An ordered metastable phase in hydrated phosphatidylethanolamine: the Y-transition (original) (raw)
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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
Chemistry and Physics of Lipids, 1997
When a fully hydrated dimyristoylphosphatidylethanolamine (DMPE) is heated from − 50°C with a slow scanning rate ( 0.1°C/min), an exothermic transition peak is observed at around 47 -48°C by differential scanning calorimetry (DSC). This paper deals with the structural change associated with this exothermic transition in a slow heating scan (0.2°C/min). Simultaneous X-ray diffraction and DSC measurements showed that at the exothermic transition, the fully hydrated DMPE cooled to −50°C converts directly from a metastable gel phase to a stable crystalline phase without the appearance of any intermediate phases. This result suggests that a following process occurs: (1) nuclei emerge partly on cooling to −50°C; (2) the nuclei remain unchanged during slow heating until about 43°C; and (3) the nucleation growth becomes active above 43°C.
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.
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.
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.
DOPC-DOPE composition dependent Lα-HII thermotropic phase transition: SAXD study
Chemistry and Physics of Lipids, 2016
The structural polymorphism and parameters of lyotropic phases formed in the mixed dioleoylphosphatidylcholine-dioleoylphosphatidylethanolamine (DOPC-DOPE) system upon heating and varying DOPC:DOPE composition were studied by means of small-angle X-ray diffraction (SAXD). In the temperature range 5-80 C a sequence of fluid lamellar Lainverse hexagonal H IIinverse cubic Q II phases was detected at DOPE mole fractions X DOPE ! 0.65. A superposition of two bicontinuous cubic Q II phases of Pn3m and Ia3d space groups was identified. The La to H II phase transition temperature, the onset of the Q II phase formation, as well as the lattice spacings of the La and H II phases were found to decrease with rising DOPE content. Moreover, evidence of structural rearrangement during the La to H II phase transition is given and change of transition mechanism with varying X DOPE is suggested. 2016 Elsevier Ireland Ltd. All rights reserved.
X-ray diffraction study of the polymorphic behavior of N-methylated dioleoylphosphatidylethanolamine
Biochemistry, 1988
The polymorphic phase behavior of aqueous dispersions of dioleoylphosphatidylethanolamine (DOPE) and its N-methylated analogues, DOPE-Me, DOPE-Me2, and DOPC, has been investigated by X-ray diffraction. In the fully hydrated lamellar (La) phase at 2 "C, the major structural difference is a large increase in the interlamellar water width from DOPE to DOPE-Me, with minor increases with successive methylation. Consistent with earlier reports, inverted hexagonal (HII) phases are observed upon heating at 5-10 OC in DOPE and at 65-75 " C in DOPE-Me and are not observed to at least 85 " C in DOPE-Me2 or DOPC. In DOPE, the L,-HII transition is facile and is characterized by a relatively narrow temperature range of coexistence of La and HI* domains, each with long-range order. DOPE-Me exhibits complex nonequilibrium behavior below the occurrence of the HII phase: Upon heating, the La lattice spontaneously disorders on a time scale of days; on cooling from the HI* phase, the disorder rises on a time scale of minutes. It is shown that, in copious water, the disordered state transforms very slowly into phases with cubic symmetry. This process is assisted by the generation of small amounts of lipid degradation products. The relative magnitudes of the monolayer spontaneous radius of curvature,
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(alpha)-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 < r < 225 degrees C/hr, and the rate-dependent apparent phase transition temperatures, T(A)...
The existence of a highly ordered phase in fully hydrated dilauroylphosphatidylethanolamine
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1983
Dilauroylphosphatidylethanolamine dispersion forms a crystalline phase at physiological pH and temperature and in the presence of excess water. This phenomenon was observed and studied by differential scanning calorimetry, scanning densitometry and X-ray diffraction. The crystalline phase is stable at pH 5.5-9.5 and below 40°C. The crystalline phase formed at pH 5.5 and pH 9.5 index according to orthorhombic cells with a = 9.41, b = 8.15, c = 46.0 and a = 9.33, b = 8.05, c = 45.8 (~,), respectively. Around 43°C, the crystalline phase is transformed into a multilayer liquid crystal phase. Cooling from 44°C results in the disappearance of the original transition at 43°C and the appearance of a second transition at around 30°C. Below 30°C the lipid forms a gel phase. This gel phase is metastable at pH 5.5 and a crystalline phase may be recovered from it by dispersing or aging methods. Suspensions of dilauroylphosphatidylethanolamine show similar phase transition behaviour at pH 5.5 and pH 9.5, although the transitions are somewhat broader at the higher pH. The thermotropic phase behaviour of dilauroylphosphatidylethanolamine dispersions may be governed by changes in hydration.
Biophysical Journal, 2001
X-ray diffraction is used to solve the low-resolution structures of fully hydrated aqueous dispersions of seven different diacyl phosphatidylethanolamines (PEs) whose hydrocarbon chains have the same effective chain length but whose structures vary widely. Both the lower-temperature, liquid-crystalline lamellar (L ␣ ) and the higher-temperature, inverted hexagonal (H II ) phase structures are solved, and the resultant internal dimensions (d-spacing, water layer thickness, average lipid length, and headgroup area at the lipid-water interface) of each phase are determined as a function of temperature. The magnitude of the L ␣ and H II phase d-spacings on either side of the L ␣ /H II phase transition temperature (T h ) depends significantly on the structure of the PE hydrocarbon chains. The L ␣ phase d-spacings range from 51.2 to 56.4 Å, whereas those of the H II phase range from 74.9 to 82.7 Å. These new results differ from our earlier measurements of these PEs (Lewis et al., Biochemistry, 28:541-548, 1989), which found near constant d-spacings of 52.5 and 77.0 -78.0 Å for the L ␣ and H II phases, respectively. In both phases, the d-spacings decrease with increasing temperature independent of chain structure, but, in both phases, the rate of decrease in the L ␣ phase is smaller than that in the H II phase. A detailed molecular description of the L ␣ /H II phase transition in these PEs is also presented.