NAD(P)H-NAD(P)+ MODELS .74. ENTROPY-CONTROLLED KINETICS, STEREOCHEMISTRY, AND TUNNELING EFFECT

Kinetics have been studied for the reactions of three NAD(P)H analogs and their 4-deuteriated compounds with 2,6-dichloro- and tetrachloro-1,4-benzoquinones. It has been elucidated that the entropy term occupies 50-90% of the Gibbs energy of activation at 298 K. Thus, the reaction is almost entropy-controlled. For certain combinations of the reducing and oxidizing reagents, quantum mechanical tunneling effect plays a large role to determine the reaction rate. The tunneling effect may be another measure of the sterochemistry.