Thermotropic phase properties of 1,2-di-O-tetradecyl-3-O-(3-O-methyl- beta-D-glucopyranosyl)-sn-glycerol (original) (raw)
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Effect of chlorophyll a on the phase behavior of hydrated monogalactosyldiacylglycerols
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1987
We have studied the effect of chlorophyll a (chl a) on the X-ray diffraction patterns and the appearance of freeze-fracture electron micrographs of aqueous dispersions of monogalactosyldiacylglycerols (MGDG), the most abundant lipid in the thylakoid membrane. In MGDG systems containing 0-18 moi% of chl a, the diffraction patterns indicate the presence of a well-ordered reverse hexagonal phase. When 30 tool% of chl a was incorporated into the MGDG, the low-angle X-ray diffraction lines of the hexagonal lattice were slightly broadened and were accompanied by additional weak lines. With higher mol percents of chl a, the low-angle lines could no longer be indexed on a hexagonal or lamellar lattice. The freeze-fracture electron micrographs of similar samples showed that the patterns characteristic of the reverse hexagonal phase of an aqueous dispersion of pure MGDG were replaced by large iiposomes, the fracture pattern of which is circular. We conclude that chl a in excess of 20 mol% destabilized the orderly reverse hexagonal phase of aqueous MGDG dispersions and disturbed the long-range order of the lipid array. These results are summarized in a temperature-composition isobaric phase diagram over a temperature range of-60 o C to 60 ° C.
Biochemistry, 1990
The polymorphic phase behavior of aqueous dispersions of a homologous series of 1,2-di-Oacyl-3-O(~-~-glucopyranosyl)-sn-glycerols was studied by differential scanning calorimetry. At fast heating rates, unannealed samples of these lipids exhibit a strongly energetic, lower temperature transition, which is followed by a weakly energetic, higher temperature transition. X-ray diffraction studies have enabled the assignments of these events to a lamellar gel/liquid crystalline (chain-melting) phase transition and a bilayer/nonbilayer phase transition, respectively. Whereas the values for both the temperature and enthalpy of the chain-melting phase transition increase with increasing acyl chain length, those of the bilayer/nonbilayer phase transition show almost no chain-length dependence. However, the nature of the bilayer/nonbilayer transition is affected by the length of the acyl chain. The shorter chain compounds form a nonbilayer 2-D monoclinic phase at high temperature whereas the longer chain compounds from a true inverted hexagonal Downloaded by UNIV OF GUELPH LIBRARY on October 15, 2009 |
Biophysical Journal, 1992
We have studied the physical properties of aqueous dispersions of 1,2-snand 2,3-sn-didodecyl-f-D-glucopyranosyl glycerols, as well as their diastereomeric mixture, using differential scanning calorimetry and low angle x-ray diffraction. Upon heating, both the chiral lipids and the diastereomeric mixture exhibit characteristically energetic L,/La phase transitions at 31.7-32.8°C and two or three weakly energetic thermal events between 490C and 890C. In the diastereomeric mixture and the 1,2-sn glycerol derivative, these higher temperature endotherms correspond to the formation of, and interconversions between, several nonlamellar structures and have been assigned to LJ/Q|l, Oll /O|l, and Q /H,, phase transitions, respectively. The cubic phases Q a and Q,, whose cell laftice parameters are strongly temperature dependent, can be identified as belonging to space groups la3d and Pn3m/Pn3, respectively. In the equivalent 2,3-sn glucolipid, the QO phase is not observed and only two transitions are seen at 490C and 770C, which are identified as LJOQb and Qb/H,, phase transitions, respectively. These phase transitions temperatures are some 10°C lower than those of the corresponding phase transitions observed in the diastereomeric mixture and the 1,2-sn glycerol derivative.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2000
The phase behaviour of aqueous dispersions of a series of synthetic 1,2-di-O-alkyl-3-O-(L-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 L /L K ) phase transition (short chain compounds, n 9 14 carbon atoms) or a lamellar gel/inverted hexagonal (L L /H II ) phase transition (longer chain compounds, n v 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 K-and L-D-glucosyl counterparts, as well as the recently published 1,2dialkyl-3-O-(L-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. ß Thermotropic phase behavior 0005-2736 / 00 / $^see front matter ß 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 5 -2 7 3 6 ( 0 0 ) 0 0 2 9 6 -
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.
