Karine Molvinger

Functionalized Chitosan as a Green, Recyclable, Biopolymer-Supported Catalyst for the 3+2 Huisgen Cycloaddition

Owing to increasing concern about environmental impact, tremendous effort has been made towards the development of new processes that minimize pollution in chemical synthesis. For this reason and others (catalyst removal, recovery, and recycling), heterogeneous catalysis is clearly on the rise, including in industry. Of the many systems that have been developed over the past decades, metallic species supported on inorganic materials (e.g. SiO2, Al2O3) or on charcoal are the most common. The immobilization of transition metals on polymer supports derived from petrochemicals (e.g. polystyrenes) has also been the focus of many efforts. Recent developments for cleaner, sustainable chemistry are being driven by a shift from petrochemical-based feedstocks to biological materials. There is considerable interest in exploiting natural polymer macrostructures, and in particular those of polysaccharides, to create high-performance and environmentally friendly catalysts. Indeed, polysaccharides present many advantages that may stimulate their use as polymeric supports for catalysis: 1) They are present in enormous quantity on earth, 2) they contain many functionalities that can be used readily for the anchoring of organometallic species, 3) they contain many stereogenic centers, and 4) they are chemically stable but biodegradable. Surprisingly, although there has been a worldwide realization that nature-derived polysaccharides can provide the raw materials needed for the production of numerous industrial consumer goods, their use as supports for catalysis is still in its infancy. Chitosan (Figure 1 A) is a particularly attractive polysaccharide for application in catalysis owing to the presence of readily functionalizable amino groups and its insolubility in organic solvents. A copolymer of b(1!4)-2-amino-2-deoxyd-glucopyranose and 2-acetamido-2-deoxy-d-glucopyranose, chitosan results from incomplete deacetylation of chitin. At least 10 gigatons of chitin are constantly present in the biosphere; thus, chitosan is a renewable green material. Of

Towards the Ultimate Size Limit of the Memory Effect in Spin‐Crossover Solids

Although the originof the spin-crossover phenomenon is purely molecular, themacroscopic behavior of these systems in the solid state isstrongly influenced by short- and long-range interactions (ofmainly elastic origin) between the transition-metal ions,giving rise to remarkable cooperative phenomena, such asfirst-order phase transitions.

Supercritical CO2 dried chitosan: an efficient intrinsic heterogeneous catalyst in fine chemistry

Chitosan microspheres are used as catalysts for the synthesis of monoglyceride by fatty acid addition to glycidol. Microspheres are obtained by drying gel beads of the natural polymer under supercritical CO2 conditions, which makes the access to the polymer functional groups easy.

Magnetic water-soluble cyano-bridged metal coordination nano-polymers

Magnetic water-soluble cyano-bridged metallic coordination polymer nanoparticles of controlled size were prepared by using water-soluble chitosan beads.

Improving Catalytic Activity by Synergic Effect between Base and Acid Pairs in Hierarchically Porous Chitosan@Titania Nanoreactors

The beneficial effect of the bifunctional character of the chitosan@titania hybrid in heterogeneous catalysis was elucidated: considering a prototypical Henry condensation, Michael addition, and Jasminaldehyde synthesis, the cohabitation of a basic site (NH(2)) and an acidic site (Ti) in the same reactor provided clear activity and selectivity enhancements, with respect to the monofunctional acidic titania and basic chitosan counterparts.

Nanosized vanadium, tungsten and molybdenum oxide clusters grown in porous chitosan microspheres as promising hybrid materials for selective alcohol oxidation

The ability of chitosan biopolymer to coordinate vanadium, tungsten and molybdenum metallic species and to control their mineralisation growth provides a new family of surface-reactive organic-inorganic hybrid microspheres. Drying the resulting materials under supercritical conditions allowed the gel network dispersion to be retained, thereby leading to a macroporous catalyst with surface areas ranging from 253 to 278 m(2) g(-1). On account of the open framework structure of these microspheres, the redox species entangled within the fibrillar network of the polysaccharide aerogels were found to be active, selective and reusable catalysts for cinamylalcohol oxidations.

Nanocomposites from Natural Templates based on Fatty Compound-Functionalised Siloxanes

This work describes the synthesis of new, environmentally friendly, robust and biocompatible organic–inorganic hybrid materials based on fatty acid methyl ester-functionalised silica. The hydrosilylation reaction was used to covalently anchor 10-undecenoic methyl ester to a cyclic and acyclic backbone based on methylsiloxane repeating units. These as-synthesised amphiphilic precursors exhibit a self-assembling ability as shown by the formation of nanoobjects evidenced by fluorescence experiments, transmission electronic microscopy (TEM) and dynamic light scattering (DLS) analyses. Spherical nanocomposites featuring unprecedented flexibility, hydrophobicity and improved hydrolytic and thermal properties were built using sol–gel condensation of tetraethoxysilane (TEOS) controlled by these new self-assembling nanobuilding blocks. The textural characteristics and the morphology of these composite materials were dependent on the type of catalyst (acidic or basic) and the nature of the solvent (polar or apolar) used during the sol–gel polymerisation. This strategy opens new opportunities for advanced applications in various fields of nanochemistry and biomaterials.

Enantioselectivity Induced by Oxazaborolidine Supported on Mesoporous Silica or by Its Analog in Homogeneous Phase

The impact of immobilization of oxazaborolidines supported on silica via different substituents on the boron and nitrogen atoms is evaluated in the enantioselective reduction of acetophenone. The performances of the homogeneous analog oxazaborolidines and silica-supported ones are compared by varying different parameters. This article deals with the synthesis, characterization and catalytic evaluation of silica-supported oxazaborolidines, their recycling capabilities and regeneration limitations.