Relative hydrophobicity and lipophilicity of β-blockers and related compounds as measured by aqueous two-phase partitioning, octanol–buffer partitioning, and HPLC

Abstract

Partitioning of 15 β-blockers and structurally related compounds was examined in aqueous dextran–PEG two-phase systems and octanol–buffer systems at pH from 2.0 up to 12.5. The same compounds were examined by gradient RP-HPLC at pH 2.0, 7.4, and 11.0. The differences between the hydrophobic character of the phases in all three systems at different pH values were characterized using a homologous series of dinitrophenyl-amino acids by measuring the free energy of transfer of a methylene group. Estimates of the relative hydrophobicity, N(CH 2), and lipophilicity, log D, of the compounds obtained by the three techniques employed were compared. The data indicate that while similar pH profiles for a given compound were established by all these techniques, the information provided is different. It is suggested that the combination of the two descriptors, log D and N(CH 2), may be useful for quantitative structure–activity relationship analysis of the biological activities involving distribution and/or transport of chemical compounds in biological systems.