Bifunctional 3-Hydroxy-4-Pyridinones as Potential Selective Iron(III) Chelators: Solution Studies and Comparison with Other Metals of Biological and Environmental Relevance

The binding ability of five bifunctional 3-hydroxy-4-pyridinones towards Cu(2+) and Fe(3+) was studied by means of potentiometric and UV–Vis spectrophotometric measurements carried out at I = 0.15 mol L(−1) in NaCl((aq),) T = 298.15 K and 310.15 K. The data treatments allowed us to determine speciation schemes featured by metal-ligand species with different stoichiometry and stability, owing to the various functional groups present in the 3-hydroxy-4-pyridinones structures, which could potentially participate in the metal complexation, and in the Cu(2+) and Fe(3+) behaviour in aqueous solution. Furthermore, the sequestering ability and metal chelating affinity of the ligands were investigated by the determination of pL(0.5) and pM parameters at different pH conditions. Finally, a comparison between the Cu(2+) and Fe(3+)/3-hydroxy-4-pyridinones data herein presented with those already reported in the literature on the interaction of Zn(2+) and Al(3+) with the same ligands showed that, from the thermodynamic point of view, the 3-hydroxy-4-pyridinones are particularly selective towards Fe(3+) and could therefore be considered promising iron-chelating agents, also avoiding the possibility of competition, and eventually the depletion, of essential metal cations of biological and environmental relevance, such as Cu(2+) and Zn(2+).