| Abstract
| - We combine two-color ultrafast infrared spectroscopy and molecular dynamics simulation toinvestigate the hydration of carbonyl moieties in a dimyristoyl−phosphatidylcholine bilayer. Excitation withfemtosecond infrared pulses of the OD stretching mode of heavy water produces a time dependent changeof the absorption band of the phospholipid carbonyl groups. This intermolecular vibrational coupling affectsthe entire CO band, thus suggesting that the optical inhomogeneity of the infrared response of carbonylin phospholipid membranes cannot be attributed to the variance in hydration. Both the experimental andthe theoretical results demonstrate that sn-1 carbonyl has a higher propensity to form hydrogen bondswith water in comparison to sn-2. The time-resolved experiment allows following the evolution of the systemfrom a nonequilibrium localization of energy in the OD stretching mode to a thermally equilibrated conditionand provides the characteristic time constants of the process. The approach opens a new opportunity forinvestigation of intermolecular structural relations in complex systems, like membranes, polymers, proteins,and glasses.
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