1,721,102 research outputs found
Matrix assisted laser desorption/ionisation (MALDI)-TOF mass spectrometry of supramolecular metalloporphyrin assemblies: a survey
No full textAnalysis of a representative series of metalloporphyrins and of their supramolecular assemblies using laser desorption/ionisation time of
flight mass spectrometry (LDI-TOF MS) revealed that non-covalent metal-ligand interactions in the complexes remain effective in the gas phase. Detectable assemblies range from simple ruthenium(II) porphyrin complexes with N- or P-donor ligands, or tin(IV) and zirconium(IV) porphyrin complexes with O-donor ligands, up to trimeric arrays. Crucial to successful recording of intact complexes is avoiding protic matrices which interfere with Lewis acidic analytes and which may induce ligand exchange reactions to form complexes with the matrix itself. Also described is the in situ generation of a series of ruthenium(II) porphyrin dimers via laser induced vaporisation of the corresponding monomers and the suppression of dimerisation by nitrogen and phosphorus ligands. Careful adjustment of instrument parameters such as incident laser energy requires special attention. relative affinities in complexation reactions are found to be consistent with liquid phase chemistry, therefore LDI-MS can provide a fast and simple, yet effective screening method for reactivity exploration. however, it also induces side-reactions such as iodine abstraction/transfer reactions. Furthermore, structurally different porphyrins show variations up to 90% in relative ion formation. Extreme caution is therefore required in the interpretation, and particularly in the quantitation, of such mass spectra
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
Ruthenium(ii) and rhodium(iii) porphyrin phosphine complexes: influence of substitution pattern on structure and electronic properties
No full textA series of ruthenium(II) and rhodium(III) porphyrin complexes with diphenyl phenylacetylene phosphine (dpap) was synthesised and fully characterised by UV-vis, 1H NMR and 31P{1H} NMR spectroscopy, and in most cases also by single-crystal X-ray diffraction. The substitution pattern of the porphyrin was varied with increasing meso-phenyl substitution, from octa-ethyl porphyrin (OEP), through diphenyl di-ethyl porphyrin (DPP), to tetraphenyl porphyrin (TPP) and 3,5-di-tbutyl tetraphenyl porphyrin (tbTPP). The dpap readily displaces the CO ligand from the parent Ru(CO)(porphyrin) and the iodide from the Rh(I)(porphyrin) to give bis-phosphine complexes M(dpap)2(porphyrin). The UV-vis spectra reveal that some of the complexes are partially dissociated at concentrations of 10?6 M, and the association constants were estimated to be in the range of 106 to 107 M?1 for the first, and 104 to 106 M?1 for the second binding event. The 1H NMR chemical shifts of the complexes vary greatly despite the fact that they display very similar geometries in the solid state, and no correlation could be discerned between the crystal structures and the spectroscopic parameters in solutio
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
Amplification of a cyclic mixed-metalloporphyrin tetramer from a dynamic combinatorial library through orthogonal metal coordination
No full textA cyclic porphyrin tetramer, consisting of two bis-phosphine substituted zinc(II) porphyrin units and two Rh(III) TPP units, is selected and amplified virtually quantitatively from a dynamic combinatorial library using 4,4'-bipy as a scaffold and using orthogonal binding modes
Phosphine-substituted porphyrins as supramolecular building blocks
No full textA route to alkyne-phosphine-substituted metalloporphyrins is presented. The X-ray structure of the methanol adduct of a diphenylphosphine Zn(II) porphyrin reveals solid state dimerisation accompanied by proton transfer from coordinated methanol to phosphine in a process reminiscent of carbonic anhydrase, The ability of the phosphine-substituted porphyrins to form non-covalent arrays with a Ru(II) porphyrin was explored using H-1/P-31 NMR and UV/vis spectroscopy as well as MALDI-TOF mass spectrometry
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