Not a normal knot

Much like a piece of string, molecules can be manipulated into knotted topologies, usually by templating using metal ions and specific binding sites along a molecular chain. The coordination number of the bound metals determines topology, which means that only one knot per molecule is usually possible. Now, David Leigh and colleagues report a molecular strand that can be knotted and unknotted into two different topologies, depending on the complexing metal ion used (copper or a lanthanide). Additionally, depending on the order of the metal ion’s coordination and its displacement, translocation of an entangled region of the strand to another region occurs, increasing the topological strain in the new knotted conformation. This forms a knot more dynamic than previous examples, suggesting that there may be more freedom in molecular design, and functionality in molecular knots, than previously thought.