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Fixed parameters used for data modeling. The molecular volumes of h-DPPC, cm-DPPC, and d62-DPPC are equal; the only difference between the sample parameters is the value of the total scattering length of the tails Σbtail. One can calculate the scattering length density (SLD) values shown considering b and Vm (SLD = Σb/Vm).

Fixed parameters used for data modeling. The molecular volumes of h-DPPC, cm-DPPC, and d62-DPPC are equal; the only difference between the sample parameters is the value of the total scattering length of the tails Σbtail. One can calculate the scattering length density (SLD) values shown considering b and Vm (SLD = Σb/Vm).

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Langmuir monolayers of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine, known as DPPC, at the air/water interface are extensively used as model systems of biomembranes and pulmonary surfactant. The properties of these monolayers have been mainly investigated by surface pressure–area isotherms coupled with different complementary techniques such as Bre...

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... has been recently demonstrated that using this model results in a better fit of the experimental curves [27]. The fixed parameters used in the fitting procedure (Table 1) are molecular volumes of DPPC heads (Vm_heads) and tails (Vm_tails) [43,44] and the total scattering length of DPPC heads (Σbheads) and tails (Σbtails). Heads-layer thickness (theads) was calculated from the Vm_heads, and finally, the roughness (r) of the three interfaces (i.e., air/tails-layer, tails-layer/heads-layer, and headslayer/subphase) was assumed identical following the approach reported by Campbell et al. [27]. ...
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... detail, the model consists of a first layer containing the lipid aliphatic tails in contact with air and, a second one, containing the polar headgroups submerged in the aqueous subphase (see Figure 1a). All parameters used to describe both layers (such as the values of Σb and molecular volumes) are included in Table 1. The best fit of the reflectivity profiles measured is also included in Figure 3a as solid lines. ...
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... value of the thickness of DPPC monolayer is 23.5 Å, with 15.0 Å corresponding to the aliphatic tails in contact with air. Using the parameters from Tables 1 and 2, the variation of the volume fraction, fDPPC(z), with the distance to the interface, was calculated using the difference of two error functions as follows ...
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... values used to calculate the cross-sectional area from Equation (11) are collected from Tables 1 and 2. ) 3.0 ± 0.1 ...


... The P-A isotherm at 21°C of a DPPC:PIP 2 (7:3) mixed monolayer and, as reference, the isotherms corresponding to pure DPPC [36] and pure PIP 2 , all of them deposited on a buffer solution containing divalent cations (Mg 2+ ), are shown in Fig. 2 A. The corresponding representation of the compressional elastic modulus (C s À1 ) versus P and A are reported in Fig. 2 B and C, respectively. ...
... Here, the LE-LC coexistence region, whose identification a priori was not straightforward from the visualization of the P-A isotherm of both monolayers, was evident from the appearance of a minimum in the C s À1 profile. This minimum has been already reported for DPPC monolayers spread onto both pure water [33] and buffer (rich in Mg 2+ ) [36] subphases. Further compression yielded a LC phase for both DPPC and DPPC:PIP 2 monolayers. ...
... This low impact of PIPs on model membranes has been also observed in bilayers [11,21]. Secondly, in buffer with Mg 2+ ions, the values of C s À1 corresponding to the LC phase for DPPC:PIP 2 mixed monolayers are much lower in comparison with the DPPC monolayer [36]. However, in both systems, the values of C s À1 are remarkably smaller in comparison to those measured for DPPC monolayers in water [33]. ...
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Hypothesis: Inositol phospholipids are well known to form clusters in the cytoplasmic leaflet of the plasma membrane that are responsible for the interaction and recruitment of proteins involved in key biological processes like endocytosis, ion channel activation and secondary messenger production. Although their phosphorylated inositol ring headgroup plays an important role in protein binding, its orientation with respect to the plane of the membrane and its lateral packing density has not been previously described experimentally. Experiments: Here, we study phosphatidylinositol 4,5-bisphosphate (PIP2) planar model membranes in the form of Langmuir monolayers by surface pressure-area isotherms, Brewster angle microscopy and neutron reflectometry to elucidate the relation between lateral (in-plane) and perpendicular (out-of-plane) molecular organization of PIP2. Findings: Different surface areas were explored through monolayer compression, allowing us to correlate the formation of transient PIP2 clusters with the change in orientation of the inositol-biphosphate headgroup, which was experimentally determined by neutron reflectometry.
... Recently, there has been significant progress in fabrication of planar nanomaterials at the air/water interface [1][2][3][4][5]. Simple, inexpensive, and effective approaches to formation of two-dimensional nanostructures with a periodic structure have been developed [6]. ...
... Raman spectra of LBFs of barium stearate on a silicon substrate (1), collapsed barium stearate monolayer obtained in a Langmuir trough (2), the film formed around the droplet of aqueous barium nitrate solution after complete n-hexane evaporation(3). ...
