Study of the structure and phase behavior of dipalmitoylphosphatidylcholine by infrared spectroscopy: characterization of the pretransition and subtransition (original) (raw)
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Biochimica Et Biophysica Acta-biomembranes, 2008
We present a combined theoretical (molecular dynamics, MD) and experimental (differential scanning calorimetry, DSC) study of the effect of 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) acyl chain-labeled fluorescent phospholipid analogs (C6-NBD-PC and C12-NBD-PC) on 1,2dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers. DSC measurements reveal that b 1 mol% of NBD-PC causes elimination of the pretransition and a large loss of cooperativity of the main transition of DPPC. Labeling with C6-NBD-PC or C12-NBD-PC shifts the main transition temperature to lower or higher values, respectively. Following our recent report on the location and dynamics of these probes (BBA 1768(BBA (2007 467-478) in fluid phase DPPC, we present a detailed analysis of 100-ns MD simulations of systems containing either C6-NBD-PC or C12-NBD-PC, focused on their influence on several properties of the host bilayer. Whereas most monitored parameters are not severely affected for 1.6 mol% of probe, for the higher concentration studied (6.2 mol%) important differences are evident. In agreement with published reports, we observed that the average area per phospholipid molecule increases, whereas DPPC acyl chain order parameters decrease. Moreover, we predict that incorporation of NBD-PC should increase the electrostatic potential across the bilayer and, especially for C12-NBD-PC, slow lateral diffusion of DPPC molecules and rotational mobility of DPPC acyl chains.
Biochimica Et Biophysica Acta - Biomembranes, 1982
The structural changes accompanying the recently described sub-transition of hydrated dipalmitoylphosphatidyicholine (Chen, S.C., Sturtevant, J.M. and Gaffney, B.J. (1980) Proc. Natl. Acad. Sci. USA 77, 5060-5063) have been defined using X-ray diffraction methods. Following prolonged storage at-4°C the usual Lt3, gel form of hydrated dipalmitoylphosphatidylcholine (DPPC) is converted into a more ordered stable 'crystal' form. The bilayer periodicity is 59.1 A and the most striking feature is the presence of a number of X-ray reflections in the wide angle region. The most prominent of these are a sharp reflection at 1/4.4 A-~ and a broader reflection at 1/3.9 j-t. This diffraction pattern is indicative of more ordered molecular and hydrocarbon chain packing modes in this low temperature 'crystal' bilayer form. At the sub-transition (T~ub=15-20°C) an increase in the bilayer periodicity occurs (d=63.6/I,) and a strong reflection at approx. I/4.2 A-l with a shoulder at approx. 1/4.1 ji,-l is observed. This diffraction pattern is identical to that of the bilayer gel (L 0,) form of hydrated DPPC. Thus, the sub-transition corresponds to a bilayer 'crystai'~ bilayer Lt3, gel structural rearrangement accompanied by a decrease in the lateral hydrocarbon chain interactions. Differential scanning calorimetry and X-ray diffraction show that on further heating the usual structural changes L 0, ~ P0' and P0, ~ L~ occur at the pre-and main transitions, at approx, 35°C and 41°C, respectively.
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.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1985
Phase transition, Fourier transform infrared spectroscopy Fourier transform infrared spectroscopy was used to characterize the lamellar phases of 1,3-dipalmitoyl-snglycero-2-pbosphocholine (1,3-DPPC), a positional isomer of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (I,2-DPPC). The molecule exists in three distinct phases over the temperature interval 0-70°C In the low-temperature (L c) phase, the spectra are indicative of acyl chains packed in an orthorhombic subcell, while the carbonyl groups and phosphate ester at the head group show evidence of only partial hydration. The transition from the low-temperature (Lc) phase to the intermediate-temperature (L,) phase at 25°C corresponds to a temperature-induced head-group hydration in which the hydration of the phosphate and carbonyl ester groups results in the reorganization of the hydrocarbon chain-packing subcell from orthorhombic to hexagonal The transition from the intermediate (L/0 to the high-temperature (L~) phase at 37°C is a gel-to-liquid-crystalline phase transition analogous to the 41.5°C transition of 1,2-DPPC The spectra of the acyl-chain carbonyi groups show evidence of significant differences in molecular conformation at the carbonyl esters in the L c phase. In the L~ and L~ phases, the carbonyl band contour becomes much more symmetric. However, two components are clearly present in the spectra indicating that the sn-I and sn-3 carbonyls experience slightly different environments. The observed differences are likely due to a preferred conformation of the phosphocholine group relative to the glycerol backbone. Indications from the infrared spectra of differences in the structure of the C=O groups provide a possible explanation for the selection of the sn-1 chain of 1,3-DPPC by phospholipase A 2 on the basis of a preferred head group conformation.
