Stilbene-bridged 1,3-alternate calix[4]arene crown ether for selective alkali ion extraction

A series of stilbene-bridged calix[4]arenes was synthesized through an intramolecular reductive McMurry coupling of bisbenzaldehyde calix[4]arene in high yields. Tetra- and pentaethylene glycol chains were tethered to the phenolic groups of calix[4]arene to form stilbene-bridged calix[4]arene crown-5 and crown-6, respectively. The presence of stilbene bridge over the calix[4]arene rim effectively prevented the connection of the polyether chains in the cone conformation resulting in the exclusive formation of 1,3-alternate stilbene-bridged calix[4]arene crown product. Compared to the cone analogues, the 1,3-alternate calix[4]arene crown ethers showed a greater extraction ability and selectivity toward Cs⁺.     

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.     

Metal ion complexation in acetonitrile by cone,di-ionised calix[4]arene-1,2-crown ethers with two pendant dansyl fluorophores

Four cone calix[4]arene-1,2-crown ethers each with two ionisable side arms containing dansyl groups are synthesised. The crown ether ring on the lower rim is varied from crown-4 to crown-5 with hydrogen or tert-butyl groups on the para position of the upper rim. Di(tetramethylammonium) salts of the di-ionised ligands are utilised for spectrofluorimetric titration experiments in MeCN. The influence of alkali metal, alkaline earth metal and selected transition and heavy metal (Co²⁺, Fe²⁺, Hg²⁺, Mn²⁺, Pb²⁺, Zn²⁺ and Fe³⁺) cations on the spectroscopic properties of the two dansyl groups linked to the lower rim of the conformationally locked, di-ionised calix[4]arene-1,2-crown ether frameworks is investigated by emission spectrophotometry. All of the metal cations induce red shifts in the emission spectra of the di-ionised ligands. The metal cations produce enhancement or quenching of the fluorescence emissions. Changes in the fluorescence emission as a function of the metal cation identity, the lower rim crown ether ring size and the absence or presence of upper rim tert-butyl groups are investigated.     

杯芳烃接枝超细SiO2的制备及其对Cu2+、Ag+萃取性能的研究

通过对杯[4]芳烃以及杯[6]芳烃上缘进行烯丙基化和硅氢加成2步衍生化反应得到硅氢化杯[4]芳烃以及硅氢化杯[6]芳烃,再将这2种硅氢化杯芳烃衍生物分别接枝到超细SiO₂上。在不同的pH值条件下,就2种杯芳烃接枝超细SiO₂衍生物对水合Cu²⁺及Ag⁺的萃取性能进行了研究。结果表明,与对叔丁基杯芳烃相比较,杯芳烃接枝超细SiO₂衍生物对Cu²⁺和Ag⁺的萃取率都有所提高,其中杯[4]芳烃接枝超细SiO₂对Ag⁺的最高萃取率达到98.78%,杯[6]芳烃接枝超细SiO₂对Cu²⁺的最高萃取率达到67.74%。     

Metal‐Ion‐Promoted Electron Transfer between Tetrathiafulvalene and Quinone Units Within a Calix[4]arene Framework and Tuning through Coordination of the Neighboring Crown Ether with a Sodium Cation

A new calix[4]arene 1 with tetrathiafulvalene (TTF), quinone, and crown ether units in the lower rim was designed and synthesized with the aim to investigate the possibility to tune the metal‐ion promoted electron transfer by coordination of the crown ether unit with additional metal ions. Both absorption and electron spin resonance (ESR) spectroscopic studies clearly indicate that electron transfer occurs efficiently from TTF to the quinone units in the presence of Sc³⁺/Pb²⁺/Zn²⁺. Moreover, the intramolecular electron transfer within 1 induced by Zn²⁺ can be switched off by addition of Na⁺ and further turned on by addition of either Sc³⁺ or Pb²⁺.     

Extraction properties of 25,27-bis(carbonylmethoxy)calix[4]arenes towards Sr2+: competitive extraction and extraction in a synthetic groundwater

The Sr²⁺ extraction properties of some 25,27-bis(carbonylmethoxy)calix[4]arenes, in which ester (–CH₂CO₂Et), keto (–CH₂COCH₃) and acid functionalities (–CH₂CO₂H) have been attached to the lower rim, are reported. Strontium ion extraction experiments were performed in a chloroform/water system, and the extraction performance analyzed by radiotracing using the short-lived radio nuclide ⁸⁵Sr. Effects of pH value, ligand to metal ratio, temperature, extraction time and strontium species on the extraction behavior were examined. It was observed that the 25,27-bis(carboxymethoxy)calix[4]arene derivatives are potent extracting agents towards the strontium ion, showing remarkable extraction performance in competition with a series of organic and inorganic impurities and in a synthetic groundwater. The crystal structure of 25,27-bis(acetonyloxy)calix[4]arene is also reported.     

