms, demonstrating conserved physiological roles of methylation during evolution. [ 26 ]
The term methylation in organic chemistry refers to the alkylation process used to describe the delivery of a CH 3 group. [ 27 ]
Methylations are commonly performed using electrophilic methyl sources such as iodomethane , [ 28 ] dimethyl sulfate , [ 29 ] [ 30 ] dimethyl carbonate , [ 31 ] or tetramethylammonium chloride . [ 32 ] Less common but more powerful (and more dangerous) methylating reagents include methyl triflate , [ 33 ] diazomethane , [ 34 ] and methyl fluorosulfonate ( magic methyl ). These reagents all react via S N 2 nucleophilic substitutions . For example, a carboxylate may be methylated on oxygen to give a methyl ester ; an alkoxide salt RO − may be likewise methylated to give an ether , ROCH 3 ; or a ketone enolate may be methylated on carbon to produce a new ketone .
The Purdie methylation is a specific for the methylation at oxygen of carbohydrates using iodomethane and silver oxide . [ 35 ]
The Eschweiler–Clarke reaction is a method for methylation of amines . [ 36 ] This method avoids the risk of quaternization , which occurs when amines are methylated with methyl halides.
Diazomethane and the safer analogue trimethylsilyldiazomethane methylate carboxylic acids, phenols, and even alcohols:
The method offers the advantage that the side products are easily removed from the product mixture. [ 37 ]
Methylation sometimes involve use of nucleophilic methyl reagents. Strongly nucleophilic methylating agents include methyllithium ( CH 3 Li ) [ 38 ] or Grignard reagents such as methylmagnesium bromide ( CH 3 MgX ). [ 39 ] For example, CH 3 Li will add methyl groups to the carbonyl (C=O) of ketones and aldehyde.:
Milder methylating agents include tetramethyltin , dimethylzinc , and trimethylaluminium . [ 40 ] | https://en.wikipedia.org/wiki/Methylation |
In molecular biology , methylation induced premeiotically ( MIP ) is a process by which cytosines within repeated DNA sequences are de novo methylated prior to the sexual cycle. This process was first described in the ascomycete Ascobolus immersens . MIP is dependent upon the gene masc1 which encodes a cytosine methyltransferase -like protein. [ 1 ] At least one major function of the process appears to be genome defense. Related functions have been found in other fungi, including Neurospora and Aspergillus species. [ 2 ]
This molecular or cell biology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Methylation_induced_premeiotically |
Methylation specific oligonucleotide microarray , also known as MSO microarray , was developed as a technique to map epigenetic methylation changes in DNA of cancer cells. [ 1 ]
The general process starts with modification of DNA with bisulfite , specifically to convert unmethylated cytosine in CpG sites to uracil, while leaving methylated cytosines untouched. [ 1 ] The modified DNA region of interest is amplified via PCR and during the process, uracils are converted to thymine. The amplicons are labelled with a fluorescent dye and hybridized to oligonucleotide probes that are fixed to a glass slide. [ 2 ] The probes differentially bind to cytosine and thymine residues, which ultimately allows discrimination between methylated and unmethylated CpG sites, respectively. [ 1 ]
A calibration curve is produced and compared with the microarray results of the amplified DNA samples. This allows a general quantification of the proportion of methylation present in the region of interest. [ 3 ]
This microarray technique was developed by Tim Hui-Ming Huang and his laboratory and was officially published in 2002. [ 1 ]
Cancer cells often develop atypical methylation patterns, at CpG sites in promoters of tumour suppressor genes . High levels of methylation at a promoter leads to downregulation of the corresponding genes and is characteristic of carcinogenesis . It is one of the most consistent changes observed in early stage tumour cells. [ 1 ] Methylation specific oligonucleotide microarray allows for the high resolution and high throughput detection of numerous methylation events on multiple gene promoters. Therefore, this technique can be used to detect aberrant methylation in tumour suppressor promoters at an early stage and has been used in gastric and colon cancers and multiple others. [ 4 ] [ 5 ] Because it allows one to detect presence of atypical methylations in cancer cells, it can also be used to reveal the major cause behind the malignancy, whether its main contributor is mutations on chromosomes or epigenetic modifications, as well as which tumour suppressor genes' transcription levels are affected. [ 2 ] [ 6 ] An interesting use of this microarray includes specific classification of cancers based on the methylation patterns alone, such as differentiating between classes of leukemia , suggesting that different classes of cancer show relatively unique methylation patterns. [ 7 ] This technique has also been proposed to monitor cancer treatments that involve modifying the methylation patterns in mutant cancer cells. [ 2 ]
This genetics article is a stub . You can help Wikipedia by expanding it .
This oncology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Methylation_specific_oligonucleotide_microarray |
Methylazoxymethanol , MAM , is a carcinogen which reduces DNA synthesis. [ 1 ] Its derivatives include methylazoxymethanol acetate and cycasin , which they are found in cycad . | https://en.wikipedia.org/wiki/Methylazoxymethanol |
Methylazoxymethanol acetate , MAM , is a neurotoxin which reduces DNA synthesis [ 1 ] used in making animal models of neurological diseases including schizophrenia [ 2 ] and epilepsy . [ 3 ] MAM is found in cycad seeds, and causes zamia staggers . It selectively targets neuroblasts in the central nervous system . In rats, administration of MAM affects structures in the brain which are developing most quickly. [ 2 ] It is an acetate of methylazoxymethanol .
In rat models, the specific effect of MAM on neural development depends on the gestational age of the subject. At the seventeenth gestational day (GD17), administration of MAM produces behavioral and histopathological patterns found in schizophrenia. [ 2 ] The molecular mechanism behind this model is not fully known. [ 4 ] Methylazoxymethanol acetate administered at GD17 reduces the thickness of the hippocampus and the thalamus . The locomotor effects of amphetamines and the spontaneous firing rate of dopaminergic neurons in the ventral tegmental area are increased. In alternating maze tests, GD17 MAM rats quickly learned the first rule, but took longer to accommodate to alterations to the rule; this is thought to indicate deficits in working spatial memory, which is also impaired in schizophrenia. [ 2 ] Another study found that mice whom methylazoxy-methanol acetate was administered on 16th gestational day, but not those whom it was administered on GD17 showed decreased parvalbumin expression in hippocampus and prefrontal cortex, and schizophrenia-like characteristics. Mice whom MAM was administered on GD16 also exhibited reduced size of hippocampus and thinning of the prefrontal cortex. PFC-dependent cognitive deficits were shown only in male MAM-treated mice. [ 5 ]
Exposure to MAM before birth increases susceptibility to epileptic seizures caused by flurothyl . [ 3 ] Prenatal MAM exposure in rats results in a model of brain malformation. In some MAM animals, video-EEG monitoring has documented the presence of spontaneous electrographic seizure activity [ 6 ] In some epilepsy rat models, MAM is administered at the fifteenth gestational day. Previous studies have found impaired cognitive function in GD15 MAM rats, and a reduced seizure threshold. [ 7 ] At the cellular level, dysplastic hippocampal neurons in the MAM model were shown to have reduced potassium current function and expression for the Kv4.2 channel subunit [ 8 ] These findings may contribute to the spontaneous seizures and reduced seizure thresholds seen in this model. | https://en.wikipedia.org/wiki/Methylazoxymethanol_acetate |
Methylcholanthrene is a highly carcinogenic polycyclic aromatic hydrocarbon produced by burning organic compounds at very high temperatures [ clarification needed ] . Methylcholanthrene is also known as 3-methylcholanthrene, 20-methylcholanthrene or the IUPAC name 3-methyl-1,2-dyhydrobenzo[j]aceanthrylene. The short notation often used is 3-MC or MCA . This compound forms pale yellow solid crystals when crystallized from benzene and ether. [ 1 ] It has a melting point around 180 °C and its boiling point is around 280 °C at a pressure of 80 mmHg. [ 2 ] Methylcholanthrene is used in laboratory studies of chemical carcinogenesis. It is an alkylated derivative of benz[ a ]anthracene and has a similar UV spectrum. The most common isomer is 3-methylcholanthrene, although the methyl group can occur in other places.
3-Methylcholanthrene, a known carcinogen which builds up in the prostate due to cholesterol breakdown, is implicated in prostate cancer . [ citation needed ] It "readily produces" primary sarcomas in mice. [ 3 ]
In 1933, the first article about methylcholanthrene was published. Here they described the synthesis of the compound. Not many years later, it became clear that this compound had toxic properties to humans and animals. Therefore, a lot of interest was shown in the compound and it was used often in toxicological research. Methylcholanthrene is often tested on mice and rats to derive information for cancer medicine development. Due to the influence of the compound on the central nervous system , its responses and change in response are compared. It is also known that due to genetic mutations, the compound causes cancer cells to develop. [ 4 ] In 1982, the last article appeared on the synthesis of methylcholanthrene. The yield of 93% was reached and therefore no further adjustments were made to the synthesis scheme.
First 3-MC was synthesized with the method of reference. [ 5 ] Later the synthesis of the compound was improved. [ 6 ] [ 7 ] The synthesis of 3-MC consists of a few steps, visualized in figure 1; the first step is the key to success for the synthesis. 4-methylindanone (1) reacts in condensation with lithium salt of N,N-diethyl-1-naphthamide (2). At -60 ̊C the reaction of 1 and 2 afforded evenly to the lactone (3), the carbonyl addition product which underwent conversion on treatment with acid. The free acid (4) was obtained when the latter was cleaved reductively with zinc and alkali. Cyclization of the product occurred when treated with ZnCl 2 in acetic acid anhydride and gave the compound 6-acetoxy-3-MC (5). Reducing this product with hydriodic acid in propionic acid resulted in 3-MC.
3-MC has an inhibitory function in a dimethylnitrosamine demethylase process in rat livers. Inhibition could happen on by interfering in demethylase conformations or by interfering in synthesis and/or degradation of demethylase. Experiments showed that the Km doesn't change after 3-MC treatment. This strongly indicates that enzyme affinity is not influenced by 3-MC. Instead, incubation with 3-MC leads to a decrease in the amount of enzyme activity . These results point towards inhibition of demethylase synthesis and/or induction of demetylase degradation. Unpublished observations of Venkatesan, Argus and Arcos suggest that demethylase synthesis inhibition is most plausible. [ 8 ]
A possible mechanism for this reaction is depicted in figure (2). 3-MC is metabolized, via epoxidation , hydrolysis and another epoxidation, to a very reactive epoxide. Epoxidations are realized by the enzyme cytochrome P450 . The second epoxide is not hydrolysed immediately because it is localized next to a bay region, which shields the epoxide. This way, the metabolite is able to travel and bind to DNA in figure (2). The mechanism is derived from the binding mechanism of benzo[ a ]pyrene to DNA. This is likely because it is plausible that two polycyclic aromatic hydrocarbons are metabolized via the same pathway. Deoxyguanosine is used in the figure, since that base appears to be bound to Benzo[a]pyrene far more often than the other bases. [ 8 ] [ 9 ]
There appears to be an equilibrium in 3-MC-free and 3-MC-bound. It is hard to determine how when the equilibrium is formed due to difficulties with radioactive measurements. A probable saturating dose is thought to be around 40 mg 3-MC/kg. [ 8 ] [ 10 ]
Research on the effect of 3-MC in rat uteri concludes that 3-MC acts as an estrogen antagonist. The sexhormone is, like 3-MC, a polycyclic aromatic hydrocarbon. 3-MC and estrogen bind to estrogenreceptors competitively, reducing the estrogen expression. [ 11 ]
MC is metabolized by rat liver microsomes into oxygenated forms which alkylate DNA. These oxygenated metabolites bind to double-stranded and single-stranded. Empirical data show that MC tends to bind mostly to G-bases8. [ 12 ] When injected in lung, kidney or liver tissue of rats, it appears that the liver is able to reverse the MC-binding to DNA. Lung and kidney tissue are not capable of doing this, which may explain why MC is more carcinogenic in lungs and kidneys than in the liver. To be carcinogenic, the MC metabolite has to be covalently bound to DNA. Therefore, it is necessary for MC to be oxygenated in order to carcinogenic. [ 9 ] [ 10 ] Injected MC does not move away from the injection site. In a rat body MC has a half-life of about 4 weeks. After 8 weeks, 80% of MC is metabolized into water-soluble metabolites. MC and its metabolites mainly exit the body via feces (a ninefold more urine). Three months after injection with MC, 85% of the rats are reported to have tumors. 82% of the tumors is a form of spindle-cell sarcoma. [ 12 ]
Methylcholanthrene is often used to induce tumors in rodents for carcinogenesis and mutagenesis research.
In a study from 1991, lung precancerous and cancerous lesions were induced in Wistar rats by one intrabronchial injection of 3-MC. After 30 days, atypical hyperplasia of bronchiolar epithelium, adenoid hyperplasia or adenomas, and squamous cell carcinoma occurred in 15 (88.2%), 12 (70.6%) and 3 (17.7%) out of 17 rats respectively. After 60 days, the incidences were 15/18 (83.3%), 4/17 (23.5%) and 7/18 (38.9%). All of the precancerous lesions and carcinomas showed positive expression of gamma-glutamyltranspeptidase (GGT). [ 13 ] Jin et al. (2013) found that the cellular redox balance is altered by acute exposure to 3-MC. This causes the nuclear factor erythroid 2-related factor 2 (Nrf2)-regulated response pathway to induce antioxidant responses. [ 14 ]
3-MC is a ligand of the aryl hydrocarbon receptor (AhR), which stimulates transcription directed by xenobiotic response elements. AhR ligands can induce formation of an AhR-estrogen receptor (ER) complex. 3-MC was found to elicit estrogenic activity by this mechanism, and by stimulation of the expression of some endogenous ER target genes. [ 15 ] 3-MC may cause respiratory tract irritation, skin irritation or eye irritation. [ 16 ]
3-MC is mutagenic to human cells. Curren et al. (1978) were the first to report successfully induced mutations in human cells with 3-MC. Skin epithelial cells are thought to metabolize the compound to mutagenic products. [ 17 ] The ability to metabolize mutagens may express genetically regulated differences within a species such as man or mouse, causing environmental chemicals to show a different level of mutagenicity and carcinogenicity to specific individuals. [ 18 ]
The administration of 3-MC to pregnant mice results in the formation of lung tumors in the offspring. Miller et al. (1990) compared the effects of fetal versus adult exposure to 3-MC on both induction of aryl hydrocarbon hydroxylase (AHH) activity in lung and dependence of lung tumorigenesis on the Ah genotype. A single ip injection (in inducible fetal lung supernatants) of 100 mg/kg of 3-MC to the mothers resulted in a maximal 50-fold induction of AHH activity by 8 hr, which persisted for 48 hr. The same injections to adult F1 mice revealed only a 4- to 7—fold increase in lung AHH activity, compared to the large fetal induction ratio. [ 19 ] | https://en.wikipedia.org/wiki/Methylcholanthrene |
The methylcitrate cycle , or the MCC , is the mechanism by which propionyl-CoA is formed, generated by β-oxidation of odd-chain fatty acids, and broken down to its final products, succinate and pyruvate . [ 1 ] The methylcitrate cycle is closely related to both the citric acid cycle and the glyoxylate cycle , in that they share substrates, enzymes and products. [ 2 ] The methylcitrate cycle functions overall to detoxify bacteria of toxic propionyl-CoA , and plays an essential role in propionate metabolism in bacteria. Incomplete propionyl-CoA metabolism may lead to the buildup of toxic metabolites in bacteria, and thus the function of the methylcitrate cycle is an important biological process. [ 3 ]
2-methyl iso citric acid, an intermediate of the methylcitrate cycle, was first synthesized in 1886 as a mixture of four isomers. The pathway of the methylcitrate cycle was not discovered until 1973 in fungi, though it was not yet fully understood. [ 4 ] Originally, the methylcitrate cycle was thought to be present only in fungal species, such as Candida lipolytica and Aspergillus nidulans . In 1999, it was discovered that the methylcitrate cycle was also present in bacteria Salmonella enterica and Escherichia coli . [ 5 ] Much research has been done on the methylcitrate cycle's role in the development and function of various fungi and strains of bacteria, as well as its virulent properties in conjunction with the glyoxylate cycle. [ 6 ]
There are three basic steps in the methylcitrate cycle, as outlined below. Additionally, the mechanism is shown with its reactants, products, intermediates, and enzymes. [ 7 ]
The major enzymes involved in this process are methylcitrate synthase (MCS) in step one, methylcitrate dehydratase (MCD) in step two, and 2-methyl iso citrate lyase (MCL) in step three.
The PrpC gene, which encodes for enzyme methylcitrate synthase in the first step of the methylcitrate cycle, is the gene responsible for propionate metabolism in the process. Without this gene, the methylcitrate cycle and ultimate metabolism would not occur, but rather catabolism. [ 9 ] The reaction of the methylcitrate cycle both overlaps and intertwines with the citric acid cycle and the glyoxylate cycle . Odd-chain fatty acids acetate and propionate are broken down by the β-oxidation cycle to form acetyl-CoA, which is further oxidized by the citric acid cycle, and propionyl-CoA, which is oxidized by the methylcitrate cycle. The substrate oxaloacetate is generated by the citric acid and glyoxylate cycles, and the product succinate is taken from the methylcitrate cycle to be used in the citric acid cycle. [ 10 ]
One of the major products of the methylcitrate cycle is pyruvate. This pyruvate can be used by metabolic enzymes for energy and biomass formation. [ 11 ] The other major product, succinate, is used in the citric acid cycle and helps to carry the reaction forward and restarts the cycle. Succinate is used by the citric acid and glyoxylate cycles to generate oxaloacetate, one of the key substrates necessary to begin the methylcitrate cycle.
[ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] | https://en.wikipedia.org/wiki/Methylcitrate_cycle |
3-Methylcrotonyl-CoA ( β-Methylcrotonyl-CoA or MC-CoA ) is an intermediate in the metabolism of leucine . [ 1 ] [ 2 ] [ 3 ]
It is found in mitochondria, where it is formed from isovaleryl-coenzyme A by isovaleryl coenzyme A dehydrogenase . It then reacts with CO 2 to yield 3-Methylcrotonyl-CoA carboxylase . [ 4 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Methylcrotonyl-CoA |
Methylcyclopentadiene is any of three isomeric cyclic di alkenes with the formula C 5 MeH 5 (Me = CH 3 ). These isomers are the organic precursor to the methylcyclopentadienyl ligand (C 5 H 4 Me, often denoted as Cp′), commonly found in organometallic chemistry .
As with cyclopentadiene , methylcyclopentadiene is prepared by thermal cracking of its Diels–Alder dimer, followed by distillation for removal of cyclopentadiene, a common impurity. [ 1 ]
Deprotonation of methylcyclopentadiene gives the aromatic methylcyclopentadienyl anion . [ 2 ] This ion is useful as a ligand for organometallic complexes . Relative to the corresponding cyclopentadienyl (Cp) complexes, complexes of Cp′ exhibit enhanced solubility in organic solvents .
Cp′ can be used to probe the structure of organometallic complexes. For example, Cp′Fe(PPh 3 )(CO)I has four different signals in the 1 H NMR spectrum for the ring hydrogens and five different signals in the 13 C NMR spectrum for the ring carbons. There is therefore no symmetry within the ring even accounting for rotation around the ring–metal axis, but instead there is a diastereotopic relationship as a result of being part of a chiral complex. The achiral precursor complex Cp′Fe(CO) 2 I has only two signals for those hydrogens and three for those carbons, indicating a symmetric structure. [ 3 ]
MgCpBr
(TiCp 2 Cl) 2 TiCpCl 3 TiCp 2 S 5 TiCp 2 (CO) 2 TiCp 2 Me 2
VCpCh VCp 2 Cl 2 VCp(CO) 4
(CrCp(CO) 3 ) 2
Fe(η 5 -C 5 H 4 Li) 2 ((C 5 H 5 )Fe(C 5 H 4 )) 2 (C 5 H 4 -C 5 H 4 ) 2 Fe 2 FeCp 2 PF 6 FeCp(CO) 2 I
CoCp(CO) 2
NiCpNO
ZrCp 2 ClH
MoCp 2 Cl 2 (MoCp(CO) 3 ) 2
RuCp(PPh 3 ) 2 Cl RuCp(MeCN) 3 PF 6 | https://en.wikipedia.org/wiki/Methylcyclopentadiene |
Methyldiazonium is an organic compound consisting of a methyl group attached to a diazo group . This cation is the conjugate acid of diazomethane , with an estimated p K a <10. [ 1 ]
It is an intermediate in methylation reactions of diazomethane with acidic hydroxyl compounds, such as conversion of carboxylic acids to methyl esters and phenols to methyl ethers . [ 2 ]
It has been implicated as the metabolite of N -nitrosodimethylamine responsible for the observed carcinogenicity of that compound. [ 3 ]
This organic chemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Methyldiazonium |
Methylene (IUPAC name: methylidene , also called carbene or methene ) is an organic compound with the chemical formula CH 2 (also written [CH 2 ] and not to be confused with compressed hydrogen , which is also denoted CH 2 ). It is a colourless gas that fluoresces in the mid-infrared range, and only persists in dilution, or as an adduct .
Methylene is the simplest carbene . [ 3 ] : p.7 [ 4 ] It is usually detected only at very low temperatures or as a short-lived intermediate in chemical reactions . [ 5 ]
The trivial name carbene is the preferred IUPAC name . [ 2 ] The systematic names methylidene and dihydridocarbon , valid IUPAC names, are constructed according to the substitutive and additive nomenclatures, respectively.
Methylidene is viewed as methane with two hydrogen atoms removed. By default, this name pays no regard to the radicality of the methylene. Although in a context where the radicality is considered, it can also name the non-radical excited state , whereas the radical ground state with two unpaired electrons is named methanediyl .
Methylene is also used as the trivial name for the substituent groups methanediyl ( >CH 2 ), and methylidene ( =CH 2 ). It was introduced as early as 1835 by French chemists Jean-Baptiste Dumas and Eugene Peligot after determining methanol 's chemical structure. They coined it the Greek μέθυ ( methy ) "wine" and ὕλη ( hȳlē ) "wood, patch of trees" (even though the correct Greek word for the substance "wood" is xylo- ) with the intention of highlighting its origins, 'alcohol made from wood (substance)'. [ 6 ]
A methylidene group is any part of a molecule that consists of a CH 2 = group. [ 7 ] The group may be represented as =CH 2 , where the '=' denotes the double bond.
In contrast, methylene is connected to the rest of the molecule by two single bonds . [ 8 ] The distinction is often important, because the double bond is chemically different from two single bonds.
The same name (methylidene) was used for the distinct molecule CH 2 , also known as carbene . [ 9 ] Formerly the methylene name was used for all three isomers (methylene, methylidene, and carbene).
Many organic compounds are named and classified as if they were the result of substituting a methylidene group for two adjacent hydrogen atoms of some parent molecule (even if they are not actually obtained that way). Thus, for example, methylenecyclopropene is named after cyclopropene .
Methylene can be prepared by decomposition of compounds with a methylidene or methanediyl group, such as ketene (ethenone) ( CH 2 =CO ), diazomethane (linear CH 2 =N 2 ), diazirine (cyclic [−CH 2 −N=N−] ) and diiodomethane ( I−CH 2 −I ). The decomposition can be effected by photolysis , photosensitized reagents (such as benzophenone ), or thermal decomposition. [ 5 ] [ 10 ] Methylene can be produced by photolysis of diazomethane . [ 11 ] In its ultraviolet spectrum, gaseous methylene absorbs at around 141.5 nm. It was shown to have a bond angle of about 140°. [ 12 ]
The reactions of methylene were also studied around 1960 by infrared spectroscopy using matrix isolation experiments. [ 13 ] [ 14 ]
Many of methylene's electronic states lie relatively close to each other, giving rise to varying degrees of radical chemistry. The ground state is a triplet radical with two unpaired electrons ( X ̃ 3 B 1 ), [ 10 ] and the first excited state is a singlet non-radical ( ã 1 A 1 ). With the singlet non-radical only 38 kJ above the ground state, [ 10 ] a sample of methylene exists as a mixture of electronic states even at room temperature, giving rise to complex reactions. For example, reactions of the triplet radical with non-radical species generally involves abstraction, whereas reactions of the singlet non-radical not only involves abstraction, but also insertion or addition.
The singlet state is also more stereospecific than the triplet. [ 10 ]
Methylene spontaneously autopolymerises to form various excited oligomers, the simplest of which, is the excited form of the alkene ethylene . The excited oligomers, decompose rather than decay to a ground state. For example, the excited form of ethylene decomposes to acetylene and atomic hydrogen. [ 10 ]
Unsolvated, excited methylene will form stable ground state oligomers.
The ground state of methylene has an ionisation energy of 10.396 eV . It has a bent configuration, with H–C–H angle of 133.84 ° , [ 10 ] and is thus paramagnetic . (The correct prediction of this angle was an early success of ab initio quantum chemistry . [ 10 ] ) However conversion to a linear configuration requires only 5.5 kcal / mol . [ 10 ]
The singlet state has a slightly higher energy (by about 9 kcal/mol) than the triplet state, [ 10 ] and its H–C–H angle is smaller, about 102°. In dilute mixtures with an inert gas, the two states will convert to each other until reaching an equilibrium. [ 10 ]
Neutral methylene complexes undergo different chemical reactions depending on the pi character of the coordinate bond to the carbon centre. A weak contribution, such as in diazomethane, yields mainly substitution reactions, whereas a strong contribution, such as in ethenone , yields mainly addition reactions. Upon treatment with a standard base, complexes with a weak contribution convert to a metal methoxide. With strong acids (e.g., fluorosulfuric acid ), they can be protonated to give CH 3 L + . Oxidation of these complexes yields formaldehyde, and reduction yields methane.
Free methylene undergoes the typical chemical reactions of a carbene . Addition reactions are very fast and exothermic. [ 15 ]
When the methylene molecule is in its state of lowest energy , the unpaired valence electrons are in separate atomic orbitals with independent spins , a configuration known as triplet state .
Methylene may gain an electron yielding a monovalent anion methanidyl ( CH •− 2 ), which can be obtained as the tetramethylammonium (( CH 3 ) 4 N + ) salt by the reaction of phenyl sodium ( C 6 H 5 Na ) with tetramethylammonium bromide (( CH 3 ) 4 N + Br − ). [ 5 ] The ion has bent geometry, with a H-C-H angle of about 103°. [ 10 ]
Methylene is also a common ligand in coordination compounds , such as copper methylene CuCH 2 . [ 16 ]
Methylene can bond as a terminal ligand, which is called methylidene , or as a bridging ligand, which is called methanediyl .
The formula of the methylene molecule (CH 2 ) was mentioned as part of a Disney comic by the Donald Duck character in a comic in 1944 in a humorous vein. In the same spirit, the comic was eventually cited in the scientific literature by Peter Gaspar and George S. Hammond . [ 17 ] [ 18 ] The comic has been cited in other sources since, including a widely adopted textbook in organic chemistry by Robert Morrison and Robert Boyd. [ 19 ] | https://en.wikipedia.org/wiki/Methylene_(compound) |
Methylthioninium chloride , commonly called methylene blue , is a salt used as a dye and as a medication. As a medication, it is mainly used to treat methemoglobinemia . It has previously been used for treating cyanide poisoning and urinary tract infections , but this use is no longer recommended. [ 5 ]
Methylene blue is typically given by injection into a vein . [ 5 ] Common side effects include headache , nausea , and vomiting .
Methylene blue was first prepared in 1876, by Heinrich Caro . [ 9 ] It is on the World Health Organization's List of Essential Medicines . [ 10 ]
Methylene blue is used to treat methemoglobinemia by chemically reducing the ferric iron in hemoglobin to ferrous iron . [ 5 ] [ 2 ] Methemoglobinemia can arise from ingestion of certain pharmaceuticals, toxins , or broad beans in those susceptible. [ 11 ] Specifically, it is used to treat methemoglobin levels that are greater than 30% or in which there are symptoms despite oxygen therapy . [ 2 ] Normally, through the NADH - or NADPH -dependent methemoglobin reductase enzymes, methemoglobin is reduced back to hemoglobin. When large amounts of methemoglobin occur secondary to toxins, methemoglobin reductases are overwhelmed. Methylene blue, when injected intravenously as an antidote, is itself first reduced to leucomethylene blue, which then reduces the heme group from methemoglobin to hemoglobin . Methylene blue can reduce the half life of methemoglobin from hours to minutes. [ 12 ] At high doses, however, methylene blue actually induces methemoglobinemia, reversing this pathway. [ 12 ]
Isobutyl nitrite is one of the compounds used as poppers , an inhalant drug that induces a brief euphoria .
Isobutyl nitrite is known to cause methemoglobinemia . [ 13 ] Severe methemoglobinemia may be treated with methylene blue. [ 14 ]
Since its reduction potential is similar to that of oxygen and can be reduced by components of the electron transport chain , large doses of methylene blue are sometimes used as an antidote to potassium cyanide poisoning, a method first successfully tested in 1933 by Matilda Moldenhauer Brooks in San Francisco, [ 17 ] although first demonstrated by Bo Sahlin of Lund University , in 1926. [ 17 ] [ 18 ]
Methylene blue increases blood pressure in people with vasoplegic syndrome (redistributive shock), but does not improve delivery of oxygen to tissues or decrease mortality. [ 19 ] [ 20 ]
Methylene blue has been used in calcium channel blocker toxicity as a possible rescue therapy for distributive shock unresponsive to first line agents. Limited to case reports , a 2024 review found low-quality evidence that methylene blue may reduce short-term mortality, duration of the need for vasopressors, and length of hospital stay. [ 21 ]
Methylene blue is used in endoscopic polypectomy as an adjunct to saline or epinephrine , and is used for injection into the submucosa around the polyp to be removed. This allows the submucosal tissue plane to be identified after the polyp is removed, which is useful in determining if more tissue needs to be removed, or if there has been a high risk for perforation. Methylene blue is also used as a dye in chromoendoscopy , and is sprayed onto the mucosa of the gastrointestinal tract in order to identify dysplasia , or pre-cancerous lesions. Intravenously injected methylene blue is readily released into the urine and thus can be used to test the urinary tract for leaks or fistulas . [ citation needed ]
In surgeries such as sentinel lymph node dissections, methylene blue can be used to visually trace the lymphatic drainage of tested tissues. Similarly, methylene blue is added to bone cement in orthopedic operations to provide easy discrimination between native bone and cement. Additionally, methylene blue accelerates the hardening of bone cement, increasing the speed at which bone cement can be effectively applied. Methylene blue is used as an aid to visualisation/orientation in a number of medical devices, including a surgical sealant film , TissuePatch. In fistulas and pilonidal sinuses , it is used to identify the tract for complete excision. [ citation needed ] It can also be used during gastrointestinal surgeries (such as bowel resection or gastric bypass ) to test for leaks. [ citation needed ]
It is sometimes used in cytopathology , in mixtures including Wright-Giemsa and Diff-Quik . It confers a blue color to both nuclei and cytoplasm, and makes the nuclei more visible. [ 22 ] When methylene blue is "polychromed" (oxidized in solution or "ripened" by fungal metabolism, [ 23 ] as originally noted in the thesis of Dr. D. L. Romanowsky in the 1890s), it gets serially demethylated and forms all the tri-, di-, mono- and non-methyl intermediates, which are Azure B , Azure A , Azure C , and thionine , respectively. [ 24 ] This is the basis of the basophilic part of the spectrum of Romanowski-Giemsa effect. If only synthetic Azure B and Eosin Y is used, it may serve as a standardized Giemsa stain ; but, without methylene blue, the normal neutrophilic granules tend to overstain and look like toxic granules. On the other hand, if methylene blue is used it might help to give the normal look of neutrophil granules and may also enhance the staining of nucleoli and polychromatophilic RBCs (reticulocytes). [ 25 ]
A traditional application of methylene blue is the intravital or supravital staining of nerve fibers, an effect first described by Paul Ehrlich in 1887. [ 26 ] A dilute solution of the dye is either injected into tissue or applied to small freshly removed pieces. The selective blue coloration develops with exposure to air (oxygen) and can be fixed by immersion of the stained specimen in an aqueous solution of ammonium molybdate . Vital methylene blue was formerly much used for examining the innervation of muscle, skin and internal organs. [ 27 ] [ 28 ] [ 29 ] The mechanism of selective dye uptake is incompletely understood; vital staining of nerve fibers in skin is prevented by ouabain , a drug that inhibits the Na/K-ATPase of cell membranes. [ 30 ]
Methylene blue has been used as a placebo ; physicians would tell their patients to expect their urine to change color and view this as a sign that their condition had improved. [ 31 ] This same side effect makes methylene blue difficult to use in traditional placebo-controlled clinical studies , including those testing for its efficacy as a treatment. One approach is to use a low dose, just enough to turn urine blue, as the placebo group. [ 32 ] However, a low dose does not guarantee inertness. [ 33 ]
Methylene blue is a monoamine oxidase inhibitor (MAOI) [ 36 ] and, if infused intravenously at doses exceeding 5 mg/kg, may result in serotonin syndrome if combined with any selective serotonin reuptake inhibitors (SSRIs) or other serotonergic drugs (e.g., duloxetine , sibutramine , venlafaxine , clomipramine , imipramine ). [ 37 ]
It causes hemolytic anemia in carriers of the G6PD enzymatic deficiency ( favism ). [ 38 ] The actual degree of this danger is a subject of controversy as the association was made based on very few cases. A 2018 meta-analysis on clinical trials against malaria in Africa, where the moderate A minus type of G6PD deficiency is prevalent, show no association between MB and hemolysis in such patients. There was, however, a clinically insignificant reduction in hemoglobin. [ 39 ]
While use during pregnancy may harm the baby, not using it in methemoglobinemia is likely more dangerous. [ 5 ] [ 2 ]
After intravenous administration in humans, methylene blue shows a multiphasic change in concentration, with a terminal half-life of 5.25 hours. The initial disappearance from blood actually reflects its movement into organs, with brain, liver, and bile all showing significantly higher concentrations than blood in rats. The overall area under the curve in oral (dry gelatin capsule) administration is only 6.5% of the AUC for iv administration; judging from rat studies, the significantly altered organ distribution plays a key role in this difference. [ 8 ]
Administration as an oral solution (500 mg in 200 mL) greatly increases the bioavailbility to 72.3±23.9%. In this newer study, the terminal half-lives were reported as 18.5±11.8 hours for iv use and 18.3±7.2 for oral use. The t max for oral use is 2.2 hours, compared to 0.5 hours for iv use. [ 40 ]
Methylene blue is a formal derivative of phenothiazine . It is a dark green powder that yields a blue solution in water . The hydrated form has 3 molecules of water per unit of methylene blue.
This compound is prepared by oxidation of 4-aminodimethylaniline in the presence of sodium thiosulfate to give the quinonediiminothiosulfonic acid, reaction with dimethylaniline, oxidation to the indamine, and cyclization to give the thiazine: [ 41 ]
A green electrochemical procedure, using only dimethyl-4-phenylenediamine and sulfide ions has been proposed. [ 42 ]
The maximum absorption of light is near 670 nm. The specifics of absorption depend on a number of factors, including protonation , adsorption to other materials, and metachromasy - the formation of dimers and higher-order aggregates depending on concentration and other interactions: [ 43 ]
Under reducing conditions, the blue-colored methylene blue cation (MB + ) gains 1H + and 2e − to become the electrically neutral and colorless leucomethylene blue (LMB). [ 44 ] The redox midpoint potential E 0 ' is +0.01 V. [ 45 ]
The redox properties can be seen in a classical demonstration of chemical kinetics in general chemistry, the " blue bottle " experiment. Typically, a solution is made of glucose (dextrose), methylene blue, and sodium hydroxide . Upon shaking the bottle, oxygen oxidizes methylene blue, and the solution turns blue. The dextrose will gradually reduce the methylene blue to its colorless, reduced form. Hence, when the dissolved dextrose is entirely consumed, the solution will turn blue again. [ 46 ]
In the mitochondrial electron transport chain reduced methylene blue (MBH 2 ) directly reduces cytochrome c rather than to oxygen, limiting the formation of superoxide . [ 47 ] [ 48 ] Methylene blue has been shown to directly accept electrons from NADH , NADPH , and FADH 2 . [ 48 ]
Methylene blue is widely used as a redox indicator in analytical chemistry . [ 46 ] [ 49 ] [ 50 ] Solutions of this substance are blue when in an oxidizing environment, but will turn colorless if exposed to a reducing agent. [ 51 ] [ 49 ]
Methylene blue is also a photosensitizer used to create singlet oxygen when exposed to both oxygen and light. It is used in this regard to make organic peroxides by a Diels-Alder reaction which is spin forbidden with normal atmospheric triplet oxygen . [ citation needed ]
With the help of light, methylene blue can be used to kill some viruses and some bacteria. [ 52 ] This kind of photo-disinfection has also been done inside of human bodies ( antimicrobial photodynamic therapy ). [ 53 ] The same process can also be used to disinfect blood plasma. [ 54 ]
Methylene blue is theoretically also applicable to other forms of photodynamic therapy , i.e. the use of oxygen, light, and a photosentizer to kill cells. Research on using it to locally kill cancer cells is in a preclinical stage. [ 55 ]
The formation of methylene blue after the reaction of hydrogen sulfide with dimethyl-p-phenylenediamine and iron(III) at pH 0.4 – 0.7 is used to determine by photometric measurements sulfide concentration in the range 0.020 to 1.50 mg/L (20 ppb to 1.5 ppm). [ 56 ] The test is very sensitive and the blue coloration developing upon contact of the reagents with dissolved H 2 S is stable for 60 min. Ready-to-use kits such as the Spectroquant sulfide test [ 57 ] facilitate routine analyses. The methylene blue sulfide test is a convenient method often used in soil microbiology to quickly detect in water the metabolic activity of sulfate reducing bacteria (SRB). In this colorimetric test, methylene blue is a product formed by the reaction and not a reagent added to the system. [ 56 ]
The addition of a strong reducing agent , such as ascorbic acid , to a sulfide-containing solution is sometimes used to prevent sulfide oxidation from atmospheric oxygen. Although it is certainly a sound precaution for the determination of sulfide with an ion selective electrode , it might however hamper the development of the blue color if the freshly formed methylene blue is also reduced, as described here above in the paragraph on redox indicator. [ 49 ]
Methylene blue is a dye behaving as a redox indicator that is commonly used in the food industry to test the freshness of milk and dairy products. [ 5 ] [ 58 ] A few drops of methylene blue solution added to a sample of milk should remain blue (oxidized form in the presence of enough dissolved O 2 ), otherwise (discoloration caused by the reduction of methylene blue into its colorless reduced form) the dissolved O 2 concentration in the milk sample is low indicating that the milk is not fresh (already abiotically oxidized by O 2 whose concentration in solution decreases) or could be contaminated by bacteria also consuming the atmospheric O 2 dissolved in the milk. [ 58 ] In other words, aerobic conditions should prevail in fresh milk and methylene blue is simply used as an indicator of the dissolved oxygen remaining in the milk. [ 51 ]
The adsorption of methylene blue serves as an indicator defining the adsorptive capacity of granular activated carbon in water filters. Adsorption of methylene blue is very similar to adsorption of pesticides from water, this quality makes methylene blue serve as a good predictor for filtration qualities of carbon. It is as well a quick method of comparing different batches of activated carbon of the same quality.
A color reaction in an acidified, aqueous methylene blue solution containing chloroform can detect anionic surfactants in a water sample. Such a test is known as an MBAS assay (methylene blue active substances assay).
The MBAS assay cannot distinguish between specific surfactants, however. Some examples of anionic surfactants are carboxylates , phosphates , sulfates , and sulfonates . [ citation needed ]
The methylene blue value is defined as the number of milliliter's standard methylene value solution decolorized 0.1 g of activated carbon (dry basis). [ 59 ] Methylene blue value reflects the amount of clay minerals in aggregate samples. [ 60 ] In materials science , methylene blue solution is successively added to fine aggregate which is being agitated in water. The presence of free dye solution can be checked with stain test on a filter paper. [ 61 ]
In biology, methylene blue is used as a dye for a number of different staining procedures, such as Wright's stain and Jenner's stain . Since it is a temporary staining technique, methylene blue can also be used to examine RNA or DNA under the microscope or in a gel: as an example, a solution of methylene blue can be used to stain RNA on hybridization membranes in northern blotting to verify the amount of nucleic acid present. While methylene blue is not as sensitive as ethidium bromide , it is less toxic and it does not intercalate in nucleic acid chains, thus avoiding interference with nucleic acid retention on hybridization membranes or with the hybridization process itself. [ citation needed ]
It can also be used as an indicator to determine whether eukaryotic cells such as yeast are alive or dead. The methylene blue is reduced in viable cells, leaving them unstained. However dead cells are unable to reduce the oxidized methylene blue and the cells are stained blue. Methylene blue can interfere with the respiration of the yeast as it picks up hydrogen ions made during the process. [ citation needed ]
It is usually used to protect newly laid fish eggs from being infected by fungus. This is useful when the hobbyist wants to artificially hatch the fish eggs. [ 62 ] For poisoning, injury (prevention of infection), or sickness, methylene blue is given as a "medicated bath" for the fish.
