Brewster Angle Microscopy Images Research Articles

Morphology Observation of Two-Dimensional Monolayers of Model Proteins on Water Surface as Revealed by Dropping Method.

We have investigated the morphology of two-dimensional monolayers of gramicidin-D (GD) and alamethicin (Al) formed on the water surface by the dropping method (DM) using surface tension measurement (STm), Brewster angle microscopy (BAM), and atomic force microscopy (AFM). Dynamic light scattering (DLS) revealed that GD in alcoholic solutions formed a dimeric helical structure. According to the CD and NMR spectroscopies, GD molecules existed in dimer form in methanol and lipid membrane environments. The STm results and BAM images revealed that the GD dimer monolayer was in a liquid expanded (LE) state, whereas the Al monolayer was in a liquid condensed (LC) state. The limiting molecular area (A0) was 6.2 ± 0.5 nm2 for the GD-dimer and 3.6 ± 0.5 nm2 for the Al molecule. The AFM images also showed that the molecular long axes of both the GD-dimer and Al were horizontal to the water surface. The stability of each monolayer was confirmed by the time dependence of the surface pressure (π) observed using the STm method. The DM monolayer preparation method for GD-dimer and Al peptide molecules is a useful technique for revealing how the model biological membrane's components assemble in two dimensions on the water surface.

Interaction of sakuranetin with unsaturated lipids forming Langmuir monolayers at the air-water interface: A biomembrane model

This study investigates the interaction between sakuranetin, a versatile pharmaceutical flavonoid, and monolayers composed of unsaturated phospholipids, serving as a surrogate for cell membranes. The phospholipids were 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE). We conducted a series of experiments to comprehensively investigate this interaction, including surface pressure assessments, Brewster angle microscopy (BAM), and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). Our findings unequivocally demonstrate that sakuranetin interacts with these phospholipids, expanding the monomolecular films. Notably, regarding POPC, the presence of sakuranetin led to a reduction in stability and a decline in surface elasticity, which can likely be attributed to intricate molecular rearrangements at the interface. The visual evidence of aggregations in BAM images reinforces the interactions substantiated by PM-IRRAS, highlighting sakuranetin's interaction with the polar and nonpolar regions of POPC. However, it is worth noting that these aggregations do not appear to contribute significantly to the viscosity of the mixed film, and our investigations did not reveal any substantial hysteresis. In contrast, when examining POPE, we observed a minor reduction in thermodynamic stability, indicative of fewer rearrangements within the monolayer. This notion was further reinforced by the limited presence of aggregations in the BAM images. Sakuranetin also increased the rigidity of the lipid monolayer; nevertheless, the monolayer remained predominantly elastic, facilitating easy re-spreading on the surface, especially for the first lipid. PM-IRRAS analysis unveiled interactions between sakuranetin and POPE's polar and nonpolar segments, compellingly explaining the observed monolayer expansion. Taken together, our data suggest that sakuranetin was more effectively incorporated into the monomolecular layer of POPE, indicating that membranes comprised of POPC might exhibit a greater degree of interaction in the presence of this pharmacologically active compound.

The effect of structural changes on the self-assembly of novel green pyridinium-carboxylate gemini surfactants in Langmuir and Langmuir-Blodgett films.

