Arene Receptor Research Articles

Novel Triphenylamine Appended 1,3-Alternate-Calix[4]arenes: Synthesis and Characterization

In the present study, two novel calix[4]arene receptors containing triphenylamine units in 1,3-alternate conformation have been synthesized and characterized in detail. First, the 25,27-dipropoxy-26,28-bis[(3-aminopropyl)oxy]-calix[4]arene 4 and 25,26,27,28-tetra[(3-aminopropyl)oxy]-calix[4]arene 7 were prepared by using convenient reagents. Then, these amino derivatives of calix[4]arene were converted to Schiff base derivatives appended to triphenylamine of calix[4]arene (5 and 8) using 4-formyltriphenylamine via condensation. The 1,3-alternate conformation of the synthesized calix[4]arenes was determined by 1H and 13C NMR analyses. Also, their structures have been characterized by using 1H and 13C NMR, infrared, and elemental analyses. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.

Heteroditopic thiacalix[4]arene receptor having ester and bipyridyl moieties for ions binding with positive/negative allosteric effect

A novel ditopic receptor possessing two complexation sites and bearing 1,3-alternate conformation based thiacalix[4]arene was prepared. The binding behaviors with Na+, K+ and Ag+ ions have been examined by 1H NMR titration experiment in (CDCl3/CD3CN; 10:1, v/v) solution. The job plots proves 1:1 complexation of 1,3-alternate-4 with Na+, K+ and Ag+ ions. Although the formation of heterogeneous dinuclear complexes was not clearly observed, the exclusive formation of mononuclear complexes of 1,3-alternate-4 with metal cations is of particular interest with positive/negative allosteric effect in thiacalix[4]arene family. These findings further demonstrate that preorganization, suitable conformational changes and affinity have a pronounced effect on the complexation process between the two different arms placed at the two edges of the thiacalix[4]arene cavity.

Improved recognition of alkylammonium salts by ion pair recognition based on a novel heteroditopic pillar[5]arene receptor

A novel pillar[5]arene-based heteroditopic receptor for ion pair recognition of alkylammonium salts with different alkyl chain lengths and different counterions was prepared, which showed the best association constant enhancement (71times) to n-BuNH3+Cl− compared with monotopic receptor 1,4-dimethoxypillar[5]arene over corresponding Br− and CF3COO− salts in chloroform.

Synthesis and Complexation Abilities of Novel Multiple-Sites Calix[4]arene Receptors: Calix[4]arene Derivatives with Anthraquinone Groups on Lower Rims and Hydrazone Groups on Upper Rims

By formylation of 1,3-bisubstituted calix[4]arene anthraquinone derivative 1 in hexamethylenetetramine/trifluoroacetic acid system, the corresponding formylated gecalix[4]arene anthraquinone derivative 2 was synthesized in yield of 63%. By further reacting compound 2 with salicylic hydrazide, 2,4-dinitrophenyl hydrazine, nicotinyl hydrazine or phenyl thiosemicarhazide, novel calix[4]arene derivatives with anthraquinone and hydrazone groups 3a–3d were obtained in yields of 74–83%. The extracting experiments for series of metallic cations showed that compounds 3a–3d possessed high extracting abilities and extracting selectivity for tested cations. The complexation UV-Vis spectra for a series of anions indicated compounds 3a–3d exhibited the strong complexation abilities for tested anions. The 1H-NMR titration study showed that compound 3d possessed excellent complexation abilities for ion-pair of NaH2PO4 in 1:1 host-guest complex with the association constant of 4.6 × 104 M−1.

