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Comparison of various calix[6]arene and calix[4]arene derivatives revealed that only analogues bearing a permanent positive charge non-covalently bind to ds-DNA and ds-RNA, by insertion into a DNA minor groove or RNA major groove. Also, these cationic analogues revealed strong and highly selective charge-dependent stabilization of AT-DNA against thermal denaturation, the calix[6]arene trication being an order of magnitude more efficient than its calix[4]arene dicationic analogue. At variance to DNA/RNA selectivity for only cationic calixarenes, both neutral and cationic calixarenes bind nucleoside monophosphates with similar efficiency, by forming tweezer-like supramolecular complexes, with nucleobases inserted between aromatic pendant arms grafted to calixarene rims. Such nucleotide-calixarene complexes were monitored by an emission change of calixarene as a function of nucleobase insertion, at variance to DNA/RNA complexes in which calixarene is inserted into the polynucleotide groove, which does not change calixarene emission – stressing the importance of the ligand insertion within a calix-basket for fluorimetric sensing. [ABSTRACT FROM AUTHOR]

Calixarenes with their three-dimensional structural architecture and ease of functionalization at the upper and/or lower rim are well-known for their plethora of applications in chemical, physical, biological and other disciplines. Herein, CuAAC click inspired p-tert-butylcalix[4]arene tethered benzotriazolyl dendrimers, for example, N-1, N-2 type 2-fold compound 6 and 7 'G(0)' and 6-fold compound 16 and 17 'G(1)' generation benzotriazolyl dendrimer, were devised and also evaluated for their therapeutic potential both in vitro and in vivo. The developed calix[4]arene tethered benzotriazolyl dendrimers have been characterized by standard spectroscopic analysis including NMR (1H and 13C), MS, and SEC. Among all the benzotriazolyl dendrimers developed, compound 7 was identified as the effective one which provided potential anti-bacterial and anti-biofilm activities against drug-resistant and slime producing organisms without imparting cytotoxicity to the eukaryotic systems. [ABSTRACT FROM AUTHOR]

The dialkylation of 2,14-dithiacalix[4]arene was studied employing various synthetic procedures known for the parent macrocycles (thiacalixarenes and/or classical calixarenes). The best results for distal dialkylation were achieved using the Mitsunobu reaction with the corresponding alcohols. Interestingly, due to the lower symmetry of the starting compound, the dialkylated derivatives represent inherently chiral systems. The introduction of chiral substituents thus leads to mixtures of diastereomers potentially useful for the separation of individual stereoisomers as demonstrated by chiral HPLC. The conformational behavior of the novel compounds was studied both in solution (NMR) and in the solid state (X-ray). [ABSTRACT FROM AUTHOR]

The meta- and para-substituted aminocalix[4]arenes immobilized in the cone conformation were acylated to yield the corresponding acyl amides. Subsequent cyclization with aryl or alkyl cyanides afforded the expected quinazolines only in the case of the para-substituted series, while only complex reaction mixtures were obtained for the meta-substituted analogues. This finding was used as a strategy for the preparation of novel inherently chiral calixarenes with strong fluorescence. The structure of the products was proved by the combination of NMR and single crystal X-ray analyses. The dynamic NMR study of quinazoline derivatives revealed the existence of two different atropisomers in solution at lower temperatures. As evidenced by resolution with a chiral HPLC column and by the fluorescence titration experiments, novel quinazolines represent inherently chiral macrocycles of high potential for the design of chiral calixarene-based receptors. [ABSTRACT FROM AUTHOR]

Phenoxathiin-based thiacalix[4]arene, accessible via acid-catalysed rearrangement of the starting spirodienone derivative, was subjected to the oxidation of sulfur bridging groups. Using an excess of the oxidation agent, systems bearing four sulfonyl groups or three sulfonyl and one sulfoxide group are available in high yields, depending on the reaction conditions. Although four different conformations can be obtained, the alkylation with various alkylating agents led stereoselectively to derivatives being immobilized in the partial cone conformation. The structure of products was assigned using a combination of NMR techniques and single crystal X-ray analysis. All compounds represent inherently chiral building blocks potentially useful in the design of novel thiacalixarene-based receptors. [ABSTRACT FROM AUTHOR]

meta-Substituted organomercury calix[4]arenes and their corresponding iodo derivatives have been used for lithiation followed by a reaction with various aldehydes or ketones. The resulting diastereomers were in some cases separable using simple column chromatography. Subsequent intramolecular Friedel–Crafts alkylation led to calix[4]arenes with an additional methylene bridge bearing two different substituents with in/out (relative to the cavity) stereochemistry. Our results indicate that the stereochemistry of the final cyclised product does not depend on the structure/stereochemistry of the starting compound, but rather it is influenced by the stability of the products. The relationship between the positions of these substituents and the complexation properties was demonstrated by 1H NMR titration experiments with N-methylpyridinium iodide. [ABSTRACT FROM AUTHOR]

