Dynamics and Kinetic Isotope Effect for the Double Proton Transfer in Formamidine Monohydrated Complex Using Direct Semiempirical Dynamics Calculation

Abstract

The dynamics of the double proton transfer in formamidine monohydrated complex has been studied by the direct semiempirical dynamics approach with variational transition-state theory using multidimensional semiclassical tunneling approximations. High-level ab initio quantum mechanical calculations were performed to estimate the energetics of the double proton transfer. Dimerization energies and the barrier height have been calculated at the G2* level of theory, which yields −7.50 and 16.6 kcal mol-1, respectively. A quantum mechanical potential energy surface has been constructed using the AM1 Hamiltonian with specific reaction parameters (AM1-SRP) which are obtained by adjusting the standard AM1 parameters to reproduce the energetics by high-level ab initio quantum mechanical calculation. The minimum energy path has been calculated on this potential energy surface, and other characteristics of the surface were calculated as needed. The two protons are transferred synchronously, so the transition state po...