Proton di-ionizable p-tert-butylcalix[4]arene-crown-6 compounds in cone, partial-cone and 1,3-alternate conformations: synthesis and alkaline earth metal cation extraction

Novel proton di-ionizable p-tert-butylcalix[4]arene-crown-6 compounds in cone, partial-cone and 1,3-alternate conformations are synthesized to compare the efficiency and selectivity with which they extract alkaline earth metal ions. In these ligands, a crown-6 polyether unit links alternate aromatic rings of the calix[4]arene framework. To the remaining lower-rim positions are attached oxyacetic acid or N-(X)sulfonyl oxyacetamide groups. Changing the conformation varies the spatial relationship between a polyether-complexed divalent metal ion and the ionized side arms of the ligands. This is found to markedly affect the efficiency and selectivity in competitive solvent extraction of alkaline earth metal ions from aqueous solutions into chloroform by the di-ionizable calix[4]arene-crown-6 ligands.     

Electrochemical investigation of nano-baskets of calix[4]-1,3-crowns-5,6 complexes

Four nano-baskets of calixarene including cone 25,27-di(carboxymethoxy)calix[4]arene-crown-5, 1,3-alternate 25,27-di[carboxymethoxy]-calix[4]arene-crown-5, cone 25,27-bis[carboxymethoxy]calix[4]arene-crown-6 and 1,3-alternate 25,27-di[carboxymethoxy]-calix[4]arene-crown-6 were synthesized and their binding abilities towards alkali and alkaline earth metals as well as some lanthanides were studied using differential pulse voltammetry. The novelty of this study was investigation of those macrocyclic complexes by voltammetric behaviors of two acidic moieties in each scaffold during complexation of crown ether ring. Their voltammetric behaviors were closely related to the complex formation by entrapment of cation into crown ether cavity and ion–dipole interaction between cation and acidic moieties in calixcrowns. The results revealed the selective changes in voltammetric behavior of synthesized scaffolds toward the cations. Moreover, the position of crown ether in 1,3-alternate instead of cone enhanced the domain of binding ability to more cations. Furthermore, it was shown that those carboxylic acid moieties, which were far from the crown ether ring in the 1,3-alternate, did not affected by encapsulated cations in the coordination space of crown ether and showed no voltammetric behavior.     

Synthesis of cone, partial-cone, and 1,3-alternate 25, 27-Bis

The preparation of 25,27-bis[1-(2-ethyl)hexyl]- and 25, 27-bis[1-(2-tert-butoxy)ethyl]calix[4]arene-crown-6 combining one polyether crown-6 and one alkylchain O-attached on each side of a calix[4]arene in the cone, partial-cone, and 1,3-alternate conformations are reported. The control over 25, 27-bisalkylcalix[4]arene-crown-6 conformation via varying specific reaction conditions was studied. The series of calix[4]arenes have been prepared by two routes, which differ in the order in which the alkyl or polyether groups were introduced. Moreover, methods have been developed to selectively prepare the cone and partial-cone conformers by using an appropriate base in the alkylation reactions. The conformations of these new derivatives have been probed by (1)H NMR analysis and X-ray crystallography. The (1)H and (13)C NMR spectra of 25,27-bis[1-(2-ethyl)hexyl]calix[4]arene-crown-6, 1, 3-alternate 1, cone 2, and partial-cone 3 are also discussed.     

Potassium-selective membrane electrodes based on macrocyclic metacyclophanes analogous to calixarenes.

