OXIDATION-KINETICS OF NADH BY HETEROPOLYANIONS

A series of selected Dawson-type mixed heteropolyanions readily oxidiz e NADH in buffered aqueous pH 7 medium. The process was monitored by U V-visible spectroscopy, which helps to establish the 2:1 stoichiometry for the oxometalate/NADH couple. The starting system for electrochemi stry consists of the one-electron reduction product of the heteropolya nions in the presence of various amounts of NADH. Cyclic voltammetry c onfirms unequivocally that the oxidized forms of the selected heteropo lyanions are capable of catalyzing efficiently the oxidation of NADH. The kinetics were studied quantitatively by double step chronocoulomet ry. The logarithm of the second order rate constant was a linear funct ion of the Eo 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 o ne-electron transfer. An estimate of the EO value for the one-electron NADH/NADH(.+) redox couple has been obtained.