3,4,3-LI(1,2-HOPO), the not-so innocent f-element chelator | Poster Board #1414

The remarkably strong chelation of tetravalent f-elements by 3,4,3-LI(1,2-HOPO), denoted HOPO herein, lies at the center of research efforts in fields spanning from radiopharmaceuticals to fundamental f-element chemistry. This is most notably observed in the recent use of HOPO as: (1) a radionuclide decorporation drug, (2) a ligand that facilitates the spontaneous oxidation-state adjustment of specific f-elements (i.e. Ce, Np, and Bk), and (3) an aqueous holdback agent in spent nuclear fuel reprocessing schemes. Despite the routine use of HOPO in these applications, which expose the ligand to a slew of strong redox agents, including metabolites, radicals, and unstable oxidation states of chelated metals, there is a lack of knowledge regarding the fundamental redox behavior of HOPO and its f-element complexes. To this end, a range of electrochemical and analytical techniques were leveraged to assess the redox behavior of HOPO and its f-element complexes. The non-innocent nature of HOPO in Ce(IV/III)-HOPO complexes is discussed and the mechanism of the oxidative degradation of HOPO is postulated. These findings undoubtedly impact the analysis of redox data related to HOPO, enabling prior and future data to be reinterpreted with new insight.