University of Manchester scientists say they have tied the tightest molecular knot yet created, an achievement that could lead to development of lighter, stronger materials.

The achievement, announced in Science, builds on research by Prof. David Leigh and his group.

Eight-way molecular knot. Credit: Stuart Jantzen/Biocinematics.comLeigh and others have speculated on potential applications for knots and braids in advanced materials design. For example, braiding a material like silk thread increases its strength. By analogy, braiding polymer strands on a nanoscale level could produce super-strong or super-elastic materials. The type of knot used to tie a molecule could be fine-tuned to yield specific material characteristics.

The new knot has eight crossings in a 192-atom loop. The largest previous knot, also created by the Leigh Group, clocked in at five loops and 160 atoms.

The molecular knots are tied—actually braided-- using a technique called self-assembly. Molecular strands are woven around metal ions, in this case, four iron ions. The first step is forming a circular triple helicate. This mixture is heated, and the loose ends are tied together using chemical catalysis. Iron ions were removed from the completed knot.

Ongoing research will investigate behaviors of different types of knots.