Pyroelectric and conduction properties of Z-type calix[4] acid Langmuir-Blodgett films

Non-centrosymmetric Z-type Langmuir-Blodgett (LB) films were prepared by transferring a calix[4] acid monolayer from a subphase of Millipore water (18 Momegacm(-1)) onto aluminised glass substrates. Electrical measurements were performed at room temperature on LB films with a sandwich structure comprising a 50 nm thick thermally evaporated aluminium film. A pyroelectric figure of merit of 2.23 microC m(-2)K(-1) is reported for this LB system. The low voltage value of conductivity is 1.82 x 10(-12) Sm(-1). The electrode-limited Schottky effect is responsible for the conduction mechanism at a relatively high field due to the dc bias and the barrier potential height is determined to be 1.72 eV. The ac conductance for both samples shows a typical power law dependence with a value of approximately 0.86 for the exponent.     

Comparison of sensing characteristics of ChemFEC devices based on spin-coated thin films of calix[n]arenes

ChemFECs (chemical field effect capacitors) or EIS (Electrolyte-Insulator-Semiconductor) devices were coated with calix[n]arene macrocycles for cation sensors development. Silicon nitride surface electrodes were spin-coated with p-tert-butylcalix[n]arene molecules for n = 8, 9 and 11. Electrochemical capacitance measurements were carried out to evaluate the sensitivity of the calix[n]arene layers towards specific cations as calcium and copper ions. Sensor responses were due to the “host-guest” specific interaction between the rigid cavity of calix[n]arene receptors (ligand) and chemical ion species. The developed chemical sensors have demonstrated good analytical characteristic in terms of: stability, selectivity and lifetime. In addition, experimental results were fitted using the site binding model in order to determine complex association constants, pK (1.9 ≤ pK ≤ 6.39) and surface density of ligands, N_L (9.10¹⁴ ≤ N_L ≤ 2.10¹⁶). All results obtained in this work were compared with those obtained using silicon dioxide EIS electrodes coated with the same calix[n]arene receptors using both spin-coating and thermal evaporation deposit processes.     

Chemical selectivity of self-assembled monolayers of calix[4]resorcinarene

Selective molecular interactions at an interface formed by self-assembly of a macrocyclic synthetic host, calix[4]resorcinarene with four thiol groups (R4SH), are investigated. The recognition of guest adsorbates from aqueous solutions is monitored using surface plasmon resonance (SPR) and the orientation of the guest-molecule is probed using polarization modulation infrared absorption spectroscopy (PM-IRRAS). The experiments reported here demonstrate that the chemical selectivity of self-assembled monolayers (SAMs) of host molecules such as calix[4]resorcinarenes extends to isomers of several different guest molecules. By using structural isomers of guest molecules such as bipyridine and nitrophenol that are multidentate hydrogen bond acceptors, it is shown that geometric match between guest and host molecules is an integral aspect of the recognition phenomena. Results from SPR and PM-IRRAS experiments reported here highlight the interplay between steric size and forces such as hydrogen bonding and hydrophobic interactions. Competitive and sequential adsorption of guest molecules such as -hydroxy-γ-butyrolactone and 4,4′-bipyridine shows that these guests compete for the same binding sites on the surface and that the interplay between steric size and molecular forces underlies the preferential selectivity of one guest molecule over another.     

Capillary Electrokinetic Chromatography Employing p-(Carboxyethyl)calix[n]arenes as Running Buffer Additives

Calixarenes, a class of macrocyclic phenolic compounds with a basket-like shape, are used as capillary electrophoresis reagents for separations of native and substituted polycyclic aromatic hydrocarbons. The p-(carboxyethyl)calix[n]arenes reported herein are a series of charged, moderately water soluble macrocyclic molecules that can form complexes with neutral molecules. Electrokinetic chromatographic separations are based on the differential distribution of molecules between a running buffer phase, which is transported by electroosmotic flow, and an electrophoretically mediated calixarene. The size of the calixarene influences separation performance, illustrating the importance of cavity size and geometry in the complexation process. p-(Carboxyethyl)calix[7]arene provides the best efficiency (>10(5) plates/m) and selectivity in these studies. The influences of pH, organic solvent, and field strength on elution range, capacity factors, efficiency, and selectivity are also reported. In general, capacity factors are rather low, but the high charge-to-mass ratios of certain calixarenes produce relatively wide elution ranges. Molecular modeling data and solubility data are used to interpret the observed selectivity.     

