Water's Thermal Pressure Drives the Temperature Dependence of Hydrophobic Hydration

With the aid of literature experimental data and reported results from molecular simulation, two thermodynamic relations are found to provide a theoretical basis for the understanding of a variety of characteristic features associated with the solvation of small nonpolar molecules in water. Thus, the large and positive solvation heat capacity, enthalpy-entropy compensation, the solubility minimum and solvation free energy maximum with respect to temperature, enthalpy convergence, and entropy convergence are rationalized in a unified way. Our key finding is that all of these phenomena are driven by the thermal pressure coefficient of pure water, which, via the isobaric thermal expansivity and the isothermal compressibility, reflects its unusual thermodynamics. Remarkably, the solubility minimum is found to be a direct consequence of water's density maximum.