Lecithin Membranes Research Articles

Orientation of Hemicyanine Dye in Lipid Membrane Measured by Fluorescence Interferometry on a Silicon Chip

Amphiphilic hemicyanine dyes are fluorescent probes for voltage transients in nerve cells. Their sensitivity is assumed to be related with an intramolecular charge shift along the oriented chromophore that interacts with the electrical field across the cell membrane. Here we report on a measurement of the molecular orientation of the hemicyanine dye Di8ANEPPS in a lecithin membrane. We took advantage of the features of dipole radiation in front of a mirror. The fluorescence intensity of a stained membrane on oxidized silicon was measured as a function of the thickness of silicon dioxide up to 1000 nm and fitted with an electromagnetic theory accounting for the interference of the exciting light, for the interference of the emitted light and for the change of fluorescence lifetime. We found an angle of 37.8 ± 1.6° between the transition dipole moment and the membrane normal for an uniaxial cone model of the angular distribution function, with an order parameter 〈P2〉 = 0.44 similar to the hydrocarbon chains...

A study of the adsorption of bile salts onto model lecithin membranes

Bile salts play a central role in the promotion of cytotoxicity or cytoprotection. In this study, we examined the interaction of different bile salts with egg lecithin vesicles using 31P NMR spectroscopy. The effects of taurochenodeoxycholate (TCDC or 3α,7α,-dihydroxy-5β-cholanoyl taurine, of tauroursodeoxycholate (TUDC) or 3α,7β,-dihydroxy-5β-cholanoyl taurine) and of tauroβmuricholate (TβMC or 3α,6β,7β,-trihydroxy-5β-cholanoyl taurine), at various bile salt/lecithin ratios, were evaluated. From the percent 31P present in vesicles, the micellar capacity of bile salts to dissolve lecithin was determined. TCDC was incorporated into vesicles for bile salt/lecithin molar ratios lower than 0.62 while for TUDC and TβMC, the critical ratios were 0.94 and 1.1, respectively. The 31P chemical shift change was markedly larger with TCDC than that found with TUDC and TβMC. In order to specify the low interactions observed between hydrophilic bile salts and lecithin, we determined the intermixed micellar/vesicular bile salt concentrations (IMVC) of bile salt/lecithin solutions using rapid ultrafiltration–centrifugation for TUDC and lecithin solubility measurements for TUDC, TβMC and TCDC. The low IMVC obtained indicate that even hydrophilic bile salts were bound mostly to the mixed aggregates. In conclusion, the low disturbance in the arrangement of lecithin induced by TUDC and TβMC appears to be due to the interfacial location of these bile salts. TCDC (7α OH) penetrates more deeply in the membrane than the 7β hydroxylated bile salts that may partly explain the distinct damaging effects of these bile salts.

Control of the size and photochemical properties of Q-CdS particles attached to the inner and/or outer surface of the lecithin vesicle bilayer membrane by the nature of its precursors

Cadmium sulfide nanoparticles have been generated in situ on the inner and/or outer surfaces of monolamellar lecithin vesicles. Chemical agents, strongly chelating or bounding the Cd 2+ cations, are shown to influence dramatically the size of CdS nanoparticles as well as their optical, luminescence and photochemical properties. The more stable is a Cd 2+-containing complex created by these chelating agents, the smaller are the CdS particles formed. In case of CdCl 2 and Cd(NO 3) 2 as the CdS precursors inside the vesicles, a steady rise in the size of growing CdS nanoparticles is observed, while in case of K 2[CdEDTA] the accumulation of mass of growing CdS occurs without a change in the nanoparticles size. The size of CdS particles and their initial growth rate depend also on pH of the vesicle suspension, modification of the lipid membrane, being, however, independent of the CdCl 2 concentration, if CdCl 2 is the CdS precursor. In the presence of a sacrificial electron donor (S 2− or EDTA), the bandgap irradiation of the lipid-vesicle-supported CdS particles yields charge separation and electron transfer to lipophilic cetylviologen bications, C 16V 2+, embedded into the lipid bilayer. The initial quantum yield of C 16V ⋅+ formation depends on the topology of vesicular systems and CdS localization on the inner or outer surface of the lecithin membrane. Presence of EDTA anions enhances sufficiently the initial quantum yield of vectorial electron phototransfer from CdS nanoparticles to cetylviologen.

