Radiolytic Evaluation of 3,4,3-LI(1,2-HOPO) in Aqueous Solutions

The octadentate hydroxypyridinone ligand 3,4,3-LI(1,2-HOPO) (abbreviated as HOPO) has been identified as a promising candidate for both chelation and f-element separation technologies, two applications that require optimal performance in radiation environments. However, the radiation robustness of HOPO is currently unknown. Here, we employ a combination of time-resolved (electron pulse) and steady-state (alpha self-radiolysis) irradiation techniques to elucidate the basic chemistry of HOPO and its f-element complexes in aqueous radiation environments. Chemical kinetics were measured for the reaction of HOPO and its Nd(III) ion complex ([Nd^III(HOPO)]⁻) with key aqueous radiation-induced radical transients (e_aq^-, H^• atom, and ^•OH and NO₃^• radicals). The reaction of HOPO with the e_aq^- is believed to proceed via reduction of the hydroxypyridinone moiety, while transient adduct spectra indicate that reactions with the H^• atom and ^•OH and NO₃^• radicals proceeded by addition to HOPO’s hydroxypyridinone rings, potentially allowing for the generation of an extensive suite of addition products. Complementary steady-state ²⁴¹Am(III)-HOPO complex ([²⁴¹Am^III(HOPO)]⁻) irradiations showed the gradual release of ²⁴¹Am(III) ions with increasing alpha dose up to 100 kGy, although complete ligand destruction was not observed.