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• Sr-morin complex spontaneously forms at Langmuir monolayers. • Sr-morin complex formation change the lipid organization at the air-liquid interface. • Complexation was followed by UV–vis absorption and fluorescence techniques. • LB films harboring the Sr-morin complex support in vitro osteoblast growth. Flavonoid-metal complexes are widely studied because of their interesting luminescent behavior and biological activity. Despite the extensive exploration of flavonoid-metal coordination processes in solution, the formation of complexes using the flavonoid molecule inserted in a lipid membrane has been little investigated. This effect could provide important insight into the biological activity of flavonoids at lipid membranes and could represent an attractive strategy to design supramolecular structures. Here, we studied the complexation between Sr2+ and morin inserted in an octadecylphosphonic acid (OPA) Langmuir monolayer. This is a relevant system due to the synergism imposed by the association of the Sr2+ ability to control bone formation/resorption with the morin antioxidative effect. Morin incorporation into the OPA monolayers and further Sr2+ complexation were monitored by surface pressure isotherms. Electronic absorption spectroscopy and fluorescence techniques showed Sr-morin complexation both in solution and at the air-liquid interface. Although morin complexation has been described to occur only at basic pH, the specific thermodynamic properties at the air-liquid interface drove metal complexation. LB films were deposited on Ti surfaces, and the resulting OPA/Sr-morin coatings exhibited high surface free energy and increase on its polar component. This optimized surface feature supported further serum protein adsorption and osteoblast growth and differentiation, indicating that these lipid-based coatings are promising for bioactive coating design. This study paves the way for the use of this lipid-based coating in the design of implants for faster osteointegration. Moreover, flavonoid-metal complexation at membranes could also help to shed light on the biological role played by flavonoids. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Sphingomyelin (SM) structure is a key factor on membrane domain formation. • PM-IRRAS spectra of 16:0 vs 24:1-SM and mixtures with DOPC and Chol were analyzed. • Acyl chains packing and orientation of polar head groups were affected by the unsaturation in 24:1-SM. • 24:1-SM amide groups remained mostly as non-H-bonded when mixed with DOPC and Chol. • These findings may play a key role in cell signaling and binding of biomolecules. Abstract Membrane structure is a key factor for the cell's physiology, pathology, and therapy. Evaluating the importance of lipid species such as N-nervonoyl sphingomyelin (24:1-SM) —able to prevent phase separation— to membrane structuring remains a formidable challenge. This is the first report in which polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) is applied to investigate the lipid-lipid interactions in 16:0 vs 24:1-SM monolayers and their mixtures with 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) and cholesterol (Chol) (DOPC/SM/Chol 2:1:1). From the results we inferred that the cis double bond (Δ15) in 24:1-SM molecule diminishes intermolecular H-bonding and chain packing density compared to that of 16:0-SM. In ternary mixtures containing 16:0-SM, the relative intensity of the two components of the Amide I band reflected changes in the H-bonding network due to SM-Chol interactions. In contrast, the contribution of the main components of the Amide I band in DOPC/24:1-SM/Chol remained as in 24:1-SM monolayers, with a larger contribution of the non-H-bonded component. The most interesting feature in these ternary films is that the C O stretching mode of DOPC appeared with an intensity similar to that of SM Amide I band in DOPC/16:0-SM/Chol monolayers (a two-phase [ Lo / Le ] system), whereas an extremely low intensity of the C O band was detected in DOPC/24:1-SM/Chol monolayers (single Le phase). This is evidence that the unsaturation in 24:1-SM affected not only the conformational properties of acyl chains but also the orientation of the chemical groups at the air/water interface. The physical properties and overall H-bonding ability conferred by 24:1-SM may have implications in cell signaling and binding of biomolecules. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Efficient uptake of inorganic nanoparticles hinders their application biomedicine. • Fluorinated ligands are a promising strategy for enhancing the cell uptake. • Experimental and computational studies describe the interaction with membrane. • Hydrophobicity provided by the fluorine atoms is key in the uptake. Abstract Fluorescent inorganic quantum dots are highly promising for biomedical applications as sensing and imaging agents. However, the low internalization of the quantum dots, as well as for most of the nanoparticles, by living cells is a critical issue which should be solved for success in translational research. In order to increase the internalization rate of inorganic CdSe/ZnS quantum dots, they were functionalized with a fluorinated organic ligand. The fluorinated quantum dots displayed an enhanced surface activity, leading to a significant cell uptake as demonstrated by in vitro experiments with HeLa cells. We combined the experimental and computational results of Langmuir monolayers of the DPPC phospholipid as a model cell membrane with in vitro experiments for analyzing the mechanism of internalization of the fluorinated CdSe/ZnS quantum dots. Surface pressure-molecular area isotherms suggested that the physical state of the DPPC molecules was greatly affected by the quantum dots. UV–vis reflection spectroscopy and Brewster Angle Microscopy as in situ experimental techniques further confirmed the significant surface concentration of quantum dots. The disruption of the ordering of the DPPC molecules was assessed. Computer simulations offered detailed insights in the interaction between the quantum dots and the phospholipid, pointing to a significant modification of the physical state of the hydrophobic region of the phospholipid molecules. This phenomenon appeared as the most relevant step in the internalization mechanism of the fluorinated quantum dots by cells. Thus, this work sheds light on the role of fluorine on the surface of inorganic nanoparticles for enhancing their cellular uptake. [ABSTRACT FROM AUTHOR]

5SO 3 H-8-hydroxyquinoline coordinated to Europium (Eu-5SO 3 -HQ) was incorporated in biomembrane models using Langmuir monolayers. Dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylserine (DPPS) were employed, representing mammalian cells and dioctadecyldimethylammonium bromide (DODAB) as a positively charged lipid to study the contrast with negatively charged lipids. Tensiometric, rheological and spectroscopic techniques were employed to characterize Eu-5SO 3 -HQ- lipid monolayer interactions. The complex condenses all the monolayer indicating interactions with the lipids' polar heads, but with distinctive effects on the mechanical and rheological properties. While the complex decreases the compression and elastic moduli of DPPC and DPPS monolayers, it increases for DODAB, also decreasing its lateral viscosity. Infrared spectroscopy shows that the interaction of Eu-5-SO 3 -HQ alters the ordering of the lipids' alkyl chains, impacting the monolayer's molecular packing. These results show that the interaction of Eu-5SO 3 -HQ with lipid monolayers at the air-water is modulated by the composition of the polar head, which can be supportive in the preparation of nanodevices for molecular probing. [Display omitted] • An Eu-hydroxyquinoline was incorporated in Langmuir monolayers. • Surface chemistry characterized molecular interactions. • Interactions with lipid polar heads depend on the charge. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The reaction between 1O 2 and unsaturated groups of DOPC and POPC leads to hydroperoxide formation. • The PM-IRRAS results confirm the migration of hydroperoxides from the hydrophobic core of the membrane toward the water/monolayer interface. • The decrease in membrane thickness inferred from GIXOS measurements is consistent with lipid hydroperoxidation for DOPC and POPC monolayers. Abstract Photodynamic therapy (PDT) efficiency depends on many factors including the incorporation of the photosensitizer (PS) in cell membranes and possible lipid hydroperoxidation. In this study, we show that hydroperoxidation may be photoinduced when eosin Y is incorporated into Langmuir monolayers that serve as cell membrane models. This occurs for Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), which have unsaturation in their hydrophobic chains. In contrast, light irradiation had no effect on monolayers of saturated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). Evidence of hydroperoxidation was obtained from the area increase in eosin-containing DOPC and POPC monolayers upon irradiation, which was accompanied by a decrease in monolayer thickness according to grazing incidence X-ray off-specular scattering (GIXOS) data. Furthermore, the changes in polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) induced by irradiation were consistent with hydroperoxide migration toward the lipid hydrophilic heads.. In summary, this combination of experimental methods allowed us to determine the effects of eosin Y interaction with cell membrane models under irradiation, which may be associated with the underlying mechanisms of eosin Y as photosensitizer in PDT. [ABSTRACT FROM AUTHOR]

