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.     

Comparative studies on the solvent extraction of transition metal cations by calixarene, phenol and ester derivatives

The ionophore solvent extraction of various alkali metal and transition metal cations from the aqueous phase to the organic phase was carried out by using diazo-coupling calix[n]arenes [p-(4-phenylazophenylazo)calix[4]arene (L1) and p-phenylazocalix[6]arene (L2)], phenol derivatives [2,6-dimethyl-3-phenylazophenol (L3), 2-(5-bromo-2-pyridylazo)-5-diethylamino phenol (L4), 2-chloro-4-nitro(phenylazo)-5-sec-butyl-2-phenol (L5) and 2-chloro-4-nitro(phenylazo)-5-tert-butyl-2-phenol (L6)], and ester derivatives [quinoline-8-benzoate (L7), phenyl-1,4-dibenzoate (L8), p-tolyltiobenzoate (L9)]. It was found that, all the compounds (L1-L9) examined showed selectivity for transition metal cations such as Ag+, Hg+ Hg2+, and poor efficiency for alkali metal cations (Na+ and K+). The best extraction efficiency was obtained with L1 and L4.     

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.     

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.     

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.     

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.     

Extraction of cesium and americium with <Emphasis Type="Italic">p</Emphasis>-alkylcalix[8]arenes from alkaline solutions

Previously unknown isononylcalix[8]arene was synthesized from commercially available isononylphenol. The properties of the product (solubility, extraction ability, tendency to aggregation) were compared with those of the known tert-butylcalix[8]arene. The extraction of ¹³⁷Cs, ^99mTc, and ²⁴¹Am from alkaline carbonate solutions with solutions of p-alkylcalix[8]arenes (alkyl = tert-butyl, isononyl) in tetrachloroethylene was studied. The dependence of the distribution ratios on pH of the aqueous phase in the interval from 11 to 13.9 and on the nature of functional groups in the calixarene core was determined. The composition of extractable solvates of cesium and americium with calix[8]arenes was found. Calix[8]arenes extract cesium from alkaline solutions more efficiently than p-tert-butylphenol, their nonmacrocyclic analog, does. tert-Butylcalix[8]arene exhibits the highest performance, which may be due to formation of aggregates 5.7 ± 0.8 nm in diameter in the organic phase at pH 13.5 of the aqueous phase. The isononyl derivative exists in the monomeric form (particle diameter 1.9 ± 0.5 nm).     

Calix[8]arene coated CdSe/ZnS quantum dots as C60-nanosensor

Here, we report an optical sensor for fullerene C(60) in water using CdSe/ZnS quantum dots coated by p-tertbutylcalix[8]arene. This C(60)-nanosensor is based on the selective host-guest interaction between fullerene C(60) and p-tertbutylcalix[8]arene. The procedure for the synthesis of p-tertbutylcalix[8]arene-CdSe/ZnS complex is described, and its fluorescent characteristics are also reported. We found that the interaction between C(60) fullerene and p-tertbutylcalix[8]arene-CdSe/ZnS complex quenches the original fluorescence of calix-QDs according to the Stern-Volmer equation. The mechanism of interaction is discussed. Finally, the potential application of the proposed method using the designed nanosensor for determination of C(60) in spiked environmental river water samples is demonstrated. For the analysis of river samples, a liquid-liquid extraction multistep preconcentration procedure is proposed. The method, which is simple and rapid, allows the detection of 5 μg L(-1) of fullerene. This sensor could be a useful tool for environmental and toxicological studies.     

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+.     

Molecular recognition of protonated polyamines at calix[4]crown-5 self-assembled monolayer modified electrodes by impedance measurements

Molecular recognition of protonated aliphatic polyamines has been studied at calix[4]crown-5 self-assembled monolayer modified gold electrodes by electrochemical impedance spectroscopic (EIS) experiments. The energy of complex formation between the calix [4]crown-5 molecule and a series of alkyl ammonium ions was shown by molecular modeling and EIS experiments to depend on the number of amine groups in the alkyl chain as well as the number of methylene groups between the amine groups. The structures of complexes formed between the crown ether on the lower rim of calix[4]arene and protonated amines were determined by minimizing the complex formation energies. The adducts thus formed on the SAM rendered the electron transfer from the electrode to the probe (Fe(CN)63-/4- pair) easier or more difficult depending on the number of ammonium groups and their arrangement in linear alkyl chains. Analytical procedures have been developed to detect protonated spermidine (a recognized cancer marker) in simulated urine, blood, erythrocyte, and cerebrospinal fluids.     

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.     

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.     

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.     

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.     

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.     

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.     

