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The application of immobilizing calixarene onto the surface of silica using a sol-gel method, as an efficient heterogeneous catalyst (CX4SO 3 HSi(n)) for multicomponent Povarov reaction has been described. Catalytic activity of the CX4SO 3 HSi(n) for the synthesis of julolidines under greener and environmentally benign conditions in simple and efficient method was explored. Notably, only 0.5 mol% of the catalyst is sufficient to catalyze the Povarov solvent-free reaction under microwave-assistance. Besides, this protocol allows the construction of four new C–C bonds and two C–N bonds in a single step. To the best of our knowledge, this consists the first silica support calix[4]arene as a heterogeneous catalyst for multicomponent synthesis of julolidines. Image 1 [ABSTRACT FROM AUTHOR]

In the present work, we synthesised a functionalised calix[4]arene with 5,11-di(N-methyl-E-(4-pyridylethylene) moiety (CX[4]), and investigated interactions of it with HemiMeQ[6], HemiMeQ[7], and Q[8]) in both water and DMSO using fluorescence spectrophotometry and 1 H NMR spectroscopy. Titration 1 H NMR spectra revealed that Q[ n ]s prefers to include the N-methyl-E-(4-pyridylethylene) moiety. In particular, the interaction of CX[4] with Q[8] in water resulted in intense fluorescence emission, and this interaction system can respond to compounds such as amantadine. [ABSTRACT FROM AUTHOR]

The one-pot reaction between bis(hydroxymethyl)phenol derivatives and diamines or triamines afforded novel azacalixarenes with bridged structures. Basket-type macrocycles of cone conformations, molecules that contained two aza[3.1.1.1]calixarene skeletons connected by a chain, or novel saucer-type azacalixarenes were obtained from the reaction. Structures of some of them were determined by crystallographic analyses. [ABSTRACT FROM AUTHOR]

The present work introduces the synthesis and characterization of upper rim dibromo-substituted bis-1,3-diketone calix[4]arenes with hydroxy and propyloxy groups at the lower rim as ligands for Gd 3+ and Tb 3+ complexes. The dibromo-substitution does not affect 1:1 complex formation with the lanthanide ions arising from their coordination via two 1,3-diketonate groups incorporated at the upper rim of the calix[4]arene. The analysis of the time-resolved luminescence spectra of the Gd 3+ complexes clearly demonstrates the notable enhancement of the decay time of the ligand triplet state, while the energy of the triplet state for the new dibromo-bis-1,3-diketones remains practically unchanged versus its non-substituted analogues. The latter tendency points to the heavy-atom effect on the energy transfer from the excited state to vibration levels of the dibromo-substituted ligand resulting in a decreased radiationless decay contribution. Measurements of Tb 3+ -centered luminescence indicate a better antenna effect (∼1.7) of dibromo-calix[4]arenes compared with its non-substituted counterpart. [ABSTRACT FROM AUTHOR]

The inclusion complex of p -sulfonatocalix[5]arene (SC5A) with N -methyl- N ′-(naphthalen-2-ylmethyl)-4,4′-bipyridinium (MVNp 2+ ) guest was successfully prepared in single-crystal form. The obtained structure shows that SC5A is significantly distorted from the common ‘cone’ conformation induced by the complexation of MVNp 2+ . Moreover, the crystal packing of MVNp 2+ ⊂ SC5A reveals that the SC5A hosts do not assemble into a typical bilayer array, but arrange themselves into an unseen face-to-back bis-chain. As a result, hydrophobic molecular channels are fabricated rarely by SC5A hosts. A host–guest solution study was further performed by using NMR spectroscopy and microcalorimetry, the results of which are in accordance with the above crystallographic results. The molecular binding behaviors of SC5A with N -methyl- N ′-adamantane carbomethyl-4,4′-bipyridinium (MVAd 2+ ) guest that is structurally similar to MVNp 2+ but with a different side group were also studied by using NMR spectroscopy and microcalorimetry in solution, the results of which are similar to those of SC5A with MVNp 2+ guest as well. [ABSTRACT FROM AUTHOR]

Six water-soluble calix[ n ]arene-based Brønsted acid-type catalysts with amphiphilic groups were successfully synthesized by incorporating sulfonic acid moieties. Their structures were characterized using FTIR, 1 H NMR, 13 C NMR, APT-NMR, and elemental analysis techniques. Moreover, their catalytic capabilities were evaluated in the coupling reaction of 2-methylfuran and/or N -methylindole with some sec -alcohols in aqueous media. The association of their surfactant abilities, and the effects of water amount used and reaction durations on the catalytic activities of these amphiphilic calix[ n ]arene derivatives were also investigated. Observations indicated that these amphiphilic calix[ n ]arene catalysts exhibited high catalytic activities in the coupling reactions of 2-methylfuran and N -methylindole with some alcohols in water. [ABSTRACT FROM AUTHOR]

