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

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.