Monolayer membranes and bilayer vesicles characterized by α- and β-anomer of sulfoquinovosyldiacyglycerol (SQDG)

Physicochemical properties of 1,2-di-O-stearoyl-3-O-(6-deoxy-6-sulfo-α-d-glucopyranosyl)-sn-glycerol (α-SQDG-C18:0) and 1,2-di-O-stearoyl-3-O-(6-deoxy-6-sulfo-β-d-glucopyranosyl)-sn-glycerol (β-SQDG-C18:0) in monolayer and bilayer membranes were examined. Surface pressure measurements in monolayer membranes indicated the molecular area of β-SQDG-C18:0 to be slightly smaller than that of α-SQDG-C18:0. In bilayer membranes, the phase transition temperature and the enthalpy of β-SQDG-C18:0 were higher than those of α-SQDG-C18:0, while the trapping efficiency of β-SQDG-C18:0 vesicles was lower. The results suggested tighter packing with β-SQDG-C18:0 than α-SQDG-C18:0, due to differences in the head group stereochemistry. High-performance liquid chromatography-electrospray ionization ion trap mass spectrometry (HPLC-ESI-MS) data and computational modeling studies provided supporting evidence for morphological differences. In both monolayer and bilayer membranes, the affinity of β-SQDG-C18:0 with cholesterol was greater than that of α-SQDG-C18:0, again due to the differences in head group properties. Turbidity measurement and microscopic examination of α- and β-SQDG-C18:0/cholesterol mixtures confirmed formation of large vesicles. The addition of cholesterol to SQDG-C18:0 optimized membrane formation and stabilized its structure.