Iron -citrate interactions

Interactions of Metal Salts with the Formation. Interactions of metal salts with the formation and distribution of the retained aluminum in a porous medium may significantly affect the location and strength of gels. This interaction was demonstrated with polyacrylamide-aluminum citrate gels [1514]. Solutions were displaced in silica sand. The major findings of this study are that as the aluminum-to-citrate ratio increases, the aluminum retention increases. Furthermore, the amount of aluminum retained by silica sand increases as the displacing rate decreases. The process is reversible, but the aluminum release rate is considerably slower than the retention rate. The amount of aluminum released is influenced by the type and the pH level of the flowing solution. The citrate ions are retained by silica sand primarily as a part of the aluminum citrate complex. Iron, cations, and some divalent cations cannot be used in the brine environment. 

FIGURE 16-10 Iron-sulfur center in aconitase. The iron-sulfur center is in red, the citrate molecule in blue. Three Cys residues of the enzyme bind three iron atoms the fourth iron is bound to one of the carboxyl groups of citrate and also interacts noncovalently with a hydroxyl group of citrate (dashed bond). A basic residue ( B) on the enzyme helps to position the citrate in the active site. The iron-sulfur center acts in both substrate binding and catalysis. The general properties of iron-sulfur proteins are discussed in Chapter 19 (see Fig. 19-5). 

A study in 6 patients found that neomycin markedly reduced the absorption of iron (iron as ferrous citrate) in 4 patients, but increased the absorption in the other 2 patients who initially had low serum iron levels. None of the patients were anaemic at any time. The importance of this is uncertain, but consider this possible interaction if the response to iron is poor. 

When galllum-67 is injected into the bloodstream as either chloride or citrate, it rapidly becomes bound to serum proteins, especially transferrin (5 53 54). Although the gallium-transferrin interaction is weaker than that of iron and... 

The electron-transferring iron-sulfur centers in the mitochondrial electron transfer chain are inaccessible to oxygen or NO for steric reasons. However, in iron-sulfur enzymes with non-redox roles [293, 294] it is frequently necessary for LMW compounds (e.g., citrate) to interact with the cluster and therefore, also NO access could not be prevented. These are generally [4Fe-4S] clusters in which three of the iron atoms have cysteine coordination, while the fourth is coordinated by inorganic sulfur. The substrate reacts at the non-cysteine coordinated iron. Most notable of these are mitochondrial and cytoplasmic aconitases. 

To establish the interaetion of the impregnating solutions with the surface of silica supports, Terorde measured the amount of water required to completely remove different iron salts applied onto the surface of silicagel in a column chromatograph [41], It appeared that an elution volume of water of 5.0 ml was required to remove the iron ammonium citrate, and of 6.2 ml to remove the Mohr s salt. Iron(III) chloride called for an elution volume of 6.3 ml, and iron(III) nitrate for a volume of 7.7 ml. Apparently, the iron species in the initially impregnated solution of iron ammonim citrate does not interact strongly with the silica surface. The relatively small interaction of the iron(III) complex of citric acid with the surface of silica indicates that the presence of the citric acid affects the adsorbed layer of water molecules that remains within the partially dried impregnated support. A thicker, less mobile layer of water molecules, citric acid anions, and iron(III) ions remains than without citric acid, where a layer of about six fairly mobile water molecules is present. 

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