Vesicle-to-micelle transition of egg yolk PC vesicles by nonionic surfactants

Abstract

The vesicle-to-micelle trarisitions of phosphatidylcholine vesicles in the presence of a homologous set of nonionic surfactants, poly (oxyethylene) alkyl ethers, were investigated by observing the changes in turbidities of vesicle-surfactant dispersions and calcein release from vesicles. From the turbidity curves, two transition points representing the total surfactant concentrations at the onset and completion of the solubilization were determined. Patterns of turbidity curves depend on either length of hydrocarbon chain or of oxyethylenemoiety. The surfactant concentrations at two break points and the widths of region indicate the structural transition of lamellar sheets and mixed micelles. As the lengths of chains or the number of hydrophile-lipophile balance varied, the solubilization of liposomes, in fact, the phase diagrams showed optimal behaviours in the middle range of the number of oxyethylenes and hydrophile-lipophile balance. From calcein release, it is believed that lamelk structures persisted up to the onset concentration of surfactant. After the onset, vesicular structures of liposomes opened and all of entrapped materials released out before solubilized. For the bilayers incorporated with cholesterol, the onset of formation of mixed micelles increased slightly, while the complete micellization greatly depended on the amounts of cholesterol. The regions of the transition to mixed micelles is different from those of phosphatidylcholine bilayers.