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In order to enhance the cost-effectiveness practicability of enzymes in many industries such as pharmaceutical, food, medical and some other technological processes, there is great need to immobilize them onto a solid supports. In this study, a new and efficient immobilization of α-amylase from Saccharomyces cerevisiae has been developed by using the surface functionalization of calix[4]arene as support. A glutaraldehyde-containing amino group functionalized calix[4]arene was used to immobilize α-amylase covalently. In this procedure, imide bonds are formed between amino groups on the protein and aldehyde groups on the calix[4]arene surface. The surface modified support was characterized using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM). The effect of various preparation conditions on the immobilized α-amylase process such as immobilization time, enzyme concentration, temperature and pH were investigated. The influence of pH and temperature on the activity of free and immobilized α-amylase was also studied using starch as substrate. The optimum reaction temperature and pH value for the enzymatic conversion catalyzed by the immobilized α-amylase were 25°C and 7, respectively. Compared to the free enzyme, the immobilized α-amylase retained 85% of its original activity and exhibited significant thermal stability than the free one and excellent durability.

Present study deals with the sorption characteristics of p-tetranitrocalix[4]arene (3) appended silica-based high-performance liquid chromatographic (HPLC) column utilized for preconcentration, determination, and purification of Cu2+ from water. The sorption characteristics of the HPLC column were investigated for Cu2+ in column agreement. The experiments were performed in five steps that were monitored using UV–visible diode-array detector. However, all the HPLC experimental results were reconfirmed by using atomic absorption spectrophotometer. The effect of concentration on the sorption efficiency of the column was evaluated for Cu2+ and data obtained was investigated using Langmuir and Freundlich sorption isotherms. The value of coefficient of determination (R2), i.e. 0.99, suggested that the Freundlich sorption isotherm was found to be the best fit model for Cu2+. The developed method was validated for system efficiency, accuracy, and precision, while the data obtained revealed that the develo...

This article describes a versatile application of 25,27-bis-N-(N,N-diethyl-2-aminoethyl)carbonylmethoxy-26,28-dihydroxycalix[4]arene (4) as an ionophore for the preparation of perchlorate ion-selective electrode. The electrode exhibits a Nernstian response over the perchlorate concentration range of 1.0×10−9 – 1.0×10−1 M with a slope of 59.24 ± 0.5 mV per decade of the concentration. The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration plot is 3.04×10−9 M. The electrode shows good selectivity toward perchlorate with respect to many common anions. The response time of the sensor was 5–10 s and it has maximum life time of 2 months in the acidic pH. The electrode was used to determine perchlorate in real water samples. The interaction of the ionophore with perchlorate ions is also demonstrated by UV–vis spectroscopy.

The present study demonstrates the successful transport of dyes specially methyl red (MR) using 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-dimethoxycalix[4]arene (1) derivative as a carrier in bulk liquid membrane (BLM). Extraction experiments were performed regarding the optimization of fundamental parameters including pH, decomplexation, dye, and salt concentration. The UV–visible data for stoichiometric ratio suggested 1:1 complexation, which is also verified by Benesi–Hildebrand equation. The high value of formation constant i.e. 8.2 × 104 mol/dm3 also suggested the strong complexation phenomenon between host and guest molecules. The transport of MR was performed through BLM under optimized conditions such as carrier concentration, type of solvent, and stirrer speed. The kinetic parameters (k1, k2, , tmax, , ) for MR transfer were examined by following kinetic laws of two consecutive irreversible first order reactions. The MR transport was augmented by rise in carrier (1) concentration ...

KEYWORDSCalixarene;Immobilization;Silica resin;Direct azo dye;Solid-phase extraction;Batch-wise sorptionAbstract The present study demonstrates the adsorption of the direct black-38 (DB-38) azo dye onpotential and newly synthesized p-tert-butylcalix[6]arene based silica resin (4). Resin 4 was synthe-sized via the modification of pure silica 1 as 2 followed by the immobilization of p-tert-butylca-lix[6]arene (3) onto modified silica (2). It was characterized by using different analyticaltechniques such as FT-IR, scanning electron microscopy (SEM) and thermo gravimetric analysis(TGA). The effect of adsorbent dosage, pH and the electrolyte effect on the removal of the DB-38 azo dye were evaluated through batch wise adsorption experiments. Maximum adsorption of91% was achieved at pH 9.0. The textile wastewater samples were used to ensure the field applica-bility of the newly synthesized adsorbent 4 for the treatment of dye contaminated effluents. Allresults regarding the removal of the DB-38 azo dye from the aqueous environment prop up resin4 as an effective adsorbent and it was found that resin 4 has high adsorption efficiency towardthe DB-38 azo dye at a wide range of pH as compared to 1 and 2.a 2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.

