Ionic liquids ILs are attractive media for electrochemistry and electroanalysis, since, in addition to other useful properties, they provide both solvent and supporting electrolyte; moreover, they feature an extremely well defined structure at the interphase with a charged electrode, resembling somehow a bulk liquid crystal, extending for many layers, also standing in the presence of water traces, and possibly tunable by in-situ present additives. [1-3] For this reason chiral ionic liquids (CILs), of which a rich palette is already available, are surprisingly still nearly unexplored by electrochemists, in spite of appearing quite attractive, since they could transmit chiral information more effectively than chiral organic solvents or chiral supporting electrolytes. [1] In this context, we have recently started a detailed investigation of (a) bio-based chiral ionic liquids and (b) inherently chiral ionic liquids (ICILs), investigating both their physico-chemical and electrochemical features and their performance as media for chiral electroanalysis experiments. Our bio-based CILs featu- re cations with a building block of natural origin, including one or more localized stereocentres, from which their chirality arises (as in most so far available CILs) [4]. Instead, in our ICILs chirality is intrinsic of the whole biheteroaromatic cation, which features a stereogenic axis related to a torsion between two equal heteroaromatic moieties, with a related energy barrier too high to be overcome at room temperature, so that the ICIL can be obtained in two stable enantiopure antipodes. In inherently chiral molecules and materials both chirality and functional properties originate from the same structural element, which can coincide with the main molecular backbone; thus their chirality manifestations can be very powerful, as recently evidenced by some of us in electroanalytical, chiroptical and magneto-electrochemistry experiments with electrodes modified by inherently chiral oligomer thin films. Actually, while interesting but (at least so far) small are the chirality effects observed working in our bio- based CILs with localized stereocentres [4], large peak potential differences have been observed for the enantiomers of very different chiral probes in CV experiments in an enantiopure bulk ICIL. Very conve- niently, impressive enantiodiscrimination is observed even using ICILs (or other related inherently chiral molecular salts, solid at room T, but of easier synthesis) as low-concentration chiral additives in common achiral ionic liquids (ILs) [5,6]. Furthermore, similar impressive performances have also been observed dissolving in an achiral IL a thiahelicene-based additive, an inherently chiral oligothiophene, but un- charged and based on a different stereogenic element, i.e. a helical scaffold. Among possible explanations we are considering the possibility of a chiral reorganization effect by the inherently chiral additives in the locally highly ordered IL structure at the interphase with the charged electrode, similarly to the well- known transitions from nematic to cholesteric order induced by chiral additives in bulk liquid crystals. The support of Fondazione Cariplo/Regione Lombardia "Avviso congiunto per l’incremento del- l’attrattività del sistema di ricerca lombardo e della competitività dei ricercatori candidati su strumenti ERC - edizione 2016” (Project 2016-0923) is gratefully acknowledged. [1] S. Arnaboldi, M. Magni, P.R. Mussini, Curr. Opin. Electrochem. 8 (2018) 60-72. [2] K. Ma, R. Jarosova, G.M. Swain, G.J. Blanchard, Langmuir 32 (2016) 9507-9512. [3] A.Lahiri Cui, T. Carstens, N. Borisenko, G. Pulletikurthi, C. Kuhl, F. Endres, J. Phys. Chem. C 120 (2016) 9341-9349. [4] M. Longhi, S. Arnaboldi, E. Husanu, S. Grecchi, I.F. Buzzi, R. Cirilli, S. Rizzo, C. Chiappe, P.R. Mussini, L. Guazzelli, Electrochim. Acta 298 (2019) 194-209. [5] 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) 2079-2082. [6] S. Rizzo, S. Arnaboldi, R. Cirilli, A. Gennaro, A.A. Isse, F. Sannicolò, P.R. Mussini, Electrochem. Comm. 89 (2018) 57-61.

Electrochemistry of, and electrochemistry in, chiral and inherently chiral ionic liquid media / S. Arnaboldi, P.R. Mussini, S. Grecchi, M. Longhi, S. Rizzo, E. Licandro, S. Cauteruccio, R. Cirilli, L. Guazzelli, C. Chiappe. ((Intervento presentato al 28. convegno Congresso Nazionale della Divisione di Chimica Analitica tenutosi a Bari nel 2019.

