A quantum chemical approach to the mechanism of the biochemical action of nicotinamide

The reaction of protonated nicotinamide with hydride ion, which models the transfer of hydrogen from a substrate to the nicotinamideadeninedinucleotide (NAD) molecule, i.e., the principal biological function of vitamin PP, was investigated by optimization of the geometry in terms of the self-consistent field (SCF) method with allowance for configuration interaction (CI) in the PM-3 approximation. It was shown that the initial event of the reaction is electron transfer, followed by the addition of a hydrogen atom to the NAD radical. The addition product is relatively stable and has a heat of formation of-68.25 kJ/mol. The geometric structure and the distribution of charges of the reagent and also the behavior of the singlet and triplet terms in the course of the reaction were analyzed. ©1999 Kluwer Academic/Plenum Publishers.