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.     

Preorganization of diglycolamides on the calix[4]arene platform and its effect on the extraction of Am(III)/Eu(III)

Different diglycolamide (DGA)-substituted calix[4]arene-based extractants were synthesized and evaluated for the extraction of Am(III) and Eu(III), representative trivalent actinide and lanthanide ions, respectively. On the narrow rim of the calix[4]arene platform, the DGA moiety was either 1,3-di- or tetrasubstituted with a varying spacer length between the oxygen and amide nitrogen atom. In addition, DGA groups were appended both to the wide rim and to both rims of calix[4]arenes and their efficiencies were compared for Am(III) and Eu(III) extraction at three different feed acidities. The extraction and separation efficiencies strongly depended on the N-alkyl substituent as well as the spacer length. 1,3-Di-DGA-substituted calix[4]arenes are inferior extractants to the corresponding tetra-DGA-substituted ones. Narrow rim DGA-functionalized derivatives resulted in high extraction efficiencies, while the wide rim DGA-functionalized calix[4]arenes showed practically no extraction.     

Multiple proton ionizable calixarene derivatives with different ring sizes and complexation ability as efficient ionophores for complexation and solvent extraction of trivalent indium

The solvent extraction behavior of multiple proton ionizable p-tert-butylcalix[4]arene and [6]arene carboxylic acid derivatives towards indium has been investigated along with an acyclic monomeric analogue from weakly acidic media into chloroform. The extraction mechanism is ion exchange and carboxylic acid groups are adequate ligating sites for extraction. The cyclic structure of calixarene ligands to accommodate the potential guest species and the cooperativity effect of multifunctional groups significantly affect the complexation behavior and calixarene derivatives are found to be excellent extractants over the monomeric analogue. The composition of the extracted complex depends on the solution pH and attempts to determine the composition of the extracted complex for the extraction of indium have been stymied by complications arising from the formation of polynuclear species of indium and bridged polymeric species of calixarene carboxylic acid derivatives. One mole of calix[4]arene derivative extracts 2.5 moles of indium whereas the calix[6]arene derivative tends to extract 4.0 moles of indium. The loaded indium is back extracted with 1 mol dm(-3) hydrochloric acid solution. Though quantitative back extraction of indium was achieved from the fully loaded calix[6]arene derivative, it was only achieved up to 85% in the case of the calix[4]arene derivative.     

Cation complexation with p-tert-butylcalix[5]arene pentacarboxylic acid derivative: an allosteric regulation of the first metal ion for stepwise extraction of the second ion

A calix[5]arene based solvent extraction reagent 3, appending carboxylic acid groups at the lower rim, has been developed and its complexation behavior towards some transition metal ions has been studied. The host 3 can selectively and quantitatively extract Pb(II) ions above pH 1.8 while other divalent ions such as Cu(II), Zn(II), Co(II), Ni(II) are extracted quantitatively only above pH 3.0. The outstanding Pb(II) selectivity of 3 comes from the size fit complementarity effect of the Pb(II) ion in the calix[5]arene cavity. One molecule of 3 extracts two Pb(II) ions in a stepwise manner. The first Pb(II) ion is extracted into the deep cavity of the calix[5]arene defined by phenoxy oxygen atoms. The first complexed Pb(II) ion acts as a template to bring the host into a cone conformation and induces a positive allosteric effect for the extraction of the second Pb(II) ion at an oxygen rich coordinating site composed of carboxyl groups. Both the Pb(II) ions are extracted through an ion exchange mechanism and the electroneutral complex in the organic phase is formed by the release of an equivalent number of hydrogen ions into aqueous solution. The loaded Pb(II) is easily back-extracted from Pb(II)-complexed 3 using dilute acid solution.     

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⁺.     

New artificial receptors from selectively functionalized calix[4]arenes

Abstract

The development of new synthetic methods for the monoalkylation of calix[4]arenes at the lower rim allows the synthesis of a new class of trihydroxamate siderophores. Three chelating hydroxamic acid units are introduced through a sequence of reactions which blocks the macrocycle in the cone conformation. The new ligands obtained form neutral 1:1 complexes (FeL) with iron (III), which are stable in EtOH/H₂O 9:1 at pH 2–7. Calix[4]arene bis-crown ethers are prepared by exploiting the selective 1,2-(proximal) functionalization of calix[4]arenes at the lower rim. These ligands are, however, less effective in complexing alkali metal cations compared with the 1,3-calix[4]arene crown-ethers which, in their partial cone structure, offer a better shielding for the complexed cations. Rigid upper rim-bridged calix[4]arenes potentially useful for the inclusion of neutral molecules are prepared by exploiting the selective 1,3-diformylation of calix[4]arene at the upper rim. Finally a new chloromethylation method for calix[4]arenes blocked in the cone conformation is described together with the synthesis of new cavitands.     

