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Reactivity of aryl and vinyl radicals: abstraction of hydrogen atom or reaction with a nucleophile
No full textThe reactivities of aryl and vinyl radicals, two fundamental transient intermediates, have been investigated with respect to two elementary processes: H-atom abstraction and reaction with a nucleophile (Y-, in the S(RN)1 reaction). The radicals of interest were generated from haloarene or haloethene precursors, either by use of the BU3SnH/AIBN system or by photostimulated electron transfer from a nucleophile, and the partition of the intermediate radical between competing pathways was investigated. Use both of indirect methods (such as the study of the reaction products in competition experiments; use of a radical-clock probe) and of direct ones (such as the detection of the radicals by flash photolysis experiments) enabled the following rate constants to be obtained (all values in m(-1.)s(-1) at 25 degreesC). For phenyl-type radicals, the rate constants for H abstraction (k(H)) from the solvents Me2SO (2.8(.)10(6)) and CH3CN (6.7(.)10(6)) and the rate constant for combination with ..
Kinetics of oxidation of benzyl alcohols by the dication and by the radical cation of ABTS. Comparison with laccase-ABTS oxidations: An apparent paradox
No full textLaccase, a blue copper oxidase, in view of its moderate redox potential can oxidise only phenolic compounds by
electron-transfer. However, in the presence of ABTS (2,2-azinobis(3-ethylbenzthiazoline-6-sulfonate) as a redox
mediator, laccase reacts with the more difficult to oxidise non-phenolic substrates, such as benzyl alcohols. The role
of ABTS in these mediated oxidations is investigated. Redox interaction with laccase could produce in situ two
reactive intermediates from ABTS, namely ABTS++ or ABTS•+. These species have been independently generated by
oxidation with Ce(IV) or Co(III) salts, respectively, and their efficiency as monoelectronic oxidants tested in a kinetic
study towards a series of non-phenolic substrates; a Marcus treatment is provided in the case of ABTS++. On these
grounds, intervention of ABTS++ as a reactive intermediate in laccase–ABTS oxidations appears unlikely, because the
experimental conditions under which ABTS++ is unambiguously generated, and survives long enough to serve as a
diffusible mediator, are too harsh (2 M H2SO4 solution) and incompatible with the operation of the enzyme.
Likewise, ABTS•+ seems an intermediate of limited importance in laccase–ABTS oxidations, because this weaker
monoelectronic oxidant is unable to react directly with many of the non-phenolic substrates that laccase–ABTS can
oxidise. To solve this paradox, it is alternatively suggested that degradation by-products of either ABTS++ or ABTS•+
are formed in situ by hydrolysis during the laccase–ABTS reactions, and may be responsible for the observed
oxidation of non-phenolics
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
Experimentally induced aggressiveness in heroin-dependent patients treated with buprenorphine: comparison of patients receiving methadone and healthy subjects
No full textObjective measures of experimentally induced aggressiveness were evaluated in heroin-dependent patients (HDP), 15 receiving buprenorphine (BUP) and 15 receiving methadone (METH) treatment. HDP were randomly assigned to BUP and METH groups. Fifteen healthy subjects (CONT) were included in the study as controls. During a laboratory task, the Point Subtraction Aggression Paradigm, subjects earned monetary reinforcement and could respond by ostensibly subtracting money from a fictitious subject (the aggressive response). Money-earning (points maintained) responses did not differ in BUP patients and in controls. In contrast, point-maintained responses were significantly lower in the group of HDP treated with METH than in both the BUP and CONT groups. Aggressive responses were significantly higher in the HDP group than in the CONT group. No significant differences in aggressive responses were found between the BUP and METH groups. Baseline concentrations of plasma adrenocorticotropic hormone (ACTH) and cortisol (CORT) were higher in HDP than in CONT. During the experimental task, ACTH and CORT increased significantly less in METH patients than in BUP patients and CONT. Norepinephrine (NE) and epinephrine (EPI) levels increased significantly more in HDP than in CONT, without any difference between the METH and BUP patients. PSAP aggressive responses positively correlated with NE and EPI changes, as well as with Buss–Durkee Hostility Inventory (BDHI) scores in both METH and BUP patients and also in CONT subjects. No correlation was found between the extent of heroin exposure, drug doses and aggressiveness levels. BUP, similarly to METH, does not seem to affect outward-directed aggressiveness, as aggressive responses related more to monoamine levels and personality traits than to the action of opioid agonists. Money-earning responses seemed to be unimpaired in BUP patients
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