Methylene blue is not without side effects to fish. [ 64 ]
Methylene blue has been described as "the first fully synthetic drug used in medicine". Methylene blue was first prepared in 1876 by German chemist Heinrich Caro . [ 65 ]
Its use in the treatment of malaria was pioneered by Paul Guttmann and Paul Ehrlich in 1891. During this period before World War I, researchers like Ehrlich believed that drugs and dyes worked in the same way, by preferentially staining pathogens and possibly harming them. Changing the cell membrane of pathogens is in fact how various drugs work, so the theory was partially correct, although far from complete. Methylene blue continued to be used in World War II, where it was not well-liked by soldiers, who observed, "Even at the loo, we see, we pee, navy blue ." [ citation needed ]
It was discovered to be an antidote to carbon monoxide poisoning and cyanide poisoning in 1933 by Matilda Brooks . [ 66 ]
Methylene blue was the original prototype or lead compound for the design of many antimalarials including chloroquine , antihistamines, and antipsychotics including chlorpromazine . [ 67 ]
Antimalarial use of the drug has recently (2009) been revived. [ 68 ] It simultaneously targets many biological processes in the apicomplexan pathogen [ 69 ] though the main mechanism seems to be causing a lethal amount of redox cycling. [ 39 ]
A 2018 meta-analysis finds that it has proven effective against P. falciparum in Africa. It effectively reduces levels of the transmission-stage gametocyte and has synergy with the standard artemisinin-based combination therapy (ACT). Its effects against other malarial species and P. falciparum populations in other locations are unclear. [ 39 ]
Another use of methylene blue is to treat ifosfamide neurotoxicity . Methylene blue was first reported for treatment and prophylaxis of ifosfamide neuropsychiatric toxicity in 1994. A toxic metabolite of ifosfamide, chloroacetaldehyde (CAA), disrupts the mitochondrial respiratory chain , leading to an accumulation of nicotinamide adenine dinucleotide hydrogen (NADH). Methylene blue acts as an alternative electron acceptor , and reverses the NADH inhibition of hepatic gluconeogenesis while also inhibiting the transformation of chloroethylamine into chloroacetaldehyde, and inhibits multiple amine oxidase activities, preventing the formation of CAA. [ 70 ] [ 71 ]
The dosing of methylene blue for treatment of ifosfamide neurotoxicity varies, depending upon its use simultaneously as an adjuvant in ifosfamide infusion, versus its use to reverse psychiatric symptoms that manifest after completion of an ifosfamide infusion. Reports suggest that methylene blue up to six doses a day have resulted in improvement of symptoms within 10 minutes to several days. [ 72 ] Alternatively, it has been suggested that intravenous methylene blue every six hours for prophylaxis during ifosfamide treatment in people with history of ifosfamide neuropsychiatric toxicity. [ 73 ] Prophylactic administration of methylene blue the day before initiation of ifosfamide, and three times daily during ifosfamide chemotherapy has been recommended to lower the occurrence of ifosfamide neurotoxicity. [ 74 ]
Methylene blue inhibits monoamine oxidase , inhibits the glutamatergic system (via inhibition of NO synthase and soluble guanylate cyclase ), modulates mitochondrial function (by acting as an electron acceptor), and decreases the activation of inflammasomes NLRP3 and NLRC4 . As a result, it's been considered potentially useful in neuropsychiatric disorders . In humans it has been tried for (listed in decreasing order of evidence quality): bipolar disorder (especially depressive symptoms), Alzheimer's disease , claustrophobia , ifosfamide encephalopathy, and schizophrenia . With methylene blue, a higher dose does not necessarily work better than a lower dose. [ 33 ]
In the late 2010s and early 2020s, a social media trend emerged promoting the use of methylene blue for various medical purposes, including anti-aging , metabolism enhancement, cognitive improvement, cancer treatment, and COVID-19 treatment. [ 75 ] [ 76 ] [ 77 ] [ 78 ] Currently there is no scientific consensus on, and no FDA approval for, its effectiveness and safety for these purposes. [ 75 ] [ 76 ] [ 78 ] Medical experts cautioned that methylene blue can be toxic in high doses and may interact with other medications , potentially reducing their effectiveness or causing unforeseen side effects. Therefore, it should only be used under a doctor's prescription. [ 75 ] [ 76 ]
This trend probably started following the publication of a few scientific papers exploring the potential of methylene blue for treating some medical conditions, [ 75 ] such as progeria , [ 79 ] and skin aging . [ 80 ] It was also explored as part of anticancer photodynamic therapy using lasers. [ 81 ] One systematic review of the studies expresses optimism but emphasizes the need for more extensive research to confirm methylene blue's clinical applications. [ 82 ] Another review takes a more critical stance, stating that "it is obvious that the clinical use of MB represents a rather controversial problem given the heterogeneity of available data and the lack of preclinical data, which is in conflict with standards of safe use of such substances in human medicinal practice". [ 83 ]
In January 2025, Robert F. Kennedy Jr ., then the U.S. health secretary nominee, was filmed adding droplets of an unidentified blue liquid to his drink during a flight. While many have speculated that it was methylene blue, Kennedy has not addressed the claims. [ 77 ] [ 84 ] [ 85 ] | https://en.wikipedia.org/wiki/Methylene_blue |
In organic chemistry , a methylene bridge , methylene spacer , or methanediyl group is any part of a molecule with formula −CH 2 − ; namely, a carbon atom bound to two hydrogen atoms and connected by single bonds to two other distinct atoms in the rest of the molecule. It is the repeating unit in the skeleton of the unbranched alkanes .
A methylene bridge can also act as a bidentate ligand joining two metals in a coordination compound , such as titanium and aluminum in Tebbe's reagent . [ 1 ]
A methylene bridge is often called a methylene group or simply methylene , as in "methylene chloride" ( dichloromethane CH 2 Cl 2 ). As a bridge in other compounds, for example in cyclic compounds, it is given the name methano . However, the term methylidene group (not to be confused with the term methylene group , nor the carbene methylidene ) properly applies to the CH 2 group when it is connected to the rest of the molecule by a double bond ( =CH 2 ), giving it chemical properties very distinct from those of a bridging CH 2 group.
Compounds possessing a methylene bridge located between two strong electron withdrawing groups (such as nitro , carbonyl or nitrile groups) are sometimes called active methylene compounds. [ 2 ] Treatment of these with strong bases can form enolates or carbanions , which are often used in organic synthesis . Examples include the Knoevenagel condensation and the malonic ester synthesis . [ 3 ]
Examples of compounds which contain methylene bridges include: | https://en.wikipedia.org/wiki/Methylene_bridge |
A methylene group is any part of a molecule that consists of two hydrogen atoms bound to a carbon atom, which is connected to the remainder of the molecule by two single bonds . [ 1 ] The group may be represented as −CH 2 − or >CH 2 , where the '>' denotes the two bonds.
This stands in contrast to a situation where the carbon atom is bound to the rest of the molecule by a double bond , which is preferably called a methylidene group , represented =CH 2 . [ 2 ] Formerly the methylene name was used for both isomers. The name “ methylene bridge “ can be used for the single-bonded isomer, to emphatically exclude methylidene. The distinction is often important, because the double bond is chemically different from two single bonds.
The methylene group should be distinguished from the CH 2 molecule called carbene . [ 3 ] This was also formerly called methylene .
The central carbon in 1,3-dicarbonyl compound is known as an activated methylene group. This is because, owing to the structure, the carbon is especially acidic and can easily be deprotonated to form a methylene group. [ 4 ]
This organic chemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Methylene_group |
Methylenedioxy is the term used in the field of chemistry , particularly in organic chemistry , for a functional group with the structural formula R−O−CH 2 −O−R′ which is connected to the rest of a molecule by two chemical bonds . The methylenedioxy group consists of two oxygen atoms connected to a methylene bridge ( −CH 2 − unit). The methylenedioxy group is generally found attached to an aromatic structure such as phenyl where it forms the methylenedioxyphenyl or benzodioxole functional group which is widely found in natural products , including safrole , and drugs and chemicals such as tadalafil , MDMA , paroxetine and piperonyl butoxide .
Enzymes within the cytochrome P450 superfamily are able to form methylenedioxy bridges by closure of an open, adjacent phenol and methoxy group. Examples of products formed by this process are canadine and berberine . Similarly, ortho -demethylenation can be carried out by other members of the superfamily to open a bridge; a process which is applied to, as examples, both MDMA and MDA during their metabolism.
MDPV and MDPHP , both belonging to the class of pyrrolidinophenones, share the street name "monkey dust," [ 1 ] [ 2 ] [ 3 ] a play on the chemical term "methylenedioxy" present in both substances.
This article about an organic compound is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Methylenedioxy |
Methylephedrine , sold under the brand name Metheph among others, is a sympathomimetic medication described as an antiasthmatic agent and used to treat coughing and nasal congestion . [ 3 ] [ 4 ] [ 1 ] It is reported to be used in various over-the-counter cough and cold preparations throughout the world, including Japan . [ 1 ]
The drug is an ephedrine -like sympathomimetic and activates α- and β-adrenergic receptors . [ 5 ] Chemically, it is a substituted amphetamine and is closely related to ephedrine. [ 3 ] [ 4 ]
Methylephedrine was discovered by 1927. [ 6 ] It is mostly no longer marketed as a prescription drug . [ 4 ] The drug is also found naturally as an alkaloid in Ephedra species including Ephedra sinica , Ephedra vulgaris , and Ephedra distachya . [ 3 ] [ 6 ]
Rarely, heart failure and stroke in association with use of methylephedrine have been reported. [ 7 ] [ 8 ] [ 9 ]
Methylephedrine shows reinforcing effects, a measure of addiction and misuse potential , in monkeys. [ 10 ]
Methylephedrine is a sympathomimetic and ephedrine -like agent. [ 5 ] [ 1 ] Ephedrine and related agents act as norepinephrine releasing agents and hence as indirectly acting sympathomimetics. [ 1 ] In relation to this, methylephedrine stimulates α- and β-adrenergic receptors . [ 5 ] [ 1 ] The drug has bronchodilator and nasal decongestant effects. [ 5 ]
The occupancy of the dopamine transporter (DAT) by racemic methylephedrine has been studied. [ 11 ]
Methylephedrine is metabolized into ephedrine and norephedrine . [ 1 ] [ 2 ] It is excreted in urine 33 to 40% unchanged, 15% as methylephedrine N -oxide, and 8% as ephedrine after 24 hours. [ 1 ] [ 2 ]
Methylephedrine, also known as (1 R ,2 S )-β-hydroxy- N , N -dimethyl-α-methyl-β-phenethylamine and as (1 R ,2 S )-β-hydroxy- N , N -dimethylamphetamine, is a substituted phenethylamine and amphetamine derivative . [ 3 ] [ 4 ] It is the N - methylated derivative of ephedrine ((1 R ,2 S )-β-hydroxy- N -methylamphetamine). [ 3 ] [ 4 ]
A closely related compound and stereoisomer of methylephedrine is N -methylpseudoephedrine . [ 3 ] Another related analogue is dimethylamphetamine ( N , N -dimethylamphetamine), which is said to be a prodrug of methamphetamine and/or amphetamine . [ 12 ] Other analogues include etafedrine ( N -ethylephedrine) and cinnamedrine ( N -cinnamylephedrine). [ 3 ]
The experimental log P of methylephedrine is 2.47 and its predicted log P ranges from 1.7 to 1.74. [ 13 ] [ 1 ] [ 14 ]
In organic chemistry , N -methylephedrine is used as a resolving agent and as a precursor to chiral supporting electrolytes , phase-transfer catalysts , and reducing agents . [ 15 ]
Methylephedrine was discovered via isolation from Ephedra by 1927. [ 6 ]
Methylephedrine is the generic name of the drug and its BAN Tooltip British Approved Name . [ 3 ] [ 4 ] [ 16 ] In the case of the hydrochloride salt , its generic name is methylephedrine hydrochloride and this is its BANM Tooltip British Approved Name . [ 3 ] [ 4 ] [ 16 ] Brand names of methylephedrine include Metheph , Methy-F , and Tybraine , among others. [ 3 ] [ 4 ] [ 16 ]
Similarly to ephedrine , methylephedrine may have misuse potential . [ 1 ] [ 17 ] The drug shows reinforcing effects in monkeys . [ 10 ] It is one of the four constituents of BRON , a Japanese over-the-counter cough medicine with reports of misuse. [ 1 ] [ 17 ] However, addiction liability of BRON was attributed primarily to the codeine component. [ 17 ] A case report of addiction to methylephedrine exists. [ 9 ]
Methylephedrine is on the World Anti-Doping Agency 's prohibited list . [ 5 ] | https://en.wikipedia.org/wiki/Methylephedrine |
Methylglyoxal ( MGO ) is the organic compound with the formula CH 3 C(O)CHO. It is a reduced derivative of pyruvic acid . It is a reactive compound that is implicated in the biology of diabetes . Methylglyoxal is produced industrially by degradation of carbohydrates using overexpressed methylglyoxal synthase . [ 1 ]
Gaseous methylglyoxal has two carbonyl groups: an aldehyde and a ketone . In the presence of water, it exists as hydrates and oligomers . The formation of these hydrates is indicative of the high reactivity of MGO, which is relevant to its biological behavior. [ 2 ]
In organisms, methylglyoxal is formed as a side-product of several metabolic pathways . [ 3 ] Methylglyoxal mainly arises as side products of glycolysis involving glyceraldehyde-3-phosphate and dihydroxyacetone phosphate . It is also thought to arise via the degradation of acetone and threonine . [ 4 ] Illustrative of the myriad pathways to MGO, aristolochic acid caused 12-fold increase of methylglyoxal from 18 to 231 μg/mg of kidney protein in poisoned mice. [ 5 ] It may form from 3-aminoacetone , which is an intermediate of threonine catabolism , as well as through lipid peroxidation . However, the most important source is glycolysis . Here, methylglyoxal arises from nonenzymatic phosphate elimination from glyceraldehyde phosphate and dihydroxyacetone phosphate (DHAP), two intermediates of glycolysis. This conversion is the basis of a potential biotechnological route to the commodity chemical 1,2-propanediol . [ 6 ]
Since methylglyoxal is highly cytotoxic , several detoxification mechanisms have evolved. One of these is the glyoxalase system . Methylglyoxal is detoxified by glutathione . Glutathione reacts with methylglyoxal to give a hemithioacetal , which converted into S - D -lactoyl-glutathione by glyoxalase I . [ 7 ] This thioester is hydrolyzed to D -lactate by glyoxalase II . [ 8 ]
Methylglyoxal is involved in the formation of advanced glycation end products (AGEs). [ 4 ] In this process, methylglyoxal reacts with free amino groups of lysine and arginine and with thiol groups of cysteine forming AGEs. Histones are also heavily susceptible to modification by methylglyoxal and these modifications are elevated in breast cancer. [ 9 ] [ 10 ]
DNA damages are induced by reactive carbonyls , principally methylglyoxal and glyoxal , at a frequency similar to that of oxidative DNA damages . [ 12 ] Such damage, referred to as DNA glycation , can cause mutation , breaks in DNA and cytotoxicity . [ 12 ] In humans, a protein DJ-1 (also named PARK7 ), has a key role in the repair of glycated DNA bases.
Due to increased blood glucose levels, methylglyoxal has higher concentrations in diabetics and has been linked to arterial atherogenesis . Damage by methylglyoxal to low-density lipoprotein through glycation causes a fourfold increase of atherogenesis in diabetics. [ 13 ] Methylglyoxal binds directly to the nerve endings and by that increases the chronic extremity soreness in diabetic neuropathy . [ 14 ] [ 15 ]
Methylglyoxal is a component of some kinds of honey, including manuka honey ; it appears to have activity against E. coli and S. aureus and may help prevent formation of biofilms formed by P. aeruginosa . [ 16 ]
Research suggests that methylglyoxal contained in honey does not cause an increased formation of advanced glycation end products (AGEs) in healthy persons. [ 17 ] [ 18 ] | https://en.wikipedia.org/wiki/Methylglyoxal |
The methylglyoxal pathway is an offshoot of glycolysis found in some prokaryotes , which converts glucose into methylglyoxal and then into pyruvate . [ 1 ] However unlike glycolysis the methylglyoxal pathway does not produce adenosine triphosphate , ATP. The pathway is named after the substrate methylglyoxal which has three carbons and two carbonyl groups located on the 1st carbon and one on the 2nd carbon. Methylglyoxal is, however, a reactive aldehyde that is very toxic to cells, it can inhibit growth in E. coli at milimolar concentrations. The excessive intake of glucose by a cell is the most important process for the activation of the methylglyoxal pathway. [ 2 ]
The methylglyoxal pathway is activated by the increased intercellular uptake of carbon containing molecules such as glucose , glucose-6-phosphate , lactate , or glycerol . Methylglyoxal is formed from dihydroxyacetone phosphate (DHAP) by the enzyme methylglyoxal synthase , giving off a phosphate group.
Methylglyoxal is then converted into two different products, either D-lactate, and L-lactate. Methylglyoxal reductase and aldehyde dehydrogenase convert methylglyoxal into lactaldehyde and, eventually, L-lactate. If methylglyoxal enters the glyoxylase pathway , it is converted into lactoylguatathione and eventually D-lactate. Both D-lactate, and L-lactate are then converted into pyruvate . The pyruvate that is created most often goes on to enter the Krebs cycle ( Weber 711–13).
The potentially hazardous effects of methylglyoxal require regulation of the reactions with this substrate. Synthesis of methylglyoxal is regulated by levels of DHAP and phosphate concentrations. High concentrations of DHAP encourage methylglyoxal synthase to produce methylglyoxal, while high phosphate concentrations inhibit the enzyme, and therefore the production of more methylglyoxal. The enzyme triose phosphate isomerase affects the levels of DHAP by converting glyceraldehyde 3-phosphate (GAP) into DHAP. The usual pathway converting GAP to pyruvate starts with the enzyme glyceraldehyde 3-phosphate dehydrogenase ( Weber 711–13). Low phosphate levels inhibit GAP dehydrogenase; GAP is instead converted into DHAP by triosephosphate isomerase . Again, increased levels of DHAP activate methylglyoxal synthase and methylglyoxal production ( Weber 711–13).
Jan Weber, Anke Kayser, and Ursula Rinas, performed an experiment to test what happened to the methylglyoxal pathway when E. coli was in the presence of a constantly high concentration of glucose. The concentration of methylglyoxal increased until it reached 20 μmol. Methylglyoxal concentration then began to decrease, once it reached this level. The decrease in the concentration of methylglyoxal was connected to the drop in respiratory activity. When respiration activity increased the concentration of methylglyoxal increased again, until it reached the 20 μmol concentration ( Weber 714–15).
This pathway does not produce any ATP, this pathway does not replace glycolysis, it runs simultaneously to glycolysis and is only initiated with an increased concentration of sugar phosphates. One believed purpose of the methylglyoxal pathway is to help release the stress of elevated sugar phosphate concentration. Also when methylglyoxal is formed from DHAP, an inorganic phosphate is given off which can be used to replenish a low concentration of needed inorganic phosphate. The methylglyoxal pathway is a rather dangerous tactic, both because less energy is produced and a toxic compound, methylglyoxal is formed. ( Weber 715).
Weber, Jan, Anke Kayser, and Ursula Rinas. Metabolic Flux Analysis of Escherichia Coli In. Vers. 151: 707-716. 6 Dec. 2004. Microbiology. 10 Apr. 2007 < http://mic.sgmjournals.org/cgi/reprint/151/3/707 >.
Saadat, D., Harrison, D.H.T. "Methylglyoxal Synthase From Escherichia Coli ." RCSB Protein Data Base. 24 Apr. 2007. RCSB Protein Data Base. 25 Apr. 2007 < http://www.pdb.org/pdb/explore.do?structureId=1B93 >.
"Methylglyoxal Synthase From Escherichia Coli." RCSB Protein Data Base. 24 Apr. 2007. RCSB Protein Data Base. 25 Apr. 2007 < http://www.pdb.org/pdb/explore.do?structureId=1B93 >.
Yun, M., C.-G. Park, J.-Y Kim, and H.-W. Park. "Structural Anayysis of Glyeraldehyde 3-Phosphate Dehydrogenase from Escherichia coli: Direct Evidence for Substrate Binding and Cofactor-Induced Confromational Changes. RCSB Protein Data Base. 24 Apr. 2007. RCSB Protein Data Base. 30 Apr. 2007 < http://www.pdb.org/pdb/explore.do?structureId=1DC4 >. | https://en.wikipedia.org/wiki/Methylglyoxal_pathway |
In organic chemistry , a methylidyne group or just methylidyne is a neutral part of a molecule (a substituent or functional group ) with formula ≡CH , consisting of a carbon atom bonded to a hydrogen atom by one single bond and to the rest of the molecule by one triple bond. [ 1 ] For example, a methylidyne group is present in n -methylidyne-1-hexanaminium , H 3 C−(CH 2 ) 5 −N + ≡CH .
The name "methylidyne" is also used for the methylidyne radical (carbyne) ⫶ CH , the same two atoms not bound to any other atom.
This organic chemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Methylidyne_group |
Methylidyne , or ( unsubstituted ) carbyne , is an organic compound whose molecule consists of a single hydrogen atom bonded to a carbon atom. It is the parent compound of the carbynes , which can be seen as obtained from it by substitution of other functional groups for the hydrogen.
The carbon atom is left with either one or three unpaired electrons (unsatisfied valence bonds), depending on the molecule's excitation state ; making it a radical . Accordingly, the chemical formula can be CH • or CH 3• (also written as ⫶ CH); each dot representing an unpaired electron. The corresponding systematic names are methylidyne or hydridocarbon(•) , and methanetriyl or hydridocarbon(3•) . However, the formula is often written simply as CH.
Methylidyne is a highly reactive gas, that is quickly destroyed in ordinary conditions but is abundant in the interstellar medium (and was one of the first molecules to be detected there). [ 4 ]
The trivial name carbyne is the preferred IUPAC name .
Following the substitutive nomenclature, the molecule is viewed as methane with three hydrogen atoms removed, yielding the systematic name "methylidyne".
Following the additive nomenclature, the molecule is viewed as a hydrogen atom bonded to a carbon atom, yielding the name "hydridocarbon".
By default, these names pay no regard to the excitation state of the molecule. When that attribute is considered, the states with one unpaired electron are named "methylylidene" or "hydridocarbon(•)", whereas the excited states with three unpaired electrons are named "methanetriyl" or "hydridocarbon(3•)".
As an odd-electron species, CH is a radical. The ground state is a doublet ( X 2 Π). The first two excited states are a quartet (with three unpaired electrons) ( a 4 Σ − ) and a doublet ( A 2 Δ). The quartet lies at 71 kJ/mol above the ground state. [ 5 ]
Reactions of the doublet radical with non-radical species involves insertion or addition:
whereas reactions of the quartet radical generally involves only abstraction:
Methylidyne can bind to metal atoms as tridentate ligand in coordination complexes . An example is methylidynetricobaltnonacarbonyl HCCo 3 (CO) 9 . [ 6 ]
Methylidyne-like species are implied intermediates in the Fischer–Tropsch process , the hydrogenation of CO to produce hydrocarbons . Methylidyne entities are assumed to bond to the catalyst 's surface. A hypothetical sequence is: [ 6 ]
The M n CH intermediate has a tridentate methylidine ligand. The methylene ligand (H 2 C) is then poised couple to CO or to another methylene, thereby growing the C–C chain. [ 7 ]
The methylylidyne group can exhibit both Lewis acidic and Lewis basic character. [ 8 ] Such behavior is only of theoretical interest since it is not possible to produce methylidyne.
In October 2016, astronomers reported that the methylidyne radical ⫶ CH, the carbon-hydrogen positive ion : CH + , and the carbon ion ⫶ C + are the result of ultraviolet light from stars , rather than in other ways, such as the result of turbulent events related to supernovas and young stars , as thought earlier. [ 9 ]
Methylidyne can be prepared from bromoform . [ 6 ] | https://en.wikipedia.org/wiki/Methylidyne_radical |
Methyllysine is derivative of the amino acid residue lysine where the sidechain ammonium group has been methylated one or more times. [ 1 ]
Such methylated lysines play an important role in epigenetics ; the methylation of specific lysines of certain histones in a nucleosome alters the binding of the surrounding DNA to those histones, which in turn affects the expression of genes on that DNA. [ 2 ] [ 3 ] The binding is affected because the effective radius of the positive charge is increased (methyl groups are larger than the hydrogen atoms they replace), reducing the strongest potential electrostatic attraction with the negatively charged DNA.
It is thought that the methylation of lysine (and arginine) on histone tails does not directly affect their binding to DNA. Rather, such methyl marks recruit other proteins that modulate chromatin structure. [ 4 ]
In Protein Data Bank files, methylated lysines are indicated by the MLY or MLZ acronyms.
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Methyllysine |
Methylmercury is an organometallic cation with the formula [CH 3 Hg] + . It is the simplest organomercury compound. Methylmercury is extremely toxic, and its derivatives are the major source of organic mercury for humans. It is a bioaccumulative environmental toxicant with a 50-day half-life . [ 1 ] [ clarification needed ] Methylmercury (derived biologically from dimethylmercury ) is the causative agent of the infamous Minamata disease .
"Methylmercury" is a shorthand for the hypothetical "methylmercury cation", sometimes written methylmercury(1+) cation or methylmercury(II) cation . This functional group is composed of a methyl group bonded to an atom of mercury . Its chemical formula is CH 3 Hg + (sometimes written as MeHg + ). The Methylmercury compound has an overall charge of +1, with Hg in the +2 oxidation state . Methylmercury exists as a substituent in many complexes of the type [MeHgL] + (L = Lewis base) and MeHgX (X = anion). [ 2 ]
As a positively charged ion, it readily combines with anions such as chloride ( Cl − ), hydroxide ( OH − ) and nitrate ( NO − 3 ). It has particular affinity for sulfur -containing anions, particularly thiols ( RS − ). Thiols are generated when the amino acid cysteine and the peptide glutathione form strong complexes with methylmercury: [ 3 ]
Methylmercury is formed from inorganic mercury by the action of microbes that live in aquatic systems including lakes , rivers , wetlands , sediments , soils and the open ocean . [ 5 ] This methylmercury production has been primarily attributed to anaerobic bacteria in the sediment. [ 6 ] Capable bacteria that can methylate mercury are mostly the sulfate-reducing bacteria (SRB), [ 7 ] [ 8 ] iron-reducing bacteria (FeRB) [ 9 ] and methanogens . [ 10 ] [ 11 ] Significant concentrations of methylmercury in ocean water columns [ 12 ] are strongly associated with nutrients and organic matter remineralization , which indicate that remineralization may contribute to methylmercury production. [ 13 ] Direct measurements of methylmercury production using stable mercury isotopes have also been observed in marine waters, [ 14 ] [ 15 ] but the microbes involved are still unknown. Increased methylmercury concentrations in water and fish have been detected after flooding of soils associated with reservoir creation (e.g. for hydroelectric power generation ) and in thermokarst wetlands that form after permafrost thaw. [ 14 ] [ 16 ] [ 17 ] The increased methylmercury concentration is due to its ability to bio-accumulate and biο-magnify in aquatic food webs. [ 18 ]
There are various sources of inorganic mercury that may indirectly contribute to the production of methylmercury from microbes in the environment. Natural sources of mercury released to the atmosphere include volcanoes , forest fires , volatilization from the ocean [ 19 ] and weathering of mercury-bearing rocks . [ 20 ] Anthropogenic sources of mercury include the burning of wastes containing inorganic mercury and from the burning of fossil fuels , particularly coal . Although inorganic mercury is only a trace constituent of such fuels, their large scale combustion in utility and commercial/industrial boilers in the United States alone results in release of some 80.2 tons (73 metric tons ) of elemental mercury to the atmosphere each year, out of total anthropogenic mercury emissions in the United States of 158 tons (144 metric tons)/year. [ 21 ]
In the past, methylmercury was produced directly and indirectly as part of several industrial processes such as the manufacture of acetaldehyde . However, currently there are few direct anthropogenic sources of methylmercury pollution in the United States. [ 21 ]
Whole-lake ecosystem experiments at IISD-ELA in Ontario , Canada, showed that mercury falling directly on a lake had the fastest impacts on aquatic ecosystems as opposed to mercury falling on the surrounding land. [ 22 ] This inorganic mercury is converted to methylmercury by bacteria. Different stable isotopes of mercury were added to lakes, wetlands , and uplands , simulating rain, and then mercury concentrations in fish were analyzed to find their source. [ 23 ] The mercury applied to lakes was found in young-of-the-year yellow perch within two months, whereas the mercury applied to wetlands and uplands had a slower but longer influx. [ 22 ] [ 23 ]
Acute methylmercury poisoning can occur either directly from the release of methylmercury into the environment or indirectly from the release of inorganic mercury that is subsequently methylated in the environment. For example, methylmercury poisoning occurred at Grassy Narrows in Ontario, Canada (see Ontario Minamata disease ), as a result of mercury released from the mercury-cell Chloralkali process , which uses liquid mercury as an electrode in a process that entails electrolytic decomposition of brine, followed by mercury methylation in the aquatic environment. An acute methylmercury poisoning tragedy occurred also in Minamata, Japan , following release of methylmercury into Minamata Bay and its tributaries (see Minamata disease ). In the Ontario case, inorganic mercury discharged into the environment was methylated in the environment; whereas, in Minamata, Japan, there was direct industrial discharge of methylmercury.
Because methylmercury is formed in aquatic systems, and because it is not readily eliminated from organisms, it is biomagnified in aquatic food chains from bacteria , to plankton , through macroinvertebrates , to herbivorous fish and to piscivorous (fish-eating) fish. [ 24 ] [ 25 ] At each step in the food chain, the concentration of methylmercury in the organism increases. The concentration of methylmercury in the top-level aquatic predators can reach a level a million times higher than the level in the water. [ 24 ] [ 25 ] This is because methylmercury has a half-life of about 72 days in aquatic organisms resulting in its bioaccumulation within these food chains. Organisms, including humans, [ 26 ] fish-eating birds, and fish-eating mammals such as otters and cetaceans (i.e. whales and dolphins ) that consume fish from the top of the aquatic food chain receive the methylmercury that has accumulated through this process, plus the toxins in their habitat. [ 24 ] [ 25 ] Fish and other aquatic species are the main source of human methylmercury exposure. [ 24 ]
The concentration of mercury in any given fish depends on the species of fish, the age and size of the fish and the type of water body in which it is found. [ 24 ] In general, fish-eating fish such as shark , swordfish , marlin , larger species of tuna , walleye , largemouth bass , and northern pike , have higher levels of methylmercury than herbivorous fish or smaller fish such as tilapia and herring . [ 27 ] [ 28 ] Within a given species of fish, older and larger fish have higher levels of methylmercury than smaller fish. Fish that develop in water bodies that are more acidic also tend to have higher levels of methylmercury. [ 24 ]
Ingested methylmercury is readily and completely absorbed by the gastrointestinal tract . It is mostly found complexed with free cysteine and with proteins and peptides containing that amino acid. The methylmercuric-cysteinyl complex is recognized by amino acids transporting proteins in the body as methionine , another essential amino acid . [ 29 ] Because of this mimicry, it is transported freely throughout the body including across the blood–brain barrier and across the placenta , where it is absorbed by the developing fetus . Also for this reason as well as its strong binding to proteins, methylmercury is not readily eliminated. Methylmercury has a half-life in human blood of about 50 days. [ 30 ]
Several studies indicate that methylmercury is linked to subtle developmental deficits in children exposed in utero such as loss of IQ points, and decreased performance in tests of language skills, memory function and attention deficits. [ 31 ] Methylmercury exposure in adults has also been linked to increased risk of cardiovascular disease including heart attack . [ 32 ] [ 33 ] [ 34 ] Some evidence also suggests that methylmercury can cause autoimmune effects in sensitive individuals. [ 35 ] There is some evidence suggesting a possible connection between post-natal mercury exposure and autism; however, it is not clear whether methylmercury intake in particular is linked in a similar way. [ 36 ] [ 37 ] [ 38 ] Although there is no doubt that methylmercury is toxic in several respects, including through exposure of the developing fetus, there is still some controversy as to the levels of methylmercury in the diet that can result in adverse effects. Recent evidence suggests that the developmental and cardiovascular toxicity of methylmercury may be mitigated by co-exposures to omega-3 fatty acids and perhaps selenium , both found in fish and elsewhere. [ 33 ] [ 39 ] [ 40 ] [ 41 ] [ 42 ]
There have been several episodes in which large numbers of people were severely poisoned by food contaminated with high levels of methylmercury, notably the dumping of industrial waste that resulted in the pollution and subsequent mass poisoning in Minamata and Niigata , Japan [ 43 ] and the situation in Iraq in the 1960s and 1970s in which wheat treated with methylmercury as a preservative and intended as seed grain was fed to animals and directly consumed by people (see Basra poison grain disaster ). These episodes resulted in neurological symptoms including paresthesias , loss of physical coordination, difficulty in speech , narrowing of the visual field , hearing impairment , blindness , and death. Children who had been exposed in utero through their mothers' ingestion were also affected with a range of symptoms including motor difficulties, sensory problems and intellectual disability .
At present, exposures of this magnitude are rarely seen and are confined to isolated incidents. Accordingly, concern over methylmercury pollution is currently focused on more subtle effects that may be linked to levels of exposure presently seen in populations with high to moderate levels of dietary fish consumption. These effects are not necessarily identifiable on an individual level or may not be uniquely recognizable as due to methylmercury. However, such effects may be detected by comparing populations with different levels of exposure. There are isolated reports of various clinical health effects in individuals who consume large amounts of fish; [ 44 ] however, the specific health effects and exposure patterns have not been verified with larger, controlled studies.
Many governmental agencies, the most notable ones being the United States Environmental Protection Agency (EPA), the United States Food and Drug Administration (FDA), Health Canada , and the European Union Health and Consumer Protection Directorate-General , as well as the World Health Organization (WHO) and the United Nations Food and Agriculture Organization (FAO), have issued guidance for fish consumers that is designed to limit methylmercury exposure from fish consumption. At present, most of this guidance is based on protection of the developing fetus; future guidance, however, may also address cardiovascular risk. In general, fish consumption advice attempts to convey the message that fish is a good source of nutrition and has significant health benefits, but that consumers, in particular pregnant women, women of child-bearing age, nursing mothers, and young children, should avoid fish with high levels of methylmercury, limit their intake of fish with moderate levels of methylmercury, and consume fish with low levels of methylmercury no more than twice a week. [ 45 ] [ 46 ]
In recent years, there has been increasing recognition that methylmercury affects fish and wildlife health, both in acutely polluted ecosystems and ecosystems with modest methylmercury levels. Two reviews [ 24 ] [ 47 ] document numerous studies of diminished reproductive success of fish, fish-eating birds, and mammals due to methylmercury contamination in aquatic ecosystems.
Reported methylmercury levels in fish, along with fish consumption advisories, have the potential to disrupt people's eating habits, fishing traditions, and the livelihoods of the people involved in the capture, distribution, and preparation of fish as a foodstuff for humans. [ 48 ] Furthermore, proposed limits on mercury emissions have the potential to add costly pollution controls on coal-fired utility boilers. Nevertheless, substantial benefits can be achieved globally by introducing mercury emission reduction measures because they reduce human and wildlife exposure to methylmercury. [ 49 ]
About 30% of the distributed mercury depositional input is from current anthropogenic sources, and 70% is from natural sources. The natural sources category includes re-emission of mercury previously deposited from anthropogenic sources. [ 50 ] According to one study, based on modeled concentrations, pre- Anthropocene tissue-bound levels in freshwater fish may not have differed markedly from current levels. [ 51 ] However, based on a comprehensive set of global measurements, the ocean contains about 60,000 to 80,000 tons of mercury from pollution, and mercury levels in the upper ocean have tripled since the beginning of the industrial revolution. Higher mercury levels in shallower ocean waters could increase the amount of the toxicant accumulating in food fish, exposing people to a greater risk of mercury poisoning. [ 52 ] | https://en.wikipedia.org/wiki/Methylmercury |
Methylotrophs are a diverse group of microorganisms that can use reduced one-carbon compounds, such as methanol or methane , as the carbon source for their growth; and multi-carbon compounds that contain no carbon-carbon bonds, such as dimethyl ether and dimethylamine . This group of microorganisms also includes those capable of assimilating reduced one-carbon compounds by way of carbon dioxide using the ribulose bisphosphate pathway. [ 1 ] These organisms should not be confused with methanogens which on the contrary produce methane as a by-product from various one-carbon compounds such as carbon dioxide.
Some methylotrophs can degrade the greenhouse gas methane , and in this case they are called methanotrophs . The abundance, purity, and low price of methanol compared to commonly used sugars make methylotrophs competent organisms for production of amino acids , vitamins, recombinant proteins, single-cell proteins , co-enzymes and cytochromes .
The key intermediate in methylotrophic metabolism is formaldehyde, which can be diverted to either assimilatory or dissimilatory pathways. [ 2 ] Methylotrophs produce formaldehyde through oxidation of methanol and/or methane. Methane oxidation requires the enzyme methane monooxygenase ( MMO ). [ 3 ] [ 4 ] Methylotrophs with this enzyme are given the name methanotrophs . The oxidation of methane (or methanol) can be assimilatory or dissimilatory in nature (see figure). If dissimilatory, the formaldehyde intermediate is oxidized completely into CO 2 {\displaystyle {\ce {CO2}}} to produce reductant and energy. [ 5 ] [ 6 ] If assimilatory, the formaldehyde intermediate is used to synthesize a 3-Carbon ( C 3 {\displaystyle {\ce {C3}}} ) compound for the production of biomass. [ 2 ] [ 7 ] Many methylotrophs use multi-carbon compounds for anabolism, thus limiting their use of formaldehyde to dissimilatory processes, however methanotrophs are generally limited to only C 1 {\textstyle {\ce {C1}}} metabolism. [ 2 ] [ 5 ]
Methylotrophs use the electron transport chain to conserve energy produced from the oxidation of C 1 {\displaystyle {\ce {C1}}} compounds. An additional activation step is required in methanotrophic metabolism to allow degradation of chemically-stable methane. This oxidation to methanol is catalyzed by MMO, which incorporates one oxygen atom from O 2 {\displaystyle {\ce {O2}}} into methane and reduces the other oxygen atom to water, requiring two equivalents of reducing power. [ 4 ] [ 5 ] Methanol is then oxidized to formaldehyde through the action of methanol dehydrogenase ( MDH ) in bacteria, [ 12 ] or a non-specific alcohol oxidase in yeast. [ 13 ] Electrons from methanol oxidation are passed to a membrane-associated quinone of the electron transport chain to produce ATP {\displaystyle {\ce {ATP}}} . [ 14 ]
In dissimilatory processes, formaldehyde is completely oxidized to CO 2 {\displaystyle {\ce {CO2}}} and excreted. Formaldehyde is oxidized to formate via the action of Formaldehyde dehydrogenase ( FALDH ), which provides electrons directly to a membrane associated quinone of the electron transport chain, usually cytochrome b or c. [ 2 ] [ 5 ] In the case of NAD + {\displaystyle {\ce {NAD+}}} associated dehydrogenases, NADH {\displaystyle {\ce {NADH}}} is produced. [ 7 ]
Finally, formate is oxidized to CO 2 {\displaystyle {\ce {CO2}}} by cytoplasmic or membrane-bound Formate dehydrogenase ( FDH ), producing NADH {\displaystyle {\ce {NADH}}} [ 15 ] and CO 2 {\displaystyle {\ce {CO2}}} .
