Binding studies of tetrathiafulvalene-calix[4]pyrroles with electron-deficient guests

The neutral meso-octamethylporphyrinogen derivative, tetraTTF-calix[4]pyrrole 1 (TTF=tetrathiafulvalene), acts as a multi-faceted receptor in that it interacts with an assortment of different guests in different ways. The conformation of receptor 1 can be reversibly switched between the 1,3-alternate conformation (i.e., 1, Fig. 1) and the cone conformation (i.e., 1·Cl⁻, Fig. 2) by the repetitive addition of chloride and sodium ions. In this paper, the results of detailed and systematic complexation studies involving both 1 and its chloride-bound complex, 1·Cl⁻, with a variety of guests are described. Receptor 1 binds quasi-planar nitroaromatic guests in its 1,3-alternate conformation, while release of these guests takes place upon addition of chloride anions. On the other hand, spherical fullerene guests are strongly bound by 1·Cl⁻. Finally, it was found that a bidentate guest, consisting of a quasi-planar 2,5,7-trinitro-9-dicyanomethylenefluorene moiety tethered to a spherical C₆₀ fullerene, could be recognized by receptor 1 in either its 1,3-alternate or its chloride-bound cone conformation, albeit through very different binding modes.     

A selective colorimetric chemosensor for lanthanide ions

The synthesis and complexing properties of a calix[4]arene derivate (6) carrying two spirobenzopyran moieties are described. The addition of lanthanide ions resulted in significant UV-vis spectral shifts (68-84 nm) in visible region. It indicates that the synthetic receptor can recognize lanthanide ions by naked eyes over other cations including Na⁺, K⁺, Mg²⁺, Ca²⁺, Fe³⁺, Cu²⁺ and Zn²⁺. The mechanism of recognition was studied with ¹H NMR, UV-vis spectra and emission spectra. The receptor may be applied to sense lanthanide ions.     

A selective colorimetric chemosensor based on calixarene framework for lanthanide ions-Dy and Er

A novel photochromic Schiff base derivative, 5,17-N,N′-(5,5′-di-methoxyl-benzlaldehyde)diimine-25,27-dipropoxy-calix[4]arene has been synthesized through incorporation of two imine groups into the upper rims of calix[4]arene. The experiments showed that the addition of Dy³⁺ or Er³⁺ ions to compound 4 results in the solution color change, but other metal ions caused less change. It indicated that the synthetic receptor can selectively recognize Dy³⁺ and Er³⁺ ion by naked eye over other lanthanide cations. Thus, these systems can be applied as chemosensor for Dy³⁺ and Er³⁺ ion in analytical chemistry.     

Calix[4]pyrrole-TCBQ assembly: a signal magnifier of TCBQ for colorimetric determining amino acids and amines

The interaction and colorimetric sensing properties of the calix[4]pyrrole-TCBQ charge-transfer complex with amino acids and amines in CHCl₃/EtOH/H₂O were investigated using UV/vis spectroscopic techniques. The obvious spectral and visual changes of the complex solution in the presence of basic amino acids (namely, lysine, arginine, and histidine) and aliphatic amines were observed, and the calix[4]pyrrole-TCBQ supramolecular assembly, like a ‘signal magnifier’, markedly improves sensing sensitivity and selectivity of TCBQ for amino acids and amines.     

Calix[4]arene-based ditopic receptor for dicarboxylates

Shape-selective recognition for the dicarboxylates in DMSO can be attained by a new calix[4]arene-based receptor 1 having two urea groups. Biologically active chorismate selectively bound in 1 over its dehydrated derivative. Molecular mechanics calculations gave a plausible explanation for the selective binding.     

Anthraquinone-modified calix[4]arene: click synthesis,selective calcium ion fluorescent chemosensor and INHIBIT logic gate

Novel anthraquinone-modified calix[4]arene was synthesized by click chemistry and exhibited selective fluorescent enhancement in the presence of Ca²⁺, which is attributed to photo-induced electron-transfer effect from the 1,2,3-triazole ring. The enhanced fluorescence was further quenched by F^?  ion. Thus, the potential Ca²⁺ and F^?  ion switched INHIBIT logic gate has been constructed.     

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⁺.     

A new colorimetric and fluorescent chemosensor based on thiacalix[4]arene for fluoride ions

A new thiacalix[4]arene based fluorescent chemosensor thiacalix[4]arene-N-(quinolin-8-yl)acetamide (TCAN8QA) has been synthesized. TCAN8QA has been found to exhibit highly selective behavior for F⁻ ions among all other anions, that is, Cl⁻, Br⁻, I⁻, PO₄⁻³, OH⁻, H₂PO₄⁻, and CH₃COO⁻ in the absorption spectra as well as in the emission spectra. Red shift and quenching in emission spectra constituting the signature for fluoride detection are due to photoinduced charge transfer (PCT) which can be attributed to deprotonation of acidic NH proton in the presence of fluoride ions.     

