CIEl team develop research on biomimetic activation of O2 by iron and copper complexes, as enzyme models, as well as studies on H+/H2 conversion by organometallic models of hydrogenases, which are extended to the activation of other small molecule resources. The main topics and projects are described below. Transition metal catalysts are powerful tools for the development of green chemistry because they allow to obtain processes generating little waste, to improve their efficiency, and selectivity. However, the use of noble metals (Ru, Os, Rh, Ir, Pd, Pt), as it is currently the case in homogeneous catalysis, is limited in long term because of their environmental impact, their scarcity as well as their high cost. Facing this problem, the metals of the first period (Mn, Fe, Co, Ni, Cu), more abundant and much less expensive, appear as promising alternatives, more respectful of the environment, but nevertheless remain less efficient than the noble metals. In this context, a bio-inspired molecular approach is very promising and aims to design new electrocatalysts inspired by some metallo-enzymes. The main constraint is to be able to understand the keys of the functioning of enzymes active sites to reproduce their activity while avoiding the complexity of the protein matrix..
Participants : L. Chatelain, C. Elleouet, F Gloaguen, C. Le Roy, F.Y Pétillon, N. Renard, C. Rouxel, P.Schollhammer
- Metal-sulfur systems.
This theme concerns the study of Metal-Sulfur systems for modeling active sites of hydrogenases or nitrogenases in order to mimic their activity, respectively, towards H+ /H2 conversion and the activation of N2. These studies require complementary skills in electrochemistry and organometallic synthesis. They are related to the activation of small resource-molecules by sulfur metallic systems.
Studies of sulfur-containing clusters, as models of natural metal-sulfur systems, their elaboration and their electrochemical behaviours, are performed.
- Organometallic models of hydrogenases.
This topic concern the synthesis and the electrochemical studies of dinuclear organometallic derivatives of iron, inspired by the active site of [Fe-Fe] hydrogenases in order to understand their functioning and to use the new molecules as electrocatalysts for the reversible conversion H+/H2. As in many natural processes, successive or coupled transfers of electron and proton are involved and these studies require the determination of parameters that control the activity of metal-sulfur sites towards substrates identified or proposed as key intermediates, or as model substrates.
- Bioinspired activation of molecular nitrogen .
Goals are to design and study new molecules bioinspired by the FeMo nitrogenase cofactor, which is able to activate N2
, in order to understand the functioning of this active site and to contribute, in the long term, to the development of new strategies for the activation of the very stable dinitrogen molecule. N2
is an inert resource-molecule but essential for the industrial and biological production of NH3
. The Haber-Bosch process is used in industry to synthesize ammonia by reacting N2
and H2 vi
a iron or ruthenium catalysts at high temperatures and pressures. On the other hand, in nature, the FeMo nitrogenase enzyme converts N2
by electron and proton transfers under a pressure of 1atm and at room temperature via an active site, the FeMo cofactor. The operating mechanism of the FeMo cofactor is still far from understood and very few molecular catalysts that are efficient in reducing N2
have been described. The development of bioinspired models of the active site of FeMo nitrogenase, which would be active with respect to the activation of N2
, remains one of the modern challenges of inorganic chemistry.
- Fe/Cu complexes: dioxygen activation
Bénédicte Douziech, Yves Le Mest, Nicolas Le Poul, Lauriane Wojcik
This research topic aims at developing bio-inspired metal complexes (Fe, Cu) for the catalytic oxidation of organic substrates by using O2. The purpose is to reproduce in structural and functional terms the active site of specific metalloenzymes which are of interest in various domains (energy, health…). The targeted enzymes are oxygenases (pMMO, sMMO, PHM) and oxidases (tyrosinase, galactose oxidase). One specificity of the team is the use of cryo-spectoelectrochemical methods for the characterization of Metal (Fe,Cu)-dioxygen species..
- pMMO (particulate methane monooxygenase) models
The pMMO is a copper-enzyme which catalyzes the oxidation of methane into methanol at room temperature. Recent studies have suggested that methane oxidation occurs likely through the formation of a dinuclear mixed-valence Cu2II,III : (µ-O)2 or a mononuclear cupryl CuII(O°) species. One of the main objectives is to be able to characterize these intermediates with the help of bio-inspired chemistry. Our strategy for that purpose is to mono-electronically oxidize dicopper(II) bis-µ-hydroxo synthetic complexes (collaborative work with Grenoble (C. Belle) and Marseille (A. J. Simaan)), by using a low-T spectroelectrochemical setup (10.1021/acs.inorgchem.6b01504, 10.1002/cplu.201600636, 10.1021/acs.inorgchem.7b00338). Other approaches using dioxygen and copper(I) complexes are also currently developed.
