CHARACTERIZATION OF SURFACTANT VESICLES AS MEMBRANE MIMETIC AGENTS .2. TEMPERATURE-DEPENDENT CHANGES OF THE TURBIDITY, VISCOSITY, FLUORESCENCE POLARIZATION OF 2-METHYLANTHRACENE, AND POSITRON-ANNIHILATION IN SONICATED DIOCTADECYLDIMETHYLAMMONIUM CHLORIDE

Sonic dispersal of dioctadecyldimethylammonium chloride (DODAC) resulted in the formation of stable bilayer vesicles. Electron micrographs showed the presence of bilayer DODAC vesicles with radii of 150±10 Å and bilayer thickness of 50±5 Å. Turbidity, viscosity, fluorescence polarization of 2-methylanthracene, and positron annihilation established phase transitions at 30.0 and 36.2°C. DODAC vesicles containing 17.2% cholesterol (w/w) had analogous phase transitions at 23.0 and 34.7°C. Placing DODAC vesicles in hyperosmolar solutions elicited osmotic shrinkage. The extent and initial rates of osmotic shrinkage have been determined as functions of the electrolyte gradients and temperature. At 25°C, DODAC vesicles act as ideal osmometers in a relatively narrow electrolyte range. At 0.10 M osmotic gradient ions permeate the vesicle. Increasing the temperature and adding cholesterol increases the extent of ion influx. DODAC vesicles are chemically the simplest functional membrane mimetic agents. © 1979, American Chemical Society. All rights reserved.