Engineered molecules with tailored molecular structures have the potential to advance various disciplines by enhancing the properties of biological membranes. In this study, we investigated the fundamental interfacial behavior of newly synthesized, water insoluble, cationic pyridinium-carboxylate based gemini surfactants (GSs) using picolinic acid (PA), nicotinic acid (NA), and isonicotinic acid (INA) and their interactions with dipalmitoylphosphatidylcholine (DPPC) in Langmuir and Langmuir-Blodgett (LB) films. Two synthetic methodologies were employed: (a) connecting two alkyl pyridinecarboxylates through the nitrogen atoms with a xylenyl spacer, namely, PAGS, NAGS1, and INAGS; and (b) dimerizing two nicotinic acid molecules through ester linkages with 1,4-benzenedimethanol, and then quaternizing the pyridine nitrogens with hexadecyl chains to yield NAGS2. A combination of Brewster angle microscopy (BAM) and atomic force microscopy (AFM) imaging techniques yielded valuable insights into the morphology of the GS films and their mixtures with DPPC. Density functional theory (DFT) calculations were used to gain further information on the GSs structures and understand their assembly. The results indicate that the film of INAGS is the most hydrophobic film, and its monolayer is the least compressible. When the nitrogen atom and a carboxylate group of the headgroup are positioned closer to each other, the GS molecules tend to form aggregates instead of a continuous film which is observed for the INAGS surfactant. This observation is consistent with the DFT energy values of pair interactions, indicating that both PAGS and NAGS1 have closely packed conformations with high stabilization energy.

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.

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.

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.

Reorganization of the outer layer of a model of the plasma membrane induced by a neuroprotective aminosterol

Trodusquemine is an amphipathic aminosterol that has recently shown therapeutic benefit in neurodegenerative diseases altering the binding of misfolded proteins to the cell membrane. To unravel the underlying mechanism, we studied the interactions between Trodusquemine (TRO) and lipid monolayers simulating the outer layer of the plasma membrane. We selected two different compositions of dioleoylphosphatidylcholine (DOPC), sphingomyelin (SM), cholesterol (Chol) and monosialotetrahexosylganglioside (GM1) lipid mixture mimicking either a lipid-raft containing membrane (Ld+So phases) or a single-phase disordered membrane (Ld phase). Surface pressure-area isotherms and surface compressional modulus-area combined with Brewster Angle Microscopy (BAM) provided the thermodynamic and morphological information on the lipid monolayer in the presence of increasing amounts of TRO in the monolayer. Experiments revealed that TRO forms stable spreading monolayers at the buffer-air interface where it undergoes multiple reversible phase transitions to bi- and tri-layers at the interface. When TRO was spread at the interface with the lipid mixtures, we found that it distributes in the lipid monolayer for both the selected lipid compositions, but a maximum TRO uptake in the rafts-containing monolayer was observed for a Lipid/TRO molar ratio equal to 3:2. Statistical analysis of BAM images revealed that TRO induces a decrease in the size of the condensed domains, an increase in their number and in the thickness mismatch between the Ld and So phase. Experiments and MD simulations converge to indicate that TRO adsorbs preferentially at the border of the So domains. Removal of GM1 from the lipid Ld+So mixture resulted in an even greater TRO-mediated reduction of the size of the So domains suggesting that the presence of GM1 hinders the localization of TRO at the So domains boundaries.Taken together these observations suggest that Trodusquemine influences the organization of lipid rafts within the neuronal membrane in a dose-dependent manner whereas it evenly distributes in disordered expanded phases of the membrane model.

Effect of Silica Microparticles on Interactions in Mono- and Multicomponent Membranes.

Advancing our understanding of the mechanism of the interaction between inhaled pollutant microparticles and cell membrane components is useful to study the impact of fine particulate matter on human health. In this paper, we focus on the effect of cholesterol (Chol) molecules on the surface properties of a model membrane in the presence of silica microparticles (MPs). Mixed monolayers containing phospholipid-dipalmitoylphosphatidylcholine (DPPC), Chol and silica particle dispersions (MPs; 0.033% w/w, 0.33% w/w and 0.83% w/w) were formed and studied using the Langmuir monolayer technique complemented by Brewster Angle Microscopy (BAM) images. It was shown that Chol caused a condensation of the DPPC monolayer, which influenced the penetration of MPs and their interactions with the model membrane. The relaxation experiments of the lipid-MP monolayer proved that the presence of Chol molecules in the monolayer led to the formation of lipid and MP complexes. Strong interactions between Chol and MPs contributed to the formation of more stable monolayers. The presented results can be useful to better comprehend the interaction between particulate materials and the lipid components of biomembranes.

