Inégalités dans l’enfance et enfance des inégalités

International audienc

Inégalités dans l’enfance et enfance des inégalités

International audienc

Inégalités dans l’enfance et enfance des inégalités

International audienc

Inégalités dans l’enfance et enfance des inégalités

International audienc

Multifunctional polyesters as key components in the design of nanostructured drug delivery and mesoporous materials

9 - Conference paper: 229th American Chemical Society National Meeting, 13-17 Mars 2005, San Diego (USA)International audienc

Multifunctional Polyester-Based Materials with Controlled Degradability

4 - Chapitre de livreHydrolytic degradability can be fine-tuned in polyester-based materials by controlling the nature and placement of comonomers introduced within the polymer structures. This contribution describes how D,L-lactide-, ε-caprolactone-, and β-hydroxyoctanoate-containing polyesters can be used to design nanostructured drug delivery vehicles and mesoporous polymeric materials. In the first part, the efficient synthesis of poly(β-hydroxyoctanoate)-based block and graft copolymers is addressed. A versatile and straightforward approach toward mesoporous functional polymers via the partial hydrolysis of poly(D,L-lactide)-based Interpenetrating Polymer Networks (IPNs) is discussed in a second part

Morphology of GaAs crystals heterogeneously integrated on nominal (001) Si by epitaxial lateral overgrowth on tunnel oxide via Ge nano-seeding

cited By 0International audienceIn this study, GaAs crystals were grown by chemical beam epitaxy on nominal (001) Si substrate over Ge nano-seeds placed within nano-holes opened through a 0.6 nm silica layer. GaAs crystal morphology and atomic organization at the interface between Ge and GaAs were studied by using complementary Scanning Transmission Electron Microscopy, energy dispersive X-ray spectrometry and dark-field electron holography. Fourfold symmetry GaAs crystals were obtained and found to be completely relaxed and twin free. Thus, the use of Ge nano-seeds to initiate the growth of GaAs results in the suppression of twins previously observed for direct GaAs growth on nominal (001) Si. Nevertheless, anti-phase domains were detected. A simple atomistic model is proposed which explains how Anti-Phase Boundaries develop at the junctions between Ge {113} facets, and {113} and {111} facets for As-stabilized GaAs growth

Nanostructured calcite precipitated under hydrothermal conditions in the presence of organic and inorganic selenium

International audienceSelenium is an important trace metalloid, whose global cycle is controlled by fluid-rock interactions in the Earth's upper crust, interactions with bio-molecules in soils and living systems, and atmospheric transport in ashes. The cycling of selenium is often intimately associated with carbonate phases, with Se being generally incorporated as an impurity in calcite crystals or adsorbed on carbonate nanoparticles. In order to better understand the interaction of aqueous selenium species with carbonates, we studied the precipitation of calcite under hydrothermal conditions (30-90 °C, 25-90 bar) in a CO2-H2O-Ca(OH)2 medium in the presence of aqueous inorganic and organic selenium compounds. Aqueous carbonation reactions in the presence of selenium at elevated temperatures and pressures, relevant for long-term CO2 sequestration in reservoirs and other natural geological systems, have until now not been investigated to the best of our knowledge. Electron microscopy (FESEM and TEM) and synchrotron X-ray absorption spectroscopy (XAS) were used in a complementary manner to investigate crystal size, structural order (crystallinity), morphology of crystal faces, crystal organization, and selenium speciation in the calcite samples. XAS data analysis showed clear evidence for the incorporation of selenite oxyanion (SeO32−) into the calcite crystal structure. At low Se content (1.3 mg/g calcite), a single site was observed with Se surrounded by six Ca atoms, whereas additional sites, probably corresponding to surface sorption sites, were found with increasing Se content. XAS also showed that seleno-L-cystine (Secys) was chemically fragmented during carbonation, and the solid phase contained elemental and oxidized Se, in hexagonal or amorphous form depending on the experimental conditions, with a minor proportion of Se(IV). Moreover, FESEM and TEM measurements revealed a very complex effect of Secys on the particle size and aggregation/agglomeration process, leading to the following calcite morphologies: rhombohedra, elongated rhombohedra (c-axis elongation), scalenohedra, star-like and shell-like crystal aggregates, and irregular calcite polycrystals. The aggregates and irregular polycrystals, which we designate as nanostructured calcite material, were constituted of nanometer-sized calcite crystallites (< 100 nm). The star and shell-like crystal aggregates, which were observed only in the presence of Secys, may be due to crystal growth in the presence of associated secondary organic compounds due to a simultaneous chemical fragmentation of Secys. Overall, the results from this study show that selenium (of biotic or abiotic origin) can be integrated into the crystallographic structure of calcite under hydrothermal conditions. This has relevance for geological processes in diverse environments, such as hydrothermal systems along mid-ocean ridges, or underground reservoirs associated with massive injection of CO2 for long-term geological sequestration

Distribution of airborne Mycosphaerella graminicola inoculum at the field scale

A network of 10 Burkard 7-day spore-recording traps was set up in the Walloon region in Belgium to monitor the airborne inoculum of wheat pathogens. Three spore traps were used to analyse the distribution of Mycosphaerella graminicola inoculum at the field scale, at 1 m above ground level. Two traps were set up in a wheat field 100 m apart. The third trap was placed 70 m away in a sugar beet field adjacent to the wheat field. Total DNA from each fragment of spore trap tape corresponding to 1 day sampling was extracted and the quantity of M. graminicola was assessed using real-time polymerase chain reaction (PCR) assay. The experiment was conducted from July to October 2009. Positive detections were obtained for between 33 and 36 days, depending on the spore traps. When detected, the daily quantities of cDNA, collected from a volume of 14.4 m3, fluctuated between 4.84E+00 and 6.10E+03. Correlation coefficients higher than 0,82 and no significant differences were observed between the quantities of M. graminicola collected by the three spore traps, indicating that, at 1 m above ground level, the distribution of inoculum can be considered as homogenous at the tested field scale. This study confirms that spore traps coupled with real-time PCR could be used to assess the airborne inoculum of M. graminicola and to understand the development of the disease at this scale

A HTS assay for the detection of organophosphorus nerve agent scavengers.

International audienceA new pro-fluorescent probe aimed at a HTS assay of scavengers is able to selectively and efficiently cleave the P-S bond of organophosphorus nerve agents and by this provides non-toxic phosphonic acid has been designed and synthesised. The previously described pro-fluorescent probes were based on a conventional activated P-Oaryl bond cleavage, whereas our approach uses a self-immolative linker strategy that allows the detection of phosphonothioase activity with respect to a non-activated P-Salkyl bond. Further, we have also developed and optimised a high-throughput screening assay for the selection of decontaminants (chemical or biochemical scavengers) that could efficiently hydrolyse highly toxic V-type nerve agents. A preliminary screening, realised on a small alpha-nucleophile library, allowed us to identify some preliminary "hits", among which pyridinealdoximes, alpha-oxo oximes, hydroxamic acids and, less active but more original, amidoximes were the most promising. Their selective phosphonothioase activity has been further confirmed by using PhX as the substrate, and thus they offer new perspectives for the synthesis of more potent V nerve agent scavengers