Synthesis and characterization of three novel azocalix[4]arene Schiff base derivatives and their selective copper extraction

The synthesis and characterization of three novel Schiff bases of azocalix[4]arene and their selective copper extraction are described. The preparation of azocalix[4]arenes (1c, 2c and 3c) has been achieved by the condensation of 2-hydroxy-3-methoxybenzaldehyde with the amine group of upper rim mono-, di- and tetra-(aminophenylazo) calix[4]arene in ethanol. The synthesized products (1c, 2c and 3c) are characterized by both ¹H and ¹³C NMR techniques, IR spectroscopy and elemental analysis. Extraction capabilities of interested derivatives of azocalix[4]arene from aqueous phase into organic phase are also examined. While extraction of Ag⁺, Hg⁺ and Hg²⁺ cations gave strong complexes with azo groups, extraction of Cu²⁺ cation is found to be highly effective with ?CCH=N?C and neighboring ?COH groups.     

Synthesis and spectral characterization of azo dyes derived from calix[4]arene and their application in dyeing of fibers

In this study, the synthesis and characterization of two new upper rim functionalized azocalix[4]arene dyes have been obtained by coupling calix[4]arene with different diazo compounds of 3,5-dicarboxyaniline and 4-aminobenzene sulphon amide. The characterization of these dyes has been carried out by elemental analysis, FT-IR and ¹H NMR spectra. The effect of varying dielectric constants of solvents on the absorption spectra of azocalix[4]arenes (1, 2, 3, 4) and commercial Isolan Gelb SGL (T) have been examined by UV–Vis spectrophotometer. These azocalix[4]arene dyes have also been used for dyeing textile fibers like cotton, wool, acetate, polyester and polyamide fibers. Their dyeing and fastness properties have also been discussed.     

Novel redox receptors for ion-pair and α-amino acid: synthesis and complexation properties of calix[4]arene derivatives bearing large conjugated ferrocene groups

By reacting calix[4]arene 1,3-bi-hydrazide derivative (2) with formacylferrocene in “1?+?2” condensation mode, novel calix[4]arene derivative bearing two conjugated ferrocene groups (3) was obtained in yield of 88%. By reacting 1,3-bi-substituted [2-(p-formylphenyloxy)ethyloxy]-p-tert-butylcalix[4]arene (5) with 1,1′-diacetylferrocene hydrazone (4) in “1?+?1” condensation mode, novel calix[4]arene derivative with 1,3-substituted large conjugated ferrocene bridge (6) was synthesized in yield of 83%. The structures and conformations of new compounds were confirmed by elemental analyses, IR spectra, ESI-MS, ¹H NMR, etc. The electrochemical cyclic voltammetry experiments revealed that compounds 3 and 6 possessed excellent reversible electrochemical properties. The ¹H NMR titration study showed that compound 6 possessed excellent complexation abilities for NaH₂PO₄ and glycine in 1:1 host–guest complex with the association constants of 3,850 and 2,460?M^?1, respectively.     

Syntheses of novel calix[4]arene hydrazone-based receptors and their cooperative complexation with soft and hard metal ions

Four novel calix[4]arene hydrazone-based receptors 3a?Cd were prepared in yields of 69?C87% by condensating formylated calix[4]arene ester (2) with salicylyl hydrazine, 2,4-dinitrophenyl hydrazine, nicotinyl hydrazine or phenyl thiosemicarhazide, respectively. New compounds were characterized through elemental analysis, IR, ESI?CMS, ¹H NMR studies. Compounds 3a?Cd containing two binding sites had the complexation abilities for hard and soft cations concurrently. The noncompetitive extracting experiments showed compounds 3a?Cd were excellent receptors for hard and soft metal cations. The competitive extracting experiments exhibited the cooperative complexation in binding hard and soft metal cations and compound 3a possessed outstanding selectivity for Na⁺ and Hg²⁺. The IR spectra of compound 3a before and after complexation revealed that the soft metal cation was binded in the cavity composed of hydrazone groups and azo groups at the upper rims of calix[4]arene units and hard metal cations was binded in cavity composed of ester groups and phenolic hydroxyl groups at the lower rims of calix[4]arene units.     