For the first time thiacalix[4]arene derivatives in 1,3-alternate conformation simultaneously containing amide, carboxyl and hydroxyl groups capable of forming 1 : 1 stoichiometry complexes with dopamine hydrochloride were obtained. The efficiency of dopamine hydrochloride binding was evaluated by a number of spectral methods. Using the methods of fluorescent, UV-Vis and NMR spectroscopy, the mechanism of interaction of the synthesized macrocycles with dopamine has been studied. It was shown that quenching of dopamine fluorescence by the studied macrocycles is carried out through a static mechanism. [ABSTRACT FROM AUTHOR]

By applying electrophilic aromatic mercuration of calix[4]arene the introduction of substituted hydroxymethyl groups at the meta position of the basic skeleton has been achieved. Subsequent intramolecular Friedel–Crafts alkylation led to a novel type of bridged calix[4]arenes with additional symmetrically substituted methylene bridges connecting to the neighbouring aromatic units. Additionally, this new efficient synthetic pathway was also used for the preparation of a double bridged analogue. These compounds with rigidified cavities can complex cations and neutral compounds using CH–π and/or cation–π interactions as demonstrated by 1H NMR titration experiments. [ABSTRACT FROM AUTHOR]

A family of calix[4]arenes with variation in steric crowding at the upper rim and incorporating pyridine and amide moieties at two of the four OH groups located in the lower rim have been synthesized and their performance as sensors for metal ions has been investigated. Two of the compounds exhibited selective interaction with Cu2+ ions with sharp colour change, observed by the naked eye. Spectroscopic and computational studies revealed that two of the compounds form 1 : 2 complexes, in which one of the Cu2+ ions interacts strongly with the phenolic OH, resulting in a colour change due to strong absorption (ICT) in the visible region. For the third compound, the Cu2+ ions coordinate with the pyridine and amide nitrogen atoms, and the Cu2+ ion could not enter inside to interact with the OH group due to restricted flexibility at the lower rim because of the bulky groups at the upper rim. The Cu2+ complexes thus formed have been used for sensing of amino acids and interestingly, one of the complexes exhibits interactions selectively with cysteine out of eighteen amino acids tested with a sharp colour change in aqueous media. The formation of the Cu2+–cysteine complex is confirmed from mass data, and the surface morphology of the complex before and after the addition of cysteine is investigated by SEM study. [ABSTRACT FROM AUTHOR]

A functionalised calixarene {4-sulphatocalix[6]arene hydrate (SC6)} stabilises MoS2/partially reduced graphene oxide (rGO) nanosheet. Such stabilised SC6–rGO/SC6–MoS2 and SC6 doped polyaniline (PANI) together form a nanocomposite hybrid material for supercapacitor electrodes. The nanocomposite is fabricated by an in situ polymerization method. Transmission electron microscopy (TEM) results suggest that PANI nanostructures grow homogeneously on the surfaces of SC6 functionalised MoS2. Calixarene acts as a dopant for PANI as well as a stabiliser for the 2D nanosheets of rGO/MoS2. The characterisation of composites and the basic components is done using various techniques, namely, solid-state FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The electrochemical performance is analysed by cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectrometry (EIS). It is found that the SC6 functionalised MoS2 and SC6 doped PANI form a uniform nanocomposite. The synthesised composites show high specific capacitance (691 F g−1) and good cycling stability during charge–discharge process when used as supercapacitor electrodes. The improvement in electrochemical performance of composites is assigned to synergistic effect of SC6 stabilised MoS2 and doped PANI. Our investigation highlights the importance of use of calixarene in composites for improved supercapacitor performance. The role of calixarene in the present study paves the way for the application of alike materials in composite supercapacitors for energy storage applications. [ABSTRACT FROM AUTHOR]