Two novel calix[4]arene macrocyclic ligands functionalized with four 1,3-diketone groups at the upper and hydroxyl ( 3 ) or propyloxy-groups ( 6 ) at the lower rims were synthesized and characterized using NMR, IR spectroscopy, mass spectrometry, and elemental analysis. UV–vis spectrophotometry and ESI mass spectrometry studies indicate 1:1 complex formation of ligands 3 and 6 with Ln(III) (Ln=Tb, Yb) in alkaline DMF solutions resulted from coordination of Ln(III) with 1,3-diketonate groups. Luminescence study of Ln(III) complexes with 3 and 6 reveals significant difference in antenna effects of their deprotonated forms on both Tb(III)- and Yb(III)-centered luminescence. Comparison of ligand-centered emission for ligands 3 and 6 points to the latter as more efficient antenna for Tb(III) and Yb(III). Different conformational behavior of ligands 3 and 6 in alkaline media is assumed as a reason for the experimentally observed difference in sensitization pathways in Ln(III) complexes with 3 and 6 . [ABSTRACT FROM AUTHOR]

Attempts at Pd-catalyzed bridging in sulfoxide-bearing calixarenes containing various substituents (phenyl, ethyl, pyrimidin-2-yl) gave the expected compound only in the case of the ethyl derivative. However, the reaction of sulfoxides with BuLi revealed the ability of the pyrimidin-2-yl group to function unexpectedly as a leaving group. This enabled, depending on the reaction conditions, preparation of unique bis-calixarenes connected together via two sulfur atoms spacers: –S–S–, –S(O)–S– or –S(O) 2 –S–. As documented by 1 H NMR titrations these compounds, otherwise not easily accessible by common synthetic methods, showed recognition ability towards selected cations of the N -methylpyridinium type. [ABSTRACT FROM AUTHOR]

A series of para - tert -butylcalix[4]arene containing amide macrocyclic and acyclic derivatives at the lower rim are synthesized in this paper and their cellular effects are evaluated. G-quadruplex interaction and stabilization are assessed with compound calix-NH 2 to relate it strong antiproliferative effect on cancer cell lines with G-quadruplex recognition. The calix-NH 2 interact and stabilize the G-quadruplexes MYC22 and h22L and show activity in MCF-7, LNCaP, U87 cancer cell lines at low micromolar range of concentrations. [ABSTRACT FROM AUTHOR]

2-(2-Hydroxynaphthalene-1-yl)pyrrolidine-1-carboxamides undergo ring opening in the presence of trifluoroacetic acid and 2-naphthol leading to the formation of new substituted dibenzoxanthenes. Reaction of 2-(2-hydroxynaphthalene-1-yl)pyrrolidine-1-carboxamides with polyatomic phenols at the same conditions was found leading to diarylmethane derivatives and calix[4]resorcinols with naphthyl fragment acting as a leaving group. [ABSTRACT FROM AUTHOR]

Several new di-ionizable p - tert -butylcalix[4]arene-1,2-crown-5 compounds were prepared in the cone conformation. For comparison with reported ligands, the systematic structural variation was a change of the pendent acidic groups from two adjacent –OCH 2 CO 2 H or –OCH 2 C(O)NHSO 2 Z (with Z=–Me, –Ph, –C 6 H 4 –4-NO 2 , –CF 3 ) units to two adjacent –O(CH 2 ) 4 CO 2 H or –O(CH 2 ) 4 C(O)NHSO 2 Z groups. Competitive solvent extractions of alkaline earth metal (AEMC) cations from aqueous solutions into chloroform by these ligands were performed. Also single species solvent extractions were conducted for the divalent heavy metal cations of Pb 2+ and Hg 2+ . Comparison of the extraction data for the new ligands with those reported reveal that the ligands with shorter proton-ionizable side arms are more effective divalent metal ion extractants. [ABSTRACT FROM AUTHOR]

