Roles of Hydrogen Bonding and the Hard Core of Water on Hydrophobic Hydration

Abstract

The roles of hydrogen bonding and the hard core of water on hydrophobic hydration are clarified using Monte Carlo simulation and the test particle method to compare the cavity formation in water with that in a Lennard-Jones (LJ) fluid with the same molecular size and density. Similarities and differences in the cavity formation in the two fluids are examined in terms of the free energy, the energy change, and the change in the coordination number upon cavity formation. The free energy of cavity formation at a given density and the decrease in the coordination number around cavities in water are similar to those in the LJ fluid. These similarities are due to geometrical restriction of the hard core of molecules. The effect of the hydrogen bonding of water can be seen in the coordination-number dependence of the average energy of one molecule, regardless of whether water is in bulk or in the hydration shell. The temperature dependence of the correlation between the coordination number and energy can explain...