Calixarenes are well known for their molecular recognition properties. Thus, the present study was carried out to explore their usage in the isolation of flavonoids [i.e. quercetin (I) and catechin (II)] from plant extracts, e.g. Alhagi camelorum through metal complexation. The synthesis of flavonoid metal complexes from plant extracts through direct complexation and their purification by using calix[4]arene based resin (R-1) was carried out simultaneously to ensure the separation efficiency of R-1. It was observed that the direct complexation of flavonoids present in plant extracts and purification using a column loaded with R-1 could be the best choice for industries requiring the isolation and purification of flavonoids or their complexes from plants.

The present article describes formation of excipient-CRL complex from water soluble calix[4]arene derivative ( 3 as excipient) and Candida rugosa lipase (CRL), which is proposed as a reusable form of enzyme that is free from steric and diffusion limitations associated with those enzymes immobilized onto porous solid supports. The excipient-CRL could completely hydrolyze 50 mM p -nitrophenyl palmitate ( p -NPP) in Tris–HCl buffer at a wide range of temperatures, i.e. 30–80 °C. It is stable under stirred conditions and could be reused multiple times without loss of enzyme activity. It was observed that excipient-CRL complex shows a significant effect on the enzyme activity with an enhancement in thermal stability, while pH and temperature affect the activity of excipient-CRL as well as free CRL. Consequently, the excipient-CRL was found more active than free CRL for the hydrolysis of p -NPP in respect of its reusability.

The present study deals with the preconcentration and determination of toxic metal ions using p-tetranitrocalix[4]arene (3) appended silica-based new HPLC column. The synthesized material was characterized using Fourier transform infrared and scanning electron microscopy techniques. The sorption characteristics of the HPLC column were investigated for three toxic metals (Cd2+, Hg2+ and Pb2+) in column agreement. The experiments were performed in five steps that were monitored using a UV–visible diode-array detector. However, all the HPLC experimental results were reconfirmed by using atomic absorption spectrophotometer. The effect of concentration on the sorption efficiency of the column was evaluated for all the three metals and the data obtained were investigated using Langmuir, Freundlich and Dubinin–Redushkevich (D–R) sorption isotherms. The value of coefficient of determination (R 2), i.e. 0.99, suggested that the Freundlich sorption isotherm was found to be the best-fit model for all the three toxic metal ions, whereas, mean free energy was calculated from the D–R isotherm as 5.3, 5.7, and 5.8 kJ/mol for Pb2+, Cd2+, and Hg2+, respectively; suggesting that physical electrostatic force is involved in the sorption process. The developed method was validated for system efficiency, accuracy, and precision.

The present article represents synthesis and As(III) sorption behavior of a novel calix[4]arene-appended functional material (DE-4 resin). The sorption ability of DE-4 resin has been evaluated at wide range of pH, i.e., pH 2–14. It has been observed that the DE-4 resin possesses greater interaction for As(III) with maximum sorption capacity (88 % at pH 4). Column sorption mechanism was studied through various parameters, i.e., change in concentration, flow rate, and bed heights. The results obtained by changing these parameters were compared with the theoretically calculated. From the results it has been observed that DE-4 resin has maximum column efficiency of 412 μg g−1. Thermal behavior of the synthesized DE-4 resin was examined at various temperatures from 298 to 338 K, which shows that column efficiency increases with increase in temperature. From the DSC study it has been observed that DE-4 resin is stable up to 439 K. Concerning regeneration ability DE-4 resin was found to be regenerable and best regeneration was achieved using 5 % solution of HNO3/NaOH. It can be deduced from the study that the resin will find its applicability in small as well as industrial-scale water purification plants.

