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Enantiomer discrimination in voltammetry in media of high structural order at the electrochemical interphase implemented with chirality
No full textEnantiomer discrimination in voltammetry in media of high structural order at the electrochemical interphase implemented with chirality
Patrizia Romana Mussini, Sara Grecchi, Serena Arnaboldi
Università degli Studi di Milano, Dipartimento di Chimica, Via Golgi 19, 20133 Milano
Discrimination of the enantiomers of electroactive chiral molecules in voltammetry is a fascinating frontier target. Of course the necessary condition to achieve it is that the two enantiomers undergo electron transfer in energetically different conditions. Since in an achiral context they would have identical physico chemical properties and thus also identical voltammetry features, this requires the implementation at the electrode|solution interphase of a suitable enantiopure chiral selector.
The so far most popular strategy consists in working on chiral electrode surfaces, and an impressive variety of approaches has been proposed [1,2]. However, working on achiral electrodes with chirality implemented in the medium has also been proposed [1,3], and very recent experiments have highlighted that this approach can yield outstanding discrimination in terms of potential differences for the enantiomers of chiral electroactive probes, when working in media of high structural order at the charged interphase, like ionic liquids ILs [3-7] and deep eutectic solvents DESs [8], implemented with chirality [5,6,9] or, even better, inherent chirality [4,7,8].
Such achievements will be comparatively presented and commented in terms of IL and DES structural order at the interphase (also compared to classical media and to ionic liquids / ionic liquid crystals [9]) as well as of possibility of probe/selector specific interactions.
Support to our chiral electroanalysis research line by Fondazione Cariplo/Regione Lombardia as well as by Università degli Studi di Milano is gratefully acknowledged.
[1] S. Arnaboldi, M. Magni, P.R. Mussini, Curr. Opin. Electrochem. 2018, 8, 60-72. (minireview)
[2] S. Arnaboldi, M. Magni, S. Grecchi, P.R. Mussini, Curr. Opin. Electrochem. 2018, 7, 188-189. (minireview)
[3] S. Grecchi, S. Arnaboldi, P.R. Mussini, Curr. Opin. Electrochem., accepted May 2021. (minireview)
[4] 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. 2017, 56, 2079 –2082.
[5] M. Longhi, S. Arnaboldi, E. Husanu, S. Grecchi, I. F. Buzzi, R. Cirilli, S. Rizzo, C. Chiappe, P. R. Mussini, L. Guazzelli, Electrochim. Acta 2019, 298, 194-209.
[6] S. Grecchi, C. Ferdeghini, M. Longhi, A. Mezzetta, L. Guazzelli, S. Khawthong, F. Arduini, C. Chiappe, A. Iuliano, P. R. Mussini, ChemElectroChem 2021.
[7] S. Rizzo, S. Arnaboldi, R. Cirilli, A. Gennaro, A. A. Isse, F. Sannicolò, P. R. Mussini, Electrochem. Commun. 2018, 89 57-61
[8] F. Fontana, G. Carminati, B. Bertolotti, P. R. Mussini, S. Arnaboldi, S. Grecchi, R. Cirilli, L. Micheli, S. Rizzo, Molecules 2021, 26, 311-324.
[9] S. Arnaboldi, A. Mezzetta, S. Grecchi, M. Longhi, E. Emanuele, S. Rizzo, F. Arduini, L. Micheli, L. Guazzelli, P. R. Mussini, Electrochim. Acta 202
Enantiomer discrimination in voltammetry in media of high structural order at the electrochemical interphase implemented with chirality
No full textDiscrimination of the enantiomers of electroactive chiral molecules in voltammetry is a fascinating frontier target. Of course the necessary condition to achieve it is that the two enantiomers undergo electron transfer in energetically different conditions. Since in an achiral context they would have identical physico chemical properties and thus also identical voltammetry features, this requires the implementation at the electrode|solution interphase of a suitable enantiopure chiral selector.
The so far most popular strategy consists in working on chiral electrode surfaces, and an impressive variety of approaches has been proposed [1,2]. However, working on achiral electrodes with chirality implemented in the medium has also been proposed [1], and very recent experiments have highlighted that this approach can yield outstanding discrimination in terms of potential differences for the enantiomers of chiral electroactive probes, when working in media of high structural order at the charged interphase, like ionic liquids ILs [3-7] and deep eutectic solvents DESs [8], implemented with chirality [3,4,8] or, even better, inherent chirality [5-7].
