Molecular motion and order in oriented lipid multibilayer membranes evaluated by simulations of spin label ESR spectra. Effects of temperature, cholesterol and magnetic field.

A simulation method to interpret electron spin resonance (ESR) of spin labelled amphiphilic molecules in oriented phosphatidylcholine multibilayers in terms of a restricted motional model is presented. Order and motion of the cholestane spin label (3-spiro-doxyl-5alpha-cholestane) incorporated into egg yolk phosphatidylcholine, dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine, pure and in mixture with cholesterol, were studied at various temperatures. With egg yolk phosphatidylcholine identical sets of motional parameters were obtained from simulations of ESR spectra obtained at three microwave frequencies (X-, K- and Q-band). With dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine analyses of the spectra show that phase transitions occur in samples containing up to 30 mol % cholesterol. The activation energy for the motion of the spin label is about three times larger above than below the phase transition, indicating a more collective motion in the lipid crystalline state than in the gel state. In the liquid crystalline state the activation energy is larger in the pure phosphatidylcholines than with cholesterol added. Additions of cholesterol to egg phosphatidylcholine induces a higher molecular order but does not appreciably affect correlation times. This is in contrast to dipalmitoylphosphatidylcholine where both order and correlation times are affected by the presence of cholesterol. The activation energies follow the same order as the transition temperatures: dipalmitoylphosphatidylcholine greater than dimyristoylphosphatidylcholine greater than egg yokd phosphatidylcholine, suggesting a similar order of the cooperativity of the motion of the lipid molecules. Magnetic field-induced effects on egg phosphatidylcholine multibilayers were found at Q-band measurements above 40 degrees C. The cholestane spin label mimics order and motion of cholesterol molecule incorporated into the lipid bilayers. This reflects order and motion of the portions of the lipid molecules on the same depth of the bilayer as the rigid steroid portions of the intercalated molecules.     

Thermal effects on motion and orientation of the cholestane spin label in planar multibilayers of dimyristoylphosphatidylcholine and dipalmitoylphosphatidylcholine

A detailed picture of the orientation and restricted motion of the cholestane spin label (3-spiro-doxyl-5α-cholestane) in planar multibilayers of dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine has been recorded by simultaneous simulation of ESR spectra obtained with the magnetic field parallel and perpendicular to the bilayers (Shimoyama, Y., Eriksson, L.E.G. and Ehrenberg, A. (1978) Biochim. Biophys. Acta 508, 213–235). The analysis has been made over the temperature range ?30°C to 60°C on samples containing 20 to 22% water. At low temperatures the cholestane spin label is tilted with respect to the lipid bilayer normal by an angle of approx. 30° which disappears at the pretransition. In this low temperature range the restricted twisting motion has an activation energy of 5.5 kJ·mol^?1. Above the main transition the twisting motion is unrestricted and has the activation energy 20 kJ·mol^?1. From below the pretransition to above the main transition the velocity of the twisting motion increases by an order of magnitude. The amplitude of the wobbling motion increases abruptly from 0° to 35° at the main transition.     

An ESR Spin label study of structural and dynamical properties of oriented lecithin-cholesterol multibilayers.

Oriented dipalmitoyllecithin-cholesterol multibilayers with 11% water have been studied with the cholestane spin label. From the ESR spectra the order parameters and the mobility of the spin label about its long axis have been calculated. The results on pure lecithin multibilayers indicate a transition from gel to liquid crystalline phase at 52 plus or minus 2 degrees C. In the gel phase the lecithin alkyl chains are highly ordered, but tilted with respect to the normal to the bilayers by about 25 degrees. Above 52 degrees C the tilt disappears and the mobility of the cholestane spin label increases, indicating an increase of mobility of the lecithin alkyl chains. When cholesterol is added, below about 52 degrees C a decrease of order is found. Furthermore, already small cholesterol contents (smaller than or equal to 10 mole %) remove the tilt. Above about 52 degrees C cholesterol improves the order by decreasing the amplitude of the librational motions. Cholesterol lowers the transition temperature of the system and reduces the mobility of the lecithin alkyl chains in the liquid crystalline phase. However an increase in mobility is found at cholesterol contents up to 10 mole %. A very broad phase transition is observed at 50 mole % cholesterol. In all systems an increase in temperature results in a reduction of order through an increase of the amplitude of the librational motions of the molecules. The librational motions are to some extent cooperative. The asymmetry of the order matrix is found to be a measure for the lateral ordering. Cholesterol increases the lateral ordering, indicating that the flat cholesterol molecules orient parallel to each other.     