In this work we propose an approach for formation of periodic two-dimensional structures on a solid substrate via self-assembly of stearic acid molecules on an aqueous subphase drop containing metal ions. It was shown that when a saturated solution of stearic acid in n-hexane was applied to the hemispherical surface of an aqueous media containing barium ions, barium stearate monolayer was formed, which spontaneously collapsed during movement from the drop surface to the substrate. By means of infrared and Raman spectroscopy, light and scanning electron microscopy, atomic force microscopy and matrix-assisted laser desorption/ionization mass spectrometry it was proved that a multi-structure of collapsed metal stearate monolayers with a developed surface was formed on the substrate surface. Thin films formed by a single application of stearic acid solution in n-hexane to a drop of aqueous lanthanum nitrate solution were used for selective enrichment of human butyrylcholinesterase adducts with diisopropyl fluorophosphate.
... However, in recent years, many researches have turned their interests towards the understanding of the relationship existing between the changes in the interfacial packing of LS layers and the worsening of their mechanical properties [22,169]. This is important because as was stated above, the LS present a very complex organization at the interface and in the adjacent liquid phase [170], and the use of techniques such as Brewster angle microscopy (BAM), AFM, surface force apparatus (SFA), ellipsometry, infrared reflection absorption spectroscopy (IRRAS), or epifluorescence microscopy, and their combinations with tensiometric techniques (mainly Langmuir film balances) are very powerful tools for deepening knowledge on the impact of particles on the organization of LS films in the micrometric and submicrometric scale [171][172][173][174]. Furthermore, there are more sophisticated tools, including neutron reflectivity or synchrotron grazing angle X-ray diffractions which may also be useful in the evaluation of the impact of particulate matter on LS interfacial organization [108,134,[175][176][177][178][179][180][181][182]. ...
... DPPC fulfills the first requirement, which has pushed the use of DPPC monolayers as minimal models for understanding some physico-chemical aspects related to the impact of particles in LS films. Furthermore, the interfacial behavior of this lipid has been extensively studied by many researchers [59,66,175,[183][184][185][186][187]. However, the use of DPPC as a model for understanding the performance of LS is rather limited because its inefficiency in the reservoir formation and its slow respreading at the interface during expansion. ...
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Pollution is currently a public health problem associated with different cardiovascular and respiratory diseases. These are commonly originated as a result of the pollutant transport to the alveolar cavity after their inhalation. Once pollutants enter the alveolar cavity, they are deposited on the lung surfactant (LS) film, altering their mechanical performance which increases the respiratory work and can induce a premature alveolar collapse. Furthermore, the interactions of pollutants with LS can induce the formation of an LS corona decorating the pollutant surface, favoring their penetration into the bloodstream and distribution along different organs. Therefore, it is necessary to understand the most fundamental aspects of the interaction of particulate pollutants with LS to mitigate their effects, and design therapeutic strategies. However, the use of animal models is often invasive, and requires a careful examination of different bioethics aspects. This makes it necessary to design in vitro models mimicking some physico-chemical aspects with relevance for LS performance , which can be done by exploiting the tools provided by the science and technology of interfaces to shed light on the most fundamental physico-chemical bases governing the interaction between LS and particulate matter. This review provides an updated perspective of the use of fluid films of LS models for shedding light on the potential impact of particulate matter in the performance of LS film. It should be noted that even though the used model systems cannot account for some physiological aspects, it is expected that the information contained in this review can contribute on the understanding of the potential toxicological effects of air pollution.
... Neutron reflectometry (NR) has been extensively used for studying structural organisation of soft matter [33][34][35][36][37][38]. This technique is advantageous when studying soft matter as it is possible to conduct experiments at atmospheric pressure and has a vertical resolution (∼0.5 nm, limited by the beam collimation and the size of the silicon blocks used) capable of resolving structure changes on the molecular scale. ...
Water-soluble nonionic surfactant, pentaethylene glycol monododecyl ether, C12E5, spontaneously blooms to the surface of spin-cast hydrophobic polyiso-prenes, generating hydrophilic surfaces. This system represents a simple model for hydrophilic chemical modification of rubbery polymers yet demonstrates surprisingly rich, complex and unexpected behaviour. The ver-tical depth profiles were quantified using neutron reflectometry (NR) and deuterated surfactant, and the surface properties were characterized using con-tact angle analysis and atomic force microscopy (AFM). Despite the low surface tension of the toluene solvent used in film preparation and the low surface en-ergy of the PI matrix, NR depth profiles revealed clear evidence of surfactant segregation. This surface layer was typically thicker than a monolayer, but incomplete, yet was remarkably stable with respect to dissolution, even when exposed to hundreds of thousands of times the volume of water required to dissolve all the surfactant on the surface. Despite the apparent resistance to removal from the surface, water exposure does alter the subsequent wettabil-ity of the surface, with a hydrophilic-to-hydrophobic transition occurring after rinsing. Complementary AFM images of these C12E5 / cis-PI films showed unexpected strand-like features on the surface of the film, which we attribute to a non-uniform lateral distribution of some of the surfactant. This surface structure becomes more evident after rinsing, and it appears that there are two distinct populations of surfactant on the PI film surface. We conclude that some of the bloomed surfactant exists as layers, which are relatively inert with respect to rinsing or surface modification, and some is laterally inhomogene-ous. This latter population is primarily responsible for surface wetting be-havior, but is not detected by specular NR.