Cyclosporin A (CsA), a hydrophobic peptide, mainly known for its immunosuppressant properties, has shown a broad range of biological activities, including antimalarial action. Since CsA was found to be active on membrane level, it was subjected for investigations involving membrane models. Our former studies on interactions between CsA and different membrane lipids using Langmuir monolayer technique indicated its affinity for sphingomyelin (SM). Inspired by this finding we have extended our experiments on multicomponent systems and performed systematic investigations of CsA behavior towards artificial membranes containing different mutual proportion of sphingomyelin and cholesterol (Chol). Langmuir monolayer results have been complemented with in-situ films structure visualization applying Brewster angle microscopy (BAM) and, after films transfer onto solid support, atomic force microscopy (AFM). Our results show that cyclosporin A introduced to SM:Chol mixed monolayers distributes differently, depending on SM-to-Chol proportion. In raft-mimicking (2:1) stoichiometry, even distribution of the drug within SM:Chol matrix was observed. However, in SM:Chol model membranes of different proportion (3:1; 1:1; 1:2), containing either the excess of unbound sphingomyelin or cholesterol in addition to model lipid raft domains, introduction of CsA induced a phase separation. [ABSTRACT FROM AUTHOR]

Some biological properties of violacein are believed to be associated with their interactions with lipid surfaces, encouraging research on the identification of membrane sites capable of drug binding. In this study, we investigated the interaction of violacein with cell membrane models represented by Langmuir monolayers of selected lipids: one representing healthy cellular membranes: dipalmitoylphosphatidylcholine, DPPC, and the other one representing tumorigenic cellular membranes, dipalmitoylphosphatidylserine, DPPS. It is shown that even small amounts of the compound affect the surface pressure-area isotherms as well as the surface vibrational spectra of the lipid monolayers, which points to a significant interaction. Such effects depend on the electrical charge of the monolayer-forming molecules, with the drug activity being particularly distinctive for negatively charged lipids in relation to zwitterionic lipids. Morphological analysis also suggests that violacein at the air-water interface is homogenized when incorporated in both lipids. Although the interaction of violacein with the lipids affects viscoelastic and structural properties of the Langmuir monolayer, it is not present permeability through lipid bilayers, as investigated using liposomes. These results therefore may have important implications in understanding how violacein acts on specific sites of the cellular membrane, and evidence the fact that the lipid composition of the monolayer modulates the interaction with the lipophilic drug. [ABSTRACT FROM AUTHOR]

Ocular inflammation is one of the most prevalent diseases in ophthalmology and it is currently treated using eye drops of nonsteroidal antiinflammatory drugs such as dexibuprofen (DXI). However, their bioavailability is low and therefore, PLGA nanoparticles constitute a suitable approach to be administered as eyedrops. Therefore, DXI has been encapsulated into PLGA nanoparticles (DXI-NPs). Although the eye, and specifically the cornea, suffers from age-related changes in its composition, current medications are not focused on these variations. Therefore, to elucidate the interaction mechanism of DXI-NPs with the cornea in relation with age, two different corneal membrane models have been developed (corresponding to adult and elder population) using lipid monolayers, large and giant unilamellar vesicles. Interactions of both DXI and DXI-NPs were studied with these models by means of Langmuir balance technique, dipole potential, anisotropy and confocal microscopy. In addition, fluorescently labelled nanoparticles were administered to mice in order to corroborate these data obtained in vitro. It was observed that DXI-NPs interact with lipid membranes through an adhesion process, mainly in the rigid regions and afterwards DXI-NPs are internalized by a wrapping process. Furthermore, differences on the dipole potential caused by DXI-NPs in each corneal membrane have been obtained due to the increase of membrane rigidity on the ECMM. Additionally, it can be confirmed that DXI-NPs adhere to L o phase and also inside the lipid membrane. Finally, in vitro and in vivo results corroborate that DXI-NPs are adhered to the more ordered phase. Finally, differences between interactions of DXI-NPs with the elder and adult corneal tissue were observed. [Display omitted] ● Two customized corneal lipid membrane have been developed and characterized. ● DXI NPs interact with lipid-based membranes through an adhesion process. ● DXI NPs interact in the rigid areas and are internalized by a wrapping process. ● DXI NPs are more retained in adult than elder membranes in vitro and in vivo. [ABSTRACT FROM AUTHOR]

Uropathogenic strains of Escherichia coli produce virulence factors, such as the protein toxin alpha-hemolysin (HlyA), that enable the bacteria to colonize the host and establish an infection. HlyA is synthetized as a protoxin (ProHlyA) that is transformed into the active form in the bacterial cytosol by the covalent linkage of two fatty-acyl moieties to the polypeptide chain before the secretion of HlyA into the extracellular medium. The aim of this work was to investigate the effect of the fatty acylation of HlyA on protein conformation and protein-membrane interactions. Polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) experiments were performed at the air-water interface, and lipid monolayers mimicking the outer leaflet of red-blood-cell membranes were used as model systems for the study of protein-membrane interaction. According to surface-pressure measurements, incorporation of the acylated protein into the lipid films was faster than that of the nonacylated form. PM-IRRAS measurements revealed that the adsorption of the proteins to the lipid monolayers induced disorder in the lipid acyl chains and also changed the elastic properties of the films independently of protein acylation. No significant difference was observed between HlyA and ProHlyA in the interaction with the model lipid monolayers; but when these proteins became adsorbed on a bare air-water interface, they adopted different secondary structures. The assumption of the correct protein conformation at a hydrophobic-hydrophilic interface could constitute a critical condition for biologic activity. [ABSTRACT FROM AUTHOR]

From the point of view of the possible medical applications of POSS (polyhedral oligomeric silsesquioxanes), it is crucial to analyse interactions occurring between POSS and model biological membrane at molecular level. Knowledge of the interaction between POSS and DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) allows prediction of the impact of POSS contained in biomaterials or cosmetics on a living organism. In the study presented, the surface properties and morphology of Langmuir monolayers formed by mixtures of POSS and the phospholipid (DPPC) at the air/water surface are examined. We selected two POSS derivatives, with completely different chemical structure of substituents attached to the corner of the silicon open cage, which allowed the analysis of the impact of the character of organic moieties (strongly hydrophobic or clearly hydrophilic) on the order of POSS molecules and their tendency to form self–aggregates at the air/water surface. POSS derivatives significantly changed the profile of the π–A isotherms obtained for DPPC but in different ways. On the basis of the regular solution theory, the miscibility and stability of the two components in the monolayer were analysed in terms of compression modulus ( C s −1 ), excess Gibbs free energy (Δ G exc ), activity coefficients ( γ ) and interaction parameter ( ξ ). The results obtained indicate the existence of two different interaction mechanisms between DPPC and POSS which depend on the chemical character of moieties present in POSS molecules. [ABSTRACT FROM AUTHOR]

