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Strategies for High Enantioselectivity on Achiral Electrode Surfaces: Implementing Inherent Chirality in Electrode|(Ionic Liquid) Interfaces
Full text linkChiral electroanalysis could be regarded as the highest recognition degree in electrochemical sensing, implying the ability to discriminate between specular images of a given electroactive molecule in terms of significant peak potential difference. Since enantiomers have identical physico-chemical properties, the electron transfer process must take place in asymmetric conditions, exploiting a suitable chiral selector, such as a chiral electrode or a chiral medium. A groundbreaking strategy was recently proposed, based on the use of inherently chiral molecular selectors, either electrode surfaces [1] or media [2]. Inherent chirality implies the chirality source of the chiral selector to be neither localized nor external, but intrinsic to the whole main molecular backbone, featuring a tailored torsion; this can result in outstanding chirality manifestations. Thus, large differences in peak potentials have been observed for the enantiomers of different chiral probes working on achiral electrodes, implementing inherent chirality at their interface with an ionic liquid medium, [2] exploiting the latter's peculiarly high order. To this aim we developed inherently chiral ionic liquids ICILs as double salts of an atropisomeric 3,3′-bipyridine scaffold with long alkyl chains and a suitable anion, resulting in melting points below room temperature. However, we found it even more convenient to employ the new ICILs, as well as other family terms solid at room temperature, as low-concentration chiral additives in commercial achiral ionic liquids: impressive peak potential differences, regularly increasing with additive concentration, have been observed for the enantiomers of different probes on achiral electrodes. Comparable results have also been obtained with other inherently chiral additives (bibenzimidazolium double salts and a thiahelicene derivative). Work is in progress to strengthen and rationalize the recognition mechanism. In this light we have found a strictly connection between our ICILs and liquid crystals; in fact our additives seem to induce a “chiral domino effect” at the electrode interface like the nematic to cholesteric transition in liquid crystals. We have also performed a physico-(electro)chemical characterization of new families of chiral ionic liquids CILs in order to compare their electrochemical properties and enantioselection performance with our ICILs.
The inherent chirality research is currently supported by Regione Lombardia and Fondazione Cariplo (Avviso congiunto per l’incremento dell’attrattività del sistema di ricerca lombardo e della competitività dei ricercatori candidati su strumenti ERC-edizione 2016, Project 2016-0923).
[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 (2014) Angewandte Chemie. International Edition, 53, 2623-2627; F. Sannicolò, P.R. Mussini, T. Benincori, R. Cirilli, S. Abbate, S. Arnaboldi, S. Casolo, E. Castiglioni, G. Longhi, R. Martinazzo, M. Panigati, M. Pappini, E.Q. Procopio, S. Rizzo (2014) Chemistry-A European Journal, 20, 15298-15302; S. Arnaboldi, T. Benincori, R. Cirilli, S. Grecchi, L. Santagostini, F. Sannicolò, P.R. Mussini (2016) Analytical And Bioanalytical Chemistry, 408, 7243-7254; E. Quartapelle Procopio, T. Benincori, G. Appoloni, P.R. Mussini, S. Arnaboldi, Carbonera, C., Cirilli, R., Cominetti, A., L. Longo, R. Martinazzo, M. Panigati, R. Pò (2017) New Journal Of Chemistry, 41, 10009-10019
[2] S. Rizzo, S. Arnaboldi, V. Mihali, R. Cirilli, A. Forni, A. Gennaro, A.A. Isse, M. Pierini, P.R. Mussini, F. Sannicolò (2017) Angewandte Chemie. International Edition, 56, 2079-2082; S. Arnaboldi, R. Cirilli, A. Forni, A. Gennaro, A. A. Isse, V. Mihali, P. R. Mussini, M. Pierini, S. Rizzo, F. Sannicolò (2015) Electrochimica Acta, 179, 250-262; S. Rizzo, S. Arnaboldi, R. Cirilli, A. Gennaro, A. A. Isse, F. Sannicolò, P. R. Mussini (2018) Electrochemistry Communications, 89, 57-6
A Simultaneous Discrimination of Two Different Probes on Achiral Electrodes
Full text linkA Simultaneous Discrimination of Two Different Probes
on Achiral Electrodes
S. Grecchia, S. Arnaboldia, S. Rizzob, F. Sannicolòa, P.R. Mussinia
a Università degli Studi di Milano, via Golgi 19, 20133 Milano, Italy
b Istituto di Scienze e Tecnologie Molecolari, CNR, Via Golgi 19, 20133, Milano, Italy
[email protected]
In literature few studies have dealt with electrochemistry or electroanalysis on achiral electrodes, the selector being provided by the medium, either having a chiral selector dissolved into it or being itself endowed with chirality. More recently, we have decided to implement the “inherent chirality” concept for the development of media to combine the powerful strategy of inherent chirality with the physico-chemical properties of the ionic liquids.
