Hydrophobic and coulombic interactions in the micellar binding of phenols and phenoxide ions

The transfer free energies of a series of substituted phenols and phenoxide ions from water to micelles of cetyltrimethylammonium bromide (CTABr) have been measured at high and low pH. The contribution of each methylene (or methyl) group to the free energy is ca. -300 cal mol-1 for both phenols and phenoxide ions, and the transfer free energies of phenol and its phenoxide ion are respectively -5680 and -6870 cal mol-1, whereas that of 2-naphthol is -6660 cal mol-1. The contribution of the Coulombic component of binding of the anions is consistent with a micellar surface potential of 50 mV, and there appears to be a major contribution from ion-dipole interactions between the cationic head groups of the surfactant and the polarizable aryl groups.