Lecithin Bilayers Research Articles

Spectral Characteristics and Functional Responses of Phospholipid Bilayers in the Terahertz Band.

Understanding the vibrational information encoded within the terahertz (THz) spectrum of biomolecules is critical for guiding the exploration of its functional responses to specific THz radiation wavelengths. This study investigated several important phospholipid components of biological membranes-distearoyl phosphatidylethanolamine (DSPE), dipalmitoyl phosphatidylcholine (DPPC), sphingosine phosphorylcholine (SPH), and lecithin bilayer-using THz time-domain spectroscopy. We observed similar spectral patterns for DPPC, SPH, and the lecithin bilayer, all of which contain the choline group as the hydrophilic head. Notably, the spectrum of DSPE, which has an ethanolamine head group, was different. Interestingly, density functional theory calculations confirmed that the absorption peak common to DSPE and DPPC at approximately 3.0 THz originated from a collective vibration of their similar hydrophobic tails. Accordingly, the cell membrane fluidity of RAW264.7 macrophages with irradiation at 3.1 THz was significantly enhanced, leading to improved phagocytosis. Our results highlight the importance of the spectral characteristics of the phospholipid bilayers when studying their functional responses in the THz band and suggest that irradiation at 3.1 THz is a potential non-invasive strategy to increase the fluidity of phospholipid bilayers for biomedical applications such as immune activation or drug administration.

High throughput onion-like liposome formation with efficient protein encapsulation under flash antisolvent mixing

Achieving a high encapsulation efficiency and loading capacity of proteins in lecithin-based liposomes has always been a challenge. Here, we use Flash Nano-Precipitation (FNP) to produce liposomes and investigated the encapsulation of model protein (Bovine Serum Albumin, BSA). Through rapid turbulent mixing, we obtained liposomes with small size, low polydispersity, and good batch repeatability at a high production rate. We demonstrated that the bilayer of liposomes prepared solely using lecithin was defective, which led to the fusion, and increased size and polydispersity. When cholesterol was added to reach a lecithin-to-cholesterol molar ratio of 5:3, a compact bilayer formed to effectively inhibit liposome fusion. The encapsulation efficiency and loading capacity of BSA was as high as ∼ 68% and ∼ 6% in lecithin-cholesterol liposome, respectively, far exceeding the values reported in the literature. Further study by Quartz Crystal Microbalance with Dissipation (QCM-D) revealed that the highly effective encapsulation was due to the rapid mutual adsorption between BSA and defective/curved lecithin double layers during the liposome formation. Such rapid mutual adsorption leads to the layer-by-layer assembly and formation of onion-like compact liposome structure as revealed by Cryo-TEM. This simple FNP method provides a scalable manufacturing approach for liposomes with efficient protein encapsulation. The revealed adsorption mechanism between protein and lecithin bilayers could also serve as a guide for similar studies.

On the role of pH and temperature on ground – and excited – state proton transfer of hydroxyflavones in lipidic bilayers of lecithin

Absorption and emission monitoring of bioactive flavonols, Hydroxyflavones (HFs), (3-HF, 3,6-diHF and 3,7-diHF), to explore their microenvironments as a function of pH and temperature in lipidic bi-layers of lecithin (EYPC), have been studied. The influence of lipidic bi-layers on the − OH groups deprotonation of HFs with several distribution in the vicinity of the polar phosphate groups of EYPC when pH changed as well as the position of −OH groups in the HFs structure on the excited-state intramolecular proton transfer (ESIPT), have been studied by fluorescence spectroscopy. It was found that at physiological pH, EYPC leads to the increase of the quantum yield of Tautomer fluorescence for HFs with multiple −OH groups. There is a temperature-dependent difference in the ESIPT process which takes place in HFs/EYPC systems. The findings are relevant for in vivo and in vitro studies of the oxidative stress process which involves cell membranes, where HFs are used as sensitive fluorescence probes.

