Nuclear Magnetic Resonance and X-ray Studies on Micellar Aggregates of Sodium Deoxycholate

X-ray studies on crystals of sodium and rubidium deoxycholates (NaDC and RbDC, respectively) and on a macromolecular fiber of NaDC provide a reasonable helical model for describing the structure of the NaDC micellar aggregates in aqueous solutions, at least within a certain concentration range and at natural pH. ‘H and 13C NMR measurements have been performed to check the validty both of this model and of a previous model, currently accepted in the literature. The results satisfactorily agree with the helical model which is characterized by an interior part formed by Na+ ions and water molecules, arranged as in a liquidlike structure, and by an outer surface covered by nonpolar groups. A very complicated network of hydrogen bonds among water molecules and hydroxyl and carboxyl groups of deoxycholate anions stabilizes the helix together with Na+- - -H,O ion-dipole and Na+- - -COO- ion-ion interactions. Therefore, hydrophobic interactions can occur among helices, but are negligible in the formation of the micelle. The investigation of the solubilization of some hydrocarbons by NaDC aqueous solutions indicates that the solubilization sites are mainly located at the boundary between the micelles and the bulk aqueous phase, near the C19 methyl group.