Bis(calix[4]diquinone) receptors: cesium- and rubidium-selective redox-active ionophores

A new class of redox-active ionophore comprised of two calix[4]diquinone moieties connected through either alkylene or pyridylene linkages has been developed. Spectroscopic and electrochemical investigations, X-ray crystal structure analyses, and molecular modeling studies show butylene- and propylene-linked members of this family of redox-active receptors exhibit remarkable selectivity preferences and substantial electrochemical recognition effects toward cesium and rubidium cations.     

Lanthanoid coordination with a tetrazole-substituted calix[4]diquinone and calix[4]dihydroquinone

The tetrazole-functionalised calixdiquinone 5,17-di-tert-butyl-26,28-bis-(1H-tetrazole-5-ylmethoxy)-calix[4]-25,27-diquinone Q was synthesised by chemical oxidation of the bis-tetrazole calix[4]arene precursor using PbO₂/HClO₄. The single crystal X-ray structure determination of Q confirmed the structure and showed binding of a water molecule in the solid state. Chemical reduction of Q to the dihydroquinone QR was achieved using N,N-diethylhydroxylamine. Comparison of the solution phase photophysical properties of Q or QR in the presence of terbium ions showed significant excitation only with QR, suggesting redox switching of the photophysical response may be possible with this or similar receptor.     

Theoretical study on conformational features and cation-binding properties of a diquinone calix[4]arene

Theoretical studies of a diquinone calix[4]arene and its interactions with the cations Li⁺, Na⁺, K⁺ and Ag⁺ have been performed. Conformational features and cation-binding properties were evaluated with the restricted hybrid Becke three-parameter exchange functional method using the 6-31G(d) basis set and its relativistic effective core potentials. To model the effect of medium, the polarisable continuum model was also used. Four typical conformations of the parent diquinone calix[4]arene were studied. The calculated results show that the most stable conformers are 1,3-alternate and partial cone in the gas phase and in CH₂Cl₂ solution, respectively. The optimised geometric structures were used to perform natural bond orbital analysis. The two main types of driving force metal–ligand and cation–π interactions are investigated. The calculated binding energy for cations (Li⁺, Na⁺, K⁺ and Ag⁺) is discussed. The calculated results indicate that cone complexes are the most stable.     

Conformational features of an actuator containing calix[4]arene and thiophene: a molecular dynamics study

Molecular dynamics simulations have been performed for poly(calix[4]arene bis(bithiophene)) in dichloromethane solution. This material responds to its electronic structure variations with significant conformational changes, producing contraction-expansion movements. Simulations have been performed for the three states of this molecular actuator (reduced, oxidized-nondeprotonated, and oxidized-deprotonated), a specific force-field being developed for each case. Results, which are fully consistent with previous ab initio quantum mechanical calculations on an isolated actuating unit, have revealed important findings about the dynamics of the system. Analyses of the flexibility/rigidity of the molecular chain with the state, the interaction of the polymer with the solvent molecules and the influence of environmental factors (as the viscosity of solvent, the counterions and the thermal agitation) on the dynamics have provided important insights to the actuation mechanism.     

Functionalized thiacalix- and calix[4]arene-based Ag ionophores: synthesis and comparative NMR study

Thiacalix[4]arene ionophores comprised of cyclic or linear O,S,N ligating and/or π-coordinate groups on the lower rim were synthesized and their Ag⁺ binding was studied by ¹H NMR methods in comparison with the respective known and novel calix[4]arene counterparts. Calix[4](O,S,N)crowns were found stronger binders than the π-coordinate molecules and thiacalixarene ionophores were generally superior to calixarenes. This study helped to develop silver ion-selective electrodes working in the subnanomolar region.     

提篮型杯[4]芳烃冠醚的合成及其对铯离子络合性能的研究

本文从去叔丁基化的杯[4]芳烃出发,先后分别在1,3-和2,4-酚羟基位点上引入正辛烯基和支链冠醚,最后通过烯烃复分解反应,合成了一种新型的提篮型杯芳烃冠醚化合物,产物结构经过1H NMR和HRMSESI表征确定.分别采用1H NMR和UV-vis方法,研究了1,3-桥联成环后张力对另一端冠醚环络合选择性的影响.结果表...     

Dual colorimetric sensoring bis(indolyl)calix[4]crown-6

Calix-chromophore, bis(indolyl)calix[4]crown-6 (1) in an oxidized form showing selective colorimetric changes for both alkaline earth cations and F⁻ in CH₃CN, has been newly synthesized. It is observed that the binding ability of 1 for the Ca²⁺ binding enhances in the presence of F⁻. Compound 1 can operate three independent combinational NOR logic gates toward metal cations and anions.     

