SYNTHESIS, STRUCTURE AND MAGNETIC-PROPERTIES OF FERRITIN CORES WITH VARYING COMPOSITION AND DEGREES OF STRUCTURAL ORDER - MODELS FOR IRON-OXIDE DEPOSITS IN IRON-OVERLOAD DISEASES

The cage-like protein ferritin was used to form nanoscale iron-contain ing mineral particles in vitro with different structures and compositi ons by reconstituting the metal-free protein (apoferritin) with iron a t different temperatures and in the presence of different quantities o f phosphate, The products of reconstitution were studied with inductiv ely coupled plasma spectrometry, transmission electron microscopy, ele ctron diffraction, extended X-ray absorption fine structure analysis, and Mossbauer spectroscopy. Reconstitution at 4 degrees C resulted in poorly ordered core structures while reconstitution at 55 degrees C re sulted in more ordered structures based on that of the mineral ferrihy drite. The more ordered structure of the 55 degrees C ferritin resulte d in stronger magnetic exchange interactions between the iron atoms wi thin each core and a larger magnetic anisotropy energy per core. Incor poration of phosphate within the core structure reduced the core densi ty. This also reduced the strength of the magnetic exchange interactio ns between the iron atoms. High levels of phosphate within the core re sulted in cores with no measurable periodicity within their structure. This in turn caused a reduction in the magnetic anisotropy energy per core. The ability to tailor the degree of structural order and phosph ate content of ferritin cores in vitro makes available a range of mode l materials for a more comprehensive study of the structural and magne tic correlations found in nanoscale iron biominerals in vivo such as n ative ferritins and haemosiderins deposited in iron-overloaded tissues .