1,721,020 research outputs found
Epoxidation and hydroxylation reactions catalyzed by the manganese and iron complexes of 5,10,15,20-tetrakis(2,6-dimethoxyphenyl)porphyrin.
No full textManganese(III) and iron(III) complexes of 5.10.15.20-tetrakis-(2,6-dimethoxyphenyl)porphyrin (H(2)TDMeOPP) were tested as catalysts in the epoxidation of alkenes and in the hydroxylation of adamantane with H2O2 (in the presence of imidazole) or PhIO as oxidants. The behavior of the two catalysts is compared with that of the corresponding manganese(III) and iron(III) complexes of 5,10,15,20-tetrakis-(2,6-dichlorophenyl)porphyrin and 5,10,15,20-tetraphenylporphyrin, and the observed differences ascribed to the electron donating effect of the methoxy groups. (C) 1997 Elsevier Science Ltd
A biomimetic approach to lignin degradation: Metalloporphyrins catalyzed oxidation of lignin and lignin model compounds
No full textAn overview of the state of the art for the use of synthetic metalloporphyrins in the catalytic oxidation of lignin and lignin model compounds is presented. The biomimetic oxidation of 5-5′ condensed and diphenylmethane lignin model compounds with several water soluble anionic and cationic iron and manganese porphyrins in the presence of hydrogen peroxide is described. Manganese porphyrins were found more effective in degrading lignin substructures than iron porphyrins. Among them the cationic manganese mesotetrakis(N-methyl-pyridinio) porphyrin pentaacetate [TPyMePMn(CH3COO)5], never used before in lignin oxidation, proved to be the best catalyst. The catalytic activity of porphyrins in hydrogen peroxide oxidation of residual kraft lignin was also investigated. TPyMePMn(CH3COO)5 was able to perform the most extensive degradation of the lignin structure, as demonstrated by the decrease of aliphatic hydroxyl groups and increase of carboxylic acids, as measured by quantitative 31P-NMR. No significant condensation reactions occurred during manganese porphyrin catalyzed oxidations of residual kraft lignin, while in the presence of iron porphyrins an increase of condensed moieties was detected
Electroactive monolayers on Si(100) from covalently bound porphyrins and metalloporphyrins: An AFM, XPS and electrochemical study
No full textJournal of Porphyrins and Phtalocyanins, Volume 10, p. 52
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
Biomimetic degradation of lignin and lignin model compounds by synthetic anionic and cationic water soluble manganese and iron porphyrins
No full textThe biomimetic oxidation of 5-5' condensed and diphenylmethane lignin
model compounds with several water soluble anionic and cationic iron and
manganese porphyrins in the presence of hydrogen peroxide is reported.
The oxidative efficiency of manganese and iron
meso-tetra(2,6-dichloro-3-sulphonatophenyl) porphyrin chloride
(TDCSPPMnCl and TDCSPPFeCl, respectively), meso-tetra-3-sulphonatophenyl
porphyrin chloride (TSPPMnCl) and manganese
meso-tetra(N-methylpyridinio)porphyrin pentaacetate
(TPyMePMn(CH3COO)(5)) was compared on the basis of the oxidation extent
of the models tested. Manganese porphyrins were found more effective in
degrading lignin substructures than iron ones. Among them the cationic
TPyMePMn (CH3COO)(5), never used before in lignin oxidation, showed to
be the best catalyst. The catalytic activity of porphyrins in hydrogen
peroxide oxidation of residual kraft lignin was also investigated. The
use of quantitative P-31 NMR allowed the focusing on the occurrence of
different degradative pathways depending on the catalyst used.
TPyMePMn(CH3COO)(5) was able to perform the most extensive degradation
of the lignin structure, as demonstrated by the decrease of aliphatic
hydroxyl groups and carboxylic acids. Noteworthy, no significant
condensation reactions occurred during manganese porphyrins catalyzed
oxidations of residual kraft lignin, while in the presence of iron
porphyrins a substantial increase of condensed substructures was
detected. (C) 1999 Elsevier Science Ltd. All rights reserved
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
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