Electrochemical Studies of Zinc/Cysteine Interactions

Abstract

The electrochemical behavior of L-cysteine has been investigated in the presence of ZnSO4 in pH 7.4 phosphate and pH 7.4 MOPS buffers. In the phosphate buffer, addition of ZnSO4 caused a cloudy appearance due to formation of zinc phosphate. A visual indication of the Zn2+/cysteine interaction was observed by the solution turning clear upon cysteine addition in a 1:2 Zn2+ : L-cysteine ratio. Voltammetry of L-cysteine at glassy carbon and gold electrodes revealed a +0.2 V shift in the L-cysteine oxidation peak potential upon addition of ZnSO4 to L-cysteine. A similar, but negative, shift in Zn2+ reduction potential was observed at glassy carbon in pH 7.4 MOPS buffer upon addition of L-cysteine. Voltammetric studies of L-cysteine at gold in pH 4.7 acetate buffer are included for comparison to those at pH 7.4