Three magnetically recoverable Brønsted acidic calix[n]arene derivatives were successfully constructed by immobilizing calix[n]arene sulfonic acids onto silica-coated magnetic nanoparticles, a process, which allows calix[n]arene derivatives to acquire magnetic properties. All of the magnetically recoverable Brønsted acidic calix[n]arenes efficiently catalyze the coupling of electron-rich arenes with some alcohols in water. After separation and recovery from the reaction mixture by a simple magnet, these Brønsted acidic calix[n]arenes can be recycled many times without losing their catalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: Two novel p-tert-butylcalix[4]arene-based chiral organocatalysts derived from l-proline have been developed to catalyze direct aldol reactions between cyclohexanone and aromatic aldehydes in water. Under the optimal conditions, high yields (up to 95%), enantioselectivities (up to 90%), and moderate diastereoselectivities (up to 65:35) were obtained. Considering the catalytic inefficiency of sole proline for the aldol reaction in water, these results clearly display the enormous effect of the hydrophobic part of calix[4]arene of compound A. [Copyright &y& Elsevier]

Abstract: A new type of calixarene-based receptor designed for the recognition of chiral anions was prepared by the introduction of (S)-2-methylbutan-1-ol moieties into the lower rim of calixarene. The immobilization of calixarene skeleton in the 1,3-alternate conformation enabled the construction of a cavity consisting of preorganised ureido functions and chiral substituents in close proximity. This cavity is capable of chiral discrimination of selected anions as demonstrated on d- and l-phenylalaninates. [Copyright &y& Elsevier]

Abstract: A novel and sensitive fluorescence sensor has been designed by click chemistry. Based on the obvious and selective fluorescence quenching of anthryl calix[4]arene, a sensitive and robust platform were developed for visual detection of picric acid (TNP) in the mixture of nitro aromatics. The computational calculations revealed the formation of host–guest complex driven by π–π stacking interactions. [Copyright &y& Elsevier]

Abstract: The syntheses, characterization and metal ion complexation and extraction capabilities of six new calix[4]arene Schiff base compounds, 5–10, are reported. The preparation of the compounds was achieved by the condensation of 5,17-diamino-11,23-di-tert-butyl-25,27-di-n-butoxy-26,28-dihydroxycalix[4]arene with the appropriate aldehyde (5-bromosalicylaldehyde for 5, 4-anisaldehyde for 6, 4-(dimethylamino)benzaldehyde for 7, 9-anthracenecarboxaldehyde for 8, 1-pyrenecarboxaldehyde for 9, and 9-fluorenecarboxaldehyde for 10) in refluxing ethanol. The compounds were characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, high-resolution mass spectrometry and elemental analysis. The X-ray crystal structures of 7, 8 and 9 (as dichloromethane solvates) revealed that the calixarene molecules adopt H-bond stabilized, distorted-cone conformations and form centrosymmetric dimers in the solid state. Compounds 5–10 did not form host–guest complexes with NEt4[(bdt)MoO2(OSiPh3)] (bdt2–=benzene-1,2-dithiolate), a potential precursor for biologically relevant oxosulfido-Mo(VI/V) enzyme models; such host–guest complexes have the potential to stabilize these sought-after but highly reactive model compounds. In addition, the capabilities of 5–10 to extract selected metal ions (Ni2+, Co2+, Cu2+, Zn2+, Ag+, Pb2+, Cd2+ and Hg2+) from an aqueous into an organic phase have been assessed by picrate extraction experiments. Compound 5 displayed exceptional selectivity towards Ni2+, compound 7 exhibited enhanced extraction towards all of the metal ions tested and compounds 6, 9 and 10 showed very high selectivity towards Hg2+. On the other hand, compound 8 exhibited negligible capacity to extract any of the metal ions tested. [Copyright &y& Elsevier]

Abstract: Self-assembly can occur spontaneously in solution for calix[4]arenes substituted at both the upper and lower rims with flexible pendant groups containing aromatic rings. This self-assembly occurs in both a head-to-tail and head-to-head manner, as proven by NOESY experiments. [Copyright &y& Elsevier]

Abstract: New di-ionizable p-tert-butylcalix[4]arene-1,2-crown-4 ligands with elongated side arms in cone, partial-cone, and 1,2-alternate conformations of the calixarene scaffold are prepared and characterized. The acidic groups on the side arms include carboxylic acid and N-(X)sulfonyl carboxamide with X variation of –Me, –Ph, –C6H4–4-NO2, and –CF3. Solvent extractions of alkaline earth metal cations, Hg2+, and Pb2+ from aqueous solutions into chloroform are employed to probe the effects of these structural modifications on the divalent metal ion complexation behavior of the new ligands. [Copyright &y& Elsevier]

