Di-ionizable p-tert-butylcalix[4]arene-1,2-monothiacrown-3 ligands in the cone conformation: synthesis and metal ion extraction

A series of di-ionizable calix[4]arene-1,2-crown-3 compounds with a sulfur-containing unit bridging the proximate phenolic oxygens have been synthesized. The ionizable groups are oxyacetic acid and N-(X)sulfonyl oxyacetamide groups with X=methyl, phenyl, 4-nitrophenyl, and trifluoromethyl, which ‘tunes’ the acidity of the latter. The efficiency and selectivity of these novel ligands are assessed for competitive solvent extractions of alkali metal cations and of alkaline earth metal cations from aqueous solutions into chloroform. Also the efficiencies for single species extractions of Pb²⁺ and of Hg²⁺ are determined. The results are compared with those reported previously for related ligands in which only oxygen heteroatoms are present in the crown ether unit.     

Novel calix[4]arene-thiacrown ether for selective and efficient extraction of Ba(II), Pb(II), and Hg(II)

A di-ionizable p-tert-butylcalix[4]arene-1,3-thiacrown-5 ether extractant was synthesized. Its cone conformation and polyether ring attachment regioselectivity were verified by NMR spectroscopy. The metal ion-complexing properties of this ligand were evaluated by solvent extractions of metal cations from aqueous solutions into chloroform. The ligand was found to be an efficient extractant with Ba²⁺ selectivity in competitive solvent extraction of alkaline earth metal cations. It also exhibits high extraction ability for Pb²⁺ and for Hg²⁺ in single species solvent extractions.     

Di-ionizable calix[4]arene-1,2-crown-5 and -crown-6 ethers in cone conformations: synthesis and divalent metal ion extraction

Two series of di-ionizable calix[4]arene-1,2-crown-5 and -crown-6 ethers in cone conformations are synthesized. The ionizable groups are oxyacetic acid moieties and N-(X)sulfonyl oxyacetamide units with X=methyl, phenyl, 4-nitrophenyl, and trifluoromethyl, which ‘tunes’ their acidity. For competitive solvent extraction of alkaline earth metal cations from aqueous solutions into chloroform, the new ligands with N-(X)sulfonyl carbamoyl groups are efficient extractants with Ba²⁺ selectivity. On the other hand, the dicarboxylic acid analogues exhibit little selectivity in extraction of alkaline earth metal cations. For single species extractions of Pb²⁺, the ligands with both types of ionizable groups show very good extractions abilities. In single species extractions of Hg²⁺, the N-(X)sulfonyl carboxamide ligands are highly efficient, in contrast to the dicarboxylic acid compounds. Influences of the ionizable group identity, the crown ether ring size, and the presence of upper-rim p-tert-butyl groups on divalent metal ion extraction are explored.     

Di-ionizable calix[4]arene-1,3-crown-4 ligands in 1,3-alternate,cone, and partial-cone conformations: synthesis and metal ion extractions

Di-ionizable calix[4]arene-1,3-crown-4 compounds locked in 1,3-alternate, cone, and partial-cone conformations are synthesized for evaluation in metal ion separations. The ionizable functions include carboxylic acid and N-(X)sulfonyl carboxamide groups in which the acidity is tuned by variation of the electron-withdrawing ability of X. Similar synthetic routes were employed for preparation of the cone and 1,3-alternate ligand series. A different preparative route utilizing protection and deprotection was required to obtain the partial-cone analogues. Ligand conformations were confirmed by their proton and/or carbon NMR spectra. X-ray diffraction verified an unusual 1,2-alternate conformation in the solid-state for one synthetic intermediate. Effects of ligand conformation and ionizable group variations on competitive solvent extractions of alkali and alkaline earth metal cations from aqueous solutions into chloroform were assessed. Single species solvent extractions of Hg²⁺ and Pb²⁺ were also performed.     

Ester and Ketone Groups Substituted Mono- and Di- Azo-coupled Azocalix[4]arenes as Extractant for Hg+ and Hg2+, or Cr3+Cations

This article describes extraction properties of mono- (A1–A8) and di- (B1–B8) substituted azocalix[4]arene analogues. The ionophore solvent extractions of alkaline-earth (Sr²⁺), basic metal (Pb²⁺) and transition metal cations (Ag⁺, Hg⁺, Hg²⁺, Co²⁺, Ni²⁺, Cu²⁺, Cr³⁺) from aqueous phase to organic phase were carried out by azocalix[4]arene derivatives. It has been observed that they show a good extraction behavior toward selected heavy metal (Hg) and toxic metal (Cr), while A4 and B4 prefer Hg⁺, Hg²⁺ and Cr³⁺ among transition metal cations, respectively. The azocalix[4]arenes (A1–A8) and (B1–B8) are not efficient extractants for all of the selected metal cations, whereas A4 and B4 are selective only for Hg metal cation.     

