Disulfides sodium tetrathionate

Figure 1.121 Sodium tetrathionate reacts with thiols to form reactive sulfenylthiosulfate intermediates. Another sulfhydryl-containing molecule may couple to this active group to create a disulfide linkage.

A final method of forming disulfide crosslinks between toxins and targeting molecules is the use of S-sulfonate formation using sodium sulfite (Na2SC>3) in the presence of sodium tetrathion-ate (Na2S40g). Tetrathionate reacts with sulfhydryls to form sulfenylthiosulfate intermediates (section 1.1.5.2). These derivatives are reactive toward other thiols to create disulfide linkages... 

Sodium tetrathionate (Na2S406) is a redox compound that under the right conditions can facilitate the formation of disulfide bonds from free sulfhydryls. The tetrathionate anion reacts with a sulfhydryl to create a somewhat stable active intermediate, a sulfenylthiosulfate (Fig. 102). Upon attack of the nucleophilic thiolate anion on this activated species, the thiosulfate (S203 =) leaving group is removed and a disulfide linkage forms (Pihl and Lange, 1962). The reduction of tetrathionate to thiosulfate in vivo was a subject of early study (Theis and Freeland, 1940 Chen et al., 1934). 

Disulfides form spontaneously by autoxidation of thiols upon exposure to air. This process is, however, relatively slow and not useful for most microgel preparation techniques. Thus, oxidizing catalysts such as diamide [21], peroxides [22], and sodium tetrathionate [23], or a catalyst based on Fenton chemistry [24], are often applied in order to shorten the oxidation time. 

The enantiomorphs of a nonplanar disulfide sometimes become separated in crystals. Thus, diphenyl disulfide (43) and probably also di-p-tolyl disulfide (43) crystallize in enantiomorphous space groups with only one enantiomorph per unit cell, and so do barium tetrasulfide monohydrate (1) and sodium tetrathionate dihydrate (101). The same applies, of course, to L-cystine and other optically active disulfides. 

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