Palladium(II) extraction by sulfur-containing calix[4,6]arenes from hydrochloric acid solutions

The comparison of the extraction properties of calixarenes, thiacalixarenes, and calix[4,6]arene thioethers showed that methyl(thiamethyl)calix[4,6]arenes 3a and 4a have the highest extraction abilities. These extractants rapidly and completely extract palladium from hydrochloric acid solutions; regarding distribution factors achieved in the kinetic mode, they three to four orders of magnitude exceed their monodentate analogue, octylbenzyl sulfide (OBnS). Approaches are considered to enhance palladium extraction via generating mixed palladium species in low-acidity solutions and via intramolecular catalysis by the protonated oxygen atoms of alkoxy groups in the lower rim. For 1 M HCl, the kinetic order of diluent effects on palladium extraction was established. The substitution of sulfur atoms for bridging CH₂ groups was discovered to enhance palladium extraction by calix[4]arene thioether 3c.     

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⁺.     

邻甲氧基羰基苄氧基取代杯[4]芳烃衍生物的合成及其性？…

杯芳烃是继冠醚、环糊精之后的第三代主体分子 [1] .据文献 [2 ,3]报道 ,在杯 [4]芳烃下沿酚氧原子上连接乙酸酯得到的四取代衍生物对 Na+ 有很高的选择性 ,核磁与晶体结构研究均证实这是由于羧酸酯的羰基和酚氧基参与了对 Na+ 的配位 ,而且配位基团所形成的包络空间大小与钠离子相匹配 .一般认为 ,随着包络空间改变 ,对金属离子的识别作用会有所变化[4] .但目前对这方面的工作并没有给予更多的重视 .我们发现 ,用 2 -溴甲基苯甲酸甲酯与杯 [4 ]芳烃反应 ,得到了一种新的四取代杯 [4]芳烃衍生物 2 ,萃取研究结果表明 ,该化合物对钾离子有较…     

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⁺.     

Rigid versus flexible: how important is ligand "preorganization" for metal ion recognition by lower rim-functionalized calix[4]arenes?

For an assessment of the outcomes from use of an appropriately "preorganized" calixarene-based ionophore versus its conformationally mobile prototype, solvent extraction propensities of flexible calix[4]arene di-[N-(X-sulfonyl)carboxamides] for alkali, alkaline earth metal cations, Pb2+, Ag+ and Hg2+ are compared with those for seven new rigid analogs fixed in the cone, partial cone and 1,3-alternate conformations. For each of the metal ions, the preferred calix[4]arene conformation was determined from the NMR spectra for the metal salt of the flexible ligand. Except for Ag+, flexible calix[4]arene di-[N-(X-sulfonyl)carboxamides] were found to provide greater metal ion extraction efficiency and better selectivity than the corresponding "preorganized" ionophores.     

杯芳烃偶氮类衍生物对金属离子的萃取作用

通过杯芳烃的酚羟基的直接烃基化反应,在杯芳烃的下缘引入2,3′-二甲基-4-氨基偶氮苯发色团,得到了一系列杯芳烃偶氮衍生物(n=4,6,8)a-c.研究了它们对碱金属,碱土金属及过渡金属等十种金属离子的萃取作用.结果表明此类杯芳烃偶氮衍生物对过渡金属离子有良好的选择性识别作用,其中空腔较大的杯[8]芳烃偶氮衍生物c的萃取效果尤为显著.     

Phosphorus-based p-tert-butylcalix[5]arene ligands

New calix[5]arene trivalent phosphorus derivatives have been synthesized which should be excellent ligands with which to study and control the interaction of a ligand atom with a metal. The larger cavity of the calix[5]arene (compared to calix[4]arene) provides a good balance between constraint and flexibility. Treatment of p-tert-butylcalix[5]arene with 2 equiv of either tris(dimethylamino)phosphine or dichlorophenylphosphine inserts two RP moieties into the calix[5]arene framework to give calix[5](PR)2(OH) (1, R = Me2N; 2, R = Ph). Further treatment of 1 with 4 equiv of HCl gives calix[5](PCl)2(OH) (3). Heating a solution of the monophosphorus compound calix[5](PNMe2)(OH)3 (4) releases dimethylamine to yield both monomeric calix[5](P)(OH)2 (6) and dimeric [calix[5](P)(OH)2](2) (7), the latter having a tubelike geometry. X-ray crystallographic studies confirm the structures and show that 1 and 2 have approximate cone conformations while 3 has an approximate 1,2-alternate conformation. The orientations of the phosphorus lone pairs and oxygen atoms in all derivatives provide a framework for both soft and hard ligand interactions within the calix[5]arene.     

