Kanazawa NanoLSI Research Podcast: Changing the handedness of molecules

24 August 2022
 
Changing the handedness of molecules
 
Researchers at Kanazawa University report in the Proceedings of the National Academy of Sciences a responsive molecular system that, inverses its chirality before becoming racemic through chemical reactions.
Learn more about their research here: WPI Kanazawa Nano Life Science Institute

https://nanolsi.kanazawa-u.ac.jp/en/research/researchers/

Transcript of this podcast
Hello and welcome to the NanoLSI podcast. 

In this episode we will feature the latest research published by Shigehisa Akine a member of the Supramolecular Chemistry group at the Kanazawa University NanoLSI.

The research described in this podcast was published in the Proceedings of the National Academy of Sciences in March 2022.  

Changing the handedness of molecules 

https://nanolsi.kanazawa-u.ac.jp/en/achievements/achievements-19316/

Researchers at Kanazawa University report in the Proceedings of the National Academy of Sciences a responsive molecular system that, inverses its chirality before becoming racemic through chemical reactions.

Molecules that can change their structure in response to a chemical or physical stimulus are called ‘responsive molecules’.  This type of molecule plays an important role in signal transduction at the nanoscale.  The typical time profile of a structural change of a responsive molecule follows an exponential relaxation.  However, molecular systems with non-typical time responses, such as e.g. chemical oscillators offer advanced functionalities and are also intensively investigated.  

Shigehisa Akine and colleagues from Kanazawa University have now designed a particular responsive molecule in which the chirality (‘handedness’) changes in a non-exponential fashion.  The achievement is a breakthrough in the field of responsive systems as the chirality change happens in a unimolecular system — and not as has often been the case before in supramolecular assemblies.

The researchers’ responsive molecule has six exchangeable sites and two forms, a ‘left-handed’ and a ‘right-handed’ version.  In solution, the two forms will occur in a given ratio.  Akine and colleagues started from the molecule with a particular chiral amine. They found that in a methanol solution the right-handed version was dominant.  The scientists then looked at what would happen when exchanging the so-called chiral A groups with piperidine (another form of amine).

Because of the achirality of the piperidine groups, the resulting solution should become ‘racemic’, which means that any effects of chirality are compensated.  This is indeed what happened, but the researchers discovered that before reaching the racemic state after two days, the solution first switched from originally P-dominant to M-dominant after 7 minutes, with maximum M-dominance after 60 – 120 minutes.  Remarkably, a similar transient chirality inversion was not observed for the reverse reaction for which the solution changed monotonically from racemic to P-dominant.

Akine and colleagues note that their responsive molecule is the first unimolecular platform displaying a transient chirality inversion, and that the unique chirality change happens on the timescale of minutes to hours, which could be potentially useful for time-dependent functional materials related to human activity.  

Quoting the scientists: “this result will provide an important insight into the science of autonomously driven materials.”

Reference

Yoko Sakata, Shuns

NanoLSI Podcast website