Controlled release of a -blocker from its silica host has been investigated by solid state NMR spectroscopy. 

Propranolol was the first successful -blocker to be developed and it is widely used in the treatment of hypertension and other heart conditions. Hubert Koller's group at the Westfälische Wilhelms University, Münster, Germany encapsulated propranolol in a silica gel host. The drug molecules are anchored to the silica using non-covalent interactions, such as hydrogen bonds and van der Waals forces. 

The group then investigated these interactions using 2D heteronuclear chemical-shift correlation (HETCOR) NMR techniques allowing the neighbourhoods between all the silicon sites and proton species in the material to be mapped. 

Controlled drug delivery, using host-guest matrixes, can make a drug more efficient and effective. The nature of the interactions between the guest molecule and the host matrix are important factors in the release of the guest from the host. 

The studies show that the hydrophobic parts of the silica gel interact more favourably with the Propranolol guest. 'This is, to the best of our knowledge, the first study of this kind,' Koller said, adding that it may allow the area of controlled drug release 'to advance more quickly in improving control of the drug release rate'. However, he admitted that for real applications 'there is a still a long way to go'.

Ruth Doherty