A Joint Effect of Cationic and Anionic Amphiphilic Compounds on the Desorption of Calcium Ions from Lecithin Liposome Membranes

Abstract The aim of the work was to determine the synergism and antagonism of mixtures of the cationic amphiphilic compounds: N-benzyl-N,N-dimethyl-N-tetradecylammonium chloride (BD TA), N-benzyl-N,N-dimethyl-N-dodecylammonium chloride (BDDA), N-methyl-N-te-tradecyl-morpholinium bromide (MTM), N,N,N-trimethyl-N-tetradecylammonium bromide (TMTA) and those of tripropyltin chloride in a mixture with amphiphilic anionic compounds (a homologous series of sodium alkylsulfonates with n = 2, 4, 6, 8, 10, 12 and 14 alkyl carbon atoms) in the process of calcium ion desorption from liposome lecithin membranes. Radioactive labels and spin labels were used in the investigations. All compounds studied caused an increase in the kinetic rate constant of calcium ion desorption from liposome membranes with increasing concentration. In case of mixtures containing cationic and anionic compounds both synergism and antagonism were observed. It was shown that the regulatory effect depended on the properties of both cationic and anionic compounds. A mixture of the most effective cationic compound (BDTA) with each of the anionic compounds decreased the effect. Mixtures of the remaining ammonium com­ pounds with sodium alkylsulfonates produced both synergism and antagonism. Anionic com­ pounds with short chains increased, and with longer chains decreased efficiency, while com­ pounds with comparable chains caused totally blocked desorption. A mixture of an organometallic compound having three short chains with anionic compounds gave a reversed effect: short-chain compounds caused a decreased and those with long-chains -increased efficiency of tripropyltin chloride. Studies with spin labels supported the conclusion that the most important factor responsi­ ble for the regulatory effect is the molecular shape of the complexes formed in a mixture of both groups of compounds -a factor that determines membrane packing density

Destruction of membranes by merocyanine 540

The effect of a photosensitizer merocyanine 540 (MC 540) on the bilayer structure of model phospholipid membranes was studied using diphenylhexatriene (DPH) fluorescence anisotropy and light-scattering techniques. A pronounced reduction of DPH anisotropy decay within 60 min of DPH incubation was induced by the presence of MC 540 in lecithin membranes. With increasing MC 540 concentrations the original fluorescence peak of DPH in liposomes at 429 nm became less distinguishable and a new fluorescence peak at 403 nm was created. The presence of MC 540 induced also a concentration dependent decrease of the scattered light intensity. The observed changes could be interpreted in terms of disturbing the bilayer structure in the presence of MC 540.

Electrochemical studies of lipophilic ion transport through BLM. The influence of sterols on its transport

AbstractCyclic voltammetry was employed to study the influence of sterols on the lipophilic ion transport through the BLM. The mole fraction of the sterols (cholesterol, oxidized cholesterol), as referred to total lipid, was varied in a range of 0–0.8. Data demonstrate that a thin‐layer model is suitable to this BLM system, By this model, the number of charges transported per lipophilic ion, the concentration of the ion in the membrane hulk phase and the aqueous/membrane phase partition coefficient could be calculated. These parameters proved that sterols had an obvious influence on the lipophilic ion transport. Cholesterol had a stronger influence on the ion transport than oxidized cholesterol. Its incorporation into egg lecithin membranes increased the partition coefficientβ of the ion up to more than 3‐fold. Yet, oxidized cholesterol incorporated into egg lecithin membranes only increased the β up to less than 2‐fold, and the β had no great variation at different oxidized cholesterol mole fractions. The higher β obtained was partly due to the trace amount of solvent existing in the core of the lipid bilayers. At the different sterol mole fractions, combining the change of β with the change of peak current, we also concluded that sterols had somewhat inhibiting effect on the ion transport at the higher sterols mole fraction (> 0.4). These results are explained in terms of the possible change of dipole potential of the membrane produced by sterols and the decrease of the membrane fluidity caused by the condensation effect of sterols and the thinning effect caused by sterols. The substituting group (in the oxidized cholesterol) had some inhibiting effects on the ion transport at higher mole fractions (oxidized cholesterol mole fraction > 0.4).

