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April 2017

Chemists tie tightest-ever knot

Self-assembly around metal ions

Scientists at the University of Manchester have produced the most tightly knotted physical structure ever known – a scientific achievement that has the potential to create a new generation of advanced materials.

The researchers, led by Professor David Leigh in Manchester’s School of Chemistry, have developed a way of braiding multiple molecular strands, enabling tighter and more complex knots to be made than has previously been possible.

The breakthrough knot has eight crossings in a 192-atom closed loop – which is about 20 nanometres long.

Being able to make different types of molecular knots means that scientists should be able to probe how knotting affects strength and elasticity of materials, which will enable them to weave polymer strands to generate new types of materials.

Leigh said: ‘Tying knots is a similar process to weaving so the techniques being developed to tie knots in molecules should also be applicable to the weaving of molecular strands.

‘For example, bulletproof 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.

‘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.’

Leigh explained that they ‘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.

The research was published in Science (doi:10.1126/science.aal1619)


Interwoven polymer strands have the potential to be more flexible than materials such as carbon fibre composite (shown).

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