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Nucleotides and their derivatives are vital biomarkers that play essential roles in biochemical reactions and influence processes of metabolism and anabolism. However, discriminating between various structurally similar nucleotides and their phosphate derivatives using convenient means still poses a challenge. Here, we designed a supramolecular fluorescence sensor array constructed with four different calixarenes loaded with dyes to discriminate between nucleotides and their phosphate derivatives. Based on the differences in the ability of calixarenes to recognise various nucleotides and nucleotide phosphates, a unique fluorescence response pattern is generated for each analyte. With the assistance of linear discriminant analysis, the discrimination of target analytes is effectively achieved. Subsequent assays involving various concentrations of nucleoside triphosphates and mixtures of nucleotide phosphates have also verified the potential of this sensor array based on calixarenes in the investigation of nucleotides. [ABSTRACT FROM AUTHOR]

Calix[4]arenes are extremely versatile ligands that are capable of supporting the formation of a wide variety of polymetallic clusters of paramagnetic metal ions. One can exert influence over cluster formation through alteration of the calix[4]arene framework and subsequent ‘expansion’ of the lower-rim polyphenolic binding site. The present contribution investigates cluster formation with calix[4]arenes substituted at all four methylene bridge positions with furan moieties. Two known cluster types have been isolated with this ligand, the structures of which lend insight into factors that may ultimately preclude the formation of mixed-metal species.

Understanding the factors that have influence on the compactness of calixarene assemblies is important for choosing or designing molecules for specific function. In this paper, we comparatively investigated the packing performances of a series of amphiphilic calixarene assemblies by fluorescence anisotropy. Calixarene frameworks, the upper-rim decoration of head groups and the length of lower-rim alkyl chains of amphiphilic calixarenes all affect their packing compactness. This work has guiding significance for further application studies. [ABSTRACT FROM AUTHOR]

This study explores the impact of a small structural modification on a biomimetic receptor. The hosting structure is a calix[6]arene capped by a tetraaza core. Two receptors are compared: one (1) presents three anisole units while the other (2) has three phenols. The latter was obtained with an excellent yield by selective demethylation thanks to a supramolecular strategy. Complexation studies showed that [2.H]+ displays strong affinities for Cl−, NO3−, HSO4−, whereas [1.H]+ is non-responsive. The anions are embedded at the level of the small rim, hydrogen-bonded to the protonated cap and the phenol groups. Ternary complexes are obtained in the presence of ammoniums. Finally, [2.H]+ shows high affinity for small zwitterions presenting a carboxylate and an ammonium groups separated by one or two carbon atom(s), not three, due to multi-point recognition. These results open routes to the design of new receptors for a variety of anionic and zwitterionic guests. [ABSTRACT FROM AUTHOR]

Four multi-component complexes based on p-sulfonatocalix[4]arene anion, the methyltriphenylphosphonium cation, lanthanide ions (Gd(III)) and different ionic liquid-based cations (1-methyl-3-butylimidazolium, 1-methyl-3-octylimidazolium and 1,4-bis((3-methylimidazolidinyl)methyl)benzene) were synthesised and structurally characterised. Common bilayer arrangements are formed in the extended structures of all four complexes, though the bilayer thicknesses varies depending on the components involved. Molecular capsule formation is facilitated by the inclusion of methyltriphenylphosphonium, 1-methyl-3-butylimidazolium and 1,4-bis((3-methylimidazolidinyl)methyl)benzene cations, but not in the case of the 1-methyl-3-octylimidazolium cation. Molecular capsule size depends on the nature of the included guest cation, and methyltriphenylphosphonium cations fill compact spaces between calixarenes in these new bilayer arrays. [ABSTRACT FROM AUTHOR]

Two new derivatives of calix[4]arene bearing on the upper rim 2-thiopenyl (Thicalix) or 2-pyridyl (Pycalix) Schiff-base substituents have been synthesised and characterised by IR, NMR, MS, and single crystal X-ray diffraction techniques. It was shown that the interaction of Thicalix with the copper(II) and palladium(II) ions is accompanied by hydrolysis of the azomethine bonds with subsequent oxidation of the aminophenolic fragment to diquinone Diquin, while the reaction of potassium tetrachloropalladate(II) with Pycalix results in the formation of metallocompex with 1:2 calix[4]arene/Pd(II) ratio. The single crystal X-ray diffraction analysis of Thicalix (1), the complex [(PdCl2)2(Pycalix)] (2) and Diquin (3) revealed that all compounds form molecular crystals as a result of numerous supramolecular interactions involving C − H···O, C − H···Cl, and C − H···π contacts. For 1 and 3 such interactions result in formation of dimers, while in 2 the dodecanuclear palladium aggregates composed of six calix[4]arene moieties are formed. [ABSTRACT FROM AUTHOR]