A Membrane Protein Model: Polypeptides with Four α-Helix Bundle Structure on 5,10,15,20-Tetrakis[2-(carboxymethoxy)phenyl]porphyrin

Abstract A novel template for the polypeptide–porphyrin hybrid, 5,10,15,20-tetrakis[2-(ethoxycarbonylmethoxy)phenyl]porphyrin (2) was synthesized in 17% yield. Four protected carboxyl groups are installed in 2 at the ortho-phenyl groups as the anchoring points, to which the N-termini of the polypeptides can be linked after the hydrolysis. Thus, 2 is a new analog of the porphyrin template tetrakis[2-(methoxycarbonyl)phenyl]porphyrin. The atropisomerization of 2 was much more rapid than that of tetrakis[2-(methoxycarbonyl)phenyl]porphyrin: At 353 K, 2 reached their equilibrium within 15 min. Such atropisomeric flexibility of 2 allows the self-organization of the α-helical peptide segments which are connected to 2. After the hydrolyses of the ethyl ester groups of 2, four α-helical 21-peptides, H–(–Gln–Leu–Leu–Gln–Ala–Leu–Ala–)3–NHCH2CH2OH were combined through the amide bonds to yield a new polypeptide–porphyrin hybrid (12). The polypeptide moieties of 12 showed typical α-helix profiles on circular dichroism measurements in methanol–water (3/1, v/v) and in Tris·HCl buffer solution. Thus, the four α-helix polypeptides are considered to fold into a bundle structure on the porphyrin template through the hydrophobic interaction. The circular dichroism spectrum of 12 in methanol showed an induced Cotton effect at the porphyrin region, and the CD band was symmetrically split. The hybrid (12) was also successfully incorporated into the egg yolk lecithin membrane almost quantitatively. When the molar ratio of egg yolk lecithin/12 was 500/1, the α-helix structure of the peptide segments in 12 was completely retained in the vesicles.

Complexation of lecithin with cationic polyelectrolytes: "Plastic membranes" as models for the structure of the cell membrane?

The complexation of bilayer-forming lipids, dihexadecyl phosphate (DHP) and soja-lecithin, with a cationic polyelectrolyte (PDADMAC) results in stable, highly ordered mesomorphous materials. For the DHP complex, a close to perfect L β ' morphology is found with SAXS. The increase of the phase transition temperature from T c = 66 °C for the free DHP membranes toward T c = 84.4 °C for the polyelectrolyte-lipid complex reflects the increased membrane stability due to polymeric counterions. Due to an extremely high glass transition of the ionic interlayers, the DHP complex is a nonplastic and brittle solid. The lecithin complex with its mixture ofhead groups and tail lengths exhibits, opposite to its clean synthetic counterpart, a quite unconventional phase structure where the stack of lamellar bilayers undulates with very high amplitudes. A similar undulated structure has recently been postulated for the natural lecithin membrane 1-3 and is obviously necessary for some biophysical membrane functions. In addition, a remarkably improved mechanical behavior of the lecithin-complex film paralleled by the depression of the glass transition of the ionic layers to T g = 10 °C is observed which allows large amplitude deformation, mechanical orientation as well as thermomechanical processing of the complex. Such systems can be understood as plastic membranes, are comparably cheap, and might be interesting as materials themselves. The observation of undulations as well as the unexpected good mechanical properties of the polymer-lecithin complex underlines that such three-dimensional materials in the bulk may act as model systems for the special properties of lecithin mesophases which arise from an appropriate mixture of tails and head groups, optimized by evolution processes.

