Synthesis and Liquid Crystals Properties of α-Methylated Galactosides (original) (raw)
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Synthesis of Branched-Chain Alkyl Glucosides and Their Liquid Crystal Behaviour
Although glycolipids exist in nature, they can also be synthesized either chemically or enzymatically. Due to their role in the nervous system and biomembranes, natural glycolipids are extensively studied by researchers, especially biochemists, but their liquid crystal state is not well understood. In this paper, starting from glucose and a series of branched-chain alcohols, novel alkyl glycosides have been synthesized. These compounds have been structurally elucidated using standard spectroscopic techniques like hydrogen (1 H) NMR, carbon-13 (13 C) NMR, and infra-red-(IR) and also using high resolution mass spectrometry (HRMS). Their thermotropic liquid crystalline properties were investigated using polarizing microscopy and differential scanning calorimetry. It was found that the shorter carbon chain analogues gave the smectic A phase while the longer ones gave only the columnar phase. The results were compared with those of the straight chain counterparts.
Thermotropic liquid crystalline properties of amphiphilic branched chain glycolipids
Liquid Crystals, 2006
Glycolipids are amphotropic liquid crystals forming lyotropic liquid crystals in aqueous solutions and thermotropic liquid crystals in their dry form. We report studies on the thermotropic properties of seven different neat glycolipids: four maltoside, two glucoside and one pyranoside lipids. Optical birefringence, electrical conductivity, differential scanning calorimetry, and dielectric spectroscopy measurements were employed to characterize the phase structures of the materials. In general, they exhibit a wide (.100uC) mesophase (smectic, columnar) range with low (0.01-0.04) birefringence. They have large (60-120) dielectric susceptibility basically proportional to the number of polar sugar heads. Depending on the temperature the relaxation frequency of the susceptibility varies between ,100 Hz and .1 MHz, mainly determined by the hydrogen bonding between the polar sugar heads.
Liquid crystal behaviour of three novel glycosides
Journal of the National Science Foundation of Sri Lanka, 2012
Novel glycosides synthesized by linking D-glucose to three different non-polar aglycones, cinnamyl alcohol, chloroxylenol and 3-pentadecylphenol showed both thermotropic and lyotropic liquid crystal phases. The effect of inclusion of a rigid spacer in between hydrophilic and hydrophobic parts on the stability of liquid crystal phases is investigated. Both acetylated and deacetylated compounds exhibited thermotropic and lyotropic liquid crystal behaviour. The liquid crystal phases were confirmed as smectic A, smectic B and hexagonal columnar by X-ray studies.
Chemistry and Physics of Lipids, 1993
The phase behaviour of a synthetic, stereochemically pure glycolipid 2,3-di-0-tetradecyl-l-O-/3-D-galactosyl-snglycerol (14-2,3-Gal) in excess water has been characterized by differential scanning calorimetry and time-resolved Xray diffraction and compared with that of the previously studied ~2-3 stereoisomer, 1,2di-0-tetradecyl-3-0-/3-Dgalactosyl-sn-glycerol (14-1,2-Gal), and 1,2-di-0-tetradecyl-3-0-8-Bglucosyl-sn-glycerol (14-1,2-Glc). The properties of 14-1,2-Gal and 14-2,3-Gal are completely different with respect to phase sequences, metastable behaviour, transition temperatures and enthalpies, but there is a rather close similarity between the phase patterns of 14-2,3-Gal and 14-1,2-Glc. The sn-3 stereoisomer, 14-1,2-Gal, exhibits a direct lamellar crystalline to inverted hexagonal phase transition U-C -H,,) on heating and a Hu -L, (metastable) -L&metastable) -L, phase sequence in subsequent cooling, while both 14-2,3-Gal and 14-1,2-Glc are characterized by an L, -L,, -H,, sequence in first heating, and reversible L, -La -H,, phase sequences in subsequent heating and cooling scans. The peak areas and temperatures of the L&9 -L, transitions are practically identical, while the L, -L, and L, -H,, temperatures for 14-2,3:Gal are about 5°C higher than the corresponding temperatures for 14-1,2-Glc. These data are interpreted in terms of a significantly greater stability and faster formation kinetics of the lamellar crystalline L, phase of 14-1,2-Gal. They show also that the property of galactose head groups of imparting higher stability on glycolipid membranes is strongly dependent on the glycerol stereoconfiguration. Changing it from sn-3 to sn-1 results in a large stability loss of the L, phase and convergence of the galactolipid phase pattern to that of the corresponding glucolipid 14-1,2-Glc.
Carbohydrate Research, 2011
Anomers and epimers aand b-gluco and -galactosides are expected to behave differently. However, recent results on a series of Guerbet glycosides have indicated similar liquid crystal clearing temperatures for pure b-glucosides and the corresponding a-galactosides. This observation has led to speculation on similarities in the self-assembly interactions between the two systems, attributed to the trans-configuration of the 4-OH group and the hydrophobic aglycon. Previous simulations on related bilayers systems support this hypothesis, by relating this clearing transition temperature to intralayer (sugar-sugar) hydrogen bonding. In order to confirm the hypothesis, the comparison was expanded to include the cis-configurated pair, that is, a-gluco/b-galactoside. A set of a-configurated Guerbet glucosides as well as octyl a-galactoside were prepared and their thermotropic phase behavior studied. The data obtained enabled a complete comparison of the isomers of interest. While the results in general are in line with a pairing of the stereo-isomers according to the indicated cis/trans-configuration, differences within the pairs can be explained based on the direction of hydrogen bonds from a simple modeling study.
