Low Surface Pressure Research Articles

Visualization of Two-Dimensional Single Chain Conformations Solubilized in a Miscible Polymer Blend Monolayer by Atomic Force Microscopy

Polymer Langmuir monolayers spread on a water surface are one of the best models for two-dimensional (2D) polymer and have been extensively studied. However, the most fundamental issue in understanding a 2D film, the polymer chain packing in the film, is still not well-understood, especially from the experimental point of view. Direct observation of the chain packing by microscopy at a molecular level, such as by atomic force microscopy (AFM), might be one of the most promising ways to study this issue; however, because of the limited resolution of the method, the chain packing of polymer cannot be resolved by AFM, except for especially large polymers. Here, we show that a mixed monolayer of vinyl polymers, poly(methyl methacrylate) (PMMA) and poly(n-nonyl acrylate) (PNA), was miscible at a low surface pressure, and if a small amount of PMMA chains was solubilized in a PNA monolayer, the isolated PMMA chains in the PNA monolayer were, for the first time, successfully visualized by AFM with a clear contrast, which originated from a difference of rigidities of the polymers due to their different glass transition temperatures (105 °C(PMMA) and -89 °C(PNA)). The PMMA chains were found to strongly interpenetrate into the PNA monolayer, with a radius of gyration (R(g(PMMA))) that was several times larger than that of the 2D ideal chain (segregated-chain). Furthermore, the radius scaled with the molecular weight of the PMMA (M(PMMA)) as R(g(PMMA)) ∝ M(PMMA)(0.63), which was between the scaling of the 2D ideal chain (segregated chain), R(g) ∝ M(0.5), and the 2D chain in good solvent, R(g) ∝ M(0.75). On the other hand, R(g(PMMA)) was independent of the molecular weight of the PNA matrix over a wide range. These results indicate that the PNA/PMMA monolayer is a strongly miscible system, although the R(g(PMMA)) scaling with M(PMMA) (0.63) is somewhat smaller than that expected for a 2D chain in good solvent systems (0.75). The generation of molecular level information by direct observation of polymer chains in 2D blend films should improve our understanding of polymer 2D films.

Headgroup specificity for the interaction of the antimicrobial peptide tritrpticin with phospholipid Langmuir monolayers

We examined the interaction of the cationic antimicrobial peptide (AMP) tritrpticin (VRRFPWWWPFLRR, TRP3) with Langmuir monolayers of zwitterionic (dipalmitoyl phosphatidylcholine, DPPC, and dipalmitoyl phosphatidylethanolamine, DPPE) and negatively charged phospholipids (dipalmitoyl phosphatidic acid, DPPA, and dipalmitoyl phosphatidylglycerol, DPPG). Both surface pressure and surface potential isotherms became more expanded upon addition of TRP3 (DPPE∼DPPC≪DPPA<DPPG). The stronger interaction with negatively charged phospholipids agrees with data for vesicles and planar lipid bilayers, and with AMPs greater activity against bacterial membranes versus mammalian cell membranes. Considerable expansion of negatively charged monolayers occurred at 10 and 30mol% TRP3, especially at low surface pressure. Moreover, a difference was observed between PA and PG, demonstrating that the interaction, besides being modulated by electrostatic interactions, displays specificity with regard to headgroup, being more pronounced in the case of PG, present in large quantities in bacterial membranes. In previous studies, it was proposed that the peptide acts by a toroidal pore-like mechanism [1,2]. Considering the evidence from the literature that PG shows a propensity to form a positive curvature as do toroidal pores, the observation of TRP3's preference for the PG headgroup and the dramatic increase in area promoted by this interaction represent further support for the toroidal pore mechanism of action proposed for TRP3.

