Effect of fatty acyl chain length and structure on the lamellar gel to liquid-crystalline and lamellar to reversed hexagonal phase transitions of aqueous phosphatidylethanolamine dispersions (original) (raw)
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European biophysics journal : EBJ, 2001
The lamellar gel to lamellar liquid-crystalline (Lbeta/Lalpha) and lamellar liquid-crystalline to inverted hexagonal (Lalpha/H(II)) phase transitions of a number of phosphatidylethanolamines (PEs) and diacyl-alpha-D-glucosyl-sn-glycerols (alpha-D-GlcDAGs) containing linear saturated, linear unsaturated, branched or alicyclic hydrocarbon chains of various lengths were examined by differential scanning calorimetry and low-angle X-ray diffraction. As reported previously, for each homologous series of PEs or alpha-D-GlcDAGs, the Lbeta/Lalpha phase transition temperatures (Tm) increase and the Lalpha/H(II) phase transition temperatures (Th) decrease with increases in hydrocarbon chain length. The Tm and the especially the Th values for the PEs are higher than those of the corresponding alpha-D-GlcDAGs. For PEs having the same effective hydrocarbon chain length but different chain configurations, the Tm and Th values vary markedly but with an almost constant temperature interval (deltaT(L...
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1989
The disaccharides, sucrose and trehalose, markedly decreased (up to 17-13C ° ) the temperature of the lamellar to hexagonal (L,, ~ Hit) phase transition and simultaneously increase by 2-4 C ° the temperature of the lamellar gel to lameUar liquid-crystal (L# ~ L a) phase transition in hydrated dihexadecylphosphatidylethanolamine and distearoylphosphatidylethanolamine. These two transitions merge and convert into a single La-Hn phase transition when disper~.,ed in 2A M sucrose. These results are inconsistent with recent reports by Crowe et at. (19g7) Biuchem. J. 242, 1-10, (1988) Biochim. Biophys. Acta 947, 367-394) which suggest that trehalnse stabilizes the L a phase relative to the Hit phase and shifts upwards beyond detectability the L,-H n transition. The present results are considered as a manifestation of the Ho|meister effect in which the sugars act a~ ltosmotropic reagents stabilizing the structure of bulk water. This t(:nds io decrease th~ area of contact between the lipid and the aqueous phases and favours the H n and IL~ phases relative to L a phase. This hypothesis is consistent with the effects of chaotropic reagents on the L,-H n phase transition (Yeagle and Sen Biochemistry 25, 7518-7522) and on the stability of the lamellar phase of dipalmitoylpbosphatidylcholine (Oku and MacDonald (1983) J. Biol. Chem. 258, 8733-8738). J J J J J
Effect of PEG-lipid conjugates on the phase behavior of phosphatidylethanolamine dispersions
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999
The phase behavior of binary mixtures of hydrated dielaidoylphosphatidylethanolamine (DEPE) with two different PEG-lipid conjugates at a molar fraction below 0.2 has been studied by using time-resolved X-ray diffraction, and partial phase diagrams have been constructed. The studied conjugates comprise two saturated hydrocarbon acyl chains 14 carbon atoms long and PEG550 or PEG5000 chains covalently attached to a phosphoethanolamine polar head group, DMPE(PEG550) and DMPE(PEGSOOO), respectively. When added in small amounts (lo-20 mol%) to DEPE aqueous dispersions, both PEG-lipids favor the lamellar liquid crystalline (L,) phase at the expense of the lamellar gel (L,) and the inverted hexagonal (H,,) phases. One of the conjugates, DMPE(PEG550), shifts the L,H,, transition of DEPE to higher temperatures by 2.5"C per mol% PEG-lipid, and induces the spontaneous formation of a cubic phase of space group Im3m in the DEPE dispersions. The cubic phase intrudes between the lamellar liquid crystalline and the inverted hexagonal phases in the DEPE/DMPE(PEG550) phase diagram. Low amounts of the DMPE(PEG5000) conjugate only shift the L,.H,, transition of DEPE to higher temperatures, at 5.2"C per mol% PEG-lipid, but does not promote the formation of additional phases. The respective slopes for the L,-L, transition temperature depression are 10-l 5 times smaller. At > 15 mol% DMPE( PEG550) and at > 5 mol% DMPE( PEG5000), the non-lamellar phases are eliminated from the phase diagrams. Structural data on the organization of the pure hydrated PEG-lipid conjugates are also provided, suggesting that these lipids form micelles and lamellae. 0 1999 Elsevier Science B.V. All rights reserved.
