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 hydroca rbon 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 eithe r a lamellar gel/liquid crystalline (L-beta/L-alpha) phase transition (shor t chain compounds, n less than or equal to 14 carbon atoms) or a lamellar g el/inverted hexagonal (L-beta/H-II) phase transition (longer chain compound s, n greater than or equal to 15 carbon atoms) by XRD. The shorter chain co mpounds may exhibit additional transitions at higher temperatures, which ha ve been identified as lamellar/nonlamellar phase transitions by XRD. The na ture of these nonlamellar phases and the number of associated intermediate transitions can be seen to vary with chain length. The thermotropic phase p roperties of these lipids are generally similar to those reported for the c orresponding 1,2-sn-diacyl alpha- and beta -D-glucosyl counterparts, as wel l 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 compoun ds. 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 hyd rogen bond donors and accepters in the polar region of the membrane. (C) 20 00 Elsevier Science B.V. All rights reserved.