Insights into water coordination associated with the Cu(II)/Cu(I) electron transfer at a biomimetic Cu centre.

International audienceThe coordination properties of the biomimetic complex [Cu(TMPA)(H2O)](CF3SO3)2 (TMPA = tris(2-pyridylmethyl)amine) have been investigated by electrochemistry combined with UV-Vis and EPR spectroscopy in different non-coordinating media including imidazolium-based room-temperature ionic liquids, for different water contents. The solid-state X-ray diffraction analysis of the complex shows that the cupric centre lies in a N4O coordination environment with a nearly perfect trigonal bipyramidal geometry (TBP), the water ligand being axially coordinated to Cu(II). In solution, the coordination geometry of the complex remains TBP in all media. Neither the triflate ion nor the anions of the ionic liquids were found to coordinate the copper centre. Cyclic voltammetry in all media shows that the decoordination of the water molecule occurs upon monoelectronic reduction of the Cu(II) complex. Back-coordination of the water ligand at the cuprous state can be detected by increasing the water content and/or decreasing the timescale of the experiment. Numerical simulations of the voltammograms allow the determination of kinetics and thermodynamics for the water association-dissociation mechanism. The resulting data suggest that (i) the binding/unbinding of water at the Cu(I) redox state is relatively slow and equilibrated in all media, and (ii) the binding of water at Cu(I) is somewhat faster in the ionic liquids than in the non-coordinating solvents, while the decoordination process is weakly sensitive to the nature of the solvents. These results suggest that ionic liquids favour water exchange without interfering with the coordination sphere of the metal centre. This makes them promising media for studying host-guest reactions with biomimetic complexes

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

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

Monocopper center embedded in a biomimetic cavity: From supramolecular control of copper coordination to redox regulation

International audienceThe electrochemical behavior of diversely substituted Cu-N-3-calix[6]arene, enzyme-like, "funnel" complexes is analyzed. The Cu(II)/Cu(I) redox process is regulated by the supramolecular organization of the Cu coordination. The presence of a "shoetree" alkyl nitrile guest molecule inside the host cavity is a prerequisite for a dynamic redox behavior. Combination of supramolecular CH-pi weak interactions with the calixarene cavity and electronic/steric effects from the N-3 substituting groups (pyridine, imidazole, pyrrolidine) enforces the preferential geometrical pattern adopted by Cu. This dictates the pathway of the electron-transfer process and, thus, the thermodynamics and kinetics of the redox reaction in the framework of a square-scheme mechanism. The present observations recall strongly the redox control exerted by the protein matrix on copper proteins through biological concepts such as induced fit mechanism, protein foldings, and entatic and allosteric effects

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

O-O bond cleavage by electrochemical reduction of a side-on peroxo dicopper model of hemocyanin.

International audienceThe redox properties of the μ-η2:η2 peroxo complex [Cu2(H6M4h)(O2)]2+ were elucidated. This study constitutes the first full electrochemical and spectroelectrochemical characterization of a side-on peroxo Cu2:O2 bioinorganic model complex. The peroxo complex is irreversibly reduced in a two- electron process localized on the peroxo ligand triggering the cleavage of the O-O bondLes propriétés redox du complexe peroxo μ-η2:η2 [Cu2(H6M4h)(O2)]2+, modèle de l’hémocyanine, ont été élucidées par des études électrochimiques et spectroélectrochimiques. La réduction du complexe peroxo est irréversible et s’effectue selon un processus à deux électrons localisé sur le ligand peroxyde, déclenchant la rupture de la liaison O-O

Aza and cyanobridged tripodal dinuclear copper(II) complexes: Electrochemical studies and structural evidence for an original azacyanocarbanion