Effect of Amidation on the Antimicrobial Peptide Aurein 2.5 from Australian Southern Bell Frogs

Aurein 2.5 is a naturally C-terminally amidated amphibian antimicrobial peptide. C-terminal amidation can increase efficacy and hence a comparison was made between aurein 2.5-CONH2 and its nonamidated analogue. Amidation of the C-terminal carboxyl of aurein 2.5 enhanced antimicrobial activity 2.5- fold against Klebsiella pneumonia. Our results demonstrate that both peptide analogues had high surface activities (23 mN m-1for aurein 2.5-COOH and 26 mN m-1 aurein 2.5-CONH2). Circular dichroism measurements suggest that the helical content of the amidated form, in the presence of trifluoroethanol, was significantly enhanced (33.66 % for aurein 2.5-COOH and 60.89 % aurein 2.5-CONH2). The interaction of aurein 2.5 with bacterial cell membrane mimics was investigated using Langmuir monolayers. Aurein 2.5-CONH2 induced stable surface pressure changes in monolayers formed from K. pneumonia (circa 4.7 mN m-1), however, lower surface pressure changes were observed for aurein 2.5- COOH (circa 3.8 mN m-1). The data shows that in the case of aurein 2.5, amidation is able to enhance antibacterial activity and it is proposed that the increase in effectiveness is due to stabilization of the α-helical structure at the membrane interface.

Interfacial layers from the protein HFBII hydrophobin: Dynamic surface tension, dilatational elasticity and relaxation times

The pendant-drop method (with drop-shape analysis) and Langmuir trough are applied to investigate the characteristic relaxation times and elasticity of interfacial layers from the protein HFBII hydrophobin. Such layers undergo a transition from fluid to elastic solid films. The transition is detected as an increase in the error of the fit of the pendant-drop profile by means of the Laplace equation of capillarity. The relaxation of surface tension after interfacial expansion follows an exponential-decay law, which indicates adsorption kinetics under barrier control. The experimental data for the relaxation time suggest that the adsorption rate is determined by the balance of two opposing factors: (i) the barrier to detachment of protein molecules from bulk aggregates and (ii) the attraction of the detached molecules by the adsorption layer due to the hydrophobic surface force. The hydrophobic attraction can explain why a greater surface coverage leads to a faster adsorption. The relaxation of surface tension after interfacial compression follows a different, square-root law. Such behavior can be attributed to surface diffusion of adsorbed protein molecules that are condensing at the periphery of interfacial protein aggregates. The surface dilatational elasticity, E, is determined in experiments on quick expansion or compression of the interfacial protein layers. At lower surface pressures (<11mN/m) the experiments on expansion, compression and oscillations give close values of E that are increasing with the rise of surface pressure. At higher surface pressures, E exhibits the opposite tendency and the data are scattered. The latter behavior can be explained with a two-dimensional condensation of adsorbed protein molecules at the higher surface pressures. The results could be important for the understanding and control of dynamic processes in foams and emulsions stabilized by hydrophobins, as well as for the modification of solid surfaces by adsorption of such proteins.

Adsorption and Dilatational Rheology of Heat-Treated Soy Protein at the Oil–Water Interface: Relationship to Structural Properties

We evaluated the influence of heat treatment on interfacial properties (adsorption at the oil-water interface and dilatational rheology of interfacial layers) of soy protein isolate. The related structural properties of protein affecting these interfacial behaviors, including protein unfolding and aggregation, surface hydrophobicity, and the state of sulfhydryl group, were also investigated. The structural and interfacial properties of soy protein depended strongly on heating temperature (90 and 120 °C). Heat treatment at 90 °C induced an increase in surface hydrophobicity due to partial unfolding of protein, accompanied by the formation of aggregates linked by disulfide bond, and lower surface pressure at long-term adsorption and similar dynamic interfacial rheology were observed as compared to native protein. Contrastingly, heat treatment at 120 °C led to a higher surface activity of the protein and rapid development of intermolecular interactions in the adsorbed layer, as evidenced by a faster increase of surface pressure and dilatational modulus. The interfacial behaviors of this heated protein may be mainly associated with more flexible conformation and high free sulfhydryl group, even if some exposed hydrophobic groups are involved in the formation of aggregates. These results would be useful to better understand the structure dependence of protein interfacial behaviors and to expand utilization of heat-treated protein in the formulation and production of emulsions.