Metal ion extraction by cone p-tert-butylcalix[4]arene-1,3-crown-5 with two N-(X)sulfonyl carbamoylmethoxy side arms and -1,3-monothiacrown-5 analogues

Four cone p-tert-butylcalix[4]arene-1,3-monothiacrown-5 ligands each with two N-(X)sulfonyl carbamoylmethoxy side arms are synthesized for comparison with analogs having only oxygen heteroatoms in the crown ether ring. Solvent extractions of hard alkali metal and alkaline earth metal cations, intermediate Pb²⁺, and soft Hg²⁺ from aqueous solutions into chloroform by these ligands are utilized to probe the effects of sulfur replacement in the crown ether ring on metal ion complexation.     

Comparison of upper and lower rim-functionalized,di-ionizable calix[4]arene-crown-6 structural isomers in divalent metal ion extraction

Upper rim-functionalized, di-ionizable calix[4]arene-crown-6 ligands are synthesized and compared with structural isomers having the two acidic side arms attached to the lower rim. Solvent extractions of selected divalent metal cations (alkaline earth metal cations, Pb²⁺, and Hg²⁺) from aqueous solutions into chloroform by the upper and lower rim-functionalized, di-ionizable calix[4]arene-crown-6 isomers are utilized to assess the effects of this structural modification on metal ion complexation abilities of the ligands. The observed effects are compared with those reported for analogous di-ionizable calix[4]arene-crown-5 structural isomers.     

Synthesis, NMR, X-ray structural analyses and complexation studies of new Ag selective calix[4]arene based dipodal hosts—a co-complexation of neutral and charged species

New podands based on the p-tert-butylcalix[4]arene unit with substitution at the lower rim incorporating imine units, have been synthesized in high yield by simple condensation method. These podands have been shown to extract and transport Ag⁺ selectively over alkali, alkaline earth metal cations, Zn²⁺, Pb²⁺ and Hg²⁺ ions, from neutral aqueous phase to organic phase. In all the ligands the calix unit has been found to be present in a cone conformation except for the one having pyridine as end group, at the ortho position. It has been isolated in two conformations; cone and 1,2-alternate. To the best of our knowledge, this may be the first 1,3-lower rim substituted calix[4]arene to exist in a 1,2-alternate conformation and is among a few known compounds with this conformation in the general class of calix[4]arenes. A complex of this ligand, which happens to be the highest extractant of Ag⁺ has been isolated and characterized using mass, ¹H and ¹³C NMR spectroscopy's and elemental analysis. The spectroscopic evidence and molecular modelling studies performed on the complex suggest a participation of the imine and pyridine nitrogens and two of the ether oxygens in coordination to the metal ion. The X-ray crystal structures of three of the ligands establish the formation of inclusion complexes with polar acetonitrile solvent molecules. The ¹H and ¹³C NMR spectra of all the compounds, taken in CDCl₃, show the presence of acetonitrile molecules in the cavity of the calix[4]arene, indicating inclusion of the neutral guest molecules in the solution phase as well. For one of the podands X-ray crystal structure has shown a formation of clatharate complex of chloroform with the ligand which has rarely been found in the case of calix[4]arenes.     

Study of Complex Formation between Kryptofix 21 with La<Superscript>3+</Superscript>, Y<Superscript>3+</Superscript> and Ce<Superscript>3+</Superscript> Cations in Some Binary Mixed Non-Aqueous Solvents Using the Conductometric Method

The complexation reactions between La³⁺, Y³⁺ and Ce³⁺ cations with the macrocyclic ligand, kryptofix 21, were studied in methanol-acetonitrile (MeOH-AN) and methanol-methylacetate (MeOHMeOAc) binary mixed solvent solutions at different temperatures using the conductometric method. The conductance data show that in most solvent systems, the kryptofix 21 forms a 1: 1 [M: L] complex with La³⁺, Y³⁺ and Ce³⁺ metal cations, but in the case of Y³⁺ cation in pure methylacetate, in addition of formation of a 1: 1 [ML] complex, 1: 2 [ML₂] and 1: 3 [ML₃] complexes are formed in solution. In the case of Ce³⁺cation, a 1: 1 [ML] and also a 1: 2 [ML₂] complexes are formed in this solvent system at all studied temperatures. The electrical conductance data in acetonitrile, show that a 1: 1 [ML] and also a 1: 2 [ML₂] complexes are formed between the ligand and La³⁺ and Ce³⁺ metal cations at different temperatures. The stability constants of the 1: 1 [ML] complexes were determined using the conductometric data and a computer program, GENPLOT. A non-monotonic relationship was observed between log_{K f} of the 1: 1 complexes with the composition of the binary solvent solutions which was discussed in term of solvent-solvent interactions and also preferential solvation of the metal cations and the ligand in solutions. The selectivity order of the ligand for the metal cations in MeOH–AN and MeOH–MeOAc binary solvent solutions, at 25°C was found to be: Y³⁺ > La³⁺ > Ce³⁺ and La³⁺ > Y³⁺ > Ce³⁺, respectively. The values of the standard thermodynamic quantities (ΔH _c ^° and ΔS _c ^° ) for formation of the 1: 1 complexes were obtained from temperature dependence of the stability constans of the complexes and the results show that the thermodynamics of the complexation reactions between kryptofix 21 and La³⁺, Y³⁺ and Ce³⁺ cations, is affected by the nature and composition of the mixed solvents systems.     

