Analysis of amino acid–water interactions by partitioning in aqueous two-phase systems. I—Amino acids with non-polar side-chains

Partition ratios of 10 l-amino acids with non-polar side chains (Gly, Ala, Val, nor-Val, Ile, Leu, nor-Leu, Phe, Trp and Pro) were measured in ten different polymer/polymer aqueous two-phase systems (ATPS) containing 0.15 M NaCl in 0.01 M phosphate buffer, pH 7.4. The solute-specific coefficients representing the solute dipole–dipole, hydrogen bonding and electrostatic interactions with aqueous environment for the compounds examined were determined by the multiple linear regression analysis using the modified linear solvation energy relationship equation. It is shown that linear combinations of these coefficients are correlated with the amino acid lipophilicity/hydrophobicity scales reported in the literature. The results obtained imply that the solute-specific coefficients may be used as solute descriptors for quantitative structure–property relationship (QSPR) analysis.