The main metabolic challenge for methylotrophs is the assimilation of single carbon units into biomass. Through de novo synthesis, methylotrophs must form carbon-carbon bonds between 1-Carbon ( C 1 {\displaystyle {\ce {C1}}} ) molecules. This is an energy intensive process, which facultative methylotrophs avoid by using a range of larger organic compounds. [ 16 ] However, obligate methylotrophs must assimilate C 1 {\displaystyle {\ce {C1}}} molecules. [ 2 ] [ 5 ] There are four distinct assimilation pathways with the common theme of generating one C 3 {\displaystyle {\ce {C3}}} molecule. [ 2 ] Bacteria use three of these pathways [ 7 ] [ 11 ] while Fungi use one. [ 17 ] All four pathways incorporate 3 C 1 {\displaystyle {\ce {C1}}} molecules into multi-carbon intermediates, then cleave one intermediate into a new C 3 {\displaystyle {\ce {C3}}} molecule. The remaining intermediates are rearranged to regenerate the original multi-carbon intermediates.
Each species of methylotrophic bacteria has a single dominant assimilation pathway. [ 5 ] The three characterized pathways for carbon assimilation are the ribulose monophosphate (RuMP) and serine pathways of formaldehyde assimilation as well as the ribulose bisphosphate (RuBP) pathway of CO 2 assimilation. [ 2 ] [ 7 ] [ 11 ] [ 18 ]
Unlike the other assimilatory pathways, bacteria using the RuBP pathway derive all of their organic carbon from CO 2 {\displaystyle {\ce {CO2}}} assimilation. [ 5 ] [ 19 ] This pathway was first elucidated in photosynthetic autotrophs and is better known as the Calvin Cycle. [ 19 ] [ 20 ] Shortly thereafter, methylotrophic bacteria who could grow on reduced C 1 {\displaystyle {\ce {C1}}} compounds were found using this pathway. [ 21 ]
First, 3 molecules of ribulose 5-phosphate are phosphorylated to ribulose 1,5-bisphosphate ( RuBP ). The enzyme ribulose bisphosphate carboxylase ( RuBisCO ) carboxylates these RuBP molecules which produces 6 molecules of 3-phosphoglycerate ( PGA ). The enzyme phosphoglycerate kinase phosphorylates PGA into 1,3-diphosphoglycerate (DPGA). Reduction of 6 DPGA by the enzyme glyceraldehyde phosphate dehydrogenase generates 6 molecules of the C 3 {\displaystyle {\ce {C3}}} compound glyceraldehyde-3-phosphate ( GAP ). One GAP molecule is diverted towards biomass while the other 5 molecules regenerate the 3 molecules of ribulose 5-phosphate. [ 7 ] [ 20 ]
A new pathway was suspected when RuBisCO was not found in the methanotroph Methylmonas methanica . [ 22 ] Through radio-labelling experiments, it was shown that M. methanica used the ribulose monophosphate (RuMP) pathway. This has led researchers to propose that the RuMP cycle may have preceded the RuBP cycle. [ 5 ]
Like the RuBP cycle, this cycle begins with 3 molecules of ribulose-5-phosphate. However, instead of phosphorylating ribulose-5-phosphate, 3 molecules of formaldehyde form a C-C bond through an aldol condensation, producing 3 C 6 {\displaystyle {\ce {C6}}} molecules of 3-hexulose 6-phosphate (hexulose phosphate). One of these molecules of hexulose phosphate is converted into GAP and either pyruvate or dihydroxyacetone phosphate ( DHAP ). The pyruvate or DHAP is used towards biomass while the other 2 hexulose phosphate molecules and the molecule of GAP are used to regenerate the 3 molecules of ribulose-5-phosphate. [ 6 ] [ 22 ]
Unlike the other assimilatory pathways, the serine cycle uses carboxylic acids and amino acids as intermediates instead of carbohydrates. [ 5 ] [ 23 ] First, 2 molecules of formaldehyde are added to 2 molecules of the amino acid glycine . This produces two molecules of the amino acid serine , the key intermediate of this pathway. These serine molecules eventually produce 2 molecules of 2-phosphoglycerate , with one C 3 {\displaystyle {\ce {C3}}} molecule going towards biomass and the other being used to regenerate glycine. Notably, the regeneration of glycine requires a molecule of CO 2 {\displaystyle {\ce {CO2}}} as well, therefore the Serine pathway also differs from the other 3 pathways by its requirement of both formaldehyde and CO 2 {\displaystyle {\ce {CO2}}} . [ 22 ] [ 23 ]
Methylotrophic yeast metabolism differs from bacteria primarily on the basis of the enzymes used and the carbon assimilation pathway. Unlike bacteria which use bacterial MDH, methylotrophic yeasts oxidize methanol in their peroxisomes with a non-specific alcohol oxidase. This produces formaldehyde as well as hydrogen peroxide. [ 24 ] [ 25 ] Compartmentalization of this reaction in peroxisomes likely sequesters the hydrogen peroxide produced. Catalase is produced in the peroxisomes to deal with this harmful by-product. [ 17 ] [ 24 ]
The dihydroxyacetone (DHA) pathway, also known as the xylulose monophosphate (XuMP) pathway, is found exclusively in yeast. [ 24 ] [ 26 ] This pathway assimilates three molecules of formaldehyde into 1 molecule of DHAP using 3 molecules of xylulose 5-phosphate as the key intermediate.
DHA synthase acts as a transferase (transketolase) to transfer part of xylulose 5-phosphate to DHA. Then these 3 molecules of DHA are phosphorylated to DHAP by triokinase . Like the other cycles, 3 C 3 {\displaystyle {\ce {C3}}} molecules are produced with 1 molecule being directed for use as cell material. The other 2 molecules are used to regenerate xylulose 5-phosphate. [ 27 ]
As key players in the carbon cycle , methylotrophs work to reduce global warming primarily through the uptake of methane and other greenhouse gases. In aqueous environments, methanogenic archaea produce 40-50% of the world's methane. Symbiosis between methanogens and methanotrophic bacteria greatly decreases the amount of methane released into the atmosphere. [ 28 ]
This symbiosis is also important in the marine environment. Marine bacteria are very important to food webs and biogeochemical cycles , particularly in coastal surface waters but also in other key ecosystems such as hydrothermal vents . There is evidence of widespread and diverse groups of methylotrophs in the ocean that have potential to significantly impact marine and estuarine ecosystems. [ 29 ] One-carbon compounds used as a carbon and energy source by methylotrophs are found throughout the ocean. These compounds include methane , methanol , methylated amines , methyl halides, and methylated sulfur compounds, such as dimethylsulfide (DMS) and dimethylsulfoxide ( DMSO ). [ 30 ] Some of these compounds are produced by phytoplankton and some come from the atmosphere. Studies incorporating a wider range of one-carbon substrates have found increasing diversity of methylotrophs, suggesting that the diversity of this bacterial group has not yet fully been explored. [ 30 ]
Because these compounds are volatile and impact the climate and atmosphere, research on the interaction of these bacteria with these one-carbon compounds can also help understanding of air-sea fluxes of these compounds, which impact climate predictions. [ 31 ] [ 29 ] For example, it is uncertain whether the ocean acts as a net source or sink of atmospheric methanol, but a diverse set of methylotrophs use methanol as their main energy source. In some regions, methylotrophs have been found to be a net sink of methanol, [ 32 ] while in others a product of methylotroph activity, methylamine , has been found to be emitted from the ocean and form aerosols. [ 29 ] The net direction of these fluxes depends on the utilization by methylotrophs.
Studies have found that methylotrophic capacity varies with the productivity of a system, so the impacts of methylotrophy are likely seasonal. Because some of the one-carbon compounds used by methylotrophs, such as methanol and TMAO , are produced by phytoplankton, their availability will vary temporally and seasonally depending on phytoplankton blooms , weather events, and other ecosystem inputs. [ 33 ] This means that methylotrophic metabolism is expected to follow similar dynamics, which will then impact biogeochemical cycles and carbon fluxes. [ 29 ]
Impacts of methylotrophs were also found in deep-sea hydrothermal vents . Methylotrophs, along with sulfur oxidizers and iron oxidizers, expressed key proteins associated with carbon fixation . [ 34 ] These types of studies will contribute to further understanding of deep sea carbon cycling and the connectivity between deep ocean and surface carbon cycling. The expansion of omics technologies has accelerated research on the diversity of methylotrophs, their abundance and activity in a variety of environmental niches , and their interspecies interactions. [ 35 ] Further research must be done on these bacteria and the overall effect of bacterial drawdown and transformation of one-carbon compounds in the ocean. Current evidence points to a potentially substantial role for methylotrophs in the ocean in the cycling of carbon but also potentially in the global nitrogen, sulfur and phosphorus cycles as well as the air-sea flux of carbon compounds, which could have global climate impacts. [ 31 ]
The use of methylotrophs in the agricultural sector is another way in which they can potentially impact the environment. Traditional chemical fertilizers supply nutrients not readily available from soil but can have some negative environmental impacts and are costly to produce. [ 36 ] Methylotrophs have high potential as alternative biofertilizers and bioinoculants due to their ability to form mutualistic relationships with several plant species. [ 37 ] Methylotrophs provide plants with nutrients such as soluble phosphorus and fixed nitrogen and also play a role in the uptake of said nutrients. [ 36 ] [ 37 ] Additionally, they can help plants respond to environmental stressors through the production of phytohormones . [ 36 ] Methylotrophic growth also inhibits the growth of harmful plant pathogens and induces systemic resistance. [ 37 ] Methylotrophic biofertilizers used either alone or together with chemical fertilizers have been shown to increase both crop yield and quality without loss of nutrients. [ 36 ] | https://en.wikipedia.org/wiki/Methylotroph |
Methyltransferases are a large group of enzymes that all methylate their substrates but can be split into several subclasses based on their structural features. The most common class of methyltransferases is class I, all of which contain a Rossmann fold for binding S -Adenosyl methionine (SAM). Class II methyltransferases contain a SET domain, which are exemplified by SET domain histone methyltransferases , and class III methyltransferases, which are membrane associated. [ 1 ] Methyltransferases can also be grouped as different types utilizing different substrates in methyl transfer reactions. These types include protein methyltransferases, DNA/RNA methyltransferases, natural product methyltransferases, and non-SAM dependent methyltransferases. SAM is the classical methyl donor for methyltransferases, however, examples of other methyl donors are seen in nature. The general mechanism for methyl transfer is a S N 2 -like nucleophilic attack where the methionine sulfur serves as the leaving group and the methyl group attached to it acts as the electrophile that transfers the methyl group to the enzyme substrate. SAM is converted to S -Adenosyl homocysteine (SAH) during this process. The breaking of the SAM-methyl bond and the formation of the substrate-methyl bond happen nearly simultaneously. These enzymatic reactions are found in many pathways and are implicated in genetic diseases, cancer, and metabolic diseases. Another type of methyl transfer is the radical S-Adenosyl methionine (SAM) which is the methylation of unactivated carbon atoms in primary metabolites, proteins, lipids, and RNA.
Methylation, as well as other epigenetic modifications, affects transcription , gene stability, and parental imprinting . [ 2 ] It directly impacts chromatin structure and can modulate gene transcription, or even completely silence or activate genes, without mutation to the gene itself. Though the mechanisms of this genetic control are complex, hypo- and hypermethylation of DNA is implicated in many diseases.
Methylation of proteins has a regulatory role in protein–protein interactions , protein–DNA interactions , and protein activation.
Examples: RCC1 , an important mitotic protein, is methylated so that it can interact with centromeres of chromosomes. This is an example of regulation of protein-protein interaction, as methylation regulates the attachment of RCC1 to histone proteins H2A and H2B . The RCC1-chromatin interaction is also an example of a protein-DNA interaction, as another domain of RCC1 interacts directly with DNA when this protein is methylated. When RCC1 is not methylated, dividing cells have multiple spindle poles and usually cannot survive.
p53 methylated on lysine to regulate its activation and interaction with other proteins in the DNA damage response. This is an example of regulation of protein-protein interactions and protein activation. p53 is a known tumor suppressor that activates DNA repair pathways, initiates apoptosis , and pauses the cell cycle . Overall, it responds to mutations in DNA, signaling to the cell to fix them or to initiate cell death so that these mutations cannot contribute to cancer.
NF-κB (a protein involved in inflammation) is a known methylation target of the methyltransferase SETD6 , which turns off NF-κB signaling by inhibiting of one of its subunits, RelA . This reduces the transcriptional activation and inflammatory response , making methylation of NF-κB a regulatory process by which cell signaling through this pathway is reduced. [ 3 ]
Natural product methyltransferases provide a variety of inputs into metabolic pathways, including the availability of cofactors, signalling molecules, and metabolites. This regulates various cellular pathways by controlling protein activity.
Histone methyltransferases are critical for genetic regulation at the epigenetic level. They modify mainly lysine on the ε-nitrogen and the arginine guanidinium group on histone tails. Lysine methyltransferases and Arginine methyltransferases are unique classes of enzymes, but both bind SAM as a methyl donor for their histone substrates. Lysine amino acids can be modified with one, two, or three methyl groups, while Arginine amino acids can be modified with one or two methyl groups. This increases the strength of the positive charge and residue hydrophobicity , allowing other proteins to recognize methyl marks. The effect of this modification depends on the location of the modification on the histone tail and the other histone modifications around it. The location of the modifications can be partially determined by DNA sequence, as well as small non-coding RNAs and the methylation of the DNA itself. Most commonly, it is histone H3 or H4 that is methylated in vertebrates. Either increased or decreased transcription of genes around the modification can occur. Increased transcription is a result of decreased chromatin condensation, while decreased transcription results from increased chromatin condensation. [ 4 ] Methyl marks on the histones contribute to these changes by serving as sites for recruitment of other proteins that can further modify chromatin. [ 5 ]
N-alpha methyltransferases transfer a methyl group from SAM to the N-terminal nitrogen on protein targets. The N-terminal methionine is first cleaved by another enzyme and the X- Proline -Lysine consensus sequence is recognized by the methyltransferase. For all known substrates, the X amino acid is Alanine , Serine , or Proline. This reaction yields a methylated protein and SAH. Known targets of these methyltransferases in humans include RCC-1 (a regulator of nuclear transport proteins) and Retinoblastoma protein (a tumor suppressor protein that inhibits excessive cell division). RCC-1 methylation is especially important in mitosis as it coordinates the localization of some nuclear proteins in the absence of the nuclear envelope . When RCC-1 is not methylated, cell division is abnormal following the formation of extra spindle poles . [ 6 ] The function of Retinoblastoma protein N-terminal methylation is not known.
DNA methylation, a key component of genetic regulation, occurs primarily at the 5-carbon of the base cytosine , forming 5’methylcytosine (see left). [ 7 ] Methylation is an epigenetic modification catalyzed by DNA methyltransferase enzymes , including DNMT1, DNMT2 (renamed TRDMT1 to reflect its function methylating tRNA, not DNA), and DNMT3. These enzymes use S-adenosylmethionine as a methyl donor and contain several highly conserved structural features between the three forms; these include the S-adenosylmethionine binding site, a vicinal proline-cysteine pair which forms a thiolate anion important for the reaction mechanism, and the cytosine substrate binding pocket. Many features of DNA methyltransferases are highly conserved throughout many classes of life, from bacteria to mammals. In addition to controlling the expression of certain genes , there are a variety of protein complexes, many with implications for human health, which only bind to methylated DNA recognition sites . Many of the early DNA methyltransferases have been thought to be derived from RNA methyltransferases that were supposed to be active in the RNA world to protect many species of primitive RNA. [ 8 ] RNA methylation has been observed in different types of RNA species viz. mRNA , rRNA , tRNA , snoRNA , snRNA , miRNA , tmRNA as well as viral RNA species. Specific RNA methyltransferases are employed by cells to mark these on the RNA species according to the need and environment prevailing around the cells, which form a part of field called molecular epigenetics . 2'-O-methylation , m6A methylation, m1G methylation as well as m5C are most commonly methylation marks observed in different types of RNA.
6A is an enzyme that catalyzes chemical reaction as following: [ 9 ]
S-adenosyl-L-methionine + DNA adenine S-adenosyl-L-homocysteine + DNA 6-methylaminopurine
m6A was primarily found in prokaryotes until 2015 when it was also identified in some eukaryotes. m6A methyltransferases methylate the amino group in DNA at C-6 position specifically to prevent the host system to digest own genome through restriction enzymes. [ 10 ]
m5C plays a role to regulate gene transcription. m5C transferases are the enzymes that produce C5-methylcytosine in DNA at C-5 position of cytosine and are found in most plants and some eukaryotes. [ 11 ]
Natural product methyltransferases (NPMTs) are a diverse group of enzymes that add methyl groups to naturally-produced small molecules. Like many methyltransferases, SAM is utilized as a methyl donor and SAH is produced. Methyl groups are added to S, N, O, or C atoms, and are classified by which of these atoms are modified, with O-methyltransferases representing the largest class. The methylated products of these reactions serve a variety of functions, including co-factors, pigments, signalling compounds, and metabolites. NPMTs can serve a regulatory role by modifying the reactivity and availability of these compounds. These enzymes are not highly conserved across different species, as they serve a more specific function in providing small molecules for specialized pathways in species or smaller groups of species. Reflective of this diversity is the variety of catalytic strategies, including general acid-base catalysis , metal-based catalysis Archived 2014-02-27 at the Wayback Machine , and proximity and desolvation effects not requiring catalytic amino acids. NPMTs are the most functionally diverse class of methyltransferases. [ 12 ]
Important examples of this enzyme class in humans include phenylethanolamine N-methyltransferase (PNMT), which converts norepinephrine to epinephrine , [ 14 ] and histamine N-methyltransferase (HNMT), which methylates histamine in the process of histamine metabolism. [ 15 ] Catechol- O -methyltransferase (COMT) degrades a class of molecules known as catecholamines that includes dopamine , epinephrine, and norepenepherine. [ 16 ]
Methanol , methyl tetrahydrofolate , mono- , di- , and trimethylamine , methanethiol , methyltetrahydromethanopterin , and chloromethane are all methyl donors found in biology as methyl group donors, typically in enzymatic reactions using the cofactor vitamin B12 . [ 17 ] These substrates contribute to methyl transfer pathways including methionine biosynthesis , methanogenesis , and acetogenesis .
Based on different protein structures and mechanisms of catalysis, there are 3 different types of radical SAM (RS) methylases: Class A, B, and C. Class A RS methylases are the best characterized of the 4 enzymes and are related to both RlmN and Cfr. RlmN is ubiquitous in bacteria which enhances translational fidelity and RlmN catalyzes methylation of C2 of adenosine 2503 (A2503) in 23 S rRNA and C2 of adenosine (A37). Cfr, on the other hand, catalyzes methylation of C8 of A2503 as well and it also catalyzes C2 methylation. [ 18 ] Class B is currently the largest class of radical SAM methylases which can methylate both sp 2-hybridized and sp 3-hybridized carbon atoms in different sets of substrates unlike Class A which only catalyzes sp 2-hybridized carbon atoms. The main difference that distinguishes Class B from others is the additional N-terminal cobalamin-binding domain that binds to the RS domain. [ 19 ] Class C methylase has homologous sequence with the RS enzyme, coproporphyrinogen III oxidase (HemN), which also catalyzes the methylation of sp 2-hybridized carbon centers yet it lacks the 2 cysteines required for methylation in mechanism of Class A. [ 18 ]
As with any biological process which regulates gene expression and/or function, anomalous DNA methylation is associated with genetic disorders such as ICF , Rett syndrome , and Fragile X syndrome . [ 2 ] Cancer cells typically exhibit less DNA methylation activity in general, though often hypermethylation at sites which are unmethylated in normal cells; this overmethylation often functions as a way to inactivate tumor-suppressor genes . Inhibition of overall DNA methyltransferase activity has been proposed as a treatment option, but DNMT inhibitors, analogs of their cytosine substrates, have been found to be highly toxic due to their similarity to cytosine (see right); this similarity to the nucleotide causes the inhibitor to be incorporated into DNA translation , causing non-functioning DNA to be synthesized.
A methylase which alters the ribosomal RNA binding site of the antibiotic linezolid causes cross-resistance to other antibiotics that act on the ribosomal RNA. Plasmid vectors capable of transmitting this gene are a cause of potentially dangerous cross resistance. [ 20 ]
Examples of methyltransferase enzymes relevant to disease:
Recent work has revealed the methyltransferases involved in methylation of naturally occurring anticancer agents to use S-Adenosyl methionine (SAM) analogs that carry alternative alkyl groups as a replacement for methyl. The development of the facile chemoenzymatic platform to generate and utilize differentially alkylated SAM analogs in the context of drug discovery and drug development is known as alkylrandomization . [ 21 ]
In human cells, it was found that m5C was associated with abnormal tumor cells in cancer. [ 22 ] The role and potential application of m5C includes to balance the impaired DNA in cancer both hypermethylation and hypomethylation. An epigenetic repair of DNA can be applied by changing the m5C amount in both types of cancer cells (hypermethylation/ hypomethylation) and as well as the environment of the cancers to reach an equivalent point to inhibit tumor cells. [ 23 ]
Examples include: | https://en.wikipedia.org/wiki/Methyltransferase |
In offshore and coastal engineering , metocean refers to the syllabic abbreviation of meteorology and (physical) oceanography .
In various stages of an offshore or coastal engineering project a metocean study will be undertaken. This, in order to estimate the environmental conditions of direct influence on the choices to be made during the project phase at hand, and to arrive at an effective and efficient solution for the problems/goals stated. In later phases of a project, more detailed and thorough metocean studies may be needed, depending on whether there is an expected additional gain with respect to the successful and efficient completion of the project.
Metocean conditions refer to the combined wind , wave and climate (etc.) conditions as found on a certain location. They are most often presented as statistics, including seasonal variations , scatter tables , wind roses and probability of exceedance . The metocean conditions may include, depending on the project and its location, statistics on:
The metocean conditions are preferably based on metocean data , which can come from measuring instruments deployed in or near the project area, global (re-analysis) models and remote sensing (often by satellites). For estimating probabilities of exceedance – for relevant physical quantities – data of extreme events during more than one year is needed.
By use of validated numerical models , the availability of metocean data can be extended. For instance, consider the case of a coastal location where no wave measurements are available. If there is long-term wave data available in a nearby offshore location (e.g. from satellites), a wind wave model can be employed to transform the offshore wave statistics to the nearshore location (provided the bathymetry is known).
Often, long-term local measurements of wave conditions due to extreme events (e.g. hurricanes) are missing. By using estimates for the wind fields during past extreme events, the corresponding wave conditions can be computed through wave hindcasts . [ 2 ] | https://en.wikipedia.org/wiki/Metocean |
The Metonic cycle or enneadecaeteris (from Ancient Greek : ἐννεακαιδεκαετηρίς , from ἐννεακαίδεκα, "nineteen") is a period of almost exactly 19 years after which the lunar phases recur at the same time of the year. The recurrence is not perfect, and by precise observation the Metonic cycle defined as 235 synodic months is just 2 hours, 4 minutes and 58 seconds longer than 19 tropical years . Meton of Athens , in the 5th century BC, judged the cycle to be a whole number of days, 6,940. [ 3 ] Using these whole numbers facilitates the construction of a lunisolar calendar .
A tropical year (about 365.24 days) is longer than 12 lunar months (about 354.36 days) and shorter than 13 of them (about 383.90 days). In a Metonic calendar (a type of lunisolar calendar ), there are twelve years of 12 lunar months and seven years of 13 lunar months.
In the Babylonian and Hebrew lunisolar calendars , the years 3, 6, 8, 11, 14, 17, and 19 are the long (13-month) years of the Metonic cycle. This cycle forms the basis of the Greek and Hebrew calendars. A 19-year cycle is used for the computation of the date of Easter each year.
The Babylonians applied the 19-year cycle from the late sixth century BC. [ 4 ]
According to Livy , the second king of Rome, Numa Pompilius (reigned 715–673 BC), inserted intercalary months in such a way that "in the twentieth year the days should fall in with the same position of the sun from which they had started". [ 5 ] As "the twentieth year" takes place nineteen years after "the first year", this seems to indicate that the Metonic cycle was applied to Numa's calendar.
Diodorus Siculus reports that Apollo is said to have visited the Hyperboreans once every 19 years. [ 6 ]
The Metonic cycle was implemented in the 2nd century BC Antikythera mechanism , which offers unexpected evidence for the popularity of the calendar based on it. [ 7 ]
The (19-year) Metonic cycle is a lunisolar cycle, as is the (76-year) Callippic cycle . [ 8 ] An important example of an application of the Metonic cycle in the Julian calendar is the 19-year lunar cycle insofar as provided with a Metonic structure. [ 9 ] Meton introduced the 19 year cycle to the Attic calendar in 432 BC. In the following century, Callippus developed the Callippic cycle of four 19-year periods for a 76-year cycle with a mean year of exactly 365.25 days.
Around AD 260 the Alexandrian computist Anatolius , who became bishop of Laodicea in AD 268, was the first to devise a method for determining the date of Easter Sunday. [ 10 ] However, it was some later, somewhat different, version of the Metonic 19-year lunar cycle which, as the basic structure of Dionysius Exiguus ' and also of Bede 's Easter table, would ultimately prevail throughout Christendom , [ 11 ] at least until in the year 1582, when the Gregorian calendar was introduced.
The Coligny calendar is a Celtic lunisolar calendar using the Metonic cycle. The bronze plaque on which it was found dates from c. AD 200, but the internal evidence points to the calendar itself being several centuries older, created in the Iron Age or late Bronze Age. [ 12 ]
The Metonic cycle is thought to be numerically encoded on the Berlin Gold Hat from central Europe, dating from c. 1000-800 BC. [ a ] [ b ] [ 13 ] [ 14 ]
The Runic calendar is a perpetual calendar based on the 19-year-long Metonic cycle. It is also known as a Rune staff or Runic Almanac. This calendar does not rely on knowledge of the duration of the tropical year or of the occurrence of leap years. It is set at the beginning of each year by observing the first full moon after the winter solstice. The oldest one known, and the only one from the Middle Ages, is the Nyköping staff , which is believed to date from the 13th century.
The Bahá'í calendar , established during the middle of the 19th century, is also based on cycles of 19 solar years.
A Small Maḥzor ( Hebrew מחזור, pronounced [maχˈzor] , meaning "cycle") is a 19-year cycle in the lunisolar calendar system used by the Jewish people . It is similar to, but slightly different in usage from, the Greek Metonic cycle (being based on a month of 29 + 13753 ⁄ 25920 days, giving a cycle of 6939 + 3575 ⁄ 5184 ≈ 6939.69 days [ c ] ), and likely derived from or alongside the much earlier Babylonian calendar. [ 15 ]
It is possible that the Polynesian kilo-hoku (astronomers) discovered the Metonic cycle in the same way Meton had, by trying to make the month fit the year. [ 16 ]
The Metonic cycle is the most accurate cycle of time (in a timespan of less than 100 years) for synchronizing the tropical year and the lunar month ( synodic month ), when the method of synchronizing is the intercalation of a thirteenth lunar month in a calendar year from time to time. [ 17 ] The traditional lunar year of 12 synodic months is about 354 days, approximately eleven days short of the solar year. Thus, every 2 to 3 years there is a discrepancy of 22 to 33 days, or a full synodic month. For example, if the winter solstice and the new moon coincide, it takes 19 tropical years for the coincidence to recur. The mathematical logic is this:
That duration is almost the same as 235 synodic months:
Thus the algorithm is correct to 0.087 days (2 hours, 5 minutes and 16 seconds).
For a lunisolar calendar to 'catch up' to this discrepancy and thus maintain seasonal consistency, seven intercalary months are added (one at a time), at intervals of every 2–3 years during the course of 19 solar years. Thus twelve of those years have 12 lunar months and seven have 13 months. Of these months, 125 were full (30 days) and 110 were deficient (29 days), to give a total of 6940 days. [ 20 ] | https://en.wikipedia.org/wiki/Metonic_cycle |
Metreleptin , sold under the brand name Myalept among others, is a synthetic analog of the hormone leptin used to treat various forms of dyslipidemia . It has been approved in Japan for metabolic disorders including lipodystrophy and in the United States as replacement therapy to treat the complications of leptin deficiency, in addition to diet, in patients with congenital generalized or acquired generalized lipodystrophy. [ 8 ]
The most common side effects include hypoglycaemia (low blood glucose) and weight loss. [ 7 ]
It was approved for medical use in Canada in January 2024. [ 1 ]
In the European Union, metreleptin is indicated in addition to diet to treat lipodystrophy, where people have a loss of fatty tissue under the skin and a build-up of fat elsewhere in the body such as in the liver and muscles. It is used in adults and children above the age of two years with generalised lipodystrophy ( Berardinelli-Seip syndrome and Lawrence syndrome ); and in adults and children above the age of twelve years with partial lipodystrophy (including Barraquer-Simons syndrome ), when standard treatments have failed. [ 7 ]
In the United States, it is indicated as an adjunct to diet as replacement therapy to treat the complications of leptin deficiency in people with congenital or acquired generalized lipodystrophy. [ 6 ]
Metreleptin is being investigated for the treatment of diabetes and/or hypertriglyceridemia , in patients with rare forms of lipodystrophy, syndromes characterized by abnormalities in adipose tissue distribution, and severe metabolic abnormalities. [ 9 ] The FDA approved Metreleptin injection for treating complications of leptin deficiency in February 2014. [ medical citation needed ]
In a three-year study of metreleptin in patients with lipodystrophy organized by the National Institute of Diabetes and Digestive and Kidney Diseases at the National Institutes of Health, metreleptin treatment was associated with a significant decrease in blood glucose (A1c decreased from 9.4% at baseline to 7.0% at study end) and triglyceride concentration (from 500 mg/dl at baseline to 200 mg/dl at study end). [ 10 ] Metreleptin is effective in most patients with generalized lipodystrophy where circulating leptin levels are extremely low. Analogous to insulin replacement for patients with type 1 Diabetes , metreleptin restores the function of a deficient hormone. However, in patients with partial lipodystrophy where there is only a relative leptin deficiency, the response to metreleptin is not universal. [ 11 ] This may or may not be due to anti-leptin antibodies.
Metreleptin is undergoing research for its potential benefit in the treatment of anorexia nervosa. [ 12 ] It is hypothesized that the gradual loss of body fat mass, and more specifically the ensuing low leptin levels, escalate the preexisting drive for thinness into an obsessive-compulsive-like and addictive-like state. It was shown that short-term metreleptin treatment of patients with anorexia nervosa had rapid on-set of beneficial cognitive, emotional, and behavioral effects. [ 13 ] Among other things, depression, drive for activity, repetitive thoughts of food, inner restlessness, and weight phobia decreased rapidly. Whether metreleptin (or another leptin analogue) is a suitable treatment for anorexia nervosa remains to be seen. Potential side effects are weight loss and the development of anti-metreleptin antibodies.
In a clinical study, metreleptin treatment improved non-alcoholic steatohepatitis (fatty liver disease) both in patients with partial lipodystrophy and in those with relative leptin deficiency. Both steatosis and hepatic injury scores decreased. [ 14 ] Metreleptin reduces body weight in overweight people with low leptin levels. [ 15 ]
Although it is not very effective as a weight loss drug, leptin levels are lowered in people who have lost weight and it is hypothesized that supplemental leptin could help them with weight loss maintenance. However, there is no regulatory pathway for drug approval for this indication. [ 16 ] | https://en.wikipedia.org/wiki/Metreleptin |
In mathematics , the metric derivative is a notion of derivative appropriate to parametrized paths in metric spaces . It generalizes the notion of "speed" or "absolute velocity" to spaces which have a notion of distance (i.e. metric spaces) but not direction (such as vector spaces ).
Let ( M , d ) {\displaystyle (M,d)} be a metric space. Let E ⊆ R {\displaystyle E\subseteq \mathbb {R} } have a limit point at t ∈ R {\displaystyle t\in \mathbb {R} } . Let γ : E → M {\displaystyle \gamma :E\to M} be a path. Then the metric derivative of γ {\displaystyle \gamma } at t {\displaystyle t} , denoted | γ ′ | ( t ) {\displaystyle |\gamma '|(t)} , is defined by
if this limit exists.
Recall that AC p ( I ; X ) is the space of curves γ : I → X such that
for some m in the L p space L p ( I ; R ). For γ ∈ AC p ( I ; X ), the metric derivative of γ exists for Lebesgue - almost all times in I , and the metric derivative is the smallest m ∈ L p ( I ; R ) such that the above inequality holds.
If Euclidean space R n {\displaystyle \mathbb {R} ^{n}} is equipped with its usual Euclidean norm ‖ − ‖ {\displaystyle \|-\|} , and γ ˙ : E → V ∗ {\displaystyle {\dot {\gamma }}:E\to V^{*}} is the usual Fréchet derivative with respect to time, then
where d ( x , y ) := ‖ x − y ‖ {\displaystyle d(x,y):=\|x-y\|} is the Euclidean metric.
This metric geometry -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Metric_derivative |
In mathematical analysis , a metric differential is a generalization of a derivative for a Lipschitz continuous function defined on a Euclidean space and taking values in an arbitrary metric space . With this definition of a derivative, one can generalize Rademacher's theorem to metric space-valued Lipschitz functions.
Rademacher's theorem states that a Lipschitz map f : R n → R m is differentiable almost everywhere in R n ; in other words, for almost every x , f is approximately linear in any sufficiently small range of x . If f is a function from a Euclidean space R n that takes values instead in a metric space X , it doesn't immediately make sense to talk about differentiability since X has no linear structure a priori. Even if you assume that X is a Banach space and ask whether a Fréchet derivative exists almost everywhere, this does not hold. For example, consider the function f : [0,1] → L 1 ([0,1]), mapping the unit interval into the space of integrable functions , defined by f ( x ) = χ [0, x ] , this function is Lipschitz (and in fact, an isometry ) since, if 0 ≤ x ≤ y ≤ 1, then
but one can verify that lim h →0 ( f ( x + h ) − f ( x ))/ h does not converge to an L 1 function for any x in [0,1], so it is not differentiable anywhere.
However, if you look at Rademacher's theorem as a statement about how a Lipschitz function stabilizes as you zoom in on almost every point, then such a theorem exists but is stated in terms of the metric properties of f instead of its linear properties.
A substitute for a derivative of f : R n → X is the metric differential of f at a point z in R n which is a function on R n defined by the limit
whenever the limit exists (here d X denotes the metric on X ).
A theorem due to Bernd Kirchheim [ 1 ] states that a Rademacher theorem in terms of metric differentials holds: for almost every z in R n , MD( f , z ) is a seminorm and
The little-o notation employed here means that, at values very close to z , the function f is approximately an isometry from R n with respect to the seminorm MD( f , z ) into the metric space X . | https://en.wikipedia.org/wiki/Metric_differential |
In the mathematical field of differential geometry , a metric tensor (or simply metric ) is an additional structure on a manifold M (such as a surface ) that allows defining distances and angles, just as the inner product on a Euclidean space allows defining distances and angles there. More precisely, a metric tensor at a point p of M is a bilinear form defined on the tangent space at p (that is, a bilinear function that maps pairs of tangent vectors to real numbers ), and a metric field on M consists of a metric tensor at each point p of M that varies smoothly with p .
A metric tensor g is positive-definite if g ( v , v ) > 0 for every nonzero vector v . A manifold equipped with a positive-definite metric tensor is known as a Riemannian manifold . Such a metric tensor can be thought of as specifying infinitesimal distance on the manifold. On a Riemannian manifold M , the length of a smooth curve between two points p and q can be defined by integration, and the distance between p and q can be defined as the infimum of the lengths of all such curves; this makes M a metric space . Conversely, the metric tensor itself is the derivative of the distance function (taken in a suitable manner). [ citation needed ]
While the notion of a metric tensor was known in some sense to mathematicians such as Gauss from the early 19th century, it was not until the early 20th century that its properties as a tensor were understood by, in particular, Gregorio Ricci-Curbastro and Tullio Levi-Civita , who first codified the notion of a tensor. The metric tensor is an example of a tensor field .
The components of a metric tensor in a coordinate basis take on the form of a symmetric matrix whose entries transform covariantly under changes to the coordinate system. Thus a metric tensor is a covariant symmetric tensor . From the coordinate-independent point of view, a metric tensor field is defined to be a nondegenerate symmetric bilinear form on each tangent space that varies smoothly from point to point.
Carl Friedrich Gauss in his 1827 Disquisitiones generales circa superficies curvas ( General investigations of curved surfaces ) considered a surface parametrically , with the Cartesian coordinates x , y , and z of points on the surface depending on two auxiliary variables u and v . Thus a parametric surface is (in today's terms) a vector-valued function
depending on an ordered pair of real variables ( u , v ) , and defined in an open set D in the uv -plane. One of the chief aims of Gauss's investigations was to deduce those features of the surface which could be described by a function which would remain unchanged if the surface underwent a transformation in space (such as bending the surface without stretching it), or a change in the particular parametric form of the same geometrical surface.
One natural such invariant quantity is the length of a curve drawn along the surface. Another is the angle between a pair of curves drawn along the surface and meeting at a common point. A third such quantity is the area of a piece of the surface. The study of these invariants of a surface led Gauss to introduce the predecessor of the modern notion of the metric tensor.
The metric tensor is [ E F F G ] {\textstyle {\begin{bmatrix}E&F\\F&G\end{bmatrix}}} in the description below; E, F, and G in the matrix can contain any number as long as the matrix is positive definite.
If the variables u and v are taken to depend on a third variable, t , taking values in an interval [ a , b ] , then r → ( u ( t ), v ( t )) will trace out a parametric curve in parametric surface M . The arc length of that curve is given by the integral
where ‖ ⋅ ‖ {\displaystyle \left\|\cdot \right\|} represents the Euclidean norm . Here the chain rule has been applied, and the subscripts denote partial derivatives :
The integrand is the restriction [ 1 ] to the curve of the square root of the ( quadratic ) differential
where
The quantity ds in ( 1 ) is called the line element , while ds 2 is called the first fundamental form of M . Intuitively, it represents the principal part of the square of the displacement undergone by r → ( u , v ) when u is increased by du units, and v is increased by dv units.
Using matrix notation, the first fundamental form becomes
Suppose now that a different parameterization is selected, by allowing u and v to depend on another pair of variables u ′ and v ′ . Then the analog of ( 2 ) for the new variables is
The chain rule relates E ′ , F ′ , and G ′ to E , F , and G via the matrix equation
where the superscript T denotes the matrix transpose . The matrix with the coefficients E , F , and G arranged in this way therefore transforms by the Jacobian matrix of the coordinate change
A matrix which transforms in this way is one kind of what is called a tensor . The matrix
with the transformation law ( 3 ) is known as the metric tensor of the surface.
Ricci-Curbastro & Levi-Civita (1900) first observed the significance of a system of coefficients E , F , and G , that transformed in this way on passing from one system of coordinates to another. The upshot is that the first fundamental form ( 1 ) is invariant under changes in the coordinate system, and that this follows exclusively from the transformation properties of E , F , and G . Indeed, by the chain rule,
so that
Another interpretation of the metric tensor, also considered by Gauss, is that it provides a way in which to compute the length of tangent vectors to the surface, as well as the angle between two tangent vectors. In contemporary terms, the metric tensor allows one to compute the dot product of tangent vectors in a manner independent of the parametric description of the surface. Any tangent vector at a point of the parametric surface M can be written in the form
for suitable real numbers p 1 and p 2 . If two tangent vectors are given:
then using the bilinearity of the dot product,
This is plainly a function of the four variables a 1 , b 1 , a 2 , and b 2 . It is more profitably viewed, however, as a function that takes a pair of arguments a = [ a 1 a 2 ] and b = [ b 1 b 2 ] which are vectors in the uv -plane. That is, put
This is a symmetric function in a and b , meaning that
It is also bilinear , meaning that it is linear in each variable a and b separately. That is,
for any vectors a , a ′ , b , and b ′ in the uv plane, and any real numbers μ and λ .
In particular, the length of a tangent vector a is given by
and the angle θ between two vectors a and b is calculated by
The surface area is another numerical quantity which should depend only on the surface itself, and not on how it is parameterized. If the surface M is parameterized by the function r → ( u , v ) over the domain D in the uv -plane, then the surface area of M is given by the integral
where × denotes the cross product , and the absolute value denotes the length of a vector in Euclidean space. By Lagrange's identity for the cross product, the integral can be written
where det is the determinant .
