ABSTRACT
Chemical and biochemical properties Pure iron is silver in appearance and melts at 1528∞C. Iron will readily combine with oxygen, the halogens, nitrogen, sulfur, and carbon on heating; all but the halogen compounds being of biological significance. Iron displays three oxidation states, the most stable being +3 (referred to as iron (III)); the +2 state is reducing (referred to as iron (II)), and the rare +6 state is extremely oxidizing (Sections G1 and I2). A simple chemical test for the presence of iron (III) ions in aqueous solution involves the use of potassium hexacyanoferrate (II); a dark blue precipitate known as Prussian blue forms:
K+ + [FeII(CN)6] 4-+ Fe3+ KI FeIII[FeII(CN)
Iron is most commonly found in the form of oxides and hydroxides, the latter being very poorly water soluble. Indeed under conditions of low soil pH (Section N3) a number of
plants have to obtain the iron they require for photosynthesis from synthetic organoiron complexes. Nevertheless in the body iron is essentially stored as particles of iron (III) hydroxide known as ferritin; these are surrounded by a protein coat and maintained until required in, for example, redox reactions (Section I2). In higher animals iron (III) is carried through the bloodstream by proteins called transferrins. In micro-organisms, iron solubilization and transport are achieved by low molecular weight proteins called siderophores.
