Electron transfer properties of mono- and diferrocenyl based Cu complexes attached as self-assembled monolayers on gold electrodes by "self-induced" electroclick

International audienceTwo new Cu complexes bearing a 6-ethynyl bis-(methyl-pyridyl) amine (6eBMPA) moiety, as an electroclickable function linked to a ferrocenyl-based triazolyl arm (ligands 3 and 4) have been synthetized and characterized by UV-Visible, EPR spectroscopies and cyclic voltammetry in acetonitrile. Two different spacer groups between the terminal ferrocene and the triazolyl group were inserted: an hexyl chain in the case of the complex Cu-3, an ethenyl-bridged diferrocenyl system for the complex Cu-4. The monoelectronic oxidation of the diferrocenyl species yields a stable mixed-valence complex. NIR-Visible spectroscopic studies show a moderate interaction between ferrocenyl units (class II according to the Robin-Day classification). The immobilization of these systems as SAMs on an azidoundecanethiol modified gold electrode has been successfully operated by using the "self-induced electroclick" procedure. The voltammetric characterization of the surface-tagged Cu complexes indicates that good surface coverage was achieved, with moderately fast electron-transfer reaction between the electrode and the redox active immobilized systems (k0(Cu) = 2-4 s−1, k0(Fc) = 20-90 s−1). Remarkably, the rate of charge transport is significantly controlled by the nature of the spacer on the ferrocenyl triazole arm

Rate enhancement of the catechol oxidase activity of a series of biomimetic monocopper(II) complexes by introduction of non-coordinating groups in N-tripodal ligands

International audienceAsymmetrical N-tripodal ligands have been synthesized in three steps. Diversity has been introduced at the first step of the synthesis by adding pyrazine, pyridine, benzyl and thiophene rings. The corresponding CuII complexes have been prepared by reaction with CuCl2 and characterized by Electron Paramagnetic Resonance (EPR), UV-Vis spectroscopies and cyclic voltammetry. The data show that the ligand coordinates to CuII in a mononuclear fashion in solution and that the complexes display a square pyramidal geometry. All complexes are characterized by a quasi-reversible one-electron redox behavior in acetonitrile. The ability of the complexes to oxidize 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone has been studied and the results show that the rate of the reaction depends on the basicity and the steric hindrance of the heterocyclic donor. Best results have been obtained with CuII complexes coordinated to bidentate ligands, since they facilitate the approach and the coordination of catechol to the metal. Particularly, the introduction of a thiophenyl group to mimic the sulfur atom at proximity to the catalytic center in the catechol oxidase protein structure improves the catalytic activity of the complex

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

Comparison of Short-Term Estrogenicity Tests for Identification of Hormone-Disrupting Chemicals

The aim of this study was to compare results obtained by eight different short-term assays of estrogenlike actions of chemicals conducted in 10 different laboratories in five countries. Twenty chemicals were selected to represent direct-acting estrogens, compounds with estrogenic metabolites, estrogenic antagonists, and a known cytotoxic agent. Also included in the test panel were 17β-estradiol as a positive control and ethanol as solvent control. The test compounds were coded before distribution. Test methods included direct binding to the estrogen receptor (ER), proliferation of MCF-7 cells, transient reporter gene expression in MCF-7 cells, reporter gene expression in yeast strains stably transfected with the human ER and an estrogen-responsive reporter gene, and vitellogenin production in juvenile rainbow trout. 17β-Estradiol, 17α-ethynyl estradiol, and diethylstilbestrol induced a strong estrogenic response in all test systems. Colchicine caused cytotoxicity only. Bisphenol A induced an estrogenic response in all assays. The results obtained for the remaining test compounds—tamoxifen, ICI 182.780, testosterone, bisphenol A dimethacrylate, 4-n-octylphenol, 4-n-nonylphenol, nonylphenol dodecylethoxylate, butylbenzylphthalate, dibutylphthalate, methoxychlor, o,p′-DDT, p,p′-DDE, endosulfan, chlomequat chloride, and ethanol—varied among the assays. The results demonstrate that careful standardization is necessary to obtain a reasonable degree of reproducibility. Also, similar methods vary in their sensitivity to estrogenic compounds. Thus, short-term tests are useful for screening purposes, but the methods must be further validated by additional interlaboratory and interassay comparisons to document the reliability of the methods

Minimum Information About a Simulation Experiment (MIASE)

