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Ruthenium tetraoxide oxidation of alkenes .7. A more complete picture
No full textThe main reaction products of the RuO4 oxidation of a number of linear and cyclic alkenes, at - 70 degrees C in acetone-water (5:1) are 1,2-diols, formed in a syn stereospecific manner, and/or alpha-ketols sometimes accompanied by small amounts of scission products, namely aldehydes and/or carboxylic acids; in some cases, 1,3-dioxolane products, formed by condensation of the 1,2-diol and aldehyde materials, are also obtained
Reaction of RuO4 with carbon-carbon double bonds. 4. Reaction of sterols containing the 7,14- or 8,14-diene system with ruthenium tetraoxide: formation of epoxysterols
No full textThe reaction of ruthenium tetraoxide with 5α-cholesta-8,14-dien-3β-yl acetate and 5α-cholesta-7,14-dien-3β-yl acetate, performed using equimolar amts. of the oxidant in acetone-water at low temp., gives mainly epoxides
Temperature Dependence of the Red-shift and Broadening of the Exciton Line in CdSe/GaAs Laser Ablated Heterostructures
No full textA detailed photoluminescence investigation of the thermal red-shift and broadening of the excitonic line of CdSe films grown on bulk GaAs substrate by laser ablation technique is presented. Material parameters related to the electron-phonon interaction have been obtained by fitting the experimental data to phenomenological models. The relative contribution of both acoustic and optical phonons to the band gap shrinkage and the dominant role of impurity scattering, at low temperatures, in the excitonic line broadening are discussed
Studies towards the synthesis of polyoxygenated steroids. Reaction of 7,9(11)-diene steroids with RuO4
No full textIn order to find an entry to C-ring oxygenated steroids, the reaction of ruthenium tetroxide with some Δ7,9(11)-sterols has been explored. The reaction has been performed both at −70°C and room temperature using an equimolecular amount of the oxidant and acetone-water as solvent system in the absence of a cooxidant. The change in the temperature conditions moderately affect the yields of the reaction products. When 3β,6α- and 3β,6β-diacetoxy-Δ7,9(11)-sterols were used the diene system was predominantly attacked at the 9(11)-double bond from the α-face of the molecule giving Δ7-9α-hydroxy-11-keto- and Δ7-9α-11α-dihydroxy-sterols. RuO4 oxidation of cholesta-7,9(11)-dien-3β-yl acetate, yielded, in addition to the above oxidation products, minor amounts of three related C-7,C-11 oxigenated 8α,9α-epoxysterols, arising from the oxidation of both double bonds of the diene system. These results, that in part parallel those we recently found on RuO4 oxidation of trisubstituted [Δ4, Δ5 and Δ7] steroidal alkenes, shed further light on the reactivity of this oxidizing agent which, neverthless, seems far from being completely understood. In addition, our procedure furnishes a reliable route to Δ7-9α,11β-dihydroxysterols via LiAlH4 reduction of the 11-keto group
Reaction of 7-dehydrocholesteryl acetate with RuO4. First isolation of cyclic ruthenium(VI) diester
No full textThe reaction of 7-dehydrocholesteryl acetate with RuO4 has been performed in acetone-water at -60°C using an oxidant substrate ratio of 1:1. The cyclic oxoruthenium(VI) diester I, likely an intermediate in the formation of 5α-cholest-7-ene-3β,5,6α-triol 3-acetate and 3β-acetoxy-5-hydroxy-5α-cholest-7-en-6-one, the final oxidn. products of the steroidal substrate with RuO4, has been isolated for the first time and characterized on the basis of spectral and chem. evidence
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
Studies towards the synthesis of polyoxygenated steroids. Reaction of some tri- and tetrasubstituted monoene steroids with ruthenium tetroxide
No full textThe course of the reaction of ruthenium tetroxide with some tri- and tetra-substituted nuclear monoene steroids, namely δ4, δ5, δ7 and δ8(14)-steroids, has been investigated in acetone-water or carbon tetrachloride as solvent systems using stoichiometric amounts of the oxidant. In contrast with results previously reported for RuO4 oxidations, we found that trisubstituted double bonds gave α-hydroxy ketones and/or 1,2-diols rather than the expected products deriving from the scission of the carbon-carbon double bond. Scission of the double bond indeed occurs when fully substituted steroidal alkenes are oxidized. Only in the case of the δ8(14)-steroid, an allylic oxidation product wa obtained in addition to the scission product. The change in the solvent system seems to profoundly affect the course of the reaction
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