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 . But making such large molecules in the lab is tough, as they tend to fall apart while they are being made.
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鈥淪ynthetic chemistry so far was simply not capable of approaching the size range of such functional units,鈥� says at the Swiss Federal Institute of Technology in Z眉rich. Previously, polystyrene was the largest stable synthetic molecule, at 40 million hydrogen masses.
To create their molecular giant, Schl眉ter 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, Schl眉ter says.
Outrageous trick
of the Max Planck Institute for Polymer Research in Mainz, Germany, is impressed by the feat and calls it an 鈥渙utrageous鈥� trick.
To synthesise PG5, Schl眉ter 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.
Schl眉ter says that because both techniques are standard, his team鈥檚 work should encourage other researchers to create synthetic macromolecules that they were previously 鈥渘ot brave enough鈥� 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. 鈥淭here is not a single entity that can challenge the loading capacity of our PG5,鈥� he says.
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Image captions have been edited since this article was first posted.
