ED mechanisms: electrodimerization of N′-methyl nicotinamide on mercury electrodes in aqueous solutions

Abstract

The electrodimerization of the NAD + model compound N′-methyl nicotinamide has been studied in aqueous media in the pH range 4–11 by direct current and differential pulse polarography and linear-sweep cyclic voltammetry. Tafel slopes and reaction orders were obtained from I- E curves traced at potentials corresponding to the foot of the polarographic wave. Controlled-potential electrolysis indicated that at pH 5 and 8 one electron is transferred per reactant molecule and a dimer must be obtained. The reduction pathways consisted of the reversible transfer of one electron, preceded by the transfer of either two (first wave) or one (second wave) H + ions, followed by an irreversible electrodimerization which was the rate-determining step, in agreement with that which occurs in the reduction of other model compounds and the NAD + coenzyme itself at these pH values. The dimerization reaction is a radical-radical coupling taking place in the reaction layer.