A bulk liquid membrane (BLM) experiment was carried out to check the Cu(II) transport efficiency of p-morpholinomethylcalix[4]arene (1) which was used as carrier. Liquid/liquid extraction experiments were also carried out to check the extraction and decomplexation efficiency of carrier 1. It has been observed that the maximum amount of Cu(II) was transported at pH = 12. The mass transfer of Cu(II) was analyzed on the basis of kinetic laws of two consecutive irreversible first order reactions. Thus, the kinetic parameters studied for the transport of Cu(II) were k1, k2, . BLM study revealed that Cu(II) transport increase with increase in concentration of carrier 1 from 1 × 10−5 to 1 × 10−4 M, rise in temperature from 298 to 308 K and at high stirring speed from 90 to 800 rpm. The effect of binary solvents on Cu(II) transport through BLM has also been studied. The values of k1, k2, decrease in the order of dichloromethane-hexane > dichloromethane-diethylether > dichloromethane > dichloromethane-ethylacetate...

The present work describes the synthesis of new 5,11,17,23-tetrakis[(propylthio)methyl]-25,26,27,28-tetrahydroxycalix[4]arene (3) based impregnated resin, its characterization, and sorption behavio...

The present article demonstrates the synthesis of p-tetraaminocalix[4]arene- and p-tetrathioureacalix[4]arene-based resins (4 and 5). The resins (4 and 5) were characterized by using different analytical techniques such as FT-IR and elemental analysis. In addition, their comparative fluoride sorption study was conducted and it was observed that 5 is highly efficient for the removal of fluoride from aqueous media at a wide range of pH as compared to 4. Consequently, on the basis of kinetic and thermodynamic studies, the pseudo first-order, pseudo second-order, entropy, enthalpy, and Gibbs free energy of fluoride sorption onto resin 5 were calculated. The experimental data were also evaluated by equations of isotherms used, i.e., Freundlich, Langmuir, and Dubinin–Radushkevich. The observations reveal that the sorption is favorable and confer the physiosorption interaction between resin 5 and fluoride.

The present study presents the adsorption behavior of p-tert-butyl-calix[4]arene based silica resin (4) for reactive black-5 (RB-5) and reactive red-45 (RR-45) azo dyes. The batchwise adsorption study was carried out to optimize various experimental parameters such as the effect of adsorbent dosage, pH, electrolyte, contact time, temperature and dye concentration. The maximum adsorption of RB-5 and RR-45 was achieved at pH 9 and pH 3, respectively. The kinetic studies revealed that the adsorption process followed the pseudo-second-order kinetic model. The positive and negative values of ∆H and ∆G demonstrated that the nature of adsorption process was endothermic and spontaneous. The adsorption behavior was analyzed by Langmuir and Freundlich isotherms. The values of correlation coefficients (R2) showed that the Freundlich isotherm model found to be best fit. Results of study showed that resin 4 proved to be highly effective for the removal of selected azo dyes.

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.

The present article describes an exploration regarding Hg(II) selective complexation behavior of 5,11,17,23-tetrakis[(N,N-dimethylamino)methyl]-25,26,27,28-tetrahydroxycalix[4]arene (4). The binding affinity of 4 toward selected transition metal ions such as Cd(II), Co(II), Cu(II), Hg(II), Ni(II), Pb(II) and Zn(II) have been investigated by UV-visible and fluorescence spectroscopies. From the results it has been noticed that 4 confers a pronounced preference for Hg(II) in complexation phenomenon even in the presence of other metal ions. The results of Job's plot analysis reveal 1:1 host-guest complex formation between Hg(II) and 4. The FT-IR spectroscopy also supports the complexation affinity of 4 for Hg(II).

The article describes transport of Pb(II) through bulk liquid membrane (BLM) containing calix[6]arene hexaester derivative (1) as a carrier. The effect of various parameters such as temperature, carrier concentration, stirring speed and type of solvent on the Pb(II) transport efficiency of the carrier through BLM was evaluated. The activation energy values for the extraction and re-extraction were found as 56.33 kJ mol−1 and 14.79 kJ mol−1, respectively. These values demonstrate that the process is diffusionally controlled by Pb(II). Observations indicate that the membrane entrance and exit rate constants (k1, k2) increase with increasing stirring speed as well as carrier concentration and decrease with increasing temperature. The effect of solvent on k1 and k2 was found to be in the order of CH2Cl2 > CHCl3 > CCl4.

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.

