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At least 19 recordsLinked to original sources

PubMed1986

Raman spectroscopy of selectively deuterated dimyristoylphosphatidylcholine: studies on dimyristoylphosphatidylcholine-cholesterol bilayers.

Dimyristoylphosphatidylcholine (DMPC), selectively deuterated in the sn-2 chain at the 3, 6, and 10 positions is used to probe DMPC-cholesterol interactions in multilamellar dispersions. Using the Raman spectral linewidths of the 2100 cm-1 C2H2 stretching modes as an index of membrane disorder, we demonstrate that cholesterol tends to order, or increase the number of trans carbon-carbon bonds within the DMPC acyl chain near the headgroup region at all temperatures. At low temperatures, cholesterol disorders the acyl chains near the methyl termini by inducing gauche conformers; cholesterol orders the entire chain at higher temperatures. These determinations are qualitatively consistent with conclusions drawn from deuterium nuclear magnetic resonance studies, but specifically reflect acyl chain trans/gauche isomerization on the 10(-12)-10(-13) s vibrational time scale.

Cholesterol↗

PubMed1983

Unusual enthalpy changes which accompany the titration of dimyristoylphosphatidylcholine vesicles with Triton X-100.

The enthalpy changes which accompany the titration of 0.1% and 0.25% small unilamellar and multiameller vesicle samples of dimyristoylphosphatidylcholine with 2% Triton X-100 in 0.067 M phosphate buffer (pH 7.4) containing 0.15 M NaCl have been determined by titration calorimetry at 21 degrees C and 28 degrees C, the enthalpy change for both type of vesicles was zero within the limits of experimental error. At 21 degrees C, the multilamellar vesicle samples exhibited an enthalpy change of 1.35 +/- 0.48 and 2.47 +/- 0.98 kcal/mol dimyristoylphosphatidylcholine which was complete at a molar ratio of dimyristoylphosphatidylcholine to Triton of 3.21 +/- 0.84 and 5.77 +/- 1.05 for 0.1% and 0.25% dimyristoylphosphatidylcholine solutions, respectively. An exothermic transition of -2.39 +/- 0.30 and -2.05 +/- 0.69 kcal/mol phospholipid followed by an endothermic transition of 1.37 +/- 0.12 and 1.94 +/- 0.20 kcal/mol dimyristoylphosphatidylcholine was observed at 21 degrees C for 0.1% and 0.25% small unilamellar vesicle samples, respectively. In addition the nearly athermal association of the small unilemellar vesicle samples at 21 degrees C was observed, which may be an appropriate model for biological membrane fusion.

Calorimetry↗

PubMed1984

Lipoprotein lipase-catalyzed hydrolysis of dimyristoylphosphatidylcholine. Effect of lipid organization and apolipoprotein C-II on enzyme activity.

The effect of phospholipid organization on the lipoprotein lipase-catalyzed hydrolysis of dimyristoylphosphatidylcholine was examined with sonicated vesicles and Triton X-100 or lysomyristoylphosphatidylcholine solubilized lipid. Triton X-100-dimyristoylphosphatidylcholine substrates were prepared at various ratios of detergent to phospholipid so as to produce lipid structures varying from bilayers to micelles. Apolipoprotein C-II, the activator protein for lipoprotein lipase, enhanced the rate of the lipoprotein lipase-catalyzed hydrolysis of dimyristoylphosphatidylcholine for each substrate tested. Although the absolute rate of lipoprotein lipase catalysis was different for each, the factor (the ratio of lipoprotein lipase activity with apolipoprotein C-II to that without the activator protein) was nearly constant, with a value of approximately 16. We conclude that the enhancement of lipoprotein lipase activity by apolipoprotein C-II is independent of the physical form of the phospholipid substrate.

Animals↗

PubMed1989

Fluorescence quenching with lindane in small unilamellar L,alpha-dimyristoylphosphatidylcholine vesicles.

