Braiding a molecular knot

Abstract

Braiding—the interlacing of three or more strands—seems fairly straightforward, but as any parent of a long-haired child will tell you, it takes skilled hands to master the technique. Braiding a molecule poses an even greater challenge because no hands are nimble enough to entwine structures on such a small scale. Using iron atoms to guide their molecular building blocks, chemists have now constructed the first braided knot (Science 2017, DOI: 10.1126/science.aal1619). This new knot, crafted by David A. Leigh and coworkers at the University of Manchester, is considerably more complex than previous examples of molecular knots, which were based on just two twisted strands. Leigh’s group made the 192-atom knot with eight different crossing points by first assembling a circular triple helicate. Helicates are helical complexes that contain metal ions. In this case, four iron ions were used to coordinate three bipyridine moieties on four identical ligand strands. The chemists