Mean Molecular Area Research Articles

Dynamic Behaviors and Morphology Change of Anionic Phospholipid DPPG Monolayer Caused by Bovine Serum Albumin at Air-Water Interface

The interaction between bovine serum albumin (BSA) and the anionic 1.2-dipalmitoyl-sn-glycero-3-(phospho-rac-(1-glycerol)) (sodium salt) (DPPG) phospholipid at different sub-phase pH values was investigated at air-water interface through surface pressure measurements and atomic force microscopy (AFM) observation. By analyzing surface pressure-mean molecular area (π-A) isotherms, the limiting molecular area in the closed packing state-the concentration of BSA (Alim-[BSA]) curves, the compressibility coefficient-surface pressure (C−1S-π) curves and the difference value of mean molecular area-the concentration of BSA (ΔA-[BSA]) curves, we obtained that the mean molecular area of DPPG monolayer became much larger when the concentration of BSA in the subphase increased at pH=3 and 5. But the isotherms had no significant change at different amount of BSA at pH=10. In addition, the amount of BSA molecules adsorbed onto the lipid monolayer reached a threshold value when [BSA]>5×10−8 mol/L for all pHs. From the surface pressure-time (π-t) data, we obtained that desorption and adsorption processes occurred at pH=3, however, there was only desorption process occurring at pH=5 and 10. These results showed that the interaction mechanism between DPPG and BSA molecules was affected by the pH of subphase. BSA molecules were adsorbed onto the DPPG monolayers mainly through the hydrophobic interaction at pH=3 and 5, and the strength of hydrophobic interaction at pH=3 was stronger than the case of pH=5. At pH=10, a weaker hydrophobic interaction and a stronger electrostatic repulsion existed between DPPG and BSA molecules. AFM images revealed that the pH of subphase and [BSA] could affect the morphology features of the monolayers, which was consistent with these curves. The study provides an important experimental basis and theoretical support to understand the interaction between lipid and BSA at the air-water interface.

Characterization of Surface-Active Biofilm Protein BslA in Self-Assembling Langmuir Monolayer at the Air-Water Interface.

Biofilm is an extracellular matrix of bacteria and serves as a protective shield of bacterial communities. It is crucial for microbial growth and one of the leading causes of human chronic infections as well. However, the structures and molecular mechanism of biofilm formation remain largely unknown. Here, we examined a protein, BslA, expressed in the biofilms of Bacillus subtilis. We characterized the Langmuir monolayers of BslA at the air/water interface. Using techniques in surface chemistry and spectroscopy, we found that BslA forms a stable and robust Langmuir monolayer at the air/water interface. Our results show that the BslA Langmuir monolayer underwent two-stage elasticity in the solid state phase upon mechanical compression: one is possibly due to the intermolecular interaction and the other is likely due to both the intermolecular compulsion and the intramolecular distortion. The Langmuir monolayer of BslA shows abrupt changes in rigidities and elasticities at ∼25 mN/m. This surface pressure is close to the one at which BlsA saturates the air/water interface as a self-assembled film without mechanical compression, corresponding to a mean molecular area of ∼700 Å2 per molecule. Based on the results of surface UV-visible spectroscopy and infrared reflective-absorption spectroscopy, we propose that the BslA Langmuir monolayer carries intermolecular elasticity before ∼25 mN/m and both intermolecular and intramolecular elasticity after ∼25 mN/m. These results provide valuable insights into the understanding of biofilm-associated protein under high mechanical force, shedding light on further investigation of biofilm structure and functionalities.

Cavity Orientation Regulated by Mixture Composition and Clustering of Amphiphilic Cyclodextrins in Phospholipid Monolayers.