The article describes the synthesis and extraction properties of a new chiral calix[4]arene Schiff base ligand 5, which has been synthesized from 5,17-diformyl-25,27-bis-(4-nitrobenzyloxy)-26,28-dihidroxycalix[4]arene (4) by treatment with (S)-(-)-1-phenylethylamine. In this synthesis, it was thought to explore the role of chiral, as well as Schiff base sites in the recognition of targeted species ions (such as dichromate anions) as well as neutral/chiral molecules. At low pH, the ligand 5 is more effective for transferring the dichromate anions from an aqueous into a dichloromethane layer; may be due to the protonation of nitrogen atoms. The extraction properties of ligand 5 towards the some selected α -amino acid methylesters are also reported. However, the ligand 5 did not display any selectivity towards the selected α-amino acid methylesters.

This article displays the synthesis of N-(2-tosylato)ethylpiperazine (ii) and 5,11,17,23-tetra-tert-butyl-25,27-bis-(2-piprazinoethyl)-26,28-dihydroxycalix[4]arene (3). Compounds (ii) and 3 were characterized through elemental analysis, FT-IR, 1H NMR and/or 13C NMR studies. The transition metal cations (Hg2+, Co2+, Ni2+, Cu2+, and Cd2+) and dichromate anion were studied by liquid–liquid extraction experiment. The results showed that compound 3 has moderate but selective extraction ability for Hg2+ and dichromate anion. Comparison between extraction properties of compound 3 with previously reported 5,11,17,23-tetra-tert-butyl-25,27-bis(isoniazidylcarbonylmethoxy)-26,28-dihydroxy-calix[4]arene (4) and protonated pyridinium form of 4 (5) is also described.

In this article unique sensor and extraction properties of p -morpholinomethylcalix[4]arene ( 3 ) has been explored. In the first phase, we have studied the complexation/sensing behavior of ligand 3 toward essential as well as beneficial metals such as Cu 2+ , Co 2+ and Ni 2+ by UV–vis and fluorescence techniques. Secondly, we have applied Pederson method for the extraction of these metal cations using their picrates in two-phase extraction experiments. From the results it has been deduced that 3 could serve as a versatile sensor for the detection of metal cations used in the experiments. Besides this, it may be employed as an ionophore for significant extraction of these metal ions in separation/transportation systems.

The article describes a convenient synthesis and Cr(VI) extraction efficiency of a novel p-tert-butylcalix[8]areneoctamide impregnated Amberlite (XAD-4) resin. Using p-tert-butylcalix[8]arene macrocyclic building block, two strategies have been developed; i.e., derivatization of p-tert-butylcalix[8]arene framework with sophisticated ionophoric groups having efficiency to extract oxoanions from aqueous media and, impregnation of p-tert-butylcalix[8]arene derivative onto the polymeric support. Liquid-liquid and solid-liquid extraction experiments have been performed to evaluate the Cr(VI) extraction efficiency of both p-tert-butylcalix[8]arene derivative and the impregnated resin. From the results, it has been deduced that solid-phase extraction method is more convenient and efficient than liquid-liquid extraction process. The impregnated XAD-4 resin has been found regenerable with better extracting efficiency as compared to the simple p-tert-butylcalix[8]areneoctamide ionophore.

The selective behavior of calix[n]arene ester derivatives in two-phase extraction systems using polarographic technique has been investigated. Calix[4]arene tetraester derivative shows remarkable Na+ over Pb2+ selectivity; whereas calix[6]arene hexaester derivative shows Pb2+ over Na+ selectivity. The interference of some selected cations (Na+, K+, Cu2+ and Mg2+) were also examined and no significant effect on the selectivity behavior as well as extraction ability of these ionophores was found except Na+. The study reveals for the first time that the calix[6]arene hexaester derivative is highly Pb2+ selective ionophore and can be employed in the field of sensor as well as separation science and technology. The work also highlights the usefulness of polarographic technique in trace metal determination.

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. © 2008 Elsevier B.V. All rights reserved.

The article describes the syntheses and extraction properties of two p‐tert‐butylcalix[6]arene nitrile derivatives (3 and 4). The trinitrile derivative 3 has been synthesized from 5,11,17,23,29,35‐hexa‐tert‐butyl‐37,38,39,40,41,42‐hexahydroxycalix[6]arene 1. The compound 1 was directly converted to its hexanitrile derivative 4. In these syntheses, it was thought to explore the role of nitrile sites in the extraction of various metal cations and HCr2O7 −/Cr2O7 2− anions. The liquid‐liquid extraction properties of 3 and 4 towards selected alkali/transition metal cations and HCr2O7 −/Cr2O7 2− anions are reported. It has been observed that receptor 3 does not extract alkali/transition metal cations effectively, but shows affinity towards HCr2O7 −/Cr2O7 2− anions at low pH. The compound 4 is an effective form for transferring Ni2+ selectively, while it shows poor transferring ability for HCr2O7 −/Cr2O7 2− anions from an aqueous into a dichloromethane layer. It was observed that the cavity size of the calix[n]a...