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-4 ligands: synthesis and high divalent metal ion extraction selectivity

Di-ionizable p-tert-butylcalix[4]arene-1,2-crown-4 ethers in the cone conformation are synthesized with their conformation and regioselectivity verified by NMR spectroscopy. The new ligands are efficient extractants with high selectivity for Ba²⁺ in competitive solvent extraction of alkaline earth metal cations from aqueous solutions into chloroform.     

Lower-rim versus upper-rim functionalization in di-ionizable calix[4]arene-crown-5 isomers. Synthesis and divalent metal ion extraction

Two series of di-ionizable calix[4]arene-crown-5 isomers in the cone conformation are synthesized to probe the effect of the pendant acidic group location on their metal ion extraction properties. In one series, the ionizable groups are attached to the lower rim of the calix[4]arene scaffold, which orients them near the crown ether cavity. In the second series, the ionizable groups are connected to the upper rim positioning them away from the crown ether ring, but close to the hydrophobic pocket of the calix[4]arene unit. The metal ion extraction behaviors of the two series of ligands are compared in extractions of alkaline earth metal cations, Hg²⁺, and Pb²⁺.     

Complexation of Cd2+, Ni2+, and Ag+ metal ions with 4,13-didecyl-l,7,10,16-tetraoxa-4,13-diazacyclooctadecane in acetonitrile-ethylacetate binary mixtures

Conductometric titrations have been performed in acetonitrile-ethylacetate (AN-EtOAc) binary solutions at 288, 298, 308, and 318 K to obtain the stoichiometry, the complex stability constants and the standard thermodynamic parameters for the complexation of Cd²⁺, Ni²⁺, and Ag⁺ cations with 4,13-didecyl-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (cryptand 22DD). The stability constants of the resulting 1: 1 complexes formed between the metal cations and the ligand were determined by computer fitting of the conductance-mole ratio data. There is a non-linear relationship between the logK _f values of complexes and the mole fraction of ethylacetate in the mixed solvent system. In addition, the conductometric data show that the stoichiometry of the complexes formed between the Cd²⁺, Ni²⁺, and Ag⁺ cations with the ligand changes with the nature of the solvent. The standard enthalpy and entropy values for the 1: 1 [ML] complexation reactions were evaluated from the temperature dependence of the formation constants. Thermodynamically, the complexation processes of the metal cations with the C22DD, is mainly entropy governed and the values of thermodynamic parameters are influenced by the nature and composition of the binary mixed solvent solutions.     

Synthesis and extraction studies of polymeric phthalimido functionalized calix[4]arene

The article comprises synthesis and extraction studies of polymeric calix[4]arene having phthalimide groups at the lower rim. The polymeric phthalimido functionalized calix[4]arene was synthesized via radical initiated reactions involving a vinylic monomer 5,11,17,23-tetra-tert-butyl-25-[4-(acrylamido)benzyloxy]-26,28-bis-(2-phthalimido-ethoxy)-27-hydroxycalix[4]arene (5) 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. From the liquid–liquid and solid–liquid extraction studies it has been concluded that the precursor 3 (5,11,17,23-tetra-tert-butyl-25-(4-nitro benzyloxy)-26,28-bis-(3-phthalimidoethoxy)-27-hydroxy-calix[4]arene) is selective for metal cations. The order of extractability of metal cations by the ligand 3 decreases in the sequence: Hg²⁺ > Cd²⁺ > Cu²⁺ > K⁺ > Co²⁺ whereas its polymeric derivative is selective in the sequence: Hg²⁺ > Cd²⁺ > K⁺ > Co²⁺ > Cu²⁺ for the metal cations used in the experiments.     

