Solvation dynamics of a single water molecule probed by infrared spectra--theory meets experiment

The dynamics and energetics of water at interfaces or in biological systems plays a fundamental role in all solvation and biological phenomena in aqueous solution. In particular, the migration of water molecules is the first step that controls the overall process in the time domain. Experimentally, the dynamics of individual water molecules is nearly impossible to follow in solution, because signals from molecules in heterogeneous environments overlap. Although molecular dynamics simulations do not have this restriction, there is a lack of experimental data to validate the calculated dynamics. Here, we demonstrate a new strategy, in which the calculated dynamics are verified by measured time-resolved infrared spectra. The coexistence of fast and slow migrations of water molecules around a CONH peptide linkage is revealed for a model system representative of a hydrate peptide.