Inorg. Chem. 2016, 55, 8263−8266
- Modèles de la DβM (Dopamine βmonooxygénase)
La dopamine β-monooxygenase (DβM) et la monooxygénase peptidylglycine α-hydroxylante (PHM) sont des enzymes essentielles dans le monde biologique. Elles catalysent la transformation de la dopamine en norepinephrine (DβM) et de peptide C-terminaux en leurs produits α-hydroxylés (PHM). Bien que leurs cibles soient foncièrement différentes, ces deux enzymes présentent des caractéristiques communes d’un point de vue du mécanisme d’hydroxylation. En effet, l’oxydation des biomolécules s’opère sur un centre cuivre mononucléaire, superoxo ou hydroperoxo. Une stratégie développée par les équipes d’O. Reinaud (Paris) et I. Jabin (Bruxelles) consiste à utiliser une plateforme calixarène N-fonctionnalisé afin de générer des complexes mononucléaires modèles de ces enzymes. Dans le cadre d’une collaboration de longue date sur ces systèmes, nous réalisons les études électrochimiques et spectroscopiques des différents complexes Cu-calixarènes synthétisés. En particulier, nous focalisons nos études sur la réactivité des complexes du Cu(I) vis-à-vis du dioxygène.
- DβM (Dopamine β monooxygénase) models
The DβM and the PHM (peptidylglycine α-hydroxylating monooxygenase) are type II dinuclear copper enzymes which catalyze the oxygenation of biologically-important molecules. These two enzymes display several analogies from the mechanistic point of view. Indeed, the oxidation of the biomolecules occurs at a mononuclear copper-oxygen center, which can be either a superoxo or a hydroperoxo species. Among the many models of these enzymes, monocopper calixarene-based complexes have been the subject of intensive electrochemical work in our group (collaboration Paris (O. Reinaud), 10.1039/c7dt03375c, 10.1021/acs.accounts.5b00152, 10.1021/acs.inorgchem.7b01225). We perform the electrochemical and spectroscopic studies of the these supramolecular models, and more particularly the reactivity of the Cu(I) complexes towards dioxygen for substrate oxidation.
- sMMO (soluble méthane monooxygenase) models
The sMMO is an iron enzyme which catalyzes the methane oxidation into methanol. This enzyme is a source of inspiration for the development of new synthetic iron-based catalysts for the activation of C-H bonds. The classical approach consists in generating mononuclear systems to produce Fe(IV)-oxo species. An alternative approach that we have developed is based on the generation of dinuclear complexes which mimic the active site of the enzyme.
- Electrode functionalization with metal complexes
Frédéric Gloaguen, Yves Le Mest, Nicolas Le Poul
Our team is interested by the surface immobilization of model complexes of enzymes, through a self-assembled monolayers (SAMs) approach. Two different strategies have been developed for the grafting onto electrode of (Cu, Fe, Ni) metal complexes: (i) the post-functionalization by a CuAAC 'electroclick' method using the in-situ electrochemical generation of a copper(I) complex to form a triazole link (10.1002/chem.201102620), and (ii) the direct immobilization, chemically assisted or not, of sulfur-based compounds (thiol, dithiolane). The electroclick approach has allowed us to monitor the in-situ immobilization on gold of a model complex of Cu-Nitrite Reductase (Cu - NIR). The catalytic activity of this complex has been tuned according to electroclick grafting conditions (10.1016/j.elecom.2013.06.014). In the field of sensors, a supramolecular Cu complex grafted by electroclick, has showed remarkable selectivity towards primary amine in an aqueous medium (10.1021/jacs.6b05317). In the pursue of these results, the current objectives concern the optimization of the methods of grafting (fundamental processes mechanistic studies), the immobilization of new metal complexes for the activation of small molecules (O2, NO2-, CO2,...). Our team is also developing physico-chemical analysis methods within the transverse axis "Spectroscopy and Reactivity" for the structural characterization and the reactivity of these molecular materials. J. Am. Chem. Soc. 2016, 138, 12841−12853
The research activity of this theme concerns the design of new materials exhibiting molecular switching and/or photoluminescent properties. Two approach have been developed: the first one is a molecular approach which concerns the design of new switchable materials, including the polyfunctional ones exhibiting a spin cross-over (SCO) behaviour and a second property such as photoluminescence (1); the second one is an hybrid organic/inorganic approach dedicated to the design of new hybrid photoluminescent materials (2).
S. Le Corre, C. Charles, F. Conan, N. Cosquer, F Thétiot, S. Triki.
- Spin cross-over and polyfunctional materials
This project concerns the study and design of new switchable materials, essentially the SCO materials, which are extended to polyfunctional systems including the SCO behaviour and photoluminescence.
