Model arenes hydrogenation with silica-supported rhodium nanoparticles:The role of the silica grains and of the solvent on catalytic activities

Silica-supported rhodium-based nanoheterogeneous catalysts were easily prepared by impregnation with a pre-stabilized colloidal suspension. The resulting catalysts contain rhodium nanoparticles well-dispersed in the silica pores with a mean size of 5 nm. Influence of the silica grains size and of the solvent was investigated in arenes hydrogenation. It appeared that the size of the silica grains has a minimal influence on the reaction rate but the supported nanocatalysts displayed higher TOFs in hexane than in water

Rhodium colloidal suspension deposition on porous silica particles by dry impregnation: Study of the influence of the reaction conditions on nanoparticles location and dispersion and catalytic reactivity

Rhodium composite nanomaterials were synthesized by an innovating process called dry impregnation in a fluidized bed. It consists in spraying an aqueous colloidal suspension of rhodium on silica porous particles. The use of this precursor solution containing preformed nanoparticles avoids calcination/activation step. Different composite nanomaterials were prepared displaying various metal loadings. The operating conditions were tuned to modify τs, the solvent vapour saturation rate value, in order to influence the deposit location: either uniform on the whole silica particles or at the particles surface like a coating. τs is defined as the ratio between solvent content in the bed atmosphere and the maximum solvent content. The obtained samples were investigated in catalytic hydrogenation of aromatic compounds under very mild conditions. Their catalytic performances were compared to those of the original colloidal suspension in one hand and of a similar catalyst prepared through wet impregnation in another hand. Interesting activity and selectivity were observed.This illustrates the interest of the dry impregnation method: this way allows an easy control of the metal loading as well as of the metal loading location in the support particles. Moreover, the support particle size and morphology are preserved

From hydroxycetylammonium salts to their chiral counterparts. A library of efficient stabilizers of Rh(0) nanoparticles for catalytic hydrogenation in water

International audienceNowadays, the nanometer-size and shape control of metallic species remains a strategic research area in material development due to their particular physical and chemical properties. Among their various applications, catalysis has emerged as one of the most pertinent due to its large range of potentialities. From now on, noble metal nanoparticles (NPs) are considered as an unavoidable family of catalysts, at the border between heterogeneous bulk materials and molecular complexes. The design of stable noble metal nanoparticles in various solvents such as ionic liquids, fluorous or organic media has become a concern over the past few years. Nevertheless, for economic and ecological purposes, the development of green approaches remains an active research area, as well as the reusability of nanocatalysts. In this context, the stabilisation in colloidal suspension of nanoparticles, thus providing a catalyst recycling thanks to a biphasic approach constitutes an efficient alternative to the heterogeneization of the nanocatalysts. Among the various water-soluble protective agents, easily modulated surfactants proved to be attractive candidates to efficiently stabilize catalytically active nanospecies in aqueous media. Here, we review our recent progresses in the hydrogenation of benzene derivatives by rhodium nanoparticles which were capped by an ammonium salts bearing an achiral or chiral polar head group

Cyclodextrin-based systems for the stabilization of metallic(0) nanoparticles and their versatile applications in catalysis

International audienceIn order to better respond to environmental standards, the development of metal nanoparticles using green approaches has exponentially grown for the last decade. Cyclodextrins, which are cyclic oligosaccharides composed of 6(α), 7(β) or 8(γ) glucopyranose units, have appeared to be interesting candidates for the synthesis of metal nanoparticles. Indeed, through the ability to form inclusion complexes or supramolecular adducts with organic molecules or metal precursors, cyclodextrins can be successfully employed to stabilize size-controlled zerovalent metallic nanoparticles active for hydrogenation reactions carried out in aqueous or gas-phase media. In this summary of our works, we report that cyclodextrins could be used in various forms and environments: (i) in free form, (ii) in complexed form with appropriate guests molecules, (iii) in combination with polymer matrices, (iv) in thermosensitive hydrogels and (v) immobilized onto porous carbons supports. All these studies highlight the fact that cyclodextrins can be seen as multi-task agents for nanocatalysis

β-Cyclodextrins grafted with chiral amino acids: A promising supramolecular stabilizer of nanoparticles for asymmetric hydrogenation?

International audienceWater-soluble ruthenium nanoparticles stabilized by randomly methylated β-cyclodextrins (RaMeCDs) grafted with chiral amino-acid moieties like l-alanine (Ala) and l-leucine (Leu) were prepared in aqueous solution by two approaches: (i) a one-step hydrogen reduction of ruthenium trichloride as metal source in the presence of appropriate cyclodextrins (one-pot method) or (ii) a NaBH4 reduction of the metal salts, followed by the stabilization of ruthenium hydrosol by the addition of chirally modified RaMeCDs (cascade method). The influence of the ligand's nature and the synthesis methodologies on the size, dispersion and surface properties of the obtained ruthenium colloids were studied by TEM and NMR analyses. The spherical ruthenium suspensions contain very small particles (0.82-1.00 nm) with narrow size distributions. Their catalytic properties were evaluated in biphasic hydrogenation of various prochiral compounds (olefins, ketones and disubstituted arenes) showing promising results in terms of activity and selectivity. Nevertheless, no significant enantiomeric excesses were observed

