Brewster Angle Microscopy Research Articles

Statin Action Targets Lipid Rafts of Cell Membranes: GIXD/PM-IRRAS Investigation of Langmuir Monolayers.

Lipid rafts are condensed regions of cell membranes rich in cholesterol and sphingomyelin, which constitute the target for anticholesterolemic drugs - statins. In this work, we use for the first time a combined grazing-incidence X-ray diffraction (GIXD)/polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS)/Brewster angle microscopy (BAM) approach to show the statin effect on model lipid rafts and its components assembled in Langmuir monolayers at the air-water interface. Two representatives of these drugs, fluvastatin (FLU) and cerivastatin (CER), of different hydrophobicity were chosen, while cholesterol (Chol) and sphingomyelin (SM), and their 1:1 mixture were selected to form condensed monolayers of lipid rafts. The effect of statins on the single components of lipid rafts indicated that both the hydrophobicity of the drugs and the organization of the layer determined the drug-lipid interaction. For cholesterol monolayers, only the most hydrophobic CER was effectively changing the film structure, while for the less organized sphingomyelin, the biggest effect was observed for FLU. This drug affected both the polar headgroup region as shown by PM-IRRAS results and the 2D crystalline structure of the SM monolayer as evidenced by GIXD. Measurements performed for Chol/SM 1:1 models proved also that the statin effect depends on the presence of Chol-SM complexes. In this case, the less hydrophobic FLU was not able to penetrate the binary layer at all, while exposure to the hydrophobic CER resulted in the phase separation and formation of ordered assemblies. The changes in the membrane properties were visualized by BAM images and GIXD patterns and confirmed by thermodynamic parameters of hysteresis in the Langmuir monolayer compression-decompression experiments.

Surfactant micellar induced aggregation control of an anionic fluorescent dye in Langmuir-Blodgett film

This work reports the formation of stable Langmuir monolayer of an anionic water soluble fluorescent dye 5(6)-carboxyfluorescein (abbreviated as CFS) by electrostatic interaction with a cationic monolayer. Formation of non-fluorescent H-dimeric sites of CFS molecules in Langmuir monolayer and Langmuir Blodgett films has been controlled by using cationic surfactant micelles of cetyltrimethylammonium bromide (CTAB). Thus the film can act as efficient fluorescence marker. Langmuir monolayer has been investigated by Surface Pressure versus Area per molecule (π-A) isotherm and in situ Brewster Angle Microscope (BAM) studies. Mono and multilayered Langmuir Blodgett films were characterized by using UV–vis absorption and steady state fluorescence spectroscopy.

Novel Insight into the Photophysical Properties and 2D Supramolecular Organization of Poly(3,4-ethylenedioxythiophene)/Permodified Cyclodextrins Polyrotaxanes at the Air-Water Interface.

Two poly(3,4-ethylenedioxythiophene) polyrotaxanes (PEDOT∙TMe-βCD and PEDOT∙TMe-γCD) end-capped by pyrene (Py) were synthesized by oxidative polymerization of EDOT encapsulated into TMe-βCD or TMe-γCD cavities with iron (III) chloride (FeCl3) in water and chemically characterized. The effect of TMe-βCD or TMe-γCD encapsulation of PEDOT backbones on the molecular weight, thermal stability, and solubility were investigated in depth. UV-vis absorption, fluorescence (FL), phosphorescence (PH), quantum efficiencies, and lifetimes in water and acetonitrile were also explored, together with their surface morphology and electrical properties. Furthermore, dynamic light scattering was used to study the hydrodynamic diameter (DH) and z-potential (ZP-ζ) of the water soluble fractions of PEDOT∙TMe-βCD and PEDOT∙TMe-γCD. PEDOT∙TMe-βCD and PEDOT∙TMe-γCD exhibited a sharp monodisperse peak with a DH of 55 ± 15 nm and 122 ± 32 nm, respectively. The ZP-ζ value decreased from -31.23 mV for PEDOT∙TMe-βCD to -20.38 mV for PEDOT∙TMe-γCD, indicating that a negatively charged layer covers their surfaces. Surface pressure-area isotherms and Brewster angle microscopy (BAM) studies revealed the capability of the investigated compounds to organize into sizeable and homogeneous 2D supramolecular assemblies at the air-water interface. The control of the 2D monolayer organization through the thermodynamic parameters of PEDOT∙TMe-βCD and PEDOT∙TMe-γCD suggests potential for a wide range of optoelectronic applications.

