A two-state model of hydrophobic hydration that produces compensating enthalpy and entropy changes

Many of the mixture models of water seek to explain the large free energy change associated with hydrophobic hydration by means of changes in the number and character of the hydrogen bonds in water. Al of these models, regardless of detail, are in clash with the idea that hydrogen bond rearrangements will produce changes in both enthalpy and entropy, which largely compensate to produce little net free energy change. One of the simplest and most recent of these mixture models is Muller's two-state model, which produces small enthalpy and large negative entropy changes. In this paper, Muller's model is examined in detail. It is found that only slight changes are required in order for the model to produce nearly compensating enthalpy and entropy changes.