Phase behaviour of a methyl branched phosphatidylethanolamine in two and three-dimensional systems (original) (raw)
Related papers
Phases and phase transitions of the hydrated phosphatidylethanolamines
Chemistry and Physics of Lipids, 1994
LIPIDAT is a computerized database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior. Here, a review of the LIPIDAT data subset refering to hydrated phosphatidylethanolamines (PE) is presented together with an analysis of these data. The PE subset represents 14% of all LIPIDAT records. It includes data collected over a 38year period and consists of 1511 records obtained from 203 articles in 35 different journals. An analysis of the data in the subset has allowed us to identify trends in synthetic PE phase behavior reflecting changes in lipid chain length, chain unsaturation (number, isomeric type and position of double bonds), chain asymmetry and branching, type of chain-glycerol linkage (ether vs. ester) and headgroup modification. Also included is a summary of the data concerning the effect of pH, stereochemical purity, and different additives such as salts, saccharides, alcohols, amino adds and alkanes on PE phase behavior. Information on the phase behavior of biologically derived PE is also presented. This review includes 236 references.
Biophysical Journal, 1996
The bilayer-to-hexagonal phase transition temperatures (TH) of di-1 8:1 C phosphatidylethanolamine with double bonds at positions 6, 9, and 11 are 370C, 80C, and 280C, respectively, as measured by differential scanning calorimetry and x-ray diffraction. Thus TH exhibits a minimum when the C=C is around position 9, similar to what has been found for the gel-to-liquid crystalline phase transition temperature in other lipids. Factors that may contribute to the dependence of TH on double bond position were studied by x-ray diffraction of the hexagonal phases in the presence and absence of added alkane, with or without the osmotic stress of polyethylene glycol, and over a wide temperature range. The lattice dimensions show that the intrinsic radius of lipid monolayer curvature increases as the double bond is moved toward the tail ends. A measure of the bending moduli of these lipid monolayers shows a higher value for the 9 position, and lower values for the other two. Consideration of the bilayer-to-hexagonal transition in terms of bending and interstitial energies provides a rationale for the relative values of TH.
An ordered metastable phase in hydrated phosphatidylethanolamine: the Y-transition
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1999
By using time-resolved X-ray diffraction, differential scanning calorimetry and scanning densitometry, we observed rapid formation at low temperature of a metastable ordered phase, termed L R1 phase, in fully hydrated dihexadecylphosphatidylethanolamine (DHPE). The L R1 phase has the same lamellar repeat period as the gel L L phase but differs from the latter in its more ordered, orthorhombic hydrocarbon chain arrangement. It forms at about 12³C upon cooling and manifests itself as splitting of the sharp, symmetric wide-angle X-ray peak of the DHPE gel phase into two reflections. This transition, designated the`Y-transition', is readily reversible and proceeds with almost no hysteresis between cooling and heating scans. Calorimetrically, the L R1 CL L transition is recorded as a low-enthalpy (0.2 kcal/mol) endothermic event. The formation of the L R1 phase from the gel phase is associated with a small, about 2 Wl/g, decrease of the lipid partial specific volume recorded by scanning densitometry, in agreement with a volume calculation based on the X-ray data. The formation of the equilibrium L c phase was found to take place from within the L R1 phase. This appears to be the only observable pathway for crystallisation of DHPE upon low-temperature incubation. Once formed, the L c phase of this lipid converts directly into L L phase at 50³C, skipping the L R1 phase. Thus, the L R1 phase of DHPE can only be entered by cooling of the gel L L phase. The data disclose certain similarities between the low-temperature polymorphism of DHPE and that of long-chain normal alkanes. ß -ray di¡raction 0005-2736 / 99 / $^see front matter ß 1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 5 -2 7 3 6 ( 9 8 ) 0 0 2 5 9 -
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.
Biochemistry Usa, 1985
The phase transition properties of dilute aqueous suspensions of "nonhydrated" (Le., lipid suspensions which had not been heated above room temperature or above the main phase transition temperature of the fully hydrated lipid, whichever was lower) and hydrated 1,2(a)-and 1,3(@)-dipalmitoylphosphatidylethanolamines with modified head groups have been determined by high-sensitivity differential scanning calorimetry at a scan rate of 0.1 K m i d. In both the 1,2 and 1,3 series, the head-group modifications Abbreviations: DSC, differential scanning calorimetry; T,, temperature of maximal excess apparent specific heat (Cmax); AT1,,, transition width in degrees centigrade at AHd, calorimetric enthalpy; AHVH, van't Hoff enthalpy; AHdT, total calorimetric enthalpy evaluated by integration of the curve of C vs. T (excess apparent specific heat vs. temperature); N, number of molecules in a cooperative unit (N = AHvH/AHEsi); TLC, thin-layer chromatography; TNH, temperature at
Determination of n-alkane partitioning within phosphatidylethanolamine Lα/HII phases
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2020
Alkanes are known to promote the fluid lamellar (L α)-to-inverted hexagonal (H II) phase transition of different phospholipids. In this work, we studied the interaction of decane and tetradecane with self-assemblies formed of 1-palmitoyl-2-oleoyl-sn-glycero-phosphoethanolamine (POPE), using sequential 2 H and 31 P solid-state NMR spectroscopy. This technique allowed calculating the partitioning constant of the alkanes between the L α and H II phases of POPE. Our results show that both alkanes are preferentially distributed in the H II phase compared to the L α phase. In the H II phase, both alkanes display a very high conformational disorder, consistent with their location in the intercylinder voids. This preferential partitioning in the H II phase is more pronounced for tetradecane than for decane. This finding is proposed to be associated with a less energetically favored insertion (limited solubility) of tetradecane in the lamellar phase. This proposition is supported by the observation that tetradecane experiences more conformational freedom than its shorter analog in POPE bilayers, suggesting that it is located, on average, closer to the middle of the bilayers. It is also established that the increase in size of the intercylinder voids, by the addition of 1-palmitoyl-2-oleoyl-sn-glycero-phosphocholine (POPC) in the H II cylinders, enhances the partitioning of decane in the H II phase compared to the L α phase. These findings propose handles to modulate the balance of the relative L α /H II phase stability.
