1,720,960 research outputs found
Biomimetic Copper(I)-mediated Activation of Dioxygen and Unexpected Non-innocence in Copper(II) complexes of Bis(oxazolines)
No full textBOX Ligands in Biomimetic Copper-Mediated Dioxygen Activation: A Hemocyanin Model
No full textThe mu-eta(2):eta(2)-peroxodicopper(II) core found in the oxy forms of the active sites of type III dicopper proteins have been a key target for bioinorganic model studies. Here, it is shown that simple bis(oxazoline)s (BOXs), which are classified among the so-called "privileged ligands", provide a suitable scaffold for supporting such biomimetic copper/dioxygen chemistry. Three derivatives (BOX)-B-R,H-Me-2 (R = H, Me, tBu) with different backbone substituents have been used. Their bis(oxazoline)-copper(I) complexes bind dioxygen to yield biomimetic mu-eta(2):eta(2)-peroxodicopper(II) species. O-2 can be reversibly released upon an increase in temperature. Their formation kinetics have been studied under cryo-stopped-flow conditions for the tBu derivative, giving activation parameters. Delta H-on(double dagger) = (2.27 +/- 0.18) kcal mol(-1), Delta H-on(double dagger) = (-46.3 +/- 0.8) cal K-1 mol(-1) for the binding event and. Delta H-off(double dagger) = (11.7 +/- 1.9) kcal mol(-1), Delta H-off(double dagger) = (-16.1 +/- 8.2) calK(-1) mol(-1) for the release of O-2, as well as thermodynamic parameters. Delta H degrees = (-10.0 +/- 1.7) kcal mol(-1) and. Delta S = (-32.7 +/- 7.4) calK(-1) mol(-1) for this equilibrium. The mu-eta(2):eta(2)-peroxodicopper(II) complexes have been isolated as surprisingly stable solids and investigated in depth by a variety of methods, both in solution and in the solid state. Resonance Raman spectroscopy revealed a characteristic isotope-sensitive stretch. (nu) over tilde (O-O) = 731-742 cm(-1) (Delta[O-18(2)] approximate to -39 cm(-1)) and an intense feature around 280 cm(-1) diagnostic for the fundamental symmetric Cu2O2 core vibration. A slight butterfly-shape of the Cu2O2 core has been derived from EXAFS data and DFT calculations. SQUID magnetic data evidenced strong antiferromagnetic coupled Cu-II(2) (-2J >= 1000 cm(-1)). Thermal degradationinsolutionyieldsbis(hydroxo)-bridged[((BOX)-B-tBu,H-Me-2)(L)-Cu(OH)](2)(PF6)(2) (L = H2O, MeCN or THF); whereas in the case of (BOX)-B-H,H-Me-2, ligand oxygenation has been detected. Preliminary reactivity studies with the substrate 2,4-di-tert-butylphenol indicate the formation of the C-C coupling product 3,3',5,5'-tetra-tert-butyl-2,2'-biphenol, whereas orthohydroxylation was not observed. The copper(I) complex [((BOX)-B-tBu,H-Me-2)Cu(MeCN)]PF6 as well as two dicopper(II) complexes [(L)((BOX)-B-tBu,H-Me-2)Cu(OH)](2)(PF6)(2) have been characterised by single-crystal X-ray diffraction. Considering the vast number of known BOX derivatives, a rich and versatile Cu/O-2 chemistry based on this platform is anticipated.European COST program [CM 1003
Tautomerism in Bis(oxazoline)s
No full textBis(oxazoline)s (BOXs) are a privileged ligand class and have found widespread use in catalysis. Herein, the tautomerism of selected BOX ligands was evidenced by X-ray diffractometry as well as by NMR and IR spectroscopy and supported by DFT calculations. In CDCl3 solution at room temperature, the new 1,1-bis(4,4-dimethyl-1,3-oxazolin-2-yl)-1-phenylmethane ((BOX)-B-Ph,H-Me-2) ligand is present as a 1:1 mixture of the diimine and iminoenamine tautomers. Thermodynamic and kinetic data for the tautomeric equilibrium were determined, which allowed comparison with related bidentate ligand classes. The other BOXs studied, (BOX)-B-H,H-Me-2, (BOX)-B-Me,H-Me-2, and (BOX)-B-tBu,H-Me-2, are largely present in the diimine form under similar conditions. IR spectroscopy was identified as a valuable tool for detecting the presence of the iminoenamine form as a minor component
C-H Activation at a Bidentate Ligand Coordinated to Palladium(II) - an Electrophilic Attack Supported by an External Base
No full text2-(2-Phenylaminopyrimidin-4-yl)pyridines undergo C-H activation at the phenyl ring in the ortho position to the amine nitrogen atom when reacted with (PhCN)2PdCl2 and finally form N,N,C-coordinated palladium(II) complexes in high yields. Five differently substituted complexes were synthesized and characterized by spectroscopy and X-ray structure analysis. The reaction mechanism for the formation of these complexes was elucidated by kinetic experiments, which allowed the calculation of the activation parameters of the complex formation
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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