Modeling Gibbs energies of solution for a non-polar solute in aqueous solutions of the protein stabilizers glycerol and ethylene glycol Original Research Article

The Hydration Shell Chemical Equilibrium Model (HSCE) has been applied to Gibbs energies of solution data for toluene in aqueous solutions of the protein stabilizers glycerol and ethylene glycol. The HSCE model fits the experimental data to nearly experimental uncertainty. This satisfactory rendering of the data provides certainty on the physical significance of the model parameters and allows a description, from the molecular point of view, of the behaviour of a non-polar solute in aqueous solutions of protein stabilizers. The toluene–stabilizer interchange energy is positive indicating a dislike between toluene and the stabilizer molecules. This dislike is, however, much less pronounced than that between the solute and water, i.e. the non-polar solute prefers to be in contact with the stabilizer rather than with water. The cohesion between water molecules is much larger than that between stabilizer molecules and it remains to be the dominant cause of the hydrophobic behaviour of the non-polar solute. Since the solute–stabilizer interactions are energetically favoured over the solute–water ones, in the vicinity of the solute the stabilizer molecules are preferred over water ones. However, there is no specific interaction leading to a distinct chemical entity (a solute–stabilizer complex). Thus, the non-polar solute–stabilizer interaction is better described by the term ‘preferential solvation of the solute by the stabilizer’.