Brewster Angle Microscopy Research Articles

Direct Comparison of Domains in DMPC/d-Cholesterol Langmuir Monolayers via Brewster Angle, Fluorescence and Light Scattering Microscopy

Direct Comparison of Domains in DMPC/d-Cholesterol Langmuir Monolayers via Brewster Angle, Fluorescence and Light Scattering Microscopy

Influence of the porphyrin structure and linker length on the interfacial behavior of phospholipid-porphyrin conjugates

HypothesisPhospholipid-porphyrin (Pl-Por) conjugates consist of porphyrin derivatives grafted to a lysophosphatidylcholine backbone. Owing to their structural similarities with phospholipids, Pl-Por conjugates can self-assemble into liposome-like assemblies. However, there is a significant lack of information concerning the impact of the porphyrin type and the length of the alkyl chain bearing the porphyrin on the interfacial behavior of the Pl-Por conjugates. We hypothesized that changing the chain length and the porphyrin type could impact their two-dimensional phase behavior and modulate the alignment between the two chains. Experiments6 Pl-Por conjugates with different alkyl chain lengths in the sn2 position of C16 lysophosphatidylcholine and coupled to either pheophorbide-a or pyropheophorbide-a were synthesized. Their interfacial behavior at the air/water interface was assessed using Langmuir balance combined to a variety of other physical techniques including Brewster angle microscopy, atomic force microscopy and X-ray reflectometry. FindingsOur results showed that all 6 Pl-Por form stable monolayers with the porphyrin moiety at the air/water interface. We also showed that changing the porphyrin moiety controlled the packing of the monolayer and thus the formation of organized domains. The chain length dictated the structure of the formed domains with no evidence of the alignment between the two chains.

Correlations between bulk and surface properties of meibomian lipids with alteration of wax-to-sterol esters content

In a recent study (Ewurum et al., 2021), wax (WE) and sterol esters (CE) from human meibum secretions (MGS) were separated and reconstituted with controlled WE/CE ratios (0%, 20%, 30%, 40%, 50%, 75% and 100% CE weight fractions). It was found that the alterations in the CE content of WE/CE mixtures modified the hydrocarbon chain conformation and packing of the mixture. A major question that emerges is whether the spectroscopic packing parameters determined for bulk meibum translate to a change in the performance of meibomian layers at the air/water interface, as it is the surface film functionality that is crucial for the performance of MGS at the ocular surface. The study of human meibum films with Langmuir surface balance was performed to access the surface properties at blink-like deformations of the film area. Surface pressure (π)-area (A) isocycles and stress relaxations were used to assess the layer’s reorganization during area cycling and dilatational elasticity, respectively. The morphology of the films was monitored by Brewster angle microscopy. It was found that the increased order and chain melting temperature of the bulk samples correlated with a raise in the maximum surface pressure attained at minimal surface area and in the transient dilatational modulus of the meibomian layers. Such correlations may allow for development of an improved understanding between the bulk and surface properties of human meibum and of other natural and synthetic tear lipid films.

DNA-mediated molecular assembly of a triphenylene–surfactant complex monolayer

Bottom-up DNA-guided molecular assembly is a technique of choice in modern organic device engineering. DNA, being a polyelectrolyte, is capable of mediating electrostatic interactions between different molecular building blocks. Here, we report DNA-mediated molecular assembly of an electrostatically driven triphenylene-surfactant complex monolayer. The monolayer, formed at air-water interface with DNA in the subphase, was studied using surface manometry and Brewster angle microscopy. Unlike that of the pristine system, the monolayer in presence of DNA showed enhanced stability and a remarkably high efficiency of deposition on solid supports. The morphologies of deposited films with controlled number of layers were studied using atomic force microscopy. In addition, UV–visible spectroscopy and grazing incidence X-ray diffraction (GIXRD) technique confirmed the presence of DNA in the deposited films. Since both triphenylene and surfactant are technologically relevant molecules, the DNA-mediated molecular assemblies deposited on solid substrates could find applications as functional materials in organic electronics.

Comparing C2=O and C2=S Barbiturates: Different Hydrogen-Bonding Patterns of Thiobarbiturates in Solution and the Solid State.

