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.     

Two novel calixarene functionalized iron oxide magnetite nanoparticles as a platform for magnetic separation in the liquid–liquid/solid–liquid extraction of oxyanions

This article focuses on the syntheses of 25,27-bis[3-(N-ethylsulfonic acid)aminopropxy]-26,28-dihydroxy-5,11,17,23-tetra-tert-butyl-calix[4]arene (3) and 25,27-bis[3-(N-ethyl-dihydrogen phosphate)aminopropxy]-26,28-dihydroxy-5,11,17,23-tetra-tert-butyl-calix[4]arene (4) as well as their immobilization onto [3-(2,3-epoxypropoxy)-propyl]-trimethoxysilane-modified Fe₃O₄ magnetite nanoparticles, and the extraction abilities of four new extractants which were characterized by a combination of FTIR, ¹H NMR, elemental analyses, transmission electron microscopy (TEM) and thermogravimetric analyses (TGA) involving electrostatic and hydrogen bonding interactions between the calixarene and oxide anions such as arsenate and dichromate anions. The extraction results indicate that these new calixarene derivatives having high extraction capabilities would be used as effective extractants for the removal of the dichromate/arsenate ions from water.     

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.     

Calixarene-based photoresponsive ion carrier for the control of Na flux across a lipid bilayer membrane by visible light

A photoresponsive ion carrier based on calix[4]arene was synthesized for the control of Na⁺ flux across lipid bilayer membranes by visible light. Calix[4]arene was chosen as a basic skeleton of a photoresponsive ion carrier because its ether derivatives are known to act as Na⁺ ion carriers in lipid bilayer membranes. For the synthesis of a photoresponsive carrier, dimethylaminoazobenzene was introduced as a photochromic moiety to an ether derivative of p-tert-butylcalix[4]arene. The ion transport ability of the dimethylaminoazobenzene appended calix[4]arene was examined by using a voltage-clamp method. When the calix[4]arene derivative was incorporated into a planar lipid bilayer membrane which separated two chambers filled with 100 mM of NaCl solutions, membrane currents resulting from Na⁺ flux were observed under applying external voltages between two chambers. The concentration dependence of the calix[4]arene derivative on the membrane currents indicated the formation of a 1:1 complex with Na⁺ ions for the calix[4]arene-mediated ion transport across the lipid bilayer membrane. By using visible light (> 400 nm), Na⁺ flux across lipid bilayer membranes containing the dimethylaminoazobenzene appended calix[4]arene derivative could be controlled.     

Interaction between calix[4]arene derivative bearing adenino units and complementary nucleosides at the air–water interface

The monolayers of the amphiphilic calix[4]arene derivatives at the lower rim with two adenino units on the surface of pure water, the aqueous subphases containing complementary nucleosides were studied by film balance measurement and relaxation experiments. LB films deposited from all subphases were investigated by UV spectra and FT-IR spectra. All the results indicate that the interaction between the adenino units in the headgroup of amphiphilic calix[4]arene derivatives and the complementary nucleosides in the subphase takes place through multiple complementary hydrogen bonding and the nucleosides in the subphases can be transferred to solid substrates along with their monolayers.     

A novel growth process of calcium carbonate crystals in silk fibroin hydrogel system

We report an interesting finding of calcium carbonate (CaCO₃) crystal growth in the silk fibroin (SF) hydrogel with different concentrations by a simple ion diffusion method. The experimental results indicate that the CaCO₃ crystals obtained from silk fibroin gels with low and high concentrations are all calcites with unusual morphologies. Time-dependent growth study was carried out to investigate the crystallization process. It is believed that silk fibroin hydrogel plays an important role in the process of crystallization. The possible formation mechanism of CaCO₃ crystals is proposed. This study provides a better explanation of the influence of silk fibroin concentration and its structure on CaCO₃ crystals growth.     

Solvent extraction and stripping of silver ions in room-temperature ionic liquids containing calixarenes

We found that a calix[4]arene-bearing pyridine is soluble in a typical room-temperature ionic liquid (RTIL), 1-alkyl-3-methylimidazolium hexafluorophosphate. Pyridinocalix[4]arene showed a high extraction ability and selectivity for silver ions. The extraction performance of the calix[4]arene was greatly enhanced by dissolution in RTILs compared to in chloroform. In a competitive extraction test using five different metal ions (Ag+, Cu2+, Zn2+, Co2+, Ni2+), only silver ions were transferred by the calix[4]arene from the aqueous feed phase into the RTILs, through a cation-exchange mechanism. The pyridinocalix[4]arene was found to form a stable 1:1 complex with silver ions, both by slope analysis and by Job's method. Since it is easy to strip silver ions from RTILs by controlling the aqueous-phase pH, the extraction performance of calix[4]arene in RTILs was maintained after five repeated uses.     

