Small-angle neutron scattering study of the lipid bilayer thickness in unilamellar dioleoylphosphatidylcholine vesicles prepared by the cholate dilution method: n-decane effect

AbstractPrevious X-ray diffraction studies on fully hydrated fluid lamellar egg phosphatidylcholine phases indicated a ∼10 Å increase of bilayer thickness in the presence of excess n-decane [Biochim. Biophys. Acta 597 (1980) 455], while the small-angle neutron scattering (SANS) on unilamellar extruded dioleoylphosphatidylcholine (DOPC) vesicles detected substantially smaller 2.4±1.3 Å bilayer thickness increase at n-decane/DOPC molar ratio of 1.2 [Biophys. Chem. 88 (2000) 165]. The purpose of the present study is to investigate the n-decane effect on the bilayer thickness in unilamellar DOPC vesicles prepared by the sodium cholate (NaChol) dilution method. Mixed DOPC+NaChol micelles at DOPC and NaChol concentrations of 0.1 mol/l were prepared in 2H2O containing 0.135 mol/l NaCl. This micellar solution was diluted in 0.135 mol/l NaCl in 2H2O to reach the final DOPC and NaChol concentrations of 0.008 mol/l. Thirty microliters of n-decane solution in methanol was added to 1 ml of this dispersion. After methanol evaporation, SANS was conducted on the dispersions. From the Kratky–Porod plot ln[I(Q)Q2] vs. Q2 of SANS intensity I(Q) in the range of scattering vector values Q corresponding to interval 0.001 Å−2≤Q2≤0.006 Å−2, the bilayer radius of gyration Rg and the bilayer thickness parameter dg=120.5Rg were obtained. The values of dg indicate that the bilayer thickness increases by 2.4±0.9 Å up to n-decane/DOPC molar ratio of 1.6. This result confirms the previous SANS findings obtained with extruded vesicles

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

AbstractLocal 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 pg and decrease the effective energy difference between gauche and trans conformation Eg 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 pg, Eg and hydration has been observed for intermediate alkyloxy chain lengths n≈4÷6

Phase Behavior of the DOPE + DOPC + Alkanol System

Small- and wide-angle X-ray diffraction was used to study the effect of 1-alkanols, as simple models of general anesthetics, (abbreviation $C_{n}OH$, n = 8–18 is the even number of carbons in the aliphatic chain) on the lamellar to hexagonal $L\alpha \rightarrow H_{II}$ phase transition in the dioleoylphosphatidylethanolamine–dioleoylphosphatidylcholine = 3 : 1 mol/mol (DOPE + DOPC) system. All studied $C_{n}OHs$ were found to decrease the phase transition temperature of the DOPE + DOPC system in a $C_{n}OH$ chain length and concentration dependent manner and thus promote the formation of the $H_{II}$ phase. Anesthetically active $C_{8}OH$ and $C_{10}OH$ were found to decrease the lattice parameter $\mathit{d}$ of the $L\alpha$ phase, however longer non-anesthetic CnOHs increased the parameter $\mathit{d}$; this effect being more pronounced with increasing $C_{n}OH$ concentration. The lattice parameter $\mathit{a}$ of the $H_{II}$ phase was decreased in the presence of all $C_{n}OHs$, even at the lowest concentrations studied. In the scope of the indirect mechanism of general anesthesia observed changes in the lattice parameter $\mathit{d}$ (reflecting changes in the bilayer thickness) due to the intercalation of $C_{8}OH$ and $C_{10}OH$ might induce changes in the activity of integral membrane proteins engaged in neuronal pathways

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 bond's 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 ∼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

Synchrotron SAX and WAX diffraction study of a hydrated very long-chain, dendritic amphiphile+DPPC mixture

The tri-headed anionic dendritic amphiphile, 4-(2-carboxyethyl)-4-[(icosyloxycarbonyl)amino]heptanedioic acid (3CCb20), forms mixed aggregates with dipalmitoylphosphatidylcholine (DPPC) in excess water at 3CCb20:DPPC = 0.91:1 molar ratio. On heating, these mixed aggregates transform into fluid bilayers stacked in the liquid crystalline lamellar L(alpha) phase at about 40 degrees C. This phase transition and the microstructure of 3CCb20 + DPPC aggregates were studied with small- and wide-angle synchrotron X-ray diffraction. The ability of 3CCb20 to solubilize solidlike lipid bilayers could contribute to the antimicrobial activities of 3CCb20, including its anti-HIV activity

