Synthesis and self-assembly of novel calix[4]arenocrowns: formation of calix[4]areno[2]catenanes

A series of novel calix[4]arenocrowns 1a-c were efficiently synthesized by a one-pot reaction of calix[4]monohydroquinone diacetate 5 with ditosylate 6 and its analogues in the presence of sodium hydroxide. It was found that the calix[4]arenocrowns could form stable pseudorotaxane-type complexes 2a-c with paraquat, and further self-assemble into calix[4]areno[2]catenanes 3a-c with dicationic salt 8 and p-bis(bromomethyl)benzene.     

Squaramide-substituted calix[4]pyrrole: Synthesis and ion binding studies

Squaramide-substituted calix[4]pyrrole 2 was synthesized and its anion-binding properties were investigated. On the basis of UV spectroscopy, ¹H NMR spectroscopic and computational DFT model analyses, compared with the parent calix[4]pyrrole 1, compound 2 shows significantly enhanced binding affinities for anions in CH₂Cl₂, and it was concluded that this increase in affinity is ascribed to participation of the squaramide unit in anion binding.     

N-confused calix[4]pyrroles

This is a first review devoted to N-confused calix[4]pyrroles (NCCPs). NCCPs are a relatively recent arrival to the family of the pyrrole-based anion binding macrocycles, being for the first time identified in 1999. Yet, in a relatively short time these calix[4]pyrrole (CP) isomers attracted attention of the community of research groups interested in anion binding and sensing. This is because they are relatively easy to synthesize, but mainly because they posses anion-binding properties that are different from that of regular calix[4]pyrroles. The difference in anion-binding properties stems from a different binding mode between the NCCP and anion. While the regular CPs adopt in the complex an ideal cone-like conformation where all four pyrroles-NHs engage in hydrogen bonding to the anion, the inverted pyrroles do not allow forming the cone. NCCPs bind anions via a confused cone (CC), by three NH hydrogen bonds with an anion and a CH–anion contact. This different binding mode results also in different anion-binding affinity and selectivity compared to regular CPs. Also, the inverted pyrroles offer a unique possibility for selective chemical modification of the receptor. The corresponding colorimetric sensors were tested for anion binding applications. The results of colorimetric assays for anions are presented and potential applications discussed.     

Effect of fluorine substitution in calix[4]pyrrole: A DFT study

Using density functional theory we investigate the ground-state geometries and electronic structures of calix[4]pyrrole (C4P) and its fluorine analogue (F-C4P). The HOMO–LUMO energy gap of C4P is 5.9 eV and remains nearly the same upon H-by-F replacement (5.7 eV). Fluorine substitution increases both the vertical and adiabatic ionization potentials of C4P by 0.8 eV while the electron affinity of either macrocycle is negative thus indicating that the corresponding radical anion in the gas-phase is thermodynamically unstable. It is shown that the topology of the LUMOs of both C4P and F-C4P have important implications for the spherical recognition of halide anions. The simulated IR, NMR, and electronic spectra display important fingerprints for the characterization of these macrocycles.     

Potentiometric sensors based on poly(3,4-ethylenedioxythiophene) (PEDOT) doped with sulfonated calix[4]arene and calix[4]resorcarenes

Potentiometric ion sensors have been prepared by galvanostatic electrosynthesis of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with p-sulfonated calix[4]arene (C[4]S) and p-methylsulfonated calix[4]resorcarenes (R_n[4]S) with alkyl substituents of different chain length (R₁=CH₃; R₂=C₂H₅; R₃=C₆H₁₃). The bowl-shape of these doping ions makes them suitable as ionic recognition sites, and their bulky character is expected to prevent them from leaching out of the conducting polymer membrane. For comparison, sensors based on PEDOT doped with poly(styrene sulfonate) (PSS) and poly(vinyl sulfonate) (PVS) were also constructed. The resulting GC/PEDOT electrodes were conditioned in 0.01 mol L^–1 AgNO₃ and their performance as Ag⁺ ion-selective electrodes (ISEs) studied. Results reveal that selectivity and lifetime of the electrodes is affected by the doping anion structure, although all electrodes show selectivity towards Ag⁺ ions. Interaction of Ag⁺ with sulfur atoms present in the conducting polymer backbone is considered to be the main reason for this behavior. A second set of electrodes was constructed and conditioned in 0.1 mol L^–1 KCl. These electrodes were tested in chloride solutions of quaternary ammonium cations, showing that C[4]S and R₂[4]S exhibit significant sensitivity towards pyridinium.Dedicated to Professor György Horányi on the occasion of his 70th birthday in recognition of his outstanding contributions to electrochemistry     

