Twisting stuff until it breaks – at the molecular level

Aromatic bonds, particularly strong chemical bonds which form in some ring-shaped molecules, are a crucial building block of the world around us. They appear in everything from proteins to aspirin, and literally millions of natural and synthetic substances in between.

The bonds are very hard to break and to control, and their properties have puzzled chemists for more than a century.

Which is just the motivation chemists needed to break and control them, and now a group of UK researchers has figured out how to twist an aromatic bond until it breaks.

The discovery could help to better understand how these perplexing bonds work, making it easier to make pharmaceuticals, polymers, and other high-tech materials.

“The precise control over the twisting of our molecules is unprecedented,” says Dr Paul McGonigal, a researcher at the University of York, UK, and co-author on a paper describing the research, published in Nature Chemistry.

“We were not only able to twist an aromatic molecule up to the maximum amount of strain it can tolerate, but also to discover what happens when we push beyond that limit.

“We hope this investigation is a step towards us being able to more routinely turn aromatic bonding ‘off’ and ‘on’ in a controlled manner.”

Read more: Turning air into metal with nitrogen, diamonds and lasers

The researchers started with a seven-pointed ring molecule made out of carbon atoms.

When they added large molecules to the carbon atoms, the ring started to twist.

The more large molecules added at the edges, the closer the ring got to breaking, eventually pinching in the middle to form two smaller, connected rings.

Two molecules with interconverting equation between them, one has a seven-pointed ring and the other has pinched the ring into a five-pointed and four-pointed ring
With enough strain, the molecule pinches in the middle and turns into two rings. Credit: provided by Durham University

The researchers found a point when their molecule switched between its big-ring and two-small-ring structures.

“The reversible pinching and reopening of an aromatic ring is truly remarkable,” says lead author Promeet Saha, a researcher at Durham University in the UK.

“Aromatic bonding is such a powerful stabilising force that we usually think of it being a constant presence. However, our findings demonstrate that it can be surprisingly dynamic.”

Please login to favourite this article.