Ecole normale supérieure de Cachan
Recent publications
Countless people have been affected by the COVID‐19 pandemic on a global scale. Favipiravir, has shown potential as an effective drug for SARS‐CoV‐2, attracting scientists’ attention. However, overuse of Favipiravir easily leads to serious side effects, requiring real‐time monitoring in body fluids. Given this, a new lanthanide metal organic framework (MOF) was prepared under solvothermal conditions from either Eu (Eu‐MOF or (1)) or Tb (Tb‐MOF or (2)) using the highly delocalized imidazoledicarboxylic acid linker H2L (H2L = 5‐(4‐(imidazol‐1‐yl) phenyl) isophthalic acid) and could be successfully applied to selective optical detection of Favipiravir. In this MOF framework, the organic linker H2L provides a high excitation energy transfer efficiency that can sensitize luminescence in lanthanides. In addition, through deliberate tuning of Eu/Tb molar ratio and reaction concentration in the lanthanide framework, ratiometric recyclable luminescent EuxTb1‐x‐MOF nanoparticles with open metal sites have been constructed, which present a high detection sensitivity (Ksv = 1×107 [M‐1], detection limit is 4.63 nM) for Favipiravir. The detection mechanism is discussed with the help of Density Functional Theory (DFT) calculations that sheds light over the selective sensing of Favipiravir over other related COVID‐19 drug candidates. Finally, to explore the practical application of Favipiravir sensing, MOF based thin films have been used for visual detection of Favipiravir and recycled 5 times.
Encapsulating ultrasmall Cu nanoparticles inside Zr‐MOFs to form core‐shell architecture is very challenging while of interest for CO 2 reduction. We report for the first time the incorporation of ultrasmall Cu NCs into series of benchmarks Zr‐MOFs without Cu NCs aggregation via a scalable room temperature fabrication approach. The Cu NCs@MOFs core‐shell composites show much enhanced reactivity in comparison to the Cu NCs confined in the pore of MOFs regardless of their very similar intrinsic properties at atomic level. Moreover, introducing polar groups on the MOF structure can further improve both the catalytic reactivity and selectivity. Mechanistic investigation reveals that the Cu(I) sites located at the interface between Cu NCs and support serve as the active sites and efficiently catalyze the CO 2 photoreduction. This synergetic effect may pave the way for the design of low‐cost and efficient catalysts for the CO 2 photoreduction into high‐value chemical feedstock.
Encapsulating ultrasmall Cu nanoparticles inside Zr‐MOFs to form core‐shell architecture is very challenging while of interest for CO 2 reduction. We report for the first time the incorporation of ultrasmall Cu NCs into series of benchmarks Zr‐MOFs without Cu NCs aggregation via a scalable room temperature fabrication approach. The Cu NCs@MOFs core‐shell composites show much enhanced reactivity in comparison to the Cu NCs confined in the pore of MOFs regardless of their very similar intrinsic properties at atomic level. Moreover, introducing polar groups on the MOF structure can further improve both the catalytic reactivity and selectivity. Mechanistic investigation reveals that the Cu(I) sites located at the interface between Cu NCs and support serve as the active sites and efficiently catalyze the CO 2 photoreduction. This synergetic effect may pave the way for the design of low‐cost and efficient catalysts for the CO 2 photoreduction into high‐value chemical feedstock.
We introduce HIGHLIGHT as a simple and general strategy to selectively image a reversibly photoactivatable fluorescent label associated with a given kinetics. The label is submitted to sine‐wave illumination of large amplitude, which generates oscillations of its concentration and fluorescence at higher harmonic frequencies. For singularizing a label, HIGHLIGHT uses specific frequencies and mean light intensities associated with resonances of the amplitudes of concentration and fluorescence oscillations at harmonic frequencies. Several non‐redundant resonant observables are simultaneously retrieved from a single experiment with phase‐sensitive detection. HIGHLIGHT is used for selective imaging of four spectrally similar fluorescent proteins that had not been discriminated so far. Moreover, labels out of targeted locations can be discarded in an inhomogeneous spatial profile of illumination. HIGHLIGHT opens roads for simplified optical setups at reduced cost and easier maintenance.