Chemistry and Physics of Lipids, 2008
Differential scanning calorimetry (DSC) measurements have been carried out simultaneously with small-and wide-angle X-ray scattering recordings on liposomal dispersions of stearoyl-oleoylphosphatidylethanolamine (PE) in a temperature range from 20 to 80 • C. The main transition temperature, T m , was determined at 30.9 • C with an enthalpy of 28.5 kJ/mol and the lamellar-to-inverse hexagonal phase transition temperature, T hex , at 61.6 • C with an enthalpy of 3.8 kJ/mol. Additionally highly resolved small angle X-ray diffraction experiments performed at equilibrium conditions allowed a reliable decomposition of the lattice spacings into hydrophobic and hydrophilic structure elements as well as the determination of the lipid interface area of the lamellar gel-phase (L ), the fluid lamellar phase (L ␣) and of the inverse hexagonal phase (H II). The rearrangement of the lipid matrix and the coincident change of free water per lipid is illustrated for both transitions. Last, possible transition mechanisms are discussed on a molecular level.
Chemistry and Physics of Lipids, 1987
Phosphatidylethanolamines are known to exhi'bit asymmetric phase transitions with a low temperature shoulder. However, in this work we demonstrate that suspensions of dielaidoylphosphatidylethanolamine can be prepared which exhibit very sharp and only slightly asymmetric phase transitions. Such preparations are made either by isolating a rapidly sedimenting fraction of a vortexed suspension of this lipid or by dialyzing a suspension which had been hydrated at pH 9.2 to pH 7.2. Smaller aggregates of the lipid can be isolated from the supernate of a vortexed suspension of dielaidoylphosphatidylethanolamine after removal of the rapidly sedimenting fraction or it can be produced by sonication of a sample at pH 9.2 followed by dialysis to pH 7.2. Such preparations exh~it very broad transitions and the transition temperature is shifted to lower values. These results demonstrate that the shape of the phase transition of dieiaidoylphosphatidylethanolamine is particularly sensitive to the method of sample preparation. Furthermore, an asymmetric phase transition with a low temperature shoulder is not necessarily an intrinsic property of phosphatidylethanoiamines.
Biochimica Et Biophysica Acta-biomembranes, 1993
1-Octadecanoyl, 2-decanoylphosphatidylethanolamine (C(18:0)C(10:0)PE) has been reported to exhibit mixed interdigitated gel-phase packing of the phospholipid acyl chains (Mason, J.T. and Stephenson, F.A. (1990) Biochemistry 29, 590–598). In contrast, ditetradecanoylphosphatidylethanolamine (C(14:0)C(14:0)PE) packs without significant interdigitation of the phospholipid acyl chains across the bilayer center. In this report, the gel-fluid transition temperatures of C(18:0)C(10:0)PE and C(14:0)C(14:0)PE in multimellar dispersion were determined by fluorescence anisotropy of cis-parinaric acid and trans-parinaric acid with a descending temperature scan rate of 0.67°C/min. The transition mid-points detected for C(18:0)C(10:0)PE with cis-parinaric acid were 19°C in water, 18°C at pH 8.1, and 14°C at pH 10. The phase diagram for C(14:0)C(14:0)PE and C(18:0)C(10:0)PE at pH 10 suggests complete mixing in the fluid phase and considerable immiscibility in the gel phase. Cross-linking of equimolar mixtures of C(14:0)C(14:0)PE and C(18:0)C(10:0)PE with dimethylsuberimidate at pH 10 revealed a random arrangement of the two species in the fluid phase, confirming the notion that C(18:0)C(10:0)PE and C(14:0)C(14:0)PE are miscible in the fluid phase, as determined from the phase diagram. In contrast, cross-linking of the equimolar mixture of C(18:0)C(10:0)PE and C(14:0)C(14:0)PE in the gel phase at 0°C revealed a non-random arrangement, demonstrating and confirming immiscibility in the gel phase.