Let M be a smooth manifold of dimension n ; for instance a surface (in the case n = 2 ) or hypersurface in the Cartesian space R n + 1 {\displaystyle \mathbb {R} ^{n+1}} . At each point p ∈ M there is a vector space T p M , called the tangent space , consisting of all tangent vectors to the manifold at the point p . A metric tensor at p is a function g p ( X p , Y p ) which takes as inputs a pair of tangent vectors X p and Y p at p , and produces as an output a real number ( scalar ), so that the following conditions are satisfied:
A metric tensor field g on M assigns to each point p of M a metric tensor g p in the tangent space at p in a way that varies smoothly with p . More precisely, given any open subset U of manifold M and any (smooth) vector fields X and Y on U , the real function g ( X , Y ) ( p ) = g p ( X p , Y p ) {\displaystyle g(X,Y)(p)=g_{p}(X_{p},Y_{p})} is a smooth function of p .
The components of the metric in any basis of vector fields , or frame , f = ( X 1 , ..., X n ) are given by [ 3 ]
The n 2 functions g ij [ f ] form the entries of an n × n symmetric matrix , G [ f ] . If
are two vectors at p ∈ U , then the value of the metric applied to v and w is determined by the coefficients ( 4 ) by bilinearity:
Denoting the matrix ( g ij [ f ]) by G [ f ] and arranging the components of the vectors v and w into column vectors v [ f ] and w [ f ] ,
where v [ f ] T and w [ f ] T denote the transpose of the vectors v [ f ] and w [ f ] , respectively. Under a change of basis of the form
for some invertible n × n matrix A = ( a ij ) , the matrix of components of the metric changes by A as well. That is,
or, in terms of the entries of this matrix,
For this reason, the system of quantities g ij [ f ] is said to transform covariantly with respect to changes in the frame f .
A system of n real-valued functions ( x 1 , ..., x n ) , giving a local coordinate system on an open set U in M , determines a basis of vector fields on U
The metric g has components relative to this frame given by
Relative to a new system of local coordinates, say
the metric tensor will determine a different matrix of coefficients,
This new system of functions is related to the original g ij ( f ) by means of the chain rule
so that
Or, in terms of the matrices G [ f ] = ( g ij [ f ]) and G [ f ′] = ( g ij [ f ′]) ,
where Dy denotes the Jacobian matrix of the coordinate change.
Associated to any metric tensor is the quadratic form defined in each tangent space by
If q m is positive for all non-zero X m , then the metric is positive-definite at m . If the metric is positive-definite at every m ∈ M , then g is called a Riemannian metric . More generally, if the quadratic forms q m have constant signature independent of m , then the signature of g is this signature, and g is called a pseudo-Riemannian metric . [ 4 ] If M is connected , then the signature of q m does not depend on m . [ 5 ]
By Sylvester's law of inertia , a basis of tangent vectors X i can be chosen locally so that the quadratic form diagonalizes in the following manner
for some p between 1 and n . Any two such expressions of q (at the same point m of M ) will have the same number p of positive signs. The signature of g is the pair of integers ( p , n − p ) , signifying that there are p positive signs and n − p negative signs in any such expression. Equivalently, the metric has signature ( p , n − p ) if the matrix g ij of the metric has p positive and n − p negative eigenvalues .
Certain metric signatures which arise frequently in applications are:
Let f = ( X 1 , ..., X n ) be a basis of vector fields, and as above let G [ f ] be the matrix of coefficients
One can consider the inverse matrix G [ f ] −1 , which is identified with the inverse metric (or conjugate or dual metric ). The inverse metric satisfies a transformation law when the frame f is changed by a matrix A via
The inverse metric transforms contravariantly , or with respect to the inverse of the change of basis matrix A . Whereas the metric itself provides a way to measure the length of (or angle between) vector fields, the inverse metric supplies a means of measuring the length of (or angle between) covector fields; that is, fields of linear functionals .
To see this, suppose that α is a covector field. To wit, for each point p , α determines a function α p defined on tangent vectors at p so that the following linearity condition holds for all tangent vectors X p and Y p , and all real numbers a and b :
As p varies, α is assumed to be a smooth function in the sense that
is a smooth function of p for any smooth vector field X .
Any covector field α has components in the basis of vector fields f . These are determined by
Denote the row vector of these components by
Under a change of f by a matrix A , α [ f ] changes by the rule
That is, the row vector of components α [ f ] transforms as a covariant vector.
For a pair α and β of covector fields, define the inverse metric applied to these two covectors by
The resulting definition, although it involves the choice of basis f , does not actually depend on f in an essential way. Indeed, changing basis to f A gives
So that the right-hand side of equation ( 6 ) is unaffected by changing the basis f to any other basis f A whatsoever. Consequently, the equation may be assigned a meaning independently of the choice of basis. The entries of the matrix G [ f ] are denoted by g ij , where the indices i and j have been raised to indicate the transformation law ( 5 ).
In a basis of vector fields f = ( X 1 , ..., X n ) , any smooth tangent vector field X can be written in the form
for some uniquely determined smooth functions v 1 , ..., v n . Upon changing the basis f by a nonsingular matrix A , the coefficients v i change in such a way that equation ( 7 ) remains true. That is,
Consequently, v [ f A ] = A −1 v [ f ] . In other words, the components of a vector transform contravariantly (that is, inversely or in the opposite way) under a change of basis by the nonsingular matrix A . The contravariance of the components of v [ f ] is notationally designated by placing the indices of v i [ f ] in the upper position.
A frame also allows covectors to be expressed in terms of their components. For the basis of vector fields f = ( X 1 , ..., X n ) define the dual basis to be the linear functionals ( θ 1 [ f ], ..., θ n [ f ]) such that
That is, θ i [ f ]( X j ) = δ j i , the Kronecker delta . Let
Under a change of basis f ↦ f A for a nonsingular matrix A , θ [ f ] transforms via
Any linear functional α on tangent vectors can be expanded in terms of the dual basis θ
where a [ f ] denotes the row vector [ a 1 [ f ] ... a n [ f ] ] . The components a i transform when the basis f is replaced by f A in such a way that equation ( 8 ) continues to hold. That is,
whence, because θ [ f A ] = A −1 θ [ f ] , it follows that a [ f A ] = a [ f ] A . That is, the components a transform covariantly (by the matrix A rather than its inverse). The covariance of the components of a [ f ] is notationally designated by placing the indices of a i [ f ] in the lower position.
Now, the metric tensor gives a means to identify vectors and covectors as follows. Holding X p fixed, the function
of tangent vector Y p defines a linear functional on the tangent space at p . This operation takes a vector X p at a point p and produces a covector g p ( X p , −) . In a basis of vector fields f , if a vector field X has components v [ f ] , then the components of the covector field g ( X , −) in the dual basis are given by the entries of the row vector
Under a change of basis f ↦ f A , the right-hand side of this equation transforms via
so that a [ f A ] = a [ f ] A : a transforms covariantly. The operation of associating to the (contravariant) components of a vector field v [ f ] = [ v 1 [ f ] v 2 [ f ] ... v n [ f ] ] T the (covariant) components of the covector field a [ f ] = [ a 1 [ f ] a 2 [ f ] … a n [ f ] ] , where
is called lowering the index .
To raise the index , one applies the same construction but with the inverse metric instead of the metric. If a [ f ] = [ a 1 [ f ] a 2 [ f ] ... a n [ f ] ] are the components of a covector in the dual basis θ [ f ] , then the column vector
has components which transform contravariantly:
Consequently, the quantity X = f v [ f ] does not depend on the choice of basis f in an essential way, and thus defines a vector field on M . The operation ( 9 ) associating to the (covariant) components of a covector a [ f ] the (contravariant) components of a vector v [ f ] given is called raising the index . In components, ( 9 ) is
Let U be an open set in ℝ n , and let φ be a continuously differentiable function from U into the Euclidean space ℝ m , where m > n . The mapping φ is called an immersion if its differential is injective at every point of U . The image of φ is called an immersed submanifold . More specifically, for m = 3 , which means that the ambient Euclidean space is ℝ 3 , the induced metric tensor is called the first fundamental form .
Suppose that φ is an immersion onto the submanifold M ⊂ R m . The usual Euclidean dot product in ℝ m is a metric which, when restricted to vectors tangent to M , gives a means for taking the dot product of these tangent vectors. This is called the induced metric .
Suppose that v is a tangent vector at a point of U , say
where e i are the standard coordinate vectors in ℝ n . When φ is applied to U , the vector v goes over to the vector tangent to M given by
(This is called the pushforward of v along φ .) Given two such vectors, v and w , the induced metric is defined by
It follows from a straightforward calculation that the matrix of the induced metric in the basis of coordinate vector fields e is given by
where Dφ is the Jacobian matrix:
The notion of a metric can be defined intrinsically using the language of fiber bundles and vector bundles . In these terms, a metric tensor is a function
from the fiber product of the tangent bundle of M with itself to R such that the restriction of g to each fiber is a nondegenerate bilinear mapping
The mapping ( 10 ) is required to be continuous , and often continuously differentiable , smooth , or real analytic , depending on the case of interest, and whether M can support such a structure.
By the universal property of the tensor product , any bilinear mapping ( 10 ) gives rise naturally to a section g ⊗ of the dual of the tensor product bundle of T M with itself
The section g ⊗ is defined on simple elements of T M ⊗ T M by
and is defined on arbitrary elements of T M ⊗ T M by extending linearly to linear combinations of simple elements. The original bilinear form g is symmetric if and only if
where
is the braiding map .
Since M is finite-dimensional, there is a natural isomorphism
so that g ⊗ is regarded also as a section of the bundle T* M ⊗ T* M of the cotangent bundle T* M with itself. Since g is symmetric as a bilinear mapping, it follows that g ⊗ is a symmetric tensor .
More generally, one may speak of a metric in a vector bundle . If E is a vector bundle over a manifold M , then a metric is a mapping
from the fiber product of E to R which is bilinear in each fiber:
Using duality as above, a metric is often identified with a section of the tensor product bundle E * ⊗ E * .
The metric tensor gives a natural isomorphism from the tangent bundle to the cotangent bundle , sometimes called the musical isomorphism . [ 6 ] This isomorphism is obtained by setting, for each tangent vector X p ∈ T p M ,
the linear functional on T p M which sends a tangent vector Y p at p to g p ( X p , Y p ) . That is, in terms of the pairing [−, −] between T p M and its dual space T ∗ p M ,
for all tangent vectors X p and Y p . The mapping S g is a linear transformation from T p M to T ∗ p M . It follows from the definition of non-degeneracy that the kernel of S g is reduced to zero, and so by the rank–nullity theorem , S g is a linear isomorphism . Furthermore, S g is a symmetric linear transformation in the sense that
for all tangent vectors X p and Y p .
Conversely, any linear isomorphism S : T p M → T ∗ p M defines a non-degenerate bilinear form on T p M by means of
This bilinear form is symmetric if and only if S is symmetric. There is thus a natural one-to-one correspondence between symmetric bilinear forms on T p M and symmetric linear isomorphisms of T p M to the dual T ∗ p M .
As p varies over M , S g defines a section of the bundle Hom(T M , T* M ) of vector bundle isomorphisms of the tangent bundle to the cotangent bundle. This section has the same smoothness as g : it is continuous, differentiable, smooth, or real-analytic according as g . The mapping S g , which associates to every vector field on M a covector field on M gives an abstract formulation of "lowering the index" on a vector field. The inverse of S g is a mapping T* M → T M which, analogously, gives an abstract formulation of "raising the index" on a covector field.
The inverse S −1 g defines a linear mapping
which is nonsingular and symmetric in the sense that
for all covectors α , β . Such a nonsingular symmetric mapping gives rise (by the tensor-hom adjunction ) to a map
or by the double dual isomorphism to a section of the tensor product
Suppose that g is a Riemannian metric on M . In a local coordinate system x i , i = 1, 2, …, n , the metric tensor appears as a matrix , denoted here by G , whose entries are the components g ij of the metric tensor relative to the coordinate vector fields.
Let γ ( t ) be a piecewise-differentiable parametric curve in M , for a ≤ t ≤ b . The arclength of the curve is defined by
In connection with this geometrical application, the quadratic differential form
is called the first fundamental form associated to the metric, while ds is the line element . When ds 2 is pulled back to the image of a curve in M , it represents the square of the differential with respect to arclength.
For a pseudo-Riemannian metric, the length formula above is not always defined, because the term under the square root may become negative. We generally only define the length of a curve when the quantity under the square root is always of one sign or the other. In this case, define
While these formulas use coordinate expressions, they are in fact independent of the coordinates chosen; they depend only on the metric, and the curve along which the formula is integrated.
Given a segment of a curve, another frequently defined quantity is the (kinetic) energy of the curve:
This usage comes from physics , specifically, classical mechanics , where the integral E can be seen to directly correspond to the kinetic energy of a point particle moving on the surface of a manifold. Thus, for example, in Jacobi's formulation of Maupertuis' principle , the metric tensor can be seen to correspond to the mass tensor of a moving particle.
In many cases, whenever a calculation calls for the length to be used, a similar calculation using the energy may be done as well. This often leads to simpler formulas by avoiding the need for the square-root. Thus, for example, the geodesic equations may be obtained by applying variational principles to either the length or the energy. In the latter case, the geodesic equations are seen to arise from the principle of least action : they describe the motion of a " free particle " (a particle feeling no forces) that is confined to move on the manifold, but otherwise moves freely, with constant momentum, within the manifold. [ 7 ]
In analogy with the case of surfaces, a metric tensor on an n -dimensional paracompact manifold M gives rise to a natural way to measure the n -dimensional volume of subsets of the manifold. The resulting natural positive Borel measure allows one to develop a theory of integrating functions on the manifold by means of the associated Lebesgue integral .
A measure can be defined, by the Riesz representation theorem , by giving a positive linear functional Λ on the space C 0 ( M ) of compactly supported continuous functions on M . More precisely, if M is a manifold with a (pseudo-)Riemannian metric tensor g , then there is a unique positive Borel measure μ g such that for any coordinate chart ( U , φ ) , Λ f = ∫ U f d μ g = ∫ φ ( U ) f ∘ φ − 1 ( x ) | det g | d x {\displaystyle \Lambda f=\int _{U}f\,d\mu _{g}=\int _{\varphi (U)}f\circ \varphi ^{-1}(x){\sqrt {\left|\det g\right|}}\,dx} for all f supported in U . Here det g is the determinant of the matrix formed by the components of the metric tensor in the coordinate chart. That Λ is well-defined on functions supported in coordinate neighborhoods is justified by Jacobian change of variables . It extends to a unique positive linear functional on C 0 ( M ) by means of a partition of unity .
If M is also oriented , then it is possible to define a natural volume form from the metric tensor. In a positively oriented coordinate system ( x 1 , ..., x n ) the volume form is represented as ω = | det g | d x 1 ∧ ⋯ ∧ d x n {\displaystyle \omega ={\sqrt {\left|\det g\right|}}\,dx^{1}\wedge \cdots \wedge dx^{n}} where the dx i are the coordinate differentials and ∧ denotes the exterior product in the algebra of differential forms . The volume form also gives a way to integrate functions on the manifold, and this geometric integral agrees with the integral obtained by the canonical Borel measure.
The most familiar example is that of elementary Euclidean geometry : the two-dimensional Euclidean metric tensor. In the usual Cartesian ( x , y ) coordinates, we can write
The length of a curve reduces to the formula:
The Euclidean metric in some other common coordinate systems can be written as follows.
Polar coordinates ( r , θ ) :
So
by trigonometric identities .
In general, in a Cartesian coordinate system x i on a Euclidean space , the partial derivatives ∂ / ∂ x i are orthonormal with respect to the Euclidean metric. Thus the metric tensor is the Kronecker delta δ ij in this coordinate system. The metric tensor with respect to arbitrary (possibly curvilinear) coordinates q i is given by
The unit sphere in ℝ 3 comes equipped with a natural metric induced from the ambient Euclidean metric, through the process explained in the induced metric section . In standard spherical coordinates ( θ , φ ) , with θ the colatitude , the angle measured from the z -axis, and φ the angle from the x -axis in the xy -plane, the metric takes the form
This is usually written in the form
In flat Minkowski space ( special relativity ), with coordinates
the metric is, depending on choice of metric signature ,
For a curve with—for example—constant time coordinate, the length formula with this metric reduces to the usual length formula. For a timelike curve, the length formula gives the proper time along the curve.
In this case, the spacetime interval is written as
The Schwarzschild metric describes the spacetime around a spherically symmetric body, such as a planet, or a black hole . With coordinates
we can write the metric as
where G (inside the matrix) is the gravitational constant and M represents the total mass–energy content of the central object. | https://en.wikipedia.org/wiki/Metric_tensor |
Routing metrics are configuration values used by a router to make routing decisions. A metric is typically one of many fields in a routing table . Router metrics help the router choose the best route among multiple feasible routes to a destination. The route will go in the direction of the gateway with the lowest metric.
A router metric is typically based on information such as path length , bandwidth , load , hop count , path cost, delay , maximum transmission unit (MTU), reliability and communications cost.
A metric can include:
In EIGRP , metrics is represented by an integer from 0 to 4,294,967,295 (The size of a 32-bit integer). In Microsoft Windows XP routing it ranges from 1 to 9999.
A metric can be considered as: [ 1 ]
Router metrics are metrics used by a router to make routing decisions. It is typically one of many fields in a routing table.
Router metrics can contain any number of values that help the router determine the best route among multiple routes to a destination. A router metric is typically based on information like path length, bandwidth, load, hop count, path cost, delay, MTU, reliability and communications cost. | https://en.wikipedia.org/wiki/Metrics_(networking) |
In topology and related areas of mathematics , a metrizable space is a topological space that is homeomorphic to a metric space . That is, a topological space ( X , τ ) {\displaystyle (X,\tau )} is said to be metrizable if there is a metric d : X × X → [ 0 , ∞ ) {\displaystyle d:X\times X\to [0,\infty )} such that the topology induced by d {\displaystyle d} is τ . {\displaystyle \tau .} [ 1 ] [ 2 ] Metrization theorems are theorems that give sufficient conditions for a topological space to be metrizable.
Metrizable spaces inherit all topological properties from metric spaces. For example, they are Hausdorff paracompact spaces (and hence normal and Tychonoff ) and first-countable . However, some properties of the metric, such as completeness , cannot be said to be inherited. This is also true of other structures linked to the metric. A metrizable uniform space , for example, may have a different set of contraction maps than a metric space to which it is homeomorphic.
One of the first widely recognized metrization theorems was Urysohn's metrization theorem . This states that every Hausdorff second-countable regular space is metrizable. So, for example, every second-countable manifold is metrizable. (Historical note: The form of the theorem shown here was in fact proved by Tikhonov in 1926. What Urysohn had shown, in a paper published posthumously in 1925, was that every second-countable normal Hausdorff space is metrizable.) The converse does not hold: there exist metric spaces that are not second countable, for example, an uncountable set endowed with the discrete metric. [ 3 ] The Nagata–Smirnov metrization theorem , described below, provides a more specific theorem where the converse does hold.
Several other metrization theorems follow as simple corollaries to Urysohn's theorem. For example, a compact Hausdorff space is metrizable if and only if it is second-countable.
Urysohn's Theorem can be restated as: A topological space is separable and metrizable if and only if it is regular, Hausdorff and second-countable. The Nagata–Smirnov metrization theorem extends this to the non-separable case. It states that a topological space is metrizable if and only if it is regular, Hausdorff and has a σ-locally finite base. A σ-locally finite base is a base which is a union of countably many locally finite collections of open sets. For a closely related theorem see the Bing metrization theorem .
Separable metrizable spaces can also be characterized as those spaces which are homeomorphic to a subspace of the Hilbert cube [ 0 , 1 ] N , {\displaystyle \lbrack 0,1\rbrack ^{\mathbb {N} },} that is, the countably infinite product of the unit interval (with its natural subspace topology from the reals) with itself, endowed with the product topology .
A space is said to be locally metrizable if every point has a metrizable neighbourhood . Smirnov proved that a locally metrizable space is metrizable if and only if it is Hausdorff and paracompact . In particular, a manifold is metrizable if and only if it is paracompact.
The group of unitary operators U ( H ) {\displaystyle \mathbb {U} ({\mathcal {H}})} on a separable Hilbert space H {\displaystyle {\mathcal {H}}} endowed
with the strong operator topology is metrizable (see Proposition II.1 in [ 4 ] ).
Non-normal spaces cannot be metrizable; important examples include
The real line with the lower limit topology is not metrizable. The usual distance function is not a metric on this space because the topology it determines is the usual topology, not the lower limit topology. This space is Hausdorff, paracompact and first countable.
The Line with two origins , also called the bug-eyed line is a non-Hausdorff manifold (and thus cannot be metrizable). Like all manifolds, it is locally homeomorphic to Euclidean space and thus locally metrizable (but not metrizable) and locally Hausdorff (but not Hausdorff ). It is also a T 1 locally regular space but not a semiregular space .
The long line is locally metrizable but not metrizable; in a sense, it is "too long".
This article incorporates material from Metrizable on PlanetMath , which is licensed under the Creative Commons Attribution/Share-Alike License . | https://en.wikipedia.org/wiki/Metrizable_space |
Metro Chicago Information Center (MCIC) was an independent nonprofit research and consulting resource based in Chicago, Illinois. MCIC was founded in 1990 by a consortium of business and philanthropic leaders at the Commercial Club of Chicago to regularly collect demographics and baseline data on social policy and human needs for the 6-county metropolitan Chicago region. [ 1 ] MCIC provided the data necessary to support public policy and social program development but did not advocate specific policy choices. Faced with a $650,000 defined benefit pension liability for staff hired before 2005, [ 2 ] MCIC closed on February 29, 2012. [ 3 ]
MCIC conducted demographic research for both local nonprofits and larger foundations such as the MacArthur Foundation and the Sprague Foundation, [ 1 ] whose findings typically went towards fundraising, advocacy, and policy making. MCIC specialized in difficult to reach and underserved populations. [ 4 ]
MCIC provided a variety of research and consulting services for branch site analysis, and strategic market planning. GIS/mapping technology, merged with unique databases like HMDA or U.S. Census information, provides in-depth analysis of delineated market areas, individual branch markets, or new site locations. [ 5 ]
MCIC was part of a group of national and community-based organizations that served as auxiliary census data distribution centers. [ 6 ]
MCIC was a founding member of the Illinois Data Exchange Affiliates (IDEA), a voluntary coalition of government agencies and nonprofit organizations working to improve and facilitate public access to public data through web-based XML data transfer. [ 7 ]
MCIC was the only National Neighborhood Indicators Partnership (NNIP) partner in the metropolitan Chicago region. The NNIP is a collaborative effort by the Urban Institute in Washington D.C. and 28 local partners around the country who work to further the development and use of neighborhood-level information systems in local policymaking and community building. [ 8 ] | https://en.wikipedia.org/wiki/Metro_Chicago_Information_Center |
A metronome (from Ancient Greek μέτρον ( métron ) ' measure ' and νόμος ( nómos ) ' law ' ) is a device that produces an audible click or other sound at a uniform interval that can be set by the user, typically in beats per minute (BPM). Metronomes may also include synchronized visual motion, such as a swinging pendulum or a blinking light. Musicians—and others including dancers, athletes, and health professionals—often practise with a metronome to improve their timing, especially the ability to maintain a steady tempo with a regular beat or pulse . Composers and conductors often use numerical metronome markings to communicate their preferred tempos to musicians preparing for a performance.
A type of metronome was among the inventions of Andalusian polymath Abbas ibn Firnas (810–887). In 1815, German inventor Johann Maelzel patented a mechanical, wind-up metronome as a tool for musicians, under the title "Instrument/Machine for the Improvement of all Musical Performance, called Metronome". [ 1 ] In the 20th century, electronic metronomes and software metronomes were invented.
When interpreting emotion and other qualities in music, performers seldom play exactly on every beat. In a musically expressive performance, the pulse generally does not align with the clicks of a metronome. [ 2 ] [ 3 ] This has led some musicians to criticize use of a metronome, because "musical time is replaced by clock time". [ 4 ]
The word metronome first appeared in English in Maelzel's 1815 patent application, and is Greek in origin, derived from metron— "measure" and nomos— "regulation, law". [ 5 ] [ 6 ] The London patent refers to the machine as "a metronome or musical time-keeper". [ 1 ]
Historical credit for the mechanical metronome is spread across Spanish, Italian, French, Dutch and German contributors.
According to historian Lynn Townsend White Jr. , the Andalusian inventor Abbas Ibn Firnas created "some sort of metronome" in the 9th century. [ 7 ] [ 8 ] Galileo Galilei studied and discovered key concepts involving the pendulum in the late 16th and early 17th centuries, famously inspired by a steadily swaying chandelier in Pisa Cathedral . [ 9 ] In 1696, musician Étienne Loulié built a pendulum-based " chronomètre ", consisting of a lead weight hanging from an adjustable string alongside a 6-foot (2 m) vertical ruler. However, his design produced no sound, and did not have an escapement mechanism to keep the pendulum in motion. [ 10 ] To get the correct tempo with this type of visual device, a musician would need to watch the pendulum as if watching a conductor's baton.
The more-familiar mechanical musical chronometre was invented by Dietrich Nikolaus Winkel in Amsterdam in 1814, based on a spring -powered, inverted pendulum rod with fixed and adjustable weights to achieve compactness. Through questionable practice, [ 11 ] Johann Maelzel , incorporating Winkel's ideas, added a numerical scale, called it a metronome, and started mass-manufacturing the pyramid-shaped device in 1816 under his own name: "Maelzel's Metronome." The original text of Maelzel's patent in England (1815) can be downloaded. [ 1 ]
Maelzel's mechanical metronome uses an adjustable weight on an inverted pendulum rod to control tempo. The weight slides up the pendulum rod to decrease tempo, or down to increase tempo. (This mechanism is also called a double-weighted pendulum, because there is a second, fixed weight on the other side of the pendulum pivot, inside the metronome case.) The pendulum swings back and forth in tempo, while a mechanism inside the metronome produces a clicking sound with each oscillation . A mechanical metronome does not need an electric battery , but runs from a spring-wound clockwork escapement. [ 1 ] For uniform beats, the metronome should be placed on a hard, level, unmoving surface, and away from any strong magnets. Small variations in pendulum speed can also result from differences in temperature, air pressure, or gravity. [ 9 ]
Since Maelzel's era, musical tempo is almost always measured in beats per minute (BPM). Metronomes often display both BPM numbers and traditional tempo markings , which are written words conveying a range of tempos and an associated character. For example, the Italian term Vivace indicates a tempo typically between 156 and 176 BPM, but it also communicates that the music should be played with a lively character. [ 12 ]
A mechanical metronome's tempo is usually adjustable from 40 to 208 BPM. The most-common arrangement of tempos on a Maelzel metronome begins with 40 beats per minute
and increases by 2 BPM: 42 44 46 48 50 52 54 56 58 60,
then by 3 BPM: 63 66 69 72,
then by 4 BPM: 76 80 84 88 92 96 100 104 108 112 116 120,
then by 6 BPM: 126 132 138 144,
then by 8 BPM: 152 160 168 176 184 192 200 208.
Some modern metronomes allow adjustment to more-precise tempos (e.g., increasing 120 to 121), but such a difference is hardly perceptible. [ 13 ]
Electromechanical metronomes were invented by Frederick Franz in the US and patented in 1953. [ 14 ] Instead of a clockwork or a quartz crystal , a plug-in electric motor operates the mechanism. Most use a mechanical variable-speed drive combination with a momentary switch and a cam wheel to time the beats. A frequent feature is an embedded neon lamp that flashes in time with the beat. Franz and Yamaha were common manufacturers in the 1960s and 1970s; a popular model was the Franz LB4.
After the fall of the Soviet Bloc in 1991, the 75-foot (23 m) electromechanical Prague Metronome was installed as a silent kinetic sculpture overlooking the city, an inverted pendulum symbolizing the passage of time. [ 15 ] It may still be the world's largest metronome, although Geneva (since 1972) and Gdańsk (since 2016) each have a larger pendulum clock . [ 16 ] [ 17 ]
Most modern metronomes are electronic and use a battery-powered quartz crystal to maintain accuracy in any position, comparable to wristwatches since the 1980s. Electronic metronomes are considerably smaller and more rugged than the earlier types. The simplest electronic metronomes have dials or buttons to control the tempo and volume. Some also produce or measure tuning notes, usually around the range of A440 (440 hertz ). Sophisticated metronomes can produce two or more distinct sounds. Tones can differ in pitch, volume and/or timbre to distinguish downbeats from other beats, as well as compound and complex time signatures . Many electronic musical keyboards have built-in metronome functions with selectable rhythm patterns .
21st-century digital software metronomes run either as standalone applications on computers and smartphones, or in music sequencing and audio multitrack software packages. In recording studio applications, such as film scoring , a software metronome may provide a click track to synchronize musicians.
Portable MP3 players including iPods can play pre-recorded MP3 metronome click tracks, which can use different sounds and samples instead of the usual metronome click or beep. Users of smartphones can install a wide range of metronome applications. The Google search engine includes an interactive metronome that can play between 40 and 218 BPM. [ 18 ] Either method avoids the need to bring a physical metronome to lessons or practice sessions.
In written musical scores since the early 1800s, composers and conductors (or editors) often indicate their preferred tempos using BPM metronome speeds, with or without descriptive tempo markings, to help musicians prepare for a performance. Even works that do not require a strictly constant tempo, such as musical passages with rubato , sometimes provide BPM markings to indicate the general tempo. Another mark that denotes tempo is M.M. (or MM), for Maelzel's Metronome. The notation M.M. is usually followed by a note value and a number that indicates the tempo, as in M.M. = 60 .
Ludwig van Beethoven , a personal acquaintance of Maelzel, became the first notable composer to indicate specific metronome markings in his music. This was done in December 1815, with the corrected copy of the score of the Cantata op. 112 containing Beethoven's first metronome mark. [ 19 ]
Musicians often practise with metronomes to develop and maintain a sense of timing and tempo. Metronomes are also used as a training tool to achieve a desired performance speed—not only by musicians, but also by dancers, [ 20 ] runners, [ 21 ] swimmers, [ 22 ] and others.
Specific uses include learning to maintain tempos and beats consistently. For example, a musician fighting a tendency to speed up might practise a phrase repeatedly while slightly slowing the BPM setting each time, to play more steadily. A musician or athlete seeking to improve technical proficiency might set the metronome to gradually higher speeds until the desired tempo is achieved. This also helps to expose unintentional slowdowns due to technical challenges or fatigue. Additionally, recording musicians use click tracks from metronomes to help audio engineers synchronize audio tracks.
In health care, metronomes can be used to maintain the desired pacing in various physiological tests and procedures. [ 23 ] For example, CPR chest compressions are significantly more likely to follow the recommended 100–120 BPM when a hospital emergency room uses an audible metronome, or when rescuers in non-hospital settings can remember a suitably paced song as a "mental metronome". [ 24 ]
"Metronome technique" is extensive and has been the subject of several books for musicians. [ 25 ] [ 26 ] [ 27 ] The "intuitive" approach is simply to practise a full musical work, in time with a metronome clicking the downbeats. With more-advanced metronome technique, musicians practise separate exercises to strengthen their sense of rhythm, tempo, and musical time, while also cultivating flexibility and expression.
The basic skill required is the ability to play "in the pocket"—that is, precisely on the click of the metronome, in a relaxed fashion. It helps musicians to develop a strong sense of time, at intervals corresponding to fractions of a second. One challenge with this approach, especially for pianists and percussionists, is the metronome click seeming to vanish (or at least be heard less distinctly) when one hits the click exactly. Musicians who attempt to play in the pocket with a metronome without established technique may find that it introduces tension and effort into their performance. To address these difficulties, musicians may first learn to play consistently behind or ahead of the click whenever they want to. As a result, they develop a clear sense of "where the click is" and can train to hit the click as well. [ 28 ] [ 29 ]
Much of modern metronome technique aims to resolve timing problems without creating overdependence on the metronome. Typical exercises are to practise maintaining a tempo while the metronome is muted for progressively longer periods of time, [ 30 ] or to practise with displaced clicks (offset from the usual downbeats) or polyrhythms against the metronome. [ 31 ]
To help build rhythmic flexibility and musical expression in performances, preparatory exercises with the metronome often incorporate a fluid sense of timing. For example, musicians may practise drifting gradually from one beat to the next, or alternately pulling behind and pushing ahead of the click. [ 32 ] As author/drummer Mac Santiago wrote: "The ability to hear the pulse and yet accelerate or decelerate slightly is a great way to incorporate human feeling into a musical performance. ... This also works for the actions of ritardando and accelerando, as they are relative to a steady pulse and are best performed gradually rather than in sudden shifts." [ 33 ]
Perhaps the most famous, and most direct, use of the metronome as an unconventional musical instrument is György Ligeti 's composition, Poème Symphonique for 100 metronomes (1962). Two years earlier, Toshi Ichiyanagi had written Music for Electric Metronomes (1960). Maurice Ravel used three metronomes at different speeds for the opening of his opera about a clockmaker, L'heure espagnole (1911). [ 34 ]
The clicking sounds of mechanical metronomes have sometimes been used to provide a soft rhythm track without using any of the usual percussion instruments . Paul McCartney did this on "Distractions" ( Flowers in the Dirt , 1989). Following the metronome, McCartney performed a rhythm track by hitting various parts of his body. [ 35 ] Also, in Ennio Morricone 's theme "Farewell to Cheyenne" (featured in the film Once Upon a Time in the West , 1968), the steady clip-clop beat is provided by the deliberately distorted and slowed-down sound of a mechanical metronome. [ 36 ]
Five metronomes begin Philip Miller 's musical score to William Kentridge 's video installation "The Refusal of Time" (2012). [ 37 ]
The metronome is usually viewed positively by performers, teachers, conservatories, and musicologists (who spend considerable time analysing metronome markings). It is considered an excellent practice tool because of its steady beat, being "mathematically perfect and categorically correct". [ 38 ] This removes guesswork and aids musicians in various ways, including keeping tempos, countering tendencies to slow down or speed up unintentionally, monitoring technical progress, and increasing evenness and accuracy, especially in rapid passages. Metronomes are thus commonly used at all skill levels, from beginners to professional musicians, and are often recommended to music students without reservation. [ 39 ] As commentator/violist Miles Hoffman wrote in 1997: "Most music teachers consider the metronome indispensable, and most professional musicians, in fact, continue to practice with a metronome throughout their careers." [ 40 ] Some musicians took this view almost as soon as the metronome was invented in the early 19th century. [ 41 ] [ 42 ] The online book Metronome Techniques includes a "Potpourri" chapter with dozens of quotations from music teachers in favour of metronome practice. [ 43 ]
The metronome has become very important in performance practice, and "largely unchallenged in musical pedagogy or scholarship since the 20th century". [ 44 ] In the 19th century, the metronome was usually not used for ticking all through a piece, but only to check the tempo and then set it aside. This is in contrast with many musicians today, who practise with the metronome in the background for the entirety of a piece of music, generally leading to steadier performances. [ 45 ]
Oboist/musicologist Bruce Haynes described the role of the metronome in modern performance style in detail in his book The End of Early Music . He emphasized that modern style is much more rhythmically rigid, compared with the effusive rubato and bluster characteristic of expressive 19th-century Romantic music . Because of this, musicologist and critic Richard Taruskin called Modernism "refuge in order and precision, hostility to subjectivity, to the vagaries of personality". [ 46 ] These qualities gave rise to the term metronomic , which music critics use to describe performances with an unyielding tempo, a mechanical rhythmic approach, and equal stress to all subintervals; violinist Sol Babitz considered it "sewing machine" style with limited flexibility. [ 46 ] Some writers have drawn parallels with a modern technological society that is ordered by the clock. [ 3 ] [ 47 ]
Unlike approximate and descriptive tempo markings , a published metronome speed indicates a highly specific tempo that cannot adapt to variations in musical aesthetics, concert hall acoustics, or the instruments themselves. [ 48 ] This is one reason why composers including Felix Mendelssohn and Richard Wagner have criticized the publication of metronome marks. [ 49 ] As Johannes Brahms once commented regarding his German Requiem : "I think here as well as with all other music, the metronome is of no value. As far at least as my experience goes, everybody has, sooner or later, withdrawn his metronome marks." [ 50 ]
A metronome only provides a fixed, continuous beat. Therefore, metronome markings on sheet music provide a reference, but cannot accurately communicate the pulse , swing , or groove of music. The pulse is often irregular, e.g., in accelerando, rallentando, or expressive musical phrasing such as rubato. [ 51 ] Even such highly rhythmical musical forms as samba , if performed in a culturally authentic style consistent with recordings by early practitioners, cannot be captured with the beats of a metronome. Performances that are unfailingly regular rhythmically might be criticized as being metronomic , lacking the characteristic swing of the genre. [ 52 ]
Some have argued that "the metronome has no real musical value", hurting rather than helping musicians' sense of rhythm. The use of a metronome has been compared to the difference between mechanically-aided and freehand drawing, in that the output with a metronome is said to be rigid and hampering creativity. [ 53 ] American composer and critic Daniel Gregory Mason wrote that the use of the metronome is "dangerous" because it leads musicians to play by the measure or beat instead of the phrase , at the expense of liveliness, instinct, and rhythmical energy, "a dead body in place of the living musical organism". [ 54 ] Even proponents of the metronome have warned that its strict speed and repetition can hinder internal rhythm and musicality when "over-used". [ 55 ]
If a musician decides not to use a metronome, other methods are required to deal with timing and tempo glitches, rushing and dragging. These strategies may also be combined with metronome technique as a complementary approach.
Humans rely on an innate sense of rhythm to perform ordinary activities such as walking, hammering nails or chopping vegetables. Even speech and thought have a rhythm of sorts. Author/drummer Andrew C. Lewis recommends working to bring these everyday rhythms into music:
"Rhythm is everywhere. Be sensitive to it, and stay aware of spontaneous occurrences that can spur rhythmic development. Listen all the time and use your imagination. Become a rhythm antenna." [ 56 ]
Until the 19th century in Europe, people used to sing as they worked , in time to the rhythms of their daily tasks. In many parts of the world today, especially tribal areas, people still sing frequently and spontaneously as they engage in daily activities. [ 57 ] Even without singing, instrumentalists can strengthen their innate sense of pulse using quieter bodily rhythms, such as breathing, walking, foot tapping, or other activities. (Likewise, listeners often adjust these movements subconsciously when hearing rhythmic music.) Musicians can deal with timing and tempo glitches by learning to "hear an ideal performance in their mind" first, and by listening carefully to recordings of themselves and others. [ 27 ] [ 56 ]
Notes inégales (unequal notes) are a common feature of French Baroque music , in which subdivided pairs of notes are written with equal duration but performed with a long/short dotted or triplet rhythm. Usually, these pairs are played with steady downbeats and the same amount of swing throughout, like modern jazz . Less commonly, the unequal rhythms are more extensive and irregular, like the constantly shifting rhythms of speech. In this view, rhythms that are subtly unsynchronized and uneven throughout can help to keep the music alive and interesting, and prevent any feeling of sameness and boredom. Musicians may practise organizing notes and phrases into " musical gestures ", patterns of motions that come naturally, rather than metronomically strict measures. Performers also may slightly delay or extend an important note of a musical phrase, to build a sense of anticipation or emphasis. This freer approach is a minority interpretation of notes inégales for early music, but noteworthy because of its perspective on musical time and rhythm, and its relevance to musicians practising to create an emotionally engaging experience for listeners. [ 58 ] | https://en.wikipedia.org/wiki/Metronome |
MEVA International is a private brand that supplies PC accessories to the international market.
The company launched its products in 2008 in Iran, but it also has sales throughout the broader middle eastern region. | https://en.wikipedia.org/wiki/Meva |
In number theory , Meyer's theorem on quadratic forms states that an indefinite quadratic form Q in five or more variables over the field of rational numbers nontrivially represents zero. In other words, if the equation Q ( x ) = 0 has a non-zero real solution, then it has a non-zero rational solution. By clearing the denominators, an integral solution x may also be found.
Meyer's theorem is usually deduced from the Hasse–Minkowski theorem (which was proved later) and the following statement:
Meyer's theorem is the best possible with respect to the number of variables: there are indefinite rational quadratic forms Q in four variables which do not represent zero. One family of examples is given by
where p is a prime number that is congruent to 3 modulo 4. This can be proved by the method of infinite descent using the fact that, if the sum of two perfect squares is divisible by such a p , then each summand is divisible by p . | https://en.wikipedia.org/wiki/Meyer's_theorem |
Methylarsonic acid is an organoarsenic compound with the formula CH 3 AsO 3 H 2 . It is a colorless, water-soluble solid. Salts of this compound, e.g. disodium methyl arsonate , have been widely used in as herbicides and fungicides in growing cotton and rice. [ 2 ]
Near physiological pH, methanearsonic acid converts to its conjugate bases, the methylarsonates . These include CH 3 AsO 3 H − and CH 3 AsO 2− 3 .