Melittin-solid phospholipid mixed films trigger amyloid-like nano-fibril arrangements at air-water interface

We used the Langmuir monolayers technique to study the surface properties of melittin toxin mixed with either liquid-condensed DSPC or liquid-expanded POPC phospholipids. Pure melittin peptide forms stable insoluble monolayers at the air-water interface without interacting with Thioflavin T (Th-T), a sensitive probe to detect protein amyloid formation. When melittin peptide is mixed with DSPC lipid at 50 % of peptide area proportion at the surface, we observed the formation of fibril-like structures detected by Brewster angle microscopy (BAM), but they were not observable with POPC. The nano-structures in the melittin-DSPC mixtures became Th-T positive labeling when the arrangement was observed with fluorescence microscopy. In this condition, Th-T undergoes an unexpected shift in the typical emission wavelength of this amyloid marker when a 2D fluorescence analysis is conducted.Even when reflectivity analysis of BAM imaging evidenced that these structures would correspond to the DSPC lipid component of the mixture, the interpretation of ATR-FTIR and Th-T data suggested that both components were involved in a new lipid-peptide rearrangement. These nano-fibril arrangements were also evidenced by scanning electron and atomic force microscopy when the films were transferred to a mica support. The fibril formation was not detected when melittin was mixed with the liquid-expanded POPC lipid. We postulated that DSPC lipids can dynamically trigger the process of amyloid-like nano-arrangement formation at the interface. This process is favored by the relative peptide content, the quality of the interfacial environment, and the physical state of the lipid at the surface.

Chemical Imaging of Lipid Segregation: Determining Different Length Scales of Heterogeneity with Compressive-Sensing Sum Frequency Generation Microscopy and Brewster Angle Microscopy

Membranes of various phospholipids may separate into different domains at micrometer length scales at the air-water interface. A significant challenge is to visualize the molecular organization and obtain chemical information on this surface. Langmuir-Blodgett monolayers of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) on fused silica were investigated with compressive sensing sum frequency generation (SFG) microscopy. Before and after mixing, SFG spectra for DSPC and DLPC revealed significant differences, indicating a structural change. Brewster angle microscopy images show phase separations that directly correlate the morphology of phospholipid mixtures with SFG images. Exploiting vibrational contrast in SFG images, exchange between the two phases was discovered, and quantitative thermodynamic analysis of lipid compositions in liquid-condensed and liquid-expanded (LE) phases was provided. Local SFG spectra reveal significant differences from one another, indicating the heterogeneity resulting from domain areas with distinct molecular orientation and conformation. Further heterogeneity across the domain boundary was presented on a finer scale, revealing an effect on DLPC due to the condensed phase DSPC, and the terminal methyl of DLPC perturbs the ordering of DSPC in the LE phase. This work demonstrates the heterogeneity of a two-dimensional binary lipid system mainly due to the aliphatic chain length and transition temperature difference.

Phospholipid acyl tail affects lipid headgroup orientation and membrane hydration.

Biomembrane hydration is crucial for understanding processes at biological interfaces. While the effect of the lipid headgroup has been studied extensively, the effect (if any) of the acyl chain chemical structure on lipid-bound interfacial water has remained elusive. We study model membranes composed of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) lipids, the most abundant lipids in biomembranes. We explore the extent to which the lipid headgroup packing and associated water organization are affected by the lipid acyl tail unsaturation and chain length. To this end, we employ a combination of surface-sensitive techniques, including sum-frequency generation spectroscopy, surface pressure measurements, and Brewster angle microscopy imaging. Our results reveal that the acyl tail structure critically affects the headgroup phosphate orientational distribution and lipid-associated water molecules, for both PE and PC lipid monolayers at the air/water interface. These insights reveal the importance of acyl chain chemistry in determining not only membrane fluidity but also membrane hydration.

