3D Coumarin Systems Based on [2.2]Paracyclophane Synthesis, Spectroscopic Characterization, and Chiroptical Properties

International audienceIn this article, we report the preparation of a series of [2.2]paracyclophane-fused coumarin systems through a simple and general procedure involving a transition-metal-catalyzed cyclization of aryl alkynoates as the key step. We also highlight the influence of the [2.2]paracyclophane (pCp) motif and its "phane" interactions on the spectroscopic properties of the newly synthesized fluorophores, which emit in the blue-green region of the visible spectrum (lambda(em), up to 560 nm) and show extremely large Stokes shifts (up to 230 nm). Finally, we demonstrate that our straightforward approach can easily be used to access optically active planar chiral 3D coumarins. Compared to previously described fluorescent paracyclophanes and other organic dyes, our compact heteroaromatic derivatives show promising chiroptical properties, both in term of circular dichroism (g(abs) similar to 8 x 10(-3)) and circularly polarized luminescence (g(lum) similar to 5 x 10(-3)), thus demonstrating a practical application of our synthetic method

Molecular approach to the synthesis and operation of cobalt hydroxyapatites : application to the selective activation of propane

L'hydroxyapatite (HAp) est un matériau bio et écocompatible dont l'attrait en catalyse hétérogène vient de la possibilité de moduler ses propriétés physico-chimiques par la synthèse. En particulier, sa modification par des métaux de transition permet de lui conférer des propriétés redox pour en faire un catalyseur hétérogène bifonctionnel. Dans un contexte d'écart croissant entre l'offre et la demande en propène, la réaction de déshydrogénation oxydante (DO) du propane suscite un regain d’intérêt et la faible réactivité du propane requiert le développement de catalyseurs permettant d'activer sélectivement la liaison C-H du propane sans suroxydation en CO et CO2. Ce travail de thèse s'intéresse ainsi à l'étude du système d'HAp modifiée au cobalt comme catalyseur de la réaction de DO du propane. L'influence de la thermodynamique et de la cinétique de la précipitation des phosphates de calcium a permis d’établir les chemins réactionnels vers différentes HAps et de rationaliser l’influence des paramètres de synthèse (pH, ordre d’introduction des réactifs, etc.) sur les propriétés structurales et texturales des supports (défauts, stœchiométrie, morphologie, surface spécifique). La modification de l'HAp calcique par le cobalt a ensuite été envisagée par dépôt sur des supports d'HAp et par précipitation. En fonction du pH, le dépôt de cations Co2+ à la surface de supports d'HAp procède par échange cationique (acide) ou complexation/adsorption électrostatique forte (basique). Ces différents mécanismes induisent, après traitement thermique, la formation respective d'espèces Co2+ isolées ou de particules d'oxyde à la surface de l'HAp. La précipitation de l'HAp en présence de cobalt permet quant à elle d'incorporer des cations Co2+ également au sein des cristallites d'HAp. Les performances catalytiques des deux séries d'échantillons (dépôt et précipitation) ont pu être comparées par atome de cobalt présent en surface grâce au développement d’une méthode de dosage basée sur la désorption en température programmée de NO. Alors que les particules d'oxyde de cobalt conduisent à une suroxydation du propane, les espèces redox Co2+ isolées à proximité d'un anion hydroxyde thermiquement activé en anion oxyde basique constituent des sites actifs sélectifs en propène impliqués dans un mécanisme du type Mars et van Krevelen. La conversion du propane en propène exprimée par la fréquence de rotation par atome de cobalt rivalise avec les meilleurs systèmes de la littérature et les catalyseurs les plus basiques préparés par échange cationique s'avèrent être les plus efficaces.Hydroxyapatite (HAp) is a bio and eco-compatible material whose attractiveness in heterogeneous catalysis comes from the possibility to modulate its physicochemical properties by synthesis. In particular, its modification by transition metals allows to confer redox properties to make it a bifunctional heterogeneous catalyst. In a context of increasing gap between the supply and the demand of propene, the oxidative dehydrogenation (ODH) reaction of propane is attracting a renewed interest and the low reactivity of propane requires the development of catalysts allowing to activate selectively the C-H bond of propane without overoxidation into CO and CO2. The aim of this PhD work is thus to study cobalt-modified HAp materials as catalysts for the ODH of propane. Firstly, the influence of thermodynamics and kinetics of calcium phosphate precipitation allowed to establish the reaction pathways to different HAps and to rationalize the influence of synthesis parameters (pH, order of introduction of reagents, etc.) on the structural and textural properties of the supports (defects, stoichiometry, morphology, specific surface). The modification of calcic HAp by cobalt was then considered by deposition on HAp supports and by precipitation. Depending on the pH, the deposition of Co2+ cations on the surface of these HAp supports proceeds by cationic exchange (acidic) or complexation/strong electrostatic adsorption (basic). After thermal treatment, these different mechanisms lead to the formation of isolated Co2+ species or oxide particles on the HAp surface, respectivly. The precipitation of HAp in the presence of cobalt allows the incorporation of Co2+ cations within the HAp crystallites. The catalytic performance of the two series (deposition and precipitation) could be compared by cobalt atom present on the surface thanks to the development of a titration method based on the temperature programmed desorption of NO. While cobalt oxide particles lead to the overoxidation of propane, redox isolated Co2+ species in the vicinity of a hydroxide anion thermally-activated to a basic oxide anion constitute propene-selective active sites involved in a Mars and van Krevelen mechanism. The conversion of propane to propene expressed as the turnover frequency per surface cobalt atom competes with the best catalysts reported in the literature to date and the most basic catalysts prepared by cation exchange are found to be the most efficient