Water soluble calixarenes are versatile mediators of protein assembly, including the fabrication of crystalline frameworks. Here, we report the X-ray crystal structure of cytochrome c (cytc) co-crystallised with two different calixarenes: phosphonato-calix[6]arene (pclx6) and sulfonato-calix[8]arene (sclx8). Each calixarene type acts as an independent molecular glue that mediates cytc dimers within the crystal. The calixarene-mediated dimers combine to yield chains of cytc-sclx8-cytc-pclx6-pclx6 repeating units. These supramolecular copolymer units pack together, via a protein-protein interface, to yield a porous dendrite-like assembly. Interestingly, the tri-component framework has features in common with previously reported structures of cytc in complex with pclx6 or sclx8. Known protein-calixarene 'building blocks' combine in novel ways to yield the tri-component assembly, highlighting the versatility of calixarene molecular glues in protein crystal engineering. [ABSTRACT FROM AUTHOR]

We present the synthesis and structure-activity relationships of sulfonatocalix[4]arene hosts bearing novel substitutions. The calix[4]arenes are modified on the upper rim at either one or two of the phenolic units, where the dual modifications are introduced regioselectively on neighbouring or opposing phenols. The calix[4]arenes are mono- or di-functionalised with nitro or formyl groups, with the remaining upper-rim sites in all cases occupied by sulphonates. Equilibrium association constants were determined between each host and the guests nicotine, nornicotine, and cotinine. Indicator displacement-based binding studies show that nicotine binds most strongly to the different members of the library followed by nornicotine, whereas cotinine displays weak to no binding. NMR titrations were carried out with nicotine and show different host-guest interaction geometries for the formyl-calix[4]arenes versus the nitro-calix[4]arenes. [ABSTRACT FROM AUTHOR]

In this study, we first used water-soluble iron oxide nanoparticles for Candida rugosa lipase immobilisation. Moreover, two new complexation phenomena of the prepared water-soluble Fe3O4 nanoparticles with an enzyme might address interesting results in terms of enzyme activity and stability in typical enzymatic reactions. The catalytic activity on pH and temperature dependence, and reusability of the immobilised lipases (p-SCX4-NP-E and p-SCX8-NP-E) were also investigated with the hydrolysis reaction of p-nitrophenyl palmitate (p-NPP). The results show that the highest catalytic affinities for p-SCX4-NP-E and p-SCX8-NP-E were obtained at pH 5.0 and pH 7.0, respectively. [ABSTRACT FROM AUTHOR]

A new bimodal triazole-bridged pyrene-appended calix[4]arene 2g has been synthesised and characterised and complexation studies showed that the binding of Cd2+ and Zn2+ occurs as demonstrated by enhanced monomer and declining excimer emission fluorescence spectral changes. With several other metal ions, quenching of both monomer and excimer emissions occurred. The observed monomer formation in the fluorescence spectra seen with Zn2+ and Cd2+ is possibly linked not just to the diminished parallel orientations of the pyrene rings but with the magnitude of the resulting HOMO-LUMO gaps and other parameters measured by DFT calculations. [ABSTRACT FROM AUTHOR]

The spontaneous preparation of well-defined functional nanoscale systems is very important, since this formulation process requires additional resources, external supply of energy and time. One of the widely used methods of their spontaneous formation is the self-assembling process using of various calixarene building blocks. The relative simplicity of the synthesis of initial calixarene skeleton, the possibility of modifying both of its rims with a wide range of chemical groups, and the presence of a hydrophobic aromatic cavity allow the use of calixarenes to create both individual and mixed aggregates. This article summarises different types of self-assembled calixarene-based amphiphilic aggregates with useful properties. Potential applications of these aggregates in biological nanotechnology are also described. [ABSTRACT FROM AUTHOR]

Selective molecular recognition is of primary importance for applications such as sensing and separation of chemicals. This work describes the host-guest and crystallisation properties of a penta-carbamated calix[6]arene designed as a molecular container with a H-donating recognition group directed towards the heart of the cavity. As demonstrated by NMR spectroscopy and X-ray diffraction studies, this macrocyclic receptor can selectively recognise small H-bond acceptors through one or two hydrogen bonds, the guests nesting inside the polyaromatic cavity surrounded by eleven bulky tert-butyl groups. [ABSTRACT FROM AUTHOR]

Calixarenes are known to form host–guest complexes and supramolecular nanoassemblies with well-defined architectures. However, the use of these materials in conjunction with drug moieties is still under explored. One reason is the insufficient biocompatibility studies. Our present study represents a systematic in vitro investigation of the cytotoxicity associated with C-methylresorcin[4]arene, C-methylpyrogallol[4]arene, p-phosphonated calix[8]arene and a metal-seamed calixarene–copper(II) complex, using human HEK293 and rat C6G cell lines and two different cell viability assays (MTT and CellTiter-Glo) to avoid species-biased results. All compounds showed low to moderate toxicity. The trend in the CC50 values indicated that the suppression of the coordination ability and the presence of phosphonate groups decrease the overall cytotoxicity of the compounds. The results of this study not only establish calixarenes and their immediate families as potential drug carriers and drug modifiers, but also reveal a pathway for fine-tuning their toxicological behaviour by appropriate chemical modification. [ABSTRACT FROM AUTHOR]

