Enantiodiscrimination in electrochemistry and electroanalysis: implementing "inherent" chirality at the electrochemical interphase

All electrochemical processes are intrinsically "intelligent" on account of the selectivity achievable by controlling the electrical potential, also providing a convenient tool for transduction of recognition events. However, chirality can make electrochemical processes even smarter, implying to discriminate between enantiomers of a given electroactive chiral molecule in terms of potential difference, for advanced analytical, synthetic or device applications. To achieve enantioselective electrochemistry and electroanalysis, electron transfer processes at the interphase must take place in the presence of a suitable enantiopure chiral selector, resulting in energetically different diastereoisomeric conditions for the two probe enantiomers [1]. Particularly effective are molecular selectors endowed with "inherently chirality", i.e. with chirality and key functional properties originating from the same structural element (in our case coinciding with the main molecular backbone, featuring a tailored torsion). Actually large enantiomer peak potential differences have been observed in voltammetry: (i) working in achiral media, on electrode surfaces modified with thin films of inherently chiral electroactive oligomers [1,2]; they can be electrodeposited from enantiopure monomers consisting of an atropoisomeric biheteroaromatic core with oligothiophene wings, or of a thiahelicene scaffold. Such films also exhibit attractive chiroptical properties (also electrochemically modulable) as well as impressive results in magnetoelectrochemistry experiments, and can be detached and tested as self-standing chiral membranes; (ii) working on achiral electrodes, implementing inherent chirality in their interphase with an ionic liquid IL medium, exploiting the latter's peculiarly high order [1,3]. We developed inherently chiral ionic liquids ICILs consisting in double salts of atropoisomeric bipyridinium scaffolds with long alkyl chains. Very conveniently, enantiodiscrimination is observed not only working in a bulk ICIL, but also using it, or other inherently chiral selectors, as low-concentration chiral additives in commercial achiral ILs. Less remarkable enantiodiscrimination was observed working with chiral (not "inherently" chiral) biobased ionic liquids CILs.