A remarkably selective nano-capsule has been created by chemists from Japan. The nanocapsule has two cavitand molecules bound to silver ions to form the 'top' and 'bottom' parts and has an internal cavity with a volume of around 580 ų.   

Takeharu Haino and colleagues at Hiroshima University found that while a variety of similar aromatic compounds fitted into the host cavity, some were incorporated up to 200 times more strongly. They think this is due to the complementary shape of the guest molecule as well as hydrogen bonding interactions. 

When mixtures of a benzoic acid derivative and acetic or propanoic acid were added to the complex, dimers with the acetic acid only were selectively formed inside the cavity. This exclusivity offers the possibility to encapsulate specific pairs of molecules from mixtures or even stabilise unstable reaction intermediates. 

Haino hopes to continue the work to create supramolecular nano-size architectures via non-covalent bonds.   

Neil Withers