Tritopic tris-calix[4]arene TC4– possessing three divergent cavities linked to a tris-aminophenylamine core – forms, in the presence of tetra-anionic Cu(ii) porphyrins CuTPPS or a combination of different metallo-porphyrins (CuTPPS, NiTPPS and MnTPPS), discrete 3 : 1 porphyrin/tris-calixarene complexes. The 3 : 1-(CuTPPS/TC4) complex in particular is shown to be a key building block for the assembly of supramolecular architectures of increasing complexity. Directional (radial vs. stacked) self-assembly of these nanostructures was achieved by alternate addition of selected hetero-components in a programmed fashion. Addition of TC4 and CuTPPS, in turn, leads to a radial growth of the assembly, whereas, addition of single-cavity calix[4]arene C4 stoppers followed by a CuTPPS topping, promotes a stacked growth. In the latter case, the use of chiral (R)- or (S)-C4 stoppers is seen to induce chirality in the whole assembly. Circular dichroism data ultimately suggest that porphyrin molecules located above/below the 3 : 1 core complex act as a “molecular glue”, by making the interaction between chiral calix[4]arenes (R)- or (S)-C4 and the achiral 3 : 1-(CuTPPS/TC4) complex stronger. [ABSTRACT FROM AUTHOR]

Herein, new fluorescent sensors based on calix[4]arene-biscrown-6 containing extended coumarin as a fluorophore were synthetized and their photophysical properties were characterized. These compounds display intense absorption and emission spectra in the visible region due to extension of the coumarin system. Moreover, complexation properties of these ligands were reported, and the Calix-COU-Benz-CN ligand was able to selectively detect cesium ions in an organoaqueous solvent. Upon the addition of cesium, a blue-shift in the absorption spectra and an enhancement of the emission spectra were observed. This ligand was incorporated in a microfluidic device for the detection of Cs+ ions, and a detection limit of 1.4 μM was achieved for these ions. [ABSTRACT FROM AUTHOR]

One major issue that precludes the application of chemical sensors for the analysis and quantification of dissolved hydrocarbon contaminants in environmental waters is interference from similar types of organic molecules. Polymer-based sensing films are used extensively to interact with certain classes of organic compounds; however, these materials have not been able to achieve sufficient selectivity when analysing complex multicomponent hydrocarbon mixtures in real aquatic systems. Polymer composite materials are an alternative approach towards improving the selectivity and analytical response of sensors for hydrocarbons. In this study, calixarene–polyisobutylene composite films were synthesised via a solvent casting method and the structural and sorption properties were investigated using infrared spectroscopy. The type and amount of calixarene in polyisobutylene was varied and it was shown that the calixarene content in the film plays a significant role on the hydrocarbon sorption mechanism. Scanning electron microscope and optical microscope studies revealed the formation of calixarene microparticles within the polymer film and that this may be responsible for the observed differences in hydrocarbon sensitivity. We demonstrate using toluene and ethylbenzene that the molecular selectivity of polymer films can be tailored by adjusting the calixarene type and concentration. [ABSTRACT FROM AUTHOR]

Herein, the multistep synthesis of eight new ligands based on either calix[4]arene or thiacalix[4]arene backbone blocked in a 1,3-alternate conformation was achieved. Both types of backbones were functionalized with pyridyl coordinating units using either imino or amino junctions. The introduction of the pyridyl units was achieved using either the position 3 (meta) or 4 (para) of the aromatic moiety. Moreover, four out of the eight ligands were structurally investigated in the solid state via X-ray diffraction methods on single crystals. [ABSTRACT FROM AUTHOR]

A table of contents for the issue is presented.

The encapsulation of paclitaxel (PTX) using amphiphilic calixarene (SC4-C6) is an attempt to improve its water solubility. The optimized nanocapsules were successfully prepared by a thin film hydration method where an organic phase containing the mixture of PTX and SC4-C6 (molar ratio of 1 : 10) was dispersed by probe sonication for 30 s into an aqueous phase. The optimized formulation of PTX loaded amphiphilic calix[4]arene nanocapsules had an average particle size of 206 ± 14 nm and an encapsulation efficiency of 82.65 ± 2.54%. Transmission electron micrographs demonstrated the sphere shape of the PTX loaded amphiphilic calix[4]arene formulation without obvious agglomeration. In vitro drug release experiments clarified the obvious sustained release behaviors of the PTX loaded amphiphilic calix[4]arene formulation compared to commercial Taxol. Furthermore, the PTX loaded SC4-C6 formulation revealed improved PTX induced cytotoxicity in human cervical cancer cell culture experiments in contrast to Taxol. The nanocapsules assembled from amphiphilic calixarenes obtained in this work displayed a desired narrow size range with acceptable drug loading and sustained release behaviors, which are beneficial for their potential application as an anti-cancer drug delivery vehicle. [ABSTRACT FROM AUTHOR]

