Liposomes from polymerizable phospholipids.

The synthesis and characterization of a great variety of single and double chain phospholipids containing the diacetylene and butadiene moiety is described. These substances can be dispersed in water by ultrasonication and the resulting vesicles can be photopolymerized with the retention of their original structure. Absorption spectra of the polymerized diacetylenic lipids show significant differences depending on the molecular structure of the monomers. By the polymerization reaction, the gel to liquid crystalline phase transition is suppressed, which does not correspond to the properties of biological membranes. Evidence for enhanced stability of polymerized vesicles is given by treatment with ethanol and detergents showing that trapped markers are released to a much smaller extent than in the case of unpolymerized vesicles. Diacetylenic lipids show a pronounced hysteresis of the phase transition. If the membrane of supercooled vesicles crystallizes, all trapped marker is released within seconds. Possibilities for overcoming this extreme rigidity of the membranes are discussed.