Langmuir trough
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The Tear Film Lipid Layer (TFLL) covering the surface of the aqueous film at human cornea forms a first barrier between the eye and environment. Its alterations are related to dry eye disease. TFLL is formed by a complex mixture of lipids, with an excess of nonpolar components and a minor fraction of polar molecules. Its thickness is up to 160 nm, hence a multilayer-like structure of TFLL is assumed. However, details of TFLL organization are mostly unavailable in vivo due to the dynamic nature of the human tear film. To overcome this issue, we employ a minimalistic in vitro lipid model of TFLL. We study its biophysical characteristics by using a combination of the Langmuir trough with fluorescence microscopy. The model consists of two-component polar-nonpolar lipid films with a varying component ratio spread on the aqueous subphase at physiologically relevant temperature. We demonstrate that the model lipid mixture undergoes substantial structural reorganization as a function of lateral pressure and polar to nonpolar lipid ratio. In particular, the film is one-molecule-thick and homogenous under low lateral pressure. Upon compression, it transforms into a multilayer structure with inhomogeneities in the form of polar-nonpolar lipid assemblies. Based on this model, we hypothesize that TFLL in vivo has a duplex polar-nonpolar structure and it contains numerous mixed lipid aggregates formed because of film restructuring. These findings, despite the simplified character of the model, seem relevant for TFLL physiology as well as for understanding pathological conditions related to the lipids of the tear film.
- Klíčová slova
- Fluorescence microscopy, Langmuir trough, Lipid films, Tear film lipid layer,
- MeSH
- fluorescenční mikroskopie MeSH
- lidé MeSH
- lipidy chemie MeSH
- povrchové vlastnosti MeSH
- rohovka chemie metabolismus MeSH
- slzy chemie MeSH
- voda chemie MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- lipidy MeSH
- voda MeSH
To elucidate the consequences of the saturated-unsaturated nature of lipid surface films, monolayers formed by an equimolar mixture of 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipids are investigated in a wide range of surface pressures. As such mixtures share some features with naturally-occurring surfactants, for example the lung surfactant, the systems are studied at the temperature relevant for human body. All-atom molecular dynamics simulations and Langmuir trough experiments are employed. The binary lipid mixture is compared with the corresponding one-component systems. Atomistic-level alterations of monolayer molecular properties upon lateral compression are scrutinized. These involve elevation of lateral ordering of lipid chains, modulation of chain and headgroup orientation, and reduction of lipid hydration. The presence of the unsaturated POPC in the DPPC/POPC mixture reduces the liquid expanded-liquid condensed coexistence region and moderates the phase transition. Simulations predict that nanoscale lipid de-mixing occurs with small transient DPPC clusters emerging due to local fluctuations of the lateral lipid arrangement. A vertical sorting of lipids induced by lateral compression is also observed, with DPPC transferred toward the water phase. Both the conformational lipid alterations due to monolayer compression as well as the existence of lateral dynamic inhomogeneities of the lipid film are potentially pertain to dynamic and non-homogeneous lipid interfacial systems.
- Klíčová slova
- Langmuir trough, Lung surfactant, Molecular dynamics, Phospholipid monolayers,
- MeSH
- 1,2-dipalmitoylfosfatidylcholin analogy a deriváty chemie MeSH
- fosfatidylcholiny chemie MeSH
- lipidy chemie MeSH
- molekulární konformace MeSH
- simulace molekulární dynamiky * MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- 1,2-dipalmitoyl-sn-glycero-3-ethylphosphocholine MeSH Prohlížeč
- 1,2-dipalmitoylfosfatidylcholin MeSH
- 1,2-oleoylphosphatidylcholine MeSH Prohlížeč
- fosfatidylcholiny MeSH
- lipidy MeSH
An electrochemical Langmuir-Blodgett trough that permits an examination of local redox processes in a layer floating on the surface of water with a scanning tunneling microscopy-tip ultramicroelectrode has been constructed and tested on a layer of 1,1'-dicarbooctadecyloxyferrocene.
