Composition of sodium taurocholate micellar solutions

The composition and range of existence of aggregates formed by sodium taurocholate in aqueous micellar solutions were studied. Electromotive force measurements were used to obtain concentrations of free hydrogen and sodium ions. Experimental data obtained at 25 degrees C and at three N(CH3)(4)Cl concentrations, used as anionic medium, can be explained by assuming the presence of aggregates with different compositions depending on the reagent concentrations and the ionic strength. Comparison with taurodeoxycholate shows wide differences. Protonated species of taurocholate are observed only at pH less than or similar to 5. At higher pH, the micellar aggregate distribution remains nearly constant at a given ionic medium concentration. As expected, the size of the micellar aggregates increases on increasing the ionic strength. A dimer is found at all concentrations of the ionic medium. All species found have aggregation numbers of anions in multiples of two. The affinity of sodium ions for micellar aggregates is greater than that of N(CH3)(4)(+) ions.