Novel hydrophilic cationic receptors for binding the pertechnetate anion in aqueous solutions. Quantum-chemical modeling, synthesis, structure and properties

Abstract

Novel water-soluble dicationic pyridinium receptors were designed, synthesized, and evaluated as masking agents for the pertechnetate anion (TcO₄⁻) in nitric acid media relevant to nuclear fuel reprocessing. Quantum-chemical calculations revealed that binding of the pertechnetate anion by these receptors involves not only electrostatic interactions, but also C–H⋯O hydrogen bonding and n → π* interactions, which determine the mutual spatial orientation of the ion pairs. A series of more than thirty new receptors was synthesized and fully characterized. Selected perrhenate complexes as analogues of pertechnetate were isolated, and their structure was studied using single-crystal X-ray diffraction. Extraction experiments demonstrated that the receptors effectively suppress TcO₄⁻ transfer into organic phases in both TODGA/F-3 and TBP/kerosene systems. In the TODGA system, suppression factors up to 5–6 were achieved, depending on the receptor structure and concentration. In the TBP/kerosene system simulating the first cycle of the PUREX process, suppression factors of 2–2.5 were observed. These results highlight dicationic pyridinium salts as accessible and tunable scaffolds for the development of practical TcO₄⁻ receptors with potential applications in nuclear fuel cycle technologies.