Behavior of cholesterol and spin-labeled cholestane in model bile systems studied by electron spin resonance and synchrotron x-ray.

The behavior of mixed bile salt micelles consisting of sodium taurocholate, egg phosphatidylcholine, and cholesterol has been studied by ESR spin labeling and synchrotron x-ray scattering. Consistent with published phase diagrams, pure and mixed bile salt micelles have a limited capacity to incorporate and, hence, solubilize cholesterol. Excess cholesterol crystallizes out, a process that is readily detected both by ESR spin labeling using 3-doxyl-5 alpha-cholestane as a probe for cholesterol and synchrotron x-ray scattering. Both methods yield entirely consistent results. The crystallization of cholesterol from mixed bile salt micelles is indicated by the appearance of a magnetically dilute powder spectrum that is readily detected by visual inspection of the ESR spectra. Both the absence of Heissenberg spin exchange and the observation of a magnetically dilute powder spectrum provide evidence for the spin label co-crystallizing with cholesterol. In mixed bile salt micelles containing egg phosphatidylcholine, the solubility of cholesterol is increased as detected by both methods. With increasing content of phosphatidylcholine and increasing mole ratio cholesterol/phosphatidylcholine, the anisotropy of motion of the spin probe increases. The spin label 3-doxyl-5 alpha-cholestane is a useful substitute for cholesterol provided that it is used in dilute mixtures with excess cholesterol: the cholesterol/spin label mole ratio in these mixtures should be greater than 100. Despite the structural similarity between the two compounds, there are still significant differences in their physico-chemical properties.(ABSTRACT TRUNCATED AT 250 WORDS)     

Physical properties of phosphatidylcholine-phosphatidylinositol liposomes in relation to a calcium effect

Physical properties of binary mixtures of dipalmitoylphosphatidylcholine and yeast phosphatidylinositol were studied by ESR analysis using TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) and lipid spin probes, freeze-fracture electronmicroscopy and particle microelectrophoresis, and they were compared with those of phosphatidylcholine/bovine brain phosphatidylserine mixtures. The phase diagram of the binary mixtures of dipalmitoylphosphatidylcholine and phosphatidylinositol was obtained from the thermal features of TEMPO spectral parameter in the lipid mixtures. The phase diagram provided evidence that these two phospholipids in various combinations were miscible in the crystalline state. The addition of 10 mM Ca2+ slightly shifted the phase diagram upward. TEMPO titration of the binary mixture of dipalmitoylphosphatidylcholine and bovine brain phosphatidylserine revealed that 10 mM Ca2+ caused the complete phase separation of this lipid mixture. Studies of phase separations using phosphatidylcholine spin probe manifested that 10 mM Ca2+ induced almost complete phase separation in egg yolk phosphatidylcholine/bovine brain phosphatidylserine mixtures but only slight phase separation in egg yolk phosphatidylcholine/yeast phosphatidylinositol mixtures. However, some phase changes around the fluidus and the solidus curves were visualized by the freeze-fracture electronmicroscopy. The molecular motion of lipid spin probe was decreased by the addition of Ca2+ in the liposomes containing phosphatidylinositol. The temperature dependence of electrophoretic mobility was also examined in the absence and presence of 1 mM Ca2+. Liposomes of dipalmitoylphosphatidylcholine-phosphatidylinositol (90 : 10, mol/mol) exhibited a clear transition in the thermal features of electrophoretic mobilities. Raising the phosphatidylinositol content up to 25 mol% rendered the transition broad and unclear. The addition of 1 mM Ca2+ decreased the electrophoretic mobility but did not change its general profile of the thermal dependence. These results suggest that the addition of calcium ions induced a small phase change in the binary mixture of phosphatidylcholine and phosphatidylinositol while Ca2+ causes a remarkable phase separation in phosphatidylcholine/phosphatidylserine mixture. The physical role of phosphatidylinositol is discussed related to the formation of diacylglycerol.     

An ESR Study of the mobility of the cholestane spin label in oriented lecithin-cholesterol multibilayers.