An Investigation of the Behavior of Binary Mixed Langmuir Monolayer of 2,2′-p-Phenylenebis (5-phenyloxazol) and Arachidic Acid

A systematic study is reported on the monolayer characteristics of 2,2′-p-phenylenebis (5-phenyloxazol) (POPOP) mixed with arachidic acid (AA) at the air-water interface, using surface pressure versus area per molecule (π-A) isotherms complemented with absorption spectroscopy as well as scanning electron microscopy. The (π-A) isotherms of POPOP mixed with AA at different mole fractions show a plateau like region at very low surface pressure, which suggests a phase transition corresponding to a reorientation of the POPOP molecules at the air-water interface. The mixing behavior was obtained from surface pressure-area isotherms by using the surface phase rule and excess area criterion. Results show that POPOP is immiscible in AA, leading to the formation of aggregates. These observations are confirmed by ultraviolet-visible absorption spectroscopy and scanning electron microscopy. Absorption spectra of the mixed LB films reveal that I-type of aggregates play their prominent role in the mixed LB films.

Ground effect on flow past a wing with a NACA0015 cross-section

Wing in ground (WIG) effects is an important aerodynamics phenomenon as it affects the aerodynamics of aircraft (during take off and landing), marine crafts like wing in ground effect (WIG) crafts and racing cars. In the present investigation, wind tunnel experiment was conducted on a wing with a NACA0015 cross-section, a chord of 0.24m and an aspect ratio of 1.46. The “ground” was simulated by a vertically mounted 0.6m (streamwise)×0.457m (same height as the wind tunnel test section) perspex plate. The wing was mounted vertically on a load cell, and the load cell on a mechanism that could traverse the wing/load cell set-up in a direction transverse to the free stream, thereby varying the distance between the wing and the ground. Measurements carried out include the pressure distribution on the wing surface at mid-span and forces on the wing, and pressure distribution on the ground. Measurements were carried out at various angles of attack, at a constant wind speed of 12m/s. The corresponding chord based Reynolds Number (Rec) is approximately 1.872×105.Mid-span surface pressure distributions were measured on the wing at both positive and negative angles of attack α, and at different ground clearance h/c. It was observed that for both positive and negative angles of attack, the pressure on the upper surface shows a much stronger angle of attack dependence, and only weak h/c dependence when the angle of attack is in the negative range. On the other hand, the lower surface pressure is influenced by both the angle of attack and h/c. Within a certain range of positive angle of attack and h/c, the “ramming effect” which is associated with a local increase in surface pressure that had been reported in the literature was observed.Streamwise pressure distribution on the ground that corresponds to the wing mid-span shows that when the wing is out of ground effect, the effects of wing angle of attack on the pressure distribution on the ground is not significant. When the ground effect are present (small to moderately small h/c), pressure distribution on the ground especially within the range −0.3<x/c<1 is affected. Different pressure versus x/c trends were observed, depending on the magnitude and sign of the wing angle of attack.Both lift coefficients obtained from integrating surface pressure distribution and from direct load cell measurements show that as h/c reduces, the sign of the lift coefficient remains unchanged but its magnitude increases. A temporary reduction in the lift coefficient is observed when h/c reduces from about 0.3 to 0.15 in the α=0–6° range, for both the pressure distribution integration and load cell measurement cases. This is believed to be the consequence of the “convergent–divergent channel effect” reported in surface pressure distribution. Generally speaking the lift estimated from integrating surface pressure distribution is slightly larger than the one measured directly from the load cell. This is consistent with the slightly more 2-D nature of the flow at the wing mid-span.The lift slope from both the pressure and load cell data show h/c dependence, with the former consistently the larger of the two. Their magnitudes generally lie within the magnitude estimated from the Thin Aerofoil Theory (2-D flow) and Prandtl’s Lifting Line Theory (3-D flow).