A new heteronuclear decoupling pulse sequence is introduced, dubbed ROtor-Synchronized Phase-Alternated Cycles (ROSPAC). It is based on a partial refocusing of the coherences (spin operator products, or cross-terms) 1,2 responsible for transverse spin-polarization dephasing, on the irradiation of a large pattern of radio-frequencies, and on a significant minimization of the cross-effects implying ¹ H chemical-shift anisotropy. Decoupling efficiency is analyzed by numerical simulations and experiments, and compared to that of established decoupling sequences (swept-frequency TPPM, TPPM, SPINAL, rCW Apa , and RS-HEPT). It was found that ROSPAC offers good ¹ H offset robustness for a large range of chemical shifts and low radio-frequency (RF) powers, and performs very well in the ultra-fast MAS regime, where it is almost independent from RF power and permits it to avoid rotary-resonance recoupling conditions ( ). It has the advantage that only the pulse lengths require optimization, and has a low duty cycle in the pulsed decoupling regime. The efficiency of the decoupling sequence is demonstrated on a model microcrystalline sample of the model protein domain GB 1 at 100 kHz MAS at 18.8 T.
The detection and quantification of exogenous metal complexes are crucial to understanding their activity in complex biological media. Mn(II) complexes are difficult to detect and quantify because of low association constants, high lability, and fast metal exchange. The superoxide dismutase (SOD) mimic (or mimetic) labelled Mn1 is based on a 1,2‐di‐aminoethane functionalized with imidazole and phenolate and has good intrinsic anti‐superoxide, antioxidant and anti‐inflammatory activities in lipopolysaccharide (LPS)‐activated intestinal epithelial HT29‐MD2 cells, similar to that of its propylated analogue labelled Mn1P. Ion mobility spectrometry‐mass spectrometry (IMS‐MS) is a powerful technique for separating low molecular weight (LMW) metal complexes and can even separate complexes with the same ligand but bound to different divalent metal cations with similar ionic radii. We demonstrated the intracellular presence of the Mn1 and Mn1P complexes, at least partly intact, in lysates of cells incubated with the complexes and estimated the intracellular Mn1P concentration using a Co‐ 13 C 6 analogue.
The detection and quantification of exogenous metal complexes are crucial to understanding their activity in complex biological media. Mn(II) complexes are difficult to detect and quantify because of low association constants, high lability, and fast metal exchange. The superoxide dismutase (SOD) mimic (or mimetic) labelled Mn1 is based on a 1,2‐di‐aminoethane functionalized with imidazole and phenolate and has good intrinsic anti‐superoxide, antioxidant and anti‐inflammatory activities in lipopolysaccharide (LPS)‐activated intestinal epithelial HT29‐MD2 cells, similar to that of its propylated analogue labelled Mn1P. Ion mobility spectrometry‐mass spectrometry (IMS‐MS) is a powerful technique for separating low molecular weight (LMW) metal complexes and can even separate complexes with the same ligand but bound to different divalent metal cations with similar ionic radii. We demonstrated the intracellular presence of the Mn1 and Mn1P complexes, at least partly intact, in lysates of cells incubated with the complexes and estimated the intracellular Mn1P concentration using a Co‐ 13 C 6 analogue.
Mechanisms combining organic radicals and metallic intermediates hold strong potential in homogeneous catalysis. Such activation modes require careful optimization of two interconnected processes: one for the generation of radicals and one for their productive integration towards the final product. We report that a bioinspired polymetallic nickel complex can combine ligand‐ and metal‐centered reactivities to perform fast hydrosilylation of alkenes under mild conditions through an unusual dual radical‐ and metalbased mechanism. This earth‐abundant polymetallic complex incorporating a catechol‐alloxazine motif as redox‐active ligand operates at low catalyst loading (0.25 mol%) and generates silyl radicals and a nickel‐hydride intermediate through a hydrogen atom transfer (HAT) step. Evidence of an isomerization sequence enabling terminal hydrosilylation of internal alkenes points towards the involvement of the nickel‐hydride species in chain walking. This single catalyst promotes a hybrid pathway by combining synergistically ligand and metal participation in both inner‐ and outer‐ sphere processes.