The article describes the syntheses and complexation properties of new calixarene-based extractants, which have been synthesized from 5,11,17,23-tetra-tert-butyl-25,26,27-tris(chlorocarbonylmethoxy)-28-hydroxycalix[4]arene and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(chlorocarbonylmethoxy)calix[4]arene by treatment with isoniazid (isonicotinic acid hydrazide) in the presence of pyridine, respectively. p-tert-Butylcalix[4]arene teraamide was converted to its methyl iodide salt by refluxing with methyl iodide in acetonitrile. In this synthesis it was thought to explore the role of pyridinium sites in the extraction of HCr2O7−/Cr2O72− anions. The complexing properties of the extractants toward selected alkali/transition metal cations and HCr2O7−/Cr2O72− anions are reported. It has been observed that both receptors do not extract alkali metal cations but show excellent selectivity toward transition metals. The protonated pyridinium forms of the receptors are effective for transferring the HCr2O7−/Cr2O72− anions from an aqueous into a dichloromethane layer.

Dye wastewater causes serious health problems that may not be solved by traditional methods. The present study deals with the removal of methyl violate (MV), methyl green (MG), and methyl blue (MB) by highly efficient and regenerable calix[4]arene based impregnated material from aqueous media. The material was characterized by different analytical techniques. Both batch and column sorption methods were used and various parameters including pH, adsorbent dosage, initial concentration, equilibrium time, temperature, and electrolyte were optimized. The kinetic and thermodynamic parameters were also evaluated. The material was 99% effective to remove these dyes from real wastewater samples. Recovery of the material and dye was achieved with 5% HCl that signifies reusability of the material again and again.

This approach disclose the selective fluorogenic ion sensing ability of 5,11,17,23-tetratertbutyl-25,27-bis((2hydroxynaphthylimino)1,2-ethylenediaminecarbonylmethoxy)-26,28 dihydroxycalix[4]arene (C4NSB). Binding property of receptor probed by using selected various cations and anions with conferring of results that demonstrates 'turn-off' fluorescence response and significantly high chromogenic selectivity toward Au(3+) and I(-). Furthermore, selective nature of receptor was investigated in the presence of different co-existing competing ions. The limit of detection (LOD) for Au(3+) and I(-) was determined as 1.5 × 10(-5) and 4.5 × 10(-6) M respectively. Receptor C4NSB form (1:1) stoichiometric complex with both ions and their binding constants were calculated as 8.0 × 10(2) for Au(3+) and 15.6 × 10(2) M(-1) for I(-). Complexes were also characterized through FT-IR spectroscopy.

Three new calix[4]arene based polymeric resins (6, 7 and 8) have been synthesized via nucleophilic substitution reactions involving 5,11,17,23-tetrakis-[(N,N-dimethylamino)methyl]-25,26,27,28-tetrahydroxycalix[4]arene 3, and 5,11,17,23-tetracyanomethyl-25,26,27,28-tetrahydroxycalix[4]arene 4 as precursors with a Merrifield resin. The extraction studies were made by using liquid–liquid extraction, solid–liquid batchwise and packed-column sorption procedures, and effect of different anion to extraction of dichromate anion was examined by using NO 3 - , Cl−, SO 4 2 - and their mixtures. The experimental results showed that these calix[4]arene based polymeric resins have high extraction abilities towards Na2Cr2O7 as compared to their monomeric precursors, and also dichromate anion was extracted in high ratios even in presence of different anions.