Computational and Theoretical Chemistry, 2017
Density functional theory calculations on three conformers, gt (gauche-trans), gg (gauche-gauche) and tg (trans-gauche) of n-octyl-α-D-glucoside (C8O-α-Glc) and n-octyl-α-D-galactoside (C8O-α-Gal) were performed for geometry optimization at the B3LYP/6-311++G** level. Both of these molecules are epimers differing only in the orientation of the hydroxyl group at the C4 position. We investigated electronically the effect of direction (axial/equatorial) of the hydroxyl group at C4 position and the orientation of hydroxymethyl rotamer on C6 position. The structure parameters of X-H•••Y intramolecular hydrogen bonds (HB) were analyzed in gas and solvent phases while the nature of these bonds was characterized using the Atoms in Molecules (AIM) approach. C8O-α-Glc (in gg and tg conformers) has two intramolecular hydrogen bonds and is more stable than the corresponding gt conformer with only one intramolecular hydrogen bond. The ellipticity of the conventional hydrogen bond (HO4…O6 and HO4…O3) is found to be much lower than the unconventional (HC7…O2). In addition, the number of intramolecular hydrogen bonds (conventional and unconventional) stabilizes the resulting self-assemblies from epimers and anomers of these glycolipids and supports the previous experimental observations. The C8O--Gal has two conventional hydrogen bonds and has the highest liquid crystal clearing transition temperature, whereas C8O--Gal and C8O--Glc with only one conventional hydrogen bond have the least clearing temperature.
Thermotropic liquid crystalline glycolipids
Chemical Society Reviews, 2007
Are the liquid crystalline properties of the materials of living systems important in biological structures, functions, diseases and treatments? There is a growing consciousness that the observed lyotropic, and often thermotropic liquid crystallinity, of many biological materials that possess key biological functionality might be more than curious coincidence. Rather, as the survival of living systems depends on the flexibility and reformability of structures, it seems more likely that it is the combination of softness and structure of the liquid-crystalline state that determines the functionality of biological materials. The richest sources of liquid crystals derived from living systems are found in cell membranes, of these glycolipids are a particularly important class of components. In this critical review, we will examine the relationship between chemical structure and the self-assembling and self-organising properties of glycolipids that ultimately lead to mesophase formation.
Hydrogen bonding DFT AIM a b s t r a c t Density functional theory calculations on three conformers, gt (gauche-trans), gg (gauche-gauche) and tg (trans-gauche) of n-octyl-aD -glucoside (C8O-a-Glc) and n-octyl-aD -galactoside (C8O-a-Gal) were performed for geometry optimization at the B3LYP/6-311++G⁄⁄ level. Both of these molecules are epimers differing only in the orientation of the hydroxyl group at the C4 position. We investigated electronically the effect of direction (axial/equatorial) of the hydroxyl group at C4 position and the orientation of hydroxymethyl rotamer on C6 position. The structure parameters of XAHÁ Á ÁY intramolecular hydrogen bonds (HB) were analyzed in gas and solvent phases while the nature of these bonds was characterized using the Atoms in Molecules (AIM) approach. C8O-a-Glc (in gg and tg conformers) has two intramolec-ular hydrogen bonds and is more stable than the corresponding gt conformer with only one intramolec-ular hydrogen bond. The ellipticity of the conventional hydrogen bond (HO4Á Á ÁO6 and HO4Á Á ÁO3) is found to be much lower than the unconventional (HC7Á Á ÁO2). In addition, the number of intramolecular hydrogen bonds (conventional and unconventional) stabilizes the resulting self-assemblies from epimers and anomers of these glycolipids and supports the previous experimental observations. The C8O-b-Gal has two conventional hydrogen bonds and has the highest liquid crystal clearing transition temperature, whereas C8O-a-Gal and C8O-b-Glc with only one conventional hydrogen bond have the least clearing temperature.
Phase Behaviour of Nature-Like Branched-Chain Glycosides
Glycolipids are remarkable biomolecule which become primary constituents of bio-membranes and may form various biologically relevance phases. Due to their diverse functions in nature, investigation on their self-assembly have obtained great attention from the fundamental point of view as well as for technological aspects. The glycolipid materials are highly in demand but, natural products such as monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) found in plant membrane are difficult to extract and purify in large quantity. Therefore, synthetic substitutes are preferred such as those of glycolipids, since these are cheap renewable resources, highly biodegradable, environmental friendly materials and have diverse biological activity. In this study, a branched-chain glycolipids based on Guerbet alcohol have been synthesized namely 2-hexyldexyl-α-D-mannopyranoside. The neat compound was measured with optical polarizing microscopy (OPM) and differential scanning calorimetry (DSC) whereas their lyotropic phase behaviour was investigated by contact penetration technique. α-Man-OC 10 C 6 formed inverse hexagonal phase in dry form whereas in water, it gave inverse bicontinuous cubic phase. The presence of non-lamellar phases implies greater potential for the material (α-Man-OC 10 C 6 ) to be used in several applications such as drug-carrier systems and membrane protein crystallization.
The geminally C-branched 6,6-di-C-n-alkyl-d-galactopyranoses 3a–d prepared in two steps from 1,2:3,4-di-O-isopropylidene-d-galacturonic acid methylester 1 and the even numbered C8-C12-alkylmagnesium bromides, represent a new group of ‘double tailed’ thermotropic mesogens forming columnar supramolecular structures based on hydrogen bridged (disc-like) multimers in accordance with the hypothesis of the Praefcke group. Furthermore, the thermal behaviour of the homologous 6-O-alkyl-d-galactopyranoses 4a–e is discussed in connection with the revised model for the molecular arrangement in smectic A phases of ‘single tailed’ carbohydrates.