Reaction of arsenous acid with methyl iodide gives methylarsonic acid. This historically significant conversion is called the Meyer reaction : [ 3 ]
The then-novel aspect of the reaction was that alkylation occurs at arsenic, leading to oxidation of arsenic from oxidation state +3 to +5.
The biomethylation of arsenic compounds is thought to start with the formation of methanearsonates. Thus, trivalent arsenic compounds are methylated to give methanearsonate. S -Adenosylmethionine is the methyl donor. The methanearsonates are the precursors to cacodylates , again by the cycle of reduction (to methylarsonous acid) followed by a second methylation. [ 4 ]
Like most arsenic compounds, it is highly toxic. [ 4 ] | https://en.wikipedia.org/wiki/Meyer_reaction |
In mathematics, a Meyer set or almost lattice is a relatively dense set X of points in the Euclidean plane or a higher-dimensional Euclidean space such that its Minkowski difference with itself is uniformly discrete . Meyer sets have several equivalent characterizations; they are named after Yves Meyer , who introduced and studied them in the context of diophantine approximation. Nowadays Meyer sets are best known as mathematical model for quasicrystals . However, Meyer's work precedes the discovery of quasicrystals by more than a decade and was entirely motivated by number theoretic questions. [ 1 ] [ 2 ]
A subset X of a metric space is relatively dense if there exists a number r such that all points of X are within distance r of X , and it is uniformly discrete if there exists a number ε such that no two points of X are within distance ε of each other. A set that is both relatively dense and uniformly discrete is called a Delone set . When X is a subset of a vector space , its Minkowski difference X − X is the set { x − y | x , y in X } of differences of pairs of elements of X . [ 3 ]
With these definitions, a Meyer set may be defined as a relatively dense set X for which X − X is uniformly discrete. Equivalently, it is a Delone set for which X − X is Delone, [ 1 ] or a Delone set X for which there exists a finite set F with X − X ⊂ X + F [ 4 ]
Some additional equivalent characterizations involve the set
defined for a given X and ε , and approximating (as ε approaches zero) the definition of the reciprocal lattice of a lattice . A relatively dense set X is a Meyer set if and only if
A character of an additively closed subset of a vector space is a function that maps the set to the unit circle in the plane of complex numbers , such that the sum of any two elements is mapped to the product of their images. A set X is a harmonious set if, for every character χ on the additive closure of X and every ε > 0, there exists a continuous character on the whole space that ε -approximates χ . Then a relatively dense set X is a Meyer set if and only if it is harmonious. [ 1 ]
Meyer sets include | https://en.wikipedia.org/wiki/Meyer_set |
The nitrite ion has the chemical formula NO − 2 . Nitrite (mostly sodium nitrite ) is widely used throughout chemical and pharmaceutical industries. [ 1 ] The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name nitrite also refers to organic compounds having the –ONO group, which are esters of nitrous acid .
Sodium nitrite is made industrially by passing a mixture of nitrogen oxides into aqueous sodium hydroxide or sodium carbonate solution: [ 2 ] [ 1 ]
The product is purified by recrystallization. Alkali metal nitrites are thermally stable up to and beyond their melting point (441 °C for KNO 2 ). Ammonium nitrite can be made from dinitrogen trioxide , N 2 O 3 , which is formally the anhydride of nitrous acid:
The nitrite ion has a symmetrical structure (C 2v symmetry ), with both N–O bonds having equal length and a bond angle of about 115°. In valence bond theory , it is described as a resonance hybrid with equal contributions from two canonical forms that are mirror images of each other. In molecular orbital theory , there is a sigma bond between each oxygen atom and the nitrogen atom, and a delocalized pi bond made from the p orbitals on nitrogen and oxygen atoms which is perpendicular to the plane of the molecule. The negative charge of the ion is equally distributed on the two oxygen atoms. Both nitrogen and oxygen atoms carry a lone pair of electrons. Therefore, the nitrite ion is a Lewis base .
In the gas phase it exists predominantly as a trans -planar molecule.
Nitrite is the conjugate base of the weak acid nitrous acid :
Nitrous acid is also highly unstable, tending to disproportionate :
This reaction is slow at 0 °C. [ 2 ] Addition of acid to a solution of a nitrite in the presence of a reducing agent , such as iron(II), is a way to make nitric oxide (NO) in the laboratory.
The formal oxidation state of the nitrogen atom in nitrite is +3. This means that it can be either oxidized to oxidation states +4 and +5, or reduced to oxidation states as low as −3. Standard reduction potentials for reactions directly involving nitrous acid are shown in the table below: [ 4 ]
The data can be extended to include products in lower oxidation states. For example:
Oxidation reactions usually result in the formation of the nitrate ion, with nitrogen in oxidation state +5. For example, oxidation with permanganate ion can be used for quantitative analysis of nitrite (by titration ):
The product of reduction reactions with nitrite ion are varied, depending on the reducing agent used and its strength. With sulfur dioxide , the products are NO and N 2 O; with tin(II) (Sn 2+ ) the product is hyponitrous acid (H 2 N 2 O 2 ); reduction all the way to ammonia (NH 3 ) occurs with hydrogen sulfide . With the hydrazinium cation ( N 2 H + 5 ) the product of nitrite reduction is hydrazoic acid (HN 3 ), an unstable and explosive compound:
which can also further react with nitrite:
This reaction is unusual in that it involves compounds with nitrogen in four different oxidation states. [ 2 ]
Nitrite is detected and analyzed by the Griess Reaction , involving the formation of a deep red-colored azo dye upon treatment of a NO − 2 -containing sample with sulfanilic acid and naphthyl-1-amine in the presence of acid. [ 5 ]
Nitrite is an ambidentate ligand and can form a wide variety of coordination complexes by binding to metal ions in several ways. [ 2 ] Two examples are the red nitrito complex [Co(NH 3 ) 5 (ONO)] 2+ is metastable , isomerizing to the yellow nitro complex [Co(NH 3 ) 5 (NO 2 )] 2+ . Nitrite is processed by several enzymes, all of which utilize coordination complexes.
In nitrification , ammonium is converted to nitrite. Important species include Nitrosomonas . Other bacterial species such as Nitrobacter , are responsible for the oxidation of the nitrite into nitrate.
Nitrite can be reduced to nitric oxide or ammonia by many species of bacteria. Under hypoxic conditions, nitrite may release nitric oxide, which causes potent vasodilation . Several mechanisms for nitrite conversion to NO have been described, including enzymatic reduction by xanthine oxidoreductase , nitrite reductase , and NO synthase (NOS), as well as nonenzymatic acidic disproportionation reactions.
Azo dyes and other colorants are prepared by the process called diazotization , which requires nitrite. [ 1 ]
The addition of nitrites and nitrates to processed meats such as ham, bacon, and sausages speeds up the curing of meat and also impart an attractive colour. [ 8 ]
The academic and industrial consensus is that nitrites also reduces growth and toxin production of Clostridium botulinum . [ 9 ] [ 10 ] [ 11 ] On the other hand, a 2018 study (full text not available) by the British Meat Producers Association determined that legally permitted levels of nitrite do not affect the growth of C. botulinum . [ 12 ] In the U.S., meat cannot be labeled as "cured" without the addition of nitrite. [ 13 ] [ 14 ] [ 15 ] In some countries, cured-meat products are manufactured without nitrate or nitrite, and without nitrite from vegetable sources. Parma ham , produced without nitrite since 1993, was reported in 2018 to have caused no cases of botulism. This is because the interior of the muscle is sterile and the surface is exposed to oxygen. [ 8 ] Other manufacture processes do not assure these conditions, and reduction of nitrite results in toxin production. [ 16 ]
In mice, food rich in nitrites together with unsaturated fats can prevent hypertension by forming nitro fatty acids that inhibit soluble epoxide hydrolase , which is one explanation for the apparent health effect of the Mediterranean diet . [ 17 ] Adding nitrites to meat has been shown to generate known carcinogens ; the World Health Organization (WHO) advises that eating 50 g (1.8 oz) of nitrite processed meat a day would raise the risk of getting bowel cancer by 18% over a lifetime. [ 8 ]
The recommended maximum limits by the World Health Organization in drinking water are 3 mg L −1 and 50 mg L −1 for nitrite and nitrate ions, respectively. [ 18 ] Ingesting too much nitrite and/or nitrate through well water is suspected to cause methemoglobinemia . [ 19 ]
95% of the nitrite ingested in modern diets comes from bacterial conversion of nitrates naturally found in vegetables. [ 20 ] However, potentially cancer-causing nitroso compounds are not made in the pH-neutral colon. They are mostly made in the acidic stomach. [ 21 ] [ 22 ]
Nitrite reacts with the meat's myoglobin by attaching to the heme iron atom, forming reddish-brown nitrosomyoglobin and the characteristic pink "fresh" color of nitrosohemochrome or nitrosyl-heme upon cooking. [ 23 ] In the US, nitrite has been formally used since 1925. According to scientists working for the industry group American Meat Institute , this use of nitrite started in the Middle Ages . [ 24 ] Historians and epidemiologists argue that the widespread use of nitrite in meat-curing is closely linked to the development of industrial meat-processing. [ 25 ] [ 26 ] French investigative journalist Guillaume Coudray [ fr ] asserts that the meat industry chooses to cure its meats with nitrite even though it is established that this chemical gives rise to cancer-causing nitroso -compounds. [ 27 ] Some traditional and artisanal producers avoid nitrites.
Addition of ascorbic acid , erythorbic acid , or one of their salts enhance the binding of nitrite to the iron atom in myoglobin. [ 23 ] These chemicals also reduce the formation of nitrosamine in the stomach, but only when the fat content of a meal is less than 10%, beyond which they instead increase the formation of nitrosamine. [ 28 ] [ 29 ]
Nitrites in the form of sodium nitrite and amyl nitrite are components of many cyanide antidote kits. [ 30 ] Both of these compounds bind to hemoglobin and oxidize the Fe 2+ ions to Fe 3+ ions forming methemoglobin . Methemoglobin, in turn, binds to cyanide (CN), creating cyanmethemoglobin, effectively removing cyanide from the complex IV of the electron transport chain (ETC) in mitochondria , which is the primary site of disruption caused by cyanide. Another mechanism by which nitrites help treat cyanide toxicity is the generation of nitric oxide (NO). NO displaces the CN from the cytochrome c oxidase (ETC complex IV), making it available for methemoglobin to bind. [ 31 ]
In organic chemistry , alkyl nitrites are esters of nitrous acid and contain the nitrosoxy functional group. Nitro compounds contain the C–NO 2 group. Nitrites have the general formula RONO, where R is an aryl or alkyl group. Amyl nitrite and other alkyl nitrites have a vasodilating action and must be handled in the laboratory with caution. They are sometimes used in medicine for the treatment of heart diseases. A classic named reaction for the synthesis of alkyl nitrites is the Meyer synthesis [ 32 ] [ 33 ] in which alkyl halides react with metallic nitrites to a mixture to nitroalkanes and nitrites.
Nitrite salts can react with secondary amines to produce N -nitrosamines , which are suspected of causing stomach cancer . The World Health Organization (WHO) advises that each 50 g (1.8 oz) of processed meat eaten a day would raise the risk of getting bowel cancer by 18% over a lifetime; processed meat refers to meat that has been transformed through fermentation, nitrite curing, salting, smoking, or other processes to enhance flavor or improve preservation. The World Health Organization's review of more than 400 studies concluded in 2015 that there was sufficient evidence that processed meats caused cancer, particularly colon cancer; the WHO's International Agency for Research on Cancer (IARC) classified processed meats as carcinogenic to humans ( Group 1 ). [ 8 ] [ 34 ]
Nitrite (ingested) under conditions that result in endogenous nitrosation , specifically the production of nitrosamine , has been classified as Probably carcinogenic to humans ( Group 2A ) by the IARC. [ 35 ] | https://en.wikipedia.org/wiki/Meyer_synthesis |
The Meyers synthesis is an organic synthesis for the preparation of unsymmetrical aldehydes via hydrolysis of an oxazine . [ 1 ] [ 2 ] [ 3 ] [ 4 ] The reaction is named after the American chemist Albert Meyers .
The starting compound is a dihydro-1,3-oxazine with an alkyl group in the 2 position. The alpha proton is acidic and can be abstracted by a strong base such as butyl lithium and subsequently alkylated by an alkyl halide ( haloalkane ). In the next step the nitrogen to carbon double bond ( imine ) is reduced with sodium borohydride and the resulting oxazine (a hemiaminal ) hydrolyzed with water and oxalic acid to the aldehyde. | https://en.wikipedia.org/wiki/Meyers_synthesis |
The Meyer–Schuster rearrangement is the chemical reaction described as an acid - catalyzed rearrangement of secondary and tertiary propargyl alcohols to α,β-unsaturated ketones if the alkyne group is internal and α,β-unsaturated aldehydes if the alkyne group is terminal. [ 1 ] [ 2 ] [ 3 ] [ 4 ]
The reaction proceeds by three major steps: (1) the rapid protonation of oxygen, (2) the slow, rate-determining step comprising the 1,3-shift of the protonated hydroxy group, and (3) the keto-enol tautomerism followed by rapid deprotonation. [ 5 ] Formation of the unsaturated carbonyl compound is irreversible. [ 6 ] Solvent is important and solvent caging is proposed to stabilize the transition state . [ 7 ]
The reaction of tertiary alcohols containing an α- acetylenic group does not produce the expected aldehydes, but rather α,β-unsaturated methyl ketones via an enyne intermediate . [ 8 ] [ 9 ] This alternate reaction is called the Rupe reaction , and competes with the Meyer–Schuster rearrangement in the case of tertiary alcohols.
The traditional Meyer–Schuster rearrangement is induced by strong acids, which introduces competition with the Rupe reaction if the alcohol is tertiary. [ 1 ] Milder conditions are possible with transition metal -based and Lewis acid catalysts (for example, Ru- [ 10 ] and Ag-based [ 11 ] catalysts). Microwave -radiation with InCl 3 {\displaystyle _{3}} catalyst to give excellent yields with short reaction times and good stereoselectivity . [ 12 ]
The Meyer–Schuster rearrangement has been used in a variety of applications, from the conversion of ω-alkynyl-ω-carbinol lactams into enamides using catalytic PTSA [ 13 ] to the synthesis of α,β-unsaturated thioesters from γ-sulfur substituted propargyl alcohols [ 14 ] to the rearrangement of 3-alkynyl-3-hydroxyl-1 H - isoindoles in mildly acidic conditions to give the α,β-unsaturated carbonyl compounds. [ 15 ] One of the most interesting applications, however, is the synthesis of a part of paclitaxel in a diastereomerically -selective way that leads only to the E -alkene. [ 16 ]
The step shown above had a 70% yield (91% when the byproduct was converted to the Meyer-Schuster product in another step). The authors used the Meyer–Schuster rearrangement because they wanted to convert a hindered ketone to an alkene without destroying the rest of their molecule.
The reaction is named after Kurt Meyer and Kurt Schuster. [ 17 ] Reviews have been published by Swaminathan and Narayan, | https://en.wikipedia.org/wiki/Meyer–Schuster_rearrangement |
Mezerein is a toxic diterpene ester found in the sap of Daphne mezereum and related plants. Plants of the genera Euphorbiaceae and Thymelaeaceae possess a wide variety of different phorbol esters, which share the capacity of mimicking diacylglycerol (DAG) and thus activating different isoforms of protein kinase C . Mezerein was first isolated in 1975. It has antileukemic properties in mice, but it is also defined as a weak promoter of skin cancers in the same species. [ 2 ] All parts of the plants contain an acrid and irritant sap that contains mezerein, thought to be the principal poison. The sap is especially prevalent in the bark and berries.
Mezerein is highly liposoluble and can cause vomiting, diarrhea and burning of the mouth. When a large dose is taken, there can be shivering, dilation of the pupils, damage to the oral passages and the intestine and even death.
It can also irritate the skin, resulting in redness by slight damage of the veins. Because of causing this redness, the sap used to be applied as rouge. [ 2 ]
Mezerein can be found in Daphne mezereum . [ 2 ] This plant has been used to make dyes, treat rheumatism and indolent ulcers and as a cosmetic. [ 3 ] [ 4 ] In homeopathy, the plant is used to treat primarily skin disorders but is also prescribed to treat anxiety related to digestive disorders and congestion. [ 5 ] Once the toxicity of the plant was discovered, these uses were abandoned. The toxicity also led to new uses. In extreme cases, the berries are used to commit suicide. [ 6 ]
The toxins mezerein and daphnetoxin are both present in the genus Daphne . Daphnetoxin has a structure similar to mezerein, with the phenyl-pentadienoyl component (top left of the mezerein structural diagram) missing. They are both PKC activators but with a different selectivity: mezerein exhibits antileukemic properties while daphnetoxin does not. [ 7 ]
Mezerein is a second stage tumor promoter. [ 8 ] According to the IPP model, tumorigenesis happens in three stages: i nitiation , p romotion , and p rogression . In the first stage, initiation, a gene-mutation with change of function occurs. These mutations often occur in oncogenes or regulatory sequences. In the promotion stage, interaction with cellular signaling pathways takes place. This leads to growth advantage for initiated cells. In the last stage, progression, the tumor has become karyotypically instable: morphological changes in the normal chromosomal structure take place. This instability is caused by additional mutations. This leads to metastasis, hyperproliferation and loss of control by the cellular environment. There is an increased risk that the tumor cells will mutate other genes. Second stage tumor promoters like mezerein do not have the capacity to initiate tumors, but can create circumstances in which initiated cells are more susceptible to additional mutations or in which initiated cells have growth advantage. [ 9 ] [ 10 ] They do not cause mutations themselves: promotion happens through interference with cellular signaling pathways.
Mezerein and other phorbol esters interact with protein kinase C (PKC). Protein kinase C controls the cell cycle , so chemicals that interact with it can have pro-proliferative or anti-proliferative effects. PKC is normally activated by diacyl glycerol (DAG). Upon DAG binding to PKC, PKC's affinity for Ca 2+ and membrane phosphoinositols is increased. After binding Ca 2+ , the DAG-PKC-Ca 2+ complex is attached to the plasma membrane by binding to membrane phosphoinositols. Now, PKC can phosphorylate various substrates, affecting the activity of several intracellular pathways that regulate cell cycle and apoptosis among others. PKC binding to the plasma membrane is reversible, because after a short period of time DAG is enzymatically degraded, causing PKC to undergo a conformational change and detach from the membrane and stop phosphorylating substrates.
Mezerein binds to PKC instead of DAG. It has a higher affinity for PKC than DAG does, and it cannot be degraded as easily as DAG. Therefore, when mezerein is bound, PKC remains in the active conformation much longer than it normally does. Furthermore, when mezerein has bound to PKC, PKC no longer requires Ca 2+ for activation. This causes overstimulation of the pathways PKC initiates, leading to more cellular proliferation and less apoptosis. [ 11 ]
However, it seems that chronic activation of PKC leads to a negative effect, that is, apoptosis. Furthermore, high doses of mezerein have been used to terminally differentiate cancer cells, preventing their growth. Thus, mezerein can have both carcinogenic and non-carcinogenic properties. Usually, low doses cause a beneficial effect and high doses cause a toxic effect. [ 12 ] [ 13 ]
Mezerein has been shown to have two effects in chick embryo fibroblasts (CEF cells) that are associated with cancer. These effects are stimulation of 2-deoxy- D -glucose (2-DG) transport and causing of fibronectin loss. These effects are known to correlate with tumorigenicity in mice. [ 14 ] Both effects are mediated by PKC. [ 15 ] [ 16 ] The ability of mezerein to decrease fibronectin levels is 46-fold lower than its ability to stimulate 2-DG transport. In related compounds, the difference between the two effects is usually 2- to 9-fold. This may have something to do with the weak tumorigenicity of mezerein.
The shape of the 2-DG transport dose-response curve has an optimum at a mezerein concentration of approximately 50 ng/mL. This is atypical, since a dose-response curve usually is S-shaped. The explanation for this behaviour is unknown. Possibly, at high concentrations, mezerein is converted by enzymes that have low affinity for it. That would lower the effective concentration and thus decrease the effects.
In this picture, a NOAE-level can be observed between mezerein concentrations of 0 to approximately 0.09 ng/mL. The concentration that gives half-maximal effects is reached for a low concentration of mezerein: about 0.7 ng/mL.
The shape of the fibronectin-decrease curve is more usual, although not quite: the separate parts of the curve are all more or less linear, which is not the case in an S-shaped curve. In this case, a maximum dose can be determined: above concentrations of about 103 ng/mL the effect remains more or less stable. A NOAE-level is visible for concentrations of up to 1 ng/mL of mezerein. The concentration that gives half-maximal effect is approximately 90 ng/mL. The difference with the half-maximal concentration for 2-DG transport is remarkable. Mezerein causes a 46-fold lower effect for fibronectin decrease than for 2-DG stimulation, and apparently only causes this effect at high concentrations. This might also correlate with mezerein being a weak tumor promoter. | https://en.wikipedia.org/wiki/Mezerein |
Mezlocillin is a broad-spectrum penicillin antibiotic . It is active against both Gram-negative and some Gram-positive bacteria . Unlike most other extended spectrum penicillins, it is excreted by the liver, therefore it is useful for biliary tract infections, such as ascending cholangitis.
Like all other beta-lactam antibiotics , mezlocillin inhibits the third and last stage of bacterial cell wall synthesis by binding to penicillin binding proteins . This ultimately leads to cell lysis . [ citation needed ]
Mezlocillin can be made in a variety of ways including reaction of ampicillin with chlorocarbamate 1 in the presence of triethylamine. Chlorocarbamate 1 itself is made from ethylenediamine by reaction with phosgene to form the cyclic urea followed by monoamide formation with methanesulfonyl chloride and then reaction of the other nitrogen atom with phosgene and trimethylsilylchloride. [ citation needed ]
The closely related analogue azlocillin is made in essentially the same manner as mezlocillin. but with omission of the methylation step. [ citation needed ] | https://en.wikipedia.org/wiki/Mezlocillin |
A mezzanine ( / ˌ m ɛ z ə ˈ n iː n / ; or in Italian , a mezzanino ) [ 1 ] is an intermediate floor in a building which is partly open to the double-height ceilinged floor below, or which does not extend over the whole floorspace of the building, a loft with non-sloped walls. However, the term is often used loosely for the floor above the ground floor, especially where a very high-ceilinged original ground floor has been split horizontally into two floors.
Mezzanines may serve a wide variety of functions. Industrial mezzanines, such as those used in warehouses, may be temporary or semi-permanent structures.
In Royal Italian architecture , mezzanino also means a chamber created by partitioning that does not go up all the way to the arch vaulting or ceiling; these were historically common in Italy and France, for example in the palaces for the nobility at the Quirinal Palace .
A mezzanine is an intermediate floor (or floors) in a building which is open to the floor below. [ 2 ] It is placed halfway ( mezzo means 'half' in Italian) up the wall on a floor which has a ceiling at least twice as high as a floor with minimum height. [ 3 ] A mezzanine does not count as one of the floors in a building, and generally does not count in determining maximum floorspace. [ 2 ] The International Building Code permits a mezzanine to have as much as one-third of the floor space of the floor below. Local building codes may vary somewhat from this standard. [ 2 ] A space may have more than one mezzanine, as long as the sum total of floor space of all the mezzanines is not greater than one-third the floor space of the complete floor below. [ 2 ]
Mezzanines help to make a high-ceilinged space feel more personal and less vast, and can create additional floor space. [ 4 ] Mezzanines, however, may have lower-than-normal ceilings [ 1 ] due to their location. The term "mezzanine" does not imply any particular function; mezzanines can be used for a wide array of purposes. [ 5 ] [ 6 ]
Mezzanines are commonly used in modern architecture , which places a heavy emphasis on light and space. [ 3 ]
In industrial settings, mezzanines may be installed (rather than built as part of the structure) in high-ceilinged spaces such as warehouses. These semi-permanent structures are usually free-standing, can be dismantled and relocated, and are sold commercially. Industrial mezzanine structures can be supported by structural steel columns and elements, or by racks or shelves. [ 7 ] Depending on the span and the run of the mezzanine, different materials may be used for the mezzanine's deck like fibre cement boards. [ 8 ] Some industrial mezzanines may also include enclosed, paneled office space on their upper levels. [ 7 ] There are three basic types of industrial mezzanines: custom, standard or modular.
A structural engineer is sometimes hired to help determine whether the floor of the building can support a mezzanine (and how heavy the mezzanine may be), and to design the appropriate mezzanine. [ 8 ]
Custom Mezzanines are steel, raised industrial platform structures that are designed specifically to match the space and capacity needs of a given facility. It will, at a minimum, include a stairway for accessing the mezzanine. These structures typically are the strongest in terms of support capacity.
Standard Mezzanines are steel, raised industrial platform structures that are completely self-supporting and are sold in predetermined sizes and shapes. These off-the-shelf structures are usually strong (in terms of support capacity) and less expensive than custom mezzanines.
Employees in material handling and manufacturing are often at risk of falls when they are on the job. Recent figures show approximately 20,000 serious injuries and nearly 100 fatalities a year in industrial facilities. [ 9 ] Falls of people and objects from mezzanines are of particular concern. [ 10 ]
In many industrial operations, openings are cut into the guardrail on mezzanines and elevated work platforms to allow picking of palletized material to be loaded and unloaded, often with a fork truck, to upper levels. The Occupational Safety and Health Administration (OSHA) [ 11 ] and International Building Council (IBC) [ 12 ] have published regulations for fall protection and The American National Standards Institute (ANSI) has published standards for securing pallet drop areas to protect workers that work on elevated platforms and are exposed to openings.
In most cases, safety gates are used to secure these openings. OSHA requires openings 48 inches or taller to be secured with a fall protection system. [ 13 ] Removable sections of railing or gates that swing or slide open would be used to open up the area and allow the transfer of material, and then close once the material is removed. However, current ANSI standards require dual-gate safety systems for fall protection. [ 14 ]
Dual-gate safety systems were created to secure these areas, allowing a barrier to be in place at all times, even while pallets are being loaded or removed. Dual-gate systems create a completely enclosed workstation providing protection for the worker during loading and off-loading operations. When the rear-side gate opens, the ledge gate automatically closes, ensuring there is always a gate between the operator and the ledge. | https://en.wikipedia.org/wiki/Mezzanine |
Magnesium perchlorate is a powerful oxidizing agent , with the formula Mg(ClO 4 ) 2 . The salt is also a superior drying agent for gas analysis.
Magnesium perchlorate decomposes at 250 °C. [ 2 ] The heat of formation is -568.90 kJ/mol. [ 3 ]
The enthalpy of solution is quite high, so reactions are done in large amounts of water to dilute it.
It is sold under the trade name anhydrone. Manufacture of this product on a semi-industrial scale was first performed by G. Frederick Smith in his garage in Urbana Illinois, but later at a permanent facility in Columbus, OH called G. Frederick Smith Chemical Co . He sold the magnesium perchlorate to A. H. Thomas Co., now Thomas Scientific, under the trade name Dehydrite.
It is used as desiccant to dry gas or air samples, [ 4 ] [ 5 ] but is no longer advised, for use as a general desiccant, due to hazards inherent in perchlorates. [ 6 ] It is dried by heating at 220 °C under vacuum.
Magnesium perchlorate and other perchlorates have been found on Mars . [ 7 ] Being a drying agent, magnesium perchlorate retains water from the atmosphere and may release it when conditions are favorable and temperature is above 273 K. Briny solutions that contain salts such as magnesium perchlorate have a lower melting point than that of pure water. Therefore the abundance of magnesium and other perchlorate salts on Mars could support the theory that liquid aqueous solutions might exist on or below the surface, where temperature and pressure conditions would ordinarily cause the water to freeze.
Magnesium perchlorate is produced by the reaction of magnesium hydroxide and perchloric acid . | https://en.wikipedia.org/wiki/Mg(ClO4)2 |
Monomagnesium phosphate is one of the forms of magnesium phosphate . It is a magnesium acid salt of phosphoric acid with the chemical formula Mg(H 2 PO 4 ) 2 . Di- and tetrahydrates are known also. It dissolves in water, forming phosphoric acid and depositing a solid precipitate of Mg(HPO 4 ) . 3H 2 O, dimagnesium phosphate . [ 2 ]
As a food additive, it is used as an acidity regulator and has the E number E343.
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Mg(H2PO4)2 |
Magnesium nitrate refers to inorganic compounds with the formula Mg(NO 3 ) 2 (H 2 O) x , where x = 6, 2, and 0. All are white solids. [ 2 ] The anhydrous material is hygroscopic , quickly forming the hexahydrate upon standing in air. All of the salts are very soluble in both water and ethanol .
Being highly water-soluble, magnesium nitrate occurs naturally only in mines and caverns as nitromagnesite (hexahydrate form). [ 3 ]
The magnesium nitrate used in commerce is made by the reaction of nitric acid and various magnesium salts.
The principal use is as a dehydrating agent in the preparation of concentrated nitric acid . [ 2 ]
Its fertilizer grade has 10.5% nitrogen and 9.4% magnesium , so it is listed as 10.5-0-0 + 9.4% Mg. Fertilizer blends containing magnesium nitrate also have ammonium nitrate , calcium nitrate , potassium nitrate and micronutrients in most cases; these blends are used in the greenhouse and hydroponics trade.
Magnesium nitrate reacts with alkali metal hydroxide to form the corresponding nitrate:
Since magnesium nitrate has a high affinity for water, heating the hexahydrate does not result in the dehydration of the salt, but rather its decomposition into magnesium oxide , oxygen , and nitrogen oxides :
The absorption of these nitrogen oxides in water is one possible route to synthesize nitric acid . Although inefficient, this method does not require the use of any strong acid .
It is also occasionally used as a desiccant. | https://en.wikipedia.org/wiki/Mg(NO3)2 |
Magnesium hydroxide is an inorganic compound with the chemical formula Mg(OH) 2 . It occurs in nature as the mineral brucite . It is a white solid with low solubility in water ( K sp = 5.61 × 10 −12 ). [ 5 ] Magnesium hydroxide is a common component of antacids , such as milk of magnesia .
Treating the solution of different soluble magnesium salts with alkaline water induces the precipitation of the solid hydroxide Mg(OH) 2 :
As Mg 2+ is the second most abundant cation present in seawater after Na + , it can be economically extracted directly from seawater by alkalinisation as described here above. On an industrial scale, Mg(OH) 2 is produced by treating seawater with lime (Ca(OH) 2 ). A volume of 600 m 3 (160,000 US gal) of seawater gives about 1 tonne (2,200 lb) of Mg(OH) 2 . Ca(OH) 2 ( K sp = 5.02 × 10 −6 ) [ 6 ] is far more soluble than Mg(OH) 2 ( K sp = 5.61 × 10 −12 ) and dramatically increases the pH value of seawater from 8.2 to 12.5. The less soluble Mg(OH) 2 precipitates because of the common ion effect due to the OH − added by the dissolution of Ca(OH) 2 : [ 7 ]
For seawater brines, precipitating agents other than Ca(OH) 2 can be utilized, each with their own nuances:
It has been demonstrated that sodium hydroxide, NaOH , is the better precipitating agent compared to Ca(OH) 2 and NH 4 OH due to higher recovery and purity rates, and the settling and filtration time can be improved at low temperatures and higher concentration of precipitates. Methods involving the use of precipitating agents are typically batch processes. [ 8 ]
It is also possible to obtain Mg(OH) 2 from seawater using electrolysis chambers separated with a cation exchange membrane . This process is continuous, lower-cost, and produces oxygen gas, hydrogen gas, sulfuric acid (if Na 2 SO 4 is used; NaCl can alternatively be used to yield HCl ), and Mg(OH) 2 of 98% or higher purity. It is crucial to deaerate the seawater to mitigate co-precipitation of calcium precipitates. [ 9 ]
Most Mg(OH) 2 that is produced industrially, as well as the small amount that is mined, is converted to fused magnesia (MgO). Magnesia is valuable because it is both a poor electrical conductor and an excellent thermal conductor. [ 7 ]
Only a small amount of the magnesium from magnesium hydroxide is usually absorbed by the intestine (unless one is deficient in magnesium). However, magnesium is mainly excreted by the kidneys; so long-term, daily consumption of milk of magnesia by someone suffering from kidney failure could lead in theory to hypermagnesemia . Unabsorbed magnesium is excreted in feces; absorbed magnesium is rapidly excreted in urine. [ 10 ]
As an antacid, magnesium hydroxide is dosed at approximately 0.5–1.5 g in adults and works by simple neutralization , in which the hydroxide ions from the Mg(OH) 2 combine with acidic H + ions (or hydronium ions) produced in the form of hydrochloric acid by parietal cells in the stomach , to produce water.
As a laxative, magnesium hydroxide is dosed at 5–10 grams (0.18–0.35 oz), and works in a number of ways. First, Mg 2+ is poorly absorbed from the intestinal tract, so it draws water from the surrounding tissue by osmosis . Not only does this increase in water content to soften the feces, it also increases the volume of feces in the intestine (intraluminal volume) which naturally stimulates intestinal motility . Furthermore, Mg 2+ ions cause the release of cholecystokinin (CCK), which results in intraluminal accumulation of water and electrolytes, and increased intestinal motility. Some sources claim that the hydroxide ions themselves do not play a significant role in the laxative effects of milk of magnesia, as alkaline solutions (i.e., solutions of hydroxide ions) are not strongly laxative, and non-alkaline Mg 2+ solutions, like MgSO 4 , are equally strong laxatives, mole for mole. [ 11 ]
On May 4, 1818, American inventor Koen Burrows received a patent (No. X2952) for magnesium hydroxide. [ 12 ] In 1829, Sir James Murray used a "condensed solution of fluid magnesia" preparation of his own design [ 13 ] to treat the Lord Lieutenant of Ireland , the Marquess of Anglesey , for stomach pain. This was so successful (advertised in Australia and approved by the Royal College of Surgeons in 1838) [ 14 ] that he was appointed resident physician to Anglesey and two subsequent Lords Lieutenant, and knighted. His fluid magnesia product was patented two years after his death, in 1873. [ 15 ]
The term milk of magnesia was first used by Charles Henry Phillips in 1872 for a suspension of magnesium hydroxide formulated at about 8 % w/v . [ 16 ] It was sold under the brand name Phillips' Milk of Magnesia for medicinal usage.
USPTO registrations show that the terms "Milk of Magnesia" [ 17 ] and "Phillips' Milk of Magnesia" [ 18 ] have both been assigned to Bayer since 1995. In the UK, the non-brand (generic) name of "Milk of Magnesia" and "Phillips' Milk of Magnesia" is "Cream of Magnesia" (Magnesium Hydroxide Mixture, BP ).
It is added directly to human food, and is affirmed as generally recognized as safe by the FDA . [ 19 ] It is known as E number E528 .
Magnesium hydroxide is marketed for medical use as chewable tablets, as capsules, powder, and as liquid suspensions , sometimes flavored. These products are sold as antacids to neutralize stomach acid and relieve indigestion and heartburn . It also is a laxative to alleviate constipation . As a laxative, the osmotic force of the magnesia acts to draw fluids from the body. High doses can lead to diarrhea , and can deplete the body's supply of potassium , sometimes leading to muscle cramps . [ 20 ]
Some magnesium hydroxide products sold for antacid use (such as Maalox ) are formulated to minimize unwanted laxative effects through the inclusion of aluminum hydroxide , which inhibits the contractions of smooth muscle cells in the gastrointestinal tract, [ 21 ] thereby counterbalancing the contractions induced by the osmotic effects of the magnesium hydroxide.
Magnesium hydroxide is also a component of antiperspirant . [ 22 ]
Magnesium hydroxide powder is used industrially to neutralize acidic wastewaters. [ 23 ] It is also a component of the Biorock method of building artificial reefs . The main advantage of Mg(OH) 2 over Ca(OH) 2 , is to impose a lower pH better compatible with that of seawater and sea life: pH 10.5 for Mg(OH) 2 in place of pH 12.5 with Ca(OH) 2 .
Natural magnesium hydroxide ( brucite ) is used commercially as a fire retardant. Most industrially used magnesium hydroxide is produced synthetically. [ 24 ] Like aluminum hydroxide, solid magnesium hydroxide has smoke suppressing and flame retardant properties. This property is attributable to the endothermic decomposition it undergoes at 332 °C (630 °F):
The heat absorbed by the reaction retards the fire by delaying ignition of the associated substance. The water released dilutes combustible gases. Common uses of magnesium hydroxide as a flame retardant include additives to cable insulation, insulation plastics, roofing, and various flame retardant coatings. [ 25 ] [ 26 ] [ 27 ] [ 28 ] [ 29 ]
Brucite , the mineral form of Mg(OH) 2 commonly found in nature also occurs in the 1:2:1 clay minerals amongst others, in chlorite , in which it occupies the interlayer position normally filled by monovalent and divalent cations such as Na + , K + , Mg 2+ and Ca 2+ . As a consequence, chlorite interlayers are cemented by brucite and cannot swell nor shrink.
Brucite, in which some of the Mg 2+ cations have been substituted by Al 3+ cations, becomes positively charged and constitutes the main basis of layered double hydroxide (LDH). LDH minerals as hydrotalcite are powerful anion sorbents but are relatively rare in nature.
Brucite may also crystallize in cement and concrete in contact with seawater . Indeed, the Mg 2+ cation is the second-most-abundant cation in seawater, just behind Na + and before Ca 2+ . Because brucite is a swelling mineral, it causes a local volumetric expansion responsible for tensile stress in concrete. This leads to the formation of cracks and fissures in concrete, accelerating its degradation in seawater.
For the same reason, dolomite cannot be used as construction aggregate for making concrete. The reaction of magnesium carbonate with the free alkali hydroxides present in the cement porewater also leads to the formation of expansive brucite.
This reaction, one of the two main alkali–aggregate reaction (AAR) is also known as alkali–carbonate reaction . | https://en.wikipedia.org/wiki/Mg(OH)2 |
Magnesium iron hexahydride is an inorganic compound with the formula Mg 2 FeH 6 . It is a green diamagnetic solid that is stable in dry air. The material is prepared by heating a mixture of powdered magnesium and iron under high pressures of hydrogen : [ 1 ]
The compound is isomorphous with K 2 PtCl 6 , i.e., their connectivities and structures are the same. The [FeH 6 ] 4− centre adopts octahedral molecular geometry with Fe-H distances of 1.56 Å. The Mg 2+ centres are bound to the faces of the octahedron, with Mg-H distances of 2.38 Å. Several related compounds are known including salts of [RuH 6 ] 4− , [OsH 6 ] 4− , and [PtH 6 ] 2− anions. [ 2 ]
Although Mg 2 FeH 6 is not soluble in ordinary solvents, related derivatives are. For example, the related salt Mg 4 Br 4 ( THF ) 4 FeH 6 is soluble as are related alkoxides . Measurements on such compounds suggest that the hydride ligand exerts a weaker crystal field than cyanide . [ 3 ] | https://en.wikipedia.org/wiki/Mg2FeH6 |
Magnesium phosphate is a general term for salts of magnesium and phosphate appearing in several forms and several hydrates: [ 1 ]
Amorphous magnesium phosphate is also claimed. [ 2 ]
Magnesium phosphates are listed on the U.S. FDA's Generally recognized as safe (GRAS) list of substances. [ 3 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Mg3(PO4)2 |
Magnesium nitride , which possesses the chemical formula Mg 3 N 2 , is an inorganic compound of magnesium and nitrogen . At room temperature and pressure it is a greenish yellow powder.
When measuring the boiling point of magnesium, Henri Étienne Sainte-Claire Deville and Henri Caron identified that molten magnesium they distilled covered itself by "small colorless and transparent needles which are destroyed fairly quickly by transforming into ammonia and magnesia". In their 1857 publication the chemists interpreted it as a likely nitride similar to those discovered by Friedrich Wöhler and Heinrich Rose . [ 2 ]
It was indeed confirmed in 1862 when Friedrich Briegleb and Johann Georg Anton Geuther synthesized the compound on purpose and first studied it. [ 3 ]
This second method is preferred despite the additional time required due to the difficulty of fully purifying nitrogen gas to prevent the formation of unwanted oxides. [ 4 ]
Magnesium nitride reacts with water to produce magnesium hydroxide and ammonia gas, as do many metal nitrides .
In fact, when magnesium is burned in air, some magnesium nitride is formed in addition to the principal product, magnesium oxide .
Thermal decomposition of magnesium nitride gives magnesium and nitrogen gas (at 700-1500 °C).