Chemistry and Physics of Lipids, 1994
The physical properties of aqueous dispersions of N-acylphosphatidylethanolamine from natural origin with long N-acyl chain (NAPE) and headgroup modified analogues have been studied. N-Acylation of PE causes a significant increase in the gel-to-liquid crystalline lamellar phase transition temperature in contrast with saturated N-acyl-(dipalmitoyl) PEs, and in addition it does not restrict the headgroup rotational mobility in gel phase, The results agree with the increase of hydration of the phosphate group compared with that in PE and suggest the formation of hydrogen bonds between amide groups. The modifications introduced modulate the headgroup size and their hydrogen bonding capability. An increasing number of methylene groups between the phosphate and amide groups does not modify the phase behaviour observed. N-methylation of the amide group, which prevents the possibility of intermolecular hydrogen bond formation, decreases the melting temperature and the cooperativity of the phase transition and does not change the phase behaviour, while the hydration at the ester carbonyl groups level is decreased. On the other hand, the addition of N-ethyl substituent to the amide group or substitution of an ester group for this group increases its tendency to form structures with inverted geometries. The behaviour of these compounds suggests that hydration forces must be more important than considerations of the lipid dynamic shape in predicting the relative stabilities of lamellar vs, non-lamellar phases for NAPEs with long saturated N-acyl chain.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1996
A new lamellar gel phase (Li~) with expanded lamellar period ~as l\~tmd at low temperatures in dihexadecylphosphatidylelhanolamine (DHPE) and dipalnfitoylphosphatidylethanolantine (DPPE) dispersions in concenuated sucrose solnlions (I-2.4 M). It forms via a cooperati,,'e, relatively broad transition upon cooling of the L~ gel phase of these lipids, According to the X-ray data, the tranfformation between L~ and L~ is rewrsible, with a temperature hysteresis of 6-10°C and a transition width of about IO°C. No specific volume changes and a wt'v small heat absorption of about 0.05 kcal/mol accompany this transition. The L~-L~ transition temperature strongly depends on the disuccharide concentration. From a value of about IO°C below the melting transition of DHPE. it drops by 25'~C with decrease of sucrose concentration from 2.4 M to I M. The low;temperature gel phase L, has a repeat spacing by 8-10 A ~ larger than that of the L~ gel phase and a single symmetric 4.2 A wide-angle peak. It has been observed in I. 1.25. 1.5 and 2.4 M solutions of sucrose, but not in 0,5 M of sucrose. The data clearly indicate that the expanded lantellar period of the L/] phase results from a cooperative. reversible with the temperature, increase of the interlamellar space of the L~ gel phase. Other st, gars (trehalose, maltose. fntctose, glucose) induce similar expanded low-temperature gel phases in DHPE and DPPE. The L~ phase is osmotic,'dly insensitive. Its lamellar period does not depend on the sucrose concentration, while the lattice spacings of the L. L~ and H, phases decrease linearly with increase of sucrose concentration. Another notable sngar efl'ect is the induction of a cubic phase in these lipids. It fom,s during the reverse H H-L,, phase mmsition and coexists with the L,, phase in the whole temperature range between the H~ and L~ phases. The cubic phase has only been observed at sucrose concentrations of I M and above. In accordance with previous data. sucrose suppresses the L,, phase in both lipids and brings about a direct Abbreviations: DHPE, 1,2-Present address: Sincmtmne Trieste. Baso,,+izza. 1-34012 Trieste. haly. 0005-2736/96/$15.00 G'?yright © 1~,~96 Elsevier Saence B.V. All rights re,,er,,cd. PII S0005-2736(96)00156-3 l I0 B. Tern'hoe el al./Biochimica et Biophysica Acta I28.5 (I 996J 109-122
