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Disulfide
In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In biology, disulfide bridges formed between thiol groups in two cysteine residues are an important component of the secondary and tertiary structure of proteins. ''Persulfide'' usually refers to compounds. In inorganic chemistry disulfide usually refers to the corresponding anion (−S−S−). Organic disulfides Symmetrical disulfides are compounds of the formula . Most disulfides encountered in organo sulfur chemistry are symmetrical disulfides. Unsymmetrical disulfides (also called heterodisulfides) are compounds of the formula . They are less common in organic chemistry, but most disulfides in nature are unsymmetrical. Properties The disulfide bonds are strong, with a typical bond dissociation energy of 60 kcal/mol (251&nbs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diphenyl Disulfide
Diphenyl disulfide is the chemical compound with the formula (C6H5S)2. This colorless crystalline material is often abbreviated Ph2S2. It is one of the more commonly encountered organic disulfides in organic synthesis. Minor contamination by thiophenol is responsible for the disagreeable odour associated with this compound. Preparation and structure Diphenyl disulfide is usually prepared by the oxidation of thiophenol: : 2 PhSH + I2 → Ph2S2 + 2 HI Hydrogen peroxide can also be used as the oxidant. Ph2S2 is rarely prepared in the laboratory because it is inexpensive, and the precursor has a disagreeable odour. Like most organic disulfides, the C–S–S–C core of Ph2S2 is non-planar with a dihedral angle approaching 85°. Reactions Ph2S2 is mainly used in organic synthesis as a source of the PhS substituent. A typical reaction entails the formation of PhS-substituted carbonyl compounds via the enolate: :RC(O)CHLiR' + Ph2S2 → RC(O)CH(SPh)R' + LiSPh Reduction Ph2S2 undergo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dimethyl Disulfide
Dimethyl disulfide (DMDS) is an organic chemical compound with the molecular formula which is the simplest disulfide. It is a flammable liquid with an unpleasant, garlic-like odor. Occurrence Dimethyl disulfide is a widespread natural odoriferous compound emitted from many sources such as bacteria, fungi, plants and animals. It is an oxidation product of methanethiol in air. Along with dimethyl sulfide and dimethyl trisulfide it has been confirmed as volatile compounds given off by the fly-attracting plant known as dead-horse arum ('' Helicodiceros muscivorus''). These flies are attracted to the odor resembling that of fetid meat, and thus help pollinate this plant. DMDS can be produced by the oxidation of methanethiol, e.g. with iodine: : Chemical reactions Important reactions include chlorination giving methanesulfenyl chloride (), methanesulfinyl chloride (), and methanesulfonyl chloride () as well as oxidation with hydrogen peroxide or peracetic acid giving the thiosulf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diphenyl Disulfide
Diphenyl disulfide is the chemical compound with the formula (C6H5S)2. This colorless crystalline material is often abbreviated Ph2S2. It is one of the more commonly encountered organic disulfides in organic synthesis. Minor contamination by thiophenol is responsible for the disagreeable odour associated with this compound. Preparation and structure Diphenyl disulfide is usually prepared by the oxidation of thiophenol: : 2 PhSH + I2 → Ph2S2 + 2 HI Hydrogen peroxide can also be used as the oxidant. Ph2S2 is rarely prepared in the laboratory because it is inexpensive, and the precursor has a disagreeable odour. Like most organic disulfides, the C–S–S–C core of Ph2S2 is non-planar with a dihedral angle approaching 85°. Reactions Ph2S2 is mainly used in organic synthesis as a source of the PhS substituent. A typical reaction entails the formation of PhS-substituted carbonyl compounds via the enolate: :RC(O)CHLiR' + Ph2S2 → RC(O)CH(SPh)R' + LiSPh Reduction Ph2S2 undergo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cysteine
Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometimes the symbol Cyz is used. The deprotonated form can generally be described by the symbol Cym as well. The thiol is susceptible to oxidation to give the disulfide derivative cystine, which serves an important structural role in many proteins. In this case, the symbol Cyx is sometimes used. When used as a food additive, it has the E number E920. Cysteine is encoded by the codons UGU and UGC. The sulfur-containing amino acids cysteine and methionine are more easily oxidized than the other amino acids. Structure Like other amino acids (not as a residue of a protein), cysteine exists as a zwitterion. Cysteine has chirality in the older / notation based on homology to - and -glyceraldehyde. In the newer ''R''/''S'' system of designating chi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cystine
Cystine is the oxidized derivative of the amino acid cysteine and has the formula (SCH2CH(NH2)CO2H)2. It is a white solid that is poorly soluble in water. As a residue in proteins, cystine serves two functions: a site of redox reactions and a mechanical linkage that allows proteins to retain their three-dimensional structure. Formation and reactions Structure Cystine is the disulfide derived from the amino acid cysteine. The conversion can be viewed as an oxidation: : Cystine contains a disulfide bond, two amine groups, and two carboxylic acid groups. As for other amino acids, the amine and carboxylic acid groups exist is rapid equilibrium with the ammonium-carboxylate tautomer. The great majority of the literature concerns the ''l,l-''cystine, derived from ''l''-cysteine. Other isomers include ''d,d''-cystine and the meso isomer d,l-cystine, neither of which is biologically significant. Occurrence Cystine is common in many foods such as eggs, meat, dairy products, and whole ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Persulfide
