Supramolecular self-assembling properties of membrane-spanning archaeal tetraether glycolipid analogues

The self-assembling properties of a new series of archaeal tetraether glycolipid analogues 1-6 that are characterized by a bipolar architecture with two similar or different glycosidic and/or phosphate polar heads and a lipid core possessing a cyclopentane unit and/or branched chains were studied by means of differential scanning calorimetry, optical microscopy, X-ray scattering, freeze-fracture electron microscopy and dynamic light scattering. Unsymmetrical phosphate derivatives 1 and 2 spontaneously formed thermostable multilamellar and unilamellar vesicles in which most of the bipolar lipids adopted a trans-membrane conformation, as revealed by freeze-fracture electron microscopy. Supramolecular aggregates of neutral glycolipids 3-6 were found to depend on both the saccharidic polar heads and the chain composition. The presence of one glycosidic residue with rather marked hydrophilic properties, such as the lactosyl moiety, was required to allow the formation of multilamellar vesicles. Surprisingly, the introduction of a cyclopentane unit in the bridging chain was able to induce an apparent two-by-two membrane association: this unusual behaviour might be the result of unsymmetrical interfacial properties of the lipid layer caused by the presence of the cyclopentane unit.