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Plessis S.,University Paris - Sud | Carrasco N.,University of Versailles | Dobrijevic M.,University of Bordeaux 1 | Dobrijevic M.,French National Center for Scientific Research | And 2 more authors.
Icarus | Year: 2012

The production rates of neutral species by dissociative recombination (DR) of molecular ions with electrons in the ionosphere of Titan are quantified by a new model, including, for the first time, all the available kinetic data on this process. The calculation is based on the ion densities measured by the INMS instrument on Cassini orbiter during flyby T19 at 1100km altitude. These production rates are compared with those predicted by photochemical models: we calculate that for many neutral species, DR has larger production rates than neutral chemistry. Concerning molecular growth in Titan's ionosphere, DR is shown to have two antagonistic effects: (1) a global chemical lysis of ions through C-C and C-N bond breaking (missed by the " H-loss" DR paradigm); and (2) an enhancement of the neutral chemistry by production of reactive radicals, such as C 2H or NH 2. Further exploration of this chemistry requires the development of ionospheric coupled models taking explicitly into account the richness of the DR process and the strong impact of ions on the budget of neutral species. This study emphasizes also the urgent need of additional experimental studies about DR of molecular ions, with two priorities: evaluation of the impact of the temperature of ions on the rates and fragmentation patterns, and the systematic study of the fragmentation patterns of CxHyNz+ ions with more than four heavy atoms (m/z>60u). © 2012 Elsevier Inc. Source

Dupre-Crochet S.,University Paris - Sud | Dupre-Crochet S.,French Institute of Health and Medical Research | Erard M.,University Paris - Sud | Erard M.,CNRS Laboratory of Chemical Physics | And 2 more authors.
Journal of Leukocyte Biology | Year: 2013

In the phagocytosis field, ROS production by the phagocyte NOX has been associated with pathogen killing for the last 50 years. Since the discovery of nonphagocyte NOX, numerous other roles for ROS production have been identified. Oxidative stress and ROS-mediated signaling have received much attention in recent years. Much lower concentrations of ROS may be required for signaling compared with microbial killing. Based on the discoveries in nonphagocytic cells, it became logical to look for ROS functions distinct from pathogen killing, even in phagocytes. ROS are now linked to various forms of cell death, to chemotaxis, and to numerous modifications of cellular processes, including the NOX itself. ROS functions are clearly concentration-dependent over a wide range of concentrations. How much is required for which function? Which species are required for how much time? Is ROS signaling only a side effect of bactericidal ROS production? One major obstacle to answer these questions is the difficulty of reliable quantitative ROS detection. Signal transduction often takes place on a subcellular scale over periods of seconds or minutes, so the detection methods need to provide appropriate time and space resolution. We present examples of local ROS production, decreased degradation, signaling events, and potentially ROS-sensitive functions. We attempt to illustrate the current limitations for quantitative spatiotemporal ROS detection and point out directions for ongoing development. Probes for localized ROS detection and for combined detection of ROS, together with protein localization or other cellular parameters, are constantly improved. © Society for Leukocyte Biology. Source

Linguerri R.,University Paris Est Creteil | Hochlaf M.,University Paris Est Creteil | Bacchus-Montabonel M.-C.,CNRS Laboratory of Ionic and Molecular Spectrometry | Desouter-Lecomte M.,CNRS Laboratory of Chemical Physics
Physical Chemistry Chemical Physics | Year: 2013

Franzreb and Williams at Arizona State University detected recently the MgO2+ molecular species in the gas phase. Here we report a very detailed theoretical investigation of the low-lying electronic states of this dication including their potentials, spin-orbit, rotational and radial couplings. Our results show that the potential energy curves of the dicationic electronic states have deep potential wells. This confirms that this dication does exist in the gas phase; it is a thermodynamically stable molecule in its ground state, and it has several excited long-lived metastable states. The potential energy curves are used then to predict a set of spectroscopic parameters for the bound states of MgO2+. We have also incorporated these potentials, rotational and radial couplings in dynamical calculations to derive the cross sections for the charge transfer Mg2+ + O → Mg+ + O+ reaction in the 1-103 eV collision energy domain via formation-decomposition of the MgO2+ dication. Our work shows the role of MgO2+ in the Earth ionosphere and more generally in atmospheric processes in solar planets, where this reaction efficiently participates in the predominance of Mg+ cations in these media compared to Mg and Mg2+. © 2013 the Owner Societies. Source

Doherty R.P.,CNRS Surface Science Lab | Doherty R.P.,University Paris - Sud | Krafft J.-M.,CNRS Surface Science Lab | Methivier C.,CNRS Surface Science Lab | And 5 more authors.
Journal of Catalysis | Year: 2012

Bimetallic AuPt nanoparticles prepared by radiolysis with Au/Pt atomic ratios of 1.2 and 1.8 were deposited onto silica and calcined to remove the stabilizing polymers. During this sequence, they lose their core-shell structure and restructure as alloys. FTIR and XPS provide evidence for further AuPt NP restructuring under CO exposure and CO oxidation with Pt surface enrichment. A promoting effect of Au is found on the CO oxidation kinetics in the AuPt catalyst with the lower Au/Pt ratio. This effect is attributed to an electron enrichment of the Pt surface atoms due to charge transfer from Au to Pt, as indicated by XPS and CO-FTIR. © 2011 Elsevier Inc. All rights reserved. Source

Ghosh S.,University Paris - Sud | Kouame N.A.,University Paris - Sud | Ramos L.,CNRS Charles Coulomb Laboratory | Remita S.,University Paris - Sud | And 8 more authors.
Nature Materials | Year: 2015

Visible-light-responsive photocatalysts can directly harvest energy from solar light, offering a desirable way to solve energy and environment issues. Here, we show that one-dimensional poly(diphenylbutadiyne) nanostructures synthesized by photopolymerization using a soft templating approach have high photocatalytic activity under visible light without the assistance of sacrificial reagents or precious metal co-catalysts. These polymer nanostructures are very stable even after repeated cycling. Transmission electron microscopy and nanoscale infrared characterizations reveal that the morphology and structure of the polymer nanostructures remain unchanged after many photocatalytic cycles. These stable and cheap polymer nanofibres are easy to process and can be reused without appreciable loss of activity. Our findings may help the development of semiconducting-based polymers for applications in self-cleaning surfaces, hydrogen generation and photovoltaics. Source

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