1,720,992 research outputs found
Graphene-Based Carbocatalysts for Thermoset Polymers and for Diastereoselective and Enantioselective Organic Synthesis
No full textThis review reports on the catalytic activity of graphene oxide (GO) and high-surface-area graphite (HSAG) for some relevant organic reactions. It is shown that the main drawbacks of graphite-based catalysts, that is, high catalyst loading and generally poor selectivity, can often be removed by operating under solvent-free conditions. Moreover, some reactions that are catalyzed by GO as well as HSAG are presented. For these reactions, stacking of the aromatic substrates with the graphitic planes plays a predominant role in the catalytic activity and the unexpected diastereoselective and enantioselective behaviors
Influence of a remote sulfinyl group on L-proline-catalyzed direct asymmetric aldol addition of acetone
No full textThe addition of acetone to rac-2-methylsulfinyl-benzaldehyde, catalyzed by secondary amines (morpholine, piperidine, L-proline, L-prolinamide and (S)-(–)-α,α-diphenyl-2-pyrrolidinemethanol trimethylsilyl ether), was realized. Interesting aspects, such as 1,4-asymmetric induction by the remote sulfinyl group of the aldehyde but also the stereochemical control and kinetic resolution of the racemic substrate by the chiral organocatalyst were examined. Finally, an unexpected stereoselective retro-aldol reaction catalyzed by L-proline was pointed out
Synthesis of multifunctionalized building blocks via vinylogous addition of Chan's diene to carbonyl and carbonyl-related electrophiles, mediated by molecular iodine
No full textThe synthesis of multifunctionalized β-ketoesters has been achieved by using molecular iodine as a catalyst under very mild conditions. The vinylogous addition of Chan's diene 1 to carbonyl and carbonyl-related compounds (aldehydes, ketones, imines and acetals) occurred with high efficiencies and with complete γ-selectivity, giving a useful method for the synthesis of interesting libraries of different δ-functionalized β-ketoesters. © 2011 Elsevier Ltd. All rights reserved
Edge-oxidation of graphites by hydrogen peroxide
No full textA simple and eco-friendly procedure of edge oxidation of high-surface area graphites, based on hydrogen peroxide treatments at 60 degrees C, is presented. Already, short-term treatments lead to O/C weight ratios higher than 0.1, leaving unaltered interlayer spacing and correlation length. This clearly indicates that all oxidized groups are located on exposed sites (mainly on lateral edges) of the graphitic layers. Short-term H2O2 treatments, as expected, increase hydrophilicity and reduce thermal stability with respect to the starting graphite. Long-term treatments, on the contrary, reduce hydrophilicity and increase thermal stability with respect to the starting graphite, mainly due to surface area reduction associated with the oxidation procedure. Exfoliation of a substantial fraction of the obtained edge-oxidized graphite can be achieved by simple procedures of dispersion and sonication in water
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Release of cationic drugs from charcoal
No full textThe goal of this research is to improve preparation of charcoal adducts in a manner suitable for cationic drug release, possibly using an eco-friendly procedure. Charcoal, widely commercialized for human ingestion, is oxidized by hydrogen peroxide in mild conditions. Adducts of a cationic drug (lidocaine hydrochloride, a medication used as local anesthetic) with charcoal are prepared after basification of charcoal and characterized mainly by elemental analysis, wide-angle X-ray diffraction, infrared spectroscopy and thermogravimetry. The drug in the prepared adducts is present in amount close to 30% by weight and can be readily released to both neutral and acidic aqueous solutions. Cation release, as studied by UV spectra of aqueous solutions, is faster in acidic solutions and is faster than for adducts with graphite oxide, which can be prepared only in harsh conditions
Solvent-free organocatalytic Mukaiyama-Michael addition of 2-trimethylsilyloxy furan to nitroalkenes catalyzed by Brønsted acids
No full textThe first organocatalytic Mukaiyama-Michael addition of 2-trimethylsilyloxy furan to nitroalkenes was promoted by Brønsted acids under solvent-free conditions. The conjugate addition took place in moderate to good yields with variously substituted nitroalkenes. The procedure is operationally simple and no workup is required
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