Changes in hydrophobic and hydrophilic hydration properties caused by raising the pressure or by lowering the temperature

We analyze entropic and energetic components of the hydration free energy (HFE) for hydrophobic and hydrophilic solutes under isochoric condition using the angle-dependent integral equation theory combined with a multipolar water model. The entropic component, which always makes a positive contribution to the HFE, becomes larger at high pressures and smaller at low temperatures for both solutes: it governs the pressure and temperature dependence of the HFE. For hydrophilic solutes at low temperatures, however, the energetic component becomes more important and makes them less hydrophilic. We discuss the validity of our previous studies on pressure and cold denaturating of proteins.