Study of the Effects of Remote Heavy Group Vibrations on the Temperature Dependence of Hydride Kinetic Isotope Effects of the NADH/NAD Model Reactions.

It has recently been observed that the temperature()-dependence of KIEs in H-tunneling reactions, characterized by isotopic activation energy difference (Δ = - ), is correlated to the rigidity of the tunneling ready states (TRSs) in enzymes. A more rigid system with narrowly distributed H-donor-acceptor distances (DADs) at the TRSs gives rise to a weaker -dependence of KIEs (i.e.