Bipolar Electrochemical Measurement of Enantiomeric Excess with Inherently Chiral Polymer Actuators

Abstract

Straightforward enantioselective analytical methods are very important for drug safety, considering that in certain cases one of the two enantiomers of a chiral molecule might be harmful for humans. In this work, we propose a simple system for the direct and easy read-out of the enantiomeric excess of 3,4-dihydroxyphenylalanine (DOPA) as a model analyte. A conducting oligomer, i.e. oligo-(3,3′-dibenzothiophene), bearing inherently chiral features, is electrogenerated on a polypyrrole film. The resulting freestanding hybrid material is used as a wireless enantioselective actuator in a bipolar electrochemical cell. Combining in a single setup two individual actuators with opposite chiral features allows a direct visual read-out of enantiomeric excess, as the bending amplitude of each of the two actuators is directly correlated with the concentration of the corresponding stereoisomer of the analyte. Optimization of the experimental parameters results in efficient bending, giving access to the percentage values of the enantiomeric excess in mixtures containing different ratios of the antipodes, thus opening the way to potential applications for chiral in situ analysis.

Autonomous Chiral Microswimmers with Self‐mixing Capabilities for Highly Efficient Enantioselective Synthesis

“…The enantiopure oligomers of an inherently chiral monomer (Scheme 1A, (R)-BT 2 T 4 and (S)-BT 2 T 4 , respectively) were deposited galvanostatically on the surface of a macroscopic Zn wire, according to a previously described procedure. [52][53][54][55][56] These monomers, with 3,3'-bibenzothiophene as a central unit, have a well-defined electroactivity and can be easily electropolymerized. The two alpha homotopic positions on the thiophene wings guarantee the regioregularity of the oligomerization process.…”

“…a new approach based on bipolar electrochemistry for the absolute on-off recognition of enantiomers of a chiral probe. [52][53][54][55] Recently, these inherently chiral oligomers have also been used to design autonomous enzyme-based swimmers, able to produce enantioselective clockwise and anticlockwise motion as a function of the enantiomer present in solution. [56] In the present work, we employ these oligomers to design selfpropelled asymmetric microswimmers, based on small pieces of zinc (Zn), partially functionalized with one of the antipodes of the inherently chiral material.…”

Autonomous Chiral Microswimmers with Self‐mixing Capabilities for Highly Efficient Enantioselective Synthesis

“…The enantiopure oligomers of an inherently chiral monomer (Scheme 1A, (R)-BT 2 T 4 and (S)-BT 2 T 4 , respectively) were deposited galvanostatically on the surface of a macroscopic Zn wire, according to a previously described procedure. [52][53][54][55][56] These monomers, with 3,3'-bibenzothiophene as a central unit, have a well-defined electroactivity and can be easily electropolymerized. The two alpha homotopic positions on the thiophene wings guarantee the regioregularity of the oligomerization process.…”

“…a new approach based on bipolar electrochemistry for the absolute on-off recognition of enantiomers of a chiral probe. [52][53][54][55] Recently, these inherently chiral oligomers have also been used to design autonomous enzyme-based swimmers, able to produce enantioselective clockwise and anticlockwise motion as a function of the enantiomer present in solution. [56] In the present work, we employ these oligomers to design selfpropelled asymmetric microswimmers, based on small pieces of zinc (Zn), partially functionalized with one of the antipodes of the inherently chiral material.…”

Cover Feature: Recent Advances in Bipolar Electrochemistry with Conducting Polymers (ChemElectroChem 1/2022)

“…Following this concept, the enantiomeric excess of unbalanced mixtures of L-and D-DOPA can be determined by using simultaneously both hybrid Ppy films, modified respectively with the S-and R-oligo-BT2T4 oligomer, as BPEs (Figure 5a). [58] A correlation between the degree of actuation and the concentration of the corresponding analyte in solution was obtained. In a very recent work, the propagation of chiral information along different scales could be achieved.…”