Hommage à Bertrand Dorny (1931-2015)

Depuis 2003, un peu avant Noël, je trouvais dans ma boîte aux lettres une enveloppe matelassée en papier kraft, légèrement bombée, et je savais qui en était l’expéditeur. C’était Bertrand Dorny. Il m’envoyait ses vœux dans une boîte d’allumettes qu’il avait eu soin de rendre unique. Elle contenait un minuscule livre manuscrit, en forme de dépliant. Le texte était de lui. Chaque année, je me promettais d’être la première à lui souhaiter la bonne année et je n’ai jamais réussi. Fin 2015, je n’a..

Nitrogen sorption as a tool for the characterisation of polysaccharide aerogels

Supercritically dried aerogels of several polysaccharides (chitin, chitosan, alginate, alginic acid, k- carrageenan, and agar) have been characterised by physisorption ofN2. Surface areas as high as 570m2 g−1 have been measured. The nature of the functional groups of the polysaccharide significantly influences the adsorption of N2 on the surface of the aerogel. The net enthalpy of adsorption increases with the polarity of the surface groups of the polymer, in the order chitin < agar≤chitosan < carrageenan < alginic acid∼alginate. The surface area and the mesopore distribution of the aerogels depend both on the dispersion of the parent hydrogel and on the behaviour of each polymer in the drying treatment. Aerogels which retain the dispersion of the parent hydrogel are mainly macroporous (pores larger than 50 nm) while materials liable to shrink upon solvent exchange form mesoporous structures

The role of argumentation in online epistemic communities: the anatomy of a conflict in Wikipedia

International audienceThis research aims to investigate the processes by which knowledge objects — in this case Wikipedia pages on astronomy — are elaborated, in online communities, focussing on the role of argumentative interactions

DNA-catalyzed Henry Reaction in Pure Water and the Striking Influence of Organic Buffer Systems

In this manuscript we report a critical evaluation of the ability of natural DNA to mediate the nitroaldol (Henry) reaction at physiological temperature in pure water. Under these conditions, no background reaction took place (i.e., control experiment without DNA). Both heteroaromatic aldehydes (e.g., 2-pyridinecarboxaldehyde) and aromatic aldehydes bearing strong or moderate electron-withdrawing groups reacted satisfactorily with nitromethane obeying first order kinetics and affording the corresponding β-nitroalcohols in good yields within 24 h. In contrast, aliphatic aldehydes and aromatic aldehydes having electron-donating groups either did not react or were poorly converted. Moreover, we discovered that a number of metal-free organic buffers efficiently promote the Henry reaction when they were used as reaction media without adding external catalysts. This constitutes an important observation because the influence of organic buffers in chemical processes has been traditionally underestimated

Mesoporosity changes from cambium to mature tension wood: a new step toward the understanding of maturation stress generation in trees

International audienceIn order to progress in the understanding of mechanical stress generation, the mesoporosity of the cell wall and its changes during maturation of poplar (Populus deltoides x P. nigra) tension wood (TW) and opposite wood (OW) were measured by nitrogen adsorption–desorption. Variations in the thickness of the gelatinous layer (G-layer) were also measured to clarify whether the mesoporosity change simultaneously with the deposition of the G-layer in TW. Results show that mesoporous structures of TW and OW were very similar in early development stages before the deposition of G-layers. With the formation of the S2 layer in OW and the G-layer in TW, the mesopore volume decreased steeply before lignification. However, in TW only, the decrease in mesopore volume occurred together with the pore shape change and a progressive increase in pore size. The different patterns observed in TW revealed that pores from G-layers appear with a different shape compared to those of the compound middle lamella, and their size increases duringthe maturation process until stabilising in mature wood. This observation strongly supports the hypothesis of the swelling of the G-layer matrix during maturation as the origin of maturation stress in poplar tension wood

Chitosan as efficient porous support for dispersion of highly active gold nanoparticles: design of hybrid catalyst for carbon-carbon bond formation