The original publication is available at www.ploscompbiol.orgReproducibility of experiments is a basic requirement for science. Minimum Information (MI) guidelines have proved a helpful means of enabling reuse of existing work in modern biology. The Minimum Information Required in the Annotation of Models (MIRIAM) guidelines promote the exchange and reuse of biochemical computational models. However, information about a model alone is not sufficient to enable its efficient reuse in a computational setting. Advanced numerical algorithms and complex modeling workflows used in modern computational biology make reproduction of simulations difficult. It is therefore essential to define the core information necessary to perform simulations of those models. The Minimum Information About a Simulation Experiment describes the minimal set of information that must be provided to make the description of a simulation experiment available to others. It includes the list of models to use and their modifications, all the simulation procedures to apply and in which order, the processing of the raw numerical results, and the description of the final output. MIASE allows for the reproduction of any simulation experiment. The provision of this information, along with a set of required models, guarantees that the simulation experiment represents the intention of the original authors. Following MIASE guidelines will thus improve the quality of scientific reporting, and will also allow collaborative, more distributed efforts in computational modeling and simulation of biological processes.The discussions that led to the definition of MIASE benefited from the support of a Japan Partnering Award by the UK Biotechnology and Biological Sciences Research Council. DW was supported by the Marie Curie program and by the German Research Association (DFG Research Training School ‘‘dIEM oSiRiS’’ 1387/1). This publication is based on work (EJC) supported in part by Award No KUK-C1-013-04, made by King Abdullah University of Science and Technology (KAUST). FTB acknowledges support by the NIH (grant 1R01GM081070- 01). JC is supported by the European Commission, DG Information Society, through the Seventh Framework Programme of Information and Communication Technologies, under the VPH NoE project (grant number 223920). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Publishers versio

Electrochemically and Chemically Induced Redox Processes in Molecular Machines

International audienceThe controlled motion of ions, molecules, or supramolecular entities has inspired scientists for more than 25 years, and the concept remains of great interest for the development of moveable nanoscale objects for applications in electronics, medicine, and materials chemistry. Artificial molecular machines that involve electron exchange processes induced by electrical, chemical, or photochemical energy, have been widely developed. More specifically, machines that are stimulated by electrochemical means have been the focus of particular attention because such systems can allow the change of states to be followed and can enable access to mechanistic pathways through direct monitoring. Furthermore, these devices have the ability to connect the nanoscale machine to the macroscopic world, for instance by surface immobilization. In this review, we report recent examples of redox-based molecular machines in both fluid solution and in organized or controllable environments such as modified electrodes, nanoparticles, polymers, gels, and liquid crystals. Basic concepts of molecular machinery and general applications are also discussed

Low-temperature electrochemistry and spectroelectrochemistry for coordination compounds

International audienceThis review is focused on the current state-of-the art of low-temperature electrochemistry and spectroelectrochemistry applied for coordination and organometallic compounds. From the first tentative steps in the 1960s to the present sophisticated spectroelectrochemical systems, low-temperature studies of redox reactions and coupled chemical processes have always fascinated chemists. The main reason is that low temperature offers the possibility not only to quantify thermodynamics/kinetics of electron transfer reactions, but also to better decipher mechanistic pathways of chemical-coupled electron transfer reactions. Various cryo-electrochemical and spectroelectrochemical set-ups have been designed leading to significant advancement of in situ detection of transient and unstable species generated by electrochemistry. In this review, we detail the novel aspects which can be discovered by performing electrochemical/spectroelectrochemical investigations at low temperature, and the means to carry out resolved electrochemistry at temperatures close to the liquid nitrogen solidification. Specific examples are given to demonstrate the powerful information which can be taken from low-temperature studies for coordination and organometallic chemistry. A conclusion and outlooks are also presented to discuss about the perspectives and remaining challenges for this research field

Theoretical aspects of electrochemistry at low temperature

International audienceThis paper aims at providing theoretical basis on electrochemical processes performed at low temperature (T) according to three different aspects. First, the effect of T-decrease is treated in terms of thermodynamics, mass-transfer, and kinetics of electron transfer (ET) heterogeneous reactions. In particular, predictions of ET kinetics at low temperature are discussed in the frame of Marcus-Hush’s model. The second part is focused on the changes associated to temperature decrease for different electrochemical methods including cyclic voltammetry (CV), chronoamperometry (CA), AC Impedance (ACI) and AC voltammetry (ACV). This section gives keys to extract electrochemical data from low-T experimental curves. In the third part, theoretical aspects of low-T cyclic voltammetry for multiple or chemically-coupled electron-transfer reactions are discussed. CVs of typical molecular mechanisms (EE, EC, ECE…) are provided in order to better visualize the impact of temperature on the redox behavior

The synthesis of flexible tetrapyridylethanes from pyridylpyrylium dications

International audienceNew tetrapyridylethanes can be prepd. as new tetradentate pyridine ligands via the aminolysis reaction of pyrylium dications, using an original oxidn. process of phenylpyridyl methylenepyrans. Crystal structure anal., and spectroscopic and electrochem. studies show the possibility for using these new ligands in coordination chem