Azocalixarenes.8: synthesis and investigation of the absorption spectra of di-substituted azocalix[4]arenes containing chromogenic groups

The synthesis of series of chromogenic di-substituted azocalix[4]arene derivatives is described. A ketone moiety as a different chelating agent is grafted on the lower rim of p-tert-butylcalix[4]arenes. Eight novel azocalix[4]arenes (1–8) are prepared by linking 2-, 3- and 4-nitroaniline, 4-phenylazoaniline, 3- and 4-chloroaniline or 2- and 4-methylaniline to 25,27-diacetonyloxy-26,28-dihydroxy-11,23-di-(tert-butyl)calix[4]arene through a diazo-coupling reaction, and characterized by UV–Vis, FT-IR and ¹H-NMR spectroscopic techniques and elemental analysis, consecutively. The absorption spectra of the di-substituted azocalix[4]arenes are discussed, according to effect of varying pH and solvent upon the absorption ability of azocalix[4]arenes. The colors of these azocalix[4]arenes are compared with respect to nature of their aromatic rings and substituents there in. Concentration effects on the visible absorption maxima of these compounds are also reported.     

Synthesis and extraction abilities of mono-formylated calix[4]-1,3-aza-crown and its hydrazone derivatives

By formylation of calix[4]-1,3-aza-crown in hexamethylenetetramine/trifluoroacetic acid system, the first formylated calix[4]-aza-crown derivative 6 was synthesized in yield of 61%. Reacting compound 6 with salicyloyl hydrazine, 2,4-dinitrophenyl hydrazine, nicotinyl hydrazine or phenyl thiosemicarbazide afforded four novel calix[4]crown hydrazone derivatives 7a–d in yields of 70–90%. By condensating compound 6 with series of bifunctional reagents, the novel mono-bridged biscalix[4]-aza-crown hydrazone derivatives 8a–c were prepared in high yields. The extraction experiments showed that all new compounds were good receptors for metal cations, especially, for soft metal cations. The extraction results suggested that the hydrazone groups produced favorable influences for binding soft cations. The two calix[4]arene units in compounds 8a–c could bind metal cations concurrently.     

Syntheses and extraction properties of novel biscalixarene and thiacalix[4]arene hydrazone derivatives

By reacting thiacalix[4]arene with p-tosyloxyethoxylbenzaldehyde 1, 3-bis(benzaldehyde-4-oxyethyloxy)-p-tert-butylthiacalix[4]arene (2) were prepared in yield of 65%. Refluxing compound 2 with aniline, salicylic hydrazide, nicotinic hydrazide and isonicotinic hydrazide, novel ringopening 1,3-bis-arylformyl-hydrazone substituted thiacalix[4]arene derivatives (3a–3d) were obtained in yields of 77–89%. Refluxing compound 2 with o-phenylendiamine, oxalyl dihydrazide, malonic dihydrazide and adipic dihydrazide in “1 + 1” intermolecular condensation mode under diluted condition, novel 1,3-bis-acyl hydrazone-bridged calix[4]arene derivatives (4a–4d) were prepared in good yields. Moreover, by condensating compound 2 with 1,3-bis(hydrazinocarbonyl-methoxy)-p-tert-butylcalix[4]arene (5), the first example of hydrazone-bridged biscalixarene (6) with calix[4]arene and thiacalix[4]arene subunits was facilely synthesized in yield of 90%. The noncompetitive and competitive extracting experiments showed that these novel hosts were good receptors for both metal cations and α-amino acids. Compounds 3a–3d and 4a–4d showed similar binding properties with high extraction percentage but low extracting selectivities. Biscalixarene 6 exhibited not only high extracting abilities but also good extracting selectivities.     

Novel deep-cavity calix[4]arene derivatives with large s-triazine conjugate systems: synthesis and complexation for dyes

Two novel deep-cavity calix[4]arenes 3 and 4 with large s-triazine π-conjugate systems were designed and synthesized in high yields by reacting calix[4]arene with mono phenyl-substituted cyanuric chloride or further substitution with aniline. The liquid–liquid extraction experiment showed that they possessed excellent extraction abilities towards one cationic and three anionic dyes (Orange I, methylene blue, neutral red, brilliant green). The highest extraction percentage of compound 4 was 88.8 % for brilliant green. The complexation UV–Vis spectra of compounds 3 and 4 with four dyes indicated the existences of complexation action between hosts and guests with 1:1 ratio of complexation in DMSO solution. The association constants suggested that the larger π-conjugate system of compound 4 possessed the stronger complexation abilities than that of compound 3. The association constant of compound 4 with BG was as high as 8.1 × 10⁶ M^?1.     

