We have developed methods for predicting and interpreting ultrafast vibrational spectra of ester groups in lipid membranes. Lipid membranes are essential to life, but their organization and dynamics remain poorly understood due to their complexity and heterogeneity. In particular, the electrostatics of lipid-water, lipid-protein, and lipid-ion interactions are not well understood.<br/><br/>Ultrafast vibrational spectroscopy, specifically two-dimensional infrared spectroscopy (2D IR), reports on the electrostatic environment near an oscillator on a sub-picosecond time scale. The combination of time resolution and sensitivity to local environment makes 2D IR a promising tool for studying dynamics and electrostatic interactions in complicated systems such as lipid membranes. Additionally, 2DIR spectra can be predicted from molecular dynamics trajectories, making interpretation of 2D IR spectra quantitative and atomistic. Unfortunately, this has been unsuccessful in the past for lipid systems, which has limited the amount of information obtained in lipid 2D IR studies.<br/><br/>We have been able to satisfactorily calculate vibrational spectra of ester stretching vibrations in lipid bilayers from molecular dynamics simulations and a computationally efficient electrostatic map. Additionally, we have found that much of the disagreement between calculated and experimental spectra comes from problems with predicting the orientations of the carbonyl bonds themselves, and that as long as the force field is able to predict these angles, reasonable spectra can be calculated.

Simulations and spectroscopy of interfacial environments in lipid membranes

255th National Meeting (2018)

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