Exploring the dynamics of calix[4]pyrrole: effect of solvent and fluorine substitution

Molecular dynamics simulations show that calix[4]pyrrole (CP) and octafluorocalix[4]pyrrole (8F-CP) are extremely flexible molecules. CP mainly adopts the 1,3-alternate conformation in all the solvents, although the percentage of alternative conformations increases in polar solvents, especially those with good hydrogen-bonding acceptor properties. However, in the case of 8F-CP, the cone conformation is the most populated in some solvents. Transitions between conformers are common and fast, and both CP and 8F-CP can adopt the cone conformation needed for optimum interaction with anions more easily than would be predicted on the basis of previous gas-phase calculations. Furthermore, the present studies show that when a fluoride anion is specifically placed initially in close proximity to CP and 8F-CP in their respective 1,3-alternate conformations, an extremely fast change to the cone conformation is observed in both cases. The results suggest that preorganization does not represent a major impediment to anion-binding for either CP or 8F-CP, and that ion-induced conformational changes can follow different mechanisms depending on the solvent and the chemical substituents present on the calix[4]pyrrole beta-pyrrolic positions.     

Diazo-coupled calix[4]arenes for qualitative analytical screening of metal ions

New chromogenic diazophenylcalix[4]arenes 1 and 2 were synthesized in cone conformation. Compound 1 with the ortho-carboxyl groups in CH₃CN solution preferentially binds with alkaline earth and transition metal ions, whereas no significant changes in absorption spectra are observed in the presence of alkali metal ions. While 2 with the ortho-ester groups shows selective complexation properties towards transition metal ions over alkali and alkaline earth metal ions. The detection of metal ions gives rise to bathochromic shifts in the absorption spectra (from orange/yellow to red), which is clearly visible even to the naked eye. According to the selective color changes using both receptors upon cation complexation, one can set up a qualitative analytical routine to screen alkali, alkaline earth, and transition metal ions.     

Synthesis of (thia)calix[4]arene oligomers: towards calixarene-based dendrimers

Thiacalix[4]arenes bearing two or four carboxylic functions on the lower rim served as starting compounds for the synthesis of novel calixarene oligomers connected by amidic functions. The cone conformers react smoothly with four molecules of 5-amino-calix[4]arene to yield the corresponding pentakis-calixarenes. On the other hand, because steric hindrance, the 1,3-alternate condenses only with two molecules leading thus to tris-calixarene, possessing a novel type of inherent chirality based on the 25,26-substitution pattern. The title compounds, which connect together ‘classical’ calixarene and thiacalixarene building blocks, represent a first step towards calixarene-based dendritic structures.     

Synthesis of bis(bora)calix[4]arenes bearing perfluoroaryl substituents

New routes to perfluoroaryl complexes of bis(bora)calix[4]arenes are described; crystallographic and spectroscopic data are presented.     

Photochemical rearrangement of calix[4]arene-derived bis(spirodienones): formation of a new macrocycle

Bis(spirodienones) of calix[4]arene undergo a facile photochemical rearrangement leading to a new macrocycle having a spirocyclic cyclopentenone-THF unit, a trisubstituted phenol, and a benzofuran moiety. The macrocyclic ring system has a 14-membered irregular cavity and resembles a partial bowl in the solid state.     

Synthesis of a novel calix[4]arene-based fluorescent ionophore and its metal ions recognition properties

A novel fluorescent ionophore derived from calix[4]arene and pyrazoline was designed and synthesized. Its molecular structure was confirmed by 1H NMR and element analysis. The resulting material shows specific fluorescent behavior toward the Zn2+ ion among the other divalent metal ions, such as Co2+, Ni2+, Cu2+. The primary results indicate this ionophore material is a potential material for developing efficient fluorescent Zn2+ chemosensors.     

