A Macrocyclic Chelator with Unprecedented Th⁴⁺ Affinity

A novel macrocyclic octadentate ligand incorporating terephthalamide binding units has been synthesized and evaluated for the chelation of Th4+. The thorium complex was structurally characterized by X-ray diffraction and in solution with kinetic studies and spectrophotometric titrations. Dye displacement kinetic studies show that the ligand is a much more rapid chelator of Th4+ than prevailing ligands (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid and diethylenetriaminepentaacetic acid). Furthermore, the resulting complex was found to have a remarkably high thermodynamic stability, with a formation constant of 1054. These data support potential radiotherapeutic applications.