Such achievements will be comparatively presented and commented in terms of IL and DES structural order at the interphase (also compared to classical media and to ionic liquids / ionic liquid crystals [9]) as well as of possibility of probe/selector specific interactions.
Support to our chiral electroanalysis research line by Fondazione Cariplo/Regione Lombardia as well as by Università degli Studi di Milano is gratefully acknowledged.
[1] S. Arnaboldi, M. Magni, P.R. Mussini, Enantioselective selectors for chiral electrochemistry and electroanalysis: Stereogenic elements and enantioselection performance, Curr. Opin. Electrochem. 8 (2018) 60-72. (minireview)
[2] S. Arnaboldi, M. Magni, S. Grecchi, P.R. Mussini, Electroactive chiral oligo- and polymer layers for electrochemical recognition, Curr. Opin. Electrochem. 7 (2018) 188-189. (minireview)
[3] M. Longhi, S. Arnaboldi, E. Husanu, S. Grecchi, I. FrancoBuzzi, R. Cirilli, S. Rizzo, C. Chiappe, P. R. Mussini, L. Guazzelli, A family of chiral ionic liquids from the natural pool: Relationships between structure and functional properties and electrochemical enantiodiscrimination tests, Electrochim. Acta 298 (2019) 194-209.
[4] S. Grecchi, C. Ferdeghini, M. Longhi, A. Mezzetta, L. Guazzelli, S. Khawthong, F. Arduini, C. Chiappe, A. Iuliano, P. R. Mussini, Chiral biobased ionic liquids with cations or anions including bile acid building blocks as chiral selectors in voltammetry, ChemElectroChem accepted March 2021.
[5] S. Rizzo, S. Arnaboldi, V. Mihali, R. Cirilli, A. Forni, A. Gennaro, A. A. Isse, M. Pierini, P. R. Mussini, F. Sannicolò, “Inherently Chiral” Ionic‐Liquid Media: Effective Chiral Electroanalysis on Achiral Electrodes, Angew. Chem. Int. Ed. 56 (2017) 2079 –2082.
[6] S. Rizzo, S. Arnaboldi, R. Cirilli, A. Gennaro, A. A. Isse, F. Sannicolò, P. R. Mussini, An “inherently chiral” 1,1′-bibenzimidazolium additive for enantioselective voltammetry in ionic liquid media, Electrochem. Commun. 89 (2018), 57-61
[7] F. Fontana, G. Carminati, B. Bertolotti, P. R. Mussini, S. Arnaboldi, S. Grecchi, R. Cirilli, L. Micheli, S. Rizzo, Helicity: A Non-Conventional Stereogenic Element for Designing Inherently Chiral Ionic Liquids for Electrochemical Enantiodifferentiation, Molecules 26 (2021) 311-324.
[8] S. Arnaboldi, A. Mezzetta, S. Grecchi, M. Longhi, E. Emanuele, S. Rizzo, F. Arduini, L. Micheli, L. Guazzelli, P. R. Mussini, Natural-based chiral task-specific deep eutectic solvents: a novel, effective tool for enantiodiscrimination in electroanalysis, Electrochim. Acta accepted March 2021.
[9] S. Grecchi, S. Arnaboldi, S. Rizzo, P. R. Mussini Advanced chiral molecular media for enantioselective electrochemistry and electroanalysis (minireview), soon to be submitted.