The Impact of Ribosome Biogenesis in Cancer: From Proliferation to Metastasis

The dysregulation of ribosome biogenesis is a hallmark of cancer, facilitating the adaptation to altered translational demands essential for various aspects of tumor progression. This review explores the intricate interplay between ribosome biogenesis and cancer development, highlighting dynamic regulation orchestrated by key oncogenic signaling pathways. Recent studies reveal the multifaceted roles of ribosomes, extending beyond protein factories to include regulatory functions in mRNA translation. Dysregulated ribosome biogenesis not only hampers precise control of global protein production and proliferation but also influences processes such as the maintenance of stem cell-like properties and epithelial-mesenchymal transition, contributing to cancer progression. Interference with ribosome biogenesis, notably through RNA Pol I inhibition, elicits a stress response marked by nucleolar integrity loss, and subsequent G1-cell cycle arrest or cell death. These findings suggest that cancer cells may rely on heightened RNA Pol I transcription, rendering ribosomal RNA synthesis a potential therapeutic vulnerability. The review further explores targeting ribosome biogenesis vulnerabilities as a promising strategy to disrupt global ribosome production, presenting therapeutic opportunities for cancer treatment

L'incidence de la culture disciplinaire sur l'évaluation des risques en éthique de la recherche

Au cours des dernières décennies, l'éthique de la recherche est devenue un enjeu social de plus de plus en plus important. Le monde de la recherche s'est progressivement vu encadré par des politiques et des codes d'éthiques. Malgré ces balises, l'évaluation des risques en recherche demeure une tâche éminemment complexe et peut donner lieu à des estimations très variables. En première lecture, cette évaluation peut apparaître très subjective. La littérature en théorie du risque suggère que la perception et l'évaluation du risque renvoient en bonne part à une démarche sociale. Malheureusement, nous savons peu de chose sur la façon dont les chercheurs exercent leur jugement éthique, quant à ses déterminants. Notre thèse s'intéresse à l'évaluation des risques éthiques en recherche. Elle étudie de manière exploratoire l'incidence de la culture disciplinaire sur les représentations des chercheurs en cette matière. Notre hypothèse de recherche est que les regroupements disciplinaires constituent des référents identitaires importants pour les représentations sociales des chercheurs en ce qui concerne l'évaluation des risques éthiques. Le cadre conceptuel développé pour les fins de cette recherche s'appuie principalement sur la théorie des représentations sociales et sur le concept de matrice disciplinaire de Kuhn. Ce dernier concept vient expliquer pourquoi et en quoi les regroupements disciplinaires constituent des référents identitaires signifiants pour les représentations sociales des chercheurs en matière d'évaluation du risque éthique. La littérature sur la théorie du risque est également mise à contribution pour expliciter le rapport au risque dans les différentes disciplines. Notre démarche empirique s'intéresse plus précisément aux représentations des chercheurs appartenant à quatre groupes disciplinaires, soit l'anthropologie, la psychologie, l'économie et la médecine spécialisée. Notre dispositif de recherche repose sur une enquête réalisée auprès de 70 chercheurs universitaires. Pour saisir les représentations sociales des chercheurs liées au jugement éthique, nous avons eu recours à la technique de la vignette. Cette vignette présente un projet de recherche en phase de conception. L'enquête était complétée d'un questionnaire à deux volets, le premier comportant des questions ouvertes, le second consistant en un ensemble de questions fermées. L'analyse des données utilise des méthodes d'analyse qualitative pour le volet I (analyse thématique et discursive) et des méthodes d'analyse quantitative simples pour le volet II. Nos résultats et analyses montrent que la culture disciplinaire des chercheurs influence la façon dont ils évaluent les risques éthiques d'un projet de recherche. Ainsi, nous avons observé que les prises de position en matière d'évaluation des risques éthiques en recherche diffèrent sensiblement selon les groupes disciplinaires de chercheurs considérés dans notre étude. D'autre part, des analyses plus interprétatives ont permis d'identifier des caractéristiques distinctives des cultures disciplinaires susceptibles d'expliquer les écarts de position observés. Ces facteurs concernent principalement la proximité des disciplines avec l'éthique, la perspective théorique du risque privilégiée dans ces disciplines, leur rapport à la «science», la méthodologie dominante utilisée, les grilles d'analyse propres aux disciplines, certains thèmes privilégiés et certaines valeurs ou attitudes véhiculées par ces groupes de chercheurs. Ces éléments sont en lien étroit avec le concept de matrice disciplinaire défini par Kuhn. Une meilleure compréhension de la façon dont les chercheurs exercent leur jugement éthique peut s'avérer utile pour orienter et adapter les politiques de renforcement de l'éthique de la recherche. Notre recherche, malgré son caractère exploratoire, apporte un éclairage utile à cet égard. Pour être efficaces, il importe que les mesures, programmes et stratégies mis de l'avant prennent en considération les spécificités disciplinaires