In a feat that breaks one of the most obscure world records in science, a team of chemists has created a microscopic circular triple helix, or put in more simple terms, the tightest knot ever made.

Researchers in Manchester in the UK built the knot from a strand of atoms which curls around in a triple loop and crosses itself eight times. Made from 192 atoms linked in a chain, the knot is only two millionths of a millimetre wide – around 200,000 times thinner than a human hair.



The construction of the knot is more than a demonstration of the precise control with which chemists can now manipulate objects on the atomic scale. In learning how to weave with strands of atoms, scientists hope to make possible a whole new world of materials.



“We know how revolutionary knotting and weaving were for people in the stone age. It had an impact on clothing, tools, fishing nets and so on. Maybe we’ll see just as great advantages from being able to do this with molecular strands,” said David Leigh, a professor of chemistry at the University of Manchester.



Facebook Twitter Pinterest X-ray crystal structure of a molecular knot with eight crossings. Credit: Robert W. McGregor/ www.mcgregorfineart.com

The tightness of a knot is defined by the distance between points where the rope, string – or chain of atoms, in this case – cross each other. For the Manchester group’s circular triple helix, each crossing point is a mere 24 atoms apart. “That’s very, very tight indeed,” said Leigh. “It is definitely the most tightly knotted physical structure known.”



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Building molecular knots has become something of a passion for Leigh. The latest knot beats the record his own team set four years ago when they created a so-called pentafoil knot from 160 atoms. That knot bested an even earlier effort called a trefoil knot with three crossing points. “There are actually billions of different knots known to mathematicians,” Leigh said in a comment that hinted at a busy future.



The new knot, designed and built with research associate Jonathan Danon and others, assembles itself from a solution that contains four strands of carbon, nitrogen and oxygen atoms. When mixed with iron and chloride ions in a heated solvent, the atomic threads form the basic shape of the knot in about a day. In a second step, the ends of each strand are fused together to make a continuous loop of atoms. The metal and chloride ions are then washed away, leaving only the knot behind.

Facebook Twitter Pinterest Assembly of a molecular knot. Photograph: David Leigh, University of Manchester

“These strands we are knotting are so small that you can’t grab the ends and tie them like you would a shoelace. Instead we use a chemical process called self assembly, where we mix the organic building blocks with ions that the building blocks then wrap around to make crossing points in the right places,” Leigh said.



The scientists designed the knot with help from computers and pipe cleaners, but until they mixed all the components together, were unsure whether it would work. The confirmation they hoped for came in x-ray crystallography images that revealed the exquisite symmetry of the molecular knot. “It’s a beautiful structure,” Leigh said.



The scientists have already found a use for the pentafoil knot they made in 2012. In recent work, it became clear that the knotted backbone of the pentafoil structure made it a good catalyst for chemical reactions.



“Knots should be just as important, versatile and useful in the molecular world as they are in our everyday world,” Leigh said. “But if we can’t tie different sorts of knots, we won’t know what those properties are and how to make use of them.”