The effect of a solvent modifier in the cesium extraction by a calix[4]arene: a molecular dynamics study of the oil phase and the oil-water interface

We report a molecular dynamics (MD) study of the effect of a fluorinated lipophilic alcohol (referred to as "cs3" by Delmau et al, Solvent Extr. Ion Exch., 2005, 23, 23) used as a phase modifier in the solvent extraction of Cs(+) NO(3)(-) by a calix[4]arene. It is shown that adding cs3 to a chloroform phase improves the solvation of all partners of the extraction system, i.e. the free calixarene ligand L, its LCs(+) complex and its counterion. This effect is most pronounced for the NO(3)(-) anion that is H-bonded to the -OH and terminal -CF(2)H protons of cs3. On the average, the dissociated nitrate interacts with 2 to 4 cs3 molecules, whereas the associated nitrate (LCs(+)NO(3)(-) complex) interacts with one cs3 dimer. The remaining modifier molecules are mainly dissolved in the solution as dimers or trimers and, to a lesser extent, as monomers and tetramers. Insights into the question of ion pairing in the organic phase are obtained via free energy perturbation (FEP) calculations, showing that the LCs(+)NO(3)(-) paired complex is more stable than its analogue with the dissociated anion. Furthermore, the nitrate dissociation energy is ca. twice as small in the cs3-modified solution than in a pure chloroform phase. We also simulated chloroform/cs3/water ternary systems, showing that the modifiers are surface active and stabilize the formation of water nanodroplets, while other modifier molecules drag some water to the organic phase. Calixarene complexes also adsorb at the aqueous interface in the presence of modifiers, confirming the importance of interfacial phenomena in the assisted cation extraction process. The microscopic insights obtained by the simulations are consistent with experimental results and allow us to better understand why the extraction is enhanced after addition of modifiers to the organic phase.     

Allosteric coextraction of sodium and metal ions with calix[4]arene derivatives 1

Solvent extraction of three alkali metal ions with p-t-octylcalix[6]arene hexacarboxylic acid, p-t-octylcalix[4]arene tetracarboxylic acid, corresponding linear trimeric and monomeric analogs was investigated. Cyclic tetramer selectively extracts sodium ion among alkali ions at extremely low pH, while the corresponding cyclic hexamer, the trimer, and the monomer exhibited only poor extraction ability for all alkali metals examined. The detailed extractive investigation of sodium ions with the cyclic tetramer was carried out. It was found that two sodium ions are simultaneously extracted by a single molecule of calix[4]arene derivative and that the second sodium extraction is facilitated by the uptake of the first sodium. The self-coextraction mechanism of sodium ions proposed in the present paper also strongly supports allosteric coextraction of sodium and other metal ions. In the competitive extraction of four alkali metal ions, potassium ion was slightly extracted as the second ion at low pH region, whereas it was hardly extracted in the individual extraction system. The result also supports the coextraction mechanism and role of the first-extracted sodium ion as an allosteric trigger. The extraction equilibrium constants of the cyclic tetramer and two sodium ions, K _ex1 and K _ex2, were estimated.     

Pyrene-armed calix[4]azacrowns as new fluorescent ionophores: "molecular taekowndo" process via fluorescence change

A series of new calixarene-based fluoroionophores were synthesized. With our new calixarene derivative bearing a crown ether and an azacrown ether as two binding sites, the metal ion was found to selectively choose its better binding pocket between these two ligands. Interesting "molecular taekowndo" processes between Ag(+)-K(+), Cu(2+)-K(+), and Ag(+)-Cs(+) pairs were easily monitored via fluorescence change.     

Synthesis of per-O-(carboxymethyl)calix[4]pyrogallols and their complexation with some alkaline metal and lanthanide ions

Complexones of a new class, viz., carboxy-functionalized calix[4]pyrrogallols, were synthesized. The per-O-(carboxymethyl)calix[4]pyrogallols obtained were established to exist in the (rel, cis, trans, trans)-configuration by 2D NMR spectroscopic data. According to the pH-potentiometric data, the interaction of these compounds with alkaline metal ions (Li⁺, Na⁺, K⁺, Cs⁺) and lanthanide ions (La³⁺, Gd³⁺, Lu³⁺) in a water—DMSO system produces 1 : 1 complexes. The specific features of complexation of per-O-(carboxymethyl)calix[4]pyrogallols, as compared to their acyclic analogs, with alkaline metal and lanthanide ions are due to the cooperative effect of donor groups preorganized on the calixarene matrix.     

Sorption of heavy metal ions by silica gel-immobilized, proton-ionizable calix[4]arenes

Silica gel-immobilized, di-ionizable calix[4]arenes are employed as stationary phases in ion-exchange chromatography for selected heavy metal ions. Sorption efficiencies for Pb²⁺ are dependent on the structure of the calix[4]arene ligand and the linker that joins the ligand to the silica gel, as well as the acidity of the sample solution. Although the resins exhibit only poor sorption of Cd²⁺, they are found to be scavengers for Hg²⁺. Competitive sorption studies are conducted with selected resins.