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.     

p-tert-butylcalix[4]arenes containing azacrown ether substituents at the lower rim as potential polytopic receptors

A series of disubstituted p-tert-butylcalix[4]arenes with N-methoxycarbonylmonoazacrown ether and N-ethoxymonoazacrown ether residues at the lower rim has been prepared via the reaction of di(carboxymethoxy)-p-tert-butylcalix[4]arene with azacrown ethers and subsequent reduction of the resulting amide derivatives. Using UV titration and ¹H NMR spectroscopy we have demonstrated the ability of the calixarene with two N-carbonylmonoaza-18-crown-6-ether substituents to form the 1:3 complexes with K⁺ and Na⁺ and the 1:2 complexes with Cs⁺, Sr²⁺, Cu²⁺, and Zn²⁺. The calixarene with two fragments of N-ethoxymonoazo-18-crown ether has formed binuclear complexes with alkali metals cations and mononuclear complexes with transition metals cations.     

A sinapic acid–calix[4]arene hybrid selectively binds Pb over Hg and Cd

The binding affinity for Pb²⁺, Cd²⁺ and Hg²⁺ of the sinapic acid–calix[4]arene hybrid 2, having four sinapyl pendants at the upper rim, has been investigated via an UV–Vis study. Compound 2 has better complexing ability than the monomeric p-phenetidine derivative 1. This highlights that the clustering of sinapyl units in a basket-like structure, dictated by the calixarene scaffold, greatly enhances the complexing properties. Ligand 2 forms complexes even with Hg²⁺, which is not complexed by 1 at all; the complexes formed by 2 with Pb²⁺ and Cd²⁺ are much stronger than the analogous complexes formed by 1. The UV–Vis investigation shows that the hybrid 2 markedly favors Pb²⁺ over Cd²⁺ and Hg²⁺. Information on the structural properties of the complex species was obtained by ¹H NMR spectroscopy. NMR data show that all three metal ions are placed into the cavity consisting of the calixarene scaffold and the sinapyl pendants, though their binding affects the coordinating regions to a different extent.     

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%。     

A new fluorogenic mono-ionizable calix[4]arene dansylcarboxamide as a selective chemosensor of soft metal ions, Tl and Hg

A new fluorogenic calix[4]arene containing one pendent N-dansylcarboxamide group has been synthesized. The ligand demonstrates selective optical recognition of Tl⁺ and Hg²⁺ in solvent extraction from aqueous solutions with high content of Na⁺. Complexation of Tl⁺ and Hg²⁺ produces contrasting changes in the fluorescence spectrum of this sensor. Partial cone is the dominant calixarene conformation in the complex with Tl⁺.     

Selective extraction of Fe3+ by a polymeric calix[4]arene

A polymeric compound containing more than one calixarene molecule was synthesized by reacting the oligomer ( 2 ) with 25,26,27-tribenzoyloxy-28-hydroxy calix[4]arene. After basic hydrolysis of 3a , the polymeric calixarene ( 3b ) was utilized for selective extraction of some metal cations from aqueous phase to organic phase. It was found that the compound ( 3b ) was selective toward Fe³⁺ from an aqueous solution containing Cu²⁺, Ni²⁺, Co²⁺ and Fe³⁺ cations. The mechanism of the extraction process was discussed. © 1994 John Wiley & Sons, Inc.     

Fluorescent chemosensors based on a new type of lower rim-dansylated and bridge-substituted calix[4]arenes

The synthesis, structural and chemosensing properties of several lower rim-dansylated calix[4]arenes bearing different methylene bridge substituents are described. Compared to bridge-unsubstituted pendants neither the conformational nor the fluorescence characteristics of the calixarene core are perceptibly influenced by the bridge substituent. X-ray structure as well as NMR measurements indicates the lower rim-propoxylated and-dansylated calixarenes to adopt the cone conformation capable of the complexation of Cu²⁺ ions at micromolar level. Fluorescent measurements point to selective 1:2 calixarene: Cu²⁺ complex formation with sensing parameters being of a suitable level to make the use as a potentially immobilisable chemosensor for the detection of Cu²⁺ ions promising.     

