3 research outputs found
Bioinspired redox-active systems for electron transfer and synthetic challenges
La nature dĂ©tient une astuce rĂ©cemment dĂ©couverte qui lui permet dâeffectuer des transformations chimiques exigeantes telles que la rĂ©duction et la valorisation du dioxyde de carbone et du diazote, des rĂ©actions dâenjeu environnemental. Ces transformations ont lieu grĂące Ă la propriĂ©tĂ© dâinversion des potentiels redox que possĂšdent certaines molĂ©cules organiques telles que les quinones et les flavines, situĂ©es dans des enzymes. Cette propriĂ©tĂ© leur permet de faciliter le second transfert Ă©lectronique par rapport au premier et leur permet de gĂ©nĂ©rer des espĂšces assez rĂ©ductrices capables de rĂ©aliser ces transformations chimiques difficiles. Cependant, les quinones et flavines ne possĂ©dant pas cette propriĂ©tĂ© dâinversion des potentiels ne sont pas capables dâeffectuer ce type de transformation. Lâordre des potentiels redox (inversion ou non) dĂ©pend de lâinteraction de la molĂ©cule organique avec son environnement dans lâenzyme. Nos travaux visent Ă reproduire ces processus naturels Ă lâaide dâun systĂšme simplifiĂ© contenant un mĂ©tal Ă©co-compatible et des ligands bio-inspirĂ©s, possĂ©dant cette propriĂ©tĂ© dâinversion en vue dâapplications en catalyse et afin dâeffectuer des rĂ©actions chimiques compliquĂ©es avec des systĂšmes plus simples que ceux utilisĂ©s par la nature. Nos rĂ©sultats montrent quâĂ lâinstar du processus naturel lâenvironnement du complexe influence fortement lâordre des potentiels redox des complexes ainsi que la rĂ©activitĂ© du complexe et permet de moduler le nombre dâĂ©lectrons transfĂ©rĂ©s. Nous exploitons aussi lâinversion des potentiels dans les transferts multiĂ©lectroniques.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