To gain knowledge about biological iron mobilization, tripodal monotopic and ditopic hydroxamate ligands (1 and 2) are prepared, and their iron-chelating properties are investigated. Ligands I and 2 contain three Ala-Ala-beta-(HO)Ala units and three [Ala-Ala-beta-(HO)Ala](2) units connected with tris(alanylaminoethyl)amine, respectively, and form six-coordinate octahedral complexes with iron(HI) in aqueous solution. Ligand 1 and I equiv of iron give Fe-1, and ligand 2 and I or 2 equiv of iron produce Fe-1-2, or Fe-2-2. These complex es exhibit absorptions at lambda (max) 425 nm of epsilon 2800-3000/Fe, characteristic of tris(hydroxamato)iron(III) complexes, and preferentially assume the Delta -cis configuration. Loading of Fe(III) on 1, 2, and M(III)-loaded ligands (M-1 and M-1-2, M = Al, Ga, In) with ammonium ferric oxalate at pH 5.4 is performed, and the second-order rate constants of loading with respect to Fe(III) and the ligand or M(Hl)-loaded ligands are determined.. The rates of loading of Fe(III) on M-1 increase in the order Al-1 < Ga-1 < In-1, and those on M-1-2,in the order Al-1-2 < Ga-1-2 < Fe-1-2 < In-1-2, indicating that the dissociation tendency of M(III) ions from the hydroxamate ligand is an important factor. The iron complexes formed with 2 are subjected to an iron removal reaction with excess EDTA in aqueous pH 5.4 solution at 25.0 C, and the collected data are analyzed by curve-fitting using appropriate first-order kinetic equations, providing the rate constants for the upper site and the lower site of 2. Similar analysis for FeM-2 affords removal rate constants for Fe-up-2, M-up-2, and Fe-low-2, and the iron residence probability at each site. The protonation constants of the hydroxamate groups for 1 and 2 (pK(1), pK(2), pK(3), and pK(1), pK(2)..., pK(6)) are determined, and the proton-independent stability constants for Fe-1, the upper site of Fe-2-2, and the lower-site of Fe-1-2 are 10(28), 10(29), and 10(28.5), respectively.