- a -Spin cross-over materials
The objective of this topic is the control the SCO characteristics such as the cooperativity, the thermal and photo-induced hysteresis, and the transition temperatures, through the design of new switchable systems requiring very intense synthesis activity. In recent years, this topic has been oriented towards the design of new triazole-based (trz) switchable systems. The main objective is to understand the origin of the strong cooperativity in coordination polymers exhibiting magnetic bistability around room temperature. Among the many original systems studied, the two most striking materials are summarized here: (i) the first systems concerns a new switchable 2D Hofmann-like spin-crossover material experiencing strong elastic frustration leading to an incomplete spin transition (Figure 1). Under light, a hidden stable low spin state (LS) is reached, revealing the existence of a hidden thermal hysteresis and multi-stability features (doi.org/10.1021/acs.inorgchem.6b01081).
The existence of these characteristics paves the way for a multi-directional photo-switching and allows potential applications for electronic devices based on ternary digits; (ii) the second system concerns the first single crystal investigations (Figure 2), in both high spin (HS
) and low spin (LS
) states of a new cooperative and robust spin transition triazole-based FeII
1-D coordination polymer (doi.org/10.1021/acs.chemmater.6b04118
This compound exhibits a sharp transition at 240 K, accompanied with an anisotropic deformation of the unit cell and a significant gliding of the chains from each other. These two features are identified as the key parameters of the non-conventional mechanical resilience of this system.
- b-Switchable polyfunctional materials
In order to reach the potential applications through the coexistence of two physical properties in the synergic way (e.g. SCO and luminescence), an extension of these switchable materials is undertaken towards the development of polyfunctional systems based on appropriate ligand involving luminophore group. In this context, we have reported recently a new example of a mononuclear iron (II) complex exhibiting a correlated SCO transition and strong fluorescence (10.1039/C9SC02331C). Overall, the results show an excellent correlation between photoluminescence (PL) and the SCO transition, indicating an extreme sensitivity of the optical activity of the ligand to the spin state of the active iron (II) centers.
Owing to this synergy between SCO and PL properties, This work open the way for conceiving new prototypes of pressure and temperature sensors (see Figure 3). With the objective to design more strongly cooperative and photoluminescent materials, around room temperature, this study will be extended to phosphorescent ligands more appropriate for the formation of monodimensional cooperative coordination polymers.
- Photoluminescent Organic-Inorganic materials
Hybrid organic-inorganic perovskites (HIOP) are a class of crystalline semiconducting materials, which emerged over the past few years owing to their outstanding technological potential in solid-state solar cells, light emitting diodes (LED) or laser devices. In the last few years, they received extraordinary community attention due to their special structure diversity and impressive optical and electrical properties, which make them highly promising candidates for applications as thin-film field-effect transistors (TFT) (10.1038/ncomms8383), laser gain media (10.1038/NPHOTON.2016.62), solid-state light-emitting diodes (LED) (10.1038/NNANO.2016.110), and photovoltaic devices (1038/NNANO.2015.90). HOIP semiconductors are characterized by a direct bandgap, large absorption coefficient, strong photoluminescence (PL), long charge carrier diffusion length (up to one micrometer in thin film) related to an exceptionally long exciton lifetime (300 ns to few hundred microseconds for single crystal); resulting in an extremely high charge carrier mobility. These properties are well appropriate for photo-induced charge transport and extraction in a solar-cell device. In the prototype 3D material Methylammonium Lead Iodide (CH3NH3)PbI3 (MAPI), the excited state is composed primarily of free carriers with low exciton binding energy (10-20 meV) and excellent electron-hole transport and mobility. Since 2009, MAPI represented an exciting new class of low-cost solar absorber materials, which have revolutionized the photovoltaic landscape by the exceptional growth of their power conversion efficiency from 3.8% to more than 22% in less than 10 years (10.1021/ja809598r and 10.1126/science.aan2301), to be compared with the nearly 25% efficiency of state-of-the-art silicon cells which have dominated the market for decades. In this context, we established since 2014 complementary national and international collaborations (Prof. K. Boukheddaden from the University of Versailles, Dr S. Pillet from the University of Nancy and Prod. Y. Abid from the university of Sfax, Tunisia) for the design of new HOIP materials exhibiting new tunable structural features and white-light emission. Soon, in the beginning of this collaboration, we and others have reported an exceptional new phenomenon, consisting on a broadband white-light emission, covering a major part of the visible region of the solar spectrum (Figure 4) with unprecedentedly large (~20%,) quantum yields (10.1021/acs.jpcc.5b06211).
