Molecular recognition: A thermodynamic study of non bonded interactions in aqueous solutions of iminoacids. Effects of steric and geometric isomerism

Enthalpies of dilution of binary and ternary aqueous solutions containing L- and D-proline, cis-L- and cis-D-4-hydroxy proline, trans-L-4-hydroxy proline, have been determined by flow calorimetry at 25°C. Pairwise self- and cross-interaction coefficients of the virial expansion of the excess enthalpies were evaluated. They are positive for solutions of unsubstituted prolines. On the contrary, upon the introduction of a hydroxy group, they become negative, reaching the largest value for the cis-L-/cis-D-4-hydroxy proline system. The results are interpreted in terms of preferential configurations, stabilized by interactions between the hydrophilic groups.