Thermodynamic considerations in co-ordination. Part XIX. In vitro studies of complexing equilibria involved in oral iron(II) therapy

Abstract

Formation constants are reported for adding protons and iron(II) ions to ligands currently in use as oral iron preparations (ascorbate, fumarate, and succinate). These constants have been used in computer models of solution equilibria in the small intestine in order to establish that iron(II)-absorption-promoting ligands preferably (i) have charge 2–, (ii) form uncharged 1 : 1 complexes, and (iii) might be low-molecular-weight polymers. These factors suggest a series of additional ligands that conceivably could possess improved absorption-promotion characteristics. Formation constants for these ligand–iron(II) complexes have been determined and the concentration distribution of these complexes over a range of physiological pH values computed, the most promising ligands being galacturonate and malate.