Octadecylamine Monolayer Research Articles

Modifying Specific Ion Effects: Studies of Monovalent Ion Interactions with Amines.

Specific ion effects in the interactions of monovalent anions with amine groups─one of the hydrophilic moieties found in proteins─were investigated using octadecylamine monolayers floating at air-aqueous solution interfaces. We find that at solution pH 5.7, larger monovalent anions induce a nonzero pressure starting at higher areas/molecules, i.e., a wider "liquid expanded" region in the monolayer isotherms. Using X-ray fluorescence at near total reflection (XFNTR), an element- and surface-specific technique, ion adsorption to the amines at pH 5.7 is confirmed to be ion-specific and to follow the conventional Hofmeister series. However, at pH 4, this ion specificity is no longer observed. We propose that at the higher pH, the amine headgroups are only partially protonated, and large polarizable ions such as iodine are better able to boost amine protonation. At the lower pH, on the other hand, the monolayer is fully protonated, and electrostatic interactions dominate over ion specificity. These results demonstrate that ion specificity can be modified by changing the experimental conditions.

The conceptual design of pH responsive ZnO-adamantane nanosystems for insulin amyloidosis

Adamantane derivatives are already being explored in amyloidogenic diseases, while ZnO nanoparticles (NPs) have the potential for affecting amyloidosis. Herein, the transformation of ZnO NPs and adamantane-1-carboxylic acid (ADA) to advanced pH responsive nanosystems is reported. Primary ZnO NPs were isolated under a simple solvothermal self-assembly synthetic procedure in the sole presence of octadecylamine (ODA). By adjusting the reaction time (8–24 h), wurtzites of crystallite sizes 19, 21 and 23 nm, respectively, were synthesized with co-crystallized ODA in monoloayer or bilayer conformation. The NPs with the bilayer of ODA have been functionalized with ADA through an amide bond, while those with the ODA monolayer were further PEGylated and ADA was loaded. Loaded ADA-ZnO nanosystems affected insulin amyloidosis in acidic pH (4.8), both in terms of final aggregation status (40 %) and by retarding the lag phase of amyloids formation. The sustained release profile of ADA was confirmed, while interaction with calf thymus DNA (CT-DNA) was evidenced by hyperchromicity. The pH of 4.8 was not enough to cleave the peptide bond, and thus the direct conjugation of ADA was effective only in prolonging the lag phase, without affecting the final amyloid formation, giving rise to the inherent properties of ZnO, foregrounding a prodrug character.

Photoinduced Stitching of Self-Assembled Triangular Silver Nanoprisms at the Air-Water Interface.

This study investigates the influence of optical excitation on the self-assembly of triangular nanoprisms of silver into a continuous monolayer at the air-water interface. Langmuir monolayers of octadecylamine (ODA) have been used to electrostatically assemble citrate-capped silver triangular nanoprisms (AgTNPs) in the presence and absence of light. Under optical excitation, the nanoprisms were observed to assemble into a well-ordered monolayer through plasmon-mediated stitching, whereas the particles were merely in close contact during assembly in the dark. These findings suggest new avenues for tailoring particle properties through light-mediated assembly in two dimensions.

Hybrid Polypyrrole and Polydopamine Nanosheets for Precise Raman/Photoacoustic Imaging and Photothermal Therapy.

The development of near-infrared light responsive conductive polymers provides a useful theranostic platform for malignant tumors by maximizing spatial resolution with deep tissue penetration for diagnosis and photothermal therapy. Herein, the self-assembly of ultrathin 2D polypyrrole nanosheets utilizing dopamine as a capping agent and a monolayer of octadecylamine as a template is demonstrated. The 2D polypyrrole-polydopamine nanostructure has tunable size distribution which shows strong absorption in the first and second near-infrared windows, enabling photoacoustic imaging and photothermal therapy. The hybrid double-layer is demonstrated to increase Raman intensity for 3D Raman imaging (up to two orders of magnitude enhancement and spatial resolution up to 1µm). The acidic environment drives reversible doping of polypyrrole, which can be detected by Raman spectroscopy. The combined properties of the nanosheets can substantially enhance performance in dual-mode Raman and photoacoustic guided photothermal therapy, as shown by the 69% light to heat conversion efficiency and higher cytotoxicity against cancer spheroids. These pH-responsive features highlight the potential of 2D conductive polymers for applications in accurate, highly efficient theranostics.

