Role of the position of unsaturation on the phase behavior and intrinsic curvature of phosphatidylethanolamines (original) (raw)
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Chemistry and Physics of Lipids, 1989
The orientational order and rotational dynamics of 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-l,3,5-hexatrienyl)phenyl]ethyl] carbon yl]-3-sn-phosphatidylchofine (DPH-PC) in dilinoleoylphosphatidylethanolamine (DLPE) and 1-palmitoyl-2-oleoylphosphatidylcholine 0aOPC) binary lipid mixtures were investigated. A previous study (Biochim. Biophys. Acta 731 (1983) 177) indicated that the empirical phase diagram of POPC/DLPE can roughly be divided into three zones. They are the lamellar (15% PC and higher), intermediate (5-15% PC) and inverted hexagonal (0-50/0 PC) phases. As the lipids changed from the lamellar to intermediate phase, the order parameter increased at all temperatures (1-50°C). On the contrary, the rotational diffusion decreased at high temperatures (20-50°C) but increased at low temperatures (I-10°C). These results indicate that the intermediate phase is in a stressed state at high temperatures but in a highly mobile amorphous state at low temperatures. As the lipid progressed from the intermediate toward hexagonal phase, the order parameter decreased abruptly at all temperatures. The ratio of order parameter in the intermediate phase to that in the hexagonal phase was calculated. This ratio was found to increase linearly with temperature, indicating that a distinct change in the packing symmetry of lipids occurred as temperature increased. From the intermediate to hexagonal phase, the rotational diffusion increased slightly at high temperatures but declined abruptly at low temperatures. These results further agreed with the stressed and amorphous natures of the intermediate phases as described above.
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.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1988
The effect el mono., di. and triaeyiglyeerols on the bilayer to hexagonal phase (1-1 n) transition was studied by. differential sc~min 8 calerimetry and StP.NMR spectresce~. The acylglycemls were mixed with either dlelaidoyl~ylethanoline or with l.palmitoyl-2.oleeyll~letbmohmine. Acylglycerols of laurie, olek and shmrte acids were mgized. All el the aeylglyeerols lowered the bilayer to H u phase transition ~.
Biochemistry, 1990
The quadrupolar splitting profiles of methylene groups along the acyl chains of perdeuteriated dimyristoylphosphatidylcholine (DMPC-dS4) in mixtures with dioleoylphosphatidylethanolamine (DOPE) were studied by 2H N M R. The quadrupolar splittings, obtained for lipid mixtures in the bilayer state, were measured as functions of temperature and PE:PC ratio and were used to obtain the approximate gauche probabilities a t a given chain position, pB. Ratios (R) ofpB for C13, C12, and C1 1 relative to that of the plateau region were used to characterize the effect of increasing P E on the gauche content of PC chains. At all temperatures studied (including the bilayer to hexagonal phase transition region), for each ratio R (e.g., RC13,P), the relative gauche content of the D M P C chains was similar over the range of 2 5 4 5 % PE. DOPE is viewed in simple terms as having a "conical" shape; if this geometry applies to the acyl chain region of the molecule, a greater lateral pressure would be expected toward the center of the bilayer as the P E content is increased, resulting in a decreased gauche content, relative to the plateau, of those methylene groups of PC. The failure to observe the predicted increase in lateral pressure has ramifications for the cone-shape molecular model. The overall "cone shape" of P E is seen to arise from the smaller size of the head-group relative to the acyl chains; however, the acyl chain region itself is not rigidly cone-shaped and is better represented by a flexible ''balloon''. These results were supported by small-angle X-ray diffraction, which showed a decreasing trend in the area per molecule with increasing P E content.
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.
Lipid concentration affects the kinetic stability of dielaidoylphosphatidylethanolamine bilayers
Chemistry and Physics of Lipids, 1993
The bilayer to hexagonal phase transition temperature (Th) of dielaidoylphosphatidylethanolamine is 65.5°C as measured by DSC heating scans at lipid concentrations below 100 mg/ml and at scan rates ranging from 1.7 to 45°C/h. However, at lipid concentrations above 100 mg/ml and at scan rates of 1-3°C/h the measured T h decreases below 65.5°C. At a lipid concentration of 500 mg/ml and a heating scan of 1.2°C/h the transition to the hexagonal phase occurs at 62.7°C. However, this same sample scanned at a rate of 34°C/h has a transition temperature of 64.6°C. Thus a combination of high lipid concentration and slow scan rate is required to significantly lower the hexagonal phase transition temperature below 65°C. These results demonstrate that the rate of conversion of the bilayer to the hexagonal phase is dependent on the concentration of the lipid suspension even under conditions of full hydration. Furthermore, a 100 mg/ml suspension of this lipid which has a Th of 64.3°C at a scan rate of 3.2°C/h has a lower hexagonal phase transition temperature of 62.8°C after pelleting the lipid with low-speed centrifugation but retaining the same amount of solvent in the supernatant above the pellet. Pelleting of the lipid also has a marked effect on the isothermal rate of conversion of the bilayer to hexagonal phase as observed by 3~p NMR. The conversion is highly temperature-dependent and is orders of magnitude more rapid for the pelleted sample than for the suspension. The NMR results also demonstrate that the lowering of the temperature of transition to non-bilayer phases is not caused by the formation of a stable cubic phase. We have demonstrated that subtle changes in the morphology of lipid suspensions, probably altering the extent of bilayer-bilayer contact, can have effects on the measured value of Th. These changes do not affect the La to L~ transition temperature. Over a wide variety of conditions, T h for dielaidoylphosphatidylethanolamine is found to be 65.6°C, but the L~ phase in the region 63-65°C is metastable.
