US-France Cooperative Research: Molecular Dynamics Simulation of Proton Transfer Reactions in Solution

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This award will support collaborative research between Dr. James Hynes, University of Colorado, and Dr. Daniel Borgis, Laboratoire de Physique Theoretique des Liquides, University of Pierre and Marie Curie, Paris, France. The objective of the project is to develop an improved theory for treating simple proton transfer reactions in solution. Protein transfer reactions in solution play a central role in chemistry, in particular in acid-base chemistry and enzyme catalysis. However, no comprehensive molecular level description of such reactions and their rates yet exist. In part, this is due to their special character, which includes quantum proton tunnelling through a barrier rather than classical thermal activation over it, and an essential involvement of the surrounding polar solvent molecules strongly coupled to the proton. Aided by recent advances in theoretical and computer simulation techniques, the investigators propose to perform molecular dynamics computer simulation of model proton transfer reactions in polar solvents. Reaction rates will be calculated and the role of solvent polarity and dynamics, and of certain molecular vibrations, will be determined. Simple yet realistic models will be initially employed to clarify the essential reaction features and to establish the simulation techniques. The systems studied will then progress to even more realistic systems directly susceptible to experimental investigation. Emphasis will be placed on calculating quantities (e.g. solvent dependence, isotope effects) which can guide the interpretation of experiments. A detailed microscopic description of proton transfer reactions is expected to result from the project. The proposed study should provide theoretical insight into understanding this important reaction class and also should provide an impetus for new experiments to probe the influence on these rates of solvent polarity and dynamics. The project will benefit for the complementary expertise of the two investigators in this rapidly developing area of physical chemistry.