SYNTHESIS OF INORGANIC NANOPHASE MATERIALS IN SUPRAMOLECULAR PROTEIN CAGES

THERE is currently great interest in the synthesis of inorganic materials of nanometre dimensions. The small size of these particles endows them with unusual structural and optical properties that may find application in catalysis and electro-optical devices. Such materials may also prove valuable as precursor phases to strong ceramics. Many approaches to the synthesis of these materials have focused on constraining the reaction environment through the use of surface-bound organic groups 1, polymers 2,3, porous glasses 4,5, zeolites 6, phospholipid vesicles 7,8 and reverse micelles 9. Nanometre-sized particles may also be produced in vivo by microorganisms 10. Here we describe a novel synthetic route based on the use of a supramolecular protein structure as a reaction cage in which to form inorganic phases. We show that the iron-storage protein ferritin can be used to generate nanometre-sized iron sulphide particles by in situ reaction of the iron oxide core of the native ferritin. Discrete nanoscale particles of manganese and uranium oxo-species can also be formed in the protein cavity. Our results highlight the potential of adapting natural biomineralization processes to problems in materials science, and suggest that the use of biological molecules and their synthetic analogues in mediating solid-state reactions constitutes a promising approach to nanophase engineering.