Not a Tiny Bit of Iceberg Near a Hydrophobic Molecule

In a lengthy article published almost 70 years ago, Frank and Evans suggested that a rare gas atom or a non-polar molecule dissolved in liquid water result in freezing of the surrounding water molecules even at room temperature. While these authors rightfully cautioned with a footnote that the word freezing or iceberg does not imply that the water structure near the solute is exactly ice-like, the behavior of water molecules at the hydrophobic surface, more specifically, the iceberg picture, has been a topic of perennial debate in physical chemistry. By an integrated description of hydrophobic hydration based on thermodynamics, molecular simulation and the scaled-particle theory (SPT), we analyzed the effect of several hydrophobic solutes on hydrogen bonding among water molecules over a broad range of temperatures. A careful analysis of different contributions of the intermolecular forces to the total solvation energy provides unequivocal evidence that a hydrophobic solute reduces the degree of hydrogen bonding in the neighboring water molecules in comparing to that in the bulk liquid at all temperatures.