Ionic liquids, organic salts with low melting points, are increasingly popular media on account of many peculiar advantageous properties respect to volatile organic solvents (low vapor pressure, chemical and thermal stability, high solvating ability, non-flammability ...). They are even more attractive for electrochemical processes, acting as both solvent and supporting electrolyte, and especially featuring an extremely well-ordered structure at the interface with a charged electrode, expanding for many layers, like a semisolid crystal, even in the presence of significant water traces, and modulated by other species possibly present at the interface. Sometimes, they even border with liquid crystals. A high degree of supramolecular organization can induce significant chirality transfer from the medium to the dissolved species. And, analogously to the electrode case, this attitude could be maximized by the “inherent chirality” strategy, that is, working in inherently chiral ionic liquids, ICILs.
To implement inherent chirality in ionic liquids, that are usually based on a heteroaromatic cation with at least one long alkyl chain (to lower the melting point), Sannicolò et al. proposed to start from biheteroaromatic scaffolds, like bipyridine or bibenzimidazole ones. [1] By dialkylation such inherently chiral scaffolds can be converted into the corresponding double salts. With at least one long alkyl chain and a suitable anion, the melting point can be lowered below room temperature; thus, two ICILs have been very recently obtained as enantiopure antipodes, starting from bicollidine, a very convenient scaffold on account of its low-cost synthesis and possibility to be separated into enantiomers by fractional crystallization, without expensive chiral HPLC. Their enantioselectivity was tested as low-concentration additives in achiral commercial ionic liquids on screen-printed electrodes, with chiral probes already used in tests with electrodes modified with inherently chiral surfaces [2]; large, specular enantiomer peak potential differences were observed. Attractively, the same behavior, as chiral additives, was also shown by family terms solid at room temperature, of faster and easier synthesis.
In this context we are studying the effect of the chiral additives on two simultaneously present chiral probes, the first of them giving a chemically reversible ET process. We have to assess the experiments on all possible binary and ternary combinations but evidence of simultaneous discrimination apparently emerges.
The inherent chirality research is currently supported by Regione Lombardia and Fondazione Cariplo (Avviso congiunto per l’incremento dell’attrattività del sistema di ricerca lombardo e della competitività dei ricercatori candidati su strumenti ERC-edizione 2016, Project 2016-0923).
[1] S. Rizzo, S. Arnaboldi, V. Mihali, R. Cirilli, A. Forni, A. Gennaro, A.A. Isse, M. Pierini, P.R. Mussini, F. Sannicolò (2017) Angewandte Chemie. International Edition, 56, 2079-2082; S. Arnaboldi, R. Cirilli, A. Forni, A. Gennaro, A. A. Isse, V. Mihali, P. R. Mussini, M. Pierini, S. Rizzo, F. Sannicolò (2015) Electrochimica Acta, 179, 250-262; S. Rizzo, S. Arnaboldi, R. Cirilli, A. Gennaro, A. A. Isse, F. Sannicolò, P. R. Mussini (2018) Electrochemistry Communications, 89, 57-61
[2] 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 (2014) Angewandte Chemie. International Edition, 53, 2623-2627; S. Arnaboldi, T. Benincori, R. Cirilli, S. Grecchi, L. Santagostini, F. Sannicolò, P.R. Mussini (2016) Analytical And Bioanalytical Chemistry, 408, 7243-7254. S. Arnaboldi, T. Benincori, R. Cirilli, W. Kutner, M. Magni, P. R. Mussini, K. Noworyta, F. Sannicolò (2015) Chemical Science, 6, 1706-171
Enantioselective voltammetry on achiral electrodes
Full text linkAn attractive target in electroanalysis is the availability of chiral media affording enantioselection in terms of significant peak potential difference between the antipodes of chiral probes in voltammetry experiments on achiral electrodes.