Calix[4]azacrowns as ionophores for liquid?Cliquid extraction and facilitated transport of biological supramolecular complexes

The native and methyl ester amino acids have been extracted by calix[4]azacrowns 1 (1,3-[ethylene-bis-aminocarbonylmethoxy)]-p-tert-butylcalix[4]arene) and 2 (1,3-[propylene-bis-aminocarbonylmethoxy)]-p-tert-butyl-calix[4]arene) from an aqueous phase into a chloroform phase and transported through a chloroform liquid membrane as ion pairs in the presence of picrate or tropaeolin 00 as counter ions aiming their separation. The amino acids under study exhibited good extractability by calix[4]azacrowns 1 and 2. Both receptors 1 and 2 showed good extractability towards amino acids under study. The results are discussed in term of correlation of structural properties of amino acids and calix[4]azacrowns involved in experiments. In this respect, the influence of chain length of receptors upon extraction and transport of amino acids, and the nature of anions used as counter ions are evaluated.     

Synthesis of a glutaraldehyde derivative of calix[4]arene as a cross-linker reagent for lipase immobilization

This article describes the synthesis of a new calix[4]arene 1,3-distal glutaraldehyde derivative 4 as a cross-linker-reagent for immobilization of Candida rugosa lipase (CRL). p-tert-Butylcalix[4]arene 1,3-distal diaminoalkyl derivative (3) synthesized via aminolysis reaction of 5,11,17,23-tert-butyl-25,27-ethoxycarbonylmethoxy-26,28-hydroxycalix[4]arene (2) with 1,8-diaminooctane. Compound 3 was converted to its aldehyde derivative (4) by the treatment with glutaraldehyde solution. 4 was used in lipase immobilization in order to see the role of calix[4]arene binding site on the lipase activity and stability. It was observed that the immobilized lipase activity was maintained at levels exceeding 95% of its original activity after 40 min.     

Synthesis and oxoanions (dichromate/arsenate) sorption study of N-methylglucamine derivative of calix[4]arene immobilized onto poly[(phenyl glycidyl ether)-co-formaldehyde]

The article describes synthesis as well as the evaluation of sorption properties of new N-methylglucamine substituted calix[4]arene and its poly[(phenyl glycidyl ether)-co-formaldehyde] immobilized product. Firstly, 5,17-bis-[(N-methylglucamine)methyl]-25,26,27,28-tetrahydroxy-calix[4]arene (3) was synthesized by the treatment of calix[4]arene with a secondary amine N-methylglucamine and formaldehyde via Mannich reaction. The immobilization of 3 onto poly[(phenyl glycidyl ether)-co-formaldehyde] to form calixarene based polymer (4) was carried out under suitable reaction conditions via nucleophilic substitution reaction. All the new compounds were characterized by a combination of FT-IR, ¹H-NMR spectroscopic and elemental analysis techniques. The sorption studies of 4 reveal that it is an excellent material for the removal of toxic oxoanions especially arsenate from aqueous environment. To understand the selectivity of 4, we also examined the retention of dichromate anions in the presence of Cl^?, NO₃ ^? and SO₄ ^2? anions at pH 1.5.     

Synthesis and metal extraction studies of a novel chromogenic 5,17-bisazocalix[4]arenes

Three novel chromogenic cone azocalix[4]arenes 5a–c, which have cavity and the azo groups as metal-binding sites and as coloration sites were synthesized. They were studied by the liquid–liquid extraction of selected metal cations (Sr²⁺, Ag⁺, Hg⁺, Hg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cr³⁺, Al³⁺). Through examination of the extraction, a novel selectivity of these compounds toward Hg²⁺ cations has been determined. Besides, it has been also found that azocalix[4]arene 5c is highly sensitive to acid–base titration, which can be detected by the naked eye.     

Syntheses of two diamine substituted 1,3-distal calix[4]arene-based magnetite nanoparticles for extraction of dichromate, arsenate and uranyl ions

The synthesis of two new calixarene derivatives 4 and 5, functionalized at the lower rim with 4-amino-1-benzylpiperidine to give diamide and diamine derivatives of p-tert-butylcalix[4]arene, is described. They were obtained by the reaction of both the diester derivative of p-tert-butylcalix[4]arene (2) and the dialkyl bromide derivative of p-tert-butylcalix[4]arene (3) with 4-amino-1-benzylpiperidine. The ¹H NMR spectra of calixarene derivatives show that 4 and 5 exist in the cone conformation. Moreover, these diamide and diamine derivatives of p-tert-butylcalix[4]arene (4 and 5) have been immobilized onto [3-(2,3-epoxypropoxy)-propyl]-trimethoxysilane-modified Fe₃O₄ magnetite nanoparticles to obtain calixarene-based magnetic nanoparticles M-DADBP-Calix (6) and M-DABP-Calix (7). The calix[4]arene immobilized materials were characterized by a combination of Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM) and Thermogravimetric Analyses (TGA) and elemental analysis. Additionally, the studies regarding the removal of As(V)/Cr(VI) ions as well as U(VI) ion from aqueous solutions were also carried out by using these compounds in liquid-liquid/solid-liquid extraction experiments.     

