Characterization of a Quasicrystalline Phase in Codispersions of Phosphatidylethanolamine and Glucocerebroside (original) (raw)
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Biophysical Journal, 1994
Hydrocarbon chain conformational and orientational order in liquid-crystalline bilayers of the highly chainasymmetric 1 -Oeicosanoyl, 2-adodecanoyl and 1 -Odecanoyl, 2-adocosanoyl phosphatidylcholines were studied by Fourier transform infrared (FTIR) and deuterium nuclear magnetic resonance (2H-NMR) spectroscopy, respectively, and compared with appropriate symmetric-chain phosphatidylcholines at comparable reduced temperatures. FTIR spectroscopy indicates that these two asymmetric-chain phospholipids contain a slightly greater number of kink, a considerably larger number of doublegauche, but a somewhat smaller number of end-gauche conformers than does dipalmitoylphosphatidylcholine, a symmetricchain phospholipid having the same total number of carbon atoms in its hydrocarbon chains. Moreover, the asymmetric-chain phospholipids also contain a larger total number of gauche conformers, suggesting that their hydrocarbon chains are more disordered overall than are those of dipalmitoylphosphatidylcholine. 2H-NMR studies of the specifically chain-perdeuterated analogs of these asymmetric-chain lipids reveal that the orientational order parameter profiles of their shorter and longer chains differ both qualitatively and quantitatively, regardless of whether they are esterified at the sn1 -or sn2 positions of the glycerol molecule. The longer hydrocarbon chains exhibit unusual orientational order profiles in which the order gradient is steepest in the middle of the chain and relatively shallower in regions adjacent to the carboxyl and methyl termini, whereas the short hydrocarbon chains exhibit orientational order profiles typical of those commonly observed with conventional symmetric chain lipids. When compared at equivalent depths in the bilayer, the shorter hydrocarbon chains of the asymmetric-chain lipids are more orientationally disordered than are their longer chain counterparts. At comparable reduced temperatures, the shorter and longer chains of the asymmetric-chain lipids are more orientationally disordered than those of appropriate short and long symmetric-chain lipids, but the chain-averaged orientational order of the symmetric-chain lipid decreases more sharply with increases in temperature than does that of the comparable chain of the asymmetric-chain species. Moreover, the order plateau regions adjacent to the carboxyl groups of the longer chains of the asymmetric-chain phosphatidylcholines are shorter than those of symmetric-chain lipids of comparable hydrocarbon chain length. Overall, the data indicate that the conformational and orientational order in the liquid-crystalline states of these highly asymmetric-chain lipids differ significantly from those of comparable symmetric-chain lipids. Also, the unusual shape of the orientational order profile of the longer chains of the former is attributed to interaction between the methyl termini regions of the long chains with hydrocarbon chains in opposing monolayers. The latter suggests that some form of hydrocarbon chain interdigitation exists in liquid-crystalline bilayers of these highly asymmetric-chain lipids.
Influence of ether linkages on the structure of double-chain phospholipid monolayers
Chemistry and Physics of Lipids, 1995
The structure c,f phosphatidylcholine monolayers has been studied by Synchrotron X-ray diffraction at the air/water interface varying the ester and ether linkages of the aliphatic tails at the glycerol backbone. All systems investigated exhibit an oblique lattice structure with extremely large tilt angles of the chains from vertical, even at high lateral pressures. Although no large difference is seen in the isotherms, the replacement of ester by ether linkages causes a reduction of the tilt angle and of the area per molecule. These changes also depend on the position of the ether group with respect to the glycerol backbone and can be understood within a model where the carbonyl group of the ester at the C2 position pulls the attached chain towards the water subphase.
Journal of Molecular Structure, 1999
The functioning of biological membranes seems to require a certain degree of fluidity of their components. The fluidity of the lipids forming the matrix of such membranes is related to the order/disorder state of their hydrocarbon chains. In this study, vibrational spectroscopy is applied to probe the chain conformation (as determining the order) of a number of phospholipids with varying intrinsic fluidities as a function of water activity (hydration). Using conventional Fourier-transform infrared (FTIR) spectroscopy and sum-frequency spectroscopy (SFS) enables one to characterize and, thus, to compare physical properties of the molecules in the bulk and in the superficial layer of a specimen, respectively. The results demonstrate the ability of FTIR spectroscopy not only to classify the lipids with respect to chain ordering, but also to detect lyotropic (hydrationdriven) phase transitions. It could be shown that the main transition of mixed-chain oleoyl/palmitoyl phosphatidylcholines (POPC, OPPC) occurs at room temperature and a defined water activity of the films investigated, as also confirmed by smallangle X-ray scattering (SAXS). Equivalent effects were found for POPC in appropriately designed SFS experiments thus evidencing lipid phase transitions by this method for the first time. This opens up a new avenue to elucidate basic aspects of lipid phase behaviour using single bilayer membranes as models of the in vivo state.
