TEMPERATURE EFFECTS ON THE HYDROPHOBIC HYDRATION OF ETHANE

A series of molecular dynamics simulations have been performed on a system comprising 256 water molecules and 1 ethane molecule at 279, 302, 320, and 352 K. The structural analysis revealed the existence of orientational restrictions for water molecules with respect to the solute in the hydration shell, while a hydrogen bond analysis showed a slight enhancement of the tetrahedral network. This behavior is consistent with the negative entropy and enthalpy functions associated with the hydrophobic hydration of nonpolar solutes near room temperature. The dynamical analysis shows that hydration-shell water molecules have slightly lower diffusion coefficients; on the other hand, calculations of hydrogen bond lifetimes reveal that this region's bonding network breaks up faster than that of the bulk The overall results suggest that the energetic environment in the hydration shell is similar to that in the bulk and reinforce the idea of a reduction in the number of low-energy paths for molecular orientational rearrangements in the vicinity of nonpolar solutes.