Interaction between acetylsalicylic acid and a cationic amphiphile model: An experimental approach using surface techniques

Mechanical and morphological effects of monolayers of octadecylamine upon aspirin adsorption are monitored by Langmuir isotherms measurements and Brewster angle microscopy. Aspirin induced a notable expansion of the corresponding isotherms and a concentration-dependence of the mechanical stability of the films as a consequence of the subtle balance between the solubility of the amine and the monolayer stabilization induced by the ion-pairs, as corroborated by Brewster Angle Microscopy images. The incorporation of the aspirin into the interface was confirmed by UV–vis reflection spectroscopy. Some comments on the feasibility of using aliphatic amines for drug delivery of anionic species are presented.

New Prediction Model of Surface and Interfacial Energies Based on COSMO-UCE.

The nature and strength of intermolecular and surface forces are the key factors that influence the solvation, adhesion and wetting phenomena. The universal cohesive energy prediction equation based on conductor-like screening model (COSMO-UCE) was extended from like molecules (pure liquids) to unlike molecules (dissimilar liquids). A new molecular-thermodynamic model of interfacial tension (IFT) for liquid-liquid and solid-liquid systems was developed in this work, which can predict the surface free energy of solid materials and interfacial energy directly through cohesive energy calculations based on COSMO-UCE. The applications of this model in prediction of IFT for water-organic, solid (n-hexatriacontane, polytetrafluoroethylene (PTFE) and octadecyl-amine monolayer)-liquid systems have been verified extensively with successful results; which indicates that this is a straightforward and reliable model of surface and interfacial energies through predicting intermolecular interactions based on merely molecular structure (profiles of surface segment charge density), the dimensionless wetting coefficient RA/C can characterize the wetting behavior (poor adhesive (non-wetting), wetting, spreading) of liquids on the surface of solid materials very well.

Sum-Frequency Vibrational Spectroscopic Study of the Cation-π Interaction: Amine and Guanidine.

The cation-π interaction is an interaction between a positively charged cation and π electrons in an aromatic group of a molecule. It is considered to play key roles in signal transduction, stabilization of the protein structure, enzyme catalysis in biology, and wet adhesion and biomolecular condensation. In this study, octadecylguanidine hydrochloride (ODG) and octadecylamine (ODA) having guanidine and amine headgroups, respectively, are found to interact with π molecules (phenol or indole) as investigated by sum-frequency vibrational spectroscopy. ODG is unstable and does not form a neat monolayer on the water surface. However, after adding π molecules into subphase water, it becomes more stable against dissolution as evidenced by the appearance of its CHx peaks and a CH peak of the aromatic ring in the sum-frequency spectrum. Unlike ODG, ODA forms a stable monolayer on the water surface at a neutral pH. After adding π molecules into the solution, the amine-π interaction promotes the protonation of the amine headgroup and the penetration of the π molecules makes the ODA monolayer more disordered. Indole is found to be more effective in binding with the ODG as compared to phenol.

Ultrathin films of functionalised single-walled carbon nanotubes: a potential bio-sensing platform

ABSTRACT The Langmuir monolayer is a special class of lyotropic liquid crystalline system wherein phase transition essentially depends on surface density, temperature and ion-content in the aqueous medium. The variety of surface phases can be transferred onto devices by the Langmuir–Blodgett (LB) technique. The Langmuir monolayer of pristine single-walled carbon nanotubes (SWCNTs) exhibited gas and liquid-like phases. The LB film of SWCNTs shows target surface pressure dependent interesting morphologies. The methane gas sensing using parallel alignment of SWCNTs was found to be better than that of randomly oriented SWCNTs. The SWCNTs can be functionalised chemically to enhance the ease of film processability and affinity towards analytes. These are essential parameters for the development of a sensor. In this article, we present our work on Langmuir monolayer and LB films of octadecylamine functionalised SWCNTs (ODACNTs) and its sensing application towards bio-analytes, e.g. L-aspartic acid and bovine serum albumin. The sensing performance of LB film of ODACNTs was compared with that of spin-coated films of ODACNTs. The sensing performance of LB films of ODACNTs indicated a potential platform for bio-sensing application.

Synthesis of Iron, Cobalt, Nickel, and Copper Hexacyanoferrates Nanoparticles Stabilized with Sodium Hexametaphosphate, and Their Use for Modification of Langmuir—Blodgett Films

Langmuir-Blodgett films were obtained on the basis of octadecylamine monolayers containing nanoparticles of various metals hexacyanoferrates. Nanoparticles were prepared using sodium hexametaphosphate as a stabilizer, their average sizes were determined by laser diffraction method. The effect of a stabilizer on the size and shape of hexacyanoferrates particles was shown by scanning electron microscopy, and the morphology of octadecylamine monolayers containing the obtained nanoparticles was studied.

