Potentiometric studies on sodium dehydrocholate micelles

The scarcely studied sodium dehydrocholate-water system was investigated at low concentration by using H+-, Na+- and dehydrocholate-ion-selective electrodes. The findings at concentrations below the critical micelle concentration are consistent with those of previous work. A dimeric chelate structure entrapping Na+ ions at very low concentration is proposed. The composition of the micelles and the degree of ionisation were studied and explained as the result of the possibility of a back-to-face mechanism of aggregation of this steroid salt. This mechanism also explains the possibility of formation of acid soaplike aggregates at intermediate concentrations.