The tetrabutyl ester derived from 9,16,25,32-tetrahydroxy[3.1.3.1]metacyclophane was an excellent ionophore for constructing a K+-selective membrane electrode. This ionophore exhibited a much higher selectivity toward K+ than the structurally similar potassium ionophore IV commercially available from Fluka. In particular, the interference from organic ammonium ions decreased remarkably. Potassium ionophore IV possessed oxygen atoms in the ring structure, while the present ionophore changed the oxygen atoms to carbon atoms. Thus, the removal of oxygen atoms in ring constituents of the metacyclophane acted to reduce the interaction with the NH3+ group of organic ammonium ions. The size of the cavity of the present ionophore was between those of calix[4]arene and calix[6]arene derivatives, which act as Na+ and Cs+ ionophores, respectively, demonstrating that the ability to recognize alkali metal cations was strongly cavity size-dependent. The present K+-selective electrode had less interference from Rb+ and Cs+ than an electrode constructed using valinomycin, but suffered greater interference from Na+.     

Protonation of 25,27-bis(1-octyloxy)calix[4]arene-crown-6 in the 1,3-alternate conformation

From extraction experiments in the two-phase water-nitrobenzene system and γ-activity measurements, the stability constant of protonated 1,3-alternate-25,27-bis(1-octyloxy)calix[4]arene-crown-6 in nitrobenzene saturated with water was determined. By using DFT calculations, the most probable structure of the 1,3-alternate-25,27-bis(1-octyloxy)calix[4]arene-crown-6 · H₃O⁺ complex species was derived. Correspondence: Emanuel Makrlík, Faculty of Applied Sciences, University of West Bohemia, Pilsen, Czech Republic.     

Effect of para-substituents on alkaline earth metal ion extraction by proton di-ionizable calix[4]arene-crown-6 ligands in cone, partial-cone and 1,3-alternate conformations

Two carboxylic acid or N-(X)sulfonyl carboxamide groups were incorporated into calix[4]arene-crown-6 compounds to afford di-ionizable ligands for use in divalent metal ion separations. Acidities of the N-(X)sulfonyl carboxamide groups were tuned by variation of the electron-withdrawing properties of X. Cone, partial-cone and 1,3-alternate conformations were obtained by different synthetic strategies and their structures verified by NMR spectroscopy. Competitive solvent extractions of alkaline earth metal cations from aqueous solutions into chloroform were performed and the results compared with those reported previously for di-ionizable p-tert-butylcalix[4]arene-crown-6 analogues to probe the influence of the para-substituent on the calix[4]arene scaffold on extraction selectivity and efficiency.     

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 and Cesium Binding Affinity of New 25,27-Bis(alkyloxy)calix[4]arene-crown-6 Conformers in Relation to the Alkyl Pendent Moiety

The preparation of new 25,27-bis(alkyloxy)calix[4]arenes-crown-6 in the cone, partial-cone and 1,3-alternate conformation is reported. We have also investigated the alkylation of the cone monoalkylated calix[4]arene-crown-6 achieved using Cs 2 CO 3 . This reaction afforded a mixture of cone and partial-cone calix[4]arenes-crown-6 having an alkyl chain anti or syn to the polyether ring. Conformations have been probed using 1 H, 13 C, 2D-NMR and NOESY analysis, and using X-ray crystallography. Extraction experiments using a two-phase solvent method involving cesium picrate were performed for these newly synthesized conformers. They reveal and confirm the strong preference for the 1,3-alternate conformers. The affinity of 1,3-alternate calixarenes for Cs + has been assessed by complexation measurements (log g ) using a spectrophotometric technique. No significant Cs + extraction difference was observed in relation to the nature of the alkyl chains on the aromatic rings. 1 H NMR studies of the 1,3-alternate calixarene Cs + complexes confirms the cation's spacial position between the two aromatic rings, due to cation- ~ interactions.     

