Interaction between iron(II) and hydroxamic acids: oxidation of iron(II) to iron(III) by desferrioxamine B under anaerobic conditions

Interaction between iron(II) and acetohydroxamic acid (Aha), alpha -alanine hydroxamic acid (alpha -Alaha), beta -alaninehydroxamic acid (beta -Alaha), hexanedioic acid bis(3-hydroxycarbamoyl-methyl)amide (Dha) or desferrioxam ine B (DFB) under anaerobic conditions was studied by pH-metric and UV-Visi ble spectrophotometric methods. The stability constants of complexes formed with Aha, alpha -Alaha, beta -Alaha and Dha were calculated and turned out to be much lower than those of the corresponding iron(III) complexes. Stab ility constants of the iron(II)-hydroxamate complexes are compared with tho se of other divalent id-block metal ions and the Irving-Williams series of stabilities was found to be observed. Above pH 4, in the reactions between iron(II) and desferrioxamine B, the oxidation of the metal ion to iron(III) by the ligand was found. The overall reaction that resulted in the formati on of the tris-hydroxamato complex [Fe(HDFB)](+) and monoamide derivative o f DFB at pH 6 is: 2Fe(2+) + 3H(4)DFB(+) = 2[Fe(HDFB)](+) + H3DFB-monoamide( +) + H2O + 4H(+) Based on these results, the conclusion is that desferrioxa mine B can uptake iron in iron(III) form under anaerobic conditions. (C) 20 01 Elsevier Science B.V. All rights reserved.