1,721,063 research outputs found
RTILs vs VOCs : the role of the electropolymerization medium on the features of inherently chiral polymer films
No full textA typical drawback of electrochemical processes consists in the employment of volatile organic solvents (VOCs), which imply safety problems and require the addition of high amounts of a supporting electrolyte to obtain the necessary conductivity. Both problems could be overcome by shifting to non-conventional media such as room temperature ionic liquids (RTILs). In fact, RTILs present various desirable advantages over molecular solvents, including negligible vapour pressure, high intrinsic conductivity without addition of supporting electrolyte and easy recyclability. Moreover, specifically dealing with electropolymerizations, preliminary studies[1,2] point to ionic liquids, both as such and as cosolvents, significantly improving the regularity and the mechanical and morphological properties of the conducting films to be employed e.g. in the energetic, optoelectronic, and sensoristic domains. In this context, we present the results obtained in our research work, concerning a class of inherently chiral polymer films[3], studied and characterized as racemates and as separated enantiomers, by means of cyclic voltammetry and electrochemical impedance spectroscopy, together with SEM imaging. In order to finely discriminate among the racemate and enantiomer film properties, and above all to achieve optimized enantiomer electrode surfaces for applications as chiral sensors, reproducibility is a necessary but hard task. In this frame, the present work is aimed to compare the polymer features obtained in different conditions (i.e., RTILs vs VOCs, on various electrode surfaces and for increasing thickness of the electrodeposited films) to select the best working medium for the preparation of the electroactive films.
[1] F. Endres, A.P. Abbott, D.R. MacFarlane, Electrodeposition from Ionic Liquids, 2008, Wiley-VCH, ISBN 978-3-527-31565-9
[2] A.Pietrzyk, W.Kutner, R.Chitta, M. E. Zandler, F. D’Souza, F. Sannicolò, P.R. Mussini, Anal. Chem., 2009, 81(24), 10061-10070.
[3] F. Sannicolò, S. Rizzo, T. Benincori, W. Kutner, K. Noworita, J.W. Sobczak, V. Bonometti, L. Falciola, P.R. Mussini, M. Pierini, Electrochim. Acta, 2010, 55(27), 8352-8364
Potential-driven Chirality manifestations and impressive enantioselectivity by inherently chiral electroactive films
Full text linkMolecular materials coupling electroactivity with enantiorecognition capability are an attractive objective in materials research. The usual strategy, hinging on attaching chiral pendants to an electroactive polyconjugated backbone, generally results in modest chirality manifestations. We have thus designed electroactive chiral polyheterocycles, where chirality is not external to the electroactive backbone, but inherent to it, resulting from a tailored torsion produced by the presence of atropisomeric, conjugatively active biheteroaromatic scaffolds. The coincidence of the stereogenic element with the whole electroactive backbone affords by electrooligomerization enantiopure electroactive films of impressive chiroptical activity, which can be finely and reversibly tuned by the electric potential, since injection of positive charges results in decrease of the atropisomeric scaffold angle to favour delocalization, as revealed by CD spectroelectrochemistry, suggesting us the image of a "breathing chirality". To test the enantiorecognition ability of the new inherently chiral conducting films we have developed an efficient protocol in ionic liquid affording preparation of very
reproducible electrode surfaces by electrooxidation of the enantiopure monomers on screen printed electrode supports. The resulting specular R and S electrodes have been tested with (R)-(+)- and S-(-)-N,N-dimethyl-1-ferrocenylethylamine specular probes. The response is highly and reproducibly enantioselective (with 100 mV separation between R and S probes with single enantiomers and even more with the racemate), specular for R vs S surfaces with respect to S and R probes, and reversible in repeated alternating sequences of S and R probe sensing on a single electrode.[1] With the contribution of Fondazione Cariplo, grant no. 2011-0417. [1] F. Sannicolò, S. Arnaboldi, T. Benincori, V. Bonometti, R. Cirilli, L. Dunsch, W. Kutner, G. Longhi, P.R. Mussini, M. Panigati, M. Pierini, S. Rizzo, Angew. Chemie 2014, 53, 2623-2627
Inherently chiral conducting polymers
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 goal 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.
Our strategy regards the development of inherent chiral conducting polymer in particular films prepared by electropolymerization of monomers like the TBTX molecule [1] (already applied as a racemate as 3-D promoter comonomer for the electrosynthesis of very efficient MIP films [2]), where chirality is owed to a tailored torsion internally produced along the whole conjugated backbone by insertion of a suitable biheteroaromatic core, and not to the presence of stereocentres external to the conjugated chain (Figure 1).
Both enantiomer films have been characterized together with the racemate one by electrochemical methods, UV-vis spectroscopy and circular dichroism with in-situ electrochemistry. Positive charge injection, reducing the torsion angle to achieve better p system conjugation, results in a fully reversible "breathing" process of the 3D chiral conducting network upon potential cycling. Enantiorecognition capability tests on chiral probe molecules are in progress.
