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

A Generic Platform for the Addressable Functionalisation of Electrode Surfaces through Self-Induced "Electroclick"

International audienceA novel and general strategy for the immobilisation of functional objects onto electrodes is described. The concept is based on the addition of two pendant ethynyl groups onto a bis(pyridyl)amine derivative, which acts as a molecular platform. This platform is pre-functionalised with an N3-tagged object of interest by Huisgen cycloaddition to one of the ethynyl groups in biphasic conditions. Hence, when complexed by CuII, this molecular-object holder can be immobilised, by a self-induced electroclick, through the second ethynyl group onto N3-alkanethiol self-assembled monolayers on a gold electrode. Two different functional groups, a redox innocent ((CH2)3?Ph) and an electrochemical probe (ferrocene), were immobilised by following this strategy. The in situ electrochemical grafting showed, for both systems, that the kinetics of immobilisation is fast. The voltammetric characterisation of the surface-tagged functionalised copper complexes indicated that a good surface coverage was achieved and that a moderately fast electron-transfer reaction occurs. Remarkably, in the case of the redox-active ferrocenyl-immobilised system, the electrochemical response highlighted the involvement of the copper ion of the platform in the kinetics of the electron transfer to the ferrocene moiety. This platform is a promising candidate for applications in surface addressing in areas as diverse as biology and materials

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

Analysis of Mesencephalic Astrocyte-derived Neurotrophic Factor in Multiple Myeloma

International audienceBackground/Aim: Multiple myeloma (MM) is characterized by high production of immunoglobulins resulting in a constant source of endoplasmic reticulum (ER)-stress. Mesencephalic astrocyte-derived neurotrophic factor (MANF) was identified as a possible circulating biomarker that could help in monitoring ER-stress mediated diseases. Materials and Methods: To assess the relevance of MANF in MM, we performed in silico and in vitro analysis in malignant cell lines including the myeloma cell line RPMI 8226. Serum MANF concentration was compared between healthy subjects (n=60), patients with MM (n=68), or those with monoclonal gammopathy of undetermined significance (MGUS) (n=73). Results: MANF mRNA expression was upregulated in the RPMI 8226 cell line, and higher secretion of MANF was measured in RPMI 8226 supernatant. Serum MANF levels were not significantly different between MM or MGUS patients and those in age-and sex-matched healthy controls. Conclusion: MANF was not validated as a biomarker of interest in MM patients. Its potential implication in myeloma pathogenesis should be investigated

Electrocatalytic reduction of nitrite ions by a copper complex attached as SAMs on gold by "self-induced electroclick": Enhancement of the catalytic rate by surface coverage decrease

International audienceA biomimetic copper complex has been attached as SAMs onto an azidoundecanethiol-modified gold electrode by the "self-induced electroclick" procedure. The immobilized complex electrocatalyzes efficiently the reduction of nitrite ions in an acidic medium. The in-situ control of the surface coverage during the grafting process by the electroclick approach has been exploited to rationalize the influence of surface concentration on the electrocatalytic properties of the immobilized Cu complex. The voltammetric analysis shows an enhancement of the catalytic rate when the surface coverage is decreased, as a consequence of steric and electronic effects. (C) 2013 Elsevier B.V. All rights reserved

Self-induced "electroclick" immobilization of a copper complex onto self-assembled monolayers on a gold electrode

International audienceWe report the self-induced "electroclick" immobilization of the [Cu(II)(6-ethynyl-TMPA)(H(2)O)](2+) complex, by its simple electro-reduction, onto a mixed azidoundodecane-/decane-thiol modified gold electrode. The redox response of the grafted [Cu(II/I)(TMPA)] at the modified electrode is fully reversible indicating no Cu coordination change and a fast electron transfer

Tetracarboxylate Ligands as New Chelates Supporting Copper(II) Paddlewheel-Like Structures

Two new ligands <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetrakis­(2-methylbenzoic acid)-1,4-diaminomethylbenzene, <b>5</b>H₄, and <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetrakis­(2-methylbenzoic acid)-4,4′-diaminomethyldiphenyl, <b>6</b>H₄, carrying four carboxylate groups suitable for bridging dinuclear centers have been prepared and their paddlewheel complexes with copper­(II) prepared. The phenyl-bridged ligand <b>5</b>H₄ gives a cyclic octanuclear species [(Cu₂)₄(<b>5</b>)₄], while the diphenyl-bridged ligand <b>6</b>H₄ gives a lantern-like tetranuclear species [(Cu₂)₂(<b>6</b>)₂]; both were characterized by X-ray crystallography. If the amine functions of <b>5</b> are protonated, intramolecular hydrogen bonds position the four carboxylates in such a way as to allow formation of the unusual compound [Cu₄(<b>5</b>H₂)₂Cl]³⁺ in which a Cu₄ square centered by a chloro ligand is sandwiched between two (<b>5</b>H₂)^2– ligands. The magnetic properties of this compound have been studied and show antiferromagnetic coupling between adjacent coppers (<i>J</i> = −33.7 cm^–1)

Electrochemical behavior and dioxygen reactivity of tripodal dinuclear copper complexes linked by unsaturated rigid spacers

International audienceNew dinucleating ligands based on two tripodal tris(2-pyridylmethyl) amine (TMPA) units linked by a series of delocalized pi-electrons spacers have been synthesized. Their di-Cu-II complexes have been prepared and structurally characterized. As compared to the corresponding monotopic complexes, these dinuclear Cu-II complexes reveal spectroscopic and voltammetric features ascribable to weakly perturbed electronic interactions. In the case of the anthracenyl spacer, observation both in the solid and in solution suggests that the existence of intramolecular pi-pi stacking interactions influences the geometry of the complex and hence its electronic properties. The bis-Cu-I complexes were prepared electrochemically. In the specific case of the complex bearing a mono-alkyne spacer, addition of dioxygen in acetonitrile leads to the slow formation of a trans-mu-1,2 peroxo Cu-2 complex which shows good stability at 268 K (t(1/2) = 240 s). Analysis of the kinetics of the peroxo formation by UV-vis spectroscopy suggests that the increased activation barrier for intramolecular binding of dioxygen is due to the rigidity of the spacer