The synthesis of novel polysiloxanes with pendant hand-basket type calix[6]crowns and their transporting properties for metal ions in a liquid membrane

Two novel polysiloxanes with pendant hand-basket type calix[6]-1,3-crown-3 and calix[6]-1,4-crown-4 were prepared by hydrosilylation of p-tert-butylcalix[6]-(2′-allyloxymethyl)-1,3-crown-3 (CA[6]C3) and p-tert-butylcalix[6]-[2′-(ω″-undecenyloxymethyl)]-1,4-crown-4 (CA[6]C4) followed by condensation reaction with silanol-terminated polydimethylsiloxane. The monomeric calix[6]crowns and two calix[6]crown-based polysiloxanes were used as carriers in a bulk membrane. All carriers showed the transport rate of the cations decreased in the order Li⁺ < Na⁺ < K⁺. The flux of K⁺ for the monomeric calix[6]crown was higher than that for polymeric carrier. In comparison with other carriers, the transport rate of calix[6]crown-4-functionalized polysiloxanes (CA[6]C4PS) towards cesium ions were increased greatly. Competitive transport experiments known to be more useful in industrial fields also revealed to give high cesium transfer rate.     

Novel Cesium‐Selective Electrodes Based on Lipophilic 1,3‐Bisbridged Cofacial‐calix[6]crowns

Five bisbridged calix[6]crowns have been investigated as Cs⁺ ionophore in PVC membrane electrodes. As ionophores, three 1,3‐bisbridged calix[6]crown‐4‐ethers( I–III ), 1,3‐bisbridged calix[6]crown‐5‐ether( IV ), and 1,3‐bisbridged calix[6]crown‐6‐ether( V ) have been evaluated. The membranes all give good Nernstian response in the concentration range from 1×10^?7 to 1×10^?1 M of cesium ion. The best detection limits (?log aequation/tex2gif-inf-1.gif=7.08–7.36) are obtained for electrode membranes containing 1,3‐bisbridged cofacial‐calix[6]crown‐4‐ethers( I‐III ), and the values are the lowest compared with those reported previously. The highest selectivity coefficients [ 3.74(Cs/K), 2.63(Cs/Rb)] are obtained for the membrane of 1,3‐bisbridged calix[6]crown‐4‐ether( II ), and these values are also the highest compared with previous reports for Cs⁺‐ISEs. The highest selectivity towards cesium ion is attributed to the geometrically cofacial positions of two crown‐ethers in calix[6]crowns in order to provide the complex of cesium ion and eight oxygens of cofacial crowns.     

Synthesis of a tweezer-like bis(arylthiaalkoxy)calix[4]arene as a cation sensor for ion-selective electrodes: an investigation of the influence of neighboring halogen atoms on cation selectivity

Two novel tweezer-like 25,27-dihydroxy-26,28-bis(phenylthiaethoxy)calix[4]arenes 6 and 7 were synthesized by the reaction of 25,27-dihydroxy-26,28-bis(bromoethoxy)calix[4]arenes 3 and 4 for the evaluation of their ion-selectivity in ion-selective electrodes (ISEs). X-ray structural analysis indicated that calix[4]arene 7 is in an interesting infinite linear aggregate via self-inclusion. For investigation of the influences of substitutes on the behavior of the ISEs, the halogen substituted aryl analogues of 25,27-dihydroxy-26,28-bis(arylthiaethoxy)calix[4]arenes 8-12 were also synthesized and their ISE performances were evaluated under the same conditions. ISEs based on 6-12 as neutral ionophores were prepared, and their selectivity coefficients for Ag+ (log KAg,M(pot)) were investigated against other alkali metal, alkaline-earth metal, lead, ammonium ions and some transition metal ions using the fixed interference method (FIM). These ISEs showed excellent Ag+ selectivity over most of the interfering cations examined, except for Hg2+ having relative smaller interference (log KAg,Hg(pot) < or = 2.1). The 19F NMR spectra of 9 and 9.AgClO4 were recorded for investigation the fluorine environments in the complex. The 19F NMR spectra strongly suggested that the fluorine atoms on ionophore 9 participated in ligation with silver cation.     

