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Zwitterion complexes of the cation dicyanobis 1,2 -bis (diphenylphosphino) ethane cobalt (III)
No full text9-Methyladenine complexes of platinum(II) stabilized by trimethylphosphine: Use of N-15 nuclear magnetic resonance spectroscopy to assign the coordination site
No full textThe new 9-methyladenine (made) complexes cis-[Pt(PMe(3))(2)(made)(2)][NO3](2) and cis-[{Pt(PMe(3))(2)(made - H)}(2)][NO3](2) have been prepared and characterized. They are formed by treating stoichiometric amounts of the nucleobase with an aqueous solution of cis-[Pt(PMe(3))(2)(NO3)(2)] at autogenous and neutral pH, respectively. A detailed multinuclear (H-1, P-31, Pt-195, C-13 and N-15 at natural abundance) NMR investigation in (CD3)(2)SO indicated that in the mononuclear complex the adenine ligands are N(1)-co-ordinated and that rotation around the metal-nitrogen bonds is slow on the NMR time-scale leading to the presence of two conformers with a relative abundance of ca. 2 : 1. In the dinuclear complex the NH2-deprotonated adenine acts as a bridging ligand through the N(1) and N(6) atoms. The sites of metal binding are clearly evidenced in the N-15 NMR spectra by the remarkable shifts shown by the co-ordinated nitrogens (60 ppm upfield for the endocyclic atom and 25 ppm downfield for the exocyclic one, with respect to the unco-ordinated nucleobase) and their coupling with the P-31 nucleus of the ligand in mutual trans position ((2)J(NP) ca. 60 Hz).The new 9-methyladenine (made) complexes cis-[Pt(PMe3)2(made)2][NO3] 2 and cis-[{Pt(PMe3)2(made - H)}2][NO3]2 have been prepared and characterized. They are formed by treating stoichiometric amounts of the nucleobase with an aqueous solution of cis-[Pt(PMe3)2(NO3)2] at autogenous and neutral pH, respectively. A detailed multinuclear (1H, 31P, 195Pt, 13C and 15N at natural abundance) NMR investigation in (CD3)2SO indicated that in the mononuclear complex the adenine ligands are N(1)-co-ordinated and that rotation around the metal-nitrogen bonds is slow on the NMR time-scale leading to the presence of two conformers with a relative abundance of ca. 2:1. In the dinuclear complex the NH2-deprotonated adenine acts as a bridging ligand through the N(1) and N(6) atoms. The sites of metal binding are clearly evidenced in the 15N NMR spectra by the remarkable shifts shown by the co-ordinated nitrogens (60 ppm upfield for the endocyclic atom and 25 ppm downfield for the exocyclic one, with respect to the unco-ordinated nucleobase) and their coupling with the 31P nucleus of the ligand in mutual trans position (2JNP ca. 60 Hz)
STRUCTURAL CHARACTERIZATION OF A TRINUCLEAR COMPLEX OF PLATINUM(II) CONTAINING BRIDGING 1-METHYLCYTOSINE LIGANDS - A COMBINED X-RAY AND MULTINUCLEAR NMR-STUDY
No full textThe dinuclear complexes cis-[(PMe3)2Pt(1-MeCy(-H))]2X2 (X = NO3- (1A), ClO4- (1B)), containing NH2-deprotonated 1-methylcytosine (1-MeCy(-H)) ligands, in aqueous or DMSO solution, at 80-degrees-C convert quantitatively into the corresponding trinuclear derivatives cis-[(PMe3)2Pt(1-MeCy(-H))]3X3(2A,B) which have been characterized in the solid state by single-crystal X-ray analysis and in solution by multinuclear (H-1, P-31, Pt-195, C-13, and N-15) NMR spectroscopy. The nitrate salt (2A) crystallizes from ethanol in the triclinic system, space group Pl. The crystals, stable only in the presence of the solvent, have the following cell dimensions: a = 13.542(5) angstrom, b = 17.352(5) angstrom, c = 20.721(6) angstrom, alpha = 113.13(2)degrees, beta = 104.30(3)degrees, gamma = 95.77(3)degrees, Z = 2. The structure, formulated as cis-[(PMe3)2Pt(1-MeCy(-H))]3(NO3)3.EtOH.H2O, was refined to R = 6.3 and R(w) = 6.3. Better structural data were obtained with the perchlorate derivative (2B), cis-[(PMe3)2Pt(1-MeCy(-H))]3(ClO4)3.2H2O, whose structure was refined to R = 4.4 and R(w) =4.9. The colorless prisms formed from aqueous solutions have the following crystallographic data: triclinic system, space group P1BAR, a = 14.634(7) angstrom, b = 14.791(9) angstrom, c = 14.980(9) angstrom, alpha = 101.93(5)degrees, beta = 103.46(5)degrees, gamma = 90.50(4)degrees, Z = 2. In both salts, the molecular structure of the cationic complex contains three cis-(PMe3)2Pt units linked to three 1-methylcytosine anions through the N(3) and N(4) atoms. The resulting 12-membered ring contains the pyrimidinic rings almost perpendicular to the plane defined by the metal atoms. Each platinum has a square-planar coordination with a Pt...Pt distance of 5.2A. The H-1, P-31, and C-13 NMR spectra indicate that the approximate S3 symmetry of the cation is maintained in solution. The compounds 1A and 2A were also characterized by N-15 NMR spectroscopy, at natural abundance. The spectroscopic data, obtained in DMSO-d6 solution, are compared with those of the derivative cis-[(PMe3)2Pt(1-MeCY)2](NO3)2 containing as ligands the neutral N(3)-bonded nucleobase. The dinuclear and trinuclear complexes exhibit very similar N-15 chemical shifts and 2J(PN) coupling constants but remarkably different from those of the mononuclear complex
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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