General ConsiderationsCaution: 254 Es (t 1/2 = 275.7 days, 70.9 TBq g −1 ) and 249 Cf (t 1/2 = 351 years, 150 GBq g −1 ) are highly radioactive, and decay to α-, β-and γ-emitting isotopes. These isotopes and their decay daughters present substantial health risks, and were manipulated only in facilities specifically designed for the safe handling of long-lived radioactive materials. All measurements were taken in controlled facilities and/or using multiple containment procedures.

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The octadentate siderophore analog 3,4,3-LI(1,2-HOPO), denoted 343-HOPO hereafter, is known to have high affinity for both trivalent and tetravalent lanthanide and actinide cations. Here we extend its coordination chemistry to the rare-earth cations Sc 3+ and Y 3+ and characterize fundamental metal-chelator binding interactions in solution via UV-Vis spectrophotometry, nuclear magnetic resonance spectroscopy, and spectrofluorimetric metalcompetition titrations, as well as in the solid-state via single crystal X-ray diffraction. Sc 3+ and Y 3+ binding with 343-HOPO is found to be robust, with both high thermodynamic stability and fast room temperature radiolabeling, indicating that 343-HOPO is likely a promising chelator for in vivo applications with both metals. As a proof of concept, we prepared a 86 Y-343-HOPO complex for in vivo PET imaging, and the results presented herein highlight the potential of 343-HOPO chelated trivalent metal cations for therapeutic and theranostic applications.