Artificial supramolecular-hierarchical structures that emulate nature represent an overcoming alternative for the design of new drug delivery systems. Thermodynamic and topographic properties of films formed by a monoacylated amphiphilic β-cyclodextrin (βCD-C16) with the phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at the air/water interface were studied. βCD-C16 formed stable mixed films with POPC at several proportions when spread together at the air/water interface. The orientation of βCD-C16 cavity at the interface depends on its mole fraction in the film as reveled by the analysis of partial mean molecular areas as a function of composition. Furthermore, βCD-C16 was able to penetrate POPC preformed films in a broad range of initial surface pressures, including that near the collapse pressure of the phospholipid. These results demonstrated the strong tendency of βCD-C16 to be inserted into this lipid matrix commonly used in liposome formulations. Topography studies show that βCD-C16 segregate from POPC forming clusters enriched in βCD-C16. Segregation of βCD-C16 was especially noticeable when βCD-C16 were incorporated by themselves into a preformed POPC matrix leading to ordered and highly birefringent structures that suggest the formation of hierarchical stacked βCD-C16 arrangement at the interface.

Supramolecular architectures of iron phthalocyanine Langmuir-Blodgett films: The role played by the solution solvents

The developing of organic-based devices has been widely explored using ultrathin films as the transducer element, whose supramolecular architecture plays a central role in the device performance. Here, Langmuir and Langmuir-Blodgett (LB) ultrathin films were fabricated from iron phthalocyanine (FePc) solutions in chloroform (CHCl3), dichloromethane (CH2Cl2), dimethylformamide (DMF), and tetrahydrofuran (THF) to determine the influence of different solvents on the supramolecular architecture of the ultrathin films. The UV–vis absorption spectroscopy shows a strong dependence of the FePc aggregation on these solvents. As a consequence, the surface pressure vs. mean molecular area (π-A) isotherms and Brewster angle microscopy (BAM) reveal a more homogeneous (surface morphology) Langmuir film at the air/water interface for FePc in DMF. The same morphological pattern observed for the Langmuir films is preserved upon LB deposition onto solid substrates. The Raman and FTIR analyses indicate the DMF-FePc interaction relies on coordination bonds between N atom (from DMF) and Fe atom (from FePc). Besides, the FePc molecular organization was also found to be affected by the DMF-FePc chemical interaction. It is interesting to note that, if the DMF-FePc leads to less aggregated FePc either in solution or ultrathin films (Langmuir and LB), with time (one week) the opposite trend is found. Taking into account the N-Fe interaction, the performance of the FePc ultrathin films with distinct supramolecular architectures composing sensing units was explored as proof-of-principle in the detection of trace amounts of atrazine herbicide in water using impedance spectroscopy. Further statistical and computational analysis reveal not only the role played by FePc supramolecular architecture but also the sensitivity of the system to detect atrazine solutions down to 10−10mol/L, which is sufficient to monitor the quality of drinking water even according to the most stringent international regulations.

Investigation of Surface Behavior of DPPC and Curcumin in Langmuir Monolayers at the Air-Water Interface.

Langmuir monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and a mixture of DPPC with curcumin (CUR) have been investigated at the air-water interface through a combination of surface pressure measurements and atomic force microscopy (AFM) observation. By analyzing the correlation data of mean molecular areas, the compressibility coefficient, and other thermodynamic parameters, we obtained that the interaction between the two components perhaps was mainly governed by the hydrogen bonding between the amino group of DPPC and the hydroxyl groups of CUR. CUR markedly affected the surface compressibility, the thermodynamic stability, and the thermodynamic phase behaviors of mixed monolayers. The interaction between CUR and DPPC was sensitive to the components and the physical states of mixed monolayers under compression. Two-dimensional phase diagrams and interaction energies indicated that DPPC and CUR molecules were miscible in mixed monolayers. AFM images results were in agreement with these analyses results of experimental data. This study will encourage us to further research the application of CUR in the biomedical field.

