1,720,964 research outputs found
Synthesis of 7,8-Dihydroxy-3-(3,4-dihydroxyphenyl)-2H-chromen-2-one Derivatives of Crown Ethers
No full textThe novel 1-(3,4-dimethoxyphenyl)-2-(2,3,4-trimethoxyphenyl)acrylonitrile was prepared from the condensation of the mixture of 2,3,4-trimethoxybenzaldehyde and 3,4-dimethoxyphenylacetonitrile in ethanol at 70 degrees C with 20% aqueous sodium hydroxide solution. Cyclization and demethylation of the acrylacetonitrile was performed using pyridine hydrochloride. The obtained 7,8-dihydroxy-3-(3,4-dihydroxyphenyl)-2H-chromen-2-one was reacted with the poly(ethylene glycol) ditosylates in CH3CN/alkali carbonate to afford bis-[12]crown-4, -[15]crown-5, and -[18]crown-6 chromenones. The chromatographically purified novel chromenone crown ethers were identified by IR, H-1 NMR, C-13 NMR, and MALDI-TOF mass spectrometry and elemental analysis
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
The synthesis of novel 4-(3,4-dimethoxyphenyl)chromenone-crown ethers and their cation binding, as determined using fluorescence spectra
No full textThe complexation of naftifine (NF) and terbinafine (TB) with cyclodextrins (CDs) has been investigated by UV/visible and 1H NMR spectroscopy, ROESY techniques and also ESI-MS. Both drugs form 1:1 inclusion complexes with all the CDs tested except with -CD, as deduced from the Benesi-Hildebrand plots and confirmed by ESI-MS and NMR spectroscopy (Job plot method). The K11 values for NF decrease in the order -CDmethylated -CD2-hydroxypropyl--CD-CD. The determination of the enthalpy and entropy provides information about the main driving forces in the process. The stability constants of the complexes NF--CD, TB--CD and TB--CD determined by 1H NMR spectroscopy are in agreement with the values obtained by UV. For TB--CD, the value is higher, due to the fact that the length of the TB aliphatic chain allows a deeper inclusion of the naphthalene group inside the corresponding -CD molecule, according to the 2D ROESY experiments
Synthesis and Spectral Characterization of a Novel Series of Methylcinnamate Derivatives of 15-Crown-5
No full textA series of novel methylcinnamate derivatives of 15-crown-5 have been synthesized. The derivatives of methylcinnamate have been prepared by a synthesis from the corresponding chromenone-crown ether with MeONa/MeOH or KOH, CH3I, and DMSO as solvent. Novel compounds were characterized by elemental analysis, IR, H-1 NMR, and MALDI-TO
The synthesis and fluorescence properties of novel chromenone-crown ethers
No full texto-Dihyroxy-3-phenylchromenone derivatives, namely, 6,7-dihydroxy-3-(3',4'-dimethoxyphenyl)chromenone and 6,7-dimethoxy-3-(3',4'-dihydroxyphenyl)chromenone, were obtained from 2,4,5-trihydroxybenzaldehyde/3,4-dimethoxyphenylacetic acid and 2-hydroxy-4,5-dimethoxybenzaldehyde/3,4-dihydroxyphenylacetic acid, respectively, in the presence of acetic anhydride and sodium acetate under an inert atmosphere, after treatment with MeOH/HCl(aq). The chromenone-crown ethers were prepared from cyclic condensation of o-dihydroxy-3-phenylchromenones with poly(ethylene glycol) ditosylates in the presence of CH3CN/alkali metal carbonates. The chromatographically purified novel chromenone-crown ethers were identified by 1H NMR, MALDI-TOF mass spectrometry and elemental analysis. The fluorescence and UV-vis spectroscopic properties of the obtained chromenone-crown ethers and their complexes with Li+, Na+ and K+ perchlorate salts were estimated in acetonitrile. The quantum yields of novel chromenone-crown ethers were determined by the comparative method. [image omitted]
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