The temperature dependence of the heat capacity of hydration water near biosurfaces from molecular simulations

The temperature dependence of the components of the potential energy and specific heat C-p of the hydration water is studied by simulations of hydrophobic and hydrophilic peptides in water. In hydration shells of both peptides, the C-p of water exceeds the bulk value and decreases upon heating. At similar to 330 K, the C-p of hydration water undergoes qualitative changes: the contribution of water-water interactions within the hydration shell to C-p sharply decreases, whereas the contribution due to interactions between hydration and bulk water to C-p sharply increases. These changes occur in the temperature interval where the hydrogen-bonded network of the hydration water breakes upon heating. The improved connectivity between the hydration water and bulk water at high temperatures makes the surface of biomolecules effectively more hydrophobic and may affect dynamics of biomolecules and their aggregation.