Complexation of amino acids derivatives in water by calix[4]arene phosphonic acids

Series of the calix[4]arene phosphonic acids with various substituents at the lower rim was synthesized. Complexing properties of these receptors towards methyl esters of six amino acids strongly depended on the calix[4]arene conformation flexibility. The complex formation processes were monitored using ¹H NMR spectroscopy (deuterated phosphate buffer at pD 7.3, 22 °C) and association constant values were evaluated. Inherently mobile calix[4]arene molecule 3 occurred in cone conformation in aqueous solution turned out to be more effective in complexation of the basic amino acids methyl esters compared to the rigid 2 and flexible 4. Mixed 1:2 and 2:1 (host–guest) complexes were observed for compound 1 with all amino acids methyl esters.     

Synthesis, characterization and electrochemical properties of two new calix[4]arene derivatives bearing two ferrocene imine or ferrocene amine units at the upper rim

A novel calix[4]arene derivative with two ferrocenyl Schiff-base groups at the upper rim 3 has been synthesized from 5,17-diformyl-25,27-dipropoxy-26,28-dihydroxy calix[4]arene and 4-ferrocenylaniline via condensation reaction. Reduction of 3 with sodium borohydride led to calix[4]arene derivative 4 with two amino ferrocenyl groups at the upper rim. The ferrocenyl Schiff-base calix[4]arene and its corresponding reduced amine have been purified and characterized by elemental analysis,¹H NMR, FTIR, Mass and UV-vis spectral data. Electrochemical properties of compounds 3 and 4 have been investigated. Cyclic voltammograms of 3 and 4 show reversible redox couples of ferrocene/ferrocinium at E_1/2=0.401 V and 0.346 V, respectively. Electrochemical studies show these redox active compounds electrochemically recognize trivalent lanthanides La³⁺ and Ce³⁺ and divalent Pb²⁺ and Cu²⁺cations. With ferrocenyl Schiff-base calix[4]arene 3 an anodic shift as large as 130 mV is observed on addition of one equivalent of Ce³⁺ ion. Also extraction properties of compound 4 towards some metal cations have been described. It has been observed that compound 4 has a good selectivity for metal cations Fe³⁺, Cu²⁺, Pb²⁺ and Cd²⁺ against Ni²⁺ and Co²⁺.     

Phosphite ligands derived from distally and proximally substituted dipropyloxy calix[4]arenes and their palladium complexes: Solution dynamics, solid-state structures and catalysis

Two bisphosphite ligands, 25,27-bis-(2,2′-biphenyldioxyphosphinoxy)-26,28-dipropyloxy-p-tert-butyl calix[4]arene (3) and 25,26-bis-(2,2′-biphenyldioxyphosphinoxy)-27,28-dipropyloxy-p-tert-butyl calix[4]arene (4) and two monophosphite ligands, 25-hydroxy-27-(2,2′-biphenyldioxyphosphinoxy)-26,28-dipropyloxy-p-tert-butyl calix[4]arene (5) and 25-hydroxy-26-(2,2′-biphenyldioxyphosphinoxy)-27,28-dipropyloxy- p-tert-butyl calix[4]arene (6) have been synthesized. Treatment of (allyl) palladium precursors [(η³-1,3-R,R′-C₃H₄)Pd(Cl)]₂ with ligand 3 in the presence of NH₄PF₆ gives a series of cationic allyl palladium complexes (3a-3d). Neutral allyl complexes (3e-3g) are obtained by the treatment of the allyl palladium precursors with ligand 3 in the absence of NH₄PF₆. The cationic allyl complexes [(η³-C₃H₅)Pd(4)]PF₆ (4a) and [(η³-Ph₂C₃H₃)Pd(4)]PF₆ (4b) have been synthesized from the proximally (1,2-) substituted bisphosphite ligand 4. Treatment of ligand 4 with [Pd(COD)Cl₂] gives the palladium dichloride complex, [PdCl₂(4)] (4c). The solid-state structures of [{(η³-1-CH₃-C₃H₄)Pd(Cl)}₂(3)] (3f) and [PdCl₂(4)] (4c) have been determined by X-ray crystallography; the calixarene framework in 3f adopts the pinched cone conformation whereas in 4c, the conformation is in between that of cone and pinched cone. Solution dynamics of 3f has been studied in detail with the help of two-dimensional NMR spectroscopy.The solid-state structures of the monophosphite ligands 5 and 6 have also been determined; the calix[4]arene framework in both molecules adopts the cone conformation. Reaction of the monophosphite ligands (5, 6) with (allyl) palladium precursors, in the absence of NH₄PF₆, yield a series of neutral allyl palladium complexes (5a-5c; 6a-6d). Allyl palladium complexes of proximally substituted ligand 6 showed two diastereomers in solution owing to the inherently chiral calix[4]arene framework. Ligands 3, 6 and the allyl palladium complex 3f have been tested for catalytic activity in allylic alkylation reactions.     

