1,721,013 research outputs found
Maximizing the reactivity of phenolic and aminic radical-trapping antioxidants: Just add nitrogen!
No full textConspectus Hydrocarbon autoxidation, the archetype free radical chain reaction, challenges the longevity of both living organisms and petroleum-derived products. The most important strategy in sloing this process is via the intervention of radical-trapping antioxidants (RTAs), hich are abundant in nature and included as additives to almost every petroleum-derived product as ell as several other commercial products. Accordingly, a longstanding objective of many academic and industrial scientists has been the design and development of novel RTAs that can outperform natural and industrial standards, such as α-tocopherol, the most biologically active form of vitamin E, and dialkylated diphenylamines, respectively.Some time ago e recognized that attempts to maximize the reactivity of phenolic RTAs had largely failed because substitution of the phenolic ring ith electron-donating groups to eaken the O-H bond and accelerate the rate of H atom transfer to radicals leads to compounds that are unstable in air. e surmised that incorporating nitrogen into the phenolic ring ould render them more stable to one-electron oxidation, enabling their substitution ith strong electron-donating groups. Guided by computational chemistry, e demonstrated that replacing the phenyl ring in very electron-rich phenols ith either 3-pyridyl or 5-pyrimidyl rings leads to phenolic-like RTAs ith good air stability and great reactivity. In fact, rate constants determined for the reactions of some compounds ith peroxyl radicals ere almost 2 orders of magnitude greater than those for α-tocopherol and implied that the reactions proceeded ithout an enthalpic barrier. Folloing extensive thermochemical and kinetic characterization, e took our studies of these compounds to more physiologically relevant media, such as lipid bilayers and human lo density lipoproteins, here the heterocyclic analogues of vitamin E shone, displaying unparalleled abilities to inhibit lipid peroxidation and prompting their current investigation in animal models of degenerative disease. Moreover, e carried out studies of these compounds in several industrially relevant contexts and in particular demonstrated that they could be used synergistically ith less reactive, less expensive, phenolic RTAs.More recently, our attention has turned to the application of these ideas to maximizing the reactivity of diarylamine RTAs that are common in additives to petroleum-derived products, such as lubricating oils, transmission and hydraulic fluids, and rubber. In doing so, e have developed the most reactive diarylamines ever reported. The 3-pyridyl- and 5-pyrimidyl-containing diarylamines are easily accessed using Pd- and/or Cu-catalyzed cross-coupling reactions, and display an ideal compromise beteen reactivity and stability. The most reactive compounds are characterized by rate constants for reactions ith peroxyl radicals that are independent of temperature, implying that-as for the most reactive heterocyclic phenols-these reactions proceed ithout an enthalpic barrier. Unprecedented reactivity as also observed hen hydrocarbon autoxidations ere carried out at elevated temperatures, real-orld conditions here diarylamines are uniquely effective because of a catalytic RTA activity that makes use of the hydrocarbon substrate as a sacrificial reductant. Our studies to date suggest that heterocyclic diarylamines have real potential to increase the longevity of petroleum-derived products in a variety of applications here diphenylamines are currently used
Substituted Diarylamines and Use of Same as Antioxidants
No full textA compound of Formula I, Formula IA, Formula IB, or Formula II, or an acid or base addition salt thereof, and use of these compounds as antioxidants. In one embodiment, a compound of Formula II, wherein each of X, Y, and Z are independently a carbon or nitrogen atom; R1 and R2 are each independently a hydrogen or an electron donating group, but are not both hydrogen, and wherein R1, and R2 are each bonded to a carbon atom in their own respective aryl ring
INHIBITOR COMBINATION, RESIN MIXTURE CONTAINING SAME AND USE OF SAME
No full textThe use of a mixture of 5-pyrimidinol derivatives with sterically hindered phenol derivatives for adjusting the reactivity and the gel time of resin mixtures and reactive resin mortars based on radically polymerizable compounds is described. Furthermore, a resin mixture containing the inhibitor combination, a reactive resin mortar containing this resin mixture and two-component mortar systems with the reactive resin mortar according to the invention and a hardener with improved stability in storage and good low-temperature hardening properties are also described. The resin mixture according to the invention is suitable in particular for chemical fastening of construction elements in boreholes in various substrates
Antioxidants and methods to maximize performance
No full textA method of preventing or reducing the level of degradation of an organic substrate is described, wherein a composition is formed that includes the organic substrate together with an effective amount of a sacrificial base and a diarylamine antioxidant
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Unprecedented Inhibition of Hydrocarbon Autoxidation by Diarylamine Radical-Trapping Antioxidants
No full textThe
reactivities of novel heterocyclic diarylamine radical-trapping
antioxidants (RTAs) are profiled in a heavy hydrocarbon at 160 °C,
conditions representative of those at which diphenylamine RTAs are
used industrially. While carboxylic acids produced during the autoxidation
are shown to deactivate these more basic RTAs, the addition of a sacrificial
base leads to efficacies that are unprecedented in the decades of
academic and industrial research in this area
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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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