This article describes the synthesis and characterization of two new calix[4]arene Schiff bases and their polymeric resins. The extraction properties of these “proton switchable extractants” with alkali, transition, post transition metal cations and for dichromate anions are reported. The two new calix[4]arene based Schiff bases (5 and 6) have been synthesized from 5,17‐diformyl‐25,27‐dipropoxy‐26,28‐dihydroxycalix[4]arene (4) by treatment with 3‐amino‐methylpyridine and 1,8‐diaminooctane in two separate reaction flasks following the same procedure. Compounds 5 and 6 have been appended to a polymeric resin by treatment with Merrifield resin through a nucleophilic substitution reaction. The receptor compounds (3 and 5–8) do not extract alkali metal cations, but show some selectivity toward transition metal cations, and a particularly high selectivity to Hg2+ and Pb2+. The protonated forms of all of the calixarene‐based receptors are good extractants for transferring Cr2O7 2−/HCr2O7 − anions from an aqueous...

The article describes the synthesis and extraction properties of new alkylnitrile and alkylbenzonitrile substituted calix[4]arene based polymers. These compounds have been synthesized via nucleophilic substitution reactions involving 5,11,17,23-tetra-tert-butyl-25,27-bis-(cyanomethoxy)-26,28-dihydroxycalix[4]arene (2a), 5,11,17,23-tetra-tert-butyl-25-(2-cyanobenzyloxy)-26,27,28-trihydroxycalix[4]arene (3a), or 5,11,17,23-tetra-tert-butyl-25,27-bis-(2-cyanobenzyloxy)-26,28-dihydroxycalix[4]arene (4a), with Merrifield’s resin (0.8 mM Cl/1.0 g resin). The two-phase extraction properties of ligands 2a–4a along with their polymers 2b–4b toward the selected metal cations and dichromate ( HCr 2 O 7 - / Cr 2 O 7 2 - ) anions are reported. Extraction studies with monomer 2a show selectivity for Hg2+, where as monomers 3a and 4a are selective for Cd2+ and Hg2+ cations. Nevertheless, due to the higher oxidative stability of nitrile groups, polymers 2b–4b have been developed as good extractants for transferring the selected metal cations and dichromate ( HCr 2 O 7 - / Cr 2 O 7 2 - ) anions from an aqueous into a dichloromethane phase.

This article describes a convenient method for the synthesis of two new polymeric resins via nucleophilic substitution reactions involving 5,11,17,23-tetrakis[(propylthio)methyl]-25,26,27,28-tetrahydroxycalix[4]arene 4 , and 5,11,17,23-tetrakis[(methylthio)methyl]-25,26,27,28-tetrahydroxycalix[4]arene 6 , as precursors with Merrifield's resin. The extraction studies were made using both liquid–liquid extraction and solid–liquid batchwise sorption procedures. The calix[4]arene based polymeric resins have high extraction ability toward metal cations and Na 2 Cr 2 O 7 as compared to their monomeric precursors.

The present work describes the synthesis of a new monomeric dibenzonitrile derivative of p‐tert‐butylcalix[4]arene containing a polymerizable group at its lower rim. This monomer with an acryl amide group has been copolymerized with styrene yielding a linear polymer with pendant calixarene groups. Extraction studies with this monomer and its copolymer show no selectivity for metal cations. Nevertheless, dibenzonitrile groups with calixarene moiety provide a suitable binding site for transferring metal salt (NaHCr2O7) as an ion‐pair.

The article describes the syntheses and extraction properties of new alkylnitrile and alkylamino substituted calix[4]arene based copolymers. These compounds have been synthesized via nucleophilic substitution reactions involving 5,11,17,23‐tetra‐tert‐butyl‐25,27‐bis(cyanomethoxy)‐26,28‐dihydroxycalix[4]arene (3), or 25,27‐bis(cyanomethoxy)‐26,28‐dihydroxycalix[4]arene (4) with 1,5‐dibromopentane and bisphenol‐A, followed by their reduction with sodium borohydride in the presence of CoCl2 · 6H2O. In addition an oligomer containing pendant calix[4]arene units with nitrile functionalities on its lower rim has been synthesized via nucleophilic reaction involving 5,11,17,23‐tetra‐tert‐butyl‐25,27‐bis(cyanomethoxy)‐26,28‐dihydroxycalix[4]arene 3 with p‐dibromoxylene. The extraction properties of polymers 5–9 toward the HCr2O7 − anion are also reported. Due to the higher oxidative stability of nitrile groups, polymers 5–7 have been developed as good extractants for transferring the HCr2O7 − anion from a...

