Kinetics of Electrochemical Reduction of NAD+ on a Glassy Carbon Electrode

Abstract

The kinetics of reduction of nicotinamide adenine dinucleotide, NAD+, was investigated on glassy carbon (GC) electrode at various temperatures, electrode potentials and NAD+ concentrations using electrochemical methods of linear polarization voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. It was shown that under the experimental conditions employed, the NAD+ reduction reaction is under diffusion control, is irreversible (requires overpotential of more than -550 mV), and is of pseudo-first order with respect to NAD+. The reduction process involves the exchange of 1.54 or 1.62 electrons, depending on reduction potential. This indicates that 54 or 62 mol% of NADH is produced, respectively, while the remaining quantity is NAD2. The kinetics of NAD+ reduction at a formal potential of the NAD+/NADH couple was found to be rather slow, and only moderately temperature dependent: the apparent formal heterogeneous electron-transfer rate constant is in the order of 10-14 cms-1, and the apparent formal Gibbs energy of activation is 53.1 kJmol–1.