Ferric iron, chelation

Rothman, R. J. Serroni, A. Farber, J. L. Cellular pool of transient ferric iron, chelatable by deferoxamine and distinct from ferritin, that is involved in oxidative cell injury. Mol. Pharmacol. 42 ... 

Coelichelin, D-hfOrn-D-aHo-Ihr-L-hOrn-D-hfOrn, a tris-hydroxamate 4-peptide discovered by Streptomyces coelicolor genome mining. The ferric-iron-chelating peptide coelichelin contains, beside D-aHo-threo-nine, two unusual amino acid residues d-5-N-formyl-5-N-hydroxyornithine (D-hfOrn) and L-5-N-hydroxyornithine (L-hOrn) [S. Lautm et al.. Nature Chem. Biol. 2005, 1, 265]. 

The classical gravimetric determination of iron now finds little application in pharmaceutical work, partly because of the readiness with which other ions are adsorbed on to the precipitate but principally because of the variety of titrimetric methods which are available. Oxidising titrants are the most widely used and these may be applied directly to ferrous iron or, after suitable reduction, to ferric iron. Reducing titrants also find some application for the direct titration of ferric iron. Chelating titrants such as EDTA may be used but, because of the formation of a highly coloured complex and because other rapid titrimetric methods are already available, these are unlikely to find routine application. 

The function of the chelant is to prevent the formation of insoluble iron compounds without interfering with the ability of the iron to undergo reduction and oxidation. In the absorption step, the sour gas stream containing hydrogen sulfide comes in contact with a liquid containing a soluble ferric iron chelate, Fe L. The hydrogen sulfide forms sulfide and hydrosul-fide ions, which are selectively oxidized to form elemental sulfur, and the ferric chelate, Fe L, is reduced to the corresponding ferrous chelate, Fe L. 

Where a stable, passivated magnetite film exists, there is little risk of corrosion when using these products, and under normal alkaline boiler conditions (above a pH of 10.0), the chelation of ferric iron [Fe(OH)3, Fe203, Fe304] does not take place (so the protective magnetite film is not disrupted). 

NOTE Although control over transported iron is critical in larger power boilers, as discussed earlier, control by the chelation of ferric iron is not possible (because of the competing anion effect). Consequently, Fe203 and Fef04 are essentially unaffected by chelants. However, it is well known that where an iron chelate (chelonate) is formed, it is stable and will not be destroyed by hydrolysis at high temperature. 

F. Awad, V. Romheld, and H. Marschner, Mobilization of ferric iron from a calcareous soil by plant-borne chelators (phytosiderophores). J. Plant Niitr. // 70l (1988). 

While much is known about siderophore-mediated ferric-iron transport, very little is known about ferrous-iron transport and iron metabolism inside the cell. It is generally assumed that Fe3+ chelated to the siderophore must be reduced to allow removal from the strong claws of the chelator. Indeed, in some cases the siderophore transported iron was found 30 minutes later in the intracellular Fe2+ pool of the cells (Matzanke et ah, 1991). 

Due to their capacity to specifically chelate ferric iron, siderophores have been used for chelation therapy to treat iron overload diseases . ... 

In the Mehansho et al. experiment, the potential for ascorbic acid to solubilize Fe was reported to be limited to low pH environments. Other investigators have reported that ascorbic acid facilitates iron absorption by forming a chelate with ferric iron at an acidic pH that remains soluble at the alkaline pH of the duodenum (Lynch and Cook, 1980). Salovaara... 

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