The synthesis of N-heterocyclic carbene (NHC) copper complexes supported by calix[4]arene is reported. Mono-substituted calix[4]arene was prepared through conventional procedures, followed by the attachment of an imidazolyl group to create the precursor of NHC ligands. Alkylation with two alkyl bromides followed by metalation resulted in fully characterized original complexes. The X-ray structure showed an “out” conformation for copper. The catalytic activity of the complexes was studied in click chemistry, and revealed good performances. In particular, three new triazoles were synthesized in high yields, under solvent-free conditions and a fast reaction time. The newly synthesized chiral complex was tested in the kinetic resolution of racemic azide. [ABSTRACT FROM AUTHOR]

Macrocycles consisting of naphthalene units connected via methylene bridges offer certain advantages as macrocylic scaffolds as compared with parent calixarenes. These advantages originate from their electron rich and enlarged cavities. Additionally, macrocycles containing 1,3-bridged naphthalene units are dissymmetric and therefore they present interesting stereochemical features, including inherent chirality. We describe here a facile, one-step synthesis of two new calix[4]naphthalenes, by the condensation of 1,6-dimethoxynaphthalene with formaldehyde catalyzed by Brønsted acid (TFA). Additionally, we show the first example of hybrid[n]arene containing a 1,6-dimethoxynaphthalene unit and 1,3-dimethoxybenzene units obtained by a simple, one-pot condensation. The conformational and complexation properties were also studied for the resulting hybrid macrocycles. [ABSTRACT FROM AUTHOR]

The introduction of nosyl moieties onto the lower rim of the calix[4]arene skeleton led to the formation of compounds immobilised in cone conformations. Subsequent reduction of the nitro group and reaction with aryl isocyanates enabled the construction of new calixarene-based ligands for anion recognition. As proven by NMR and UV/vis titration experiments, diaryl urea moieties with electron-withdrawing substituents on both sides represent very efficient tools for the complexation of selected anions (AcO−, BzO−, H2PO4−) even in highly competitive solvents such as DMSO-d6. [ABSTRACT FROM AUTHOR]

This study describes the synthesis, characterization and application of a new amino-substituted p-tert-butylcalix[4]arene-based magnetic sporopollenin, Calix-EPPTMS-MS (4), for the removal of two toxic organophosphorus pesticides, namely chlorpyrifos and diazinon, from contaminated water. The synthesized Calix-EPPTMS-MS (4) was characterized using FT-IR spectroscopy, a UV-Vis spectrophotometer, an elemental analyzer, scanning electron microscopy and energy dispersive spectroscopy. The pesticide removal efficiency of Calix-EPPTMS-MS (4) was evaluated through a batch-wise method and gas chromatography using a micro-electron capture detector (GC-μECD). Experimental parameterssuch as adsorbent dosage, pesticide concentration, solution pH and contact time were optimized. Excellent removal efficiencies of 96% for chlorpyrifos and 88% for diazinon were achieved at pH 7 within 10 min of contact time. Kinetic studies showed that both pesticides followed the pseudo-second-order rate model with a coefficient of determination (R2) of 0.999. The Langmuir and Dubinin–Radushkevich isotherms with high values of R2 revealed that chlorpyrifos and diazinon adsorption on the Calix-EPPTMS-MS (4) adsorbent follows the chemisorption mechanism. Pesticide contaminated wastewater samples were used to assess the field applicability of the Calix-EPPTMS-MS (4) adsorbent. The results obtained showed that the newly fabricated adsorbent material Calix-EPPTMS-MS (4) is an efficient adsorbent and exhibits great potential as an alternative adsorbent for pesticide removal. [ABSTRACT FROM AUTHOR]

While all the alkylation methods commonly used in the chemistry of classical calixarenes failed, tetranitrothiacalix[4]arene was easily alkylated using various alcohols under Mitsunobu reaction conditions. The products thus obtained were immobilized in the 1,3-alternate conformation as suggested by 1H NMR and proven unequivocally by X-ray analysis. The introduction of chiral alkyl substituents into the lower rim of thiacalixarene gave us an opportunity to form well-preorganized ureido cavities on both sites of the system. As revealed by 1H NMR titration experiments, such compounds were capable of chiral anion recognition even in DMSO-d6 which is a highly competitive solvent towards hydrogen bonding interactions. The highest chiral discrimination was achieved for free serine with a selectivity factor of 3.13 for the d-isomer. [ABSTRACT FROM AUTHOR]

