Electroactive bio-based chiral tweezers: Attractive selectors for enantioselective voltammetry

Ionic liquids (ILs), either chiral in themselves (CILs) or modified with small quantities of CILs or related chiral molecular salts as chiral additives, have been proposed as an effective tool to achieve enantiodiscrimination in terms of potential differences in voltammetric electroanalysis, on account of their high local order at the electrode | solution interphase. Successful cases already explored range from biobased CILs (or related chiral additives) including terpenol or bile acid building blocks, having stereocentres as stereogenic elements, to CILs (or related chiral additives) with “inherently chiral” scaffolds based on biheteroaromatic atropisomeric cores. A further attractive family of CILs and related compounds worthy to be explored is based on chiral “tweezer” dications consisting of a biobased isomannide or isosorbide chiral core with two cation arms which include heteroatoms and aromatic systems, thus providing many coordination elements for selector/probe interactions. A wide, systematic series of such chiral tweezers is presented, characterized in terms of thermal features (by thermal gravimetric analysis and differential scanning calorimetry) and stereochemical properties (by electronic circular dichroism spectroscopy), and submitted to an exhaustive electrochemical study to highlight and rationalize their redox properties. Successful preliminary chiral voltammetry tests, performed employing rac-N-3,5-dinitrobenzoyl phenylglycine methyl ester (DNB-PhGly) as well as 2,2,2-trifluoro-1-(9-anthryl)ethanol (TFAE) as chiral electroactive probes in combination with selected tweezers, confirm the attractiveness of the biobased tweezer family as chiral selectors for enantioselective electroanalysis.