DIFFERENTIAL SCANNING CALORIMETRY AND X-RAY-DIFFRACTION STUDIES OF A SERIES OF SYNTHETIC BETA-D-GALACTOSYL DIACYLGLYCEROLS

We have investigated the physical properties of a homologous series of synthetic, saturated 1,2-di-O-acyl-3-O-(beta-D-galactopyranosyl)-sn-glycerols using calorimetry and X-ray diffraction. Unannealed aqueous dispersions of these compounds exhibit a lower temperature, moderately energetic, chain-melting (L(beta)/L(alpha)) phase transition and a higher temperature, weakly energetic, bilayer/nonbilayer phase transition. On annealing below the L(beta)/L(alpha)) phase transition, the L(beta) phase converts to an L(C) phase, which may undergo a highly energetic L(C)/L(alpha) or L(C)/H(II) phase transition at very high temperatures on reheating. The temperatures of these phase transitions are higher than those seen in the corresponding alpha- and beta-D-glucosyl diacylglycerols. However, the L(beta)/L(alpha) and bilayer/nonbilayer phase transition temperatures of the beta-D-galactosyl diacylglycerols are lower than those of the corresponding diacyl phosphatidylethanolamines. These observations are discussed in terms of the hydration and hydrogen bonding properties of their respective headgroups.