Surface mechanical behavior of water-spread poly(styrene)–poly(ethylene glycol) (PS–PEG) micelles at the air–water interface: Effect of micelle size and polymer end/linking group chemistry

Hypothesis:The surface mechanical properties of poly(styrene)-poly(ethylene glycol) (PS–PEG) micelles are influenced by the PEG corona structure. Changes in micelle aggregation number as well as changes in the PEG end group and linking group chemistry of the PS–PEG block copolymer are expected to alter PEG corona characteristics and therefore affect surface mechanical properties of the resulting micelle film. Experiments:Different sized micelles comprised of PS–PEG block copolymer chains were formulated by equilibrating micelles in different ratios of acetone/water mixtures and subsequently removing acetone using dialysis. Additionally, micelles of a similar size and PS–PEG molecular weight but slightly different chemistry were formulated. The micelles were characterized using dynamic light scattering (DLS), transmission electron microscopy (TEM), 1H NMR, surface pressure–area isotherms and Brewster angle microscopy (BAM). Findings:The reduction in micelle aggregation number results in the subsequent monolayer having higher compressibility moduli and bending stiffnesses and collapsing at lower surface pressures. Micelle hydrophobicity was shown to improve readsorption of micelles to interface after collapse. Analysis of Brewster angle microscopy images of out-of-plane wrinkle structures which formed upon monolayer collapse indicates the presence of continuous 1 nm thick PEG layer which allows micelle monolayers to bend under high compression.

Penicillin-binding proteins (PBPs) determine antibiotic action in Langmuir monolayers as nanoarchitectonics mimetic membranes of methicillin-resistant Staphylococcus aureus

The membrane of methicillin-resistant Staphylococcus aureus (MRSA) contains penicillin-binding proteins (PBPs) in the phospholipidic bilayer, with the protein PBP2a being linked with the resistance mechanism. In this work we confirm the role of PBP2a with molecular-level information obtained with Langmuir monolayers as cell membrane models. The MRSA cell membrane was mimicked with a mixed monolayer of dipalmitoyl phosphatidyl glycerol (DPPG) and cardiolipin (CL), also incorporating PBP2a. The surface pressure-area isotherms and the Brewster angle microscopy (BAM) images for these mixed monolayers were significantly affected by the antibiotic meropenem, which is PBP2a inhibitor. The meropenem effects were associated with the presence of PBP2a, as they were absent in the Langmuir monolayers without PBP2a. The relevance of PBP2a was confirmed with results where the antibiotic methicillin, known to be unsuitable to kill MRSA, had the same effects on mixed DPPG/CL and DPPG/CL-PBP2a monolayers since it prevented PBP2a from incorporating in the monolayer. The biological implication of the findings presented here is that a successful antibiotic against MRSA should be able to interact with PBP2a, but in the membrane.

Morphological Behavior of DPPC-DMPC Two-dimensional Mixed Monolayer on Water Surface by Dropping Method

We have investigated the morphology of dipalmitoyl phosphatidyl choline (DPPC)-dimyristoyl PC (DMPC) mixed monolayer formed on the water surface by the dropping method using surface tension measurement (STm), Brewster angle microscopy (BAM), and infrared external reflection spectroscopy (IERS). The limiting molecular area (A0) obtained by STm showed that the negative deviation at < mole fraction (xDMPC)= 0.4 whereas the positive deviation at > xDMPC =0.6 when DMPC was added to the DPPC monolayer. BAM images also showed that the condensed rigid monolayer at xDMPC < 0.4 changed to the expandable monolayer at xDMPC > 0.5. Moreover, IER spectra showed that the alkyl chains of both DPPC and DMPC molecules are in trans conformation in mixed monolayer at xDMPC =0.2 whereas gauche conformation existed at xDMPC = 0.8. Above findings have justified the transition of flexible gauche conformation alkyl chains of DMPC molecule into rigid trans conformation by the addition of DPPC molecule at xDMPC < 0.4 whereas alkyl chains retained flexible gauche conformation in both DPPC and DMPC molecules at xDMPC > 0.6.

Influence of solvents on the morphology of Langmuir and Langmuir-Schaefer films of PCBM and PCBM-based oligomers and polymers.

