Phase diagrams of monoacylated amide-linked disaccharide glycolipids

A series of monoacylated glycolipids with even-numbered acyl chain lengths ranging from saturated C11 to C15 and an unsaturated C17:1 fatty acid connected by an amide in linkage to the disaccharide head groups maltose, melibiose and lactose were synthesized. The structural polymorphism of the glycolipids was investigated using Fourier-transform infrared spectroscopy and differential scanning calorimetry for the detection of the gel to liquid-crystalline acyl chain melting behaviour and small-angle X-ray scattering for the elucidation of the physical structure of the lipid aggregates. Also, the phase morphology was studied by polarizing microscopy in contact preparations. The data clearly show the existence of uni- and multilamellar structures. Although only one acyl chain is present, there is no evidence for the existence of micelles – of spherical or of cylindrical (HI) type – or of interdigitated phases. The preference for lamellar phases seems to be correlated with the intrinsic high conformational order of the amide linkage of these compounds which inhibits the formation of highly curved structures.