MERCAPTANS (the modern name — thiols) — a class of the organic compounds containing group at carbon atom — SH (sulphhydryl, or mercaptogroup). Groups M. contain the proteins (including many enzymes) including the remains of mercaptoamino acid cysteine (see), so-called thiol cofactors — glutathione (see), KOA, dihydrolipoic to - that etc., and other connections. Nek-ry multifunctional M. find application in medicine. 1,2 Dithiols — 2,3 dimercaptopropyl alcohol, Unithiolum (see), dimercaptoamber to - that are used as antidotes at poisonings with arsenic, mercury and other heavy metals and at other intoxications, and also at the arrhythmias of heart, hepatocerebral dystrophy, a scleroderma and other diseases which are followed by disturbances of exchange of collagen etc. Aliphatic mercaptoamines (2 mercaptoethylamine, 2-merkaptoiropilamin) are recognized radio protective agents. Their radio protective action is connected with reduction of an exit of aberation chromosomes in leukocytes of the persons which underwent radiation, and with increase in their fabrics by the number of the induced SH-group and the recovered glutathione. Application in clinic as pharmaceuticals was found by heterocyclic M. (6 Mercaptopurinum, 8 mercaptoadenines, a 1-methyl-2-mercaptoimidazole). Nek-rye M. is used also as pesticides, in production of polymers and in other fields of the national economy.
M are eurysynusic in the nature, many M. have plant or animal origin (pro-pan-thiol contains in onions, butantiol — in release of protective glands of a skunk, etc.), in very small amounts of M. contain in foodstuff (e.g., CH 3 SH in cheese, milk, coffee, etc.).
On a structure and a nek-eye to properties M. are similar to alcohols and are called sometimes thioalcohols. Names M. are formed as names of alcohols (C 2 H 5 SH — thioethyl alcohol, () — 2 pro-pan-thiol, HSCH 2 CH 2 CH 2 SH — 1,3 pro-pan-dithiol); for multifunctional M. the prefix «merkapto-» is used (e.g., HSCH 2 CH 2 IT — 2 mercaptoethanol).
Low-molecular aliphatic M. represent liquids, temperature of boiling to-rykh much lower than temperature of boiling of the corresponding alcohols, with lengthening of a carbon chain this difference smoothes out and the highest alkanethiols are already low-melting solid matters. M.'s solubility in water is much lower, than at the corresponding alcohols (for C 2 H 5 SH ⩽ 1% at 20 °). Characteristic property of M. (especially the lowest aliphatic M.) — strong off-flavor, notable even in insignificant concentration (for CH 3 To SH such concentration is equal to 2*10 - 9 mg/l of air) therefore M. (e.g., isoamylthiol) use as odorants of gas. Low-molecular M. can be received by interaction of alkyl halides with NaSH.
M — very weak to - you, at effect of alkalis form easily hydrolyzed salts (tiolyata, mercaptides). Formation of difficult water soluble mercaptides of heavy metals is characteristic of M. (especially mercury); the formation of such mercaptides blocking SH groups of proteins (enzymes) happens at poisonings with compounds of heavy metals. M — very reactive connections. Easily happening M.'s oxidation in disulfides plays an important role in chemistry of SH-group in biol., in particular in enzymatic processes (see. Sulphhydryl groups ). Exchange reaction of M. with disulfides is used for prevention of an autookisleniye of SH-group in proteins (by means of mercaptoethanol, a ditiotrektol). M are easily alkylated and acylated on sulfur atom to sulfides and thioacylic connections respectively; in biochemical, processes in an organism of animals and the person tioatsilovy ethers serve as carriers of acyl (see. Coenzymes ). With aldehydes and ketones M. form thioacetals and thioketals. Addition reaction of M. to the activated double bond is used, e.g., at a research of SH proteins by means of N-etilmaleimida.
For M.'s detection staining reactions with Sodium nitroprussidum, ions of Pb serve 2+ and Hg 2+ , nitrogenous to - that, isatin and a chamois to - that, etc. M.'s number determine by methods yodo-, argento-and merkurimetriya, colorimetry with use phosphatotungstic to - you and other ways. In proteins apply amperometrichesky titration with AgNO to definition of SH-group 3 , spectrophotometric methods with participation of n-hlormerkuribenzoata, N-etilmaleimida and other methods.
Bibliography Biological activity of some aminothiols and aminosulfides, under the editorship of M. N. Volkov, M., 1974; At e of N Y. and Veyl, Methods of organic chemistry, the lane with it., t. 2, page 582, M., 1967; Roberts D. and To and with e r and about M. Fundamentals of organic chemistry, the lane with English, t. 2, page 150, M., 1978; Torchinsky Yu. M. It is gray in proteins, M., 1977; With t about y-the p e in Ts. Biologichn aktivnost on tiolo-Vit of a sjedineniye, Sofia, 1975; E 1 u h and-t at A. L. Biochemistry of the thiol group, in book: The chemistry of the thiol group, ed. by S. Patai, pt 2, p. 589, L., 1974.
A. I. Tochilkin; V. P. Fisenko (pharm).