NOTA: Si tratta di abstract inviato, che è stato in seguito definito "invited lecture" (e così inserito nel programma) dall'organizzatore del simposio in cui è stato presentato
Enantiorecognition towards L- and D-DOPA on easy-to-prepare inherently chiral film electrodes
No full textWe have recently shown [1,2] that oligomers endowed with “inherent chirality” display high chirality manifestations plus a pool of unprecedented properties. In particular, in the very last months we have demonstrated that electrooligomerization (especially in ionic liquids) of our inherently chiral monomers on screen-printed electrodes and on glassy carbon tip electrodes affords inherently chiral electroactive films of outstanding enantiodiscrimination ability towards a series of chiral probes of quite different bulkiness and chemical nature (also of pharmaceutical interest like DOPA, common antibiotics and FANS) [3]. The general validity of the "inherent chirality" concept has been confirmed by characterizing monomers and related films based on different atropisomeric biheteroaromatic scaffolds (i.e. bis-benzothiophene, bis-indole, and “all thiophene” core). In this work the enantiorecognition ability of our smart films towards L- and D-DOPA will be presented focusing on the variation in voltammetric peak separation of the probe enantiomers when changing i) the medium (e.g. increasing pH, figure below), ii) the nature of electrode material and iii) the probe carboxylic unit (i.e. DOPA methyl ester). The impressive enantiomer peak potential separation combined with the peak current linear dynamic ranges enables to estimate enantiomeric excesses in probe enantiomeric
mixtures. Such synthetic electrode surfaces able to neatly discriminate the antipodes of chiral probes as separate peaks are unprecedented in literature, opening the way to the development of
efficient chiral voltammetric sensors. This work was supported by Fondazione Cariplo (Grant no. 2011-0417)
[1] F. Sannicolò, S. Arnaboldi et al. Angewandte Chemie Int. Ed., 53 (2014),
2623
[2] F. Sannicolò, P. R. Mussini, S. Arnaboldi et al. Chemistry-A European Journal
10, (2014), 15261
[3] S. Arnaboldi et al. Chemical Science, 6 (2015), 170
Enantiorecognition towards L- and D-DOPA on easy-to-prepare inherently chiral film electrodes
No full textWe have recently shown1,2 that oligomers endowed with “inherent chirality” display high chirality manifestations plus a pool of unprecedented properties. In particular, in the very last months we have
demonstrated that electrooligomerization (especially in ionic liquids) of our inherently chiral monomers on screen‐printed electrodes and on glassy carbon tip electrodes affords inherently chiral electroactive films of outstanding enantiodiscrimination ability towards a series of chiral probes of quite different bulkiness and chemical nature (also of pharmaceutical interest like DOPA, common antibiotics and FANS)3. The general validity of the "inherent chirality" concept has been confirmed by characterizing monomers and related films based on different atropisomeric biheteroaromatic scaffolds (i.e. bis‐benzothiophene, bis‐indole, and “all thiophene” core). In this work the enantiorecognition ability of our smart films towards L‐ and D‐DOPA will be presented focusing on the variation in voltammetric peak separation of the probe enantiomers when changing i) the medium (e.g. increasing pH), ii) the nature of electrode material and iii) the probe carboxylic unit (i.e. DOPA
methyl ester). The impressive enantiomer peak potential separation combined with the peak current linear dynamic ranges enables to estimate enantiomeric excesses in probe enantiomeric mixtures. Such synthetic electrode surfaces able to neatly discriminate the antipodes of chiral probes as separate peaks are unprecedented in literature, opening the way to the development of efficient chiral voltammetric sensors.
Figure. Effect of the variation in the pH medium on the enantiorecognition ability of our bithianaphthene‐based (BT2‐T4)n inherently chiral electrodes with L‐ and D‐DOPA probes, superimposed on a speciation plot of DOPA.
This work was supported by Fondazione Cariplo (Grant no. 2011‐0417)
References
[1] F. Sannicolò, S. Arnaboldi, T. Benincori, V. Bonometti, R. Cirilli, L. Dunsch, W. Kutner, G. Longhi, P. R. Mussini, M.
Panigati, M. Pierini and S. Rizzo, Angewandte Chemie Int. Ed., 53 (2014), 2623
[2] 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. Quartapelle Procopio, S. Rizzo, Chemistry‐A European Journal 10, (2014), 15261
[3] S. Arnaboldi, P. Mussini, M. Magni, F. Sannicolò, T. Benincori, R. Cirilli, K. Noworyta and W. Kutner, Chemical
Science, 6 (2015), 170
Strategies for High Enantioselectivity on Achiral Electrode Surfaces: Implementing Inherent Chirality in Electrode|(Ionic Liquid) Interfaces
No full textChiral 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
Innovative Chiral Materials and Media for Enantioselection in Chiral Electrochemistry and Advanced Applications in Spintronics
No full textThe highest degree of selectivity in electrochemical recognition is achieved with enantioselective electroanalysis, implying the ability to discriminate specular images of a given electroactive molecule, an issue particularly important in the biological and pharmaceutical fields [1]. In fact the enantiomers of a chiral molecule have identical physico-chemical properties and would have identical electrochemical behaviour excepting when reacting in a diastereomeric context (diastereoisomers are energetically different). Unprecedented enantiorecognition in terms of large potential differences was recently observed in analytical experiments by our research group[2], implementing:
1) enantiopure electrode surfaces based on inherently chiral heterocycle-based electroactive films (with different stereogenic elements, C2 axis vs helix);
2) enantiopure media based on inherently chiral (or simply chiral) ionic liquids or related additives dissolved in an achiral medium [3,4];
3) Deep Eutectic Solvents (DES), commonly defined as systems composed of a mixture of at least two components, a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD).
