ja029796n_si_001.pdf (625.8 kB)
A New Angle on Heat Capacity Changes in Hydrophobic Solvation
journal contribution
posted on 2003-07-19, 00:00 authored by Kelly R. Gallagher, Kim A. SharpThe differential solubility of polar and apolar groups in water is important for the self-assembly
of globular proteins, lipid membranes, nucleic acids, and other specific biological structures through
hydrophobic and hydrophilic effects. The increase in water's heat capacity upon hydration of apolar
compounds is one signature of the hydrophobic effect and differentiates it from the hydration of polar
compounds, which cause a decrease in heat capacity. Water structuring around apolar and polar groups
is an important factor in their differential solubility and heat capacity effects. Here, it is shown that joint
radial/angular distribution functions of water obtained from simulations reveal quite different hydration
structures around polar and apolar groups: polar and apolar groups have a deficit or excess, respectively,
of “low angle hydrogen bonds”. Low angle hydrogen bonds have a larger energy fluctuation than high
angle bonds, and analysis of these differences provides a physical reason for the opposite changes in
heat capacity and new insight into water structure around solutes and the hydrophobic effect.