524—NAD/NADH as a model redox system: Mechanism, mediation, modification by the environment

• Published in: Journal of electroanalytical chemistry and interfacial electrochemistry 1982, Vol.141 (3), p.365-378
• Main Authors: Elving, Philip J., Bresnahan, William T., Moiroux, Jacques, Samec, Zdenek
• Format: Article
• Language: English
• ISSN: 0022-0728
• DOI: 10.1016/0022-0728(82)85223-6

The biologically important redox couple, β-nicotinamide adenine dinucleotide/1,4,β-dihydronicotinamide adenine dinucleotide, provides a grossly reversible prototype system for an overall electrode reaction consisting of two successive one-electron (1 e −) transfer steps coupled with (a) dimerization of an intermediate free radical product, (b) protonation—deprotonation of an intermediate product, (c) other chemical reactions, (d) adsorption of reactant, intermediate and product species, and (e) mediation by electrode surface species. Cathodic reduction of NAD + proceeds through two 1 e − steps well separated in potential; protonation of the free radical produced on the first step occurs prior to the second electron-transfer; a first-order chemical reaction coupled to the latter may involve rearrangement of an initial dihydro product to 1,4-NADH (and some 1,6-NADH). In the apparently single stage 2 e − anodic oxidation of NADH, the initial step is an irreversible heterogeneous electron transfer, which proceeds to at least some extent through mediator redox systems located close to the electrode surface; the resulting cation radical, NADH + −, loses a proton (first order reaction) to form a neutral radical, NAD −, which may participate in a second heterogeneous electron transfer (ECE mechanism) or may react with NAD + − (disproportionation mechanism DISP 1 or half-regeneration mechanism) to yield NAD +.