Unconventional Electrochemical Approaches for the Direct Readout of Chiral Information

Among the different strategies to endow conducting polymers with chiral features, the concept of inherent chirality is extremely attractive and efficient for several reasons. [1] Inherent chirality is an intrinsic propriety of the whole molecule in which the stereogenic element responsible for chirality coincides with the functional group responsible for the specific properties of the molecular material. The racemization barrier of these molecules is high enough to allow the separation into stable enantiomers by chiral HPLC. Their electro-oligomerization results in chiral electrode surfaces able to discriminate the antipodes of chiral species by differences in peak potential recorded by voltammetry.[2] This is a true advantage from an analytical point of view, because it is possible to achieve the enantioselective discrimination in racemic mixtures of the analyte, in contrast to most of the approaches presented in literature for which the recognition is only based on differences in current intensity. In this context the high enantioselectivity of such chiral surfaces was used in combination with the mechanical and electrical properties of polypyrrole (Ppy) films to develop i) a new approach based on bipolar electrochemistry for the absolute on-off recognition of enantiomers of a chiral probe (Fig. A), [3] and ii) new autonomous enzymes based swimmers able to convert chiral information present at the molecular level into macroscopic enantioselective trajectories (Fig. B). [4] Both approaches allow correlating the output signal with the concentration of the enantiomers present in solution, even in the case of mixtures containing different ratios of the molecular antipodes.