Biophysical Journal, 1978
Raman spectroscopic data indicate that the conformations of the two hydrocarbon chains of dipalmitoyl phosphatidyicholine in aqueous dispersions of the lipid differ significantly. The compounds I-palmitoyl, 2-palmitoyl-d3l-3-sn-phosphatidylcholine and l-palmitoyl-d3l, 2-palmitoyl-3-sn-phosphatidylcholine were synthesized. Aqueous dispersions of these phospholipids display very similar phase behavior, with both premelting and melting transitions at nearly identical temperatures, midway between the comparable transition temperatures of undeuterated and completely deuterated dipalmitoyl phosphatidylcholine. We have monitored the state of chains I and 2 of these molecules simultaneously and independently by Raman spectroscopy. Raman difference spectra taken between samples of the two compounds under identical conditions show significant features. We attribute these spectral differences to nonequivalent conformations of the fatty acyl chains attached at positions 1 and 2 on the glycerol backbone. Below the pretransition the conformation of chain 2 is, on average, slightly less all-trans than is the chain at position 1. There is some evidence that the conformations of the terminal methyl group of the two chains are significantly different at low temperatures.
Theoretical models of phospholipid systems have indicated that both intramolecular and intermolecular forces are important in governing their acyl chain order. Knowledge of the nature and magnitude of these interactions is central to understanding the balance of forces present in lipid lamellar phases, which in turn is related to their microscopic and macroscopic behavior. It is possible to explore the contribution of intermolecular interactions using lipid systems with the same headgroup and acyl chain identity by variation of the ratio of the headgroups to acyl chains. In this paper, deuterium (2H) NMR spectroscopy has been used to gain information on the orientational order of an acyl chain perdeuterated lipid, l-perdeuteriopalmitoyl-sn-Bly~3-phosphocholine (PaLpc-d31), in various molecular environments. The orientational order of PaLpGd31 was studied in four different lamellar phases, including pure PaLPC-d31 (containing 10 wt % H20), diplmitoyl-phosphatidyl~holine/PaLPC-d3~ (3:1), palmitic a~id/PaLPC-d~~ (l:l), and ch~lesterol/PaLPC-d~~ (1:l) (each containing 50 wt % HzO). ' H NMR spectra were obtained for the low-temperature and liquid-crystalline (L,) states of each of these mixtures. In the low-temperature state, the f i t three systems yielded ZH NMR spectra characteristic of all-trans chains undergoing axial diffusion, with the methyl groups rotating about their C3 axes. The molecular order, as judged by the presenoe of spectral discontinuities and moment analysis, was found to be almost identical in the low-tempratwe phases. A different behavior was observed for the ch~lesterol/PaLPC-d~~ (1:l) sample in that the maximum splitting was close to the all-trans rotating value, with a profile of quadrupolar splittings due to inmased disorder near the chain ends. The f i t three systems underwent orderdisorder phase transitions near the same midpoint temperature (range of T, values 40-48 "C), whereas the ch~lesterol/PaLPC-d~~ (1:l) sample did not display a transition over the temperature range studied. In the L, phase, where order profdm were determined as a function of acyl chain segmglt position, the segmental ordering d i f f e r e d significantly among the samples. The differences were interpreted using a simple diamond lattice model for the acyl chain configurational statistics, as a means of comparing the effective lengths, (L), projected along the bilayer normal and estimated chain cross-sectional areas, (A), of PaLPC-d31 in the various mixtures. The derived values of (L) and (A) can be understood qualitatively in terms of average packing parameters related to the balance of forces in the headgroup and acyl chain regions, or alternatively the curvature free energy of the membrane lipid-water interface. In lamellar phases of pure P~L P C-C~~~ the curvature stnap is potentially large, and interdigitation of the acyl chains of the appoaed monolayers may occur. However, in mixtures of PaLPC-d31 with 1 , 2-d i p a l m i t o y l-s n-B l y~~3-p h o s p~~~e (DPPC), the curvature elaatic stress is apparently relieved by an increase in the cross-sectional acyl chain area, (A), Le. corresponding to an increase in configurational f d o m. The data were also compared to the results of statistical theories to yield additional knowledge of the intermolecular forces. These studies indicate how the segmental ordering reflects intermolecular interactions within a given lamellar phase. Avmge properties of the entire system such as average cross-sectional arm accessible to each acyl chain relative to the headgroup area can be modulated by these interactions. Such intermolecular interactions may be related to the prcaence of lipid diversity in biological membranes.
Physica B: Condensed Matter, 1995
Small-angle neutron scattering and small-angle X-ray scattering studies have been performed to investigate the structural phase transition in the dipalmitoylphosphatidylcholine(DPPC~wate~salt system. We found that there is a minimum at around 25°C in the relaxation time r for ordering of the L~, structure. The strong diffuse scattering in SANS indicates that the direction of the ripple propogation of the bilayer has only weak correlation with the neighbouring bilayers in the cooling process. The repeat distance of the rippled structure dr increased as the temperature T decreased. We found that the rippled structure appears even when the thickness of water between the lipid bilayers increases up to 130 A. These results show that the rippled structure originates mainly in the intralayer interaction.
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.
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.
Order–disorder transition in bilayers of diphytanoyl phosphatidylcholine
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2000
A comparative study on bilayers of diphytanoyl phosphatidylcholine (DPhPC) and bilayers of dimyristoyl phosphatidylcholine (DMPC) was made by X-ray lamellar diffraction as a function of temperature and the degree of hydration. An order^disorder phase transition of DPhPC reveals an interesting contrast to the standard model of DMPC. Electron density profiles allow us to deduce the conformational changes which occur in the headgroup-glycerol region and in the chain region. The important conclusion is that the lipid headgroup may have different conformational energetics in lipids of different chains. We explain why this is important to protein^membrane interactions.