1,721,001 research outputs found
Selective Synthesis and Biological Application of Flavonoids
Get PDFSecondary metabolites such as alkaloids, polyphenols, and isoprenoids are produced by plants. From these, flavonoids are one of the most naturally found polyphenol organic compounds. Flavonoids have a wide range of biological uses such as anti-diabetic activity and anti-cancer activity as well as antioxidant properties. This review article presents the various chemical synthetic methods of flavonoids. Flavonoids are prepared from chalcones, coumarin, 1,3-diones, eugenol using cyclic oxidation, Wacker oxidation, Suzuki-Miyaura reaction, and Knoevenagel condensation. Flavonoids can be divided into three main classes such as flavones, isoflavonoids and neoflavonoids (4-arylcoumarins). Flavones are successfully synthesized by Baker and Venkatraman synthesis and Claisen-Schmidt condensation method while Isoflavonoids are prepared using deoxybenzoin, Suzuki-reaction, oxidative rearrengement, and chalcone routes. Neoflavonoids are synthesized from coumarin using Suzuki-Miyaura reaction and Knoevenagel condensation system
Recent Advances in Synthesis of Coumarins: Coumarin Derivatives and Their Biological Application
No full textCoumarin was first extracted from Tonka bean by Vogel in 1820. Coumarin and its derivatives are important groups of compounds due to their medicinal and pharmacological properties. These compounds have a significant role in the development of new drugs. Many different conventional methods and non-conventional methods have been developed to synthesize coumarin derivatives. The objective of this review paper is to present the various methods of coumarin synthesis, both conventional and green synthesis. Techniques such as heating, microwave, and ultrasound irradiation were employed. Moreover, various solvents and catalysts were employed to obtain better yields. The present review revealed that the conventional methods are time-consuming, environmentally polluting, and lower in yield whereas the green synthesis of coumarin derivatives is better in yield, environmentally eco-friendly, and rapid. This review summarized several conventional methods, non-conventional methods and reaction conditions for the synthesis of coumarin derivatives from various precursors such as aldehydes, carboxylic acids, ketones and phenols. Literature collection was conducted using various search engines
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Phytochemical Investigation and Antibacterial Activity Assessment of Zehneria scabra (L.f) Sond (ሀረግ ሬሣ) Leaves Extract
No full textThis study was intended to identify chemical constituents of methanol (99%) leaves extract of Zehneria scabra (L.f) Sond. The crude extract fractions were tested against Staphylococcus aureus and Escherichia coli using the agar well diffusion method at 100 mg/ml concentrations in the presence of positive control. The phytochemical was isolated and purified by using preparative thin-layer chromatography (in a solvent system of 10% ethyl acetate: 90% chloroform). The structure of the isolated component was determined by using a combination of spectroscopic techniques such as IR, 1H NMR, 13C NMR, and DEPT-135 spectra. The phytochemical screening of methanol crude extract indicated the presence of alkaloids, flavonoids, terpenoids, glycosides, and tannins. The chloroform and ethyl acetate fraction revealed more potent antibacterial activities
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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