Free energy of solubility of non-polar particles in water: The role of pressure

The behavior of aqueous solutions of non-polar substances at different temperatures has been studied extensively. The interpretation of the behavior of these systems under pressure is somewhat controversial when the attempt is made to connect the hydrocarbon model with the folding-unfolding of proteins under pressure. We consider the free energy of solubility of non-polar substances in water by molecular dynamics simulation to compute changes in the free energy of transference of a Lennard-Jones particle to an existent cluster of such particles in water from 1 to 1500 bar and 300 +/- 4 K. The critical cluster size needed to form an aggregate increase with pressure. Using the values of the free energy of transference, an analytical expression is proposed to describe its behavior. The formation of clusters requires a tetrahedral structure to allow hydrophobic interaction, then, decrease of cluster size is due to the change of water properties under pressure. (C) 2014 Elsevier B. V. All rights reserved.