Room temperature Suzuki coupling of aryl iodides, bromides, and chlorides using a heterogeneous carbon nanotube-palladium nanohybrid catalyst

International audiencePalladium nanoparticles were immobilized on multi-walled carbon nanotubes by a layer-by-layer approach, resulting in a well-defined assembly. The nanohybrid was found effective in promoting Suzuki cross couplings of various halogenated aromatics, including chlorinated ones, with arylboronic acids under sustainable conditions. The heterogeneous catalyst could also easily be recovered from the reaction mixture and reused with no loss of activity over several cycles

Selective conversion of nitroarenes using a carbon nanotube-ruthenium nanohybrid

International audienceRuthenium nanoparticles were assembled on carbon nanotubes and the resulting nanohybrid was used in the hydrazine-mediated catalytic hydrogenation of various nitroarenes, at room temperature. Depending on the solvent, a selective transformation occurred, giving either access to the corresponding aniline or hydroxylamine derivative

Mild and selective catalytic oxidation of organic substrates by a carbon nanotube-rhodium nanohybrid

International audienceA heterogeneous catalyst was assembled by stabilization of rhodium nanoparticles on carbon nanotubes. The nanohybrid was used for the catalytic aerobic oxidation of diverse substrates such as hydroquinones, hydroxylamines, silanes, hydrazines and thiols, at room temperature. The system proved very efficient on the investigated substrates and demonstrated high selectivity. The selective oxidation of organic compounds under mild conditions is of practical importance in synthetic chemistry. In addition to classical stoichiometric processes, catalytic systems have been devised to perform oxidation reactions. 1 Further improvements in terms of sustainability were also achieved by supporting the catalysts, thus allowing their reclaim and reuse. 2 Among the various catalyst supports, nanostructured carbon allotropes, in particular carbon nanotubes (CNTs), have emerged as highly promising platforms that provide unique advantages such as chemical, thermal, and mechanical stability in liquid media, inertness, high specific surface area, and chemically tunable topography. 3 We previously reported supramolecular assemblies of metallic nanoparticles (e.g. Au, Pd, Ru) on carbon nanotubes. These assemblies afforded metal-coated CNTs that were subsequently used in the heterogeneous catal-ysis of various organic transformations. 4 In the course of our investigations we demonstrated that CNTs acted as synergistic support capable of enhancing the performances of the catalytic metal. With these critical features in mind, we sought to expand the scope of our nanohybrid systems by developing a catalyst that would promote a broad scope of oxidation reactions under mild and sustainable conditions

Risk of peanut- and tree-nut-induced anaphylaxis during Halloween, Easter and other cultural holidays in Canadian children.

BACKGROUND: It is not established whether the risk of anaphylaxis induced by peanuts or tree nuts in children increases at specific times of the year. We aimed to evaluate the risk of peanut-and tree-nut-induced anaphylaxis during certain cultural holidays in Canadian children. METHODS: We collected data on confirmed pediatric cases of anaphylaxis presenting to emergency departments in 4 Canadian provinces as part of the Cross-Canada Anaphylaxis Registry. We assessed the mean number of cases per day and incidence rate ratio (IRR) of anaphylaxis induced by unknown nuts, peanuts and tree nuts presenting during each of 6 holidays (Halloween, Christmas, Easter, Diwali, Chinese New Year and Eid al-Adha) versus the rest of the year. We estimated IRRs and 95% confidence intervals (CIs) using Poisson regression. RESULTS: Data were collected for 1390 pediatric cases of anaphylaxis between 2011 and 2020. Their median age was 5.4 years, and 864 (62.2%) of the children were boys. During Halloween and Easter, there were higher rates of anaphylaxis to unknown nuts (IRR 1.66, 95% CI 1.13-2.43 and IRR 1.71, 95% CI 1.21-2.42, respectively) and peanuts (IRR 1.86, 95% CI 1.12-3.11 and IRR 1.57, 95% CI 0.94-2.63, respectively) compared to the rest of the year. No increased risk of peanut- or tree-nut-induced anaphylaxis was observed during Christmas, Diwali, Chinese New Year or Eid al-Adha. Anaphylaxis induced by unknown nuts, peanuts and tree nuts was more likely in children aged 6 years or older than in younger children. INTERPRETATION: We found an increased risk of anaphylaxis induced by unknown nuts and peanuts during Halloween and Easter among Canadian children. Educational tools are needed to increase awareness and vigilance in order to decrease the risk of anaphylaxis induced by peanuts and tree nuts in children during these holidays

