Mechanistic Aspects of the Electrochemical Oxidation of Dihydronicotinamide Adenine Dinucleotide (NADH)

Article abstract of DOI:10.1021/ja00541a024

The apparently single stage anodic oxidation of NADH involving removal of two electrons and a proton to form NAD⁺ has been examined with particular attention to the deprotonation step and its relationship to the initial potential-determining electron-transfer step, primarily at glassy carbon electrodes (GCE) in aqueous media with supplementary studies at pyrolytic graphite and platinum electrodes in aqueous media and at GCE in Me2SO; the carbon electrodes were generally first covered with an adsorbed NAD⁺ layer in order to eliminate adsorption-controlled faradaic processes.The initial step is an irreversible heterogeneous electron transfer (transfer coefficient β = 0.37 at carbon electrodes and 0.43 at platinum).The resulting cation radical NAD.H⁺ loses a proton (first-order reaction; rate constant k) to form the neutral radical NAD. which may participate in a second heterogeneous electron transfer (ECE mechanism) or in a homogeneous electron transfer with NAD.H⁺ (disproportionation mechanism DISP 1 or half-regeneration mechanism), yielding NAD⁺.The near identities of current functions, viscosity-corrected diffusion coefficients D and β values, point to essentially similar solute species and charge-transfer paths being involved in different media and at different electrodes.D is ca. 2 x 10^-6 cm² s^-1 in aqueous solution; k is ca. 60 s^-1 at the GCE covered with adsorbed NAD⁺.