Synthesis, structure and property of three divalent metal complexes of the piperidinoacetyl-containing calix[4]arene

Three new mononuclear complexes [Cd(L)](ClO₄)₂·4(MeCN) (1) (L?=?5,11,17,23-tetra-t-butyl-25,26,27,28-tetrakis(piperidinocarbonylmethoxy)calix[4]arene), [Zn(L)](ClO₄)₂·4(MeCN)·CH₂Cl₂ (2), [Cu(L)](ClO₄)₂·3(MeCN)·Et₂O (3) have been synthesized and characterized by elemental analysis and X-ray single crystal diffraction (CCDC: 838342, 838343 and 838344). The results of the crystal structural analyses show that calix[4]arene backbones in 1, 2, 3 are fixed in the cone conformation while the divalent metal cations (Cd, Zn and Cu) are coordinated with the discrepant geometry. The cadmium ion in 1 is eight-coordinated with four carbonyl oxygen atoms and four ethereal oxygen atoms in the low rim of calix[4]arene, whereas zinc ion in 2 and copper ion in 1 are four-coordinated with the acyl oxygen atoms. The atomic net charges distribution and frontier molecular orbital energies were obtained by Gaussian 98 program with DFT method at B3LYP/lanl2dz level. Furthermore, the SOD-like activities of 3 were measured by xanthine/xanthine oxidase-NBT assay at pH 7.2 and 7.8.     

Metal ions recognition by 1,2,3-triazolium calix[4]arene esters synthesized via click chemistry

Two triazole-modified calix[4]arene diesters were synthesized via Huisgen 1,3-dipolar cycloaddition between azides esters and alkynylcalixarenes. Their structures had been deduced from ¹H NMR, element analysis and ESI-MS. Two-phase extraction experiments indicated that triazole-modified calix[4]arene diethylester 3a exhibited Cs⁺ selectivity.     

CMPO-substituted calix[6]- and calix[8]arene extractants for the separation of An/Ln from radioactive waste

Three calix[6]arene derivatives (1a-c) and two calix[8]arene derivatives (2a,b), with six and eight CMPO residues, respectively, attached to the narrow/lower rim via ether links, were synthesised. Preliminary liquid-liquid extraction studies for Eu(III) and Am(III) from aqueous nitric acid to o-nitrophenylhexyl ether reveal remarkable properties with respect to efficiency and selectivity, especially for the tert-butylcalix[6]arene derivative with a -(CH₂)₃- spacer.     

Alkali Metal Complexation. Binding Properties of cone and partial-cone Calix[4]arenes Bearing a Mixed (O 2 , O 2 ') Donor Set (O = Phosphine Oxide; O ' = Amide or Ester)

The stability constants of alkali metal complexes obtained from the followingO-substituted calix[4]arenes were determined by UV/Vis spectroscopy inmethanol at 20°C: 5,11,17,23-tetra-tert-butyl-25,27-bis(diethylcarbamoylmethoxy)-26,28-bis(diphenylphosphinoylmethoxy)calix[4]arene(cone-1), 25,27-syn-26,28-anti-5,11,17,23-tetra-tert-butyl-25,27-bis(diethylcarbamoylmethoxy)-26,28-bis(diphenylphosphinoylmethoxy)calix[4]arene (paco-1),5,11,17,23-tetra-tert-butyl-25,27-diethoxycarbonylmethoxy-26,28-bis(diphenylphosphinoylmethoxy)calix[4]arene(cone-2) and25,27-syn-26,28-anti-5,11,17,23-tetra-tert-butyl-25,27-diethoxycarbonylmethoxy-26,28-bis(diphenylphosphinoylmethoxy)calix[4]arene(paco-2). All ligands form 1:1 complexes with alkali metal cations. The amide-containing calixarenes were found to be more efficient for alkali metalcomplexation than those bearing ester substituents. While sodium ions are selectivelycomplexed by the two mixed amide-(phosphine oxide) calixarenes, the twoester-containing isomers cone-2 and paco-2 turned out to be selective towards potassium and rubidium ions, respectively. With allfour ligands the lowest stability constants were found for the lithium andcesium ions.