... [5,[14][15][16][17] At the air/water interface, lipid monolayers are generally formed by dropwise spreading of a lipid solution from a highly volatile organic solvent (typically chloroform or a methanol:chloroform mixture) directly at the interface. This protocol is widely applied to monolayer studies at the air/water interface [11,[18][19][20] and to prepare solid-supported lipid membranes by Langmuir-Blodgett or Langmuir-Schaefer depositions.[1, 9,21] Spread lipid monolayers at the air/water interface are very stable thanks to the low solubility of lipid molecules in aqueous media as well as the many interactions between hydrophobic moieties (chains) exposed to air. ...
The properties of lipid monolayers at the interface between two immiscible electrolyte solutions (ITIES) have attracted much attention over the last 30 years. This is mainly because of the biological relevance of lipids and the possibility of controlling ion and electron transfer across one leaflet of a cellular membrane. In the last decade, the electrochemical characterization of phosphatidylcholine (PC) adsorbed monolayers at ITIES suggested that the transfer of aqueous cations across the interface is facilitated by the complexation of aqueous cations with the PC zwitterionic head groups, followed by the depletion of lipids from the interface. In this work, we present a study on the effects of applied electric fields and electrolyte concentration on the interfacial structure of the ITIES by combining neutron reflectometry (NR) and electrochemical characterization techniques including the effects of an adsorbed lipid layer. Our results confirm that lipid depletion occurs as cations are transferred. However, we found that the presence of lipids favors the intermixing of the two-liquid phases on a length scale of a few tens of nanometers. To our knowledge, this has been the first NR-electrochemistry study of the ITIES. We believe that our findings could open new possibilities for coupling bioelectrochemical characterization and scattering based techniques at the liquid-liquid interface.
The pulmonary surfactant (PS) is a complex mixture of lipids and proteins dispersed in the aqueous lining layer of the alveolar surface. Such a layer plays a key role in maintaining the proper lung functionality. It acts as a barrier against inhaled particles and pathogens, including viruses, and may represent an important entry point for drugs delivered via aerosols. Understanding the physico-chemical properties of PS is therefore of importance for the comprehension of pathophysiological mechanisms affecting the respiratory system. That can be of particular relevance for supporting the development of novel therapeutic interventions against COVID-19-induced acute respiratory distress syndrome. Due to the complexity of the in vivo alveolar lining layer, several in vitro methodologies have been developed to investigate the functional and structural properties of PS films or interfacial films made by major constituents of the natural PS. As breathing is a highly dynamic interfacial process, most applied methodologies for studying pulmonary surfactants need to be capable of dynamic measurements, including the study of interfacial dilational rheology. We provide here a review of the most frequently and successfully applied methodologies that have proven to be excellent tools for understanding the biophysics of the PS and of its role in the respiratory mechanics. This overview also discusses recent findings on the dynamics of pulmonary surfactant layers and on the impact of inhalable particles or pathogens, such as the novel coronavirus, on its functionality.
This review focuses on the description of the structure and composition of a variety of Langmuir monolayers (LMs) deposited at the air/water interface by using ellipsometry, Brewster Angle microscopy and scattering techniques, mainly neutron and X-ray reflectometry. Since the first experiment done by Angels Pockels with a homemade trough in her home kitchen until today, LMs of different materials have been extensively studied providing not only relevant model systems in biology, physics and chemistry but also precursors of novel materials via their deposition on solid substrates. There is a vast amount of surface-active materials that can form LMs and, therefore, far from a revision of the state-of-the-art, we will emphasize here: (i) some fundamental aspects to understand the physics behind the molecular deposition at the air/water interface; (ii) the advantages in using in situ techniques, such as reflectometry or ellipsometry, to resolve the interfacial architecture and conformation of molecular films; and, finally, (iii) a summary of several systems that have certain interest from the experimental or conceptual point of view. Concretely, we will report here advances in polymers confined to interfaces and surfactants, from fatty acids and phospholipids monolayers to more unconventional ones such as graphene oxide.
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Fluid interfaces are promising candidates for the design of new functional materials by confining different types of materials, e.g., polymers, surfactants, colloids, or even small molecules, by direct spreading or self-assembly from solutions. The development of such materials requires a deep understanding of the physico-chemical bases underlying the formation of layers at fluid interfaces, as well as the characterization of the structures and properties of such layers. This is of particular importance, because the constraints associated with the assembly of materials at the interface lead to the emergence of equilibrium and dynamic features in the interfacial systems that are far from those found in traditional 3D materials. These new properties are of importance in many scientific and technological fields, such as food science, cosmetics, biology, oil recovery, electronics, drug delivery, detergency, and tissue engineering. Therefore, the understanding of the theoretical and practical aspects involved in the preparation of these interfacial systems is of paramount importance for improving their usage for designing innovative technological solutions.