Investigating the mechanism of proton translocation in solution: from small chemical systems to biomolecules

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The major theme of research outlined in this proposal is the investigation of the mechanism of proton transfer reactions in aqueous solutions using computational approaches. These processes play a fundamental role in numerous chemical and biochemical transformations, including acid-base reactions, enzyme catalysis, substrate binding and energy transduction. Theoretical investigations of proton transfer reactions in bulk water, at the interface between aqueous and hydrophobic media, as well as in biologically-relevant systems have been actively pursued for at least two decades. However, with the recent advent of ultrafast, time-resolved vibration spectroscopy techniques, the aforementioned proton transfer processes can for the first time be directly probed with the relevant space and time resolution. This opens new opportunities for computational chemistry to contribute to the advancement of our fundamental understanding of proton transfer reactions.******A key objective of the present research program is to improve the existing arsenal of computational methods that can complement the aforementioned spectroscopy techniques. In this vein a novel methodology will be presented, which allows us to perform first-principles molecular dynamics calculations that can be related to a recently reported series of state-of-the-art, femtosecond-resolved UV pump/mid-IR probe acid-base neutralization experiments. An important goal of these theoretical studies will be to establish the elementary steps comprising acid-base neutralization in water, but the information thus obtained will also be relevant to processes at surfaces and interfaces. ******The investigation of proton translocation in the 3D H-bond network of bulk water will be complemented by a study of nuclear quantum effects. The latter project will involve adapting and developing existing computational methodologies that allow one to compute and interpret first-principles thermodynamic and kinetic isotope effects.