The motion of the cholestane spin label in oriented lecithin-cholesterol multibilayers is described in terms of a rotational diffusion about the long molecular axis with diffusion coefficient D parrell and a restricted random librational motion about axes perpendicular to the long axis with diffusion coefficient D1. The diffusion coefficients have been determined from the angular dependence of the ESR line shape at various temperatures and cholesterol contents. The temperature dependence of D parrell and D1 clearly shows the transition from the gel to liquid crystalline phase. Increasing amounts of cholesterol reduce the transition temperature. A strong reduction is found from o to 10 mole % cholesterol. At 50 mole % no longer a sharp transition is observed. In the temperature range from 40 to 80 degrees C the range of D is about 10 times larger than the range of D parrell, indicating a high activation energy for the librational motion arising from a strong hindrance by interaction with surrounding molecules. Cholesterol contents up to 10-20 mole % give an increase of D parrell and D1, arising from strong decrease of the transition temperature in this range. Above 10-20 mole % a reduction of D parrell and D1 is found. However, the effect of cholesterol is much stronger on D1 than on D parrell. In the liquid crystalline phase at about 60 degrees C the effect of cholesterol on D parrell is even negligible, while D1 strongly changes. This indicates that in the liquid crystalline phase only the librational motion is influenced by cholesterol, due to a denser packing of the molecules in the bilayer.     

Magnetic resonance study of the distribution of 2,2,6,6-tetramethylpiperidine-N-oxyl in phosphatidylcholine bilayers.

With the aid of paramagentic praseodymium ions the resonances at 60 MHz of the inward and outward facing choline methyl protons of sonicated egg yolk phosphatidylcholine vesicles were resolved. The subsequent addition of 2,2,6,6,-tetramethylpiperidine-N-oxyl (TEMPO) to the vesicle suspension broadened the inner and outer resonances equally. TEMPO easily penetrates the egg yolk phosphatidylcholine vesicles and has free access to the entire lipid volume above the gel to liquid crystalline transition temperature. The electron spin resonance (ESR) spectrum of TEMPO in the egg yolk phosphatidylcholine suspension exhibits features indicating that TEMPO dissolves principally in the hydrocarbon portion of the egg yolk phosphatidylcholine bilayer. The egg yolk phosphatidylcholine methylene chain proton resonances are also broadened by TEMPO notably to a greater extent than the choline methyl resonances. These data indicate that TEMPO should be more sensitive to the melting behavior of the fatty acyl chains of phospholipid suspensions than to the polar head groups.     

Effects of polar carotenoids on dimyristoylphosphatidylcholine membranes: a spin-label study.

Spin labeling methods were used to study the structure and dynamic properties of dimyristoylphosphatidylcholine (DMPC) membranes as a function of temperature and the mole fraction of polar carotenoids. The results in fluid phase membranes are as follows: (1) Dihydroxycarotenoids, zeaxanthin and violaxanthin, increase order, decrease motional freedom and decrease the flexibility gradient of alkyl chains of lipids, as was shown with stearic acid spin labels. The activation energy of rotational diffusion of the 16-doxylstearic acid spin label is about 35% less in the presence of 10 mol% of zeaxanthin. (2) Carotenoids increase the mobility of the polar headgroups of DMPC and increase water accessibility in that region of membrane, as was shown with tempocholine phosphatidic acid ester. (3) Rigid and highly anisotropic molecules dissolved in the DMPC membrane exhibit a bigger order of motion in the presence of polar carotenoids as was shown with cholestane spin label (CSL) and androstane spin label (ASL). Carotenoids decrease the rate of reorientational motion of CSL and do not influence the rate of ASL, probably due to the lack of the isooctyl side chain. The abrupt changes of spin label motion observed at the main phase transition of the DMPC bilayer are broadened and disappear at the presence of 10 mol% of carotenoids. In gel phase membranes, polar carotenoids increase motional freedom of most of the spin labels employed showing a regulatory effect of carotenoids on membrane fluidity. Our results support the hypothesis of Rohmer, M., Bouvier, P. and Ourisson, G. (1979) Proc. Natl. Acad. Sci. USA 76, 847-851, that carotenoids regulate the membrane fluidity in Procaryota as cholesterol does in Eucaryota. A model is proposed to explain these results in which intercalation of the rigid rod-like polar carotenoid molecules into the membrane enhances extended trans-conformation of the alkyl chains, decreases free space in the bilayer center, separate the phosphatidylcholine headgroups and decreases interaction between them.     