Aggregation behavior of star-shaped fluoropolymers containing polyhedral oligomeric silsesquioxane (POSS) at the air–water interface

Aggregation behavior of three star-shaped fluoropolymers containing polyhedral oligomeric silsesquioxane (POSS) and different monomers poly(methyl methacrylate) (PMMA), poly(trifluoroethyl methacrylate) (PTFEMA) and poly[poly(ethylene glycol)methyl ether methacrylate] (PMPEGMA), POSS-(PMMA-b-PTFEMA)8, POSS-(PTFEMA-b-PMMA)8, and POSS-(PTFEMA-b-PMPEGMA)8) was investigated at the air–water interface. The interfacial rheology and surface morphology were studied through surface pressure and compression modulus measurements, hysteresis, relaxation, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The surface pressure–mean molecular area (Π-MMA) isotherms exhibited four regions, and it was found that the pseudoplateau observed corresponds to a “pancake-to-brush” transition. The compression modulus isotherms showed two peak values which were related to the phase transition of the monolayer. The hysteresis behaviors were compared in two different regions during the compression–expansion process. In addition, the relaxation of the monolayer was discussed using the step compression method. The relaxation process was proposed that related to the adsorption–desorption exchange of molecules and polymer segments on the surface (fast relaxation process) and the reconformation of the adsorbed macromolecules inside the adsorption layer (slow relaxation process). Furthermore, the Langmuir–Blodgett (LB) films prepared at different surface pressures from the three copolymers were scanned by AFM and a variety of morphologies were observed. Finally, the structure evolutions for the three star-shaped copolymers that aggregate at the air–water interface were proposed.

Imidazolium-Based Lipid Analogues and Their Interaction with Phosphatidylcholine Membranes.

4,5-Dialkylated imidazolium lipid salts are a new class of lipid analogues showing distinct biological activities. The potential effects of the imidazolium lipids on artificial lipid membranes and the corresponding membrane interactions was analyzed. Therefore, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) was employed to create an established lipid monolayer model and a bilayer membrane. Mixed monolayers of DPPC and 4,5-dialkylimidazolium lipids differing by their alkyl chain length (C7, C11, and C15) were characterized by surface pressure-area (π-A) isotherms using a Wilhelmy film balance in combination with epifluorescence microscopy. Monolayer hysteresis for binary mixtures was examined by recording triplicate consecutive compression-expansion cycles. The lipid miscibility and membrane stability of DPPC/imidazolium lipids were subsequently evaluated by the excess mean molecular area (ΔAex) and the excess Gibbs free energy (ΔGex) of mixing. Furthermore, the thermotropic behavior of mixed liposomes of DPPC/imidazolium lipids was investigated by differential scanning calorimetry (DSC). The C15-imidazolium lipid (C15-IMe·HI) forms a thermodynamically favored and kinetically reversible Langmuir monolayer with DPPC and exhibits a rigidification effect on both DPPC monolayer and bilayer structures at low molar fractions (X ≤ 0.3). However, the incorporation of the C11-imidazolium lipid (C11-IMe·HI) causes the formation of an unstable and irreversible Langmuir-Gibbs monolayer with DPPC and disordered DPPC liposomes. The C7-imidazolium lipid (C7-IMe·HI) displays negligible membrane activity. To better understand these results on a molecular level, all-atom molecular dynamics (MD) simulations were performed. The simulations yield two opposing molecular mechanisms governing the different behavior of the three imidazolium lipids: a lateral ordering effect and a free volume/stretching effect. Overall, our study provides the first evidence that the membrane interaction of the C15 and C11 derivatives modulates the structural organization of lipid membranes. On the contrary, for the C7 derivative its membrane activity is too low to contribute to its earlier reported potent cytotoxicity.

