COORDINATION CHEMISTRY OF THE AMONABACTINS, BIS(CATECHOLATE) SIDEROPHORES FROM AEROMONAS-HYDROPHILA

The amonabactins are a series of four bis(catecholate) siderophores is olated from the pathogenic organism, Aeromonas hydrophila. As tetraden tate ligands, they cannot singly satisfy the octahedral coordination s phere of iron. The solution coordination chemistry of the amonabactins has been elucidated using potentiometric and spectrophotometric titra tions, circular dichroism, and mass spectroscopy. They form 2:3 metal: ligand complexes at high pH and excess Ligand. Their complexation beha vior is essentially identical to one another, with log beta(230) = 86. 3. At lower pH, they preferentially form a 1:1 bis(catecholato)bis(aqu a) iron(III) species, with log beta(110) = 34.3. The 2:3 complexes sho w a very slight Delta preference in chirality at the metal center, whi le the 1:1 complexes are achiral. The biological implications of these properties are discussed.