Conductometric and Potentiometric Studies of the Association of α-Cyclodextrin with Ionic Surfactants and Their Homologs

Abstract

Abstract The conductometric determination was made of the association constants of α-cyclodextrin (αCD) with ionic surfactants and their homologs. For 1-alkanesulfonate ions with carbon atoms (n) of 5–12, the association constant was found to increase regularly with n and become abruptly constant at n=10. The association constants for sodium 1-dodecanesulfonate, dodecylammonium chloride, dodecyltrimethylammonium chloride, and 1-dodecylpyridinium chloride were all similar in their magnitude. The effect of complexation on the micellar properties of sodium dodecyl sulfate and dodecyltrimethylammonium chloride were also studied potentiometrically by determining the counterion activities. In both cases, the critical micelle concentration increased regularly, while the degree of counterion association to the micelle decreased almost linearly with increasing αCD concentrations. It was suggested that the αCD-surfactant ion complex is solubilized in the hydrophilic surface region of surfactant micelle to give rise to a decrease in the surface charge density.