A Langmuir and AFM study on interfacial behavior of binary monolayer of hexadecanol/DPPE at the air-water interface

Hexadecanol is chemically stable and can be used as an effective addition in synthetic clinical lung surfactant preparations to improve their spreading properties. In this work, a detailed thermodynamic and structural characterization of a simple model system, which based on a hexadecanol-phospholipid mixture is reported. Langmuir monolayers of binary mixtures of hexadecanol/1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) have been studied with thermodynamic parameters and monolayer structure. The extent of the thermodynamic parameters has been evaluated by the direct related parameters, such as mean molecular area, percent of condensation, surface excess Gibbs free energies, isothermal compressibility, interaction energy parameter, activity coefficient and two-dimensional phase diagram. Monolayer film structure has been characterized by atomic force microscopy (AFM) technique. Combining thermodynamic and AFM data indicate that there exist repulsive and attractive interactions between the two film forming molecules and the binary films behave as non-ideal mixtures, which can be portrayed by the mole fraction of hexadecanol. At low mole fraction of hexadecanol, the monolayer is phase-separated and the interactions between hexadecanol and DPPE is more repulsive; while the content of hexadecanol up to 0.6, the monolayer becomes miscible and stable, the interaction between different molecules is more attractive. The addition of hexadecanol in the DPPE monolayer clearly affects the lateral organization of membranes and improves its surface tension kinetics. The results discussed in this context will be expected to be potential contribution for exogenous lung surfactant researches.

Improved prediction of bilayer and monolayer properties using a refined BMW-MARTINI force field

Coarse-grained (CG) models allow enlarging the size and time scales that are reachable by atomistic molecular dynamics simulations. A CG force field (FF) for lipids and amino acids that possesses a polarizable water model has been developed following the MARTINI parametrization strategy, the BMW-MARTINI [1]. We tested the BMW-MARTINI FF capability to describe some structural and thermodynamical properties of lipid monolayers and bilayers. We found that, since the surface tension values of oil/water interfaces calculated with the model are not correct, compression isotherms of lipid monolayers present artifacts. Also, this FF predicts DPPC and DAPC bilayers to remain in the Lα phase at temperatures as low as 283K, contrary to the expected from their experimental Tm values. Finally, simulations at constant temperature of bilayers of saturated lipids belonging to PC homologous, showed an increase in the mean molecular area (Mma) upon increasing the chain length, inversely to the experimental observation.We refined BMW-MARTINI FF by modifying as few parameters as possible in order to bring simulated and experimental measurements closer. We have also modified structural parameters of the lipid geometry that do not have direct influence in global properties of the bilayer membranes or monolayers, but serve to approach the obtained CG geometry to atomistic reference values. The refined FF is able to better reproduce phase transition temperatures and Mma for saturated PC bilayers than BMW-MARTINI and MARTINI FF. Finally, the simulated surface pressure-Mma isotherms of PC monolayers resemble the experimental ones and eliminate serious artifacts of previous models.

Synthesis of an Open-Cage Structure POSS Containing Various Functional Groups and Their Effect on the Formation and Properties of Langmuir Monolayers.

Recently, silsesquioxanes have been recognized as a new group of film-forming materials. This study has been aimed at determining the effect of the kind of functional groups present in two different open-cage structure POSS molecules on the possibility of the formation of Langmuir monolayers and their properties. To achieve this goal, two new POSS derivatives (of open-cage structures) containing polyether and fluoroalkyl functional groups have been synthesized on the basis of a hydrosilylation process. An optimization of the process was performed, which makes it possible to obtain the above-mentioned derivatives with high yields. In the next step, the Langmuir technique was applied to measurements of the surface pressure (π) - the mean molecular area (A) isotherms during the compression of monolayers formed by molecules of the two POSS derivatives considered. Subsequently, the monolayers were transferred onto quartz plates according to the Langmuir-Blodgett technique. Both derivatives are able to form insoluble Langmuir films at the air-water interface, which can be transferred onto a solid substrate and effectively change its wetting properties.

