Inhibition of aggregation of a biomimic peptidolipid Langmuir monolayer by Congo red studied by UV-vis and infrared spectroscopies

A synthetic peptidolipid consisted of a hydrocarbon chain with a chain length of C18 and a peptide moiety of IIGLM terminated with an amine group, designated as C18IIGLM-NH2, has been employed as a biomimic model compound of amyloid peptide for exploring molecular interaction and orientation with the use of the Langmuir monolayer and Langmuir-Blodgett film techniques. Inspired by a well-known fact that a stain reagent, Congo red (CR), binds well to the amyloid-mimic part (IIGLM), inhibition of molecular aggregation of C18IIGLM-NH2 by interaction with CR was expected, and it has been investigated by use of surface pressure-area isotherm, surface dipole moment-area isotherm, Brewster-angle microscopy, and UV-vis/infrared spectroscopies. It has been revealed that monomeric CR molecules whose long axis is parallel to the Langmuir monolayer surface are penetrating the C18IIGLM-NH2 Langmuir monolayer, which plays a role of inhibition of molecular aggregation via hydrogen bonding.     

Interaction of FtsZ protein with a DPPE Langmuir film

FtsZ is the key protein in cell division in bacteria. We have proposed that lipid domains in the cytoplasmic membrane play a role in the localisation of FtsZ. In order to test this hypothesis, we used a model system based on Langmuir films to simulate the bacterial membrane. In this simple system we used a single phospholipid, dipalmytoylphosphatidylethanolamine, which is the major constituent of the inner membrane in Escherichia coli. The first results show clearly the importance of the GTP-controlled assembly process in the appearance of circular or fibrillar structures.     

Polymerization of an Elaidic Acid Langmuir Film Prepared on a Terbium-Containing Subphase

The UV-induced polymerization of an elaidic acid Langmuir film prepared on a terbium-containing subphase has been studied. The polymerization caused changes in pressure/area isotherms. The irradiated film in its more condensed state is in a liquid phase while the monomer film is in a solid phase. The dynamics of the irradiated films was investigated by following the evolution of the film area at a constant pressure. For the longer irradiation times, an expansion of the film area was observed. Scanning force microscopy and IR spectroscopy have been used to study the monolayer after its transfer onto a solid support. IR spectroscopic measurements indicated the presence of an oxygen-containing copolymer. Scanning force microscopy images revealed a modification of the structure of the film after irradiation. Copyright 1999 Academic Press.     

Continuous water purification system for Langmuir film studies

A system for continuous purification of water to make it suitable for use in Langmuir film studies has been designed and implemented in our laboratory. The system incorporates particulate filtration, activated carbon adsorption, deionization by reverse osmosis, and continuous distillation under a nitrogen sweep. Surface tension in excess of 99% of theoretical and resistivity of 18 Megohm-cm at 25°C have been achieved without the use of organic ion exchange resins.     

Sum frequency generation study of Langmuir Blodgett film architecture

We present sum frequency generation vibrational spectroscopy data on monolayer films of pure stearonitrile and mixed films of stearonitrile and ferric stearate deposited by the Langmuir Blodgett technique. Films ranging in composition from pure stearonitrile to 65% stearonitrile/35% ferric stearate deposit in a head-to-tail, Z-type architecture while films of composition <65% stearonitrile deposit in a head-to-head, tail-to-tail, Y-type structure. The vibrational spectra of the monolayer films corresponding to these two different architectures show distinct and characteristic features in their CH stretching regions. Spectral analysis indicates little difference in the modes associated with the terminal methyl groups but large differences in the methylene CH(2) vibrational modes. These spectral differences are consistent with alkyl chains that possess uncompensated methylene oscillator strength arising from portions of the chain that are bent. This behavior is consistent with the energetics expected from a close-packed monolayer of stearonitrile molecules whose CN headgroups possess sizable dipole moments and are expected to adopt a large center-to-center angle to minimize electrostatic, dipole-dipole repulsive interactions.     

Langmuir monolayers of a photoisomerizable macrocycle surfactant

An amphiphilic photoisomerizable macrocycle has been prepared that forms stable Langmuir monolayers at the air-water interface. The hydrophilic core of the molecule switches between closed and open isomers upon irradiation by the appropriate wavelengths of light. Isotherm measurements, Brewster angle microscope images, and atomic force micrographs (of transferred Langmuir-Blodgett films) suggest a phase transition between a face-on to a tilted edge-on molecular orientation as a function of surface concentration. In the face-on phase, in situ photoisomerization results in a reversible increase in surface pressure due to greater molecular crowding in the open configuration.     

