1H NMR Study of the Rates and Isotope Effects of the NADH Model Hydride Transfer Reaction

The kinetics of reaction of [4,4-(H,H)]-BzNADH and [4,4-(H,D)]-BzNADH with methyl benzoylformate (MBF) and p-benzoquinone (BQ) in CD3CN and in the presence of Mg(ClO4)2 has been studied by 1H NMR spectroscopy. Prior investigations of mechanisms of 1,4-dihydropyridine oxidations have employed the less informative methods of uv/vis spectrophotometry. No 1H NMR evidence was found for the hydration of BzNADH nor for the reaction of starting BzNADH and product BzNAD+ which would lead to isotope scrambling in the course of reaction. Calculated values of PKIE and SKIE suggest a mechanism change from a single step H− transfer for BzNADH oxidation with MBF to a multistep e−, H+, e− transfer for BzNADH oxidation with BQ.