1,720,964 research outputs found
Potentiometric and spectroscopic studies on transition metal complexes of GlyLys(Gly) and Asp-epsilon-Lys
No full textCopper(II), nickel(II) and zinc(II) complexes of the peptides GlyLys(Gly) and Asp-epsilon-Lys, containing the amide functions at the c-amino groups of the lysyl residues were studied by potentiometric, UV-VIS and EPR spectroscopic methods. The stoichiometry of the major species formed in the copper(II)-GlyLys(Gly) system is [CuH-1L] and the EPR spectroscopic data indicate the existence of two isomeric forms of the complex. The nickel(II) and zinc(II)-GlyLys(Gly) systems have been characterised by the formation of stable [ML](+) complexes containing bis(NH2,CO) co-ordination and a macrochelate. Deprotonation and co-ordination of the amide groups were detected in the copper(II) and nickel(II) complexes. The co-ordination chemistry of Asp-epsilon-Lys is best described by the metal binding ability of the amino acid residues and it's high affinity for dimerisation. The stoichiometry of the dinuclear complexes can be given as [M2L2]. containing only amino acid binding sites. Deprotonation and co-ordination of the amide functions were suggested only in the copper(II)-containing systems, resulting in the formation of the [Cu2H-2L2](2-) dinuclear complex
Copper(II) complexes of N-terminal protected tri- and tetrapeptides containing histidine residues
No full textCopper(II) complexes of peptides containing two or three histidyl residues (Ac-HisGlyHis-OH, Ac-HisGlyHis-NHMe, Ac-HisHisGlyHis-OH and Ac-HisHisGlyHis-NHMe) have been studied by potentiometric, UV-Vis, EPR and CD spectroscopic measurements. The imidazole nitrogen atoms are described as the primary metal binding sites of all ligands resulting in the formation of various macrochelates in the pH range 4 to 7. The (N-im, N-, N-im)-co-ordinated [CuH-1L](0(+)) complexes were mainly detected in samples containing free carboxylates at the C-termini, whilst the [CuH-2L](-(0)) complexes were the predominant species in slightly alkaline solution and their binding modes were described via 4N-co-ordination (N-im, N-, N-, N-im) in (7,5,6)- membered fused chelate rings. Deprotonation and co-ordination of the third amide nitrogens were detected above pHsimilar to9 in all cases
Copper(II) complexes of oligopeptides containing aspartyl and glutamyl residues. Potentiometric and spectroscopic studies
No full textCopper(II) complexes of di-, tri- and tetra-peptides built up from Asp and/or Glu residues were studied by potentiometric and various spectroscopic techniques including UV-visible, circular dichroism and electron paramagnetic resonance measurements. The ligands contain two to five carboxylate functions and it generally results in the enhanced metal binding ability of the ligands, which is especially true for the oligopeptides of aspartic acid. In the case of peptides containing aspartyl residue in the N-terminal position the stability enhancement is reflected in the equilibrium data of the species [CuL] containing the (NH2, beta-COO-)-coordination mode in a 6-membered chelate. In the case of AspAsp and AspAspAsp the (NH2, N-, beta-COO-) and (NH2, N-, N-, beta-COO-)-coordination modes will be favoured, which contain (5,6) and (5,5,6)-joined chelate ring systems, respectively. The outstanding stability of the latter binding mode and the high negative charge of the corresponding species suppresses the metal ion coordination of the third amide function of AspAspAspAsp. It is also important to note that the presence of side chain carboxylate functions results in the formation of carboxylato-bridged polynuclear complexes in medium pH range. The extent of oligomerisation can be significantly enhanced by the increase of concentration and by the decrease of temperature. (c) 2005 Elsevier Inc. All rights reserved
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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