Optical and electrical study of chromogenic calix[4]arene derivatives

New chromogenic calix[4]arene derivatives proved many applications in optical and electrical fields. Organic diodes formed by sandwiching azo-calix[4]arene layers between indium-thin oxide (ITO) and (Al) contacts have been elaborated and measured. In this paper, studies of devices by current–voltage characteristics I(V) and electrical impedance spectroscopy measurements in a wide frequency range have been reported. The electrical characteristics follow a space charge limited conduction behaviour (SCLC). Therefore, the Cole–Cole plots were modelled by an equivalent circuit. Relaxation processes have been identified too from the impedance spectroscopy. The optical excitation of the organic structure revealed enhancement in electrical properties.     

Grafting of calix[4]arene derivative on activated carbon surface

A new material has been synthesised by reaction between a calix[4]arene amine derivative and an oxidized activated carbon in DMF. Each reactant was characterized by thermogravimetric analysis (TGA) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). In addition, the BET surface area of activated carbon, oxidized carbon and calixarene-modified carbon, were measured and are equal to 737, 519 and 351 m²/g, respectively. Results show that calixarene is linked to superficial oxygen functional groups through a covalent bond. A percentage of grafted calixarene of the order of 35% have been calculated from the results of elemental analysis.     

Evaluation of polymer based third order nonlinear integrated optics devices

Nonlinear polymers are promising materials for high speed active integrated optics devices. In this paper we evaluate the perspectives polymer based nonlinear optical devices can offer. Special attention is directed to the materials aspects. In our experimental work we applied mainly Akzo Nobel DANS side-chain polymer that exhibits large second and third order coefficients. This material has been characterized by third harmonic generation, z-scan and pump-probe measurements. In addition, various waveguiding structures have been used to measure the nonlinear absorption (two photon absorption) on a ps time-scale. Finally an integrated optics Mach Zehnder interferometer has been realized and evaluated. It is shown that the DANS side-chain polymer has many of the desired properties: the material is easily processable in high-quality optical waveguiding structures, has low linear absorption and its nonlinearity has a pure electronic origin. More materials research has to be done to arrive at materials with higher nonlinear coefficients to allow switching at moderate light intensity ( < 1 W peak power) and also with lower nonlinear absorption coefficients.     

Preparation and application of calix[4]arene-grafted magnetite nanoparticles for removal of dichromate anions

Magnetic Fe₃O₄ nanoparticles were prepared by the chemical co-precipitation of Fe(III) and Fe(II) ions. Then, the nanoparticles were modified directly by 3-aminopropyltrimethoxy silane (APTMS) to introduce reactive groups onto the particles' surface, and diester derivative of calix[4]arene was immobilized onto the surface of modified-Fe₃O₄ nanoparticles by aminolysis reaction. The prepared magnetite nanoparticles (Calix-GM) were characterized by a combination of IR, TGA and TEM analyses. The extraction properties of the new material toward dichromate anions were also studied. It was observed that the prepared magnetite nanoparticles were an effective extractant for the removal of dichromate anions at pH 2.5–4.5.     

杯[4]芳烃乙酸/TiO2的制备及其光催化活性

以Ti(OBu)4和杯[4]芳烃乙酸为前驱体,采用溶胶-凝胶法制备了不同TiO2含量的杯[43芳烃乙酸/TiO2(CA/TiO2)材料.通过FT-IR测试表明,材料中有机无机两相间存在着化学键,并通过XRD对材料的结构进行表征.为了测试材料的光催化性能,以甲基橙溶液为模拟水样,进行了光催化降解的对比实验.结果表明:当T...     

Ionic interactions and multilayer structures on self-assembled surfaces of calix[4]resorcinarene

The ionization of a self-assembled monolayer of tetrathiol calix[4]resorcinarene, which is a synthetic host in guest-host recognition phenomena, was investigated. Using surface plasmon resonance measurements, it was found that ionization of the self-assembled surface occurred in water at a pH of approximately 11.5. These ionized surfaces of calix[4]resorcinarene were used to bind ionic guests such as metallic copper ions that were further exploited in the formation of supramolecular ionic assemblies of calix[4]resorcinarene. The structure of the molecular assemblies was characterized using polarization modulation infrared reflection absorption spectroscopy. The use of ionic interactions to attach molecules such as 11-mercapotundecanoic acid to the upper rim of the calix[4]resorcinarene host was also investigated as a method for simple and non-covalent modification of the host cavity.     

