Efficient synthesis of unsymmetrical bolaamphiphiles for spontaneous formation of vesicles and disks with a transmembrane organization

Unsymmetrical bolaamphiphiles 1a-1d bearing a neutral glycosidic polar head and an electropositive ammonium group at opposite ends of a polymethylene bridging spacer were efficiently synthesized. An additional alkoxy group was introduced at the anomeric site of the carbohydrate in order to yield anomerically defined compounds, to allow the modulation of hydrophobic-hydrophilic balance (HLB), and to increase the dissymmetry of the monomers. The self-assembling properties of the bolaphiles 1a-1d were investigated in both concentrated and more diluted aqueous media and were characterized in a variety of ways. An appropriate modulation of the HLB allowed us to obtain spontaneous formation of stable vesicles characterized by a transmembrane conformation of the lipids. Freeze fracture electron microscopy clearly demonstrated an unusual transformation of the vesicular systems into disks upon heating.