The Role of Inorganic Phosphate in Iron Oxide Biomineralization
The involvement of inorganic phosphate in the formation of biogenic iron-oxides such as ferrihydrite (5Fe2O3·9H2O) in the iron-storage protein ferritin and goethite (α-FeOOH) in the radula teeth of the limpet Patella vulgata is discussed from a chemical perspective. The structural characteristics and spatial distribution of biominerals in these systems has been studied by high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray analysis (EDXA), proton-induced X-ray emission (PIXE) analysis and Mössbauer spectroscopy. The results indicate that phosphate is an important component in the mediation of these solid state processes, for example, in the regulation of structural and redox states, and nucleation and growth phenomena. Phosphate-rich domains in limpet teeth and bacterial ferritin are non-crystalline whereas the absence or low level of phosphate results in the deposition of crystalline phases. Phosphate interactions also influence the morphology, magnetic properties and composition of these biominerals. A general rationalization of phosphate-iron-oxide interactions is presented based on the results of chemical studies in vitro. Several possible roles for phosphate are identified; (a) crystal growth inhibition, (b) crystal growth mediation (morphological enhancement, microcrystalline states), (c) kinetic stabilization with respect to phase transformation (dynamic behaviour in homeostasis), (d) solubility control via complexation, and (e) redox control over Fe(II) oxidation and reductive dissolution of Fe(III) oxides.
KeywordsHigh Resolution Transmission Electron Microscopy Reductive Dissolution Mossbauer Spectrum High Phosphate Content Crystal Growth Inhibition
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