The present work deals with the theoretical study of conformational equilibrium of calix[4]tetrolarenes (1,2,3 trimethoxy substituted calix[4]arene) in gaseous and solvation phases. A total of 64 calculations (four conformations at eight level of theories) were performed using Density Functional Theory (DFT) functionals viz. wB97XD, B97D, B3LYP, CAM-B3LYP with diffused (6-31 + G(d)) and non-diffused basis sets (6-31G(d)). It has been found that the conformational profile of calix[4]tetrolarene changes from cone to 1,3-Alternate upon incorporating - OMe group. The B97D and wB97XD functionals gave the most accurate result having rmsd value ~0.73Å followed by B3LYP and CAM-B3LYP > 0.78Å. Furthermore, NBO calculations demonstrated that reduction in charges at lower rim oxygens reduces the chances of hydrogen bonding. Moreover, global reactivity parameters and molecular dynamics also complement the observed trend. Owing to the methoxy substitutions, anion binding study of these new molecules indicates towards the promising capability to bind Cl− and F− ions. [ABSTRACT FROM AUTHOR]

Preferential crystallization from a mixture of C-methylresorcin[4]arene (RsC1) and calix[6]arene (Calix6) in the presence of different bases has been investigated. In the presence of pyridine, a boat conformer of RsC1 crystallizes, whereas in the presence of triethylamine, Calix6 crystallizes in a symmetrically distorted conformation. The packing arrangements of the macrocycles show discrete solvent pockets for calixarenes and channels for resorcinarenes. [ABSTRACT FROM AUTHOR]

Amphiphilic PEGylated calix[5]arenes 1 and 2 were obtained in one step from the parent p-tert-butylcalix[5]arene and p-methylcalix[5]arene. Very low critical micellar concentrations (0.5 and 4.5 μM for 1 and 2 respectively) were determined by the Rose Bengal micellization method. Aggregation features were studied by means of 1H and DOSY NMR as well as by AFM. Release of Rose Bengal from the micellar environment was accomplished by increasing the temperature. [ABSTRACT FROM AUTHOR]

Calix[4]arene dihydroxyphosphonic acid has been demonstrated to possess an interesting range of biological properties, including atypical anti-cancer activity. The robustness of calix[4]arene dihydroxyphosphonic acid and its ubiquitous dimeric motif offers perspectives for pre-defined solid state complexation with small molecules. In the current article we describe co-crystals (organic salts) of calix[4]arene dihydroxyphosphonic acid with four nucleic base cations: adeninium, cytosinium, guaninium and uracilium. A number of characteristic interactions between the components in the four co-crystals are pointed out also using the Hirshfeld surface analysis. All the four co-crystals are based on layers of calix[4]arene dimers, alternating with layers of nucleic acid molecules. Two of the reported crystal structures (cytosinium and guaninium) are 1D channel-type structures, while the two others (adeninium and uracilium) represent 2D channel-type structures. In three out of four reported structures, interactions between the cations of nucleic bases are present generating 1D chains of cations. A constant motif is that the nucleic base is present in a type of cavity formed by one aromatic ring and a phosphonic acid moiety. [ABSTRACT FROM AUTHOR]

An organic material, p-tert-butyltetrasulfonylcalix[4]arene, self-assembles via hydrogen bonding to form a diamondoid supramolecular network. Possessing discrete, zero-dimensional (0D) microcavities, the thiacalixarene derivative adsorbs CO2 at high pressures. [ABSTRACT FROM AUTHOR]

Calix[4]arenes are extremely versatile ligands that are capable of supporting the formation of a wide variety of polymetallic clusters of paramagnetic metal ions. One can exert influence over cluster formation through alteration of the calix[4]arene framework and subsequent ‘expansion’ of the lower-rim polyphenolic binding site. The present contribution investigates cluster formation with calix[4]arenes substituted at all four methylene bridge positions with furan moieties. Two known cluster types have been isolated with this ligand, the structures of which lend insight into factors that may ultimately preclude the formation of mixed-metal species. [ABSTRACT FROM AUTHOR]

The solid state structure of the co-crystal between proximal p-tert-butylcalix[4]dihydroquinone, ethylacetate and 4,4’-bipyridine shows an interesting interplay of H-bond and van der Waals interactions that allow to rationalise the assembly possibilities of the calixarene compound under study. [ABSTRACT FROM AUTHOR]

