Mixed micelle formation in aqueous solutions of alkyltrimethylammonium cholates

Abstract

Critical micelle concentrations, conductivities, aggregation numbers and intrinsic viscosities of the mixed micelles of hexadecyl, tetradecyl, and dodecyl-trimethylammonium cholates (long-chain cations and trihydroxy-substituted steroidal anion) have been determined in aqueous solution at 25°C using surface tension, conductivity, light-scattering, and viscosity techniques. The results indicate that the mixed micelles were small, approximately spherical, and only slightly charged. Critical micelle concentrations were of the order of 0.4 to 2.1 × 10 −4 mole 1 −1; areas occupied by the alkyltrimethylammonium cholate complexes at the surface of aqueous solutions were in the range 84–132 Å 2 aggregation numbers were 19–32. A model of the mixed micelle consists of a bimolecular leaflet-type of arrangement of the long-chain cations, each leaflet being enclosed by a circumference of cholate ions; the hydroxyl groups of which are orientated towards the surrounding aqueous medium.