Chelated forms of iron

For a 2 pm3 bacterial cell this amounts to just one free Fe34 ion in almost 100 million cells at any single moment. The importance of chelated forms of iron becomes obvious. It is also evident from Eq. 16-1 that, in addition to chelation, a low external pH can also facilitate uptake of Fe3+ by organisms. 

Sustained-release and chelated forms of iron (see above) have the advantage that poisoning is less serious if a mother s supply is consumed by young children, a real hazard. 

New forms of iron are now being considered by those who would seek to reduce the need for subsequent infusions. Such forms could include iron lignosite, which would increase the solubility and residence time of iron in the surface waters. Since this is a chelated form of iron, problems of rapid precipitation are reduced. In addition, iron lig-nosulfonate is about 15% Ee by weight, making it a space-efficient form of iron to transport. As yet untested is the extent to which such a compound would reduce the need for re-infusion. 

The intrinsic kinetics of the reactions taking place in the scrubber, i.e. the reaction of NO with the iron chelate forming an iron nitrosyl complex (eq. 1) and the undesired oxidation reaction of the iron chelate (xanpla (eq. 2) wae deteimined in dedicated stirred cell contactors. Typical process conditions were T = 25-55 °C [Fe"(EDTA) "] = 1-100 mol/m [NO] = 1-1000 ppm pH = 5-8 and an oxygen level ranging between 1 and 20 vol%. 

Levashkevich (1968) experimentally studied the ability of specific humic acids in several types of soils to form chelated compounds with ionic forms of iron (Fe " "). It was established that in the reactions of chelate formation Fe203 is bound with humic acids into compounds in which the iron loses the properties of an independent ion, and fulvic acids have higher complexforming capability than humic. The maximum amount of Fe that can be bound with fulvic acids reaches 650-711 mg per 1 g of organic matter, with humic acids, 119-152 mg. Chelated compounds of FcjOj with fulvic acids are considerably mobile, but solution of humate complexes occurs only in alkaline environments (at pH = V.3-7.7). In acid environments these com-... 

The foregoing discussion provides a basis for selection of a reliable indicator of iron availability. Figure 1 summarizes in schematic form the changes that occur as food moves through the digestive tract. The assumption is made that absorbable iron is present in the duodenum as a low molecular weight soluble chelate. It is further assumed that the other forms of iron that may be present do not contribute significantly to absorbable iron. 

Iron may be absorbed as the intact chelate or the chelate may transfer its iron to an acceptor on the mucosal cell surface. Absorption and exchange would be much more rapid with soluble forms of iron since insoluble forms would have limited contact with the mucosal cell surface. 

Organic Acids. Ascorbic acid has been most extensively studied and its absorption promoting property is well documented (Table V). Ascorbic acid has been shown to increase iron uptake in proportion to its concentration in the diet (29). Tea inhibited iron absorption from a corn-cereal diet, but supplementation with ascorbic acid overcame the inhibition (30). Ascorbic acid also increased the absorption of iron from fairly insoluble forms of iron such as rust and ferric hydroxide (30). Brise and Hallberg presented evidence that the absorption promoting effect of ascorbic acid was mainly due to reducing action within the lumen, preventing or delaying formation of less soluble ferric compounds (31). Conrad and Schade (32) found that ascorbic acid formed a soluble chelate with ferric chloride at an acid pH, but not at an alkaline pH. However, the acid iron chelate was stable and remained in a soluble form when the pH was raised. 

Often added as sodium silicate, this chelating agent is able to keep ferrous ions in solution and avoid their oxidation to the insoluble ferric form of iron. Silicate can therefore reduce the extent of red water iron discolouration problems. Silicate does not reduce the dissolution of lead, but it may reduce particulate lead problems arising from iron discolouration. 

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