Funnel complexes with CoII and NiII: New probes into the biomimetic coordination ability of the calix[6]arene-based tris(imidazole) system

cited By 30International audienceThe coordination properties of the calix[6]arene-based tris-(imidazole) ligand X6Me3Imme3 were further explored with CoII and NiII. This imidazole system stabilizes tetrahedral mononuclear CoII complexes with an exchangeable fourth exogenous ligand (water, alcohol, amide) located at the heart of the hydrophobic calixarene cavity. With a weak donor ligand such as a nitrile, both four-coordinate tetrahedral and five-coordinate trigonal bipyramidal complexes were obtained. The latter contains a second nitrile molecule trans to the included guest nitrile. These complexes were characterized in solution as well as in the solid state. The NiII complexes are square-based pyramidal five-coordinate edifices with a guest nitrile inside the cavity and a water molecule outside. A comparison with previously described ZnII and CuII complexes emphasizes the flexibility of this ligand. A comparison with carbonic anhydrase, a mononuclear zinc enzyme with a tris(histidine) coordination core, shows that X6Me 3Imme3 displays many structural features of this enzyme except for the cis coordination of the exogenous ligands. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004

Supramolecular control of an organic radical coupled to a metal ion embedded at the entrance of a hydrophobic cavity

cited By 5International audienceA novel N3ArO-calix[6]arene-based system is presented. It allows the formation of an aryloxy radical bound to a metal ion (CuII or ZnII) that presents a free coordination site in a concave cavity. Its oxidative activity appears highly controlled by the supramolecular system hence providing a good model for radical enzymes such as Galactose oxidase. © 2003 The Royal Society of Chemistry

Supramolecular assembly with calix[6]arene and copper ions - Formation of a novel tetranuclear core exhibiting unusual redox properties and catecholase activity

International audienceThe supramolecular biomimetic chemistry based on calix[6]arene N-ligands has been further explored. A tris(imidazole)CuI complex was treated with 1 mol-equiv. of cuprous ion under dioxygen to produce a tetranuclear cupric species, X-ray structural determination of this novel Cu4 complex revealed that the self-inclusion of an imidazolyl coordinating arm into the hydrophobic calixarene cavity provides the base of coordination for a _ClImCu(OH)2CuIm2₂ assembly. The Cu4 core is maintained in solution and is stable even in a coordinating solvent such as acetonitrile. Magnetic susceptibility measurements evidenced a strong antiferromagnetic coupling in each Cu(OH)2Cu subunit with J = -408 cm-1. The complex displayed catecholase activity in the presence of 3,5-di-tert-butylcatechol behaving as a four-electron hole with, however, a sluggish Cu4 I → Cu4 II regeneration through O2 autooxidation. Finally, electrochemical studies revealed two oxidative reversible processes that successively gave rise to a _CuIICuIII__Cu2 II_ and a _CuIICuIII₂ mixed-valence species that could be characterized by UV/Vis and EPR spectroscopy, The overall structure and behavior of this tetranuclear complex is reminiscent of multicopper enzymes. © Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002

Electrochemical behavior of the tris(pyridine) - Cu funnel complexes: An overall induced-fit process involving an entatic state through a supramolecular stress

International audienceThe electrochemical behavior of the tris(pyridine) calix[6]arene Cu adducts is unique as compared to that of most classical Cu complexes in a strain-free environment. The presence of MeCN buried inside the cavity is a prerequisite for a quasi-reversible behavior in a dynamic mode. The CV behavior assisted by simulation outlines that the coordination adaptability of the Cu(II)/Cu(I) redox states is completely reversed, with a Td geometry enforced at either redox states. Hence, the supramolecular control of the Cu coordination by a protein-like pocket determines the dynamics of the electron transfer process, its thermodynamics, and the kinetics of the reorganizational barrier and generates a preorganized state for oxidation. This redox behavior corresponds to an overall induced-fit process generating a truly entatic highly oxidizing Cu(II) state through a protein-like strain by involvement of the secondary coordination sphere

Architecture-controlled ``SMART'' calix[6]arene self-assemblies in aqueous solution

International audienceSelf-assemblies of a calix[6]arene (1) functionalized at the small rim by three imidazolyl arms and at the large rim by three hydrophilic sulfonato groups have been studied in water. Transmission electron microscopy, atomic force microscopy, and in situ dynamic light scattering showed that 1 forms multilamellar vesicles at a concentration equal to or higher than 10(-4) M. At pH 7.8 and 10(-4) M, the multilamellar vesicles present a relatively large polydispersity (50-250 nm in diameter). However, after sonication unilamellar vesicles of much lower polydispersity and smaller size are obtained. The impact of the pH and the presence of Ag+ ions have also been investigated. Whereas increasing the pH led to the formation of giant vesicles (450 nm), monodisperse vesicules of 50 nm were obtained at a pH (6.5) that is only slightly higher than the pK(a) of the tris(imidazole) core of 1. Most interestingly, in the presence of silver ions, micelles (2.5 nm large) were obtained instead of vesicles. These observations are attributable to the imidazole core in 1 that is not only sensitive to the presence of protons but also can bind a silver cation. The resulting geometrical change in the monomeric units triggers the collapse of the vesicles into micelles. This shows that the implementation of an acid-base functionality such as an imidazole group in the hydrophobic core of the amphiphilic calix[6]arene makes the aggregation architecture responsive to the pH and to metal ions