Kinetic Hydrogen/Deuterium Isotope Effects in Multiple Proton Transfer Reactions

Abstract

Abstract In this paper, a description of multiple kinetic isotope effects (MKIE) of degenerate double, triple and quadruple proton transfer reactions in terms of formal kinetics is developped. Both single and multiple barrier processes are considered, corresponding to so-called “concerted” and “stepwise” reaction pathways. Each step is characterized by a rate constant and the transfer of a given H isotopes or ensemble of H isotopes. The MKIE are expanded in terms of kinetic H/D isotope effects P contributed by single sites in which a proton is transferred in the rate limiting steps. By combination with a modified Bell tunneling model the formalism developed can be used in order to take into account tunneling effects of both concerted and stepwise multiple proton transfers at low temperatures.