High-Resolution Investigation of Nanoparticle Interaction with a Model Pulmonary Surfactant Monolayer

The pulmonary surfactant film spanning the inner alveolar surface prevents alveolar collapse during the end-exhalation and reduces the work of breathing. Nanoparticles (NPs) present in the atmosphere or nanocarriers targeted through the pulmonary route for medical purposes challenge this biological barrier. During interaction with or passage of NPs through the alveolar surfactant, the biophysical functioning of the film may be altered. However, experimental evidence showing detailed biophysical interaction of NPs with the pulmonary surfactant film are scant. In this study, we have investigated the impact of a hydrophobic polyorganosiloxane (AmOrSil20) NPs on the integrity as well as on the structural organization of the model pulmonary surfactant film. Primarily, scanning force microscopic techniques and electron microscopy have been used to visualize the topology as well as to characterize the localization of nanoparticles within the compressed pulmonary surfactant film. We could show that the NPs partition in the fluid phase of the compressed film at lower surface pressure, and at higher surface pressure, such NPs interact extensively with the surface-associated structures. Major amounts of NPs are retained at the interface and are released slowly into the aqueous subphase during repeated compression/expansion cycles. Further, the process of vesicle insertion into the interfacial film was observed to slow down with increasing NP concentrations. The hydrophobic AmOrSil20 NPs up to a given concentration do not substantially affect the structural organization and functioning of pulmonary surfactant film; however, such NPs do show drastic impacts at higher concentrations.

Analysis of satellite-derived Arctic tropospheric BrO columns in conjunction with aircraft measurements during ARCTAS and ARCPAC

Abstract. We derive tropospheric column BrO during the ARCTAS and ARCPAC field campaigns in spring 2008 using retrievals of total column BrO from the satellite UV nadir sensors OMI and GOME-2 using a radiative transfer model and stratospheric column BrO from a photochemical simulation. We conduct a comprehensive comparison of satellite-derived tropospheric BrO column to aircraft in-situ observations of BrO and related species. The aircraft profiles reveal that tropospheric BrO, when present during April 2008, was distributed over a broad range of altitudes rather than being confined to the planetary boundary layer (PBL). Perturbations to the total column resulting from tropospheric BrO are the same magnitude as perturbations due to longitudinal variations in the stratospheric component, so proper accounting of the stratospheric signal is essential for accurate determination of satellite-derived tropospheric BrO. We find reasonably good agreement between satellite-derived tropospheric BrO and columns found using aircraft in-situ BrO profiles, particularly when satellite radiances were obtained over bright surfaces (albedo &gt;0.7), for solar zenith angle &lt;80° and clear sky conditions. The rapid activation of BrO due to surface processes (the bromine explosion) is apparent in both the OMI and GOME-2 based tropospheric columns. The wide orbital swath of OMI allows examination of the evolution of tropospheric BrO on about hourly time intervals near the pole. Low surface pressure, strong wind, and high PBL height are associated with an observed BrO activation event, supporting the notion of bromine activation by high winds over snow.

Electrochemical behaviour of mixed LB films of ubiquinone – DPPC

The structure and the electrochemical behaviour of Langmuir and Langmuir–Blodgett (LB) films of the biological ubiquinone-10 (UQ) and a mixture of dipalmytoilphosphatidylcholine (DPPC) and UQ at the molar ratios DPPC:UQ 5:1 and 10:1 have been investigated. The surface pressure-area isotherms of the Langmuir films and the AFM images of the LB films show the formation of a monolayer in the DPPC:UQ mixture till a certain surface pressure is attained, and then at higher surface pressures the UQ is progressively expelled. The cyclic voltammograms of DPPC:UQ LB films formed on indium tin oxide, ITO, at different surface pressures show one reduction and one oxidation peak at low surface pressures, but two or even more reduction and oxidations peaks at medium and high surface pressures. The electrochemical behaviour is correlated with the film structure.

In Vitro Application of Langmuir Monolayer Model to Study In Vivo Biological Systems