The interactions between hydrochloride salts of biologically relevant amines and micelles formed by a water-soluble p-tert-butylcalix[5]arene were investigated by means of 1H NMR spectroscopy, using a combination of NOESY and DOSY techniques. DOSY measurements were conveniently employed to assess the micelle affinity towards the target guests (phenylethylamine ≈ histamine ≈ serotonin ＞ tyramine ＞ dopamine ＞ norepinephrine), whereas NOESY studies revealed the approximate position of these cationic guests within the different micellar regions. In general, all the guests were located in the palisade region of the micelle, with the exception of phenethylamine and histamine, the former being bound to the micellar core as well as the palisade, the latter preferring the outer shell of the micelle. [ABSTRACT FROM AUTHOR]

The present study describes the extraction of lead(ii) from acidic medium with supercritical carbon dioxide using various calixarenes. It involves the investigation of the effect of temperature, acid molarity, and the metal to complexing agent molar ratio on supercritical fluid extraction efficiency. Efficient extraction of Pb(ii) was observed for p-t-butylcalix(4)arene with (92 ± 3)% extraction at 323 K, 20.27 MPa, 30 minute static time followed by 30 minute dynamic time and a metal to complexing agent molar ratio of 1 : 5. The complexing ability of Pb(ii) with calixarene was established by absorption and energy dispersive spectroscopy. The scanning electron micrograph of calixarene and the lead–calixarene complex was studied. The structure of the Pb(ii)–calixarene complex has been proposed based on solvent extraction in hexane and IR spectroscopic analysis of the extract. Thermodynamic aspects of extraction were also studied and the extraction reaction was found to be entropy driven. Interference from other metal ions, on Pb(ii) extraction behaviour, has been investigated. The developed method has been utilized for extraction of Pb(ii) from real samples viz. paints, batteries, tobacco and wastewater. [ABSTRACT FROM AUTHOR]

Two new calix[4]arene based fluorescence sensors (L1 and L2) have been synthesized and characterized. L1 was found to selectively quench fluorescence intensity upon addition of Cu2+ ions through host–guest complexation and display “on–off” behavior while L2 was not that efficient. The in situ generated L1·Cu2+ complex could further recognize CN− from the anionic broth with a distinct “off–on” behavior in the fluorescence titration. [ABSTRACT FROM AUTHOR]

Carbon nanomaterials (CNMs) stabilised by p-phosphonated calix[8]arene are decorated with Pd nano-particles via hydrogen reduction of H2PdCl4 in a vortex fluidic device, with control over particle size (1.3 nm to 7 nm). The composite is readily incorporated into sensors for up to 10% hydrogen detection, using a drop casting method. [ABSTRACT FROM AUTHOR]

A new thioacetate-bearing cone-conformer calix[4]arene has been synthesized and shown to be a sensitive microcantilever self-assembled monolayer coating for calcium ion detection in aqueous solutions. [ABSTRACT FROM AUTHOR]

The conformational distribution in distally functionalized adamantylated calix[4]tubes was analyzed with NMR and quantum-chemical calculations. Without any intramolecular interactions, ester-, acid-, amino-, alcohol-, isocyanate-, phthalimide- and urea-substituted calixtubes preferred less sterically hindered flattened cone conformers in solution. In contrast, in a non-polar medium (CDCl3) for calixtubes bearing two 3-carboxymethyl-1-adamantyl or 3-(2-ureidoethyl)-1-adamantyl units, the less sterically preferable flattened cone conformation with bulky substituents connected by intramolecular hydrogen bonds was found to be more favorable. On the other hand, for a calixtube with two positively charged units, only the conformer with distanced substituents was exclusively detected. Thus, the conformational equilibrium in functionalized calix[4]tubes can be controlled by intramolecular hydrogen bonding between appropriately arranged carboxylic groups or urea moieties, or by electrostatic repulsion of positively charged substituents. [ABSTRACT FROM AUTHOR]

A series of pyrazine-based calix[4]arene extractants was prepared by a stepwise functionalization, comprising palladium-catalyzed exhaustive cross-coupling of di- and tetrasubstituted calix[4]arenes bearing chloropyrazine moieties. The extraction behavior of the synthesized ligands was studied on Am–Eu mixtures under acidic feed conditions similar to those prevailing in nuclear wastes. Phosphorylpyrazine-bearing extractants exhibited a very high acid resistivity and a high affinity for americium giving D values as high as 794 at pH 1. The synergistic effect of the chlorinated cobalt bis(dicarbollide) anion [(B9C2H8Cl3)2Co]− (CCD-anion), as well as the effect of the calix[4]arene platform compared to monovalent ligands, was investigated. The presence of 1 mM CCD resulted in a 105 times increase in the D value. [ABSTRACT FROM AUTHOR]

