1,720,983 research outputs found
Simple model system to study sugar/aromatic interactions
No full textA molecular scaffold was identified which enables the establishment of intramolecular interactions between a monosaccharide and a nearby phenyl ring. A group of molecules containing four different monosaccharides (glucose, galactose, N-acetyl-glucosamine and N-acetyl-galactosamine) was synthesized and used to investigate the extent and nature of this carbohydrate-arene interaction, as well as the effect on the overall 3D structure of the molecules involved. The sugar-aromatic distance was evaluated by rigorous NMR studies supported by molecular modeling, and found to be constant throughout the series, independent of the nature of the sugar, and of the conformational behaviour of the fragment connecting the two elements. Ab initio calculations at the B3LYP/DZV(2d,p) level of theory enable the analysis of the electronic nature of the interaction. The study shows that, given the opportunity, persistent intramolecular aromatic-sugar interactions can be established and can significantly influence overall molecular shape and energetics. These results have important implications in the design of structural mimics of oligosaccharide
Clemmensen reduction of diosgenin and kryptogenin: synthesis of [16,16,22,22,23,23-H-2(6)]-(25R)-26-hydroxycholesterol.
No full textA new experimental protocol has been established for the Clemmensen reduction of diosgenin and kryptogenin with the aim to prepare deuterated isotopomers of (25R)-26-hydroxycholesterol. Uncontrolled deuteration has been achieved from diosgenin, whereas [16,16,22,22,23,232 H-2(6)]-(25R)-26-hydroxycholesterol (1) can be synthesized from kryptogenin
Synthesis of deuterated isotopomers of 7 alpha- and (25R,S)-26-hydroxycholesterol, internal standards for in vivo determination of the two biosynthetic pathways of bile acids.
No full textDeuterated isotopomers of 7alpha- and (25R,S)-26-hydroxycholesterol, internal standards for in vivo determination of the two biosynthetic pathways of bile acids formation from cholesterol, were prepared from [2,2,3,4,4,6-H-2(6)]-cholesterol and (20S)-[7,7,21,21-H-2(4)]-3beta-(tert-butyldimethylsilyl)oxy-20-methylpregna-5-en-21-ol, respectively
Adenylate deaminase (5 '-adenylic acid deaminase, AMPDA)-catalyzed deamination of 5 '-deoxy-5-substituted and 5 '-protected adenosines: A comparison with the catalytic activity of adenosine deaminase (ADA)
No full textThe enzyme adenylate deaminase (AMPDA) is able to catalyze the hydrolytic deamination of 5'-substituted and 5'-protected 5'-deoxyedenosines, whereas limited or no activity is shown by adenosine deaminase (ADA) towards the same substrates
Lipase-catalyzed selective benzoylation of 1,2-diols with vinyl benzoate in organic solvents
No full textLipases from Mucor miehei (MML) and Candida antarctica (CAL) are able to catalyze the benzoylation of the primary hydroxy group of 1.2-diols with vinyl benzoate in organic solvents. We have studied the MML-catalyzed benzoylation that proceeds with high regioselectivity and moderate enantioselectivity, whereas in the dibenzoylation reaction activity of MML and stereoselectivity of the enzymatic process is strongly influenced by steric factors
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
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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