Search

Your search keyword '"Costentin, Guylène"' showing total 150 results
Start Over Author "Costentin, Guylène"
150 results on '"Costentin, Guylène"'

5. Acidic Osteoid Templates the Plywood Structure of Bone Tissue

Author

Robin, Marc, primary, Djediat, Chakib, additional, Bardouil, Arnaud, additional, Baccile, Niki, additional, Chareyron, Camille, additional, Zizak, Ivo, additional, Fratzl, Peter, additional, Selmane, Mohamed, additional, Haye, Bernard, additional, Genois, Isabelle, additional, Krafft, Jean‐Marc, additional, Costentin, Guylène, additional, Azaïs, Thierry, additional, Artzner, Franck, additional, Giraud‐Guille, Marie‐Madeleine, additional, Zaslansky, Paul, additional, and Nassif, Nadine, additional

Published
2023
Full Text
View/download PDF

6. Acidic Osteoid Templates the Plywood Structure of Bone Tissue.

Author

Robin, Marc, Djediat, Chakib, Bardouil, Arnaud, Baccile, Niki, Chareyron, Camille, Zizak, Ivo, Fratzl, Peter, Selmane, Mohamed, Haye, Bernard, Genois, Isabelle, Krafft, Jean‐Marc, Costentin, Guylène, Azaïs, Thierry, Artzner, Franck, Giraud‐Guille, Marie‐Madeleine, Zaslansky, Paul, and Nassif, Nadine

Subjects
PLYWOOD, GLYCOSAMINOGLYCANS, LIQUID crystals, COMPACT bone, CANCELLOUS bone, COLLAGEN
Abstract

Bone is created by osteoblasts that secrete osteoid after which an ordered texture emerges, followed by mineralization. Plywood geometries are a hallmark of many trabecular and cortical bones, yet the origin of this texturing in vivo has never been shown. Nevertheless, extensive in vitro work revealed how plywood textures of fibrils can emerge from acidic molecular cholesteric collagen mesophases. This study demonstrates in sheep, which is the preferred model for skeletal orthopaedic research, that the deeper non‐fibrillar osteoid is organized in a liquid‐crystal cholesteric geometry. This basophilic domain, rich in acidic glycosaminoglycans, exhibits low pH which presumably fosters mesoscale collagen molecule ordering in vivo. The results suggest that the collagen fibril motif of twisted plywood matures slowly through self‐assembly thermodynamically driven processes as proposed by the Bouligand theory of biological analogues of liquid crystals. Understanding the steps of collagen patterning in osteoid‐maturation processes may shed new light on bone pathologies that emerge from collagen physico‐chemical maturation imbalances. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

22. Controlled Formation of Native Defects in Ultrapure ZnO for the Assignment of Green Emissions to Oxygen Vacancies

Author

Averseng, Fredeŕic, Zhang, Miao, Averseng, Frederic, Krafft, Jean-Marc, Borghetti, Patrizia, Costentin, Guylène, Stankic, Slavica, Laboratoire de Réactivité de Surface (LRS), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Institut des Nanosciences de Paris (INSP), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), and Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Materials science, chemistry.chemical_element, 02 engineering and technology, [CHIM.MATE]Chemical Sciences/Material chemistry, 010402 general chemistry, 021001 nanoscience & nanotechnology, 01 natural sciences, Crystallographic defect, Oxygen, 0104 chemical sciences, Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials, General Energy, Chemical engineering, chemistry, [CHIM]Chemical Sciences, Physical and Theoretical Chemistry, 0210 nano-technology
Abstract

