Differential scanning calorimetry and X-ray diffraction studies of the thermotropic phase behavior of the diastereomeric di-tetradecyl-beta-D-galactosyl glycerols and their mixture

Abstract

We have investigated the thermotropic phase behavior of aqueous dispersions of the 1,2- and 2,3-di-O-tetradecyl-1(3)-O-(beta-D-galactopyranosyl)-sn- glycerols and their diastereomeric mixture using differential scanning calorimetry and low-angle and wide-angle x-ray diffraction. Upon heating, unannealed aqueous dispersions of these compounds all exhibit a lower temperature, moderately energetic phase transition at approximately 52 degrees C and a higher temperature, weakly energetic phase transition at approximately 63 degrees C, both of which are reversible on cooling. X-ray diffraction measurements identify these events as the L beta (or L' beta)/L alpha and L alpha/HII phase transitions, respectively. The structures of the L beta, L alpha, and HII phases of these lipids, as determined by x-ray diffraction measurements, are identical within the error bars for all of these lipids. On annealing below the L beta/L alpha phase transition temperature, the L beta phase converts to an Lc phase at a rate which is strongly dependent on the chirality of the glycerol backbone (1,2-sn > 1,2-rac > 2,3-sn). The temperature of the phase transition from the Lc phase seen on reheating is also dependent on the glycerol chirality. In addition, the nature of the Lc phase changes on subsequent heating in the 1,2-sn and 1,2-rac lipids, but we have not been able to detect this Lc1/Lc2 phase transition by calorimetry. However, wide-angle x-ray diffraction measurements indicate that these Lc phases differ mostly in their hydrocarbon chain packing modes. The Lc2 phase does not appear to be present in the 2,3-sn compound, suggesting that its formation is not favored in this diastereomeric isomer. These observations are discussed in relation to the effect of glycerol chirality on the molecular packing of these glycolipids, particularly on hydrogen bonding and hydration in the interfacial region of the bilayer.

Bilayer Properties of Totally Synthetic C16:0-Lactosyl-Ceramide

“…For example, the monoglycosyl-glycerolipids favor the formation of the nonbilayer hexagonal phase, whereas addition of a second sugar promotes the formation of bilayer lamellar phases (for example, see original studies of plant galactolipids by Shipley et al, 1973). Systematic studies of synthetic glycoglycerolipids differing in sugar structure, fatty acid chain length, and chain unsaturation have been reported by Quinn, Hinz, and McElhaney and their colleagues (for example, Sen et al, 1981;Hinz et al, 1991;Sen et al, 1990;Mannock et al, 1994). These extensive studies have essentially confirmed and extended the concept of an important structure-determining role for the lipid-linked sugar moiety.…”

Lactosylceramide: Effect of Acyl Chain Structure on Phase Behavior and Molecular Packing

“…The marginal capability of the lactose disaccharide headgroup to disrupt the stable gel phase of LacCer is noteworthy because glycerol-based glycolipids such as digalactosyldiglyceride do not share this feature. Rather, the presence of the disaccharide sugar headgroup in the glycerol-based glycolipids dramatically lowers the phase transition temperature compared to chain-matched diglycerides containing monosaccharide headgroups (Sen et al, 1981(Sen et al, , 1983(Sen et al, , 1990Hinz et al, 1991, Mannock et al, 1994. On an absolute basis, the main endothermic transition temperature of 18:0 LacCer is ϳ30°C higher than that of di-18:0 digalactosyldiglyceride, while 18:0 GalCer's main endothermic transition temperature is only a few degrees higher than that of 18:0 monogalactosyldiglyceride (Sen et al, 1983;Reed and Shipley, 1989;Koynova and Caffrey, 1995).…”

Hydrophilic/Hydrophobic Balance Determines Morphology of Glycolipids with Oligolactose Headgroups

“…Effects of the ethyleneglycol chain on the phase behavior and the interface activity have been discussed using various methods (Kuhl et al, 1994(Kuhl et al, , 1998Kenworthy et al, 1995a, b;Naumann et al, 1999;Mathe et al, 2000). Morphology of synthetic glycolipids with mono-or disaccharide headgroups has intensively been studied (Sen et al, 1982;Mannock et al, 1994;Hinz et al, 1991). However, only several reports have been conducted on the glycolipids with linear oligosaccharide headgroups (Hinz et al, 1991;Hato and Minamikawa, 1996;Tamada et al, 1996;Köberl et al, 1998;Hato et al, 1999;Saxena et al, 2000).Recently, we reported the thermodynamic properties and swelling behavior of ether-linked glyco-glycerolipids with linear oligolactose headgroups (Schneider et al, 2001).…”