The role of sphingomyelin in regulating phase coexistence in complex lipid model membranes: competition between ceramide and cholesterol

The structure, thermotropic phase behavior, dynamic motion and order parameters of bilayer dispersions of egg phosphatidylcholine, egg sphingomyelin, egg ceramide and cholesterol have been determined. The coexistence of gel, liquid-ordered and liquid-disordered structure has been determined by peak fitting analysis of synchrotron X-ray powder patterns. Order parameters and extent of distribution of 16-doxyl-stearic acid spin probe between ordered and disordered environments has been estimated by ESR spectral simulation methods. The presence of ceramide in proportions up to 20 mol% in phosphatidylcholine is characterized by gel-fluid phase coexistence at temperatures up to 46 degrees C depending on the amount of ceramide. Cholesterol tends to destabilize the ceramide-rich domains formed in phosphatidylcholine while sphingomyelin, by formation of stable complexes with ceramide, tends to stabilize these domains. The stability of sphingomyelin-ceramide complexes is evident from the persistence of highly ordered structure probed by ESR spectroscopy and appearance of a sharp wide-angle X-ray reflection at temperatures higher than the gel-fluid transition of ceramide alone in egg phosphatidylcholine bilayers. The competition between ceramide and cholesterol for interaction with sphingomyelin is discussed in terms of control of lipid-mediated signaling pathways by sphingomyelinase and phospholipase A2.     

Haptenic activity of galactosyl ceramide and its topographical distribution on liposomal membranes. I. Effect of cholesterol incorporation

The relation between the immune-reaction of phosphatidylcholine liposomes containing spin-labeled galactosyl ceramide with or without cholesterol and the topographical distribution of the glycolipid in membranes was studied. In egg yolk phosphatidylcholine liposomes, both immune agglutination and antibody binding occurred, irrespectively of the presence of cholesterol, though the motion of the fatty acyl chain of spin-labeled galactosyl ceramide was restricted by cholesterol. In dipalmitoyl phosphatidylcholine liposomes, unlike in egg yolk phosphatidylcholine liposomes, the immune-reaction depended on the cholesterol content. The electron spin resonance (ESR) spectra of spin-labeled galactosyl ceramide in dipalmitoyl phosphatidylcholine liposomes indicated that cholesterol affected the topographical distribution of spin-labeled galactosyl ceramide in the liposomes. Without cholesterol, most of the spin-labeled galactosyl ceramide was clustered on the dipalmitoyl phosphatidylcholine membrane, but with increase of cholesterol, random distribution of hapten on the membrane increased. The cholesterol-dependent change in the topographical distribution of hapten on the membranes was parallel with that of immune reactivity. 'Aggregates' composed solely of galactosyl ceramide did not show any binding activity with antibody. The findings suggest that the recognition of galactosyl ceramide by antibody depended on the topographical distribution of hapten molecules. Phosphatidylcholine and/or cholesterol may play roles as 'spacers' for the proper distribution of 'active' haptens on the membranes. The optimum density of haptens properly distributed on liposomal membranes is discussed.     

Different effects of propofol and nitrosopropofol on DMPC multilamellar liposomes

The mechanisms of reaction of propofol with nitrosoglutathione lead to the formation of an active species which was identified, and then synthesised, as 2,6-diisopropyl-4-nitrosophenol. In the present work, we demonstrate the in vitro formation of 2,6-diisopropyl-4-nitrosophenol, then we discuss the interaction of propofol and 2,6-diisopropyl-4-nitrosophenol with dimyristoylphosphatidylcholine and egg yolk phosphatidylcholine multilamellar liposomes using differential scanning calorimetry and spin labelling techniques. It was demonstrated that both molecules are highly lipophylic and absorb almost entirely in the lipid phase. The thermotropic profiles showed that these molecules affect the temperature and the co-operativity of the gel-to-fluid state transition of the liposomes differently: the effects of 2,6-diisopropylphenol on the lipid organisation are quite similar to phenol and coherently interpretable in terms of the disorder produced in the membrane by a bulky group; 2,6-diisopropyl-4-nitrosophenol is a stronger perturbing agent, and ESR spectra suggest that this is due to a relative accumulation of the molecule into the interfacial region of the bilayer.     

Transfer of cholestane spin label between lipid bilayer membranes and its molecular motion in membranes.