The ‘one-pot’ reaction of 2-hydroxy-3,5-di-tert-butylsalicylaldehyde with in situ generated ‘amino calixarene’ (from {Mo[(2-NC6H4)2CH2CH2]Cl2(DME)}, KOtBu and p-tert-butylcalix[4]areneH4LH4) afforded, after work-up, the heterobimetallic salt K(NCMe)2[Mo(NCMe)(OEt)(2-C6H4CH2CH2C6H4NH2-2)L] (1∙2MeCN). By constrast, use of the ‘amino calixarene’ [Mo(NCMe)(2-C6H4CH2CH2C6H4NH2-2)L] afforded the potassium/ethoxide-free complex [Mo(NCMe)(2-C6H4CH2CH2C6H4N-2-CHC6H2-2′-(OH)-3′,5′-tBu)L] (2∙2MeCN). Reaction of the ‘amino calixarene’ (two equivalents) with the dialdehyde [1,3-(CHO)2-5-MeC6H3OH-2] led, following work-up, to the isolation of the cation-anion pair [C46H42N4O2]2+[Mo6O19]2−·C2H3N (3∙MeCN). The molecular structures of 1·2MeCN, 2·2MeCN and 3·MeCN are reported, for which it was necessary to use synchrotron radiation for data collection. Complex 1 contains an eliptical calixarene conformation as a result of π-interactions between the K+ and the arene groups and a distorted O5N octahedral geometry at the molybdenum centre, whereas in ‘K+/ethoxide-free’ 2, the calixarene retains the cone conformation and the metal possesses a distorted octahedral O4N2 coordination environment. In 3, a protonated macrocyclic cation, formed via hydrolysis, has weak intermolecular interactions with the polyoxomolybdate anion. [ABSTRACT FROM AUTHOR]

An organic material, p-tert-butyltetrasulfonylcalix[4]arene, self-assembles via hydrogen bonding to form a diamondoid supramolecular network. Possessing discrete, zero-dimensional (0D) microcavities, the thiacalixarene derivative adsorbs CO2 at high pressures. [ABSTRACT FROM AUTHOR]

Calix[4]arenes are extremely versatile ligands that are capable of supporting the formation of a wide variety of polymetallic clusters of paramagnetic metal ions. One can exert influence over cluster formation through alteration of the calix[4]arene framework and subsequent ‘expansion’ of the lower-rim polyphenolic binding site. The present contribution investigates cluster formation with calix[4]arenes substituted at all four methylene bridge positions with furan moieties. Two known cluster types have been isolated with this ligand, the structures of which lend insight into factors that may ultimately preclude the formation of mixed-metal species. [ABSTRACT FROM AUTHOR]

The ‘one-pot’ reaction of 2-hydroxy-3,5-di-tert-butylsalicylaldehyde with in situ generated ‘amino calixarene’ (from {Mo[(2-NC6H4)2CH2CH2]Cl2(DME)}, KOtBu and p-tert-butylcalix[4]areneH4LH4) afforded, after work-up, the heterobimetallic salt K(NCMe)2[Mo(NCMe)(OEt)(2-C6H4CH2CH2C6H4NH2-2)L] (1∙2MeCN). By constrast, use of the ‘amino calixarene’ [Mo(NCMe)(2-C6H4CH2CH2C6H4NH2-2)L] afforded the potassium/ethoxide-free complex [Mo(NCMe)(2-C6H4CH2CH2C6H4N-2-CHC6H2-2′-(OH)-3′,5′-tBu)L] (2∙2MeCN). Reaction of the ‘amino calixarene’ (two equivalents) with the dialdehyde [1,3-(CHO)2-5-MeC6H3OH-2] led, following work-up, to the isolation of the cation-anion pair [C46H42N4O2]2+[Mo6O19]2−·C2H3N (3∙MeCN). The molecular structures of 1·2MeCN, 2·2MeCN and 3·MeCN are reported, for which it was necessary to use synchrotron radiation for data collection. Complex 1 contains an eliptical calixarene conformation as a result of π-interactions between the K+ and the arene groups and a distorted O5N octahedral geometry at the molybdenum centre, whereas in ‘K+/ethoxide-free’ 2, the calixarene retains the cone conformation and the metal possesses a distorted octahedral O4N2 coordination environment. In 3, a protonated macrocyclic cation, formed via hydrolysis, has weak intermolecular interactions with the polyoxomolybdate anion. [ABSTRACT FROM AUTHOR]

The solid state structure of the co-crystal between proximal p-tert-butylcalix[4]dihydroquinone, ethylacetate and 4,4’-bipyridine shows an interesting interplay of H-bond and van der Waals interactions that allow to rationalise the assembly possibilities of the calixarene compound under study. [ABSTRACT FROM AUTHOR]

A novel calixarene-based diimine, 1,3-bis(pyren-1-yliminomethyl)calix[4]arene (5), serves as a turn-on-type fluorescent sensor, which selectively detects Hg2+in THF/H2O (99:1, v/v) in the presence of various other metal ions. Such selectivity is not seen with half salen1derived from salicylaldehyde and 1-aminopyrene.1H NMR analysis reveals that it is a chemodosimetric sensor based on its hydrolysis mediated by Hg2+to release 1-aminopyrene molecules as fluorescent chromophores. [ABSTRACT FROM PUBLISHER]

In this study, a tetramine-substituted calix[4]arene derivative, which was synthesised from calix[4]arene by treatment with dimethylamine in one step via Mannich reaction, was used to fabricate a new calix[4]arene-embedded polysulphone membrane (calix@membrane). Its structure and surface morphology were determined using thermogravimetric analysis and scanning electron microscopy, and elemental analysis techniques. Moreover, a Donnan dialysis system was employed to investigate Cr(VI) transport efficacy of calix@membrane at different pH values. Results showed that calix@membrane represented a promising transport capability for HCr2O7−due to their efficient complexation behaviour. [ABSTRACT FROM PUBLISHER]

