Braiding a molecular knot with eight crossings
Authors: Jonathan J. Danon, Anneke Krüger, David A. Leigh, Jean-François Lemonnier, Alexander J. Stephens, Iñigo J. Vitorica-Yrezabal, Steffen L. Woltering
Publication Date: 13 January, 2017
Department of: Chemistry
Tying the tightest knot
As every fisherman and sailor knows, different types of knots have different characteristics that make them more or less suited for a particular task: ‘bend knots’ give the strongest binding between two lengths of rope; ‘hitches’ are best for tying rope around an object; and ‘loop knots’, or ‘nooses’, allow degrees of movement between the components they connect. There is no reason to believe that different types of knots won’t be just as important, versatile and useful in the molecular world. But we can’t find out about that until we can make them.
Knots occur in DNA and approximately 1% of proteins, and they form spontaneously in polymer chains (just as happens with plates of spaghetti and headphone cables!). However, until now synthetic chemists have only been able to make the simplest types of molecular knot, such as trefoil (three crossing) and pentafoil (five crossing) knots. This is partly because the most widely used methods to make molecular knots twist two ligand strands around one another. The unavailability of all but the simplest molecular knots hinders the investigation of the effects of different knot types in materials and other molecular applications.
Now scientists at the University of Manchester have developed a way of braiding three molecular strands enabling tighter and more complex knots to be made than has previously been possible. The Manchester scientists made a molecular knot with eight crossings in a loop just 192 atoms long. The synthesis of the eight-crossing molecular knot illustrates a strategy (the braiding of three strands) that should be applicable to the synthesis of many more, and more diverse, types of molecular knots. By making different types of molecular knot we can find out about their properties (such as at which point are entangled molecular strands prone to breaking?) and which knots have properties best suited for a particular purpose, just as a fisherman or sailor knows which knot is best suited for each task.
- This is the most tightly knotted physical structure known (eight crossings in a thread just 20 nanometers long)
- The left-hand picture shows the precise molecular structure of the knot, which contains iron ions (shown in purple), oxygen atoms (red), nitrogen atoms (dark blue), carbon atoms (shown in metallic grey, with one of the building blocks shown in light blue) and a single chloride ion (green) at the centre of the structure.
- Chemists have 'braided' molecules to make the tightest knot ever - Forbes, 13 Jan 2017
- Knotty professors: chemists break world record to create tightest knot ever made - The Guardian, 12 Jan 2017
- Eight crossings and 192 atoms long: the tightest knot ever tied - The New York Times, 16 Jan 2017
- Molecules tied into beautiful 'octofoil' knot for first time - New Scientist, 12 Jan 2017
- Knot not easy to knot - Scientific American 60 Second Science (audio clip), 18 Jan 2017
- Twisted science: Tying the strongest molecular knot - Science Friday (US radio), 13 Jan 2017
- Scientists have twisted molecules into the tightest knot ever - Morning Edition, NPR (US radio), 12 Jan 2017