Molecular knots

The arrangement of the two most complex molecular knots yet made — a composite knot (left) and a catenane — is depicted by this diagram. Credit: Adapted from L. Zhang et al./Nature Chem.

Chemistry

The world’s most complex molecular knot ties up a record

Metal framework allows triple knot to be created in the lab.

Researchers have tied strings of molecules into a complicated knot whose strands cross one another nine times — an unprecedented feat.

In nature, a DNA molecule often takes the form of one large knot composed of smaller knots. But in the lab, such ‘composite knots’ are difficult to produce in a specific configuration.

To create a composite knot, David Leigh and his colleagues at the University of Manchester, UK, used six iron atoms as scaffolding. Around those atoms, the researchers wove six molecular strands that, between them, contained 324 atoms. The team carefully designed the strands to control their connections with the iron atoms.

This allowed the authors to join the strands’ 12 loose ends to form one of two different patterns. One was a composite knot made of three identical tangles; the second was a structure known as a catenane, which was composed of three twisted loops linked to each other. In both cases, the strands crossed each other nine times.

Synthesizing complex knots could aid in the study of processes such as the part knotted DNA plays in the spread of viruses, the authors write.