Abstract: The syntheses and conformational structures of various functionalized tetraoxacalix[2]arene[2]triazines were studied. Applying the fragment coupling approach and the post-macrocyclization chemical manipulations, a number of tetraoxacalix[2]arene[2]triazines that contain, on the lower rim, one or two aldehyde, ester, carboxylic acid, hydroxymethyl, and aminomethyl functional groups were prepared in moderate to high chemical yields from cheap and commercially available materials. On the basis of X-ray crystallography and NMR spectroscopy, all tetraoxacalix[2]arene[2]triazines containing electron-withdrawing group(s) adopted 1,3-alternate conformation both in solution and in the solid state, while tetraoxacalix[2]arene[2]triazines bearing hydroxymethyl and aminomethyl substituent(s) existed as pinched or distorted partial cone conformers due to the formation of intramolecular hydrogen bond between hydroxyl or amino group and triazine ring. [Copyright &y& Elsevier]

Abstract: Upper rim-functionalized, di-ionizable calix[4]arene-crown-6 ligands are synthesized and compared with structural isomers having the two acidic side arms attached to the lower rim. Solvent extractions of selected divalent metal cations (alkaline earth metal cations, Pb2+, and Hg2+) from aqueous solutions into chloroform by the upper and lower rim-functionalized, di-ionizable calix[4]arene-crown-6 isomers are utilized to assess the effects of this structural modification on metal ion complexation abilities of the ligands. The observed effects are compared with those reported for analogous di-ionizable calix[4]arene-crown-5 structural isomers. [Copyright &y& Elsevier]

Abstract: A series of novel calix[4]arene-based Mannich (5 and 6) and Schiff base (9–11) receptors have been synthesized and characterized by various analytical techniques. Competitive two-phase extraction experiments of these novel calix[4]arene amine- and imine-containing derivatives revealed a strong affinity for dichromate anions . The protonated alkylinium form of 5, 6 and 9–11 proved to be effective extractants for transferring the dichromate anions from an aqueous into an organic phase. Moreover, the extraction of dichromate anions by 5 and 9 in the presence of competitive anions such as F−, Cl−, Br−, , , and showed that 5 and 9 could be selective anion receptors for dichromate anions in the presence of those anions. [Copyright &y& Elsevier]

Abstract: An inherently chiral biscalix[4]arene carboxylic acid cone–partial cone conformer was optically resolved into individual enantiomers by chemical resolution method using (S)-BINOL as a chiral auxiliary. The partial cone calix[4]arene component plays a crucial role in optical resolution. The title compound may interact enantiodiscriminantly with chiral aminoalcohols, especially 2-phenylglycinol. [Copyright &y& Elsevier]

Abstract: Different diglycolamide (DGA)-substituted calix[4]arene-based extractants were synthesized and evaluated for the extraction of Am(III) and Eu(III), representative trivalent actinide and lanthanide ions, respectively. On the narrow rim of the calix[4]arene platform, the DGA moiety was either 1,3-di- or tetrasubstituted with a varying spacer length between the oxygen and amide nitrogen atom. In addition, DGA groups were appended both to the wide rim and to both rims of calix[4]arenes and their efficiencies were compared for Am(III) and Eu(III) extraction at three different feed acidities. The extraction and separation efficiencies strongly depended on the N-alkyl substituent as well as the spacer length. 1,3-Di-DGA-substituted calix[4]arenes are inferior extractants to the corresponding tetra-DGA-substituted ones. Narrow rim DGA-functionalized derivatives resulted in high extraction efficiencies, while the wide rim DGA-functionalized calix[4]arenes showed practically no extraction. [Copyright &y& Elsevier]

Abstract: Methods are described for the selective diametrical functionalization of calix[4]arenes at the upper rim by formamide and isocyanide functional groups. The adaptation of Ugi-4-CR to calix[4]arenes leading to α-acylaminocarboxamide derivatives is also discussed. [Copyright &y& Elsevier]

Abstract: A novel protection/deprotection method leading to the regioselective ipso-substitution of calix[4]arenes is described. The introduction of nosyl (p-nitrobenzenesulfonyl) groups into the lower rim of partly alkylated tert-butylcalix[4]arenes leads subsequently to the exclusive ipso-nitration of the alkylated phenol rings, while the protecting groups can be easily removed in the next step. This method gives dialkoxy- or trialkoxy-substituted calix[4]arenes with nitro groups on the alkylated rings and tert-butyl groups on the remaining ones. The above substitution pattern is complementary to the isomers so far known in the chemistry of calix[4]arenes and could be used in the design of novel type of calixarene-based receptors. [Copyright &y& Elsevier]