Tirilazad mesylate protects stored erythrocytes against osmotic fragility

The hypoosmotic lysis curve of freshly collected human erythrocytes is consistent with a single Gaussian error function with a mean of 46.5 ± 0.25 mM NaCl and a standard deviation of 5.0 ± 0.4 mM NaCl. After extended storage of RBCs under standard blood bank conditions the lysis curve conforms to the sum of two error functions instead of a possible shift in the mean and a broadening of a single error function. Thus, two distinct sub-populations with different fragilities are present instead of a single, broadly distributed population. One population is identical to the freshly collected erythrocytes, whereas the other population consists of osmotically fragile cells. The rate of generation of the new, osmotically fragile, population of cells was used to probe the hypothesis that lipid peroxidation is responsible for the induction of membrane fragility. If it is so, then the antioxidant, tirilazad mesylate (U-74,006f), should protect against this degradation of stored erythrocytes. We found that tirilazad mesylate, at 17 μM (1.5 mol% with respect to membrane lecithin), retards significantly the formation of the osmotically fragile RBCs. Concomitantly, the concentration of free hemoglobin which accumulates during storage is markedly reduced by the drug. Since the presence of the drug also decreases the amount of F 2-isoprostanes formed during the storage period, an antioxidant mechanism must be operative. These results demonstrate that tirilazad mesylate significantly decreases the number of fragile erythrocytes formed during storage in the blood bank.

Ultra‐Long‐Duration Local Anesthesia Produced by Injection of Lecithin‐Coated Tetracaine Microcrystals

This study was designed to determine if microencapsulated tetracaine would provide a longer duration of local anesthesia than nonmicroencapsulated (neat) tetracaine. Local anesthesia was determined by monitoring the response of the rat to tail clamping after the installation of a subcutaneous ring block. Ten percent microencapsulated tetracaine was found to provide local anesthesia of the tail for a 43-hour duration. Ten percent tetracaine solution was toxic. One percent tetracaine solution provided a tail block lasting 8 hours. Lecithin membranes without drug provided no block. This study demonstrates that lecithin-coated tetracaine microcrystals produce a local anesthetic effect that is ultra-long in duration, reversible, and not systemically toxic.

Tumoristatic Activity of Liposomes Reconstituted from Tumor Associated Antigens and Interleukin 2 for Immunotherapy of Fibrosarcomas in BALB/C MICE

AbstractHuman Interleukin 2 (IL 2) was entrapped into liposomes prepared from egg lecithin and plasma membranes of fibrosarcoma cells, including tumor associated antigens (TAA). The animal model was the Balb/c mouse. The efficiency of interleukin incorporation by the dehydration/rehydration technique was 51% measured with radiolabelled IL 2. The inhibition of tumor growth by the TAA-presenting liposomes was studied in syngeneic mice which had received the tumor subcutaneously. Peritumor injections of liposomes containing both IL 2 and TAA inhibited the tumor growth significantly.- With lower doses of this special liposomal IL 2, the inhibition was more pronounced than with IL 2 alone. In addition, systemic therapeutic effects on contralateral untreated tumors were discernible.

Nature of alcohol and anesthetic action on cooperative membrane equilibria.

A generalized, colligative thermodynamic framework is used to treat the action of solutes on cooperative membrane equilibria. Configurational entropy, the randomness imparted by solutes through the partitioning or mixing process, is implicated as the energetic driving force for the action of anesthetics on cooperative membrane equilibria. The equilibria predicted to be most sensitive to solute action--in which the dilute solute causes a perturbation equivalent to a large change in temperature--are (1) low-enthalpy processes that coincide with (2) large partitioning differences between states. The model stresses that solutes do not act at a single site, but on both states in an equilibrium, and that the perturbation is determined by the difference in entropy. Evidence for the thermodynamic framework is obtained from the partitioning behavior of the general anesthetic 1-hexanol into a model lecithin (DMPC; 1,2-dimyristoyl-sn-glycero-3-phosphocholine) membrane as a function of temperature and alcohol concentration. The low-enthalpy equilibrium between the gel (L beta') and ripple states (P beta') (pretransition) is more sensitive to 1-hexanol than the high-enthalpy equilibrium between the ripple (P beta') and fluid bilayer states (L alpha) (main transition). The perturbations of both equilibria are accurately described by the colligative thermodynamic framework. The results suggest that alcohols and anesthetics act through entropy to upset the natural thermal balance that maintains native membrane architecture.

