Ferritin Core Structure

The mineral phase of ferritin displays properties similar to the iron oxyhydroxide ferryhydrite which is widespread in nature. This mineral has been traditionally described as amorphous or colloidal ferric hydroxide - Fe(OH3) - due to its poor X-ray diffracting properties. The actual composition however, is Fe5HO8 • 4 H2O and recent X-ray absorption studies (Fe K-edge XANES and EXAFS spectroscopy) have shown that most of the Fe(III) ions are situated in identical, structurally well-defined coordination environments. A highly hydrated ferrihydrite slowly precipitates from Fe(III)-containing solutions at pH > 2 at room temperature. The Fe(III) hexaqua cations first oligomerize to yield chains of water-soluble poly-cations in which octahedrally coordinated Fe(III) ions are bridged by hydroxide anions. Further deprotona-tion and polymerization yield ferrihydrite, which, at close to its zero point of charge at pH 7-8, slowly and irreversibly dehydrates and rearranges to the thermo-dynamically more stable iron oxide hematite (a-Fe2O3). Although the details of the crystal structure and surface properties of ferrihydrite are still controversial, the current data support a structural model in which double chains of edge-sharing iron(III) octa-hedra are cross-linked via corners (Figure 2, top), similar to the essential structural elements of the mineral goethite (a-FeOOH). The dimensions of coherent X-ray scattering domains for synthetic ferrihydrite are within the range of 1-6 nm, which accounts for the characteristic broadening of X-ray diffraction lines. Temperature-dependent 57Fe Moss-bauer spectra of synthetic ferrihydrite and ferritin cores display identical features, indicating a super-paramagnetic behaviour of the crystalline phase at room temperature and below. Therefore synthetic ferrihydrite precipitates, as well as ferritin cores, may be better described as nanocrystals rather than nanocolloids.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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