Abstract: We synthesized the new calix[4]arene amines bearing two and four imidazole or tert-butylamine moieties (9a,b/10a,b) by the reaction of di- or tetra-tosylated calix[4]arene derivatives (7 and 8, respectively) with 1-(3-aminopropyl)imidazole and/or tert-butylamine, respectively. After the characterization of 9a,b/10a,b their extraction abilities toward Cr(VI) anionic species (CAS) was evaluated and compared by the liquid–liquid extraction method. The extraction results revealed that calix[4]arene amine having four imidazole groups (10a) was an efficient anion receptor for CAS. Moreover, the extraction of CAS by 10a in the presence of other anions such as Cl−, NO3 −, and PO4 3− showed that 10a could be a selective anion receptor for CAS in the presence of those anions. [Copyright &y& Elsevier]

Abstract: The interactions between diquat (DQ) and p-sulfonatocalix[4]arene (C4S) were studied in an aqueous solution as a function of the ionic strength. Evidence for the formation of a complex between DQ and C4S was obtained using fluorescence measurements, while the stoichiometry of the complex was confirmed as 1:1 for DQ/C4S using UV–vis spectroscopy. The ionic strength had no influence on the stoichiometry of the complex, but exerted a significant influence on the complexation constant, K c, decreasing with an increase in the ionic strength. The thermodynamic complexation constant, K c′, was computed as 5.25±1.11×107 using the extended Debye–Hückel law. The rate constants for the heterogeneous electron transfer for the reduction of DQ at an electrode surface were evaluated as 0.150±0.010cms−1 in the absence of C4S and 0.065±0.010cms−1 when C4S was added to the solution in a 1:1 ratio. [Copyright &y& Elsevier]

Abstract: Di-ionizable calix[4]arene-1,3-crown-4 compounds locked in 1,3-alternate, cone, and partial-cone conformations are synthesized for evaluation in metal ion separations. The ionizable functions include carboxylic acid and N-(X)sulfonyl carboxamide groups in which the acidity is tuned by variation of the electron-withdrawing ability of X. Similar synthetic routes were employed for preparation of the cone and 1,3-alternate ligand series. A different preparative route utilizing protection and deprotection was required to obtain the partial-cone analogues. Ligand conformations were confirmed by their proton and/or carbon NMR spectra. X-ray diffraction verified an unusual 1,2-alternate conformation in the solid-state for one synthetic intermediate. Effects of ligand conformation and ionizable group variations on competitive solvent extractions of alkali and alkaline earth metal cations from aqueous solutions into chloroform were assessed. Single species solvent extractions of Hg2+ and Pb2+ were also performed. [Copyright &y& Elsevier]

Abstract: We now report the formation and characterization of water-soluble hetero-capsules 1·2 resulting from the ionic interactions between positively charged flexible aniline hydrochloride 1 and negatively charged phosphonate 2 having rigid homooxacalix[3]arene units. The formation of the molecular capsules was studied by NOESY, DOSY NMR spectroscopy and ESI-Mass spectrometry. The water solubility of the capsules is improved by the introduction of mono- or triethylene glycol substituents in the homooxacalix[3]arene-based phosphonate units 2. [Copyright &y& Elsevier]

Abstract: The regioselective nitration of 25,26,27,28-tetrapropoxythiacalix[4]arene (1,3-alternate) led to the formation of mono- and dinitro derivatives bearing NO2 groups in the meta positions at the same side of the molecule. Their reduction and subsequent condensation with arylisocyanates gave the new types of anion receptors with a so far unknown meta-substitution pattern. In a highly HB-competitive solvent like DMSO, the novel ligands showed good complexation abilities. Moreover, as can be documented by higher complexation constants, achiral receptors 9a, 9b are better preorganized for anion binding than corresponding stereoisomers 10a, 10b. Our results indicate that anion receptors based on meta-substituted thiacalixarenes possess complexation abilities fully comparable with common para-substituted analogues. [Copyright &y& Elsevier]

