Relative hydrophobicity of organic compounds measured by partitioning in aqueous two-phase systems

Partitioning of a variety of organic compounds, the majority of which repre sent therapeutic drugs, was examined in an aqueous dextran-polyethylene gly col (Dex-PEG) two-phase system containing 0.15 M NaCl in 0.01 M sodium phos phate buffer at pH 7.3 and in an octanol-buffer (0.15 M NaCl in 0.01 M sodi um phosphate buffer, pH 7.3) system. The possibility of introducing compoun ds to be partitioned in an aqueous two-phase system with dimethyl sulfoxide , and the effect of this solvent on the solute partitioning was explored. R elative hydrophobicity of the compounds was estimated and expressed in equi valent numbers of methylene units. Comparison of the results obtained for s everal subsets of compounds in the octanol-buffer and in aqueous Dex-PEG tw o-phase systems clearly demonstrates the advantage of aqueous two-phase par titioning for the hydrophobicity measurements over partitioning in octanol- buffer system. (C) 2000 Elsevier Science B.V. All rights reserved.