The relation between the molecular motion of a steroid in lipid membranes and the transfer rate between membranes was examined using radioactive cholestane spin label. Order parameters of the molecule were determined in bilayers composedof dipalmitoylglycerophosphocholine or egg yolk phosphatidylcholine at various temperatures. The line widths of the ESR signal of the cholestane spin label in membranes, which depend upon the rate of molecular axial rotation in the membranes, were also measured. The temperature dependences of these two parameters and of the transfer rate suggest a close correlation between the rate of molecular axial rotation and the transfer rate.     

The influence of cholesterol on molecular motion in egg lecithin bilayers--a variable-frequency electron spin resonance study of a cholestane spin probe

Electron spin resonance spectra at 9.5, 24. and 35 GHz were obtained for a cholestane spin probe in oriented multibilayers of egg lecithin of varying cholesterol content. In agreement with earlier studies, cholesterol induced a higher degree of spectral anisotropy in the multibilayers—the variation of the hyperfine separations with cholesterol content was in agreement with the model of Lapper et al. (Can. J. Biochem.50, 969 (1972)) where the amplitude of anisotropic probe motion decreased with increasing cholesterol content. Analysis of the electron spin resonance line shapes was done using the relatively simple modified Bloch equation approach, and correlation times for anisotropic probe motion were extracted from the spectra at three frequencies. The data demonstrate that increasing cholesterol content results in a decreased rate of anisotropic motion of the probe, providing further insight into the molecular mechanism of the condensing effect of cholesterol.     

Slow-motion ESR of cholestane spin labels in planar multibilayers of diacyldigalactosyldiglycerides

The orientation and restricted motion of the cholestane spin label (3-spiro-doxyl-5α-cholestane) incorporated into planar multibilayers of diacyldigalactosyldiglycerides extracted from the thylakoid membranes of chloroplasts from different plant leaves has been studied. The experimental ESR spectra were simulated in terms of the slow-tumbling ESR formalism of Freed and co-workers (Polnaszek, C.F., Bruno, G.V. and Freed, J.H. (1973) J. Chem. Phys. 58, 3185–3199). The analysis shows that the degree of orientational order is low. The spin label molecules undergo a faster reorientational motion about their long molecular axes than perpendicular to them. At room temperature the reorientational rate around the long molecular axis falls within the fast-motional limit, while the reorientation rate of the long axis itself corresponds to the slow-tumbling regime. The results indicate that the motion of the labels in bilayers of diacyldigalactosyldiglycerides is considerably slower than that of the same label incorporated into bilayers of saturated phosphatidylcholines above the main phase transition. Differences between bilayers of diacyldigalactosyldiglycerides extracted from different plant membranes have been observed.     

A photogrammetric method to measure fluid movement across isolated frog retinal pigment epithelium.

P-31 single-pulse and cross-polarization (CP) nuclear magnetic resonance spectra were obtained of aqueous dispersions of pure phospholipids. Dimyristoyl phosphatidylcholine, dipalmitoylphosphatidylcholine, 1-palmitoyl-2-oleoyl phosphatidylcholine, egg phosphatidylcholine, bovine brain sphingomyelin, and transphosphatidylated (from egg phosphatidylcholine) phosphatidylethanolamine were studied. The spectra from all the phospholipids, taken in the usual single-pulse mode, showed the pseudo-axially symmetric powder pattern typical of phospholipids in a hydrated lamellar form. P-31 CP spectra of all the phosphatidylcholines and phosphatidylethanolamine revealed a decrease in intensity in the vicinity of the isotropic chemical shift as long as the lipid was above the gel-to-liquid crystalline phase transition temperature. This intensity pattern has been observed previously for C-13 CP spectra of molecules rotating rapidly about a single well-defined axis (e.g., solid benzene) (Pines, A., M.G. Gibby, and J.S. Waugh, 1973, J. Chem. Phys., 59:569-590). Pure lipid dispersions below their gel-to-liquid crystalline phase transition temperature, including dipalmitoylphosphatidylcholine and sphingomyelin, do not exhibit a local minimum in the CP spectrum at the position of the isotropic chemical shift. Thus, below the phase transition temperature, there is not the same rapid rotation of the headgroup about a well-defined axis. A dramatic change in the rate of headgroup rotation is shown to take place at the pretransition of dipalmitoylphosphatidylcholine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fusion and lipid exchange in vesicles containing lipophilic spin labels