A novel calix[4]arene fluorescent receptor for selective recognition of acetate anion

A novel bridged fluorescent calix[4]arene with 1,8-diaminoanthracene and glycine at the upper rim has been prepared, which exhibited selective recognition towards AcO⁻ over other anions such as F⁻, Cl⁻, Br⁻, , , I⁻ and by fluorescence spectroscopy and ¹H NMR method.     

Calix[4]quinones. Part 4: The ClO2 oxidation of calix[4]arene dialkyl ethers

Except for the special case of calix[4]arene diethyl ether 1, the chlorine dioxide oxidation of dialkyl ethers 2-5 yielded only the corresponding calix[4]diquinone dialkyl ethers 8-11. Chlorine dioxide oxidation of calix[4]arene diethyl ether 1 produced two isomeric products 6 and 7, which were stable enough to be isolated by column chromatography. However, a slow conformational interconversion between isomeric pair 6 and 7 was observed at room temperature, and the equilibrium was reached after 400 h at 18 °C with an amount of 5:3 in favor of syn-isomer.     

Siloxane-functionalized calix[4]pyrrole: synthesis, characterization and modification of silica-based solid supports

A siloxane-functionalized calix[4]pyrrole derivative was synthesized starting from the corresponding alcohol-functionalized calix[4]pyrrole. Structural elucidation was carried out by using NMR spectroscopy, mass spectrometry and X-ray diffraction analysis. The use of this siloxane-functionalized calix[4]pyrrole for modification of various silica solid supports (silica gel 60, fume silica, and SiO₂ nanopowder) was studied. Characterization of the modified silica solid supports was achieved by FTIR, TGA, and elemental analysis. It was also shown that the production of silica nanoparticles is possible via a sol-gel reaction of siloxane-functionalized calix[4]pyrrole and tetraethoxysilane (TEOS). Calix[4]pyrrole modified silica solid supports were found to sense chloride anions of Azure A dye.     

The synthesis of calix[4]crown based dendrimer

A second generation of dendrimer with calixcrown as repeat unit was first synthesized. Its structure and conformation was determined by ¹H NMR and MALDI-TOF mass spectra.     

Highly selective transport of silver ion through a supported liquid membrane using calix[4]pyrroles as suitable ion carriers

Facilitated transport of silver ion across a supported liquid membrane (SLM) by calix[4]pyrroles, as selective ion carriers, dissolved in kerosene has been investigated. The influences of fundamental parameters affecting the transport of silver ion including ion carrier concentration in the membrane phase, thiosulfate concentration in strip phase, picric acid concentration in the feed phase, stirring speed of aqueous phases, type of membrane solvent and time of transport have been studied. In the presence of thiosulfate as a suitable metal ion acceptor in the strip phase and picrate ion as ion pairing agent in the source phase, transport of silver occurs almost quantitatively after 75 min. The selectivity and efficiency of silver transport from aqueous solution containing Cu²⁺, Mg²⁺, Ni²⁺, Ca²⁺, Zn²⁺, Pb²⁺, Co²⁺, Al³⁺, Hg²⁺, Cd²⁺, Fe³⁺, Fe²⁺ and Cr³⁺ were investigated.     

Synthesis and Properties of Functionalized Schiff Bases of 5α,10α-Di（4-hydroxylphenyl）calix[4]pyrrole and 5α,15β-Di（4-hydroxylphenyl）calix｜4] pyrrole

A series of calix[4]pyrrole meso-substituted Schiff bases was synthesized with 5α,10α-di（4- hydroxylphenyl）calix[4]pyrrole or 5α,15β-di（4-hydroxylphenyl）calix[4]pyrrole as starting materials. The synthetic routes included alkylation with methyl a-chlroroaceate, ammonolysis with alkylene diamine, and condensation with salieylladehyde or 2-hydroxynaphthaldehyde. The crystal structures of the new calix[4]pyrroles and their Schiff bases were determined by X-ray diffraction. The coordination properties of the representative ealix[4]pyrrole Sehiff bases to transition metal ions were also investigated by UV-Vis spectra.     

