Arachidic Acid Langmuir Monolayers Research Articles

A study of the local atomic structure the environment of zinc ions of different concentrations during their interaction with the arachidic acid Langmuir monolayer

Vital cellular processes depend on the controlled transport of metal ions across biological membranes. A biological membrane is a complex system consisting of lipids and proteins, that is why simplified systems, in particular monomolecular layers, are used to model it. This work presents the results of a study of the interaction of zinc ions from the aqueous subphase with the Langmuir monolayer of arachidic acid. The study was carried out for the first time and used total external reflection X-ray absorption spectroscopy. It considers the influence of the concentration of a ZnCl2 aqueous subphase solution on the local environment of zinc ions when interacting with the lipid monolayer immediately after its formation. The theoretical analysis of experimental XANES spectra showed that one of the interaction ways of arachidic acid molecules with zinc ions immediately after the monolayer formation is an intramolecular interaction with the formation of spodium bonds between the zinc cation and the OH carboxyl group of arachidic acid

Diamond-rich crystalline nanosheets seeded with a Langmuir monolayer of arachidic acid on water.

The enigmatic self-assembling ability of nanodiamond (ND) particles has been discovered herein. Diamond-rich crystalline nanosheets with thickness of approximately ∼25 nm were grown from a Langmuir monolayer of arachidic acid (AA) at the interface between air and a dilute aqueous ND solution. Their fine rectangular shapes with uniform uniaxial birefringence indicate appreciable crystallinity, thus supporting that they are hydrated colloidal crystals of homogeneous ND particles.

Lipid-matrix effects on tyrosinase immobilization in Langmuir and Langmuir-Blodgett films.

The immobilization of the enzyme tyrosinase (Tyr) in lipid matrices can be explored to produce biosensors for detecting polyphenols, which is relevant for the food industry. Herein, we shall demonstrate the importance of the lipid composition to immobilize the enzyme tyrosinase in Langmuir-Blodgett (LB) films. Tyr could be incorporated into Langmuir monolayers of arachidic acid (AA), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (sodium salt) (DPPG), having as the main effect an expansion in the monolayers. Results from polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) pointed to electrostatic interactions between the charged residues of Try and the lipid headgroups, in addition to changes in the order of lipid chains. The interaction between Tyr and DPPC in Langmuir monolayers can be correlated with the superior performance of DPPC/Tyr LB films used as biosensors to detect catechol by cyclic voltammetry. The molecular-level interactions assessed via PM-IRRAS are therefore believed to drive an immobilization process for Tyr in the lipid LB matrix and may serve as a general criterion to identify matrices that preserve enzyme activity.

The Formation of arachidic acid Langmuir monolayers on the NiCl2 solution

The article describes the features of the formation of arachidic acid Langmuir monolayers on a water or NiCl2 solution subphase surface. Monolayers structure was investigated by analyzing the compression isotherms and Brewster angle microscopy methods. Films on the solid substrate (glass plates) were investigated by atomic force microscopy method for morphology. Film structure was studied as a function of the concentration of salt in subphase and exposure time. It is shown that the structure of films obtained by using NiCl2solution as subphase is not homogeneous and we can see some grains in thin films.

Charging of Carboxylic Acid Monolayers with Monovalent Ions at Low Ionic Strengths: Molecular Insight Revealed by Vibrational Sum Frequency Spectroscopy

The charging of arachidic acid Langmuir monolayers as a function of subphase pH and monovalent ion concentration below 100 mM was investigated using vibrational sum frequency spectroscopy. Molecular information was obtained by targeting the vibrational modes of the carboxylic acid headgroups, alkyl chains, and water molecules in the immediate surface and diffuse double layers. The surface charge in the monolayer was experimentally determined by monitoring the hydrated carboxylate stretching modes. The charging behavior was found to be in excellent agreement with that predicted by Gouy–Chapman theory using a thermodynamic pKa of 5.1 ± 0.2. This resulted in an apparent pKa of ∼10.8 when the only ions present in solution were those associated with adjusting the pH. Water molecules with a preferred orientation in the immediate surface region were found to primarily interact with the uncharged carboxylic acid moiety, decreasing in number as the monolayer further deprotonated. Contributions from water molecules...

