Catalytic activity for decomposition of hydrogen peroxide by metal complexes of water-soluble thiacalix[4]arenetetrasulfonate on the modified anion-exchangers

The catalytic activity for the decomposition of hydrogen peroxide by anion-exchangers modified with metal complexes of thiacalix[4]arenetetrasulfonate (Me(n+)-TCAS[4], Me(n+)=Mn(3+), Mn(2+), Fe(3+), Co(3+), Co(2+), Cu(2+), Zn(2+) and Ni(2+)) was investigated. As a reference, calix[4]arenetetrasulfonate, calix[6]arenehexasulfonate and calix[8]areneoctasulfonate were also examined. Mn(3+)- and Fe(3+)-TCAS[4] on the modified anion-exchangers showed high catalytic activity in alkaline buffer solutions among metal complexes tested. Mn(3+)- and Fe(3+)-TCAS[4] on the modified anion-exchangers exhibited high and constant levels of catalytic activity even after having been used 5 times, and showed catalytic activity in the presence of an excess of H(2)O(2) over Mn(3+)- and Fe(3+)-TCAS[4] on the modified anion-exchangers. Only Mn(3+)-TCAS[4] on the modified anion-exchangers exhibited high catalytic activity at around a neutral pH.     

Novel anion receptors based on thiacalix[4]arene derivatives

Starting from the thiacalix[4]arene tetraacetate, novel derivatives bearing four ureido or thioureido functions on the lower rim have been prepared. As proven by NMR titrations, these compounds can bind anions via hydrogen bonding interactions and represent the first example of anion receptors in the thiacalixarene series.     

Spectrofluorometric determination of hydrogen peroxide based on oxidative catalytic reactions of p-hydroxyphenyl derivatives with metal complexes of thiacalix[4]arenetetrasulfonate on a modified anion-exchanger.

The peroxidase-like catalytic activity of metal complexes of thiacalix[4]arenetetrasulfonate (TCAS[4]) on a modified anion-exchanger (Me(n+)-TCAS[4]A-500; Me(n+) = H2, Fe3+, Fe2+, Mn3+, Co3+, Co2+, Cu2+, Zn2+, Ni2+) for the oxidation of p-hydroxyphenyl derivatives to produce fluorescent substances in the presence of hydrogen peroxide has been investigated. Among the Me(n+)-TCAS[4]A-500 tested, Fe(3+)-TCAS[4]A-500 exhibited the highest level of catalytic activity for the oxidation of p-acetoamidophenol in a carbonate buffer solution of pH 10. The catalytic activity of Fe(3+)-TCAS[4]A-500 was then used for the spectrofluorometric determination of hydrogen peroxide. The calibration curve for the Fe(3+)-TCAS[4]A-500 method was linear over a range spanning from 0.1 to 5.0 microg of hydrogen peroxide in a 1.0 ml sample solution.     

Comparative study on the transition metal complexes of a novel thiacalix[4]arene derivative

A comparative study on Zn²⁺ and Cu²⁺ complexes of the novel compound 5,11,17,23-tetra-tert-butyl-25,27-bis{[4-(methoxycarbonyl)phenyl]methoxy}-2,8,14,20-tetrathiacalix[4]arene, that possesses potential as a core unit for the construction of molecular receptors, is presented using semiempirical AM1 calculation. The possible structures of each metal complex and their corresponding energetic data are compared with the parent 5,11,17,23-tetra-tert-butyl-2,8,14,20-tetrathiacalix[4]arene. The complexation ability of both thiacalix[4]arenes towards the two metal ions is discussed on the basis of binding energies. Both thiacalix[4]arene 1:1 complexes show higher complexation ability towards Cu²⁺. However, 5,11,17,23-tetra-tert-butyl-25,27-bis{[4-(methoxycarbonyl)phenyl]methoxy}-2,8,14,20-tetrathiacalix[4]arene presents lower complexation ability when compared with the 5,11,17,23-tetra-tert-butyl-2,8,14,20-tetrathiacalix[4]arene. The results of liquid–liquid extraction experiments of the thiacalix[4]arenes are in good agreement with the theoretical calculations.     