New redox anion receptors based on calix[4]pyrrole bearing ferrocene amide

Two redox anion receptors based on calix[4]pyrrole and ferrocene have been synthesized. The electrochemical investigation revealed that these compounds can be response to the anions with different shifts of Fc/Fc⁺ couple. With the ¹H NMR titration study, the selectivity to F⁻ and AcO⁻ ions in CD₃CN solution was confirmed. The conformations of the mono-aromatic meso-substituted calix[4]pyrroles, which were the synthetical intermediate of the ferrocene based receptors, and their anion complexes in the solid state have also been studied by single X-ray crystallography, and the rationality of the crystal conformations was proved by theoretical study.     

Mono Halogen Substituted Calix[4]pyrroles: Fine-tuning the Anion Binding Properties of Calix[4]pyrrole

Abstract

Single halogen atom (i. e. I, Br, Cl and F) substituted calix[4]pyrroles, compounds 2, 3, 4 and 5, were synthesized. Studies of these systems reveal that replacement of a single β-pyrrolic hydrogen atom can increase the anion binding ability of calix[4]pyrroles for a variety of anions (e. g. Cl^?, Br^?, H₂PO₄ ^? and HSO^? ₄) relative to normal non-halogen substituted calix[4]pyrrole 1. In the case of chloride anion, the expected relative affinity sequence of 5 > 4 > 3 > 2 was observed. This was not found to be true for Br^?, H²PO^? ₄, and HSO^? ₄. Here, the chlorine substituted calix[4]pyrrole 4 was found to display a slightly higher affinity in the case of each anion than the fluorine-bearing derivative 5. This was rationalized in terms of intermolecular NH … F hydrogen bonding interactions being present in CD₂Cl₂ solutions of 5. Support for this latter conclusion came from concentration and temperature-dependent NMR spectroscopic studies.

A matched set of mono halogen substituted calix[4]pyrroles was used to study in detail, the extent to which halogen substituents may be used to fine-tune the anion binding properties of calix[4]pyrroles.     

Head-to-tail connected double calix[4]arenes

Summary New macrotricyclic compounds consisting of two calix[4]arene substructures connected by aliphatic chains of various length (three to five carbon atoms) between two oppositep-positions and two distal phenolic oxygens have been synthesized. Starting withp-tert-butyl-calix[4]arene, two O-protected phenolic units are attachedvia ether links in 1,3-position by reaction with the corresponding tosylates. After deprotection, the new calix[4]arene is formed by fragment condensation with 2,6-bisbromomethylated 4-alkylphenols. The structure of one example (8c) has been confirmed by single crystal X-ray analysis. Both calixarene parts assume the cone conformation, a molecule of acetonitrile being included in both cavities.

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Doppelte Calix[4]arene in Kopf-Schwanz-Verknüpfung

Zusammenfassung Neue makrotricyclische Verbindungen, in denen zwei Calix[4]aren-Einheiten durch aliphatische Ketten unterschiedlicher Länge (drei bis fünf C-Atome) zwischen zwei gegenüberliegendenp-Positionen und zwei gegenüberliegenden Phenolsauerstoffen verknüpft sind, wurden hergestellt. Ausgehend vonp-tert-Butyl-calix[4]aren werden zunächst zwei O-geschützte Phenolbausteine in 1,3-Stellung durch Umsetzung mit den entsprechenden Tosylaten etherartig gebunden. Nach Abspaltung der Benzylether-Schutzgruppe wird durch Fragmentkondensation mit 2,6-bisbrommethylierten 4-Alkylphenolen das neue Calix[4]aren gebildet. Für8c wurde die Struktur durch Einkristallröntgenstrukturanalyse bestätigt. Beide Calixarenteile nehmen diecone-Konformation ein, wobei in die beiden Hohlräume je ein Molekül Acetonitril eingeschlossen wird.

