Thermodynamics of transfer of glycine, diglycine, p-nitroaniline and benzoic acid from water to aqueous solutions of polyhydroxy compounds

Abstract

The enthalpies, entropies and free energies of transfer of glycine, diglycine, p-nitroaniline and benzoic acid from water to aqueous solutions of mannitol and sucrose have been determined from solubility measurements at different temperatures. The sign of transfer entropies (ΔS^°_t) are dominated by the nature of the solute (hydrophobic/hydrophilic) rather than the solvent structure. Analysis of the results in terms of the overlap cosphere model of solute hydration indicates that these polyhydroxy compounds have a structure-breaking effect. The unfavourable free energies of transfer for glycine and diglycine in spite of the favourable enthalpy term have been explained in terms of the entropy-controlled nature of the process.