Dependence of the bilayer to hexagonal phase transition on amphiphile chain length
Biochemistry, 1989
Several series of amphiphiles of increasing chain length were tested for their abilities to modify the L,-HII transition of dielaidoylphosphatidylethanolamine using differential scanning calorimetry. Acylcarnitines, alkyl sulfates, alkylsulfobetaines, and phosphatidylcholines, with chain lengths between about 6 and 12 carbon atoms, show an increasing capacity to raise the L,-HII phase transition temperature of phosphatidylethanolamine. This is ascribed to increased partitioning of the added amphiphile from water into the membrane as the chain length increases. Alkyl sulfates and alkyltrimethylammonium bromides have diminished capacities to raise the La-H,I transition temperature as the chain length is increased from 12 to 16. This is caused by an increase in the hydrophobic portion of the amphiphile leading to a change in the intrinsic radius of curvature and a decrease in the hydrocarbon packing constraints in the HII phase relative to the shorter chain amphiphiles. The La-HII transition temperature of phosphatidylethanolamine with acylcarnitines of chain length 14-20 carbon atoms, alkylsulfobetaines above 14 carbon atoms, and phosphatidylcholines with acyl groups having above 10 carbon atoms is relatively insensitive to chain length. We suggest that this is caused by a balance between increasing hydrocarbon volume promoting the HII phase through decreased intrinsic radius of curvature and greater relief of hydrocarbon packing constraints vs greater intermolecular interactions favoring the more condensed L, phase. This latter effect is more important
Biophysical Journal, 2002
The thermodynamic properties of fully-hydrated lipids provide important information about the stability of membranes and the energetic interactions of lipid bilayers with membrane proteins (Nagle and Scott, Physics Today, 2:39, 1978). The lamellar/inverse hexagonal (L ␣-H II) phase transition of 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) water mixtures is a first-order transition and, therefore, at constant pressure, must have a thermodynamically well-defined equilibrium transition temperature. The observed transition temperature is known to be dependent upon the rate at which the temperature is changed, which accounts for the many different values in the literature. X-ray diffraction was used to study the phase transition of fully-hydrated DOPE to determine the rate-independent transition temperature, T LH. Samples were heated or cooled for a range of rates, 0.212 Ͻ r Ͻ 225°C/hr, and the rate-dependent apparent phase transition temperatures, T A (r) were determined from the x-ray data. By use of a model-free extrapolation method, the transition temperature was found to be T LH ϭ 3.33 Ϯ 0.16°C. The hysteresis, ͉T A (r) Ϫ T LH ͉, was identical for heating and cooling rates, Ϯr, and varied as ͉r͉  for  Ϸ 1 ⁄4. This unexpected power-law relationship is consistent with a previous study (Tate et al., Biochemistry, 31:1081-1092, 1992) but differs markedly from the exponential behavior of activation barrier kinetics. The methods used in this study are general and provide a simple way to determine the true mesomorphic phase transition temperatures of other lipid and lyotropic systems.
BMC biophysics, 2011
Although biological membranes are organized as lipid bilayers, they contain a substantial fraction of lipids that have a strong tendency to adopt a nonlamellar, most often inverted hexagonal (HII) phase. The polymorphic phase behavior of such nonbilayer lipids has been studied previously with a variety of methods in the fully hydrated state or at different degrees of dehydration. Here, we present a study of the thermotropic phase behavior of the nonbilayer lipids egg phosphatidylethanolamine (EPE) and monogalactosyldiacylglycerol (MGDG) with a focus on interactions between the lipid molecules in the interfacial and headgroup regions. Liposomes were investigated in the dry state by Fourier-transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC). Dry EPE showed a gel to liquid-crystalline phase transition below 0°C and a liquid-crystalline to HII transition at 100°C. MGDG, on the other hand, was in the liquid-crystalline phase down to -30°C and showed a nonb...
Biophysical Journal, 2002
The thermodynamic properties of fully-hydrated lipids provide important information about the stability of membranes and the energetic interactions of lipid bilayers with membrane proteins (Nagle and Scott, Physics Today, 2:39, 1978). The lamellar/inverse hexagonal (L ␣ -H II ) phase transition of 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) water mixtures is a first-order transition and, therefore, at constant pressure, must have a thermodynamically well-defined equilibrium transition temperature. The observed transition temperature is known to be dependent upon the rate at which the temperature is changed, which accounts for the many different values in the literature. X-ray diffraction was used to study the phase transition of fully-hydrated DOPE to determine the rate-independent transition temperature, T LH . Samples were heated or cooled for a range of rates, 0.212 Ͻ r Ͻ 225°C/hr, and the rate-dependent apparent phase transition temperatures, T A (r) were determined from the x-ray data. By use of a model-free extrapolation method, the transition temperature was found to be T LH ϭ 3.33 Ϯ 0.16°C. The hysteresis, ͉T A (r) Ϫ T LH ͉, was identical for heating and cooling rates, Ϯr, and varied as ͉r͉  for  Ϸ 1 ⁄4. This unexpected power-law relationship is consistent with a previous study (Tate et al., Biochemistry, 31:1081-1092 but differs markedly from the exponential behavior of activation barrier kinetics. The methods used in this study are general and provide a simple way to determine the true mesomorphic phase transition temperatures of other lipid and lyotropic systems.