In this present work, the adsorption of the enzyme lactase onto Langmuir monolayers of the phospholipid dimyristoylphosphatidic acid (DMPA) was investigated and characterized with surface pressure-area isotherms, surface potential-area isotherms and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). The adsorption of the enzyme at the air-water interface expanded the lipid monolayer and increased the film compressibility at high surface pressures. Amide bands in the PM-IRRAS spectra were identified, with the C N and C O dipole moments lying parallel to the monolayer plane, revealing that the structuring of the enzyme into β-sheets was kept in the mixed monolayer. The enzyme-lipid films were transferred from the floating monolayer to solid supports as Langmuir-Blodgett (LB) films and characterized with fluorescence spectroscopy and atomic force microscopy. The catalytic activity of the films was measured and compared to the homogenous medium. The enzyme accommodated in the LB films preserved more than 80% of the enzyme activity after 20 days, in contrast for the homogeneous medium, which preserved less than 60% of the enzyme activity. The method presented in this present work not only allows for an enhanced catalytic activity toward lactose, but also can help explain why certain film architectures exhibit better performance. [ABSTRACT FROM AUTHOR]

The tear film lipid layer (TFLL) is a unique biological membrane of importance to the maintenance of ocular surface health. The underlying factors at play, e.g. the ability to retard evaporation and offer protection from the environment, are all closely connected to the properties of individual lipid components and their interplay. The TFLL contains unique ultra-long polar lipid species such as O -acyl-ω-hydroxy fatty acids, type I-St diesters and type II diesters, which are considered important for its proper function. Herein, we have synthesized model compounds from these categories and studied their biophysical and surface rheological properties at the aqueous interface. Altogether, we provide insights on the distinct biophysical profiles of these lipid classes and discuss how their interplay may affect the structure and function of the TFLL. [Display omitted] • Protocols for the synthesis of TFLL lipids is supplied. • Detailed characterization data of OAHFAs and type II/type I-St diesters is supplied. • Langmuir monolayer experiments reveal the biophysical profiles of these species. • Unique features of ultra-long OAHFAs are revealed through studies on mixtures. • The possible roles of these lipids in the nonpolar/polar lipid layer is discussed. [ABSTRACT FROM AUTHOR]

Antimicrobial resistance has reached alarming levels in many countries, thus leading to a search for new classes of antibiotics, such as antimicrobial peptides whose activity is exerted by interacting specifically with the microorganism membrane. In this study, we investigate the molecular-level mechanism of action for Labaditin (Lo), a 10-amino acid residue cyclic peptide from Jatropha multifida with known bactericidal activity against Streptococcus mutans. We show that Lo is also effective against Staphylococcus aureus ( S. aureus ) but this does not apply to its linear analogue (L 1 ). Using polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), we observed with that the secondary structure of Lo was preserved upon interacting with Langmuir monolayers from a phospholipid mixture mimicking S. aureus membrane, in contrast to L 1 . This structure preservation for the rigid, cyclic Lo is key for the self-assembly of peptide nanotubes that induce pore formation in large unilamellar vesicles (LUVs), according to permeability assays and dynamic light scattering measurements. In summary, the comparison between Labaditin (Lo) and its linear analogue L 1 allowed us to infer that the bactericidal activity of Lo is more related to its interaction with the membrane. It does not require specific metabolic targets, which makes cyclic peptides promising for antibiotics without bacteria resistance. [ABSTRACT FROM AUTHOR]

The interaction between chitosans and Langmuir monolayers mimicking cell membranes has been explained with an empirical scheme based on electrostatic and hydrophobic forces, but so far this has been tested only for dimyristoyl phosphatidic acid (DMPA). In this paper, we show that the mode of action in such a scheme is also valid for dipalmitoyl phosphatidyl choline (DPPC) and dipalmitoyl phosphatidyl glycerol (DPPG), whose monolayers were expanded and their compressibility modulus decreased by interacting with chitosans. In general, the effects were stronger for the negatively charged DPPG in comparison to DPPC, and for the low molecular weight chitosan (LMWChi) which was better able to penetrate into the hydrophobic chains than the high molecular weight chitosan (Chi). Penetration into the hydrophobic chains was confirmed with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and sum frequency generation (SFG) spectroscopy. A slight reduction in conformational order of the lipid chains induced by the chitosans was quantitatively estimated by measuring the ratio between the intensities of the methyl (r + ) and methylene (d + ) peaks in the SFG spectra for DPPG. The ratio decreased from 35.6 for the closely packed DPPG monolayer to 7.0 and 6.6 for monolayers containing Chi and LMWChi, respectively. Since in both cases there was a significant phospholipid monolayer expansion, the incorporation of chitosans led to chitosan-rich and lipid-rich condensed domains, which mantained conformational order for their hydrophobic tails. The stronger effects from LMWChi are ascribed to an easier access to the hydrophobic tails, as corroborated by measuring aggregation in solution with dynamic light scattering, where the hydrodynamic radius for LMWChi was close to half of that for Chi. Taken together, the results presented here confirm that the same mode of action applies to different phospholipids that are important constituents of mammalian (DPPC) and bacterial (DPPG) cell membranes. [ABSTRACT FROM AUTHOR]

Preserving the catalytic activity of enzymes immobilized in bioelectronics devices is essential for optimal performance in biosensors. Therefore, ultrathin films in which the architecture can be controlled at the molecular level are of interest. In this work, the enzyme rhodanese was adsorbed onto Langmuir monolayers of the phospholipid dimyristoylphosphatidic acid and characterized by surface pressure-area isotherms, polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS), and Brewster angle microscopy (BAM). The incorporation of the enzyme (5% in mol) in the lipid monolayer expanded the film, providing small surface domains, as visualized by BAM. Also, amide bands could be identified in the PM-IRRAS spectra, confirming the presence of the enzyme at the air–water interface. Structuring of the enzyme into α-helices was identified in the mixed monolayer and was preserved when the film was transferred from the liquid interface to solids supports as Langmuir–Blodgett (LB) films. The enzyme-lipid LB films were then characterized by fluorescence spectroscopy, PM-IRRAS, and atomic force microscopy. Measurements of the catalytic activity towards cyanide showed that the enzyme accommodated in the LB films preserved more than 87% of the enzyme activity in relation to the homogeneous medium. After 1 month, the enzyme in the LB film maintained 85% of the activity in contrast to the homogeneous medium, which 24% of the enzyme activity was kept. The method presented in this work not only points to an enhanced catalytic activity toward cyanide, but also may explain why certain film architectures exhibit an improved performance. [ABSTRACT FROM AUTHOR]

Sulfated glycosaminoglycans are precursors of the extracellular matrix used to treat diseases related to blood clotting and degenerative joint diseases. These medical applications have been well established, but the mode of action at the molecular level, which depends on the interaction with cell membranes, is not known in detail. In this study, we investigated the interaction between chondroitin sulfate (CS) and phospholipid monolayers that mimic cell membranes. From surface pressure isotherms and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), CS was found to interact mainly with the polar groups of dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylglycerol (DPPG), with negligible penetration into the hydrophobic tails and only small changes in monolayer elasticity for the packing corresponding to a real cell membrane. The changes in surface pressure and surface potential isotherms depended on CS concentration and on the time allowed for its adsorption onto the monolayer, which points to a dynamic adsorption-desorption process. The charge of the phospholipid was also relevant, since CS induced order into DPPC monolayers while the opposite occurred for DPPG, according to the PM-IRRAS spectra. In summary, interaction with polar groups is responsible for the CS effects on model cell membranes. [ABSTRACT FROM AUTHOR]