In chemistry, persulfide refers to the functional group R-S-S-H. Persulfides are intermediates in the biosynthesis of iron-sulfur proteins and are invoked as precursors to hydrogen sulfide, a signaling molecule. Nomenclature The nomenclature used for organosulfur compounds is often non-systematic. Sometimes persulfides are called hydrodisulfides to further avoid confusion with disulfides with the grouping R-S-S-R, by emphasizing the presence of an H at one end of a disulfide bond. Properties Compared to thiols (R-S-H), persulfides are uncommon. They are thermodynamically unstable with respect to loss of elemental sulfur: :RSSH → RSH + 1/8 S8 Nonetheless, persulfides are often kinetically stable. The S-H bond is both more acidic and more fragile than in thiols. This can be seen in the bond dissociation energy of a typical persulfide, which is 22 kcal/mol weaker than a typical thiol, and the lower pKa of about 6.2 for persulfides compared to 7.5 for thiols. Thus, persulfides e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thiol
In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl group, or a sulfanyl group. Thiols are the sulfur analogue of alcohols (that is, sulfur takes the place of oxygen in the hydroxyl () group of an alcohol), and the word is a blend of "''thio-''" with "alcohol". Many thiols have strong odors resembling that of garlic or rotten eggs. Thiols are used as odorants to assist in the detection of natural gas (which in pure form is odorless), and the "smell of natural gas" is due to the smell of the thiol used as the odorant. Thiols are sometimes referred to as mercaptans () or mercapto compounds, a term introduced in 1832 by William Christopher Zeise and is derived from the Latin ('capturing mercury')''Oxford American Dictionaries'' (Mac OS X Leopard). because the thiolate group () bonds very strong ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lipoic Acid
Lipoic acid (LA), also known as α-lipoic acid, alpha-lipoic acid (ALA) and thioctic acid, is an organosulfur compound derived from caprylic acid (octanoic acid). ALA is made in animals normally, and is essential for aerobic metabolism. It is also manufactured and is available as a dietary supplement in some countries where it is marketed as an antioxidant, and is available as a pharmaceutical drug in other countries. Lipoate is the conjugate base of lipoic acid, and the most prevalent form of LA under physiological conditions. Only the (''R'')-(+)-enantiomer (RLA) exists in nature and is essential for aerobic metabolism because RLA is an essential cofactor of many enzyme complexes. Physical and chemical properties Lipoic acid (LA), also known as α-lipoic acid, alpha-lipoic acid (ALA), and thioctic acid is an organosulfur compound derived from octanoic acid. LA contains two sulfur atoms (at C6 and C8) connected by a disulfide bond and is thus considered to be oxidized althou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Functional Group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest of the molecule's composition. This enables systematic prediction of chemical reactions and behavior of chemical compounds and the design of chemical synthesis. The reactivity of a functional group can be modified by other functional groups nearby. Functional group interconversion can be used in retrosynthetic analysis to plan organic synthesis. A functional group is a group of atoms in a molecule with distinctive chemical properties, regardless of the other atoms in the molecule. The atoms in a functional group are linked to each other and to the rest of the molecule by covalent bonds. For repeating units of polymers, functional groups attach to their nonpolar core of carbon atoms and thus add chemical character to carbon chains. Fun ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrogen Peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%–6% by weight) in water for consumer use, and in higher concentrations for industrial use. Concentrated hydrogen peroxide, or " high-test peroxide", decomposes explosively when heated and has been used as a propellant in rocketry. Hydrogen peroxide is a reactive oxygen species and the simplest peroxide, a compound having an oxygen–oxygen single bond. It decomposes slowly when exposed to light, and rapidly in the presence of organic or reactive compounds. It is typically stored with a stabilizer in a weakly acidic solution in a dark bottle to block light. Hydrogen peroxide is found in biological systems including the human body. Enzymes that use or decompose hydrogen peroxide are classified as peroxidases. Properties The boiling poi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic Luster (mineralogy), luster and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname of ''fool's gold''. The color has also led to the nicknames ''brass'', ''brazzle'', and ''Brazil'', primarily used to refer to pyrite found in coal. The name ''pyrite'' is derived from the Greek language, Greek (), 'stone or mineral which strikes fire', in turn from (), 'fire'. In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel; Pliny the Elder described one of them as being brassy, almost certainly a reference to what we now call pyrite. By Georgius Agricola's time, , the term had become a generic term for all of the pyrite group, sulfide minerals. Pyrite is usua ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrophile
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carries a partial positive charge, or have an atom that does not have an octet of electrons. Electrophiles mainly interact with nucleophiles through addition and substitution reactions. Frequently seen electrophiles in organic syntheses include cations such as H+ and NO+, polarized neutral molecules such as HCl, alkyl halides, acyl halides, and carbonyl compounds, polarizable neutral molecules such as Cl2 and Br2, oxidizing agents such as organic peracids, chemical species that do not satisfy the octet rule such as carbenes and radicals, and some Lewis acids such as BH3 and DIBAL. Organic chemistry Addition of halogens These occur between alkenes and electrophiles, often halogens as in halogen addition reactions. Common reactions i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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