INVESTIGATION OF THE REDUCTION-MECHANISM OF THE NAD(-COMPOUND N'-METHYL NICOTINAMIDE ON MERCURY-ELECTRODES IN STRONGLY ACIDIC SOLUTIONS() MODEL)

The electroreduction of the NAD(+) model compound N'-methyl nicotinami de has been studied in acidic media (5 M H2SO4 to pH 5) by de and DP p olarography and linear-sweep cyclic voltammetry. Tafel slopes and reac tion orders were obtained from I-E curves traced at potentials corresp onding to the foot of the polarographic wave. The protonation pK of th e heterocyclic nitrogen was obtained from spectroscopic (UV) and poten tiometric measurements, having a value of 3.50 +/- 0.15. Controlled-po tential electrolysis indicated that at pH < 2.5 two electrons are tran sferred per reactant molecule and that the carbonyl group is reduced t o hydroxyl. The reduction pathway consists of the reversible transfer of an electron and an Hf ion followed by an irreversible one-electron transfer, which is the rate-determining step, in agreement with what o ccurs in the reduction of NAD(+) coenzyme at these pH values.