Ferrihydrite Particle Encapsulated within a Molecular Organic Cage.

Metal oxides with sizes of a few nanometers show variable crystal and electronic structures depending on their dimensions, and the synthesis of metal oxide particles with a desired size is a key technology in materials science. Although discrete metal oxide particles with an average diameter ( d) smaller than 2 nm are expected to show size-specific properties, such ultrasmall metal oxide particles are significantly limited in number. In nature, on the other hand, nanosized ferrihydrite (Fh), which is ferric oxyhydroxide, occurs as a result of biomineralization in ferritin, an iron storage protein cage.