Chiral discrimination is of crucial importance for many applications, including drug cross checking and electronic tongue type devices. In a typical sensing scheme, an enantiomeric selector is combined with an appropriate transduction mechanism. We propose here a hybrid material composed of an electrically conducting oligomer i.e. oligo-(3, 3'-dibenzothiophene) bearing inherently chiral features, and polypyrrole as a support which can undergo electrochemical actuation. The combination of both leads to a freestanding film that is addressable in a wireless way based on the principle of bipolar electrochemistry. The induced redox reactions lead to wellpronounced actuation when DOPA with the right chirality is present in solution as a model analyte, whereas absolutely no electromechanical response is measured for the wrong enantiomer. This constitutes a straightforward and absolute read out of chiral information where the amplitude of actuation is correlated with the concentration of the analyte. Optimization of the scheme results in highly efficient bending, and thus opens up new directions in the field of chiral technologies.
A key approach for designing bioinspired machines is to transfer concepts from nature to manmade structures by integrating biomolecules into artificial mechanical systems. This allows the conversion of molecular information into macroscopic action. In the present contribution, we describe the design and dynamic behavior of hybrid bioelectrochemical swimmers, which move spontaneously at the air/water interface. Their motion is governed by the diastereomeric interactions between immobilized enantiopure oligomers and the antipodes of a chiral probe molecule present in solution. These dynamic systems are able to convert chiral information present at the molecular level into enantiospecific macroscopic trajectories. Depending on the enantiomer in solution, the swimmers will move clockwise or anti-clockwise and the concept can also be used for the direct visualization of the degree of enantiomeric excess by analyzing the curvature of the trajectories.
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.
Bipolar electrochemistry has gained increasing attention in recent years as an attractive transduction concept in analytical chemistry in general and, more specifically, in the frame of chiral recognition. Herein, we use this concept of wireless electrochemistry, based on the combination of the enantioselective oxidation of a chiral probe with the emission of light from a light‐emitting diode (LED), as an alternative for an easy and straightforward readout of the presence of chiral molecules in solution. A hybrid polymer‐microelectronic device was designed, using an inherently chiral oligomer, that is, oligo‐(3,3′‐dibenzothiophene) and a polypyrrole strip as the anode and cathode of a miniaturized LED. The wireless induced redox reactions trigger light emission when the probe with the right chirality is present in solution, whereas no light emission is observed for the opposite enantiomer. The average light intensity shows a linear correlation with the analyte concentration, and the concept opens the possibility to quantify the enantiomeric excess in mixtures of the molecular antipodes.
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