Sodium tetrathionate

Sodium tetrathionate (Na2S40g) 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 (S2O3 =) 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). 

The macromolecule containing sulfhydryl residues to be blocked or protected is dissolved in a buffer suitable for its individual stability requirements. The blocking process may be done on a purified protein or during the early stages of a purification process to protect sulfhydryl-active centers from oxidation. PBS buffers containing 1 mM EDTA work well. 

To remove the sulfenylthiosulfate blocking group, add a 300-fold excess of DTT over the amount of blocked sulfhydryls present. Alternatively, add DTT to obtain a 0.01—0.1 M final concentration. Cysteine also may be utilized to regenerate some enzymes to full activity. 

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The amount of sodium hypochlorite in a bleach solution can be determined by using a given volume of bleach to oxidize excess iodide ion to iodine CIO- is reduced to Cl-. The amount of iodine produced by the redox reaction is determined by titration with sodium thiosulfate, Na2S203 I2 is reduced to I-. The sodium thiosulfate is oxidized to sodium tetrathionate, Na2S406. In this analysis, potassium iodide was added in excess to 5.00 ml of bleach d = 1.00 g/cm3). If 25.00 mL of 0.0700 MNa2S203 was required to reduce all the iodine produced by the bleach back to iodide, what is the mass percent of NaCIO in the bleach ... 

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... 

Theis, F.V., and Freeland, M.R. (1941) Thrombo-angiids obliterans clinical observations and arterial blood oxygen studies during treatment of the disease with sodium tetrathionate and sodium thiosulfates. Ann. Surg. 113(3), 411-423. 

Fig. 6 (a) SQ and (b) DQ rotor-synchronized 2H MAS NMR spectra of sodium tetrathionate dihydrate-d4 (solid lines). The dashed line in (a) represents the exact numerical simulation of the SQ spectrum for random molecular motion with the rate constant k given in the figure, (c) The corresponding experimental and simulated static 2H quadrupolar-echo spectra, (d) Simulated SQ (solid line) and DQ (dashed line) linewidths as functions of k. (Reproduced with permission from [88])... 

Baskin S, Kirby S. 1990. Effect of sodium tetrathionate on cyanide conversion to thiocyanate by enzymatic and non-enzymatic mechanisms [Abstract], The Toxicologist 10 326. 

Theory Iodine solution may also be standardized by using sodium thiosulphate (AR-Grade) whereby the latter gets oxidized to sodium tetrathionate as expressed below ... 

Sodium thiosulfate is a common reducing agent. It reduces iodine to iodide anion forming sodium tetrathionate. This reaction is utilized in the so-called iodometric titration ... 

Additional Exercise Sodium tetrathionate, Na2S406-2Hs0. 

Tetrathionic Acid, H2S4Oe.—Formation.—(l) From Thiosulphates As is well known, sodium tetrathionate is produced by the interaction of sodium thiosulphate and iodine ... 

Figure 102 Sodium tetrathionate reacts with thiols to form reactive sulfenylthiosulfate intermediates.

The crude product contains about 40 g. of sodium selenopentathionate 3-hydrate and about 4 mol per cent of sodium tetrathionate. It is dissolved in 50 ml. of 0.2 N hydrochloric acid at about 30°, and the solution is filtered with suction. One hundred milliliters of methanol is added, and the mixture is cooled in an ice-salt mixture. Pure sodium selenopentathionate 3-hydrate precipitates and is filtered, washed with ethanol, and dried in vacuo over sulfuric acid. The yield is about 25 g. (55%). 

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. 

With hydrogen peroxide the first product is sodium tetrathionate, and the solution becomes alkaline ... 

Sodium thiosulphate is employed in iodometry, being converted by the action of iodine into sodium tetrathionate ... 

Sodium tetrathionate, Na2S408.—The tetrathionate is prepared from the thiosulphate either by the action of iodine (p. 124) or by oxidation with cupric chloride.15 It can be precipitated from solution by addition of alcohol. With sodium carbonate it yields sodium thiosulphate 16... 

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