Influence of humectants on the thermotropic behaviour and nanostructure of fully hydrated lecithin bilayers

Humectants are used widely in topical formulations as they provide cosmetic and health benefits to skin. Of particular interest to our laboratories is the interaction of humectants in phospholipid based topical skin care formulations. This study probed the effects of three exemplary humectants on a fully hydrated lecithin system (DPPC) by use of X-ray scattering and differential scanning calorimetry. While the three humectants affected the nanostructure of 1, 2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC, bilayers in a similar manner, leading to an increased membrane order, differences in the effect on the thermal behaviour of DPPC suggest that betaine and sarcosine interacted via a different mechanism compared to acetic monoethanolamide, AMEA. At concentrations above 0.4 M, betaine and sarcosine stabilised the gel phase by depletion of the interfacial water via the preferential exclusion mechanism. At the same time, a slight increase in the rigidity of the membrane was observed with an increase in the membrane thickness. Overall, the addition of betaine or sarcosine resulted in an increase in the pre- and main transition temperatures of DPPC. AMEA, on the other hand, decreases both transition temperatures, and although the interlamellar water layer was also decreased, there was evidence from the altered lipid chain packing, that AMEA molecules are present also at the bilayer interface, at least at high concentrations. Above the melting point in the fluid lamellar phase, none of the humectants induced significant structural changes, neither concerning the bilayer stacking order nor its overall membrane fluidity. An humectant-induced increase in the Hamaker constant is the most plausible explanation for the observed reduction of the inter-bilayer distances, both in the gel and fluid phase.

Preparation of Barije (Ferula gummosa) Essential Oil–Loaded Liposomes and Evaluation of Physical and Antibacterial Effect on Escherichia coli O157:H7

The aim of this study was to load liposomes with Barije (Ferula gummosa) essential oil (EO) and to evaluate their physical and antibacterial properties. Liposomes were produced with specific ratios of lecithin/cholesterol by thin-film hydration and sonication. The chemical composition of the EO was analyzed by gas chromatography and mass spectroscopy. The physical properties of the liposomes (particle size, polydispersity index, zeta potential, and encapsulation efficiency) were evaluated. The antimicrobial effects of these liposomes against Escherichia coli O157:H7 were determined based on the MIC and disk diffusion results. The effect of subinhibitory concentrations (sub-MICs) of EO against the growth of the bacterium over 24 h was evaluated before and after encapsulation. The major components of EO were β-pinene (60.84%) and α-pinene (9.14%). The mean liposome radius of EO-loaded liposomes was 74.27 to 99.93 nm, which was significantly different from that of the empty liposomes (138.76 nm) (P < 0.05). Addition of cholesterol to the lecithin bilayer increased the particle size and reduced the encapsulation efficiency (P < 0.05). The electrostatic stability of the empty liposomes was improved by adding cholesterol, but when the EO was replaced in the liposomes, there was no significant change in electrostatic stability of liposomes with cholesterol (P < 0.05). MICs were 14.5 μg/mL for the EO-loaded nanoliposomes containing 30 mg of lecithin and 30 mg of cholesterol and 10 μg/mL for nonencapsulated EO. This trend was confirmed by measuring the inhibition zone diameter. Sub-MICs of liposomal EO (containing 60 mg of lecithin) decreased bacterial levels to a greater degree than did free EO, especially at 50 and 75% of the MIC.