Interaction of Arachidic Acid Langmuir Monolayers with Trivalent Ions La<sup>3+</sup> and Fe<sup>3+</sup> Studied by Vibrational Sum-Frequency Spectroscopy

Interaction of Arachidic Acid Langmuir Monolayers with Trivalent Ions La<sup>3+</sup> and Fe<sup>3+</sup> Studied by Vibrational Sum-Frequency Spectroscopy

Study of Langmuir Monolayers of Arachidic Acid on Saline Solutions Using Sum-frequency Generation Vibrational Spectroscopy

Abstract: In this report, we studied the effect of halide salt concentration on Arachidic Acid (AA) Langmuir monolayers formed on salt solutions, such as NaCl, NaI, NaF by using a Sum-Frequency Generation Vibrational Spectroscopy. In the SFG spectra, we observed the peak intensities of CH3FR and CH3SS vibrational modes decreased when increasing the salt concentration. This observation indicates that the structure of the AA monolayer was disordered by the interaction of the dissolved ions with the carboxyl head groups of the monolayer.

Three-Dimensional Analysis of the Collapse of a Fatty Acid at Various Compression Rates using In Situ Imaging Ellipsometry

The collapse of Langmuir monolayers of arachidic acid (AA) on water at various rates of molecular area compression has been investigated in situ by imaging ellipsometry (IE). The thickness of the collapsed AA molecules, which are inherently inhomogeneous, was determined by IE with a spatial resolution of a few microns. For the analysis, we determined the dielectric function of AA monolayers from 380 to 1690 nm by conventional spectroscopic ellipsometry. Compression rates ranged from 0.23 to $0.94{\AA}^2/min$ . A change of multilayer domains was observed in the in situ IE images. Lower compression rates resulted in more uniform collapsed films. Our experimental results correspond with previous theoretical simulations.

Ion-Specific Induced Charges at Aqueous Soft Interfaces

Ionic specificity effects, i.e., ions of the same valence leading to different macroscopic effects, are studied by considering a Langmuir monolayer of arachidic acid over a solution containing either Fe(3+) or La(3+). We systematically vary pH levels as a way to control the interfacial surface charge and characterize the system by surface-sensitive x-ray scattering and spectroscopic techniques. We show that the critical surface pressure at the tilted (L2) to untilted (LS) transition is ionic specific and varies with pH. While the maximum density of surface bound La(3+) per head group of arachidic acid is ∼0.3, the amount necessary to neutralize the surface charge, for Fe(3+) it is nearly 0.6 and it is accompanied with a significant accumulation of the coions Cl(-) as revealed by surface x-ray spectroscopy. We account for the experimental observations by a statistical mechanical model including ion specificity.

Preparation and Characterization of Porous and Composite Nanoparticulate Films of CdS at the Air/Water Interface

CdS nano-particulate films were prepared at the air/water interface under Langmuir monolayers of arachidic acid (AA) via interfacial reaction between <TEX>$Cd^{2+}$</TEX> ions in the subphase and <TEX>$H_2S$</TEX> molecules in the gaseous phase. The films were made up of fine CdS nanoparticles with hexagonal Wurtzite crystal structure after reaction. It was revealed that the formation of CdS nano-particulate films depends largely on the experimental conditions. When the films were ripened at room temperature or an increased temperature (<TEX>$60^{\circ}C$</TEX>) for one day, numerous holes were appeared due to the dissolution of smaller nanoparticles and the growth of bigger nanoparticles with an improved crystallinity. When the films were ripened further, CdS rodlike nanoparticles with cubic zinc blende crystal structure appeared due to the re-nucleation and growth of CdS nanoparticles at the stacking faults and defect structures of the hexagonal CdS grains. These structures were characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and X-ray diffraction (XRD). These results declare that CdS semiconductor nanoparticles formed at the air/water interface change their morphologies and crystal structures during the ripening process due to dissolution and recrystallization of the particles.