Inclusion behavior of thiacalix[4]arenetetrasulfonate toward water-miscible organic molecules studied by salting-out and X-ray crystallography

[reaction: see text] Inclusion ability of thiacalix[4]arenetetrasulfonate (TCAS) toward water-miscible organic molecules such as alcohols, ketones, cyclic ethers, and so on was studied by salting-out of the inclusion complex. NMR spectra of the recovered precipitates showed size selectivity to include the guest molecules. X-ray crystallographic analyses of TCAS salts including acetone and 1,4-dioxane suggested that guests are retained with the aid of cation coordination and H-bonding.     

Regulation of metal ion recognition by allosteric effects in thiacalix[4]crown based receptors

Three new ditopic receptors 3a-c based on thiacalix[4]arene of 1,3 alternate conformation possessing two different complexation sites have been designed and synthesized for both soft and hard metal ions. The imino nitrogens bind soft metal ion (Ag⁺/Pb²⁺/Cu²⁺) and the crown moiety binds K⁺ ion. The preliminary investigations show that 3a-c behave as ditopic receptors for Ag⁺/K⁺, Pb²⁺/K⁺, and Cu²⁺/K⁺ ions, respectively. In all the three receptors it was observed that the formation of 3a·Ag⁺/3b·Pb²⁺/3c·Cu²⁺ complex triggers the decomplexation of K⁺ ion from crown moiety and acts as a gateway, which regulates the binding of alkali metal to crown moiety. Thus, allosteric binding between metal ions ‘switch off’ the recognition ability of crown ether ring.     

Alkylation of thiacalix[4]arenes

Thiacalix[4]arenes were alkylated using procedures well established in ‘classical’ calixarene chemistry (PrI/K₂CO₃/acetone or PrI/NaH/DMF) to reveal conformational preferences in the thiacalixarene series. Surprisingly, the conformer distribution of tetraalkylated products is different from that of calix[4]arene. The 1,3-alternate conformers are well accessible in high yields (>60%) while the cone conformation forms only in very low yields (<20%). Moreover, the conformational outcome of the alkylation strongly depends on the upper rim substitution (tert-butyl versus H).     

Stereoselective alkylation of thiacalix[4]arenes

A direct tetraalkylation of thiacalix[4]arenes using procedures well established in ‘classical’ calixarene chemistry usually gives the 1,3-alternate conformers as the main product (n-PrI/K₂CO₃/acetone) while the cone conformers are obtained only in very poor yields (n-PrI/NaH/DMF). Surprisingly, the so far almost inaccessible cone conformers can be prepared in high yields using the two-step procedure: dialkylation-dialkylation, opening the way for their further utilisation in supramolecular chemistry.     

Alkali-metalated forms of thiacalix[4]arenes

The alkali metal salts [TCALi4] (1), [TCANa4] (2), and [TCALK4] (3) of fully deprotonated p-tert-butyltetrathiacalix[4]arene (H(4)TCA) are readily available from the reactions of thiacalix[4]arene and n-BuLi, NaH, or KH as deprotonating reagents. Crystals of the sodium salts 2 and the potassium salt 3 suitable for X-ray diffraction were obtained in the form of the pyridine solvates [(TCA)2Na8.8py] (2.8py) and [(TCA)2K(8).8py] (3.8py). These molecules are dimers in the solid state but are structurally not related. In addition, the reaction of H(4)TCA and lithium hydroxide afforded the structurally characterized complex [(TCA)Li5(OH).4THF] (4). The molecular structure of 4 as well as the structures of 2.8py and 3.8py reveal a close relationship to the corresponding alkali metal salts of the calix[4]arenes.     

Composition of thiacalix[4]arene complexes with monovalent metal ions in the gas phase: MALDI mass spectrometry

MALDI-TOF mass spectrometry was used to study the reaction of p-tert-butylthiacalix[4]arene (1) and a number of its derivatives disubstituted at the lower rim (2—9) with monovalent metal salts (Li, Na, K, Cs, Cu, Ag) in the gas phase. It was shown that the thiacalixarenes under study bind the metal ions through the substitution of hydrogen atoms of the hydroxy groups. The reactions of silver and copper salts with the thiacalix[4]arenes were found to form the cluster ions, which represent the macrocycle dimers with several metal ions, while the formation of such clusters is impossible in the case of alkali metal salts. The peak intensities of the cluster ions increase in the weakly basic medium, reaching in some cases 100%.     

