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Electrochemically induced Asymmetry: from materials to molecules and back

Periodic Reporting for period 2 - ELECTRA (Electrochemically induced Asymmetry: from materials to molecules and back)

Reporting period: 2019-03-01 to 2020-08-31

Asymmetry is a very common feature of many systems, objects and molecules, that we use in our daily life. Actually, it is in a majority of cases the absolutely crucial ingredient for conferring a useful property to a system. A prominent example is the chiral nature of pharmaceutically active compounds, where only one of the two mirror images of a molecule is useful from a medical point of view, whereas the other one is in the best case useless or in the worst case even toxic. This nicely illustrates that the controlled generation of asymmetry is an issue of societal relevance, which deserves important research efforts, from an applied and from a very fundament point of view. Chemists have developed various approaches to generate asymmetry, from the molecular to the macroscopic scale, but are still facing major challenges when exploring efficient alternative physico-chemical concepts for symmetry breaking. In this context, the global aim of the ELECTRA project is to propose so far unexplored and versatile strategies, based on the unconventional use of electrochemical phenomena, to generate asymmetry in chemical systems at different length scales.
We are currently investigating simultaneously wired and wireless electrochemistry in order to open up unique possibilities for advancing the topic of asymmetry generation in an original and cross-disciplinary way. We are testing the utility of these strategies in the frame of two major challenges that are:
-unconventional detection, separation and synthesis of enantiomers, based on metal structures which are encoded with chiral information, a topic that has been pioneered by us in the last few years;
-design and characterization of Janus systems with complex structures, composition and reactivity
We have carefully designed experiments that enable us to gain a better understanding of the different mechanisms involved in symmetry breaking, covering various characteristic length scales, from the molecular level to macroscopic objects and systems. New concepts with respect to their efficiency, yield and selectivity are crucial steps currently under investigation. This allows us chosing the most innovative approaches of symmetry breaking, in view of the numerous highly relevant applications, ranging from analysis to catalysis and energy conversion. Furthermore, due to the interdisciplinary character of asymmetry, our findings should not only have a major impact in various areas of chemistry, but might also be very interesting for other scientific disciplines like physics and biology.
The project is organized around two complementary physico-chemical approaches to break the symmetry of chemical systems, namely wired and wireless electrochemistry. For both axis, we have already made substantial progress, going beyond the state of the art.

Wired electrochemistry:

There are three different challenges in this part of the project .

A) The first major challenge is the optimization of the synthesis of chiral imprinted mesoporous metals. A very difficult task is changing the nature of the metal in order to replace noble metals, which we used up to now, by cheap non-noble metals. So far, we were already able to imprint chiral information into mesoporous nickel electrodes, despite their chemical and mechanical more fragile nature (Press release: https://inc.cnrs.fr/fr/cnrsinfo/un-film-poreux-de-nickel-pour-selectionner-les-enantiomeres ).

B) A second goal of the project concerns the use of chiral metal matrices for enantioselective separation. We’ve succeeded so far in integrating these metals into microfluidic channels and use these modified channels as intrinsically chiral stationary phases for the microseparation of mixtures of enantiomers (Press release https://inc.cnrs.fr/fr/cnrsinfo/molecules-chirales-separer-linseparable )

C) The third important challenge is to adapt these new materials for enantioselective synthesis and push the enantiomeric excess (% ee) into regions of practical interest. We were able to circumvent several practical problems and could reach unexpected % ee values of over 90%. Such a selectivity is unprecedented in chiral electrosynthesis and also constitutes a change of paradigm in heterogeneous chiral synthesis (Press release: https://inc.cnrs.fr/fr/cnrsinfo/molecules-therapeutiques-lelectrochimie-pulsee-pour-une-synthese-selective ).

Wireless electrochemistry:

In the frame of this part of the project, our objective is to push the limits of the concept of bipolar electrochemistry and the corresponding progress we already made is illustrated by a few highlights.

The first challenge concerns the synthesis of asymmetric, so-called Janus objects with an unprecedented degree of complexity in terms of used materials and design. While working on this task we’ve considerably enlarged the notion of Janus object by not only considering classic Janus particles, but by integrating also other very original asymmetric systems. We were able to propose completely unusual dynamic asymmetric systems based on conducting polymers which can be addressed in a wireless way and behave as actuators. In these cases, the induced bifunctionality can be used either for generating controlled motion of the polymer object (see Youtube video: https://www.youtube.com/watch?v=CCXtQm9Ncu0 ) or for developing a new tool for the electromechanical readout of analytical information (J.Am.Chem.Soc.140 (2018) 15501). In combination with the activities described in the section about chiral recognition, we even could design a dynamic device able to distinguish between two enantiomers (Chem.Comm. 55 (2019) 10956). Additional and very original bifunctional Janus objects have also been developed in parallel, based on the asymmetric modification of miniaturized light-emitting diodes (Angew.Chem.Int.Ed. (2020) in press doi.org/10.1002/anie.201915705).