Neuronal Calcium Sensor-1 (NCS1) belongs to the family of Neuronal Calcium Sensor (NCS) proteins. NCS1 is composed of four EF-hand motifs and an N-terminal myristoylation. However, the presence of a calcium–myristoyl switch in NCS1 and its role in the membrane binding are controversial. The model of Langmuir lipid monolayers is thus used to mimic the cell membrane in order to characterize the membrane interactions of NCS1. Two binding parameters are calculated from monolayer measurements: the maximum insertion pressure, up to which protein binding is energetically favorable, and the synergy, reporting attractive or repulsive interactions with the lipid monolayers. Binding membrane measurements performed in the presence of myristoylated NCS1 reveal better binding interactions for phospholipids composed of phosphoethanolamine polar head groups and unsaturated fatty acyl chains. In the absence of calcium, the membrane binding measurements are drastically modified and suggest that the protein is more strongly bound to the membrane. Indeed, the binding of calcium by three EF-hand motifs of NCS1 leads to a conformation change. NCS1 arrangement at the membrane could thus be reshuffled for better interactions with its substrates. The N-terminal peptide of NCS1 is composed of two amphiphilic helices involved in the membrane interactions of NCS1. Moreover, the presence of the myristoyl group has a weak influence on the membrane binding of NCS1 suggesting the absence of a calcium–myristoyl switch mechanism in this protein. The myristoylation could thus have a structural role required in the folding/unfolding of NCS1 which is essential to its multiple biological functions. [ABSTRACT FROM AUTHOR]

Drug-induced phospholipidosis indicates an accumulation of phospholipids within lysosomes, which can occur during therapeutic treatment. Whether or not phospholipidosis represents a toxicological phenomenon is still under investigation, and in the last decade the Food and Drug Administration has been raising concerns about the possible consequences of this adverse event. Cationic amphiphilic drugs represent the majority of phospholipidosis inducers, followed by aminoglycoside and macrolide antibiotics. Although the mechanism of phospholipidosis induction is still uncertain, the interaction of drugs with phospholipids in the lysosomal membrane represents a key step. Therefore, the study of the drug/lipid complex formation will provide valuable insight into the causation of phospholipidosis at the molecular level and to identify the potential phospholipidosis risk associated with drug. In this study, we investigated the insertion profile of eleven drugs with known phospholipidosis effect into preformed Langmuir monolayers of various lipid compositions, to evaluate for the first time the drug/lipid interaction for phospholipidosis inducers and non-inducers in a dynamic approach. We found that the addition of dipalmitoylphosphatidylserine (DPPS) to dipalmitoylphosphatidylcholine (DPPC) to form the lipid monolayer allowed a clear identification of the phospholipidosis effect of the selected drugs based on the variation of the surface pressure, not only for cationic amphiphilic drugs but also for the aminoglycoside and the macrolide antiobiotics tested. Compared to a standard PAMPA assay, the new method appears to be more effective for the study of poorly soluble drugs. [ABSTRACT FROM AUTHOR]

The incorporation of silica nanoparticles (NPs) from the subphase into Langmuir lipid monolayers formed by three components, 1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) and Cholesterol (Chol), modifies the thermodynamic and rheological behavior, as well as the structure of the pristine lipid film. Thus, the combination of structural characterization techniques, such as Brewster Angle Microscopy (BAM) and Atomic Force Microscopy (AFM), with interfacial thermodynamic and dilational rheology studies has allowed us to deepen on the physico-chemical bases governing the interaction between lipid molecules and NPs. The penetration of NPs driven by the interaction (electrostatic or hydrogen bonds) with the polar groups of the lipid molecules affects the phase behaviour (surface pressure-area, П − A , isotherm) of the monolayer. This can be easily rationalized considering the modification of the packing and cohesion of the molecules at the interface as revealed BAM and AFM images. Furthermore, oscillatory barrier experiments have allowed obtaining information related to the effect of NPs on the monolayer response under dynamic conditions that presents a critical impact on the characterization of biological relevant systems because most of the processes of interest for these systems present a dynamic character. [ABSTRACT FROM AUTHOR]

Chitosan is a versatile and biocompatible cationic antimicrobial polymer obtained from sustainable sources that is effective against a wide range of microorganisms. Although it is soluble only at low pH, chitosan oligomers (ChitO) are soluble in pure water and thus more appropriate for antibacterial applications. Although there is a vast literature on chitosan's antimicrobial activity, the molecular details of its interaction with biomembranes remain unclear. Here we investigate these molecular interactions by resorting to phospholipid Langmuir films (zwitterionic DPPC and anionic DPPG) as simplified membrane models (for mammalian and bacterial membranes, respectively), and using SFG vibrational spectroscopy to probe lipid tail conformation, headgroup dynamics and interfacial water orientation. For comparison, we also investigate the interactions of another simple cationic antimicrobial polyelectrolyte, poly(allylamine) hydrochloride – PAH. By forming the lipid films over the polyelectrolyte solutions, we found that both have only a very small interaction with DPPC, but PAH adsorption is able to invert the interfacial water orientation (membrane potential). This might explain why ChitO is compatible with mammalian cells, while PAH is toxic. In contrast, their interaction with DPPG films is much stronger, even more so for ChitO, with both insertion within the lipid film and interaction with the oppositely charged headgroups. Again, PAH adsorption inverts the membrane potential, while ChitO does not. Finally, ChitO interaction with DPPG is weaker if the antimicrobial is injected underneath a pre-assembled Langmuir film, and its interaction mode depends on the time interval between end of film compression and ChitO injection. These differences between ChitO and PAH effects on the model membranes highlight the importance of molecular structure and intermolecular interactions for their bioactivity, and therefore this study may provide insights for the rational design of more effective antimicrobial molecules. [Display omitted] • Interaction between antimicrobial polymers and cell membrane models were studied. • Surface pressure isotherms and SFG spectroscopy are important tools to assess interaction mechanism. • Antimicrobial interaction with lipid monolayers depends on electrostatics and their structure. • Methodology affects results: subphases containing the antimicrobial vs. its injection under a lipid film. • Results provide insights for the rational design of effective antimicrobial molecules. [ABSTRACT FROM AUTHOR]

Studying interactions between potential anticancer drugs and cell membrane models is of great interest to explore the capability of novel drugs in the development of anticancer treatments. Lipid membrane models are useful to understand cellular interactions and to discern drug mechanism action. Here, the interactions of curcumin, as a bioactive natural compound with anti-cancer properties, with both healthy and cancerous or tumor cell membrane models, based on Langmuir monolayers, have been studied. The healthy-cell membrane model is composed of cholesterol 67%, and saturated lipid dipalmitoylphosphatidylcholine 33%. The cancerous-cell-membrane-model is composed of a lower proportion of cholesterol, 25%, and unsaturated lipid sphingomyelin 75%. To compare their interaction with curcumin we report the compression isotherms registered for both lipid membrane models and curcumin in different proportions, their compression moduli and the thermodynamic interaction parameters. From this analysis, we evidence a destabilizing interaction between curcumin and the cancerous cell membrane model in comparison with the healthy one. This interaction is further visualized by micro-Brewster Angle and Atomic Force Microscopies. Our experiments show that the drug enhances cohesion in the healthy membrane model whereas it fluidifies the cancerous cell membrane model causing thermodynamic destabilization. These are useful results to improve the selectivity of the drug avoiding adverse side effects of most current anticancer therapies. [Display omitted] • Langmuir monolayers as Biotechnological platform to study relevant interactions. • Interactions between curcumin drug and healthy and tumor cell membrane models. • Curcumin enhances cohesion in the healthy membrane model and fluidifies the tumor one. • Evidence of destabilizing interactions between curcumin and tumor membrane model. • The interactions have been visualized by BAM and AFM microscopies [ABSTRACT FROM AUTHOR]