Chemistry and Physics of Lipids, 1990
Fourier transform infrared (FTIR) and time-resolved fluorescence spectroscopy have been employed to examine the structural dynamics of lipid fatty acyl chains and lipid/water interfaciai region of a binary lipid mixture containing unsaturated phosphatidylethanolamine (PE) and diacylgiycerol (DG). Infrared vibrational frequencies of the CH 2 symmetric stretching and the C = O stretching bands of the lipids were measured at different lipid compositions and temperatures. For 0% DG, the lamellar gel to lamellar liquid crystalline (L0-L) and the L, to inverted hexagonal (L-Hu) phase transitions were observed at 'x,15° and 55°C, respectively. As the DG content increased gradually from 0% to 15%, the Lo-HI~ phase transition temperature decreased drasticaily while the LFL ° phase transition temperature decreased only slightly. At 10% DG, a merge of these two phase transitions was noticed at ~I0°C. For the composition study at 23°C, the La-H u transition occurred at ~6-10% DG as indicated by abrupt increases in both the CH 2 and C = O stretching frequencies at those DG contents. Using time-resolved fluorescence spectroscopy, abrupt decreases in both the normalized long time residual and the initial slope of the anisotropy decay function of lipid probes, ~-paimit~y~-2-[[2-[4-(6-pheny~-trans-~'3~5-hexatrieny~)pheny~]ethy~]carb~ny~]~3-sn-ph~sphatidy~ch~ine~ in these PE/ DG mixtures were observed at the Lo-H H phase transition. These changes in the anisotropy decay parameters suggested that the rotational dynamics and orientationai packing of the lipids were altered at the composition-induced L-H~j transition, and agreed with a previous temperature-induced L-H u transition study on pure unsaturated PE (Cheng (1989) Biophys. J. 55, 1025-1031). The fluorescence lifetime of water soluble probes, 8,1-anilinonapthalenes sulfonate acid, in PE/DG mixtures increased abruptly at the L,-H, phase transition, suggesting that the conformation and hydration of the lipid/water interfacial region also undergo significant changes at the Lo-H~ transition.
Low amounts of PEG-lipid induce cubic phase in phosphatidylethanolamine dispersions
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1997
Ž . By using time-resolved X-ray diffraction we demonstrate that low amounts 5-10 mol% of a phospholipid with two saturated hydrocarbon acyl chains 14 carbon atoms long and PEG550 chain covalently attached to its phosphoethanolamine Ž . Ž polar head group, DMPE PEG550 , induce spontaneous formation of a cubic phase with lattice constant 20.5 nm cubic . Ž. aspect a8, space group Im3m in aqueous dispersions of dielaidoylphosphatidylethanolamine DEPE . This phase displays a highly resolved X-ray diffraction pattern with 17 low-angle reflections. The cubic phase was found to intrude in the Ž . Ž . temperature range between the lamellar liquid crystalline L phase and the inverted hexagonal phase H known to form a II Ž . in pure DEPErwater dispersions. A higher DMPE PEG550 amount of 20 mol% was found to eliminate the non-lamellar phases in the temperature scale up to 1008C. DMPE grafted with PEG5000 only shifts the L -H transition of DEPE to a II higher temperatures but does not promote formation of cubic phase. These findings indicate that, consistent with their bulky head groups, the PEG-lipids decrease the tendency for negative interfacial mean curvature of the DEPE bilayers.