Evaluation of the performance of calix[8]arene derivatives as liquid phase extraction material for the removal of azo dyes

This paper presents a study on the removal of azo dyes (Reactive Black 5, Trapaeolin 000, Methyl Orange and Direct Violet 51) with calix[n]arene derivatives from aqueous solution into the organic phase in order to explore the potential use of calixarenes as low-cost efficient extractants for wastewater dye removal. The carboxylic acid derivative of calix[8]arene shows highest affinity towards the azo dyes. The influence of NaCl (present in the solution) on extraction process was also studied. The extent of the dye removal increased with the addition of NaCl. The proposed extraction mechanism involves several kinds of interactions: electrostatic repulsion between carboxylic acid groups of calix[8]arenes and sulfonate groups of azo dyes, hydrogen bonding and formation of an inclusion complex due to three dimensional cavity type calix[n]arene molecules through host-guest interactions.     

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.     

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.     

Biological synthesis of calcite crystals using <Emphasis Type="Italic">Scindapsus aureum</Emphasis> petioles

We report a novel strategy for the biological synthesis of calcite crystals using the petioles of the plant Scindapsus aureum. The resultant calcite crystals were characterized by scanning electron microscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffractometry, and electron diffraction. The biomolecules of S. aureum petioles were confirmed by UV–Vis and FT-IR analysis. The results showed that the spherical or rhombohedral calcite crystals were obtained in the cells of S. aureum petioles. Biomimetic synthesis of calcium carbonate (CaCO₃) in aqueous solution containing extracts of S. aureum petioles was also performed to investigate the soluble biomolecules’ influence on crystal growth of CaCO₃. It was found that twinborn spherical calcite crystals were formed, suggesting that the soluble biomolecules of S. aureum play a crucial role in directing the formation of calcite spherical particles. The possible mechanism of formation of CaCO₃ crystals using S. aureum is also discussed; the biomolecules of S. aureum may induce and control the nucleation and growth of CaCO₃ crystals.     

Extraction of americium and europium with functionalized calixarenes from alkaline solutions

Extraction of ²⁴¹Am and ¹⁵²Eu from alkaline carbonate solutions with solutions of functionalized calix[4]arenes and their nonmacrocyclic analogs in m-nitrobenzotrifluoride was studied. The dependence of the distribution ratios and separation factors of the radionuclides on pH of the aqueous phase in the interval from 9.8 to 13.5 and on the position and electronic nature of functional groups (alkyl, pyridine, phosphoryl) in the calixarene core was examined. The composition of the extractable solvates of americium and europium with functionalized calix[4]arenes was determined. From both alkaline and nitric acid solutions, calixarenes extract americium more efficiently than their nonmacrocyclic analogs do. The calix[4]arene with the pyridine functional group exhibits the highest selectivity, with the Am/Eu separation factor exceeding 3. Calix[4]arenebis-(methanediphosphonates) extract europium and americium from both alkaline and nitric acid solutions with similar magnitude of the cooperative effect.     

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.     

Raman Spectroscopy and Structure of InBO<Subscript>3</Subscript>

The structure of boron-oxygen groups in InBO₃ single crystals (calcite type) is investigated by Raman spectroscopy. The fundamental vibrational modes of indium orthoborate are analyzed using detailed studies of polarized Raman spectra. The polarization and relative intensities of lines in the spectra of InBO₃ are shown to differ markedly from those in the spectra of other calcite-structure crystals (LuBO₃ and CaCO₃) and alkali and alkaline-earth orthoborates and their melts. This effect is tentatively attributed to the large covalent contribution to the energy of bonding between In³⁺ and the oxygens of the [BO₃] groups.     

Optical spectroscopy studies of the complexation of chromogenic azo-calix[4]arene with Eu3+, Ag+ and Cu2+ ions

Due to their potential applicability as selective receptors in electrochemical and/or optical sensors (optodes) a new family of chromogenic calix[4]arenes derivatives were investigated. The complexing properties of these molecules towards metallic cations and lanthanides and the photophysical properties of the formed compounds in acetonitrile solution have been studied by UV/Vis spectroscopy. The molar ratio method revealed that the stoichiometry of calix[4]arenes 1a and 1b to Eu(III) in the complex is 1 : 1. The stability constants of the complexes have been determined.     

