1,720,956 research outputs found
An investigation into the molecular recognition and sensing of anions, especially of alkylcarbamates and related species
No full textThis thesis reports the synthesis and study of the anion recognition properties of a variety of synthetic organic and inorganic receptors. A series of known anion receptors containing a common urea and varying alkyl and aryl substituents have been investigated for their ability to bind the alkylcarbamate portion of two alkylammonium-alkylcarbamate salts and the CO2 adduct of a cyclic amidine, in an investigation into novel CO2 fixation strategies. Chemical shift changes were used to observe relative binding strengths for interactions between the alkylcarbamate and the receptors in DMSO-d6. The results show that it is possible to bind the alkylcarbamate anion in the presence of the primary alkylammonium cation, when a receptor of sufficient strength is employed. The strength of this interaction was increased when 18-crown-6 was added, which acts as a receptor for the alkylammonium cation. The CO2 adduct of the cyclic amidine, (1,4,5,6, tetrahydropyrimidine) was shown to have the strongest interactions with the receptor series. Several Schiff-base and urea containing receptors have been synthesised and assessed for anion complexation properties in solution using 1H NMR in DMSO-d6 : water mixtures. These are selective for acetate, benzoate and dihydrogen phosphate over chloride and hydrogen sulfate, and exhibit a mixture of 1:1 and 2:1, (guest:host), binding stoichiometries in several cases. Zinc(II) and cobalt(II) chloride complexes of one of this series were synthesised. The cobalt(II)chloride complex was observed to be a stark colorimetric indicator for chloride and dihydrogen phosphate. A number of isophthalamide derivatives containing activated NH and / or CH protons have been synthesised and assessed for anion complexation solution using 1H NMR in DMSOd6. Their interactions with fluoride, chloride and bromide were investigated, which demonstrate a significant contribution from the activated CH proton
Stabilisation of alkylcarbamate anions using neutral hydrogen bond donors
No full textThe interactions of a series of urea-based anion receptors and alkylcarbamate species formed by the reaction of carbon dioxide with primary amines have been investigated by 1H NMR. Significant downfield shifts in the NH proton signals of the receptors in the presence of the alkylcarbamates were observed, consistent with classical host:anion hydrogen-bonding. This observation demonstrates that neutral hydrogen bond donor receptors can compete with ammonium cations to bind carbamates in DMSO-d6 solution.<br/
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
Carboxylate complexation by a family of easy-to-make ortho-phenylenediamine based bis-ureas: studies in solution and the solid state
No full textSimple bis-urea compounds based on ortho-phenylenediamine function as excellent receptors for carboxylate anions in DMSO-d(6)-0.5% water solution. By varying the functional groups in these compounds, the binding affinity of carboxylate anions can be modulated. Solid-state studies illustrate the cleft-like arrangement of the DDDD hydrogen bond array in the carboxylate complexes of these compounds
Carbamate complexation by urea-based receptors: studies in solution and the solid state
No full textThe interactions of a series of urea based neutral hydrogen bond donor anion receptors have been investigated with i) alkylcarbamate anions formed by the reaction of carbon dioxide with primary aliphatic amines and ii) the zwitterionic species formed by the reaction of carbon dioxide with 1,4,5,6-tetrahydropyrimidine. Significant downfield chemical shift changes were observed for the urea NH protons in many cases, consistent with host:anion hydrogen bonding interactions, and thus stabilisation of the carbon dioxide bound species. In the case of the alkylammonium-alkylcarbamate salts, this represents successful competition with electrostatic interactions between the alkylcarbamate and alkylammonium components of the salt. A synchrotron structure of a ternary complex formed by an amide appended diindolylurea, the ammonium carbamate salt formed by 1,3-diaminopropane and CO2 and 18-crown-6, was elucidated and shows the carbamate group bound by six hydrogen bonds (accepting five and donating one) to the functionalised diindolylurea
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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