Biophysical Journal, 2006
To investigate the properties of a pure liquid ordered (L o ) phase in a model membrane system, a series of saturated phosphatidylcholines combined with cholesterol were examined by variable temperature multinuclear ( 1 H, 2 H, 13 C, 31 P) solidstate NMR spectroscopy and x-ray scattering. Compositions with cholesterol concentrations $40 mol %, well within the L o phase region, are shown to exhibit changes in properties as a function of temperature and cholesterol content. The 2 H-NMR data of both cholesterol and phospholipids were used to more accurately map the L o phase boundary. It has been established that the gel-L o phase coexistence extends to 60 mol % cholesterol and a modified phase diagram is presented. Combined 1 H-, 2 H-, 13 C-NMR, and x-ray scattering data indicate that there are large changes within the L o phase region, in particular, 1 H-magic angle spinning NMR and wide-angle x-ray scattering were used to examine the in-plane intermolecular spacing, which approaches that of a fluid L a phase at high temperature and high cholesterol concentrations. Although it is well known for cholesterol to broaden the gelto-fluid transition temperature, we have observed, from the 13 C magic angle spinning NMR data, that the glycerol region can still undergo a ''melting'', though this is broadened with increasing cholesterol content and changes with phospholipid chain length. Also from 2 H-NMR order parameter data it was observed that the effect of temperature on chain length became smaller with increasing cholesterol content. Finally, from the cholesterol order parameter, it has been previously suggested that it is possible to determine the degree to which cholesterol associates with different phospholipids. However, we have found that by taking into account the relative temperature above the phase boundary this relationship may not be correct. angle spinning; CSA, chemical shift anisotropy; Chol-d 1 , cholesterol deuterated at the C3 position or Cholesterol-3a-d 1 ; T m , temperature of the gel to fluid transition (chain melting); T*, temperature above the gel-L o to L o phase boundary.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1986
Dynamic properties of phosphatidylcholine-cholesterol membranes in the fluid phase and water accessibility to the membranes have been studied as a function of phospholipid alkyl chain length, saturation, mole fraction of cholesterol, and temperature by using spin and fluorescence labelling methods. The results are the following: (1) The effect of cholesterol on motional freedom of 5-doxyl stearic acid spin label (5-SASL) and 16-doxyl stearic acid spin label (16-SASL) in saturated phosphatidylcholine membrane is significantly larger than the effects of aikyl chain length and introduction of unsaturation in the aikyi chain. (2) Variation of alkyl chain length of saturated phospholipids does not alter the effects of cholesterol except in the case of dilauroylphosphatidylcholine, which possesses the shortest alkyl chains (12 carbons) used in this work. (3) Unsaturation of the alkyl chains greatly reduces the ordering effect of cholesterol at C-5 and C-16 positions although unsaturation alone gives only minor fluidizing effects. (4) Introduction of 30 mol% cholesterol to dimyristoylphosphatidylcholine membranes decreases the lateral diffusion constants of lipids by a factor of four, while it causes only a slight decrease of lateral diffusion in dioleoylphosphatidylcholine membranes. (5) If compared at the same temperature, 5-SASL mobilities plotted as a function of mole fraction of cholesterol in the fluid phases of dimyristoylphosphatidylcholine-, dipalmitoylphosphatidylcholine-and distearoylphosphatidylcholine-cholesterol membranes are similar in wide ranges of temperature (45-82°C) and cholesterol mole fraction (0-50%). (6) In isothermal experiments with saturated phosphatidylcholine membranes, 5-SASL is maximally immobilized at the phase boundary between Regions I and lII reported by other workers (Recktenwald, D.J. and McConnell, H.M. (1981) Biochemistry 20, 4505-4510) and becomes more mobile away from the boundary in Regions I and IIl. (7) 5-SASL in unsaturated phosphatidylcholine membranes showed a gradual monotonic immobilization with increase of cholesterol mole fraction without showing any maximum in the range of cholesterol fractions studied. (8) By rigorously determining rigid-limit
Biochemistry, 1993
The lipid chain dynamics in the interdigitated gel phase of dipalmitoylphosphatidylcholine (DPPC) dispersed in glycerol and in the fully hydrated noninterdigitated gel phase in aqueous buffer were compared by using conventional and saturation transfer electron spin resonance (ESR) spectroscopy. Twelve different positional isomers of phosphatidylcholine spin-labeled in the sn-2 chain were used to characterize the chain motion. The outer hyperfine splittings of the conventional ESR spectra and the line height ratios at the diagnostic spectral positions in the saturation transfer ESR spectra were taken as indices of the rotational mobility of the labeled chain segments in the gel phase ( 0 4 0 "C). The conventional spin label ESR spectra revealed a gradient of increasing mobility on proceeding down the chain toward the terminal methyl end in the fully hydrated DPPC gel phase bilayer structure. This gradient was absent in the interdigitated gel phase, Le., the rotational mobility throughout the length of the lipid chain was comparable to that near the polar interface, on the conventional ESR time scale. Values of the outer hyperfine splitting for spin labels at the 5-and 14-C atom positions in the chain were 65.5 and 61.0 G in buffer, respectively, and 67.0 G for both positions in glycerol, at 0 OC. At 35 OC, still in the gel phase, these differences between the two systems were much greater. Saturation transfer ESR measurements revealed that the motion throughout the chain was restricted on the microsecond time scale in the interdigitated phase. The motional I Abbreviations: DPPC, 1,2-dipalmitoyl-sn-glyctre3-phosphccholine; n-PCSL, l-acyl-2-(n-(4,4-dimethyloxazolidineN-oxy)stearoy~)-~n-glycero-3-phosphccholine; n-SASL, n-(4,4-dimethyloxazolidine-iV-oxy)stearic acid; ESR, electron spin resonance; STESR, saturation transfer ESR; VI, first harmonic ESR absorption signal detected in-phase with respect to the field modulation; Vz', second harmonic ESR absorption signal detected 90° out-of-phase with respect to the fieldmodulation; L$, lamellar gel phase with interdigitated chains; Lp, lamellar gel phase with tilted and noninterdigitated chains; Pp, rippled gel phase of oblique lattice with noninterdigitated chains; La, fluid lamellar phase.
