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Driven by an interest in the impact of the para-substituent of calix[4]arenes on metal complexation and structural chemistry, studies of p-cyclohexylcalix[4]arene (L) have been carried out. The 1:1 dichloromethane and dimethylformamide solvates were found to be isostructural, and different to the typical bilayer structure often observed for p-t-butylcalix[4]arene solvates. The methanol solvate, in contrast, does form a bilayered structure but is also a 1:1 solvate, unlike the p-t-butylcalix[4]arene·2MeOH system. Lanthanoid complexation was investigated, resulting in the structural characterisation of two different DMF solvates of a 2:2 dimeric europium complex, Eu2(L–3H)2(DMF)4. A tetrazole derivative, 5,11,17,23-tetracyclohexyl-25,27-dihydroxy-26,28-bis(tetrazole-5-ylmethoxy)calix[4]arene, has been synthesised via the intermediate 5,11,17,23-tetracyclohexyl-25,27-dihydroxy-26,28-dicyanomethoxycalix[4]arene, with the latter compound being structurally characterised. Attempts to isolate lanthanoid clusters supported by the tetrazole derivative under conditions known to form Ln19 clusters with the p-t-butyl analogue were unsuccessful, resulting only in isolation of the ligand from the reaction mixture. [ABSTRACT FROM AUTHOR]

Human Papillomavirus (HPV) is the leading cause of cervical cancer, with only some HPV types prevented with vaccines and no treatments for the viral infection itself. One way to target viral infection is by inhibiting the assembly of the L1 monomer into a pentamer, which forms the viral capsid. Four calix[4]arene compounds functionalised with D- and L-aspartic and glutamic acid and an iminodiacetic functionalised calix[4]arene were synthesised and tested for L1 pentamer formation inhibition. The amino acid functionalised calix[4]arene derivatives showed millimolar inhibition (IC50 = 0.72 to 2.67 mM) of pentamer formation, with little difference between the stereoisomers. The iminodiacetic acid calix[4]arene derivative showed no inhibitory properties, despite sharing structural similarities with the four other calix[4]arenes. Confirmation of binding the negatively charged compounds to the positive residues of the L1 protein was achieved by trypsin digestion. This study is helpful in the development of cost-effective inhibitors to prevent HPV assembly. [ABSTRACT FROM AUTHOR]

The tetrazole-functionalised calixdiquinone 5,17-di-tert-butyl-26,28-bis-(1H-tetrazole-5-ylmethoxy)-calix[4]-25,27-diquinone Q was synthesised by chemical oxidation of the bis-tetrazole calix[4]arene precursor using PbO2/HClO4. The single crystal X-ray structure determination of Q confirmed the structure and showed binding of a water molecule in the solid state. Chemical reduction of Q to the dihydroquinone QR was achieved using N,N-diethylhydroxylamine. Comparison of the solution phase photophysical properties of Q or QR in the presence of terbium ions showed significant excitation only with QR, suggesting redox switching of the photophysical response may be possible with this or similar receptor. [ABSTRACT FROM AUTHOR]

The preparation of discrete tetranuclear lanthanide/alkali metal (Ae) assemblies bearing a tribenzoylmethane ligand (LH) is discussed. These assemblies have the general formula [Ln(Ae·HOEt)(L)4]2, where Ln3+ = Gd3+, Tb3+, Dy3+, Ho3+and Ae+ = Na+, K+, Rb+. The coordination geometries of the lanthanide species were analyzed and compared, revealing a trend between an eight-coordinate square antiprism and triangular dodecahedron dependent on the nature of lanthanide, alkali metal, and lattice solvent. The potassium-containing analogs were also analyzed for their magnetic susceptibility. [ABSTRACT FROM AUTHOR]

Lanthanoid complexes of a tetra-amide substituted calix[4]arene in the cone conformation are characterised by single crystal X-ray structure determination. The structural analysis shows that the metal ions are coordinated to the calixarene through the eight O donor atoms, along with one aqua ligand which is located within the cavity of the calixarene. The calixarene ligand was covalently incorporated into a polymethylmethacrylate monolith throughp-allyl functional groups, followed by loading with a range of lanthanoid cations giving rise to light-emitting materials. The emission from the hydrid materials was found to be comparable to the solution phase emission. [ABSTRACT FROM AUTHOR]

