Effects of Base on Oxidation of an NADH Model Compound by Iron(III) Complexes and Tetracyanoethylene

Article abstract of DOI:10.1039/P29840000673

Effects of base on both an electron-transfer reaction from an NADH model compound, 1-benzyl-1,4-dihydronicotinamide (BNAH) to (3+) (N-N = 2,2'-bipyridine and 1,10-phenanthroline) and a hydride transfer from BNAH to tetracyanoethylene (TCNE) in acetonitrile have been examined.The stoicheiometry of the electron transfer from BNAH to (3+) in the absence of a base indicates that BNAH is a one-electron donor.In the presence of a base, however, BNAH acts as an apparent two-electron donor, when the two-electron transfer proceeds via a multistep process; a fast one-electron transfer from BNAH to (3+) occurred, followed by the rate-determining deprotonation of BNAH^+. by base and the subsequent fast electron transfer from BNA^. to (3+).The rate constants for the proton transfer from BNAH^+. to a series of pyridine derivatives have been determined.In the reduction of TCNE by BNAH, BNAH appears to be a two-electron donor in both the absence and presence of a base.Rates of the reduction of TCNE by BNAH increased with inceasing base concentration, suggesting the involvement of BNAH^+. as an intermediate in the hydride transfer from BNAH to TCNE.The kinetic analyses have led to the evaluation of the proton transfer rate constants for the deprotonation of BNAH^+. with various bases, which accord with those obtained from the electron-transfer reactions of BNAH with (3+) in the presence of bases.Based on the Broensted plot of the proton transfer rate constants as well as the variation of the primary kinetic isotope effects k_H/k_D with the pK_a of the base, the pK_a value for BNAH^+. has been evaluated as 3.6 +/-0.4.

Full text of DOI:10.1039/P29840000673

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