Oxidation kinetics of NADH by heteropolyanions

A series of selected Dawson-type mixed heteropolyanions readily oxidize NADH in buffered aqueous pH 7 medium. The process was monitored by UV-visible spectroscopy, which helps to establish the 2:1 stoichiometry for the oxometalate/NADH couple. The starting system for electrochemistry consists of the one-electron reduction product of the heteropolyanions in the presence of various amounts of NADH. Cyclic voltammetry confirms unequivocally that the oxidized forms of the selected heteropolyanions are capable of catalyzing efficiently the oxidation of NADH. The kinetics were studied quantitatively by double step chronocoulometry. The logarithm of the second order rate constant was a linear function of the E^o of the first redox systems of the heteropolyanions with a slope of 16.4 V^?1. This result indicates that the oxidation of NADH proceeds by a multistep mechanism involving an initial rate-limiting one-electron transfer. An estimate of the E^o value for the one-electron NADH/NADH^·+ redox couple has been obtained.