Oxidation of NADH Involving Rate-Limiting One-Electron Transfer

Article abstract of DOI:10.1021/ja00335a062

The kinetics and the mechanism of the oxidation of NADH by ferrocenium cation (1a) and several substituted ferrocenium cations in aqueous 1-propanol are reported.All reactions were found to be first order in both NADH and ferrocenium cation.The rate of oxidation of NADH by 1a was found to be independent of pH and showed no change in rate when <4-1H,4-2H>NADH or <4-2H,4-2H>NADH was used.All of these results are consistent with rate-limiting one-electron transfer.A plot of log k vs.E^o for the ferrocenium/ferrocene couples gave a straight-line segment with slope = 16.0 V^-1.By extrapolation of this line to the diffusion-controlled rate limit the E^o for the NADH/NADH^+. couple was found to be 1.05 V vs.NHE in PrOH/H2O.When the Rehm-Weller relationship was used, the ΔG(excit.) value for NADH/NADH^+. self-exchange was calculated to be 5.6 kcal mol^-1.The best estimates in aqueous solution are E^o = 0.93 V and ΔG(excit.) = 5.6 kcal mol^-1.The mechanistic implications of these results are briefly discussed.