Triphenylamine (TP) derivatives such as two-branch cationic vinylbenzimidazolium triphenylamine TP-2Bzim are promising turn-on fluorescent probes suitable for two-photon imaging, labelling mitochondria in live cells. Here, we designed two TP-2Bzim derivatives as bimodal probes suitable for X-ray fluorescence imaging. The conjugation of the TP core with a rhenium tricarbonyl moiety in the TP-RePyta probe altered the localisation in live cells from mitochondria to lysosomes. The introduction of bromine on the TP core generated the TP-Br probe retaining good photophysical properties and mitochondria labeling in live cells. The influence of calcium channels in the uptake of TP-Br was studied. Synchrotron Radiation X-ray Fluorescence (SXRF) imaging of bromine enabled the detection of TP-Br and suggested a negligible presence of the probe in an unbound state in the incubated cells, a crucial point in the development of these probes. This study paves the way towards the development of TP probes as specific organelle stainers suitable for SXRF imaging.
Red-to-NIR absorption and emission wavelengths are key requirements for intravital bioimaging. One of the way to reach such excitation wavelengths is to use two-photon excitation. Unfortunately, there is still a lack of two-photon excitable fluorophores that are both efficient and biocompatible. Thus, we design a series of biocompatible quadrupolar dyes in order to study their ability to be used for live-cell imaging, and in particular for two-photon microscopy. Hence, we report the synthesis of 5 probes based on different donor cores (phenoxazine, acridane, phenazasiline and phenothiazine) and the study of their linear and non-linear photophysical properties. TD-DFT calculations were performed and were able to highlight the structure-property relationship of this series. All these studies highlight the great potential of three of these biocompatible dyes for two-photon microscopy, as they both exhibit high two-photon cross-sections (up to 3650 GM) and emit orange to red light. This potential was confirmed through live-cell two-photon microscopy experiments, leading to images with very high brightness and contrast.
The emergence of new piezoelectric materials makes it possible to offer high performances in terms of power densities and integration. These new materials can be used in DC-DC power converters as a solution to replace the magnetic components and to meet the growth in demand of miniaturization, high power densities and high efficiency applications. This paper deals with a new topology of a DC-DC converter based on piezoelectric resonator . The conversion mechanism, based on energy and charge balance, is explained in details through an analytical model and validated by experimental results. A prototype has been designed for an input-output voltage up to 250-125 V and a power range of 100 W. It provides an efficiency higher than 93% for wide operating points in radial mode vibration. As an example, we obtain an efficiency 93.8 % of for 250 -117 V input-output voltage at 50 W output power. In addition, the thickness mode operation is experimentally validated at 1 MHz, and exhibited a peak output power of 175 W with an efficiency of 80 % for 200 60 V input-output voltage. The experimental results show the promising performances of the proposed DC-DC power converter based on piezoelectric resonator for high- to-low voltage, high efficiency and low-to-medium power applications.
Richard Ernst, Pionier der NMR-Spektroskopie und Chemie-Nobelpreisträger, ist am 4. Juni 2021 in seiner Geburtsstadt Winterthur verstorben. Er war an der Entwicklung der Puls-Fourier-Transform-NMR-Spektroskopie beteiligt und realisierte die zwei- und später mehrdimensionale NMR-Spektroskopie. Seine Arbeiten bilden die Grundlage für die heutige Nutzung der NMR-Spektroskopie zur Untersuchung von Materialien und chemisch und biologisch relevanten Molekülen.
