1,720,963 research outputs found
Bis-triazolyl diguanosine derivatives as synthetic transmembrane ion channels
No full textIn nature, ion channels facilitate the transport of ions across biological membranes. The development of artificial ion channels that can mimic the fundamental functions of the natural ones would be of great importance to biological research. Artificial ion channels based on nucleoside derivatives are expected to be biocompatible with functions that can be controlled by the presence or absence of biologically relevant molecules. This protocol describes the detailed procedures for the synthesis and ion-channel activity of four diguanosine derivatives, each made up of two guanosine moieties separated by a covalent linker (e.g., PEG). The procedure describes the preparation of guanosine azide and guanosine alkine building blocks, as well as the preparation of four distinct synthetic linkers each containing either two alkynes or two azides. The diguanosine derivatives are synthesized using a 'one-pot' modular synthetic approach based on Cu(I)-catalyzed azide and alkyne cycloaddition. The ion-channel activity of these diguanosine derivatives for the transportation of ions across a phospholipid bilayer is investigated using voltage-clamp experiment. By using the PEG-containing diguanosine as an example, we describe how to determine the ion-channel activity in the presence of different metal ions (e.g., Na+, K+ and Cs+) and the inhibition of the ion-channel activity using the nucleobase cytosine. The approximate time frame for the synthesis of the PEG dinucleoside is 3 d, and that for the experiments to evaluate its ability to transport K+ ion across a phospholipid bilayer is similar to 8-10 h
A DNA-Inspired Synthetic Ion Channel Based on G-C Base Pairing
No full textA dinucleoside containing guanosine and cytidine at the end groups has been prepared using a modular one-pot azide-alkyne cycloaddition. Single channel analysis showed that this dinucleoside predominantly forms large channels with 2.9 nS conductance for the transport of potassium ions across a phospholipid bilayer. Transmission electron microscopy, atomic force microscopy, and circular dichroism spectroscopy studies reveal that this dinucleoside can spontaneously associate through Watson-Crick canonical H-bonding and pi-pi stacking to form stable supramolecular nanostructures. Most importantly, the ion channel activity of this G-C dinucleoside can be inhibited using the nucleobase cytosine
Triazole-Tailored Guanosine Dinucleosides as Biomimetic Ion Channels to Modulate Transmembrane Potential
No full textA click ion channel platform has been established by employing a clickable guanosine azide or alkyne with covalent spacers. The resulting guanosine derivatives modulated the traffic of ions across the phospholipid bilayer, exhibiting a variation in conductance spanning three orders of magnitude (pS to nS). Forster resonance energy transfer studies of the dansyl fluorophore with the membrane binding fluorophore Nile red revealed that the dansyl fluorophore is deeply embedded in the phospholipid bilayer. Complementary cytosine can inhibit the conductance of the supramolecular guanosine channels in the phospholipid bilayers
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
Self-Assembly of a Guanosine Derivative To Form Nanostructures and Transmembrane Channels
No full textWe herein report the self-assembly of a lipophilic bromoguanosine derivative (G1) in homogeneous solution, in the solid state and in planar bilayer membranes. The self-assembly of G1, driven by H-bonding and π–π stacking interactions can form different nano-structures depending on incubation time. The G1 nanostructure is able to bind a bioactive dye like Rose Bengal. In crystal state, it shows ribbon type H-bonding pattern and exhibits birefringence in polarized light. And further, the self-assembled nanostructure of G1 can form discrete transmembrane ion channels in lipid bilayer membranes, enabling passage of potassium ions
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