1,720,970 research outputs found
Using the 'Chemical Tunability' of Ionic Liquids to Increase Sustainability in the Electrophilic Bromination of Unsaturated Compounds
No full textTribromide-based ionic liquids have been synthesized and investigated as efficient bromination agents. The different physicochemical properties of the reaction media, which depend on the cation structure, have been used to improve the efficiency of the bromination process
Assessing the bio-compatibility of a click DNA backbone linker
No full textClick chemistry has the potential to be employed for the assembly of large DNA fragments, by purely chemical methods. However to enable this, the bio-compatibility of the resulting click-linked DNA must be examined. Click DNA linkers were incorporated into a plasmid within the gene encoding for an ampicillin resistance marker. The plasmid was transformed into E. coli and resulting colonies found to survive on LB agar plates supplemented with ampicillin. This indicated that the click DNA linker was replicated and transcribed correctly by the cellular machinery of E. coli. The observed bio-compatibility was further probed by demonstrating the functionality of the click-linked DNA in nucleotide excision repair deficient cells line. The bio-compatibility of the click DNA linker was then investigated in a non-essential gene by constructing a click-linked variant of the gene encoding for the fluorescent mCherry protein. Experiments carried out using a plasmid containing two click DNA linkers in the region of the gene encoding for the mCherry fluorophore provided further evidence that the click DNA linker was functional in E. coli. Moreover, using a coupled in vitro transcription/translation system the yield and fluorescence of the mCherry protein expressed from the plasmid containing the click DNA linker was similar to that from canonical DNA. Investigation of the bio-compatibility of the click DNA linker in mammalian cells showed that a plasmid containing the click-linked DNA, had the same viability of a plasmid containing canonical DNA. Finally, the use of click ligation for the assembly of the first 229 bp of the mCherry gene was investigated. Two different approaches referred as “templated click assembly” and “one-pot click assembly” were employed and the bio-compatibility of the click DNA linker was confirmed in both cases
Styrene oxidation by hydrogen peroxide in ionic liquids: the role of the solvent on the competition between two Pd-catalyzed processes, oxidation and dimerization
No full textA series of hydrophilic N,N-dimethylpyrrolidinium-and N,N-dimethylpiperidinium-based ionic liquids (ILs) have been prepared and applied as reaction media in the Wacker oxidation of styrene by hydrogen peroxide using PdCl(2) as the catalyst. The efficiency of these ILs was compared with hydrophilic and hydrophobic imidazolium systems (including those with nitrile functionalities). The nature of the ionic liquid strongly influences the product distribution. In particular, in hydrophobic ILs, relevant amounts of 1,3-diphenyl-1-butene arising from styrene dimerization were detected, in addition to the expected phenylmethylketone. The formation of 1,3-diphenyl-1-butene may be attributed to the formation of Pd(0) species from "ClPdOH" (probably formed during the Wacker process) in a side-reaction. Consequently, the ability of the IL to favor or disfavor the reoxidation of "ClPdOH" to "ClPdOOH" by hydrogen peroxide, giving an homogeneous phase or a biphasic system, appears to be the main factor affecting selectivity
Basic ionic liquids based on monoquaternized 1,4-diazobicyclo[2.2.2]octane (dabco) and dicyanamide anion: Physicochemical and solvent properties
No full textIn this paper, we report on the synthesis and application of monosubstituted diazabicyclo[.2.2.2]octane (dabco) cations associated with a basic anion, dicyanamide. Key properties of these salts-phase transitions, density, and conductivity-were measured and compared to those of other common ionic liquids (ILs). Moreover, solvatochromic dyes were used to assess their solvation properties. The Heck cross-coupling reaction was evaluated in dabco-based ILs and compared with the behavior in common unfunctionalized ILs, evidencing good catalyst stability and a high recyclability in these basic ILs
The pH- And salt-controlled self-assembly of [1]benzothieno[3,2-b][1]-benzothiophene-peptide conjugates in supramolecular hydrogels
No full textHere, we report a [1]benzothieno[3,2-b][1]-benzothiophene (BTBT) derivative functionalized with a β-sheet-forming peptide which alternates in its sequence Phe and Glu residues. The BTBT core is a popular structural motif in the design of high-mobility organic semiconductors. The insertion of the self-assembling subunit allows control of the supramolecular organization. This molecule self-assembles in water to give hydrogels over a broad range of pH values. Hydrogelation is triggered by both pH changes and variations in salt concentrations. Transmission electron microscopy shows the formation of long-range self-assembled 1D structures. The key role of hydrogen bonding and π-π interactions in hierarchical self-assembly is investigated using absorption, emission, infrared and circular dichroism spectroscopy. This is the first example of demonstrating the formation of supramolecular hydrogels containing the BTBT structure
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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