7 research outputs found
Applications des polyoxométalates en catalyse hétérogÚne
The aim of this work was preparation and characterization of catalysts based on polyoxometalates and their use in various catalytic reactions in heterogenous conditions. Methane C-H activation on silica-supported polyoxometalates was shown already at room temperature. Methoxy species [SiMo12O40(CH3)]3- from the 13C-enriched methane adsorption at 200°C on the surface of a silicadispersed silicomolybdic acid was detected by means of 13C SS NMR. Its hydrolysis led to methanol formation, thus completing the catalytic cycle. After 13C-enriched MeOH adsorption presence of two distinct methoxy species on the surface of polyoxometalates was shown, located on terminal (single coordinated) and bridging (double coordinated) oxygen atoms and resulting in the resonances at 58 and 77 ppm in 13C SS NMR. Grafting of PtMe2COD on the surface of various polyoxometalate supports led to methane or combined methane and ethane release, explained by means of oxidative addition/reductive elimination mechanism on metal centers. Ammonium salts of phosphotungstic acid catalyzed efficiently n-butane to isobutane skeletal isomerisation at mild conditions (225 °C, atmospheric pressure). Successful heterogenization of copper catalysts, active in enantioselective C-H carbene insertion reactions, on polyoxometalate supports have been shownLâobjectif de la thĂšse Ă©tait la prĂ©paration et la caractĂ©risation des catalyseurs hĂ©tĂ©rogĂšnes Ă base de polyoxomĂ©talates. LâĂ©tude mĂ©canistique dâoxydation du mĂ©thane jusquâau mĂ©thanol a montrĂ© que sur des polyoxomĂ©talates supportĂ©s sur la silice lâactivation C-H a lieu dĂ©jĂ Ă la tempĂ©rature ambiante. Lâadsorption du mĂ©thane-13C sur H4SiMo12O40 supportĂ©, suivie par RMN solide a mis en Ă©vidence la crĂ©ation de lâespĂšce mĂ©thoxy [SiMo12O40(CH3)]3-. Le cycle catalytique est complĂ©tĂ© par lâhydrolyse de cette espĂšce - mĂ©thanol est formĂ© et une molĂ©cule de lâeau recrĂ©e la structure du dĂ©part de polyoxomĂ©talate. Lâadsorption du mĂ©thanol-13C sur des polyoxomĂ©talates a montrĂ© la crĂ©ation de deux types des espĂšces methoxy, localisĂ©es sur des atomes dâoxygĂšnes terminaux ou pontants est caractĂ©risĂ©es par deux signaux RMN distincts â Ă 58 et 77 ppm, respectivement. En greffant un complexe de platine PtMe2COD sur les sels de cĂ©sium de polyoxometalates, le dĂ©gagement du mĂ©thane ou de la mĂ©lange du mĂ©thane et de lâĂ©thane a Ă©tĂ© observĂ© et expliquĂ© par la sĂ©quence de lâaddition oxydative du proton de polyoxometalate au centre mĂ©tallique, couplage C-H ou C-C et finalement lâĂ©limination rĂ©ductrice et libĂ©ration dâune molĂ©cule de gaz. Sels dâammonium de lâacide phosphotungstique H3PW12O40 ont Ă©tĂ© montrĂ©es de catalyser lâisomĂ©risation du n-butane a lâisobutane dans des conditions douces (225°C, 1 atm.). ComposĂ© du cuivre Cu(OTf)2 sur la surface des sels inorganiques des polyoxometalates donne des catalyseurs trĂšs actifs en insertion des carbĂšnes aux liaisons C-H des Ă©thers cycliques
Synergistic catalysis: highly diastereoselective benzoxazole addition to MoritaâBaylis-Hillman carbonates
An expedited method has been developed for the diastereoselective synthesis of highly functionalized alkyl-azaarene systems with good yields and high diastereoselectivities (>15 : 1 dr). The methodology includes a synergistic catalysis event involving organometallic (10 mol% AgOAc) activation of an alkyl azaarene and Lewis base (10 mol% DABCO) activation of a MoritaâBaylisâHillman carbonate. The structure and relative configuration of a representative product were confirmed by X-ray analysis
