Evidence for Anomalous Hydration Dynamics near a Model Hydrophobic Peptide

We present new quasi-elastic neutron scattering experiments and simulation analysis for studying the hydration water dynamics of N-acetyl-leucine-methylamide (NALMA) solutions as a function of concentration and temperature. The experiments show non-Arrhenius translational dynamics over the temperature range of −3 to +37 °C for all concentrations, and fits to the experimental intermediate scattering function show nonexponential relaxation dynamics. While the lower-concentration NALMA solution could be classified as an intermediate to strong liquid, the higher concentration is legitimately defined as a fragile liquid, and the hydration dynamics of the most concentrated solution exhibits very good correspondence with the same signatures of non-Arrhenius behavior and nonexponential dynamics as that observed for supercooled water well below −20 °C. The corresponding molecular dynamics simulation analysis of the high concentration data using the SPC water model, a common companion water model used in protein si...