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Organic macromolecules with dendrimeric architectures are polymeric materials potentially useful as nanocarriers for therapeutic drugs. In this work, we evaluate a series of Newkome-type dendrons in Langmuir and Langmuir-Blodgett films as platforms capable of interacting with a potential antitumoral agent. The nanocomposite is proposed as model for the development of surface mediated drug delivery systems. We were successful in the formation and characterization of pure (dendrons) and composite (drug-dendron) stable and reproducible monolayers, and their transfer to solid substrates. A detailed study of topographic characteristics of the generated surfaces by atomic force microscopy was conducted. Furthermore, we probed dendron monolayer films as anchorage surfaces for mammalian cells. Normal cell attachment and proliferation on the surfaces were observed. No evident cytotoxic effects were detected, demonstrating the adequate biocompatibility of the surfaces. [ABSTRACT FROM AUTHOR]

A new class of anionic, gemini surfactants based on N , N ’-dialkyl- N - N ’-diacetate ethylenediamine has recently been reported in the literature, with the compounds exhibiting controllable and, in some cases reversible, aggregation in response to solution pH and the presence of inorganic cations. In this work, the response of one member of this surfactant family (12 carbon long tail) to subphase Na + and Ca 2+ at basic pH was investigated at the air-water interface using Langmuir monolayer approaches. It was found that the anionic monolayer exhibited marked expansion in response to subphase cation concentration, with Ca 2+ leading to significantly greater film expansion than Na + . The film’s response to inorganic ions in the subphase was modeled using a simple ion-binding model, with association constants that were generally smaller than those reported for comparator systems such as phospholipids, and a 1:1 and 2:1 surfactant to cation binding ratio, respectively. However, Brewster angle microscope measurements revealed that monolayer film expansion was accompanied by the formation of multimolecular aggregates, tentatively assigned to the formation of poorly-dispersed deposits of cation chelated with the surfactant. The impact of this effect on the apparent magnitude of film expansion, ion-binding and controlling aggregation in these systems, and the potential for this system in terms of controlling surfactant aggregation is discussed. [ABSTRACT FROM AUTHOR]

The dynamic surface properties of mixed monolayers of 1,2-Dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and negatively charged polystyrene particles (PS) of different size were investigated with the aim to model the interactions of particles with biointerfaces. Special attention was paid to the aggregation of the particles at the water/air interface. The particle aggregates have a weaker influence on the dynamic properties of DPPC monolayers as compared with non-aggregated particles because of a shorter three phase contact line. The incorporation of particles into a DPPC monolayer leads to disordering of the monolayer structure, decreases the changes of surface properties in the course of two-dimensional phase transitions and the dynamic surface elasticity of the condensed lipid film. The influence of particles on the properties of mixed monolayers depends strongly on the ratio of lipid molecules and particles, and decreases with the decrease of particle surface concentration. The Brewster angle microscopy gives direct evidence of the PS particle aggregation in the course of compression of mixed monolayers. [ABSTRACT FROM AUTHOR]

Langmuir monolayers at the air/water interface are widely used as biomembrane models and for amphiphilic molecules studies in general. Under controlled intermolecular organization (lateral molecular area), surface pressure, surface potential, reflectivity ( R ) and other magnitudes can be precisely determined on these planar monomolecular films. However, some physical parameters such as the refractive index of the monolayer ( n ) still remain elusive. The refractive index is very relevant because (in combination with R ) it allows for the determination of the thickness of the film. The uncertainties of n determine important errors that propagate non-linearly into the calculation of monolayers thickness. Here we present an analytical method for the determination of n in monolayers based on refractive index matching. By using a Brewster angle microscopy ( BAM ) setup and monolayers spread over subphases with variable refractive index ( n 2 ), a minimum in R is search as a function of n 2 . In these conditions, n equals n 2 . The results shown correspond to monolayers of myelin lipids. The n values remain constant at 1.46 upon compression and equals the obtained value for myelin lipid bilayers in suspension. The values for n and R allow for the determination of thickness. We establish comparisons between these thicknesses for the monolayer and those obtained from two X-ray scattering techniques: 1) GIXOS for monolayers at the air/water interface and 2) SAXS for bilayers in bulk suspension. This allows us to conclude that the thickness that we measure by BAM includes the apolar and polar headgroup regions of the monolayer. [ABSTRACT FROM AUTHOR]

