100,619 research outputs found
L.Marchese, E. Gianotti, T. Maschmeyer, G. Martra, S. Coluccia, J.M. Thomas Spectroscopic Tools for Probing the Isolated Titanium Centres in MCM41 Mesoporous Catalysts
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An exploration of Silsesquioxanes and Zeolites using High-Speed experimentation
No full textCombinatorial Chemistry and High-Speed Experimentation techniques allow the rapid preparation and testing of large numbers of samples by using automated workstations. These techniques are increasingly applied to various fields of chemical research and particularly to catalysis. In this project, High-Speed Experimentation techniques were used to study two families of compounds with a silicon-oxygen framework: silsesquioxanes and zeolites. Silsesquioxanes are inorganic-organic hybrid materials with broad applications as model compounds for silica surfaces and as ligands in coordination chemistry and catalysis. Here, the synthesis of incompletely condensed silsesquioxanes as precursors for titanium catalysts active in the epoxidation of alkenes was optimised by means of High-Speed Experimentation techniques. This thorough study led to the identification of a number of trends, to new and more efficient methods to synthesise known silsesquioxanes and to the discovery of new silsesquioxane precursors for active catalysts. The most interesting results were reproduced at a conventional laboratory scale and the silsesquioxane products were fully characterised. One of these silsesquioxane structures was used to prepare an osmium complex that proved to be a useful model compound for a known heterogeneous catalyst and an active and safe homogenous catalyst for the dihydroxylation of alkenes. Zeolites are microporous crystalline materials with applications as heterogeneous catalysts, ion-exchangers and molecular sieves. The synthesis of aluminium-rich zeolite beta was investigated by means of High-Speed Experimentmation techniques in order to identify the lowest Si/Al ratio to obtain pure zeolite beta with hydrothermal methods.Applied Science
Chiral dirhodium catalysts immobilised in porous hosts: Synthesis and performance
No full textThe main objective of this research is to modify the catalytic properties of homogeneous chiral dirhodium catalysts upon immobilisation on the porous support materials silica, MCM-41 and TUD-1. The catalysts were immobilised via ligand exchange of one chiral ligand with a carboxylate tether group. This influences the enantio- and trans/cis selectivity of the catalysts in the cyclopropanation reaction of styrene with ethyl or tert-butyl diazoacetate and the Si-H insertion reaction of dimethylphenylsilane with methyl phenyldiazoacetate. The results show that it is possible to influence the selectivity of these catalysts by immobilising them. Leaching of the catalyst from the carrier materials remains a problem. Full conversions are still possible upon recycling, but analysis shows that a significant amount of rhodium leaches. In some cases the active catalyst leaches, in others the filtrate is not active, so non-active rhodium leaches. Future work needs to be addressed to the optimisation of the constraint induced by the pore walls as well as to the problem of leaching. The former would be greatly facilitated by computational modelling studies and the latter by ligands that are giving a more stable complex (e.g. four- or six-dentate ones).Applied Science
Murine T-Cell Transfer Colitis as a Model for Inflammatory Bowel Disease.
No full textInflammatory bowel disease (IBD) is a group of severe chronic inflammatory conditions of the human gastrointestinal tract. Murine models of colitis have been invaluable tools to improve the understanding of IBD development and pathogenesis. While the disease etiology of IBD is complex and multifactorial, CD4+ T helper cells have been shown to strongly contribute to the disease pathogenesis of IBD. Here, we present a detailed protocol of the preclinical model of T-cell transfer colitis, which can easily be utilized in the laboratory to study T helper cell functions in intestinal inflammation
Letter, [Author unclear] to Paulina T. Merritt
No full textHandwritten letter to Paulina Merritt from an unknown author, October 1, 1876.
Synthesis, Characterization and Catalytic Testing of a 3-D Mesoporous Titanosilica, Ti-TUD-1
No full textProbing the titanium sites in Ti-MCM41 by diffuse reflectance and photoluminescence UV-vis spectroscopies
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