Carbonyl-centered hydrogen bonds with various strength and geometries are often exploited in materials to embed dynamic and adaptive properties, with the use of thiocarbonyl groups as hydrogen-bonding acceptors remaining only scarcely investigated. We herein report a comparative study of C2=O and C2=S barbiturates in view of their differing hydrogen bonds, using the 5,5-disubstituted barbiturate B and the thiobarbiturate TB as model compounds. Owing to the different hydrogen-bonding strength and geometries of C2=O vs. C2=S, we postulate the formation of different hydrogen-bonding patterns in C2=S in comparison to the C2=O in conventional barbiturates. To study differences in their association in solution, we conducted concentration- and temperature-dependent NMR experiments to compare their association constants, Gibbs free energy of association ∆Gassn., and the coalescence behavior of the N-H‧‧‧S=C bonded assemblies. In Langmuir films, the introduction of C2=S suppressed 2D crystallization when comparing B and TB using Brewster angle microscopy, also revealing a significant deviation in morphology. When embedded into a hydrophobic polymer such as polyisobutylene, a largely different rheological behavior was observed for the barbiturate-bearing PB compared to the thiobarbiturate-bearing PTB polymers, indicative of a stronger hydrogen bonding in the thioanalogue PTB. We therefore prove that H-bonds, when affixed to a polymer, here the thiobarbiturate moieties in PTB, can reinforce the nonpolar PIB matrix even better, thus indicating the formation of stronger H-bonds among the thiobarbiturates in polymers in contrast to the effects observed in solution.

Direct causality between film formation and water-retaining effect of surfactant-based film-forming curing compound for concrete

Surfactant-based film-forming curing compounds (SFCCs) are widely used to retain water on fresh concrete by forming multilayered films. However, the water-retaining mechanism is not yet fully understood; therefore, we aimed to clarify this mechanism, thereby potentially aiding in evaluating the effect of SFCC or to develop more effective SFCCs. It was confirmed that SFCC does not hinder the setting and hardening properties or strength development. Thus, we examined water evaporation from cement pastes on which SFCC was sprayed. Consequently, the water-retaining effect lasted up to 8 h, which indicating that 8 h after spraying SFCC is enough time for suppression of plastic cracking. We then observed the water surface on which SFCC was spread under a Brewster angle microscope and discovered that SFCC on the water surface forms continuous thin film and agglomerates. The water-retaining effect was higher when a continuous thin film was formed; thus, the observation of this thin film facilitated the evaluation of the effect of SFCC. • This study focused on a surfactant-based film-forming curing compound (SFCC). • The water-retaining effect of SFCC continued up to 8 h. • SFCC on the water surface forms continuous thin film and agglomerates. • The water-retaining effect was higher when the continuous thin film was formed.

Formation of Surface Wrinkles in Collapsed Langmuir Films of a Polyhedral Oligomeric Silsesquioxane Containing Diblock Copolymer.

Surface pressure versus mean molecular area isotherms of Langmuir films of a hybrid diblock copolymer of poly(ethylene glycol) (PEG) and poly(methacrylo polyhedral oligomeric silsesquioxane) P(MA-POSS) together with Brewster angle microscopy reveal details of the phase transitions. The formation of a periodic wrinkling pattern in collapsed films is observed by epifluorescence microscopy after applying several compression-expansion cycles above the surface pressure of ≈18 mN/m. The wrinkle formation is reversible upon compression and expansion of the Langmuir films. Two distinct orientations of POSS molecules are assumed in Langmuir films upon compression, vertically for chains close to the water surface and horizontally orientated upper layers with significant amounts of PEG in between them. Thus, the wrinkling forms mainly in the top stiffer MA-POSS blocks above a certain compressional stress. The wrinkles disappear during the Langmuir-Blodgett (LB) transfer. Nevertheless, atomic force microscopy and grazing incidence wide-angle X-ray scattering experiments reveal the formation of highly ordered POSS molecules in LB films.