Influence of oxidized lipids on palmitoyl-oleoyl-phosphatidylcholine organization, contribution of Langmuir monolayers and Langmuir–Blodgett films

In this work, we studied the interaction of two oxidized lipids, PoxnoPC and PazePC, with POPC phospholipid. Mean molecular areas obtained from (π–A) isotherms of mixed PoxnoPC–POPC and PazePC–POPC monolayers revealed different behaviors of these two oxidized lipids: the presence of PoxnoPC in the monolayers induces their expansion, mean molecular areas being higher than those expected in the case of ideal mixtures. PazePC–POPC behave on the whole ideally. This difference can be explained by a different conformation of oxidized lipids. Moreover the carboxylic function of PazePC is protonated under our experimental conditions, as shown by (π–A) isotherms of PazePC at different pH values. Both oxidized lipids induce also an increase of the monolayer elasticity, PoxnoPC being slightly more efficient than PazePC. These monolayers were transferred from the air–water interface onto mica supports for a study by AFM. AFM images are on the whole homogenous, suggesting the presence of only one lipid phase in both cases. However, in the case of PazePC–POPC monolayers, AFM images show also the presence of areas thicker of 7nm to 10nm than the surrounding lipid phase, probably due to the local formation of multilayer systems induced by compression.

Miscibility of dl-α-tocopherol β-glucoside in DPPC monolayer at air/water and air/solid interfaces

The role of newly synthesized tocopherol glycosidic derivative in modifying molecular organization and phase transitions of phospholipid monolayer at the air/water interface has been investigated. Two-component Langmuir films of dl-α-tocopheryl β-D-glucopyranoside (BG) mixed with dipalmitoyl phosphatidylcholine (DPPC) in the whole range of mole fractions were formed at the water surface. An analysis of surface pressure versus mean molecular area (π-A) isotherms and Brewster angle microscope images showed that the presence of BG molecules changes the structure and packing of the DPPC monolayer in a BG concentration dependent manner. BG molecules incorporated into DPPC monolayer inhibit its liquid expanded to liquid condensed phase transition proportionally to the BG concentration. The monolayers were also transferred onto solid substrates and visualized using an atomic force microscope. The results obtained indicate almost complete miscibility of BG and DPPC in the monolayers at surface pressures present in the biological cell membrane (30-35·10-3 N·m-1) for a BG mole fraction as high as 0.3. This makes the monolayer less packed and more disordered, leading to an increased permeability. The results support our previous molecular dynamics simulation data.

Combined effect of synthetic protein, Mini-B, and cholesterol on a model lung surfactant mixture at the air–water interface

The overall goal of this work is to study the combined effects of Mini-B, a 34 residue synthetic analog of the lung surfactant protein SP-B, and cholesterol, a neutral lipid, on a model binary lipid mixture containing dipalmitolphosphatidylcholine (DPPC) and palmitoyl-oleoyl-phosphatidylglycerol (POPG), that is often used to mimic the primary phospholipid composition of lung surfactants. Using surface pressure vs. mean molecular area isotherms, fluorescence imaging and analysis of lipid domain size distributions; we report on changes in the structure, function and stability of the model lipid-protein films in the presence and absence of varying composition of cholesterol. Our results indicate that at low cholesterol concentrations, Mini-B can prevent cholesterol's tendency to lower the line tension between lipid domain boundaries, while maintaining Mini-B's ability to cause reversible collapse resulting in the formation of surface associated reservoirs. Our results also show that lowering the line tension between domains can adversely impact monolayer folding mechanisms. We propose that small amounts of cholesterol and synthetic protein Mini-B can together achieve the seemingly opposing requirements of efficient LS: fluid enough to flow at the air–water interface, while being rigid enough to oppose irreversible collapse at ultra-low surface tensions.