Influence of Surface Flows on the Shape of Fractal Domains.

Tidal breathing is associated with a 30% change of the surfactant-covered alveolar surface occurring about 16 times per minute. To model this highly dynamic process, erucic acid monolayers at the air-water interface were compressed fast. Brewster angle microscopy imaged the fractal liquid-condensed (LC) domains and quantified the surface flow in size, direction, and duration. Radial branch distribution of the domains has a minimum in the flow direction, as was shown with directionality histograms. The fast Fourier transform of the domains shows a preferential growth perpendicular to the flow direction. Additionally, at the beginning of the flow, the downstream side of the domain grows faster than the upstream side. Surface flows act on the mm to cm scale, cause an anisotropic flow in the liquid expanded phase surrounding the LC domain, and affect the overall domain shape. On the μm-scale, the dendritic or seaweed domains' branches were only slightly disturbed. These results may help to understand pulmonary surfactant layers.

Stimuli-Responsive Langmuir Films Composed of Nanoparticles Decorated with Poly(N-isopropyl acrylamide) (PNIPAM) at the Air/Water Interface.

The nanotechnology shift from static toward stimuli-responsive systems is gaining momentum. We study adaptive and responsive Langmuir films at the air/water interface to facilitate the creation of two-dimensional (2D) complex systems. We verify the possibility of controlling the assembly of relatively large entities, i.e., nanoparticles with diameter around 90 nm, by inducing conformational changes within an about 5 nm poly(N-isopropyl acrylamide) (PNIPAM) capping layer. The system performs reversible switching between uniform and nonuniform states. The densely packed and uniform state is observed at a higher temperature, i.e., opposite to most phase transitions, where more ordered phases appear at lower temperatures. The induced nanoparticles' conformational changes result in different properties of the interfacial monolayer, including various types of aggregation. The analysis of surface pressure at different temperatures and upon temperature changes, surface potential measurements, surface rheology experiments, Brewster angle microscopy (BAM), and scanning electron microscopy (SEM) observations are accompanied by calculations to discuss the principles of the nanoparticles' self-assembly. Those findings provide guidelines for designing other adaptive 2D systems, such as programable membranes or optical interfacial devices.

Perylene nanostructured films optimization for organic electronics: Molecular, structural, and electrochemical characterization

The deposition technique, structure, and thermal treatment can influence the optical and electrical properties of perylene derivatives films. In this work, the nanostructured Langmuir-Schaefer films of bis(n-propylimide) perylene (PTCD-Pr) with thermal treatment were optimized for an electrochemical application. The PTCD-Pr film before and after thermal treatment was characterized by ultraviolet-visible absorption, infrared absorption spectroscopy, micro-Raman scattering, and voltammetry. Brewster angle microscopy images confirmed the higher aggregation degree of molecules on Langmuir film. The PTCD-Pr deposition showed a linear growth, forming H, J, and null aggregates. The infrared absorption spectroscopy indicates a preferential head-on orientation with a slight chromophore deviation. After thermal treatment (200 °C for 2 h), the PTCD-Pr film showed a decrease in the contribution of null aggregates while maintaining the same molecular orientation. The Raman and surface-enhanced Raman spectroscopy measurements also confirmed the presence of PTCD-Pr molecules distributed throughout the substrate surface, and the thermal treatment conditions did not degrade the PTCD-Pr molecule. Moreover, thermal treatment contributes to the increase of stability of the film at the electrode surface for electrochemical measurements. In the presence of active species (paraquat in this case), the thermally treated film showed promising electrocatalytic properties compared to the unmodified electrode.

