Vesicle and tubular microstructure formation from synthetic sugar-linked amphiphiles. Evidence of vesicle formation from single-chain amphiphiles bearing a disaccharide headgroup

Abstract

Altogether eight sugar-based amphiphiles were synthesized. Out of these, four amphiphiles contained only one hydrocarbon chain in their hydrophobic segment. Two of these single-chain amphiphiles contained fully cyclic, disaccharide headgroups, while the other two were made of one cyclic sugar unit connected to the hydrocarbon chain via open, reduced alditol units. The first two single-chain amphiphiles formed vesicles upon suspension in water as indicated by transmission electron microscopy and dye entrapment experiments. The diameters of these vesicles ranged from 500 to 800 Å. Upon aging, these vesicles transformed into tubular and lamellar microstructures. However, the other two single-chain amphiphiles produced micelles in water. Four double-chain systems including two glycolipid analogues, N-hexadecyl-(1-hexadecylamido)-β-D-lactoside and N-hexadecyl-(1-hexadecylamido)-β-D-maltoside, were also synthesized. The other two double-chain (dihexadecyl ether) lipids were based on a pseudoglyceryl backbone where the headgroup residues were made of amino-β-D-maltoside and amino-β-D-lactoside, respectively. All the double-chain amphiphiles formed vesicles upon suspension in water as indicated by transmission electron microscopy and dye entrapment experiments. The diameters of these vesicles ranged from 1000 to 1100 Å. X-ray diffraction of the cast films of the vesicle-forming amphiphiles indicated a lamellar thickness of ~58-60 Å for these membranous organizations. The vesicular aggregates showed sharp, solid-to-fluid thermal transitions that ranged from ~52 to 62 °C. Formation of giant-sized vesicles from the single-chain amphiphiles could also be triggered by complex formation with Cu²⁺ ions under ambient pH conditions.