Thermodynamic properties of Langmuir layers created of monoimide perylenetetracarboxylic acid derivatives

Langmuir films formed of some fluorescent dyes, 3,4-bis-pentyl ester of 9,10-N-(n-pentylimide)-perylenetetracarboxylic acid, as well as their mixtures with arachidic acid, were studied. Surface pressure versus mean molecular area isotherms for Langmuir films were reordered and the alignment of molecules at the air–water interface was estimated. The isotherms show that the dye molecules do not lie flat onto the water surface but are tilted with respect to the normal to the interface. The surface pressure–area isotherms of Langmuir films formed from the dye/arachidic acid mixture provide evidence for phase separation of the components within almost the entire range of mole fractions. A repulsive interaction between molecules was observed in all two components of Langmuir films.

Interaction of polyhedral oligomeric silsesquioxane containing epoxycyclohexyl groups with cholesterol at the air/water interface

Binary mixtures of cholesterol and fully-condensed octakis[{2-(3,4-epoxycyclohexyl) etyl}dimethyl-silyloxy]octasilsesquioxane (OE-POSS) were characterized using Langmuir trough for obtaining surface pressure-area isotherms. The most characteristic feature of the mixed films is the presence of two collapse points on the isotherms. The first one is attributed to the collapse of less stable OE-POSS and it occurs at similar surface pressures for all compositions, while the second one corresponds to cholesterol collapse. Brewster angle microscopy observations confirmed the collapse behavior of the mixed film. Strong condensing effect was observed for the mean molecular areas dependence on cholesterol content in the film. Moreover, formation of microdomains of each component in the matrix of the other one was confirmed by BAM images. For the reasons of molecular structures and interactions a true mixed and homogenous film did not form in the systems considered. Phase separation was observed for all the compositions experimented. The lack of the interactions of OE-POSS with biomembrane components represented by cholesterol is beneficial for applications of OE-POSS in biomedical devices.

The Effect of Ambient Ozone on Unsaturated Tear Film Wax Esters.

Tear film lipid layer (TFLL) is constantly exposed to reactive ozone in the surrounding air, which may have detrimental effects on ocular health. Behenyl oleate (BO), a representative tear film wax ester, was used to study the reaction with ozone at the air-water interface. Time-dependent changes in mean molecular area of BO monolayers were measured at different ozone concentrations and surface pressures. In addition, the effect of ascorbic acid on the reaction rate was determined. Reaction was followed using thin-layer chromatography and reaction products were identified using liquid chromatography-electrospray ionization mass spectrometry (LC-MS). Tear fluid samples from healthy subjects were analyzed with LC-MS for any ozonolysis reaction products. Behenyl oleate was found to undergo rapid ozonolysis at the air-water interface at normal indoor ozone concentrations. The reaction was observed as an initial expansion followed by a contraction of the film area. Ascorbic acid was found to decrease the rate of ozonolysis. Main reaction products were identified as behenyl 9-oxononanoate and behenyl 8-(5-octyl-1,2,4-trioxolan-3-yl)octanoate. Similar ozonolysis products were not detected in the tear fluid samples. At the air-water interface, unsaturated wax esters react readily with ozone in ambient air. However, no signs of ozonolysis products were found in the tear fluid. This is most likely due to the antioxidant systems present in tear fluid. Last, the results show that ozonolysis needs to be controlled in future surface chemistry studies on tear film lipids.

Thermodynamic and structural studies of DMPC and DSPC with DOTAP mixed monolayers at the air–water interface

According to the method of Langmuir-Blodgett the thermodynamic behavior and the miscibility of the two phospholipids 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) with 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) in the mixed monolayer were evaluated in terms of the excess mean molecular area, excess Gibbs free energy and compressibility coefficient. DMPC and DOTAP were miscible and a repulsive interaction appeared between DMPC and DOTAP molecules at most of selected ratios and surface pressures. Meanwhile, the interaction between DSPC and DOTAP were attractive and the most stable monolayers were formed at the 3: 2 and 1: 4 stoichiometry. The morphology observations by fluorescence microscopy reveals that the size of the domains composed of DSPC were larger than DMPC.

Spectroscopic and Structural Studies of a Surface Active Porphyrin in Solution and in Langmuir-Blodgett Films.

