21 research outputs found
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 matĂ©riau bio et Ă©cocompatible dont l'attrait en catalyse hĂ©tĂ©rogĂšne vient de la possibilitĂ© de moduler ses propriĂ©tĂ©s physico-chimiques par la synthĂšse. En particulier, sa modification par des mĂ©taux de transition permet de lui confĂ©rer des propriĂ©tĂ©s redox pour en faire un catalyseur hĂ©tĂ©rogĂšne bifonctionnel. Dans un contexte d'Ă©cart croissant entre l'offre et la demande en propĂšne, la rĂ©action de dĂ©shydrogĂ©nation oxydante (DO) du propane suscite un regain dâintĂ©rĂȘt et la faible rĂ©activitĂ© du propane requiert le dĂ©veloppement de catalyseurs permettant d'activer sĂ©lectivement la liaison C-H du propane sans suroxydation en CO et CO2. Ce travail de thĂšse s'intĂ©resse ainsi Ă l'Ă©tude du systĂšme d'HAp modifiĂ©e au cobalt comme catalyseur de la rĂ©action de DO du propane. L'influence de la thermodynamique et de la cinĂ©tique de la prĂ©cipitation des phosphates de calcium a permis dâĂ©tablir les chemins rĂ©actionnels vers diffĂ©rentes HAps et de rationaliser lâinfluence des paramĂštres de synthĂšse (pH, ordre dâintroduction des rĂ©actifs, etc.) sur les propriĂ©tĂ©s structurales et texturales des supports (dĂ©fauts, stĆchiomĂ©trie, morphologie, surface spĂ©cifique). La modification de l'HAp calcique par le cobalt a ensuite Ă©tĂ© envisagĂ©e par dĂ©pĂŽt sur des supports d'HAp et par prĂ©cipitation. En fonction du pH, le dĂ©pĂŽt de cations Co2+ Ă la surface de supports d'HAp procĂšde par Ă©change cationique (acide) ou complexation/adsorption Ă©lectrostatique forte (basique). Ces diffĂ©rents mĂ©canismes induisent, aprĂšs traitement thermique, la formation respective d'espĂšces Co2+ isolĂ©es ou de particules d'oxyde Ă la surface de l'HAp. La prĂ©cipitation de l'HAp en prĂ©sence de cobalt permet quant Ă elle d'incorporer des cations Co2+ Ă©galement au sein des cristallites d'HAp. Les performances catalytiques des deux sĂ©ries d'Ă©chantillons (dĂ©pĂŽt et prĂ©cipitation) ont pu ĂȘtre comparĂ©es par atome de cobalt prĂ©sent en surface grĂące au dĂ©veloppement dâune mĂ©thode de dosage basĂ©e sur la dĂ©sorption en tempĂ©rature programmĂ©e de NO. Alors que les particules d'oxyde de cobalt conduisent Ă une suroxydation du propane, les espĂšces redox Co2+ isolĂ©es Ă proximitĂ© d'un anion hydroxyde thermiquement activĂ© en anion oxyde basique constituent des sites actifs sĂ©lectifs en propĂšne impliquĂ©s dans un mĂ©canisme du type Mars et van Krevelen. La conversion du propane en propĂšne exprimĂ©e par la frĂ©quence de rotation par atome de cobalt rivalise avec les meilleurs systĂšmes de la littĂ©rature et les catalyseurs les plus basiques prĂ©parĂ©s par Ă©change cationique s'avĂšrent ĂȘtre 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 molĂ©culaire de la synthĂšse et du mode de fonctionnement dâhydroxyapatites au cobalt : application Ă lâactivation sĂ©lective 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 matĂ©riau bio et Ă©cocompatible dont l'attrait en catalyse hĂ©tĂ©rogĂšne vient de la possibilitĂ© de moduler ses propriĂ©tĂ©s physico-chimiques par la synthĂšse. En particulier, sa modification par des mĂ©taux de transition permet de lui confĂ©rer des propriĂ©tĂ©s redox pour en faire un catalyseur hĂ©tĂ©rogĂšne bifonctionnel. Dans un contexte d'Ă©cart croissant entre l'offre et la demande en propĂšne, la rĂ©action de dĂ©shydrogĂ©nation oxydante (DO) du propane suscite un regain dâintĂ©rĂȘt et la faible rĂ©activitĂ© du