Natural emulsion gels and lecithin-based sorbents: A potential treatment method for organic spills on surface waters

Natural sorbents for the removal of a free toluene phase from water were made using lecithin, food-grade oils (canola, sunflower, safflower and corn oil) and water, or lecithin, hydroxystearic acid (HSA) and canola oil, or lecithin, HSA and soy wax. Lecithin (5 g), food-grade oils (5 mL), and water (5 mL) formed emulsions, in which clusters of water droplets were dispersed in oil, as probed using confocal microscopy and cryo-scanning electron microscopy (cryo-SEM). These emulsions were gel-like, with shear elastic moduli (G’) greater than the shear viscous moduli (G”). Emulsion gels obtained with lecithin, canola oil and water could absorb up to 47% (volume based) of toluene freely floating on deionised water in 20 h. G’ increased from 1621 ± 203 Pa to 6372 ± 168 Pa upon mixing with up to 20% of toluene (volume based), and decreased to 2130 ± 376 Pa and to 846 ± 60 Pa with 33% and 47% toluene (volume based), respectively. However, the gels remained cohesive enough to be recovered from water even with 47% toluene, facilitating it removal. The gels lost instead cohesiveness with 67% of toluene. Similar trends were observed with all other food-grade oils used and in the presence of CaCl2 salt. With 35 g/L NaCl and 33% toluene gels less cohesive than with DI or CaCl2 salt. Optical microscopy showed that lecithin formed thick, heterogeneous films at the oil-water interface in the absence of toluene. Toluene addition to lecithin in canola decreased the interfacial tension (as probed with the pendant drop method), rendered the lecithin interfacial films homogeneous and improved the miscibility between the oil and the water phase, as observed through confocal microscopy. Toluene addition also affected the lamellar swelling of lecithin bilayers, which were studied using Wide and Small Angle X-ray Scattering (WAXS and SAXS). Addition of HSA or HSA and soy wax to the emulsion gels increased their shear viscoelastic moduli before and after mixing with toluene. Gels comprised of HSA (0.5 g), lecithin (4.5 g), canola oil (2.5 mL) and water (5 mL) or of HSA (0.5 g), lecithin (3 g), soy wax (1.5 g) and water (5 mL) could absorb approximately 10 mL of toluene (i.e. 67% of the lecithin gel volume) in 20 h. Addition of HSA also increased the cohesiveness of gels with toluene and 35 g/L NaCl.

Effect of Sodium and Chloride Binding on a Lecithin Bilayer. A Molecular Dynamics Study.

The effect of ion binding on the structural, mechanical, dynamic and electrostatic properties of a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer in a 0.5 M aqueous NaCl solution is investigated using classical atomistic molecular dynamics simulation with different force-field descriptions for ion-ion and ion-lipid interactions. Most importantly, the repulsive Lennard–Jones parameters for the latter were modified, such that approximately similar binding of cations and anions to the lipid membrane is achieved. This was done to qualitatively improve the apparent ion-lipid binding constants obtained from simulations with the original force field (Berger lipids and GROMOS87 ions in combination with the SPC water model) in comparison to experimental data. Furthermore, various parameters characterizing membrane structure, elasticity, order and dynamics are analyzed. It is found that ion binding as observed in simulations involving the modified in comparison to the original force-field description leads to: (i) a smaller salt-induced change in the area per lipid, which is in closer agreement with the experiment; (ii) a decrease in the area compressibility and bilayer thickness to values comparable to a bilayer in pure water; (iii) lipid deuterium order parameters and lipid diffusion coefficients on nanosecond timescales that are very similar to the values for a membrane in pure water. In general, salt effects on the structural properties of a POPC bilayer in an aqueous sodium-chloride solution appear to be reproduced reasonably well by the new force-field description. An analysis of membrane-membrane disjoining pressure suggests that the smaller salt-induced change in area per lipid induced by the new force-field description is not due to the alteration of membrane-associated net charge, but must rather be understood as a consequence of ion-specific effects on the arrangement of lipid molecules.