Triangular Single-Crystalline Nanorings of PbS Formed at the Air/Water Interface

Triangular single-crystalline nanorings of PbS were prepared at the air/water interface and characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV−vis spectroscopy. The nanorings were transformed from triangular PbS nanopyramids that were formed under Langmuir monolayers of arachidic acid (AA) through interfacial reactions between Pb2+ ions in the subphases and H2S in the gaseous phase. The basal plane of the pyramids is a (111) face of PbS crystals with rock salt crystal structure, which is parallel to the air/water interface. The tips of the pyramids beneath the interface dissolved gradually due to selective etching of Pb2+ in the nanocrystals by Cl− ions in the subphase because of their higher surface energy, resulting in the formation of the rings. The size of the rings could be tuned by changing the experimental conditions, and the optical properties changed when the rings formed.

In-Situ IR Spectral Measurement in Organic Matrix-Mediated Hydroxyapatite Formation

Organic template-directed crystallization of hydroxyapatite (HAp) was studied in-situ via Fourier transform IR external reflection spectroscopy. Langmuir monolayer of arachidic acid was formed on a surface of simulated body fluid, which possesses inorganic ion concentrations and a pH value almost equal to those of human blood plasma. Owing to the chemical interactions between inorganic ions and carboxyl groups, heterogeneous nucleation of HAp occurred below the monolayer. The absorbances of the antisymmetric and symmetric methylene stretching bands in the IR spectra varied during the nucleation process, which means that conformational change of hydrocarbon chain occurred. Interfacial interactions between organic templates and induced crystals are often discussed only through static experimental models. However, the organic matrices should also be treated as elastic template and their structural changes due to the formation of HAp crystals should be recognized, when the biomineralization mechanism is discussed.

Dynamics and Equilibrium of the Penetration of Soluble Cetyltrimethylammonium Bromide into Langmuir Monolayers of Arachidic Acid under Different pH Conditions

Experimental and theoretical studies of the equilibrium and dynamics of the penetration of the soluble cationic surfactant cetyltrimethylammonium bromide (CTAB) into arachidic acid monolayers are reported. The experimental studies of the system are performed at different pH values in acidic, alkaline, and neutral media. The penetration of CTAB from the alkaline subphase into the arachidic acid monolayer is shown to result in a significant increase of the surface pressure of the mixed monolayer, whereas the surface pressure jump for the penetration from the acidic subphase does not differ from that corresponding to the adsorption from the single CTAB solution with the same concentration onto the pure aqueous surface. This phenomenon is explained by the fact that the dissociation degrees of arachidic acid are different (the dissociation is the largest in the alkaline subphase, and nearly no dissociation exists in the acidic subphase), and in the alkaline subphase, strong Coulombic interaction exists between...

Morphological investigation of hybrid Langmuir-Blodgett films of arachidic acid with a hydrotalcite/dendrimer nanocomposite.

A hydrotalcite clay/dendrimer nanocomposite prepared by the ionic exchange process was adsorbed from suspension of the nanocomposite on a Langmuir monolayer of arachidic acid at the air/water interface, followed by compressing and transferring onto an arachidic acid monolayer Langmuir-Blodgett (LB) film on mica. For comparison, the hydrotalcite-adsorbed hybrid film was also prepared. The morphology of hydrotalcite and the nanocomposite studied by transmission electron microscopy indicated the layered structures with respectively 1.2 +/- 0.3 and 3.2 +/- 0.5 nm repeating distances. The hybrid Langmuir films displayed the occupied surface area of 0.24 nm2 for both hydrotalcite and the nanocomposite. The formation of hybrid Langmuir films was confirmed by Brewster angle microscopy. Atomic force microscopic images of hybrid LB films revealed the formation of plateau domains with the height difference of 6 nm for hydrotalcite and 12 nm for the nanocomposite and the presence of dendrimers adsorbed on the clay surface of the nanocomposite.

Langmuir−Blodgett Mixed Films of Titanyl(IV) Pthalocyanine and Arachidic Acid. Molecular Orientation and Film Structure

Langmuir and Langmuir−Blodgett (LB) films of neat titanyl(IV) phthalocyanine (TiOPc) and mixed (TiOPc)−arachidic acid (AA) films were studied. The surface pressure−area isotherms (π−A) were recorded, and an unusual expansion of the surface area per molecule was detected for mixed TiOPc−AA Langmuir monolayers. The expansion is attributed to the TiOPc molecular orientation in the neat films being different from that in the mixed films with arachidic acid. The molecular orientation in LB films was monitored using reflection−absorption infrared spectroscopy (RAIRS). It was found that the TiOPc molecules are tilted with respect to the substrate in the neat film, changing to a preferential face-on orientation in the TiOPc−AA mixed films. Complementary information about molecular organization and film structure was obtained using UV−visible absorption and micro-Raman imaging.

