Hexadentate β-Dicarbonyl(bis-catecholamine) Ligands for Efficient Uranyl Cation Decorporation: Thermodynamic and Antioxidant Activity Studies

The special linear dioxo cation structure of the uranyl cation, which relegates ligand coordination to an equatorial plane perpendicular to the O═U═O vector, poses an unusual challenge for the rational design of efficient chelating agents. Therefore, the planar hexadentate ligand rational design employed in this work incorporates two bidentate catecholamine (CAM) chelating moieties and a flexible linker with a β-dicarbonyl chelating moiety (β-dicarbonyl(CAM)₂ ligands). The solution thermodynamics of β-dicarbonyl(CAM)₂ with a uranyl cation was investigated by potentiometric and spectrophotometric titrations. The results demonstrated that the pUO₂²⁺ values are significantly higher than for the previously reported TMA(2Li-1,2-HOPO)₂, and efficient chelation of the uranyl cation was realized by the planar hexadentate β-dicarbonyl(CAM)₂. The efficient chelating ability of β-dicarbonyl(CAM)₂ was attributed to the presence of the more flexible β-dicarbonyl chelating linker and planar hexadentate structure, which favors the geometric arrangement between ligand and uranyl coordinative preference. Meanwhile, β-dicarbonyl(CAM)₂ also exhibits higher antiradical efficiency in comparison to butylated hydroxyanisole. These results indicated that β-dicarbonyl(CAM)₂ has potential application prospects as a chelating agent for efficient chelation of a uranyl cation.