Effect of triterpene and steroid saponins on lecithin bilayers

We describe the effect of four triterpene (α-hederin, hederacoside C, ammonium glycyrrhizate, Quillaja bark saponins (QBS)) and one steroid (digitonin) saponins on lecithin and lecithin-cholesterol (4:1mol/mol) model bilayers. For this purpose the Giant Unilamellar Vesicles (GUV), Large Unilamellar Vesicles (LUV) and Supported Lipid Bilayers (SLB) were probed with fluorescence microscopy, dynamic light scattering and neutron reflectivity, respectively. In most cases the results provided from the three techniques were consistent. In cholesterol-free systems, only α-hederin was able to penetrate SLB and induce macroscopic changes in LUV and GUV. Digitonin can adsorb to a small extent on the surface of cholesterol-free SLB, but does not affect macroscopically the LUV and GUV. In the presence of cholesterol, not only α-hederin but also QBS and digitonin affect the liposomes both microscopically and macroscopically. The present data clearly confirm that cholesterol significantly enhances the effect of membrane-active saponins on bilayers and that the effect on model bilayers correlates well with the membrane-activity of the saponins.

The impact of model peptides on structural and dynamic properties of egg yolk lecithin liposomes - experimental and DFT studies.

Electron spin resonance (ESR), (1) H-NMR, voltage and resistance experiments were performed to explore structural and dynamic changes of Egg Yolk Lecithin (EYL) bilayer upon addition of model peptides. Two of them are phenylalanine (Phe) derivatives, Ac-Phe-NHMe (1) and Ac-Phe-NMe2 (2), and the third one, Ac-(Z)-ΔPhe-NMe2 (3), is a derivative of (Z)-α,β-dehydrophenylalanine. The ESR results revealed that all compounds reduced the fluidity of liposome's membrane, and the highest activity was observed for compound 2 with N-methylated C-terminal amide bond (Ac-Phe-NMe2 ). This compound, being the most hydrophobic, penetrates easily through biological membranes. This was also observed in voltage and resistance studies. (1) H-NMR studies provided a sound evidence on H-bond interactions between the studied diamides and lecithin polar head. The most significant changes in H-atom chemical shifts and spin-lattice relaxation times T1 were observed for compound 1. Our experimental studies were supported by theoretical calculations. Complexes EYLAc-Phe-NMe2 and EYLAc-(Z)-ΔPhe-NMe2 , stabilized by NH⋅⋅⋅O or/and CH⋅⋅⋅O H-bonds were created and optimized at M06-2X/6-31G(d) level of theory in vacuo and in H2 O environment. According to our molecular-modeling studies, the most probable lecithin site of H-bond interaction with studied diamides is the negatively charged O-atom in phosphate group which acts as H-atom acceptor. Moreover, the highest binding energy to hydrocarbon chains were observed in the case of Ac-Phe-NMe2 (2).

Engineering of a lipid-polymer nanoarchitectural platform for highly effective combination therapy of doxorubicin and irinotecan.

We developed a highly stable lipid-polymer nanoarchitectural platform for effective combination therapy of doxorubicin and irinotecan in the polyelectrolyte complex nanoparticle core, followed by incorporation of the whole assembly into a lecithin bilayer. It shows great potential for the treatment of a broad range of cancers.

Formulation of nanoliposomal vitamin d3 for potential application in beverage fortification.

Vitamin D, a liposoluble vitamin has many benefits on health. Encapsulation of bioactives in lipid-based carrier systems like nanoliposomes preserves their native properties against oxidation over time along with providing its stable aqueous dispersion. In the current study, vitamin D3 nanoliposomes were prepared using thin-film hydration-sonication method and fully characterized by different instrumental techniques. According to FTIR and DSC results, no interaction was observed between encapsulated nutraceutical and liposome constituents. The particle size and size distribution (Span value) were calculated 82-90 nm and 0.70-0.85, respectively. TEM analysis showed nano sized globular and bilayer vesicles. In all formations, the encapsulation efficiency of vitamin D3 was calculated more than 93%. Addition of cholesterol to lecithin bilayer increased the negative zeta potential from -29 to -43mV. The results of this study concluded that the liposomal nanoparticles may be introduced as a suitable carrier for fortification of beverages with vitamin D3.