Surface characterization and interfacial activity of chitinase chi18-5 against chitosan in langmuir monolayers

One of the challenges for producing active chitinase formulations relies on the gap between the laboratory tests and the biological scenarios where the enzyme will perform its function. In this work, we have employed different Langmuir monolayer arrays to evaluate the interfacial behavior of a recently purified recombinant chitinase, Chi18–5. We have demonstrated that two conformations exist for the chitinase at pH values close to its pI, showing very distinct structural properties at the air/aqueous interface. Enzyme activity was assessed by implementing different kinetic approaches and using a chitosan-1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) mixed film as organized substrate model membrane. Combining these strategies, we demonstrated that better catalytic efficiencies can be obtained for Chi18–5 at pH 5. Moreover, the chitinase activity at the air/aqueous interface can be tuned by introducing in situ pH modifications over the surrounding milieu. We also studied the changes in the topography at the mesoscale level using Brewster Angle Microscopy (BAM). We found that Chi18–5 segregated onto the chitosan domains of the membrane, showing differences in homogeneity depending on the pH imposed. Alternatively, pure Chi18–5 was tested for immobilization onto a hydrophilic activated solid support using the Langmuir-Blodgett technique. Atomic Force Microscopy (AFM) analyses showed successfully stabilization and preservation of molecular features attributed to the pH at which the enzyme deposition was performed.

Revealing the Impacts of Chemical Complexity on Submicrometer Sea Spray Aerosol Morphology.

Sea spray aerosol (SSA) ejected through bursting bubbles at the ocean surface is a complex mixture of salts and organic species. Submicrometer SSA particles have long atmospheric lifetimes and play a critical role in the climate system. Composition impacts their ability to form marine clouds, yet their cloud-forming potential is difficult to study due to their small size. Here, we use large-scale molecular dynamics (MD) simulations as a "computational microscope" to provide never-before-seen views of 40 nm model aerosol particles and their molecular morphologies. We investigate how increasing chemical complexity impacts the distribution of organic material throughout individual particles for a range of organic constituents with varying chemical properties. Our simulations show that common organic marine surfactants readily partition between both the surface and interior of the aerosol, indicating that nascent SSA may be more heterogeneous than traditional morphological models suggest. We support our computational observations of SSA surface heterogeneity with Brewster angle microscopy on model interfaces. These observations indicate that increased chemical complexity in submicrometer SSA leads to a reduced surface coverage by marine organics, which may facilitate water uptake in the atmosphere. Our work thus establishes large-scale MD simulations as a novel technique for interrogating aerosols at the single-particle level.

Atomic force microscopy study of the complexation of sterols and the glycoalkaloid α-tomatine in Langmuir-Blodgett monolayers.

Glycoalkaloids are secondary metabolites produced by plants that aid in their protection from pathogens and pests. They are known to form 1:1 complexes with 3β-hydroxysterols such as cholesterol causing membrane disruption. So far, the visual evidence showcasing the complexes formed between glycoalkaloids and sterols in monolayers has been mainly restricted to some earlier studies using Brewster angle microscopy which were of low resolution showing the formation of floating aggregates of these complexes. This study is aimed at using atomic force microscopy (AFM) for topographic and morphological analysis of the aggregates of these sterol-glycoalkaloid complexes. Langmuir-Blodgett (LB) transfer of mixed monolayers of the glycoalkaloid α-tomatine, sterols, and lipids in varying molar ratios onto mica followed by AFM examination was performed. The AFM method allowed visualization of the aggregation of sterol-glycoalkaloid complexes at nanometer resolution. While aggregation was observed in mixed monolayers of α-tomatine with cholesterol and in mixed monolayers with coprostanol, no sign of complexation was observed for the mixed monolayers of epicholesterol and α-tomatine, confirming their lack of interaction found in prior monolayer studies. Aggregates were observed in transferred monolayers of ternary mixtures of α-tomatine with cholesterol and the phospholipids 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) or egg sphingomyelin (egg SM). The formation of aggregates was found to be less prevalent for mixed monolayers of DMPC and cholesterol containing α-tomatine than it was for mixed monolayers containing egg SM and cholesterol with α-tomatine. The observed aggregates were generally elongated structures, of a width ranging from about 40-70nm.

