Partition coefficients of 20 polar molecules between water and trimethyldodecylammonium bromide micelles: Correlation with the water + octanol system

Abstract

The partition coefficient P between trimethyldodecylammonium bromide micelles and water of 20 nonaromatic polar molecules was determined at 298.15°K by a combination of salting constant and critical micelle concentration determinations; included are amines, alcohols, ethers, esters, ketones, and some high dipole moment molecules. The partition coefficients obtained for the alcohols are about one-half their value in aqueous micellar sodium dodecylsulfate solutions. It is shown that for straight, branched, and cyclic amines, alcohols, esters, and ketones there is an excellent correlation between partition coefficients in the aqueous cationic micelles and in the classical octanol + water system. Some ethers and halogenated alkanes do not follow this correlation; the P values in these cases in the micellar solutions are about one-third of the values predicted from the correlation. The same observation can be made for halogenated alkanes in aqueous sodium dodecylsulfate solutions. The behavior of simple polar solutes in the micellar systems studied resembles that found with dimyristoyl lecithin liposomes. The average solubilization site of the nonaromatic solutes onto the cationic micelles may be looked upon as having the properties of a solvent such as isobutanol saturated with water.