Mixed monolayers were prepared using phospholipids in order to mimic cell membranes and fractions of capsaicinoids (extracted from Malagueta, Caps-M, and Bhut Jolokia, Caps-B, peppers). According to their surface-pressure isotherms and polarization-modulated infrared reflection absorption spectra (PM-IRRAS), weak molecular-level interactions were observed between Caps and phospholipids. Both Caps-M and Caps-B penetrated into the alkyl tail region of the monolayer, interacted with the phosphate group of the phospholipids and affected hydration of their C O groups. Since the physiological activity of Caps is not governed solely by interaction with cell membranes, it should require participation of a neuronal membrane receptor, e.g. vanilloid receptor (TRPV1). [ABSTRACT FROM AUTHOR]

Anionic phospholipids cardiolipins (CL) and phosphatidylglycerols (PG) dominate in the biomembranes of the majority of soil bacteria. CL to PG ratio differs between the species and is also dependent on the external conditions. CL/PG ratio is different in polluted than in unspoiled soils and it was hypothesized that it is connected with the activity of the membranelytic enzymes from the phospholipase A2 class (PLA2) as it was proved that persistent soil pollutants can activate PLA2. In our studies we applied the Langmuir monolayer technique and Brewster angle microscopy to elucidate the mechanism of the interactions of PLA2 with the model membranes formed by anionic phospholipids. It turned out that there are significant differences between CL and PG. The monolayer of PG is hydrolyzed readily and entirely, whereas for CL approximately 30% of the phospholipid molecules are hydrolyzed after which the enzyme is inhibited. The observed differences between PG and CL are strictly connected with the hydrophobicity of the generated lysolipids: lyso-PG and lyso-CL. Lyso-PG is water soluble and leaves the interface whereas lyso-CL is water-insoluble remains at the interface and modifies the monolayer properties. The second hydrolysis product – myristic acid (MA) forms crystallites of calcium myristate when generated from PG, whereas when generated from CL it is shielded by the lysolipid and does not interact with calcium. Therefore, on the basis of our study it can be concluded that the increase in CL content protects the soil bacteria from PLA2 activity and from the loss of calcium homeostasis. [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]

Properties of microbicide drugs are believed to be associated to their interactions with biointerfaces such as cell membranes, encouraging research on the identification of membrane sites capable of drug binding. In this study, we investigated the interaction of bacitracin, a known antibiotic peptide, with cell membrane models represented by Langmuir monolayers of selected phospholipids. It is shown that even small amounts of bacitracin affect the surface pressure-area isotherms, as well as the vibrational spectra and the morphology of phospholipid monolayers, which points to a specific interaction for each phospholipid. Such effects depend on the chemical nature of the monolayer-forming molecules, with the drug activity being distinctive for dipalmitoyl-sn-glycero-3-phospho- l -serine sodium salt in contrast to what was observed for 1,2-dipalmitoyl- sn -glycero-3-phospho- l -choline and 1,2-dipalmitoyl- sn -glycero-3-phospho-(1′- rac -glycerol) sodium salt. As a result, the phospholipid composition of the monolayer modulates the interaction with the peptide, which may have important implications in understanding how the drug acts on specific sites of cell membranes. [ABSTRACT FROM AUTHOR]

We studied the surface properties of monolayers composed of polyunsaturated conjugated ethylene glycol phospholipids (carotenoid lipids), compared the data with monolayers of dipalmitoylphosphatidylcholine (DPPC) to which carotenoids were added and evaluated the impact of the unsaturated glycol lipids on monolayers with the glycerolipid DPPC. The carotenoid based glycol lipids formed monolayers at the air/water interface. Using the Langmuir method we obtained series of pressure-area ( π-A ) isotherms and determined the limiting area A per molecule of three glycol lipids, C30:9-C 0 A = 42.6 ± 1.4 Å 2 , C30:9-C 2 A = 76.1 ± 2.5 Ǻ 2 and C30:9-C 12 A = 354.0 ± 12.0 Å 2 and their mixtures with DPPC at various mole fraction X . C30:9-C 0 and C30:9-C 2 did not affect significantly the shape of the isotherm, but caused their slight shift toward a lower and larger molecular area, respectively. C30:9-C 12 at mole fractions X > 0.02 affected the shape of isotherm. The compressibility modulus C s −1 of monolayers depended on the surface pressure. C s −1 value was substantially higher for DPPC monolayers in comparison with those of pure glycol lipids. At low surface pressure π = 5–10 mN/m and low mole fractions X < 0.02 the glycol lipids formed complexes with DPPC; at higher surface pressure the separation of pure components took place. The dipole potential of the monolayers composed of cationic glycol lipids C30:9-C 2 and C30:9-C 12 was higher in comparison with those of zwitterionic DPPC and C30:9-C 0 . This may be connected with various contributions of dipole moments of the molecules and their orientation in the monolayer. [ABSTRACT FROM AUTHOR]

