Multiple Pathways in the Oxidation of a NADH Analogue

Abstract

Oxidation of the NADH analogue, <i>N</i>-benzyl-1,4-dihydronicotinamide (BNAH), by the 1e^– acceptor, [Os­(dmb)₃]³⁺, and 2e^–/2H⁺ acceptor, benzoquinone (Q), has been investigated in aqueous solutions over extended pH and buffer concentration ranges by application of a double-mixing stopped-flow technique in order to explore the redox pathways available to this important redox cofactor. Our results indicate that oxidation by quinone is dominated by hydride transfer, and a pathway appears with added acids involving concerted hydride-proton transfer (HPT) in which synchronous transfer of hydride to one O-atom at Q and proton transfer to the second occurs driven by the formation of the stable H₂Q product. Oxidation by [Os­(dmb)₃]³⁺ occurs by outer-sphere electron transfer including a pathway involving ion-pair preassociation of HPO₄^2– with the complex that may also involve a concerted proton transfer