Sucrose influence on lecithin and polypyrrole lecithin bilayer membranes

Lecithin and polypyrrole+lecithin membranes were coated with sucrose from a water solution. Changes of the membrane properties were investigated. A significant increase in the mechanical membrane stability was observed. The optimum sucrose concentration was determined.

Sucrose influence on lecithin and polypyrrole lecithin bilayer membranes

Lecithin and polypyrrole+lecithin membranes were coated with sucrose from a water solution. Changes of the membrane properties were investigated. A significant increase in the mechanical membrane stability was observed. The optimum sucrose concentration was determined.

A statistical mechanical model of the pre- and subtransitions of lecithin membranes

A statistical mechanical model with experimentally proved facts as starting points is presented. This model explains on molecular level, the pre- and subtransitions appearing in lipid membranes. The model describes the main features of the transitions, the hysteresis of the subtransition and the mobility changes of the heads and chains at these transitions. The model was expanded for phosphatidylcholine homologues with arbitrary chain lengths, and a qualitative agreement in the case of pretransition as far as a quantitative one for the subtransition were found.

Pentachlorophenol-induced change of ζ-potential and gel-to-fluid transition temperature in model lecithin membranes

We have determined ζ-potentials for dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) membranes by measuring the electrophoretic mobility of multilayered vesicles and the temperatures of the gel-to-ripple-to-fluid phase transitions of sonicated vesicles by a photometric method. Some conclusions are: (1) The ζ-potentials of DMPC and DPPC vesicles become negative due to adsorption of ionized pentachlorophenol (PCP), (2) their magnitude changes, step-like, on gel-to-fluid transition and (3) the temperature of the step-like change in ζ-potential decreases with an increase in PCP concentration. (4) PCP exhibits a large effect on membrane structure: It induces an isothermal phase change from the ordered to disordered state, which is enhanced by monovalent salt in the aqueous phase. (5) Both ionized and unionized PCP decrease the melting phase transition temperature and abolish the pretransition, (6) the unionized species increases the melting transition width and (7) the ionized species is more potent in abolishing the pretransition. (8) The shorter chain lipid (DMPC) is more sensitive to the presence of PCP; the maximum decrease in ΔT t is 13 K (DMPC) and 7 K (DPPC) in the presence of ionized PCP. We have shown experimentally, by comparing the ΔT t from photometric studies with the density of adsorbed PCP derived from ζ-potential isotherms, that (9) the shift of the melting phase transition temperature increases linearly with the density of adsorbed PCP. (10) In contrast to membranes made of negatively charged lipids, the transition temperature of DMPC and DPPC membranes in the presence of PCP further decreases in the presence of monovalent salt. The salt effect is due to screening of the membrane surface leading to enhanced adsorption of ionized PCP and a depression in transition temperature. (11) It is shown that both the adsorption and the changes of gel-to-fluid phase transition temperature can be described in terms of the Langmuir-Stern-Grahame model and (12) proposed that future studies of membrane toxicity of PCP should be focused on its pH dependence.

Mutual adhesion of lecithin membranes at ultralow tensions

We present an extensive light-microscopic study of mutual adhesion of egg (and dimyristoyl) lecithin bilayers in highly swollen samples, including adhesion brought about by osmotic inflation of vesicles. The lateral tensions associated with adhesion, if below ca. 3 x 10-4 dyn cm-1 , could be read from a rounding of the membrane next to the contact area. The contact angle of symmetric adhesion, i.e. of two membranes under equal tension, had a maximum of 45°. While showing some scatter, it did not seem to depend on tension down to 3 x 10-6 dyn cm-1, the lowest tension observed. The maximum contact angle of single membranes adhering to bundles of membranes was near 70°. The data indicate that mutual adhesion of lecithin membranes is always induced by lateral tension. The constancy of the contact angles appears to be compatible with undulation theory, but their magnitude compels us to postulate an unknown, optically unresolvable roughness of lecithin membranes which serves as an area reservoir.

