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 stereochemistry.