Membrane-active calixarenes: toward ‘gating’ transmembrane anion transport

This paper describes on-going efforts to develop calixarene amides as transmembrane anion transporters. We report on the transport of Cl⁻ anions across phospholipid membranes as mediated by some lipophilic calixarenes, all fixed in the cone conformation. We present significant findings regarding use of these calixarenes as transmembrane Cl⁻ transporters: (1) the cone conformer cone-H 2a, like its 1,3-alt and paco isomers, transports Cl⁻ across liposomal membranes; (2) the conformation of the calixarene (paco-H 1 vs cone-H 2a) is important for modulating Cl⁻ transport rates; (3) the substitution pattern on the calixarene's upper rim is crucial for Cl⁻ transport function; and (4) at least one of the four arms of the calixarene can be left unmodified without loss of function, enabling development of a pH-sensitive anion transporter (TAC-OH 3). This last finding is useful given the interest in gating the activity of synthetic ion transporters with external stimuli.     

(1+1) or (2+2) Coupling for bis(tosyloxyethoxy)benzenes with calix[4]arene and thiacalix[4]arene

As bifunctional reagents, bis(tosyloxyethoxy)benzenes can react with p-tert-butylcalix[4]arene or p-tert-butylthiacalix[4]arene to afford intramolecularly bridged (1+1) or intermolecularly bridged (2+2) products. It was found that the bridging pattern strongly depended on the structure of bis(tosyloxyethoxy)benzene and the kind of calixarene. For the ortho-isomer of bis(tosyloxyethoxy)benzene, intramolecularly bridged calix[4]arene and thiacalix[4]arene were the main products. For the para-isomer, the bridging reaction was in a (2+2) fashion. As for the meta-isomer, double thiacalix[4]arene and intramolecularly bridged calix[4]crown were synthesized.     

ABSORPTIVE IONOPHORES FOR Fe3+ CATION BY PARENT CALIX[n]ARENES

The absorption of Fe³⁺ ion from the aqueous phase to the solid phase was carried out by using p-tert-butyl calix[6]arene (L₁), calix[6]arene (L₂), p-tert-butyl calix[8]arene (L₃), and calix[8]arene (L₄). The effect of varying pH upon the absorption capability of parent calixarenes was examined. It was found that the compounds (L₁, L₂, L₃, and L₄) showed the highest extractability toward Fe³⁺ ion at 4.5–5.4. The calixarene L₂ shows a strong binding ability to Fe³⁺ ion. Based on the continuous variation method, calixarene L₂ formed 1:1 complex with Fe³⁺ ion.     

High extraction ability of 1,3-dialkynyl calixarene towards mercury（Ⅱ） ion

The reaction of 1,3-dipropyn-2-yloxycalix[4]arene with mercury(II)acetate could give mercury-containing alkynyl calixarenepolymer.The extraction behavior of 1,3-dipropyn-2-yl-oxycalix[4]arene towards mercury(II)ion was examined.When the moleratio of Hg~(2 )/calixarene was 1:1,the extractive percent can reach to 99.1%,and the extraction capacity was up to 431 mg/g.It couldalso decrease the Hg~(2 )concentration from 5 to 0.85 mg/L,which was only 17%of the national standard of effluent and satisfied thenational standard of drinking water.The extraction process included chemical reaction.     

A new fluorescent chemosensor for transition metal cations and on/off molecular switch controlled by pH

A new fluorescent chemosensor with imidazole as ionophore was synthesized by the selective derivation of calixarene, which can effectively recognize Cu²⁺ and Zn²⁺ leading to different fluoroscopic behaviors in CH₃OH-H₂O. This system could be considered as a molecular switch. By modulating the pH of the solution, on-off-on fluorescent switching is carried out upon combinatory addition of acid, base and Cu²⁺.     

Determination of alkali metal ion binding selectivities of calixarenes by matrix-assisted laser desorption ionization and electrospray ionization in a quadrupole ion trap

Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS) are used to evaluate the alkali metal ion binding selectivities of a series of calixarenes. Each calixarene of interest is mixed with one or more alkali metal salts (1:100 ratio of calixarene to metal), either in the ESI solution or on the MALDI probe surface, and the relative binding selectivities are directly determined from the intensities of the calixarene/metal complexes in the mass spectra. For t-butylcalix[4]arene-tetraacetic acid tetraethyl ester (calixarene 1), complexation of Na⁺ is favored over complexation of K⁺, in agreement with prior solution results obtained by conventional methods. For the three calixarenes that do not have t-butyl groups on the upper rims, the calixarenes preferentially bind K⁺ over Na⁺, thus demonstrating that size selective complexation can be probed with both the ESI and MALDI methods. Collision-activated dissociation results indicate that the phenyl oxygens, but not necessarily the ethoxy ethyl oxygens of the lower rims, are the primary binding sites for the alkali metal ions.     

