1,720,981 research outputs found
Absolute configuration of furanogermacrenones from Commiphora erythraea by computational analysis of ECD and ORD spectra
No full textSynthesis, electronic properties, structural studies, and catalytic activity of peripherally metalated β-η1-Pd(II)-thioalkyl porphyrazine
No full textThe β-η1-Pd(II)-thioethyl porphyrazine complex 1 was isolated as an intermediate in the Suzuki-Miyaura cross-coupling of β-bromo thioethyl porphyrazine with palladium complexes. The same complex was also synthesized via a direct reaction of the bromo porphyrazine with Pd(PPh3)4 and its structure was assessed by NMR and single-crystal X-ray diffraction analysis, representing one of the very few cases of crystallographic resolution of a thioalkyl porphyrazine obtained to date. This organometallic thioethyl porphyrazine derivative constitutes the first example of an η1 organometallic complex of tetrapyrroles in which the metal is coordinated at the β position of the macrocycle rather than at the meso position, as observed in some porphyrin complexes. Spectroscopic and electrochemical studies, including UV-vis absorption and cyclic voltammetry, supported by time-dependent density functional theory calculations revealed that compared to symmetrically substituted thioalkyl porphyrazines, this complex exhibits a reduced HOMO-LUMO bandgap and a charge transfer transition involving the metal and the macrocycle at the typical tetrapyrrole Soret band. This behavior markedly contrasts with that observed in peripherally aryl-substituted thioalkyl porphyrazines, where a charge transfer HOMO-LUMO transition occurs between the aryl substituent and the macrocycle core in correspondence to the Q bands region. Furthermore, the complex demonstrated good catalytic activity in both Suzuki-Miyaura and Sonogashira Pd(ii)-catalyzed coupling reactions of aryl halides with boronic acids or alkynes, respectively. In both reactions, the porphyrazine complex performed with comparable efficiency to the commonly used Pd(PPh3)2Cl2 catalyst
Characterization of "Free Base" and Metal Complex Thioalkyl Porphyrazines by Magnetic Circular Dichroism and TDDFT Calculations
No full textUV-vis absorption and magnetic circular dichroism (MCD) spectra of octakis thioethyl "free base" porphyrazine H2OESPz and its metal complexes MOESPz (M = Mg, Zn, Ni, Pd, Cu), as well as of [MnOESPz(SH)] were recorded. In the last case, MCD proved to have quite good sensitivity to the coordination of this complex with 1-methylimidazole (1-mim) in benzene. Time-dependent density functional theory (TDDFT) calculations were carried out for the considered porphyrazine complexes and showed good performance on comparing with MCD and UV-vis experimental spectra, even in the open-shell Cu and Mn cases. Calculations accounted for the red shift observed in the thioalkyl compounds and allowed us to reveal the role of sulfur atoms in spectroscopically relevant molecular orbitals and to highlight the importance of the conformations of the thioethyl external groups. Calculated MCD spectra of [MnOESPz(SH)] confirm the Mn(III) → Mn(II) redox process, which leads to the [Mn(OESPz)(1-mim)2] species, and the relevance of the spin state for MCD is revealed
Absolute configuration of bioactive furanogermacrenones from Commiphora erythraea (Ehrenb) Engl. by computational analysis of their chiroptical properties
No full textAbsolute configurations (+)-(4S), (+)-(3S,4R), (-)-(2S,4S), and (-)-(1R,2R,4S) were assigned, for the first time, to bioactive furanogermacranes extracted from Commiphora erythraea resin by DFT computational analysis of their ORD curves and ECD spectra. This analysis established that all of these compounds share the same absolute configuration at the methyl-substituted carbon thus allowing us to hypothesize a biosynthetic relationship among these structurally related metabolites
Absolute configuration of furanogermacrenones from Commiphora erythraea resin by computational analysis of ORD curves and ECD spectra
No full text
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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