Quantum localization, dephasing and vibrational energy flow in a trans-formanilide (TFA)-H2O complex

Recent stimulated emission pumping-population transfer spectroscopic studies are providing measurements of energy barriers to hydrogen bond rearrangements involving biological molecules and water. To determine the kinetics of hydrogen bond rearrangements we need in addition information about energy flow in the biomolecule-water complex. We address the problem of quantum energy flow in one such complex system using a random matrix approach. We report here calculations of energy flow in the peptide trans-formanilide (TFA) that account for the hydrogen bonding of a water molecule to one of two sites on the peptide. Coupling to the water is found to enhance energy flow in the peptide. At energies near the hydrogen bond rearrangement barrier the rate of energy flow in TFA is nevertheless sufficiently sluggish to have a significant impact on the kinetics of water shuttling between hydrogen-bonding sites.