Biochemistry, 1991
The role carbohydrate moieties play in determining the structure and energetics of glycolipid model membranes has been investigated by small-and wide-angle X-ray scattering, differential scanning densitometry (DSD), and differential scanning microcalorimetry (DSC). The dependence of a variety of thermodynamic and structural parameters on the stereochemistry of the OH groups in the pyranose ring and on the size of the sugar head group has been studied by using an homologous series of synthetic stereochemically uniform glyceroglycolipids having glucose, galactose, mannose, maltose, or trimaltose head groups and saturated ether-linked alkyl chains with 10, 12, 14, 16, or 18 carbon atoms per chain. The combined structural and thermodynamic data indicate that stereochemical changes of a single OH group in the pyranose ring can cause dramatic alterations in the stability and in the nature of the phase transitions of the membranes. The second equally important determinant of lipid interactions in the membrane is the size of the head group. A comparison of lipids with glucose, maltose, or trimaltose head groups and identical hydrophobic moieties has shown that increasing the size of the neutral carbohydrate head group strongly favors the bilayer-forming tendency of the glycolipids. These experimental results provide a verification of the geometric model advanced by Israelachvili et al. to explain the preferences lipids exhibit for certain structures. Generally galactose head groups confer highest stability on the multilamellar model membranes as judged on the basis of the chain-melting transition. This is an interesting aspect in view of the fact that galactose moieties are frequently observed in membranes of thermophilic organisms. Glucose head groups provide lower stability but increase the number of stable intermediate structures that the corresponding lipids can adopt. Galactolipids do not even assume a stable intermediate L, phase for lipids with short chain length but perform only L, -Hn transitions in the first heating. The CZ isomer, mannose, modifies the phase preference in such a manner that only L, -Hu changes can occur. Maltose and trimaltose head groups prevent the adoption of the Hu phase and permit only L, -L, phase changes. The DSD studies resulted in a quantitative estimate for the volume change associated with the L, -Hu transition of 14-Glc. The value of AB = 0.005 mL/g supports the view that the volume difference between L, and Hn is minute. Analogously, it was found that the enthalpy input required to transform the lamellar L, phase into the inverted hexagonal structure is only approximately 10% of that of the L, -+ L, transition.
Glycobiology, 2005
Glycolipids are important components of almost all biological membranes. They possess unique properties that have only been incompletely characterized so far. The plant glycolipid digalactosyldiacylglycerol (DGDG) strongly influences the physical behavior of phospholipid model membranes in both the dry and hydrated state. It was, however, unclear whether the strong effect of DGDG on the gel to liquid-crystalline phase transition temperature (T m ) in dry phosphatidylcholine (PC) bilayers is mainly due to the high degree of unsaturation of the DGDG fatty acyl chains or to interactions between the DGDG and PC headgroups. Also, no information on the relative effectiveness of membrane bound and free sugars on membrane phase behavior was available. We have used Fourier-transform infrared spectroscopy (FTIR) to investigate the phase properties and H-bonding patterns in dry membranes made from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) containing one saturated and one monounsaturated (16:0/18:1) fatty acid and different fractions of DGDG or 1,2-dilinolenoyl-sn-glycero-3-phosphatidylcholine (DLPC) (18:3/18:3). This was compared to the effects of galactose (Gal) and digalactose (diGal). All additives depressed T m of the dry membranes, but DGDG was much more effective than DLPC or Gal. diGal had a similar effect as DGDG, pointing to the sugar headgroup as the component with the strongest influence on membrane phase behavior. A combination of DLPC and diGal, which should theoretically be equivalent to DGDG, was much more effective than the galactolipid. H-bonding interactions with the P=O group of PC were also stronger for free diGal than for DGDG, indicating that the free sugar may be structurally more flexible to adopt an optimal conformation for interactions with the PC headgroup.