A novel bis-naphthalimidocalix[4]arene-Cu(II) supramolecular complex has been observed to provide an efficient recognition system for CN−ions in aqueous medium. The binding stoichiometry of bis-naphthalimidocalix[4]arene and copper ion has been found to be 1:1 while that for bis-naphthalimidocalix[4]arene-Cu(II) and cyanide ion it has been determined to be 1:2. [ABSTRACT FROM AUTHOR]

Calix[4]arene-based cation receptor 1 has been synthesised by following a multi-step synthetic procedure. The fluorescence properties of 1 upon the addition of various metal ions were investigated by fluorescence spectroscopy. As a result, it was revealed that 1 displayed dramatic quenching effect upon the exposure to Cs+. In contrast, no significant quenching effects were observed upon the addition of other metal ions such as Li+, Na+, K+, Mg2+, Ca2+, Sr2+, Ag+, Zn2+and Ni2+. Compound 1 was also found by Job plot to form a 1:1 complex with Cs+. In addition, we also prepared 1-embedded electrospun nanofibrous film (NF-1) as an adsorbent for Cs+. NF-1 is proved to adsorb Cs+effectively from an aqueous solution, indicating that it would be usefully utilised as an adsorbent to remove Cs+. [ABSTRACT FROM PUBLISHER]

Tris-(N-phenylureido)-calix[6]arenes are heteroditopic non-symmetric molecular wheels that, in apolar media, bind viologen-based molecular axles in a pseudorotaxane-type fashion. Because of the precise kinetic requirements associated with the threading process, in apolar solvents, the dicationic portion of the axle enters the calixarene annulus exclusively from the upper rim. With the general aim to develop new prototypes of molecular devices and machines whose functions could be governed through a wider set of control elements, we envisaged that the unique properties of these calixarene wheels could be transferred to the synthesis of new catenanes for the construction of unidirectional rotary motors. Herein, we describe the synthesis of a tris(N-phenylureido)calix[6]arene-based catenane by applying the intramolecular ring-closing metathesis reaction for the catenation step on a pre-formed pseudorotaxane. [ABSTRACT FROM AUTHOR]

The octaanionic 5,11,17,23-tetrasulfonato-25,26,27,28-tetrakis(hydroxycarbonylmethoxy)-calix[4]arene (cone conformation) (C4TsTc) was investigated as a sensor for the biogenic tetracationic polyamine, spermine.(H4Spe4+). Fluorescence titration experiments of the water-soluble calixarene with spermine showed the formation of the 2:1 and 1:1 calixarene:spermine complexes in solution. The single crystal X-ray diffraction analysis of [(NaC4TsTc)4·(H4Spe)7] confirmed the formation of 2:1 and 1:1 calixarene:spermine species and showed that the water-soluble calixarene binds the spermine either by partially hosting it in the inner cavity or through the carboxylate groups on the lower rim. In order to investigate the effect of multivalent systems, supramolecular assemblies of octaanionic calixarene molecules templated bymeso-tetrakis(4-N-methylpyridyl)porphyrin (H2T4) in different stoichiometric porphyrin:calixarene ratios (1:4 and 3:4) were also tested for spermine binding in solution. Fluorescence titration experiments with the 1:4 and 3:4 H2T4:C4TsTc supramolecular complexes showed that the multivalent assemblies are more sensitive to the presence of spermine than the calixarene alone. [ABSTRACT FROM AUTHOR]

Selective binding of fluoride anion and its alkali metal cation ion pairs by a fluorescent calix[4]arene (L) derivative bearing tryptophan moieties was studied in acetonitrile at 25 °C. It was found thatLF−andLF22&#x2212.complexes were formed and their stability constants were determined by means of UV and1H NMR titrations. Both amide and indole NH groups were involved in the stabilisation of the fluoride complexes, i.e.Lafforded two anion-binding sites.1H NMR titrations provided evidence of simultaneous complexation of both Na+cation and fluoride anion resulting in the formation of a ternary NaLF complex. In this ion pair complex, the Na+cation was most probably bound primarily by the calixarene ether and amide oxygen atoms, whereas the indole NH groups interacted with the fluoride ion. A highly favourable ion pairing between Na+and F–in acetonitrile was studied using potentiometric measurements. The results pointed out the importance of fluoride pairing with alkali metal cations in aprotic organic solvents and the necessity of taking these reactions into account in the course of speciation studies of such solutions. [ABSTRACT FROM AUTHOR]

Nε-methylation of lysine within proteins is a critical biological process that, among other roles, is involved in the control of gene expression. Compounds that recogniseNε-methylated lysine may therefore be useful probes for the study of the associated biological mechanisms and have therapeutic potential. Here, we show that tetracyanoresorcin[4]arene (1) selectively recognisesNε-trimethyllysine and binds toNε-trimethyllysine within the context of a short peptide. Its binding properties compare favourably to a previously characterisedNε-trimethyllysine binder,p-sulfonatocalix[4]arene (2). We also show that both1and2inhibit the demethylation ofNε-trimethyllysine within a histone-derived peptide by the histone demethylase KDM4A. [ABSTRACT FROM AUTHOR]

