A new model for the origin of kinetic hydrogen isotope effects

Measurements of kinetic hydrogen isotope effects in enzymatic C-H bond cleavage reactions have generated a body of data that is inconsistent with either a semi-classical formalism for the origin of the isotope effects or a semi-classical formalism together with a modest degree of hydrogen tunneling. A model that treats the movement of hydrogen as a wave, and whose behavior is dictated by the heavy atom environment, is presented and discussed. A list of unanswered questions and challenges is given at the end of this paper. Copyright (C) 2010 John Wiley & Sons, Ltd.