At high pressures, the stability and formation of new nitrogen-rich nitrides (N/Mg ratio equal or greater to one) were suggested and later discovered. [ 5 ] [ 6 ] [ 7 ] These include the Mg 2 N 4 and MgN 4 solids which both become thermodynamically stable near 50 GPa. [ 8 ] The Mg 2 N 4 is composed of exotic cis -tetranitrogen N 4− 4 species with N-N bond orders close to one. This Mg 2 N 4 compound was recovered to ambient conditions, along with the N 4− 4 units, marking only the fourth polynitrogen entity bulk stabilized at ambient conditions.
When isolating argon , William Ramsay passed dry air over copper to remove oxygen and over magnesium to remove the nitrogen , forming magnesium nitride.
Magnesium nitride was the catalyst in the first practical synthesis of borazon (cubic boron nitride ). [ 9 ]
Robert H. Wentorf, Jr. was trying to convert the hexagonal form of boron nitride into the cubic form by a combination of heat, pressure, and a catalyst. He had already tried all the logical catalysts (for instance, those that catalyze the synthesis of diamond ), but with no success.
Out of desperation and curiosity (he called it the "make the maximum number of mistakes" approach [ 10 ] ), he added some magnesium wire to the hexagonal boron nitride and gave it the same pressure and heat treatment. When he examined the wire under a microscope, he found tiny dark lumps clinging to it. These lumps could scratch a polished block of boron carbide , something only diamond was known to do.
From the smell of ammonia, caused by the reaction of magnesium nitride with the moisture in the air, he deduced that the magnesium metal had reacted with the boron nitride to form magnesium nitride, which was the true catalyst.
Magnesium nitride has also been applied to synthesize aluminum nitride nanocrystals, cubic boron nitride and nitrides of aluminum and Group 3 [ 11 ] It has also been proposed as an intermediate in a fossil-fuel-free nitrogen fixation process. [ 12 ] | https://en.wikipedia.org/wiki/Mg3N2 |
Magnesium phosphate is a general term for salts of magnesium and phosphate appearing in several forms and several hydrates: [ 1 ]
Amorphous magnesium phosphate is also claimed. [ 2 ]
Magnesium phosphates are listed on the U.S. FDA's Generally recognized as safe (GRAS) list of substances. [ 3 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Mg3O8P2 |
Talc , or talcum , is a clay mineral composed of hydrated magnesium silicate , with the chemical formula Mg 3 Si 4 O 10 (OH) 2 . Talc in powdered form, often combined with corn starch , is used as baby powder . This mineral is used as a thickening agent and lubricant . It is an ingredient in ceramics , paints , and roofing material . It is a main ingredient in many cosmetics . [ 6 ] It occurs as foliated to fibrous masses, and in an exceptionally rare crystal form. It has a perfect basal cleavage and an uneven flat fracture, and it is foliated with a two-dimensional platy form.
The Mohs scale of mineral hardness, based on scratch hardness comparison , defines value 1 as the hardness of talc, the softest mineral. When scraped on a streak plate , talc produces a white streak, though this indicator is of little importance, because most silicate minerals produce a white streak. Talc is translucent to opaque, with colors ranging from whitish grey to green with a vitreous and pearly luster . Talc is not soluble in water, and is slightly soluble in dilute mineral acids . [ 7 ]
Soapstone is a metamorphic rock composed predominantly of talc.
The word talc derives from Persian : تالک tālk . In ancient times, the word was used for various related minerals, including talc, mica , and selenite . [ 8 ]
Talc dominantly forms from the metamorphism of magnesian minerals such as serpentine , pyroxene , amphibole , and olivine , in the presence of carbon dioxide and water. This is known as "talc carbonation" or "steatization" and produces a suite of rocks known as talc carbonates .
Talc is primarily formed by hydration and carbonation by this reaction:
Talc can also be formed via a reaction between dolomite and silica, which is typical of skarnification of dolomites by silica-flooding in contact metamorphic aureoles:
Talc can also be formed from magnesium chlorite and quartz in blueschist and eclogite metamorphism by the following metamorphic reaction :
Talc is also found as a diagenetic mineral in sedimentary rocks where it can form from the transformation of metastable hydrated magnesium-clay precursors such as kerolite , sepiolite , or stevensite that can precipitate from marine and lake water in certain conditions. [ 9 ]
In this reaction, the ratio of talc and kyanite depends on aluminium content, with more aluminous rocks favoring production of kyanite. This is typically associated with high-pressure, low-temperature minerals such as phengite , garnet , and glaucophane within the lower blueschist facies . Such rocks are typically white, friable, and fibrous, and are known as whiteschist .
Talc is a trioctahedral layered mineral; its structure is similar to pyrophyllite , but with magnesium in the octahedral sites of the composite layers. [ 2 ] The crystal structure of talc is described as TOT , meaning that it is composed of parallel TOT layers weakly bonded to each other by weak van der Waals forces . The TOT layers in turn consist of two tetrahedral sheets ( T ) strongly bonded to the two faces of a single trioctahedral sheet ( O ). It is the weak bonding between TOT layers that gives talc its perfect basal cleavage and softness. [ 10 ]
The tetrahedral sheets consist of silica tetrahedra, which are silicon ions surrounded by four oxygen ions. The tetrahedra each share three of their four oxygen ions with neighboring tetrahedra to produce a hexagonal sheet. The remaining oxygen ion (the apical oxygen ion) is available to bond with the trioctahedral sheet. [ 11 ]
The trioctahedral sheet has the structure of a sheet of the mineral brucite . Apical oxygens take the place of some of the hydroxyl ions that would be present in a brucite sheet, bonding the tetrahedral sheets tightly to the trioctahedral sheet. [ 12 ]
Tetrahedral sheets have a negative charge, since their bulk composition is Si 4 O 4− 10 . The trioctahedral sheet has an equal positive charge, since its bulk composition is Mg 3 (OH) 4+ 2 The combined TOT layer thus is electrically neutral. [ 13 ]
Because the hexagons in the T and O sheets are slightly different in size, the sheets are slightly distorted when they bond into a TOT layer. This breaks the hexagonal symmetry and reduces it to monoclinic or triclinic symmetry. [ 14 ] However, the original hexahedral symmetry is discernible in the pseudotrigonal character of talc crystals. [ 3 ]
Talc is a common metamorphic mineral in metamorphic belts that contain ultramafic rocks , such as soapstone (a high-talc rock), and within whiteschist and blueschist metamorphic terranes . Prime examples of whiteschists include the Franciscan Metamorphic Belt of the western United States, the western European Alps especially in Italy, certain areas of the Musgrave Block , and some collisional orogens such as the Himalayas , which stretch along Pakistan , India , Nepal , and Bhutan .
Talc carbonate ultramafics are typical of many areas of the Archaean cratons , notably the komatiite belts of the Yilgarn craton in Western Australia . Talc-carbonate ultramafics are also known from the Lachlan Fold Belt , eastern Australia , from Brazil , the Guiana Shield , and from the ophiolite belts of Turkey , Oman , and the Middle East .
China is the key world talc and steatite-producing country with an output of about 2.2 million tonnes (2016), which accounts for 30% of total global output. The other major producers are Brazil (12%), India (11%), the U.S. (9%), France (6%), Finland (4%), Italy, Russia, Canada, and Austria (2%, each). [ 15 ]
Notable economic talc occurrences include the Mount Seabrook talc mine, Western Australia, formed upon a polydeformed, layered ultramafic intrusion. The France-based Luzenac Group is the world's largest supplier of mined talc. Its largest talc mine at Trimouns near Luzenac in southern France produces 400,000 tonnes of talc per year.
Extraction in disputed areas of Nangarhar province , Afghanistan, has led the international monitoring group Global Witness to declare talc a conflict resource , as the profits are used to fund armed confrontation between the Taliban and Islamic State . [ 16 ]
Talc is used in many industries, including paper making, plastic , paint and coatings (e.g. for metal casting molds), rubber, food, electric cable, pharmaceuticals, cosmetics, and ceramics. A coarse grayish-green high-talc rock is soapstone or steatite , used for stoves, sinks, electrical switchboards, etc. It is often used for surfaces of laboratory table tops and electrical switchboards because of its resistance to heat, electricity, and acids.
In finely ground form, talc finds use as a cosmetic ( talcum powder ), as a lubricant , and as a filler in paper manufacture. It is used to coat the insides of inner tubes and rubber gloves during manufacture to keep the surfaces from sticking. Talcum powder, with heavy refinement, has been used in baby powder, an astringent powder used to prevent diaper rash (nappy rash). The American Academy of Pediatrics recommends that parents avoid using baby powder because it poses a risk of respiratory problems, including breathing trouble and serious lung damage if inhaled. The small size of the particles makes it difficult to keep them out of the air while applying the powder. Zinc oxide -based ointments are a much safer alternative. [ 17 ]
Soapstone (massive talc) is often used as a marker for welding or metalworking . [ 18 ] [ 19 ]
Talc is also used as food additive or in pharmaceutical products as a glidant . In medicine, talc is used as a pleurodesis agent to prevent recurrent pleural effusion or pneumothorax . In the European Union , the additive number is E553b . Talc may be used in the processing of white rice as a buffing agent in the polishing stage.
Due to its low shear strength, talc is one of the oldest known solid lubricants. Also, limited use is made of talc as a friction-reducing additive in lubricating oils. [ 20 ]
Talc is widely used in the ceramics industry in both bodies and glazes. In low-fire art-ware bodies, it imparts whiteness and increases thermal expansion to resist crazing . In stonewares , small percentages of talc are used to flux the body and therefore improve strength and vitrification . It is a source of MgO flux in high-temperature glazes (to control melting temperature). It is also employed as a matting agent in earthenware glazes and can be used to produce magnesia mattes at high temperatures.
ISO standard for quality (ISO 3262)
Patents are pending on the use of magnesium silicate as a cement substitute. Its production requirements are less energy-intensive than ordinary Portland cement (at a heating requirement of around 650 °C for talc compared to 1,500 °C for limestone to produce Portland cement), while it absorbs far more carbon dioxide as it hardens. This results in a negative carbon footprint overall, as the cement substitute removes 0.6 tonnes of CO 2 per tonne used. This contrasts with a positive carbon footprint of 0.4 tonnes per tonne of conventional cement. [ 21 ]
Talc is used in the production of the materials that are widely used in the building interiors such as base content paints in wall coatings. Other areas that use talc to a great extent are organic agriculture , the food industry, cosmetics, and hygiene products such as baby powder and detergent powder .
Talc is sometimes used as an adulterant to illegal heroin , to expand volume and weight and thereby increase its street value. With intravenous use, it may lead to pulmonary talcosis , a granulomatous inflammation in the lungs .
Sterile talc powder ( NDC 63256-200-05) is a sclerosing agent used in the procedure of pleurodesis . This can be helpful as a cancer treatment to prevent pleural effusions (an abnormal collection of fluid in the space between the lungs and the thoracic wall ). It is inserted into the space via a chest tube, causing it to close up, so fluid cannot collect there. The product can be sterilized by dry heat, ethylene oxide , or gamma irradiation . [ 22 ]
Suspicions have been raised that talc use contributes to certain types of disease, mainly cancers of the ovaries and lungs. According to the IARC , talc containing asbestos is classified as a group 1 agent (carcinogenic to humans), talc use in the perineum is classified as group 2B (possibly carcinogenic to humans), and talc not containing asbestos is classified as group 2A (probably carcinogenic to humans). [ 23 ] Reviews by Cancer Research UK and the American Cancer Society conclude that some studies have found a link, but other studies have not. [ 24 ] [ 25 ]
The studies discuss pulmonary issues, [ 26 ] lung cancer , [ 27 ] [ 28 ] and ovarian cancer . [ 29 ] One of these, published in 1993, was a US National Toxicology Program report, which found that cosmetic grade talc containing no asbestos -like fibres was correlated with tumor formation in rats forced to inhale talc for 6 hours a day, five days a week over at least 113 weeks. [ 27 ] A 1971 paper found particles of talc embedded in 75% of the ovarian tumors studied. [ 30 ] In 2018, Health Canada issued a warning against inhaling talcum powder or women's using it perineally. [ 31 ]
In contrast, however, research published in 1995 and 2000 concluded that, although it was plausible that talc could cause ovarian cancer, no conclusive evidence had been shown. [ 32 ] [ 33 ] Further, a 2008 European Journal of Cancer Prevention review of ovarian cancer and talc use studies pointed out that, although many of them examined the duration, frequency, and accumulation of hygienic talc use, few found a positive association among these factors and some found a negative one: “It may be argued that the overall null findings associated with talc-dusted diaphragms and condom use is more convincing evidence for a lack of a carcinogenic effect, especially given the lack of an established correlation between perineal dusting frequency and ovarian tissue talc concentrations and the lack of a consistent dose-response relationship with ovarian cancer risk." Instead, the authors credited powdered talc with "a high degree of safety.” [ 34 ]
Similarly, in a 2014 article published in a leading cancer journal, the Journal of the National Cancer Institute , researchers reported the results of a survey of 61,576 postmenopausal women, more than half of whom had used talc powder perineally. The researchers compared the subjects’ reports of their own talc use with their reports of having had ovarian cancer diagnosed by their doctors, and found, regardless of subjects’ age and tubal ligation status, “Ever use of perineal powder ... was not associated with risk of ovarian cancer compared with never use,” nor was any greater individual cancer risk associated with longer use of talc powder. On this basis, the article concluded, “perineal powder use does not appear to influence ovarian cancer risk.” [ 35 ] The Cosmetic Ingredient Review Expert Panel concluded in 2015 that talc, in the concentrations currently used in cosmetics, is safe. [ 36 ]
In July 2024, the International Agency for Research on Cancer listed talc as "probably" carcinogenic for humans. The study is based on limited evidence it could cause ovarian cancer in humans. [ 37 ] [ better source needed ]
In the United States, the Occupational Safety and Health Administration and National Institute for Occupational Safety and Health have set occupational exposure limits to respirable talc dusts at 2 mg/m 3 over an eight-hour workday. At levels of 1000 mg/m 3 , inhalation of talc is considered immediately dangerous to life and health . [ 38 ]
The United States Food and Drug Administration considers talc (magnesium silicate) generally recognized as safe (GRAS) to use as an anticaking agent in table salt in concentrations smaller than 2%. [ 39 ]
One particular issue with commercial use of talc is its frequent co-location in underground deposits with asbestos ore. Asbestos is a general term for different types of fibrous silicate minerals, desirable in construction for their heat resistant properties. [ 40 ] There are six varieties of asbestos; the most common variety in manufacturing, white asbestos , is in the serpentine family. [ 41 ] Serpentine minerals are sheet silicates ; although not in the serpentine family, talc is also a sheet silicate, with two sheets connected by magnesium cations. The frequent co-location of talc deposits with asbestos may result in contamination of mined talc with white asbestos, which poses serious health risks when dispersed into the air and inhaled. Stringent quality control since 1976, including separating cosmetic- and food-grade talc from that destined for industrial use, has largely eliminated this issue, but it remains a potential hazard requiring mitigation in the mining and processing of talc. [ 42 ] A 2010 US FDA survey failed to find asbestos in a variety of talc-containing products. [ 43 ] A 2018 Reuters investigation asserted that pharmaceuticals company Johnson & Johnson knew for decades that there was asbestos in its baby powder, [ 44 ] and in 2020 the company stopped selling its baby powder in the US and Canada. [ 45 ] There were calls for Johnson & Johnson's largest shareholders to force the company to end global sales of baby powder, and hire an independent firm to conduct a racial justice audit as it had been marketed to African American and overweight women. [ 46 ] On August 11, 2022, the company announced it would stop making talc-based powder by 2023 and replace it with cornstarch-based powders. The company said the talc-based powder is safe to use and does not contain asbestos. [ 47 ]
In 2006 the International Agency for Research on Cancer classified talcum powder as a possible human carcinogen if used in the female genital area. Despite this, no federal agency in the US acted to remove talcum powder from the market or add warnings. [ 48 ]
In February 2016, as the result of a lawsuit against Johnson & Johnson (J&J), a St. Louis jury awarded $72 million to the family of an Alabama woman who died from ovarian cancer . The family claimed that the use of talcum powder was responsible for her cancer.
In May 2016, a South Dakota woman was awarded $55 million as the result of another lawsuit against J&J. [ 49 ] The woman had used Johnson & Johnson's Baby Powder for more than 35 years before being diagnosed with ovarian cancer in 2011. [ 50 ]
In October 2016, a St. Louis jury awarded $70.1 million to a Californian woman with ovarian cancer who had used Johnson's Baby Powder for 45 years. [ 51 ]
In August 2017, a Los Angeles jury awarded $417 million to a Californian woman, Eva Echeverria, who developed ovarian cancer as a "proximate result of the unreasonably dangerous and defective nature of talcum powder", her lawsuit against Johnson & Johnson stated. [ 52 ] On 20 October 2017, Los Angeles Superior Court judge Maren Nelson dismissed the verdict. The judge stated that Echeverria proved there is "an ongoing debate in the scientific and medical community about whether talc more probably than not causes ovarian cancer and thus (gives) rise to a duty to warn", but not enough to sustain the jury's imposition of liability against Johnson & Johnson stated, and concluded that Echeverria did not adequately establish that talc causes ovarian cancer. [ 53 ] [ 54 ]
In July 2018, a court in St. Louis awarded a $4.7bn claim ($4.14bn in punitive damages and $550m in compensatory damages) against J&J to 22 claimant women, concluding that the company had suppressed evidence of asbestos in its products for more than four decades. [ 55 ]
At least 1,200 to 2,000 other talcum powder-related lawsuits were pending as of 2016 [update] . [ 51 ] [ 56 ]
In 2020 J&J stopped sales of its talcum-based baby powder, which it had been selling for 130 years. J&J created a subsidiary responsible for the claims in an effort to resolve the lawsuits in bankruptcy court. In 2023 J&J proposed a nearly $9bn settlement with 50,000 claimants saying the claims were "specious" but it wanted to move on from the issue, but judges blocked the plans, ruling that the subsidiary was not in financial distress and could not use the bankruptcy system to resolve the lawsuits. [ 57 ]
In July 2023 J&J sued researchers who linked talc to cancer alleging they used junk science to disparage company's products, while defendants say the lawsuits are meant to silence scientists. [ 58 ] | https://en.wikipedia.org/wiki/Mg3Si4O10(OH)2 |
The magnesium argide ion, MgAr + is an ion composed of one ionised magnesium atom, Mg + and an argon atom. It is important in inductively coupled plasma mass spectrometry and in the study of the field around the magnesium ion. [ 1 ] The ionization potential of magnesium is lower than the first excitation state of argon, so the positive charge in MgAr + will reside on the magnesium atom. Neutral MgAr molecules can also exist in an excited state .
The spectrum of MgAr + can be observed. It resembles that of Mg + , however some lines are blue shifted and others red shifted. In Mg + the ground state is termed 2 S. A first excited state has a 3s electron moved to the 3p orbital and the state is termed 2 P. But because of spin-orbit coupling it is actually split into 2 P 1 / 2 and 2 P 3 ⁄ 2 with energy 35,669 and 35,761 cm −1 . [ 1 ] In comparison the ionic molecule has a ground state called 2 Σ + . The corresponding excited state is significantly split into two depending on whether the p orbital of the magnesium is pointing to the argon or is perpendicular. When the electron in the p orbital is perpendicular to the Mg-Ar axis, the argon sees a greater electrostatic force from the magnesium atom and is more tightly bound. This lowers the energy level of what is called the 2 Π level. This too is split into 2 Π 1 / 2 and 2 Π 3 ⁄ 2 . When the excited electron is in line with the argon the state is called 2 Σ + and corresponds only to 2 P 3 ⁄ 2 and so is not split. [ 1 ]
The MgAr + spectrum shows bands, with the first one at 31,396 cm −1 , which is redshifted 4300 cm −1 from Mg + . The band is blue degraded. The band consists of a series of doublets. The two lines in the doublet are separated by 75 cm −1 , and from one pair to the next one is 270 cm −1 . This band is due to A 2 Π ← X 2 Σ + . [ 1 ]
In the ground state the binding energy or MgAr + is 1281 cm −1 and in the A 2 Π 1 / 2 state is 5554 cm −1 (3.66 kcal/mol). [ 1 ] The A 2 Π 1 / 2 state has a stronger bond because a p electron overlaps the argon atom less, and thus has less repulsion. [ 2 ] The dissociation energy of the ground state ion is 1295 cm −1 (15 kJ/mol). [ 3 ]
The bond length is 2.854 Å for the ground state, and 2.406 Å for the excited state. The 2 Π state is predicted to have a radiative lifetime of about 6 nanoseconds. [ 2 ]
Unionized MgAr (magnesium argon) can also exist as a van der Waals molecule or temporarily in an excited state termed a Rydberg molecule . [ 4 ] The neutral molecule can be formed by evaporating magnesium metal using a laser into argon gas, and then expanding it through a supersonic jet. [ 5 ] When evaporated many magnesium atoms are excited into a 3s3p state (from the ground 3s3s). These can then attach an argon atom by way of a three body collision to yield Mg(3s3pπ 3 P J )Ar 3 Π. Then this excited state can lose energy via collisions to form Mg(3s3pπ 3 P J )Ar 3 Π 0+,0− . [ 6 ] MgAr is mainly held together with dispersion forces which vary as the inverse sixth power of the separation. The ground state MgAr has electron configuration Mg(3s3s 1 S 0 )Ar 1 Σ + . [ 7 ] The triplet states with one excited electron include Mg(3s3pπ 3 P 0 )Ar 3 Π 0+ , Mg(3s4s 3 S 1 )Ar 3 Σ + , Mg(3s3dδ 3 D J )Ar 3 Δ, and Mg(3s4pπ 3 P J )Ar 3 Π 0+ . A singlet single excited electron state is Mg(3s3pπ 1 P)Ar 1 Π. [ 7 ]
The different excited states can be studied by resonance-enhanced two-photon ionization and mass spectroscopy. [ 6 ] The absorption spectrum of MgAr shows bands due to electronic transitions combined with vibrational and rotational transitions. The spectrum involving electronic transition in the argon atom and a change in the d orbital of the magnesium, is very complex with 18 different branches [ 6 ]
A doubly excited state, where two electrons on the magnesium atom are boosted to 3p sub-orbitals, has a strong binding energy, even higher than in MgAr + . [ 5 ] Normally an ion would bond an inert gas atom more strongly, as attraction varies as 1/R 4 , compared to 1/R 6 for a van der Waals molecule, and in an ion, the electron cloud shrinks due to the more positive charge attracting it. However in the doubly excited state both of the magnesium atoms are in p suborbitals, which can be arranged so that electron density is on a line perpendicular to a potential argon atom bond. This allows the two atoms to approach each other closer. [ 8 ]
The neutral molecule has cas number 72052-59-6. [ 9 ]
Under pressures over 250 gigapascals , MgAr is predicted to be stable as a solid with either an anti-NiAs or CsCl structure dependent on pressure. Mg 2 Ar is predicted to be a stable solid with localized electrons in the structure, making it an electride . [ 10 ] These pressures are higher than found in the Earth's mantle, but magnesium argides could form minerals in super-Earths .
MgAr + can interfere with determination of copper or zinc isotopes when using inductively coupled plasma mass spectrometry , particularly when using a desolvated plasma. When analysing mineral specimens, magnesium is a common element found in rock matrix. It can react with the argon ions present in the plasma. [ 11 ] In analysis of soil, MgAr + interferes with detection of 65 Cu , though common isotopomer has a molecular weight of 64.95 compared to 64.93 for the copper 65 isotope. [ 12 ] This is called isobaric interference. | https://en.wikipedia.org/wiki/MgAr |
The magnesium argide ion, MgAr + is an ion composed of one ionised magnesium atom, Mg + and an argon atom. It is important in inductively coupled plasma mass spectrometry and in the study of the field around the magnesium ion. [ 1 ] The ionization potential of magnesium is lower than the first excitation state of argon, so the positive charge in MgAr + will reside on the magnesium atom. Neutral MgAr molecules can also exist in an excited state .
The spectrum of MgAr + can be observed. It resembles that of Mg + , however some lines are blue shifted and others red shifted. In Mg + the ground state is termed 2 S. A first excited state has a 3s electron moved to the 3p orbital and the state is termed 2 P. But because of spin-orbit coupling it is actually split into 2 P 1 / 2 and 2 P 3 ⁄ 2 with energy 35,669 and 35,761 cm −1 . [ 1 ] In comparison the ionic molecule has a ground state called 2 Σ + . The corresponding excited state is significantly split into two depending on whether the p orbital of the magnesium is pointing to the argon or is perpendicular. When the electron in the p orbital is perpendicular to the Mg-Ar axis, the argon sees a greater electrostatic force from the magnesium atom and is more tightly bound. This lowers the energy level of what is called the 2 Π level. This too is split into 2 Π 1 / 2 and 2 Π 3 ⁄ 2 . When the excited electron is in line with the argon the state is called 2 Σ + and corresponds only to 2 P 3 ⁄ 2 and so is not split. [ 1 ]
The MgAr + spectrum shows bands, with the first one at 31,396 cm −1 , which is redshifted 4300 cm −1 from Mg + . The band is blue degraded. The band consists of a series of doublets. The two lines in the doublet are separated by 75 cm −1 , and from one pair to the next one is 270 cm −1 . This band is due to A 2 Π ← X 2 Σ + . [ 1 ]
In the ground state the binding energy or MgAr + is 1281 cm −1 and in the A 2 Π 1 / 2 state is 5554 cm −1 (3.66 kcal/mol). [ 1 ] The A 2 Π 1 / 2 state has a stronger bond because a p electron overlaps the argon atom less, and thus has less repulsion. [ 2 ] The dissociation energy of the ground state ion is 1295 cm −1 (15 kJ/mol). [ 3 ]
The bond length is 2.854 Å for the ground state, and 2.406 Å for the excited state. The 2 Π state is predicted to have a radiative lifetime of about 6 nanoseconds. [ 2 ]
Unionized MgAr (magnesium argon) can also exist as a van der Waals molecule or temporarily in an excited state termed a Rydberg molecule . [ 4 ] The neutral molecule can be formed by evaporating magnesium metal using a laser into argon gas, and then expanding it through a supersonic jet. [ 5 ] When evaporated many magnesium atoms are excited into a 3s3p state (from the ground 3s3s). These can then attach an argon atom by way of a three body collision to yield Mg(3s3pπ 3 P J )Ar 3 Π. Then this excited state can lose energy via collisions to form Mg(3s3pπ 3 P J )Ar 3 Π 0+,0− . [ 6 ] MgAr is mainly held together with dispersion forces which vary as the inverse sixth power of the separation. The ground state MgAr has electron configuration Mg(3s3s 1 S 0 )Ar 1 Σ + . [ 7 ] The triplet states with one excited electron include Mg(3s3pπ 3 P 0 )Ar 3 Π 0+ , Mg(3s4s 3 S 1 )Ar 3 Σ + , Mg(3s3dδ 3 D J )Ar 3 Δ, and Mg(3s4pπ 3 P J )Ar 3 Π 0+ . A singlet single excited electron state is Mg(3s3pπ 1 P)Ar 1 Π. [ 7 ]
The different excited states can be studied by resonance-enhanced two-photon ionization and mass spectroscopy. [ 6 ] The absorption spectrum of MgAr shows bands due to electronic transitions combined with vibrational and rotational transitions. The spectrum involving electronic transition in the argon atom and a change in the d orbital of the magnesium, is very complex with 18 different branches [ 6 ]
A doubly excited state, where two electrons on the magnesium atom are boosted to 3p sub-orbitals, has a strong binding energy, even higher than in MgAr + . [ 5 ] Normally an ion would bond an inert gas atom more strongly, as attraction varies as 1/R 4 , compared to 1/R 6 for a van der Waals molecule, and in an ion, the electron cloud shrinks due to the more positive charge attracting it. However in the doubly excited state both of the magnesium atoms are in p suborbitals, which can be arranged so that electron density is on a line perpendicular to a potential argon atom bond. This allows the two atoms to approach each other closer. [ 8 ]
The neutral molecule has cas number 72052-59-6. [ 9 ]
Under pressures over 250 gigapascals , MgAr is predicted to be stable as a solid with either an anti-NiAs or CsCl structure dependent on pressure. Mg 2 Ar is predicted to be a stable solid with localized electrons in the structure, making it an electride . [ 10 ] These pressures are higher than found in the Earth's mantle, but magnesium argides could form minerals in super-Earths .
MgAr + can interfere with determination of copper or zinc isotopes when using inductively coupled plasma mass spectrometry , particularly when using a desolvated plasma. When analysing mineral specimens, magnesium is a common element found in rock matrix. It can react with the argon ions present in the plasma. [ 11 ] In analysis of soil, MgAr + interferes with detection of 65 Cu , though common isotopomer has a molecular weight of 64.95 compared to 64.93 for the copper 65 isotope. [ 12 ] This is called isobaric interference. | https://en.wikipedia.org/wiki/MgAr+ |
Magnesium bromide are inorganic compounds with the chemical formula MgBr 2 (H 2 O) x , where x can range from 0 to 9. They are all white deliquescent solids. Some magnesium bromides have been found naturally as rare minerals such as: bischofite and carnallite . [ 2 ] [ 3 ]
Magnesium bromide can be synthesized by treating magnesium oxide (and related basic salts) with hydrobromic acid . [ 3 ] It can also be made by reacting magnesium carbonate and hydrobromic acids, and collecting the solid left after evaporation. [ 2 ]
As suggested by its easy conversion to various hydrates , anhydrous MgBr 2 is a Lewis acid . In the coordination polymer with the formula MgBr 2 (dioxane) 2 , Mg 2+ adopts an octahedral geometry. [ 4 ]
Magnesium bromide is used as a Lewis acid catalyst in some organic synthesis , e.g., in aldol reaction . [ 5 ]
Magnesium bromide also has been used as a tranquilizer [ 2 ] and as an anticonvulsant for treatment of nervous disorders. [ 6 ]
Magnesium bromide modifies the catalytic properties of palladium on charcoal . [ 7 ]
Magnesium bromide hexahydrate has properties as a flame retardant. [ 8 ]
Treatment of magnesium bromide with chlorine gives magnesium chloride. This reaction is employed in the production of magnesium chloride from brines. [ 9 ]
Two hydrates are known, the hexahydrate and the nonahydrate. Several reports claim a decahydrate, but X-ray crystallography confirmed that it is a nonahydrate. The hydrates feature [Mg(H 2 O) 6 ] 2+ ions.<ref> Hennings, Erik; Schmidt, Horst; Voigt, Wolfgang (2013). "Crystal Structures of Hydrates of Simple Inorganic Salts. I. Water-Rich Magnesium Halide Hydrates MgCl 2 ·8H 2 O, MgCl 2 ·12H 2 O, MgBr 2 ·6H 2 O, MgBr 2 ·9H 2 O, MgI 2 ·8H 2 O and MgI 2 ·9H 2 O". Acta Crystallographica Section C Crystal Structure Communications . 69 (11): 1292– 1300. doi : 10.1107/S0108270113028138 . PMID 24192174 . </ref it can also cause violently convulsing and potential release of bowels | https://en.wikipedia.org/wiki/MgBr2 |
Magnesium oxalate is an organic compound comprising a magnesium cation with a 2+ charge bonded to an oxalate anion . It has the chemical formula MgC 2 O 4 . Magnesium oxalate is a white solid that comes in two forms: an anhydrous form and a dihydrate form where two water molecules are complexed with the structure. Both forms are practically insoluble in water and are insoluble in organic solutions.
Magnesium oxalate has been found naturally near Mill of Johnston, which is located close to Insch in northeast Scotland. This naturally occurring magnesium oxalate is called glushinskite and occurs at the lichen /rock interface on serpentinite as a creamy white layer mixed in with the hyphae of the lichen fungus. A scanning electron micrograph of samples taken showed that the crystals had a pyramidal structure with both curved and striated faces. The size of these crystals ranged from 2 to 5 μm. [ 9 ]
Magnesium oxalate can by synthesized by combining a magnesium salt or ion with an oxalate.
A specific example of a synthesis would be mixing Mg(NO 3 ) 2 and KOH and then adding that solution to dimethyl oxalate , (COOCH 3 ) 2 . [ 10 ]
When heated, magnesium oxalate will decompose. First, the dihydrate will decompose at 150 °C into the anhydrous form.
With additional heating the anhydrous form will decompose further into magnesium oxide and carbon oxides between 420 °C and 620 °C. First, carbon monoxide and magnesium carbonate form. The carbon monoxide then oxidizes to carbon dioxide , and the magnesium carbonate decomposes further to magnesium oxide and carbon dioxide. [ 8 ]
Magnesium oxalate dihydrate has also been used in the synthesis of nano sized particles of magnesium oxide, which have larger surface are to volume ratio than conventionally synthesized particles and are optimal for various applications, such as in catalysis . By using a sol-gel synthesis , which involves combining a magnesium salt, in this case magnesium oxalate, with a gelating agent, nano sized particles of magnesium oxide can be produced. [ 11 ]
Magnesium oxalate is a skin and eye irritant. If inhaled, it will irritate the lungs and mucous membranes . Magnesium oxalate has no known chronic effects nor any carcinogenic effects. Magnesium oxalate is non-flammable and stable, but in fire conditions it will give off toxic fumes. According to OSHA, magnesium oxalate is considered to be hazardous. [ 4 ] [ 12 ] | https://en.wikipedia.org/wiki/MgC2O4 |
Magnesium malate , the magnesium salt of malic acid , is a mineral supplement often used for nutritional concerns. It is represented by the chemical formula C4H4MgO5 [ 1 ] and has a molecular weight of 156.376 g/mol. Magnesium malate is discussed as being a more bioavailable form of magnesium, along with other forms such as citrate and glycinate . [ 2 ]
This drug article relating to the gastrointestinal system is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/MgC4H4O5 |
Magnesium carbonate , Mg CO 3 (archaic name magnesia alba ), is an inorganic salt that is a colourless or white solid. Several hydrated and basic forms of magnesium carbonate also exist as minerals .
The most common magnesium carbonate forms are the anhydrous salt called magnesite ( MgCO 3 ), and the di, tri, and pentahydrates known as barringtonite ( MgCO 3 ·2H 2 O ), nesquehonite ( MgCO 3 ·3H 2 O ), and lansfordite ( MgCO 3 ·5H 2 O ), respectively. [ 6 ] Some basic forms such as artinite ( Mg 2 CO 3 (OH) 2 ·3H 2 O ), hydromagnesite ( Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O ), and dypingite ( Mg 5 (CO 3 ) 4 (OH) 2 ·5H 2 O ) also occur as minerals . All of those minerals are colourless or white.
Magnesite consists of colourless or white trigonal crystals . The anhydrous salt is practically insoluble in water , acetone , and ammonia . All forms of magnesium carbonate react with acids . Magnesite crystallizes in the calcite structure wherein Mg 2+ is surrounded by six oxygen atoms. [ 3 ]
The dihydrate has a triclinic structure, while the trihydrate has a monoclinic structure.
References to "light" and "heavy" magnesium carbonates actually refer to the magnesium hydroxy carbonates hydromagnesite and dypingite , respectively. [ 7 ] The "light" form is precipitated from magnesium solutions using alkali carbonate at "normal temperatures" while the "heavy" may be produced from boiling concentrated solutions followed by precipitation to dryness, washing of the precipitate, and drying at 100 C. [ 8 ]
Magnesium carbonate is ordinarily obtained by mining the mineral magnesite . Seventy percent of the world's supply is mined and prepared in China. [ 9 ]
Magnesium carbonate can be prepared in laboratory by reaction between any soluble magnesium salt and sodium bicarbonate :
If magnesium chloride (or sulfate) is treated with aqueous sodium carbonate, a precipitate of basic magnesium carbonate – a hydrated complex of magnesium carbonate and magnesium hydroxide – rather than magnesium carbonate itself is formed:
High purity industrial routes include a path through magnesium bicarbonate , which can be formed by combining a slurry of magnesium hydroxide and carbon dioxide at high pressure and moderate temperature. [ 6 ] The bicarbonate is then vacuum dried, causing it to lose carbon dioxide and a molecule of water:
Like many common group 2 metal carbonates, magnesium carbonate reacts with aqueous acids to release carbon dioxide and water :
At high temperatures MgCO 3 decomposes to magnesium oxide and carbon dioxide . This process is important in the production of magnesium oxide. [ 6 ] This process is called calcining :
The decomposition temperature is given as 350 °C (662 °F). [ 10 ] [ 11 ] However, calcination to the oxide is generally not considered complete below 900 °C due to interfering readsorption of liberated carbon dioxide.
The hydrates of the salts lose water at different temperatures during decomposition. [ 12 ] For example, in the trihydrate MgCO 3 ·3H 2 O , which molecular formula may be written as Mg(HCO 3 )(OH)·2H 2 O , the dehydration steps occur at 157 °C and 179 °C as follows: [ 12 ]
The primary use of magnesium carbonate is the production of magnesium oxide by calcining . Magnesite and dolomite minerals are used to produce refractory bricks . [ 6 ] MgCO 3 is also used in flooring , fireproofing , fire extinguishing compositions , cosmetics , dusting powder , and toothpaste . Other applications are as filler material , smoke suppressant in plastics, a reinforcing agent in neoprene rubber, a drying agent , and colour retention in foods.
Because of its low solubility in water and hygroscopic properties, MgCO 3 was first added to table salt ( NaCl ) in 1911 to make it flow more freely. The Morton Salt company adopted the slogan "When it rains it pours", highlighting that its salt, which contained MgCO 3 , would not stick together in humid weather. [ 13 ]
Powdered magnesium carbonate, known as climbing chalk or gym chalk is also used as a drying agent on athletes' hands in rock climbing , gymnastics , powerlifting, weightlifting and other sports in which a firm grip is necessary. [ 9 ] A variant is liquid chalk .
As a food additive , magnesium carbonate is known as E504. Its only known side effect is that it may work as a laxative in high concentrations. [ 14 ]
Magnesium carbonate is used in taxidermy for whitening skulls. It can be mixed with hydrogen peroxide to create a paste, which is spread on the skull to give it a white finish.
Magnesium carbonate is used as a matte white coating for projection screens . [ 15 ]
It is a laxative to loosen the bowels .
In addition, high purity magnesium carbonate is used as an antacid and as an additive in table salt to keep it free flowing. Magnesium carbonate can do this because it does not dissolve in water, only in acid, where it will effervesce (bubble). [ 16 ]
Magnesium carbonate is non-toxic and non-flammable. | https://en.wikipedia.org/wiki/MgCO3 |
Magnesium chloride is an inorganic compound with the formula Mg Cl 2 . It forms hydrates MgCl 2 · n H 2 O , where n can range from 1 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in nature, have a variety of practical uses. Anhydrous magnesium chloride is the principal precursor to magnesium metal, which is produced on a large scale. Hydrated magnesium chloride is the form most readily available. [ 2 ]
Magnesium chloride can be extracted from brine or sea water . In North America and South America, it is obtained primarily from Great Salt Lake brine. In the Jordan Valley , it is obtained from the Dead Sea . The mineral bischofite ( MgCl 2 ·6H 2 O ) is extracted (by solution mining) out of ancient seabeds, for example, the Zechstein seabed in northwest Europe. Some deposits result from high content of magnesium chloride in the primordial ocean. [ 3 ] Some magnesium chloride is made from evaporation of seawater.
In the Dow process , magnesium chloride is regenerated from magnesium hydroxide using hydrochloric acid :
It can also be prepared from magnesium carbonate by a similar reaction.
MgCl 2 crystallizes in the cadmium chloride CdCl 2 motif, therefore it loses water upon heating: n = 12 (−16.4 °C), 8 (−3.4 °C), 6 (116.7 °C), 4 (181 °C), 2 (about 300 °C). [ 4 ] In the hexahydrate, the Mg 2+ is also octahedral , being coordinated to six water ligands . [ 5 ] The octahydrate and the dodecahydrate can be crystallized from water below 298K. As verified by X-ray crystallography , these "higher" hydrates also feature [Mg(H 2 O) 6 ] 2+ ions. [ 6 ] A decahydrate has also been crystallized. [ 7 ]
Anhydrous MgCl 2 is produced industrially by heating the complex salt named hexamminemagnesium dichloride [Mg(NH 3 ) 6 ] 2+ (Cl − ) 2 . [ 2 ] The thermal dehydration of the hydrates MgCl 2 · n H 2 O ( n = 6, 12) does not occur straightforwardly. [ 8 ]
As suggested by the existence of hydrates, anhydrous MgCl 2 is a Lewis acid , although a weak one. One derivative is tetraethylammonium tetrachloromagnesate [N(CH 2 CH 3 ) 4 ] 2 [MgCl 4 ] . The adduct MgCl 2 ( TMEDA ) is another. [ 9 ] In the coordination polymer with the formula MgCl 2 ( dioxane ) 2 , Mg adopts an octahedral geometry. [ 10 ] The Lewis acidity of magnesium chloride is reflected in its deliquescence , meaning that it attracts moisture from the air to the extent that the solid turns into a liquid.
