The Electrochemistry of Disulfides and Related Compounds

At mercury electrodes Lee reported that cystine dissolved in perchloric acid was reduced to cysteine (Reaction 5.3) at a potential of —0.43 V, but that there was also evidence of the transient formation of mercurous cysteinate as a reaction 

Injection of excessive amounts of DTT also rapidly degrades electrodes, particularly Au/Hg electrodes. Newer reductants based on phosphine chemistry are claimed to be more efficient. Tri-n-butylphosphine is efiicient, but can be explosive in excess Triphenylphosphine is also an efficient reductant, but tris-(2-carboxyethyl)-phosphine solves most problems. Dithionite (sodium hydrosulfite) has also been used. 

Since disulfides can be completely reduced to thiols at voltages below — IV, off-line EC reduction can be useful. Saetre and Rabenstein reduced D-penicillamine-containing disulfides in plasma and blood after protein precipitation at a mercury-pool electrode held at —6 V. This procedure was also adopted by Bergstrom et A disadvantage of this approach is the assumption that only one disulfide is present and that it is totally reduced. No chromatographic identification of the disulfides is possible since only the reduced thiols are analysed. 

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