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+.
Highlights
Copper (Cu) and iron (Fe) are essential metals for plants, animals and humans, ensuring their normal biochemical and physiological functions [1,2]
We have recently explored a small family of compounds, namely bifunctional bidentate 3,4-HP ligands, with the aim of improving their lipophilic–hydrophilic balance, bioavailability and affinity towards biological membranes, Molecules 2021, 26, 7280 and UV–Vis (Ultraviolet–Visible) spectrophotometric investigation on the interaction of five bifunctional 3‐hydroxy‐4‐pyridinones (Figure 1) with Cu2+ and Fe3+, metal cations with a borderline and a hard character, respectively, that are 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 the speciation schemes featured by metal-ligand species with different stoichiometry and stability, due 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 an aqueous solution
Summary
Copper (Cu) and iron (Fe) are essential metals for plants, animals and humans, ensuring their normal biochemical and physiological functions [1,2]. In humans and other mammals, iron is a fundamental constituent of myoglobin and haemoglobin, proteins able to transport oxygen along the body It is important for the normal functions of hormones and cells, being the cofactor of many enzymes, like in cytochromes B5, C and P450 [8]. Since its disclosure and later approval [16,17], many 3,4HP derivatives, have been developed with the aim of overcoming some DFP drawbacks and efficacy improving [3] Following this strategy, we have recently explored a small family of compounds, namely bifunctional bidentate 3,4-HP ligands, with the aim of improving their lipophilic–hydrophilic balance, bioavailability and affinity towards biological membranes, Molecules 2021, 26, 7280 and UV–Vis (Ultraviolet–Visible) spectrophotometric investigation on the interaction of five bifunctional 3‐hydroxy‐4‐pyridinones (Figure 1) with Cu2+ and Fe3+, metal cations with a borderline and a hard character, respectively, that are carried out at I = 0.15 mol L−1 in NaCl(aq), T = 298.15 K and 310.15 K. The equilibrium constants, concentrations and ionic strengths are expressed in the molar (c, mol L−1) concentration scale
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