Biseugenol (1), a neolignan with antiprotozoal activity against Trypanosoma cruzi , was partially methylated, and the compound obtained – methyl biseugenol (2) – had its activity evaluated against the extracellular (trypomastigotes) and intracellular (amastigotes) forms of T. cruzi. It was observed that both compounds 1 and 2 exhibited similar effects against trypomastigotes (IC 50 of 11.7 and 16.2 μM, respectively), whereas compound 2 displayed higher activity against amastigotes (IC 50 = 8.2 μM) in comparison with biseugenol (IC 50 = 15.4 μM). Additionally, reduced toxicity against NCTC cells for compound 2 was observed (CC 50 > 200 μM), differently from compound 1 with CC 50 = 58.0 μM. Aiming to understand better the molecular mechanism of the biological action of compound 2 , the prodrug was incorporated into cellular membrane models constituted of Langmuir monolayers of the lipids dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE), dipalmitoylphosphatidylserine (DPPS), and dipalmitoylphosphatidylglycerol (DPPG). The lipid-drug interaction was inferred through tensiometry, surface potential, infrared spectroscopy (PM-IRRAS), and Brewster angle microscopy (BAM). The prodrug expanded DPPC and DPPG monolayers and condensed DPPE ones, as well as presented characteristic behaviors regarding the chemical structure of the lipid considering expansion-compression curves, surface potential-area isotherms, and stability of previously compressed monolayers to relevant-biological surface pressures. PM-IRRAS indicated a molecular disorder for DPPC and DPPS alkyl chains in the presence of the drug. BAM revealed the presence of domains in the DPPG and DPPE monolayers, which was probably induced by the prodrug. These data suggest, in general, that the lipid composition modulates the interaction of compound 2 , whose results are expected to correlate to its trypanocidal activity, which involves the plasma membrane of T. cruzi as the primary target, i.e., the first barrier that the compound should encounter to interact with the microorganism. [Display omitted] • Dehydrodieugenol was isolated from plants and partially methylated. • Dehydrodieugenol presented toxicity to parasites. • Molecular mechanism with cell membranes was investigated. • Interaction with lipid is modulated by the film fluidity. [ABSTRACT FROM AUTHOR]

Langmuir monolayers are advantageous systems used to investigate how lipid membranes get involved in the physiology of many living structures, such as collapse phenomena in alveolar structures. Much work focuses on characterizing the pressure-bearing capacity of Langmuir films, expressed in the form of isotherm curves. These show that monolayers experience different phases during compression with an according evolution of their mechanical response, incurring into instability events when a critical stress threshold is overcome. Although well-known state equations, which establish an inverse relationship between surface pressure and area change, are able to properly describe monolayer behaviour during liquid expanded phase, the modelling of their nonlinear behaviour in the subsequent condensed region is still an open issue. In this regard, most efforts are addressed to explain out-of-plane collapse by modelling buckling and wrinkling mainly resorting to linearly elastic plate theory. However, some experiments on Langmuir monolayers also show in-plane instability phenomena leading to the formation of the so-called shear bands and, to date, no theoretical description of the onset of shear banding bifurcation in monolayers has been yet provided. For this reason, by adopting a macroscopic description, we here study material stability of the lipid monolayers and exploit an incremental approach to find the conditions that kindle shear bands. In particular, by starting from the widely assumed hypothesis that monolayers behave elastically in the solid-like region, in this work a hyperfoam hyperelastic potential is introduced as a new constitutive strategy to trace back the nonlinear response of monolayer response during densification. In this way, the obtained mechanical properties together with the adopted strain energy are successfully employed to reproduce the onset of shear banding exhibited by some lipid systems under different chemical and thermal conditions. [ABSTRACT FROM AUTHOR]