ABSTRACTLangmuir monolayer model is applied to study molecular interactions between phospholipids and surface active compounds and to determine the lateral elasticity and compressibility of the surface films at air-liquid interface. The interaction of the synthetic Methionine-enkephalin (Met-enk) and its amidated derivative (Met-enk-NH2) with monolayers of the zwitterionic dimyristoylphosphatidylcholine and the negatively charged dimyristoylphosphatidylglycerol were evaluated by measurements of surface tension (γ, mN/m) - time dependencies after injection of enkephalins under the Langmuir monolayer. The decrease of γ values during time showed that there was a strong penetration effect of both types of Met-enk molecules into the monolayers, being significantly stronger for the amidated derivate, Met-enk-NH2.The behavior of tear film lipid layer (TFLL) is studied in dynamic conditions by compression/expansion cycling of Langmuir films. It allows determining reciprocal compressibility, CS−1, and reversibility, Rv, of the tear films at air-liquid interface. Our results showed very high lateral elasticity (i.e. low reciprocal compressibility) and high structural reversibility of the meibomian surface films which was confirmed by Brewster Angle Microscopy images. It is shown that even at low surface pressures (between 0.5 and 10 mN/m) human meibum forms rough continuous multilayer films at the air/water interface that get more uniform when surface pressure increases.Our results demonstrate the potential of lipid monolayers formed in Langmuir's through to be successfully used as an elegant and simple model to study molecular interactions and properties of surface films at the air/water interface.

Insertion properties of cholesterylcyclodextrins in phospholipid membranes: a molecular study

Amphiphilic cyclodextrins (CDs) are good candidates to functionalize natural membranes, as well as synthetic vesicles. In this paper, we fully describe and compare the insertion properties of the permethylated mono-cholesteryl α-CD (TASC) and its mono- and di-cholesteryl β-CD analogues (TBSC and TBdSC) in dipalmitoyl-L-α-phosphatidylcholine (DPPC) mono- and bi-layers as membrane models from the macroscopic to the molecular scale. By calculating the inverse compressibility moduli and free excess Gibbs energies from the Langmuir isotherms, the influence of the CD type, CD ratio and number of cholesteryl anchors on the membrane properties have been established. TBdSC, with its two cholesteryl residues, seems to be anchored best to the membrane compared to CD derivatives with only one anchor. Furthermore, TASC appears to be more firmly inserted into the membrane than TBSC. The in-plane structure is characterized by Brewster angle microscopy (BAM) at the air–water interface and atomic force microscopy (AFM) of the mono- and bi-layers deposited on mica. Depending on the compression, full miscibility of the cholesteryl CDs and the phospholipids is observed at low surface pressures and a clear demixing tendency is apparent during compression. CD-modified bilayers are stable and are subject to a gel–liquid phase transition upon heating. Due to their bulky CD moiety, the amphiphilic CDs exhibit a distinct fluidizing effect, shifting the DPPC's gel–liquid transition. The structure of the mixed TASC/DPPC mono- and bi-layers perpendicular to the surface is investigated with Angstrom resolution by neutron reflectivity. In this way a molecular model of the insertion has been established, which suggests that the CD cavities partly protrude into the subphase, which should leave them accessible for complex formation.

Conformational Change of HIV Nef upon Insertion into Lipid Membranes Resolved by Neutron Reflectivity

Nef is one of several HIV-1 accessory proteins and directly contributes to AIDS progression. Nef has no catalytic activity but instead realizes its functions by interacting with cellular proteins. Nef is myristoylated on the N-terminus, associates with membranes, and undergoes a transition from a solution conformation to a membrane-associated conformation. It has been hypothesized that conformational rearrangement enables membrane-associated Nef to interact with cellular proteins. Despite its obvious disease importance, there is little or no direct information about the conformation of membrane-bound Nef. In this work we used neutron reflection to reveal details of the conformation of membrane-bound Nef. The conformation of myristoylated Nef was studied upon binding to Langmuir monolayers of negatively-charged lipids. By adjusting the surface pressure, the extent of insertion of the myristate group could be controlled. At sufficiently high surface pressure such that the myristate group did not insert, adsorbed Nef was in a condensed state with the core domain directly against the lipid headgroups. At lower surface pressure such that the myristate group inserted into the membrane, adsorbed Nef was found to be in an extended state with the core domain displaced ∼ 70 A from the lipid headgroups. Thus, insertion of the myristate group triggers a conformational transition to an open configuration. This has important ramifications for the ability of Nef to interact with host proteins.