Ditopic Receptors based on Lower‐ and Upper‐Rim Substituted Hexahomotrioxacalix[3]arenes: Cation‐Controlled Hydrogen Bonding of Anion

Heteroditopic hexahomotrioxacalix[3]arene receptors that are capable of binding an anion and a cation simultaneously in a cooperative fashion were synthesized. The structure of one of the triamide derivatives was confirmed by single-crystal X-ray diffraction. The binding of alkali metals at the lower rim, and the binding of anions (chloride, bromide) at the upper rim, has been investigated by using (1)H NMR titration experiments. Alkali metal binding at the lower rim controls the calix cavity. Li(+)-ion binding to the lower rim can improve the binding ability of anions at the upper rim amide moiety by a factor of 15, thus suggesting a strong positive allosteric effect for anion recognition. However, when a Na(+) cation is bound to the ionophoric site on the lower rim, the calix cavity is changed from a "flattened cone" to a more-upright form, which is favored for intramolecular hydrogen bonding between the neighboring NH and C=O groups; this change can block the inclusion of anions onto the amide moiety at the upper rim, which strongly suggests a negative allosteric effect of Na(+)-ion binding, which controls the cooperative recognition system.

Anion Recognition by Charge Neutral Electron-deficient Arene Receptors

Anion-π interactions are newly emerging non-covalent interactions and have attracted considerable attention from both theoreticians and supramolecular chemists. This short review article summarizes the recent advances in anion recognition using charge neutral electron-deficient aromatic compounds.

An ONIOM investigation on anion recognition of alkali–metal complexes with diurea calix[4]arene receptor

The ONIOM(B3LYP/6-31G(d):AM1) optimized structures of complexes of diurea calix[4]arene receptor (L) with alkali metals Li(+), Na(+) and K(+) and their complexes with halide ions F(-), Cl(-), Br(-), oxygen-containing anions HCO(3)(-), HSO(4)(-) and CH(3)COO(-) ions were obtained. Binding energies and thermodynamic properties of complex receptors LiL(+), NaL(+) and KL(+) with these anions were determined. The binding stabilities according to binding energies of LiL(+), NaL(+) and KL(+) associated with anions computed either at the ZPVE-corrected ONIOM(B3LYP/6-31G(d):AM1) or BSSE-corrected B3LYP/6-31 + G(d,p)//ONIOM(B3LYP/6-31G(d):AM1) are in the same order: F(-) >> CH(3)COO(-) ≈ HCO(3)(-) > Br(-) ≈ HSO(4)(-) ≈ Cl(-). All the receptors LiL(+), NaL(+) and KL(+) were found to be selective toward fluoride ion.

Synthesis and electrochemical properties of calix[4]arene derivatives containing ferrocene units in the cone and 1,3-alternate conformation

Two novel calix[4]arene receptors containing ferrocene units in cone ( L 1 ) and 1,3-alternate ( L 2 ) conformations have been synthesized from 25,27-dihydroxy-26,28-bis[(3-aminopropyl)oxy]calix[4]arene 4 or 25,26,27,28-tetra[(3-aminopropyl)oxy]calix[4]arene 6 and ferrocenecarboxaldehyde via condensation, respectively. Their structures have been characterized by 1H, 13C, APT, COSY NMR, FTIR, HSMR, and UV–vis spectral data. The electrochemical behavior of L 1 and L 2 has been investigated in the presence of F −, Cl −, Br −, H 2PO 4 −, CH 3COO − anions. Electrochemical studies show that these receptors electrochemically recognize CH 3COO −, H 2PO 4 −, and Cl −, anions. Using an UV–vis study, the selectivity to these anions in DMSO solution was confirmed.

Rhodamine appended thiacalix[4]arene of 1, 3-alternate conformation for nanomolar detection of Hg 2+ ions

Rhodamine appended thiacalix[4]arene receptors 4 and 5 are synthesized, of which receptor 4 of 1, 3-alternate conformation shows high selectivity towards Hg 2+ ions with fluorescence enhancement among various metal ions tested and thus, behaves as an efficient ‘Turn On’ fluorescent chemosensor for Hg 2+ ions with a detection limit up to nanomolar range.

