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Transport of the anti-diabetic VO2+ complexes formed by pyrone derivatives in the blood serum
No full textThe biotransformation in the blood serum of the two anti-diabetic agents [VO(ema)2] – or BEOV – and [VO(koj)2] formed by ethylmaltol (Hema) and kojic acid (Hkoj) was studied with EPR spectroscopy, pH-potentiometry and DFT calculations. For comparison, the behavior of the systems with tropolone (Htrop) was also analyzed. The interaction of [VO(ema)2] and [VO(koj)2] with the most important bioligands of the serum, lactic (Hlact) and citric acid (H3citr), human serum transferrin (hTf), human serum albumin (HSA) and immunoglobulin G (IgG) was examined and discussed. Among the several mixed species observed, cis-VO(carrier)2(hTf), cis-VO(carrier)2(HSA) and cis-VO(carrier)2(IgG), where carrier is ethylmaltolate or kojate, with a His-N of the protein coordinated in the equatorial position, are plausible candidates for the transport processes of the drug toward the target organs. The values of the logβ are in the range 19.6–19.8 for the species formed by ethylmaltol and 17.4–17.6 for those formed by kojic acid. The formation of such species was confirmed through pH-titrations of the model systems VO2 +/carrier/1-MeIm and VO2 +/carrier/Ac-his, where 1-MeIm and Ac-his are 1-methylimidazole and N-acetylhistamine, and DFT calculations of 51V Az of the model species cis-[VO(carrier)2(1-MeIm)] and cis-[VO(carrier)2(Ac-his)]. The values of the stability constants for the mixed species observed were used to predict the biodistribution of VO2 + ion between the blood serum components for concentrations of 1, 10 and 50 μM
VIVO and CuII complexation by ligands based on pyridine nitrogen donors
No full textThe binary and ternary systems formed by (VO)-O-IV and Cu-II ions with ligands (L) based on the pyridine ring (1,10-phenanthroline (phen), 2,2'-bipyridine (bpy), 2,2': 6',2 ''-terpyridine (terpy), 2,2'-bipyrimidine (bpm) and 2,3-bis(2-pyridyl)pyrazine (bpp)) were studied, combining spectroscopic (EPR and UV-vis), pH-potentiometric and computational (DFT calculations) methods. In the systems with (VO)-O-IV, the formation of mono-chelated complexes with equatorial-equatorial and equatorial-axial (phen, bpy, bpm and bpp) or equatorial-equatorial-equatorial and equatorial-axial-equatorial coordination (terpy) and bis-chelated species with cis-octahedral geometry, with a water or a hydroxido ion in the fourth equatorial position, is demonstrated. Phen, bpy, bpm and bpp form also a dinuclear [(VO)(2)L-2(H2O)(2)(OH)(2)](2+) complex with an anti-coplanar arrangement of the two (VO)-O-IV ions and a ferromagnetic coupling between the metal ions. Due to the low basicity of the nitrogen donors, the potentially tetradentate 2,2'-bipyrimidine and 2,3-bis(2-pyridyl)pyrazine behave like simple bidentate ligands, and in the ternary systems with 2,2'-bipyridine the expected dinuclear species, in which the former ligands would act as a bridge between the two metal ions using all four nitrogen donors, are not formed. The interaction of phen and Cu-II-phen complexes with human serum albumin (HSA) was also studied at pH 7.4 by circular dichroism and EPR spectroscopy, the formation of several HSA-Cu-II-phen containing species being confirmed and their binding constants determined
Characterization and biotransformation in the plasma and red blood cells of VIVO2 + complexes formed by ceftriaxone
No full textThe coordination mode and geometry in aqueous solution of oxidovanadium(IV) complexes formed by a third-generation cephalosporin, ceftriaxone (H3cef), were studied by spectroscopic (EPR, electron paramagnetic resonance), pH-potentiometric and computational (DFT, density functional theory) methods. The behavior of the model systems containing 6-hydroxy-2-methyl-3-thioxo-3,4-dihydro-1,2,4-triazine-5(2H)-one (H2hmtdt) and 3-benzylthio-6-hydroxy-2-methyl-1,2,4-triazine-5(2H)-one (Hbhmt) was examined for comparison. The stability of the tautomers of ceftriaxone and 6-hydroxy-2-methyl-3-thioxo-3,4-dihydro-1,2,4-triazine-5(2H)-one in the neutral, mono- and bi-anionic form was calculated by DFT methods, both in the gas phase and in aqueous solution, and the electron density on the oxygen atoms of the hydroxytriazinone ring was related to the pKa of the ligands. The data demonstrate that ceftriaxone coordinates VIVO2 + forming mono- and bis-chelated complexes with (Oket, O−) donor set and formation of five-membered chelate rings. The geometry of the bis-chelated complex, cis-[VO(Hcef)2(H2O)]2 −, is cis-octahedral and this species can deprotonate, around physiological pH, to form the corresponding mono-hydroxido cis-[VO(Hcef)2(OH)]3 −. The interaction of cis-[VO(Hcef)2(H2O)]2 − with apo-transferrin (apo-hTf) was studied and the results suggest that VIVO2 + distributes between (VO)apo-hTf/(VO)2apo-hTf and cis-[VO(Hcef)2(H2O)]2 −, whereas mixed complexes are not formed for charge and steric effects. The interaction of cis-[VO(Hcef)2(H2O)]2 − with red blood cells shows that ceftriaxone helps VIVO2 + ion to cross the erythrocyte membrane. Inside the cell cis-[VO(Hcef)2(H2O)]2 − decomposes and the same species formed by inorganic VIVO2 + are observed. The relationship between the biotransformation in the plasma and red blood cells and the potential pharmacological activity of VIVO2 + species of ceftriaxone is finally discussed
Tuning the hydrolytic properties of half-sandwich-type organometallic cations in aqueous solution
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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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