The lateral mobility and lipid-water partition of the pesticide lindane was studied by fluorescence quenching of N-isopropylcarbazole (NIPC) and L,alpha-palmitoyl-beta-(N-carbazolyl) undecanoylphosphatidylcholine (PCUPC) in liposomes of dimyristoylphosphatidylcholine at 50 degrees C. In isotropic solvents the quenching reaction was highly inefficient. A scheme for dynamic quenching, in which the monomolecular quenching rate constant is small, was valid. In lipid bilayers the same scheme was applied to describe the quenching results but the rate constant of the back-reaction of the excited complex to quencher and excited probe was of comparable magnitude to the monomolecular quenching rate constant. This phenomenon results in biexponential decays of the fluorescent probe in the presence of quencher. All the rate constants of the scheme could be determined. Stern-Volmer plots at different membrane concentrations were obtained from fluorescence intensity and decay time measurements. From these plots the true bimolecular quenching rate constant, Kq, and the rate constant for lateral diffusion, kd, were determined: kq[NIPC] = 3.2 +/- 0.5 x 10(8) M-1 s-1, kq[PCUPC] = 1.9 +/- 0.4 x 10(8) M-1 s-1, kd[NIPC] = 6.6 +/- 0.8 x 10(8) M-1 s-1. The smaller value of kq compared to kd for the quenching reaction of NIPC with lindane indicates that this quenching reaction is not diffusion controlled. The lateral diffusion coefficient D of lindane was found to be 1.7 +/- 0.2 x 10(-6) cm2/s in dimyristoylphosphatidylcholine vesicles at 50 degrees C. The partition coefficient of lindane in these lipid bilayers is very high (greater than 2000).

Dimyristoylphosphatidylcholine↗

PubMed1991

EPR studies on the influence of chain length on the segmental motion of spin-labelled fatty acids in dimyristoylphosphatidylcholine bilayers.

The rotational dynamics of spin-labelled fatty acids of different chainlengths (9, 10, 12, 14, 16 and 18 C-atoms) and different positions of labelling (5-C, 6-C and 7-C) have been studied in dimyristoylphosphatidylcholine bilayers using EPR spectroscopy. The segmental flexibility at a given label position is found to vary considerably with the length of the lipid chain, when this is less than that of the dimyristoylphosphatidylcholine host lipid. For both the charged and protonated forms of labelled fatty acids with chainlengths of 9, 10, and 12 C-atoms, the spectral anisotropy decreases steadily with decreasing chainlength in fluid phase bilayers. The differences become especially pronounced at the 7-C position of caprylic acid and the 6-C position of nonanoic acid, where the label is located close to the terminal methyl end of the chain. An unusually high degree of motional freedom is found for both these spin-labels, even in gel phase bilayers. There is relatively little effect of chainlength of the labelled fatty acid when this is longer or comparable to that of the host lipid (i.e., for fatty acid chainlengths of 18, 16 and 14 C-atoms), except if the label position is close to the terminal methyl end of the chain. The implications for the heterogeneous lipid chain composition in biological membranes are discussed.

Dimyristoylphosphatidylcholine↗

PubMed1988

Probucol reduces the rate of association of apolipoprotein C-III with dimyristoylphosphatidylcholine.

The effect of low concentrations of probucol and cholesterol on the association of dimyristoylphosphatidylcholine with human plasma apolipoprotein C-III was studied. Liposomes of dimyristoylphosphatidylcholine with or without probucol or cholesterol were prepared by swelling the lipids in buffer at 37 degrees C. The association of apolipoprotein C-III with the liposomes was determined at 24 degrees C by measuring the rate of clearing of turbidity at 400 nm following addition of protein. At a weight ratio of probucol/dimyristoylphosphatidylcholine of 1:25 (5 mol% probucol), the rate of clearing of liposomes was decreased by 60%; 5 mol% cholesterol had no effect on the clearing rate. Liposomes were then added to the preformed apolipoprotein C-III/lipid micelles. In the absence of probucol, the added liposomes cleared rapidly regardless of the presence or absence of cholesterol. With 5 mol% probucol, almost no decrease in absorbance was noted on addition of liposomes to the micelles. These data show that probucol reduces the rate of association of an apolipoprotein with lipid and suggests that the interaction of probucol with lipid may modify the assembly and/or metabolism of lipoproteins.

Apolipoprotein C-III↗

PubMed1993

The kinetics and thermodynamics of bleaching of rhodopsin in dimyristoylphosphatidylcholine. Identification of meta-I, meta-II, and meta-III intermediates.

