%0 Journal Article %A Sundar, J. Vijaya %A Subramanian, V. %D 2012 %T Mechanistic Studies on the pH-Controllable Hydrogenation of NAD+ by H2 and Generation of H2 from NADH by a Water-Soluble Biomimetic Iridium Complex %U https://acs.figshare.com/articles/journal_contribution/Mechanistic_Studies_on_the_pH_Controllable_Hydrogenation_of_NAD_sup_sup_by_H_sub_2_sub_and_Generation_of_H_sub_2_sub_from_NADH_by_a_Water_Soluble_Biomimetic_Iridium_Complex/2457550 %R 10.1021/om300812k.s001 %2 https://acs.figshare.com/ndownloader/files/4100230 %K NAD %K nicotinamide adenine dinucleotide %K H 2 %K NADH %K pH %K medium %K activation barrier height %K mechanism %K Ir %X Functional biomimicking of hydrogenases at ambient conditions is challenging. Recently an Ir­(III)-cyclometalated complex (J. Am. Chem. Soc. 2012, 134, 367) has been shown to catalyze the pH-dependent reversible reduction of NAD+ (nicotinamide adenine dinucleotide) by dihydrogen in water medium. Yet, the reaction mechanism for the catalysis has not been unravelled comprehensively. Hence in this work, mechanisms for catalytic hydrogenation of NAD+ to the reduced form of NAD+ (NADH) and the reverse reaction catalyzed by the Ir­(III)-cyclometalated complex have been proposed using the results obtained from density functional theory based calculations. The mechanism suggests that the carboxylate group of the Ir­(III) complex can act as a proton relay between hydrogen and water molecules. As a consequence, the direction of the reaction is controlled by the pH of the medium. Splitting of H2 and generation of H2 are the rate-determining steps in the two directions with the same activation barrier height of 34.6 kcal/mol. Also, the mechanism supports that the σ-bond metathesis is preferred over oxidative addition of hydrogen. Results show that NADH may act as an inhibitor of the substrate at high basic pH. %I ACS Publications