Controlling aggregation of the dual sensitizer-emitter (S-E) zinc tetraphenylporphyrin (ZnTPP) is an important consideration in solid state noncoherent photon upconversion (NCPU) applications. The Langmuir-Blodgett (LB) technique is a facile means of preparing ordered assemblies in thin films to study distance-dependent energy transfer processes in S-E systems and was used in this report to control the aggregation of a functionalized ZnTPP on solid substrates. This was achieved by synthetic addition of a short polar tail to one of the pendant phenyl rings in ZnTPP in order to make it surface active. The surface active ZnTPP derivative formed rigid films at the air-water interface and exhibited mean molecular areas consistent with approximately vertically oriented molecules under appropriate film compression. A red shift in the UV-vis spectra as well as unquenched fluorescence emission of the LB films indicated formation of well-ordered aggregates. However, NCPU, present in the solution phase, was not observed in the LB films, suggesting that NCPU from ZnTPP as a dual S-E required not just a controlled aggregation but a specific orientation of the molecules with respect to each other.

The influence of an antitumor lipid - erucylphosphocholine - on artificial lipid raft system modeled as Langmuir monolayer.

Outer layer of cellular membrane contains ordered domains enriched in cholesterol and sphingolipids, called 'lipid rafts', which play various biological roles, i.e., are involved in the induction of cell death by apoptosis. Recent studies have shown that these domains may constitute binding sites for selected drugs. For example alkylphosphocholines (APCs), which are new-generation antitumor agents characterized by high selectivity and broad spectrum of activity, are known to have their molecular targets located at cellular membrane and their selective accumulation in tumor cells has been hypothesized to be linked with the alternation of biophysical properties of lipid rafts. To get a deeper insight into this issue, interactions between representative APC: erucylphosphocholine, and artificial lipid raft system, modeled as Langmuir monolayer (composed of cholesterol and sphingomyelin mixed in 1:2 proportion) were investigated. The Langmuir monolayer experiments, based on recording surface pressure-area isotherms, were complemented with Brewster angle microscopy results, which enabled direct visualization of the monolayers structure. In addition, the investigated monolayers were transferred onto solid supports and studied with AFM. The interactions between model raft system and erucylphosphocholine were analyzed qualitatively (with mean molecular area values) as well as quantitatively (with ΔG(exc) function). The obtained results indicate that erucylphosphocholine introduced to raft-mimicking model membrane causes fluidizing effect and weakens the interactions between cholesterol and sphingomyelin, which results in phase separation at high surface pressures. This leads to the redistribution of cholesterol molecules in model raft, which confirms the results observed in biological studies.

CoenzymeQ10 localizations in model membranes. A Langmuir monolayer study

The interaction of coenzyme Q10 (CoQ10) in a monolayer of 1,2-dipalmitoyl-sn-glysero-3-phospho-L-choline (DPPC), in a monolayer of 1,2-dierucoyl-sn-glysero-3-phospho-L-choline (DEPC), in a monolayer of 1-palmitoyl-2-oleoyl-sn-glysero-3-phospho-L-serine (POPS) and in a monolayer of total lipid extract from pig brain (PB) has been investigated by using the Langmuir monolayer technique. Surface pressure (π)-mean molecular area (mma) isotherms have been measured for pure lipid monolayers and lipid monolayers with 0.5, 1.0, 2.0, 5.0 and 10.0 mol% CoQ10 concentrations. At the biological concentration (1.0-3.0 mol%) of CoQ10, intercalation of CoQ10 occurs in the lipid acyl chains of DPPC, POPS and PB monolayers. Above the biological concentration of CoQ10, the CoQ10 molecule induces domain formation in the monolayers of DPPC, POPS and PB lipids. The DEPC monolayer behavior deviates from the other lipids in this study. At 2.0 mol% the CoQ10 promotes very dense lipid packing, and the CoQ10 molecule is located parallel to the DEPC acyl chains at all concentrations.