A pair of linear and cyclic peptide-based trihydroxamate ligands (1 and 2) have been prepared through fragment condensation of suitably protected Ala-Ala-beta(HO)Ala units. These ligands have an eight-atom spacing between hydroxamic acid groups and compare in chain length with natural desferrioxamines of a nine-atom spacing. Ligands 1 and 2 form hexadentate octahedral complexes with iron(III), Fe(III)-1 and Fe(III)-2, in aqueous solution. The complexes show absorptions at lambda(max) 425 nm with epsilon ca. 2800, characteristic of a 1:3 iron(III) complex with a hydroxamato group. Absorption vs pH profiles give ranges of pH 4-9.5 and 6.7-8.7 for Fe(III)-1 and Fe(III)-2, respectively, where each of them exists as the 1:3 complex. The ligand protonation constants (pK(1) pK(2), pK(3)) are determined, and the stability constants [10(27) for Fe(III)-1 and 10(28) for Fe(III)-2] obtained are rather close to values of 10(30) s for ferrioxamines. However, the absorption vs pH profile for the complexes and their iron(III)-exchange kinetics with EDTA show that the iron(III)-holding capacity of these complexes is still lower than that of ferrioxamine B. The kinetic data indicate that Fe(III)-2 holds iron more tightly than Fe(III)-1. The alanine residues exert their chiral influence on the coordination. Fe(III)-1 and Fe(III)-2 reveal large negative and positive Cotton effects at 445 and 360 nm in their CD spectra, showing that the complexes are preferentially in the Delta configuration around the metal ion. Thus, it is concluded that the Ala-Ala-beta(HO)Ala sequence is a useful unit for making chiral ligands which form stable iron(III) complexes of well-defined structure.