Influence of membrane organization on the interactions between persistent pollutants and model membranes

Langmuir monolayer studies and electrochemical methods were employed to investigate the effect of model membrane organization on the interactions with persistent pollutants such as perfluorinated carboxylic acids (PFCAs). 1,2-dimyristoyl-sn-glycero-3-phosphoethanoloamine (DMPE) was employed to construct the model lipid membrane and perfluorooctanesulphonic acid (PFOS) was chosen as the representative of perfluorinated pollutants. We demonstrate that perfluorinated compounds penetrate a model membrane only when it is less condensed. Such liquid-expanded phase was achieved by compressing the Langmuir monolayer to lower surface pressures. PFOS incorporation into model DMPE membrane during membrane formation was observed in liquid-expanded region, while at higher surface pressures, in the well-organized monolayer the expulsion of perfluorinated compound occurred as the result of a strong attraction between the DMPE molecules. The DMPE monolayers prepared by the Langmuir–Blodgett/Langmuir–Schaefer method were transferred onto gold electrode under surface pressure of 3mN/m and 20mN/m. The model membrane organization depends on surface pressure during transfer and time of exposure to PFOS solution and is shown to affect the electrode accessibility by three electroactive compounds used as the probes of the blocking properties of the monolayer: menadione, potassium ferricyanide and hexaamineruthenium chloride, differing in the properties and kinetics of electron transfer.

Amphiphilic Behavior of New Cholesteryl Cyclodextrins: A Molecular Study

Amphiphilic cyclodextrins (CDs) are good candidates to functionalize natural membranes as well as synthetic vesicles. In this paper, we describe the synthesis of the amphiphilic permethylated monocholesteryl α-CD (TASC). Its interfacial behavior is compared with that of the permethylated mono- and dicholesteryl β-CD analogues (TBSC and TBdSC). Langmuir isotherms suggest a reorganization upon compression for all compounds, which is quantified using neutron as well as X-ray reflectivity. The in-plane structure is characterized by atomic force microscopy (AFM) on monolayers deposited on solid substrates. A model involving a reorientation of the CD with respect to the interface to adjust its conformation to the available area per molecule is proposed. Although we observe for TBSC a rearrangement similar to TASC and TBdSC, it is already achieved at lower surface pressures compared with its disubstituted derivative. This specific behavior is explained by an increased structural flexibility and compressibility compared with TBdSC and TASC. The average number of water molecules per CD was determined using the neutron data and validated from X-ray data, which also allows the determination of the CD's molecular volume. The permethylated CD molecules are strongly hydrated in the film, but the α-CD analogue is less hydrated than the β-CD derivatives, and hydration decreases with compression.

A spectroscopic study of water-soluble pyronin B and pyronin Y in Langmuir–Blodgett films mixed with stearic acid

Mono and multilayer of water-soluble pyronin B (PyB) and pyronin Y (PyY) mixed with stearic acid (SA) have been incorporated in Langmuir–Blodgett (LB) films. The surface pressure–area (π–A) isotherm studies pointed out that pure PyB and PyY are incapable of forming stable films at air–water interface and collapsed readily at low surface pressures. However, mixture of PyB or PyY with SA easily formed stable films at the air–water interface and they were easily transferred onto solid substrates. The average area per molecule of mixed films of PyB and PyY at the air–water interface was observed to decrease with increasing concentrations of PyB and PyY. The spectroscopic characteristics of PyB and PyY in chloroform, in SA containing chloroform and in LB films have also been investigated by using absorption and steady-state and time-resolved fluorescence spectroscopy techniques. The morphology of the LB film surfaces has been characterized by using atomic force microscopy (AFM).

Spectrin-like Repeats 11–15 of Human Dystrophin Show Adaptations to a Lipidic Environment

