Impact of Oxoanion on Formation and Dissolution of Iron Mineral: Implication in Understanding the Ferritin Core

Abstract

Iron, a crucial element, is inextricably intertwined in various stages of living and non-living systems. Its existence in two different oxidation states (Fe 2+ /Fe 3+ ) is not only a virtue but also troublesome (low solubility of Fe3+ at neutral pH and Fenton’s reaction by Fe 2+ ). As a solution to this essentiality and toxicity dilemma, nature devised a globular multimeric protein nanocage: ferritin, to detoxify and store iron in soluble ferrihydrite bio-mineral form. Bio-minerals of native ferritins are associated with variable amounts of phosphate depending upon their source (Pi : Fe ~0.1 in animals, and Pi : Fe ~0.5 -1.0 in plant/bacteria). Whether the occurrence of a low Pi : Fe ratio in animal ferritins is just a coincidence or a consequence of ferritin electrostatics at the pore/cage is not well understood. Moreover, the natural selectivity of phosphate over other oxoanion is intriguing. Similar to phosphate other oxoanions may stabilize Fe3+ to modulate the redox and optoelectronic properties of bare and ferritin-encapsulated ferrihydrite minerals. Therefore, a comparison of bare and protein-encapsulated oxoanion-doped iron minerals may give insights into the impact of oxoanion on the structure, stability, and reactivity of iron bio-mineral. So a detailed investigation was performed on a series of oxoanion-doped ferrihydrite which closely resembles, the iron mineral found in nature. The physicochemical properties of oxoanion doped iron mineral were compared to justify their percentage incorporation by natural selection.