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Mono- and Polynuclear Complexes of the Model Nucleobase 1-Methylcytosine. Synthesis and Characterization of cis-[(PMe2Ph)2Pt{1-MeCy(-H)}]3(NO3)3 and cis-[(PPh3)2Pt{1-MeCy}]NO3
No full textStabilization of the iminooxo tautomer of 1-methylcytosine in PtII complexes: Role of the ancillary ligands
No full textRole of the ancillary ligands on the stabilization of the imino-oxo tautomer of 1-methyl-cytosine in PtII complexes
Full text linkThe mixed nucleobases complexes cis-[L2Pt{1-MeTy(-H)}(1-MeCy,N3)]NO3 (L = PPh3, 1a; PMePh2, 1b), containing the N(3)-deprotonated 1-methylthymine (1-MeTy(-H)) and the neutral 1-methylcytosine (1-MeCy) have been prepared and characterised. The compounds were obtained by reacting the hydroxo complexes cis-[L2Pt(μ-OH)]2(NO3)2 with 1-methylthymine (1-MeTy), followed by the addition of 1 equivalent of 1-MeCy. In solution of DMSO, DMF or chlorinated solvents, 1a converts quantitatively into the isomer cis-[L2Pt{1-MeTy(-H)}(1-MeCy,N4)]NO3 (2a) containing the tautomeric form of the cytosine stabilized through the coordination at the N(4) atom, as shown by single-crystal X-ray analysis. The structural determination of 2a shows the presence in the unit cell of two crystallographic independent complexes having similar conformation, with a different orientation of the two nucleobases (head–head and head–tail) according to the presence of both isomers in solution. Complex 1b, having the less hindered PMePh2 ligands, in DMSO solution, contains the tautomeric forms of the cytosine in equilibrium and the migration of the metal from the N(3) to N(4) site occurs only to a minor extent
Role of the phosphine ligands on the stabilization of monoadducts of the model nucleobases 1-methylcytosine and 9-methylguanine in platinum(II) complexes
Full text linkThe addition of 1-methylcytosine (1-MeCy) or 9-methylguanine (9-MeGu) to solutions of cis-(PPh3)2Pt(ONO2)2 (1a), in a molar ratio of 1:1, affords the monoadducts cis-[(PPh3)2Pt(1-MeCy)(ONO2)]NO3 (2a) and cis-[(PPh3)2Pt(9-MeGu)(ONO2)]NO3 (3a) and only trace amounts of the bisadducts cis-[(PPh3)2Pt(1-MeCy)2](NO3)2 (4a) and cis-[(PPh3)2Pt(9-MeGu)2](NO3)2 (5a), respectively. The X-ray structural determination of 2a and 3a indicates a strong π−π stacking interaction between one of the PPh3 phenyl groups and the pyrimydinic N3-platinated cytosine or the imidazole part of the N7-coordinated guanine base. The addition of a further equiv of nucleobase to the monoadducts forms quantitatively the bisadducts that have been isolated as pure compounds 4a and 5a. Under the same experimental conditions, the dinitrato analogue cis-[(PMePh2)2Pt(ONO2)2] (1b) forms the monoadducts 2b and 3b in equilibrium with a relatively high concentration (20–30%) of the bisadducts cis-[(PMePh2)2Pt(1-MeCy)2](NO3)2 (4b) and cis-[(PMePh2)2Pt(9-MeGu)2](NO3)2 (5b), which have been structurally characterized by single-crystal X-ray analysis. The characterization of the isolated complexes by multinuclear NMR spectroscopy is also described
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
Irreversible Insertion of Benzonitrile into Platinum(II)-Nitrogen Bonds of Nucleobase Complexes. Synthesis and Structural Characterisation of Stable Azametallacycle Compounds
Full text linkDeprotonation of 1-methylcytosine (1-MeCy) and 9-methyladenine (9-MeAd) promoted by cis-[L2Pt(μ-OH)]2(NO3)2 (L = PPh3, PMePh2, 1/2dppe) in PhCN causes the irreversible insertion of a nitrile molecule into the Pt−N4 and Pt−N6 bonds of the cytosinate and adeninate ligands, respectively, to form the stable azametallacycle complexes cis-[L2PtNH═C(Ph){1-MeCy(−2H)}]NO3 (L = PPh3, 1; PMePh2, 2; 1/2dppe, 3) and cis-[L2PtNH═C(Ph){9-MeAd(−2H)}]NO3 (L = PPh3, 4; PMePh2, 5) containing the deprotonated form of the molecules (Z)-9-N-(1-methyl-2-oxo-2,3-dihydropyrimidin-4(1H)-ylidene)benzimidamide and (Z)-N-(9-methyl-1H-purin-6(9H)-ylidene)benzimidamide. Single-crystal X-ray analyses of 2 and 4 show the metal coordinated to the N3 cytosine site [Pt−N3 = 2.112(7) Å̊] and to the N1 site of adenine [Pt−N1 = 2.116(6) Å̊] and to the nitrogen atom of the inserted benzonitrile [Pt−N2 = 2.043(6) and 2.010(6) Å̊ in 2 and 4, respectively], with the exocyclic nucleobase amino nitrogen bound to the carbon atom of the CN group. Complex 2, in solution, undergoes a dynamic process related to a partially restricted rotation around Pt−P bonds, arising from a steric interaction of the oxygen atom of the cytosine with one ring of the phosphine ligands. The reaction of 4 with acetylacetone (Hacac) causes the quantitative protonation of the anionic ligand, affording the acetylacetonate complex cis-[(PPh3)2Pt(acac)]NO3 and the free benzimidamide NH═C(Ph){9-MeAd(−H)}. In the same experimental conditions, complex 3 reacts with Hacac only partially
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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