2D-monolayer formation of 3-monoacyl-sn-glycerols at the air/water interface. A comprehensive quantum chemical approach

Thermodynamic and structural aspects of the monolayer film formation of 3-monoacyl-sn-glycerol homologous series with the alkyl chain length n = 7–18 at the air/water interface are considered. The calculations are carried out within the framework of the semiempirical quantum chemical method PM3 and supported experimentally using surface pressure-area per molecule (π–A) isotherms, Brewster angle microscopy (BAM), as well as grazing incidence X-ray diffraction analysis (GIXD). A conformational analysis of 3-monoacyl-sn-glycerol monomers reveals three stable conformations of monomers with Monomer 1 as the possible basis for the construction of the most energetically advantageous structures of small clusters, which subsequently can form a 2D monolayer. Optimized tetramer structure of 3-monoacyl-sn-glycerol is considered as a unit cell of the 2D film with geometric parameters: a= 4.82 Å, b= 4.92 Å, and the angle between them θ = 91°. The molecular tilt angle of surfactant molecules with respect to the normal to the interface is 23.5°. These structural parameters are in good agreement with existing experimental data. The spontaneous clusterization threshold of 3-monoacyl-sn-glycerol at the air/water interface is 16 carbon atoms in the alkyl chain at standard temperature. The temperature dependences of the Ac area per film molecule at the beginning of the liquid-expanded–liquid-condensed (LE–LC) phase transition are analyzed. The values of the Ac change per 1 °C for 3-monoacyl-sn-glycerol are commensurable with corresponding values of other surfactant classes confirming the dominating role of intermolecular CH···HC interactions in the clusterization energy of surfactants.

Role of Sn(II) in Mediating the Formation and Organization of a Langmuir Monolayer.

The influence of the Sn(II) ion on the formation and morphology of an arachidic acid (AA) monolayer was investigated using Langmuir film formation technology, pressure-area (Π-A) isotherm measurements, and Brewster angle microscopy (BAM). Our findings indicate that AA Langmuir monolayers exhibit organization that depends on subphase pH and Sn2+ concentration. There are multiple equilibria that are relevant to the complexation of AA monolayers, and the balance of Sn(OH)n equilibria and Sn(AA)n equilibria gives rise to unusual monolayer structural effects. With Sn2+ in the subphase, the AA monolayer exhibits an isotherm characterized by the absence of a collapse point and with a pH-dependent change in isotherm shape not consistent with the formation of an ordered solid phase. The amphiphile headgroup equilibrium mediates the absence of collapse seen experimentally and the ability of the monolayer to retain organization at a surface pressure of ca. 70 mN/m. BAM images show that the morphology of the monolayer depends on the Sn2+ concentration, consistent with several species of Sn(AA)n, where n = 1, 2, or 3, contributing to the overall monolayer order.

Interaction between acetylsalicylic acid and a cationic amphiphile model: An experimental approach using surface techniques

Mechanical and morphological effects of monolayers of octadecylamine upon aspirin adsorption are monitored by Langmuir isotherms measurements and Brewster angle microscopy. Aspirin induced a notable expansion of the corresponding isotherms and a concentration-dependence of the mechanical stability of the films as a consequence of the subtle balance between the solubility of the amine and the monolayer stabilization induced by the ion-pairs, as corroborated by Brewster Angle Microscopy images. The incorporation of the aspirin into the interface was confirmed by UV–vis reflection spectroscopy. Some comments on the feasibility of using aliphatic amines for drug delivery of anionic species are presented.