[1] An effective multipurpose building block for 3D electropolymerisations:2,2’-bis(2,2’-bithiophene-5-yl)-3,3’-bi-1-benzothiophene / F. Sannicolò, S. Rizzo, T. Benincori, W. Kutner, K. Noworita, J.W. Sobczak, V. Bonometti, L. Falciola, P.R. Mussini, M. Pierini, Electrochimica Acta. - ISSN 0013-4686. - ISSN 1873-3859. - 55:27(2010 Nov), 8352-8364.
[2] Melamine Acoustic Chemosensor Based on Molecularly Imprinted Polymer Film / A.Pietrzyk, W.Kutner, R.Chitta, M. E. Zandler, F. D’Souza, F. Sannicolò, P.R. Mussini, Analytical chemistry. - ISSN 0003-2700. - ISSN 1520-6882. - 81:24(2009), 10061-10070
RTILs vs VOCs : the role of the electropolymerization medium on the features of inherently chiral polymer films
No full textA typical drawback of electrochemical processes consists in the employment of volatile organic solvents (VOCs), which imply safety problems and require the addition of high amounts of a supporting electrolyte to obtain the necessary conductivity. Both problems could be overcome by shifting to non-conventional media such as room temperature ionic liquids (RTILs). In fact, RTILs present various desirable advantages over molecular solvents, including negligible vapour pressure, high intrinsic conductivity without addition of supporting electrolyte and easy recyclability.
Moreover, specifically dealing with electropolymerizations, preliminary studies[1,2] point to ionic liquids, both as such and as cosolvents, significantly improving the regularity and the mechanical and morphological properties of the conducting films to be employed e.g. in the energetic, optoelectronic, and sensoristic domains.
In this context, we present the results obtained in our research work, concerning a class of inherently chiral polymer films[3], studied and characterized as racemates and as separated enantiomers, by means of cyclic voltammetry and electrochemical impedance spectroscopy, together with SEM imaging.
In order to finely discriminate among the racemate and enantiomer film properties, and above all to achieve optimized enantiomer electrode surfaces for applications as chiral sensors, reproducibility is a necessary but hard task. In this frame, the present work is aimed to compare the polymer features obtained in different conditions (i.e., RTILs vs VOCs, on various electrode surfaces and for increasing thickness of the electrodeposited films) to select the best working medium for the preparation of the electroactive films.
[1] F. Endres, A.P. Abbott, D.R. MacFarlane, Electrodeposition from Ionic Liquids, 2008, Wiley-VCH, ISBN 978-3-527-31565-9
[2] A.Pietrzyk, W.Kutner, R.Chitta, M. E. Zandler, F. D’Souza, F. Sannicolò, P.R. Mussini, Anal. Chem., 2009, 81(24), 10061-10070.
[3] F. Sannicolò, S. Rizzo, T. Benincori, W. Kutner, K. Noworita, J.W. Sobczak, V. Bonometti, L. Falciola, P.R. Mussini, M. Pierini, Electrochim. Acta, 2010, 55(27), 8352-8364
The thiophene-based inherently chiral monomer family grows: molecular design and electrochemical properties
Full text linkOur group has recently presented electroactive thiophenebased polyconjugated films of unprecedented chirality manifestations and enantiorecognition ability,[1] based on the "inherent chirality" concept, implying that the whole electroactive backbone coincides with the stereogenic element, consisting in a tailored torsion induced by an atropisomeric bi-benzothiophene scaffold. Such films are easily prepared as enantiopure electrode surfaces by electrooligomerization of (R) and (S) enantiopure monomer 1.
Now, concurrently with the exploration of the applicative potentialities of this "parent" molecular material, both racemic and enantiopure, we are widening the class of available monomers designed according the same strategy, but with different atropisomeric heteroaromatic scaffolds, different side chains, and/or with the addition of a further stereogenic element. The electrochemical properties of a selection of the new inherently chiral monomers now available will be presented in detail and rationalized as a function of their molecular structure, also in the perspective of potential applications.
With the contribution of Fondazione Cariplo, grant no. 2011-0417.
[1] F. Sannicolò, S. Arnaboldi, T. Benincori, V. Bonometti, R. Cirilli, L. Dunsch, W. Kutner, G.
Longhi, P.R. Mussini, M. Panigati, M. Pierini, S. Rizzo, Angew. Chemie 2014, 53, 2623-2627
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
Molecularly printed polymer, process for preparation thereof and chemical piezoelectric sensor for detection and identification of biologically active substances selected from the group of biogenic amines, especially melamine
No full textMolecularly printed polymer, process for preparation thereof and chemical piezoelectric sensor for detection and identification of biologically active substances selected from the group of biogenic amines, especially melamin
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
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
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