Jana Gallová

Areas of Monounsaturated Diacylphosphatidylcholines

We have studied the structural properties of monounsaturated diacylphosphatidylcholine lipid bilayers (i.e., diCn:1PC, where n = 14, 16, 18, 20, 22, and 24 is the number of acyl chain carbons). High-resolution x-ray scattering data were analyzed in conjunction with contrast-varied neutron scattering data using a technique we recently developed. Analyses of the data show that the manner by which bilayer thickness increases with increasing n in monounsaturated diacylphosphatidylcholines is dependent on the double bonds position. For commonly available monounsaturated diacylphosphatidylcholines, this results in the nonlinear behavior of both bilayer thickness and lipid area, whereas for diC18:1PC bilayers, lipid area assumes a maximum value. It is worthwhile to note that compared to previous data, our results indicate that lipid areas are smaller by approximately 10%. This observation highlights the need to revisit lipid areas, as they are often used in comparisons with molecular dynamics simulations. Moreover, simulators are encouraged to compare their results not only to x-ray scattering data, but to neutron data as well.

Interaction of surfactants with model and biological membranes.: II. Effect of N-alkyl-N,N,N-trimethylammonium ions on phosphatidylcholine bilayers as studied by spin probe ESR

The interaction of N-alkyl-N,N,N-trimethylammonium (CnTMA, n = 6-18) salts (iodides and/or bromides) with model membranes prepared by hydration of egg yolk phosphatidylcholine (EYPC) over aqueous salt solutions has been studied by m-doxyl stearic acid (m-DSA, m = 12 and 16) spin probe method. In disoriented EYPC bilayers the CnTMA salts decrease the orientational order parameter S33 of m-DSA evaluated from the powder pattern ESR spectra. This effect is maximal for C6TMA. In oriented EYPC bilayers prepared by the parallel-beam sputtering method and hydrated over saturated NaCl solution the order parameter S33 calculated from the angular dependence of the nitrogen hyperfine splitting is decreased in the presence of C6TMA. The order parameter S11 obtained from the angular dependence of line positions indicates deviation of m-DSA motion from axial symmetry. C6TMA increases the probability of gauche conformations of the lipid chains by about 13-14%, and decreases the effective energy difference between the trans and gauche conformations by about 420-480 J/mol, at molar ratio of EYPC/C6TMA = 2:1. The angular dependence of linewidths is analysed by employing a theory of spin relaxation based on the strong collision model for molecular reorientations. The correlation time tau 0 of the reorientation of an axis orthogonal to the doxyl ring of 16-DSA is decreased in the presence of C6TMA, while that of 12-DSA is not influenced by it. The ratio of tau 2/tau 0 is increased in the presence of C6TMA for the both spin probes. The results are explained using the free-volume model of the CnTMA-EYPC membrane interaction.

Hydrophobic thickness, lipid surface area and polar region hydration in monounsaturated diacylphosphatidylcholine bilayers: SANS study of effects of cholesterol and β-sitosterol in unilamellar vesicles

The influence of a mammalian sterol cholesterol and a plant sterol beta-sitosterol on the structural parameters and hydration of bilayers in unilamellar vesicles made of monounsaturated diacylphosphatidylcholines (diCn:1PC, n=14-22 is the even number of acyl chain carbons) was studied at 30 degrees C using small-angle neutron scattering (SANS). Recently published advanced model of lipid bilayer as a three-strip structure was used with a triangular shape of polar head group probability distribution (Kucerka et al., Models to analyze small-angle neutron scattering from unilamellar lipid vesicles, Physical Review E 69 (2004) Art. No. 051903). It was found that 33 mol% of both sterols increased the thickness of diCn:1PC bilayers with n=18-22 similarly. beta-sitosterol increased the thickness of diC14:1PC and diC16:1PC bilayers a little more than cholesterol. Both sterols increased the surface area per unit cell by cca 12 A(2) and the number of water molecules located in the head group region by cca 4 molecules, irrespective to the acyl chain length of diCn:1PC. The structural difference in the side chain between cholesterol and beta-sitosterol plays a negligible role in influencing the structural parameters of bilayers studied.

