STRUCTURE OF AN IRON CORE ANALOG OF FERRITIN

The structure of a synthetic ferritin-like polymer of approximate composition Fe4O3(OH)4- (NO3)2 ·1.5H2O has been investigated using X-ray scattering from aqueous solution, infrared and Möss- bauer spectroscopy, and magnetic susceptibility measurements. The ferric ions are all tetrahedrally coordinated by O2-, OH-, and H2O in a corner-sharing bridged structure, with Fe-O-Fe bond angles of 125 ± 30°. The nitrate ions are not coordinated directly to the iron, but act only as counterions to the positively charged polymer spheres. As with natural ferritin, the Mössbauer spectrum of the synthetic iron polymer has a paramagnetic doublet spectrum above 77°K and a magnetic hyperfine-split spectrum at 5°K, while in the range 40-70°K, both spectra appear simultaneously, as expected for superparamagnetic particles. The magnetic susceptibility demonstrates that the 70-A spheres of the synthetic polymer are antiferrmagnetic with a Néel point above 300°K, and a blocking temperature of 8°K. © 1968, American Chemical Society. All rights reserved.