Stuart Jantzen/BioCinematics.com

Scientists Have Tied Molecules Into the Tightest Knot Ever Created

This is the key to making new materials.

FIONA MACDONALD
13 JAN 2017
 

Scientists have successfully manipulated strands of molecules to create the tightest physical knot ever, with eight crossings twisting molecules into a Celtic knot-structure.

That might not sound too impressive, but researchers have only ever managed to tie a few, very simple molecular knots to date. And figuring out how to make these braided formations will be the key to unlocking powerful new materials.

 

Just picture bullet-proof material that's as light and flexible as cotton. 

"Historically, knotting and weaving have led to all kinds of breakthrough technologies," one of the researchers, David Leigh, from the University of Manchester in the UK, told Nell GreenfieldBoyce at NPR.

Just think about clothes, fishing nets, even shoe laces - all inventions that came about thanks to our ability to tie knots.

"Knots should be just as important at the molecular level, but we can't exploit that until we learn how to make them, and that's really what we're beginning to do," added Leigh.

The first molecular knot was tied back in 1989 by chemist Jean-Pierre Sauvage, who went on to win last year's Nobel Prize in Chemistry for related work.

Sauvage's knot was the simplest knot possible - a 'trefoil knot' that looked kind of like a three-leaf clover. But it took scientists another 25 years to achieve another molecular knot.

 

They knew it was possible - mathematicians have predicted billions of possible molecular knots - but it's much harder to get chemicals to weave together than it sounds.

You can't just grab two molecules like shoelaces and wrap them around each other - you actually need to nudge chemicals to bond with each other in specific ways.

Over the past few years, Leigh and his colleagues, along with several other teams, have managed to produce a few more molecular knots - but they've been limited to two molecular strands, and little more than three crossings.

This latest knot is the tightest and most intricate yet. It looks a lot like a Celtic knot, with three strands, and eight crossings holding it together. Here it is in all its glory:

In order to create it, the researchers actually had to take three molecular braids, and get them to self-assemble in a test tube and tie themselves up into the structure. 

The 'rope' that they used was just 192 atoms long - or 500 times smaller than a red blood cell - and yet, they were able to put an unheard-of eight crossings in it, knitting the structure together into the tightest molecular knot ever created. 

To form these crossings, the team wrapped the molecular strands around metal ions to manipulate their formation.

"We 'tied' the molecular knot using a technique called 'self-assembly', in which molecular strands are woven around metal ions, forming crossing points in the right places just like in knitting - and the ends of the strands were then fused together by a chemical catalyst to close the loop and form the complete knot," explained Leigh in a press release.

"The eight-crossings molecular knot is the most complex regular woven molecule yet made by scientists."

The fact that the team is now able to take regular molecules and braid them together means we could be on the verge of creating materials with fascinating new properties.

For example, if we could learn to weave together the molecules in bullet-proof vests, we could develop materials that are lighter, more flexible, but even stronger than kevlar. 

"Bullet-proof vests and body armour are made of kevlar, a plastic that consists of rigid molecular rods aligned in a parallel structure - however, interweaving polymer strands have the potential to create much tougher, lighter and more flexible materials in the same way that weaving threads does in our everyday world," said Leigh.

"Some polymers, such as spider silk, can be twice as strong as steel so braiding polymer strands may lead to new generations of light, super-strong and flexible materials for fabrication and construction."

It could also lead to applications beyond what we can picture at the moment, seeing as knots also play an important role in the formation of DNA and proteins. 

"Knots are really fascinating objects or geometric shapes. They have always been around; you observe them in art, in nature. As a Boy Scout, you learn how to tie knots," chemist Rigoberto Advincula from Case Western Reserve University, who wasn't involved in the study, told NPR.

"It's one of the fascinating things to stretch chemistry in terms of your ability to make synthetic objects."

The research has been published in Science.

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