Monolayers of Surfactants Containing Nanoparticles of Hexacyanoferrates of Various Metals

Abstract In this article the possibility of obtaining Langmuir-Blodgett films on the basis of octadecylamine monolayers containing nanoparticles of hexacyanoferrates of various metals was shown. A comparison was made between different methods for obtaining these particles. Nanoparticles were produced using sodium hexametaphosphate as a stabilizer, their average size were determined by laser diffraction. The isotherms of compression were studied for monolayers on a subphase containing nanoparticles. Optimal conditions for the transfer of monolayers to a solid substrate were chosen according to the data obtained and their morphology was studied by scanning electron microscopy. The cyclic voltammetry method also confirmed the successful transfer of a monolayer to a solid substrate and showed the manifestation of the electrochemical properties of the obtained substrates.

Electrochemical properties of Langmuir-Blodgett films containing cobalt hexacyanoferrate nanoparticles

Langmuir-Blodgett films modified by an electrochemically active compound, such as cobalt hexacyanoferrate, are of interest to create water-insoluble film electrodes with a high concentration of active centers and a low response time. The possibility of introducing cobalt hexacyanoferrate nanoparticles stabilized by sodium hexametaphosphate in octadecylamine monolayers with subsequent transfer them to a solid substrate by the Langmuir-Blodgett method is shown. Cobalt hexacyanoferrate nanoparticles were obtained by gradual mixing of an equimolar reagents mixture with the addition of sodium hexametaphosphate as a stabilizer. The size of nanoparticles were determined by the laser diffraction method, the size of their main number was about 12 nm. The hydrosol of the nanoparticles stability was studied photometrically in the pH range 2–4. The π-A octadecylamine monolayers isotherms on a subphase containing cobalt hexacyanoferrate nanoparticles were studied at the same pH values. According to the obtained data, optimal conditions for the monolayers transfer to a solid substrate by the Langmuir-Blodgett method were chosen. The morphology of the resulting films was studied on the surface of solid substrates. The electrochemical properties of electrodes based on Langmuir-Blodgett films in various solutions of electrolytes were studied by using the cyclic voltammetry and potentiometry.

Preparation of Patterned Ultrathin TiO2 Films by Langmuir–Blodgett Method Using Mixed Monolayers of Octadecylamine and 1H,1H-Perfluoro-1-dodecanol

An approach for the preparation of patterned ultrathin TiO2 films is demonstrated by using phase-separated Langmuir monolayers, wherein the mixed monolayer of long-chain alkylamine and perfluoroalcohol is formed on an aqueous subphase containing potassium titanium oxalate, followed by deposition onto a solid substrate as a single-layer Langmuir–Blodgett (LB) film. Atomic force microscope observation of the LB films shows that ring-like TiO2 domains are formed on the surface of the substrate and that the size and shape of the TiO2 domains can be tuned by concentration of spreading solution as well as mixing ratio of the two film materials. Subsequent heat-treatment at 500 °C results in TiO2 films of 1.6 nm in thickness maintaining the ring-like pattern.

Unveiling the interaction of DNA–octadecylamine at the air–water interface by ultraviolet-visible reflection spectroscopy

In this work, ultraviolet-visible reflection spectroscopy is proposed as a technique that, in combination with classical surface pressure–area isotherms, allows to study in situ the adsorption of DNA to octadecylamine monolayers.

Formation of J-aggregates in Langmuir-Blodgett films: Effect of stearic acid and nano clay platelets

ABSTRACTIn the present communication, a water soluble prophyrin derivative, tetra-cationic dye 5, 10, 15, 20-tetrakis (1-methyl-4-pyrindino) porphyrin tetra (p-toluenesulfonate) (abbreviated as TMPyP) has been used to prepare stable Langmuir monolayer at the air–water interface by allowing it to adsorb from the aqueous subphase, into the preformed Langmuir monolayer of anionic stearic acid (SA) and cationic octadecylamine (ODA). Anionic nano clay platelets Laponite acted as mediator to initiate adsorption of cationic TMPyP into the cationic ODA monolayer. Surface pressure versus area per molecule (π-A) isotherm studies of SA-TMPyP complex monolayer gave valuable information about the TMPyP molecular area. Organizations of TMPyP molecules were greatly affected in the two different kinds of anionic and cationic matrices. Adsorption led to the flattening of TMPyP molecules in both the matrices. The organization of TMPyP tagged nano clay platelets in preferred direction led to the development of J-band resulting due to the formation J-aggregates in the Langmuir-Blodgett (LB) films. This has been confirmed by UV-vis absorption spectroscopic studies.

High enzymatic activity preservation of malate dehydrogenase immobilized in a Langmuir–Blodgett film and its electrochemical biosensor application for malic acid detection

Malate dehydrogenase was immobilized on a cation octadecylamine monolayer and transferred onto an indium tin oxide coated glass substrate. The enzyme immobilized electrode was then used to electrochemically sense malic acid in the range of 2.2–50 mM.