Synthesis and application of calix[4]arene based resin for the removal of azo dyes

The present study describes a novel synthetic method for the immobilization of calix[4]arene (II) onto the surface of modified Amberlite XAD-4 resin (4), which does not require the derivatization of calixarene moiety. The novel calix[4]arene based resin (C4 resin) 5 was used as sorbent for the removal of azo dyes. Batch-wise sorption study was carried out and observed that the C4 resin (5) is more effective as compared to compound II as well as pure Amberlite XAD-4 resin (1) to remove the selected dyes [i.e. Reactive Black-5 (RB-5), Reactive Red-45 (RR-45) and Congo Red (CR)]. The effect of sorbent dosage and pH on % sorption was studied. During the extraction process, various kinds of interactions such as electrostatic repulsion, deprotonation of the hydroxyl groups of C4 resin, dissociation of reactive dyes into anions/cations and structural variations were monitored and found that they are highly pH dependent.     

An efficient calix[4]arene based silica sorbent for the removal of endosulfan from water

The present work explores sorption behavior of calix[4]arene based silica resin to remove α and β endosulfan isomers from aqueous solution. The efficiency of resin was checked through both batch and column sorption methods. In both methods, the sorption parameters, i.e. pH, equilibrium time, shaking speed and sorbent dosage were optimized as 2, 60 min, 125 rpm and 50 mg, respectively. Freundlich and Langmuir sorption isotherm models were applied to validate the sorption process. The data obtained in both models reveal that the sorption is favorable. Column sorption data were analyzed through Thomas model to calculate kinetic coefficient k(TH) and maximum sorption capacity q(o) of the resin, which were found to be 6.18 and 5.83 cm(3) mg(-1) min(-1) as well as 1.11 and 1.08 mg g(-1) for α and β endosulfan, respectively. Kinetics of sorption shows that it follows pseudo second order rate equation. The optimized method has also been applied to real water samples and the results show that calix[4]arene based silica resin is an effective sorbent to remove endosulfan from waste waters.     

Extraction of americium and europium with functionalized thiacalix[4]arenes from alkaline solutions

The extraction of ²⁴¹Am and ¹⁵²Eu from alkaline carbonate solutions with solutions of functionalized thiacalix[4]arenes in m-nitrobenzotrifluoride was studied. The dependence of the radionuclide distribution ratios and separation factors on pH of the aqueous phase in the interval from 10 to 13.5, kind of the organic diluent, and position and electronic characteristics of functional groups in the thiacalixarene platform was examined. The composition of the extractable solvates of Am and Eu with functionalized thiacalix[4]arenes was determined by slope analysis. The hydrolytic stability of tert-butylthiacalix[4]arene in alkaline and acid solutions was evaluated. Thiacalix[4]arenes efficiently extract Am from alkaline solutions. The bromine-substituted thiacalix[4]arene exhibits the maximal selectivity, with the Am/Eu separation factor in extraction with this agent exceeding 30.     

Observation by atomic force microscopy of calix[n]arene thin films and their thermal rearrangement

Vapor deposited thin films of various calix[n]arenes have been investigated by contact mode atomic force microscopy. Two classes of thin films have been defined. For para-H-calix-4-arene, para-H-calix-6-arene, and para-iso-propyl-calix-4-arene pre-organized structures are observed on deposition. For para-iso-propyl-calix-6-arene, para-tert-butyl-calix-4-arene, para-tert-butyl-calix-6-arene, para-tert-butyl-calix-8-arene glassy unordered systems are obtained on deposition. Annealing of para-iso-propyl-calix-6-arene, para-tert-butyl-calix-4-arene, para-tert-butyl-calix-6-arene at 100°C leads to crystallization either directly from the glass or by migration of nano-crystallites to form microstructures.     