Biophysical Journal, 2000
We have examined the effects of cholesterol on the thermotropic phase behavior and organization of aqueous dispersions of a homologous series of linear disaturated phosphatidylserines by high-sensitivity differential scanning calorimetry and Fourier transform infrared spectroscopy. We find that the incorporation of increasing quantities of cholesterol progressively reduces the temperature, enthalpy, and cooperativity of the gel-to-liquid-crystalline phase transition of the host phosphatidylserine bilayer, such that a cooperative chain-melting phase transition is completely or almost completely abolished at 50 mol % cholesterol, in contrast to the results of previous studies. We are also unable to detect the presence of a separate anhydrous cholesterol or cholesterol monohydrate phase in our binary mixtures, again in contrast to previous reports. We further show that the magnitude of the reduction in the phase transition temperature induced by cholesterol addition is independent of the hydrocarbon chain length of the phosphatidylserine studied. This result contrasts with our previous results with phosphatidylcholine bilayers, where we found that cholesterol increases or decreases the phase transition temperature in a chain length-dependent manner (1993. Biochemistry, 32:516 -522), but is in agreement with our previous results for phosphatidylethanolamine bilayers, where no hydrocarbon chain length-dependent effects were observed (1999. Biochim. Biophys. Acta, 1416:119 -234). However, the reduction in the phase transition temperature by cholesterol is of greater magnitude in phosphatidylethanolamine as compared to phosphatidylserine bilayers. We also show that the addition of cholesterol facilitates the formation of the lamellar crystalline phase in phosphatidylserine bilayers, as it does in phosphatidylethanolamine bilayers, whereas the formation of such phases in phosphatidylcholine bilayers is inhibited by the presence of cholesterol. We ascribe the limited miscibility of cholesterol in phosphatidylserine bilayers reported previously to a fractional crystallization of the cholesterol and phospholipid phases during the removal of organic solvent from the binary mixture before the hydration of the sample. In general, the results of our studies to date indicate that the magnitude of the effect of cholesterol on the thermotropic phase behavior of the host phospholipid bilayer, and its miscibility in phospholipid dispersions generally, depend on the strength of the attractive interactions between the polar headgroups and the hydrocarbon chains of the phospholipid molecule, and not on the charge of the polar headgroups per se.
Glycosphingolipid phase behaviour in unsaturated phosphatidylcholine bilayers: A 2H-NMR study
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1992
H-NMR was employed to consider the art mgement of a glycosphingolipid, N-(lignoeeroyl-d4?)galactosylceramide, in bilayers of the mono-uusaturated phospholipid, bstearoyb2-oleoylphosphatidylcholine. The deuterated glycolipiO prepared by partial synthesis was incorporated at co,~centrations ranging from 5 mid% to 53 mol% into unsonlcate'l liposemcs, and its spectra were recorded from ~-76°C to-i,~°C. First spectral moments were plotted as a function of temperature for each sample composition and, along with inspection of the spectra, were ~-mpioyed to infer a phase diagram describing glycolipid bchaviour in the unsaturated phospholipid host ma~'ix. It was possib!c to refine the result using 2H-lqMR difference sp,.'ctroscopy. Tile phase diagram obtained was indicative of perite:tic behaviour. At glycnlipid concentrations exceeding about 20 tool% tIler¢ was considerable tendency to glyco!ipid phase scpelration-as indicated by coexistence of fluid phospholipid-¢nric.hed and gel phase glycolipid-cnriched domains over a wide rang,: of temperatures, and by coexistence of distinct ordered phase domains at lower temperature, lu contrast, al lower g!yco!ipid c,'mceatrations reflective of many biological membranes, the lipid components were ntiscible in both the liquid crystal and gel pha: us, wi:h only a narrow temperature range of fluid and ordered phase coe~iqtence. For tile fluid phase at low glycolipid concen.'rattons, ~peetra of the 0euterated glycolipid 24-carbon fatty acid suggest that or!.'ntattonal order is low for a number of methyler~.e groups near the methyl end of the chain.