Aqueous peptides as experimental models for hydration water dynamics near protein surfaces.

We report quasi-elastic neutron scattering experiments to contrast the water dynamics as a function of temperature for hydrophilic and amphiphilic peptides under the same level of confinement, as models for understanding hydration dynamics near chemically heterogeneous protein surfaces. We find that the hydrophilic peptide shows only a single non-Arrhenius translational process with no evidence of spatial heterogeneity unlike the amphiphilic peptide solution that exhibits two translational relaxations with an Arrhenius and non-Arrhenius dependence on temperature. Together these results provide experimental proof that heterogeneous dynamical signatures near protein surfaces arise in part from chemical heterogeneity (energy disorder) as opposed to mere topological roughness of the protein surface.