Achieving Effective Inherently Chiral Electroanalysis on Chiral and Achiral Screen-Printed Supports

“Inherently chiral” polyconjugated thiophene-based electroactive films [1] have recently been shown to afford impressive chirality manifestations and enantiorecognition ability [1,2]. The "inherent chirality" strategy followed in their design implies that both the stereogenic element responsible for chirality and the electroactivity source coincide with the main molecular backbone, where an atropisomeric 3,3’-bithianaphthene scaffold induces a left- or right-handed torsion; this unique threefold identity enhances the functional properties of the material and connects them together as well. Thus, unprecedented results are being obtained in chiroptical and electroanalytical experiments with inherently chiral electroactive films [1-3]; in particular, inherently chiral screen-printed electrode surfaces have been proposed as a tool opening the way to chiral voltammetry, especially for enantiodiscrimination and enantiomeric excess quantification of pharmaceutically relevant probes, in aqueous and nonaqueous achiral media, without preliminary separation steps [3]. By analogy, high enantioselectivity can be expected to be achievable as well by implementing inherent chirality in the working medium, which would provide an interesting alternative to the use of a chiral active surface. Ionic liquids, increasingly popular media with many attractive features, look ideal for such implementation, for instance they are intrinsically much more ordered than organic solvents. In this context we have started working on the application of the inherent chirality strategy to develop "inherently chiral ionic liquids". Suitable systems are long-chain dialkyl salts of the 3,3'-bipyridine scaffold of bicollidine, easily accessible and featuring a very high interconversion barrier as well as a very large electrochemical window. This 3,3'-bipyridine is particularly interesting since the two enantiomers can be separated by fractional crystallization as diastereomeric salts with enantiopure chiral acids, therefore avoiding the use of much more expensive chiral HPLC. The scaffold chirality is preserved also upon conversion into their corresponding dialkylated salts. This study is still in its early stage, but several tests seem to indicate that, also in this case, significant enantioselectivity could be achieved using unmodified screen-printed supports by applying the inherent chirality concept. References [1] Angew. Chem. 2014, 53, 1. [2] Chem. Eur. J. 2014, 20, 15298. [3] Chemical Science 2015, 6, 1706 Fondazione Cariplo: Grants no. 2011-0417 (inherently chiral electrodes) and no. 2011-1851 (inherently chiral ionic liquids)