Electrochemical lability of glycine in acid media

Abstract

Electrochemical lability of different glycine species is considered on the basis of voltammetric data obtained for hydrogen evolution on the copper electrode in weakly acidic glycine solutions at different potential sweep rates (v). Voltammograms contain well-defined current peaks the height of which depends on both solution pH and glycine concentration. Current peaks and their potentials vary linearly with √−v and log v, respectively, this being typical of the electrochemical processes controlled by diffusion and charge transfer.
To characterise system lability, peak coordinates and convolutive transforms of voltammograms are analysed. The results show that protons attached to different groups in a glycine molecule exhibit different mobility. In contrast to the protonated amino group, the release of a proton from the carboxylic group proceeds significantly faster. Consequently, protonated species +H3N–CH2–COOH can be treated as labile proton donors, whereas zwitterions +H3N–CH2–COO– do not fall into this category.