Abstract: Calix[4]arene 3, which contains two distal triazole groups on the lower rim and two distal o-methoxyphenylazo groups on the upper rim, was synthesized and found to be a specific and ratiometric sensor for Hg2+ in a polar protic solvent. A series of o-methoxyphenylazo derivatives (3, 4, 5, 7, and 9) were synthesized, which proved that the lower-rim triazoles and the hydroxyl azophenol(s) were the major ligands for metal ion binding. Though analogues 4 and 10 showed some sensitivity for Hg2+, compound 3 was the only ratiometric chemosensor for Hg2+ among the series of azocalix[4]arenes synthesized in this work. The formation of 3·Hg2+ complex was supported by UV/vis and NMR titration studies and Mass spectrometry. Based on the symmetrical features of NMR spectra of 3·Hg2+, the complex is believed to be symmetrical with respect to the calix[4]arene cavity. Furthermore, the complex was determined to be 1:1 binding stoichiometry by Job’s plot, and the association constant was determined to be 4.02×103 M−1 using Benesi–Hildebrand plot. [Copyright &y& Elsevier]

Abstract: Six p-(1-adamantyl)calix[4]arenes 7, 8 with four differently attached diphenyl-carbamoylmethylphosphine oxide (CMPO) functions at the narrow rim were synthesized. This series was extended by adamantylcalix[4]arenes with two CMPO and two ester, acid or (diethylphosphono)acetylamino groups. Structures of new compounds were proved by NMR, mass-spectrometry and a single-crystal X-ray analysis for the intermediate di-phthalimide 103 . The extraction studies towards selected lanthanides and thorium showed that the ligands 7 surpassed the corresponding p-H, p-tert-butyl and p-tert-octyl analogues 3–5 in lanthanide extraction while thorium was extracted with the same or lesser extent. For the lanthanide extraction D Ln(74 )>D Ln(73 )≈D Ln(72 ), which follows the order established earlier for ligands 3–5. Among the tetra-CMPO derivatives of type 8, the ligand 83 /4 was the best extractant for which the D Ln and D Th values were comparable with those for 74 . [Copyright &y& Elsevier]

Abstract: To investigate alkali metal complexation with sulfur-linked calixarene analogues and their guest-binding properties for gaseous organic guest molecules, we elucidated a crystal structure of a cesium complex with p-H-thiacalix[4]arene (1·4H) ligands and guest-binding properties of the cesium complex (2) and the previously reported rubidium complex (3). In crystals of the complex 2, a ‘sandwich-like’ binuclear complex was formed by inter-molecular coordination of cesium cations to the thiacalixarene molecules and methanol molecules, mutually interacting by aromatic-H⋯S hydrogen bonding and alkali metal cation–π interactions between the alkali metal cation and thiacalixarene aromatic rings outside of the cavities. On the guest-binding behaviors both complexes 2 and 3 toward organic guest molecules, methanol, ethanol, and 1-propanol as polar molecules, the complex 2 has no methanol adsorption ability, but the complex 3 showed vapor adsorption properties for all guest molecules. In particular, both complexes exhibited a high adsorption capability toward ethanol molecule. As results of gaseous guest adsorption measurements for alcohol molecules, the guest-binding of these complexes are significantly different because the properties depend heavily on structural natures between complexes 2 and 3. [Copyright &y& Elsevier]

Abstract: 2-(ω-Chloroalkyl)tetramethoxycalix[4]arenes are converted to 2-(ω-azidoalkyl)tetramethoxy- and cone-2-(ω-azidoalkyl)tetrapropoxycalix[4]arenes, the former by substitution and the latter by demethylation to 2-(ω-chloroalkyl)tetrahydroxycalix[4]arenes, which are O-propylated before substitution of azide for chloride. The azide-terminated calixarenes undergo Cu(I)-catalyzed 1,3-cycloaddition to terminal alkynes to give 1,4-disubstituted 1,2,3-triazoles, demonstrating the potential to couple calixarenes from a tether at the 2-position (methylene bridge) to substrates that bear a terminal alkyne group. The cone conformation of cone-2-(4-chlorobutyl)tetrapropoxycalix[4]arene has been confirmed by X-ray diffraction. [Copyright &y& Elsevier]

Abstract: This study reports the synthesis of calix[4]arene-based phase-transfer catalysts derived from the reaction of 5,17-di-tert-butyl-25,27,26,28-tetrahydroxycalix[4]arene with N-ethylpiperazine, diallylamine or 4-benzylpiperidine. The catalytic efficiency of the calix[4]arenes alkylamine derivatives was evaluated by carrying out the ester-forming reaction of alkali metal carboxylates (sodium butyrate or sodium caprylate) with p-nitrobenzyl bromide. It has been observed that the ester-forming reaction of alkali metal carboxylates with p-nitrobenzyl bromide, using the N-ethylpiperazine amine derivative of calix[4]arene as a phase-transfer catalyst in dichloromethane at 25 °C, provided the best yields. [Copyright &y& Elsevier]