Calix[4]arenes are versatile ligands capable of forming a wide range of cluster motifs when reacted with 3d, 4for 3d/4fmetal ions. Synthetic modification at the calix[4]arene methylene bridge offers a unique opportunity to explore cluster formation with these alternative building blocks. Here, we present the synthesis of a range of bis-calix[4]arenes that are tethered by alkyl chains, as well as exploratory structural studies into cluster-forming reactions. Single crystals were formed in four cases, and from the X-ray structures elucidated it is possible to conclude that sufficiently long alkyl tethers allow for the formation of established cluster topologies without disruption to the core coordination chemistry. Synthetic modification at the calix[4]arene methylene bridge offers a unique opportunity to synthesise alternative supramolecular building blocks. This paper describes the synthesis of a range of alkyl-tethered bis-calix[4]arenes, as well as exploratory structural studies into polymetallic cluster formation. [ABSTRACT FROM AUTHOR]

Recognition ability of both cationic pillar[5]arene and calix[4]arene has been studied in aqueous media. Anion complexation can be evaluated from their ability to complex their counterions as well as an added external organic anion. DOSY NMR experiments and fluorescence quenching show that pillararenes have a larger ability for including their own counterions than calixarenes irrespective of the anion (tetrafluoroborate or chloride or bromide) and the structure of the cationic moiety (trimethylammonium or methylimidazolium). Counterion complexation shows a picture where four to five positive charges of the pillar[5]arene are neutralised, meanwhile only one positive charge of the calixarene is neutralised for a 1 mM solution of the macrocycle. Irrespective of the smaller net positive charge in the pillar[5]arene, its binding ability for organic anions (toluenesulfonate or hydroxybenzoate) is larger than for calix[4]arene allowing a better accommodation of the guest in its cavity. The larger separation between the cationic groups of the receptor and its electron-rich aromatic region improves the anion recognition ability for pillar[5]arene. [ABSTRACT FROM AUTHOR]

Polyoxomolybdate-based organic−inorganic hybrid architectures were synthesised and characterised by X-ray crystallography. The supramolecular assemblies present rows of metallic clusters H-bonded by ammonium cations, with a 1:2 molybdate/ammonium ratio. The organic moieties of the ammonium cations establish hydrophobic contact among them such as van der Waals, C–H⋯πandπ⋯πinteractions that stabilise the supramolecular architectures. In particular, for compound5then-alkyl tails pack closely together giving a lipid-like bilayer. In compound6, the aromatic phenyl rings of the organic cation allow the stabilisation of the supramolecular architecture by C–H⋯πandπ⋯πinteractions. Regarding the X-ray structure of the compound11,the tetraanionic octa-molybdate [Mo8O26]4−cluster is surrounded by four ethyl-triphenyl-phosphonium cations. Running along theb-axis open channels are occupied by DMF solvent molecules. Interestingly, a soaking experiment inn-pentane with the corresponding crystals of compound11afforded to a crystal structure very different from the native one. Van der Waals, C–H⋯πandπ⋯πinteractions between large organic moieties are fundamental in the stabilization of hybrid organic-inorganic POM architectures. [ABSTRACT FROM AUTHOR]

Amphiphilic calixarenes are interesting building blocks with high propensity to assemble in well-defined supramolecular architectures. In this work, we report that a succinyl-calix[4]arene derivative (2), exposing four terminal carboxylic acid groups at the calixarene upper rim and four dodecyl chains at the lower rim, forms discrete and stable nanoaggregates in aqueous medium. Field-emission scanning electron microscopy and transmission electron microscopy images showed that the aggregates of2possess a spherical shape and a vesicular structure with a multilamellar wall. The vesicular nature was confirmed by encapsulation of a hydrophilic dye rhodamine B. A preliminary study also evidenced that compound2increases water solubility of a hydrophobic drug such as curcumin. [ABSTRACT FROM AUTHOR]

The synthesis of two amido-thiourea based receptors/sensors1and2, formed by functionalisation of the lower rim of a calix[4]arene, and the photophysical analysis of these with Zn(II) and various anions is described. The two structures, differing by the substituent on the thiourea moiety, were found to bind Zn(II) effectively in ethanol (EtOH); the recognition giving rise to significant changes in the UV-vis absorption spectra, which was red-shifted for both chemosensors. The changes in the absorption spectra were further analysed using nonlinear regression analysis programme (using the global analysis software ReactLab™ Equilibria), which revealed high binding constants for both systems. The resulting dimetallic complexes(1,2)–Zn2were (pre-formed and) then used to coordinate anionic species such as AcO− , H2PO4− and Br− through electrostatic interactions, showing high affinity towards these anions. In all cases, nonlinear regression analysis showed both 1:1 or 1:2 sensor:anion depending on the anion used. Although the2-Zn2complex showed high affinity for acetate, phosphate and bromide, the1-Zn2complex showed selectivity towards the recognition of phosphate in EtOH. [ABSTRACT FROM AUTHOR]