Anhydrous MgCl 2 is the main precursor to metallic magnesium. The reduction of Mg 2+ into metallic Mg is performed by electrolysis in molten salt . [ 2 ] [ 11 ] As it is also the case for aluminium , an electrolysis in aqueous solution is not possible as the produced metallic magnesium would immediately react with water, or in other words that the water H + would be reduced into gaseous H 2 before Mg reduction could occur. So, the direct electrolysis of molten MgCl 2 in the absence of water is required because the reduction potential to obtain Mg is lower than the stability domain of water on an E h –pH diagram ( Pourbaix diagram ).
The production of metallic magnesium at the cathode (reduction reaction) is accompanied by the oxidation of the chloride anions at the anode with release of gaseous chlorine . This process is developed at a large industrial scale.
Magnesium chloride is one of many substances used for dust control, soil stabilization , and wind erosion mitigation. [ 12 ] When magnesium chloride is applied to roads and bare soil areas, both positive and negative performance issues occur which are related to many application factors. [ 13 ]
Ziegler-Natta catalysts , used commercially to produce polyolefins , often contain MgCl 2 as a catalyst support . [ 14 ] The introduction of MgCl 2 supports increases the activity of traditional catalysts and allowed the development of highly stereospecific catalysts for the production of polypropylene . [ 15 ]
Magnesium chloride is also a Lewis acid catalyst in aldol reactions . [ 16 ]
Magnesium chloride is used for low-temperature de-icing of highways , sidewalks , and parking lots . When highways have dangerous ice buildup, road maintainers apply magnesium chloride to deter ice from bonding to the pavement, allowing snow plows to clear treated roads more efficiently.
For the purpose of preventing ice from forming on pavement, magnesium chloride is applied in three ways: anti-icing, which involves spreading it on roads to prevent snow from sticking and forming; prewetting, which means a liquid formulation of magnesium chloride is sprayed directly onto salt as it is being spread onto roadway pavement, wetting the salt so that it sticks to the road; and pretreating, when magnesium chloride and salt are mixed together before they are loaded onto trucks and spread onto paved roads. Calcium chloride damages concrete twice as fast as magnesium chloride. [ 17 ] The amount of magnesium chloride is supposed to be controlled when it is used for de-icing as it may cause pollution to the environment. [ 18 ]
Magnesium chloride is used in nutraceutical and pharmaceutical preparations . The hexahydrate is sometimes advertised as " magnesium oil ". Magnesium Chloride is also an electrolyte .
Magnesium chloride ( E511 [ 19 ] ) is an important coagulant used in the preparation of tofu from soy milk .
In Japan it is sold as nigari ( にがり , derived from the Japanese word for "bitter"), a white powder produced from seawater after the sodium chloride has been removed, and the water evaporated. In China, it is called lushui ( 卤水 ).
Nigari or Iushui is, in fact, natural magnesium chloride, meaning that it is not completely refined (it contains up to 5% magnesium sulfate and various minerals). The crystals originate from lakes in the Chinese province of Qinghai , to be then reworked in Japan.
Because magnesium is a mobile nutrient, magnesium chloride can be effectively used as a substitute for magnesium sulfate (Epsom salt) to help correct magnesium deficiency in plants via foliar feeding . The recommended dose of magnesium chloride is smaller than the recommended dose of magnesium sulfate (20 g/L). [ 20 ] This is due primarily to the chlorine present in magnesium chloride, which can easily reach toxic levels if over-applied or applied too often. [ 21 ]
It has been found that higher concentrations of magnesium in tomato and some pepper plants can make them more susceptible to disease caused by infection of the bacterium Xanthomonas campestris , since magnesium is essential for bacterial growth. [ 22 ]
It is used to supply the magnesium necessary to precipitate phosphorus in the form of struvite from agricultural waste [ 23 ] as well as human urine.
Magnesium concentrations in natural seawater are between 1250 and 1350 mg/L, around 3.7% of the total seawater mineral content. Dead Sea minerals contain a significantly higher magnesium chloride ratio, 50.8%. Carbonates and calcium [ clarification needed ] are essential for all growth of corals , coralline algae , clams , and invertebrates . Magnesium can be depleted by mangrove plants and the use of excessive limewater or by going beyond natural calcium, alkalinity , and pH values. [ 24 ] The most common mineral form of magnesium chloride is its hexahydrate, bischofite. [ 25 ] [ 26 ] Anhydrous compound occurs very rarely, as chloromagnesite. [ 26 ] Magnesium chloride-hydroxides, korshunovskite and nepskoeite, are also very rare. [ 27 ] [ 28 ] [ 26 ]
Magnesium ions are bitter-tasting, and magnesium chloride solutions are bitter in varying degrees, depending on the concentration.
Magnesium toxicity from magnesium salts is rare in healthy individuals with a normal diet, because excess magnesium is readily excreted in urine by the kidneys . A few cases of oral magnesium toxicity have been described in persons with normal renal function ingesting large amounts of magnesium salts, but it is rare. If a large amount of magnesium chloride is eaten, it will have effects similar to magnesium sulfate , causing diarrhea, although the sulfate also contributes to the laxative effect in magnesium sulfate, so the effect from the chloride is not as severe.
Chloride ( Cl − ) and magnesium ( Mg 2+ ) are both essential nutrients important for normal plant growth. Too much of either nutrient may harm a plant, although foliar chloride concentrations are more strongly related with foliar damage than magnesium. High concentrations of MgCl 2 ions in the soil may be toxic or change water relationships such that the plant cannot easily accumulate water and nutrients. Once inside the plant, chloride moves through the water-conducting system and accumulates at the margins of leaves or needles, where dieback occurs first. Leaves are weakened or killed, which can lead to the death of the tree. [ 29 ] | https://en.wikipedia.org/wiki/MgCl2 |
MgCu 2 is a binary intermetallic compound of magnesium (Mg) and copper (Cu) adopting cubic crystal structure , more specifically the C15 Laves phase . The space group of MgCu 2 is Fd 3 m with lattice parameter a = 7.04 Å. [ 2 ]
MgCu 2 can be prepared by hydrogenation of Mg 2 Cu or the reaction of magnesium hydride and metallic copper at elevated temperature and pressure: [ 3 ]
MgCu 2 can also be prepared by reacting of stoichiometric amounts of metals at about 380 °C in the presence of excess copper. [ 4 ]
MgCu 2 can react with boron or its oxide to form magnesium borides . [ 5 ] It can also react with magnesium hydride to produce orthorhombic Mg 2 Cu , liberating hydrogen. [ 6 ] | https://en.wikipedia.org/wiki/MgCu2 |
Magnesium fluoride is an ionically bonded inorganic compound with the formula Mg F 2 . The compound is a colorless to white crystalline salt and is transparent over a wide range of wavelengths , with commercial uses in optics that are also used in space telescopes . It occurs naturally as the rare mineral sellaite .
Magnesium fluoride is prepared from magnesium oxide with sources of hydrogen fluoride such as ammonium bifluoride , by the breakdown of it:
Related metathesis reactions are also feasible:
The compound crystallizes as tetragonal birefringent crystals. The structure of the magnesium fluoride is similar to that of rutile , [ 4 ] [ 5 ] featuring octahedral Mg 2+ cations and 3- coordinate F − anions . [ 6 ]
In the gas phase, monomeric MgF 2 molecules adopt a linear molecular geometry . [ 4 ] [ 5 ]
Magnesium fluoride is transparent over an extremely wide range of wavelengths . Windows, lenses , and prisms made of this material can be used over the entire range of wavelengths from 0.120 μm ( vacuum ultraviolet ) to 8.0 μm ( infrared ). High-quality, synthetic magnesium fluoride is one of two materials (the other being lithium fluoride ) that will transmit in the vacuum ultraviolet range at 121 nm ( Lyman alpha ).
Magnesium fluoride is tough and polishes well but is slightly birefringent and should therefore be cut with the optic axis perpendicular to the plane of the window or lens. [ 6 ] Due to its suitable refractive index of 1.37, magnesium fluoride is commonly applied in thin layers to the surfaces of optical elements as an inexpensive anti-reflective coating . [ citation needed ] Its Verdet constant is 0.00810 arcmin ⋅ G −1 ⋅cm −1 at 632.8 nm. [ 8 ]
Chronic exposure to magnesium fluoride may affect the skeleton, kidneys, central nervous system, respiratory system, eyes and skin, and may cause or aggravate attacks of asthma. [ 9 ] | https://en.wikipedia.org/wiki/MgF2 |
Magnesium monohydride is a molecular gas with formula MgH that exists at high temperatures, such as the atmospheres of the Sun and stars . [ 2 ] It was originally known as magnesium hydride, although that name is now more commonly used when referring to the similar chemical magnesium dihydride .
George Downing Liveing and James Dewar are claimed to be the first to make and observe a spectral line from MgH in 1878. [ 3 ] [ 4 ] However they did not realise what the substance was. [ 5 ]
A laser can evaporate magnesium metal to form atoms that react with molecular hydrogen gas to form MgH and other magnesium hydrides. [ 6 ]
An electric discharge through hydrogen gas at low pressure (20 pascals) containing pieces of magnesium can produce MgH. [ 7 ]
Thermally produced hydrogen atoms and magnesium vapour can react and condense in a solid argon matrix . This process does not work with solid neon, probably due to the formation of MgH 2 instead. [ 8 ]
A simple way to produce some MgH is to burn magnesium in a bunsen burner flame, where there is enough hydrogen to form MgH temporarily. Magnesium arcs in steam also produce MgH, but also produce MgO. [ 5 ]
Natural formation of MgH happens in stars, brown dwarfs , and large planets, where the temperature is high enough. The reaction that produces it is either 2 Mg + H 2 → 2 MgH or Mg + H → MgH. Decomposition is by the reverse process. Formation requires the presence of magnesium gas. The amount of magnesium gas is greatly reduced in cool stars by its extraction in clouds of enstatite , a magnesium silicate. Otherwise in these stars, below any magnesium silicate clouds where the temperature is hotter, the concentration of MgH is proportional to the square root of the pressure, and concentration of magnesium, and 10 −4236/T . MgH is the second most abundant magnesium containing gas (after atomic magnesium) in the deeper hotter parts of planets and brown dwarfs. [ 9 ] [ 10 ]
The reaction of Mg atoms with H 2 (dihydrogen gas) is actually endothermic and proceeds when magnesium atoms are excited electronically. The magnesium atom inserts into the bond between the two hydrogen atoms to create a temporary MgH 2 molecule, which spins rapidly and breaks up into a spinning MgH molecule and a hydrogen atom. [ 11 ] The MgH molecules produced have a bimodal distribution of rotation rates. When Protium is changed for Deuterium in this reaction the distribution of rotations remains unchanged. ( Mg + D 2 or Mg +HD ). The low rotation rate products also have low vibration levels, and so are "cold". [ 12 ]
The far infrared contains the rotational spectrum of MgH ranging from 0.3 to 2 THz. This also contains hyperfine structure. [ 7 ] 24 MgH is predicted to have spectral lines for various rotational transition for the following vibrational levels. [ 13 ]
The infrared vibration rotation bands are in the range 800–2200 cm −1 . [ 14 ] The fundamental vibration mode is at 6.7 μm. [ 15 ] Three isotopes of magnesium and two of hydrogen multiply the band spectra with six isotopomers : 24 MgH 25 MgH 26 MgH 24 MgD 25 MgD 26 MgD. Vibration and rotation frequencies are significantly altered by the different masses of the atoms. [ 14 ]
The visible band spectrum of magnesium hydride was first observed in the 19th century, and was soon confirmed to be due to a combination of magnesium and hydrogen. Whether there was actually a compound was debated due to no solid material being able to be produced. Despite this the term magnesium hydride was used for whatever made the band spectrum. This term was used before magnesium dihydride was discovered. The spectral bands had heads with fluting in the yellow green, green, and blue parts of the visible spectrum. [ 5 ]
The yellow green band of the MgH spectrum is around the wavelength 5622 Å. The blue band is 4845 Å [ 16 ]
The main band of MgH in the visible spectrum is due to electronic transition between the A 2 Π→X 2 Σ + levels combined with transitions in rotational and vibrational state . [ 17 ]
For each electronic transition, there are different bands for changes between the different vibrational states. The transition between vibrational states is represented using parenthesis (n,m), with n and m being numbers. Within each band there are many lines organised into three sets called branches. The P, Q and R branch are distinguished by whether the rotational quantum number increases by one, stays the same or decreases by one. Lines in each branch will have different rotational quantum numbers depending on how fast the molecules are spinning. [ 18 ] For the A 2 Π→X 2 Σ + transition the lowest vibrational level transitions are the most prominent, however the A 2 Π energy level can have a vibration quantum state up to 13. Any higher level and the molecule has too much energy and shakes apart. For each level of vibrational energy there are a number of different rates of rotation that the molecule can sustain. For level 0 the maximum rotational quantum number is 49. Above this rotation rate it would spin so fast it would break apart. Then for subsequently higher vibrational levels from 2 to 13 the number of maximum rotational levels decreasing going through the sequence 47, 44, 42, 39, 36, 33, 30, 27, 23, 19, 15, 11 and 6. [ 19 ]
The B' 2 Σ + →X 2 Σ + system is a transition from a slightly higher electronic state to the ground state. It also has lines in the visible spectrum that are observable in sunspots . The bands are headless. The (0,0) band is weak compared to the (0,3), (0,4), (0,5), (0,6), (0,7), (1,3), (1,4), (1,7), and (1,8) vibrational bands. [ 15 ]
The C 2 Π state has rotational parameters of B = 6.104 cm −1 , D = 0.0003176 cm −1 , A = 3.843 cm −1 , and p = -0.02653 cm −1 . It has an energy level of 41242 cm −1 . [ 20 ]
Another 2 Δ electronic level has energy 42192 cm −1 and rotation parameters B = 6.2861 cm −1 and A = -0.168 cm −1 . [ 20 ]
The ultraviolet has many more bands due to higher energy electronic states. [ 21 ] [ 22 ] [ 23 ]
The UV spectrum contains band heads at 3100 Å due to a vibrational transition (1,0) 2940 Å (2,0) 2720 Å (3,0) 2640 Å (0,1) 2567 Å (1,3). [ 24 ] [ 25 ] [ 26 ] [ 27 ] [ 28 ]
[ 31 ]
The magnesium monohydride molecule is a simple diatomic molecule with a magnesium atom bonded to a hydrogen atom . The distance between hydrogen and magnesium atoms is 1.7297Å. [ 32 ] The ground state of magnesium monohydride is X 2 Σ + . [ 1 ] Due to the simple structure the symmetry point group of the molecule is C ∞v . [ 32 ] The moment of inertia of one molecule is 4.805263×10 −40 g cm 2 . [ 32 ]
The bond has significant covalent character. [ 33 ] The dipole moment is 1.215 Debye . [ 34 ] [ 35 ]
Bulk properties of the MgH gas include enthalpy of formation of 229.79 kJ mol −1 , [ 32 ] entropy 193.20 J K −1 mol −1 [ 32 ] and heat capacity of 29.59 J K −1 mol −1 . [ 32 ]
The dissociation energy of the molecule is 1.33 eV. [ 36 ] Ionization potential is around 7.9 eV with the MgH + ion formed when the molecule loses an electron. [ 37 ]
In noble gas matrices MgH can form two kinds of dimer: HMgMgH and a rhombic shaped (◊) (HMg) 2 in which a dihydrogen molecule bridges the bond between two magnesium atoms. MgH also can form a complex with dihydrogen HMg·H 2 . Photolysis increases reactions which form the dimer. [ 6 ] The energy to break up the dimer HMgMgH into two MgH radicals is 197 kJ/mol. Mg(μ-H 2 )Mg has 63 kJ/mol more energy than HMgMgH. [ 38 ] In theory gas phase HMgMgH can decompose to Mg 2 and H 2 releasing 24 kJ/mol of energy exothermically. [ 38 ] The distance between the magnesium atoms in HMgMgH is calculated to be 2.861 Å. [ 39 ] HMgMgH can be considered a formal base compound for other substances LMgMgL that have a magnesium to magnesium bond. In these magnesium can be considered to be in oxidation state +1 rather than the normal +2. However these sorts of compounds are not made from HMgMgH. [ 40 ] [ 41 ] [ 42 ]
MgH + can be made by protons hitting magnesium, or dihydrogen gas H 2 interacting with singly ionized magnesium atoms ( H 2 + Mg + → MgH + + H ). [ 43 ]
MgH − , [ 44 ] MgH − 3 and MgH − 2 are formed from low pressure hydrogen or ammonia over a magnesium cathode. [ 44 ] The trihydride ion is produced the most, and in a greater proportion when pure hydrogen is used rather than ammonia. The dihydride ion is produced the least of the three. [ 44 ]
HMgO and HMgS have been theoretically investigated. MgOH and MgSH are lower in energy. [ 45 ]
The spectrum of MgH in stars can be used to measure the isotope ratio of magnesium, the temperature, and gravity of the surface of the star. [ 46 ] In hot stars MgH will be mostly disassociated due to the heat breaking the molecules, but it can be detected in cooler G, K and M type stars. [ 47 ] It can also be detected in starspots or sunspots . The MgH spectrum can be used to study the magnetic field and nature of starspots. [ 48 ]
Some MgH spectral lines show up prominently in the second solar spectrum , that is the fractional linear polarization. The lines belong to the Q 1 and Q 2 branches. The MgH absorption lines are immune to the Hanle effect where polarization is reduced in the presence of magnetic fields, such as near sunspots. These same absorption lines do not suffer from the Zeeman effect either. The reason that the Q branch shows up in this way is because Q branch lines are four times more polarizable, and twice as intense as P and R branch lines. These lines that are more polarizable are also less subject to magnetic field effects. [ 49 ] | https://en.wikipedia.org/wiki/MgH |
Magnesium hydride is the chemical compound with the molecular formula MgH 2 . It contains 7.66% by weight of hydrogen and has been studied as a potential hydrogen storage medium. [ 2 ]
For comparison, one cubic meter can contain 45 kg of hydrogen pressurized at 700 atm, 70 kg of liquid hydrogen, or up to 106 kg of hydrogen bound in magnesium hydride. [ 3 ]
Magnesium hydride is also investigated for use in thermobaric weapons and incendiary weapons , standalone or as a mixture with a solid oxidizer; China tested a (non-nuclear) "hydrogen bomb" using the substance. [ 4 ] It can be also used in emulsion explosives as a source of bubbles and additional fuel. [ 5 ] It can be added to improve heat release of aluminized explosive compositions and to improve burn rate of propellants . [ 6 ] [ 7 ]
In 1951 preparation from the elements was first reported involving direct hydrogenation of Mg metal at high pressure and temperature (200 atmospheres, 500 °C) with MgI 2 catalyst: [ 8 ]
Lower temperature production from Mg and H 2 using nanocrystalline Mg produced in ball mills has been investigated. [ 9 ] Other preparations include:
The room temperature form α-MgH 2 has a rutile structure. [ 12 ] There are at least four high pressure forms: γ-MgH 2 with α-PbO 2 structure, [ 13 ] cubic β-MgH 2 with Pa-3 space group , [ 14 ] orthorhombic HP1 with Pbc2 1 space group and orthorhombic HP2 with Pnma space group. [ 15 ] Additionally a non stoichiometric MgH (2-δ) has been characterised, but this appears to exist only for very small particles [ 16 ] (bulk MgH 2 is essentially stoichiometric, as it can only accommodate very low concentrations of H vacancies [ 17 ] ).
The bonding in the rutile form is sometimes described as being partially covalent in nature rather than purely ionic; [ 18 ] charge density determination by synchrotron x-ray diffraction indicates that the magnesium atom is fully ionised and spherical in shape and the hydride ion is elongated. [ 19 ] Molecular forms of magnesium hydride, MgH, MgH 2 , Mg 2 H, Mg 2 H 2 , Mg 2 H 3 , and Mg 2 H 4 molecules identified by their vibrational spectra have been found in matrix isolated samples at below 10 K, formed following laser ablation of magnesium in the presence of hydrogen. [ 20 ] The Mg 2 H 4 molecule has a bridged structure analogous to dimeric aluminium hydride , Al 2 H 6 . [ 20 ]
MgH 2 readily reacts with water to form hydrogen gas:
At 287 °C it decomposes to produce H 2 at 1 bar pressure. [ 21 ] The high temperature required is seen as a limitation in the use of MgH 2 as a reversible hydrogen storage medium: [ 22 ] | https://en.wikipedia.org/wiki/MgH2 |
Magnesium iodide is an inorganic compound with the chemical formula Mg I 2 . It forms various hydrates MgI 2 · x H 2 O . Magnesium iodide is a salt of magnesium and hydrogen iodide . These salts are typical ionic halides , being highly soluble in water.
Magnesium iodide has few commercial uses, but can be used to prepare compounds for organic synthesis .
Magnesium iodide can be prepared from magnesium oxide , magnesium hydroxide , and magnesium carbonate by treatment with hydroiodic acid : [ 3 ]
Magnesium iodide is stable at high heat under a hydrogen atmosphere, but decomposes in air at normal temperatures, turning brown from the release of elemental iodine . When heated in air, it decomposes completely to magnesium oxide. [ 4 ]
Another method to prepare MgI 2 is mixing powdered elemental iodine and magnesium metal . In order to obtain anhydrous MgI 2 , the reaction should be conducted in a strictly anhydrous atmosphere; dry-diethyl ether can be used as a solvent.
Usage of magnesium iodide in the Baylis-Hillman reaction tends to give ( Z )- vinyl compounds. [ 5 ]
Demethylation of certain aromatic methyl ethers can be afforded using magnesium iodide in diethyl ether . [ 6 ]
Two hydrates are known, the octahydrate and the nonahydrate, both verified by X-ray crystallography These hydrates feature [Mg(H 2 O) 6 ] 2+ ions. [ 7 ] | https://en.wikipedia.org/wiki/MgI2 |
Magnesium oxide ( MgO ), or magnesia , is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide ). It has an empirical formula of MgO and consists of a lattice of Mg 2+ ions and O 2− ions held together by ionic bonding . Magnesium hydroxide forms in the presence of water (MgO + H 2 O → Mg(OH) 2 ), but it can be reversed by heating it to remove moisture.
Magnesium oxide was historically known as magnesia alba (literally, the white mineral from Magnesia ), to differentiate it from magnesia nigra , a black mineral containing what is now known as manganese .
While "magnesium oxide" normally refers to MgO, the compound magnesium peroxide MgO 2 is also known. According to evolutionary crystal structure prediction, [ 11 ] MgO 2 is thermodynamically stable at pressures above 116 GPa (gigapascals), and a semiconducting suboxide Mg 3 O 2 is thermodynamically stable above 500 GPa. Because of its stability, MgO is used as a model system for investigating vibrational properties of crystals. [ 12 ]
Pure MgO is not conductive and has a high resistance to electric current at room temperature . The pure powder of MgO has a relative permittivity inbetween 3.2 to 9.9 k {\displaystyle k} with an approximate dielectric loss of tan(δ) > 2.16x10 3 at 1kHz. [ 5 ] [ 6 ] [ 7 ]
Magnesium oxide is produced by the calcination of magnesium carbonate or magnesium hydroxide . The latter is obtained by the treatment of magnesium chloride MgCl 2 solutions, typically seawater, with limewater or milk of lime. [ 13 ]
Calcining at different temperatures produces magnesium oxide of different reactivity. High temperatures 1500 – 2000 °C diminish the available surface area and produces dead-burned (often called dead burnt) magnesia, an unreactive form used as a refractory . Calcining temperatures 1000 – 1500 °C produce hard-burned magnesia, which has limited reactivity and calcining at lower temperature, (700–1000 °C) produces light-burned magnesia, a reactive form, also known as caustic calcined magnesia. Although some decomposition of the carbonate to oxide occurs at temperatures below 700 °C, the resulting materials appear to reabsorb carbon dioxide from the air. [ citation needed ]
MgO is prized as a refractory material , i.e. a solid that is physically and chemically stable at high temperatures. It has the useful attributes of high thermal conductivity and low electrical conductivity. According to a 2006 reference book: [ 14 ]
By far the largest consumer of magnesia worldwide is the refractory industry, which consumed about 56% of the magnesia in the United States in 2004, the remaining 44% being used in agricultural, chemical, construction, environmental, and other industrial applications.
MgO is used as a refractory material for crucibles . It is also used as an insulator in heat-resistant electrical cable .
Among metal oxide nanoparticles, magnesium oxide nanoparticles (MgO NPs) have distinct physicochemical and biological properties, including biocompatibility, biodegradability, high bioactivity, significant antibacterial properties, and good mechanical properties, which make it a good choice as a reinforcement in composites. [ 15 ]
It is used extensively as an electrical insulator in tubular construction heating elements as in electric stove and cooktop heating elements. There are several mesh sizes available and most commonly used ones are 40 and 80 mesh per the American Foundry Society . The extensive use is due to its high dielectric strength and average thermal conductivity. MgO is usually crushed and compacted with minimal airgaps or voids.
MgO is one of the components in Portland cement in dry process plants .
Sorel cement uses MgO as the main component in combination with MgCl 2 and water.
MgO has an important place as a commercial plant fertilizer [ 16 ] and as animal feed. [ 17 ]
It is a principal fireproofing ingredient in construction materials. As a construction material, magnesium oxide wallboards have several attractive characteristics: fire resistance, termite resistance, moisture resistance, mold and mildew resistance, and strength, but also a severe downside as it attracts moisture and can cause moisture damage to surrounding materials. [ 18 ] [ 14 ] [1]
Magnesium oxide is used for relief of heartburn and indigestion, as an antacid , magnesium supplement, and as a short-term laxative . It is also used to improve symptoms of indigestion . Side effects of magnesium oxide may include nausea and cramping. [ 19 ] In quantities sufficient to obtain a laxative effect, side effects of long-term use may rarely cause enteroliths to form, resulting in bowel obstruction . [ 20 ]
Magnesium oxide is used extensively in the soil and groundwater remediation , wastewater treatment, drinking water treatment, air emissions treatment, and waste treatment industries for its acid buffering capacity and related effectiveness in stabilizing dissolved heavy metal species. [ according to whom? ]
Many heavy metals species, such as lead and cadmium , are least soluble in water at mildly basic conditions (pH in the range 8–11). Solubility of metals increases their undesired bioavailability and mobility in soil and groundwater. Granular MgO is often blended into metals-contaminating soil or waste material, which is also commonly of a low pH (acidic), in order to drive the pH into the 8–10 range. Metal-hydroxide complexes tend to precipitate out of aqueous solution in the pH range of 8–10.
MgO is packed in bags around transuranic waste in the disposal cells (panels) at the Waste Isolation Pilot Plant , as a CO 2 getter to minimize the complexation of uranium and other actinides by carbonate ions and so to limit the solubility of radionuclides . The use of MgO is preferred over CaO since the resulting hydration product ( Mg(OH) 2 ) is less soluble and releases less hydration heat . Another advantage is to impose a lower pH value (about 10.5) in case of accidental water ingress into the dry salt layers, in contast to the more soluble Ca(OH) 2 which would create a higher pH of 12.5 (strongly alkaline conditions). The Mg 2+ cation being the second most abundant cation in seawater and in rocksalt , the potential release of magnesium ions dissolving in brines intruding the deep geological repository is also expected to minimize the geochemical disruption. [ 21 ]
Magnesia is used in brake linings for its heat conductivity and intermediate hardness. [ 33 ] It helps dissipate heat from friction surfaces, preventing overheating, while minimizing wear on metal components. [ 34 ] Its stability under high temperatures ensures reliable and durable braking performance in automotive and industrial applications. [ 35 ]
In thin film transistors(TFTs) , MgO is often used as a dielectric material or an insulator due to its high thermal stability, excellent insulating properties, and wide bandgap . [ 36 ] Optimized IGZO/MgO TFTs demonstrated an electron mobility of 1.63 cm²/Vs, an on/off current ratio of 10⁶, and a subthreshold swing of 0.50 V/decade at −0.11 V. [ 37 ] These TFTs are integral to low-power applications, wearable devices, and radiation-hardened electronics, contributing to enhanced efficiency and durability across diverse domains. [ 38 ] [ 39 ]
Inhalation of magnesium oxide fumes can cause metal fume fever . [ 41 ] | https://en.wikipedia.org/wiki/MgO |
Magnesium sulfate or magnesium sulphate is a chemical compound , a salt with the formula MgSO 4 , consisting of magnesium cations Mg 2+ (20.19% by mass) and sulfate anions SO 2− 4 . It is a white crystalline solid , soluble in water but not in ethanol .
Magnesium sulfate is usually encountered in the form of a hydrate MgSO 4 · n H 2 O , for various values of n between 1 and 11. The most common is the heptahydrate MgSO 4 ·7H 2 O , [ 1 ] known as Epsom salt , which is a household chemical with many traditional uses, including bath salts . [ 2 ]
The main use of magnesium sulfate is in agriculture, to correct soils deficient in magnesium (an essential plant nutrient because of the role of magnesium in chlorophyll and photosynthesis ). The monohydrate is favored for this use; by the mid 1970s, its production was 2.3 million tons per year. [ 3 ] The anhydrous form and several hydrates occur in nature as minerals , and the salt is a significant component of the water from some springs .
Magnesium sulfate can crystallize as several hydrates , including:
As of 2017, the existence of the decahydrate apparently has not been confirmed. [ 9 ]
All the hydrates lose water upon heating. Above 320 °C, only the anhydrous form is stable. It decomposes without melting at 1124 °C into magnesium oxide (MgO) and sulfur trioxide ( SO 3 ).
The heptahydrate takes its common name "Epsom salt" from a bitter saline spring in Epsom in Surrey , England, where the salt was produced from the springs that arise where the porous chalk of the North Downs meets the impervious London clay .
The heptahydrate readily loses one equivalent of water to form the hexahydrate.
It is a natural source of both magnesium and sulphur . Epsom salts are commonly used in bath salts , exfoliants , muscle relaxers and pain relievers. However, these are different from Epsom salts that are used for gardening, as they may contain aromas and perfumes not suitable for plants. [ 10 ]
Magnesium sulfate monohydrate, or kieserite, can be prepared by heating the heptahydrate to 120 °C. [ 11 ] Further heating to 250 °C gives anhydrous magnesium sulfate. [ 11 ] Kieserite exhibits monoclinic symmetry at pressures lower than 2.7 GPa after which it transforms to phase of triclinic symmetry. [ 6 ]
The undecahydrate MgSO 4 ·11H 2 O , meridianiite , is stable at atmospheric pressure only below 2 °C. Above that temperature, it liquefies into a mix of solid heptahydrate and a saturated solution . It has a eutectic point with water at −3.9 °C and 17.3% (mass) of MgSO 4 . [ 7 ] Large crystals can be obtained from solutions of the proper concentration kept at 0 °C for a few days. [ 7 ]
At pressures of about 0.9 GPa and at 240 K , meridianiite decomposes into a mixture of ice VI and the enneahydrate MgSO 4 ·9H 2 O . [ 9 ]
The enneahydrate MgSO 4 ·9H 2 O was identified and characterized only recently, even though it seems easy to produce (by cooling a solution of MgSO 4 and sodium sulfate Na 2 SO 4 in suitable proportions).
The structure is monoclinic, with unit-cell parameters at 250 K: a = 0.675 nm , b = 1.195 nm, c = 1.465 nm, β = 95.1°, V = 1.177 nm 3 with Z = 4. The most probable space group is P21/c. Magnesium selenate also forms an enneahydrate MgSeO 4 ·9H 2 O , but with a different crystal structure. [ 9 ]
As Mg 2+ and SO 2− 4 ions are respectively the second most abundant cation and anion present in seawater after Na + and Cl − , magnesium sulfates are common minerals in geological environments. Their occurrence is mostly connected with supergene processes. Some of them are also important constituents of evaporitic potassium -magnesium (K-Mg) salts deposits.
Bright spots observed by the Dawn Spacecraft in Occator Crater on the dwarf planet Ceres are most consistent with reflected light from magnesium sulfate hexahydrate. [ 12 ]
Almost all known mineralogical forms of MgSO 4 are hydrates. Epsomite is the natural analogue of "Epsom salt". Meridianiite , MgSO 4 ·11H 2 O , has been observed on the surface of frozen lakes and is thought to also occur on Mars. Hexahydrite is the next lower hydrate. Three next lower hydrates – pentahydrite , starkeyite , and especially sanderite – are rare. Kieserite is a monohydrate and is common among evaporitic deposits. Anhydrous magnesium sulfate was reported from some burning coal dumps .
Magnesium sulfate is usually obtained directly from dry lake beds and other natural sources. It can also be prepared by reacting magnesite ( magnesium carbonate , MgCO 3 ) or magnesia ( oxide , MgO) with sulfuric acid ( H 2 SO 4 ):
Another possible method is to treat seawater or magnesium-containing industrial wastes so as to precipitate magnesium hydroxide and react the precipitate with sulfuric acid .
Also, magnesium sulfate heptahydrate ( epsomite , MgSO 4 ·7H 2 O ) is manufactured by dissolution of magnesium sulfate monohydrate ( kieserite , MgSO 4 ·H 2 O ) in water and subsequent crystallization of the heptahydrate.
Magnesium sulfate relaxation is the primary mechanism that causes the absorption of sound in seawater at frequencies above 10 kHz [ 13 ] ( acoustic energy is converted to thermal energy ). Lower frequencies are less absorbed by the salt, so that low frequency sound travels farther in the ocean. Boric acid and magnesium carbonate also contribute to absorption. [ 14 ]
Magnesium sulfate is used both externally (as epsom salt) and internally.
The main external use is the formulation as bath salts , especially for foot baths to soothe sore feet. Such baths have been claimed to also soothe and hasten recovery from muscle pain, soreness, or injury. [ 15 ] Health effects of magnesium sulfate that have been proposed include resistant depression [ 16 ] and as an analgesic for migraine and chronic pain . [ 17 ] Magnesium sulfate has also been studied in the treatment of asthma , [ 18 ] preeclampsia , and eclampsia . [ 19 ]
Magnesium sulfate is usually the main component of the concentrated salt solution used in isolation tanks to increase its specific gravity to approximately 1.25–1.26. This high density allows an individual to float effortlessly on the surface of water in the closed tank, eliminating stimulation of as many of the external senses as possible.
In the UK , a medication containing magnesium sulfate and phenol , called "drawing paste", is useful for small boils or localized infections [ 20 ] and removing splinters. [ 21 ]
Internally, magnesium sulfate may be administered by oral, respiratory, or intravenous routes. Internal uses include replacement therapy for magnesium deficiency , [ 22 ] treatment of acute and severe arrhythmias , [ 23 ] as a bronchodilator in the treatment of asthma , [ 24 ] preventing eclampsia [ 25 ] and cerebral palsy , [ 26 ] [ 27 ] a tocolytic agent, [ 28 ] and as an anticonvulsant . [ 28 ] The effectiveness and safety of magnesium sulfate for treating acute bronchiolitis in children under the age of 2 years old is not well understood. [ 29 ]
It also may be used as laxative . [ 30 ]
In agriculture , magnesium sulfate is used to increase magnesium or sulfur content in soil . It is most commonly applied to potted plants, or to magnesium-hungry crops such as potatoes , tomatoes , carrots , peppers , lemons , and roses . The advantage of magnesium sulfate over other magnesium soil amendments (such as dolomitic lime ) is its high solubility , which also allows the option of foliar feeding . Solutions of magnesium sulfate are also nearly pH neutral, compared with the slightly alkaline salts of magnesium as found in limestone ; therefore, the use of magnesium sulfate as a magnesium source for soil does not significantly change the soil pH . [ 28 ] Contrary to the popular belief that magnesium sulfate is able to control pests and slugs, helps seeds germination, produce more flowers, improve nutrient uptake, and is environmentally friendly, it does none of the purported claims except for correcting magnesium deficiency in soils. Magnesium sulfate can even pollute water if used in excessive amounts. [ 31 ]
Magnesium sulfate was historically used as a treatment for lead poisoning prior to the development of chelation therapy , as it was hoped that any lead ingested would be precipitated out by the magnesium sulfate and subsequently purged from the digestive system . [ 32 ] This application saw particularly widespread use among veterinarians during the early-to-mid 20th century; Epsom salt was already available on many farms for agricultural use, and it was often prescribed in the treatment of farm animals that had inadvertently ingested lead. [ 33 ] [ 34 ]
Magnesium sulfate is used as:
Anhydrous magnesium sulfate is commonly used as a desiccant in organic synthesis owing to its affinity for water and compatibility with most organic compounds. During work-up , an organic phase is treated with anhydrous magnesium sulfate. The hydrated solid is then removed by filtration , decantation , or by distillation (if the boiling point is low enough). Other inorganic sulfate salts such as sodium sulfate and calcium sulfate may be used in the same way.
Magnesium sulfate is used to prepare specific cements by the reaction between magnesium oxide and magnesium sulfate solution, which are of good binding ability and more resistance than Portland cement . This cement is mainly utilized in the production of lightweight insulation panels, although its poor water resistance limits its usage.
Magnesium (or sodium) sulfate is also used for testing aggregates for soundness in accordance with ASTM C88 standard, when there are no service records of the material exposed to actual weathering conditions. The test is accomplished by repeated immersion in saturated solutions followed by oven drying to dehydrate the salt precipitated in permeable pore spaces . The internal expansive force, derived from the rehydration of the salt upon re-immersion, simulates the expansion of water on freezing .
Magnesium sulfate is also used to test the resistance of concrete to external sulfate attack (ESA).
Magnesium sulfate heptahydrate is also used to maintain the magnesium concentration in marine aquaria which contain large amounts of stony corals , as it is slowly depleted in their calcification process. In a magnesium-deficient marine aquarium, calcium and alkalinity concentrations are very difficult to control because not enough magnesium is present to stabilize these ions in the saltwater and prevent their spontaneous precipitation into calcium carbonate . [ 39 ]
Double salts containing magnesium sulfate exist. There are several known as sodium magnesium sulfates and potassium magnesium sulfates . A mixed copper -magnesium sulfate heptahydrate (Mg,Cu)SO 4 ·7H 2 O was found to occur in mine tailings and was given the mineral name alpersite . [ 40 ] | https://en.wikipedia.org/wiki/MgO4S |
Magnesium polonide (MgPo) is a salt of magnesium and polonium . It is a polonide , a set of very chemically stable compounds of polonium. [ 3 ]
Magnesium polonide can be produced by heating a mixture of elemental magnesium and polonium at 300–400 °C. [ 1 ]
Magnesium polonide has the nickeline (NiAs) structure. [ 1 ] [ 3 ] It is unusual among polonides in not being isomorphous with the corresponding sulfide , selenide and telluride ; only mercury polonide (HgPo) shares this property. [ 2 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/MgPo |
Magnesium sulfide is an inorganic compound with the formula Mg S . It is a white crystalline material but often is encountered in an impure form that is brown and non-crystalline powder. It is generated industrially in the production of metallic iron.
MgS is formed by the reaction of sulfur or hydrogen sulfide with magnesium . It crystallizes in the rock salt structure as its most stable phase, its zinc blende [ 1 ] and wurtzite [ 2 ] structures can be prepared by molecular beam epitaxy . The chemical properties of MgS resemble those of related ionic sulfides such as those of sodium, barium, or calcium. It reacts with oxygen to form the corresponding sulfate, magnesium sulfate . MgS reacts with water to give hydrogen sulfide and magnesium hydroxide . [ 3 ]
In the BOS steelmaking process, sulfur is the first element to be removed. Sulfur is removed from the impure blast furnace iron by the addition of several hundred kilograms of magnesium powder by a lance. Magnesium sulfide is formed, which then floats on the molten iron and is removed. [ 4 ]
MgS is a wide band-gap direct semiconductor of interest as a blue-green emitter , a property that has been known since the early 1900s. [ 5 ] The wide-band gap property also allows the use of MgS as photo-detector for short wavelength ultraviolet light. [ 6 ]
Aside from being a component of some slags , MgS is a rare nonterrestrial mineral niningerite detected in some meteorites . It is also a solid solution component along with CaS and FeS in oldhamite . MgS is also found in the circumstellar envelopes of certain evolved carbon stars , i. e., those with C/O > 1. [ 7 ]
MgS evolves hydrogen sulfide upon contact with moisture. | https://en.wikipedia.org/wiki/MgS |
Magnesium sulfite is the magnesium salt of sulfurous acid with the formula MgSO 3 . Its most common hydrated form has 6 water molecules making it a hexahydrate , MgSO 3 ·6 H 2 O . When heated above 40 °C (104 °F), it is dehydrated to magnesium sulfite trihydrate , or MgSO 3 ·3 H 2 O . [ 1 ] The anhydrous form is hygroscopic , meaning that it readily absorbs water from the air.