Substituted p-phenylene ethynylene trimers as fluorescent sensors for nitroaromatic explosives

New sensory materials based on p-phenylene ethynylene trimers integrating calix[4]arene receptors ( CALIX-PET) and tert-butylphenol ( TBP-PET) moieties have been synthesized and their sensitivity and selectivity for the detection of nitroaromatic compounds (NACs) such as nitrobenzene (NB), 2,4-dinitrotoluene (2,4-DNT), 2,4,6-trinitrotoluene (TNT) and picric acid (PA) investigated in fluid phase and solid-state. It was found that both fluorophores displayed high sensitivities toward NACs detection in solution as evaluated by the Stern–Volmer formalism. For all the tested explosives, the ratio of fluorescence intensities ( F 0/ F) is a linear function of the quencher concentration only after appropriate correction of fluorescence quenching data for inner-filter effects. The quenching efficiencies for CALIX-PET and TBP-PET follow the order PA ≫ TNT > DNT > NB, which correlate well with the quenchers electron affinities as evaluated from their LUMOs energies thereby suggesting a photoinduced electron transfer as the dominant mechanism of fluorescence quenching. The selectivity of these sensors was checked against exemplar interferents possessing differentiated electronic properties (benzoic acid, 2,4-dichlorophenol and benzoquinone) and reduced quenching activity was detected. The quenching efficiencies and response times of the two fluorophores in the solid-state toward NB, 2,4-DNT and TNT vapors were evaluated through steady-state fluorescence quenching experiments with the materials dispersed in polymeric matrices or as neat films. The most significant fluorescence quenching responses were achieved for drop-casted films of TBP-PET upon exposure to nitroaromatics.

Transportation of Poorly Soluble Drug Molecules from the Organic Phase to the Aqueous Phase by Using Phosphorylated Calixarenes

This study is the first report on the extraction of poorly soluble drug molecules such as nifedipine, niclosamide, and furosemide from the organic phase to the aqueous phase by water-soluble p-phosphonate calix[n]arene receptors via a liquid–liquid phase extraction process. These water-soluble calixarene derivatives were easily obtained from the reaction between their corresponding chloromethylated derivatives and trimethyl phosphite. From the liquid–liquid phase extraction studies, it was observed that the size of the p-phosphonate calix[n]arenes changed the extraction percentage of selected drug molecules.

Absorption Spectrophotometric, NMR and Quantum Chemical Investigations of Ground State Non-Covalent Interactions between Fullerenes and a Designed Trihomocalix[6]arene in Solution

Ground state non-covalent interactions between a newly designed macrocyclic 1,3,5-trihomo calix[6]arene receptor, designated as 1, and the C60 and C70 fullerenes have been studied in toluene solutions. It was observed that the absorbances of both C60 and C70 solutions increased upon the addition of increasing concentrations of compound 1. Job’s method of continuous variation established 1:1 stoichiometry for these fullerene-1 complexes. The binding constant (K) data reveal that compound 1 binds to C70 more strongly compared to C60, i.e., \(K_{C60\mbox{-}\boldsymbol{1}} = 230~\mathrm{dm}^{3}{\cdot}\mathrm{mol}^{-1}\) and \(K_{C70\mbox{-}\boldsymbol{1}}= 517~\mathrm{dm}^{3}{\cdot}\mathrm{mol}^{-1}\). Proton NMR analysis provides very good support for strong binding between C70 and 1. Estimations of the solvent reorganization energy (RS) suggest that the C70-1 complex is stabilized more than the corresponding C60-1 complex, with \(R_{S(C60\mbox{-}\boldsymbol{1})} = -1.970~\mathrm{eV}\) and \(R_{S(C70\mbox{-}\boldsymbol{1})}= -2.300~\mathrm{eV}\). Molecular mechanics force field method calculations established that the binding pattern of C70 towards 1 occurs in the side-on rather than end-on orientation, and that the C70-1 complex gains 5.23 kJ⋅mol−1 of extra stabilization energy with this side-on geometrical arrangement.

Potentiometric Sensors Based on Polyaniline and Thiacalixarenes for Green Tea Discrimination

AbstractThe performance of potentiometric sensors based on carbon screen‐printed and glassy carbon electrodes covered with polyaniline (PANI) and thiacalix[4]arene receptors have been compared in the determination of some ions and discrimination of green tea brands. The optimization of PANI electropolymerization provided satisfactory characteristics of screen‐printed electrodes comparable with those of conventional sensors based on glassy carbon. The potentiometric sensors make it possible to determine 1×10−2–1×10−6 M Fe3+ ions. Also, successful discrimination of twelve tea brands was performed with three‐sensor array. The 100 % true prediction was confirmed by principal component analysis (PCA) and linear discriminant analysis (LDA).

