A conductimetric study of the interaction of p-cyclodextrin or hydroxypropyl-beta-cyclodextrin with dodecyltrimethylammonium bromide in water solution

Solutions of the ternary systems formed by beta-cyclodextrin (beta-CD) or hydroxypropyl-beta-cyclodextrin (HP-beta-CD), dodecyltrimethylammonium bromide (D(12)TAB), and water were studied using a computerized electrical conductivity technique. The measurements were carried out at 25 degrees C as a function of [D(12)TAB] with varying concentrations of cyclodextrin, as a function of [CD] at various concentrations of D(12)TAB, and as a function of [CD] and [D(12)TAB] with [CD]/[D(12)TAB] constant at stoichiometric concentration. A model has been proposed to evaluate the binding constant (K) from conductivity, considering the association of the surfactant counterion with the inclusion complex and the variation of the ionic molar conductivities with the concentration. The stoichiometry, A, of the complexes, the apparent critical micellar concentration, cmc*, and the free surfactant concentration of D(12)TAB have been also obtained. The influence of the presence of the inclusion complex on the micellization process of the surfactant has been studied.