Structure and Phase Equilibria of the Soybean Lecithin/PEG 40 Monostearate/Water System

PEG stearates are extensively used as emulsifiers in many lipid-based formulations. However, the scheme of the principles of the lipid-surfactant polymer interactions are still poorly understood and need more studies. A new phase diagram of a lecithin/PEG 40 monostearate/water system at 30 °C is reported. First, we have characterized the binary PEG 40 monostearate/water system by the determination of the critical micelle concentration value and the viscous properties. Then, the ternary phase behavior and the influence of phase structure on their macroscopic properties are studied by a combination of different techniques, namely, optical microscopy, small-angle X-ray scattering, differential scanning calorimetry, and rheology. The phase behavior is complex, and some samples evolve even at long times. The single monophasic regions correspond to micellar, swollen lamellar, and lamellar gel phases. The existence of extended areas of phase coexistence (hexagonal, cubic, and lamellar liquid crystalline phases) may be a consequence of the low miscibility of S40P in the lecithin bilayer as well as of the segregation of the phospholipid polydisperse hydrophobic chains. The presence of the PEG 40 monostearate has less effect in the transformation to the cubic phase for lecithin than that found in other systems with simple glycerol-based lipids.

Recording ion channels across soy-extracted lecithin bilayer generated by water-soluble quantum dots

We report on the quantum dot (QD)-induced ion channels across a soya-derived lecithin bilayer supported on a laser drilled of ~100 μm aperture of cellulose acetate substrate that separates two electrolytic chambers. Adequate current bursts were observed when the bilayer was subjected to a gating voltage. The voltage-dependent current fluctuation, across the bilayer, was attributed to the insertion of ~20 nm sized water-soluble CdSe QDs, forming nanopores due to their spontaneous aggregation. Apart from a closed state, the first observable conductance levels were found as 6.3 and 11 nS, as for the respective biasing voltages of −10 and −20 mV. The highest observable conductance states, at corresponding voltages were ~14.3 and 21.1 nS. Considering two simplified models, we predict that the non-spherical pores (dnspore) can be a better approximation over spherical nanopores (dspore) for exhibiting a definite conductance level. At times, even dnspore ≤ 4dspore and that the non-spherical nanopores were associated with a smaller No. of QDs than the case for spherical nanopores, for a definite conductance state. It seems like the current events are partly stochastic, possibly due to thermal effects on the aggregated QDs that would form nanopores. The dwell time of the states was predicted in the range of 384–411 μs. The ion channel mechanism in natural phospholipid bilayers over artificial ones will provide a closer account to understand ion transport mechanism in live cells and signaling activity including labelling with fluorescent QDs.

Mass-Action Model Analysis of the Apparent Molar Volume and Heat Capacity of Pluronics in Water and Liposome Suspensions at 25 °C

Pluronics are block copolymers composed of a central block of polypropylene oxide and two side chains of polyethylene oxide. They are used in water to generate aggregates and gels or added to phospholipid suspensions to prepare microparticles for drug delivery applications. The structure of these systems has been widely investigated. However, little is known about the mechanisms leading to these structures. This investigation compares the apparent molar volumes and heat capacities of Pluronics F38, F108, F127, P85, P104, and P103 at 25 °C in water and in the presence of lecithin liposomes. The changes in molar volumes, heat capacities, and enthalpies generated by a mass-action model are in good agreement with the loss of hydrophobic hydration of the polypropylene oxide central block of the Pluronics. However, the molecularity of the endothermic transitions is much smaller than the aggregation numbers reported in the literature for the same systems. It is suggested that Pluronics go through dehydration of their central block to form unimolecular or small entities having a hydrophobic polypropylene oxide core. In water, these entities would assemble athermally to form larger aggregates. In the presence of liposomes, they would be transferred into the hydrophobic lecithin bilayers of the liposomes. Light transmission experiments suggest that the liposome suspensions are significantly altered only when the added Pluronics are in the dehydrated state.

