OXIDATION OF CYSTEINE, CYSTEINESULFINIC ACID AND CYSTEIC ACID ON A POLYCRYSTALLINE GOLD ELECTRODE

The mechanism electro-oxidation of cysteine, cysteinesulfinic acid and cysteic acid in perchloric acid solutions has been studied using cycl ic voltammetry. All the compounds investigated have been found to be c hemisorbed on a polycrystalline gold electrode, and oxidized with four , two or one electron respectively. The water molecule coadsorbed with cysteine participates in the cysteine one-electron oxidation with a l ower energy requirement, whereas bulk water is involved in multiple el ectron transfer reactions at the completely covered electrode surface. A strong inhibiting effect of chloride anions on the cysteine oxidati on has been observed at the partially covered electrode surface. The e ffect of the adsorbate surface coverage on the reaction mechanism in a nodically catalyzed reactions involving oxygen transfer is discussed.