More recently, we have reported a new organic–inorganic hybrid material, (C6H22N4)[Pb2Br8], exhibiting infinite 1D ladder‐like structure. Under UV excitation, this compound emits white light due to radiative recombinations of self‐trapped excitons associated with a structural distortion of the PbBr6 octahedra (Figure 5). Thin films of TETAPb2Br8 show a photoluminescence (PL) quantum yield of ≈11% (https://doi.org/10.1002/adom.201900763).
After this first work concerning mainly the 1D and 2D hybrid Organic/Inorganic systems exhibiting white light emission, the second step will be dedicated to the crystal engineering to design new 3D hybrid organic-inorganic MOFs (HOI-MOFs) with different and various structural topologies.
The cross-disciplinary sub-team “Spectroscopy and Reactivity” is involved in the development of new analytical methods based on spectroelectrochemistry, mass spectrometry, and electrochemical and molecular modeling to support the research activity of the team CIEl.
- Cryo-spectroelectrochemical methods
Y. Le Mest, N. Le Poul, L. Wojcik
Our team has developed since 2014 low-temperature spectroelectrochemical setups (UV-Visible-NIR, EPR). The aim is to perform in-situ and time-resolved (10 ms) characterization of transient redox species including inorganic and organic compounds. Our first studies on copper enzyme model complexes have allowed us to study the redox process associated to Cu2:O2 peroxo/superoxo intermediates at T = -90 °C (10.1002/chem.201705066). Our setup has also been recently employed for kinetic studies of molecular organic switches (collaborative work with the team of Lannion, 10.1021/acs.joc.7b02199).
- Analytical method development using chemometrics and tandem mass spectrometry
Participants : Alicia Maroto, Antony Memboeuf
Structural and quantitative analysis of mixtures of isobars and isomers can be very challenging to perform. It may require sophisticated methods or necessitate tedious optimization procedures. In this context, we have developed a tandem mass spectrometric method (MS/MS) in which unequivocal structural and quantitative information of such mixtures can be obtained. This information is obtained by direct infusion of the sample mixtures, i.e. without the need for any chromatographic separation, then speeding up the analytical process by taking advantage of the rapidity, sensitivity and selectivity of mass spectrometry measurement (10.1007/s13361-011-0195-8). The method is based on tandem mass spectrometry (MS2 and/or MS3) performed using the CID technique (Collision Induced Dissociation with an inert gas, such as Ar). Experiments are performed at different excitation voltages and using different data representations such as the Survival Yield (rate of parent ions surviving the excitation process) or mass-energy diagrams (10.1021/ac902463q).
This method has been applied to various mixtures of biological and synthetic polymers including isobars and isomers (10.1021/acs.analchem.6b03490, 10.1039/c4py01087f). Chemometric tools (method validation, experimental design, data analysis and multivariate calibration …) are used to evaluate and improve its performances in various experimental conditions and types of samples.
- Electrochemical and molecular modeling combined with spectroelectrochemistry and mass spectrometry F. Gloaguen, A. Lebon, N. Le Poul, A. Memboeuf
Molecular catalysts for water splitting and CO2 and N2 electrochemical reduction are usually employed under varied experimental conditions (e.g. solvent and proton source), which make any rationalization of their intrinsic performances a difficult task. To decipher the effects of the nature on the metal center and of the steric and electronic properties of the ligands on the catalytic performances, we have developed mathematical models allowing for systematic analysis of electrochemical responses (10.1021/acs.inorgchem.5b02245). Besides, mechanistic studies usually achieved by electrochemistry are complemented with original results obtained from spectroelectrochemistry, mass spectrometry and molecular modeling (quantum chemistry and micro-kinetic calculations, 10.1021/acs.jpca.7b05399).
Optimization of catalytic performances can be achieved by implementation of the “reactive collisions”; a mass spectrometry technique that is able to provide a complete energetic diagram of the catalytic mechanism in gas phase using out-of-thermal equilibrium micro-kinetic modeling (10.1002/anie.201307745, 10.1016/j.ijms.2012.05.002). Then the effects of structural modifications of the catalyst on the kinetic and bottlenecks are more easily rationalized (10.1002/chem.201603518). Here we mainly focus on biomimetic systems in order support research of the team CIEl on “biomimetic activation”.
For the development of application solutions, it will be necessary to organize and assemble molecules to produce soft materials that retain catalytic properties. Different bottom-up approaches (e.g. SAM and chemical grafting) will be explored (10.1039/C5CP01210D). In this context, the new analytical techniques and mathematical models developed by the cross disciplinary sub-team “Spectroscopy and Reactivity” will be invaluable to improve fabrication process and to determine the structure/catalytic activity relationship of soft materials.