Surface-enhanced micro-Raman detection and characterization of calix[4]arene-polycyclic aromatic hydrocarbon host-guest complexes

Surface-enhanced micro-Raman spectroscopy (micro-SERS) was used to detect traces of the hazardous pollutant polycyclic aromatic hydrocarbons (PAHs) pyrene and benzo[c]phenanthrene deposited onto a calix[4]arene-functionalized Ag colloidal surface. High spectral reproducibility and very low molecular detection limits (10(-8) M) were obtained by using 25,27-carboethoxy-26,28-hidroxy-p-tert-butylcalix[4]arene as host molecule. Films of immobilized aggregated Ag nanoparticles, obtained by chemical reduction with hydroxylamine, were prepared by direct adhesion on a glass surface. The influence of the aggregation degree of the initial Ag nanoparticles on the micro-SERS detection effectiveness was checked. Different relative concentrations of the host (calixarene receptor) and the guest (PAHs) were attempted in order to optimize detection of the pollutant. The obtained results indicated that the detection limit is much lower in the case of benzo[c]phenanthrene than in pyrene when exciting with the 785 nm line of a diode laser. A detailed interpretation of the Raman spectra was accomplished in order to obtain more information about the interaction mechanism of the host-guest complex, which could be useful in the future for the design of powerful detection systems.     

Transition metal cations extraction by ester and ketone derivatives of chromogenic azocalix[4]arenes

The molecule of azocalix[n]arene is a macrocyclic used effectively in the complexation of the heavy metal pollutants (like silver and mercury). In this work, our main aim is to prepare new chromogenic azocalix[n]arene molecules to elaborate an extractant with high extractant selectivity for metal ions able to detect this type of pollutant. The solvent extraction properties of four acetyls, four methyl ketones and four benzoyls derivatives from azocalix[4]arenes which were prepared by linking 4-ethyl, 4-n-butyl, 4-acetamid anilin and 2-aminothiazol to calix[4]arene through a diazo-coupling reaction, the alkaline earth (Sr2+) and the transition (Ag+, Hg2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Cr3+) metal cations have been determined by extraction studies with metal picrates. Both ketones are better extractants than esters, and show a strong preference for Ag+, while Cu2+ and Cr3+ are the most extracted cation with the esters. Both acetyl and benzoyl esters are good carriers for Ag+ and Hg2+.     

Removal efficiency of a calix[4]arene-based polymer for water-soluble carcinogenic direct azo dyes and aromatic amines

A Mannich base derivative of 5,11,17,23-tetrakis-[(1,4-dioxa-8-azaspiro-[4.5]decanyl)methyl]-25,26,27,28-tetrahydroxy calix[4]arene 3 was synthesized by the treatment of calix[4]arene with a cyclic secondary amine (1,4-dioxa-8-azaspiro-[4.5]decane) and formaldehyde. The compound 3 was treated with dibromoxylene to obtain a calix[4]arene-based copolymer 4. In batch sorption experiments of selected carcinogenic azo dyes and aromatic amines, the compounds 3 and 4 were found to be a better sorbent for azo dyes than for the aromatic amines. It was observed that the percentage of azo dye removal was 95-99% for compound 3 and 83-97% for 4 when the pH of the dye solution was in the range of 2.0-8.0. The sorption of azo dyes and aromatic amines by calix[4]arenes-based compounds indicates that amino groups play the major role for the formation of hydrogen bonds and electrostatic interactions.     

A model study of artificial linker system using self-assembled calix[4]arene derivative monolayers for protein immobilization

The attachment of biomolecules, in particular proteins, onto solid supports is fundamental in the development of advanced biosensors, biochips, bioreactors, and many diagnostic techniques. In addition, the effective investigation of biomolecular structure and function with chip-based modern instruments often requires effective attachment of the biomolecule to a substrate. For this reason, it is very important to construct well-characterized linker system that can immobilize protein efficiently. Here, we investigate the formation of self-assembled monolayers (SAMs) with calix[4]arene ethylester and carboxylic acid derivatives that can serve as a model system for protein immobilization at solid surfaces. The calix[4]arene derivative monolayers were formed on Au surface and carefully characterized by atomic force microscopy (AFM), Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS) and surface plasmon resonance (SPR). Immobilization process of protein using bovine serum albumin (BSA) on the artificial linker layer was measured by SPR. The surface concentration of BSA was calculated by simulation of experimental SPR data. The surface concentration of BSA on the carboxylic acid form was higher than that of the ethylester. These results can help in modeling and understanding of protein immobilization on the linker layer.