Calix[6]arene hexacarboxylic acid binds instantly and with low symmetry to Pb, Sr and Ba. Later a highly symmetric up-down alternating conformation emerges. The solution structures are identical to their p-tert-butylcalix[6]arene hexacarboxylic acid counterparts. With either receptor, an octahedral cage is formed around the metal. The transformation from low to high symmetry however proceeds at significantly faster rates for the de-t-butylated host. [ABSTRACT FROM AUTHOR]

The sorption behaviour of three kinds of macrocyclic sorbents – amidoamine tetradodecyloxyphenylencalix[4]resorcinarene1and tetramethyloxyphenylencalix[4]-resorcinarene2; composition of calix[4]resorcinarene1+2, and novelP.1andP.2polymers with amidoamine calix[4]resorcinarene units towards three water-soluble azo dyes – methyl orange (MO), acid orange (AO5) and Congo red (CR) was studied. All sorbents form supramolecular complexes with the aforesaid dyes. The best sorbent forMOwas shown to be polymerP.1, for theAO5– composition1+2and for theCR– macrocycle 2, with high sorption capacities (373, 497 and 625 mg/g, respectively). The main factor in the binding of dyes by all studied sorbents proved to be surface electrostatic interactions. In addition to the Coulomb interactions, the most important factor for the polymers appeared to be the ‘net’ structure of the polymer with a high concentration of binding sites, providing electrostatic, hydrogen, dipole–dipole and hydrophobic interaction. Hydrophobic substituents in the sorbents exert a significant influence on the dye sorption. The increase of the sorbents' hydrophobicity leads to a lower sorption capacity forMOandCRand a higher sorption capacity forAO5. It was shown that sorption efficiency of the sorbent depends on the ‘dye–sorbent’ structure conformity. [ABSTRACT FROM AUTHOR]

The current study comprises synthesis of pyrimidylthioamide derivatized calix[4]arene (5), and its comparative liquid–liquid extraction properties with the compound4towards the selected transition metal ions (Cu2+, Co2+, Ni2+, Pb2+, Hg2+and Cd2+) were investigated. Experimental results revealed that the compound5shows better efficiency and affinity for Pb2+and Hg2+ions as compared to compound4. The antibacterial and antifungal effects of compound5were also investigated on various bacteria and fungi. It has been observed that compound5has some effects againstSalmonella typhimuriumNRRLB 4420,Bacillus cereusATCC 11778,Staphylococcus aureusNRRL B767 andBacillus subtilisNRS 744. [ABSTRACT FROM PUBLISHER]

In recent years, calixarene-based fluorescent chemosensors for mercury(II) are mushroom growth because of its intrinsic sensitivity. The design of the highly selective calixarene-based chemosensors towards mercury(II) is still a challenging task. In this paper, the progress of highly selective fluorescent sensor for mercury(II) based on calixarene derivatives is reviewed according to a mono-fluorophore chemosensor and a bi-fluorophore chemosensor. Some new developments such as calixarene-modified nanoparticles are also covered. [ABSTRACT FROM PUBLISHER]

A series ofp-tert-butylcalix[4]arene 1,3-diimidazolium salts were successfully prepared by the alkylation ofp-tert-butylcalix[4]arene with dibromoalkanes, and sequential substitution reaction with 1-alkylimidazole. Furthermore, coordination reactions ofp-tert-butylcalix[4]arene 1,3-diimidazolium salts with silver oxide and mercury acetate gave novel Ag and Hg complexes of bis(N-heterocyclic carbenes) onp-tert-butylcalix[4]arene platform. The single-crystal structures of fourp-tert-butylcalix[4]arene 1,3-diimidazolium salts and three metal complexes were successfully determined by X-ray diffraction. An Ag–Ag argentophilic interaction (Ag–Ag bond length is 3.1599(6) Å) is formed between the two Ag–NHC complexes and a dimetallic coordination mode exists in Hg–NHC complexes. [ABSTRACT FROM PUBLISHER]

The binding abilities and thermodynamic origin for the intermolecular complexation of two water-soluble calixarenes,p-sulfonatocalix[4]arene (SC4A) and 5,11,17,23-tetrasulfonato-25,26,27,28-tetrakis(n-butyl)-calix[4]arene (SC4A-Bu), with six organic cations: 1,4-diazabicyclo[2,2,2]octane (G1), 3,5,6,8,-tetrahydropyrazino[1,2,3,4-Imn][1,10]phenanthroline (G2), diquat (G3), paraquat (G4), 1-methylpyridin-1-ium (G5) and 1,3-dimethylimidazolium (G6), have been determined by means of isothermal titration calorimetry in aqueous solutions at pH 7.0, 298.15 K, and their binding modes have been investigated by NMR spectroscopy. The obtained results indicate that the binding modes of SC4A-Bu and SC4A change a little but their binding affinities show great difference, resulting from the distinguishable binding thermodynamics. The binding selectivity of G1 is up to 688 times for the SC4A/SC4A-Bu hosts, and SC4A-Bu prefers to include planer molecules of large π system with low electron density. The aggregation behaviours of SC4A-Bu before and after complexation with G3 were then investigated, showing that G3 is able to induce the aggregation of SC4A-Bu. [ABSTRACT FROM PUBLISHER]