Previous literature attempts pointed to enantioselectivity increasing with the structural order of the chiral medium; on the other hand, outstanding enantioselection performance has been recently observed working on electrode surfaces consisting in "inherently chiral" oligomer films [1-2].
Combining both strategies, we have recently developed two inherently chiral ionic liquids, ICILs, consisting of dialkylated bicollidinium salts, with an atropoisomeric bipyridinium cation featuring at least one octyl chain and bistrifilimide counteranions. They showed high enantioselectivity when tested even as low concentration additives in commercial achiral ionic liquid media [3] and also as chiral bulk media.
Importantly, similar ability was also shown by other terms of the same family,
having shorter alkyl chains and/or different counteranions, solid at room temperature but of easier synthesis. As a first tentative explanation we are considering the high supramolecular order of even simple ionic liquids at the interphase with a charged surface. A chiral additive could result in chiral reorganization of this peculiar interphase, as in the case of nematic-to-cholesteric transitions induced by chiral dopants in liquid crystals.
This allowed us to include in our chiral voltammetry experiments a quite larger number of inherently chiral selectors based on different stereogenic elements, i.e., the bicollidine and bibenzimidazole atropoisomeric scaffolds and the tetrathielicene helicoidal scaffold. They all proved successful.
The support of Fondazione Cariplo/Regione Lombardia "Avviso congiunto per l’incremento dell’attrattività del sistema di ricerca lombardo e della competitività dei ricercatori candidati su strumenti ERC - edizione 2016” (Project 2016-0923) is gratefully acknowledged.
[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. Chem. Int. Ed. 53 (2014) 2623
[2] S. Arnaboldi, P. Mussini, M. Magni, F. Sannicolò, T. Benincori, R. Cirilli, K. Noworyta, W. Kutner, Chem. Sci. 6 (2015) 1706
[3] S. Rizzo, S. Arnaboldi, V. Mihali, R. Cirilli, A. Forni, A. Gennaro, A. A. Isse, M. Pierini, P. R. Mussini, F. Sannicolò, Angew. Chem. Int. Ed 56 (2017) 207
Electronic and Spectroscopic Properties of Thiophene-based Organic Polyconjugated Semiconductors Built from Inherently Chiral Monomers
No full textThe availability of materials which could couple electroactivity properties and enantiorecognition capability is an ambitious objective of the modern chemical research. Chirality is generally introduced in these materials by attaching chiral pendants to an electroactive polyconjugated backbone through suitable linkers and a great variety of substituents have been employed either chosen from the chiral pool, like sugar and amino-acids, or man-made, designed and synthesized for specific applications. We have developed a new strategy for preparing electroactive chiral polymers, consisting in the oxidative polymerization of chiral oligothiophene monomers in which chirality results from a tailored torsion produced along the oligothiophene backbone by an atropisomeric bithiophene or bipyrrole scaffold (Scheme 1).1 The structural design of the monomers requires that the biheteroaromatic core could take part in the conjugative communication between the bithiophene termini. Furthermore, the polymerization sites of the monomers should be homotopic, thus granting the perfect constitutional regularity of the polymers. The 2,2’-bis(2,2’-bithiophene-5-yl)-3,3’-bithianaphthene and the 1,1’-dimethyl-3,3’-bis(2,2’-bithiophene-5-yl)- 2,2’-biindole are the first examples of this strategy. The antipodes have been obtained in an enantiopure state and submitted to the electropolymerization process yielding materials exhibiting outstanding chirality manifestations.
References
1) F. Sannicolò, S. Rizzo, T. Benincori, W. Kutner, K. Noworyta, J. W. Sobczak, V. Bonometti, L. Falciola, P. R. Mussini, M. Pierini, Electrochimica Acta, in press
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
Typhlitis in a post-chemotherapy lymphoma patient; images in clinical medicine
Full text linkTyphlitis, also known as neutropenic enterocolitis, occurs primarily in severely immunosuppressed patients undergoing chemotherapy for haemathological and solid tumors. We report a case of a 57 years-old patient who presented typhlitis as a complication during chemotherap
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