International audience; Ultrapure ZnO nanopowders were synthesized via vapor-phase based methods under oxygen deficient conditions. The type and relative proportions of intrinsic point defects were studied by photoluminescence (PL) and EPR spectroscopies performed under strictly controlled conditions. Besides coupled PL/EPR signals recently assigned to Zni + (2.80 eV / g=1.96) two green emissions were systematically detected at 2.50 eV and 2.22 eV without EPR counterparts whereas their contributions were observed to depend on synthesis' oxygen partial pressure (PO2). Among diamagnetic defects likely to be formed in O2-poor conditions, Zni 0 and Zni 2+ were discarded based on their reported energy levels-with transitions associated rather to match the violet light. Conversely, the involvement of oxygen vacancies (VO 0 and VO 2+) as recombination centers for the green emission in ZnO was supported by Raman and XPS data. In line with the expected trends based on formation energies, the always dominant green luminescence (2.50 eV) was assigned to VO 2+ and the weaker one (2.22 eV) to VO 0. The involvement of an electron containing defect (VO 0) was confirmed by visible light absorption observed in DR UV-Vis spectra. We also showed that the Zni + / VO 2+ ratio can be tuned by PO2 or by the choice of static or flow synthesis conditions. Overall, this study demonstrates that by controlling the conditions during synthesis, processing and spectroscopic investigations, the 2 ultrapure ZnO nanopowders represent reliable models for the identification of photoluminescent crystal defects-an approach that can be widely applied on other systems.

Published
2020

34. Synergistic Effect Between Ca4V4O14 and Vanadium‐Substituted Hydroxyapatite in the Oxidative Dehydrogenation of Propane.

Author

Petit, Sarah, Thomas, Cyril, Millot, Yannick, Averseng, Frederic, Brouri, Dalil, Krafft, Jean‐Marc, Dzwigaj, Stanislaw, Rousse, Gwenaelle, Laberty‐Robert, Christel, and Costentin, Guylène

Subjects
OXIDATIVE dehydrogenation, CATALYSTS, HYDROXYAPATITE, PROPANE, ELECTRON delocalization, INTIMACY (Psychology)
Abstract

The present work reports on a new type of V‐based catalysts, namely V‐substituted hydroxyapatites, and the influence of the synthesis conditions on their catalytic performance in the oxidative dehydrogenation of propane (ODHP) reaction. Vx‐substituted hydroxyapatite materials prepared with the periodic addition of ammonia during the maturation step (Vx‐HAp‐pH‐per) were shown to exhibit a Ca4V4O14 phase in addition to the V‐substituted hydroxyapatite phase for x greater than or equal to 3.5. TEM characterization of the biphasic samples allowed us to demonstrate that the Ca4V4O14 phase was grown epitaxially on the Vx‐HAp nanorods. The close intimacy between the two phases was confirmed by NMR suggesting the involvement of V4+ species. Consistently EPR data of the fresh and spent samples showed that V4+ species may be stabilized at the boundaries of these two phases. The strong promotion of the oxidative dehydrogenation reaction to propene observed from 723 K for the V4‐HAp‐pH‐per composition is attributed to a synergistic effect between the Vx‐HAp nanorods that enable the activation of propane and the Ca4V4O14 phase that helps the redox exchanges. This synergy may be attributed to an easier electron delocalization on the V4O14 units located at the phases' boundaries. [ABSTRACT FROM AUTHOR]

Published
2021
Full Text
View/download PDF

38. Unraveling the Direct Decomposition of NOxover Keggin Heteropolyacids and Their Deactivation Using a Combination of Gas-IR/MS and In Situ DRIFT Spectroscopy

Author

Schnee, Josefine, Delannoy, Laurent, Costentin, Guylène, and Thomas, Cyril

Abstract

Keggin heteropolyacids (HPAs) have been known to be efficient NOxabsorbers for many years, and to be able to decompose a significant fraction of NOxspecies preabsorbed at 100–150 °C into harmless N2and O2upon rapid heating to 450 °C. However, this capability of Keggin HPAs to directly decompose NOxin the absence of a reducing agent in the feed has never been studied under more realistic reaction conditions, for example, under continuous NOxfeeding and in the presence of O2in the feed. This was done for the first time in the present work over the widely used H3PW12O40Keggin HPA at 380 °C. H3PW12O40was shown to be active in the direct decomposition of continuously fed NOx, with the decomposition process occurring through the involvement of NOH+adspecies. O2was found to play a dual role. On the one hand, it led to the oxidation of NO into NO2in the feed, with NO2deactivating the HPA units. On the other hand, it was found to initiate the diffusion of NOxinto the bulk of the HPA crystals, which significantly enhanced the durability of the activity of the HPA in the direct decomposition of these NOx, provided that the diffusion pathway in between the bulk Keggin units was already accessible, thanks to the presence of NOxspecies preabsorbed at room temperature. By providing the key factors involved in the direct decomposition of continuously fed NOxover H3PW12O40, the present work paves the way for future investigations that might focus, for instance, on tuning the chemical composition of the heteropolyanions in order to make the HPA more resistant to deactivation.

