The influence of the molar ratio of cholesteryl hemisuccinate/dipalmitoylphosphatidylcholine on 'liposome' formation after lipid film hydration.

The morphology of the structures formed after hydration of lipid films of cholesteryl hemisuccinate/dipalmitoylphosphatidylcholine (CHEMS/DPPC) was investigated in low ionic strength solutions. The importance of addition of a charge inducing agent/geometrical structure such as CHEMS for the formation of stable vesicle dispersions upon hydration was demonstrated. The encapsulated volume measured for CHEMS/DPPC ratios below 1:50 was low. For a ratio of CHEMS/DPPC of 1:30 EM micrographs showed mainly small unilamellar vesicles, with particle sizes between 0.07 and 0.3 microns, together with a small number of much larger vesicles. For ratios of CHEMS/DPPC above 0.1 only unilamellar vesicles and no bilayer stacks were found. The results confirm the hypothesis by Hauser (Biochim. Biophys. Acta 772 (1984) 37-50), that the structures formed upon hydration of charged phospholipid films are unilamellar vesicles, while for neutral phospholipid films upon hydration bilayer stacks and multilamellar vesicles are formed. The effect of CHEMS on the liposome bilayer structure can be mainly ascribed to its charge inducing properties and presumably to a minor extent to its molecular geometry, or to a combination of both.