1,721,054 research outputs found
Improving Spin Probe Methodologies to Investigate Supramolecular Assemblies
Full text linkIn this report, our work describing the use of spin probes in the field of supramolecular chemistry and how electron spin resonance (EPR) has been used for detecting and identifying supramolecular assemblies is shortly reviewed. Selected examples are reported, including paramagnetic host-guest complexes, self-assembled systems doped with spin probes, spin-labelled macrocycles and open shell mechanically interlocked structures (MIMs) such as rotaxanes, in which the dumbbell, the wheel or both are tagged with nitroxide radicals
Nitroxides in Supramolecular Chemistry
No full textWith the advance of supramolecular chemistry, the need for diverse analytical methodologies as a tool to exploit basic principles for the rational design of the building blocks used to assembly supramolecular aggregates is continuously increasing. In this respect, electron paramagnetic resonance (EPR) and related methods offer particular opportunities to study supramolecular systems. The main advantages of EPR are the sensitivity of the method; the possibility of obtaining kinetic information in the submicrosecond time range; the ability to measure tumbling rates on the nanosecond timescale and distances between spin labels in the 0–100 Å range. The strength of EPR lies also in its possible application to heterogeneous and solid samples.
Because of these EPR favourable features, in recent years spin probing and labelling methodologies have largely expanded beyond the classical context of biology and structural biochemistry and are now commonly used in the characterization of supramolecular assemblies. Both spin probe and spin label terminology refer to the methodology in which one (or more) paramagnetic species (in most cases a nitroxide radical) is used to report EPR information on the chemical environment experienced by the radical itself. Generally speaking, nitroxides are considered spi
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
Aerobic Oxidation of Alkylaromatics using a LipophilicN-Hydroxyphthalimide: Overcoming the Industrial Limit of Catalyst Solubility
Full text link4,4′-(4,4′-Isopropylidenediphenoxy)bis(N-hydroxyphthalimide), which is a new lipophilic analogue of N-hydroxyphthalimide, can act as an effective catalyst in the aerobic oxidation of alkylaromatics under reduced amounts of polar cosolvent. The catalyst was selected on the basis of an in-depth study of the influence that substituents on the aromatic ring of N-hydroxyphthalimide exert on determining the NO[BOND]H bond dissociation energy (BDE). BDE values for a range of model molecules are calculated by DFT and measured by EPR spectroscopy. The new catalyst can be successfully employed in the aerobic oxidation of cumene, ethylbenzene, and cyclohexylbenzene, affording, in all cases, good conversions and high selectivity for the corresponding hydroperoxide. The effect of solvent, catalyst, and temperature has also been investigated
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
Supramolecular Control of Spin Exchange in a Spin-Labelled [2]Rotaxane Incorporating a Tetrathiafulvalene Unit
No full textThe EPR properties of a novel triradical obtained
by single-electron oxidation of a nitroxide-spin-labelled rotaxane
containing a tetrathiafulvalene unit and cyclobis-
(paraquat-p-phenylene) ring is reported. Rotaxanation is
proved to have a dramatic effect on through-space magnetic
interactions between radical fragments. Analysis of
the EPR spectra by a three-jump model, allowed us to
obtain structural information on the interlocked structure
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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