The synthesis and characterisation ofp-t-butylcalix[4]arene functionalised at the lower rim with four tetrazole moieties is reported. The macrocycle is found to be a poorer ionophore for lanthanoid cations than the bis-tetrazole–substituted analogue. Solution-phase photophysical studies strongly suggested that the cations interacted only weakly with the calixarene ligand. A mixed sodium/triethylammonium salt of the calixarene ligand was crystallised in the presence of lanthanoid cations and structurally characterised. Strong intramolecular interactions are hypothesised to be the cause of the observed behaviour. [ABSTRACT FROM AUTHOR]

Calix[4]arenes functionalised at the upper rim with acidic amino acid residues are found to have a significant impact on the crystal growth of model mineral systems, calcium carbonate and barium sulphate. The aspartic acid derivative is found to be most efficacious, matching or exceeding the impact of commercial phosphonate-based scale inhibitors. In some cases, the modified morphologies are found to be similar to those induced by proteins isolated from biomineralised systems. [ABSTRACT FROM AUTHOR]

The field of low molecular weight supramolecular gels, also known as physical gels, has grown rapidly over the last decade. In these gels, small molecules (gelators) self-assemble through non-covalent interactions, usually into a network of fibres, to trap solvent. Many physical gels are responsive to stimuli and often these types of gels can be reversibly converted from gel to sol. These properties make them ideal candidates for investigation into a range of potential applications, including biomedical, smart materials, sensors and catalysts. This review provides an overview of macrocyclic compounds, particularly the calixarenes, that can form supramolecular gels. [ABSTRACT FROM AUTHOR]

X-ray crystal structures of three dicarboxylato-bis-α-hydroxyoximenickel(II) complexes have been obtained. These contain a short chained (C8) analogue of LIX®63 hydroxyoxime, along with either benzoate, isobutyrate or propionate. All have pseudo-octahedral structures with monodentate carboxylate anions located cis to one another and neutral, chelating α-hydroxyoxime ligands. Intra-molecular hydrogen bonding between each anionic acid's carboxylate group and an adjacent oxime hydroxyl group is evident. Inter-molecular hydrogen bonding is also observed. These provide the first definitive structural elucidation of the types of nickel complexes that could be formed during synergistic extraction by LIX®63 and carboxylic acids. [ABSTRACT FROM AUTHOR]

The tetra-isopropyl ethers of calix[4]arene and p-t-butylcalix[4]arene have been isolated in the cone conformation, and structurally characterised as chloroform solvates. Thermogravimetric analysis demonstrated that the parent isopropylcalix[4]arene solvate is significantly more stable than the p-t-butylcalix[4]arene analogue, retaining the solvent up to a temperature of 125°C. It was found that the calix[4]arene ether sublimes at atmospheric pressure, and solvent-free crystals appropriate for structure determination were produced at reduced pressure. The p-t-butylcalix[4]arene ether was also isolated without solvent in the lattice, but in this case the calixarene was crystallised from acetone, as sublimation did not produce crystals of sufficient quality. [ABSTRACT FROM AUTHOR]

A versatile synthon with formyl and allyl groups at the upper rim of calix[4]arene has been synthesized in two steps. Selective formylation of 25,27-diallyloxy-26,28-dihydroxycalix[4]arene, along with the Claisen rearrangement of the allyl groups, was achieved by reaction with hexamethylenetetraamine (hexamine) in glacial acetic acid. A control reaction of the dipropyl analogue shows that the selective formylation takes place independently of the Claisen rearrangement. The crystal structure of the dimethylacetal derivative of 5,17-diformyl-11,23-diallylcalix[4]arene is reported. [ABSTRACT FROM AUTHOR]

The syntheses and structures of uranyl complexes of p - t -Bu-calix[6]arene (calix[6]H 6 ) and p - t -Bu-calix[9]arene (calix[9]H 9 ) are reported, further developing the role of calixarenes as 'cluster keepers'. The calix[6]arene complex, formulated as [(HO){UO 2 (calix[6]H 4 )(dmso)} 3 H], is trinuclear and linked symmetrically by the hydroxyl O atom. The calix[9]arene complex is binuclear, with a carbonate atom bridging between the two uranyl cations to give the complex, (HNEt 3 ) 3 [(OCO 2 )(UO 2 ) 3 (calix[9]H 4 )]. [ABSTRACT FROM AUTHOR]