Selective assembling of calixarenes and pseudorotaxanes on Si(100) and polycrystalline copper

We report the first compared study of the anchoring mode of calix[6]arene derivatives and pseudorotaxanes on Si(100) and polycrystalline Cu. Calixarenes have been chosen for their flexibility as linkers, being, i.a., efficient building blocks for the constructing of molecular devices based on pseudorotaxanes and rotaxanes. A covalent functionalization on Si or Cu surfaces requires the molecules to be differently modified: thiol (-SH) or C double bond C terminations are respectively suitable for Cu or H-Si(100). Anchoring on Cu was reached by dipping a clean substrate in a calix[6]arene-SH solution, while a wet-chemistry recipe was followed for Si(100), combined with an extra-mild photochemical activation via visible light. Molecular adhesion onto either surfaces has been demonstrated by the presence of XPS signals from specific elements in the molecules: calix[6]arene designed for H-Si were derivatized with NO2 groups on the upper rim of the calix, while the S atom was used as the molecular identifier on Cu. A further extension is represented by the anchoring reaction of rotaxanes on Si(100) and Cu surfaces. A pseudorotaxane species was first formed in solution by reacting a calix[6]arene "wheel," bearing three N-phenylureido groups on the upper rim, with viologen (4,4'-bipyridinium) containing axle. The resulting species has then been anchored on either Cu and Si via its distinct termination of the axle. This two-step reaction has produced a threaded pseudorotaxane covalently bound to either surfaces, as shown by XPS results. These species are ready to respond to external stimuli. We also cross-checked the two different anchoring groups for their reactivity on Cu and Si surfaces. No molecular uptake was observed when two solutions, containing calixarenes with the anchoring arms intended either for Si or Cu surfaces, were exchanged.     

Tuning and enhancing enantioselective quenching of calixarene hosts by chiral guest amines.

The synthesis of a propranolol amide derivative of p-allylcalix[4]arene is described, which has been designed to behave as a molecular sensor capable of distinguishing chiral amines on the basis of their shape and chirality. This molecule can discriminate between the enantiomers of phenylalaninol through the quenching of the fluorescence emission in methanol in contrast to an (S)-dinaphthylprolinol calix[4]arene derivative, which can discriminate between the enantiomers of phenylglycinol, but not phenylalaninol. The separation between the naphthyl fluorophores and the hydrogen-bonding sites within the chiral cavity can be tuned to recognize guest amines with similar separation between aryl groups and hydrogen-bonding sites. The formation of metal ion complexes of the p-allylcalix[4]arene propranolol amide derivative is shown to induce a more regular and rigid cone conformation in the calix[4]arene macrocycle, which generates a significant enhancement in the observed enantiomeric discrimination.     

The extraction of thorium by calix[6]arene columns for urine analysis

Thorium is a natural alpha-emitting element occurring in various ores and has numerous industrial applications. Routine monitoring of potentially exposed workers is generally achieved through radiobioassay (urine and faeces). The procedures currently used for analysing actinides such as thorium in urine require lengthy chemical separation associated with long counting times by alpha-spectrometry due to low activity levels. Thus, their main drawback is that they are time-consuming, which limits the frequency and flexibility of individual monitoring. In this context, this study developed new radiochemical procedures based on the use of tertbutylcalix[6]arenes bearing three carboxylic acid groups or three hydroxamic acid groups. These previous works demonstrated that these macrocyclic molecules immobilised on an inert solid support are excellent extractants for uranium, plutonium and americium. In this study, the authors investigated the thorium extraction by calix[6]arene columns. Experiments were performed on synthetic solutions and on real urine samples. The influence of various parameters, such as the thorium solution pH and the column flow rate on thorium extraction, was studied. The results showed that both calix[6]arenes are efficient to extract thorium. Thorium extraction is quantitative from pH = 2 for synthetic solution and from pH = 3 for real urine samples. This study has demonstrated that the column flow rate is a crucial parameter since its value must not be too high to achieve the steady-state complexation equilibrium. Finally, these results will be compared with those obtained for other actinides (U, Pu and Am) and the conditions of actinides' separation will be discussed.     

Photoluminescence and thermoanalytical studies of complexes based on 5-Cl-8-hydroxyquinoline and calix[4]arene ligands

A innovative 5-Cl-8-oxyquinolinepropoxycalix[4]arene ligand (2) have been prepared, exhibiting, at room temperature, blue fluorescent light emission and resulting in shift band to green fluorescent light (fluorescence mode) in the presence of coordinated Eu(III) and Tb(III) ions. Terbium complex presented phosphorescence emission as noted by typical bands at 490 nm, 545 nm and 585 nm. TG/DTG data exhibited typical thermal behavior for these compounds, however DSC curves showed the melting temperature near 300 °C for the samples, demonstrating an unusual thermal stability when quinoline derivatives are attached to calix[4]arene matrix. This fact strongly suggests an effective approach to preparing the photoluminescent compound associating high chemical and thermal stability.