Sulfide formation from sulfite

Since there is no simple assay available for sulfite reductase activity, and the electron donor for sulfite reduction is not known (50), only indirect evidence exists for the involvement of sulfite reductase. Reduction of 2,4-diamino-6-hydroxylaminotoluene by cell suspensions of the isolate is inhibited by carbon monoxide and also by hydroxyl-amine, which is known to be a substrate for the sulfite reductase of Desulfovibrio vulgaris (26). Because not all sulfite reductases in sulfidogenic bacteria are CO-sensitive, the inhibition of sulfide formation from sulfite by carbon monoxide and hydroxylamine was tested. Indeed, carbon monoxide as well as hydroxylamine inhibited sulfide formation in cell suspensions of the isolate. Assuming that diaminohydroxylaminotoluene and/or DANT can be alternative, non-physiological substrates of sulfite reductase, an inhibition of sulfide formation by 2,4-DAHAT and/or DANT can be envisaged and was actually confirmed (39). 

Kobayashi, K., Seki, Y. and Ishimoto,M., 1974. Biochemical studies on sulfate-reducing bacteria. XIII Sulfite reductase from Desulfovibrio vulgaris — mechanism of trithio-nate, thiosulfate and sulfide formation and enzymatic properties. J. Biochem., Tokyo, 75 519—529. 

Barium sulfide solutions undergo slow oxidation in air, forming elemental sulfur and a family of oxidized sulfur species including the sulfite, thiosulfate, polythionates, and sulfate. The elemental sulfur is retained in the dissolved bquor in the form of polysulfide ions, which are responsible for the yellow color of most BaS solutions. Some of the mote highly oxidized sulfur species also enter the solution. Sulfur compound formation should be minimized to prevent the compounds made from BaS, such as barium carbonate, from becoming contaminated with sulfur. 

In heavily sulfited white wines containing over 0.5 ppm copper and stored in sealed containers, a reddish-brown deposit may form. This occurs in the absence of oxygen and ferric ions but redissolves readily upon exposure to oxygen. Its formation may be accelerated by exposure to sunlight or heat, and it is believed to consist of colloidal cupric sulfide (14, 29). More commonly, copper casse may arise from reactions between copper and sulfur-containing amino acids, peptides, and proteins (15,16,17). 

The average concentrations of reduced inorganic sulfur species in the anoxic zone of the Black Sea measured using a new colorimetric method developed by Volkov [61,62] are summarized in Table 3. Presented elemental sulfur data refer to the stun of elemental sulfur allotropes (zero-valent sulfur) and the zero-valent sulfur derived from some fraction (n - 1) of the original polysulfide S 2. Thiosulfate data in the table represent the total amount of thiosulfate, sulfite, and polythionates. At some stations in the Black Sea, Volkov [61] observed a concentration maximum of elemental sulfur at the oxic/anoxic interface associated with sulfide oxidation by dissolved oxygen and/or Mn oxyhydroxides. Increasing with depth, elemental sulfur concentrations are probably explained by the ongoing process of polysulfide formation... 

Visible Light-Induced Formation of Addition of sulfite shown to enhance the clea-Hydrogen and Thiosulfate from vage of H2S into H2 and S. See also Refs. 495-Aqueous Sulfide/Sulfite Solutions 497 and Ref. 500 for follow-up work, in CdS Suspensions. 499... 

The typical S-oxidation with BVMOs allows the formation of chiral sulfoxides from organic sulfides. This oxidation has received much interest in organic chemistry due to its use in the synthesis of enantiomerically enriched materials as chiral auxiliaries or directly as biologically active ingredients. This reaction has been studied extensively with CHMO from Adnetohacter showing high enantioselectivi-ties in the sulfoxidation of alkyl aryl sulfides, disulfides, dialkyl sulfides, and cychc and acyclic 1,3-dithioacetals [90]. CHMO also catalyzes the enantioselective oxida-hon of organic cyclic sulfites to sulfates [91]. 

For the influence of the specific surface area of the semiconductor powder on the rate of product formation, two opposite effects are of major importance [81]. One is concerned with the rate of electron-hole recombination which increases linearly with surface area, and accordingly the reaction rate should decrease. The other is a linear increase in the reaction rate of the reactive electron-hole pair with the adsorbed substrates, which should increase product formation. It is therefore expected that, depending on the nature of semiconductor and substrates, the reaction rate, or increasing surface area. This is nicely reflected by the CdS/Pt-catalyzed photoreduction of water by a mixture of sodium sulfide and sulfite. The highest p values are observed with small surface areas and are constant up to 2 m g". From there a linear decrease to almost zero at a specific surface area of 6 m g" takes place. Upon further increase to 100 m g" this low quantum yield stays constant [82]. 

The reaction of polysulfides with peroxide depends on the polysulfide ion present (see above). Once higher polysulfides are produced, the reaction should result in a peroxide-polysulfide intermediate (similar to II) that transfers two electrons from the polysulfide ion to the peroxide as readily as the sulfide and peroxide reaction. At low peroxide levels, partial oxidation of the polysulfide ions should result in the direct formation of sulfate (through thiosulfate and perhaps sulfite) and S ... 

Sulfite reductases contain siroheme and iron-sulfur centers. Siroheme, also present in some nitrite reductases, is an iron tetrahydroporphyrin of the isobacteriochlorin type with eight carboxylic acid side-chains (Fig. 1). Siroheme isolated from Desulfovibrio species was found to be a monoamide, heptamethyl ester derivative, rather than the usual octamethyl ester derivative, which suggests that in these organisms an amidated form of the siroheme may be the physiologically active prosthetic group [93]. Sulfite reductases are divided into two classes, the assimilatory and the dissimilatory enzymes. The assimilatory sulfite reductases produce sulfide for use in the cell biosynthetic pathways. The dissimilatory enzymes are present in the sulfate-reducing organisms, and reduce sulfite as a respiratory substrate in a process coupled to ATP formation. 

The sulfite formed would react with excess hydrogen sulfide to produce sulfur directly from the sulfoxylic or thiosulfurous intermediate, Reactions 25 and 26, without polythionate formation. The overall reaction between hydrogen sulfide and sulfite would be ... 

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