Electrochemical reduction of NAD+ on a polycrystalline gold electrode

A range of dc and ac electrochemical techniques was used to investigate the kinetics of NAD(+) reduction on a polycrystalline gold electrode surface. It has been shown that the reduction of NAD(+) on gold is irreversible and occurs at cathodic overpotentials larger than -0.2 V Depending on the reduction potential applied, the ratio between the amount of enzymatically active 1,4-NADH and inactive NAD(2) formed changes from 0.78 at overpotential -0.515 V down to 0.28 at overpotential -0.715 V. The NAD(+) reduction reaction was found to be mass-transport controlled, and of first order with respect to NAD(+). It was shown that the reversible adsorption of NAD(+) reduction reaction products, NAD(2) and NADH, occurs if the stationary electrode is polarized for a longer time in the potential region of NAD(+) reduction, causing electrode fouling. An NAD(+) reduction reaction kinetic model was proposed and successfully validated. A set of kinetic parameters was calculated and verified independently using various experimental techniques: the apparent transfer and diffusion coefficients, the apparent formal heterogeneous electron-transfer rate constant, and the apparent Gibbs energy of activation. (c) 2006 Elsevier B.V. All rights reserved.