Chemistry and Physics of Lipids, 1996
The effect of 1-palmitoyl lysophosphatidylcholine (PLPC) on the phase behaviour of 1,2-dipalmitoyl phosphatidylethanolamine (DPPE) in excess water (34 wt%) has been examined by differential scanning calorimetry, scanning dilatometry and isothermal compressibility measurements. Mole percentages of PLPC in DPPE between 14 and 62% have been studied over the temperature range 30-75°C. The temperature dependence of orientational ordering at selected sites in 2H-labelled PLPC and 2H20 has been determined from measurement of time-averaged chemical shift anisotropies and quadrupole splittings in the 3~p_ and 2H-NMR spectra. These data have been used to further characterize phase behaviour. At less than equimolar contents of PLPC, when a single phase transition with a reduced transition temperature is observed, spectral and calorimetric data indicate complete miscibility of the two lipid components. An equimolar mixture of PLPC and DPPE shows a sharp first order transition at 47.3°C and a second order transition at 62.5°C. NMR data are consistent with the existence of a defective bilayer at intermediary temperatures. In this range it is proposed that PLPC molecules prefer regions with high curvature in the vicinity of the defects, while DPPE molecules are mostly confined to flatter regions of the bilayer. A possible molecular model is described. At temperatures above 62.5°C, PLPC and DPPE are completely miscible and exist as lamellae. At higher PLPC content ( > 50 mol"/,,), thermodynamic and spectral data are indicative of phase separation of the two components over the temperature range examined.
Biochemistry, 1987
Cholesterol lowers the bilayer to hexagonal phase transition temperature of phosphatidylethanolamines up to a mole fraction of about 0.1. At cholesterol mole fractions above about 0.3, the effect of this sterol is to stabilize the bilayer phase. The relatively weak effects of cholesterol in altering the bilayer to hexagonal phase transition temperature can be explained on the basis of lateral phase separation. This is indicated by the horizontal liquidus line for the gel to liquid-crystalline transition in the phase diagram for mixtures of cholesterol with dielaidoylphosphatidylethanolamine (DEPE) as well as the fact that cholesterol does not greatly decrease the cooperativity of the bilayer to hexagonal phase transition. The enthalpy of this latter transition increased with increasing mole fractions of cholesterol. Two oxidation products of cholesterol are 5-cholesten-3P,7a-diol and cholestan-3P,5a,6P-triol. Compared with cholesterol, 5-cholesten-3@,7a-diol had a greater effect in decreasing the bilayer to hexagonal phase transition temperature and broadening this transition. It is suggested that its effectiveness is due to its greater solubility in the DEPE. In contrast, cholestan-3P,5a,6P-t1.iol raises the bilayer to hexagonal phase transition temperature of DEPE. This is due to its larger and more hydrophilic head group. In addition, its length, being shorter than that of DEPE, would not allow it to pack efficiently in a hexagonal phase arrangement. We suggest that this same effect is responsible for cholesterol raising the bilayer to hexagonal phase transition temperature at higher mole fractions.
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.
The polymorphic phase behavior of dielaidoylphosphatidylethanolamine. Effect of n-alkanols
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1989
The polymoqflfic phase bcha~im" of dielaidoylphusphatidylethanolamine (DEPE) has been investigated using spectrophogometry and 31p tnldear ~ resolgall~ (NMR). It has been demonstrated that the bilayer to invermd hexagonal phase transition can be observed by spectrophotometry. The effects of the methanol, ethano[, and Wopanol on both the gel to liquid crystal transition and the hilayer to inverted hexagonal transition were invesfigat,~ by spectrophotometry. It was shown that these alcohols shift the gel to liquid-crystalline phase transition to lower temperature, ~hereas the b|layec to inverted hexagonal phase transition is shifted to higher temperatures by these alcohols. The structural transition between the bilayer and inverted hexagonal phase of pure DEPE was also investigated by 31 P-NMIL