Thermometric and Surfactant Selective Potentiometric Titration Studies of Surfactant Binding to Phospholipid Vesicles

Abstract

The interactions between sodium dodecyl sulphate and dodecyltrimethylammonium bromide with Asolectin (phospholipid extract from soybeans) vesicles has been studied using titration calorimetry, potentiometry using surfactant selective electrodes,and gel filtration chromatography. Exothermic heat changes were observed on mixing which depend on the concentration of Asolectin. The emf data were also observed to be related to the concentration of phospholipid. At low ratios of surfactant to Asolectin, the data were consistent with a mechanism in which there is a steady amount of surfactant bound to the vesicles until the apparent critical micelle concentration is reached. The free surfactant at that concentration, or the true critical micelle concentration, is always less than the critical micelle formation without Asolectin. All of the evidence points to the formation of mixed surfactant-phospholipid micelles when the apparent critical micelle concentration is reached.