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PHOTONUCLEASE ACTIVITY OF FAGOPYRIN, A PERYLENEQUINONE ISOLATED FROM Fagopyrum esculentum FLOWERS
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Structural Analysis of Fagopyrin Extracts by HPLC-MS, NMR and CD
No full textFagopyrin is a phenantro-perylenequinone present in the flowers of Fagopyrum aesculentum (buckwheat), endowed with photodynamic activity and responsible of a certain number of photosensitizing syndromes in grazing animals (fagopyrism)1. This molecule was firstly extracted, more than 30 years ago, by Brockmann, who ascertained its chemical constitution.2
More accurate structural investigations, performed on the related compound hypericin, showed that a high degree of structural and conformational complexity might be present,3 as the aromatic system is involved in different equilibria of tautomerism, dissociation, torsional isomerism, and homoassociation. In the case of fagopyrin, the presence of two piperidine rings at positions 2 and 5 introduces two new stereogenic centres, in addition to the axial chirality of the aromatic system. Apart from the fundamental work of Brockmann, who did not establish the absolute configuration of the isolated fagopyrin, no other study has appeared, reporting a detailed analysis of the various stereogenic centres.
Here, we wish to report our results regarding the stereochemistry of fagopyrin, as well as the composition of fagopyrin extracts; which actually proved to be complex mixtures of up to twenty molecules. Some of them are constituted by the same perylene-quinone, linked not only to piperidine, but also to pirrolidine moieties. This generates three different groups of closely related molecules (see Figure), depending on the nature of the linked heterocycles, with the generation of up to 8 stereoisomers within each family. The configuration of each stereocenter has been established by NMR and CD measurements, combined with ab-initio calculations (Gaussian03). Finally, the highly acidic hydroxyl groups allow the formation of zwitterionic species constituted by ion-pairs between the protonated amino groups and the negatively charged hypericinate ion.
1. Wender S. H., Gortner R. A., Inman O. L., J. Am. Chem. Soc., 1943, 65, 1733-1735.
2. Brockmann H., Lackner H., Tetrahedron Lett., 1979, 1575-1578.
3. Falk H., Angew. Chem. Int. Ed., 1999, 38, 3116-3136
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
Identification and characterization of a Bowman-Birk inhibitor active towards trypsin but not chymotrypsin in Lupinus albus seeds
No full textThe paper describes the purification, structural characterization and inhibitory properties of a trypsin inhibitor from Lupinus albus L., a leguminous plant believed to be devoid of any protease inhibitor. The protein has been isolated by a newly set-up procedure and characterized by direct amino acid sequencing, MALDI-TOF mass spectroscopy and circular dichroism. Inhibitory properties toward bovine trypsin and chymotrypsin, as well as its thermal and pH stabilities, have been also assessed. The inhibitor is 63 amino acid long (Mr 6858; pI 8.22) and it is capable to inhibit two trypsin molecules simultaneously, with a Kd of 4.2 ± 0.4 nM, but not chymotrypsin. BLAST search against UniProtKB/TrEMBL database indicates that the inhibitor belongs to the Bowman-Birk inhibitor (BBI) family. The interest in these serine-protease inhibitors arises from the ability to prevent or suppress carcinogen-induced transformation, as shown in various in vitro and in vivo model systems
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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