Preparation, reactivity and controlled release of SAMs of calix[4,6]arenes and calix[6]arene-based rotaxanes and pseudorotaxanes formed on polycrystalline Cu

Specific and reversible binding of guest molecules from a solution to a surface pre-treated with host molecules is a recent and active field of research. Self-assembled monolayers may result from supramolecular interactions, adding distinct functionalities to the surface. In this frame, the first compared study is given here of the anchoring on the technologically relevant Cu surface of calix[4]arene receptors and calix[6]arene-based rotaxanes and pseudorotaxanes. These molecules, which belong to the most representative classes of compounds in supramolecular chemistry, have been chosen for their synthetic accessibility and versatility, which make them useful building blocks for the synthesis of new advanced supramolecular structures. Covalent functionalisation of calix[4,6]arenes on Cu was reached via a dip-coating procedure, optimizing the various synthetic aspects in order to obtain good coverages and copper passivation. Molecular adhesion has been demonstrated by the presence and relative quantitation of XPS signals from specific elements in the molecules. We have successfully tested the combination of different functionalities by producing a mixed film, prepared by ligand exchange of calix[4]arene with undecanethiol. The availability of the calix[4]arene cavity to reversibly host further species after anchoring on Cu has been demonstrated by a sequence of uptake and release cycles with pyridinium salts. Rotaxane and pseudorotaxane species, composed of a calix[6]arene wheel functionalized with N-phenylurea groups on the upper rim, and a viologen-containing axle, have been anchored on Cu via the SH-termination of the axle. XPS demonstrated the successful self-assembly of fully threaded rotaxanes and pseudorotaxanes from their solutions and the controlled release upon biasing of full rotaxanes and of the pseudorotaxane wheel.

Functional characterization of a supramolecular affinity switch at the single molecule level

Surface-immobilized and switchable resorcin[4]arene receptor molecules were quantitatively investigated with atomic force microscopy (AFM) and AFM-single molecule force spectroscopy (AFM-SMFS). The upper rim of the supramolecular receptor cavities was modified with two photodimerizable anthracene moieties. The molecular constitution can be externally switched and controlled by exposure to ultraviolet (UV) light and heat. The topography as well as the complexation affinity against small ammonium guest ions of the two isomers were investigated at the single molecule level. Our results demonstrate the feasibility to externally control the supramolecular receptor's affinity and simultaneously quantify and associate these binding properties with the structural change of the resorcin[4]arenes structure on the basis of the measured molecule corrugation height.

Tetrahedral Anions Selective Fluorescent Calix[6]arene Receptor Containing Urea and Pyrene Moieties

Selective binding of ions is an important aspect of ion de-tection and ion transport. Selective complexation of anions is more demanding than that of cations due to low charge density and strong solvation. Furthermore, it has to be kept in mind that anions are subject to pH-dependent acid-base equilibria.

1,3-Alternate Calix[4]arene Bifuntional Fluorescent Receptor Containing Urea and Crown Ether Moieties