Physicochemical Characteristics of Model Membranes Composed of Legionella gormanii Lipids

Legionella gormanii is one of the species belonging to the genus Legionella, which causes atypical community-acquired pneumonia. The most important virulence factors that enable the bacteria to colonize the host organism are associated with the cell surface. Lipids building the cell envelope are crucial not only for the membrane integrity of L. gormanii but also by virtue of being a dynamic site of interactions between the pathogen and the metabolites supplied by its host. The utilization of exogenous choline by the Legionella species results in changes in the lipids' composition, which influences the physicochemical properties of the cell surface. The aim of this study was to characterize the interfacial properties of the phospholipids extracted from L. gormanii cultured with (PL+choline) and without exogenous choline (PL-choline). The Langmuir monolayer technique coupled with the surface potential (SPOT) sensor and the Brewster angle microscope (BAM) made it possible to prepare the lipid monomolecular films (model membranes) and study their properties at the liquid/air interface at 20 °C and 37 °C. The results indicate the effect of the choline addition to the bacterial medium on the properties of the L. gormanii phospholipid membranes. The differences were revealed in the organization of monolayers, their molecular packing and ordering, degree of condensation and changes in the components' miscibility. These findings are the basis for further research on the mechanisms of adaptation of this pathogen, which by changing the native composition and properties of lipids, bypasses the action of antimicrobial compounds and avoids the host immune attack.

Investigating Adsorption of Cellulose Nanocrystals at Air–Liquid and Substrate–Liquid Interfaces after pH Manipulation

AbstractCoatings of anisotropic nanoparticles such as cellulose nanocrystals (CNCs) can provide tuneable physicochemical surface properties to a substrate such as modifying wettability. These coatings are often formed using dip coating, with CNCs enriched at the air–water interface transferred to a substrate as a monolayer. This process is commonly facilitated by surfactants, which can remain present in the final product, affecting coating properties. In this work, an “additive free” method for creating CNC coatings by exploiting electrostatic interactions within the pH window between pH 2–4 is demonstrated. Within this pH window, the air–water interface is positively charged and CNCs are negatively charged, with surface pressure tensiometry, X‐ray reflectivity, and Brewster angle microscopy indicating that CNCs are driven to the air–water interface. The optimal condition for monolayer coverage was pH 3; at pH 2 charge screening causes localized flocculation at the air–water interface, and at pH 4 interparticle repulsion leads to incomplete, patchy coverage. These findings successfully translate to dip coated CNC monolayers as characterized by atomic force microscopy, showing that the manipulation of pH can facilitate the surfactant‐free dip coating of CNCs, with advantages over the surfactants that are more typically used.

Phase behaviour and adsorption of deoxyribonucleic acid onto an azobenzene liquid crystalline ligand at the interfaces

Azobenzene liquid crystalline (ALC) ligand contains a cholesteryl group linked to an azobenzene moiety through a carbonyl dioxy spacer (C7) and terminated with an amine group as a polar head. The phase behaviour of the C7 ALC ligand at the air-water (A-W) interface is investigated employing surface manometry. The surface pressure-area per molecule isotherm shows that C7 ALC ligand exhibit two different phases following the phase sequence viz., liquid expanded (LE1 and LE2) and then collapse to three-dimensional crystallites. Further, our investigations under different pH conditions and in the presence of DNA reveal the following. Compared to the bulk, the acid dissociation constant (pKa) of an individual amine reduces to 5 at the interfaces. For pH (3.5) < pKa, the protonation of amine groups of C7 ALC ligand facilitates the condensation of the film and enhances the stability. For pH values > pKa, the phase behaviour of the ligand remains the same due to the partial dissociation of the amine groups. The presence of DNA in the sub-phase result in the expansion of isotherm to the higher area per molecule and the compressional modulus extracted reveals the phase sequence; liquid expanded, liquid condensed, followed by a collapse. Further, the kinetics of adsorption of DNA to the amine groups of the ligand is investigated, suggesting the interactions are influenced by surface pressure corresponding to different phases and pH of the sub-phase. Brewster angle microscope studies are carried out at different surface densities of the ligand as well as in the presence of DNA also supports this inference. Atomic force microscope is employed to acquire the surface topography and height profile of C7 ALC ligand (1 layer) after transferring on onto a silicon substrate using Langmuir Blodgett deposition. The difference in the surface topography and thickness of the film indicates the adsorption of DNA onto the amine groups of the ligand. The characteristic UV–visible absorption bands of the ligand films (10 layers) at the air-solid interface are tracked and the hypsochromic shift of these bands is also attributed to these DNA interactions.