A convenient synthesis and Cr(VI) extraction properties of a new calix[4]arene-based receptor (5), which has been synthesized from 5,17-diformyl-25,27-dimethoxycarbonylmethoxycalix[4]arene (4) by treatment with 3-aminomethylpyridine in one step, are described. The receptor 5 contains four pyridinyl groups, two on each rim. Two of them are joined by an amide linkage onto the lower rim, and other two are linked by an imine-type linkage onto the upper rim of the calix[4]arene moiety. Receptor 5 is very soluble in water at low pH (

The synthesis of the cone conformers of 5,11,17,23-tetra-tert-butyl-25,27-bis[(4-nitrobenzyloxy)-26,28-dihydroxy]-calix[4]-arene (2), 5,11,17,23-tetra-tert-butyl-25,27-bis[(4-nitrobenzyloxy)]calix[4]arene-crown-6 (3) and 5,11,17,23-tetra-tert-butyl-25,27-bis[(4-aminobenzyloxy)]calix[4]arene-crown-6 (4) containing polymerizable side arms, along with their oligomeric analogue 5, is reported. Extraction studies with monomers 3 and 4 and the oligomer 5 show no difference in their extraction behavior and selectivity, whereas, ionophore 2 is a poor extractant for alkali metal cations. These observations suggest that, substitution of side arms on the lower rim of calix moiety can enhance the calix[4]-crown-6 cone conformers function to extract alkali metal cations in two phase extraction systems.

Four new calix(aza)crown oligomers (5–8) have been synthesized by reacting p-tert-butylcalix[4](aza)crowns (3 and 4) with triethylene glycol ditosylate or 1,5-dibromopentane. Their phase transfer studies were performed by using liquid–liquid extraction procedure. It has been deduced from the observations that, the oligomers 5 and 7 are good extractants, whereas, oligomers 6 and 8 show different extraction behavior toward selected alkali (Li+, Na+, K+, Cs+) and transition metal cations (Ni+2, Cu+2, Co+2, Cd+2, Hg+2, Pb+2).

Three newly synthesized polymer supported calix[4]arene ionophores (7–9) were synthesized, and their ion binding properties toward selected alkali (Li+, Na+, K+, Cs+) and transition metal (Hg2+, Ni2+, Cu2+, Co2+, Cd2+, and Pb2+) cations were investigated. It has been observed that these ionophores are not selective toward a particular metal cation but show better ion binding property as compared to monomeric calixarene derivatives (2 and 6). Ionophore 6 and its supported polymer were also employed in dichromate anion extraction experiments. The polymeric ionophore (9) was found an effective extractant for dichromate anion even at pH 7.

A new oligomeric calix[4]arene-thiacrown-4 (5) was synthesized via a condensation reaction of 5,11,17,23-tetra-tert-butyl-25,27-bis-(4-aminobenzyloxy)-calix[4]arene-thiacrown-4 (4) with adipoyl dichloride. In this oligomerization reaction only five/six calix[4]arene-thiacrown-4 units were linked in the oligomeric chain. The complexation studies of 5 were made with liquid–liquid- extraction and solid–liquid-sorption procedures. For comparison, the extraction efficiencies of monomers 1, 3, and 4 to selected transition metals are reported. The selectivity of monomers 3 and 4 toward Cu2+, Hg2+, and Pb2+ was lost after oligomerization in the two-phase extraction systems. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 186–193, 2004

In this study the selective derivatization of p-tert-butylcalix[4]arene was carried out and two new calix[4]arene-based azacrown ionophores, 5,17-di-tert-butyl-11, 23-di-(methyl-3,5-dioxaoctane-1,8-diimine)-25,26,27,28-tetrahydroxycalix[4]arene ( 6 ), and 5,17-di-tert-butyl-11,23-di-(methyl-3,5-dioxaoctane-1,8-diimine)-25,27-diethoxyformyl-methoxy-26,28-dihydroxycalix[4]arene ( 7 ) have been synthesized. Treatment of 5,17-di-tert-butyl-11,23-diformylcalix[4]arene-25,26,27,28-tetrol ( 5 ) with 1,8-diamino-3,6-dioxaoctane gave the ionophore 6 which was converted to its diester derivative 7 by reaction with ethylbromoacetate in the presence of potassium carbonate. In the synthesis, the upper and lower rims of p-tert-butylcalix[4]arene were modified in order to acquire binding sites for the recognition of metal cations and dichromate anions. It was observed that receptor 7 is a better extractant for Cr2O72− anions than receptor 6 . The protonated alkylinium form of 7 is an effective extractant for transferring the Cr2O72− anions from aqueous into a dichloromethane layer and failed in transferring Na+ cations due to the allosteric effect produced by the crown part of the calix moiety present at the p-position.

