BIOMIMETIC SYNTHESIS AND CHARACTERIZATION OF MAGNETIC PROTEINS (MAGNETOFERRITIN)

A new synthesis of the magnetic protein magnetoferritin is reported. A ddition of increments of Fe(II) to anaerobic solutions of the demetala ted protein, apoferritin, at pH 8.6 and 65 degrees C, followed by stoi chiometric amounts of the oxidant trimethylamine-N-oxide (Me3NO), resu lts in the formation of a dispersed magnetic bioinorganic nanocomposit e. By limiting the Fe:protein ratio to not more than similar to 140 at oms/protein molecule and the Fe(II): Me3NO ratio to 3:2 in each increm ent, ferrimagnetic nanocrystals of magnetite/maghemite (Fe3O4)/(gamma- Fe2O3) are synthesized in the 8 nm diameter protein cage. Controlling the number of stepwise cycles of the Fe(II)/oxidant additions produces biomimetic proteins with different iron loadings (100, 260, 530, 1000 , 2040, and 3150 Fe atoms/protein molecule) and concomitant changes in the size of the inorganic nanocores. Magnetoferritins prepared with l e ss than 1000 Fe atoms/molecule were discrete nanocomposites with pro tein-encapsulated magnetic cores. Samples with higher iron loadings we re aggregated on the TEM grid and showed a progressive increase in the number of cores with dimensions greater than the protein cavity. The temperature-dependent magnetic properties of magnetoferritins with dif ferent Fe loadings were studied by SQUID magnetometry. An approximatel y linear dependence of the superparamagnetic blocking temperature with iron loading was determined.