Bioinspired redox-active systems for electron transfer and synthetic challenges

La nature détient une astuce récemment découverte qui lui permet d’effectuer des transformations chimiques exigeantes telles que la réduction et la valorisation du dioxyde de carbone et du diazote, des réactions d’enjeu environnemental. Ces transformations ont lieu grâce à la propriété d’inversion des potentiels redox que possèdent certaines molécules organiques telles que les quinones et les flavines, situées dans des enzymes. Cette propriété leur permet de faciliter le second transfert électronique par rapport au premier et leur permet de générer des espèces assez réductrices capables de réaliser ces transformations chimiques difficiles. Cependant, les quinones et flavines ne possédant pas cette propriété d’inversion des potentiels ne sont pas capables d’effectuer ce type de transformation. L’ordre des potentiels redox (inversion ou non) dépend de l’interaction de la molécule organique avec son environnement dans l’enzyme. Nos travaux visent à reproduire ces processus naturels à l’aide d’un système simplifié contenant un métal éco-compatible et des ligands bio-inspirés, possédant cette propriété d’inversion en vue d’applications en catalyse et afin d’effectuer des réactions chimiques compliquées avec des systèmes plus simples que ceux utilisés par la nature. Nos résultats montrent qu’à l’instar du processus naturel l’environnement du complexe influence fortement l’ordre des potentiels redox des complexes ainsi que la réactivité du complexe et permet de moduler le nombre d’électrons transférés. Nous exploitons aussi l’inversion des potentiels dans les transferts multiélectroniques.Nature has a recently discovered trick that allows it to perform demanding chemical transformations such as the reduction of carbon dioxide and dinitrogen, reactions of environmental concern. These transformations take place thanks to the property of redox potential inversion that certain organic molecules such as quinones and flavines possess, located in enzymes. This property allows them to facilitate the second electronic transfer compared to the first one and allows them to generate reducing species capable of carrying out these difficult chemical transformations. However, quinones and flavines that do not possess the property of potential inversion are not able to carry out this type of transformation. The order of the redox potentials (inversion or not) depends on the interaction of the organic molecule with its environment in the enzyme. Our work aims at reproducing these natural processes with a simplified system containing an eco-compatible metal and bio- inspired ligands, possessing this property of potential inversion for applications in catalysis and in order to perform complicated chemical reactions with simpler systems than those used in nature. Our results show that, as in the natural process, the environment of the complex strongly influences the order of the redox potentials of the complexes as well as the reactivity of the complex and allows to modulate the number of electrons transferred. We also exploit potential inversion in reaction that require multi-electron transfers

Assessing the Extent of Potential Inversion by Cyclic Voltammetry: Theory, Pitfalls, and Application to a Nickel Complex with Redox-Active Iminosemiquinone Ligands

International audiencePotential inversion refers to the situation where a protein cofactor or a synthetic molecule can be oxidized or reduced twice in a cooperative manner, that is the second electron transfer (ET) is easier than the first. This property is very important regarding the catalytic mechanism of enzymes that bifurcate electrons and the properties of bidirectional redox molecular catalysts that function in either direction of the reaction with no overpotential. Cyclic voltammetry is the most common technique for characterizing the thermodynamics and kinetics of ET to or from these molecules. However, a gap in the literature is the absence of analytical predictions to help interpret the values of the voltammetric peak potentials when potential inversion occurs ; the cyclic voltammograms are therefore often analyzed by simulating the data, with no discussion of the possibility of overfitting and often no estimation of the error on the determined parameters. Here we formulate the theory for the voltammetry of freely-diffusing or surface-confined two-electron redox species in the experimentally relevant irreversible limit where the peak separation depends on scan rate. We explain why the model is intrinsically underdetermined, and we illustrate this conclusion by the analysis of the voltammetry of a Ni complex with redox-active iminosemiquinone ligands. Being able to characterize the thermodynamics of two-electron transfer reactions will be crucial for designing more efficient catalysts

Photoactive Organic/Inorganic Hybrid Materials with Nanosegregated Donor-Acceptor Arrays

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