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Electrochemically induced Asymmetry: from materials to molecules and back

Periodic Reporting for period 4 - ELECTRA (Electrochemically induced Asymmetry: from materials to molecules and back)

Reporting period: 2022-03-01 to 2023-02-28

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 have simultaneously investigated 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 tested the utility of these strategies in the frame of two major challenges that were:
-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 enabled 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 we elucidated during the last five years. This allowed 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 will have a major impact in various areas of chemistry, but should also be very interesting for other scientific disciplines like physics and biology.
A summary of the progress is indicated below for the two subtopics.

1. Wired electrochemistry:

We have succeeded in proposing in a convincing way the encoding of chiral information in bulk metal structures, not only for rather stable metals such as platinum, but even for chemically and mechanically much more fragile non-noble metals such a nickel. This allowed us to use these sophisticated matrices for the very first time not only for separating enantiomers in a microfluidic channel, but, most importantly, to employ these electrode structures also for the highly selective electrosynthesis of chiral molecules. An absolutely unprecedented enantiomeric excess of over 90% has been achieved in this way. This novel methodology represents a complete change of paradigm, not only in the context of organic electrosynthesis, but also for heterogeneous catalysis in the more general sense. The findings are therefore of primary importance especially for pharmaceutical industries and thus we plan for the near future to work on a scale-up of these approaches.

2. Wireless electrochemistry:

We were able to propose a completely new approach for electrically addressing conducting polymer objects in a wireless way by bipolar electrochemistry. The concept allows triggering different redox reactions at the two opposite extremities of the bipolar object, resulting in a controlled deformation of the polymer due to spatially localized shrinking and swelling. We have explored this phenomenon for the very first time to achieve wireless actuation of these objects either for developing active elements such as valves and pumps, or for designing new analytical tools based on an electromechanical transduction, which allows a straightforward readout of chemical information. We believe that this new concept opens up very interesting perspectives for a large variety of applications, ranging from controlled drug delivery to soft robotics. In addition we have used this concept of wireless electrochemistry for the very first time to address biological objects, namely cable bacteria. These microorganisms are currently a very hot topic for fundamental studies, because an interdisciplinary scientific community tries to understand how these entities manage to conduct electricity and to use this feature to drive their metabolism. We were able to demonstrate with a series of quite complicated experiments, that the cable bacteria have an integrated molecular system allowing them to act as bifunctional catalysts performing in a reversible way oxygen reduction and oxygen evolution. This conceptual breakthrough adds an important brick to the mosaic of scientific evidence for the peculiar behavior of these microorganisms.
An equally important break-through at the very fundamental level is our discovery that by integrating a circularly polarized light source into the classic Miller-Urey experiment it is possible to change the relative kinetics of the synthesis of the different natural amino acids. This insight has far-reaching consequences, especially with respect to the eternal question about the origin of homochirality on earth. We therefore expect that our results will have an impact on the scientific community working actively on this still open question.
Some of the achievements of the project can be considered as true breakthroughs in various fields of chemistry and also in neighboring disciplines. A significant fraction of our findings go beyond the state of the art, illustrated also by the fact that they were published in very high-impact journals.

A couple of highlights that illustrate the progress beyond mainstream strategies:

1. Wireless Electromechanical Readout of Chemical Information
J. Am. Chem. Soc. 140 (2018) 15501

2. Potential-Induced Fine-tuning of the Enantioaffinity of Chiral Metal Phases
Angew. Chem. Int. Ed., 58 (2019) 3471

3. Lorentz Force-Driven Autonomous Janus Swimmers
J. Am. Chem. Soc. 143 (2021) 12708

4. Direct dynamic readout of molecular chirality with autonomous enzyme driven swimmers
Nature Chem. 13 (2021) 1241

5. Nanoengineered chiral Pt-Ir alloys for high-performance enantioselective electrosynthesis
Nature Comm. 12 (2021) 1314

Some of these results were planned and/or expected, but others are the fruit of a synergy between different intra-project research topics, leading to an unexpected cross-fertilization. This is exactly what makes an ERC project so appealing, as it is possible to follow without restrictions new research opportunities, which initially seem to be side-roads, but turn out to be extremely interesting because they open a whole original avenue of additional activities.
Journal Cover illustrating enantioselective separation
Journal Cover illustrating a wireless light emitting actuator
Journal Cover illustrating chiral imprinted nickel electrode
Complex Janus particle obtained by bipolar electrochemistry