Formation of a new stable phase of phosphatidylglycerols
Biophysical Journal, 1992
Dilauroyl and dimyristoylphosphatidylglycerol (DMPG) form a more stable gel state when aqueous suspensions are incubated several days at low temperature (O-20C), pH 7.4 with 0.15 M NaCI. This gel state is characterized by a higher transition temperature and a higher transition enthalpy. The geometry of this gel state is distinguishable from the metastable gel state that forms rapidly upon hydration on the basis of its x-ray diffraction pattern. Infrared spectra in the CH2 scissoring region indicate that the stable gel phase of DMPG is also characterized by reduced reorientational fluctuations of acyl chains and increased interchain interactions. Analysis of vibrational bands due to ester carbonyl groups of DMPG suggests that the transition to a new gel phase is initiated by changes in the interfacial and/or headgroup region of the bilayer, most likely via formation of interlipid hydrogen bonds. The melting of the stable gel phase of DMPG is accompanied by a gross morphological change resulting in vesiculation.
Chemistry and Physics of Lipids, 2007
The thermotropic phase behaviour of aqueous dispersions of some synthetic 1,2-di-O-alkyl-3-O-(-d-galactosyl)-rac-glycerols (rac--d-GalDAGs) with both odd and even hydrocarbon chain lengths was studied by differential scanning calorimetry (DSC), small-angle (SAXS) and wide-angle (WAXS) X-ray diffraction. DSC heating curves show a complex pattern of lamellar (L) and nonlamellar (NL) phase polymorphism dependent on the sample's thermal history. On cooling from 95 • C and immediate reheating, rac--d-GalDAGs typically show a single, strongly energetic phase transition, corresponding to either a lamellar gel/liquid-crystalline (L  /L ␣ ) phase transition (N ≤ 15 carbon atoms) or a lamellar gel/inverted hexagonal (L  /H II ) phase transition (N ≥ 16). At higher temperatures, some shorter chain compounds (N = 10-13) exhibit additional endothermic phase transitions, identified as L/NL phase transitions using SAXS/WAXS. The NL morphology and the number of associated intermediate transitions vary with hydrocarbon chain length. Typically, at temperatures just above the L ␣ phase boundary, a region of phase coexistence consisting of two inverted cubic (Q II ) phases are observed. The space group of the cubic phase seen on initial heating has not been determined; however, on further heating, this Q II phase disappears, enabling the identification of the second Q II phase as Pn3m (space group Q 224 ). Only the Pn3m phase is seen on cooling.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1993
The lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) forms a lamellar liquid crystalline phase (L~) in arbitrary mixtures of glycerol and water. The phase has been characterized by means of X-ray diffraction, 31p-NMR spectroscopy and differential scanning calorimetry (DSC). In the L,~ state, and for DOPC concentrations greater than 50% (w/w), the thickness of the lipid bilayer decreases, while the area of the polar head group increases Kith increasing glycerol concentration. The phase transition from gel to L~ state occurs in the range of 240 to 260 K. Contrary to a previous (McDaniel, R.V., Mclntosh, T.J. and Simon, S.A. (1983) Biochim. Biophys. Acta 731, 97) study of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) we find that in the gel state, the thickness of the DOPC lipid bilayer is greater than that in the L~ state. This suggests that in the gel state, the lipid acyl chains of DOPC are in extended configuration. The lamellar phase reaches its maximum swelling at about 50% (w/w) of DOPC. At lower DOPC concentrations a two-phase system is formed where the lamellar phase exists in equilibrium with excess Of solvent. Unilamellar vesicles can be prepared from a diluted suspension of the lamellar phase either by using the sonicator or extruder technique. We show this by means of 31p-NMR, EPR and fluorescence spectroscopy. The mean radius of the vesicles, p.repared by a sonicator, has been determined at different glycerol/water mixtures. It is found to decrease continously from 100 A at 100% water to a minimum of 75 ,~ at about 50% water in the solvent mixture. By further decreasing the water content in the solution, the radius rapidly increases, and a mean radius of 450 .~ is estimated at a water content of 10%. The rotational relaxation times of a fluorescent probe and two EPR spin probes, solubilized in DOPC vesicles, have been measured at different glycerol/water mixtures. It is found that the rotational rates are always much slower in the systems containing glycerol.