Fullerene-based polymers and oligomers combined with non-fullerene acceptors show extremely high efficiencies in organic photovoltaic devices. Furthermore, fullerene-based materials are of interest for use in anti-cancer and anti-viral treatments, where their presence can enhance the efficacy of medication considerably. Therefore, it remains important to understand their morphology and electronic properties to improve devices and technological applications. The main goal of this study is to prepare and characterize Langmuir and Langmuir-Schaefer films of PCBM-based materials to investigate the influence of different solvents such as chloroform, toluene, and xylene, and co-components on their morphology. PCBM-based materials were thus studied either alone or in mixtures with a polythiophene derivative (poly(3-hexythiophene), P3HT) commonly used in organic photovoltaic devices. The formation of Langmuir films was studied using surface pressure isotherms and Brewster's angle microscopy (BAM), where the homogeneity, phase behavior, and morphology of the films were investigated. In addition, Langmuir-Schaefer films were characterized by UV-visible absorption spectroscopy, atomic force microscopy (AFM), and Raman spectroscopy, providing information on the morphology of the solid films. This study has shown that it is possible to successfully fabricate Langmuir and Langmuir-Schaefer films of PCBM and PCBM-based oligomers and polymers, both pure and in mixtures with P3HT, to compare their organization, roughness, and optical properties. With the Langmuir films, it was possible to estimate the area of the molecules and visualize their aggregation through BAM images, establishing a relationship between the area occupied by these materials and the solvent used. All characterization techniques corroborate that the use of chloroform significantly reduced the roughness of the LS films mixed with P3HT and also presented a higher ordering compared to films prepared with xylene solutions.

Triglyceride Lenses at the Air-Water Interface as a Model System for Studying the Initial Stage in the Biogenesis of Lipid Droplets.

Lipid droplets (LD) are intracellular structures consisting of an apolar lipid core, composed mainly of triglycerides (TG) and steryl esters, coated by a lipid-protein mixed monolayer. The mechanisms underlying LD biogenesis at the endoplasmic reticulum membrane are a matter of many current investigations. Although models explaining the budding-off of protuberances of phase-segregated TG inside bilayers have been proposed recently, the assumption of such initial blisters needs further empirical support. Here, we study mixtures of egg phosphatidylcholine (EPC) and TG at the air-water interface in order to describe some physical properties and topographic stability of TG bulk structures in contact with interfaces. Brewster angle microscopy images revealed the appearance of microscopic collapsed structures (CS) with highly reproducible lateral size (∼1 μm lateral radius) not varying with lateral packing changes and being highly stable at surface pressures (π) beyond collapse. By surface spectral fluorescence microscopy, we were able to characterize the solvatochromism of Nile Red both in monolayers and inside CS. This allowed to conclude that CS corresponded to a phase of liquid TG and to characterize them as lenses forming a three-phase (oil-water-air) system. Thereby, the thicknesses of the lenses could be determined, observing that they were dramatically flattened when EPC was present (6-12 nm compared to 30-50 nm for lenses on EPC/TG and TG films, respectively). Considering the shape of lenses, the interfacial tensions, and the Neumann's triangle, this experimental approach allows one to estimate the oil-water interfacial tension acting at each individual microscopic lens and at varying compression states of the surrounding monolayer. Thus, lenses formed on air-water Langmuir films can serve to assess variables of relevance to the initial step of LD biogenesis, such as the degree of dispersion of excluded-TG phase and shape, spatial distribution, and oil-water interfacial tension of lenses.