Non steroidal anti-inflammatory drugs (NSAIDs) are those of the most common over the counter (OTC) medications widely used by millions of people every day. Unfortunately, despite their popularity those drugs can cause serious side effects in the digestive system (ulcers, bleeding, and pain). These inconveniences are caused by the changes in the structures of the outer phospholipid layers of gastric mucus and mucosa. As a result the H+ ions from the stomach acid can pass easily through these natural protective barriers and damage the epithelial cells which causes ulcers and bleeding. Chitosan as a polysaccharide known for its unique biocompatibility, drug delivery possibilities and wound healing effect has been chosen to examine if it can induce the reduction of undesirable effects of naproxen. This paper focuses on the interactions of the naproxen with a model biological membrane with and without the presence of chitosan. Applying the Langmuir technique coupled with the surface potential measurements and the Brewster angle microscope imaging allowed to characterize successfully examined systems in terms of the monolayer compressibility, thickness, stability, electric properties and morphology. The results proved that the presence of naproxen alters the mechanical and electrical properties of the model membrane depending on its surface pressure. Moreover, the addition of chitosan to the lipid-drug system causes significant changes in the properties of the layer, i.e. a reduction of its compressibility, thickness and morphology modification. Nevertheless, chitosan suppresses some changes induced by naproxen such as alteration of the apparent dipole moment and film stability. [Display omitted] • The presence of the naproxen and chitosan in the model membrane environment caused its significant perturbations. • Naproxen can remain in the hydrocarbon area of the lipid membrane affecting its electrical properties and thickness. • Chitosan molecules can accumulate in the polar areas of the lipid membrane then penetrate it. • This can act as a shield repelling hydrogen ions from the lipid membrane disrupted by NSAIDs in an acidic environment. [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]

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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Symmetrical triblock semifluorinatedn-alkane, di(perfluorohexyl)hexane of the formula F(CF2)6(CH2)6(CF2)6F (abbreviated F6H6F6), has been synthesised and investigated at the air/water interface. Our results show for the first time that this unusual film-forming material, completely hydrophobic in nature and possessing no polar group, is capable of stable film formation at the free water surface. The surface pressure–area isotherm of the studied compound exhibited two regions: corresponding to monotonous pressure rise, followed by a pseudo-plateau region. Visualisation of film structure with Brewster angle microscope (BAM) proved the formation of domains within the pseudo-plateau region. A closer insight into the structure of these domains with atomic force microscope (AFM) proved their ordered, circular shape. The average area of F6H6F6domain was found to depend on surface pressure value, as it is 4.98 ± 1.75 μm2at π = 1.2 mN/m to 16.54 ± 0.31 μm2at π = 1.7 mN/m. Following performed quantum-chemical calculations, it can be concluded that the observed surface aggregates from F6H6F6are formed by linear conformers with shifted CF and CH parts. The calculated domain thickness is between 20 and 21 Å, which perfectly agrees with the experimental value estimated from AFM measurements (20.3 ± 1.4 Å). [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]

It was demonstrated that, in contrast to a solution in an organic solvent, the relaxation of the excited state of a fluorophore moiety proceeds mainly radiationless upon the formation of naphthalimide fluoroionophore complexes with complementary cations in a monolayer on a water surface. Apparently, this is due to the fact that the distribution of the energy levels of molecular orbitals in the fluoroionophore complexes with cations at the air-water interfaces changes in such a way that relaxation of the excited state via charge transfer within the complex molecule remains possible. [ABSTRACT FROM AUTHOR]

A bstract The aggregation behavior of 2-(2-decenyl) succinic acid (C10SA) in alkaline aqueous media was extensively studied and found interesting properties. The CMC (critical micelle concentration) is lower than expected for a compound with two carboxylate groups and an alkenyl chain of 10–12 carbon atoms. We identified that among the factors that affect the CMC, the double bond and the arrangement of the carbonyl group play a crucial role. They favor an ease packing of the head group of the surfactant resulting in a reduction of their mutual repulsion in the micelle. This particular conformation influences the solubilization/aggregation behavior and is responsible of the high tendency to self-assembly forming micelles of spherical shape and small size. An important feature of C10SA molecules is their ability to orient the carboxyl groups in a way that allow them been packed in the aggregates and this property may be of interest for many future applications. [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]