A New Family of Indoaniline-Derived Calix[4]arenes: Synthesis and Optical Recognition Properties as a Chromogenic Receptor(1)

A new family of indoaniline-derived calix[4]arenes has been synthesized for the purpose of developing a new chromogenic receptor. A condensing reaction of calix[4]arene (1) with 4-(diethylamino)-2-methylaniline hydrochloride (2) in the presence of an oxidizing agent under alkaline conditions affords mono- (3), 1,2-bis- (4), 1,3-bis- (5), and tetrakisindoaniline-derived (6) calix[4]arenes after careful column chromatography. Compound 3 is crystallized from a CHCl(3)-MeOH solution, and the crystal structure was determined by X-ray analysis. The crystal is monoclinic, space group P2(1)/n, Z = 4, a = 19.507(6) ?, b = 18.591(6) ?, c = 8.524(2) ?, beta = 94.69(2) degrees. The final R value for 2406 reflections of F(o) > 3sigma(F(o)) is 0.085. A unique intramolecular hydrogen-bonding network involving the carbonyl oxygen of indoaniline for 3 implied that the quinone carbonyl group as an acceptor of the chromophore can easily be subjected to an electrostatic interaction in the lower rim. Indeed, 1,3-bis(indoaniline)-derived 2,4-bis((ethoxycarbonyl)methoxy)calix[4]arene 7, prepared by the reaction of 5 with ethyl bromoacetate in the presence of NaH, is capable of undergoing an efficient ion-dipole interaction between the binding cation and the two quinone carbonyl groups of the chromophores, so that a selective Ca(2+)-induced pronounced color change (wavelength change > 100 nm) occurs with an association constant on the order of 10(6) in 99% EtOH, making 7 of potential use as an optical sensor for Ca(2+) detection. The IR and NMR studies have indicated that Ca(2+) is encapsulated in the cavity made by the distally located OCH(2)CO(2) groups on the lower rim of the cone-shaped calix[4]arene segment. Interestingly, however, the shape of the cavity in which Ca(2+) has been encapsulated does not have a C(2) axis of symmetry, as inferred from the (1)H-(1)H COSY experiment. On the other hand, 1,2-bis(indoaniline)-derived analogue 8 shows no response with metal ions, which can be interpreted to mean the absence of a cavity for encapsulation on the lower rim.     

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.     

Syntheses of Lower-Rim-1,3-Crowned Calix[6]Arenes and their Complexation Abilities Toward Cations

An approach to lower-rim-1,3-crowned calix[6]arene and its derivatives in one-pot process has been accomplished. In the presence of very excess Na2C03 (27-150 equivalent per mole p-tert-butyleal ix[6]arene 1) in acetonitrile, the lower-rim-1,3-bridged calix[6]crown-3 (4), the bistosylethoxy-ethyl derivative of 4 (5), as well as the intermediate of 4, monotosylethoxyethyl p-tert-butylcalix[6]arene 3, were obtained in rational yields, the distribution of the three compounds varied with the amount of the base used and other selected experimental conditions. 4 exhibits high selectivity towards Li⁺. 3 may be the first example of ionophore with high Et2NH2⁺ selectivity.     

Synthesis of calix[4]arene-crown-6 with alkoxysilyl-containing substituents

An efficient procedure has been proposed for the synthesis of calix[4]arene-crown-6 conjugate having triethoxysilyl fragments in the para positions. The calixarene fragment adopts a 1,3-alternate conformation. Unlike known methods of synthesis of analogous structures, the proposed procedure ensures introduction of two ethoxysilyl groups into the oppositely located benzene rings in the macrocycle.     

