Thermotropic phase properties of 1,2-di-O-tetradecyl-3-O-(3-O-methyl- beta-D-glucopyranosyl)-sn-glycerol (original) (raw)

The hydration properties and the phase sbtucture of 1,2-di-O-tetradecyl-3-O(3-O-methyl-fo-Dglucopyranosyl)sn-glycerol (3-O-Me-o -GlcDAIG) in water have been studied via differential scanning calorimetry, 'H-NMR and 2H-NMR spectroscopy, and x-ray diffction. Results indicate that this lipid forms a crystalline (O phase up to temperatures of 60 70oC, where a transition through a metastable reversed hexagonal (H.) phase to a reversed micellar solution (L2) phase occurs. Experiments were carried out at water concentrations in a range from 0 to 35 wt %, which indicate that all phases are poorty hydrated, taking up <5 mol water/mol lipid. The absence of a lamellar liquid crystalline (L) phase and the low levels of hydration measured in the discemible phases suggest that the methylation of the saccharide moiety alters the hydrogen bonding properfies of the headgroup in such a way that the 3-O-Me-fro-GIcDAIG headgroup cannot achieve the same level of hydration as the unmethylated forn. Thus, in spite of the small increase in steric bulk resulting from methylation, there is an increase in the tendency of 3-OMe--H-GIcDAIG to form nonlamellar strures. A similar phase behavior has previously been observed for the Actxleplasma laidlawiiA membrane lipid 1 ,2-diacy 6(aacyl-a--glucopyranosyl)-sn-glycerol in water (Undblom et al. 1993. J. Bol. Chem. 268:16198-16207). The phase behavior of the two lipids suggests that hydrophobic substituton of a hydroxyl group in the sugar ring of the glucopyranosylglycerols has a very strong effect on their physicochemical properfies,