1,721,060 research outputs found
Direct identification of phenolic constituents in Boldo Folium (Peumus boldus Mol.) infusions by high-performance liquid chromatography with diode array detection and electrospray ionization tandem mass spectrometry
Get PDFA very simple and direct method was developed for the qualitative analysis of polyphenols in boldo (Peumus boldus Mol., Monimiaceae) leaves infusions by high-performance liquid chromatography with diode array detection (HPLC-DAD) and electrospray ionization tandem mass spectrometry (HPLC-MSn). The phenolic constituents identified in infusions of the crude drug Boldo Folium were mainly proanthocyanidins and flavonol glycosides. In the infusions, 41 compounds were detected in male and 43 compounds in female leaf samples, respectively. Nine quercetin glycosides, eight kaempferol derivatives, nine isorhamnetin glycosides, three phenolic acids, one caffeoylquinic acid glycoside and twenty one proanthocyanidins were identified by HPLC-DAD and ESI-MS for the first time in the crude drug. Isorhamnetin glucosyl-di-rhamnoside was the most abundant flavonol glycoside in the male boldo sample, whereas isorhamnetin di-glucosyl-di-rhamnoside was the main phenolic compound in female boldo leaves infusion. The results suggest that the medicinal properties reported for this popular infusion should be attributed not only to the presence of catechin and boldine but also to several phenolic compounds with known antioxidant activity. The HPLC fingerprint obtained can be useful in the authentication of the crude drug Boldo Folium as well as for qualitative analysis and differentiation of plant populations in the tree distribution range.Fil: Simirgiotis, Mario Juan. Universidad de Talca; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Schmeda Hirschmann, Guillermo. Universidad de Talca; Chil
Determination of phenolic composition and antioxidant activity in fruits, rhizomes and leaves of the white strawberry (Fragaria chiloensis spp. chiloensis form chiloensis) using HPLC-DAD-ESI-MS and free radical quenching techniques
Get PDFA comparative analysis of methanol extracts from fruits, rhizomes and leaves of the Chilean white strawberry (Fragaria chiloensis spp. chiloensis var chiloensis) was performed by means of reversed phase high-performance liquid chromatography coupled to diode array detection and electrospray ionization mass spectrometry (HPLC-DAD and HPLC-ESI-MS). The total phenolic, total flavonoid and total anthocyanin content of the extracts was measured and compared. For the first time, some 18 phenolic compounds were tentatively identified in rhizomes and 18 in leaves of the Chilean strawberry. The products were mainly procyanidins, ellagitannins, ellagic acid and flavonol derivatives. The different extracts of the native strawberry presented antioxidant activity, which was close to that exhibited by the white fruits. The rhizomes and leaves proved to be a good source of phenolic antioxidants. The obtained information can be used to characterize the local cultivars by metabolite profiling and provide a reference HPLC fingerprint for future comparison of chemical changes associated to the plant response towards environmental factors and pathogens.Fil: Simirgiotis, Mario Juan. Universidad de Talca; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; ArgentinaFil: Schmeda Hirschmann, Guillermo. Universidad de Talca; Chil
Chemistry of the Chilean Strawberry (Fragaria chiloensis spp. chiloensis)
Get PDFThe Chilean strawberry (Fragaria chiloensis spp. chiloensis) is one of the progenitors of the cultivated strawberry, Fragaria × ananassa.Recent studies have started to disclose the chemical composition of the native fruit, the secondary metabolite occurrence and distributionin different plant parts as well as the biological activity of the main fruit constituents. This article revises the chemistry of the Chileanstrawberry and compares some of the most characteristic constituents with that of the highly cultivated and worldwide known F. ×ananassa. The main phenolic in the white strawberry are ellagic acid or hexahydroxydiphenolic acid-based hydrolysable tannins and procyanidinsas well as flavonoid glycosides from quercetin and kaempferol. The general trend in the plant is the accumulation of condensedtannins of increasing molecular weight in the rhizomes while the leaf contains mainly hydrolysable tannins and flavonoids.Fil: Schmeda Hirschmann, Guillermo. Universidad de Talca; ChileFil: Simirgiotis, Mario Juan. Universidad de Antofagasta; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; ArgentinaFil: Cheel, José. CPN Ltd.; República Checa. Univerzita Karlova; República Chec
New Dammarane Triterpenes from the aerial parts of Ibicella lutea grown in Argentina
Get PDFTwo new dammarane triterpenes have been isolated from the aerial parts of Ibicella lutea, 3-acetyl-24- epi-polacandrin (1) and 1,3-diacetyl-24-epi-polacandrin (2), and were obtained along with the known compounds 20S*,24S*-epoxy-3â,12â,25-trihydroxydammarane (3) and apigenin. The structures of compounds 1 and 2 were deduced by spectroscopic studies and by chemical transformations leading to the preparation of derivatives 4-11. The structure and relative stereochemistry of 1 were verified by single-crystal X-ray analysis. The natural compounds and selected semisynthetic derivatives were evaluated against several tumor cells.Fil: Simirgiotis, Mario Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; ArgentinaFil: Jiménez, Carlos. Universidad da Coruña; EspañaFil: Rodríguez, Jaime. Universidad da Coruña; EspañaFil: Giordano, Oscar Santiago. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; ArgentinaFil: Tonn, Carlos Eugenio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; Argentin
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
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
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