Binding of Phenol Derivatives to Nonionic Surfactant Micelles as Studied by Capillary Zone Electrophoresis

Abstract

Binding constants of 13 kinds of phenols as neutral and anionic species to nonionic surfactant micelles were determined using their mobility changes in capillary zone electrophoresis. Electrophoretic mobility of the phenolate ions at alkaline regions decreased with increasing the concentrations of nonionic surfactant. Analyzing such mobility decreases provided the binding constants of the ions (KB,A). The KB,A values are larger in the anions which are more hydrophobic. Binding constants of the phenols as their neutral species to nonionic surfactant micelles (KB,HA) were also determined by using the difference in acid dissociation constants between in the absence of and in the presence of nonionic surfactant micelles: in the presence of the surfactant, the apparent pKa values became larger, which indicates that the neutral species are more likely bound to the micelles. The KB,A and KB,HA values determined were compared with each other on the basis of hydrophobicity, basicity, and position of the substituents.