Bulk organic solvent-water systems as a possible model to predict alkyl p-aminobenzoate partitioning in liposomes

This study compares the bilayer-water distribution coefficients of a homologous series of n-alkyl p-aminobenzoates in liposomes with their respective distribution coefficients in octanol-water, oleyl alcohol-water, and hexane-water systems. The data indicate that the bilayer-water distribution coefficient is quite sensitive to changes in solute structure and to the structural organization of the bilayer and that octanol, oleyl alcohol, and hexane are able to reflect the partitioning changes that occur in the liposomal bilayer with respect to increasing the alkyl chain length of n-alkyl p-aminobenzoates. For this particular homologous series, the hexane-water system tended to underestimate the bilayer-water distribution coefficients, whereas octanol-water and oleyl alcohol-water systems overestimated solute partitioning into the bilayer. The similarity of the lipid environment, with respect to solute partitioning, in the organic solvent system and that in liposomes can be ascertained by using the Collander relationship.