The structural diversity of DNA-neutral phospholipids-divalent metal cations aggregates: a small-angle synchrotron X-ray diffraction study

We investigate the structure of aggregates formed due to DNA interaction with saturated neutral phosphatidylcholines [dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine] in presence of Ca(2+) and Mg(2+) cations using simultaneous synchrotron small- and wide-angle X-ray diffractions. For DPPC:DNA = 3:1 mol/base and in the range of 1-50 mM Ca(2+), the diffractograms show structural heterogeneity of aggregates. We observe the coexistence of two lamellar phases in aggregates prepared at 1 mM Ca(2+): L(x) phase with the DNA strands (of unknown organization) intercalated in water layers between adjacent lipid bilayers and L(DPPC) phase of DPPC bilayers without any divalent cations and DNA strands. Aggregates prepared in the range 2-50 mM Ca(2+) show a condensed gel lamellar phase L (g) (c) with the lipid bilayer periodicity d approximately 8.0 nm, and the DNA-DNA interhelical distance d (DNA) approximately 5.1 nm. The increase of temperature induces the decrease in the intensity and the increase in the width of the DNA related peak. In the fluid state, the condensed lamellar phase L (alpha) (c) gradually converts into L(x) phase. The aggregates do not exhibit rippled P(beta) phase. The thermal behaviour of aggregates was investigated in the range 20-80 degrees C. Applying heating-cooling cycles, the aggregates converted into energetically more favourable structure: a condensed lamellar phase L(c) (or L(x)) is preserved or we observe lateral segregation of the DNA strands and metal cations (L(x) phase) in coexistence with L(PC) phase of pure phospholipids

The effects of cholesterol and beta-sitosterol on the structure of saturated diacylphosphatidylcholine bilayers

The structures of DMPC and DPPC bilayers in unilamellar liposomes, in the presence of 33.3 mol% cholesterol or the plant sterol β-sitosterol, have been studied by small-angle neutron scattering. The bilayer thickness d(L) increases in a similar way for both sterols. The repeat distance in multilamellar liposomes, as determined by small-angle X-ray diffraction, is larger in the presence of β-sitosterol than in the presence of cholesterol. We observe that each sterol modifies the interlamellar water layer differently, cholesterol reducing its thickness more efficiently than β-sitosterol, and conclude that cholesterol suppresses bilayer undulations more effectively than β-sitosterol

Influence of cholesterol and beta-sitosterol on the structure of EYPC bilayers

The influence of cholesterol and β-sitosterol on egg yolk phosphatidylcholine (EYPC) bilayers is compared. Different interactions of these sterols with EYPC bilayers were observed using X-ray diffraction. Cholesterol was miscible with EYPC in the studied concentration range (0-50 mol%), but crystallization of β-sitosterol in EYPC bilayers was observed at X ≥ 41 mol% as detected by X-ray diffraction. Moreover, the repeat distance (d) of the lamellar phase was similar upon addition of the two sterols up to mole fraction 17%, while for X ≥ 17 mol% it became higher in the presence of β-sitosterol compared to cholesterol. SANS data on suspensions of unilamellar vesicles showed that both cholesterol and β-sitosterol similarly increase the EYPC bilayer thickness. Cholesterol in amounts above 33 mol% decreased the interlamellar water layer thickness, probably due to "stiffening" of the bilayer. This effect was not manifested by β-sitosterol, in particular due to the lower solubility of β-sitosterol in EYPC bilayers. Applying the formalism of partial molecular areas, it is shown that the condensing effect of both sterols on the EYPC area at the lipid-water interface is small, if any. The parameters of ESR spectra of spin labels localized in different regions of the EYPC bilayer did not reveal any differences between the effects of cholesterol and β-sitosterol in the range of full miscibility