1,721,413 research outputs found
The Depth of Molecular Recognition: Voltage-Sensitive Blockage of Synthetic Multifunctional Pores with Refined Architecture
No full textVoltage-sensitive blockage by ADP, ATP and phytate (IP6) demonstrates that active-site contraction toward the middle of newly synthesized rigid-rod beta-barrels provides a general strategy to rationally create and modulate the voltage sensitivity (and to increase the efficiency) of molecular recognition by synthetic multifunctional pores
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
Introduction to the Art of Chemistry
Get PDFThe author describes his undergraduate and graduate studies at the University of Zurich. His interest in large complex molecules at the interface between chemistry and biology led him to Columbia University, New York and Georgetown University, Washington before he accepted a professorship
at the University of Geneva
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
Microfluidic Electric-Field Catalysis on Carbon Nanotubes and the Origin of Anion-π Autocatalysis
No full textAnion-π interactions, the anionic counterparts to well-known cation-π interactions, have emerged as a novel and powerful tool in organic synthesis. These noncovalent forces enable the stabilization of anionic intermediates and transition states (TS) on π-acidic surfaces, laying the foundation for innovative catalytic strategies. This work explores their potential not only as a stabilizing interaction but as a dynamic catalytic tool that can be actively tuned using external stimuli.
Central to this approach is the concept of induced π-acidity—whereby a π-system becomes polarized in response to an approaching anionic TS. Multiwalled carbon nanotubes (MWCNTs), with their exceptional polarizability and extended π-networks, serve as ideal scaffolds for this purpose. Aromatic and alkyl-substituted epoxides undergo efficient cyclization in MWCNT suspensions, with reaction rates increasing proportionally to nanotube loading, confirming the catalytic role of induced anion-π interactions. Enhanced performance with pyrene-tagged epoxides underscores the importance of electronic communication between substrate and catalyst.
To further control reactivity, an oriented external electric field (OEEF) was applied to modulate MWCNT polarization. Using a microfluidic device with MWCNT-coated electrodes, we demonstrate reversible electric-field-driven catalysis: switching the field direction enabled or inhibited the conversion of pyrene epoxide to its product. This dynamic control of catalysis introduces the concept of electricity as a “smart reagent.”
To study the selectivity of epoxide cyclization under OEFF, a series of methylated epoxides were synthesized. These were designed to bias the reaction pathway toward either cation-π or anion-π catalysis, depending on field polarity and substrate structure. Results revealed that reaction mechanisms could be steered toward Baldwin or anti-Baldwin pathways by simply changing the field direction, unlocking new control over chemoselectivity under bulk conditions. Subtle changes in molecular design, such as the position of aromatic tags, further fine-tuned this selectivity.
Beyond external control, we investigated the intriguing autocatalytic behavior of epoxide cyclizations under anion-π catalysis. Two bulky epoxides displayed sigmoidal kinetics, with acceleration linked to product concentration. Attempts at asymmetric induction through chiral product co-catalysts were unsuccessful, pointing to a mechanism not reliant on close-range interactions. Experimental data and computational modeling supported a novel TS involving water-mediated long-range activation from product to substrate—an unprecedented mode of remote control in catalysis.
Together, these findings position anion-π interactions as a tunable, field-responsive platform for catalysis. The dual compatibility with both cation-π and anion-π mechanisms, electric-field-directed reactivity, and discovery of water-mediated autocatalysis point toward a new paradigm: catalysis that is not only selective and efficient, but also remotely programmable. This work opens exciting opportunities for scalable, smart catalysis in synthetic chemistry and beyond.</p
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
Rigid-rod ß-barrel pores as enzyme sensors
No full textCe travail présente le design et la synthèse d'une baguette formée d'un octiphényle portant sur chaque phényle: le pentapeptide -Leu-Arg-Leu-His-Leu. L'auto-assemblage de cette baguette forme une barrique ß qui agit comme un pore dans les doubles couches lipidiques, perméable au passage d'anions. Les études de blocage avec l'acide poly-glutamique ont mis en évidence la formation d'un complexe entre le polymère et la barrique transmembranaire ainsi qu'une coopérativité dipôle-potentiel. La mise au point et l'utilisation de la structure supramoléculaire comme senseur d'enzymes ont été largement illustrées sur des biopolymères ou des enzymes intervenant dans différents processus biologiques. L'utilisation d'un seul pore permet la détection d'une large variété d'enzymes et de substrats à intérêt biologiques, sans requérir aucune modification chimique des composés impliqués. Des applications telles que la recherche d'inhibiteurs d'enzymes ou la quantification du sucre dans les boissons ont découlé de cette recherche
Anion-π Catalysis with Peptides and Synthesis of Thiol-Mediated Uptake Inhibitors
No full textIn the first topic of this thesis, peptide secondary structure was explored in the design of new anion-π catalysts. The rigid peptide skeleton allows to control the positions of each amino acid residue above the naphthalenediimide surface precisely. When a tertiary amine is placed at different amino acid side chains along the peptide, the catalytic activity of the catalysts could be modulated in a predictable manner. The scope of electron-poor aromatic surface was extended to perylenediimides (PDIs) in the second topic. The helix-like conformation for the peptide backbone has been confirmed with NMR spectroscopy. Overall performance of PDI catalysts was significantly improved in comparison with the NDI analogs. Finally, the application of peptide secondary structures was examined in thiol-mediated uptake. Highly reactive γ-turn peptides were synthesized as potential thiol-mediated uptake inhibitors. With the intention to identify more efficient inhibitors, a large library of thiol-reactive reagents has also been synthesized
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