Partial area of cholesterol in monounsaturated diacylphosphatidylcholine bilayers

The influence of cholesterol on the structural parameters of phosphatidylcholine bilayers is studied by small-angle neutron scattering on unilamellar liposomes. Monounsaturated diacylphosphatidylcholines diCn:1PC with the length of acyl chains n=14, 18 and 22 carbons are used. We confirm that the bilayer thickness increases with increasing concentration of cholesterol for all studied diCn:1PCs. However, partial areas per diCn:1PC and cholesterol molecule on lipid-water interface are found not to depend of cholesterol concentration. The partial area per cholesterol molecule is 0.24nm². In addition, the partial area per diC18:1PC is larger than that for diC14:1PC and diC22:1PC.

Interaction of local anesthetic heptacaine homologs with phosphatidylcholine bilayers: spin label ESR study

Local anesthetic monohydrochlorides of [2-(alkoxy)phenyl]-2-(1-piperidinyl)ethyl esters of carbamic acid (CnA, n = 2, 3, 4, 6, 8, 10, 12 is the number of carbon atoms in the alkyloxy substituent) increase the probability of formation of gauche isomers p(g) and decrease the effective energy difference between gauche and trans conformation E(g) in egg yolk phosphatidylcholine (EYPC) acyl chains, as determined by electron spin resonance spectroscopy using dipalmitoylphosphatidylcholines labeled with the paramagnetic dimethyloxazolidinyl group on the 12-th or 16-th carbon atoms of their sn-2 acyl chain, and oriented EYPC bilayers hydrated at 81% relative water vapour pressure. CnAs also increase the hydration of EYPC in non-oriented bilayers at the same relative water vapour pressure. At the molar ratio of CnA:EYPC = 0.4:1, the maximum effect on p(g), E(g) and hydration has been observed for intermediate alkyloxy chain lengths n approximately 4/6.

Partial volumes of cholesterol and monounsaturated diacylphosphatidylcholines in mixed bilayers

Dispersions of multilamellar liposomes prepared from monounsaturated diacylphosphatidylcholines having 18-24 carbons and from varying amounts of cholesterol were studied by densitometry. Ideal mixing of the studied phosphatidylcholines with cholesterol in the fluid phase was observed. The temperature dependence of partial volumes of both phosphatidylcholines and cholesterol was determined. A slight decrease in the partial volume of cholesterol with the lengthening of the acyl chain of the host phosphatidylcholine was observed. By measuring the density of multilamellar liposomes of dinervonoylposphatidylcholine and cholesterol below the main phase transition temperature, the phase boundary between the solid ordered phase and the area of coexistence of the solid ordered and liquid ordered phases was detected.

Effect of alkan-1-ols on the structure of dopc model membrane

Abstract The effect of general anaesthetics alkan-1-ols (CnOH, where n = 10, 12, 14, 16 and 18 is the number of carbon atoms in the molecule) on the structure of dioleoylphosphatidylcholine (DOPC) model membrane was studied by small-angle neutron scattering (SANS) and small-angle neutron diffraction (SAND). Fluid bilayers were prepared at CnOH:DOPC = 0.3 molar ratio. The results of both the experiments show that bilayer thickness - a thickness parameter dg in the case of SANS and lamellar repeat distance D in the case of SAND - increases with increasing n. A coexistence of two lamellar phases with different D was detected by measuring the C18OH+DOPC oriented sample.

Site-specific effect of radical scavengers on the resistance of low density lipoprotein to copper-mediated oxidative stress: influence of α-tocopherol and temperature

