Structure and water dynamics of aqueous peptide solutions in the presence of co-solvents

Abstract

We perform neutron diffraction and quasi-elastic neutron scattering (QENS) to probe hydration water structure, and dynamics down to supercooled temperatures, of a concentrated amphiphilic peptide system with the co-solvents glycerol and dimethyl sulfoxide. We find that the kosmotropic co-solvent glycerol preserves the hydration structure near the peptide that is observed in the water solvent alone, that in turn preserves the dynamical temperature trends of two water relaxation processes—one corresponding to a localized relaxation process of the peptide bound surface water and a second relaxation process of the outer hydration layers. By contrast the chaotropic co-solvent, by disrupting the hydration layer near the peptide surface, eliminates the inner hydration layer relaxation process induced by the peptide, to show a single time scale for translational water dynamics.