Effect of Zn(II) and its complexes on the kinetics of the hydride transfer reduction of an NAD+ model by isopropanol

ORGN 144

Donald Endicott, dendico@siue.edu, William E Kuester, wkueste@siue.edu, and Yun Lu, yulu@siue.edu. Department of Chemistry, Southern Illinois University Edwardsville, Edwardsville, IL 62026
We recently reported a kinetic study of the hydride transfer reaction from isopropanol to an NAD+ model, N-methylacridinium ion (MA+) (Tetrahedron Lett. 2007, 48, 6356). The reaction is believed to be an effective model of the alcohol dehydrogenase reaction. The complexed Zn(II) in the active site of the enzyme catalyzes the hydride reduction of the NAD+ with alcohols by forming a reactive zinc alkoxide. We report the study of the effect of Zn(II) and its complexes on the kinetics of our model reaction in order to provide insights into the role of the Zn(II) during the biochemical process. No rate acceleration was observed for the reactions in the presence of either the free or complexed form of Zn (II). This may be explained in terms of electrostatic repulsion effect between MA+ and the positively charged zinc(II) associated with the alkoxide so that the chances for the two species to react are little.