Direct and co-catalytic oxidative aromatization of 1,4-dihydropyridines and related substrates using gold nanoparticles supported on carbon nanotubes

International audienceA heterogeneous catalyst was assembled by stabilization of gold nanoparticles on carbon nanotubes. The resulting nanohybrid was used in the catalytic aerobic oxidation of 1,4-dihydropyridines. The system proved very efficient on the investigated substrates either directly or in the presence of a quinone co-catalyst. Pyridines have found applications in various domains such as in the synthesis of drugs, 1 herbicides, 2 or insecticides. 3 In addition, the pyridine scaffold plays a central role in living systems since nicotinamide adenine dinucleotide (NAD + / NADH) and nicotinamide adenine dinucleotide phosphate (NADP + /NADPH) are key pyridine-incorporating co-factors involved in oxido-reduction processes. 4 Among the various methods developed for the synthesis of pyridine derivatives, 5 the oxidation of Hantzsch 1,4-dihydropyridines is likely one of the most straightforward approaches. The Hantzsch pyridine synthesis is a multi-component process which involves an aldehyde, two equivalents of a β-keto ester, and a nitrogen atom source. The initial condensation affords a dihydro-pyridine intermediate which can be oxidized, in a second step, into the corresponding pyridine. This reaction was reported for the first time in 1881 by Arthur Hantzsch. 6 Numerous reagents have been reported to promote the second step-oxidative aromatization reaction and include, for example , copper bromide, 7 ferric chloride, 8 palladium on carbon, 9 manganese dioxide, 10 and tert-butylhydroperoxide. 11 However, the oxidation of dihydropyridines is not always easy when substrates bear sensitive functional groups and there is still the quest for mild and general protocols. Also, some of the reported procedures lead to the formation of by-products which can be difficult to remove from the reaction mixture. Therefore, the development of milder, sustainable, and more effective methods for the oxidative aromatization of 1,4-dihydropyridines is sound. In the present article, we report the assembly and use of a recyclable CNT-supported gold catalyst for the selective and mild aerobic oxidation of 1,4-dihydropyridines (DHPs) and related substrates (Fig. 1). The CNT-gold catalyst was assembled using a layer-by-layer approach according to a previously reported procedure Fig. 1 Overview of the catalytic assembly and catalyzed oxidation process studied in the present work

Biogenèses et synthèses biomimétiques des alcaloïdes isolés de plantes du genre Nitraria

CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocSudocFranceF

Auto-construction et synthèse biomimétique d alcaloïdes polycycliques complexes

Au cours de ce travail, nous avons abordé la synthèse biomimétique de plusieurs alcaloïdes polycycliques complexes selon une philosophie générale d auto-construction, tentant de tirer partie de la réactivité spontanée de précurseurs chimiques, sélectionnés après une étape importante de réflexion sur la biogenèse des molécules ciblées. La synthèse totale de la nitraramine, alcaloïde spiranique complexe isolé de plantes du genre Nitraria (Zygophyllaceae), a pu être réalisée en une seule étape avec une efficacité bien supérieure à ce que la littérature décrivait jusqu alors. La très grande stéréosélectivité de la cascade réactionnelle impliquée a également été mise en évidence, en montrant une absence totale de formation d épinitraramine, permettant ainsi la correction des données de la littérature concernant cette molécule.Throughout this work, the biomimetic syntheses of several complex polycyclic alkaloids have been studied following a general self-construction philosophy, aiming at taking advantage of the spontaneous reactivity of simple chemical precursors that were selected with the target molecules biogenesis in mind. The total synthesis of nitraramine, a complex spiro-alkaloid isolated from plants of the Nitraria genus (Zygophyllaceae), was achieved in one step with great efficacy. The stereoselectivity of the implied reaction cascade was highlighted as no formation of epinitraramine was observed, and in the process, the literature data concerning that compound were revised. Studies carried out around the total synthesis of two other Nitraria alkaloids, tangutorine and nitrarine, led to the design of simple reactive compounds (derived from (E)-hept-3-ene-1,3,7-tricarbaldehyde) designed as tetrahydroanabasine analogs.CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocSudocFranceF

Fullerenes make copper catalysis better

International audienceEthylene glycol can be reliably produced by mild hydrogenation of dimethyl oxalat

Where do nanometric micelles stand for biomedical applications?

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Catalytic Processes for the Neutralization of Sulfur Mustard

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