A number of calix[4]arene-based fluorescent chemosensors containing amide as a binding site and quinoline as a fluorogenic unit have been synthesised and characterized by a single crystal X-ray diffraction study. These compounds have been designed with variations in conformation and steric crowding in the calix moiety to investigate its effect on ion selectivity and thereby on excimer emission. The ion-binding property of these fluoroionophores has been investigated with a large number of cations and anions and the ion-recognition event was monitored by luminescence, UV-Vis and 1H NMR (for anions) spectral changes. Out of a large number of cations, Hg2+, Pb2+, Fe3+ and Cu2+ exhibited strong complexation with all of the ionophores, as evident from luminescence and UV-vis spectroscopy. In the case of anions, F− and HSO4− exhibited strong complexation with two of the ionophores, as shown by fluorescence and NMR spectroscopy. Interestingly, complexation with metal ions resulted in a new band at lower energy due to excimer emission, which was not observed for anions. The binding constants for all of the three fluoroionophores with strongly interacting ions have been determined from fluorescence, UV-vis and NMR titration data. The DFT calculations for all of the three compounds were performed and the results show that the modulation of frontier molecular orbital energies upon complexation of metal ions causes the fluorescent excimer emission. [ABSTRACT FROM AUTHOR]

Crystallisation of a tris-p-carboxylatocalix[4]arene from various pyridine derivatives leads, in some cases, to further self-assembly into triply helical nanotubes, demonstrating the degree of tolerance of the structure motif towards the introduction of alkyl groups around the aromatic ring of the guest template. [ABSTRACT FROM AUTHOR]

The calixarenes and resorcinarenes are macrocyclic phenolic molecules that can be modified “à façon” and a wide range of chemical modification strategies have been published over the last 30 years. Because of their remarkable structural properties and their relative ease of chemical modification, they represent excellent and highly versatile bases to design complex building blocks capable of self-assembly and molecular recognition. They have been widely studied for their ability to form supramolecular structures targeting a wide range of applications. The possibility to regio(rim)-selectively modify these macrocycles with different polar and apolar moieties provides synthetic chemists with an unlimited range of possibilities for the design of complex amphiphiles with a high control over the position of the grafted moieties in the three dimensions. These amphiphiles have been shown to possess outstanding self-assembling and/or molecular recognition properties. This short review describes the developments of the chemistry of amphiphilic calixarenes and resorcinarenes with a clear focus on the synthetic paths used for their production and their self-assembly properties in water. [ABSTRACT FROM AUTHOR]

A number of calix[4]arene-azacrowns with variation in ring size and substituents at the upper and lower rims have been synthesized to investigate the effect of steric crowding towards ion selectivity. The structural elucidation of these ionophores has been carried out mainly by 1H NMR and ES-MS in solution and by single crystal X-ray study in the solid state. Interaction of these ionophores with a large number of cations has been investigated by NMR studies. The ionophore with tert-butyl at the upper rim (3) exhibits selectivity towards Na+ only whereas an ionophore of the same size but without tert-butyl at the upper rim (1) shows selectivity towards both Na+ and K+. An ionophore of the same size but with three tosyl substituents at the lower rim (4) exhibits no complexation with any cation. The ionophore with the larger crown ring and without tert-butyl at the upper rim (2) exhibits complexation with K+, Rb+, Ba2+ and weak interaction with Na+. Binding constants with these metal ions have been determined by NMR titration. Molecular modeling studies performed by a molecular mechanics force field (MMFF94) using the Monte Carlo search method and DFT calculations predicted the observed higher selectivity for sterically crowded receptor. [ABSTRACT FROM AUTHOR]

Calixarenes are versatile platforms for the design and synthesis of molecular receptors and multivalent ligands that are able to mimic or affect specific biological functions. This review illustrates examples spanning the recognition of small peptides and carbohydrates to ion transport through membranes, biomimetic catalysis, DNA condensation and cell transfection, protein binding, sensing and inhibition, and gives perspectives for using calixarene macrocycles in bio-supramolecular chemistry. [ABSTRACT FROM AUTHOR]