The effects of light on rhodopsin reconstituted into dimyristoylphosphatidylcholine at a molar ratio of 1:70 have been studied as a function of temperature and time. The lipid phase behavior and thermal stability of rhodopsin in the system used to measure the photolytic reactions were also determined. Thus, it was shown that the gel-to-fluid phase transition of the reconstituted membrane had a marked influence on the bleaching kinetics and thermodynamics of rhodopsin-bleaching equilibria, whereas lipid-protein interactions were also directly involved. Rhodopsin photolysis resulted in temperature-sensitive equilibria between three main photoproducts, with absorption maximal of approximately 480, 380, and 465 nm. Below the lipid phase transition temperature, the main photoproduct had an absorption maximum at 480 nm. With increasing temperature progressively more of the 380 nm-absorbing species was formed. The photoproduct with a spectral-maximum at 465 nm absorption was formed more slowly. Increasing temperatures decreased the ratio of the 465:380 nm-absorbing species. The thermal reactions were reversible: on cooling the higher-temperature products were converted back to the lower-temperature products. The results indicate that rhodopsin has extensive photochemical activity when reconstituted in dimyristoylphosphatidylcholine. The equilibria that we have measured resemble those of rhodopsin in the disk membrane. However, the kinetics of meta-II and meta-III formation appear to be considerably faster in the reconstituted membranes and the meta-I-to-meta-II equilibrium is displaced in the direction of the meta-I state relative to native rod outer segment disk membranes. The displacement of the meta-rhodopsin equilibrium from its position in the rod outer segment is attributed mainly to the effects of lipid-lipid interactions in the membrane bilayer and correlates with the difference in gel-to-fluid phase transition temperature of the different lipids.

Animals↗

PubMed1985

Effects of lipid environment on the light-induced conformational changes of rhodopsin. 1. Absence of metarhodopsin II production in dimyristoylphosphatidylcholine recombinant membranes.

Photolysis of bovine rhodopsin in dimyristoylphosphatidylcholine recombinant membranes results in the production of a relatively stable metarhodopsin I like photointermediate that decays slowly to a species with a broad absorbance maximum centered at about 380 nm [O'Brien, D. F., Costa, L. F., & Ott, R. A. (1977) Biochemistry 16, 1295-1303]. On the basis of the results of a variety of chemical and spectroscopic tests, we show that this process corresponds to the production of free retinal plus opsin and not to the slow production of metarhodopsin II. Electron spin resonance studies using a novel disulfide spin-label that is covalently linked to rhodopsin indicate that the apparent arrest of the protein at the metarhodopsin I stage is not due to simple aggregation of the protein in this short-chain, saturated lipid bilayer but must be understood in terms of the effect of the lipid host on the conformational energies of individual protein molecules. Limited production of metarhodopsin II is observed under acidic conditions. Thus, the rhodopsin-dimyristoylphosphatidylcholine recombinants offer a unique system for the study of the effect of the phospholipid bilayer environment on the conformation of an intrinsic membrane protein.

Animals↗

PubMed1986

Microemulsions of cholesteryl oleate and dimyristoylphosphatidylcholine: a model for cholesteryl ester rich very low density lipoproteins.

This study describes the preparation, purification, and characterization of a cholesteryl oleate/dimyristoylphosphatidylcholine microemulsion as a model for the interaction of lipid domains in cholesteryl ester rich very low density lipoproteins. These lipids were chosen specifically because their thermal transitions were distinct from each other, and their differences in chemical structure permitted the motion(s) of each lipid component to be monitored independently by 13C nuclear magnetic resonance (NMR). The model particles were formed by cosonication of cholesteryl oleate and dimyristoylphosphatidylcholine in a 4:1 molar ratio for 45 min at 55-60 degrees C (above both lipid phase transition temperatures). The crude microemulsion was fractionated by low-speed centrifugation and Sepharose CL-2B chromatography. Microemulsion particles which eluted from the column at a volume similar to that of cholesteryl ester rich very low density lipoproteins had high cholesteryl ester:phospholipid ratios (2.5:1----6:1). Electron micrographs of negatively stained particles showed them to be large spheres devoid of multilamellar or unilamellar vesicle structures. Particle size calculated from a simple compositional model correlated well with sizes determined by electron microscopy (500-1000 A) for various column fractions. Differential scanning calorimetry studies of the microemulsion revealed two thermal transitions for the model particles, at 31.0 and 46.6 degrees C, which were tentatively assigned to the surface phospholipid and core cholesteryl ester domains, respectively. These assignments were confirmed by 13C NMR which demonstrated that, at temperatures near the lower thermotropic transition, only resonances derived from carbon atoms of dimyristoylphosphatidylcholine (DMPC) were observable. As the temperature was raised to 38.6 degrees C, resonances from the olefinic carbons in the cholesteryl ester acyl chain appeared in the spectrum. At 46.6 degrees C, the center of the higher temperature endotherm, resonances from both the steroid ring and remaining acyl chain carbons of cholesteryl oleate became observable in the spectrum. Further increases in temperature did not result in the appearance of new resonances; however, those that were present narrowed and increased in intensity. The elevation in transition temperature for DMPC in these particles (31 degrees C) as compared to that for DMPC in small unilamellar (18 degrees C) and large multilamellar (23 degrees C) vesicles suggested a stabilization of the phospholipid monolayer, possibly by interaction with the nonpolar core lipids.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1981

