Hydration of dioxaalkanes in aqueous solutions

The interactions between water and linear dioxaalkane molecules were invest igated by water-heptane partition. Two homologous series: dimethoxyalkanes and diethoxyalkanes were studied, with the oxygen atoms separated by a numb er of methylene groups (changing from 1 to 5). Free energy and enthalpy of partition were calculated from partition constants and from their temperatu re dependence. Hydration of these amphiphilic solutes in the aqueous phase was evaluated. The separation between the oxygen atoms in the molecule affects hydrophilic -hydrophobic properties of dioxaalkanes. The effect is due not only to a di fferent number of hydrophobic groups in the molecule, but also to different degrees of their hydrophobicity as well as of hydrophilicity of the oxygen atoms at different separations. The contribution from different parts of t he molecules is, therefore, not additive and the group-contribution model c annot be used to describe physicochemical properties of aqueous solutions o f dioxaalkanes without taking into account the structure of the solute mole cules. (C) 2000 Elsevier Science B.V. All rights reserved.