The extraction pathway of lanthanide ions from simulated nuclear waste solutions and the synergistic effects of a calixarene and a cobalt dicarbollide anion (CD) have been investigated on a model system by the combined use of electrospray ionization MS, FTMS ICR, together with 1H and 11B high field NMR spectroscopy techniques. Moreover, the extracting capabilities of the calixarene/BrCD mixture were determined by liquid–liquid extraction tests. An enhanced extraction efficiency of the calixarene/BrCD mixture with respect to the calixarene alone was observed. MS analysis allowed the assessment of a supramolecular ternary association, while the NMR data gave information on the calixarene binding sites for lanthanide ions. Herein, we report the experimental evidence of the formation of a ternary lanthanide/calixarene/Co-dicarbollideaggregate, which allowed us for the first time to assess the mechanism of the synergistic action of calixarenes and CD anions in lanthanide ion extraction. [ABSTRACT FROM AUTHOR]

Bowl shaped p-sulfonatocalix[4]arene is a versatile anion in building multi-component self-assembled materials, with a design strategy of incorporating small organic cations including imidazolium or pyrrolidinium cations within the cavity of the calixarene through their polar head groups, which is also established in solution for the two components. Another design strategy is the assembly of interlocking (embracing) large phosphonium cations around the outer (exo-) surface of the cavity of the calixarene. The selectivity of interplay of the different cations with the endo- and exo-surfaces of the calixarene requires the presence of aquated lanthanide(iii) ions, but these ions are not necessarily incorporated into the extended structures. [ABSTRACT FROM AUTHOR]

The tri-carboxylatomethylene-mono-alkoxy calix[4]arenes have been shown by fluorescence spectroscopy to bind to the NBD1 domain of MRP1 protein in a magnesium dependent manner. The observed associations constants are of the same order as that observed for ATP–Mg, the natural substrate for this protein. [ABSTRACT FROM AUTHOR]

Silver nanoparticles less than 5 nm in diameter are accessible by a simple photochemical reduction in water, templated by p-phosphonated calix[4]arene and its O-alkyl derivatives, in a way depending on the pH of the reagent solution. [ABSTRACT FROM AUTHOR]

Improvement of the design of inherently chiral calix[4]arenes as organocatalysts was accomplished viathe introduction of a diarylmethanol structure. Novel, inherently chiral calix[4]arenes bearing a tertiary amine or a quaternary ammonium moiety, together with a diarylmethanol moiety, were synthesized from previously reported chiral calix[4]arene amino acid derivatives in an optically pure form. These chiral calix[4]arenes were applied to asymmetric reactions as organocatalysts, and a positive effect of the diarylmethanol structure on enantioselectivity was observed. [ABSTRACT FROM AUTHOR]

The article focuses on a study related to multi-component solid state structures containing 1-octyl-2,3-dimethylimidazolium cations, anionic p-sulfonatocalix[4]arenes and large mono-phosphonium cations, and lanthanide metal ions. It shows that the imidazolium ring is confined in the calixarene cavity, forming ''molecular capsules'' based on two calixarenes with the nature of the calixarene-dimethylimidazolium interplay mapped out using Hirshfeld surface analysis.

In order to prepare new molecular hosts able to discriminate enantiomers of amino-acid derivatives, we have synthesized chiral thiacalix[4]arenes. Extensive studies using NMR and mass spectrometry techniques allow us to determine the major supramolecular interactions involved in the recognition process. Moreover, a titration study enables us to determine the binding constant between these new hosts and a series of amino-acid derivatives. Finally, we have also demonstrated that these calixarenes are able to discriminate enantiomers of amino-acid guests. [ABSTRACT FROM AUTHOR]

A series of triazole-modified calix[4]crowns, 3, containing hard and soft ion binding sites were synthesized in good yields viaclick chemistry. The hard and soft ion binding sites may selectively complex alkali metal or transition metal cations. Compound 3ashows good complex selectivity towards Pb2+and 3cshows the highest Li+/K+extraction ratio, suggesting that the triazole groups play an important role in metal ion binding. [ABSTRACT FROM AUTHOR]

New calix[4]arene derivatives (3–5, 7–8) of coneand 1,3-alternateconformations possessing thiourea/urea moieties have been synthesized and examined for their anion recognition abilities towards different anions like fluoride, chloride, bromide, iodide, nitrate and acetate by 1H NMR and UV-Vis spectroscopy. Fitting the changes in the absorption spectra using nonlinear regression analysis indicates that all these compounds have strong binding affinity for chloride ions. The stoichiometry of the hydrogen bonded complexes is 1 : 1 (H : G) for receptor 3–5, while it is 2 : 1 (H : G) with 7–8. Chloride ion selective electrodes (ISEs) were also formed which showed excellent selectivity over all other anions tested. [ABSTRACT FROM AUTHOR]

