PG5 could store drugs within its complex, tree-like folds (Image: Angewandte Chemie)

Meet PG5, the largest stable synthetic molecule ever made.

With a diameter of 10 nanometres and a mass equal to 200 million hydrogen atoms, this huge molecule festooned with tree-like appendages, paves the way to sophisticated structures capable of storing drugs within their folds, or bonding to a wide variety of different substances.

Complex macromolecules abound in nature and PG5 is about the same size as tobacco mosaic virus. But making such large molecules in the lab is tough, as they tend to fall apart while they are being made.


“Synthetic chemistry so far was simply not capable of approaching the size range of such functional units,” says Dieter Schlüter at the Swiss Federal Institute of Technology in Zürich. Previously, polystyrene was the largest stable synthetic molecule, at 40 million hydrogen masses.

To create their molecular giant, Schlüter and his colleagues started with standard polymerisation, in which smaller molecules join up to form a long chain. To this carbon and hydrogen backbone, they added branches made of benzene rings and nitrogen, as well as carbon and hydrogen.

They then performed several similar cycles, adding sub-branches to each existing branch, to build tree-like structures. The result was PG5. In total, the whole synthesis required 170,000 bond formations, Schlüter says.

Outrageous trick

Klaus Mullen of the Max Planck Institute for Polymer Research in Mainz, Germany, is impressed by the feat and calls it an “outrageous” trick.

To synthesise PG5, Schlüter combined standard polymerisation reactions, which assemble small molecules into a long chain or backbone, with reactions from other areas of organic chemistry which attached groups of atoms to the backbone in a radial fashion.

Schlüter says that because both techniques are standard, his team’s work should encourage other researchers to create synthetic macromolecules that they were previously “not brave enough” to attempt.

He says molecules like PG5 could find applications in delivering drugs, which could either dock to their surface via the different branches, or nestle in the spaces produced by the molecule folding in on itself. “There is not a single entity that can challenge the loading capacity of our PG5,” he says.

Journal reference: Angewandte Chemie, DOI: 10.1002/anie.201005164

Image captions have been edited since this article was first posted.