Hypothesis Owing to structural similarities between sulfobetaine lipids and phospholipids it should be possible to form stable Langmuir monolayers from long tail sulfobetaines. By modification of the density of lipid tail group (number of carbon chains) it should also be possible to modulate the two-dimensional phase behaviour of these lipids and thereby compare with that of equivalent phospholipids. Potentially this could enable the use of such lipids for the wide array of applications that currently use phospholipids. The benefit of using sulfobetaine lipids is that they can be synthesised by a one-step reaction from cheap and readily available starting materials and will degrade via different pathways than natural lipids. The molecular architecture of the lipid can be easily modified allowing the design of lipids for specific purposes. In addition the reversal of the charge within the sulfobetaine head group relative to the charge orientation in phospholipids may modify behaviour and thereby allow for novel uses of these surfactants. Experiments Stable Langmuir monolayers were formed composed of single and double tailed sulfobetaine lipids. Surface pressure-area isotherm, Brewster Angle Microscopy and X-ray and neutron reflectometry measurements were conducted to measure the two-dimensional phase behaviour and out-of-plane structure of the monolayers as a function of molecular area. Findings Sulfobetaine lipids are able to form stable Langmuir monolayers with two dimensional phase behaviour analogous to that seen for the well-studied phospholipids. Changing the number of carbon tail groups on the lipid from one to two promotes the existence of a liquid condensed phase due to increased Van der Waals interactions between the tail groups. Thus the structure of the monolayers appears to be defined by the relative sizes of the head and tail groups in a predictable way. However, the presence of sub-phase ions has little effect on the monolayer structure, behaviour that is surprisingly different to that seen for phospholipids. [ABSTRACT FROM AUTHOR]

The main scope of the present study was to analyze the membrane interaction of members of different classes of polyphenols, i.e. resveratrol, naringenin, epigallocatechin gallate and enterodiol, in model systems of different compositions and phase states. In addition, the possible association between membrane affinity and membrane protection against both lipid oxidation and bilayer-disruptive compounds was studied. Gibbs monolayer experiments indicated that even though polyphenols showed poor surface activity, it readily interacted with lipid films. Actually, a preferential interaction with expanded monolayers was observed, while condensed and cholesterol-containing monolayers decreased the affinity of these phenolic compounds. On the other hand, fluorescence anisotropy studies showed that polyphenols were able to modulate membrane order degree, but again this effect was dependent on the cholesterol concentration and membrane phase state. In fact, cholesterol induced a surface rather than deep into the hydrophobic core localization of phenolic compounds in the membranes. In general, the polyphenolic molecules tested had a better antioxidant activity when they were allowed to get inserted into the bilayers, i.e. in cholesterol-free membranes. On the other hand, a membrane-protective effect against bilayer permeabilizing activity of lysozyme, particularly in the presence of cholesterol, could be assessed. It can be hypothesized that phenolic compounds may protect membrane integrity by loosely covering the surface of lipid vesicles, once cholesterol push them off from the membrane hydrophobic core. However, this cholesterol-driven distribution may lead to a reduced antioxidant activity of linoleic acid double bonds. [ABSTRACT FROM AUTHOR]

During the last decades opioid peptides, like enkephalins (Tyr-Gly-Gly-Phe-Met/Leu) are subject to extensive studies due to their antinociceptive action in organism. According to the membrane catalysis theory, in order to adopt a proper conformation for binding to their receptors, opioid peptides interact with the lipid phase of the membrane receptor surrounding. With this regard, the aim of the present work was to study the effects of synthetic leucine-enkephalin and leucine-enkephalinamide on surface characteristics and morphology of lipid monolayers, composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, sphingomyelin, and cholesterol alone and with their mixtures. The lipids were chosen to represent a model of a membrane raft, since it is known that G-protein-coupled receptors, including opioid receptors, are located preferably in membrane rafts. By using Langmuir's monolayer method, the change in surface pressure of the model membranes before and after the addition of the synthetic enkephalins was studied, and the compressional moduli of the lipids and lipid-peptides monolayers were determined. In addition, by Brewster angle microscopy, the surface morphology of the lipid monolayers alone and after the injection of both enkephalins was monitored. Our results showed that both leucine-enkephalins affected the lipid monolayers surface characteristics, and led to an increase in surface density of the mixed surface lipids/enkephalins films at loose lipid packing. This effect was more pronounced for the enkephalinamide, suggesting a different mechanism of interaction for the amidated enkephalin with the lipid phase, as compared to leucine-enkephalin. [ABSTRACT FROM AUTHOR]

The interaction of ions with interfaces and, in particular, the high specificity of these interactions to the particular ions considered, are central questions in the field of surface forces. Here we study the effect of different salts (NaI, NaCl, CaCl2 and MgCl2) on monolayers made of cholesterol molecules, both experimentally (surface area vs. lateral pressure isotherms measured by a Langmuir Film Balance) and theoretically (molecular dynamics (MD) all-atomic simulations). We found that surface isotherms depend, both quantitatively and qualitatively, on the nature of the ions by altering the shape and features of the isotherm. In line with the experiments, MD simulations show clear evidences of specific ionic effects and also provide molecular level details on ion specific interactions with cholesterol. More importantly, MD simulations show that the interaction of a particular ion with the surface depends strongly on its counterion, a feature ignored so far in most theories of specific ionic effects in surface forces. [ABSTRACT FROM AUTHOR]

