Computing the Nonlinear Vibrational Response of Liquids and Biomolecules

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Roger Loring of Cornell University is supported by the Theoretical and Computational Chemistry Program to develop methods for modeling nonlinear infrared spectroscopy in liquids and biomolecules with an atomistic level of description. Experimental observables in two-pulse and three-pulse vibrational echo measurements will be computed using classical molecular dynamics simulations. The fundamental theoretical issue underpinning this research is determining the optimal use of classical mechanical molecular dynamics data for complex systems to calculate nominally quantum mechanical observables. Two closely coupled research directions will be pursued: (1) to establish rigorously the validity regime of classical mechanical echo calculations, by performing numerically exact classical and quantum calculations for the same model system, and (2) to perform classical echo calculations for liquid-state and biomolecular models, for which quantum treatment is not feasible. Calculations will focus on myoglobin-CO, for which experiments are now characterizing the nature and time scales of protein fluctuations. Computing vibrational echoes in myoglobin-CO will identify the specific protein dynamics sensed by the CO ligand, and will guide the application of these new laser laboratory techniques to other bimolecular systems.Molecular motions in liquid solvents and in the heterogeneous environments of proteins are an integral part of the dynamics of chemical reactions and biological processes. A new generation of spectroscopic techniques can probe these motions directly. This research will allow for a detailed molecular picture of these processes by interpreting these new measurements.