Molecular self-assembly of nucleosides is important, and the self-assembled nanostructures may be used for drug delivery and targeting. Gemcitabine (GEM) is an important anticancer nucleoside analog though deactivation and multi-drug resistance frequently happen. Four N-fatty acyl derivatives of cyclic phosphoryl GEM were prepared based on the theory of self-assembled drug delivery systems and the HepDirect prodrug technique wherein the prodrug could be degraded by the cytochrome P 450 isozymes in hepatocytes to release active drugs. They are cyclic phosphoryl N-octyl gemcitabine (CPOG), cyclic phosphoryl N-dodecanoyl gemcitabine (CPDG), cyclic phosphoryl N-hexadecanoyl gemcitabine (CPHG), and cyclic phosphoryl N-octadecanoyl gemcitabine (CPODG). Their amphiphilicity and self-assembling property were explored. The self-assembled nanostructures of them were prepared and simulated. The in vitro anticancer activities of the nanostructures were investigated. The derivatives formed the Langmuir monolayers at the air/water interface, though their surface pressure–molecular area isotherms were different with dependency of the length of lipid chains. The derivatives self-assembled into the vesicular or rice-like nanostructures based on the hydrophobic interaction between lipid chains when injected into water, in accordance with the results of computer simulation. The nanostructures showed higher anticancer effects on HepG2 cells than GEM. The nanostructures are promising anticancer nanomedicines. [ABSTRACT FROM AUTHOR]

α-Amyrin (AMalf) and ursolic acid (Urs) are ursane-type pentacyclic triterpenes which exhibit wide spectrum of antibacterial activity. These surface active compounds can be incorporated into bacterial membranes and alter their structure and function; however, the exact mechanism of their action still needs to be elucidated. Thus, we decided to study the interactions of these terpenes with specific anionic phospholipids:cardiolipins and phosphatidylglycerols extracted from Escherichia coli in the model environment of Langmuir monolayers. To characterize the ordering of the terpene molecules in one-component films as well as to study their interactions with the bacterial phospholipids in binary monolayers we applied grazing incidence X-ray diffraction (GIXD). It turned out that amyrins and ursolic acid molecules form crystalline hexagonal phases in Langmuir monolayers, in which the molecules are oriented uprightly. Regarding the mixtures, it was found that in the monolayers with Urs crystalline domains are present till moderate or even low Urs proportion. In contrast, in the mixtures with AMalf crystalline domains were observed only at the highest terpene concentration. In the interpretation of our results we underlined the significance of the interactions between the cyclopropane ring present in the hydrophobic part of the bacterial phospholipids and the terminal ring of the terpene structure. We proposed that the significant differences between the systems with AMalf and Urs are connected with the formation of hydrogen bonds between the Urs hydrophobic moieties. It can be inferred from the results that Urs is a more membrane-active agent than AMalf. [ABSTRACT FROM AUTHOR]

Bioelectronic devices, such as biosensors, can be constructed with enzymes immobilized in ultrathin solid films, for which preserving the enzymatic catalytic activity is fundamental for optimal performance. In this sense, nanostructured films in which molecular architectures can be controlled are of interest. In this present work, the adsorption of the enzyme penicillinase onto Langmuir monolayers of the phospholipid dimyristoylphosphatidic acid was investigated and characterized with surface pressure–area isotherms and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). The incorporation of the enzyme in the lipid monolayer not only caused the film to expand, but also could be identified through amide bands in the PM-IRRAS spectra, with the C N and C O dipole moments being identified, lying parallel to monolayer plane. Structuring of the enzyme into α-helices was identified in the mixed enzyme–phospholipid monolayer and preserved when transferred to solid as a Langmuir–Blodgett (LB) film. The enzyme–lipid LB films were then characterized with PM-IRRAS, atomic force microscopy and fluorescence spectroscopy. Measurements of the catalytic activity showed that the enzyme accommodated in the LB films preserved 76% of the enzyme activity in relation to the homogeneous medium. The method presented here not only allows for enhanced catalytic activity toward penicillin, but also can be useful to explain why certain film architectures exhibit better enzyme activity. [ABSTRACT FROM AUTHOR]

Pectin, a polysaccharide with potential bioactivity, was inserted in the aqueous subphase of monolayers of the selected lipids DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and DPPE (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine), representing mammalian and bacterial membranes, respectively. Pectin condensed both monolayers but made the DPPC monolayer more fluid, while for DPPE, it made its monolayer more rigid, as detected with dynamic interfacial rheology. Complementary data using surface potential, infrared spectroscopy, and Brewster angle microscopy also showed distinctive effects of pectin on DPPE and DPPC. We believe these data can be correlated with the action of this polysaccharide with biological lipidic surfaces with different polar heads, which may be relevant, generally speaking, to understanding the molecular mechanism of this bioactive compound for pharmaceutical purposes. [Display omitted] • Pectin adsorbs on polar groups of DPPC and DPPE. • Pectin condenses both lipids but increases elasticity only for DPPE. • Pectin adsorption on the polar heads distorts the alkyl chains. • Interaction is modulated by the lipid composition. [ABSTRACT FROM AUTHOR]

In this work systematic investigations on the influence of zymosterol (zymo), which is one of cholesterol precursors, on lipid monolayers were done. The aim of these studies was to perform thorough comparison of zymosterol vs cholesterol membrane activity and fill the gap in the studies on the effect of sterols on membranes. The Langmuir monolayers experiments combined with Brewster angle microscopy studies were performed on binary (SM:zymo, POPC:zymo, GM3:zymo) and ternary (SM:POPC:zymo, SM:GM3:zymo) films differing in the sterol content. The obtained results evidenced differences in the influence of both sterols on lipid monolayers, which was manifested in the parameters calculated based on the isotherms as well is in monolayers morphology. It was found that zymosterol is of condensing, ordering and domain promoting abilities thus this molecule can be included to the group of membrane active sterols. However, zymosterol is much less effective than cholesterol as condensing and ordering agent. These findings were attributed to the differences in the structure of both sterols and their ability to pack tightly with other lipids in the mixed systems. [ABSTRACT FROM AUTHOR]

In this study, we tested the hypothesis according to which chitosan reduces lipid digestion by blocking the access of lipases to ingested fat. Because lipase action takes place mostly at interfaces, we produced Langmuir films of 1,2-didecanoyl-glycerol (DDG), which is the substrate for human pancreatic lipase (HPL). The experimental assays were carried out in acidic medium, at pH 3.0, to ensure that chitosan is completely soluble. Chitosan was found to affect strongly the surface activity of HPL that forms a Gibbs monolayer at the air/water interface, but did not inhibit the enzymatic action of HPL toward the DDG monolayer. The latter was observed using two surface-specific spectroscopic techniques, namely polarization-modulated infrared reflection–absorption and sum-frequency generation (SFG). The extension of DDG hydrolysis calculated using SFG spectroscopy was 33% in the absence of chitosan, and ranged from 29 to 50% in the presence of chitosan at concentrations of 0.20 g L −1 and 0.30 g L −1 , respectively. Therefore, fat “protection” by chitosan is unlikely to be an important factor in fat reduction. [ABSTRACT FROM AUTHOR]

Lipid derivatives of nucleoside analogs and their nanoassemblies have become the research hotspot due to their unique function in cancer therapy. Six lipid derivatives of 3′-hydroxyurea-deoxythymidine were prepared with zidovudine as the raw material. The 5′-substituted lipid chains in the derivatives were from the various fatty acids including octanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid and octadecanoic acid corresponding to the derivatives OHT, DHT, DDHT, TDHT, HDHT and ODHT. The amphiphilic derivatives formed Langmuir monolayers at the air/water interface with different surface pressure-molecular area isotherms depending on the length of lipid chains. The nanoassemblies of OHT, DHT, DDHT, TDHT and HDHT and the nanoscale precipitates of ODHT were obtained after we injected their tetrahydrofuran solutions doped with hydrophilic long chained polymers into water. Electron microscopy showed that the morphology of nanoassemblies may be vesicles or nanotubes depending on the length of lipid chains. The shorter the lipid chains were, the softer the nanoassemblies. Computer simulation supported the experimental results. The nanoassemblies and the nanoscale precipitates showed much higher anticancer effects on SW620 cells than the parent drug hydroxyurea. The nanostructures of the derivatives are promising anticancer nanomedicines. [ABSTRACT FROM AUTHOR]

