Préparation, criblage et utilisation de catalyseurs hétérogènes à base de polysaccharides

Les contraintes environnementales poussent les chimistes à développer de nouveaux systèmes générant un minimum de déchets. La mise au point de catalyseurs hétérogènes bien définis permet de répondre à ces contraintes notamment par la récupération et le recyclage du catalyseur. Alors que de nombreux systèmes catalytiques hétérogènes à base de supports inorganiques ou organiques, sont d ores et déjà rapportés dans la littérature, peu de travaux mettent en œuvre des systèmes à base de matériaux biologiques, tels que des macrostructures polymériques naturelles. Dans cette optique, nous avons entrepris de développer des catalyseurs hétérogènes à base de polysaccharides, en tant que supports renouvelables, sous la forme de billes macroscopiques poreuses. Les différents catalyseurs obtenus ont été criblés à l aide de tests fluorescents. Dans un premier temps, l efficacité catalytique d une douzaine de systèmes hétérogènes à base de chitosane comme support pour des complexes cuivre-ligand a pu être étudiée via la réaction de cycloaddition 1,3-dipolaire de Huisgen. Puis dans un second temps, l efficacité catalytique d une quarantaine de systèmes hétérogènes à base de nanoparticules de palladium supportées sur alginate a pu être étudiée via la réaction de couplage de Suzuki. Nos résultats montrent que des systèmes hétérogènes fortement actifs peuvent être obtenus en combinant les propriétés texturales des polysaccharides et les propriétés catalytiques de métaux de transition ou de complexes métal-ligand .Environmental constraints push chemists to develop new systems for generating minimal waste. The development of well-defined heterogeneous catalysts can respond to these constraints in particular by the recovery and the recycling of catalyst. While many heterogeneous catalytic systems based on inorganic or organic materials are already reported in the literature, few works implement systems based on biological materials such as natural polymeric macrostructures. In this context, we have undertaken to develop heterogeneous catalysts based on polysaccharides as renewable materials, in the form of macroscopic porous beads. Different catalysts obtained were screened using fluorescent test. Firstly, the catalytic efficiency of a dozen heterogeneous catalysts based on chitosan as support for copper-ligand complexes has been studied through the 1,3-dipolar Huisgen s cycloaddition. Secondly, the catalytic efficiency of around forty heterogeneous systems based on palladium nanoparticles supported on alginate have been studied through the Suzuki s coupling reaction. Our results show that highly active heterogeneous systems can be obtained by combining the structural properties of polysaccharides and catalytic properties of transition metals or metal-ligand complexes.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Dramatic Effect of the Gelling Cation on the Catalytic Performances of Alginate-Supported Palladium Nanoparticles for the Suzuki-Miyaura Reaction

International audienceThis work describes the preparation and characterization of a library of alginate-supported palladium nanoparticles together with their catalytic capabilities to promote the Suzuki-Miyaura reaction. Using the chelating properties of the carboxylate functions of the alginate matrix a series of Ca, Ba, Mn, Zn, Ni, Ce, Cu, and Co alginate gels were first prepared and then reacted with Pd2+ salts. Partial exchange of metal cations followed by Pd reduction into palladium nanoparticles and supercritical CO2 drying generated a panel of bimetallic alginate aerogels. Physical characterizations of these materials showed a significant influence of both the gelling metal nature and the Pd loading on surface areas and nanoparticles size. A comparative study of the catalytic performances of these heterogeneous catalytic systems is then reported for the Suzuki-Miyaura reaction. This study highlighted the superior performances of palladium nanoparticles supported on copper-alginate aerogels. This heterogeneous catalyst showed high catalytic activities as illustrated by a TOF value of 10 s(-1) and a TON value close to 10(6). The robustness of the catalyst allowed several reuses with no significant loss of activity or metal leaching

Linking of Antitumor trans NHC-Pt(II) Complexes to G-Quadruplex DNA Ligand for Telomeric Targeting

International audienceG-quadruplex structures (G4) are promising anticancer-ous targets. A great number of small molecules targeting these structures have already been identified through biophysical methods. In cellulo, some of them are able to target either telomeric DNA and/or some sequences involved in oncogene promotors, both resulting in cancer cell death. However, only a few of them are able to bind to these structures G4 irreversibly. Here we combine within the same molecule the G4-binding agent PDC (pyridodicarboxamide) with a N-heterocyclic carbene−platinum complex NHC-Pt already identified for its antitumor properties. The resulting conjugate platinum complex NHC-Pt-PDC stabilizes strongly G-quadruplex structures in vitro, with affinity slightly affected as compared to PDC. In addition, we show that the new conjugate binds preferentially and irreversibly the quadruplex form of the human telomeric sequence with a profile in a way different from that of NHC-Pt thereby indicating that the platination reaction is oriented by stacking of the PDC moiety onto the G4-structure. In cellulo, NHC-Pt-PDC induces a significant loss of TRF2 from telomeres that is considerably more important than the effect of its two components alone, PDC and NHC-Pt, respectively