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

We show, through molecular dynamics, that the hydration free energy of model hydrocarbons, exhibits a convergence temperature in supercooled water, T*(G) similar to 255 K +/- 10 K, around which, hydration entropy and enthalpy minima are observed. Further, although entropy convergence at T*(S) similar to 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 T*(G), specifically, the occurrence of an orientational order maximum. (C) 2021 Elsevier B.V. All rights reserved.