Evaluation of the permeability and potential toxicity of polycyclic aromatic hydrocarbons to pulmonary surfactant membrane by the parallel artificial membrane permeability assay model

Polycyclic aromatic hydrocarbons (PAHs) can penetrate and accumulate in the pulmonary surfactant (PS) membranes, leading to abnormalities of biological macromolecules and the destruction of membrane structure and properties. In the present study, the bioavailability, apparent permeability, effective permeability and residual coefficient of 10 PAHs on PS membrane was assessed by the parallel artificial membrane permeability assay (PAMPA). The influence of various forces on permeability is obtained by analyzing the correlation between parameters and physicochemical properties. Research shows that octanol-water partition coefficient (Kow) cannot directly predict permeability, and permeability has no significant relationship with polarity. Dispersion, induction, coupling/polarization promote permeation, while hydrogen bonded acid and n-n electron pair inhibit permeation. Further surface pressure-area (π-A) isotherms test and Brewster angle microscope observation manifested that there are huge differences in the transmembrane ability and effects on the membrane of PAHs with different structures. This work has considerable significance that will help to evaluate the bioavailability and human health risk of PAHs.

Interactions of model airborne particulate matter with dipalmitoyl phosphatidylcholine and a clinical surfactant Calsurf

HypothesisLung surfactant protects lung tissue and reduces the surface tension in the alveoli during respiration. Particulate matter with an aerodynamic diameter of less than 2.5 μm (PM2.5), which invades primely through inhalation, can deposit on and interact with the surfactant layer, leading to changes in the biophysical and morphological properties of the lung surfactant. ExperimentsLangmuir monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and clinical surfactant Calsurf were investigated with a PM2.5 model injected into the water subphase, which were characterized by surface pressure-area isotherms, Brewster angle microscopy, atomic force microscopy, fluorescent microscopy, and x-ray photoelectron spectroscopy. The binding between DPPC/Calsurf and PM2.5 was studied using isothermal titration calorimetry. FindingsPM2.5 induced the expansion of the monolayers at low surface pressure (п) and film condensation at high п. Aggregation of PM2.5 mainly occurred at the interface of liquid expanded/liquid condensed (LE/LC) phases. PM2.5 led to slimmer and ramified LC domains on DPPC and the reduction of nano-sized condensed domains on Calsurf. Both DPPC and Calsurf showed fast binding with PM2.5 through complex binding modes attributed to the heterogeneity and amphiphilic property of PM2.5. This study improves the fundamental understanding of PM2.5-lung surfactant interaction and shows useful implications of the toxicity of PM2.5 through respiration process.

Effect of lipopolymer (DSPE-PEG750) on phospholipid monolayers and bilayers differing in the structure of the polar head group

Phospholipid liposomes are the most popular kind of vesicles used in drug delivery due to their high biocompatibility with biomembranes. However, this type of liposomes show some limitations related with their short half-life in bloodstream. This problem can be resolved by the coating of their surface with the application of PEG molecules which form steric and entropic barrier, avoiding recognition of encapsulated liposomes by the reticuloendothelial system (RES). Such modification of liposomes significantly affects the physicochemical characteristics of PEGylated liposomes, which is related to the intermolecular interactions between the lipopolymer molecules and the phospholipid that builds the liposome membrane. In our work we investigated the influence of the PEG-ylated lipid (DSPE-PEG750) on physicochemical properties of phospholipid monolayers and bilayers with different structure of the polar group (DPPC, DPPE, DPPS). The phospholipid monolayers were examined with the application of Langmuir monolayer technique and Brewster angle microscopy (BAM) as well as grazing incidence x-ray diffraction (GIXD). The studies performed on phospholipid bilayer systems were related to dynamic light scattering and zeta potential measurements and the experiments with the calcein release and steady-state fluorescence anisotropy of DPH. The obtained results showed that the type of polar group of phospholipid as well as the addition of PEG-ylated lipid significantly changes the molecular organization of phospholipid monolayers. Moreover, these parameters also influence the properties of phospholipid bilayers such as size, surface charge, stability and permeability.

Composition, functionality and structural correlates of mixed lipid monolayers at air-water interface

