1,720,973 research outputs found
Redox Isomeric Ferrocenyl Styrylruthenium Radical Cations with Diphenyl-Substituted β-Ketoenolato Ligands
No full textTailoring Valence Tautomerism by Using Redox Potentials: Studies on Ferrocene‐Based Triarylmethylium Dyes with Electron‐Poor Fluorenylium and Thioxanthylium Acceptors
No full textThree new electrochromic ferrocenyl triarylmethylium dyes with fluorenylium ( 1a + , 1b + ) or thioxanthylium ( 1c + ) residues were selected in order to keep the intrinsic differences of redox potentials for ferrocene oxidation and triarylmethylium reduction small and to trigger valence tautomerism. UV/Vis/NIR and quantitative EPR spectroscopy identified paramagnetic diradical isomers 1a +•• ‐1c +•• alongside diamagnetic forms 1a + ‐1c + , which renders these complexes magnetochemical switches. The diradical forms 1a +•• ‐1c +•• as well as the one‐electron reduced triarylmethyl forms of the complexes were found to dimerize in fluid solution. For radical 1a • , dimerization occurs on the timescale of cyclic voltammetry, which allowed us to determine the kinetics and equilibrium constant for this process by digital simulation. Mößbauer spectroscopy indicated that 1a + and 1b + retain VT even in the solid state. UV/Vis/NIR spectroelectrochemistry revealed the polyelectrochromic behaviour of these complexes by establishing distinctly different electronic absorption profiles of the corresponding oxidized and reduced form s.publishe
In-cell approaches in electron paramagnetic resonance spectroscopy to study conformations of DNA G-quadruplexes
No full textThe current work deals with the development of EPR for biological applications. Based on existing in vitro techniques, in-cell approaches for determination of distance constraints by double electron-electron resonance (DEER) were established. After proof-of-principle experiments on rigid model systems, in-cell DEER has been applied to study formation of G-quadruplexes adopted by human telomeric DNA oligomers upon their microinjection into living cells.Distances between two spin labels are derived from a DEER experiment. Their incorporation into DNA oligomers was achieved by inserting nitroxide-modified 2′-deoxyuridines at places of thymidines during solid-phase synthesis. By means of CD spectroscopy it was shown that nitroxides incorporated in this way in loop regions of G-quadruplexes do not disturb their initial structures. In spite of the inherent flexibility of loops, measured interspin distances are characteristic: they vary significantly for different G-quadruplex topologies providing a criterion for identification of those topologies. The most probable interspin distance can be predicted from existing high-resolution structural data and compared with reference measurements of known structures allowing for allocation to a certain structure. Even several conformations can be identified within a single experiment if the difference between the most probable interspin distances exceeds 0.3 nm. In the ion-dependent folding of the d[AGGG(TTAGGG)3] the antiparallel-basket topology was found for Na+ (in agreement with high-resolution NMR structure) and for the first time a 1:1 mixture of the antiparallel-basket and the parallel-propeller in the presence of K+ ions was identified.G-quadruplexes may alter folding topology if they are formed one after another within a long DNA sequence. This influence of neighboring G-quadruplexes was studied in a sequence with three G-quadruplex-forming blocks where one of them – in the middle or at the side – was selectively labeled with nitroxides. Consequent distance measurements allowed for conclusion on topologies adopted solely by the middle or the terminal part of the DNA sequence and thus allowed for building models for the folded human telomeric DNA in solution.The intracellular environment is known to reduce nitroxides to EPR-silent hydroxylamines. Therefore, prior to novel in-cell distance measurements free nitroxides were deposited into cells via microinjection. Here, the reduction kinetics of two types of nitroxides was described within Michaelis-Menten formalism for enzymatic processes. Thus, an enzymatic origin of reduction in cellulo was proposed. It was found that inside X. laevis oocytes and in their extract the five member ring nitroxides (like PCA) are reduced much slower than their six member ring analogs. In principle, both six and five member ring nitroxides are suitable for in-cell DEER if no long incubation time is required. However, five member ring nitroxides are preferable due to longer half-life and thus easier handling.Conformations of the d[AGGG(TTAGGG)3] inside oocytes where nucleus-like conditions preside were studied after incubating the unfolded sequence for 15 min after injection. Two conformations at 1:1 ratio were found inside cells. These were the antiparallel-basket and the parallel-propeller. This result is the same as found in K+-containing buffer. Thus, a dominant role of K+ in in-cell folding of the human telomeric oligonucleotide was established. This result was also confirmed by in-extract measurement providing an alternative way to study conformations in cellulo. A time-dependent experiment allowed monitoring of the folding process.DEER was shown to be applicable for structural identification goals of biological objects under their native conditions. In-cell DEER can provide means to analyze conformations and folding of nucleic acid structures inside living cells which has hitherto been unachievable.publishe
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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