On the Possibility of Detecting Low Barrier Hydrogen Bonds with Kinetic Measurements

Recent experimental evidence has pointed to the possible presence of a short, strong hydrogen bond in the enzyme-substrate transition states in some biochemical reactions. To date, most experimental measures of these short, strong hydrogen bonds have monitored their equilibrium properties. In this work we show that kinetic measurements can also be used to detect the presence of short, strong hydrogen bonds. In particular, we find nontrivial differences among rate constant ratios of protonated to deuterated hydrogen bonds between strong and weak hydrogen bonds for proton transfer between donor-acceptor sites. We quantify this kinetic isotope effect by performing dynamical calculations of these rate constants by computing reactive flux through a dividing surface. This reactive flux is computed by evolving trajectories on an effective quantum mechanical potential energy surface.