Human bestrophin-1 (hBest1) is a transmembrane channel protein, predominantly expressed in the membrane of retinal pigment epithelium (RPE) cells. Although it is clear that hBest1's interactions with lipids are crucial for its function such studies were not performed as the protein was not purified. Here we describe an effective purification of hBest1 from Madin-Darby Canine Kidney (MDCK) cells via simple gel-filtration and affinity chromatographic steps, which makes possible to probe the protein interplay with lipids. The interaction of the purified hBest1 with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was studied in Langmuir monolayers. The surface pressure ( π )–area ( A ) isotherms and compression/expansion isocycles of POPC monolayer were recorded in absence and presence of hBest1 in the subphase. The π ( A ) isotherms were analyzed in terms of surface compressional modulus and via two-dimensional virial equation of state. The dilatational rheological properties of the surface films and their surface potential were also measured. The morphology of the films was observed by Brewster angle microscopy. The inclusion of the protein in the film subphase does not lead to in-depth penetration of hBest1 but interaction takes place in the headgroup region of the monolayer. The hBest1/POPC interaction resulted in formation of more condensed films, which rheological properties and lateral structure differed significantly from the pure POPC monolayers. Our study sheds light on the still unclear question how hBest1 gets in touch with biomembrane phospholipids of eukaryotic cells that might be of key importance for the proper structure and function of RPE biomembranes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biomembranes are mimicked with Langmuir monolayers. [•] Sucrose phosphorylase are incorporated into the lipid monolayer. [•] Enzyme adsorption is confirmed with tensiometry and infrared spectroscopy. [•] Langmuir–Blodgett films of the enzyme presents enzyme activity. [Copyright &y& Elsevier]

Highlights: [•] Limited miscibility of sterols with choline plasmalogen in Langmuir monolayers. [•] Stronger interactions of sterols with phosphatidylcholine vs. choline plasmalogen. [•] Vinyl ether bond in choline plasmalogen affects its interactions with sterols. [•] Phytosterols strongly affect model cancer membranes of elevated plasmalogen content. [Copyright &y& Elsevier]

Highlights: [•] Tetracaine fluidizes lipid membranes and may induce swelling or even solubilization. [•] The tetracaine action depends on the membrane model and its immobilization state. [•] Tetracaine affects more lipid Langmuir monolayers than liposomes in solution. [•] Tetracaine affects more liposomes in solution than supported liposomes. [Copyright &y& Elsevier]

Highlights: [•] The synthesis of bitailed amphiphilic nitrone antioxidants is reported. [•] The antioxidant efficiency was demonstrated in Langmuir monolayers and liposomes. [•] The antioxidant efficiency varies with the biomimetic system and the oxidation mode. [•] The degree of amphiphilicity of nitrones alters their antioxidant properties. [Copyright &y& Elsevier]

Photoinduced hyperthermia with nanomaterials has been proven effective in photothermal therapy (PTT) of tumor tissues, but a precise control in PTT requires determination of the molecular-level mechanisms. In this paper, we determined the mechanisms responsible for the action of photoexcited gold shell-isolated nanoparticles (AuSHINs) in reducing the viability of MCF7 (glandular breast cancer) and especially A549 (lung adenocarcinoma) cells in vitro experiments, while the photoinduced damage to healthy cells was much smaller. The photoinduced effects were more significant than using other nanomaterials, and could be explained by the different effects from incorporating AuSHINs on Langmuir monolayers from lipid extracts of tumoral (MCF7 and A549) and healthy cells. The incorporation of AuSHINs caused similar expansion of the Langmuir monolayers, but Fourier-transform infrared spectroscopy (FTIR) data of Langmuir-Schaefer films (LS) indicated distinct levels of penetration into the monolayers. AuSHINs penetrated deeper into the A549 extract monolayers, affecting the vibrational modes of polar groups and carbon chains, while in MCF7 monolayers penetration was limited to the surroundings of the polar groups. Even smaller insertion was observed for monolayers of the healthy cell extract. The photochemical reactions were modulated by AuSHINs penetration, since upon irradiation the surface area of A549 monolayer decreased owing to lipid chain cleavage by oxidative reactions. For MCF7 monolayers, hydroperoxidation under illumination led to a ca. 5% increase in surface area. The monolayers of healthy cell lipid extract were barely affected by irradiation, consistent with the lowest degree of AuSHINs insertion. In summary, efficient photothermal therapy may be devised by producing AuSHINs capable of penetrating the chain region of tumor cell membranes. [Display omitted] • Photothermal mechanisms of action of gold-shell isolated nanoparticles (AuSHINs). • Dependence of photothermal efficiency on membrane-AuSHINs interaction. • The degree of AuSHINs penetration modulates the photochemical reactions. • More significant effects in reducing tumor cells viability. • Slightly photoinduced damage to healthy cells. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biomembranes are mimicked with Langmuir monolayers. [•] Carrageenans are incorporated into the monolayer. [•] Interactions at the molecular level depend on the number of sulfate groups. [•] Molecular expansion of the monolayers is related to anticoagulant effects. [ABSTRACT FROM AUTHOR]

Highlights: [•] The effect of lipid oxidation on protein's binding parameters has been determined [•] Measurements were performed using lipids oxidized in different conditions. [•] Large decreases of the maximum insertion pressure, ΔΠ 0 and ΔΠ were observed. [•] The presence of different oxidized lipid species is unfavorable for protein binding. [•] Diseases producing oxidized lipids could lead to aberrant protein binding. [Copyright &y& Elsevier]

Abstract: The growing use of nanoparticles in a variety of applications calls for detailed studies of their toxicology, which in turn require understanding the interactions between nanoparticles and living cells. Since simulating the interaction with real cell membranes is rather complex, Langmuir monolayers (LMs) have been used to mimic the first barrier encountered by a nanoparticle as it approaches a biological membrane to assess molecular-level interactions. In this study, we show how oppositely charged gold nanoparticles (Au-NPs) interact with monolayers of the zwitterionic dipalmitoylphosphatidyl choline (DPPC) and negatively charged dipalmitoylphosphatidyl glycerol (DPPG). The monolayers were spread on subphases containing two concentrations of either negatively charged Au-NPs coated with citrate anions or positively charged Au-NPs functionalized with the cationic polyelectrolyte poly(allylamine hydrochloride) (PAH). For DPPG, electrostatic effects dominated which depended strongly on the NPs capping agent, being obviously larger for the positive nanoparticles. The in-plane elasticity for DPPG monolayers within the surface pressure range corresponding to real cell membranes increased with adsorption of positively charged NPs, but decreased with the negative ones. For the zwitterionic DPPC, on the other hand, significant effects only occurred for negatively charged NPs, including a decrease in elasticity. Therefore, it is concluded that the nature, namely the charge of the capping agents, is crucial for the interaction of charged NPs with the cell membrane. [Copyright &y& Elsevier]