A calorimetric study of peptide-phospholipid interactions: the glucagon-dimyristoylphosphatidylcholine complex.

The isothermal enthalpy of reaction glucagon with dimyristoylphosphatidylcholine is found to be large and markedly temperature dependent, changing from -150 kcal/mol of glucagon at 25 degrees C to + 80 kcal/mol of glucagon at 23 degrees C. The observed enthalpy is shown to arise mainly from the glucagon-induced alteration of the distribution of the phospholipid between gel and liquid crystalline phases. The reaction is accompanied by a large change in the apparent heat capacity around the phase transition temperature of the pure lipid which explains the small variation of the free energy of binding with temperature despite the large changes in enthalpy. The equilibrium binding constant calculated from the enthalpy as a function of lipid-peptide ratio is in good agreement with that previously found from fluorescence titrations, but the number of lipid molecules bound per glucagon molecule at 25 degrees C is increased from 20 to 50, suggesting that glucagon can bind to 50 lipid molecules but that only 20 of these are close enough to affect the fluorescence of the hormone. Differential scanning calorimetry of dimyristoylphosphatidylcholine in the presence of glucagon shows a transition curve composed of two components. The major component, corresponding to 80% of the enthalpy change, is centered at 26.1 degrees C and has a cooperative unit of 45 lipid molecules. The total enthalpy change for the transition in the presence of glucagon is only +3.2 kcal/mol, compared with +4.8 kcal/mol for the pure lipid.

Animals↗

PubMed1988

[Formation of micellar complexes of apolipoprotein A-I with dimyristoylphosphatidylcholine].

Structural changes of apolipoprotein AI from human plasma high density lipoproteins in 2-chloroethanol solutions were studied using spin label and fluorescence techniques. Reversible changes in spectral parameters occur in 2-chloroethanol concentration range 0-40% and are affected by dimyristoylphosphatidylcholine, of 2-chloroethanol concentration does not exceed 30%. Dialysis experiments demonstrated the absence of binding of monomer phosphatidylcholine with apolipoprotein AI. It thus follows that formation of complexes of apolipoprotein AI with dimyristoylphosphatidylcholine is caused by lipid micella aggregation.

Apolipoprotein A-I↗

PubMed1976

Evidence for phase boundary lipid. Permeability of Tempo-choline into dimyristoylphosphatidylcholine vesicles at the phase transition.

The existence of distinct regions of mismatch in molecular packing at the interfaces of the fluid and ordered domains during the phase transition of dimyristoylphosphatidylcholine vesicles has been demonstrated by measuring the temperature dependence of the permeability to a spin-label cation and comparing this with a statistical mechanical calculation of the fraction of interfacial lipid. The kinetics of uptake and release of the 2,2,6,6-tetramethylpiperidinyl-1-oxycholine (Tempo-choline) spin label by single-bilayer dimyristoylphosphatidylcholine vesicles were measured using electron spin resonance spectroscopy to quantitate the amount of spin label present within the vesicles after removal of the external spin-label by ascorbate at 0 degrees C. Both the uptake and release experiments show that the Tempo-choline permeability peaks to a sharp maximum at the lipid-phase transition, the vesicles being almost impermeable to Tempo-choline below the transition and having a much reduced permeability above. The temperature profile of the permeability is in reasonable quantitative agreement with calculations of the fraction of interfacial boundary lipid from the Zimm and Bragg theory of cooperative transitions, which use independent spin-label measurements of the degree of transition to determine the cooperativity parameter. The relatively high intrinsic permeability of the interfacial regions (P approximately 0.2-1.0 X 10(-8) cm/s) is attributed to the mismatch in molecular packing of the lipid molecules at the ordered-fluid boundaries, which could have important implications not only for permeability in natural membranes (e.g., in transmitter release), but also for the function of membrane-bound enzymes and transport proteins.