An even more striking feature implying inherently chiral films was obtained in the frame of the CISS (Chiral Induced Spin Selectivity) effect, recently unveiled by Ron Naaman and co-workers, where spin polarization in photo-ejected electrons transmitted through a thin layer of enantiopure material on gold was observed [5]. In this frame we present an innovative set-up which includes i) a non-ferromagnetic electrode (ITO) modified with a thin electroactive chiral film (the spin filter), ii) achiral redox couples dissolved in aqueous or organic solutions and iii) an external permanent magnet which was placed near the chiral film. A spectacular unforeseen effect was observed by means of cyclovoltammetry (CV), in fact CV peaks recorded in the presence of achiral redox couples reveal an impressive potential shift by flipping the magnet orientation (north vs south). This effect was also specular by changing the spin injector configuration. The importance of these studies includes possible applications in the field of spintronics, electronics, chemical sensoristic and so on and provides a striking evidence of the spin selectivity properties of chiral thin films [6].
References:
[1]S. Arnaboldi, T. Benincori, R. Cirilli, S. Grecchi, L. Santagostini, F. Sannicolò, P. R. Mussini, (2016), ABC, 408, 26, 7243.
[2]S. Arnaboldi, S. Grecchi, M. Magni, P. Mussini, (2018), Curr. Opinion, 8, 60
[3]S. Arnaboldi, M. Magni, P. Mussini, (2018), Curr. Opinion, 7, 188.
[4]M. Longhi, S. Arnaboldi, E. Husanu, S. Grecchi, I. F. Buzzi, R. Cirilli, S. Rizzo, C. Chiappe, P. R. Mussini, L. Guazzelli, (2019), Electrochimica Acta, 298, 194.
[5]B Dor, S. Yochelis, S. P. Mathew, R. Naaman, Y. Paltiel, (2013) Nat. Commun. 4, 3256.
[6]Benincori, S. Arnaboldi, M. Magni, S. Grecchi, R. Cirilli, C. Fontanesi, P. R. Mussini, (2019), Chem. Sci, 10, 2750
Optimizing the electrodeposition protocol of enantioselective inherently chiral electrode surfaces: a multi-technique investigation
No full textWe have recently introduced "inherently chiral" enantiopure electrode surfaces of outstanding chirality manifestations, including circularly polarized luminescence, reversibly potential-driven circular dichroism, and large potential differences for the enantiomers of chiral probes in voltammetry experiments performed on such surfaces. [1-3]
The outstandingly powerful “inherent chirality” concept implies a molecular structure where the stereogenic element does not consist in an isolated stereocentre or an external chirality source, but originates from a tailored torsion in the whole main backbone endowing the molecule with its key functional property (here electroactivity).
A key issue is now to investigate the enantioselection mechanism and to optimize the experimental protocols for the deposition of our inherently chiral surfaces. For both aims it is important to study the thickness and regularity of the chiral oligomer films as a function of the experimental conditions. We started a systematic profilometry study correlated to electrochemical impedance spectroscopy measurements of the oligomer films obtained by carefully controlled electrodeposition, varying one by one different experimental parameters. The study is also important to properly compare enantioselection by films prepared from different inherently chiral monomers, including e.g. bisindole and tetrathiahelicene ones.
[1] S. Arnaboldi, S. Grecchi, M. Magni, P. Mussini, Electroactive chiral oligo- and polymer layers for electrochemical enantiorecognition, Current Opinion in Electrochemistry, 7 (2018) 188-199.
