Thermotropic behavior of glycosphingolipids in aqueous dispersions

Abstract

The thermotropic behavior of 20 chemically related glycosphingolipids (GSL) of high purity, containing neutral and anionic carbohydrate residues in their oligosaccharide chains, was studied by high-sensitivity differential scanning calorimetry. In general, the polar head group of GSL appears to be one of the major determinants of their phase behavior. Compared to phospholipids, the presence of the carbohydrate rather than the phosphorylcholine moiety in the polar head group and a sphingosine base in the hydrocarbon portion of GSL reduces the effect on the transition temperature (Tm) brought about by increasing the number of methylene groups in the amide-linked fatty acyl chains. For simple neutral GSL, the Tm were 20.degree.-40.degree. C higher than those of phospholipids with comparable hydrocarbon chains. As the oligosaccharide chain of GSL becomes more complex, the excess heat capacity, Tm, enthalpy (.DELTA.Hcal) and entropy of the transition decrease proportionally to the number of carbohydrate residues present in the polar head group. The Tm and .DELTA.Hcal for anionic GSL were 16.degree.-25.degree. C and 1-3 kcal mol-1 lower than those of neutral GSL with comparable oligosaccharide chains. A linear dependence of .DELTA.Hcal with Tm was found. The slopes of these plots were different for neutral and for anionic GSL, suggesting different types of intermolecular organizations for the 2. The Tm and .DELTA.Hcal were linearly dependent on the molecular area of both neutral and anionic GSL; this indicated that the influence of the complexity of the polar head group in GSL for establishing the thermodynamic behavior may be mediated by the intermolecular spacings.