Synthesis and thermotropic characterization of a homologous series of racemic beta-D-glucosyl dialkylglycerols.

The phase behaviour of aqueous dispersions of a series of synthetic 1,2-di-O-alkyl-3-O-(beta-D-glucosyl)-rac-glycerols with both odd and even hydrocarbon chain lengths was studied by differential scanning calorimetry and low angle X-ray diffraction (XRD). Thermograms of these lipids show a single, strongly energetic phase transition, which was shown to correspond to either a lamellar gel/liquid crystalline (L(beta)/L(alpha)) phase transition (short chain compounds, n < or =14 carbon atoms) or a lamellar gel/inverted hexagonal (L(beta)/H(II)) phase transition (longer chain compounds, n > or =15 carbon atoms) by XRD. The shorter chain compounds may exhibit additional transitions at higher temperatures, which have been identified as lamellar/nonlamellar phase transitions by XRD. The nature of these nonlamellar phases and the number of associated intermediate transitions can be seen to vary with chain length. The thermotropic phase properties of these lipids are generally similar to those reported for the corresponding 1,2-sn-diacyl alpha- and beta-D-glucosyl counterparts, as well as the recently published 1, 2-dialkyl-3-O-(beta-D-glycosyl)-sn-glycerols. However, the racemic lipids studied here show no evidence of the complex patterns of gel phase polymorphism exhibited by the above mentioned compounds. This suggests that the chirality of the glycerol molecule, by virtue of its position in the interfacial region, may significantly alter the phase properties of a lipid, perhaps by controlling the relative positions of hydrogen bond donors and acceptors in the polar region of the membrane.