Abstract: A new series of water-soluble tetravalent glycoclusters incorporating β-lactosyl residues attached to a central calix[4]arene core was synthesised using azide–alkyne Cu(I)-catalysed cycloaddition (‘click chemistry’). Carbohydrate moieties were attached either to the upper or lower rim of rigid cone-shaped or partial cone macrocycles via 14–21 atom spacer arms. The glycoclusters with a C4-symmetrical arrangement of β-lactosyl residues showed trypanocidal activity, with one of them showing comparable activity to established anti-trypanosomal drug benznidazole in in vitro anti-parasite assays. [Copyright &y& Elsevier]

Abstract: A series of calix[4]arenes bearing various substituents including alkyl, p-bromobenzyl, carboxy and allyl at opposite methylene bridges has been synthesized via successive metallation followed by nucleophilic substitution. In a first step, mono-lithiated calix[4]arenes react with terminal bromoalkanes to give 2-alkylated calix[4]arenes or with CO2 the respective calixarene-2-carboxylic acid in good yields. A second lithiation step of the monosubstituted products with subsequent attachment of both polar and non-polar substituents yields several new diametrally bridge-disubstituted calix[4]arenes. 2D-NMR measurements establish the disubstituted calixarenes to predominantly adopt the 1,2-alternate conformation in solution. First examples of X-ray crystal structures of the new type of disubstituted calix[4]arenes are described featuring the calix[4]arene also in the rare 1,2-alternate conformation. [Copyright &y& Elsevier]

Abstract: The electrophilic substitution of 25,27-dipropoxy-26,28-dinosyloxycalix[4]arene leads exclusively to the para-substitution of the alkylated phenol rings, while in the next step, the protecting nosyl group can be easily removed using a basic hydrolysis. The overall process yields dialkoxycalix[4]arenes with the substitution on the alkylated rings—the substitution pattern, which is complementary to the common dialkoxycalix[4]arenes with substituted nonalkylated phenolic units. The usefulness of this protection/deprotection procedure was documented by the synthesis of novel type of calixarene dipropoxy derivatives, and by the preparation of a novel anion receptor based on this substitution pattern. [Copyright &y& Elsevier]

Abstract: The hemisphere-shaped calixarene 1a and its split-hemisphere-shaped isomer 1b were synthesized from [2.1.2.1]metacyclophane (MCP) 3 by pinacol rearrangement and subsequent intramolecular acetalization. Their structures were revealed by X-ray crystallography and 1H NMR spectroscopy. The temperature-dependence of the intramolecular acetalization to provide 1a and 1b was examined. The results indicated that 1a is the dominant product at high temperatures, and the values of ΔH° and ΔS° were estimated to be −18.3±0.37 kJ mol−1, −59.1±1.12 kJ mol−1 K−1, respectively. The dinitro derivative 7 and tetranitro derivatives 8 were obtained by ipso-nitration at the upper rims of 1a. The optical resolution and chiral recognition ability of racemic mixture 7 were investigated by HPLC systems. [Copyright &y& Elsevier]

Abstract: Fluorogenic tert-butylcalix[4]arenes bearing two pyrene pendant groups at the lower rim were synthesized. Based on ratiometric changes of monomer and excimer emissions, the pyrene amine derivative of calix[4]arene has been found to act as a selective sensor for Pb2+ and Cu2+ ions, respectively, due to a conformational change upon chelation of these ions. [Copyright &y& Elsevier]

Abstract: The development of selective electrochemical iron sensor is still a challenging task. One promising possibility is to use organically functionalized inorganic particles, for instance silica, as sensitive element. Herein, we report on the design and synthesis of calix[4]arene-based platforms modified with ICL670 iron chelator and alkylamino chain(s). These new molecular edifices could be easily grafted on silica particles. The strategy relies on selective calix[4]arenes functionalizations by alkylamino chains at the lower rim, in partial-cone or 1,3-alternate conformations. The different synthesis routes are presented and discussed. [Copyright &y& Elsevier]

Abstract: Two series of di-ionizable calix[4]arene-crown-5 isomers in the cone conformation are synthesized to probe the effect of the pendant acidic group location on their metal ion extraction properties. In one series, the ionizable groups are attached to the lower rim of the calix[4]arene scaffold, which orients them near the crown ether cavity. In the second series, the ionizable groups are connected to the upper rim positioning them away from the crown ether ring, but close to the hydrophobic pocket of the calix[4]arene unit. The metal ion extraction behaviors of the two series of ligands are compared in extractions of alkaline earth metal cations, Hg2+, and Pb2+. [ABSTRACT FROM AUTHOR]