The radical scavenging capacity of active nitroxide spin label radicals located at different depths in the surface monolayer of native and alpha-tocopherol enriched low density lipoprotein (LDL) has been evaluated at early stages of copper-mediated lipid peroxidation. Spin labels induced a concentration-dependent prolongation in lag time and a pronounced decrease in the initial rate of conjugated diene (CD) formation. These effects strongly argue for a protective, antioxidative action of spin labels, which in turn become destroyed with the extent of oxidation by radical recombination reactions. The results revealed that the decrease in spectral intensity proceeds at a higher rate for nitroxide radicals located in a more hydrophobic environment. The loss in spin label activity is accompanied by simultaneous alpha-tocopherol consumption and progresses rather independently of initial alpha-tocopherol content. The data provided no evidence that spin labels either save alpha-tocopherol or compete with it for radicals. The authors, therefore, deduce that due to enhanced accessibility and mobility, spin labels located in the interior of LDL eliminate lipid-derived radicals, which otherwise would promote lipid peroxidation. Lowering of temperature clearly below the core-lipid phase transition temperature of LDL exerts a significant effect on the kinetics of copper-induced LDL oxidation, whereas the characteristics of the radical scavenging mechanisms of the spin label molecules located in the surrounding phospholipid monolayer are conserved. Taken together, the susceptibility of LDL to primary oxidative stress conditions was efficiently retarded by small amounts of radical scavengers. This effect was more pronounced for nitroxide radicals embedded deeper in the phospholipid monolayer and was rather independent of alpha-tocopherol enrichment.

Partial molecular volumes of cholesterol and phosphatidylcholine in mixed bilayers

Abstract Dispersion of multilamellar liposomes of dimyristoylphosphatidylcholine (DMPC) and cholesterol (CHOL) were studied by vibrational densitometer for the CHOL mole fractions X = 0−0.54 in the temperature range 18−50 °C, both below and above the main phase transition. DMPC-CHOL bilayers served as a simple model for lipidic part of biological membrane. Volumetric parameters are essential not only to evaluate the data obtained by scattering and diffraction methods on model membranes but can provide valuable information about molecular packing in bilayers and the phase behaviour of lipid-CHOL mixtures. In this paper, preliminary results regarding the changes in the specific volume of lipid bilayer with increasing temperature and CHOL content are presented. Different values of apparent molecular volume of CHOL for different CHOL mole fraction pointed out the non-ideal mixing of DMPC and CHOL.

Effect of N-dodecyl-N,N-dimethylamine N-oxide on unilamellar liposomes

Received September 1, 2013, accepted September 29, 2013 Original research article Comenius University in Bratislava, Faculty of Pharmacy, Department of Physical Chemistry of Drugs, Bratislava, Slovak Republic / Univerzita Komenského v Bratislave, Farmaceutická fakulta, Katedra fyzikálnej chémie liečiv, Bratislava, Slovenská republika Efekt N-dodecyl-N,N-dimetylamín N-oxidu (C12NO) na unilamelárne lipozómy (ULL) pripravené z vaječného fosfatidylcholínu (EYPC) bol študovaný metódou turbidimetrie a fluorescenčnej spektroskopie. Koncentrácia C12NO vyvolávajúca saturáciu a úplnú solubilizáciu membrány bola vyhodnotená turbidimetricky. Pre fluorescenčné merania boli použité lipozómy naplnené hydrofilnou fluorescenčnou sondou kalceínom. Závislosť intenzity fluorescencie od koncentrácie C12NO môže byť rozdelená na tri priamkové sekcie. Zlomové body, získané z priesečníkov priamok, zodpovedajú dvom koncentráciám C12NO, pri ktorých nastáva vznik malých štrukturálnych defektov resp. veľkých perforácií v membráne lipozómov. Tieto defekty sú natoľko veľké, že dochádza k úplnému vyplaveniu kalceínu z lipozómov. Výsledky získané z dvoch metód sme následne porovnali. Meranie fluorescenčnou metódou ukázalo, že voľná difúzia kalceínu cez póry v EYPC dvojvrstvách prebieha pri koncentráciách C12NO, kedy saturácia membrány nie je ukončená a tvar lipozómov zostáva zachovaný. Ku solubilizácii, teda k fázovej premene z dvojvrstiev na micely sú potrebné vyššie koncentrácie C12NO. slovak abstract Acta Fac. Pharm. Univ. Comen. LX, 2013, (2), p. 7–13 ISSN 1338-6786 (online) and ISSN 0301-2298 (print version) DOI 10.2478/afpuc-2013-0021 * sisa.hulakova@gmail.com