Syntheses and Metal-ion Binding Properties of Calix[4]arene Derivatives Containing Soft Donor Atoms: Highly Selective Extraction Reagents for Ag+

A series of calix[4]arene derivatives containing N or S atoms atthe lower rim were synthesized by etherification of OH groups and their metal-ion extraction abilities were studied. The extraction selectivity for Ag⁺ over other ions with these novel receptors was outstanding. Among these ligands, calix[4]arene podand, which possessed two linear ligands, has shown better binding ability with Ag⁺ than calix[4]crowns.     

Synthesis and metal ion complexation studies of proton-ionizable calix

A series of novel N-chromogenic calix[4]arene azacrown ethers were synthesized as selective extractants of potassium ion. 1,3-Alternate calix[4]arene azacrown ethers were prepared by reacting 25,27-dipropyloxy-26,28-bis(5-chloro-3-oxapentyloxy) calix[4]arenes with p-toluenesulfonamide in the presence of potassium carbonate. The coupling reaction of calix[4]arene azacrown ether with 2-hydroxy-5-nitrobenzyl bromide in the presence of triethylamine in THF gave the chromogenic calix[4]arene azacrown ether in moderate yield. These compounds show high potassium selectivity over other metal ions as shown by two-phase extraction, bulk liquid membrane, and 1H NMR studies on a ligand-metal complex. It is assumed that the OH of the chromogenic group attached on nitrogen can assist the complexation by encapsulation of the metal.     

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⁺.     

Potassium Sensing Calix[4]arene Crown Ethers

1,3-Alternate calix[4]arene crown-5 (1) and corresponding biscrown-5 (2) were synthesized and the complexation behavior with alkali metal ions examined. For both 1 and 2, potassium ion was selectively extracted from aqueous phase into organic phase over other alkali metal ions based on two phase extraction experiment. The complexation ratio between calix[4]arene biscrown-5 (2), in which two crown cavities connect to the calix[4]arene framework by 1,3-alternate fashion and potassium metal ion is found to 1:1 by proton NMR spectroscopy and extraction equilibria. Association constants (logK_a) for 1 and 2 were determined to give 2.51 and 3.49, respectively.     

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.     

Synthesis and cationic selectivity studies of novel calix[4]arene derivatives containing heteroatom at the lower rim

A series of calixarene derivatives 2―5 containing heteroatom at the lower rim have been synthesized. 1H NMR studies and crystallographic structures demonstrated that the calix[4]arene derivatives adopted cone conformations. Their cationic binding abilities and selectivities towards heavy and tran- sition metal ions have been evaluated by solvent extraction of aqueous metal picrates. The obtained results indicated that the introduction of nitrogen, sulfur, and/or phosphor atoms to the calix[4]arene framework could effectively enhance their binding ability and selectivity for heavy and transition metal ions, such as Pb2 or Ag .     

Complexation and extraction of non-ferrous metals by calix[n]arene phosphine oxides

The extraction of non-ferrous metal (M²⁺) nitrates by the calix[4,6]arenes (L), bearing four or six phosphine oxide donor groups at the upper or at the lower rim, was quantitatively described in the form of [M_n(NO₃)_2nL] (n = 1, 2) complexes. The extraction constants (Zn²⁺ > Cu²⁺ > Co²⁺ > Ni²⁺) for the both types of L coincide with Irving-Williams sequence. Calix[4]arenes, phosphorylated at the lower (narrow) rim, provide better stability of ML complexes because of the best spatial fitting of M²⁺ by the donor groups. For the upper (wide) rim phosphorylated calix[4]arenes M₂L and ML₂ complexes are more stable. Unusual zwitterionic [Co₂(NO₃)₄L] complex of the lower rim tetraphosphorylated calix[4]arene 1 was determined by X-ray structural analysis.     

Liquid-liquid extraction of transition and alkali metal cations by a new calixarene: Diphenylphosphino calix[4]arene methyl ether

The liquid-liquid extraction of various metal ions by a diphenylphosphino calix[4]arene (1) using picrate counter ion has been studied and compared with those ofp-tert-butyl-calix[4]arene methyl ether (2) and triphenylphosphine (3). The calixarene 1 shows strong binding ability to almost all metal cations examined, but calixarene 2 shows little ability to extract any of them. Based on the continuous variation method, calixarene 1 formed 1: 2 complexes with copper(II) ion.     

