A group of chemists has designed what must be the world’s smallest bottle: a carbon cage that can hold just a single water molecule.

Many researchers have used the carbon spheres called fullerenes to surround molecules. An international team has now taken the crucial next step and designed a ‘stopper’ that can plug an open fullerene but can also be removed to allow a molecule of water in and out. In the future such ‘molecular vials’ could be used to transport radioactive atoms or small molecules for medical purposes such as imaging, they suggest.

The team behind the advance – reported in Angewandte Chemie – have previously reported the synthesis of the main part of their molecular vial. This involves modifying the classic Carbon-60 form of fullerene to create an orifice big enough for water to pass through.

Now they show that a phosphate group can be easily attached and removed from the edge of the orifice and acts as a plug for the fullerene vial. With the stopper in place, water is encapsulated into the carbon cage at a far slower rate than with it detached.

The design “works perfectly as a lockable molecular container for a single water molecules”, write Wim Klopper of the Karlsruhe Institute of Technology, Liangbing Gan of Peking University in Beijing, and their colleagues. Or in other words, the world’s smallest water bottle.

Image: Angewandte Chemie