Published
2020
Full Text
View/download PDF

39. Incorporation of vanadium into the framework of hydroxyapatites: importance of the vanadium content and pH conditions during the precipitation step

Author

Petit, Sarah, primary, Gode, Thrimurthulu, additional, Thomas, Cyril, additional, Dzwigaj, Stanislaw, additional, Millot, Yannick, additional, Brouri, Dalil, additional, Krafft, Jean-Marc, additional, Rousse, Gwenaelle, additional, Laberty-Robert, Christel, additional, and Costentin, Guylène, additional

Published
2017
Full Text
View/download PDF

40. Acidic Properties of Alkaline-Earth Phosphates Determined by an Experimental-Theoretical Approach

Author

Blanco, Elodie, Gu, Qingyi, Couble, Julien, Martin, Lucile, Onfroy, Thomas, Costentin, Guylène, Paul, Jean-François, Michel, Carine, and Loridant, Stéphane

Abstract

Alkaline-earth phosphates efficient in the dehydration of lactic acid to acrylic acid were previously shown to contain a surface mono/dihydrogen phosphate amorphous layer composed of M2+cations and both P═O and POH groups. In this work, acidic properties of such a layer were determined combining Fourier transform infrared (FTIR) spectra achieved at the dehydrated state and under water vapor and density functional theory (DFT) simulations of nondefective and defective MPOH structure. The FTIR spectra of adsorbed pyridine and lutidine revealed the presence of moderate Lewis acid sites (LAS) and of POH groups interacting by H-bonding without significant protonation. DFT calculations were key to interpret FTIR spectra after adsorption of NH3: when solely adsorbed, NH3interacts with the LAS on both the nondefective surface and the defective surface, whereas the POH for which H points up toward the gas phase are reoriented downward. Brønsted acid sites (BAS) were shown to form under water vapor. This phenomenon was shown by DFT to arise from a more acidic character of HPO42–species for the nondefective surface and casual formation of nondefective surface leading to higher amount of H2PO4–species, which are more acidic BAS.

Published
2020
Full Text
View/download PDF

42. Importance of the Nature of the Active Acid/Base Pairs of Hydroxyapatite Involved in the Catalytic Transformation of Ethanol to n‐Butanol Revealed by Operando DRIFTS.

Author

Osman, Manel Ben, Krafft, Jean‐Marc, Thomas, Cyril, Yoshioka, Tetsuya, Kubo, Jun, and Costentin, Guylène

Subjects
HYDROXYAPATITE, BUTANOL, ETHANOL, CARBON, ACETALDEHYDE, ALDOL condensation
Abstract

Operando DRIFTS is used to identify the nature and the role of the surface sites of hydroxyapatites (HAps) involved in the catalytic transformation of ethanol to n‐butanol. The surface processes occurring upon a first reaction step followed by a step under He flow greatly influence the reactivity of HAps in a subsequent second reaction step. Ethanol is found to be mostly activated by the basic OH− groups of HAps, as indicated by the concomitant recovery of ethanol conversion and OH− groups under He flow. The drastic changes in selectivity observed during the second reaction step reveal the key role of acidic sites cooperatively acting with basic sites for basic reaction steps. Once the POH groups are poisoned by extensive formation of polymeric carbon species and the Ca2+ sites are available, the production of acetaldehyde is drastically promoted at the expense of that of n‐butanol. It is concluded that i) acetaldehyde acts as an intermediate in the formation of n‐butanol, and ii) various active sites are involved in the key basic reaction steps such as Ca2+−OH− and POH−OH− acid‐base pairs in the dehydrogenation of ethanol to acetaldehyde and the aldol condensation for n‐butanol formation, respectively. Drifting away. Atypical active sites were revealed on hydroxyapatite catalysts: Ca2+−OH− and POH−OH− are proposed to act as acid‐base pairs in the dehydrogenation of ethanol to acetaldehyde and the aldol condensation for n‐butanol formation, respectively. [ABSTRACT FROM AUTHOR]

