Solvation in modified water models: towards understanding hydrophobic effects

The solvation of small hydrophobic solutes, modelled as hard spheres or Lennard-Jones particles, is characterized in several modified water liquids. In the hybrid family of liquids the SPC/E model is partially transformed to a Lennard-Jones liquid with the same number density. In this family, hydrophobic solutes become less soluble as the liquid structure becomes more close packed. In the bent family of models the network structure is altered by geometrical changes from SPC/E which increase the solubility of hydrophobic groups. Solvophobicity in the isotropic model, which has the same radial distribution function as SPC/E water by construction, is greater than in SPC/E water. This shows the importance of three-body correlations. In addition to excess chemical potentials, contact densities and the agreement with the Gaussian distributions predicted by information theory are investigated. Dielectric constants and surface tensions have been determined approximately and are used in the discussion of the results.

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