1,720,957 research outputs found
Studies on organic synthesis through sustainable catalysis
No full textToday the development of sustainable processes in the chemical industry is critical, and Green Chemistry represents an evolution from the conventional concepts of process efficiency. Twenty years ago, Paul Anastas and John Warner introduced this concept within the twelve principles. In this work, many aspects the twelve principles are applied, developing sustainable methods involving the use of metal catalysis and biocatalysis through one pot and cascade reactions.In the first part of the PhD period, the use of the micellar catalysis was investigated, to perform reactions in water avoiding (or limiting) the use of the traditional organic solvents. The possibility to apply the micellar conditions for the hydrogen borrowing (HB) reaction to prepare amines was explored. Different Ru catalysts were screened using water as medium, under Microwave (MW) dielectric heating. Once optimized, the scope of the reaction was investigated using differently substituted amines and alcohols. Besides, the use of a biomass-derived solvent (GVL) was explored in Pd/C catalysed transformations to avoid the arching phenomena frequently observed using conventional solvents (e.g. toluene). A sustainable protocol for the synthesis of benzimidazoles employed different aliphatic and aromatic amines through a hydrogen transfer Pd/C. A heating profile and various studies of stability have been reported. A biocatalytic approach to pyridine and furans is also reported. These heterocycles are fundamental building blocks for the synthesis of pharmaceuticals, agrochemicals and organic material. Furthermore, these compounds are also employed in flavour and fragrance industry owing to their peculiar olfactory properties. Classical methodologies for their synthesis are based on low-yielding multistep methods, which involve the use of harsh conditions. Therefore, novel mild and greener methodologies for the preparation of heterocycles compounds are highly desirable. Aromatization of substituted 1,2,3,6-tetrahydropyridines (THPs) was performed using whole-cell monoamine oxidase MAO-N (variants from Aspergillus niger) catalyst. The aromatization of the tetrahydropyridine starting materials into the pyridine products was monitored through 1H NMR spectroscopy. During the optimization, different pyridine compounds are prepared to screen the best co-solvents and MAO-N variants. The kinetic profile of the biocatalytic transformation by MAO-N was also monitored via in situ 19F NMR experiments. Aromatization of different 2,5-dihydrofurans into corresponding furans was also performed using the Laccase/TEMPO catalytic system using mild conditions. A chemo- enzymatic cascade reaction starting directly from acyclic aliphatic precursor has been developed
showing that metathesis Grubb's catalyst and the Laccase/TEMPO system can be used in combination for an efficient protocol
Avoiding hot-spots in Microwave-Assisted Pd/C catalysed reactions by using the biomass derived solvent γ-Valerolactone
Full text linkHerein, we report the use of γ-valerolactone as a new biomass-derived reaction medium for microwave assisted organic synthesis. The interaction of this solvent with microwaves and its heating profile under microwave irradiation has been fully characterized for the first time, demonstrating its stability and the applicability in microwave assisted Pd/C catalysed reactions avoiding the arcing phenomena frequently observed in these conditions. The use of γ-valerolactone demonstrated to be compatible with aliphatic and aromatic amines in the hydrogen transfer Pd/C mediated synthesis of benzimidazoles
In water alkylation of amines with alcohols through a borrowing hydrogen process catalysed by ruthenium nanoparticles
No full textA simple and environmentally benign procedure for the synthesis of secondary amines in water has been developed. Combining Ru3(CO)12, tetraphenylcyclopentadienone and a small quantity of TGPS-750-M surfactant, primary and secondary alcohols were alkylated at N employing equimolar amounts of aromatic amines in water. The reaction occurs under microwave (MW) dielectric heating with high conversion and high yield. When required, the use of biomass-derived 2-MeTHF or GVL as a co-solvent is possible. Under the influence of MWs, a Ru nanoparticle–nanomicelle combination was formed acting as an effective and recyclable catalyst. This protocol was also employed for “in water” cyclisation to synthesise biologically relevant pyrrolobenzodiazepines (PBDs).
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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