Thermodynamics of distribution of p-substituted phenols between aqueous solution and organic solvents and phospholipid vesicles.

The distribution of p-substituted phenols between 0.15 M NaCl and a range of organic solvents (including 1-octanol) was examined over a range of temperatures. The thermodynamic parameters of transfer, delta G, delta H, and delta S, were determined and the values examined in the light of Hildebrand and Scott's solubility parameter theory, and the collision complexes between solute and organic solvent. Delta H of transfer was positive for nonpolar solvents and negative for 1-octanol; the transfer processes were entropy and enthalpy dominated, respectively. The distribution of the phenols into phospholipid vesicles was examined below the phase-transition temperature. Although delta G of transfer for vesicle-water systems was similar to that for octanol-water systems, the full thermodynamic analysis indicated that the two systems were dissimilar. The use of vesicle distribution data in structure-activity studies is discussed.