Physicochemical properties of lipid monolayer depend on its composition where a blend of lipids exhibit superior behaviour than the individual component. Surface pressure ( π ) – area ( A ) isotherms of mixed monolayer (PC mix ) formed by dipalmitoylphosphatidylcholine (DPPC), palmitoleylphosphatidylcholine (POPC), soyphosphatidylcholine (SPC) and hydrogenated soy phosphatidylcholine (HSPC) in combination with 30 mole % cholesterol (Chol) were obtained by using Langmuir trough. Effects of dipalmitoylphosphatidyethanolamine (DPPE) on its mutual miscibility at the air-water interface with DPPC ​+ ​Chol, POPC ​+ ​Chol, HSPC ​+ ​Chol and SPC ​+ ​Chol were also investigated separately, followed by studying the effects of DPPE and dipalmitoylphosphatidylglycerol (DPPG) to PC mix ​+ ​Chol and PC mix ​+ ​DPPE ​+ ​Chol respectively. Lift-off area, minimum molecular area, excess molecular area, collapse pressure, Gibbs free energy of interfacial mixing, compressibility modulii values were evaluated by analyzing the isotherms. Deviations from the ideal mixing behaviours were dependent on the composition of the lipid blends. Surface dilatational rheology studies could assess monolayer elasticity, whereas the film morphologies were analysed by Brewster angle microscopic (BAM) studies. DPPC induced formation of condensed monolayer, whereas film rigidity was increased with the incorporation of DPPE and DPPG into mixed systems. Interactions among the lipid components of the investigated mixed systems were thoroughly discussed from the point of view of polar head and acyl chain saturation and obtained results follow the sequence: PC mix ​+ ​DPPE ​+ ​DPPG ​+ ​Chol ​> ​PC mix ​+ ​DPPE ​+ ​Chol ​> ​individual PC ​+ ​DPPE ​+ ​Chol which could be translated into the bilayer studies. Such investigation of mixed lipid is important for class of its own composition and combined results are expected to contribute in better understanding the interaction of selected lipid in proposed blend.

The hydrophobic core effect in model bacterial membranes upon interaction with tetra-p-guanidinoethylcalix[4]arene

The calixarene derivative used in this study (tetra-p-guanidinoethylcalix[4]arene) shows in vitro activity against different Gram-positive and Gram-negative bacteria. The interaction between bacterial cell membranes and the water-soluble calixarene was investigated using model lipids spread as monomolecular films at the air–water interface. Compression and adsorption experiments, as well as Brewster angle microscopy, polarization modulation-infrared reflection–absorption spectroscopy and computer modeling permitted understanding of the intra- and intermolecular interaction in several lipid-calixarene systems. Because the affinity of the calixarene derivative for the membranes may be linked to the interaction with negative charges, phosphatidylglycerols were used as model lipids; the phosphatidylglycerols contained saturated or unsaturated hydrocarbon chains with different lengths. It was showed that the affinity of the calixarene for the monolayer depends on the structure of the phosphatidylglycerols side chains. This observation may be of interest for a further development of new antibiotics.

Synthesis, Photophysics, and Langmuir Films of Polyfluorene/Permodified Cyclodextrin Polyrotaxanes.

In the present study, we investigated the effect of permodified 2,3,6-tri-O-trimethylsilyl β- and γ-cyclodextrin (TMS·β-CD, TMS·γ-CD) encapsulation on the optical, electrochemical, morphological, and supramolecular arrangements of a poly[2,7'-(9,9-dioctylfluorene-alt-2',7-fluorene)] PF copolymer. For this purpose, the photophysical properties and Langmuir monolayer formation of PF·TMS·β-CD and PF·TMS·γ-CD polyrotaxanes were investigated and compared with those of the reference PF. Surface pressure-area isotherms and Brewster angle microscopy studies indicated the capability of both polyrotaxanes to organize into larger and homogeneous 2D supramolecular assemblies at the air-water interface. The obtained results suggest that the presence of the surrounding TMS·β-CD and TMS·γ-CD macrocycles on the PF backbones leads to changes in the conformation and hydrophobicity of the film surfaces. Our investigation offers a method to assess the impact of TMS-CD encapsulation on the control of 2D monolayer formation, with particular attention on the generation of stable PF monolayers for organic electronic devices.

The Role of Molecular Packing in Dictating the Miscibility of Some Cholesteryl n-Alkanoates at Interfaces.