Synthesis and Molecular Structures of Tetrasilyl Ethers of Calix[4]arenes

The tetrasilyl ethers calix[4]areneOSiMe₂R (R = Me, H, vinyl, allyl) were prepared by salt elimination; the calix[4]arene was deprotonated with sodium hydride and subsequently reacted with chlorosilanes ClSiMe₂R. In general, DMF was chosen as solvent in order to steer the reactions in terms of a preference for the cone‐conformation of the products. In the case of calix[4]areneOSiMe₃ both, partial‐cone‐ and cone‐conformers, were synthesised. All products were characterised by NMR (¹H, ¹³C, ²⁹Si) spectroscopy, mass spectrometry and single‐crystal X‐ray diffraction.     

A new fluorescent chemosensor for copper(II) and molecular switch controlled by light

A novel fluorescent chemosensor with two 5-nitro-salicylaldehyde groups at the upper rim of calix[4]arene has been synthesized. The chemosensor can effectively recognize copper(II) ion. This system could be considered as a molecular switch. By alternating the light irradiation of mixed solution formed by the host and Cu²⁺, off-on-off fluorescent switching is carried out.     

Interface Host?Guest Interaction Between Calix[4]pyrrole and Neutral Derivatives of Phenol as the Base for Their Potentiometric Discrimination

Calix[4]pyrrole liquid membrane electrodes display a potentiometric response towards the neutral form of phenol derivatives. They do not respond towards the corresponding anionic forms. The mechanism of the generation of the potentiometric signal relies on: (1) The creation of supramolecular complex calix[4]pyrrole? nitrophenol at the organic/aqueous interface; (2) The increasing of the acidity of OH group from nitrophenol molecules due to formation of hydrogen bond between calix[4]pyrrole? nitrophenol at the interface; (3) The dissociation of the OH group from calix[4]pyrrole? nitrophenol complex and the ejection of H⁺ to the aqueous layer adjusted to the membrane organic phase boundary. The sensitivity and selectivity of the calix[4]pyrrole liquid membrane electrodes are governed by the lipophilicity and acidity of the phenolic guests. Also, the affinity to create a hydrogen bond between the host and the target molecule is a parameter which has a strong influence on the phenomena studied.     

Water-soluble calixarenes—self-aggregation and complexation of noncharged aromatic guests in buffered aqueous solution

Water-soluble calix[4]arenes are useful receptors for hydrophobic substrates in aqueous buffered solution. The inclusion of 22 aromatic guests as well as the self-aggregation behavior of amphiphilic hosts was studied by ¹H NMR spectroscopy. The association constants obtained range from 10 to 1000 L mol⁻¹. In all cases, the aromatic moiety is included into the hydrophobic pocket of the calixarenes maximizing hydrophobic contacts. Additionally, substituents such as methyl or chlorine exhibit a preference for inclusion in the pocket of the macrocycles owing to CH/π or Cl/π interactions. In case self-aggregation is observed, millimolar CMC values are to be found.     

Synthesis of (thia)Calixarene-based exTTF Derivatives and Their Electron Transfers Towards p-Chloranil and C60

Two novel (thia)calixarene-based exTTF derivatives(3a and 3b) were prepared by Mitsunobu reactions in toluene using diethyl azodicarboxylate(DEAD) and triphenylphosphine(PPh₃) system. The cyclic voltammograms of compounds 3a and 3b were provided, and two electron-irreversible waves with redox potentials were observed. Meanwhile, the intermolecular electron transfer(ET) properties of both compounds 3a and 3b towards p-chloranil(Q) and C₆₀ were investigated via UV-Vis and fluorescent spectroscopies, respectively. The results indicated that the introduced nonoxidable metal ions(Al³⁺, Pb²⁺, Sc³⁺) might promote the intermolecular ET from compounds 3a and 3b towards Q ensembles, whereas the effects of Sc³⁺ were the most impressive. Furthermore, the effects of the same metal ions(Al³⁺, Pb²⁺, Sc³⁺) added for compound 3b were greater than those for compound 3a. Additionally, the photoinduced intermolecular ET from compounds 3a and 3b towards C₆₀ was observed.     

Click-modified hexahomotrioxacalix[3]arenes as fluorometric and colorimetric dual-modal chemosensors for 2,4,6-trinitrophenol

A new type of chemosensor-based approach to the detection of 2,4,6-trinitrophenol (TNP) is described in this paper. Two hexahomotrioxacalix[3]arene-based chemosensors 1 and 2 were synthesized through click chemistry, which exhibited high binding affinity and selectivity toward TNP as evidenced by UV–vis and fluorescence spectroscopy studies. ¹H NMR titration analysis verified that CH?O hydrogen bonding is demonstrated as the mode of interaction, which possibly facilitates effective charge-transfer.     

Investigation of the retention mechanism of naphthol and benzenediol on calix[4]arene stationary phase based on quantum chemistry calculations

Calixarenes are macrocyclic oligomers having the shape of a conical vase. Their inner cavity can accommodate various guest molecules, i. e. form supramolecules. Thus, calixarenes can be employed to manipulate selectivity in separation sciences. The essential step of separation is the interaction between calixarene and analytes. Therefore, in the present work, the retention mechanisms of benzenediol and naphthol positional isomers on a calix[4]arene column were investigated. The optimized supramolecular structures showed that there exist hydrogen bonding and pi-pi interactions for benzenediol, and for naphthol the pi-pi interactions dominate. Thermodynamic results from quantum chemistry calculations using DFT-B3LYP/STO-3G** basis set were consistent with the retention behaviors of benzenediol and naphthol positional isomers on the calix[4]arene column. This work will provide theoretical support for the design of new calixarene stationary phases.     

