1,720,996 research outputs found
Uv-a Photolysis of Khellin - Products and Reaction-mechanism
No full textPhotolysis at 365 nm of khellin in various solvents was studied: the degradation rate strongly depends on solvent but not on polarity, since it is related to the singlet oxygen lifetime in each solvent. Eight products were isolated and characterized, some of which had previously been described as coming from chemical oxidation of khellin. Both facts support an oxic pathway for photolysis involving singlet oxygen and leading to unstable intermediates. These are rapidly decomposed by nucleophiles, suggesting possible interference-if they are also formed in vivo-with physiological processes during photochemotherapeutic treatment with khellin
Inibitori delle fosfodiesterasi
No full textIl capitolo illustra la progettazione, le proprietà chimico-fisiche, farmacocinetiche e farmacodinamiche dei principali inibitori selettivi delle fosfodiesterasi, con particolare attenzione verso gli agenti terapeutici
Activity of 3-carbethoxyangelicin photolysis products
No full text3-Carbethoxyangelicin (3-CA), carrying an electron-withdrawing group at the pyrone side, has been prepared to have a fully monofunctional angelicin derivative. 3-CA does not photoreact with DNA and induces a moderate antiproliferative activity. 3-CA proved to be extremely sensitive to ultraviolet A (UVA) light, undergoing rapid photolysis. Only one photolysis product has been isolated and identified. By means of alkaline elution, we observed that 3-CA and its photolysis products are able to induce a large amount of single-strand breaks in DNA in vivo. The results obtained from studying the capacity to produce singlet oxygen suggest that the photodynamic mechanism of action of 3-CA very likely results from its capacity-as well as that of its photolysis products-to produce singlet oxygen. (C) 1997 Elsevier Science S.A
The Photodegradation of Quercetin: Relation to Oxidation
Full text linkThe photostability of quercetin in alcoholic solutions was studied. Both UVA and UVB light induced degradation of quercetin, yielding a single product <strong>1</strong> deriving from oxidation and addition of an alcohol molecule to the 2,3 double bond. The same mechanism operated when quercetin was dissolved in alkaline solutions, and again a product <strong>2</strong> due to oxidation and addition of water was characterized. Comparison with quercetin analogs confirmed that, despite the presence of five hydroxy groups in quercetin, those in positions 3, 3′, and 4′ are mainly involved in the antioxidant activity of the compound , as well as in its photolability
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
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