MICRO-PHASE SEPARATION IN BINARY MIXED LANGMUIR MONOLAYERS: CORRELATION BETWEEN MOLAR FRACTION AND AREA FRACTION

Correlation between molar fraction and area fraction in micro-phase separated structures formed in binary mixed Langmuir monolayers of arachidic acid (C20) and a perfluoropolyether amphiphile (PFPE) has been examined. On the water surface, C20 and PFPE separate into fully condensed micro-domains and a largely expanded phase, respectively. The area fraction of the condensed phase domains is estimated by two different ways: one is by analyzing atomic force microscope (AFM) images and the other is calculated from π–A isotherm data assuming complete immiscibility of the film components in the monolayers. Two area fractions are in agreement with each other, and increase exponentially with increase in molar fraction. Our results ensure the complete phase separation of the two film components on the water surface, the monolayer transfer without any structural changes, and the fruitfulness of digital image analysis for the evaluation of two-dimensional organized structures.

Effect of Cations on the Dissociation of Arachidic Acid Monolayers on Water Studied by Polarization-Modulated Infrared Reflection−Absorption Spectroscopy

We report on the variation of the dissociation of a Langmuir monolayer of arachidic acid at the air/water interface as a function of the subphase pH and for several cations (Cd2+, Ca2+, Mg2+, and Na+) with the help of the polarization-modulated infrared reflection−absorption spectroscopy (PM-IRRAS) method. The infrared spectra give access to the relative concentration of acid and salt molecules and allow us to determine the influence of the subphase pH on the acid dissociation reaction for each cation. It is shown that Na+ obeys the purely electrostatic Gouy−Chapman theory quite well, whereas the behavior of Mg2+, and even more so that of Ca2+ and Cd2+, requires the introduction of some complexation constant to be understood.

Oriented Crystallization of KH2PO4 under a Compressed Langmuir Monolayer

Oriented growth of KH2PO4 (KDP) under a compressed Langmuir monolayer of arachidic acid (AA) has been studied by using π−A isotherms, X-ray diffraction (XRD), Brewster angle microscope (BAM), and atomic force microscopy (AFM) techniques. All produced crystals are almost connected with the monolayer by the crystal face (100), epitaxial forming multilayer structures along the vertical direction. BAM observation shows that KDP crystals induced by the Langmuir monolayer are nearly homogeneous and uniform in crystal size. Crystallization induction time is reduced evidently. The optical second harmonic generation (SHG) experiment indicates that the SHG signal of the sample of 25 layers deposited in Z type is better than that of the crystals in the absent of a monolayer, which demonstrates that oriented KDP crystals are homogeneous with a uniform orientation.

Fabrication of nano-sized particles of metallic copper and copper sulfide in Langmuir–Blodgett films

Langmuir monolayers of arachidic acid on a subphase of 0.3 mM CuSO 4/17 mM NH 3 were transferred to hydrophobic glass and mica substrates to give Langmuir–Blodgett films of cupric arachidate (CuAr). Transfer ratios of close to 1 were observed and regular “Y”-type deposition was demonstrated with hydrophobic glass. With mica as the substrate, “Z”-type deposition occurred. The films were exposed to H 2S and hydrazine, and evidence for the formation of copper sulfide and metallic copper particles, respectively, was obtained by ultraviolet/visible spectrophotometry, X-ray photoelectron spectroscopy and atomic force microscopy.

In-situ measurement of lead(II) ion binding to an arachidic acid langmuir monolayer using a quartz crystal microbalance

A quartz crystal microbalance (QCM) was used to measure the in situ binding of lead (II) ions to a Langmuir monolayer of arachidic acid (ArH) at the air-water interface. A horizontally oriented QCM was lowered onto an ArH monolayer and an analiquot of a Pb 2+ solution was injected beneath the monolayer. A decrease in the QCM frequency was observed, consistent with Pb 2+ binding to the ArH monolayer. Models for a fatty acid to divalent metal ion ratio ( F: M) of 2 and 1 were considered. The experimental data was consistent with 2:1 binding.