Preparation and characterization of large dioctadecyldimethylammonium chloride liposomes and comparison with small sonicated vesicles.

Dioctadecyldimethylammonium chloride (DODAC) unilamellar liposomes with a mean external diameter of 0.5 micron and sharp gel-to-liquid-crystalline phase transition temperatures (Tc) were obtained by chloroform vaporization and compared with small sonicated DODAC vesicles. Sucrose, impermeant through large DODAC liposomes and sonicated vesicles, was used for internal volume determinations. The internal volumes for large DODAC liposomes and sonicated DODAC vesicles were 9.0 +/- 1.3 and 0.13 +/- 0.2 l/mol, respectively. Ideal osmometer behaviour, towards KCl (0-50 mM) and sucrose, was observed only for large DODAC liposomes. Sonicated DODAC vesicles were osmotically non-responsive towards sucrose and flocculated upon addition of KCl. At temperatures near the Tc, a steep increase in the initial shrinkage rate and a minimum for the total extent of shrinkage were observed for large DODAC liposomes. Large DODAC liposomes are proposed as an adequate synthetic membrane model.