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

Abstract

The binding ability of five bifunctional 3-hydroxy-4-pyridinones towards Cu2+ and Fe3+ 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 Cu2+ and Fe3+ behaviour in aqueous solution. Furthermore, the sequestering ability and metal chelating affinity of the ligands were investigated by the determination of pL0.5 and pM parameters at different pH conditions. Finally, a comparison between the Cu2+ and Fe3+/3-hydroxy-4-pyridinones data herein presented with those already reported in the literature on the interaction of Zn2+ and Al3+ with the same ligands showed that, from the thermodynamic point of view, the 3-hydroxy-4-pyridinones are particularly selective towards Fe3+ 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 Cu2+ and Zn2+.

Hydroxypyridinone-Based Metal Chelators towards Ecotoxicity: Remediation and Biological Mechanisms

“…Bifunctional 3-hydroxy-4-pyridinones ( L1 – L5 , Figure 2 ), featured by a single 3,4-HP chelating core and various functional groups attached to the pyridinone moiety by different N -alkyl spacers, were synthesized and thermodynamically evaluated as possible strong chelators of hard metal cations of environmental relevance (Al 3+ , Fe 3+ ) [ 7 , 8 ], using potentiometric and spectrophotometric techniques; the potential thermodynamic competition, and eventually depletion, of other hard (Ca 2+ , Mg 2+ ) and borderline (Zn 2+ , Cu 2+ ) character metals of environmental interest was also evaluated [ 8 , 9 , 10 ]. The main experimental conditions chosen by the authors was I = 0.15 M in NaCl (aq) and T = 298.15 K. Sodium chloride was selected as ionic medium, since it is the main inorganic constituent of many natural fluids [ 11 , 12 ], or it can also be found in soils as contaminant (saline soils) [ 13 ].…”

“…The main experimental conditions chosen by the authors was I = 0.15 M in NaCl (aq) and T = 298.15 K. Sodium chloride was selected as ionic medium, since it is the main inorganic constituent of many natural fluids [ 11 , 12 ], or it can also be found in soils as contaminant (saline soils) [ 13 ]. In some cases, studies at different ionic strengths ( I = 0.50–1.00 M) and temperatures ( T = 288.15–310.15 K) were reported, providing useful information for the determination of thermodynamic parameters allowing us to simulate the real conditions of natural fluids and other environmental matrices [ 8 , 9 , 10 ].…”

“…Comparisons between the different M n+ /mono-3,4-HP systems [ 7 , 8 , 9 , 10 ], and also with the literature data reported for deferiprone (3-hydroxy-1,2-dimethyl-pyridin-4(1 H )-one, dmmp, DFP, L8b , Figure 3 ) [ 14 ], widely diffused as hard metals chelating agent, were performed based on the pM parameter (pM = −log [M n+ ], for c Metal = 1 μM and c Ligand = 10 μM) [ 15 ], to gain information on the ligands affinity towards the different metal cations, as reported in Table 1 . In the literature, the pL 0.5 parameter [ 16 ], indicating the total concentration of ligand required to sequester the 50% of M n+ if present in trace (10 −6 μM) in the solution, was proposed to compare the sequestering ability of 3-hydroxy-4-pyridinones towards one or more metal ions.…”

“…In the literature, the pL 0.5 parameter [ 16 ], indicating the total concentration of ligand required to sequester the 50% of M n+ if present in trace (10 −6 μM) in the solution, was proposed to compare the sequestering ability of 3-hydroxy-4-pyridinones towards one or more metal ions. The pL 0.5 calculation can find applications for the remediation of polluted systems, in processes of water treatment and in the activities involving the employment of a chelating agent, since the knowledge of the ligand concentration to be used can be useful for optimization of the working conditions [ 8 ].…”

“…The five mentioned bifunctional mono-(3-hydroxy-4-pyridinones) ( L1 – L5 , Figure 2 ), were developed and tested as chelators of several metal ions (Al 3+ [ 7 ], Fe 3+ , Cu 2+ [ 8 ], Zn 2+ [ 10 ], Ca 2+ , Mg 2+ [ 9 ]) and the sequestering ligands are featured by carboxylic ( L1 ), amide-amino-carboxylic ( L2 , L3 ), amino-carboxylic ( L4 ) and amino ( L5 ) groups in the N -alkyl chain attached to the pyridinone ring. L1 was proposed as a good aluminum(III) chelating ( Table 1 ) and sequestering agent (pL 0.5 = 6.3 (Al 3+ ), 4.8 (Cu 2+ ), 2.5 (Zn 2+ ), <1.0 (Ca 2+ )), excluding the possibility of an effective ligand M 2+ chelation instead of the Al 3+ remediation.…”