Scheme 1. Synthetic routes to fluorescent chemosensor 1 Calix[4]arenes are important building blocks in supramolecular chemistry. The calixarene framework provides a unique possibility to organize several binding sites in an array complementary to a potential guest. A variety of calixarene-based receptors for cations, anions and neutral molecules have been synthesized in the past decade. Though anion recognition appears to be a relatively new area of research, both positively charged and neutral receptors for anionic species have been prepared in the last few years. As fluorogenic units, pyrenes are one of the most useful because of their relatively efficient excimer formation and emission. Since the intensity ratio of the excimer to the monomer emission (IE/IM) is sensitive to conformational changes of the pyrene-appended receptors, changes in IE/IM upon metal ion complexation can be an informative parameter in various sensing systems. The simultaneous binding of cationic and anionic guest species by ditopic receptors is a rapidly developing new field for ion pair recognition of environment and biological importance. By taking advantage of calixarene framework, a few neutral bifunctional receptors were developed and showed the simultaneous complexation properties of hydrophilic anions and cations in organic media. Those receptors are, however, only focused on the cone conformers of calix[4]arene. It has been known that 1,3-alternate conformation of calix[4]arene could provide the two excellent binding sites for guest molecules when the proper functionalization could be achieved. We have previously reported 'bifunctional calix[4]arene receptors' containing two urea groups and crown ether moieties at the calix[4]arene fixed in the 1,3-alternate conformation. It was shown the simultaneous binding properties of cation and anion guests with enhanced binding affinity of halide anions in the presence of potassium cation. Here we report a new bifunctional receptor 1 based on 1,3alternate conformer of calix[4]arene, which contains urea linking pyrene fluorophores instead of phenylurea and crown ether moieties at the opposite side of lower rim of calix[4]arene fixed in the 1,3-alternate conformation. Also, we studied binding affinity of various anions in the present of potassium ion.

ChemInform Abstract: Thermodynamic Study on Supramolecular Complex Formation of Fullerene with Calix[5]arenes in Organic Solvents.

Abstract Thermodynamic parameters for the supramolecular complex formation of fullerene C 60 with calix[5]arene receptors are reported. The entropy change in chloroform is negative, but in toluene is positive, suggesting the tight solvation around the guest in toluene. Desolvation of the guest plays an important role in the supramolecular complex formation in toluene.

Dipyrenylcalix[4]arene—A Fluorescence‐Based Chemosensor for Trinitroaromatic Explosives

A new chemosensor-based approach to the detection of nitroaromatics is described. It involves the analyte-induced quenching of excimer emission of a dipyrenyl calix[4]arene (L). The chemical and photophysical properties of the complexes formed between L and mono-, di-, and trinitrobenzene, and di- and trinitrotoluene were studied in acetonitrile and chloroform by using (1)H NMR, UV/Vis, and fluorescence spectroscopy. Fluorescence spectroscopy revealed that the trinitroaromatics engendered the largest response among the various substrates tested, with the sensitivity for these analytes being correspondingly high. Quantitative analysis of the fluorescence titration profile generated from the titration of L with TNT provided evidence that this particular functionalized calix[4]arene receptor allows for the detection of TNT down to the low ppb level in CH(3)CN. A single-crystal X-ray diffraction analysis revealed that in the solid state the complex L.TNT consists of a supramolecular crystalline polymeric structure, the formation of which appears to be driven by intermolecular pi-pi interactions between two pyrene units and a TNT molecule held at a distance of 3.2-3.6 A, as well as by intra- and intermolecular hydrogen-bonds among the amide linkages. Nevertheless, the changes in the (1)H NMR, UV/Vis, and fluorescence spectrum, including sharp color changes, are ascribed to a charge-transfer interaction arising from complementary pi-pi overlap between the pyrene subunits and the bound trinitroaromatic substrates. A number of ab initio calculations were also carried out and, considered in concert, they provide further support for the proposed charge-transfer interactions, particularly in the case of L.TNT.

Water-soluble aminocalix[4]arene receptors with hydrophobic and hydrophilic mouths

Water-soluble aminocalix[4]arene hosts, the one with hydrophilic function and the other with hydrophobic function on the top of the deep hydrophobic cavity representing hydrophobic mouth and hydrophilic mouth, respectively. We report the new water-soluble aminocalix[4]arene hosts 1 and 2 with deep hydrophobic cavity facilitating hydrophobic mouth and hydrophilic mouth, respectively. The 1 H NMR titrations revealed that host 1 shows high selectivity for neutral guests 9 and 10 , with log K of 4.2 and 4.6, respectively. The host 2 shows log K of 4.9 for binding with guest 15 . Moreover, the binding ability of the host 2 for guest 14 is stronger by a factor of 1000 than that of the host 1 .