     

Conformational instability of a proximally-difunctionalized calix[4]-diquinone

We have recently described the electrochemical oxidation of 5,11,17,23-tetra-tert-butyl-25, 26-bis(diphenylphosphinoylmethoxy)-27,28-dihydroxycalix[4]arene into the corresponding diquinone 1. The solid state structure of 1 has now been determined by a single crystal X-ray diffraction study. Diquinone 1 crystallizes in the monoclinic space group with a=10.3507(12), b=25.219(4), c=20.2315(14) Å, β=101.166(8)°, V=5181.1(10) Å³, Z=4, and D_x=1.273 g cm⁻³. The calixarene skeleton adopts a partial cone conformation in which one quinone ring is anti-oriented with respect to the other three rings of the calixarene core. A variable temperature NMR study shows that 1 is dynamic in solution, each quinone unit undergoing fast oscillation about the axis that passes through the two meta carbon atoms bonded to the adjacent methylene groups. The motion of the quinone rings was confirmed by 2D NMR experiments.     

A novel calix[4]arene-based neutral semicarbazone receptor for anion recognition

A series of novel calix[4]arene-based neutral semicarbazone and thiosemicarbazone receptors have been synthesized and characterized. The molecular receptor 4a recognizes in preference to other anions (Cl⁻, Br⁻, I⁻, , and ) through a 1:1 binding-stoichiometry.     

Dendritic octa-CMPO derivatives of calix[4]arenes

Calix[4]arenes substituted at the narrow or wide rim by eight carbamoylmethyl-phosphine oxide (CMPO) functions in a dendritic manner were synthesised and studied in extraction of Eu³⁺ and Am³⁺ from aqueous nitric acid into o-nitrophenylhexyl ether. ¹H NMR relaxivity titrations for a wide rim octa-CMPO reveal the clear formation of a solvent-free 1:2 ligand/metal complex, while the wide rim tetra-CMPO formed oligomeric complexes under similar conditions.     

Aminolysis reaction of calix [ 4 ] arene esters and crystal structures and conformational behaviors of calix[4]arene amides

We first make use of aminolysis of calix[4]arene esters to synthesize calix[4]arene amides. When the two ethyl esters of the calix[4]arene esters are aminolysized, the 1, 3-amide derivative is formed selectively. The crystal structures of the calix-[4]arene with two butyl amide (3b) and four butyl amide moieties (4b) were determined. The intermolecular hydrogen bonds make 4b form two-dimensional net work insolid state. The 1H NMR spectra prove that 3b is of a pinched cone conformation, while 4b and tetraheptylamide-calix[4]arene (6b) take fast interconversion between two C2v isomers in solution and appear an apparent cone conformation at room temperature. As decreasing temperature, the interconversion rate decreases gradually and, finally, the interconversion process is frozen at Tc = -10℃, which makes both conformations of 4b and 6b the pinched cone structures. The hydrogen bond improves the interconversion barrier, and the large different values of the potential barrier between 6b and 4b (or 6b) may     

Molecular octopus: octa functionalized calix[4]resorcinarene-hydroxamic acid [C4RAHA] for selective extraction, separation and preconcentration of U(VI)

A solvent extraction separation of uranium, in the presence of thorium, cerium and lanthanides with a new calix[4]resorcinarene bearing eight hydroxamic acid groups (C4RAHA) is described. Quantitative extraction of uranium is possible in ethyl acetate solution of C4RAHA at pH 8.0. The lambda(max) and molar absorptivity (varepsilon) for uranium is 356nm and 8352Lmol(-1)cm(-1). The Binding ratio of uranium with C4RAHA as evaluated by Job's method is 4:1. The system obeys Beer's law over the range 0.075-6.0mugml(-1) of uranium with Sandell sensitivity 0.0284mugcm(-2). A preconcentration factor of 142 was achieved by directly aspirating the extract for GF-AAS measurements. The two-phase stability constant evaluated at 25 degrees C for uranium is 15.91. The complexation is characterized by favorable enthalpy and entropy changes. A liquid membrane transport study of uranium was carried out from source to the receiving phase under controlled conditions and a mechanism of transport is proposed. Uranium has been determined in standard and environmental samples.