Actinium-225 (t1/2=10 d) is an extremely promising isotope for the treatment of metastatic cancers. During the decay of Ac-225 and daughters, a total of 4 alpha particles are emitted, which gives Ac-225 uniquely high cytotoxicity. However, the use of Ac-225 has been hindered by both the limited understanding of the fundamental chemistry of Ac and the insufficient supply. At Los Alamos National Laboratories (LANL), we have been part of the Tri-Lab project to develop an accelerator production capability using the proton irradiation of natural thorium. In addition to the production aspects, we have also been engaged in a cutting-edge research program focused on developing a wide variety of spectroscopic and physical techniques to interrogate the chemistry of Ac. Contrary to Ac-225, Ac-227 (t1/2=22 y) is available in microgram amounts enabling the use of traditional chemical techniques. We have developed multiple spectroscopic and theoretical approaches to help understand Ac coordination chemistry, including X-ray absorption fine structure (XAFS), electronic absorption, nuclear magnetic resonance (NMR), and fluorescence spectroscopies.<br/>While Ac-227 has a much lower specific activity than Ac-225, the strong alpha/beta/gamma emissions of the daughter products have necessitated the development of careful handling protocols, both at LANL and at the Stanford Synchrotron Radiation Laboratory (SSRL). Additionally, the limited supply of Ac-227 necessitates full recovery of all material, ruling out any destructive measurements. We will present our latest results on Ac coordination chemistry, involving the use of phosphonate armed crown ethers (DOTP). These results will be contrasted with trivalent lanthanides and actinides to determine some of the subtleties of Ac chemistry.

Spectroscopic studies of actinium coordination chemistry

255th National Meeting (2018)

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