International audienceThe reactivity of the mononuclear [Cu(TMPA)(L)] n+ complex (TMPA: tris(2-methylpyridine) amine, L: CH3CN, H2O) towards two different bridging species (tetracyanoethylene, 4,40-bipyridine) was investigated. The dinuclear complex [(mu-4,40-bipy)Cu-II(TMPA)(2)](CF3SO3)(4) (1) was synthesised and analysed by Xray diffraction (XRD). Magnetic studies revealed that this derivative displays very weak antiferromagnetic interactions between the two metal centres (2J = -0.69 cm(-1)). Solution studies (EPR spectroscopy and voltammetry) evidenced the lability of the bridged neutral bipyridine ligand in acetonitrile. The reaction of TCNE (TCNE: tetracyanoethylene) with the copper(I) complex [CuI(TMPA)(CH3CN)](PF6) afforded the salts [(mu-CN)Cu-II(TMPA)(2)](PF6)(C14N8) (2) and [(mu-CN)Cu(TMPA)(2)](PF6)(3) (3). Both compounds were characterised at solid state (XRD) and in solution. Compound (2) shows the presence of the organocyanide entity C14N82 corresponding to the new N-(tetracyanocyclopentadienyl)-3-aza-1,1,2-tricyanoprop- 1-enide ion. (C) 2013 Elsevier B. V. All rights reserved

Dioxygen activation at a mononuclear Cu(I) center embedded in the calix[6]arene-tren core.

The reaction of a cuprous center coordinated to a calix[6]arene-based aza-cryptand with dioxygen has been studied. In this system, Cu(I) is bound to a tren unit that caps the calixarene core at the level of the small rim. As a result, although protected from the reaction medium by the macrocycle, the metal center presents a labile site accessible to small guest ligands. Indeed, in the presence of O2, it reacts in a very fast and irreversible redox process, leading, ultimately, to Cu(II) species. In the coordinating solvent MeCN, a one electron exchange occurs, yielding the corresponding [CalixtrenCu-MeCN](2+) complex with concomitant release of superoxide in the reaction medium. In a noncoordinating solvent such as CH2Cl2, the dioxygen reaction leads to oxygen insertions into the ligand itself. Both reactions are proposed to proceed through the formation of a superoxide-Cu(II) intermediate that is unstable in the Calixtren environment due to second sphere effects. The transiently formed superoxide ligand either undergoes fast substitution for a guest ligand (in MeCN) or intramolecular redox evolutions toward oxygenation of Calixtren. Interestingly, the latter process was shown to occur twice on the same ligand, thus demonstrating a possible catalytic activation of O2 at a single cuprous center. Altogether, this study illustrates the oxidizing power of a [CuO2](+) adduct and substantiates a mechanism by which copper mono-oxygenases such as DbetaH and PHM activate O2 at the Cu(M) center to produce such an intermediate capable of C-H breaking before the electron input provided by the noncoupled Cu(H) center.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Synthesis and study of new biomimetic calix[6]tren based complexes

More than 30% of enzymes present a metal ion in their active site that is key forcatalysis. Interesting sub-families present a mononuclear active site where a single metal ion(Zn2+ or Cun+) is coordinated to a polyhistidine core. The elaboration of model compounds isimportant for understanding the fundamental mechanisms involved in their bio-catalyticcycles.1 We have developed calix[6]arene based ligands presenting an aza cap covalentlylinked to the calixarene moiety, which offers a metal coordination site and a well-definedhydrophobic cavity. This assembly allows and controls exogenous ligand binding to a metalcenter. One of these ligands, calix[6]tren (1), shows versatile host-guest properties oncecomplexed to Cun+ but is also a remarkable receptor for ammonium ions and polar neutralmolecules,2 as well as a trigger for host/guest interconverion3 and for dioxygen activation.4The development of efficient synthetic methodologies for the selective functionalization ofcalix[6]tren is now required in order to tune its properties by the modification of thecoordination sphere of the metal and by obtaining surface graftable analogues that can bestudied in water.For these purposes, different calixarenes were synthesized:- A “two-story” calix[6]amidotren (2) to expand the available space underneath thecap to allow simultaneous coordination of several guests and to study its catalytic properties;- A calix[6]tren-trisPhOH (3) amending the first and second coordination sphere of themetal in order to study its effects on coordination and reactivity;- A calix[6]tren decorated with an arm on the cap bearing an azide function (4) inorder to be immobilized on the surface and study its properties in water: these functionalizedsurfaces will present unique electrocatalytic and redox detection properties in aqueousmedium.Synthesis, complexation, characterization and electrochemical behavior of thedifferent compounds in solution and immobilized on surface will be presented and discussed.0info:eu-repo/semantics/nonPublishe