EXAFS - A NEW APPROACH TO THE STRUCTURE OF MICELLAR AGGREGATES

A helical model was previously proposed for sodium (NaDC) and rubidium (RbDC) deoxycholate micellar aggregates in aqueous solutions. SAXS, NMR, ESR, and CD meehurements verified the helical model. Here we report an EXAFS study by the spherical wave formalism on the coordination of the Rb' ions in the crystal, macromolecular fiber, and micellar aqueous solution of RbDC together with measurements carried out on rubidium oxalate (crystal and aqueous solution). The results show that the Rb" ions of the micellar aggregates have the same (or very similar) peculiar coordination as that inside the helices of the crystal and macromolecular fiber. Moreover, their coordination remarkably differs from that observed in the aqueous solutions of rubidium oxalate, where the situation would be similar to that of a classical micelle. Thus, the helical model is unquestionably confirmed.