Interactions between Nonionic Surfactants and Sterically Stabilized Phophatidyl Choline Liposomes

The interactions between sterically stabilized (EPC/PEG-lipid) liposomes and the nonionic surfactants octyl glucoside (OG) and octa(ethylene glycol) n -dodecyl monoether (C 12 E 8 ) have been studied. Cryogenic transmission electron microscopy revealed that poly(ethylene glycol)-lipids (PEG-lipids) affected the OG-mediated solubilization of the liposomes. Long-lived small bilayer disks were observed at OG concentrations saturating the bilayers. In addition, the macroscopic phase separation observed in EPC/OG systems, at OG concentrations such that the bilayers were close to being solubilized, was entirely inhibited by the inclusion of PEG-lipids in the membrane. OG was more efficient in destabilizing sterically stabilized liposomes than conventional ones, whereas for C 12 E 8 the effective molar ratio of surfactant to lipid at bilayer saturation was essentially the same for both types of liposomes. Furthermore, the results reported illuminate the effect of PEG-lipids on, and the mechanism of, surfactant-induced growth of small unilamellar vesicles.