Sulfhydryl sulfide

In the presence of sulfide or sulfhydryl anions, the quinonemethide is attacked and a benzyl thiol formed. The P-aryl ether linkage to the next phenylpropane unit is broken down as a result of neighboring-group attack by the sulfur, eliminating the aryloxy group which becomes reactive phenolate ion (eq. 2). If sulfide is not present, a principal reaction is the formation of the stable aryl enol ether, ArCH=CHOAr. A smaller amount of this product also forms in the presence of sulfhydryl anion. 

Schwefelwasserstoff, m. hydrogen sulfide, -rest, m. mercapto group, sulfhydryl, SH. -saure, /. hydrosulfuric acid (H2S). -Strom,... 

Gold(I) thiolates also undergo reactions with disulfides. An example is 2,2-dithio-bis(2-nitrobenzoic acid) (ESSE) used as a kinetic probe of sulfhydryl reactivity in metallothioneins [39-42]. ESSE is readily attacked by metal-bound thiolates. The reaction with the open chain form of AuSTm seems to occur in two stages. The first attack involves the terminal sulfides and the second attack involves the bridging thiolates [19] ... 

Humans may be exposed to hydrogen sulfide both from its endogenous production or from exogenous sources. Most endogenous production apparently results from the metabolism of sulfhydryl-containing amino acids, e.g., cysteine, by bacteria present in both the intestinal tract and the mouth (Beauchamp et al. 1994 Tonzetich and Carpenter 1971) however, it is also produced in the brain and several smooth muscles, e.g., thoraic aorta, by enzymes found in these tissues (Abe and Kimura 1996 Hosoki et al. 1997). 

Hydrogen sulfide in the air is oxidized at a relatively slow rate by molecular oxygen (02) but at a much faster rate by hydroxide (OH) radicals, forming the sulfhydryl radical and ultimately sulfur dioxide or sulfate compounds (Hill 1973 NSF 1976). Sulfur dioxide and sulfates are eventually removed from the atmosphere through absorption by plants and soils or through precipitation (Hill 1973). 

Hydrogen sulfide is produced in the large intestine of mammals by metabolism of sulfhydryl proteins by anaerobic bacteria, and may compose 0-10% of intestinal gases (Beauchamp et al. 1984 EPA 1978). It is produced in the human mouth by microbial petrification (Rosenberg et al. 1991). 

Bosma W, Kamminga G, De Kok LJ. 1990. Hydrogen sulfide-induced accumulation of sulfhydryl compounds in leaves of plants under field and laboratory exposure. In Rennenberg H et al., eds. Sulfur nutrition and sulfur assimilation in higher plants Fundamental environmental and agricultural aspects. The Hague, Netherlands SPB Academic Publishing, 173-175. 

De Kok LJ, Thompson CR, Mudd JB, et al. 1983. Effect of hydrogen sulfide fumigation on water-soluble sulfhydryl compounds in shoots of crop plants. Z Pflanzenphysiol Bd 111 85-89. 

FIGURE 6.21 (A) Removal of trityl and acetamidomethyl from sulfhydryl by oxidative cleavage by iodine. (B) Cleavage of terf-butylsulfanyl by mercury(II) acetate,88 followed by displacement of the metal ion by hydrogen sulfide. 

All attempts of identifying the sulfides in the surface have been unsuccessful so far. Sulfhydryl groups (—SH) seem to be present in minor quantities in some samples, as was shown by their ability to... 

Hahn. Reasoning from the observation that proteins and other substances which contain sulfhydryl groups produce hydrogen sulfide on addition of sulfur, Heffter denied that a biochemical reduction process took place at all. As a generalization this negation seems definitely unjustified (see pp. 93 and 95). 

There are several non heme iron-sulfur proteins that are involved in electron transfer. They have received considerable attention in the last few years. They contain distinct iron-sulfur clusters composed of iron atoms, sulfhydryl groups from cysteine residues, and inorganic or labile sulfur atoms or sulfide ions- The latter are readily removed by washing with acid ... 

A few mechanisms were postulated for this reaction (6). No matter what mechanism is considered, the oxidation of elemental sulfur or thiosulfate is accompanied by reductive cleavage of the sulfur-sulfur bridges. In the case of sulfur, the intermediate involved is a cyclic form of sulfur, probably Ss, although there is little difference observed for different allotrophic forms of sulfur such as rhombic, precipitated, and amphorous. These cyclic sulfides form the basis of polysulfanes and polythionates which could be metabolized readily by Thiobacilli (as shown in Figure 3). Actually, sulfur oxidation begins with its reduction, in which the gluathione-sulfhydryl groups located near the cell surface take part ... 

Literally hundreds of complex equilibria like this can be combined to model what happens to metals in aqueous systems. Numerous speciation models exist for this application that include all of the necessary equilibrium constants. Several of these models include surface complexation reactions that take place at the particle-water interface. Unlike the partitioning of hydrophobic organic contaminants into organic carbon, metals actually form ionic and covalent bonds with surface ligands such as sulfhydryl groups on metal sulfides and oxide groups on the hydrous oxides of manganese and iron. Metals also can be biotransformed to more toxic species (e.g., conversion of elemental mercury to methyl-mercury by anaerobic bacteria), less toxic species (oxidation of tributyl tin to elemental tin), or temporarily immobilized (e.g., via microbial reduction of sulfate to sulfide, which then precipitates as an insoluble metal sulfide mineral). 

Lovenberg, Buchanan, and Rabinowitz found that treatment of ferredoxin with iodoacetate or N-ethylmaleimide in either the presence or absence of 8 M urea had no effect on its spectral characteristics. Less than 1 mole of carboxymethyl cysteine was formed per mole of protein when native ferredoxin was treated with iodoacetate-1-C14 (Table 10). Sobel and Lovenberg (96) showed recently that C14-iodoacetate did not react appreciably with reduced ferredoxin. However, Table 10 shows that if ferredoxin was treated with 2-mercaptoethanol in 8 M urea, it was alkylated with iodoacetate. This demonstrated that the half-cystine residues of native ferredoxin were not present as free sulfhydryls, and the mercurial titration data given above showed that they were not present as disulfides. The two observations were consistent, therefore, with a structure in which the half-cystine residues are present as cysteine and are bonded with the iron by a sulfide bridge. 

The aminodithiole (301) obtained from 234 and ammonia in benzene solution can also be isolated at room temperature. It can again be completely reconverted into 234 by means of perchloric acid. Compound 301 decomposes in boiling ethanol, with liberation of hydrogen sulfide in addition to a little elementary sulfur, a little desoxybenzoin, thiobenzamide, and triphenyl 1,3-thiazole, the dithiole (300) was isolated in 20% yield. Leaver has explained this result on the basis of the equilibrium between 301 and 302 and the exchange of the amino group for the sulfhydryl group.24... 

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