A new Schiff-base type oligocalix[4]arene containing two nitrile ligating sites at narrow rim was synthesized via a simple condensation reaction through a wide rim of the calixarene moiety. The extraction ability of the oligomer with selected alkali and transition metals is compared with its monomeric analogous. It has been observed that the oligomer 6 is not selective as compared to its analogae 2 and 3, but shows a remarkable high affinity towards toxic metal cations such as Cu2+, Hg2+ and Pb2+.

Two different oligomeric calix[4]arene-crowns ( 2b and 3b ) were synthesized ( via ) the condensation reaction of p- tert -butylcalix[4]arene-oxacrown-4 ( 2a ) and p- tert -butylcalix[4]arene-thiacrown-4 ( 3a )(calix[4]arene-crown monomers) with 1,5-dibromopentane. In these oligomerization reactions, it has been found that only three or four calix[4]arene-crowns-4 units have been linked together through alkyl bridges. Their comparative complexing properties with selected alkali and transition metals are reported here. It has been deduced that the selectivity of monomer 2a toward alkali metals has not been reserved, but a pronounced increase in its complexing ability was observed after the oligomerization. However, the selectivity of the monomer 3a toward Cu 2+ , Hg 2+ , and Pb 2+ has also been lost after oligomerization, and it has been found that oligomer 3b is an efficient extractant for the transition metal cations employed in the two-phase extraction systems.

The article describes the syntheses and extraction properties of two new calixarene based receptors ( 3 and 4 ); the receptor 3 was synthesized from 25,27-diacetonyloxy-26,28-dihydroxy-5,11,17,23-tetra- tert -butylcalix[4]arene 2 by treatment with tetraethylene glycol ditosylate and then the compound 3 was converted to its Schiff base derivative 4 by refluxing 3 with 1,8-diamino-3,6-dioxaoctane. In the synthesis, the lower rim of p - tert -butylcalix[4]arene has been modified in order to acquire soft and hard binding sites for the recognition of metal cations and Cr 2 O 7 2− anions. The complexing properties of 3 and 4 toward selected alkali, transition metal cations and Cr 2 O 7 2− anions are reported. It has been observed that receptor 4 is a better extractant for all metal cations, but not selective as compared to the receptor 3 . The protonated alkylinium form of 4 is an effective extractant for transferring the Cr 2 O 7 2− anions from an aqueous into a dichloromethane layer.

Three new polymers containing pendant calix[4]crown-4 units have been synthesized via radical initiated reactions involving a vinylic monomer 7 (5,7,11,23-tetra- tert -butyl-25-[2-(Acryloxy)ethoxy]-27-methoxycalix[4]arene-crown-4) and with styrene. A five atom spacer group was incorporated between the bulky calixarene core and the acrylate moiety in order to minimize steric interactions which proved to impede the polymerization. The complexation studies were made by using liquid–liquid and solid–liquid extraction procedures. It has been deduced from the observations that the precursor 5 (5,7,11,23-tetra- tert -butyl-25-hydroxy-27-methoxycalix[4]arene-crown-4) is selective for Hg 2+ , whereas the polymers are not selective but better extractants for all used metal cations. The extraction data support the conformational change of the calix[4]crown from cone to the other various conformations of calixarene moiety.

A series of different bridged biscalix[4]arenes in which the lower rims are linked via a single site on each calixarene were synthesized and converted to their alcoholic, ketonic, and esteric derivatives. Their complexing abilities were studied by the liquid–liquid extraction of selected alkali (Li+, Na+, K+, Cs+) and transition (Cu2+, Co2+, Cd2+, Ni2+, and Hg2+) metal cations. Through extraction examination it has been deduced from the observations that the alcoholic derivatives are very poor extractants as compared to the ketonic and esteric derivatives. The ketonic derivative is selective for Hg2+, whereas the esteric derivative is not selective but a good extractant and showed higher affinity towards Na+, Cu2+, Co2+, and Hg2+. The results indicate that the ligands containing π-system functional groups and having a proper conformation of calixarene cavity form novel binding sites for the comlexation of metal cations.