Lipophilic non-electrolyte spin labels greatly accelerate the fusion of unilamellar vesicles of dipalmitoylphosphatidylcholine when the system is maintained below the lipid phase transition. Differential scanning calorimetry and centrifugation measurements show that the transformed vesicles are large and probably unilamellar. Differential scanning calorimetry and fluorescence depolarization measurements were also carried out on mixtures of labeled dipalmitoylphosphatidylcholine vesicles and of vesicles composed of pure dimyristoylphosphatidylcholine. A mixing of the membrane components is observed when the vesicles are incubated above the transition temperature of the two constituent lipids. However, the process does not involve a real fusion of the entire vesicles. An exchange of lipid and label monomers between the two lipid phases seems to occur. These observations are discussed in view of the molecular organization of the spin label within the dipalmitoylphosphatidylcholine matrix below and above the lipid transition temperature.     

Spin label study of local anesthetic-lipid membrane interactions. Phase separation of the uncharged form and bilayer micellization by the charged form of tetracaine

The interaction between tetracaine and egg phosphatidylcholine (egg PC) multibilayers was examined. ESR spectra of an ester spin label indicate that at low uncharged anesthetic: lipid ratios, membrane organization decreases. At higher ratios, saturation and phase separation occur, as suggested by a second spectral component which appears when the water solubility of tetracaine is reached. However, experiments with the drug in the absence and in the presence of membranes, making use of a phospholipid spin label, suggest that the new phase does not consist of solid tetracaine alone. Location of the new phase in the membrane would require a change in partition coefficient, while its location outside would imply a mechanism whereby the anesthetic would come off the membrane as an aggregate containing spin probe and phospholipid. Charged tetracaine forms micelles which disrupt-unilamellar egg PC vesicles (Fernandez, M.S. (1981) Biochim. Biophys. Acta 646, 27-30). Micellar tetracaine added to bilayers containing a PC spin probe changes the spectrum from one typical of a bilayer into one typical of micelles, indicating the formation of a tetracaine-egg PC mixed micelle. The effect is reversible upon dilution to concentrations below the critical micelle concentration of tetracaine. When membranes are prepared in the presence of a water-soluble spin label, TEMPOcholine, ascorbate destroys the signal of untrapped label; when mixed phospholipid-tetracaine are formed by addition of micellar tetracaine, this leads to a complete loss of the ESR signal. High drug concentrations are often used for anesthesia and could be related to morphological nerve damage caused by large doses of anesthetics.     

Factors affecting the motion of the polar headgroup in phospholipid bilayers. A 31P NMR study of unsonicated phosphatidylcholine liposomes.

(1) The 129 MHZ and 36.4 MHZ 31 P NMR spectra of unsonicated liposomes consisting of phosphatidylcholines of varying chain length and unsaturation have been investigated. (2) In the liquid crystalline state the 31 P NMR liposome spectra are similar for both saturated and unsaturated phosphatidylcholines, demonstrating that the motion of the polar headgroup is not sensitive to the fatty acid composition in the disordered liquid crystalline state. (3) Below the hydrocarbon phase transition temperature there is a marked increase in the linewidth of the 31P NMR liposome spectra, indicating a reduction in the motion of the polar headgroup. (4) The addition of equimolar concentrations of cholesterol to phosphatidylcholine eliminates phase transition effects experienced by the polar headgroup. The motion of the polar headgroup is then very similar to that obtained in the liquid crystalline state for pure phosphatidylcholine bilayers. (5) In the liquid crystalline state the motion of the polar headgroup in the phosphate region is insensitive to changes in the available area per phosphatidy-choline molecule.     

A study of mobility and order in model membranes using 2H NMR relaxation rates and quadrupole splittings of specifically deuterated lipids

²H NMR spectra have been observed for several selectively deuterated phospholipid and fatty acid probes intercalated in the liquid crystalline phase of egg phosphatidylcholine in aqueous dispersion. For unsonicated lamellar dispersions and planar multibilayers, quadrupole splittings may be observed which lead directly to a value for the order parameter for the carbon-deuterium bond. Sonicated dispersions yield high-resolution spectra, from which spin-lattice relaxation rates and correlation times for rotational diffusion can be obtained. The presence of cholesterol in the dispersion has no effect on the quadrupole splittings and relaxation rates for ²H in the choline methyl groups, in contrast to its profound effect on the spectra for ²H in the hydrocarbon chains.