Solubility tables of MgSO 3 hydrates PDF: [ 2 ] | https://en.wikipedia.org/wiki/MgSO3 |
Magnesium sulfate or magnesium sulphate is a chemical compound , a salt with the formula MgSO 4 , consisting of magnesium cations Mg 2+ (20.19% by mass) and sulfate anions SO 2− 4 . It is a white crystalline solid , soluble in water but not in ethanol .
Magnesium sulfate is usually encountered in the form of a hydrate MgSO 4 · n H 2 O , for various values of n between 1 and 11. The most common is the heptahydrate MgSO 4 ·7H 2 O , [ 1 ] known as Epsom salt , which is a household chemical with many traditional uses, including bath salts . [ 2 ]
The main use of magnesium sulfate is in agriculture, to correct soils deficient in magnesium (an essential plant nutrient because of the role of magnesium in chlorophyll and photosynthesis ). The monohydrate is favored for this use; by the mid 1970s, its production was 2.3 million tons per year. [ 3 ] The anhydrous form and several hydrates occur in nature as minerals , and the salt is a significant component of the water from some springs .
Magnesium sulfate can crystallize as several hydrates , including:
As of 2017, the existence of the decahydrate apparently has not been confirmed. [ 9 ]
All the hydrates lose water upon heating. Above 320 °C, only the anhydrous form is stable. It decomposes without melting at 1124 °C into magnesium oxide (MgO) and sulfur trioxide ( SO 3 ).
The heptahydrate takes its common name "Epsom salt" from a bitter saline spring in Epsom in Surrey , England, where the salt was produced from the springs that arise where the porous chalk of the North Downs meets the impervious London clay .
The heptahydrate readily loses one equivalent of water to form the hexahydrate.
It is a natural source of both magnesium and sulphur . Epsom salts are commonly used in bath salts , exfoliants , muscle relaxers and pain relievers. However, these are different from Epsom salts that are used for gardening, as they may contain aromas and perfumes not suitable for plants. [ 10 ]
Magnesium sulfate monohydrate, or kieserite, can be prepared by heating the heptahydrate to 120 °C. [ 11 ] Further heating to 250 °C gives anhydrous magnesium sulfate. [ 11 ] Kieserite exhibits monoclinic symmetry at pressures lower than 2.7 GPa after which it transforms to phase of triclinic symmetry. [ 6 ]
The undecahydrate MgSO 4 ·11H 2 O , meridianiite , is stable at atmospheric pressure only below 2 °C. Above that temperature, it liquefies into a mix of solid heptahydrate and a saturated solution . It has a eutectic point with water at −3.9 °C and 17.3% (mass) of MgSO 4 . [ 7 ] Large crystals can be obtained from solutions of the proper concentration kept at 0 °C for a few days. [ 7 ]
At pressures of about 0.9 GPa and at 240 K , meridianiite decomposes into a mixture of ice VI and the enneahydrate MgSO 4 ·9H 2 O . [ 9 ]
The enneahydrate MgSO 4 ·9H 2 O was identified and characterized only recently, even though it seems easy to produce (by cooling a solution of MgSO 4 and sodium sulfate Na 2 SO 4 in suitable proportions).
The structure is monoclinic, with unit-cell parameters at 250 K: a = 0.675 nm , b = 1.195 nm, c = 1.465 nm, β = 95.1°, V = 1.177 nm 3 with Z = 4. The most probable space group is P21/c. Magnesium selenate also forms an enneahydrate MgSeO 4 ·9H 2 O , but with a different crystal structure. [ 9 ]
As Mg 2+ and SO 2− 4 ions are respectively the second most abundant cation and anion present in seawater after Na + and Cl − , magnesium sulfates are common minerals in geological environments. Their occurrence is mostly connected with supergene processes. Some of them are also important constituents of evaporitic potassium -magnesium (K-Mg) salts deposits.
Bright spots observed by the Dawn Spacecraft in Occator Crater on the dwarf planet Ceres are most consistent with reflected light from magnesium sulfate hexahydrate. [ 12 ]
Almost all known mineralogical forms of MgSO 4 are hydrates. Epsomite is the natural analogue of "Epsom salt". Meridianiite , MgSO 4 ·11H 2 O , has been observed on the surface of frozen lakes and is thought to also occur on Mars. Hexahydrite is the next lower hydrate. Three next lower hydrates – pentahydrite , starkeyite , and especially sanderite – are rare. Kieserite is a monohydrate and is common among evaporitic deposits. Anhydrous magnesium sulfate was reported from some burning coal dumps .
Magnesium sulfate is usually obtained directly from dry lake beds and other natural sources. It can also be prepared by reacting magnesite ( magnesium carbonate , MgCO 3 ) or magnesia ( oxide , MgO) with sulfuric acid ( H 2 SO 4 ):
Another possible method is to treat seawater or magnesium-containing industrial wastes so as to precipitate magnesium hydroxide and react the precipitate with sulfuric acid .
Also, magnesium sulfate heptahydrate ( epsomite , MgSO 4 ·7H 2 O ) is manufactured by dissolution of magnesium sulfate monohydrate ( kieserite , MgSO 4 ·H 2 O ) in water and subsequent crystallization of the heptahydrate.
Magnesium sulfate relaxation is the primary mechanism that causes the absorption of sound in seawater at frequencies above 10 kHz [ 13 ] ( acoustic energy is converted to thermal energy ). Lower frequencies are less absorbed by the salt, so that low frequency sound travels farther in the ocean. Boric acid and magnesium carbonate also contribute to absorption. [ 14 ]
Magnesium sulfate is used both externally (as epsom salt) and internally.
The main external use is the formulation as bath salts , especially for foot baths to soothe sore feet. Such baths have been claimed to also soothe and hasten recovery from muscle pain, soreness, or injury. [ 15 ] Health effects of magnesium sulfate that have been proposed include resistant depression [ 16 ] and as an analgesic for migraine and chronic pain . [ 17 ] Magnesium sulfate has also been studied in the treatment of asthma , [ 18 ] preeclampsia , and eclampsia . [ 19 ]
Magnesium sulfate is usually the main component of the concentrated salt solution used in isolation tanks to increase its specific gravity to approximately 1.25–1.26. This high density allows an individual to float effortlessly on the surface of water in the closed tank, eliminating stimulation of as many of the external senses as possible.
In the UK , a medication containing magnesium sulfate and phenol , called "drawing paste", is useful for small boils or localized infections [ 20 ] and removing splinters. [ 21 ]
Internally, magnesium sulfate may be administered by oral, respiratory, or intravenous routes. Internal uses include replacement therapy for magnesium deficiency , [ 22 ] treatment of acute and severe arrhythmias , [ 23 ] as a bronchodilator in the treatment of asthma , [ 24 ] preventing eclampsia [ 25 ] and cerebral palsy , [ 26 ] [ 27 ] a tocolytic agent, [ 28 ] and as an anticonvulsant . [ 28 ] The effectiveness and safety of magnesium sulfate for treating acute bronchiolitis in children under the age of 2 years old is not well understood. [ 29 ]
It also may be used as laxative . [ 30 ]
In agriculture , magnesium sulfate is used to increase magnesium or sulfur content in soil . It is most commonly applied to potted plants, or to magnesium-hungry crops such as potatoes , tomatoes , carrots , peppers , lemons , and roses . The advantage of magnesium sulfate over other magnesium soil amendments (such as dolomitic lime ) is its high solubility , which also allows the option of foliar feeding . Solutions of magnesium sulfate are also nearly pH neutral, compared with the slightly alkaline salts of magnesium as found in limestone ; therefore, the use of magnesium sulfate as a magnesium source for soil does not significantly change the soil pH . [ 28 ] Contrary to the popular belief that magnesium sulfate is able to control pests and slugs, helps seeds germination, produce more flowers, improve nutrient uptake, and is environmentally friendly, it does none of the purported claims except for correcting magnesium deficiency in soils. Magnesium sulfate can even pollute water if used in excessive amounts. [ 31 ]
Magnesium sulfate was historically used as a treatment for lead poisoning prior to the development of chelation therapy , as it was hoped that any lead ingested would be precipitated out by the magnesium sulfate and subsequently purged from the digestive system . [ 32 ] This application saw particularly widespread use among veterinarians during the early-to-mid 20th century; Epsom salt was already available on many farms for agricultural use, and it was often prescribed in the treatment of farm animals that had inadvertently ingested lead. [ 33 ] [ 34 ]
Magnesium sulfate is used as:
Anhydrous magnesium sulfate is commonly used as a desiccant in organic synthesis owing to its affinity for water and compatibility with most organic compounds. During work-up , an organic phase is treated with anhydrous magnesium sulfate. The hydrated solid is then removed by filtration , decantation , or by distillation (if the boiling point is low enough). Other inorganic sulfate salts such as sodium sulfate and calcium sulfate may be used in the same way.
Magnesium sulfate is used to prepare specific cements by the reaction between magnesium oxide and magnesium sulfate solution, which are of good binding ability and more resistance than Portland cement . This cement is mainly utilized in the production of lightweight insulation panels, although its poor water resistance limits its usage.
Magnesium (or sodium) sulfate is also used for testing aggregates for soundness in accordance with ASTM C88 standard, when there are no service records of the material exposed to actual weathering conditions. The test is accomplished by repeated immersion in saturated solutions followed by oven drying to dehydrate the salt precipitated in permeable pore spaces . The internal expansive force, derived from the rehydration of the salt upon re-immersion, simulates the expansion of water on freezing .
Magnesium sulfate is also used to test the resistance of concrete to external sulfate attack (ESA).
Magnesium sulfate heptahydrate is also used to maintain the magnesium concentration in marine aquaria which contain large amounts of stony corals , as it is slowly depleted in their calcification process. In a magnesium-deficient marine aquarium, calcium and alkalinity concentrations are very difficult to control because not enough magnesium is present to stabilize these ions in the saltwater and prevent their spontaneous precipitation into calcium carbonate . [ 39 ]
Double salts containing magnesium sulfate exist. There are several known as sodium magnesium sulfates and potassium magnesium sulfates . A mixed copper -magnesium sulfate heptahydrate (Mg,Cu)SO 4 ·7H 2 O was found to occur in mine tailings and was given the mineral name alpersite . [ 40 ] | https://en.wikipedia.org/wiki/MgSO4 |
Enstatite is a mineral; the magnesium endmember of the pyroxene silicate mineral series enstatite (MgSiO 3 ) – ferrosilite (FeSiO 3 ). The magnesium rich members of the solid solution series are common rock-forming minerals found in igneous and metamorphic rocks. The intermediate composition, (Mg,Fe)SiO 3 , has historically been known as hypersthene , although this name has been formally abandoned and replaced by orthopyroxene. When determined petrographically or chemically the composition is given as relative proportions of enstatite (En) and ferrosilite (Fs) (e.g., En 80 Fs 20 ).
Most natural crystals are orthorhombic ( space group P bca ) although three polymorphs are known. The high temperature, low pressure polymorphs are protoenstatite and protoferrosilite (also orthorhombic, space group P bcn ) while the low temperature forms, clinoenstatite and clinoferrosilite, are monoclinic (space group P2 1 /c ).
Weathered enstatite with a small amount of iron takes on a submetallic luster and a bronze-like color. This material is termed bronzite , although it is more correctly called altered enstatite.
Bronzite and hypersthene were known long before enstatite, which was first described by G. A. Kenngott in 1855. [ 5 ]
An emerald-green variety of enstatite is called chrome-enstatite and is cut as a gemstone . The green color is caused by traces of chromium , hence the varietal name. In addition, black, chatoyant hypersthene and brownish bronzite are also used as semi-precious gemstones.
Enstatite and the other orthorhombic pyroxenes are distinguished from those of the monoclinic series by their optical characteristics, such as straight extinction, much weaker double refraction and stronger pleochroism . [ 5 ] They also have a prismatic cleavage that is perfect in two directions at 90 degrees. Enstatite is white, gray, greenish, or brown in color; its hardness is 5–6 on the Mohs scale , and its specific gravity is 3.2–3.3. This prismatic form is used in gemstones, and for academic purposes.
Isolated crystals are rare, but orthopyroxene is an essential constituent of various types of igneous rocks and metamorphic rocks . Magnesian orthopyroxene occurs in plutonic rocks such as gabbro (norite) and diorite . It may form small idiomorphic phenocrysts and also groundmass grains in volcanic rocks such as basalt , andesite , and dacite .
Enstatite, close to En 90 Fs 10 in composition, is an essential mineral in typical peridotite and pyroxenite of the Earth's mantle . Xenoliths of peridotite are common in kimberlite and in some basalt. Measurements of the calcium , aluminum , and chromium contents of enstatite in these xenoliths have been crucial in reconstructing the depths from which the xenoliths were plucked by the ascending magmas.
Orthopyroxene is an important constituent of some metamorphic rocks such as granulite . Orthopyroxene near pure enstatite in composition occurs in some metamorphosed serpentines . Large crystals, a foot in length and mostly altered to steatite , were found in 1874 in the apatite veins traversing mica - schist and hornblende -schist at the apatite mine of Kjørstad, near Brevik in southern Norway . [ 5 ]
Enstatite is a common mineral in meteorites. Crystals have been found in stony and iron meteorites , including one that fell at Breitenbach in the Ore Mountains , Bohemia . In some meteorites, together with olivine it forms the bulk of the material; it can occur in small spherical masses, or chondrules , with an internal radiated structure. [ 5 ]
Enstatite is one of the few silicate minerals that have been observed in crystalline form outside the Solar System , particularly around evolved stars and planetary nebulae such as NGC 6302 . Enstatite is thought to be one of the early stages for the formation of crystalline silicates in space. Many correlations have been noted between the occurrence of the mineral and the structure of the object around which it has been observed. [ citation needed ]
Enstatite is thought to be a main component of the E-type asteroids . [ 6 ] The Hungaria asteroids are the main examples in the Solar System.
A layer of quartz and enstatite clouds above an iron cloud deck are thought to exist in the atmosphere of the young brown dwarf 2M2224-0158 . [ 7 ] | https://en.wikipedia.org/wiki/MgSiO3 |
mhchem is a LaTeX package designed to simplify the typesetting of chemical formulae and equations. It allows users to write chemical expressions using a concise and intuitive syntax that is then rendered into properly formatted chemical notation. [ 1 ]
The command:
will render as:
To use mhchem , include the package in the LaTeX document preamble:
Then, chemical equations can be typed using the \ce{} command.
mhchem is supported by MathJax , enabling its use on the web for rendering chemical equations in HTML documents, including Wikipedia and other wikis using MathJax extensions. | https://en.wikipedia.org/wiki/Mhchem |
miR-122 is a miRNA that is conserved among vertebrate species. miR-122 is not present in invertebrates , and no close paralogs of miR-122 have been detected. [ 1 ] miR-122 is highly expressed in the liver , where it has been implicated as a regulator of fatty-acid metabolism in mouse studies. Reduced miR-122 levels are associated with hepatocellular carcinoma . miR-122 also plays an important positive role in the regulation of hepatitis C virus replication.
miR-122 was originally identified by cloning of tissue-specific microRNAs in mouse. [ 2 ] The liver-specific expression of miR-122 is conserved in zebrafish . [ 3 ] miR-122 expression increases during embryogenesis until it constitutes 72% of total miRNA in adult human liver, making it one of the most highly expressed miRNAs in any tissue. [ 4 ] In humans, miR-122 is encoded at a single genomic locus in chromosome 18 . The primary miR-122 transcript (pri-miR-122) is a long non-coding RNA . Transcription is regulated by HNF4α . [ 5 ] The miR-122 hairpin precursor consensus shown here is predicted based on base pairing and cross-species conservation. The mature sequence is excised from the 5' arm of the hairpin. [ 2 ] [ 6 ]
There is evidence that miR-122 is regulated by Rev-ErbA alpha which is involved in circadian gene expression , suggesting that miR-122 is a circadian metabolic regulator . miR-122 regulates the expression of several mRNA molecules that are important in the circadian cycle, such as PPARβ/δ . [ 7 ] Mature miR-122 is subject to modification by the poly(A) polymerase GLD-2, which adds a single adenosine to the miRNA 3' end. This results in an increase in miR-122 stability. [ 8 ]
miR-122 regulates the synthesis of the protein CAT-1 by binding to sites in the mRNA 3'UTR such that translation is repressed and the mRNA is targeted to P bodies . This repression can be relieved by the protein HuR , which is released from the nucleus under conditions of cell stress and binds to the CAT-1 3'UTR. The HuR interaction leads to release of the mRNA from the P bodies and resumption of active translation. [ 9 ]
A number of other miR-122 targets, including CD320 , AldoA and BCKDK , have been identified by microarray analysis of changes in mRNA expression in the liver of mice treated with miR-122 inhibitors. [ 10 ] [ 11 ] [ 12 ] The overall effect of miR-122 inhibition is to reduce the plasma cholesterol level , although the pathways involved in this regulation have not been fully elucidated. miR-122 also regulates systemic iron homeostasis via the target mRNAs Hjv and Hfe . [ 13 ] miR-122 inhibition in mice or primates does not result in any detectable liver toxicity . [ 14 ]
miR-122 levels are frequently reduced in hepatocellular carcinoma (HCC) compared to normal liver, and low miR-122 levels correlate with poor prognosis . [ 15 ] [ 16 ] Overexpression of miR-122 reduces tumorigenic properties in HCC cell lines, suggesting that it functions as a tumor suppressor gene , and increases the response of cells to the chemotherapeutic drugs sorafenib and doxorubicin . [ 17 ] [ 18 ] Several miR-122 target genes have been implicated in tumorigenesis, including ADAM10 , IGF1R , CCNG1 and ADAM17 . [ 17 ] [ 18 ] [ 19 ]
Recent studies demonstrated that miR-122 may directly regulate different aspects of the interferons (IFNs) signaling pathway [ 20 ] [ 21 ] to enhanced induction of anti-viral genes and inhibition of various virus. [ 21 ] [ 22 ] [ 23 ] [ 24 ] [ 25 ] [ 26 ] [ 27 ] [ 28 ] [ 29 ] [ 30 ] Moreover,
miR-122 have been shown to target various genes, [ 31 ] [ 32 ] [ 29 ] [ 33 ] [ 28 ] resulting in enhancement of IFN signaling and subsequent antiviral innate immunity. [ 31 ] [ 27 ] Interferons (IFNs, includes type I and III interferon) treatment leads to a significant reduction in the expression of the liver-specific miR-122. [ 21 ] [ 34 ] [ 35 ] [ 36 ] [ 28 ] HepG2 cells with overexpressed microRNA-122 mount an effective antiviral interferon response and innate immune response to hepatitis C virus (HCV), other RNA viruses and viral mimetics (e.g. poly(I:C)). [ 22 ]
Recent studies have shown that replication of hepatitis C virus (HCV) is dependent on miR-122 expression. [ 37 ] miR-122 regulates HCV by binding directly to two adjacent sites close to the 5' end of HCV RNA. [ 38 ] Although these experiments were conducted using genotype 1a and 1b HCV RNA, the miR-122 binding sites are highly conserved across different genotypes, and miR-122 is also required for replication of infectious type 2a HCV. [ 39 ] As miRNAs generally function to repress gene expression by binding to 3'UTR sites, this positive regulation of viral replication via a 5'UTR represents a novel function for miR-122. The mechanism of regulation is not yet clear. miR-122 stimulates translation of HCV RNA, but not to a sufficient extent to explain its effects on viral replication, indicating that a second stage of the viral replication cycle must also be regulated. [ 40 ] [ 41 ] HCV RNA synthesis is not affected by miR-122, suggesting that regulation of other processes such as RNA stability may occur. [ 42 ] [ 43 ] The extent to which the miRNA-induced silencing complex (miRISC) is involved in this regulation has not been fully determined. The Argonaute proteins (Ago1–4), which are essential for miRNA-directed repression, appear to be necessary for miR-122 to regulate HCV, [ 44 ] although miR-122 overexpression may overcome this requirement. [ 45 ] The crystal structure of Ago2:miR-122 bound to the miR-122 binding site at the 5'-end of the HCV genome, in combination with functional experiments, suggests that the viral RNA has evolved to maximize protection from cytoplasmic exoribonucleases by altering the molecular behavior of Ago2. [ 46 ] Another miRISC component, the DEAD-box RNA helicase DDX6, does not play a role in miR-122-facilitated HCV replication. [ 47 ]
The existing HCV therapy of PEG-IFNα plus ribavirin is poorly tolerated and frequently ineffective, [ 48 ] [ 26 ] so there is an urgent need for new drugs, and miR-122 inhibitors are an attractive possibility. The association between low miR-122 levels and hepatocellular carcinoma suggests that caution will be necessary when testing miR-122 inhibitors, and that long-term treatment might be undesirable. However, miR-122 is a promising target as it can be very selectively and effectively inhibited with antisense oligonucleotides, and as it is a conserved host factor it is hoped that the virus would not be able to acquire resistance mutations to an anti-miR-122 therapeutic. Moreover, engineering HepG2 cells to express miR-122 (HepG2-HFL cell, HepG2 cells expressing miR-122) mount an effective antiviral interferon-lambda (IFNλ) based innate immune response to hepatitis C virus (HCV) infection. [ 22 ] [ 25 ] HepG2 cells (stably expressing miR-122) produced a more robust IFN Response (type I and type III interferons) when challenged with other RNA viruses [ IAV-ΔNS1 and SeV ] and viral mimetics than Huh-7 and Huh-7.5 cells. HCV Induces an IFN-λ (IL28 and IL29), ISG, and Cytokine Response in these HepG2 cells with stably expressing miR-122. [ 22 ] [ 23 ] [ 24 ] [ 31 ] [ 27 ]
As of 2017, Santaris Pharma was developing miravirsen , a locked nucleic acid -based antisense oligonucleotide that inhibits miR-122, as a potential treatment for HepC. [ 49 ]
miR-122 has recently been explored as a potential biomarker for various hepatic conditions. A change in levels of miR-122 in the blood has been confirmed as an indicator for viral-, alcohol- and chemical-induced liver injury [ 50 ] [ 51 ] [ 52 ] as well as Transplant rejection after Liver transplantation . [ 53 ] [ 54 ] This change is noted before increased amino- transferase activity, making it an early indicator of liver disease and hepatocellular injury of liver grafts prior to liver transplantation. [ 53 ] [ 55 ]
There is a great deal of research into the use of miR-122 as a biomarker for hepatitis C . While some studies dispute its efficacy for diagnosing Hep C, [ 56 ] other research indicates that it may be useful in diagnosing specific forms of hepatitis. [ 57 ] In addition, decreased levels of miR-122 in liver biopsies have been linked to a strain of hepatitis C that is resistant to interferon therapy. [ 26 ]
miR-122 has also been suggested as a biomarker for hepatectomy-induced liver injury in patients with hepatocellular carcinoma . [ 58 ]
Detection of miR-122 and other microRNAs in Body fluid like blood can be interfered by heparin contaminated. The commonly used anticoagulant heparin profoundly inhibits the by reverse transcription polymerase chain reaction (RT-PCR) used for microRNA quantification. [ 59 ] [ 60 ] | https://en.wikipedia.org/wiki/MiR-122 |
miR-208 is a family of microRNA precursors found in animals , including humans . The ~22 nucleotide mature miRNA sequence is excised from the precursor hairpin by the enzyme Dicer . [ 1 ] This sequence then associates with RISC which effects RNA interference . [ 2 ]
In humans, the gene for miR-208 is located in an intron of MYH7 . [ 3 ]
miR-208 has been deemed a "myomiR" [ 3 ] as it is specifically expressed, or found at much higher levels, in cardiac tissue . Other myomiRs include miR-1 and miR-133 . [ 3 ] miR-208 is thought to be dysregulated in various cardiovascular diseases . [ 4 ] [ 5 ]
miR-208 functions in cardiomyocytes regulating the production of the myosin heavy chain during development. [ 3 ] It also responds to stress and forms part of a hormonal signalling cascade in cardiac cells. [ 6 ]
A preliminary study has shown a potential use in the prognosis of dilated cardiomyopathy . [ 7 ] Another application has been suggested as using plasma concentration of miR-208 as a biomarker of damaged cardiac muscle cells. [ 8 ] | https://en.wikipedia.org/wiki/MiR-208 |
miR-324-5p is a microRNA that functions in cell growth, apoptosis , cancer, [ 1 ] epilepsy , [ 2 ] [ 3 ] neuronal differentiation, [ 4 ] psychiatric conditions, [ 5 ] cardiac disease pathology, [ 6 ] [ 1 ] and more. [ 7 ] As a microRNA, it regulates gene expression through targeting mRNAs . Additionally, miR-324-5p is both an intracellular miRNA, meaning it is commonly found within the microenvironment of the cell, and one of several circulating miRNAs found throughout the body. [ 8 ] Its presence throughout the body both within and external to cells may contribute to miR-324-5p's wide array of functions and role in numerous disease pathologies – especially cancer – in various organ systems.
miR-324-5p first appeared in literature in a paper published by John Kim et al. in early 2004 that identified 32 entirely new miRNAs from cultured rat cortical neurons using miRNA cloning and RNA analysis. [ 9 ] The miRNA quickly gained traction in scientific literature, appearing in articles about the evolutionary conservation of microRNAs, [ 10 ] HIV , [ 11 ] cancer, [ 12 ] and other topics within a few years. Today, the functions and roles of miR-324-5p are still not yet fully characterized. [ 13 ]
miR-324-5p is a reverse strand miRNA, meaning it is produced from the 5' end of the associated RNA, and spans from position 7,223,342 to 7,223,364 on chromosome 17. [ 14 ] Its sequence is CGCAUCCCCUAGGGCAUUGGUG. [ 15 ] [ 16 ]
miRNA forms following cleavage of pre-miRNA at the hairpin loop by the enzyme dicer within the cytosol. Interestingly, both strands of miR-324's pre-miRNA hairpin loop structure, miR-324-5p and miR-324-3p, become active miRNAs with distinct targets and functions. [ 17 ] miR-324-5p has between 166 and 469 predicted targets, [ 18 ] [ 19 ] [ 14 ] including regulators of cell growth, proliferation, survival, cytoskeletal structure, ATP transport, and ion channels. [ 18 ] Though miR-324-5p is found on chromosome 17, its targets span across all chromosomes. [ 16 ]
miR-324-5p likely regulates cell growth and survival through interaction with multiple pathways. Published research demonstrates that this miRNA interacts with the Hedgehog (HH) signaling pathway via interactions with HH transcription factor Gli1 [ 20 ] and HH protein receptor Smo , [ 21 ] often contributing to tumorigenesis. miR-324-5p's activating interaction with the protein NfkB also regulates numerous components of cell survival, including cell cycle control, enzyme synthesis, and cell adhesion. [ 22 ] In addition, miR-324-5p regulates components of the MAPK pathway , influencing cell growth, proliferation, and survival. Specifically, miR-324-5p downregulates RAF and ERK and is necessary for normal levels of cell growth. Reduced expression leads to increased cell growth and proliferation, and overexpression limits growth, leading to its role in oncogenesis. [ 23 ]
Both up and downregulation of miR-324-5p is shown to contribute to various types of cancer. [ 17 ]
miR-324-5p plays a role in inflammation and tumorigenesis in colorectal cancer through regulation of CUEDC2, which regulates inflammation via interaction with NF-kB signaling. [ 12 ] miR-324-5p can inhibit glioma proliferation, [ 20 ] suppress hepatocellular carcinoma and nasopharyngeal carcinoma cell invasion, [ 24 ] [ 25 ] and regulate growth and pathology in multiple myeloma . [ 26 ] Additionally, chromosome 17 deletions, which include deletion of miR-324-5p, are present in 10% of multiple myeloma patients and are associated with poorer prognosis. [ 26 ]
In contrast, overexpression of miR-324-5p in gastric cancer cells reduces cell death and promotes growth and proliferation. [ 27 ] miR-324-5p has also been shown to reduce the viability of gastric cancer cells via downregulation of TSPAN8 , and miR-324-5p expression increased apoptosis in these same gastric cancer cells. [ 28 ]
Seizures are characterized by high levels of synchronized neuronal activity. One important regulator of neuronal activity is the hyperpolarizing A-type current mediated by potassium channel KV4.2 . [ 29 ] miR-324-5p downregulates KV4.2, exacerbating conditions that lead to seizure onset, and downregulation of miR-324-5p in mouse models of epilepsy is seizure-suppressive. [ 3 ]
Changes in miRNA expression are seen in epileptogenesis and in other disease pathologies. [ 30 ] [ 31 ] In epilepsy, miR-324-5p expression has been shown to increase [ 32 ] and decrease [ 33 ] at different timepoints and loci.
Importantly, miR-324-5p has increased association with the RISC complex following seizure in mice, indicating more suppressive activity. [ 3 ] [ 34 ]
Overall, this suggests that miR-324-5p plays a role in epileptogenesis via targeting of potassium channel KV4.2.
miR-324-5p contributes to cardiac disease pathophysiology and cardiomyocite death through translational inhibition of Mtfr1 , leading to reduced mitochondrial fission , apoptosis, and myocardial infarction . [ 6 ]
MiRNA expression profiles are altered in psychiatric conditions, including depression , [ 5 ] anxiety , [ 35 ] and PTSD . [ 36 ] It has been demonstrated that miR-324-5p expression is altered in the brains of suicide victims with depression [ 5 ] and in the amygdala , the fear center of the brain, in PTSD. [ 36 ] MiRNAs are an underexplored potential biomarker and target for treatment for psychiatric disease. [ 37 ]
miRNA-324-5p is a relatively new and understudied microRNA. It is an important regulator in several diseases, and its effects span across the body from neuronal dysregulation in seizure to hepatocellular carcinoma and cardiac disease. Because microRNAs have numerous targets, they are capable of regulating multiple pathways and circuits, an ability that may be useful in the treatment of complex disorders like epilepsy in which many subsystems are dysregulated. However, the wide-ranging functions of miRNAs may be limiting as well. microRNA expression modulation could lead to unanticipated physiological effects and not provide adequate specificity. [ 38 ] | https://en.wikipedia.org/wiki/MiR-324-5p |
MiTAC Holdings Corporation was formed on September 12, 2013, through a stock swap from MiTAC International Corp . As part of a restructuring aimed at future operational objectives, the Group established MiTAC Computing Technology Corporation on September 1, 2014, to focus on designs and manufactures servers for data centers and enterprises, offering solutions from edge to cloud computing, including hyperscale data centers, AI /HPC systems, and energy-efficient technologies like liquid cooling. [ 1 ]
MiTAC entering the server ODM business in 1999, has designed and manufactured servers utilizing various processors, including Intel x86, SPARC, IBM Power ISA, and ARM architectures. The company expanded its capabilities in 2007 by acquiring Tyan Computer, that strengthened its ability to offer high-performance server solutions. [ 2 ]
In 2015, MiTAC Computing entered a distribution agreement with Avnet Embedded to distribute its cloud database and computing equipment. [ 3 ] [ 4 ] The company has maintained partnerships with industry leaders, including AMD and Intel, contributing to advancements in server technology. [ 5 ] In 2023, MiTAC Computing acquired Intel’s Data Center Solutions Group (DSG) server business, further expanding its market presence. [ 6 ] [ 7 ] [ 8 ] [ 9 ]
In 2024, MiTAC Computing integrated the Tyan server brand into its operations, consolidating product branding under the MiTAC Computing name and updating its logo and website. [ 10 ]
MiTAC Computing Technology Corporation offers a range of products, including:
This article about a Taiwanese corporation or company is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/MiTAC_Computing_Technology_Corp. |
MiWi is a proprietary wireless protocol supporting peer-to-peer , star network connectivity. It was designed by Microchip Technology . MiWi uses small, low-power digital radios based on the IEEE 802.15.4 standard, and is designed for low-power, cost-constrained networks, such as industrial monitoring and control, home and building automation, remote control, wireless sensors, lighting control, and automated meter reading. [ 1 ]
The MiWi protocol is supported on Microchip's SAMR30 (sub-gigahertz) [ 2 ] and SAMR21 (2.4 GHz) [ 3 ] ARM Cortex-M 0+ devices and modules. Legacy MiWi protocol code supporting PIC and dsPIC microcontrollers has been frozen and is no longer recommended for new designs; however, it is still available in the Microchip Library for Applications (MLA) [ 4 ] for the MPLAB Integrated Development Environment. [ 5 ]
Microchip Technology released technical information on MiWi. [ 6 ] [ 7 ] These are not primarily protocol specifications and are focused on implementing the MiWi protocol on Microchip microcontrollers.
As of 2019, interoperable third party implementations have not appeared. Unless they do, it will not be clear if those specifications are complete or accurate enough to serve roles other than supporting Microchip's code or being one more proprietary example of a lightweight WPAN stack. Many developers trying to use WPAN technologies have observed that the competing Zigbee WPAN protocol seems undesirably complex. Accordingly, there exists a technical niche for simpler protocols, of which MiWi is a proprietary example.
The MiWi protocol is a small foot-print alternative (3K-32K [ vague ] ) to Zigbee (40K-180K [ vague ] ), for cost-sensitive applications with limited memory.
The MiWi protocol stack supports star network and peer-to-peer wireless-network topologies, useful for simple, short-range, wireless node-to-node communication. Additionally, the stack provides sleeping-node, active-scan and energy-detect features while supporting the low-power requirements of battery-operated devices.
Microchip Technology released MiWi support on the SAMR30 [ 2 ] and SAMR21 [ 3 ] RF-MCU's in 2018. Both devices are ARM Cortex M0+, and have 256 KB Flash and up to 40 KB RAM and utilize OQPSK RF Modulation defined in IEEE 802.15.4 for a +3dB advantage in power efficiency vs. FSK modulation. [ 8 ] Legacy devices supporting MiWi include several PIC Microcontrollers paired with the MRF89XA [ 9 ] (Proprietary Sub-GHz Transceiver) or the MRF24J40 [ 10 ] (an IEEE 802.15.4 2.4 GHz transceiver).
MiWi Modules
In 2018 Microchip released the SAMR30M, [ 11 ] a module based on the SAMR30 Cortex M0+ sub-GHz RF-MCU.
In 2008, Microchip released a 2.4 GHz wireless transceiver module with a standard 4-wire SPI interface paired with several Microchip PIC and dsPIC microcontrollers (the Microchip MRF24J40MA, MRF24J40MD, MRF24J40ME), and can be used in production devices. Being ZigBee compliant, and capable of communicating using MiWi wireless protocols, it is based on the IEEE 802.15.4 Wireless PAN standard. Option are for PCB antenna or u.FL connected antenna. The modules are regulatory-agency certified for the USA ( Federal Communications Commission (FCC) Part 15, Subpart C), Canada ( Industry Canada ) and European - Radio Equipment Directive (RED) 2014/53/EU, eliminating the need for users to receive independent FCC certification for their wireless products. [ 12 ]
Microchip Technology's ZENA (Zigbee Enhanced Network Analyzer) is a wireless packet sniffer and network analyzer following the IEEE 802.15.4 specification on the 2.4 GHz band. The ZENA analyzer supports both the ZigBee and MiWi protocols. Accompanying software can analyze network traffic and graphically display decoded packets. It can also display the network topology and the messages as they flow through the network. With the provided key of the network, data on encrypted MiWi networks can be sniffed and viewed as well. | https://en.wikipedia.org/wiki/MiWi |
The Miami Science Barge (also known as the Science Barge ) was a floating marine laboratory and education platform docked in Museum Park , Miami , FL since 2016. [ 1 ] The Barge, designed to help support a more sustainable city, had three main areas of focus: marine ecology and conservation, sustainability, and alternative agriculture. It is completely off-grid and off-pipe and provided approximately enough energy and food production to support an average American family. [ 2 ] In its first year, over 3000 students came aboard to learn about the innovative technology on the Barge. The vessel opened to the public on Saturdays.
The Miami Science Barge was conceived by Nathalie Manzano and designed by Manzano and Ted Caplow . They were inspired by the Science Barge built in 2006 by New York Sun Works, designed by Caplow. The vessels were of similar size and both had a sustainable technology focus, but they responded to very different local environments and housed differing technology and unique public education programs. The Miami Science Barge emphasized aquaculture.
The Miami Science Barge was donated in April 2017 to the brand-new Philip and Patricia Frost Museum of Science, who took over operations. The Miami Science Barge is no longer in use.
In 2015, Nathalie Manzano and Ted Caplow of CappSci won the Knight Cities Challenge grant competition from the John S. and James L. Knight Foundation with a proposal to build the Miami Science Barge. [ 3 ] The Barge was a 120x30 steel construction barge from Grady Marine retrofitted with 2nd-hand shipping containers in 2015. With the generosity of Beau Payne of P & L Towing, the staff of CappSci were able to design and build the power system and exhibits of the Barge on the Miami River prior to moving it to its official location in Museum Park in downtown Miami, FL.
The Miami Science Barge opened on Earth Day , April 22, 2016. The following April, the Barge was gifted to Phillip and Patricia Frost Museum of Science .
The Miami Science Barge has three main areas of focus:
The Barge is fully off-grid . It utilizes 48 solar panels (donated by JinkoSolar) to generate enough power to run all of its systems. These panels are set into five arrays including a solar dance floor and a solar tracking system . Power is stored into two sets of batteries: lead-acid batteries , and experimental Aquion M-Line battery modules . The panels provide about 75Kwh. [ 4 ] It is also off-pipe , meaning that all of its fresh water comes from a rainwater catchment system located about the classroom area. The water is stored in a 900-gallon cistern. The salt water comes directly from Biscayne Bay . No discharge is released from the Barge. Waste water is collected in constructed wetland troughs where the water is filtered or in some cases may evaporate.
Furthermore, the Barge aimed to utilize only sustainable material in construction, i.e. the Kebony deck throughout the farm area. Kebony is an eco-friendly alternative to tropical hardwoods, using a bio-based seal instead of a synthetic one. [ 5 ] The staff on the Barge also follow strict habits of sustainability, including prohibiting single-use plastics from being used on board for events and by diligently cleaning debris found in the notch.
On board are a variety of sustainable and unconventional agriculture systems including hydroponics , aeroponics , aquaculture, and aquaponics. [ 6 ] Hydroponics and aeroponics are forms of growing produce that utilizes water and nutrients most efficiently. Aquaculture systems grow fish and other marine creature for consumption so as not to harm the balance in the ocean and aquaponics is a combination of aquaculture and aquaponics, where marine life produce waste which is consumed by plants.
On board is also a vertically integrated greenhouse (patented by Caplow and Zak W. Adams).
Along with the aquaponic and aquaculture tanks, there are multiple tanks showcasing marine life. Towards the entrance of the Barge, there is a coral tank, developed with the help of Dr. Diego Lirman at the University of Miami and Rescue a Reef. It is the only tank in South Florida representing what coral restoration in the wild looks like. Other exhibit tanks show sea life from Biscayne Bay, including sea horses , a giant hermit crab , erosion-preventing sea grasses , mangroves , and a myriad of local fish.
These tanks are used to educate about the importance of diversity in Miami’s local ecology. Guest scientists are invited most weekends and on the 3rd Wednesday of every month for Sip of Science to promote the conservation of the environment.
The Miami Science Barge opened on Earth Day , April 22, 2016 and was attended by dignitary speakers including City of Miami Commissioner Frank Carollo , who in his remarks called the Barge "a symbol of Miami's diversity not only in people, but in ideas, as well as, a symbol of our community's commitment to environmental education, [ 7 ] " Miami Dade County Public Schools Superintendent Alberto Carvalho, Knight Foundation’s Miami Program Director Matt Haggman, and Children Trust’s Founding Board Chair David Lawrence, Jr.
In December 2016, Miami Science Barge was named one of “The Ten Best Things to Do in Downtown Miami” by Miami New Times [ 8 ] | https://en.wikipedia.org/wiki/Miami_Science_Barge |
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