Electrocatalytic Oxidation of NADH at Polythionine-modified Electrodes as Studied by Rotating Disk Voltammetry

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