1,721,056 research outputs found
Synthetic Pores with Reactive Signal Amplifiers as Artificial Tongues
No full textThe sensation of taste is mediated by activation or deactivation of transmembrane pores(1,2). Artificial stimulus-responsive pores are enormously appealing as sensor components because changes in their activity are readily detectable in many different ways(3-9). However, the detection of multiple components in complex matrices (such as foods) with one pore sensor has so far remained elusive because the specificity necessary for sensing a target compound in complex mixtures is incompatible with the broad applicability needed for the detection of multiple components(7). Here, we present synthetic pores that, like our tongues, can sense flavours in food and in addition make them visibly detectable. Differential sensing and pattern recognition are solutions based on empirical and biomimetic approaches. They have been explored with synthetic receptor arrays(10-15) and electronic tongues(16). In contrast, our approach is non-empirical as it exploits reactive amplifiers that covalently capture elusive analytes after enzymatic signal generation(17-22) and drag them into synthetic pores for blockage. Reactive amplification proved to be highly sensitive and adaptable to various analytes and pores. Moreover, it can be combined with reactive filtration for minimizing interference. The system was tested on real food samples for detection of sucrose, lactose, lactate, acetate, citrate and glutamate to demonstrate the feasibility of these synthetic pores as universal sensors
Études computationnelles de complexes non-covalents et de leurs applications dans des architectures supramoléculaires ainsi qu'en organocatalyse
No full textLes interactions non-covalentes telles que les liaisons hydrogène, les interactions π-π, les interactions cation/anion-π, les liaisons halogène sont à la base de la chimie supramoléculaire. Ces interactions ont permis la conception de nouveaux systèmes possédant des fonctions intéressantes dans des domaines variés comme l'électronique organique, le transport transmembranaire ou l'organocatalyse. Dans cette thèse, différents outils de la chimie computationnelle (DFT, dynamique moléculaire…) ont été utilisés pour évaluer la contribution des interactions non-covalentes assurant la cohésion et la fonction dans des systèmes bioorganiques. Ces modélisations ont permis de comprendre et d'expliquer les observations macroscopiques faites en laboratoire à l'aide des informations obtenues au niveau computationnel. Des modélisations concernant les possibles fonctions catalytiques de systèmes supramoléculaires faisant appel aux interactions de type anion-π ont également été réalisées. Les résultats issus de ces études théoriques pourront servir de base de travail pour les chimistes de synthèse quant à l'existence réelle de telles fonctions
Synthetic Multifunctional Pores that Open and Close in Response to Chemical Stimulation
No full textStudies on synthetic multifunctional pores with external and internal active sites for ligand gating and noncompetitive blockage are presented, with emphasis on the contribution of external ligands to the characteristics of the pore. A comparison between different synthetic multifunctional pores reveals that the location of functional groups in rigid-rod beta-barrel pores is precisely reflected in the function: molecular recognition at the outer barrel surface results in pore opening, while molecular recognition at the inner barrel surface results in pore closing. Negligible nonspecific leakage, disappearance of pH gating, inhibition of intervesicular pore transfer, and maybe also the flickering of currents of single open pores characterize external ligands as adhesive cushions that liberate the pore from lateral pressure exerted by the surrounding membrane. Refined molecular models show good agreement with pore design and experimental facts with regard to function
Ab initio investigations of perhydrotriquinacenyl and other bridgehead carbocations
No full textAb initio MO calculations at the SCF level using 6–31 G* basis sets show that only 2.1 kcal mol–1 more energy is needed to form perhydrotriquinacenyl cation 1 from the corresponding hydrocarbon than to form the tert-butyl cation from 2-methylpropane; such a stabilisation energy is comparable to those computed for 1-noradamantyl cation 2, 3-noradamantyl cation 3, and bicyclo[3.2.1]octan-1-yl cation 4, which are shown to be stabilized efficiently by C–C hyperconjugation
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
Steric effects on reaction rates. XI. Solvolysis of tertiary carbon substrates rationalized by molecular mechanics calculations
No full textThe steric energy difference (Est) between tertiary carbenium ions (R+) and the corresponding alcohols has been calculated by MM2 for a series of tertiary nonbridgehead substrates and correlated with their rate of solvolytic reactivity. Satisfactory correlation is obtained, except for p-nitrobenzoates of highly congested substrates. The slope and intercept of the correlations remain almost unchanged if bridge-head substrates are included in the plot. However, the quality of the fit is better for bridgehead substrates alone
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