A phenanthrene-based calix[4]arene as a fluorescent sensor for Cu and F

A new phenanthrene-based fluorescent calix[4]arene (4) has been synthesized in cone conformation. This compound was examined for its fluorescent properties towards different metal ions (Na⁺, Li⁺, Mg²⁺, Ni²⁺, Ba²⁺, Ca²⁺, Cu²⁺, Pb²⁺) and anions (F⁻, Cl⁻, Br⁻, H₂₄PO⁻,${{\text{H}}_2{\text{PO}}_4}^{-}\text{,}$₃NO⁻,${{\text{NO}}_3}^{-}\text{,}$₄HSO⁻,${{\text{HSO}}_4}^{-}\text{,}$ CH₃COO⁻) by fluorescence spectroscopy. The properties of the compound were evaluated and show that it is a fluorescence sensor for Cu²⁺ and F⁻. With the addition of Cu²⁺ and F⁻, the fluorescence was severely quenched.     

Preparation of Calix[4]arene Alkylamine Derivatives by Mannich Reaction and use as Phase-Transfer Catalysts for Esterification Reaction

In this study, 5,11,17,23-tetrakis[(N-ethylpiperazine)methyl]-25,26,27,28-tetrahydroxycalix[4]arene (3) and 5,11,17,23-tetrakis[(4-carboethoxy-N-piperidino) methyl]-25,26,27,28-tetrahydroxycalix[4]arene (4) were synthesized in one step according to the Mannich reaction by the treatment of calix[4]arene with a secondary amine (N-ethylpiperazine, ethyl-4-piperidincarboxylate) and formaldehyde. The calix[4]arene derivatives (3, 4) were characterized by a combination of FTIR, ¹H NMR and elemental analyses. The synthesized compounds were used in an esterification reaction as the phase transfer catalyst. The catalytic efficiency of the calix[4]arenes 3 and 4 was evaluated by carrying out the ester-forming reaction of alkali metal carboxylates (sodium butyrate or sodium caprylate) with p-nitrobenzyl bromide. It was observed that the ester-forming reaction of alkali metal carboxylates with p-nitrobenzyl bromide, using calix[4]arene-based catalyst 3 as a phase-transfer catalyst in dichloromethan, provided the best yields.     

A Surface Fluorescent Sensing Membrane for Rapid Detection of Sodium

Abstract

A sensitive fluorescent sensing membrane has been developed for the rapid detection of sodium ions by immobilizing the membrane onto a glass slide surface. The membrane consists of a fluorophore, an ionophore, a plasticizer, and an anionic site of a lipophilic salt in a polyvinyl chloride (PVC) matrix. Based on the ion‐exchange response and photoinduced electron transfer mechanisms, the ionophore first captures target sodium ions from the solution into the membrane, and then the fluorophore emits a fluorescent signal based on the amount of sodium ions captured. To effectively transmit the signal and avoid the leaching of the fluorophore from the membrane, a newly synthesized fluorescent compound was used as a fluorophore in the fabrication of the membrane. Due to the special structure of the fluorophore, it remains trapped inside the membrane and thus gives a reliable fluorescent signal when sodium ions exist in the solution. Calix[4]arene tetraester acts as a sodium ion carrier, the crown size in its molecular structure is compatible with the sodium ionic size, making the membrane highly selective to sodium ions. Furthermore, the membrane demonstrates a rapid response to sodium ions—less than 1 min is required to reach a stable fluorescent signal. The sodium content in various real samples, such as mineral water, urine, and serum, were determined by the sensing membrane. The results highly correlate with the atomic absorption spectrometry method, confirming the validity of the fluorescent sensing membrane for sodium ion detection.     

A highly selective fluorescence chemosensor for Pb(II) in neutral buffer aqueous solution

A 3,4-dimethylthieno[2,3-b]thiophene-based fluorogenic probe bearing benzo[d]-thiazole-2-thio unit (sodium 3,4-bis ((benzo[d]thiazol-2-ylthio)methyl) thieno [2, 3-b]thio-phene-2, 5-dicarboxylate) was developed as a novel fluorescent chemosensor with high selectivity towards Pb(II) over other cations tested. The new probe exhibited good water solubility and only sensed Pb(II) among metal ions examined in neutral 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer solution. The selectivity and sensitivity of fluorogenic probe to Pb(II) were discussed on the basis of experimental results.     

A novel method for the upper rim alkoxy-substitution of calix[4]arene via a bis(spirodienone) route

A mild and efficient one-step procedure for the upper rim modification of calix[4]arene via a bis(spirodienone) is described. The bis(spirodienone) on reaction with alcohols in the presence of p-TSA affords mono- and 1,3-disubstituted alkoxy derivatives in moderate to good yields.