Guests inducing p-sulfonatocalix[4]arenes into nanocapsule and layer structure

Reaction of sodium p-sulfonatocalix[4]arene and TbCl₃ in the presence of 2,2′-bipyridine-N,N′-dioxide (bpdo) gives the 2:1 supramolecular nanocapsule [[Tb(bpdo)₂·4H₂O]³⁺?{p-sulfonatocalix[4]arene⁴⁻}₂], which further interacts with the [Tb(bpdo)₄]³⁺ through charge-assisted π-stacking interactions forming a channel structure 1. In further investigation, we tried to use the terpyridine-1,1′,1′-trisoxide (tpto) instead of bpdo. Although we failed to isolate a supramolecular capsules based on the tpto, lanthanide and p-sulfonatocalix[4]arene, a layer structure derived from p-sulfonatocalix[4]arene with an unusual [Cu(tpto)₂]²⁺ incorporation into the cavity of the calixarene and an outside [Cu(tpto)₂]²⁺ balancing the charge, has been obtained. Fluorescence spectra show clearly that compound 1 possesses the luminescence characteristics of Tb³⁺ and the ligand bpdo can sensitize Tb³⁺ ion. Gas sorption experiment shows the channel structure 1 has highly selective gas sorption properties for water and methanol.     

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.     

A calixarene-based ion-selective electrode for thallium(I) detection

Three new calixarene Tl⁺ ionophores have been utilized in Tl⁺ ion-selective electrodes (ISEs) yielding Nernstian response in the concentration range of 10⁻²–10⁻⁶ M TlNO₃ with a non-optimized filling solution in a conventional liquid contact ISE configuration. The complex formation constants (log β_IL) for two of the calixarene derivatives with thallium(I) (i.e. 6.44 and 5.85) were measured using the sandwich membrane technique, with the other ionophore immeasurable due to eventual precipitation of the ionophore during these long-term experiments. Furthermore, the unbiased selectivity coefficients for these ionophores displayed excellent selectivity against Zn²⁺, Ca²⁺, Ba²⁺, Cu²⁺, Cd²⁺ and Al³⁺ with moderate selectivity against Pb²⁺, Li⁺, Na⁺, H⁺, K⁺, NH₄⁺ and Cs⁺, noting that silver was the only significant interferent with these calixarene-based ionophores. When optimizing the filling solution in a liquid contact ISE, it was possible to achieve a lower limit of detection of approximately 8 nM according to the IUPAC definition. Last, the new ionophores were also evaluated in four solid-contact (SC) designs leading to Nernstian response, with the best response noted with a SC electrode utilizing a gold substrate, a poly(3-octylthiophene) (POT) ion-to-electron transducer and a poly(methyl methacrylate)–poly(decyl methacrylate) (PMMA–PDMA) co-polymer membrane. This electrode exhibited a slope of 58.4 mV decade⁻¹ and a lower detection limit of 30.2 nM. Due to the presence of an undesirable water layer and/or leaching of redox mediator from the graphite redox buffered SC, a coated wire electrode on gold and graphite redox buffered SC yielded grossly inferior detection limits against the polypyrrole/PVC SC and POT/PMMA–PDMA SC ISEs that did not display signs of a water layer or leaching of SC ingredients into the membrane.     

Interactions of a water-soluble calix[4]arene with spermine: solution and solid-state characterisation

Abstract

The octaanionic 5,11,17,23-tetrasulfonato-25,26,27,28-tetrakis(hydroxycarbonylmethoxy)-calix[4]arene (cone conformation) (C₄TsTc) was investigated as a sensor for the biogenic tetracationic polyamine, spermine _.(H₄Spe⁴⁺). Fluorescence titration experiments of the water-soluble calixarene with spermine showed the formation of the 2:1 and 1:1 calixarene:spermine complexes in solution. The single crystal X-ray diffraction analysis of [(NaC₄TsTc)₄·(H₄Spe)₇] confirmed the formation of 2:1 and 1:1 calixarene:spermine species and showed that the water-soluble calixarene binds the spermine either by partially hosting it in the inner cavity or through the carboxylate groups on the lower rim. In order to investigate the effect of multivalent systems, supramolecular assemblies of octaanionic calixarene molecules templated by meso-tetrakis(4-N-methylpyridyl)porphyrin (H₂T₄) in different stoichiometric porphyrin:calixarene ratios (1:4 and 3:4) were also tested for spermine binding in solution. Fluorescence titration experiments with the 1:4 and 3:4 H₂T₄:C₄TsTc supramolecular complexes showed that the multivalent assemblies are more sensitive to the presence of spermine than the calixarene alone.     

