Challenges of the element with atomic number 85: strengthening the metal-astatide bond by complex formation with triazacyclononane ligands

Astatine has only radioactive isotopes, which strongly limits its application possibilities. Its major use appears in nuclear medicine, where the isotope 211 At has a sincere potential for targeted alpha therapy (TAT). The development of stable carriers for this application is under active research. The present paper contributes to this field by probing selected chelate complexes using density functional theory (DFT) calculations. In these molecules At is bonded to a metal ion captured by the chelator ligand. In the study triazacyclononane-based macrocyclic chelators containing various pendant arms are probed with appropriate trivalent metals (Rh, Co, Y, Lu and Ir). The thermodynamic stabilities were assessed by computed dissociation energies. Trends in the structures were rationalized on the basis of the bonding properties evaluated with the natural energy decomposition method and topological analysis of the electron density distribution.