Pharmacological inactivation of antitumor drugs toward healthy cells is a critical factor in prodrug development. Typically, pharmaceutical chemists graft temporary moieties to existing antitumor drugs to reduce their pharmacological activity as much as possible. Here, we report a platform where the structure of the prodrug excludes the preexisting antitumor drug motif and is based on an inactive synthetic precursor able to generate the cytotoxic agent by bioorthogonal cyclization within a tumor environment. Using phenanthridines as cytotoxic model compounds, we designed ring-opened biaryl precursors that generated the phenanthridines through bioorthogonal irreversible imination. This reaction was triggered by reactive oxygen species, commonly overproduced in cancer cells, able to convert a vinyl boronate ester function into a ketone that subsequently reacted with a pendant aniline. An inactive precursor was shown to engender a cytotoxic phenanthridine against KB cancer cells. Moreover, the kinetic of cyclization of this prodrug was extremely rapid (˂ 10 ms) inside living cells of KB cancer spheroids so as to circumvent drug action.
Pharmacological inactivation of antitumor drugs toward healthy cells is a critical factor in prodrug development. Typically, pharmaceutical chemists graft temporary moieties to existing antitumor drugs to reduce their pharmacological activity as much as possible. Here, we report a platform where the structure of the prodrug excludes the preexisting antitumor drug motif and is based on an inactive synthetic precursor able to generate the cytotoxic agent by bioorthogonal cyclization within a tumor environment. Using phenanthridines as cytotoxic model compounds, we designed ring‐opened biaryl precursors that generated the phenanthridines through bioorthogonal irreversible imination. This reaction was triggered by reactive oxygen species, commonly overproduced in cancer cells, able to convert a vinyl boronate ester function into a ketone that subsequently reacted with a pendant aniline. An inactive precursor was shown to engender a cytotoxic phenanthridine against KB cancer cells. Moreover, the kinetic of cyclization of this prodrug was extremely rapid (˂ 10 ms) inside living cells of KB cancer spheroids so as to circumvent drug action.
The main protease of SARS-CoV-2 (called Mpro or 3CLpro) is essential for processing polyproteins encoded by viral RNA. Macromolecules adopt several favored conformations in solution depending on their structure and shape, determining their dynamics and function. Integrated methods combining the lowest-frequency movements obtained by Normal Mode Analysis (NMA), and the faster movements from Molecular Dynamics (MD), and data from biophysical techniques, are necessary to establish the correlation between complex structural dynamics of macromolecules and their function. In this article, we used a hybrid simulation method to sample the conformational space to characterize the structural dynamics and global motions of WT SARS-CoV-2 Mpro and 48 mutants, including several mutations that appear in P.1, B.1.1.7, B.1.351, B.1.525 and B.1.429+B.1.427 variants. Integrated Hybrid methods combining NMA and MD have been useful to study the correlation between the complex structural dynamics of macromolecules and their functioning mechanisms. Here, we applied this hybrid approach to elucidate the effects of mutation in the structural dynamics of SARS-CoV-2 Mpro, considering their flexibility, solvent accessible surface area analyses, global movements, and catalytic dyad distance. Furthermore, some mutants showed significant changes in their structural dynamics and conformation, which could lead to distinct functional properties.
Liquid water confined within nanometer‐sized channels exhibits a strongly reduced local dielectric constant perpendicularly to the wall, especially at the interface, and this has been suggested to induce faster electron transfer kinetics at the interface than in the bulk. We study a model electron transfer reaction in aqueous solution confined between graphene sheets with classical molecular dynamics. We show that the solvent reorganization energy is reduced at the interface compared to the bulk, which explains the larger rate constant. However, this facilitated solvent reorganization is due to the partial desolvation by the graphene sheet of the ions involved in the electron transfer and not to a local dielectric constant reduction effect.