Abstract: Binary Langmuir monolayers composed of 1,2-dipalmitoyl-sn-phosphatidylcholine (DPPC) and erucylphosphocholine (ErPC) – a new generation anti-cancer drug of phospholipids-like structure, have been studied with classical Langmuir technique complemented with Brewster angle microscopy (BAM) and Grazing Incidence X-ray Diffraction (GIXD). In the course of surface pressure (π)–area (A) isotherms for film containing mole fraction of ErPC (X ErPC) equal to 0.1, 0.2 and 0.3, two collapses appear – the value of the first one is close to the collapse pressure observed for pure ErPC, while the second one occurs at the pressure similar to that for pure DPPC. Such a behavior could imply that the investigated system is immiscible – the expulsion of a component collapsing at a lower pressure (ErPC) from mixed monolayer occurs at the first transition while DPPC (collapsing at a higher pressure value) is expelled at the final collapse. To confirm this hypothesis further analysis has been performed. Namely, thermodynamic analysis based on the calculation of the excess free enthalpy of mixing () evidenced for mutual miscibility of DPPC and ErPC in the region of surface pressures below the first collapse, which has been additionally confirmed with BAM images. On the other hand, at high surface pressures, above the first collapse (50mN/m) GIXD experiments complemented with BAM images proved phase separation of the investigated lipids and 2D crystalline domains formation. The interpretation of the X-ray scattering results enabled us to propose a possible model of molecular packing, according to which only condensed domains of the 1:1 lipids ratio are periodically ordered; whereas at the other proportions the lipids are located randomly within the domains. [Copyright &y& Elsevier]

Abstract: Langmuir monolayers of Cholesterol (Chol) and a mixture of Chol with 1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), at a ratio of 17:83 in weight, spread on pure water and on silica nanoparticle dispersions, have been investigated measuring the compression isotherms as well as the surface pressure response to harmonic area variation of the monolayer. Aim of this study was to evaluate the effects of the interaction of silica nanoparticles with Chol and the conditions for the incorporation in the monolayer. In previous works on different kind of lipid monolayers, it has been shown that hydrophilic silica nanoparticles dispersed in the sub-phase may transfer into the monolayer, driven by the interaction with the lipid molecules that make them partially hydrophobic. The results here obtained indicate that also for Chol and Chol–DPPC mixtures the presence of silica nanoparticles may have important effects on the phase behaviour and structural properties of the monolayer. As confirmed by complementary structural characterisations, BAM, AFM and ellipsometry, the principal effect of the nanoparticle incorporation is the disruption of the monolayer packing, owing to the alteration of the cohesive interactions of lipid components. [Copyright &y& Elsevier]

Abstract: Competitive adsorption is a general problem both in polymer and in biological systems. The equilibrium composition at a surface in contact either with polymer solutions or biological fluids depends on the competition between all the surface active material present in the medium. Such competition is particularly important in cell membranes where membrane proteins generated on ribosomes have to incorporate in the cell. Here we use fluovideo microscopy to study the competition for adsorption at the air/water interface between the enzyme glucose oxidase (GOx) and fluid monolayers of pentadecanoic acid (PDA). Although water soluble, GOx has a strong affinity for the air/water interface. We show that under certain conditions it inserts in the monolayer and causes a contraction of the Langmuir film and the formation of condensed domains. When exposed to a heterogeneous surface it is inserted in the less dense regions. Its crystallization leads to the deformation of the condensed domains followed by the destruction of their initial shape. By compressing the layer the protein is not removed from the interface where it eventually forms three-dimensional structures. [Copyright &y& Elsevier]

Abstract: In this work the Langmuir monolayers were used to prepare multicomponent systems mimicking outer and inner layer of human erythrocyte membranes. The aim of performed experiments was to compare the influence of cholesterol on complex artificial membranes reflecting compositional diversity of the respective membranes leaflets. The properties of both systems in the presence of cholesterol at various concentrations were analyzed by means of thermodynamic description of the interactions between molecules in the investigated monolayers, complemented by the analysis of their morphology performed with the application of Brewster Angle Microcopy. It was found that cholesterol induces highly favorable stabilizing effect on the studied monolayers, increases their condensation and strengthens intermolecular forces. However, the influence of cholesterol was found to be stronger on the mixed film imitating outer membrane layer. Detailed discussion of the obtained results proved that the behavior of cholesterol in the model outer vs. inner layers is strongly determined by their compositional differences. The most important findings resulting from these experiments concern the problem of transbilayer distribution of cholesterol in membranes, which despite numerous investigations seems to be still unclear. The data obtained in this work allow one to suggest that cholesterol tends to accumulate preferentially in outer membrane leaflet or it is localized symmetrically in both layers rather than in inner leaflet. [Copyright &y& Elsevier]

Abstract: The presence of dietary phytocompounds – plant sterols and stanols – in human plasma and membranes raises the question on their influence on membrane properties. A good way to get an insight into interactions of these biomolecules with membranes at molecular level is to perform experiments on artificial systems, e.g. Langmuir monolayers, composed of membrane lipids. In this paper the influence of plant stanol – β-sitostanol – on monolayers imitating the inner leaflet of human membrane, composed of phosphatidylethanolamine (POPE)/phosphatidylserine (POPS)/cholesterol (Chol) was studied. Two effects have been investigated and compared, namely the systematic increase of plant stanol (β-sitostanol) content in the mixed film as well as the replacement of cholesterol by β-sitostanol in POPE/POPS/Chol monolayer. The analysis of the collected data evidenced that the plant stanol strongly influences the condensation and interactions in POPE/POPS/Chol film. BAM images taken for the studied monolayers demonstrated that the presence of β-sitostanol in the mixture leads to the formation of 3D crystallites within the film, which seems to result from a limited solubility of plant stanol in phospholipids environment. All these effects have got intensified upon systematic elimination of cholesterol and its replacement by plant stanol in the mixed monolayer. The obtained results evidence that the presence of plant stanol may significantly alter organization of the inner leaflet of human membrane. [Copyright &y& Elsevier]

Abstract: Three single-chained ether lipids of comparable chemical structure but different biological activities (namely natural platelet activating factor – PAF, its deacetylated precursor – lyso-PAF and synthetic compound – edelfosine – ED) have been investigated in mixed Langmuir monolayers with phosphatidylethanolamines, PEs (DSPE, SOPE and DOPE), serving as model of inner shell of cellular membrane. The aim of undertaken studies was to verify the correlation between minor differences in chemical structures of the investigated ether lipids and their behavior in membrane-mimicking environment. To reach this goal the interactions between particular ether lipids and PEs have been analyzed with ΔG Exc values derived from the surface pressure–area isotherms. To get insight into miscibility between film components, Brewster angle microscopy, enabling direct visualization of monolayers structure, has been applied. The obtained results prove significant differences in both mixing properties and the interactions in the investigated systems. On one hand, they are related to the structure of polar head-groups of the studied ether lipids, which determine their capability of hydrogen bond(s) formation with head-groups of PEs. Edelfosine, lacking this property, interacts with PEs the most unfavorably among all the investigated compounds. Another important parameter in this context is the structure of PEs monolayers – the most closely packed DSPE film was found to be most unfavorable for incorporation of ether lipid molecules. Our results prove that the analysis of the interaction between ether lipids and components of biomembrane in Langmuir monolayers is a potent method to explain differences in biological activity of the investigated ether lipids. [Copyright &y& Elsevier]

