1,721,026 research outputs found
Analytical, biological and chemical investigations on selected classes of alkaloids
No full textAbstract: This PhD project focuses on the phytochemical, antiviral and analytical investigation of selected classes of alkaloids. The thesis contains two distinct parts; the first one dealing with Amaryllidaceae alkaloids and potential antiviral agents, more in particular against SARS-CoV-2; and the second one dealing with quality control of alkaloid-containing food supplements based on Maca (Lepidium meyenii). A general structure elucidation workflow was established, combining the power of computer-assisted structure elucidation (CASE) by DFT (density functional theory) calculations with various chromatographic and spectroscopic techniques. The workflow was successfully applied to determine 2D and 3D structures of all compounds in this study. In addition, the structure of a mistakenly assigned compound named \u201cmacaridine\u201d was revised to macapyrrolin C by DFT calculation of chemical shifts. The phytochemical investigations of the four plant species (Hymenocallis littoralis, Pancratium maritimum, Scadoxus multiflorus, Lepidium meyenii) led to the discovery of nine novel alkaloids as well as extended the phytochemical profiles of the plant species. A library of Amaryllidaceae alkaloids was built and screened in vitro against the emerging SARS-CoV-2 and cytotoxicity on Vero-E6 cell line. As a result, thirteen compounds displayed moderate inhibition of SARS-CoV-2 replication (EC50 = 39 \u2013 100 \ub5M); ten compounds were devoid of activity and cytotoxicity, and twelve compounds lacked selective activity, since they were cytotoxic. Preliminary evaluation of structure-activity relationships revealed four skeleton-types (lycorine, homolycorine, crinine, and galanthamine) as promising scaffolds for further research. A new UPLC-TQD-MS/MS method was developed and validated for quality control of alkaloids in Maca-containing food supplements, because of their suspected toxicity. This represents the first analytical method for this purpose. Results obtained from analyses of commercial products indicate the alkaloid content of 500 \u2013 600 ppm in pure Maca powder. From a regulatory point of view, and based on safety concerns about the alkaloidal constituents of L. meyenii, it may be advisable to establish a maximum level of particular alkaloids or alkaloid classes in food supplements containing Maca, rather than to request their total absence. Also, we recommend the use of lepidilines as chemical markers for characterization of Maca in all types of commercial preparation due to their high content, exclusive existence in Maca and ultra-sensitivity to MS detection
Cyclopeptide alkaloids : isolation, structure elucidation, antiplasmodial activity and AGEs inhibiting properties
No full text
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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