Formation of giant liposomes from lipids in chaotropic ion solutions

Liposomes with diameters in the range of 10–20 μm, evidently uni- and oligolamellar, were generated upon removal of sodium trichloroacetate by dialysis or dilution from a solution containing egg phospholipids and sodium trichloroacetate. At room temperature, giant liposomes were formed only from concentrations of sodium trichloroacetate which induced the transformation of phosphatidylcholine from the lamellar to the micellar phase. The yield of giant liposomes increases with increasing phospholipid concentration in the sodium trichloroacetate solution. Inclusion of a freeze-thaw step reduced the concentration of sodium trichloroacetate needed to generate giant liposomes to less than 0.1 M and substantially lowered the minimum lipid concentration. Apparently sodium trichloroacetate is concentrated during freezing to above the critical concentration which solubilizes phospholipids. The micelles, so generated, also become concentrated so that giant liposomes form upon thawing as the melting ice dilutes the trichloroacetic acid and the micellar phase reverts to the lamellar phase. Other chaotropic solutions, such as guanidine-HCl and urea, which did not solubilize lipids at room temperature, also generated giant liposomes when their solutions, containing dispersed lipids, were frozen, thawed and then dialyzed to remove the solutes. In the case of chaotropic anions such as thiocyanate and nitrate, potassium salts are more effective than sodium salts.