Published
2019
Full Text
View/download PDF

43. Discrimination of infrared fingerprints of bulk and surface POH and OH of hydroxyapatites

Author

Manel Ben Osman, Costentin Guylène, Sarah Diallo-Garcia, Jean-Marc Krafft, Souhir Boujday, Laboratoire de Réactivité de Surface (LRS), and Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Infrared, Chemistry, Analytical chemistry, Infrared spectroscopy, Protonation, General Chemistry, Photochemistry, Acidic and basic probe molecule, Catalysis, Hydroxypatite, Isotopic labeling, Surface, Adsorption, Deuteration, Molecule, Hydroxyapatites
Abstract

International audience; The identification of the nature of the surface acid base pairs present on hydroxyapatites surface is a key point to rationalize their catalytic properties. To investigate the possible involvement of acidic protonated phosphate (POH) and/or of basic OH emerging from the channels, the spectroscopic fingerprints of the surface sites have to be discriminated from bulk HPO42− and OH− groups. This was monitored by infrared spectroscopy (i) using isotopic H-D exchanges, either implemented in mild conditions (353-373 K) or at higher temperature (573 K) to selectively label the lone surface or to achieve deep deuteration, respectively (ii) following then the perturbation induced upon adsorption probe molecules. Two bulk contributions are observed in the νOH region, one at 3572 cm−1 that is associated to OH− from the channels, and one at 3657 cm−1 that was assigned to HPO42−. Five surface contributions perturbated upon CO adsorption at 77 K can be ascribed to protonated forms of the various terminated phosphates. The formation of hydrogenocarbonate species upon CO2 adsorption evidences the presence of basic surface OH−. However, due to complex material restructuring occurring upon CO2 adsorption that greatly modifies the H-bonding interactions, the related νOH fingerprint could not be formally identified. Whatever, from the formation of low intense band at 2633 or 3572 cm−1 under soft deuteration or protonation conditions respectively, it is inferred that the related bands could be ascribed to both surface and bulk OD or OH.

Published
2014

49. Study of the structure of the OH groups on MgO by 1D and 2D 1MAS NMR combined with DFT cluster calculations

Author

Chizallet, Céline, Costentin, Guylène, Lauron-Pernot, Hélène, Che, Michel, Bonhomme, Christian, Maquet, Jocelyne, Delbecq, Françoise, Sautet, Philippe, Laboratoire de Réactivité de Surface (LRS), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Chimie de la Matière Condensée de Paris (site Paris VI) (LCMCP (site Paris VI)), Université Pierre et Marie Curie - Paris 6 (UPMC)-Collège de France (CdF (institution))-Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[CHIM.INOR]Chemical Sciences/Inorganic chemistry, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2007

50. A microGC study of the deactivation process during conversion of methylbutynol on basic zeolites

Author

Massiani, Pascale, Groust, Jean-François, Costentin, Guylène, Teyssier, Laurent, Laboratoire de Réactivité de Surface (LRS), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), and Dechema

Subjects
[CHIM.CATA]Chemical Sciences/Catalysis
Abstract

The initial deactivation occurring during conversion of methylbutunol on basic alkali-faujasite catalysts was studied by microGC. Both the product selectivity and the formation of water during the first minutes of run permit to conclude on the deactivation process and on the nature of the adsorbed inhibiting products that were also identified by in situ thermal activation in O2 or N2 of used catalysts, followed by mass spectrometry. Interestingly, the level of activity at steady state after thermal regeneration in O2 is significantly higher than on the fresh catalyst.

Published
2006

Catalog

Books, media, physical & digital resources
See catalog results