Calixarene-based surfactants: evidence of structural reorganization upon micellization

The self-aggregation of five amphiphilic p-sulfonatocalix[n]arenes bearing alkyl chains at the lower rim was investigated by NMR spectroscopy and electrical conductivity. The critical micelle concentration was determined, and the tendency of this special class of surfactants to self-aggregate in aqueous solution was analyzed as a function of the alkyl chain length and the number of aromatic units in the macrocyclic ring. The structure of the surfactants in the monomeric and micellized states was elucidated by means of (1)H NMR and, in the case of the calix[6]arene derivative, with 2D NMR experiments. While all amphiphilic calix[4]arenes studied here are blocked in the cone conformation, in the monomeric state the calix[6]arene adopts a pseudo-1,2,3-alternate conformation and the calix[8]arene is conformationally mobile. These calixarenes undergo an aggregation-induced conformational change, adopting the cone conformation in the micelles. The structure and size of the aggregates were studied by diffusion ordered spectroscopy (DOSY) experiments, and the results indicate that these surfactants self-assemble into ellipsoidal micelles.     

Transition metal-directed self-assembly of calix[4]arene based dithiocarbamate ligands

The transition metal-directed self-assembly of dithiocarbamate ligand functionalized upper and lower rim calix[4]arenes affords novel dimeric bimetallic bis(calix[4]arene) species as determined by a combination of analytical methods including X-ray crystallography. An exception is a zinc(II) dithiocarbamate upper rim calix[4]arene assembly which is monomeric in nature. Electrochemical investigations reveal the bimetallic copper(II) bis(calix[4]arene) systems can electrochemically sense dihydrogen phosphate and carboxylate anions via significant cathodic perturbations of the respective copper(II)/(III) dithiocarbamate oxidation wave.     

Synthesis of upper rim calix[4]arene divalent glycoclusters via amide bond conjugation

Synthetic routes for linking two sugar units at the upper rim of cone calix[4]arenes, through the formation of amide bonds, have been explored. Steric effects prevent the coupling of calix[4]arene dicarboxylic acid with simple aminoglycosides, whereas the corresponding reaction with carbohydrates bearing a two or three carbon atoms spacer, terminating with a primary amino group, allows the synthesis of several difunctionalized calix[4]arene neoglycoconjugates, attractive in chemical glycobiology and supramolecular chemistry.     

The selective preparation of partial cone O-aryl calix[4]arene ethers from 1,3-dimethoxycalix[4]arene: a new platform for the preparation of non-aggregated dyes

We report a new direct route for the selective preparation of novel partial cone O-aryl ether calix[4]arenes to be used as new platforms for the preparation of non-aggregated dyes. These partial cone conformers have the aromatic substituents lying within the calix[4]arene annulus via the upper rim.     

邻甲氧基羰基苄氧基取代杯[4]芳烃衍生物的合成及其性能研究

杯芳烃是继冠醚、环糊精之后的第三代主体分子[1].据文献[2,3]报道,在杯[4]芳烃下沿酚氧原子上连接乙酸酯得到的四取代衍生物对Na+有很高的选择性,核磁与晶体结构研究均证实这是由于羧酸酯的羰基和酚氧基参与了对Na+的配位,而且配位基团所形成的包络空间大小与钠离子相匹配.一般认为,随着包络空间改变,对金属离子的识别作用会有所变化[4].但目前对这方面的工作并没有给予更多的重视.我们发现,用2-溴甲基苯甲酸甲酯与杯[4]芳烃反应,得到了一种新的四取代杯[4]芳烃衍生物[2]萃取研究结果表明,该化合物对钾离子有较好的选择性.此外,在合成该衍生物的过程中,还得到了另一新的二取代衍生物(3).     

Selective transmembrane carriers for hydroxycarboxylic acids: Influence of a macrocyclic calix[4]arene platform

Selective transmembrane carriers for a-hydroxy acids, acyclic a-amino phosphonates and calix[4]arenes containing a-aminophosphonate substituents at the lower rim have been synthesized; analytical HPLC has been used to monitor the selective separation of dicarboxylic, a-hydroxy and a-amino acid mixtures by membrane extraction; the attachment of a-aminophosphonate fragments to the macrocyclic calix[4]arene platform results in receptors with markedly modified efficiency and selectivity relative to those of only aminophosphonates.     

杯芳烃衍生物液－液萃取和液膜传输银的对比研究及机理探讨

以4类含硫、硒、氮等杂原子基团二取代的杯[4]芳烃五衍生物（1－14）为中 性载体，在H2O-CHCl3-苦味酸体系萃取银和H2O-CHCl3-H2O液膜体系中传输银进行 了对比研究。萃取和传输结果具有一致性，除了苯并噻唑取代的杯[4]芳烃衍生物 （3－6）外，其它10个含硫、硒、氮的杯[4]芳烃衍生物1－14均对软重金属银和汞 有很高的选择性，而吡啶取代的杯[4]芳烃衍生物7－10对铅有一定的萃取选择性， 其中羟基硫醚取代的杯[4]芳烃衍生物11－14对银的萃取率和传输速率最大。并且 就杯[4]芳烃衍生物对银的传输机理进行了探讨，发现传输速率随源相中金属离子 浓度和有机相中载体浓度的增加而增大，因此推论这是由金属离子浓度梯度推动下 的传输。