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.