Homooxacalix[3]arene Derivatives as Ionophores for Serotonin‐Selective Membrane Electrodes

Homooxacalix[3]arene derivatives are effective ionophores for constructing serotonin‐selective membrane electrodes. An electrode based on one of the derivatives, tris(methoxyphenylpropyloxy)hexahomooxacalix[3]arene‐triethyl ether, with potassium tetrakis(p‐chlorophenyl)borate (20 mol% relative to the ionophore) as an ionic additive and bis(2‐ethylhexyl) sebacate as a solvent mediator in a poly(vinyl chloride) membrane matrix, displayed much better selectivity for serotonin than for various organic ammonium ions and inorganic cations. The electrode exhibited a near‐Nernstian response to serotonin in the concentration range of 2×10^?4 to 1×10^?2 M with a slope of 56.4 mV per concentration decade in physiological saline containing 150 mM NaCl and 10 mM Na₂HPO₄/NaH₂PO₄ (pH 7.4). The limit of the detection was 8×10^?5 M. The selectivity pattern of this electrode was quite different from that of an electrode using calix[6]arene‐hexaacetic acid hexaethyl ester, a well‐known ionophore for primary organic ammonium ions, which did not induce an enhanced response to serotonin. The developed electrode was used for the active loading of serotonin in liposomes induced by transmembrane pH gradients.     

Selectivity of calix[4]arene-bis(benzocrown-6) in the complexation and transport of francium ion

It is shown for the first time that a representative member of the "cesium-selective" calix[4]arene-crown-6 family exhibits a high affinity for Fr+ ion. In the investigation, the transport of 221Fr+ and Cs+ ions by calix[4]arene-bis(benzocrown-6) from an aqueous sodium nitrate solution into the water-immiscible diluent 1,2-dichloroethane was measured and compared to address the question of selectivity of the calix-crown-6 cavity toward alkali metal ions of increasing size. Selective separation of 221Fr+ from its parent 225Ac and from the matrix Na+ ions was demonstrated. Higher distribution ratios were obtained than those for the Cs+ ion. The extraction equilibria were determined for the case of the Cs+ ion, and the same equilibria were shown to be applicable to the case of Fr+ with inclusion of additional competitive effects.     

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.     

Calix[4]resorcinarene Ionophore in the Ion-Selective Electrodes with Plasticized Poly(vinylchloride) Membranes

Synthetic ionophore calix[4]resorcinarene was incorporated into the poly(vinyl chloride) (PVC) plasticized membrane of an ion-selective electrode (ISE). Calixarene interactions with quaternary ammonium and alkaline metals cations in the organic and water-organic media were carefully investigated by various authors. We studied the effects of choline and Na⁺ cations present in the working solution on the ionophore which was incorporated into a membrane phase. Due to the pH sensitivity of the ionophore, a study was undertaken in a wide range of pH values. The different characteristics of calix[4]resorcinarene interactions with these cations were discovered by the ISE with the PVC plasticized membrane containing this ionophore, which respond to both the choline and Na⁺ cations due to the variation of working solution pH.     

Self-assembled monolayers of organosulphur molecules bearing calix[4]arene moieties

We investigate the self-assembly of modified calix[4]arene on gold surfaces. Calix[4]arene was modified through a reaction sequence which led to assembling of the crown-5 moiety and to the insertion of two thioether groups into the starting molecule. The so-obtained calix[4]arene-crown-5 bis(7-thiatridecyloxy) (hereafter called calix[4]arene) was in the stable 1,3-alternate conformation. The calix[4]arene/gold interface was investigated by means of spectroscopic ellipsometry (SE), scanning tunneling microscopy (STM) and cyclic voltammetry (CV). SE data indicate a layer thickness compatible with the formation of a monomolecular layer. This result is confirmed by STM imaging which shows the formation of a high density of small pits, one gold layer deep, a typical feature of self-assembled organosulphur monolayers on gold. CV measurements performed in presence of the [Ru(NH(3))(6)(2+/3+)] redox couple indicate a passivation of the metal electrode, resulting in a reduction of the redox current, after the layer deposition. CV has also been used to investigate the selectivity properties of calix[4]arene-covered gold electrodes by measuring the redox current decrease in the presence of different salt solutions. It is found that calix[4]arene-covered electrodes are able to complex K(+) and Ba(2+), while no complexation is observed in the case of Li(+), Na(+), Cs(+), Mg(2+) and Ca(2+).