Scientists have braided a molecule into a knot with eight crossings, the most complex yet made in the lab.

Credit: Jean-Francois Lemonnier/Univ. Manchester

Flexible polymers can twist themselves into complex knots, but scientists have struggled to create all but the simplest structures. David Leigh and his colleagues at the University of Manchester, UK, weaved three organic strands — totalling 192 atoms — around four iron ions to assemble a tight knot with eight crossings (pictured). Bipyridine groups embedded in the strands bonded to each ion at three points to hold the structure in place.

Such techniques should enable the creation of more complex knots, which could be used to produce new kinds of tough, flexible material.

Science 355, 159–162 (2017)