[2] S. Arnaboldi, M. Magni, P. R. Mussini, Enantioselective selectors for chiral electrochemistry and electroanalysis: Stereogenic elements and enantioselection performance, Current Opinion in Electrochemistry, 8 (2018) 60-72.
[3] S. Arnaboldi, T. Benincori, R. Cirilli, S. Grecchi, L. Santagostini, F. Sannicolò, P.R. Mussini, “Inherently chiral” thiophene-based electrodes at work: a screening of enantioselection ability toward a series of pharmaceutically relevant phenolic or catecholic amino acids, amino esters, and amine, Analytical and Bioanalytical Chemistry, 408 (2016) 7243-7254
Electroactive Inherently Chiral Surfaces at Work: Clues Toward the Elucidation of the Enantioselection Mechanism
No full textChirality is a concept strictly related to life and to its evolution. Capability to discriminate antipodes and/or produce enantiopure chiral chemicals through cheap and efficient protocols is a crucial task for our modern civilization. So identification of increasingly effective and robust chiral selectors is a challenging task also for the electrochemical community [1,2].
In this frame our research group is working on the so called “inherently chiral functional molecular materials”, ICFMMs; the idea is simple: make the stereogenic element responsible for chirality coincident with the functional group responsible for the material specific property (Figure, left). This approach has constituted an actual breakthrough in chiral electrochemistry, resulting in the preparation of efficient chiral electroactive surfaces [3,4,5] (and chiral additives/media, too [6]) invariably characterized by outstanding enantiodiscrimination ability in quite different working conditions and with chemically different chiral electroactive analytes. Notwithstanding plenty of proofs pointing to a general validity of the ICFMMs concept, a clear rationalization of the enantiodiscrimination mechanism still lacks.
To fill the gap a deeper knowledge of the behavior of our electrodeposited chiral films is mandatory. As a first step some of the most important experimental parameters governing the growth of the conductive coatings have been changed, one by one, to evaluate their impact on the morphological, optical and electronic properties of the final deposit. Results of the multi-technique characterization will be discussed, including profilometry, electrochemical impedance spectroscopy (Figure, right) and spectroelectrochemistry data, all aimed to collect clues useful to rationalize the way in which ICFMMs work.
The support of Fondazione Cariplo/Regione Lombardia (Project 2016-0923) and SmartMatLab are gratefully acknowledged.
References:
[1] S. Arnaboldi, M. Magni, P. Mussini, Curr. Opin. Electrochem., 2018, 8, 60.
[2] S. Arnaboldi, S. Grecchi, M. Magni, P. Mussini, Curr. Opin. Electrochem., 2018, 7, 188.
[3] F. Sannicolò, P.R. Mussini, T. Benincori, R. Martinazzo, S. Arnaboldi, G. Appoloni, M. Panigati, E. Quartapelle Procopio, V. Marino, R. Cirilli, S. Casolo, W. Kutner, K. Noworyta, A. Pietrzyk-Le, Z. Iskierko, K. Bartold, Chem. Eur. J., 2016, 22, 10839.
[4] S. Arnaboldi, P.R. Mussini, M. Magni, F. Sannicolò, T. Benincori, R. Cirilli, K. Noworyta, W. Kutner, Chem. Sci., 2015, 6, 1706.
[5] 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., 2014, 53, 2623.
[6] 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., 2017, 56, 2079
The Breakthrough in Enantioselective Electrochemistry: Inherently Chiral Functional Molecular Materials
No full textIn Nature chirality has played a key role since the appearance of the first living being. Nowadays in our modern society capability to discriminate antipodes is still crucial; let us think to pharmaceutical industry: effective chiral selectors are mandatory both from an analytical and a synthetic point of view. Identifying chiral selectors able to effectively discriminate enantiomers of chiral analytes is a challenging task also for electrochemists [1,2].
In this frame our research group is working on the so called “inherently chiral functional molecular materials”, ICFMMs; the idea is simple: make the stereogenic element responsible for chirality coincident with the functional group responsible for the material specific property. This approach has constituted an actual breakthrough in chiral electrochemistry, resulting in the preparation of both chiral electroactive surfaces [3,4] and chiral media [5] invariably characterized by outstanding enantiodiscrimination ability in quite different working conditions and with chemically different chiral analytes.
