IRON(III) REDUCTION BY D-GALACTURONIC ACID .3. INFLUENCE OF THE PRESENCE OF ADDITIONAL METAL-IONS AND OF 2-AMINO-2-DEOXY-D-GLUCONIC ACID

The effects of the presence of an aminosugar, namely 2-amino-2-deoxy-D-gluconic acid, on the reduction of iron(III) to iron(II) by D-galacturonic acid when copper(II), uranyl(VI), lead(II), nickel(II) or cadmium(II) ions are also present in the solution have been investigated. Lowering of the yield in iron(III) reduction has been found at any time in the cases of those metals whose addition to the system iron(III)-D-galacturonic acid favours iron(II) formation. Stoichiometries and stability constants of the complexes formed in the binary systems comprising one of the above-mentioned metal ions and the aminosugar ligand, as well as in the ternary systems with D-galacturonic acid as additional ligand, have been preliminarily determined by potentiometry. Relations between the compositions of the systems and the results of the kinetic tests have been suggested. The importance of similar reduction-complexation processes in the mobilization and consequent bioavailability of iron in biological systems, in particular at the root-soil interface, is emphasized.