Study of Interactions between Saponin Biosurfactant and Model Biological Membranes: Phospholipid Monolayers and Liposomes

The aim of this study was to determine the effect of saponins-rich plant extract on two model biological membranes: phospholipid monolayers and liposomes. The Langmuir monolayer technique was used to study the interactions of model phospholipid membranes with saponins. The π-A isotherms were determined for DPPE (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine) monolayer with the addition of various concentrations of licorice saponins extracts and subjected to qualitative as well as quantitative analysis. Additionally, relaxation studies of the obtained monolayers were carried out and morphological changes were examined using Brewster angle microscopy. Moreover, changes in the structure of phospholipid vesicles treated with solutions of saponins-rich plant extracts were assessed using the FTIR technique. The size and zeta potential of the liposomes were estimated based on DLS methods. The obtained results indicated that the saponins interact with the phospholipid membrane formed by DPPE molecules and that the stability of the mixed DPPE/saponins monolayer strongly depends on the presence of impurities in saponins. Furthermore, it was found that the plant extract rich in saponins biosurfactant interacts mainly with the hydrophilic part of liposomes.

Effect of partial O-methylation in dehydrodieugenol on its antitrypanosomal activity - correlation with the toxicity using cell membrane models

Biseugenol (1), a neolignan with antiprotozoal activity against Trypanosoma cruzi, was partially methylated, and the compound obtained – methyl biseugenol (2) – had its activity evaluated against the extracellular (trypomastigotes) and intracellular (amastigotes) forms of T. cruzi. It was observed that both compounds 1 and 2 exhibited similar effects against trypomastigotes (IC50 of 11.7 and 16.2 μM, respectively), whereas compound 2 displayed higher activity against amastigotes (IC50 = 8.2 μM) in comparison with biseugenol (IC50 = 15.4 μM). Additionally, reduced toxicity against NCTC cells for compound 2 was observed (CC50 > 200 μM), differently from compound 1 with CC50 = 58.0 μM. Aiming to understand better the molecular mechanism of the biological action of compound 2, the prodrug was incorporated into cellular membrane models constituted of Langmuir monolayers of the lipids dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE), dipalmitoylphosphatidylserine (DPPS), and dipalmitoylphosphatidylglycerol (DPPG). The lipid-drug interaction was inferred through tensiometry, surface potential, infrared spectroscopy (PM-IRRAS), and Brewster angle microscopy (BAM). The prodrug expanded DPPC and DPPG monolayers and condensed DPPE ones, as well as presented characteristic behaviors regarding the chemical structure of the lipid considering expansion-compression curves, surface potential-area isotherms, and stability of previously compressed monolayers to relevant-biological surface pressures. PM-IRRAS indicated a molecular disorder for DPPC and DPPS alkyl chains in the presence of the drug. BAM revealed the presence of domains in the DPPG and DPPE monolayers, which was probably induced by the prodrug. These data suggest, in general, that the lipid composition modulates the interaction of compound 2, whose results are expected to correlate to its trypanocidal activity, which involves the plasma membrane of T. cruzi as the primary target, i.e., the first barrier that the compound should encounter to interact with the microorganism.

Organization of the Interfacial Film of Nanoemulsions Stabilized by Porphyrin Derivatives.