Upper rim substituted thiacalix[4]arenes

The synthesis and structure of new tetrahydroxythiacalix[4]arenes, existing in the cone conformation and possessing reactive bromide, chloromethyl or diorganylphosphoryl groups on the upper rim of the macrocycle are described. The molecular structure of tetrakis(diisopropoxyphosphorylmethyl)thiacalix[4]arene was examined by X-ray crystallography.     

A series of octanuclear-nickel(II) complexes supported by thiacalix[4]arenes

A series of discrete complexes, [Ni(8)(BTC4A)(2)(μ(6)-CO(3))(2)(μ-CH(3)COO)(4)(dma)(4)]·H(2)O (1), [Ni(8)(BTC4A)(2)(μ(6)-CO(3))(2)(μ-Cl)(2)(μ-HCOO)(2)(dma)(4)]·2DMF·2CH(3)CN (2), [Ni(8)(PTC4A)(2) (μ(6)-CO(3))(2)(μ-CH(3)COO)(4)(dma)(4)]·DMF (3), and [Ni(8)(PTC4A)(2)(μ(6)-CO(3))(2)(μ-OH)(μ-HCOO)(3) (dma)(4)] (4) (p-tert-butylthiacalix[4]arene = H(4)BTC4A, p-phenylthiacalix[4]arene = H(4)PTC4A, dma = dimethylamine, and DMF = N,N'-dimethylformamide), have been prepared under solvothermal conditions and structurally characterized by single-crystal X-ray diffraction analyses, powder XRD, and IR spectroscopy. These four complexes are stacked by dumbbell-like building blocks with one chairlike octanuclear-nickel(II) core, which is capped by two thiacalix[4]arene molecules and connected by two in situ generated carbonato anions and different auxiliary anions. This work implied that not only the solvent molecules but also the upper-rim groups of thiacalix[4]arenes have significant effects on the self-assembly of the dumbbell-like building blocks. The magnetic properties of complexes 1-4 were examined, indicating strong antiferromagnetic interactions between the nickel(II) ions in the temperature range of 50-300 K.     

Anion receptors based on ureido-substituted thiacalix[4]arenes and calix[4]arenes

The regioselective nitration of 25,27-dipropoxythiacalix[4]arene was carried out as a key step in the synthesis of thiacalix[4]arene derivative bearing two arylureido functions on the upper rim. The preorganisation of ureido units using the thiacalix[4]arene/calix[4]arene moieties as a molecular scaffold gave novel anion receptors. These compounds, albeit based on hydrogen bonding interactions, show good complexation ability even in highly HB-competitive solvent, such as DMSO. Direct comparison of otherwise identical structures 6a and 7a revealed remarkable dominance of the thiacalix[4]arene derivative over its classical analogue in anion binding.     

Synthesis and complexation properties towards metal ions of new tri-substituted thiacalix[4]arenes

New thiacalix[4]arenes appended with three amide functions have been prepared. Their conformations have been solved thanks to ¹H NMR 2D correlation spectroscopy (COSY) and nuclear overhauser and exchange spectroscopy (NOESY). The complexation ability of these ligands towards various metal ions (Cd^2 + , Pb^2 + , Pd^2 + , Ni^2 + , Hg^2 + , Hg⁺, Ag⁺, Zn^2 +  and Cu^2 + ) has been investigated by the UV–vis absorption and the stoichiometry of the metal–ligand complexes was determined.     