Calix[4]arenes Bridged with Two Different Crown Ether Loops: Influence of Crown Size on Metal Ion Recognition

A series of calix[4]arene-bis-crownethers were synthesized in a fixed 1,3-alternateconformation with good yields by the reaction of amonocyclic calixcrown ether with multi-ethyleneglycoldi-p-toluenesulfonate in the presence of cesiumcarbonate. In the preparation of the monocycliccalixcrown ethers (1 and 2), the use ofpotassium carbonate as a base provided the best yieldregardless of the template concept. In two phaseextraction and competitive transport experiments forligand-metal complexation, calix[4]arene biscrown(5) provided the best selectivity for potassiumion. When a calixbiscrown ether (4) bearingdifferent sized crown ether loops coordinates to K⁺and Cs⁺, respectively, the changes of peak splittingpatterns and chemical shift on ¹H NMR spectra aredependent on the complexed metal ion species.     

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.     

Preorganized, cone-conformational calix[4]arene possessing four propylenephosphonic acids with high extraction ability and separation efficiency for trivalent rare earth elements

p-t-Octylcalix[4]arene with tetraphosphonic acid at lower rim in cone conformation has been designed and synthesized as a new extraction reagent to investigate the extraction behavior of the nine trivalent rare earth elements: La, Pr, Nd, Sm, Eu, Gd, Ho, Y, and Er. The extraction of rare earth metals with the present extractant occurs by a simple ion-exchange mechanism. The stoichiometry of the extractant to rare earth metal ion was determined to be 2:1 based on the extraction equation, half pH values, pH_1/2, and the difference in the values of the extraction equilibrium constants of nine trivalent rare earth elements and separation factors between adjacent rare earth elements. This allowed for comparison of the estimated extraction efficiency and selectivity. The present extractant exhibited extremely high extractability and sufficiently high separation efficiency of rare earth metals, compared with calix[4]arene tetraphosphonic acid at upper rim, calix[4]arene tetraacetic acid at lower rim as previously reported and the commercial extraction reagent. This results was attributed to size and multidentate effects based on the preorganized cyclic structure of calix[4]arene and to the original selectivity of functional group for heavier rare earth elements.     

The Preorganization Effect of the Calix[4]arene Platform on the Extraction Properties of Acetylhydrazide Groups with Transition Metal Ions

The binding properties of the cone conformer of O,O,O,O-tetrakis[hydrazinocarbonylmethyl]-4-tert-butylcalix[4]arene, the cone and the 1,3-alternate conformers of the corresponding thia analogue have been evaluated by means of liquid–liquid extraction for a large variety of metal ions. The extraction constants and the stoichiometries of the complexes formed have been determined. Comparison of the extraction properties of calix[4]arenes with their acyclic monomeric analogue clearly demonstrated, that the preorganization of acetylhydrazide groups on the calix[4]arene platform is the cause for a significant improvement of its binding properties. The presence of additional “soft” nitrogen binding sites in acetylhydrazide derivatives of calix[4]arenes compared to their amide derivatives leads to a shift from their classical selectivity for alkali and alkaline earth cations to transition metals. The cone conformer of tetrathiacalix[4]arene shows higher selectivity in a series of d-metal ions compared with its “classical” analogue. The 1,3-alternate conformer exhibits an excellent extraction selectivity for Cu²⁺ and Hg²⁺.     

基于四丹磺酰胺杯[4]芳烃的汞离子荧光化学传感器

我们方便地合成了上沿修饰四丹磺酰胺基团的杯[4]芳烃衍生物1,发现该化合物在含50％水的乙腈中显示出对汞离子高选择性和灵敏性的识别作用,竞争实验表明多数金属离子对其检测干扰较小。机理研究结果表明荧光萃灭源于由丹磺酰胺基团到汞离子的光致电子转移过程。另外,通过研究1和1-Hg2+的荧光衰减实验,以及对比双丹磺酰胺杯[4]芳烃2和单丹磺酰胺杯[4]芳烃3对汞离子的识别作用,发现化合物1的四丹磺酰胺基团具有很好的预组织和协同作用。化合物1对汞离子的检测限为3.41×10-6 mol·L-1,这可以使1成为一个潜在的汞离子荧光化学传感器。     

Synthesis of calix[4]arene(amido)monocrowns and their photoresponsive derivatives

A series of new calix[4]arene(amido)mono-crown compounds have been synthesized through aminolysis of calix[4]arene esters and intramolecular cyclization of the intermediates. The title compounds were converted into their nitro and azo substituted derivatives to provide novel photoresponsive molecular receptors for transition metal ions. Single crystal X-ray analysis of calix[4]arene(ethyleneamido)mono-crown (2a) revealed that the compound is present in a cone conformation with an amido loop that caps the lower rim of calix[4]arene cavity to result in stacking along axis a and axis c to provide supramolecular aggregates in the solid state. Evaluation of synthesized macrocycles in the solution phase for recognition of transition metal cations (Cr³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Cd²⁺, Pb²⁺, Hg⁺, Hg²⁺, Pd²⁺, and Pt²⁺) by UV-visible spectroscopy revealed that p-tert-butyl-calix[4]arene mono-(amidocrown) 1c selectively shows a blue shift at 38 nm on interaction with Hg⁺ ions.