1,720,960 research outputs found
Photochemical, photophysical and electrochemical properties of six dansyl-based dyads
No full textWe have prepared six dyads containing a fluorescent propyldansylamide (PD) unit covalently linked to nitrobenzene (NB), naphthalene (NA), trans- and cis-azobenzene (tAZ and cAZ), 2,2′-bipyridine (BPY), and [Ru(bpy)3]2+ (RU) moieties. The photochemical, photophysical, and electrochemical properties of the dyads have been investigated in acetonitrile solution. In the PD-NB dyad, the fluorescence of the PD unit is quenched by electron transfer to the NB unit at 298 K, but it is not quenched in a rigid matrix at 77 K. In the PD-NA dyad, the fluorescence of the naphthalene unit is completely quenched by competing energy (80% efficiency) and electron transfer processes. In the case of PD-tAZ, the dansyl fluorescence is quenched without sensitization of the trans → cis photoisomerization reaction of the tAZ moiety, whereas in the PD-cAZ dyad the dansyl fluorescence quenching is accompanied by the sensitisation of the cis → trans photoisomerization of the cAZ moiety. In the PD-BPY dyad the fluorescence of the dansyl moiety is sensitized by the BPY unit; upon protonation or Zn2+ complexation of the BPY unit, however, the dansyl fluorescence is quenched by electron transfer. In the PD-RU dyad, the fluorescence of the dansyl unit is quenched by competing energy (25% efficiency) and electron transfer processes, whereas the emission of the RU moiety is unaffected
Effect of protons and metal ions on the fluorescence properties of a polylysin dendrimer containing twenty four dansyl units
No full textThe interaction of protons, Co2+, Ni2+ and Zn2+ ions (as nitrate salts) with a polylysin dendrimer, D, functionalized in the periphery with 24 5-dimethylamino-l-naphthalenesulfonamido (dansyl) units has been investigated in acetonitrile-dichloromethane solution. The dendrimer consists of a benzene core branched in the 1, 3, and 5 positions. Each branch starts with a (dialkyl)carboxamide-type moiety and carries (i) six aliphatic amide groups and (ii) eight fluorescent dansyl units. For comparison purposes, the behaviour of a monodansyl reference compound (I) has also been investigated. The absorption spectrum and the fluorescence properties of the dendrimer are those expected for a species containing 24 non-interacting dansyl units. Both for the model compound and for the dendrimer, protonation causes a shift of the absorption and fluorescence bands towards higher energies; for the dendrimer, however, the changes in fluorescence intensity during the acid titration reveal the occurrence of intradendrimer quenching processes, with signal amplification. Addition of Co2 or Ni2+ ions to a basic solution of the model compound I does not cause any effect in the absorption and emission properties, whereas in the case of dendrimer D a strong fluorescence quenching is observed. At low metal ion concentration each metal ion quenches about 9 dansyl units; the fluorescence quenching takes place by a static mechanism involving co-ordination of metal ions in the interior of the dendrimer. Addition of Zn2+ to a basic solution of the dendrimer causes only a very small decrease in the fluorescence intensity. The co-ordinated Co2+ and Ni2+ ions are fully displaced by addition of Zn2 or H"1" with revival of the dansyl fluorescence. The results obtained show that a dendrimer can exhibit an unusual co-ordinating ability and sensory signal amplification. © The Royal Society of Chemistry 2000
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
Fluorescent guests hosted in fluorescent dendrimers
No full textWe have investigated the formation of host-guest complexes between dendrimers of the poly(propylene amine) family functionalized with dansyl units at the periphery (hosts) with dye molecules (guests). Each dendrimer nD, where the generation number n goes from 1 to 5, comprises 2′′+1 (i.e. 64 for 5D) dansyl functions in the periphery and 2′′+1 -2 (i.e. 62 for 5D) tertiary amine units in the interior. The most thoroughly investigated systems were those with eosin as a guest. The results obtained show that: (i) the nD dendrimers dissolved in dichloromethane solution extract eosin from aqueous solutions; (ii) the maximum number of eosin molecules hosted in the dendrimers increases with increasing dendrimer generation, up to a maximum of 12 for the 5D dendrimer; (iii) the fluorescence of the peripheral dansyl units of the dendrimers is completely quenched via energy transfer by the hosted eosin molecules; (iv) the fluorescence of the hosted eosin molecules is partially quenched; (v) the eosin molecules can occupy two different sites (or two families of substantially different sites) in the interior of the dendritic structure; (vi) excitation of eosin hosted in the dendrimers causes sensitization of the dioxygen emission via eosin triplet excited state. The behavior of fluorescein and rose bengal is qualitatively similar to that of eosin, whereas naphthofluorescein is not extracted. The maximum number of dye molecules extracted by the 4D dendrimer is 25 for rose bengal and ca. 1 for fluorescein, showing that the formation of host-guest species is related to the electronic properties rather than to the size of the dye molecules. © 2002 Elsevier Science Ltd. All rights reserved
Eosin molecules hosted into a dendrimer which carries thirty-two dansyl units in the periphery: A photophysical study
No full textEosin in dendrime
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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