Free energy convergence in short- and long-length hydrophobic hydration

Abstract

We show, through molecular dynamics, that the hydration free energy of model hydrocarbons, exhibits a convergence temperature in supercooled water, TG∗ ~ 255 K ± 10 K, around which, hydration entropy and enthalpy minima are observed. Further, although entropy convergence at TS∗ ~ 400 K ± 10 K is found to be violated by large non-spherical hydrocarbons, due to “folding”, a free energy maximum is still observed, opposite to hard spheres. Evidence is provided that the entropy and enthalpy minima are associated with shell-bulk water structural differences, also observed between low-density liquid and high-density liquid water, around TG∗, specifically, the occurrence of an orientational order maximum.