Aqueous solutions of non electrolytes have been studied for their importance as model molecules of structural units of polypeptide chains and proteins. The pairwise enthalpic interaction coefficients obtained from the excess enthalpies are interpreted according to an interaction model which provides the presence of a preferential configuration between two hydrated molecules, stabilized by the simultaneous juxtaposition of groups having the same effect on water structure. This model accounts for the enhanced cooperativity of hydrophobic interactions when sustained by hydrophilic interactions. Up to now, the proposed model has proved to be useful to explain the difference in the behaviour of positional, geometric and stereo isomers, and also to predict the value of the enthalpic interaction coefficient of polyhydroxylated substances in aqueous solution.

For α-aminoacids, the preferential configuration model rationalizes chiral recognition, namely the differences between the values of the homochiral and heterochiral pairwise enthalpic interaction coefficients, assigning a major role to the zwitterionic interaction and to the nature of the alkyl chain. In concentrated aqueous urea solutions, the trends of homochiral coefficients for unsubstituted α-aminoacids underlines that hydrophobic interactions are attenuated, and that an interaction mechanism holds, not different from that occurring in water.