Binding Sites↗

PubMed1975

Proton magnetic resonance relaxation studies on the structure of mixed micelles of Triton X-100 and dimyristoylphosphatidylcholine.

Proton magnetic resonance and gel chromatographic studies on mixtures of phospholipid and the nonionic surfactant Triton X-200 have shown that at temperatures above the thermotropic phase transition of the phospholipid and below the cloud point of Triton, mixed micelles are present at molar ratios above about 2:1 Triton/phospholipid. Proton T1 and T2 (from line widths) relaxation times are reported for protons in Triton micelles and in mixed micelles of Triton and dimyristoylphosphatidylcholine at a molar ratio of 3:1 Triton/phospholipid. The T1 values and their temperature dependence and the activation energies of the various Triton proton groups appear to reflect internal motions of the Triton molecules in the micelle. Measurements of the T1/T2 ratio and frequency dependence (55-220 MHz) suggest that the hydrophobic tert-butyl group in Triton is observed under extreme narrowing conditions. The T1 and T2 values of Triton are unchanged in the presence of phosphatidylcholine. The T1 values of various protons of dimyristoylphosphatidylcholine in mixed micelles are similar to those reported for the phospholipid in sonicated vesicles, which are used as membrane models, and presumably the same coupled trans-gauche motions dominate. The T2 values for the terminal methyl and choline methyl protons in the phospholipid are longer than those reported for these groups in vesicles. Hence, the motion of the phospholipid in the mixed micelles appears to be less restricted than in vesicles. T1 measurements in H20/D20 mixtures are consistent with the idea that water does not penetrate the hydrophobic core of the mixed micelles, while water does solvate the polar oxyethylene and choline methyl groups. Titration with Mn2+ confirms that the oxyethylene and choline methyl groups are on the exterior of the mixed micelle while the hydrophobic groups are located in the micellar interior.

Colloids↗

PubMed1982

Quantitative composition and characterization of the proteins in membrane vesicles released from erythrocytes by dimyristoylphosphatidylcholine. A membrane system without cytoskeleton.

Membrane vesicles were prepared by incubation of human erythrocytes with dimyristoylphosphatidylcholine [3] and isolated by isopycnic centrifugation on Dextran density gradients. Protein analyses were carried out with crossed immunoelectrophoresis and dodecylsulfate polyacrylamide gel electrophoresis. The right-side-out-oriented membrane vesicles contained membrane and cytoplasmic proteins of the erythrocyte but lacked cytoskeletal components. Comparison of proteins in vesicles and erythrocyte membranes showed that acetylcholinesterase was enriched two to six times in the vesicles relative to both membrane-spanning proteins, band 3, and glycophorin. Two further, hitherto unidentified, sialic acid-containing membrane antigens were found in the vesicles. Both faced the outside of the membranes and were enriched two to seven times. Ankyrin was not present in the membrane vesicles and spectrin could not be detected by dodecylsulfate polyacrylamide gel electrophoresis. We suggest that the redistribution of proteins in the vesicles reflects differences in their interactions with other membrane components and their relative mobility within the erythrocyte membrane.

Dimyristoylphosphatidylcholine↗

PubMed1984

Characteristics of drug-phospholipid coprecipitates I: Physical properties and dissolution behavior of griseofulvin-dimyristoylphosphatidylcholine systems.

Solid dispersions of griseofulvin and dimyristoylphosphatidylcholine (lecithin) have been prepared as both coprecipitates and physical mixtures, and their physical characteristics and dissolution behavior compared with pure griseofulvin. The dissolution of the physical mixtures was similar to pure drug, but the coprecipitates yielded a 3.5-fold greater initial dissolution rate and a limiting concentration after 60 min which was 72% greater at a griseofulvin-lecithin weight ratio of 19:1. Increasing the lecithin content to 1.5:1 compositions resulted in only a further 50% increase in the initial dissolution rate and a further 12% increase in the limiting concentration. The effect of the pH of the medium on dissolution was slight, but varied with the composition of the system. The phase diagram indicated that these systems have no significant eutectic or solid solution formation. X-ray diffraction spectra further showed that freshly prepared or aged coprecipitates contained griseofulvin crystals, and photomicrographs showed that the crystals essentially retained their characteristic shapes and sizes in all systems. Differential thermal analysis yielded heats of fusion that gave a good linear correlation with the percent of griseofulvin dissolved from coprecipitates at all time intervals, but not with physical mixtures. Furthermore, aged coprecipitates underwent a slower rate of dissolution compared with fresh samples. The results are interpreted to suggest that griseofulvin undergoes improved dissolution from coprecipitates due to the formation of crystals of lower stability. In addition, the rapid dispersion of lecithin in the aqueous medium (as seen microscopically) entraps griseofulvin in myelinic structures and liposomes and effectively increases the saturation concentration of drug in the diffusion layer during the dissolution process.

