The equilibrium solvation structure for the solvent-separated hydrophobic bond

Abstract

We present a detailed geometrical analysis of the solvent in an aqueous solution containing two nonpolar atomic solutes which are constrained to an interatomic distance corresponding to a solvent‐separated free energy minimum. The results are obtained from a molecular dynamics simulation using ST2 water. The interpretation of structural features attributed to the hydrophobiceffect are facilitated by a time averaging procedure which removes the high frequency librational excitation from the underlying liquid structure.Solvent reordering within the hydration shell surrounding the solutes is clearly revealed by octahedral resolution of orientational correlations and is consistent with the widespread view of ‘‘clathrate‐like’’ structure promotion induced by apolar moieties. Of particular interest, the relatively lengthy simulation reveals a rich variety of cage‐like solvation shell structures which encompass the solvent separated solute particles. The librational freedom of the shell molecules is briefly examined; the simulation reveals a decrease in librational amplitudes for the shell solvent.