Mode of iron(III) chelation by hexadentate hydroxypyridinones.

Tripodal hexadentate hydroxypyridin-4-ones are increasingly utilised as iron(III) and gallium(III) ligands, their attachment to proteins being particularly useful for positron emission tomography (PET). A widely studied tripodal ligand NTA(BuHP)3, which is reported to form 1:1 iron(III) and gallium(III) complexes in aqueous, media forms 2:2 complexes under physiological conditions. This important difference has implications for both iron chelation therapy and PET imaging.