1,721,002 research outputs found
Inherently chiral electrodes, the effective tool for chiral voltammetry
No full textAn attractive issue in electroanalysis is the development of artificial “intelligent” electrodes, capable to discriminate as well as quantify the enantiomers of chiral analytes, particularly of biological and pharmaceutical interest. For this aim, many approaches have been proposed in the last years. However, even the most successful attempts at chiral discrimination almost invariably resulted in the detection of a difference in current intensity between the signals of the two antipodes of a chiral probe, without differentiation of their redox potentials; the chiral enantioselective layer is in many instances not of general use, but tailored for a given probe; many preparation procedures are very sophisticated and/or the active films fragile.
A winning solution comes from a new class, which we have recently presented and patented1, of “inherently chiral” molecular semiconductors, in which the coincidence of the element granting both electroactivity and chirality with the entire molecular backbone results in extraordinary chiroptical manifestations, which can be finely and reversibly tuned by the electric potential. Above all, enantiopure electrode surfaces can be easily prepared e.g. by electrooligomerization; they mostly consist of cyclic oligomers, highly electroactive and chiral, idealizing conducting polymers without ends and of high complexing ability.
Such electrode surfaces are able to discriminate enantiomers of chiral molecules in terms of large peak potential differences (80-200 mV and more), with linear dynamic ranges for peak currents, thus affording enantiomeric ratio evaluation. The same spectacular enantioselectivity is obtained on chemically different surfaces of the same structural concept, which demonstrates the general validity of our proposed strategy. A simple reconditioning protocol affords performing more experiments on a single electrode.The new electrodes have been tested with very good results on chiral probes even very different and of applicative interest2 (Dopa, methyl-Dopa, ofloxacin, norepinephrine, tyrosine, naproxen, catechines, ascorbic acid...), on different supports, including commercial screen printed ones, and in different media (aqueous and nonaqueous ones, as well as small ionic liquid drops on SPEs).
As an interesting alternative strategy to effective enantiodiscrimination, preliminary results about inherently chiral ionic liquid media applied on achiral electrodes will be also presented.
This work was supported by Fondazione Cariplo (Grants no. 2011-0417 and 2011-1851)
References
(1) Sannicolò, F. et al., Angew. Chem. Int. Ed. 2014, 53, 2623; Sannicolò, F. et al., Chem. Eur. J. 2014, 20, 15296; Sannicolò F. et al., Patent appl. MI2014A000948 (2014).
(2) Arnaboldi S., Benincori T., Cirilli R., Kutner W., Magni M., Mussini P.R., Noworyta K., Sannicolò F., Chemical Science, 2015, 6, 2041
Inherent Chirality in Electrochemically Active Molecular Materials: Strategy and Panoramic Overview
No full textThe introduction of chirality in organic conjugated polymers has been considered for a wide variety of purposes and applications, i.e., in optics and sensoristics. In this frame, the possibility of coupling electroactivity and enantiorecognition capability is an ambitious objective of the modern chemical research. As commonly reported in literature, chirality in organic semiconductors has mostly been introduced by attaching chiral pendants to the electroactive conjugated backbone through suitable linkers; however, this approach usually leads to poor chirality manifestations.
In our strategy, instead, chirality results from a tailored torsion internally produced along the conjugated backbone, and it is not due to the presence of any external stereogenic element. The general structure is here illustrated: the stereogenic core responsible for chirality interconnects two bithiophene pendants and the connectivity of the bi-heteroaromatic scaffold maintains the conjugation between the bithiophene termini. The symmetry of the monomer is C2, and the thiophene a–positions involved in the electrochemical polymerization are homotopic, so full regioregularity of the polymers is guaranteed. Several members of this innovative class of inherently chiral molecules have been designed, synthesized, characterized and submitted to electrochemical polymerization. Chirality is maintained even in the solid state, as proved by CD experiments carried out on polymer films. CD investigations performed under different polarization states revealed a tendency of the structure to flatten when the polymer is p-doped. This phenomenon is reversible and suggested the image of a breathing system.
The electrochemical properties and the polymerization ability of a complete series of inherently chiral thiophene- and pyrrole-based monomers, both as racemates and as pure enantiomers, will be described and discussed
Inherently chiral electrodes, tool for chiral voltammetry
No full textRecently we have devised an innovative approach to chiral conducting thiophene oligomers, based on the concept of "inherent chirality": the stereogenic element is a tailored torsion intrinsic to the whole electroactive backbone, arising from insertion of atropisomeric biheteroaromatic scaffolds, rather than stereocentres localized in attached pendants. [1] Thus the stereogenic element responsible for chirality is also responsible for electroactivity, since it constitutes the conjugated backbone. An example are the films obtained by electrooligomerization of the 2,2-bis[2-(5,2-bithienyl)]3,3-bithianaphthene (BT2-T4) parent monomer, mostly yielding cyclic oligomers (BT2-T4)n, predominantly dimers and trimers. They constitute rings of fully conjugated thiophene units, idealizing conducting polymers without ends. [2] This outstanding feature combination endows the electroactive films with exceptional chirality manifestations, like e.g. circularly polarized luminescence, and, above all, the capability, as electrode materials, to pronouncedly separate (in many cases by 100-200 mV and even more) voltammetry peaks of enantiomers of chiral probes of quite different chemical and electrochemical properties, and of quite different structural features, including pharmaceutically and/or biological relevant ones, like DOPA, ofloxacin and many others. Concurrently, peak currents display a linear dynamic range, to be exploited e.g. to quantify enantiomeric excesses on disposable SPEs. [3] Similar enantioselectivity is also shown by oligomer films obtained by electrooligomerization of other inherently chiral monomers, having different chemical and structural features. This proves the general validity of this approach to obtain highly enantioselective enantiopure surfaces, attractive tools for chiral voltammetry.
[1] Angew.Chem. 2014, 53, 2623
[2] Chem.Eur. J. 2014, 20, 5298
[3] Chem.Sci. 2015, 6,1706
Keywords: chiral electrodes, chiral voltammetry, inherently chiral oligomer films,
enantioselectivity in electroanalysis
Acknowledgements: The Authors gratefully acknowledge the support provided by
FONDAZIONE CARIPLO (grant no. 2011-0417
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
Novel spider-like multithiophene architectures: redox properties and electrochemical polymerization
No full textVariations 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
Inherently chiral thiophene-based electrode surfaces
No full textThe general strategy followed for “chiralizing” electroactive materials is to hang chiral pendants to the polyconjugated chain which assumes a form of chirality which is somewhat “reflected” from outside. The consequences of the diastereomeric interactions of this kind of materials with chiral species are generally modest, even though some exceptions are present in the chemical literature.
In this context, we are currently developing electroactive materials in which the conducting polyconjugated chain is chiral by itself (inherently chiral), with no help from external chiral decorations, since chirality results from a tailored torsion internally produced in the oligothiophene backbone. It is expected that the enantiorecognition process directly effected by the chiral chain could be followed by relevant conformational modifications, in turn associated with significant variations in its electronic and electric properties.
In particular we have recently developed and studied a purposedly non-planar, inherently chiral multithiophene-based monomer showing an intrinsically high ability for fast and regular electropolymerisation, and performing outstandingly as a 3D promoter building block in copolymerizations. The racemate of the new oligomer was resolved, the CD spectra of the antipodes being perfect mirror images. This allowed us to perform preliminary experiments of enantiopure TX electropolymerizations, followed by characterization of the resulting conducting films. The solid-state dichroism measurements point to the solid-state films fully retaining the dissimmetry of enantiopure monomers. The preliminary tests on this innovative surfaces will be reported and discussed
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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