propane requiert le dĂ©veloppement de catalyseurs permettant d'activer sĂ©lectivement la liaison C-H du propane sans suroxydation en CO et CO2. Ce travail de thĂšse s'intĂ©resse ainsi Ă l'Ă©tude du systĂšme d'HAp modifiĂ©e au cobalt comme catalyseur de la rĂ©action de DO du propane. L'influence de la thermodynamique et de la cinĂ©tique de la prĂ©cipitation des phosphates de calcium a permis dâĂ©tablir les chemins rĂ©actionnels vers diffĂ©rentes HAps et de rationaliser lâinfluence des paramĂštres de synthĂšse (pH, ordre dâintroduction des rĂ©actifs, etc.) sur les propriĂ©tĂ©s structurales et texturales des supports (dĂ©fauts, stĆchiomĂ©trie, morphologie, surface spĂ©cifique). La modification de l'HAp calcique par le cobalt a ensuite Ă©tĂ© envisagĂ©e par dĂ©pĂŽt sur des supports d'HAp et par prĂ©cipitation. En fonction du pH, le dĂ©pĂŽt de cations Co2+ Ă la surface de supports d'HAp procĂšde par Ă©change cationique (acide) ou complexation/adsorption Ă©lectrostatique forte (basique). Ces diffĂ©rents mĂ©canismes induisent, aprĂšs traitement thermique, la formation respective d'espĂšces Co2+ isolĂ©es ou de particules d'oxyde Ă la surface de l'HAp. La prĂ©cipitation de l'HAp en prĂ©sence de cobalt permet quant Ă elle d'incorporer des cations Co2+ Ă©galement au sein des cristallites d'HAp. Les performances catalytiques des deux sĂ©ries d'Ă©chantillons (dĂ©pĂŽt et prĂ©cipitation) ont pu ĂȘtre comparĂ©es par atome de cobalt prĂ©sent en surface grĂące au dĂ©veloppement dâune mĂ©thode de dosage basĂ©e sur la dĂ©sorption en tempĂ©rature programmĂ©e de NO. Alors que les particules d'oxyde de cobalt conduisent Ă une suroxydation du propane, les espĂšces redox Co2+ isolĂ©es Ă proximitĂ© d'un anion hydroxyde thermiquement activĂ© en anion oxyde basique constituent des sites actifs sĂ©lectifs en propĂšne impliquĂ©s dans un mĂ©canisme du type Mars et van Krevelen. La conversion du propane en propĂšne exprimĂ©e par la frĂ©quence de rotation par atome de cobalt rivalise avec les meilleurs systĂšmes de la littĂ©rature et les catalyseurs les plus basiques prĂ©parĂ©s par Ă©change cationique s'avĂšrent ĂȘtre 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 Sylwanâs 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 âtransmutationâ or âimprintingâ. 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 alignĂ©s verticalement sur feuilles dâaluminium pour application supercondensateurs : synthĂšse en une Ă©tape, Ă partir de prĂ©curseurs biosourcĂ©s et caractĂ©risation Ă©lectrochimique
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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 (ÎŽ13C) 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 GCâMS-C-IRMS to explore the ÎŽ13C 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 GCâMS-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 ÎŽ13C values. This robust, precise, and accurate methodology allows VOC identification and ÎŽ13C CSIA in plastic materials in the low nanogram concentration range. Results show that the monomer styrene displays a different ÎŽ13C value (â 22.2 ± 0.2â°), compared to the ÎŽ13C value of the bulk polymer sample (â 27.8 ± 0.2â°). 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 ÎŽ13C patterns, with toluene showing specific ÎŽ13C values for polystyrene (â 25.9 ± 0.1â°), polyethylene terephthalate (â 28.4 ± 0.5â°), and polylactic acid (â 38.7 ± 0.5â°). These results illustrate the potential of VOC ÎŽ13C 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