Distribution of acetylcholine chloride between the micellar and bulk phases as studied by ultrafiltration.

Abstract

The distribution of acetylcholine chloride (Ach) between the aqueous and micellar phases has been measured by means of ultrafiltration and the binding parameters have been estimated. The results indicate that Ach enters not only anionic micelles of sodium dodecyl sulfate (SDS), but also cationic micelles of dodecyltrimethylammonium chloride (DTAC). Furthermore, in the cases of ionic micelles and mixed micelles composed of ionic and nonionic, (heptaethylene glycol dodecyl ether (HED)), surfactants, it has been found that Ach molecules are bound to one locus within the surfactant micelles. The Ach molecule has higher affinity but lower saturated adsorption amount for DTAC micelles than SDS micelles, indicating that Ach molecules are probably situated at the surface of the SDS micelles, but penetrate more deeply and bind more tightly to DTAC micelles. For nonionic micelles, the bound Ach concentration (percent) was very small, but for mixed micelles, the percentage increased with mole fraction of ionic surfactants. Furthermore, in the system of negatively charged mixed micelles and Ach, the bound Ach concentration (percent) was found to depend on the surface potential of the micelles, and the dependence was explained well by the Gouy-Chapman theory.