- Publikační typ
- časopisecké články MeSH
To modify the surface of poly(L-lactide) (PLA) supports, we have investigated the feasibility to deposit on the PLA surface Langmuir-Blodgett films of amphiphilic block copolymers based on poly(L-lactide). AB and ABA block copolymers were prepared with PLA as the A block and either poly(ethylene oxide), alpha-methoxy-omega-hydroxy poly(ethylene oxide), alpha-carboxy-omega-hydroxy poly(ethylene oxide) or poly(L-aspartic acid) as the B blocks. Films with phase-separated hydrophilic and hydrophobic blocks in a bilayer "brush" structure were prepared by compression of the copolymer Langmuir films on the water/air interface. The interfacial behavior of the monolayers and the effect of the copolymer composition on the phase separation was followed by measurements of the surface-pressure/area isotherms using a Langmuir trough and by contact angle measurement of deposited Langmuir-Blodgett (LB) films. The phase separation of the hydrophilic and PLA blocks is more effective in diblock AB copolymers compared with triblock ABA copolymers. The presence of ionic groups in the hydrophilic chains facilitates penetration of hydrophilic segments into the water subphase. Dynamic contact angle measurements were used to study the stability of the LB-films transferred on the PLA support and the changes in the surface properties upon incubation of surfaces in water.
- Publikační typ
- časopisecké články MeSH
For future use in self-assembly of surface structures, the adsorption on the surface of mercury of a series of tetraphenylcyclobutadienecyclopentadienylcobalt double-decker sandwich complexes with five mercury and sulfur containing "tentacles" on the cyclopentadienyl deck has been examined by combined electrochemical and Langmuir trough techniques.
- Publikační typ
- časopisecké články MeSH
The tear film at the ocular surface is covered by a thin layer of lipids. This oily phase stabilizes the film by decreasing its surface tension and improving its viscoelastic properties. Clinically, destabilization and rupture of the tear film are related to dry eye disease and are accompanied by changes in the quality and quantity of tear film lipids. In dry eye, eye drops containing oil-in-water emulsions are used for the supplementation of lipids and surface-active components to the tear film. We explore in detail the biophysical aspects of interactions of specific surface-active compounds, cetalkonium chloride and poloxamer 188, which are present in oil-in-water emulsions, with tear lipids. The aim is to better understand the macroscopically observed eye drops-tear film interactions by rationalizing them at the molecular level. To this end, we employ a multi-scale approach combining experiments on human meibomian lipid extracts, measurements using synthetic lipid films, and in silico molecular dynamics simulations. By combining these methods, we demonstrate that the studied compounds specifically interact with the tear lipid film enhancing its structure, surfactant properties, and elasticity. The observed effects are cooperative and can be further modulated by material packing at the tear-air interface.
- Klíčová slova
- Langmuir trough, dilatation rheology, fluorescence microscopy, meibum, molecular dynamics, tear film, tear film lipid layer,
- MeSH
- fluorescenční mikroskopie * metody MeSH
- kvartérní amoniové sloučeniny chemie MeSH
- lidé MeSH
- lipidy * chemie MeSH
- mastné alkoholy chemie MeSH
- meibomské žlázky metabolismus MeSH
- poloxamer chemie MeSH
- simulace molekulární dynamiky * MeSH
- slzy * chemie MeSH
- teoretické modely MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- cetalkonium chloride MeSH Prohlížeč
- kvartérní amoniové sloučeniny MeSH
- lipidy * MeSH
- mastné alkoholy MeSH
- poloxamer MeSH
We introduce and study a multicomponent lipid film mimicking lipid composition of the human lung surfactant. It consists of phospholipids with various lipid headgroups and tail saturation. Furthermore, it includes cholesterol and oxidized lipids. Langmuir trough and fluorescence microscopy experiments are combined with fully atomistic molecular dynamics simulations. The considered lipid mixtures form complex interfacial films with properties modulated by lateral compression. Cholesterol laterally condenses, and oxidized lipids laterally expand the films; both types of molecules increase film miscibility. Oxidized lipids also alter the lipid-water interface enhancing film hydration; this effect can be partially reversed by cholesterol. Regarding presentation of different chemical moieties toward the aqueous subphase, the zwitterionic phosphatidylcholine groups dominate at the lipid-water interface, while both the negatively charged phosphatidylglycerol and hydroxyl group of cholesterol are less exposed. The investigated synthetic lipid-only mimic of the lung surfactant may serve as a basis for further studies involving nonlipid pulmonary surfactant components.