Dystrophin is essential to skeletal muscle function and confers resistance to the sarcolemma by interacting with cytoskeleton and membrane. In the present work, we characterized the behavior of dystrophin 11-15 (DYS R11-15), five spectrin-like repeats from the central domain of human dystrophin, with lipids. DYS R11-15 displays an amphiphilic character at the liquid/air interface while maintaining its secondary α-helical structure. The interaction of DYS R11-15 with small unilamellar vesicles (SUVs) depends on the lipid nature, which is not the case with large unilamellar vesicles (LUVs). In addition, switching from anionic SUVs to anionic LUVs suggests the lipid packing as a crucial factor for the interaction of protein and lipid. The monolayer model and the modulation of surface pressure aim to mimic the muscle at work (i.e. dynamic changes of muscle membrane during contraction and relaxation) (high and low surface pressure). Strikingly, the lateral pressure modifies the protein organization. Increasing the lateral pressure leads the proteins to be organized in a regular network. Nevertheless, a different protein conformation after its binding to monolayer is revealed by trypsin proteolysis. Label-free quantification by nano-LC/MS/MS allowed identification of the helices in repeats 12 and 13 involved in the interaction with anionic SUVs. These results, combined with our previous studies, indicate that DYS R11-15 constitutes the only part of dystrophin that interacts with anionic as well as zwitterionic lipids and adapts its interaction and organization depending on lipid packing and lipid nature. We provide strong experimental evidence for a physiological role of the central domain of dystrophin in sarcolemma scaffolding through modulation of lipid-protein interactions.

Aggregation of non-amphiphilic bathophenanthroline in the restricted geometry of Langmuir–Blodgett films with two different matrices

The behavior of binary mixed Langmuir monolayers from the mixture of non-amphiphilic bathophenanthroline (BPH) and behenic acid (BA)/poly(methyl methacrylate) (PMMA) spread on aqueous subphase was investigated on the basis of the analysis of surface pressure–average area per molecule (π–A) isotherms complemented with UV–vis absorption spectroscopy and scanning electron microscopy. In addition, the miscibility of the components in the two investigated mixed systems (BPH/BA and BPH/PMMA) was also tested by using additivity and surface phase rules. The plots of area per molecule versus mole fraction suggest that BPH and BA are immiscible, whereas BPH and PMMA mixtures show non-ideal behavior at low surface pressures and complete miscibility or immiscibility at higher surface pressures. Spectroscopic study reveals that J-type of aggregates is formed in the mixed films. Scanning electron microscopic study supports the presence of aggregates.

Interfacial Behavior of OEG–Linear Dendron Monolayers: Aggregation, Nanostructuring, and Electropolymerizability

We report on the interesting interfacial behavior of oligoethylene glycol or OEGylated linear dendron monolayers at the air-water interface as a function of (a) carbazole dendron generation, (b) the length of the OEG units, and (c) the surface pressure applied upon compression. Surface pressure-area isotherms, hysteresis studies, and isobaric creep measurement revealed a structure-property relationship consistent with the hydrophilic-lipophilic balance of a linear dendron with the OEG group serving as the surface anchor to the water subphase. AFM studies revealed that all the OEGylated carbazole dendrons self-assemble into spherical morphology at low surface pressures but form ribbonlike structures as the surface pressure is increased. This nanostructuring is primarily imparted by the increase in van der Waals forces with increasing amount of carbazole units per dendron generation on a hydrophilic mica surface. Further, electrochemical cross-linking of the carbazole molecules by cyclic voltammetery (CV) on doped Si wafer has enabled the formation of an LB film monolayer with a secondary level of organization in the monolayer imparted by the inter- and intramolecular cross-linking among the carbazole units. This study should provide a basis for monolayer film materials based on combining the LB technique and electrochemical cross-linking for nanostructuring superstructures at the air-water interface.

Atomic force microscopy analysis of rat pulmonary surfactant films

Pulmonary surfactant facilitates breathing by forming a surface tension reducing film at the air–liquid interface of the alveoli. The objective was to characterize the structure of surfactant films using endogenous rat surfactant. Solid-support surfactant films, at different surface pressures, were obtained using a Langmuir balance and were analyzed using atomic force microscopy. The results showed a lipid film structure with three distinct phases: liquid expanded, liquid ordered and liquid condensed. The area covered by the liquid condensed domains increased as surface pressure increased. The presence of liquid ordered phase within these structures correlated with the cholesterol content. At a surface pressure of 50 mN/m, stacks of bilayers appeared. Several structural details of these films differ from previous observations made with goat and exogenous surfactants. Overall, the data indicate that surfactant films demonstrate phase separation at low surface pressures and multilayer formation at higher pressure, features likely important for normal surfactant function.