ED MECHANISMS - ELECTRODIMERIZATION OF N'-METHYL NICOTINAMIDE ON MERCURY-ELECTRODES IN AQUEOUS-SOLUTIONS

The electrodimerization of the NAD(+) model compound N'-methyl nicotin amide has been studied in aqueous media in the pH range 4-11 by direct current and differential pulse polarography and linear-sweep cyclic v oltammetry. Tafel slopes and reaction orders were obtained from I-E cu rves traced at potentials corresponding to the foot of the polarograph ic 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 transf er of one electron, preceded by the transfer of either two (first wave ) or one (second wave) H+ ions, followed by an irreversible electrodim erization 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 rad ical-radical coupling taking place in the reaction layer.