The effects of oligosaccharide stereochemistry on the physical properties of aqueous synthetic glycolipids

Effects of the stereochemistry of oligosaccharide head groups on the physical properties of aqueous synthetic glycolipids, 1,3-di-O-dodecyl-2-(beta-glycosyl)glycerols bearing cellooligosaccharides (beta-1,4-O-glycosidic bonds) and maltooligosaccharides (alpha-1,4-O-glycosidic bonds) as hydrophilic groups have been studied. The increase in the number of glucose residues, N, in the two different headgroups exhibited opposite effects on the physical properties of the aqueous glycolipids. For the maltooligosaccharide-containing lipid, Mal(N)(C-12)(2), increasing N in the head groups decreases the hydrated solid/liquid crystalline phase transition temperature T-m and increases the ''hydrophilicity'' of the lipids. However, the T-m of the cellooligosaccharide-containing lipids Cel(N)(C-12)(2) increases with increasing N of the cellooligosaccharide head groups. It is noteworthy that T-m jumps from 59 degrees C (for N = 4) to above 160 degrees C (N = 5), so that the Cel(5)(C-12)(2) cannot form a liquid crystalline phase and was totally insoluble in water, The results can be explained in terms of different conformations of the head groups, i.e., a ''helical'' conformation of the maltooligosaccharides and an ''extended'' conformation of the cellooligosaccharides.