Selective sensing of Hg2+ by a proton-ionizable calix[4]arene fluoroionophore

A fluorogenic derivative of a calix[4]arene with two proton-ionizable N-(phenyl)sulfonyl carboxamide-containing side arms in the 1,3-positions on the lower rim is employed for the selective sensing of Hg²⁺ at low concentration levels in water/MeCN (1:1, v/v) solutions containing Pb²⁺ and Cd²⁺. All three metal ions quench the fluorescence of the ligand in pure MeCN. However, in water/MeCN mixed solvent, the recognition of such cations occurs differently as only Hg²⁺ complexation quenches the fluorescence of the calixarene. Experiments carried out in the presence of an acid and a bulky non-complexing cation shows that the quenching of the calixarene fluorescence upon Hg²⁺ addition is likely due to proton displacement from the proton-ionizable side arms of the ligand. The system may be employed as a simple tool for the selective and efficient mercury sensing in mixed water/organic solvent.     

Aminopyridyl derivative of thiacalix[4]arene-carboxylic acid as ionizable highly selective Ag+ ionophore

A novel mono-ionizable receptor 2 possessing three aminopyridyl and one carboxylic group in 1,3-alternate conformation based on thiacalix[4]arene, confirmed by single crystal X-ray analysis, was prepared. For competitive solvent extraction of alkali metal (Na⁺, K⁺ and Cs⁺) and some transition metal (Cu²⁺, Zn²⁺, TI⁺, Ag⁺) cations from aqueous solutions into chloroform, it was found that the introduction of proton-ionizable group (carboxylic acid moiety) into the aminopyridyl-thiacalix[4]arene derivative could further improve its Ag⁺ extractability with high selectivity.     

Synthesis and complexation study of calix[4]arene diamine derivative incorporated in a polymeric backbone with chiral monomers

The novel chiral polymeric compounds containing more than one calix[4]arene have been synthesized by reacting a new calix[4]arene diamine derivative with two chiral monomers. These newly prepared compounds were studied by extraction of toxic heavy metal (Cu²⁺, Co²⁺, Cd²⁺, Hg²⁺), silver and alkali metal (Na⁺, K⁺) cations from aqueous phase. It was observed that the resulting calixarene-based polymers have a good complexing ability towards silver, alkali metal and toxic heavy metal cations.     

Intramolecular hydrogen bonding effect on metal ion complexation of homooxacalix[4]arene bearing tetraamides

N,N-Dipentylamido homooxacalix[4]arene (3) in the C-1,2-alternate conformation provided Pb²⁺ ion selectivity over other metal cations. N-Monopentylamido homooxacalix[4]arene in C-1,2-alternate conformation has an intramolecular hydrogen bonding, causing decrease of the metal ion complex ability.     

One stone kills four birds: a novel diazaperinone 12H-pyrazino[2′,3′:3,4]pyrrolo[1,2-a]perimidin-12-one recognizes four different metal ions

A novel diazaperinone 12H-pyrazino[2′,3′:3,4]pyrrolo[1,2-a]perimidin-12-one has been successfully synthesized through a one-step condensation. Single crystal X-ray analysis shows that the product is of planar structure with strong π?π interactions and H-bonding. Interestingly, the 12H-pyrazino[2′,3′:3,4]pyrrolo[1,2-a]perimidin-12-one can recognize three different metal cations Cu²⁺, Ag⁺ and Hg²⁺ via naked eye visualization, and shows turn-on fluorescence for Fe³⁺ and Ag⁺ among the 22 metal cations.     

Di-ionizable p-tert-butylcalix[4]arene-1,3-crown-4 ligands: synthesis and alkaline earth metal cation extraction

A series of di-ionizable calix[4]arene-1,3-crown-4 compounds has been synthesized. The ionizable groups are oxyacetic acid and N-(X)sulfonyl oxyacetamide groups with X=methyl, phenyl, 4-nitrophenyl and trifluoromethyl, which ‘tunes’ the acidity of the latter. The efficiency and selectivity of these novel ligands are assessed with competitive solvent extractions of alkaline earth metal cations from aqueous solutions into chloroform. The results are compared with those reported previously for calix[4]arene-crown analogues with crown-6 and crown-5 rings.     

Efficient divalent metal cation extractions with di-ionizable calix[4]arene-1,2-crown-4 compounds

Di-ionizable calix[4]arene-1,2-crown-4 ethers in the cone conformation were synthesized and their conformation and regioselectivity verified by NMR spectroscopy. These new ligands exhibited high Ba²⁺ selectivity in competitive solvent extraction of alkaline earth metal cations from aqueous solutions into chloroform. The selectivity order was Ba²⁺>>Sr²⁺>Ca²⁺>Mg²⁺ with Ba²⁺/Sr²⁺ selectivity exceeding 100. The ligands also exhibited high extraction ability for Pb²⁺ and for Hg²⁺ in single species extraction. With variation of proton-ionizable groups, which are oxyacetic acid moieties and N-(X)sulfonyl oxyacetamide units with X=methyl, phenyl, 4-nitrophenyl, and trifluoromethyl, ‘tunable’ ligand acidity was obtained.