Surface and electrochemical properties of lipid raft model membranes and how they are affected by incorporation of statin

Cerivastatin belongs to the class of statins, drugs lowering blood cholesterol level by inhibiting the enzyme HMG-CoA reductase. The enzyme is located in the endoplasmic reticulum (ER) membrane, which is enriched in cholesterol and sphingolipids. Therefore, in the present study an equimolar mixture of 1,2-dioleoylo-sn‑glycero-3-phosphocholine (DOPC), cholesterol (Chol) and egg sphingomyelin (SM) was used to prepare a simple model of the ER membrane using the Langmuir technique. DOPC:Chol:SM 1:1:1 monolayers were characterized by surface pressure measurements and Brewster angle microscopy (BAM). The lipid raft formation was confirmed by a characteristic kink on the surface pressure – area per molecule (π-A) isotherm. Exposure of the model membrane to solutions containing cerivastatin led to the fluidization of the membranes, confirmed by the BAM images. The lipid monolayers were next transferred using the combined Langmuir-Blodgett (LB) – Langmuir-Schaefer (LS) approach onto the gold (111) substrates and the resulting supported bilayer was studied using electrochemical impedance spectroscopy (EIS). EIS measurements showed inhomogeneity of the bilayer and the presence of defects occurring on the borders of the raft islands. However, upon exposure to cerivastatin, part of these defects disappeared – they were filled with the statin molecules, which changed the properties of the bilayer. The disappearance of the minimum on the phase angle plot and impedance measurement data confirmed the decrease in the defectiveness of the layer – the resistance of the membrane increased while its capacitance decreased. The hydrophobic drug penetration into the hydrophobic core of the lipid layer led to increased barrier properties of the film despite its increased fluidity. Such serious modification of lipid membranes under influence of cerivastatin is one of the unwanted side effects of this drug and although it effectively decreased cholesterol levels in the body, its withdrawal from the pharmaceutical market had to be considered.

Morphological and Interaction Characteristics of Surface-Active Ionic Liquids and Palmitic Acid in Mixed Monolayers.

A series of water soluble, surface-active ionic liquids (SAILs), namely, 1-alkyl-3-methyl imidazolium chlorides ([Cn -mim]Cl) and their mixtures with palmitic acid (PA) are investigated in Langmuir monolayers and Langmuir-Blodgett films. It is inferred from the surface pressure-area isotherms that C16 -mim-IL mixes non-ideally with PA and stabilizes the binary mixed films. In addition, the residence of mim-IL at the water surface is enhanced as a function of the increasing alkyl side chain length. Generally, the compressional moduli values decrease upon increasing the content of the mim-ILs over a wide range of compositions. Furthermore, film relaxation measurements indicate that the IL component is selectively excluded from the mixed films upon achieving a certain target pressure. Brewster angle microscope images demonstrate minimal changes on the PA domains in the presence of either C4 - and C8 -mim-ILs, whereas presence of the hexadecyl counterpart results in the formation of condensed sheets. Atomic force microscopy imaging of deposited films show the formation of propeller-like aggregates when C8 - or C16 -mim-IL is present in the mixed films.

The impact of blue light in monolayers representing tumorigenic and nontumorigenic cell membranes containing epigallocatechin-3-gallate

Natural products such as epigallocatechin-3-gallate (EGCG) have been suggested for complementary treatments of cancer, since they lower toxic side effects of anticancer drugs, and possess anti-inflammatory and antioxidant properties that inhibit carcinogenesis. Their effects on cancer cells depend on interactions with the membrane, which is the motivation to investigate Langmuir monolayers as simplified membrane models. In this study, EGCG was incorporated in zwitterionic dipalmitoyl phosphatidyl choline (DPPC) and anionic dipalmitoyl phosphatidyl serine (DPPS) Langmuir monolayers to simulate healthy and cancer cells membranes, respectively. EGCG induces condensation in surface pressure isotherms for both DPPC and DPPS monolayers, interacting mainly via electrostatic forces and hydrogen bonding with the choline and phosphate groups of the phospholipids, according to data from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). Both monolayers become more compressible upon interaction with EGCG, which may be correlated to the synergy between EGCG and anticancer drugs reported in the literature. The interaction with EGCG is stronger for DPPC, leading to stronger morphological changes in Brewster angle microscopy (BAM) images and higher degree of condensation in the surface pressure isotherms. The changes induced by blue irradiation on DPPC and DPPS monolayers were largely precluded when EGCG was incorporated, thus confirming its antioxidant capacity for both types of membrane.