A series of triblock semifluorinated n-alkanes of the general formula: F(CF 2 ) m (CH 2 ) n (CF 2 ) m F, (in short F m H n F m ), where m = 10, 12, and n = 6, 8, and 12 have been synthesized and employed for liquid crystalline studies and Langmuir monolayer characterization. Differential scanning calorimetry (DSC) measurements together with texture observation with polarizing microscope (POM) revealed the presence of liquid crystalline smectic phases for all the investigated homologs. The behavior of the studied molecules spread at the free water surface has also been investigated. Our results show for the first time that these unusual film-forming materials, which are completely hydrophobic in nature and do not possess any polar group in their structure, are surface active and form insoluble (Langmuir) monolayers at the air/water interface. Due to the fact that these molecules are chemically inert and, similar to the semifluorinated diblocks, are not toxic, they may be destined for biomedical uses as gas carriers and contrast agents, as well as in drug delivery systems. [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]

This study employed surface pressure isotherms and spectroscopic techniques to investigate the effect of quantum dots on the interaction between porphyrins and phospholipids using Langmuir monolayers and Langmuir-Blodgett films formed from negatively charged DMPA (the sodium salt of dimyristoyl- sn-glycero-phosphatidyl acid) and zwitterionic DPPC (1,2-dipalmitoyl- sn-glycero-3-phosphocholine) as cell membrane models in the presence of 5,10,15,20-tetrakis(4-N-tetradecyl-pyridyl) porphyrin (TMPyP), 5,10,15,20-tetrakis( p-sulfonato-phenyl) porphyrin (TPPS) and PEG-coated CdSe/ZnS quantum dots (QD). The porphyrins present at the monolayer subphase affected the organization of the lipids at the air/liquid interface, as shown by the changes in the surface pressure-surface area isotherms. QDs enhanced the interaction of TMPyP with DMPA, improving their transference from the liquid monolayers to solid supports. A higher amount of TMPyP was transferred to DMPA-Langmuir-Blodgett films when the QDs were present in the subphase as evidenced by the UV-Vis data. For DPPC the surface effects due to the presence of QDs are less evident. [ABSTRACT FROM AUTHOR]

The interactions between parabens (PBs) and lipid components of mammalian and bacterial cell membranes were investigated in model systems of Langmuir monolayers. Me-, Et-, Pr- and Bu-paraben studied in this paper are frequently applied as cosmetics and food preservatives, since they possess broad antimicrobial activity. The mode of PB action is connected with their incorporation into the membrane of bacterial organisms, however; it is not known what is the role of the respective lipid species in this mechanism. This problem is crucial to understand the differences in paraben activity toward individual microorganisms and to shed the light onto the problem of PB cytotoxicity reported in studies on mammalian cells. In this paper, the mentioned aspects were investigated with application of the Langmuir monolayer technique complemented with BAM and GIXD. Our experiments revealed that the influence of PBs depends on their chemical structure, solution concentration and on the class of lipid. The strongest modification of the monolayer characteristics, leading to its collapse at low surface pressure, occurred in the presence of BuPB, having the largest chain. PBs interact preferentially with the monolayers possessing low degree of condensation, whereas for LC state, the effect was weaker and observed only as modification of the 2D unit cells. In the model systems, PBs interact with phospholipids characteristic for mammalian membranes (phosphatidylcholine) stronger than with bacterial (phosphatidylglycerol and cardiolipin). This strong influence of parabens on the model systems composed of animal lipids may explain cytotoxic activity of these preservatives. [ABSTRACT FROM AUTHOR]