International audienceMacroporous catalyst was obtained by dispersing nanosized gold in the fibrils of the chitosan matrix, followed by CO2 supercritical drying of the resulting hybrid material. The accessible gold nanoparticles are highly active for carbon–carbon cross coupling reactions

De la complexation des cations aux matériaux d'intérêt (les gels ionotropiques d'alginate)

Les alginates, polysaccharides extraits des algues brunes, sont des copolymères à blocs linéaires formés d'unités mannuronates (M) et guluronates (G). Leur structure dépend de la source naturelle. La complexation de cations divalents ou trivalents (sauf Mg2+) par les fonctions carboxylates conduit à la formation d'un hydrogel. Pour approfondir l'étude de la formation des gels ionotropiques d'alginate, des hydrogels et des aérogels séchés en conditions supercritiques ont été caractérisés à plusieurs échelles par différentes techniques. L'analyse orbitalaire ab initio de petits complexes a montré la formation de liaisons covalentes fortes avec les métaux de transition alors que les alcalino-terreux ne mettent en jeu que des interactions électrostatiques. Selon le rapport M/G et la nature des cations, différents régimes structuraux ont pu être identifiés par des mesures SAXS (~10-200Å) : des gels fibrillaires ou formés d'agglomérats interconnectés. Les propriétés mécaniques des hydrogels et les surfaces spécifiques des aérogels correspondants sont directement reliées à ces morphologies. La présence simultanée de plusieurs métaux dans les gels peut induire des effets coopératifs dans la formation mais aussi dans les propriétés des matériaux. De nouvelles méthodes ont été mises au point pour contrôler la synthèse de gels hétéro-cationiques, en considérant les effets d'affinité.Sur la base de cette étude, des synthèses originales de matériaux fonctionnels nano-structurés ont été développées. Certains ont été construits directement dans le réseau d'alginate en exploitant les cations de gélification ; d'autres ont nécessité le sacrifice de la matrice pour former des oxydes simples ou mixtes nanocristallins.Alginates, polysaccharides produced by brown algae, are linear block-copolymers formed by mannuronate (M) and guluronate (G) units. Their structure depends on the natural source. The coordination of divalent or trivalent cations (except Mg2+) with the carboxylate functions leads to the formation of a hydrogel. In order to get some insight in ionotropic alginate gel formation, hydrogels and supercritical dried aerogels were analysed through various characterizations at different scales. The ab initio molecular orbital analysis on small complexes revealed strong coordination-covalent bonds in the transition metal complexes, whereas only ionic interaction occurs between the alkaline-earth cations and the carboxylates. Depending on the M/G ratio and the nature of the cation, different structural regimes were identified by SAXS analysis (~10-200Å) : well-defined fibrillar gels or gels with multiple junction nature. The mechanical properties of the hydrogels and surface areas of the resulting aerogels are directly related to these morphologies. The concomitant presence of different metals in the gel can bring cooperative effect for the formation but also for the properties of the materials. New methods to control the synthesis of hetero-cationic gels were implemented, taking into account the affinity effects. On the basis of this study, we developed new nanostructured functional materials synthesis. Some were built directly in the alginate network using the gelling cations. Others needed to sacrifice the matrix to form nanocrystalline single or mixed oxides.MONTPELLIER-Ecole Nat.Chimie (341722204) / SudocSudocFranceF

15 000 volumes à la réserve des livres rares

Si le département des estampes s\u27est spécialisé dans la collection des artist\u27s book, un genre né à la fin des années 1960 (lire l\u27article de Marie-Cécile Miessner en page 36), la réserve des livres rares a constitué une collection de livres d\u27artistes dont l\u27origine remonte aux livres illustrés par des peintres, dans le dernier quart du XIXe siècle. Responsable des collections des XX et XXIe siècles, Marie-Françoise Quignard présente la constitution du fonds, l\u27un des plus importants au monde

Editorial on Special Issues “Aerogels” and “Aerogels 2018”

International audienc

Des hydrocolloïdes aux matériaux mésoporeux (application en catalyse)

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF