1,721,009 research outputs found
A perspective on enantioselective chromatography by comparing ultra-high performance supercritical fluid chromatography and normal-phase liquid chromatography through the use of a pirkle-type stationary phase
No full textSince their discovery, the Pirkle-type chiral stationary phases, and in particular the Whelk-O1, have been used in a large number of applications and theoretical studies. Although they can be used in many elution modes, their main field of application is in normal phase liquid chromatography and more recently in supercritical fluid chromatography. In this review, we tried to compare the two techniques using the Whelk-O1 stationary phase as a trait d'union. The main milestones obtained in the last decades of research in enantioselective chromatography and possible lights and shadows of the two techniques have been described. There is still a long way to go to achieve the full potential in the field of enantioselective separations, and especially ultra-high supercritical fluid chromatography, given its great potential, is a technique still to be improved
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
Molecular recognition of the hplc whelk-o1 selector towards the conformational enantiomers of nevirapine and oxcarbazepine
Full text linkThe presence of stereogenic elements is a common feature in pharmaceutical compounds, and affording optically pure stereoisomers is a frequent issue in drug design. In this context, the study of the chiral molecular recognition mechanism fundamentally supports the understanding and opti-mization of chromatographic separations with chiral stationary phases. We investigated, with molecular docking, the interactions between the chiral HPLC selector Whelk-O1 and the stereoisomers of two bioactive compounds, the antiviral Nevirapine and the anticonvulsant Oxcarbazepine, both char-acterized by two stereolabile conformational enantiomers. The presence of fast-exchange enantiomers and the rate of the interconversion process were studied using low temperature enantioselective HPLC and VT-NMR with Whelk-O1 applied as chiral solvating agent. The values of the energetic barriers of interconversion indicate, for the single enantiomers of both compounds, half-lives suffi-ciently long enough to allow their separation only at critically sub-ambient temperatures. The chiral selector Whelk-O1 performed as a strongly selective discriminating agent both when applied as a chiral stationary phase (CSP) in HPLC and as CSA in NMR spectroscopy
Tetrasubstituted cyclopentadienones as suitable enantiopure ligands with axial chirality.
No full textA series of thermally stable atropisomeric phencyclone ligands (ΔG‡
rac > 35 kcal mol−1), bearing two chiral
axes, has been successfully synthesized, taking into account the results of DFT calculations on model
systems. The absolute configurations of the novel atropisomers have been assigned using TD-DFT simulation
of ECD spectra. Atropisomeric phencyclones herein presented pave the way towards new ruthenium-
based enantioselective hydrogenation catalyst
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
Polysorbate 20 vesicles as multi-drug carriers: in vitro preliminary evaluations
No full textThis study focuses on the physico-chemical characterization of surfactant nanovectors according to the evidence that the knowledge of nanocarrier properties is a necessary step to translate their potentiality to nanomedicine applications. In particular, in this investigation we have prepared multi-drug surfactant vesicles (niosomes) and characterized them in terms of dimensions, zeta-potential and stability. Also the potential application of analyzed carriers was evaluated in terms of lidocaine and ibuprofen entrapment efficiency and in vitro permeation experiments. The obtained results suggest the potential application of niosomes in dermal administration of the two drugs at the same time in the same pharmaceutical formulation, as useful carriers for the treatment of various skin diseases, such as acute and chronic inflammations in presence of pain
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