Magnetic resonance measurements of solubilizate distribution coefficients and surface probabilities in some micelles

Abstract

Proton relaxation rates have been used to measure (i) distribution coefficients of solubilizates in a variety of micelles, (ii) surface probabilities (which provide information on the orientation of a surfactant molecule with respect to the micelle surface). For both types of work, paramagnetic ions are added to the solutions and it has been established that for (i) the paramagnetic ions must not complex with the head groups and be completely insoluble in the micelle: Fremy's salt has been used with some negatively charged surfactants to refine a method for the measurement of distribution coefficients. For (ii) the paramagnetic ion must be associated with the head groups hence transition metal ions such as those of copper(II) and chromium(III) are suitable. The surface probabilities obtained for most of the surfactants are consistent with a simple linear orientation; however, some types of surfactant have unusual conformations. It has also been shown that the location of solubilizates can be determined from surface probability measurements.