Formation of inverted lipid micelles in aqueous dispersions of mixed sn-3-galactosyldiacylglycerols induced by heat and ethylene glycol.

The formation of 'lipidic' particles corresponding to inverted lipid micelles in freeze-fracture replicas of aqueous dispersions of mono- and digalactosyldiacylglycerols can be greatly enhanced either by increasing the temperature from which the samples are thermally quenched or by the addition of cryoprotectants such as ethylene glycol. In the case of the heated samples, the lipids tend to form quasi-crystalline structures consisting of sheets of 8-9 nm diameter particles organised on an orthorhombic lattice. The orientation of alternate sheets varies giving rise to a characteristic herring-bone pattern. Ethylene glycol-treated samples, in contrast, form more regular structures consisting of 13-16 nm diameter particles. Lowering the temperature from which the samples are quenched and/or decreasing the concentration of ethylene glycol reduces the frequency of formation of such structures. A number of intermediate states associated with the reincorporation of the lipid molecules of the inverted micelles into the lamella phase are also identified. The factors influencing particle formation are briefly discussed. It is concluded that the destabilisation of lipid-water interactions play a major role in this process.