Design and Synthesis of Covalently Tethered "IsoG-Star" as Recyclable Host for Selective Cesium Separation

The isoguanosine self-assembled pentamer (isoG-star) has exhibited remarkable selectivity for Cs⁺ binding over competing alkali and alkali earth metal cation, rendering it a promising extractor for radioactive waste ¹³⁷Cs separation. However, to make isoG-star a pracrtical material for Cs⁺ isolation, the development of recyclable isoG-star material is required. In this study, a systematic screening of functional isoG derivatives was performed. By employing well-defined complex formation and post-assembly modification, a covalently tethered isoG₅-star was prepared through olefin metathesis, utilizing a designed isoG monomer. The application of this newly developed covalently linked isoG-star enabled selective Cs⁺ extraction, followed by controled solvent-induced H-bond dessociation. This resulted in the creation of a recyclable Cs⁺ extractor, demonstrating excellent cation selectivity and good reusability (over seven cycles) the first time. Consequently, this new supramolecular macrocycle offers a practical new platform for the treatment of radiocesium (¹³⁴Cs and ¹³⁷Cs) in an environmentally friendly and highly effective manner.