Electronic and Magnetic Characterization of in vivo Produced vs. in vitro Reconstituted Horse Spleen Ferritin
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1056-HH03-27
Electronic and Magnetic Characterization of in vivo Produced vs. in vitro Reconstituted Horse Spleen Ferritin Georgia C. Papaefthymiou1,2, Arthur J. Viescas1, Eamonn Devlin2, and Athanassios 2 Simopoulos 1 2Physics, Villanova, Villanova, PA, 19085 Institute of Materials Science, NCSR Demokritos, Aghia Paraskevi, Greece ABSTRACT Magnetic nanophases nucleated within horse spleen apoferritin, under in vivo physiological conditions and in vitro reconstitution, were characterized by Mössbauer spectroscopy in lyophilized form. Mössbauer spectra at 80 K indicate that for the in vivo produced ferritin the presence of phosphates within the iron biomineral core results in larger quadrupole splittings, at interior and surface sites, 0.62 mm/s and 1.06 mm/s, respectively, as compared to 0.56 mm/s and 0.75 mm/s for the reconstituted ferritin. Data collected at lower temperatures give blocking temperatures of 55 and 40 K for in vitro and in vivo samples. At 4.2 K, both samples give similar hyperfine field values for the interior (495 kOe) and surface (450 kOe) iron sites. The temperature dependence of the hyperfine fields at the interior sites is consistent with the collective magnetic excitations model, due to the precession of the particle’s magnetization about the anisotropy axis. In contrast, a marked decrease in the hyperfine field at surface sites with increasing temperature indicates a more complex spin excitation energy landscape at the surface.
INTRODUCTION The study of the iron storage protein ferritin is of interest not only for its important physiological function [1], but also as a model system in biomimetic materials synthesis, fundamental studies in cluster nucleation and crystal growth processes [2] and the macroscopic quantum tunneling of magnetization [3]. Ferritin-inspired biocompatible nano-systems are of great current interest for a variety of bio-technological applications as directed drug delivery carriers [4], MRI enhancement agents [5], and magnetic separation agents in genomic and proteomic applications [6]. The biological function of ferritin is to maintain iron in an available non-toxic form. Its structure [1] presents 24 amino acid chains, of two types, L (light) and H (heavy), interlocked to form a robust spherical shell of interior diameter ca. 7 nm. The cavity is used for the storage and detoxification of iron in biological organisms ranging from bacteria to mammals. In addition, the protein exhibits enzymatic action for the reversible oxidation of ferrous ions (Fe2+) and the hydrolytic polymerization of ferric ions (Fe3+). The iron is stored in a compact antiferromagnetic biomineral form of ferrihydrite (5Fe2O3·9H2O). L-chain rich proteins seem to be associated with long term iron storage, while H-chain rich proteins participate more actively in iron metabolism through the function of their ferroxidase center [7]. Scheme 1 depicts a model of ferritin as proposed
Ferritin
Shell by Brooks et. al. [8] where a crystalline ferrihydrite core is surrounded by an amorphous ferrihydrite s
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