Structural changes in vesicle membranes and mixed micelles of various lipid compositions after binding of different bile salts

Binding equilibria of common bile salts (BS) and different mixtures of membrane lipids were correlated with BS-induced structural changes of large unilamellar vesicles, with transition of vesicles to mixed micelles (MM), and with successive transformations of MM. At very low BS concentrations, in the outer vesicle monolayer definite BS/lipid aggregates are formed, the size and BS binding strength of which depend on the BS and lipid species involved. At increasing BS concentrations, binding to the membranes is hampered, and above a critical BS content, membrane stress due to asymmetric BS binding leads to formation of transient membrane holes, as shown by inulin release from the vesicles. Independent of the BS and lipid species, membrane solubilization starts at a ratio r = 0.3 of bound BS/lipid. Increasing phosphatidylserine, phosphatidylethanolamine, and cholesterol contents stabilize the lecithin membrane against BS to different degrees and in different ways, whereas the destabilization by sphingomyelin is probably due to the enhancement of the membrane gel-liquid transition temperature. Conjugation of the BS with glycine or taurine has a modulating effect on membrane hole formation, rather than on lipid solubilization. Diphenylhexatriene fluorescence anisotropy indicates a BS-induced drop of the internal membrane order and its restoration during membrane solubilization. At higher concentrations ursodeoxycholate induces additional condensation, whereas the other BS cause internal disorder in the MM. Above ratios r of approximately 8:1, we found a release of BS from these MM and suggest a rodlike structure for them. The results were discussed with respect to BS/membrane interactions during lipid excretion from the liver cell.

NMR study of the interactions of polymyxin B, gramicidin S, and valinomycin with dimyristoyllecithin bilayers

The interactions of three polypeptide antibiotics (polymyxin B, gramicidin S, and valinomycin) with artificial lecithin membranes were studied by nuclear magnetic resonance (NMR). Combination of 31P and 2H NMR allowed observation of perturbations of the bilayer membrane structure induced by each of the antibiotics in the regions of the polar headgroups and acyl side chains of the phospholipids. The comparative study of the effects of these membrane-active antibiotics and the lipid bilayer structure demonstrated distinct types of antibiotic-membrane interactions in each case. Thus, the results showed the absence of interaction of polymyxin B with the dimyristoyllecithin membranes. In contrast, gramicidin S exhibited strong interaction with the lipid above the gel to liquid-crystalline phase transition temperature: disordering of the acyl side chains was evident. Increasing the concentration of gramicidin S led to disintegration of the bilayer membrane structure. At a molar ratio of 1:16 of gramicidin S to lecithin, the results are consistent with coexistence of gel and liquid-crystalline phases of the phospholipids near the phase transition temperature. Valinomycin decreased the phase transition temperature of the lipids and increased the order parameters of the lipid side chains. Such behavior is consistent with penetration of the valinomycin molecule into the interior of the lipid bilayers.

13C-NMR Investigation of the insertion of the bee venom melittin into lecithin vesicles

The orientation of melittin in lecithin membranes was investigated by means of 13C-NMR spectroscopy. Phospholipase-free melittin was labeled with 13C-methyl groups at the ω-amino side chains of lysine 7, 21, and 23. From the pH dependence of the corresponding 13C resonances, pK values of the lysine residues were derived that were different for free and membrane-bound melittin. The shift reagent Pr(NO3)3 induced shifts in the 13C resonance position of all three lysines when melittin and the shift reagent were added to a lecithin vesicle suspension, whereas Pr3+ ions included in the inner volume of the vesicles did not affect the 13C resonances of melittin bound to the outer vesicle membrane. A wedge-like structure was derived for the membrane-bound melittin, the lysine side chains of which are freely accessible to the aqueous solvent.