July 13, 2024

I, Science

The science magazine of Imperial College

Researchers at the University of Manchester have broken the record for creating the tightest knot ever, using a strand of 192 atoms.

Tying a knot may seem like a trivial thing– in fact few people over the age of 5 would ever call tying their shoelaces a great achievement. However, researchers at the University of Manchester have broken a new record we didn’t even know existed. This team of scientists created the tightest knot ever: the microscopic circular triple helix. This knot consists of a very thin strand of atoms, 200,000 times thinner than a human hair, which curls around in a triple loop, crossing itself a total of 8 times. The strand uses only 192 atoms in total.

How tight is ‘tight’? 

Although you can generally gauge the tightness of a knot by feeling its tension against your fingers, a more quantitative definition of tightness is required for these intangible atomic knots. In this case, the tightness of a knot is related to the distance between points where the strand crosses itself. The shorter the distance, the tighter the knot. In the circular triple helix, each crossing point is situated only 24 atoms apart; “that’s very, very tight indeed,” says David Leigh, a professor of chemistry at the University of Manchester, “it is definitely the most tightly knotted physical structure known”.

How is it made? 

The new knot assembles itself from a solution that contains four strands of carbon, nitrogen, and oxygen atoms. When they are mixed with iron and chloride ions in a heated solvent, the atomic threads form the basic shape of the knot. The ends of each strand are then attached together to generate an uninterrupted loop of atoms. The metal and chloride ions can then be washed away, leaving behind only the knot. The team was unsure whether it would work, and would only find out when all components were mixed together. The good news was revealed by x-ray crystallography images, which displayed the breath-taking intricacy and symmetry of the knot.

What can it be used for? 

From the Anchor bend to the Zepellin loop, knots contain a rich history and an enormous variety, allowing their different shapes, sizes, and mechanics to be used in different scenarios. Although impressive, the circular triple helix is much more than just a demonstration of precise control. By studying how these strands of atoms are constructed and weaved, an entirely new domain of material science can be explored. For example, the comparable pentafoil knot, which Leigh had discovered in 2012, is very good at catalysing chemical reactions. “Knots should be just as important, versatile, and useful in the molecular world as they are in our everyday world,” Leigh said– although we probably don’t have to worry about shoelaces getting replaced by atomic strands anytime soon.

Gaia Stucky de Quay is a postgraduate researcher in Earth and Planetary Sciences

Banner Image: Knotted Rope, Roman Tsubin