Inorganic—Protein Interactions in the Synthesis of a Ferrimagnetic Nanocomposite

Abstract

The iron-storage protein ferritin provides a spatially constrained reaction environment within a catalytically active bio-polymer. These properties have facilitated the synthesis of a ferrimagnetic iron oxide-protein composite, formed by tailoring conditions for the synthesis of magnetite. The controlled partial oxidation of Fe(II), at high pH and elevated temperature, in the presence of apo-ferritin resulted in the formation of a colloidal composite with a narrow particle size distribution. This material combines characteristics of both the protein and the inorganic phase. Direct magnetic measurements indicated 13,100 Bohr magnetons per particle. Electron and x-ray diffraction data indicated the presence of a cubic iron oxide mineral phase but could not distinguish between magnetite and maghemite. Data from Mössbauer spectroscopy, measured both in the presence and absence of an applied field as well as at low temperature, suggested that the predominant mineral phase was maghemite rather than magnetite