In this presentation a panoramic overview of our recent results will be given, pointing to a general validity of the aforementioned concept. In particular the following topics will be discussed: ICFMMs with various stereogenic elements (all of which assure a tailored torsion in the molecular backbone), screening of different chiral analytes (with different stereogenic element, too) and working media (e.g. pH, counter-ions).
Very recently efforts have been focused on understanding the enantioselection mechanism, which still lacks. Results of a multi-technique characterization of the inherently chiral oligomer films will be presented, including profilometry, electrochemical impedance spectroscopy and spectroelectrochemistry measurements.
References
(1) Arnaboldi, S.; Magni, M.; Mussini, P. Curr. Opin. Electrochem. 2018, 8, 60.
(2) Arnaboldi, S.; Grecchi, S.; Magni, M.; Mussini, P. Curr. Opin. Electrochem. 2018, 7, 188.
(3) Sannicolò, F.; Arnaboldi, S.; Benincori, T.; Bonometti, V.; Cirilli, R.; Dunsch, L.; Kutner, W.; Longhi, G.; Mussini, P.R.; Panigati, M.; Pierini, M.; Rizzo S. Angew. Chem. Int. Ed. 2014, 53, 2623.
(4) Arnaboldi, S.; Mussini, P.R.; Magni, M.; Sannicolò, F.; Benincori, T.; Cirilli, R.; Noworyta, K.; Kutner W. Chem. Sci. 2015, 6, 1706.
(5) Rizzo S.; Arnaboldi, S.; Mihali, V.; Cirilli, R.; Forni, A; Gennaro, A.; Isse, A.A.; Pierini, M.; Mussini, P.R.; Sannicolò, F. Angew. Chem. Int. Ed. 2017, 56, 2079
Highly Enantioselective “Inherently Chiral" Film Electrodes at Work
No full textThe usual approaches to chiral electroactive molecular materials, relying on attaching chiral pendants to an electroactive polyconjugated backbone, generally result in modest chirality manifestations; other approaches, such as chiral templating agents, chiral counteranions, etc. actually imply the chirality source to be external to the electroactive material.
Very recently, our research group has unveiled by electrochemical experiments the unprecedented enantioselectivity properties of molecular films based on a new family of "inherently chiral" polyheterocycles, where chirality is not external to the electroactive backbone, but inherent to it, resulting from a tailored torsion produced by the periodical presence of atropoisomeric, conjugatively active biheteroaromatic scaffolds (e.g. 3,3'-bithiophene [as in the monomers (R)- and (S)-BT2T4 represented in Figure 1], 2,2'-biindole and 3,3' bithiophene). [1]
The electroactive films obtained by electrooligomerization mostly consist of cyclic electroactive oligomers, constituted by several fully conjugated thiophene units.
These ringlets, which can also be obtained by chemical oligomerization, are endowed with an outstanding pool of attractive properties both as racemates and as enantiopure antipodes. [1,2] The neat peak separation for two enantiomers of electroactive chiral probes (Figure 2) together with the linearity of the peak currents with enantiomer concentration affords estimation of the enantiomeric excess when both enantiomers are present [3].
The new electrodes have been tested with very good results towards several chiral probes, quite different in molecular structure and of applicative interest, on different supports, and in different media. Moreover, we have verified that the same spectacular enantioselectivity is obtained on surfaces prepared starting from monomers designed according to the same structural concept but chemically different, which demonstrates the general validity of the new strategy.
Albeit preliminary, such unprecedented outstanding results open the way to chiral voltammetry.
References
[1] F. Sannicolò, S. Arnaboldi, T. Benincori, V. Bonometti, R. Cirilli, L. Dunsch, W. Kutner, G. Longhi, P. R. Mussini, M. Panigati, M. Pierini and S. Rizzo, Angewandte Chemie Int. Ed., 2014, 53, 2623
[2] 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. Quartapelle Procopio and S. Rizzo, Chemistry-A European Journal, 2014, 10, 15261
[3] S. Arnaboldi, P. Mussini, M. Magni, F. Sannicolò, T. Benincori, R. Cirilli, K. Noworyta and W. Kutner, Chemical Science, 2015, 6, 170
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