- MeSH
- cholesterol chemie MeSH
- fluorescenční mikroskopie MeSH
- lidé MeSH
- lipidy chemie MeSH
- oxidace-redukce MeSH
- plicní surfaktanty chemie MeSH
- simulace molekulární dynamiky * MeSH
- voda chemie MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- cholesterol MeSH
- lipidy MeSH
- plicní surfaktanty MeSH
- voda MeSH
In situ grazing-incidence X-ray scattering shows that a monolayer of artificial rod-shaped dipolar molecular rotors produced on the surface of an aqueous subphase in a Langmuir trough has a structure conducive to a 2D ferroelectric phase. The axes of the rotors stand an average of 0.83 nm apart in a triangular grid, perpendicular to the surface within experimental error. They carry 2,3-dichlorophenylene rotators near rod centers, between two decks of interlocked triptycenes installed axially on the rotor axle. The analysis is based first on simultaneous fitting of observed Bragg rods and second on fitting the reflectivity curve with only three adjustable parameters and the calculated rotor electron density, which also revealed the presence of about seven molecules of water near each rotator. Dependent on preparation conditions, a minor and variable amount of a different crystal phase may also be present in the monolayer.
The interaction of L-phenylalanine with a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer at the air-water interface was explored using a combination of experimental techniques and molecular dynamics (MD) simulations. By means of Langmuir trough methods and Brewster angle microscopy, L-phenylalanine was shown to significantly alter the interfacial tension and the surface domain morphology of the DPPC film. In addition, confocal microscopy was used to explore the aggregation state of L-phenylalanine in the bulk aqueous phase. Finally, MD simulations were performed to gain molecular-level information on the interactions of L-phenylalanine and DPPC at the interface. Taken together, these results show that L-phenylalanine intercalates into a DPPC film at the air-water interface, thereby affecting the surface tension, phase morphology, and ordering of the DPPC film. The results are discussed in the context of biological systems and the mechanism of diseases such as phenylketonuria.
- MeSH
- 1,2-dipalmitoylfosfatidylcholin analogy a deriváty chemie MeSH
- deuterium chemie MeSH
- fenylalanin chemie MeSH
- mikroskopie MeSH
- molekulární struktura MeSH
- povrchové vlastnosti MeSH
- simulace molekulární dynamiky MeSH
- voda chemie MeSH
- vzduch * MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, N.I.H., Extramural MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
- Názvy látek
- 1,2-dipalmitoylfosfatidylcholin MeSH
- colfosceril palmitate MeSH Prohlížeč
- deuterium MeSH
- fenylalanin MeSH
- voda MeSH
Phenylalanine has an important role both in normal biological function and in disease states such as phenylketonuria (PKU) and amyloid fibril diseases. Two crucial aspects of phenylalanine behavior in biological systems are its preferential partitioning into membranes and its propensity to cluster. In order to examine the intermolecular interactions that give rise to this behavior, the surface partitioning behavior was investigated for a series of molecules structurally related to phenylalanine (phenylglycine, phenylacetic acid, and tyrosine) both experimentally and by molecular dynamics simulations. Surface tension measurements were performed over time for aromatic solutions both in the presence and in the absence of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) monolayer films, which functioned as simple model membranes. The observed trends in surface activity defy simple predictions based on solubility and hydrophobicity. The possibility of clustering is investigated through a combination of Langmuir trough, nuclear magnetic resonance (NMR), fluorescence self-quenching, and mass spectroscopy measurements. It is concluded that clustering does not occur in solution to a significant extent for these molecules, but interfacial clustering is likely. An explanation for observed trends in surface activity is presented on the basis of cluster stability and molecular conformational flexibility.
- MeSH
- 1,2-dipalmitoylfosfatidylcholin chemie MeSH
- fenylalanin chemie MeSH
- fluorescenční spektrometrie MeSH
- hmotnostní spektrometrie MeSH
- magnetická rezonanční spektroskopie MeSH
- povrchové vlastnosti MeSH
- rozpustnost MeSH
- shluková analýza MeSH
- simulace molekulární dynamiky MeSH
- tyrosin chemie MeSH
- unilamelární lipozómy chemie MeSH
- voda chemie MeSH
- vzduch * MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, N.I.H., Extramural MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
- Názvy látek
- 1,2-dipalmitoylfosfatidylcholin MeSH
- fenylalanin MeSH
- tyrosin MeSH
- unilamelární lipozómy MeSH
- voda MeSH