Photodynamic therapies combining the action of a photosensitizer (PS), molecular oxygen, and light make it possible to destroy certain infectious sites and tumors. The incorporation of photosensitizers in nanocarriers allows for better control of their distribution in tissues and increases their concentration in the area that will be then illuminated. Nanoemulsions of glyceryl trioctanoate (GTO) have been designed in which pyropheophobide a (Pyro-A) or its lipid conjugate (Pyro-Lipid) are both stabilizing and photostimulable agents. In this work, we studied by surface pressure measurements and Brewster angle microscopy (BAM) analysis the organization of the interfacial films of nanodroplets. Comparison of preformed porphyrin nanoemulsions and two porphyrin-GTO mixtures, one mimicking the composition of the nanoemulsions and the other that of a porphyrin-rich interfacial film, highlighted the role of GTO and porphyrin derivatives in the formation, organization, and elasticity of the interfacial films in nanoemulsions. Pyro-Lipid and GTO can mix, and some of the GTO molecules remain inserted in the interfacial film at high surface pressures. In contrast, Pyro-A and GTO do not mix well and tend to segregate, leaving Pyro-A alone in the condensed interfacial film. The results of this study demonstrate the importance of characterizing the interfacial properties of porphyrin derivatives and their interaction with the oil to design stable nanoemulsions with well-controlled optical properties.

The Effect of Selected Flavonoids and Lipoic Acid on Natural and Model Cell Membranes: Langmuir and Microelectrophoretic Methods.

The influence of kaempferol (K), myricetin (M) and lipoic acid (LA) on the properties of natural erythrocytes, isolated from animal blood and biological membrane models (monolayers and liposomes) made of phosphatidylcholine (PC), cholesterol (CHOL), and sphingomyelin (SM), CHOL in a ratio of 10:9, was investigated. The Langmuir method, Brewster angle microscopy (BAM) and microelectrophoresis were used. The presented results showed that modification of liposomes with kaempferol, myricetin and lipoic acid caused changes in the surface charge density and the isoelectric point value. Comparing the tested systems, several conclusions were made. (1) The isoelectric point for the DPPC:Chol:M (~2.2) had lower pH values compared to lipoic acid (pH~2.5) and kaempferol (pH~2.6). (2) The isoelectric point for the SM-Chol with myricetin (~3.0) had lower pH values compared to kaempferol (pH~3.4) and lipoic acid (pH~4.7). (3) The surface charge density values for the DPPC:Chol:M system in the range of pH 2-9 showed values from 0.2 to -2.5 × 10-2 C m-2. Meanwhile, for the DPPC:Chol:K and DPPC:Chol:LA systems, these values were higher at pH~2 (0.7 × 10-2 C m-2 and 0.8 × 10-2 C m-2) and lower at pH~9 (-2.1 × 10-2 C m-2 and -1.8 × 10-2 C m-2), respectively. (4) The surface charge density values for the SM:Chol:M system in the range of pH 2-9 showed values from 0.5 to -2.3 × 10-2 C m-2. Meanwhile, for the DPPC:Chol:K and DPPC:Chol:LA systems, these values were higher at pH~2 (0.8 × 10-2 C m-2), and lower at pH~9 (-1.0 × 10-2 C m-2 and -1.8 × 10-2 C m-2), respectively. (5) The surface charge density values for the erythrocytes with myricetin in the range of pH 2-9 showed values from 1.0 to -1.8 × 10-2 C m-2. Meanwhile, for the erythrocytes:K and erythrocytes:LA systems, these values, at pH~2, were 1.3 × 10-2 C m-2 and 0.8 × 10-2 C m-2 and, at pH~9, -1.7 × 10-2 C m-2 and -1.0 × 10-2 C m-2, respectively.

Investigation on the relationship between lipid composition and structure in model membranes composed of extracted natural phospholipids

HypothesisUnravelling the structural diversity of cellular membranes is a paramount challenge in life sciences. In particular, lipid composition affects the membrane collective behaviour, and its interactions with other biological molecules. ExperimentsHere, the relationship between membrane composition and resultant structural features was investigated by surface pressure-area isotherms, Brewster angle microscopy and neutron reflectometry on in vitro membrane models of the mammalian plasma and endoplasmic-reticulum-Golgi intermediate compartment membranes in the form of Langmuir monolayers. Natural extracted yeast lipids were used because, unlike synthetic lipids, the acyl chain saturation pattern of yeast and mammalian lipids are similar. FindingsThe structure of the model membranes, orthogonal to the plane of the membrane, as well as their lateral packing, were found to depend strongly on their specific composition, with cholesterol having a major influence on the in-plane morphology, yielding a coexistence of liquid-order and liquid-disorder phases.