Thermal decomposition of ferritin core

Abstract

Ferritin is an iron storage protein found in living organisms. It is an antiferromagnetic nanoparticle system consisting of an inorganic core surrounded by a protein shell. Ferritin is characterized by X-ray diffractometer, transmission electron microscope, atomic absorption spectrometer and thermogravimetric analyzer. We find that the ferritin core is poorly crystalline, 8 nm in size and consists of 10 wt% iron. It is believed that cores of ferritin consist of single-phase inorganic mineral ferrihydrite. Recently, we have shown that ferrihydrite decomposes directly to $\alpha$-$\hbox {Fe}_{{2}}\hbox {O}_{3}$ on heating in air at 440 $^{\circ }$C. In the present work, we show that ferritin cores gradually decompose to a mixture of $\gamma$-$\hbox {Fe}_{{2}}\hbox {O}_{{3}}$ and $\alpha$-$\hbox {Fe}_{{2}}\hbox {O}_{{3}}$ on heating in air. This mixture finally stabilizes to $\alpha$-$\hbox {Fe}_{{2}}\hbox {O}_{{3}}$ on further heating. The magnetic behaviour of final sample is also studied. This work confirms that the ferritin cores contain more than one phase.