Interaction Metal Ions with NADH Model Compounds. Cupric Ion Oxidation of Dihydronicotinamides

摘要

Kinetic studies on cupric ion (Cu2+) oxidation of 1-benzyl- and 1-aryl-1,4-dihydronicotinamides (XNAH) in aqueous solution were performed. In the presence of dioxygen (O2), the reaction followed first order kinetics with respect to both XNAH and Cu2+. The oxidation reaction was found to be independent and parallel to the acid-catalyzed hydration reaction of XNAH. The catalytic role of Cu2+ for the oxidation of XNAH in the presence of O2 was attributed to Cu2+/Cu+ redox cycle by the reactions with XNAH and O2. The second order rate constants of the Cu2+ oxidation reaction kCu, and acid-catalyzed hydration reaction kH were strongly dependent on the nature of the substituents in 1-aryl moiety. The slopes of log kCu vs log KH and log kCu vs ヲp of the substituents plots were 1.64 and -2.2, respectively. This revealed the greater sensitivity of the oxidation reaction rate to the electron density on the ring nitrogen than the hydration reaction rate. A concerted two-electron transfer route involving XNAH-Cu2+ complex was proposed for mechanism of the oxidation reaction.