THERMODYNAMICS OF ALIPHATIC AND AROMATIC-HYDROCARBONS IN WATER

Makhatadze and Privalov have analyzed the thermodynamics of transfer o f aliphatic and aromatic hydrocarbons from the gas phase into water. F inding that the hydration free energy of aliphatic and aromatic hydroc arbons have different signs, they conclude that the mechanism causing hydrophobicity of these solutes is of a different nature. Here, we off er an alternative analysis of the dissolution of these non-polar compo unds into water based on a recently published interpretation scheme fo r thermodynamic transfer functions. Our analysis shows that the hydrop hobicity of aromatic and aliphatic hydrocarbons is qualitatively the s ame, i.e. its causes are the same namely the extremely high cohesive e nergy of water which overcomes the favorable solute-solute and solute- water interactions. However, both analyses conclude that the experimen tally observed quantitative difference between the interactions of wat er with aliphatic and aromatic hydrocarbons, can be assigned to the fo rmation of aromatic ring-water H-bonds. (C) 1998 Published by Elsevier Science B.V. All rights reserved.