Influence of the alkyl chain length of some mesogenic molecules on their Langmuir film formation ability

Langmuir films of members of two homologous series, the 4‐n‐alkyl‐4′‐cyanobiphenyls (nCB) for n = 2–14 and trans‐4‐n‐alkyl(4′‐cyanophenyl)cyclohexanes (PCHn) for n = 2–12, have been studied by recording surface pressure/area isotherms and by Brewster angle microscopy. It has been found that the compounds with very short chains (n3) and very long chains (n>12 for nCB, n>10 for PCHn) are unable to form compressible monolayers at the air–water interface. Other members of both series can form stable Langmuir films, but both their rigidity and stability as well as the molecular packing vary with the alkyl chain length. The isotherms and BAM images imply that the organization of the liquid crystal molecules in the films is to some extent correlated with their ability to form corresponding mesophase in the bulk: nematogenic compounds tend to form rounded droplet‐like domains, whereas smectogenic compounds tend to form flat domains.     

Surface properties of "jellyfish": Langmuir monolayer and Langmuir-Blodgett film studies of recombinant aequorin

In this paper, we studied the surface properties of recombinant aequorin at the air-water interface. Using the Langmuir monolayer technique, the surface properties of aequorin were studied, including the surface pressure and surface potential-area isotherms, compression-decompression cycles, and stability on Trizma Base (Tris/HCl) buffer at pH 7.6. The results showed that aequorin formed a stable Langmuir monolayer and the surface pressure-area isotherms were dependent on both pH and ionic strength. At a pH higher or lower than 7.6, the limiting molecular area decreased. The circular dichroism (CD) spectra of aequorin in aqueous solutions explained this result: when the pH was higher than 7.6, the alpha-helix conformation changed to unordered structures, whereas at a pH lower than 7.6, the alpha-helix conformation changed to beta-sheet. The addition of calcium chloride to the Tris/HCl buffer subphase (pH 7.6) caused an increase of the limiting molecular area of the aequorin Langmuir monolayer. The fluorescence spectra of a Langmuir-Blodgett (LB) film of aequorin in the presence of calcium chloride indicated that the aequorin transformed to the apoaequorin.     

Glutathionylation of beta-actin via a cysteinyl sulfenic acid intermediary

Background  

Cysteinyl residues in actin are glutathionylated, ie. form a mixed disulfide with glutathione, even in the absence of exogenous oxidative stress. Glutathionylation inhibits actin polymerization and reversible actin glutathionylation is a redox dependent mechanism for regulation of the cytoskeleton structure. The molecular mechanism that mediates actin glutathionylation in vivo is unclear.     

Dangling OD confined in a Langmuir monolayer

Novel structural features of water confined in lipid Langmuir monolayers are revealed. Using vibrational sum frequency generation spectroscopy at the air/D2O/monolayer interface, dangling OD bonds were investigated. Upon increasing the monolayer surface coverage, the dangling OD stretching mode showed a marked frequency red-shift as well as spectral structure. Furthermore, the dangling OD was found to exist even when a D2O surface was fully covered by the lipid molecules. This phenomenon was observed in monolayers formed with dipalmitoylphosphatidylcholine and with palmitic acid. The frequency red-shift of the dangling OD is interpreted to be due to the perturbation imposed by the lipid hydrophobic tail groups. The observed persistence of the dangling OD at full surface coverage is related to hydrophobicity-induced drying.     

Growth of anisotropic domains in a Langmuir monolayer

We studied the growth of solid anisotropic domains in a monolayer made of pure NBD-stearic acid spread on water. These domains have a needle-like shape. We found that the growth process is limited by the interface kinetics, and not by the diffusion of impurities. Moreover the longitudinal growth velocity of these needles is simply proportional to the overpressure, as for a rough interface. No such law was found for the width of the needles.     

Sequential collapse transitions in a Langmuir monolayer

Unusual sequential collapse transitions are investigated in a lignoceric acid Langmuir monolayer. The nucleation of monolayer collapse is first initiated in the solid, S, phase but at remarkably low surface pressure where small three-dimensional (3D) granular dots appear. The density of nucleation centers increases, and the 3D dots prevail over the monolayer (surface roughening regime) as the surface pressure increases, but individual dots neither grow very much in size nor evolve into other shapes such as stripes or elongated dots. On further compression the second collapse mode manifests itself by highly anisotropic, global crack arrays (anisotropic cracking regime) where the surface pressure "kink" appears in the isotherm. In the latter regime, various forms of 3D curved filaments develop in the crack regions, and they break into smaller fragments with a typical relaxation time (approximately 60 ms).     

Anisotropy in Langmuir layers of a bent-core liquid crystal

Langmuir layers of a symmetric bent-core molecule with hydrocarbon end chains and two chlorine atoms substituted on the central phenyl ring of the bent core were characterized by a combination of surface pressure isotherms, Brewster angle microscopy, and surface potential measurements. These layers were found to be optically anisotropic, in contrast to Langmuir layers of similar molecules with different substitutions on the core. After compression, the orientation of the optical axis was essentially uniform over the film. Upon decompression, the film broke into uniform islands or domains. Measuring domain reflectivity while changing the domain orientation allowed the determination of the tilt angle with respect to both domain features and the film normal, as well as the refractive index anisotropy. The tilt angle, near 90 degrees, suggests that the bent-core molecules lie quite flat on the surface.     

