Electrocatalytic properties of vitamin B-12 towards oxidation and reduction of nitric oxide

This paper reports on the catalytic behaviour of cyanocobalamin (VB12) towa rds the reduction and oxidation of nitric oxide. When VB12 is adsorbed on g lassy carbon electrodes, it catalyses the reduction of nitric oxide (NO) in pH 4 and 9 buffers. In the absence of NO, cyclic voltammetry shows that VB 12 is reduced by a one-step two-electron reduction from Co-III to the Co-I species. Addition of NO at pH 9 to solutions of VB,, resulted in the splitt ing of the cyclic voltammetry peaks as a result of a consecutive one-electr on reduction of the central Co-III metal in VB12 to Co-II and finally to Co -I. Th, catalytic peak for oxidation of NO on a glassy carbon electrode mod ified with VB12 was observed at 1.71 V versus Ag\AgCl. at pH 9. The product s of the catalytic reduction of nitric oxide include ammonia and hydroxylam ine. (C) 2000 Elsevier Science Ltd. All rights reserved.