Innovative Chiral Materials and Media for Enantioselection in Chiral Electrochemistry and Advanced Applications in Spintronics

The 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.