Influence of the liquid crystal behaviour on the Langmuir and Langmuir-Blodgett film supramolecular architecture of an ionic liquid crystal

Novel fluorescent poly(2-(acetoacetoxy)ethyl methacrylate)(PAAEMA) latexes have been synthesized by miniemulsion polymerization employing a polymeric costabilizer. Nanoscale aggregates of macromolecules bearing β-dicarbonyl are formed in the prepared latex particles. Ammonia and the β-dicarbonyl aggregates assemble a supramolecular complex, which exhibits strong visible fluorescence under UV light. The formation of the complex is confirmed by the characteristic absorption peak located at about 275 nm in UV-Vis spectra. The absorption spectrum has been found to be applicable for ammonia detection. Atomic Force Microscopy (AFM) studies of surface morphology reveal that gas-sensing properties of the PAAEMA thin films involve the reversible absorption and desorption of ammonia. PAAEMA thin films are sensitive to ammonia gas and have a short response time of 80s when exposed to 54 ppm of ammonia gas concentration.     

Flow-induced patterning of Langmuir monolayers

Insoluble monolayers on water have been patterned at the macroscopic scale (i.e., at the centimeter scale of the flow apparatus) as well as the mesoscopic scale (i.e., down to the micron scale resolvable via optical microscopy). The macroscopic patterning at the air/water interface results from a hydrodynamic instability leading to a steadily precessing flow pattern. The velocity field is measured, and the associated shear stress at the interface is shown to be locally amplified by the flow pattern. The resulting hydrodynamic effects on two different monolayer systems are explored: (1) the pattern in a model monolayer consisting of micron-size, surface-bound particles is visualized to show that the particles are concentrated into isolated regions of converging flow with high shear, and (2) Brewster angle microscopy of a Langmuir monolayer (vitamin K1) shows not only that the monolayer is patterned at the macroscopic scale but also that the localized high-shear flow further patterns the monolayer at the mesoscale.     

Capillary isotachophoretic determination of cysteinyl leukotrienes.

The cysteinyl leukotrienes (LTs) C4, D4 and E4 are among the most potent lipid mediators of anaphylaxis and inflammation. A capillary isotachophoretic method is described for the determination of these cysteinyl LTs. The method is based on anionic separation and detection using UV (254 nm) and conductivity detectors. The total analysis time is of the order of 30 min. The limit of detection of the method was determined to be 0.5 nmol of LTE4. Despite of similar chemical structures, all three cysteinyl LTs can be determined simultaneously.     

Polymerization of diacetylene phospholipid bilayers on solid substrate: influence of the film deposition temperature

Micropatterned phospholipid bilayers on solid substrates offer an attractive platform for various applications, such as high throughput drug screening. We have previously developed a photopolymerization-based methodology for generating micropatterned bilayers composed of polymerized and fluid lipid bilayers. Lithographic photopolymerization of a diacetylene-containing phospholipid (DiynePC) allowed facile fabrication of compartmentalized arrays of fluid lipid membranes. Herein, we report on a key experimental parameter that significantly influences the homogeneity and quality of the fabricated polymeric bilayers, namely the temperature at which monolayers of monomeric DiynePC were formed on the water surface and transferred onto solid substrates by the Langmuir-Blodgett/Langmuir-Schaefer (LB/LS) technique. Using fluorescence microscopy and atomic force microscopy, it was found that polymerized bilayers were homogeneous, if bilayers of DiynePC were prepared below the triple point temperature (ca. 20 degrees C) of the monolayer, where a direct transition from the gaseous state to the liquid condensed state occurred. Bilayers prepared above this temperature had a markedly increased number of crack-like line defects. The differences were attributed to the domain structures in the monolayer that were transferred from the water surface to the substrate. Domain size, rather than the molecular packing in each domain, was concluded to play a critical role in the formation of defects. The spontaneous curvature and area changes of bilayers were postulated to cause destabilization and detachment of the films from the substrate upon polymerization. Our present results highlight the importance of controlling the domain structures for the homogeneity of polymerized bilayers required in technological applications.     

Self-organization of a sulfonamido-porphyrin in Langmuir monolayers and Langmuir-Blodgett films

Langmuir monolayers (LM) and Langmuir-Blodgett (LB) films of pure lipophilic meso-tetra(4-dodecylaminosulfophenyl)porphyrin (PC12) and mixed with the anionic surfactant sodium hexadecylsulfate (SHS) were studied. The molecular packing and structure of PC12 and PC12-4SHS with variable surface pressure were investigated by surface pressure-area measurements, steady-state absorption, fluorescence emission and anisotropy, as well as by fluorescence lifetime imaging microscopy (FLIM). At low surface pressure, the porphyrin molecules are organized with the rings tilted on the water surface whereas at high surface pressure the porphyrin rings achieve a more perpendicular arrangement. Using the FLIM images a gradual change of aggregates into large "islands" is observed. Different patterns are observed in the pure PC12 multilayer films (n = 3 and 5) with ordered patches superimposed which are not observed in the PC12-4SHS multilayer LB films.