Anodic oxidation of dihydronicotinamide adenine dinucleotide at solid electrodes; mediation by surface species

Abstract

The mechanism and kinetics for the two-electron oxidation of 1.4-dihydronicoeueamide adenine dinucleotide (NADH) to NAD+ at gold, platinum and glassy carbon (GC) rotating case electrodes at various solution pH and NADH concentrations can be rationalized in terms of the electron transfer occurring through mediator redox systems, located close to the electrode surface, such as the redox couples formed by oxygen-containing species adsorbed at Au and Pi surfaces. Analogous catalysis of NADH oxidation is provided by sulfide species adsorbed on a gold electrode surface. An important factor in differentiating the behavior of the three types of electrodes is the strong adsorption of NADH at Pt and Au, and of NAD+ at GC. Since oxidation of adsorbed NADH starts at more positive potential than oxidation of bulk NADH, the latter occurs at Au or Pt electrode surfaces covered by adsorbed NADH, or at GC electrodcs surfaces covered to ionic extent by adsorbed NAD+. The theory for the surface EC catalytic mechanism is considered.