Synthesis of a deep-cavity thiacalix[4]arene

A novel thiacalix[4]arene derivative bearing four phenyl groups on the upper rim was prepared by the direct condensation of biphenyl-4-ol with elemental sulphur. As revealed by X-ray diffraction analysis, this compound adopts the cone conformation in the solid state, thus creating a cavity with an extended π-aromatic system potentially applicable for solid-state inclusion of suitable molecules. Subsequent alkylation (RI/K₂CO₃/acetone, R=Me, Et, Pr) yielded tetraalkylated derivatives, which were studied for their conformational preferences using ¹H NMR spectroscopy. While the Me or Et derivatives are conformationally mobile and exhibit thermodynamic equilibria of several conformers in solution (CDCl₃ or CD₂Cl₂), the corresponding propoxy derivative is infinitely stable at room temperature.     

Determination of hydrogen peroxide by iron(III) complex of thiacalix[4]arenetetrasulfonate on a modified ion-exchanger with peroxidase-like catalytic activity.

An iron(III) complex of thiacalix[4]arenetetrasulfonate on a modified anion-exchanger (Fe3+-TCAS(A-500)) has shown high peroxidase-like activity at pH 5 - 6 for the reaction of quinoid-dye formation between 3-methyl-2-benzothiazolinone hydrazone and N-(3-sulfopropyl)aniline in the presence of hydrogen peroxide. Utilizing the peroxidase-like activity of Fe3+-TCAS(A-500) for this reaction, a method using Fe3+-TCAS(A-500) was applied for the spectrophotometric determination of hydrogen peroxide. The calibration curve by the method using Fe3+-TCAS(A-500) was linear over the range from 1 to 10 microg of hydrogen peroxide in a 1 ml sample solution. The apparent molar absorptivity for hydrogen peroxide was 2.4 x 10(4) l mol(-1) cm(-1). which was about 80% of that by peroxidase under the same conditions. This determination method of hydrogen peroxide using Fe3+-TCAS(A-500) was applied for the determination of glucose in diluted normal and abnormal control serum I and II.     

Monosubstituted lower rim thiacalix[4]arene derivatives

A clean and partially green route to monoalkyled thiacalix[4]arenes has been demonstrated. We have discovered that tetraalkylammonium halide can cleave selectively one of the two aryl alkyl ethers of dialkylated para-tert-butylthiacalix[4]arenes. Thus, p-tert-butyl thiacalix[4]arenes differently monoalkyled at the lower rim with acetyl, propyl, and benzyl group were synthesized in good yield.     

Synthesis and metal complexation studies of [2n]thiacalix[m]arene[m]pyrazine

Novel [2_n]thiacalixarenepyrazine and [2_n]thiacalixarenetriazine systems were synthesised by one-pot S_NAr reactions. A screening of the metal-complexing ability of [2₆]hexathiacalix[3]arene[3]pyrazine revealed its affinity for Cu^I, Cu^II and Ag^I metal salts.     

Pyridinyl hydrazone derivatives of thiacalix[4]arene as selective extractants of transition metal ions

The recognition ability of pyridinyl hydrazone derivatives of cone- and 1,3-alternate tetrathiacalix[4]arenes towards transition and alkali metals has been investigated by picrate extraction method. The stoichiometry of complexes and the extraction constants have been determined. It has been found that hydrazones do not extract alkali metal ions but show an excellent affinity towards transition and heavy metal cations. The removal of tert-butyl groups from calix[4]arene platform in the case of cone and 1,3-alternate isomers leads to an increase of d-ion extraction selectivity or efficiency.     

Unique self-assembly patterns based on thiacalix[4]arene-silver interactions

Novel self-assembled supramolecular networks were prepared by the interactions of thiacalix[4]arenes bearing simple alkyl groups on the lower rim (4×MeO-, 4×n-PrO-) with silver triflate. Contrary to the classical calix[4]arenes (with CH₂ bridges between the aromatic moieties), the presence of four sulfur atoms enables the formation of S-Ag-S connections between the individual molecules leading to the coordination topology so far unknown in calixarene chemistry. These systems form infinite 1-D coordination polymeric structures in the solid state, where the thiacalixarene moieties are preorganized in a side-by-side arrangement. Interestingly, the linear coordination polymers were obtained using both the conformational immobilised (4×n-PrO, cone, 1,3-alternate conformers) and the conformational mobile (4×MeO) thiacalix[4]arenes, which indicates the generality of this behaviour in thiacalixarene series.