An Efficient Way for the Recognition of Zinc Ion via the Fluorescence Enhancement

This study concentrates on the spectral and complexing properties of a tetraoxycalix[2]arene[2]triazine derivative bearing two bipyridines (Calix‐BIPY2) in a mixture of acetonitrile:chloroform (4:1, V:V). The results show that Calix‐BIPY2 has a highly selectivity and sensitivity towards Zn²⁺ over various competing cations (K⁺, Cu²⁺, Cd²⁺, Co²⁺, Fe²⁺, Hg²⁺, Ag⁺, Al³⁺ and Pb²⁺). The complexation of Zn²⁺ induces a remarkable fluorescence enhancement due to combination effects of the binding strength, electron spins state of metal ions, photoinduced charge transfer (PCT) and the rigidity of the complexing unit offered by calixarene‐based hosts.     

Number of species in complexation equilibria of SNAZOXS or Naphtylazoxine 6S and Cd(2+), Co(2+), Cu(2+), Ni(2+), Pb(2+) and Zn(2+) ions by PCA of UV-vis spectra

A critical comparison of the various PCA methods on the absorbance matrix data concerning the complexation equilibria between SNAZOXS and Cd²⁺, Co²⁺, Cu²⁺, Ni²⁺, Pb²⁺ and Zn²⁺ or Naphtylazoxine 6S and Cd²⁺, Cu²⁺, Ni²⁺ and Zn²⁺ at 25 °C is performed. The number of complex species in a complex-forming equilibria mixture is the first important step for further qualitative and quantitative analysis in all forms of spectral data treatment. Therefore, the accuracy of the nine selected index functions for the prediction of the number of light-absorbing components that contribute to a set of spectra is critically tested using the principal component PCA algorithm INDICES in S-Plus software. Four precise methods based upon a knowledge of the experimental error of the absorbance data and five approximate methods requiring no such knowledge are discussed. Precise methods always predict the correct number of components even a presence of the minor species in mixture. Due to the large variations in the index values and even at logarithmic scale they do not reach an obvious point where the slope changes. An improved identification with the second or third derivative and derivative ratio function for some indices is preferred. Behind the number of various complexes formed the stability constants of species ML, ML₂, (and ML₃, respectively) type log β₁₁, log β₁₂, (and log β₁₃, respectively) for the system of SNAZOXS (ligand L) with six metals (the standard deviation s(log β_pq) of the last valid digits are in brackets) Cd²⁺ (4.50(3), 8.36(7)), Co²⁺ (5.75(6), 9.79(9), 13.05(2)), Cu²⁺ (6.69(6), 11.40(7)), Ni²⁺ (6.44(8), 10.91(11), 15.07(10)), Pb²⁺ (5.63(5), 9.97(9)) and Zn²⁺ (5.11(3), 8.84(5)) and for system of Naphtylazoxine 6S with Cd²⁺ (6.08(4), 11.44(7), 16.06(11)), Cu²⁺ (7.80(8), 13.41(14)), Ni²⁺ (6.35(12), 11.43(19), 16.68(24)) and Zn²⁺ (7.01(8), 12.65(15)) at 25 °C are estimated with SQUAD(84) nonlinear regression of the mole-ratio spectrophotometric data. The proposed strategy of an efficient experimentation in a stability constants determination, followed by a computational strategy, is presented with goodness-of-fit tests and various regression diagnostics able to prove the reliability of the chemical model proposed.     

EPR of Mn2+ in [Co(H2O)6] PtCl6 single crystals: Estimation of Co2+ spin-lattice relaxation time

EPR of Mn²⁺ in single crystals of [Co(H₂O)₆]PtCl₆ has been studied from room temperature to 77 K at ∼ 9.35 GHz. Mn²⁺ has been found to substitute for Co²⁺ exhibiting a unique magnetic complex. The observation of resolved Mn²⁺ spectra has been interpreted in terms of a random modulation of the interaction between the Mn²⁺ and Co²⁺ ions by the rapid spin-lattice relaxation of Co²⁺ ions. It has been found that the effective spin-relaxation time T₁αT⁻ⁿ where n = 1.8 for 105 < T< 293 K.