Cholesteryl n-alkanoates of saturated fatty acids and their mixtures are widely studied in different physical states and also due to their significance in biology. Here, we address the miscibility of some homologues of cholesteryl n-alkanoates at interfaces, which are known to exhibit different (cholesteryl octanoate, ChC8, and cholesteryl stearate, ChC18) or the same (cholesteryl nonanoate, ChC9, and cholesteryl laurate, ChC12) molecular packing in bulk. Surface manometry and Brewster angle microscopy studies on ChC8 (cholesteryl-cholesteryl interaction, referred to as m-i packing)/ChC9 (cholesteryl-chain interaction, referred to as m-ii packing) and also on ChC18 (chain-chain interactions, referred to as the crystalline bilayer)/ChC9 mixtures reveal phase separation at the air-water (A-W) interface plausibly due to the difference in the molecular packing. In contrast, ChC12/ChC9 (both m-ii packing) mixtures form a homogeneous phase and exhibit a higher collapse pressure (almost twice) than that of ChC9 indicating higher stability. At the air-solid (A-S) interface, the height profiles extracted from the surface topography images using an atomic force microscope yielded thicknesses of 3.6 ± 0.1 and 5.6 ± 0.1 nm for ChC18/ChC9 mixtures (at 0.66 and 0.5 mole fractions (MF)) corresponding to individual assembly, whereas a uniform thickness of 3.5 ± 0.2 nm is obtained for the case of ChC12/ChC9 mixtures (at 0.2, 0.5, and 0.8 MF) corresponding to m-ii packing. Ellipsometry studies reveal that the desorption temperature increases with the mole fraction of ChC9 and attains a maximum at 406.8 ± 4.8 K for 0.4 MF of ChC9, beyond which it decreases. Raman spectroscopy studies are carried out for ChC12/ChC9 mixtures in the homogeneous phase and in the collapsed state. Here, the dependency of peak positions on different physical states was assessed. Our studies offer new insights into the compatibility of molecular packing influencing the phase behavior and may be of relevance to tear film studies and on the formation of crystals in atherosclerosis.

Behavior comparison of films of Mexican bitumen and its asphaltene and maltenes fractions at interfaces

The oil industry has been focused on bitumens and heavy oils due to the depletion of petroleum reservoirs. For this reason, we studied the interfacial behavior comparison of films of bitumen and their asphaltene and maltene fractions by means of the Langmuir balance and Brewster angle microscopy at the air–water interface. The films were transferred by Langmuir-Blodgett technique onto mica and grids to be further analyzed by AFM and SEM at different surface pressures. We found that the isotherm behavior of the bitumen depends on the amount of its asphaltene and maltene fractions, although the isotherm behavior of asphaltene and maltene fractions are quite different. BAM images of the bitumen and asphaltene samples show the formation of two- and three-dimensional domains, being the asphaltene domains the most rigid and compact structures. Maltenes seems to form large areas of mono- or bi-molecular films, and their structures are like those reported for lipid monolayers. The AFM images for the bitumen morphology exhibited polydisperse mesostructures with spherical and disk-like shapes, while asphaltene images revealed disk-like microstructures and some of these microstructures coalesce, resulting in the formation of worm-like and other small structures. AFM images of the maltene film revealed that they form a fine plaster that might agglutinates the asphaltenes. SEM images of bitumen film show a smooth and slightly porous surface with some layer detachments, holes and bright spots embedded, while asphaltene images presented porous surfaces with spherical- or drumstick-like structures. Maltene SEM images showed a surface with irregular pores. The results support a better understanding of the bitumen, asphaltene, and maltene fractions and suggest that the interfacial behavior of bitumen presents a synergy between its asphaltene and maltene fractions.

Designing a Useful Lipid Raft Model Membrane for Electrochemical and Surface Analytical Studies.

A model biomimetic system for the study of protein reconstitution or drug interactions should include lipid rafts in the mixed lipid monolayer, since they are usually the domains embedding membrane proteins and peptides. Four model lipid films composed of three components: 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), cholesterol (Chol) and sphingomyelin (SM) mixed in different molar ratios were proposed and investigated using surface pressure measurements and thermodynamic analysis of the monolayers at the air–water interface and imaged by Brewster angle microscopy. The ternary monolayers were transferred from the air–water onto the gold electrodes to form bilayer films and were studied for the first time by electrochemical methods: alternative current voltammetry and electrochemical impedance spectroscopy and imaged by atomic force microscopy. In excess of DOPC, the ternary systems remained too liquid for the raft region to be stable, while in the excess of cholesterol the layers were too solid. The layers with SM in excess lead to the formation of Chol:SM complexes but the amount of the fluid matrix was very low. The equimolar content of the three components lead to the formation of a stable and well-organized assembly with well-developed raft microdomains of larger thickness, surrounded by the more fluid part of the bilayer. The latter is proposed as a convenient raft model membrane for further physicochemical studies of interactions with drugs or pollutants or incorporation of membrane proteins.