Approche moléculaire de la synthèse et du mode de fonctionnement d’hydroxyapatites au cobalt : application à l’activation sélective du propane

Hydroxyapatite (HAp) is a bio and eco-compatible material whose attractiveness in heterogeneous catalysis comes from the possibility to modulate its physicochemical properties by synthesis. In particular, its modification by transition metals allows to confer redox properties to make it a bifunctional heterogeneous catalyst. In a context of increasing gap between the supply and the demand of propene, the oxidative dehydrogenation (ODH) reaction of propane is attracting a renewed interest and the low reactivity of propane requires the development of catalysts allowing to activate selectively the C-H bond of propane without overoxidation into CO and CO2. The aim of this PhD work is thus to study cobalt-modified HAp materials as catalysts for the ODH of propane. Firstly, the influence of thermodynamics and kinetics of calcium phosphate precipitation allowed to establish the reaction pathways to different HAps and to rationalize the influence of synthesis parameters (pH, order of introduction of reagents, etc.) on the structural and textural properties of the supports (defects, stoichiometry, morphology, specific surface). The modification of calcic HAp by cobalt was then considered by deposition on HAp supports and by precipitation. Depending on the pH, the deposition of Co2+ cations on the surface of these HAp supports proceeds by cationic exchange (acidic) or complexation/strong electrostatic adsorption (basic). After thermal treatment, these different mechanisms lead to the formation of isolated Co2+ species or oxide particles on the HAp surface, respectivly. The precipitation of HAp in the presence of cobalt allows the incorporation of Co2+ cations within the HAp crystallites. The catalytic performance of the two series (deposition and precipitation) could be compared by cobalt atom present on the surface thanks to the development of a titration method based on the temperature programmed desorption of NO. While cobalt oxide particles lead to the overoxidation of propane, redox isolated Co2+ species in the vicinity of a hydroxide anion thermally-activated to a basic oxide anion constitute propene-selective active sites involved in a Mars and van Krevelen mechanism. The conversion of propane to propene expressed as the turnover frequency per surface cobalt atom competes with the best catalysts reported in the literature to date and the most basic catalysts prepared by cation exchange are found to be the most efficient.L'hydroxyapatite (HAp) est un matériau bio et écocompatible dont l'attrait en catalyse hétérogène vient de la possibilité de moduler ses propriétés physico-chimiques par la synthèse. En particulier, sa modification par des métaux de transition permet de lui conférer des propriétés redox pour en faire un catalyseur hétérogène bifonctionnel. Dans un contexte d'écart croissant entre l'offre et la demande en propène, la réaction de déshydrogénation oxydante (DO) du propane suscite un regain d’intérêt et la faible réactivité du propane requiert le développement de catalyseurs permettant d'activer sélectivement la liaison C-H du propane sans suroxydation en CO et CO2. Ce travail de thèse s'intéresse ainsi à l'étude du système d'HAp modifiée au cobalt comme catalyseur de la réaction de DO du propane. L'influence de la thermodynamique et de la cinétique de la précipitation des phosphates de calcium a permis d’établir les chemins réactionnels vers différentes HAps et de rationaliser l’influence des paramètres de synthèse (pH, ordre d’introduction des réactifs, etc.) sur les propriétés structurales et texturales des supports (défauts, stœchiométrie, morphologie, surface spécifique). La modification de l'HAp calcique par le cobalt a ensuite été envisagée par dépôt sur des supports d'HAp et par précipitation. En fonction du pH, le dépôt de cations Co2+ à la surface de supports d'HAp procède par échange cationique (acide) ou complexation/adsorption électrostatique forte (basique). Ces différents mécanismes induisent, après traitement thermique, la formation respective d'espèces Co2+ isolées ou de particules d'oxyde à la surface de l'HAp. La précipitation de l'HAp en présence de cobalt permet quant à elle d'incorporer des cations Co2+ également au sein des cristallites d'HAp. Les performances catalytiques des deux séries d'échantillons (dépôt et précipitation) ont pu être comparées par atome de cobalt présent en surface grâce au développement d’une méthode de dosage basée sur la désorption en température programmée de NO. Alors que les particules d'oxyde de cobalt conduisent à une suroxydation du propane, les espèces redox Co2+ isolées à proximité d'un anion hydroxyde thermiquement activé en anion oxyde basique constituent des sites actifs sélectifs en propène impliqués dans un mécanisme du type Mars et van Krevelen. La conversion du propane en propène exprimée par la fréquence de rotation par atome de cobalt rivalise avec les meilleurs systèmes de la littérature et les catalyseurs les plus basiques préparés par échange cationique s'avèrent être les plus efficaces