Electrochemistry of, and electrochemistry in, chiral and inherently chiral ionic liquid media

S. Arnaboldi;P.R. Mussini;S. Grecchi;M. Longhi;E. Licandro;S. Cauteruccio;
2019

Abstract

Ionic liquids ILs are attractive media for electrochemistry and electroanalysis, since, in addition to other useful properties, they provide both solvent and supporting electrolyte; moreover, they feature an extremely well defined structure at the interphase with a charged electrode, resembling somehow a bulk liquid crystal, extending for many layers, also standing in the presence of water traces, and possibly tunable by in-situ present additives. [1-3] For this reason chiral ionic liquids (CILs), of which a rich palette is already available, are surprisingly still nearly unexplored by electrochemists, in spite of appearing quite attractive, since they could transmit chiral information more effectively than chiral organic solvents or chiral supporting electrolytes. [1] In this context, we have recently started a detailed investigation of (a) bio-based chiral ionic liquids and (b) inherently chiral ionic liquids (ICILs), investigating both their physico-chemical and electrochemical features and their performance as media for chiral electroanalysis experiments. Our bio-based CILs featu- re cations with a building block of natural origin, including one or more localized stereocentres, from which their chirality arises (as in most so far available CILs) [4]. Instead, in our ICILs chirality is intrinsic of the whole biheteroaromatic cation, which features a stereogenic axis related to a torsion between two equal heteroaromatic moieties, with a related energy barrier too high to be overcome at room temperature, so that the ICIL can be obtained in two stable enantiopure antipodes. In inherently chiral molecules and materials both chirality and functional properties originate from the same structural element, which can coincide with the main molecular backbone; thus their chirality manifestations can be very powerful, as recently evidenced by some of us in electroanalytical, chiroptical and magneto-electrochemistry experiments with electrodes modified by inherently chiral oligomer thin films. Actually, while interesting but (at least so far) small are the chirality effects observed working in our bio- based CILs with localized stereocentres [4], large peak potential differences have been observed for the enantiomers of very different chiral probes in CV experiments in an enantiopure bulk ICIL. Very conve- niently, impressive enantiodiscrimination is observed even using ICILs (or other related inherently chiral molecular salts, solid at room T, but of easier synthesis) as low-concentration chiral additives in common achiral ionic liquids (ILs) [5,6]. Furthermore, similar impressive performances have also been observed dissolving in an achiral IL a thiahelicene-based additive, an inherently chiral oligothiophene, but un- charged and based on a different stereogenic element, i.e. a helical scaffold. Among possible explanations we are considering the possibility of a chiral reorganization effect by the inherently chiral additives in the locally highly ordered IL structure at the interphase with the charged electrode, similarly to the well- known transitions from nematic to cholesteric order induced by chiral additives in bulk liquid crystals. The support of Fondazione Cariplo/Regione Lombardia "Avviso congiunto per l’incremento del- l’attrattività del sistema di ricerca lombardo e della competitività dei ricercatori candidati su strumenti ERC - edizione 2016” (Project 2016-0923) is gratefully acknowledged. [1] S. Arnaboldi, M. Magni, P.R. Mussini, Curr. Opin. Electrochem. 8 (2018) 60-72. [2] K. Ma, R. Jarosova, G.M. Swain, G.J. Blanchard, Langmuir 32 (2016) 9507-9512. [3] A.Lahiri Cui, T. Carstens, N. Borisenko, G. Pulletikurthi, C. Kuhl, F. Endres, J. Phys. Chem. C 120 (2016) 9341-9349. [4] M. Longhi, S. Arnaboldi, E. Husanu, S. Grecchi, I.F. Buzzi, R. Cirilli, S. Rizzo, C. Chiappe, P.R. Mussini, L. Guazzelli, Electrochim. Acta 298 (2019) 194-209. [5] 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) 2079-2082. [6] S. Rizzo, S. Arnaboldi, R. Cirilli, A. Gennaro, A.A. Isse, F. Sannicolò, P.R. Mussini, Electrochem. Comm. 89 (2018) 57-61.
Settore CHIM/01 - Chimica Analitica
Società Chimica Italiana. Divisione di Chimica Analitica
Electrochemistry of, and electrochemistry in, chiral and inherently chiral ionic liquid media / S. Arnaboldi, P.R. Mussini, S. Grecchi, M. Longhi, S. Rizzo, E. Licandro, S. Cauteruccio, R. Cirilli, L. Guazzelli, C. Chiappe. ((Intervento presentato al 28. convegno Congresso Nazionale della Divisione di Chimica Analitica tenutosi a Bari nel 2019.
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