The hydrophobic effect Gibbs energy

Abstract

A new method of experimental determination of thermodynamic functions of the hydrophobic effect is proposed. It is based on regarding the thermodynamic functions of hydration as the sum of thermodynamic functions of nonspecific hydration, specific hydration and the hydrophobic effect. In addition to the previously developed method to determine the hydrophobic effect enthalpies, we present a new method to calculate the hydrophobic effect Gibbs energies. The hydrophobic effect Gibbs energies of noble and simple substance gases, alkanes, arenes, and their halogenated derivatives are determined. For all the compounds studied, the hydrophobic effect Gibbs energy is found to be positive. From the values of the Gibbs energies and the enthalpies of the hydrophobic effect, the entropies of the hydrophobic effect are calculated. They are found to be negative for all the compounds. An excellent linear correlation between the hydrophobic effect Gibbs energy and McGowan characteristic molecular volume of the solute is found. The method was applied to a large molecule of fullerene C60. The hydrophobic effect Gibbs energy of fullerene does not deviate from the linear dependence observed for small solutes. © 2007 Elsevier B.V. All rights reserved.