Aerobic Oxidation of Alcohols in Carbon Dioxide with Silica-Supported Ionic Liquids Doped with Perruthenate

The replacement of toxic CrVI for O2 and of chlorinated solvents for supercritical carbon dioxide (or ionic liquids) in the oxidation of alcohols remains hindered by the low selectivity and activity of the current heterogeneous catalysts. Using an integrated approach that combines sol–gel entrapped perruthenate as aerobic catalyst, an encapsulated ionic liquid as solubility promoter, and scCO2 as the reaction solvent, we have developed a system capable of rapidly converting different alcohols into carbonyl compounds with complete selectivity, including substrates which are otherwise difficult to oxidise. The methodology is generally applicable and may easily be extended to other waste-free, catalytic syntheses of fine chemicals

Linking Two Immuno-Suppressive Molecules: Indoleamine 2,3 Dioxygenase Can Modify HLA-G Cell-Surface Expression1

Nonclassical human leukocyte antigen (HLA) class I molecule HLA-G and indoleamine 2,3 dioxygenase (INDO) in humans and mice, respectively, have been shown to play crucial immunosuppressive roles in fetal-maternal tolerance. HLA-G inhibits natural killer and T cell function by high-affinity interaction with inhibitory receptors, and INDO acts by depleting the surrounding microenvironment of the essential amino acid tryptophan, thus inhibiting T cell proliferation. We investigated whether HLA-G expression and INDO function were linked. Working with antigen-presenting cell (APC) lines and monocytes, we found that functional inhibition of INDO by 1-methyl-tryptophan induced cell surface expression of HLA-G1 by HLA-G1- negative APCs that were originally cell-surface negative, and that in reverse, the functional boost of INDO by high concentrations of tryptophan induced a complete loss of HLA-G1 cell surface expression by APCs that were originally cell-surface HLA-G1-positive. This mechanism was shown to be posttranslational because HLA-G protein cell contents remained unaffected by the treatments used. Furthermore, HLA-G cell surface expression regulation by INDO seems to relate to INDO function, but not to tryptophan catabolism itself. Potentia

Influence of Alkylene Chain Length on the Morphology of Chiral Bridged Silsesquioxanes

International audienceFour chiral diureido derivatives of trans-(1R,2R)- and trans-(1S,2S)-diaminocyclohexane with different carbon chain lengths (n = 3, 4, 5, 10) were synthesized and were hydrolyzed in aqueous acidic conditions in order to examine the role of the carbon chain spacer on the resulting hybrid bridged silsesquioxanes. Solid state NMR (29Si and 13C) studies demonstrated the presence of covalently bonded organo-bridged silica networks in these materials. Scanning electron microscopy (SEM) showed the materials obtained from the short chain derivatives to consist of fibers (n = 3 and 4). In contrast, plate-like shapes were formed from the longer chain precursors (n = 5 and 10). A lamellar structure was observed via transmission electron microscopy (TEM) for the hybrid obtained from the precursor with the longest chain (n = 10). This lamellar form was confirmed by powder X-ray diffraction (PXRD) measurement of the hybrid

Chiral amino-urea derivatives of (1R,2R)-1,2-diaminocyclohexane as ligands in the ruthenium catalysed asymmetric reduction of aromatic ketones by hydride transfer

International audienceSeveral new chiral urea and thiourea ligands have been prepared by reaction of (1R,2R)-1,2-diaminocyclohexane with various organic isocyanates and isothiocyanates. These were used as ligands in the ruthenium catalysed enantioselective reduction of aromatic ketones by isopropanol. The reduction proceeded at room temperature using 2 mol% of ruthenium catalyst to give good yields of the (R)-alcohol with enantiomeric excesses of up to 83%. By contrast, the use of bis-urea ligands gave much lower enantioselectivities. Amino-thiourea ligands led to the (S)-alcohol with low enantiomeric excess

Shape-Controlled Bridged Silsesquioxanes: Hollow Tubes and Spheres

International audienceA new approach for the morphological control of bridged silsesquioxanes has been achieved by the hydrolysis of silylated organic molecules bearing urea groups. The urea groups are responsible for the auto-association of the molecules through intermolecular hydrogen-bonding interactions. The self-assembly leads to supramolecular architectures that have the ability to direct the organization of hybrid silicas under controlled hydrolysis. The hydrolysis of the chiral diureido derivatives of trans-(1,2)-diaminocyclohexane 1 under basic conditions has been examined. The solid-state NMR spectra (29Si and 13C) showed the hybrid nature of these materials with wholly preserved SiC covalent bonds throughout the silicate network. Hybrid silicas with hollow tubular morphologies were obtained by the hydrolysis of the enantiomerically pure compounds, (R,R)-1 or (S,S)-1, whereas the corresponding racemic mixture, rac-1, led to a hybrid with ball-like structures. The tubular shape is likely to result from a combination of two phenomena: the auto-association abilities and a self-templating structuration of the hybrid materials by the organic crystalline precursor. Electronic microscopy techniques (SEM and TEM) gave evidence for the self-templating pathway. The formation of the ball-like structures occurs through a usual nucleation growth phenomenon owing to a higher solubility of the corresponding crystals in the same medium

Hybrid silica with molecular recognition properties

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New Hybrid Organic-Inorganic Solids with Helical Morphology via H-Bond Mediated Sol-Gel Hydrolysis of Silyl Derivatives of Chiral (R,R)- or (S,S)-Diureidocyclohexane

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Lamellar organo-bridged silicones

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Hybrid Organic-Inorganic Materials Derived from a Monosilylated Hoveyda-type Ligand as Recyclable Diene and Enyne Metathesis Catalysts

International audienceThe synthesis of a monosilylated Hoveyda-type monomer is described as well as the preparation of several organic-inorganic hybrid materials derived from it by sol-gel processes and by anchoring to commercial silica gel and MCM-41. The resulting materials were treated with first and/or second generation Grubbs catalyst to generate Hoveyda-Grubbs type alkylidene ruthenium complexes covalently bonded to the silica matrix. These materials are efficient recyclable catalysts for the ring-closing metathesis reaction of dienes and enynes, even for the formation of tri- and tetrasubstituted olefins

Facile Cleavage of Si-C Bonds during the Sol-Gel Hydrolysis of Aminomethyltrialkoxysilanes - A New Method for the Methylation of Primary Amines

International audienceThe reaction of chloromethyltriethoxysilane with (1R,2R)-bis(methylamino)cyclohexane (1) afforded the corresponding bis-silylated compound 2. The sol-gel hydrolysis of 2 did not give the expected bridged silsesquioxane owing to quantitative Si-C-bond cleavage. Instead, silica and (1R,2R)-bis(dimethylamino)cyclohexane (3) were obtained. This reaction was exploited to propose a new route for the methylation of amines. Such methylation reaction of amines could be extended to other amines and provides a new method for the selective monomethylation of primary amines