In this study, two new Cu(II) complexes ofp-tert-butylcalix[4]arene amide derivatives (8,9) have been synthesised and investigated their DNA cleavage and antimicrobial activities. On the basis of spectral studies, a smaller distortion of square planar geometry has been proposed for both of the copper(II) complexes. The DNA cleavage studies show that the ligands are not efficacious, whereas the complexes have high activity. Futhermore, in order to determine the site of DNA cleavage, the DNA interactions of these compounds were investigated with some restriction enzymes. In addition, all synthesised compounds were screened for antimicrobial activities against some bacteria and for antifungal activities against yeast strains. The results showed that ethyl ester and furfuryl amide derivatives of the calixarenes are more efficient than other compounds against tested bacteria. However, complexes have not been effective. In case of DNA interaction studies, compounds were very effective against plasmid DNA. [ABSTRACT FROM AUTHOR]

The metal cation binding ability ofcone-p-tert-butylhexahomotrioxacalix[3]arene tris(acetic acid) was investigated by1H NMR and complementary semi-empirical calculations. NMR showed significant shifts with Na+, K+, Ag+and, to a lesser extent, Pb2+. The macrocyclic protons undergoing the greatest shifts imply that these cations bind inside the cavity composed of the phenoxy and carbonyl oxygen atoms. Metal complexes were modelled using a semi-empirical approach and, in general, their geometry optimised structures were in agreement with NMR data. U-tube transport experiments demonstrated that the macrocycle actively transported Cr3+, Fe3+, Co2+and Cu2+through the organic phase. [ABSTRACT FROM AUTHOR]

Alkali metal cation extraction behaviour for two series of 1,3-alternate, mono-ionisable calix[4]arene-benzocrown-6 compounds is examined. In Series 1, the proton-ionisable group (PIG) is a substituent on the benzo group of the polyether ring that directs it away from the crown ether cavity. In Series 2, the PIG is attached to oneparaposition in the calixarene framework, thereby positioning it over the crown ether ring. Competitive solvent extraction of alkali metal cations from aqueous solutions into chloroform shows high Cs+efficiency and selectivity. Single-species extraction pH profiles of Cs+for Series 1 and 2 ligands with the same PIG are very similar. Thus, association of Cs+with the calixcrown ring is more important than the position of the PIG relative to the crown ether cavity. Solid-state structures of two unionised ligands from Series 2 are presented. Also described is a crystal containing two different ionised ligand–Cs+complexes. [ABSTRACT FROM AUTHOR]

So, David Gutsche's legacy is a wealth of chemistry and a class of building blocks for supramolecular chemistry that resulted from the meticulous synthetic procedures developed in his labs. Although he was not the first chemist to explore these cyclic reaction products of phenols and aldehydes, it is due to his work that a vast and diverse chemistry could develop. David Gutsche was the godfather of calixarene chemistry, one of the major building blocks in supramolecular chemistry. [Extracted from the article]

A series of thiacalix[4]arenes bearing one, two or four chelating dibutylphopshinoylmethoxy groups have been synthesised and studied in the context of this paper. The synthesis consisted of precise Williamson alkylation of thiacalixarene tetrols with tosylate of dibutylhydroxymethyl phosphine oxide in the presence of alkali metal carbonates or sodium hydride. Stereochemical yield of the reaction (coneor 1,3-alternateconformer) depends on the nature of alkali metal. Small-sized ‘hard’ sodium cation organises the macrocyclic platform in theconeconformation, but larger and ‘soft’ potassium and cesium cations stabilise the macrocycle in the1,3-alternateconformation. All synthesised compounds (except monophosphine monoxide) possess either moderate or high extraction ability towards pertechnetate ion. Thecone-shaped thiacalix[4]arene tetraphosphine tetraoxide due to cooperative (macrocyclic) effect of eight oxygen atoms of the phosphinoylmetoxy-binding groups effectively extract spherical americium, europium cations due to cooperative (macrocyclic) effect of eight oxygen atoms of the phosphinoylmetoxy-binding groups. The extraction ability is very similar to that of calix[5]arene pentaphosphine pentaoxide existing in theconeconformation. [ABSTRACT FROM AUTHOR]

The synthetic approaches to mono-isopropoxytrihydroxycalix[4]arenes bearing two or three diphenylphosphino groups at the upper macrocycle rim were elaborated. Due to reactive hydroxyl groups at the lower rim capable of binding with silica gel surface, the calixarenes, especially the enantiomerically pure inherently chiral diphosphinocalixarene, are promissing ligands for creation of hybride organic–inorganic metallocomplexing catalysts of organic (asymmetric) reactions. [ABSTRACT FROM AUTHOR]