Abstract: A series of large-ringed calix[6,7,8]arene analogues have been synthesised and their affect against Mycobacterium tuberculosis in vivo established. In general, when p-phenylcalixarenes and tert-butylcalixarenes were not functionalised at the lower rim, low biological activities were observed. However on going from partially to fully lower rim pegylated calixarenes the anti-mycobacterial properties improved. The addition of cyanopropoxy groups at the lower rim gave rise to low activities, whereas the addition of acetate moieties interestingly had pro-TB effects. Two upper rim sulfonated calixarenes showed promising properties. In the course of this work, a high yielding procedure to synthesise p-phenylcalix[7]arene was also established. [Copyright &y& Elsevier]

Abstract: Although originally designed for anion recognition, bis(N′-p-nitrophenylureido)calix[4]arenes immobilised in the 1,3-alternate conformation can act as receptors for small neutral molecules, such as sulfoxides and ketones. Their binding ability was studied both in solution and in the solid state using the combination of UV/vis, NMR, and X-ray crystallography. [Copyright &y& Elsevier]

Abstract: A seemingly ipso-like nucleophilic substitution of the upper rim of p-tert-butylcalix[4]arene is accomplished by an indirect method involving calix[4]arene derived bis(spirodienone). This method not only provides both mono and 1,3-diaryloxy calixarenes but also enables the synthesis of upper rim monothio substituted calix[4]arenes. A modification of the methodology can be successfully extended for the selective synthesis of mono- and 1,3-diquinone calix[4]arenes having free hydroxyl groups at the lower rim, in fewer steps. [Copyright &y& Elsevier]

Abstract: (1,3)-Calix[5]arene-crown-3 derivatives 1a and 1b, bearing either three n-butylureido or 1-naphthylureido moieties at the lower rim, respectively, have been synthesised. Their cationic and anionic binding domains have been investigated by a combination of 1D- and 2D-NMR, UV/vis absorption and fluorescence and ESIMS techniques. Complexation data show that the attachment of 1-naphthyl groups at the lower rim of calix[5]crown-3 1b dramatically increases its anion-binding ability over the n-butyl-bearing derivative 1a. Overall, both 1a and 1b act as highly efficient heteroditopic receptors for n-butylammonium halides and in so doing bind these salt species—as spatially-separated ions—much more effectively than the single ionic components. The X-ray crystal structure of the pivotal tris-[2-(2-chloroethoxy)ethoxy]-calixcrown precursor 2 is also reported. [Copyright &y& Elsevier]

Abstract: A novel calix[4]arene derivative with two ferrocenyl Schiff-base groups at the upper rim 3 has been synthesized from 5,17-diformyl-25,27-dipropoxy-26,28-dihydroxy calix[4]arene and 4-ferrocenylaniline via condensation reaction. Reduction of 3 with sodium borohydride led to calix[4]arene derivative 4 with two amino ferrocenyl groups at the upper rim. The ferrocenyl Schiff-base calix[4]arene and its corresponding reduced amine have been purified and characterized by elemental analysis,1H NMR, FTIR, Mass and UV–vis spectral data. Electrochemical properties of compounds 3 and 4 have been investigated. Cyclic voltammograms of 3 and 4 show reversible redox couples of ferrocene/ferrocinium at E 1/2=0.401V and 0.346V, respectively. Electrochemical studies show these redox active compounds electrochemically recognize trivalent lanthanides La3+ and Ce3+ and divalent Pb2+ and Cu2+cations. With ferrocenyl Schiff-base calix[4]arene 3 an anodic shift as large as 130mV is observed on addition of one equivalent of Ce3+ ion. Also extraction properties of compound 4 towards some metal cations have been described. It has been observed that compound 4 has a good selectivity for metal cations Fe3+, Cu2+, Pb2+ and Cd2+ against Ni2+ and Co2+. [Copyright &y& Elsevier]

Abstract: A series of calix[4]arene-dithiacrown-5 and -dithiacrown-6 compounds in cone and 1,3-alternate conformations has been synthesized. Responses of these ionophores to Hg2+ and competing metal ions were determined in solvent polymeric membrane electrodes. High potentiometric selectivity for Hg2+ over Na+ and a variety of transition and heavy metal ions was obtained. [Copyright &y& Elsevier]