Pairwise-additive hydrophobic effect for alkanes in water.

Pairwise additivity of the hydrophobic effect is indicated by reliable experimental Henry's constants for a large number of linear and branched low-molecular-weight alkanes in water. Pairwise additivity suggests that the hydrophobic effect is primarily a local phenomenon and that the hydrophobic interaction may be represented by a semiempirical force field. By representing the hydrophobic potential between two methane molecules as a linear function of the overlap volume of the hydration layers, we find that the contact value of the hydrophobic potential (-0.72 kcal/mol) is smaller than that from quantum mechanics simulations (-2.8 kcal/mol) but is close to that from classical molecular dynamics (-0.5 approximately -0.9 kcal/mol).