Octadecylamine-based Langmuir-Blodgett films containing iron and copper hexacyanoferrates

Octadecylamine (ODA)-based Langmuir-Blodgett films modified with metal hexacyanoferrates are promising ion-exchange systems. The analysis of compression isotherms has led to the conclusion that iron and copper hexacyanoferrates are embedded into ODA monolayers. Optimal conditions have been determined for transferring these hybrid films onto a solid substrate by the Langmuir-Blodgett method. The optimal time required for the formation of iron and copper hexacyanoferrates in the monolayer has been established with the use of spectrophotometric measurements. The transfer of ODA monolayers modified with iron and copper hexacyanoferrates onto a conducting substrate has been confirmed by atomic force microscopy. The EMF values of galvanic cells developed based on the ODA/Fe4[Fe(CN)6]3-KCl and ODA/Cu3[Fe(CN)6]2-NH4Cl systems have been shown to be close to the theoretical ones.

Adsorption of a water soluble cationic dye into a cationic Langmuir monolayer

This communication reports the successful adsorption of a water soluble cationic fluorescent dye Rhodamine B (RhB) into a cationic Langmuir monolayer of Octadecylamine (ODA). Anionic nano clay platelets Hectorite played an important role in the process of adsorption. Surface pressure vs. area per molecule (π–A) isotherms were studied to monitor the adsorption process. In-situ fluorescence Imaging Microscopic (FIM) technique was employed to visualize the domain structures formed at the air–water interface. Atomic Force Microscopic (AFM) image of the monolayer Langmuir–Blodgett (LB) films were taken to study the morphology and ultrastructure of the film. Detailed spectroscopic investigations were carried out on the mono- and multilayer Langmuir–Blodgett (LB) films.

Light-induced contraction and extension of single macromolecules on a modified graphite surface.

Synthetic rigid-rod polymers incorporating multiple azobenzene photoswitches in the backbone were deposited from solution onto a monolayer of octadecylamine covering the basal plane of graphite. Large contractions and extensions of the single macromolecules on the surface were induced by irradiation with UV and visible light, respectively, as visualized by scanning force microscopy. Upon contraction, the single polymer chains form more compact nanostructures and also may move across the surface, resembling a crawling movement. We attribute the efficiency of these processes to the low mechanical and electronic coupling between the surface and polymers, the high density of azobenzenes in their backbones, and their rigidity, allowing for maximized photodeformations. The visualization of on-surface motions of single macromolecules directly induced by light, as reported herein, could help promote the development of optomechanical nanosystems.

Adsorption behavior of DNA onto a cationic surfactant monolayer at the air–water interface

This communication reports the adsorption of DNA to the preformed Langmuir monolayer of cationic surfactant Octadecylamine (ODA) at the air–water interface and thereby formation of ODA/DNA complex monolayer at the interface. Effect of concentration of DNA in the subphase as well as subphase pH on the adsorption of DNA onto ODA monolayer assemblies have been studied by monitoring the change in surface pressure of ODA/DNA complex monolayer as a function of time. The complex monolayer was also transferred onto solid substrate to prepare ODA/DNA Langmuir–Blodgett films which were analyzed by UV–vis absorption, ATR–FTIR spectroscopic techniques. The most significant observations is that the extent of interactions between ODA and DNA at the air–water interface increases with increasing concentration of DNA in the subphase and also subphase pH. At higher pH, hydrophobic interaction dominates over electrostatic interaction between DNA and ODA in the aqueous subphase. DNA immobilized in the backbone of ODA lies almost flat or extended onto solid substrate at neutral pH whereas, they lie aggregated and compacted coil rather than flat when adsorbed from high pH namely, 11.5 of the subphase. This was confirmed by atomic force microscopy of these complex LB films onto solid substrate.

Incorporation of Erythrosin B Within the Restricted Geometry of Langmuir Monolayer and Langmuir-Blodgett Films of Octadecylamine

This paper reports the monolayer characteristics of cationic octadecylamine (ODA) on both distilled water and aqueous Erythrosine B (EB) dye solution at the air-water interface. From the pressure-area isotherms at various pHs, EB anions in the subphase were found to interact with the insoluble monolayer of cationic octadecylamine (ODA). Adsorption kinetics shows that the amount of dye adsorbed depends on the concentration of the dye present in the subphase. It was observed that the adsorption process mainly occurred due to the electrostatic interaction between the cationic amino group of long chain amine and the anionic part of EB. The spectroscopic characteristics of the mixed LB films, solution, have been compared using UV-vis absorption and fluorescence spectroscopic data. These studies indicate the formation of aggregates in the thin films. Scanning electron microscopic study certainly confirms the presence of aggregates of EB dye in the (ODA-EB) mixed LB films.