A neurons-astrocyte network model: from synaptic boosting to epilepsy

Recent findings indicate that astrocytes might play a functional role in triggering epileptic seizures. To test both the role of astrocytes on neuronal firings under normal conditions and the role they could play in epilepsy, we build here a computational model where four neurons and an astrocyte interact. Based on a mathematical model previously described in the literature, our model allows to investigate the dynamics of neuronal firing in this mini-network. In particular, we describe the conditions that can lead to hypersynchronous firings

A Testing Framework for Background Subtraction Algorithms Comparison inIntrusion Detection Context

International audienceIdentifying objects from a video stream is a fundamentaland critical task in many computer-vision applications.A popular approach is the background subtraction, whichconsists in separating foreground (moving objects) frombackground. Many methodologies have been developed forautomatic background segmentation but this fundamentaltask is still challenging. We focus here on a particular applicationof computer vision: intrusion detection in videosurveillance.We propose in this paper a multi-level methodology forevaluating and comparing background subtraction algorithms.Three levels are studied: first, pixel level to evaluatethe accuracy of the segmentation algorithm to attribute theright class to each pixel. Second, image level, measuringthe rate of right decision on each frame (intrusion vs nointrusion) and finally sequence level, measuring the accordancewith the time span where objects appear. Moreover,we also propose a new similarity measure, called D-Score,adapted to the context of intrusion detection

Studying archaeological mineralised textiles. A perspective from sixteenth to nineteenth century scholars.

International audienceIn temperate latitudes, archaeological textiles are rarely found during excavations, except when they have been mineralised in contact with metal artefacts, copper or iron-based. Mineralised textiles are often the only direct source of information on the textile techniques and processes of ancient civilisations. Vivi Sylwan’s description of textiles along the Silk Road in the early 20th century is often considered the first detailed archaeological description of mineralised textiles, while the physico-chemist Leo Biek pioneered their microscopic description. In this paper, we examine how antiquaries and scholars from the 18th and the first half of the 19th century identified and studied the presence of textile remains on metal objects, seemingly aware of the significance of these findings. These descriptions share common concepts and vocabulary with writings from the 16th to the early 18th century on petrification of wood. The authors not only show an awareness of and an interest in textile remains, but also question, including experimentally, the process of mineralisation, shaping the modern perception of it with concepts such as “transmutation” or “imprinting”. These ancient sources had a lasting impact on our contemporary appraisal of these materials, as we shall discuss in the second stage of this review, which will be devoted to contemporary methods of studying archaeological mineralised textiles

Croissance de nanotubes de carbone alignés verticalement sur feuilles d’aluminium pour application supercondensateurs : synthèse en une étape, à partir de précurseurs biosourcés et caractérisation électrochimique

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Vertically aligned carbon naanotubes on aluminum foils: one-step synthesis from bio-sourced precursors and electrochemical characterization

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Volatile organic compounds identification and specific stable isotopic analysis (δ13C) in microplastics by purge and trap gas chromatography coupled to mass spectrometry and combustion isotope ratio mass spectrometry (PT-GC-MS-C-IRMS)

Microplastics (MPs) have become one of the major global environmental issues in recent decades due to their ubiquity in the environment. Understanding MPs source origin and reactivity is urgently needed to better constrain their fate and budget. Despite improvements in analytical methods to characterize MPs, new tools are needed to help understand their sources and reactivity in a complex environment. In this work, we developed and applied an original Purge-&-Trap system coupled to a GC–MS-C-IRMS to explore the δ13C compound-specific stable isotope analysis (CSIA) of volatile organic compounds (VOC) embedded in MPs. The method consists of heating and purging MP samples, with VOCs being cryo-trapped on a Tenax sorbent, followed by GC–MS-C-IRMS analysis. The method was developed using a polystyrene plastic material showing that sample mass and heating temperature increased the sensitivity while not influencing VOC δ13C values. This robust, precise, and accurate methodology allows VOC identification and δ13C CSIA in plastic materials in the low nanogram concentration range. Results show that the monomer styrene displays a different δ13C value (− 22.2 ± 0.2‰), compared to the δ13C value of the bulk polymer sample (− 27.8 ± 0.2‰). This difference could be related to the synthesis procedure and/or diffusion processes. The analysis of complementary plastic materials such as polyethylene terephthalate, and polylactic acid displayed unique VOC δ13C patterns, with toluene showing specific δ13C values for polystyrene (− 25.9 ± 0.1‰), polyethylene terephthalate (− 28.4 ± 0.5‰), and polylactic acid (− 38.7 ± 0.5‰). These results illustrate the potential of VOC δ13C CSIA in MP research to fingerprint plastic materials, and to improve our understanding of their source cycle. Further studies in the laboratory are needed to determine the main mechanisms responsible for MPs VOC stable isotopic fractionation

International study day on "New research on mineralised textiles"

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