1,720,973 research outputs found
Synthesis, characterization and chemisorption on gold of a Beta-cyclodextrin-lipoic acid conjugate.
No full textMono-6-lipoyl-amido-2,3,6-O-permethyl-beta -cyclodextrin, TM beta CDLA, was synthesized in 79% isolated yield by coupling the mono-6-amino-permethyl-beta -cyclodextrin with lipoic acid in the presence of 1-(3-dimethylamino)ethyl carbodiimide. The identity of cyclodextrin-lipoic acid conjugate was confirmed by NMR spectroscopy and electrospray mass spectrometry. Chemiadsorption of TM beta CDLA on colloidal gold was shown to occur by colloid flocculation test analysis
Synthesis of 6(I)-amino-6(I)-deoxy-2(I-VII)-tetradeca-O-methyl-cyclomaltoheptaose
No full textThe preparation of 6(I)-amino-6(I)-deoxy-2(I-VII),3(I-VII)-tetradeca-O-methyl-cyclomaltoheptaose is reported. Two different routes (A and B), both starting from beta-cyclodextrin (betaCD), have been examined. Route A involved: (i) synthesis of heptakis(6-0-tert-butyldimethylsilyl)-betaCD from betaCD; (ii) permethylation of the secondary hydroxyl groups with methyl iodide and sodium hydride; (iii) desilylation of the primary hydroxyls with ammonium fluoride; (iv) monotosylation at O-6 position of per-(2,3-O-methyl)-betaCD,- (5) nucleophilic replacement of the tosyl group with azide anion; (v) reduction of the azido group by catalytic transfer hydrogenation using hydrazine hydrate in the presence of Pd/C in methanol/water. Route B started from the known 6(I)-monoazido-6(I)-monodeoxy-beta-CD (two steps from beta-CD) and entailed: (i) protection of the remaining primary hydroxyls using tert-butyldimethylsilylchloride (TBDMSCI); (ii) exhaustive methylation of the secondary hydroxyls with methyl iodide and sodium hydride; (iii) removal of the TBDMS protecting groups with ammonium fluoride; (iv) reduction of the azido group as above. Route A was found to be less convenient than Route B due to the inherent difficulty of controlling the monotosylation of per-(2,3-O-methyl)-betaCD
External vs. internal interactions in the enantiodiscrimination of fluorinated alpha-amino acid derivatives by heptakis[(2,3-di-O-acetyl-6-O-(tert-butyldimethylsilyl)]-beta-cyclodextrin, a powerful chiral solvating agent for NMR spectroscopy
No full textNMR spectroscopic investigations involving extensive use of ROESY and DOSY techniques and comparison with silylated-acetylated linear dextrins as acyclic model compounds
shed light on the origin of the phenomenon of enantiodiscrimination of fluorinated α-amino acid derivatives by heptakis[2,3-di-O-acetyl-6-O-(tert-butyldimethylsilyl)]-β-
cyclodextrin. The effectiveness and versatility of the cyclic derivatized oligosaccharide as a chiral solvating agent for the
NMR determination of enantiomeric purity in the same class of compounds is demonstrated. A regular correlation between the relative positions of enantiomers’ signals and absolute configurations is observed
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
Water soluble heptakis(6-deoxy-6-thio)cyclomaltoheptaose capped gold nanoparticles via metal vapor synthesis: NMR structural characterization and complexation properties
No full textThe complexation of heptakis(6-deoxy-6-thio)cyclomaltoheptaose to gold nanoparticles prepared by using the Metal Vapour Synthesis (MVS) led to water soluble gold nanoaggregates, thermally stable at 25 C. The role of gold concentration in the MVS-derived starting solution as well as of the cyclodextrin to gold molar ratio on the size of cyclodextrin-capped gold nanoparticles were investigated. The ability of cyclodextrin bonded to gold nanoparticles to include deoxycytidine was also probed in comparison with
that of 1-thio-b-D-glucose sodium salt
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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