1,720,960 research outputs found
Interactions Between Quercetin and Warfarin for Albumin Binding: A New Eye on Food/Drug Interference
No full textThe interaction between quercetin, a popular antioxidant flavonoid, and human serum albumin (HSA) is investigated and characterized by means of induced circular dichroism and saturation transfer difference NMR. These techiques demonstrate the reversible binding of quercetin to the carrier protein, which is responsible for its dissolution in aqueous medium. Competition experiments with two classical probes for HSA binding sites, namely Ibuprofen and Warfarin (a common anticoagulant coumarin), demonstrate that quercetin has a primary binding site located in the subdomain IIA, where coumarins are hosted. The affinity for this site is large and we found that quercetin may effectively displace warfarin from HSA. This may have relevant consequences in rationalizing the interferences of common dietary compounds and food supplements to anticoagulant treatments
The structure of metal adducts of anthracyclines probed by absorption, circular dichroism and paramagnetic NMR
No full textA structural study of metal ion adducts of a new anthracycline disaccharide (MEN 10755) was undertaken. The trivalent lanthanide ion Yb(III) was employed as paramagnetic structural probe for H-1 NMR analysis. Through a comparative spectroscopic investigation [UV-Vis absorption and circular dichroism (CD), H-1 NMR], the isomorphism between its adducts with lanthanide ions (La3+, Yb3+, Lu3+) and calcium (one of the most representative biological cations) was verified. Solution behavior and cation binding were also investigated by means of optical titrations. In agreement with other anthracyclines, MEN 10755 was found to dimerize in aqueous solution [estimated K-dim (pH 7.6) = 7 x 10(3)], but not in methanol. A prevalent complex Yb3+-MEN 10755 (1:1) in both buffered aqueous and methanolic solutions (estimated K-compl = 2100 M-1) was observed. A numerical analysis of the LIR and LIS H-1 NMR literature data for a similar adduct (Yb3+-daunorubicin) was performed using newly developed software, PERSEUS (Paramagnetic Enhanced Relaxation and Shifts for Eliciting Ultimate Structures), and the structure of the complex was characterized, locating definitely the binding site on the O-11, O-12 quinone system. The components of the anisotropic part of the magnetic susceptibility tensor were also determined. Finally, a study of the time-dependent formation of an Yb3+-MEN 10755 complex through H-1 NMR, UV-Vis CD and induced NIR CD was carried out
The solution structure of a Lasalocid A metal complex in lipophilic solvents
No full textLasalocid A (LasNa), a common antibiotic in veterinary medicine, is a polyetheral ionophore, disrupting cation equilibria through the cell wall. By means of circular dichroism (in the UV and in the near-IR), paramagnetic NMR, and with the aid of the program PERSEUS, we determined the solution geometry of the 1: 1 Las-Yb(3+) complex in CD(3)CN and CDCl(3), following a protocol similar to the one successfully used for the anthracycline-metal adduct. The resulting structure is in full agreement with the expectation of the ligand wrapping around the cation in a horseshoe shape. The oxygen atoms participate in the coordination either through a direct, first sphere, or a longer range interaction
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
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