Phase Behaviors of Giant Surfactants with Different Numbers of Fluorinated Polyhedral Oligomeric Silsesquioxane "Heads" and One Poly(ethylene oxide) "Tail" at the Air-Water Interface.

Giant surfactants with different numbers of aryl-trifluorovinyl ether-functionalized polyhedral oligomeric silsesquioxane (FVPOSS) heads and one poly(ethylene oxide) (PEO) tail, (FVPOSS)n-PEO227, are precisely synthesized. The phase behaviors of (FVPOSS)n-PEO227 at the air-water interface were investigated through surface pressure measurements (isotherm and hysteresis experiments) and the Brewster angle microscopy. Upon increasing the number of FVPOSS heads, the interfacial behaviors of these giant surfactants greatly change. More phase transitions occur during the compression as the number of FVPOSS heads increased from one to two and three. The evolution of morphologies of Langmuir films and compression-expansion hysteresis curves further illustrate phase transitions at the air-water interface. Furthermore, molecular mechanisms to describe phase transitions of (FVPOSS)n-PEO227 at the interface are put forward. This study deepens the understanding of interfacial phase behaviors of special giant surfactants and provides knowledge of nanostructure design and construction at the interface.

Gangliosides smelt nanostructured amyloid Aβ(1–40) fibrils in a membrane lipid environment

Gangliosides induced a smelting process in nanostructured amyloid fibril-like films throughout the surface properties contributed by glycosphingolipids when mixed with 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC)/Aβ(1–40) amyloid peptide. We observed a dynamical smelting process when pre-formed amyloid/phospholipid mixture is laterally mixed with gangliosides. This particular environment, gangliosides/phospholipid/Aβ(1–40) peptide mixed interfaces, showed complex miscibility behavior depending on gangliosides content. At 0% of ganglioside covered surface respect to POPC, Aβ(1–40) peptide forms fibril-like structure. In between 5 and 15% of gangliosides, the fibrils dissolve into irregular domains and they disappear when the proportion of gangliosides reach the 20%. The amyloid interfacial dissolving effect of gangliosides is taken place at lateral pressure equivalent to the organization of biological membranes.Domains formed at the interface are clearly evidenced by Brewster Angle Microscopy and Atomic Force Microscopy when the films are transferred onto a mica support. The domains are thioflavin T (ThT) positive when observed by fluorescence microscopy.We postulated that the smelting process of amyloids fibrils-like structure at the membrane surface provoked by gangliosides is a direct result of a new interfacial environment imposed by the complex glycosphingolipids. We add experimental evidence, for the first time, how a change in the lipid environment (increase in ganglioside proportion) induces a rapid loss of the asymmetric structure of amyloid fibrils by a simple modification of the membrane condition (a more physiological situation).

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

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

Effects of Carboxyl or Amino Group Modified InP/ZnS Nanoparticles Toward Simulated Lung Surfactant Membrane.

Quantum dots (QDs) as a promising optical probe have been widely used for in vivo biomedical imaging; especially enormous efforts recently have focused on the potential toxicity of QDs to the human body. The toxicological effects of the representative InP/ZnS QDs as a cadmium-free emitter are still in the early stage and have not been fully unveiled. In this study, the DPPC/DPPG mixed monolayer was used to simulate the lung surfactant monolayer. The InP/ZnS-COOH QDs and InP/ZnS-NH2 QDs were introduced to simulate the lung surfactant membrane’s environment in the presence of InP/ZnS QDs. The effects of InP/ZnS QDs on the surface behavior, elastic modulus, and stability of DPPC/DPPG mixed monolayer were explored by the surface pressure-mean molecular area isotherms and surface pressure-time curves. The images observed by Brewster angle microscope and atomic force microscope showed that the InP/ZnS QDs affected the morphology of the monolayer. The results further demonstrated that the InP/ZnS QDs coated with different surface groups can obviously adjust the mean molecular area, elastic modulus, stability, and microstructure of DPPC/DPPG mixed monolayer. Overall, this work provided useful information for in-depth understanding of the effects of the −COOH or −NH2 group coated InP/ZnS QDs on the surface of lung surfactant membrane, which will help scientists to further study the physiological toxicity of InP/ZnS QDs to lung health.