1,720,957 research outputs found
Anti-tyrosinase and antioxidant activity of meroterpene bakuchiol from Psoralea corylifolia (L.)
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Role of Sulphur and Heavier Chalcogens on the Antioxidant Power and Bioactivity of Natural Phenolic Compounds
Full text linkThe activity of natural phenols is primarily associated to their antioxidant potential, but is
ultimately expressed in a variety of biological effects. Molecular scaffold manipulation of this large
variety of compounds is a currently pursued approach to boost or modulate their properties. Insertion
of S/Se/Te containing substituents on phenols may increase/decrease their H-donor/acceptor ability
by electronic and stereo-electronic effects related to the site of substitution and geometrical constrains.
Oxygen to sulphur/selenium isosteric replacement in resveratrol or ferulic acid leads to an increase
in the radical scavenging activity with respect to the parent phenol. Several chalcogen-substituted
phenols inspired by Vitamin E and flavonoids have been prepared, which in some cases prove to
be chain-breaking antioxidants, far better than the natural counterparts. Conjugation of catechols
with biological thiols (cysteine, glutathione, dihydrolipoic acid) is easily achieved by addition to
the corresponding ortho-quinones. Noticeable examples of compounds with potentiated antioxidant
activities are the human metabolite 5-S-cysteinyldopa, with high iron-induced lipid peroxidation
inhibitory activity, due to strong iron (III) binding, 5-S-glutathionylpiceatannol a most effective
inhibitor of nitrosation processes, and 5-S-lipoylhydroxytyrosol, and its polysulfides that proved
valuable oxidative-stress protective agents in various cellular models. Different methodologies
have been used for evaluation of the antioxidant power of these compounds against the parent
compounds. These include kinetics of inhibition of lipid peroxidation alkylperoxyl radicals, common
chemical assays of radical scavenging, inhibition of the OH mediated hydroxylation/oxidation
of model systems, ferric- or copper-reducing power, scavenging of nitrosating species. In addition,
computational methods allowed researchers to determine the Bond Dissociation Enthalpy values
of the OH groups of chalcogen modified phenolics and predict the best performing derivative.
Finally, the activity of Se and Te containing compounds as mimic of glutathione peroxidase has been
evaluated, together with other biological activities including anticancer action and (neuro)protective
effects in various cellular models. These and other achievements are discussed and rationalized to
guide future development in the field
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
Entangling imidazolium-based ionic liquids and melanins: A crossover study on chemical vs electronic properties and carrier transport mechanisms
No full textMelanins (mel) are a class of pigments that are nearly ubiquitous and among the oldest compounds found in nature. However, their practical application has been limited due to their low solubility in water and in most organic solvents. Recent research on polydopamine has revealed that ionic liquids (ILs) not only enhance melanin's dissolution but also fine-tune its redox properties through specific dipolar interactions. In this study, we expand upon previous investigations by customizing new suspensions on a broader range of melanins. Concerning ILs, we focus on imidazolium based ILs, tailoring their chemical properties (pKa) and structural characteristics (cation radius, anion radius). The melanins under consideration include synthetic polymers derived from the oxidative polymerization of 5,6-dihydroxyindole (DHI) and its 2 -carboxylic acid counterpart (DHICA), as well as the natural pigment Sepiomelanin (Sepiomel), which is isolated from the ink sack of cuttlefish. Our comparative analysis between neat ILs and ILs-mel responses reveals several key findings: the increase in solubility, the tuning of the redox ability, the decrease of the ionic charge resistance (from M Omega To k Omega); the partial removal of the electrical polarization effects and the delocalized ionic charge hopping mechanisms in conductivity; the increase of the free ionic diffusion mobility and Debye lengths. Notably, electrical transport is influenced by both the chemical features and the steric hindrance in the ILs as well as the specific type of melanin employed. These factors contribute to the high order correlation between free ionic charge densities and their corresponding Debye lengths. Consequently, our findings suggest that for these complex systems, an improved model extending beyond a simplified electrostatic interaction mechanism is required
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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