Electrocatalytic oxidation of NADH at polythionine-modified electrodes as studied by rotating disk voltammetry

The electrocatalytic oxidation of NADH at polythionine-modified electrodes was studied by linear potential-sweep voltammetry, rotating disk voltammetr y, and ultraviolet spectroscopy, The high overpotential of NADH was decreas ed by 0.5 V by modifying GC electrode with polythionine. The rate constant for oxidation of NADH decreased with increasing NADH concentration in solut ion at each, pH values, indicating that the electrooxidation of NADH occurs via a intermediate complex [NADH-pTh]. The electrooxidation of NADH at a p olythionine-modified electrode was limited by the rate of the conversion of the intermediate complex to NAD(+) and pTh. The rate constant for the diss ociation of the intermediate complex decreased with decreasing pH value. Th is decrease may be due to a poor electron-donating property of NADH in an a cidic solution or most probably to the great stability of protonated interm ediate complex in an acidic solution.