Credit: © 2006 ACS

There are a variety of weak intermolecular forces that can be used to direct the self-assembly of molecules into well-defined and organized structures. The hydrophobic effect — the process in which oily molecules or oily parts of molecules arrange themselves in water to minimize their contact with it — is of fundamental importance in nature and is responsible for the bilayer structure of cell membranes.

Now, Corinne Gibb and Bruce Gibb from the University of New Orleans in the USA have used the hydrophobic effect to drive the formation of molecular capsules that can trap small hydrocarbon gases in their interior1. They show that bowl-shaped molecules can come together in pairs — a process know as dimerization — to form capsules inside which propane or butane can be trapped. The dimerization process results from the stacking of hydrophobic aromatic groups along the rims of two face-to-face bowls. Moreover, this assembly only occurs in the presence of either propane or butane, which act as templates around which the capsule forms.

The affinity of the capsule for the hydrocarbons is so strong that they can be captured directly from the gas phase. Furthermore, competition experiments show that butane can be selectively trapped over propane, suggesting that this approach could be useful for the separation of structurally similar gases.