Resumo: A obra de Afrikan Spir é uma importante fonte para entender a discussão de Nietzsche com a filosofia crítica. Ele procura superar a crítica transcendental através de uma investigação genética sobre a origem dos conceitos; ao mesmo tempo, tenta revelar os preconceitos e as idiossincrasias que se ocultam por detrás da vontade de manter a cisão entre mundo fenomenal e mundo numenal. A aversão pela mudança, pelo vir-a-ser, pelo testemunho dos sentidos, a predileção por verdades lógicas e conceitos contraditórios constituem, segundo Nietzsche, a forma específica de superstição dos filósofos críticos, dos quais a filosofia de Spir é o exemplo mais consequente.
With the widespread application of convolutional neural networks (CNNs), the traditional model based denoising algorithms are now outperformed. However, CNNs face two problems. First, they are computationally demanding, which makes their deployment especially difficult for mobile terminals. Second, experimental evidence shows that CNNs often over-smooth regular textures present in images, in contrast to traditional non-local models. In this letter, we propose a solution to both issues by combining a nonlocal algorithm with a lightweight residual CNN. s solution gives full latitude to the advantages of both models. We apply this framework to two GPU implementations of classic nonlocal algorithms (NLM and BM3D) and observe a substantial gain in both cases, performing better than the state-of-the-art with low computational requirements. Our solution is between 10 and 20 times faster than CNNs with equivalent performance and attains higher PSNR. In addition the final method shows a notable gain on images containing complex textures like the ones of the MIT Moiré dataset.
Among all the chemical and biotechnological strategies implemented to extract energy from oxygenic photosynthesis, several concern the use of intact photosynthetic organisms (algae, cyanobacteria…). This means rerouting (fully or partially) the electron flow from the photosynthetic chain to an outer collecting electrode generating thus a photocurrent. While diverting photosynthetic electrons from living biological systems is an encouraging approach, this strategy is limited by the need to use an electron shuttle. Redox mediators that are able to interact with an embedded photosynthetic chain are rather scarce. In this respect, exogenous quinones are the most frequently used. Unfortunately, some of them also act as poisoning agents within relatively long timeframes. It thus raises the question of the best quinone. In this work, we use a previously reported electrochemical device to analyze the performances of different quinones. Photocurrents (maximum photocurrent, stability) were measured from suspensions of Chlamydomonas reinhardtii algae/quinones by chronoamperometry and compared to parameters like quinone redox potentials or cytotoxic concentration. From these results, several quinones were synthesized and analyzed in order to find the best compromise between bioelectricity production and toxicity.
Hybrid excited synchronous machines (HESM) combine permanent-magnet (PM) excitation and wound field (WF) excitation. The goal of hybrid excitation is to combine the advantages of PM excited machines and wound field synchronous machines. HESM have been identified as one of the emerging technologies for modern energy conversion systems. They have been the subject of many review papers. The principle of hybrid excitation allows solving many drawbacks related to permanent magnet electric machines operation: flux weakening, energy efficiency, and permanent magnets price fluctuation. It helps to introduce an additional degree of freedom in the design of synchronous machines, and allows therefore an easier adaptation of PM synchronous machines to a wider applications scope. To this additional degree corresponds the possibility of adjusting the contribution of the two magnetic field sources, PM and WF. The use of this technology for electric traction has been the subject of many scientific and technical contributions. In this contribution, the emphasis will be put on the use of these machines as generators in transportation applications and renewable energy applications. The design and operation of three particular structures will be presented. Two of them have been designed as generators for transportation applications, and the third one has been designed as generator for renewable energy conversion. All of them are flux switching hybrid excited synchronous structures (FSHESM).
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Nabil Anwer
  • Automated Production Research Laboratory
Sylvie Noelle Pommier
  • Laboratoire de mécanique et de Technologie - LMT
Jacques A Delaire
  • Department of Chemistry
Jacques Prioux
  • Sciences Du Sport Et Education Physique (2SEP)
Michel Arock
  • Laboratoire de biologie et de pharmacologie appliquee
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Cachan, France