1,721,177 research outputs found
CHROMIUM(III) COMPLEXES WITH DIETHYLENTRIAMINEPENTAACETIC ACID
No full textAbstract Complex formation by chromium(III) with diethylentriaminepentaacetic acid (DTPA) has been studied by potentiometry and spectrophotometry. In equimolar solutions or with a ligand excess, complexation is practically complete at pH > 1 and protonation equilibria have been calculated. Molar absorbtivities of the different species have been evaluated. Equilibrium constants for complex formation have been calculated in 1 mol dm−3 (Na,H)ClO4 at 20°C
On the reaction of dioxouranium(VI) with diethylene triaminepentaacetic acid (DTPA) and with chromium(III)-DTPA chelating agent
No full textFormation of complexes by dioxouranium(VI) with chromium(III)DTPA as "chelating agent" has been investigated, by potentiometry, in aqueous solution. Two chelates, a monomer and a dimer, with the same 1:1 dioxouranium(VI)/chromium(III)-DTPA molar ratio have been evidenced. The monomer, uncharged, has also been obtained in the solid state and has been characterised by IR and thermoanalytical techniques.
Complexes of dioxouranium(VI) with DTPA alone were also studied. These were 1:1, with a different degree of protonation, or 2:1 metal to ligand molar ratio and were evidenced in aqueous solution. The stability constants of the above equilibria have been calculated at 20 degrees C, in NaClO4 1.0 mol/dm(3). In the solid state, several compounds were prepared and no stoichiometric metal to ligand molar ratios are found (the values range from 1.2 to 1.8). Tn the case of these fractional values a polymeric structure may be assumed for the solid compounds
Binuclear chelates of DTPA with aluminum(III) and chromium(III) ions
No full textThe reaction of aluminum(III) with chromium(III)DTPA "complex chelating agent" has been investigated, in aqueous solution, at 20 degreesC in NaClO4 1.0 mol dm(-3) by potentiometric methods. In acidic medium and with ligand excess three different complex species (AlCrL+, Al(OH)CrL and Al(CrL)(2) over bar) were evidenced and, knowing the protonation constants of the chromium(III)-DTPA complex, the stability constants were calculated. The comparison of these constants with those of the corresponding complexes of aluminium(III) with iminodiacetic acid proved the coordination of aluminum(III) occurs in all cases by iminodiacetic groups. The mononuclear [H2AlL(H2O)] and the heterobinuclear [Al(OH)CrL(H2O)(6)] complexes were also obtained as solid compounds and were characterized by X-ray and IR spectroscopy and thermoanalytical techniques (TG and DSC)
Thermoanalytical behaviour of the captopril- cobalt(II) complex
No full textAbstract
Captopril (H2L) reacts with cobalt(II) in aqueous solution at a neutral pH forming a deep red complex. The reaction rate depends on the temperature, pH, metal ion and ligand concentrations. A solid compound precipitates by acidification of the solution. The chemical, potentiometric, and spectroscopic analyses of the solid complex give the simplest formula, Co(HL)2·H2O, and suggest that the sequence of the bonds is S-Co-S, with the carboxylic group of the ligand remaining uncoordinated.
The thermal behaviour of the captopril and its cobalt complex was studied by thermogravimetry, differential thermal analysis and differental scanning calorimetry in dynamic nitrogen and oxygen atmospheres.
Copyright © 1990 Published by Elsevier B.V
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
On the reaction of iron(III) with chromium(III)-DTPA chelating agent
No full textThe reaction of iron(III) with chromium(III)-DTPA 'chelating agent' has been investigated, in aqueous solution, by measuring both hydrogen ion concentration and emf of the iron(III)/iron(II) couple. In acidic medium (pH C in NaClO4 1.0 mol dm(-3). The comparison of these constants, considering the basicity of the ligands, proved the coordination of iron(III) occurs by one iminodiacetic group. The iron(III)-chromium(III)-DTPA complex has been precipitated and the solid compound characterized by IR and thermoanalytical techniques
Thermal behaviour of iminodiacetic, oxydiacetic and thiodiacetic acids
No full textThe thermal decomposition of iminodiacetic, oxydiacetic, and thiodiacetic acids in helium atmosphere has been studied by means of thermogravimetry (TG), differential thermal analysis (DTA) and temperature-programmed pyrolysis directly coupled with mass spectrometry (TPPy-MS). Evolved gas analysis (EGA) profiles of iminodiacetic and oxydiacetic acids were obtained and compared with TG and DTA profiles. The decomposition of iminodiacetic acid forms water, CO, CO2, CH3CN, HCN and some hydrocarbons. After water evolution a cyclic anhydride is formed, as well as for oxydiacetic acid. Thiodiacetic acid vaporizes without decomposition
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
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