A series of diureido-calix[4]arenes immobilised in the 1,3-alternateconformation was synthesised and systematically studied for their complexation ability. As revealed by 1H NMR and UV/vis titrations, this structural motif leads to very efficient ligands for anion recognition with high binding constants in nonpolar solvents. The comparison with the corresponding ligands possessing the coneconformation indicates that diureido-calix[4]arene in a 1,3-alternateconformation are very promising anion receptors with pronounced binding ability towards carboxylates. [ABSTRACT FROM AUTHOR]

The ability of pyridine N-oxide molecules to form host–guest complexes with p-sulfonatocalix-[5]arene was probed and resulted in the formation of europium complexes incorporating 2- or 4-picoline N-oxide, and 4,4′-dipyridine N,N′-dioxide. Relative to lanthanide complexes of p-sulfonatocalix[5]arene incorporating pyridine N-oxide, the presence of a methyl group on the aromatic ring for the picoline N-oxides, or a larger dipyridine dioxide guest dramatically alters the self-assembly, resulting in the formation of three new supramolecular motifs for the calixarene. [ABSTRACT FROM AUTHOR]

The first synthesis and optical resolution of an inherently chiral calix[4]arene amino acid has been achieved. [ABSTRACT FROM AUTHOR]

The synthesis of a series of novel tris[(carboxy)methyl]-monoalkoxy-trihydroxycalix[4]arenes is described. Treatment of the tris[(dimethylamino)methyl]-monoalkoxy-trihydroxycalix[4]arene derivatives with iodomethane, followed by sodium cyanide as a nucleophile, gave the corresponding tris[(cyano)methyl]-monoalkoxy-trihydroxycalix[4]arenes in excellent yield, and these latter compounds were converted by hydrolysis to their tris[(carboxy)methyl]-monoalkoxy derivatives. The solid-state structures of four of the intermediate tris[(cyano)methyl]-monoalkoxy-trihydroxycalix[4]arenes show inclusion of an acetonitrile guest in the ethoxy derivative and intermolecular inclusion of the hydrophobic terminal region of the alkoxy groups for longer chain lengths. The packing of both structural types show 1-D inclusion polymer behaviour. At pH values above 5.5, all the trianionic tris[(carboxy)methyl]-monoalkoxy-trihydroxycalix[4]arene derivatives showed self-assembly to yield micellar systems, for which there was a clear odd–even effect in the observed surface tensions at the critical micelle concentrations. [ABSTRACT FROM AUTHOR]

A new class of functionalized calix[4]arenes have been synthesized and evaluated for colorimetric detection of fluoride ions. The molecular receptor 4bselectively recognizes fluoride ions viaH-bonds and subsequent deprotonation to elicit a distinct colour change from yellow to dark purple. [ABSTRACT FROM AUTHOR]

A family of chiral lower-rim substituted calixarene ligands 1–14 is synthesized and characterized as prospective ligands for synthesis of asymmetric active sites for heterogeneous catalysis and adsorption using a surface organometallic approach. The ligands possess asymmetric centers directly attached to lower-rim oxygens; the asymmetric centers are tailored with sterically bulky naphthyl and electron withdrawing CF3 substituents. 1H and 13C NMR spectroscopies demonstrate that mono- and 1,3-di-alkylated calixarenes synthesized using this procedure adopt the cone-shaped conformation, which is stabilized by multiple hydrogen bonds at the lower rim. Smaller pendant groups and polar solvents increase the dialkylation/monoalkylation ratio. The reaction proceeds with full inversion of configuration as established via single crystal X-ray diffraction of an N-Cbz-protected aminocyclopentoxy-modified calixarene. The calixarenes synthesized by this approach are characterized using circular dichroism (CD) spectroscopy and ab initio modeling, which is used to identify the minimal molecular fragment responsible for the observed lowest energy Cotton effect in the CD spectrum. Factors that influence the intramolecular induction of asymmetry throughout the calixarene scaffold are investigated by systematically varying substituent steric bulk, connectivity of the asymmetric center to the calixarene core, and the extent of hydrogen bonding at the calixarene lower rim. The asymmetry of the calixarene core is quantified using 1H NMR spectroscopic shifts of aromatic meta and methylene bridge hydrogens and supported using ab initio calculations. The results demonstrate that calixarene core asymmetry is most strongly induced for rigid calixarene cores—an attribute that is expected to be preserved upon metal complexation and anchoring of these prospective ligands. [ABSTRACT FROM AUTHOR]

We demonstrate for the first time the utility of oxacalixarenes as hosts and investigate the forces that influence the thermodynamics of binding. [ABSTRACT FROM AUTHOR]