Abnormal polymorph conversion of calcium carbonate from calcite to vaterite

Inspired by mineralization in biological organisms, the production of higher ordered CaCO₃ crystals modified by surfactants has received much attention. Normal micelles formed by anionic surfactant, sodium bis-2-ethylhexyl-sulfosuccinate (aerosol OT, AOT), was used as a template to direct the growth of CaCO₃ crystals in the present work. When the concentration of the AOT increased from 0.5 to 5.0 mM, the polymorph of CaCO₃ crystals changed from almost pure aragonite to almost pure vaterite at 150 °C. In the meantime, various morphologies of vaterite were obtained, such as astral and hexagonal structures. Based on the time-resolved experiments, we suggested that AOT micelles induced the formation of these structures. And the micelles were wrapped in the hexagonal structures, and dissolved in the aqueous solution with increase of the experimental time. Thus, hollow shells were produced. Abnormal polymorph transformation of CaCO₃ crystals from the calcite to the vaterite was found. These effects of AOT on polymorph and morphology of CaCO₃ crystals have not been reported as far as we know.     

Cadmium-sensitive electrode based on tetracetone derivatives of p-tert-butylcalix[8]arene

The performance of a cadmium-sensitive electrode based on the tetracetone derivatives of p-tert butylcalix[8]arene was investigated. The ion-sensitivity of the calix[8]arene was examined via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectrometry, UV/Vis spectroscopy and FT-IR spectroscopy. The sensitive membrane containing the active ionophore was cast onto the surface of a gold electrode. The electrode exhibited a linear relationship between the charge transfer resistance (R_ct) and the logarithm of the detected ion concentration. The cathodic peak at a potential of 0.56 V increased linearly as the Cd^2 + ion concentration increased. The detection limit of the device reached 10^? 7 M with high sensitivity toward cadmium.     

Experimental investigations on the effects of asparagine and serine on the polymorphism of calcium carbonate

The present study investigated the effects of the amino acids asparagine and serine, as additives, on the polymorphic transformation of calcium carbonate (CaCO₃) within the concentration range of 25–100 ppm at 30 °C and pH 12. The structural composition and morphology of the samples prepared with and without additives were evaluated experimentally through X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) analysis. The XRD results showed that the calcite composition of CaCO₃ samples prepared with asparagine and serine reduced with increasing concentrations of both additives. SEM images showed that CaCO₃ prepared with asparagine and serine had three coexisting crystal forms: cubic-shaped calcite, spherical shaped vaterite, and needle-like aragonite crystals. Moreover, the addition of both additives separately was found to increase the average particle size and Brunauer–Emmett–Teller (BET) specific surface area of the crystals. Higher concentrations of serine and asparagine individually in the crystallization media resulted in a more negative zeta potential. Meanwhile, the thermal behavior, kinetics, and thermodynamics of the CaCO₃ crystals were simultaneously evaluated by means of by thermogravimetric analysis (TGA) coupled with Fourier transform infrared (FTIR) and mass spectrometry (MS). The master plots method combined with the Friedman method revealed that the decomposition of CaCO₃ prepared in pure media followed the contracting volume mechanism, R₃. Positive values of ΔH and ΔG were obtained for CaCO₃ decomposition.     

Ultra-high-sensitive extraction-photometric determination of sodium ion using flow injection analysis with a chromogenic calix[4]arene derivative and a laser interferometric photothermal detector

A novel flow injection analysis (FIA) system for ultra-high-sensitive determination of Na(+), which involves laser interferometric photothermal equipment as the detector, was designed using a proton-dissociable chromogenic calix[4]arene derivative with a dinitrophenol moiety as the extraction-photometric reagent. The chromogenic calix[4]arene derivative showed an excellent extractability toward Na(+), which reflected the cation-complexing property of the tetraethyl ester derivative of calix[4]arene. As the calibration graph of the Na(+) concentration could be successfully obtained at the nanomolar level by this method, the proposed FIA system was found to be promising for highly sensitive determination of Na(+) in very dilute samples such as supply water and cooling water in power plants.     

Effect of surface properties of calcium carbonate on aggregation process investigated by molecular dynamics simulation

The control of the morphology and polymorphs of CaCO₃ has been required, since their capabilities are dependent on particle characteristics of CaCO₃. It is difficult to clarify the formation mechanism only by the experimental approaches because the nucleation and crystal growth of CaCO₃ occurred at nanoscale. The objective of the present work is to investigate the effect of surface properties including in the charge density and the dielectric constant of water on the aggregation process of primary particles by means of molecular dynamics simulations. The grain boundary energy was also calculated by molecular dynamics simulation to investigate the change of energy in the aggregation process of primary particles. From the results of molecular dynamics simulation, we found that the interface of (001)Ca and (001)CO₃ contacted with water charged positively and negatively and the interface of (100) and (104) contacted with water charged neutrally. When the distance of interfaces between CaCO₃ particles came close to colliding, the dielectric constant of water became small except the interface of (001)CO₃. The boundary energy of interface between (001)Ca and (001)CO₃ was the lowest among five types of interfaces. It indicates that the aggregation of (001)Ca and (001)CO surface is the easiest among all types of interfaces.