Bisphenol A (BPA) and other bisphenols constitute a class of organic pollutants, which because of their estrogenic properties, low dose activity and bioaccumulation pose considerable risk for public health as well as for the environment. Accumulated in the sediment bisphenols can endanger the decomposers' populations being incorporated into their cellular membranes; however, the mechanism of their membrane activity is unknown. Therefore, to study these phenomena we applied anionic phospholipid Langmuir monolayers as simple but versatile models of decomposers biomembranes. Phosphatidylglycerols and cardiolipins are not only the main components of bacterial membranes but also of crucial importance in mitochondrial and thylakoid membranes in eukaryotic cells. In our investigations we applied five compounds of the bisphenol class most commonly detected in the environment. To characterize the bisphenols–model membrane interactions we applied multiple mutually independent methods of physical chemistry; namely: the Langmuir monolayer technique, surface potential measurements, Brewster angle microscopy for the visualization of the monolayers' texture and grazing incidence X-ray diffraction for the discussion of the phospholipids packing within the monolayers. Our studies indicated that all the investigated bispenols interact with the model membrane, but the strength of the interactions is dependent on the bisphenol structure and hydrophobicity and the fluidity of the model membranes. We proved that bisphenol S often treated as the least toxic BPA analog can also be incorporated to the model membranes changing their structure and fluidity. [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]

The molecular packing, thermodynamics and surface topography of binary Langmuir monolayers of Insulin and DPPC (dipalmitoylphosphatidylcholine) or POCP (1-palmitoyl-2-oleoylphosphatidylcholine) at the air/water interface on Zn 2+ containing solutions were studied. Miscibility and interactions were ascertained by the variation of surface pressure-mean molecular area isotherms, surface compressional modulus and surface (dipole) potential with the film composition. Brewster Angle Microscopy was used to visualize the surface topography of the monolayers. Below 20 mN/m Insulin forms stable homogenous films with DPPC and POPC at all mole fractions studied (except for films with X INS = 0.05 at 10 mN/m where domain coexistence was observed). Above 20 mN/m, a segregation process between mixed phases occurred in all monolayers without squeezing out of individual components. Under compression the films exhibit formation of a viscoelastic or kinetically trapped organization leading to considerable composition-dependent hysteresis under expansion that occurs with entropic–enthalpic compensation. The spontaneously unfavorable interactions of Insulin with DPPC are driven by favorable enthalpy that is overcome by unfavorable entropic ordering; in films with POPC both the enthalpic and entropic effects are unfavorable. The surface topography reveals domain coexistence at relatively high pressure showing a striped appearance. The interactions of Insulin with two major membrane phospholipids induces composition-dependent and long-range changes of the surface organization that ought to be considered in the context of the information-transducing capabilities of the hormone for cell functioning. [ABSTRACT FROM AUTHOR]

CPT-11 and SN-38 are camptothecins with strong antitumor activity. Nevertheless, their severe side effects and the chemical instability of their lactone ring have questioned the usual forms for its administration and have focused the current research on the development of new suitable pharmaceutical formulations. This work presents a biophysical study of the interfacial interactions of CPT-11 and SN-38 with membrane mimetic models by using monolayer techniques and Differential Scanning Calorimetry. The aim is to get new insights for the understanding of the bilayer mechanics after drug incorporation and to optimize the design of drug delivery systems based on the formation of stable bilayer structures. Moreover, from our knowledge, the molecular interactions between camptothecins and phospholipids have not been investigated in detail, despite their importance in the context of drug action. The results show that neither CPT-11 nor SN-38 disturbs the structure of the complex liposome bilayers, despite their different solubility, that CPT-11, positively charged in its piperidine group, interacts electrostatically with DOPS, making stable the incorporation of a high percentage of CPT-11 into liposomes and that SN-38 establishes weak repulsive interactions with lipid molecules that modify the compressibility of the bilayer without affecting significantly neither the lipid collapse pressure nor the miscibility pattern of drug–lipid mixed monolayers. The suitability of a binary and a ternary lipid mixture for encapsulating SN-38 and CPT-11, respectively, has been demonstrated. [ABSTRACT FROM AUTHOR]

Myelin is the self-stacked membrane surrounding axons; it is also the target of several pathological and/or neurodegenerative processes like multiple sclerosis. These processes involve, among others, the hydrolytic attack by phospholipases. In this work we describe the changes in isolated myelin structure after treatment with several secreted PLA 2 (sPLA 2 ), by using small angle x-ray scattering (SAXS) measurements. It was observed that myelin treated with all the tested sPLA 2 s (from cobra and bee venoms and from pig pancreas) preserved the lamellar structure but displayed an enlarged separation between membranes in certain zones. Additionally, the peak due to membrane asymmetry was clearly enhanced. The coherence length was also lower than the non-treated myelin, indicating increased disorder. These SAXS results were complemented by Langmuir film experiments to follow myelin monolayer hydrolysis at the air/water interface by a decrease in electric surface potential at different surface pressures. All enzymes produced hydrolysis with no major qualitative difference between the isoforms tested. [ABSTRACT FROM AUTHOR]

