Panoramic Overview on the Enantioselection Performance of Inherently Chiral Surfaces in Electroanalysis

A powerful tool is provided by electroactive heterocycle-based oligomer films endowed with “inherent” chirality (that is, following F. Sannicolò's definition [1], originating from the same element responsible for the key functional property, here electroactivity) on account of the presence of atropisomeric (i.e., with hindered rotation) or helicoidal elements in the main conjugated backbone, resulting in a regular torsion with an energy barrier far too high to be overcome in the working operating conditions. We have recently observed outstanding chirality manifestations and enantioselectivity in electrochemistry experiments [2,3] with enantiopure electrodes prepared from thiophene-based starting monomers endowed with inherent chirality and able to neatly discriminate as separate peaks (in terms of potential values) the antipodes of chiral probes (both as enantiopure and racemate). We have confirmed the general validity of the inherent chirality concept, which does not depend from the chemical nature of the atropisomeric scaffold. In this frame we have also tested chiral surfaces, electrooligomerized from starting monomers, with different molecular design (i.e. bithiophene, bibenzothiophene and biindole) and different stereogenic elements (stereogenic axis vs helix). In order to fully elucidate the enantioselection capability of all of these heteroaromatic systems, we propose a detailed comparison of our powerful surfaces together with a surface characterization in order to determine the thickness and the morphology of deposited films. Extending the same experiments to inherently chiral electroactive films with other stereogenic elements is of huge interest. Quite recently an additional confirmation came with the outstanding enantioselection observed working on achiral electrodes in inherently chiral media [4]. References [1] S. Arnaboldi, M. Magni, P.R. Mussini, Enantioselective selectors for chiral electrochemistry and electroanalysis: Stereogenic elements and enantioselection performance, Curr. Opin. Electrochem. (2018) doi.org/10.1016/j.coelec.2018.01.001 [2] S. Arnaboldi, T. Benincori, R. Cirilli, W. Kutner, M. Magni, P.R. Mussini, K. Noworyta, F. Sannicolò, Inherently chiral electrodes: the tool for chiral voltammetry, Chemical Science 6 (2015) 1706-1711 [3] 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, Potential-Driven Chirality Manifestations and Impressive Enantioselectivity by Inherently Chiral Electroactive Organic Films, Angew. Chem. Int. Ed. 53 (2014) 2623–2627. [4] 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. Acknowledgements: 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.