Gaussian deconvolution: a useful method for a form-free modeling of scattering data from mono- and multilayered planar systems

A new method for analysis of scattering data from lamellar bilayer systems is presented. The method employs a form-free description of the cross-section structure of the bilayer and the fit is performed directly to the scattering data, introducing also a structure factor when required. The cross-section structure (electron density profile in the case of X-ray scattering) is described by a set of Gaussian functions and the technique is termed Gaussian deconvolution. The coefficients of the Gaussians are optimized using a constrained least-squares routine that induces smoothness of the electron density profile. The optimization is coupled with the point-of-inflection method for determining the optimal weight of the smoothness. With the new approach, it is possible to optimize simultaneously the form factor, structure factor and several other parameters in the model. The applicability of this method is demonstrated by using it in a study of a multilamellar system composed of lecithin bilayers, where the form factor and structure factor are obtained simultaneously, and the obtained results provided new insight into this very well known system.

Linear free-energy relationships for water/hexadec-1-ene and water/deca-1,9-diene partitions, and for permeation through lipid bilayers; comparison of permeation systems

Linear free energy relationships based on Abraham descriptors have been obtained for partition from water and the gas phase into hexadec-1-ene and into deca-1,9-diene, and for permeation through egg lecithin bilayers. Comparison with equations for partition into a large number of organic solvents shows that hexadec-1-ene and deca-1,9-diene are excellent models for permeation through egg lecithin bilayers. Wet octanol is a poor model, as are all polar organic solvents. The egg lecithin bilayer is non-polar and has only weak hydrogen bond acidity and weak hydrogen bond basicity. Comparison of equations for permeation through egg lecithin bilayers, through the human intestinal membrane, through the blood-brain membrane and through human skin shows that these four permeation processes are chemically far apart. It is not possible to obtain any general model for permeation: each permeation process requires a different model system.

Sponge Mesoporous Silica Formation Using Disordered Phospholipid Bilayers as Template

Lecithin/dodecylamine/lactose mixtures in ethanol/aqueous media led to the formation of sponge mesoporous silica (SMS) materials by means of tetraethoxysilane (TEOS) as silica source. SMS materials show a "sponge-mesoporous" porosity with a pore diameter of about 5-6 nm, in accordance to the length of a lecithin bilayer. SMS synthesis was developed to create a new class of powerful biocatalysts able to efficiently encapsulate enzymes by adding a porosity control to the classical sol-gel synthesis and by using phospholipids and lactose as protecting agents for the enzymes. In the present study, the formation of SMS was investigated by using electron paramagnetic resonance (EPR) probes inserted inside phospholipid bilayers. The influence of progressive addition of each component (ethanol, dodecylamine, lactose, TEOS) on phospholipid bilayers was first examined; then, the time evolution of EPR spectra during SMS synthesis was studied. Parameters informative of mobility, structure, order, and polarity around the probes were extracted by computer analysis of the EPR line shape. The results were discussed on the basis of solids characterization by X-ray diffraction, nitrogen isotherm, transmission electron microscopy, and scanning electron microscopy. The results, together with the well-known ability of ethanol to promote membrane hemifusion, suggested that the templating structure is a bicontinuous phospholipid bilayer phase, shaped as a gyroid, resulting of multiple membrane hemifusions induced by the high alcohol content used in SMS synthesis. SMS synthesis was compared to hexagonal mesoporous silica (HMS) synthesis accomplished by adding TEOS to a dodecylamine/EtOH/water mixture. EPR evidenced the difference between HMS and SMS synthesis; the latter uses an already organized but slowly growing mesophase of phospholipids, never observed before, whereas the former shows a progressive elongation of micelles into wormlike structures. SMS-type materials represent a new class of biocompatible materials and open a bright perspective for biomolecule processing for pharmaceutical, biocatalysis, biosensors, or biofuel cell applications.