Chemical Phenomena↗

PubMed2000

Interaction of linear mono- and diamines with dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol multilamellar liposomes.

The effect of linear monoamines on dimyristoylphosphatidylglycerol and dimyristoylphosphatidylcholine multilamellar liposomes was studied as a function of their length and compared with the behavior of linear carboxylic acids. The role of the hydrophobic interactions was demonstrated and the free energy of the binding for each interacting carbon atom was determined. The thermotropic behavior of the liposomes was characterized by differential scanning calorimetry and it was shown that these molecules affect the temperature and the cooperativity of the gel to fluid state transition of the membrane differently. In particular, it appeared that membrane perturbation was maximum when the chain length of the amphipathic molecules ranged between 7 and 9 carbon atoms, with more pronounced effects in the case of monoamines. Molecules shorter than 3-4 carbon atoms did not produce any observable change in the transition temperature. The study was extended to linear alpha,omega-diamines to investigate the amphipathic character of long diamines and to investigate the role of bridging bonds established with neighboring phospholipids.

Amines↗

PubMed1989

Interaction of filipin with dimyristoylphosphatidylcholine membranes studied by 2H-NMR, circular dichroism, electronic absorption and fluorescence.

Interaction of the pentene antibiotic filipin with dimyristoylphosphatidylcholine (DMPC) membranes has been monitored by 2H-NMR, circular dichroism (CD), electronic absorption and fluorescence in the temperature range 10 degrees to 60 degrees C. Interaction appears to depend on whether filipin is added before or after membrane formation and also upon the temperature of the system. When filipin is added to preformed DMPC large unilamellar vesicles (LUV), the association constants, as determined by electronic absorption are 39 x 10(3) M-1, 15 x 10(3) M-1 and 0.6 x 10(3) M-1 at 15 degrees, 30 degrees and 50 degrees C, respectively. Under identical conditions, CD spectra of bound filipin exhibit features characteristic of an aggregation over the whole temperature range. When filipin is incorporated in membranes during their preparation, the 2H-NMR spectra of deuterated DMPC indicate that the drug has a slight disordering effect on the lipid matrix below the temperature, Tc, of the gel-to-fluid phase transition and above Tc + 11 degrees C. Between these two temperature boundaries the system consists of two lipid regions of very different dynamic properties. One of the regions, which is attributed to a filipin-lipid complex, has the properties of gel-like lipids whereas the other has those of fluid-like lipids. The latter domain is however more ordered than the pure lipid at corresponding temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)

Antifungal Agents↗

PubMed2003

Determination of bilayer thickness and lipid surface area in unilamellar dimyristoylphosphatidylcholine vesicles from small-angle neutron scattering curves: a comparison of evaluation methods.

Small-angle neutron scattering (SANS) experiments were performed on unilamellar 1,2-dimyristoylphosphatidylcholine (DMPC) vesicles prepared in heavy water by extrusion through polycarbonate filters with 500 A pores. The data obtained at 30+/-0.1 degrees C were evaluated using a five-strip function model of the bilayer coherent neutron scattering length density, three different approximate form factors describing scattering from vesicles, and different methods of evaluation of the experimental data. It is shown that the results obtained from the SANS data in the range of scattering vector values 0.0316 A(-1)< q<0.0775 A(-1) are not sensitive to the vesicle form factor, nor to the evaluation method. Using the hollow sphere model of vesicles convoluted with the Gaussian distribution of their sizes, a constrained bilayer polar region thickness of 9 A and a DMPC headgroup volume of 325.5 A(3), it was possible to obtain from the experimental data the DMPC surface area as 58.9+/-0.8 A(2), the bilayer thickness as 44.5+/-0.3 A and the number of water molecules as 6.8+/-0.2 per DMPC located in the bilayer polar region.

Algorithms↗