Temperature Dependence of the Primary Kinetic Isotope Effect in Hydride Transfer Reactions with NAD+and NADH Models

N1-(2,6-dichlorobenzyl)-1,4-(1H2)dihydronicotinamide and N1-(2,6-dichlorobenzyl)-1,4-(1H,2H)dihydronicotinamide were oxidized with nitrosobenzene (NOB), 2,6-dichloroindophenol (DCPIP), 2,4,6-trinitrobenzenesulfonic acid (TNBS), 10-methyl-acridinium ion (MAI), and 10-methyl-9-phenyl-acridinium ion (MPAI). In addition, 2-propanol-h8and 2-propanol-d8were oxidized by NAD+in the presence of yeast alcohol dehydrogenase. Investigation of the temperature dependence of the kinetic isotope effect indicated that the redox reactions with MAI and MPAI have very similar thermodynamic characteristics and proceed via a linear transition state. Redox reactions with NOB, DCPIP, and TNBS have entirely different thermodynamic characteristics, and probably proceed via a different transition state. Thermodynamic characteristics of enzymatic reaction are very similar to model redox reactions with MAI and MPAI.