Abstract: The aim of this study is to deepen the understanding of the behavior of human serum albumin (HSA) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) mixed monolayers. For this purpose, different amounts of DPPC were spread at 25°C on the water surface containing a monolayer of HSA. Surface film balance and Brewster angle microscopy techniques have been used to analyze the structural and energetic characteristics (structure, topography, thickness, miscibility and interactions) of these mixtures. HSA/DPPC mixed monolayers exhibit two phase transitions evidenced by two discontinuities in the corresponding π–A isotherms and by two minimum values in the compressional modulus (C s −1)–surface pressure (π) curves. The plot of the molecular areas occupied by the mixed monolayers as function of the mass fraction of DPPC shows the absence of deviations from linearity, a typical behavior for ideal or inmiscible system. This result was confirmed from the values calculated for the free energy of excess (ΔG exc), which are practically zero whatever the composition of the mixtures and the surface pressures at which ΔG exc values were calculated. In addition, relative thickness values of HSA/DPPC mixed monolayers showed the existence of an exclusion surface pressure (π exc), below which the monolayer is composed of a mixture of both components, while above π exc the HSA molecules are squeezed out the interface, but not totally. In fact, although in this region DPPC domains predominate at the interface, the existence of protein molecules in a packing “loops” configuration can be observed in BAM images. Moreover, relative thickness measurements confirm this hypothesis. [Copyright &y& Elsevier]

Abstract: β-Carotene, positively recognized in literature as regards its film-forming abilities at the water/air interface, was subjected to further Langmuir monolayer investigations. A wide variety of organic solvents and their mixtures have been tested in order to choose the best spreading solvents for monolayer experiments. A constant surface pressure rise, without characteristic for collapse spike or plateau, was observed upon compressing films dropped onto the air/water interface from all the solvents studied. However, a surface pressure increase alone is an insufficient criterion to evidence a true monolayer formation. The application of Brewster angle microscopy (BAM) indicated the presence of crystalline domains even at large molecular areas, contrary to homogeneous monolayer, which has been expected based on the above-mentioned reports. The addition of surface active substances (n-pentanol or iso-propanol) into β-carotene solution does not improve whatsoever its spreading behaviour. Our experiments indicate that β-carotene is not capable of forming monomolecular films at the free water surface and therefore is not suitable material for investigations with the Langmuir technique. Thus, this study shows the importance of using complementary – to classical surface manometry – techniques to confirm the true monolayer formation from molecules of interest. [Copyright &y& Elsevier]

Abstract: The molecular recognition activities of flavonoid derivatives toward other guest molecules have been the focus of interest recently. This study reports the metal-complexation behavior of nitrogen-containing rutin (RuCn) in the organized Langmuir films. Three model compounds with different lipid chain lengths (n =8, 12 and 18) were designed and synthesized. The monolayer structures and metal-binding activities of RuCn were studied by the monolayer technology, FT-IR spectroscope and thermodynamic calculations (experimentally and theoretically). Results showed that hard Lewis acid-type metal cations, such as Na(I), K(I), Ca(II) and Fe(III), and soft metal cations, such as Cu(II), exhibited clearly different binding activities to RuCn monolayers. The sequence of the effects of metal ions on the monolayer properties and thermodynamic stability varies in the order: univalent ions

Abstract: Surface pressure (π)–molecular area (A) curves were used to characterize the packing of pseudo-ternary mixed Langmuir monolayers of egg phosphatidylcholine (EPC), 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) and l-α-dioleoyl phosphatidylethanolamine (DOPE). This pseudo-ternary mixture EPC/DOPE/DOTAP has been successfully employed in liposome formulations designed for DNA non-viral vectors. Pseudo-binary mixtures were also studied as a control. Miscibility behavior was inferred from π–A curves applying the additivity rule by calculating the excess free energy of mixture (ΔG Exc). The interaction between the lipids was also deduced from the surface compressional modulus (C s −1). The deviation from ideality shows dependence on the lipid polar head type and monolayer composition. For lower DOPE concentrations, the forces are predominantly attractive. However, if the monolayer is DOPE rich, the DOTAP presence disturbs the PE–PE intermolecular interaction and the net interaction is then repulsive. The ternary monolayer EPC/DOPE/DOTAP presented itself in two configurations, modulated by the DOPE content, in a similar behavior to the DOPE/DOTAP monolayers. These results contribute to the understanding of the lipid interactions and packing in self-assembled systems associated with the in vitro and in vivo stability of liposomes. [ABSTRACT FROM AUTHOR]

Abstract: The studies on the influence of cholesterol on phospholipids accumulated in inner leaflet of membrane are performed rather rarely, especially in the presence of electrolytes, which are present in membrane environment. Therefore, in this work the interactions between cholesterol and saturated phosphatidylethanolamine (PE) and phosphatidylserine (PS) were studied in binary (phospholipid/cholesterol) and ternary (PS/PE/cholesterol) monolayers in the presence and absence of sodium and calcium ions. The composition of ternary films was estimated to reflect the proportion of PSs to PEs in inner layer of human erythrocyte membrane. The influence of electrolytes on pure PS and PE films was also analyzed. It was found that both sodium and calcium ions affect the condensation of DPPS films, and influence the interactions in DPPS/cholesterol monolayers. On the other hand, no effect of these ions on DPPE films as well as on DPPE/cholesterol interactions in the mixed systems was observed. The results obtained for ternary mixtures prove that in the presence of Na+ the interactions between the lipids are more favorable than in the absence of these ions. This is in contrast to the effect of Ca2+. All the results were thoroughly analyzed in the context of the structure of polar heads of the investigated phospholipids. [ABSTRACT FROM AUTHOR]

Abstract: The wide variability in composition and molecular weight of natural polymers has hampered understanding of their physicochemical properties and ultimately their use in noble applications, especially in the cases where surface properties need to be probed at the molecular level. A useful approach to analyse data from surface monolayers of complex mixtures is to try distinguishing the effects from the distinct fractions in such mixtures. The cork suberin extract investigated here is known to contain aliphatic monomers with terminal carboxylic acid and methyl ester groups as well as long esterified aliphatic chains dispersed in a polymeric aliphatic matrix. The role of such terminal groups was studied and the results showed that depending on the nature of the terminal groups the monolayers present distinct isotherms due to the different interactions with the water subphase. Fractionation strategies based on different solubilities of the cork suberin components in chloroform were also employed to probe their effect on the monolayer characteristics. From the two sets of experiments it is clear that the presence of monomers with terminal carboxylic acids in the suberin extract affects considerably the monolayer-forming ability. This approach may be used as a complementary, relatively simple route to assess suberin genetic engineering strategies towards resistance to environmental stress. [Copyright &y& Elsevier]

Abstract: The surface interactions of Meibomian gland secretion (MGS) with polar lipid (PL), Egg Sphingomyelin (SM) or Dipalmitoylphosphatidylcholine (DPPC), are studied in mixed pseudo-binary films formed at the air/water interface of Langmuir surface balance. The behavior of the mixed films during slow quasi-equilibrium compression and during fast dynamic compression–decompression is registered by measurements of surface pressure and surface potential, and by monitoring film morphology with Brewster Angle Microscopy (BAM). Quasi-equilibrium compression isotherms are used to calculate the excess Gibbs and Helmholtz energy of mixing between MGS and PLs and thus to evaluate the interactions between the lipid compounds at the interface. The effects of PLs on the mixed film''s elastic moduli of area compressibility, morphology and capability to attain high surface pressures are also examined. PLs interact with MGS with different strength and in different manner: MGS–SM interaction is weak and might lead to interfacial disaggregation of the thick meibium domains when SM is in excess, while MGS–DPPC interaction is strong and results in the formation of thick lipid aggregates. Both PLs increase the mixed films reciprocal compressibility and capability to achieve higher surface pressures. The results demonstrate that in vitro studies of the surface interactions between MGS and PLs might be beneficial in the selection of PLs for artificial tear formulations and for examination on molecular scale of the possible role of PLs at the ocular surface. [Copyright &y& Elsevier]