New Discovery: Molecular Knot with Only 54 Atoms Identified

Picture a knot so small that it's invisible to the naked eye, and then imagine something even smaller.

A team of chemists have successfully linked just 54 atoms to create the smallest molecular knot to date. The knot, mentioned in the January 2nd issue of Nature Communications, is a combination of gold, phosphorus, oxygen and carbon atoms, interlaced to form a three-crosses pretzel-like structure known as a trefoil. This new discovery breaks the previous record for the smallest molecular knot, which was made of 69 atoms and was reported in 2020.

The new knot was accidently created by chemist Richard Puddephatt and his colleagues from the Chinese Academy of Sciences in Dalian while they were trying to build interlocked ring molecules called catenanes. These complex structures could potentially be used in molecular machines - switches and motors operating at a molecular level. Currently, however, scientists are still trying to understand the inner workings of these catenanes which in this case, lead to the unintentional creation of an entirely new molecular structure.

Puddephatt, from the University of Western Ontario in London, Canada, describes it as a fortunate discovery in scientific research which comes as a welcome surprise after many setbacks and challenges.

This new trefoil knot is not only the smallest, but it's also the tightest of its kind. The tightness is calculated by a ratio known as the backbone crossing ratio, or BCR. This is obtained by dividing the number of atoms in the chain by the number of chain intersections. The lower the BCR, the tighter the knot. The newly created knot has a BCR of 18, which surpasses the previous smallest trefoil knot with a BCR of 23.

The exploration of small molecular knots may open doors to the discovery of new materials in the future. However, at present, the team is focused on understanding why this particular mix of atoms forms a knot.