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Partitioning of a series of free amino acids, their derivatives, and homo-oligopeptides in aqueous dextran-PEG two-phase systems and octanol buffer systems was examined at pH values from 2.0 up to 12.5. The pH-dependent partition behavior of free amino acids and peptides in the two-phase systems was compared with that of monofunctional drug-like compounds and found to be clearly different. The differences observed indicate that the information provided by the techniques of partitioning in octanol buffer (log(D)(pH)) and in aqueous two-phase systems, N(CH2), is different. It is suggested that the combination of the two descriptors, log(D) (lipophilicity) and N(CH2) (relative hydrophobicity), may be useful for QSAR analysis of the biological activities involving distribution and/or transport of chemical compounds in biological systems.