A series of semifluorinated thiols of the general formula C m F 2 m +1 C n H 2 n SH ( abbr . F m H n SH) have been synthesized and characterized in Langmuir monolayers with surface pressure-area isotherms, complemented with polarization-modulated reflection absorption spectroscopy (PM-IRRAS) and sum-frequency generation (SFG) techniques. A comparative analysis was performed for compounds having the same length of fluorinated segment (F 10 ) and variable length of the hydrogenated part (H 6 , H 10 , H 12 ), and having identical hydrogenated segment (H 12 ) connected to a fluorinated moiety of different lengths (F 6 , F 8 , F 10 ). For the sake of comparison, an alkanethiol (H 18 SH) was also examined, and F 10 H 10 COOH and F 10 H 10 OH molecules were used for helping the assignment of SFG spectra of CH stretches. SFG was applied to investigate the hydrocarbon chain and the terminal CF 3 group, while PM-IRRAS was used to probe CF 2 groups. The number of gauche defects in the hydrocarbon chain increased with the increasing length of the molecule, either by elongation of the hydrogenated or perfluorinated part. SFG measurements recorded at three polarization combinations ( ppp , ssp , sps ) enabled us to estimate the tilt angle of the terminal CF 3 group in semifluorinated thiol molecules as ranging from 35° to 45°, which is consistent with nearly vertical fluorinated segments. Upon increasing the surface pressure, the fluorinated segment gets slightly more upright, but the hydrocarbon chain tilt increases while keeping the same average number of gauche defects. The extent of disorder in the hydrogenated segment may be controlled by varying the size of the fluorinated segment, and this could be exploited for designing functionalized surfaces with insertion of other molecules in the defect region. [ABSTRACT FROM AUTHOR]

Mixed Langmuir monolayers of 10,12-Pentacosadiynoic acid (DA) and amphiphilic hemicyanine (HSP) have been fabricated at the air–water interface. The mixed monolayer has been proved to be completely homogeneous. The DA molecules are arranged in a single monolayer within the mixed Langmuir monolayer, as opposed to the typical trilayer architecture for the pure DA film. Brewster angle microscopy has been used to reveal the mesoscopic structure of the mixed Langmuir monolayer. Flower shape domains with internal anisotropy due the ordered alignment of hemicyanine groups have been observed. Given the absorption features of the hemicyanine groups at the wavelength used in the BAM experiments, the enhancement of reflection provoked by the absorption process leads to the observed anisotropy. The ordering of such groups is promoted by their strong self-aggregation tendency. Under UV irradiation at the air–water interface, polydiacetylene (PDA) has been fabricated. In spite a significant increase in the domains reflectivity has been observed owing to the modification in the mentioned enhanced reflection, the texture of the domains remains equal. The PDA polymer chain therefore grows in the same direction in which the HSP molecules are aligned. This study is expected to enrich the understanding and design of fabrication of PDA at interfaces. [ABSTRACT FROM AUTHOR]

Cyclosporin A (CsA), a hydrophobic cyclic peptide produced by the fungus Tolypocladium inflatum, is well known for its high efficiency as an immunosuppressor for transplanted organs and anti-inflammatory properties; however, it is also active as antiparasitic (antimalarial) drug. Antimalarial mechanism of CsA action lacks a detailed understanding at molecular level. Due to a high lipophilicity of CsA, it is able to interact with lipids of cellular membrane; however, molecular targets of this drug are still unknown. To get a deeper insight into the mode of antimalarial activity of CsA, it is of utmost importance to examine its interactions with membrane components. To reach this goal, the Langmuir monolayer technique, which serves as a very useful, easy to handle and controllable model of biomembranes, has been employed. In this work, the interactions between CsA and main membrane lipids, i.e., cholesterol (Chol), 2-oleoyl-1-palmitoyl-3-phosphocholine (POPC), and sphingomyelin (SM), have been investigated. Attractive interactions are observed only for CsA mixtures with SM, while repulsive forces occur in systems containing remaining membrane lipids. Taking into consideration mutual interactions between membrane lipids (Chol-SM; Chol-POPC and SM-POPC), the behavior of CsA in model erythrocyte membrane of normal and infected cells has been analyzed. Our results prove strong affinity of CsA to SM in membrane environment. Since normal and parasitized erythrocytes differ significantly in the level of SM, this phospholipid may be considered as a molecular target for antimalarial activity of CsA. [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]