Evolution of Structure and of Grafting Properties of Îł-Alumina with Pretreatment Temperature
In this study, the nature of the hydroxyl groups present on Îł-alumina, Îł-Al<sub>2</sub>O<sub>3</sub>, pretreated at various temperatures has been reinvestigated by <sup>1</sup>H NMR spectroscopy. The peaks are assigned by comparison between experimental and simulated spectra, in agreement with previous IR studies. The lowest chemical shifts ÎŽ correspond to OH groups strongly bound to the most acidic Al atoms (Al<sub>IV</sub> and Al<sub>V</sub>). High chemical shifts ÎŽ are assigned to OH groups making hydrogen bonds. A large range of values is found depending on the strength of these bonds. The structure of the surface complexes obtained by grafting Hf(CH<sub>2</sub><i>t</i>Bu)<sub>4</sub>, <b>1</b>, on Îł-Al<sub>2</sub>O<sub>3</sub> at various pretreatment temperatures <i>T </i>(350, 500, 700 °C), referred to as <b>1-</b>Îł-Al<sub>2</sub>O<sub>3â(T)</sub>, and of their thermolysis products has been determined, by a combined experimental (mass balance, in situ IR,) and theoretical (DFT calculations) study. These results unambiguously prove the presence of two kinds of neopentylâmetal bonds, HfâCH<sub>2</sub><i>t</i>Bu and AlâCH<sub>2</sub><i>t</i>Bu for <b>1</b>-Îł-Al<sub>2</sub>O<sub>3â(500)</sub> and <b>1</b>-Îł-Al<sub>2</sub>O<sub>3â(700)</sub>, hence the existence of surface cationic low coordinated hafnium complexes. In contrast, for <b>1</b>-Îł-Al<sub>2</sub>O<sub>3â(350)</sub>, only neutral species exist. Hence, temperature pretreatment has a key role for controlling the chemistry of the alumina surface (density of OH groups, presence of highly Lewis acidic Al), the grafting mode of the Hf precursor, and the formation of cationic low coordinated active centers
Sequential development of several RT-qPCR tests using LNA nucleotides and dual probe technology to differentiate SARS-CoV-2 from influenza A and B
Sensitive and accurate RT-qPCR tests are the primary diagnostic tools to identify SARS-CoV-2-infected patients. While many SARS-CoV-2 RT-qPCR tests are available, there are significant differences in test sensitivity, workflow (e.g. hands-on-time), gene targets and other functionalities that users must consider. Several publicly available protocols shared by reference labs and public health authorities provide useful tools for SARS-CoV-2 diagnosis, but many have shortcomings related to sensitivity and laborious workflows. Here, we describe a series of SARS-CoV-2 RT-qPCR tests that are originally based on the protocol targeting regions of the RNA-dependent RNA polymerase (RdRp) and envelope (E) coding genes developed by the Charite Berlin. We redesigned the primers/probes, utilized locked nucleic acid nucleotides, incorporated dual probe technology and conducted extensive optimizations of reaction conditions to enhance the sensitivity and specificity of these tests. By incorporating an RNase P internal control and developing multiplexed assays for distinguishing SARS-CoV-2 and influenza A and B, we streamlined the workflow to provide quicker results and reduced consumable costs. Some of these tests use modified enzymes enabling the formulation of a room temperature-stable master mix and lyophilized positive control, thus increasing the functionality of the test and eliminating cold chain shipping and storage. Moreover, a rapid, RNA extraction-free version enables high sensitivity detection of SARS-CoV-2 in about an hour using minimally invasive, self-collected gargle samples. These RT-qPCR assays can easily be implemented in any diagnostic laboratory and can provide a powerful tool to detect SARS-CoV-2 and the most common seasonal influenzas during the vaccination phase of the pandemic