Voltammetrically Controlled Electron Transfer Reactions from Alkanethiol Modified Gold Electrode Surfaces to Low Molecular Weight Molecules Deposited within Lipid (Lecithin) Bilayers

A procedure was developed for initiating electron transfer from a gold electrode to a low molecular weight electron acceptor present inside supported lipid (lecithin) bilayers, followed by further electron transfer to an electron acceptor present in an aqueous solution. The electron acceptors present in the lecithin bilayers and aqueous phase were 7,7,8,8-tetracyanoquinodimethane (TCNQ) and [Fe(III)(CN)(6)](3-), respectively. A polished planar gold disk electrode was first coated via self-assembly procedures with an alkanethiol monolayer. A phospholipid layer consisting of multiple bilayers of lecithin containing TCNQ was subsequently deposited onto the alkanethiol monolayer. The Au/alkanethiol/lecithin-TCNQ electrode was placed in an aqueous solution containing various amounts of [Fe(III)(CN)(6)](3-) and [Fe(II)(CN)(6)](4-), with 0.5 M KCl as the supporting electrolyte. In the absence of TCNQ inside the alkanethiol/lecithin layers, only a small background current was observed. When TCNQ was included in the alkanethiol/lecithin layers, the voltammetry showed features typical of a catalytic process, due to the TCNQ being reduced to TCNQ(-*) within the lecithin bilayers and then undergoing oxidation back to TCNQ via interaction with [Fe(III)(CN)(6)](3-) at the lecithin-aqueous solution interface. The procedures for preparing the alkanethiol/lecithin-TCNQ coatings were optimized in order to obtain the most reproducible voltammetric response. Experiments were also performed using tetrathiafulvalene (TTF) as an electron donor in the lipid bilayer phase.

Dopant-Mediated Interactions in a Lecithin Lamellar Phase

Interactions induced by dopants in a lamellar phase constructed from the lecithin and water are analyzed by the small angle x-ray scattering (SAXS) technique. From SAXS patterns, scattering peak or curve shape changes disclose information on phase structure as well as the interactions between dopant and host matrices. At a certain concentration, two amphiphilic tri-block copolymers (Pluronic P123 and F127) as dopants squeeze themselves into the lecithin bilayers with PPO hydrophobic blocks and produce various effects on the lamellar phase depending on the length of PEO hydrophilic groups. Coexistence of two different lamellar phases is observed in P123-doped systems.

Preferential location of lidocaine and etidocaine in lecithin bilayers as determined by EPR, fluorescence and 2H NMR

We have examined the effect of the uncharged species of lidocaine (LDC) and etidocaine (EDC) on the acyl chain moiety of egg phosphatidylcholine liposomes. Changes in membrane organization caused by both anesthetics were detected through the use of EPR spin labels (5, 7 and 12 doxyl stearic acid methyl ester) or fluorescence probes (4, 6, 10, 16 pyrene-fatty acids). The disturbance caused by the LA was greater when the probes were inserted in more external positions of the acyl chain and decreased towards the hydrophobic core of the membrane. The results indicate a preferential insertion of LDC at the polar interface of the bilayer and in the first half of the acyl chain, for EDC. Additionally, 2H NMR spectra of multilamellar liposomes composed by acyl chain-perdeutero DMPC and EPC (1:4 mol%) allowed the determination of the segmental order ( S mol) and dynamics ( T 1) of the acyl chain region. In accordance to the fluorescence and EPR results, changes in molecular orientation and dynamics are more prominent if the LA preferential location is more superficial, as for LDC while EDC seems to organize the acyl chain region between carbons 2–8, which is indicative of its positioning. We propose that the preferential location of LDC and EDC inside the bilayers creates a “transient site”, which is related to the anesthetic potency since it could modulate the access of these molecules to their binding site(s) in the voltage-gated sodium channel.