Chemists in the US have provided verification of the structure of their acclaimed nanoscale Borromean rings, and suggest that they can now find practical applications for the rings.

The attractive Borromean ring motif, dating from the 15th century, is characterised by three inseparable, interlocked rings. Yet cutting one circle destroys all the remaining links. Fraser Stoddart and his group at the University of California, Los Angeles, were the first to design a completely synthetic molecular representation of the Borromean ring.  

The researchers have managed to remove zinc ion templates from their Borromean rings to produce the free structure, dubbed the Borromeand by Stoddart, who said, 'People were constantly asking, "Can you demetallate the complex?" Now we can say, "Yes, we can".' 

However, extracting the metal template from the complex can also make the rings fall apart - the reaction conditions cause one ring to be cleaved open, irreversibly. NMR spectroscopy and mass spectrometry confirm that this produces an unlocked mixture of released rings and their broken analogue. This is chemical proof that the complex has an intrinsic Borromean nature. 

David Leigh, an expert in functional molecular architectures at the University of Edinburgh, UK, explains: 'The Borromean ring assembly is probably the most impressive designed one- pot synthesis of any molecular structure.' He adds that the chemistry that Stoddart has now performed on this 'extraordinary molecule' is 'chemical proof of the molecular topology'. 

Stoddart describes the Borromean ring complex as a 'precisely defined nanoparticle with the opportunity to introduce functionality', suggesting that the Borromeand represents not only an elaborate molecule, but also has real potential for applications. 

Sula Armstrong