THE REACTIONS OF CYSTINE AT MERCURY-ELECTRODES

Cystine in aqueous solutions reacts chemically with mercury, forming t he surface-bound cysteine mercuric thiolate. When the potential of mer cury is made less positive this compound is transformed (at a partiall y free mercury surface in a currentless process and at an occupied ele ctrode under the passage of current) into cysteine mercurous thiolate. The latter compound is also formed in a reversible interaction of cys tine with mercury in the potential range where cystine is adsorbed. At the negative end of this range the electroreduction of cystine occurs by the reduction of cysteine mercurous thiolate. At negatively charge d mercury, where cystine is not adsorbed, two electrons are transferre d directly to the cystine -S-S- bond in an overall irreversible proces s. On the positive side the dissolution of mercury into solutions cont aining cystine starts by anodic formation of slightly soluble mercuric cystinate near the electrode surface.