1,721,179 research outputs found
From catechol-tocopherol to catechol-hydroquinone polyphenolic antioxidant hybrids
No full textMultidefence antioxidants represent a valuable solution for the protection against oxidative stress. From the planned synthesis of a catechol-tocopherol hybrid, we isolated a catechol-hydroquinone hybrid through a BBr3-mediated benzochromene-fluoren-1-ol transposition. The compound prepared showed a remarkable chain-breaking antioxidant in the catechol portion, while the very sensitive hydroquinone moiety revealed to be an efficient generator of hydroperoxyl radicals
Teacher’s Thinking About Sensory Impairments and Technologies: An Exploratory Study Within a Specialisation Course
No full textGoing 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
A Straightforward Route to Potent Phenolic Chain-Breaking Antioxidants by Acid-Promoted Transposition of 1,4-Benzo[b]oxathiines to Dihydrobenzo[b]thiophenes
No full textThe transformation of simple phenols with limited antioxidant activity into potent chain-breaking antioxidants was achieved by a three-step protocol, consisting of the conversion of phenols into 1,4-benzo[b]oxathiines followed by an unprecedented acid-promoted transposition to o-hydroxydihydrobenzo[b]thiophenes, or dihydrobenzo[de]thiochromenes, starting from phenols or naphthols, respectively. These derivatives, bearing a benzo-fused heterocycle with a sulfide sulfur ortho to the phenolic OH, have a rate constant of reaction with alkylperoxyl radicals (kinh) comparable to that of a-tocopherol. A solid rationale for the transposition mechanism as well as for the structure-antioxidant activity relationship is presente
A Base-Mediated Mild Sulfenylation of Indoles and Pyrrole with α-Acylthiones
No full textA new procedure for the sulfenylation of indoles and pyrroles based on an aromatic substitution with α-acylthiones used as electrophiles is described. The sulfenylating species were obtained, under very mild reaction conditions, from N-thiophthalimides, using a weak base (pyridine or triethylamine) as promoter. The overall yields obtained are comparable with those obtained by other known sulfenylation protocols, which typically require harsher reaction conditions and/or metal-containing Lewis acids as promoters.
Magnetic nanoantioxidants with improved radical-trapping stoichiometry as stabilizers for inhibition of peroxide formation in ethereal solvents
No full textGraphite-coated magnetic cobalt nanoparticles (CoNPs) decorated with hindered phenolic antioxidant analogues of 2,6-di-tert-butyl-4-methylphenol (BHT, E321) provided easily removable nanoantioxidants capable of preventing the autoxidation of organic solvents as tetrahydrofuran (THF)
Synthesis of heterohelicenes by a catalytic multi-component povarov reaction
No full textA multi-component Povarov reaction was used for the preparation of [4], [5] and [6]aza- and azaoxahetero helical-shaped compounds. The oxidation of the tetrahydroquinolinic primary Povarov adducts to the aromatic quinolines is mandatory to achieve a helical-shaped structure and can be carried out in a one-pot fashion with DDQ. Resolution of [5] and [6]heterohelicenes was successfully performed by chiral HPLC
- …
