Plutonium sequestering agents: Their chemistry and biological evaluation

The biological hazard posed by plutonium is caused by the combination of its relatively high specific activity as an alpha emitter (239Pu) and its chemical similarity to iron. As a trace contaminant much of the plutonium distribution and long-term storage in mammals is a result of its incorporation into iron transport and storage sites. This has led to the development of synthetic complexing agents intended to be specific for plutonium based on the ligand functionalities found in siderophores (low molecular weight complexing agents of microbial origin that have a high affinity and specificity for ferric iron and are utilized as iron uptake agents for bacteria and other microbes). The existing treatment for plutonium incorporation involves DTPA (diethylenetriaminepentaacetic acid); however, this complexing agent is not particularly specific for actinide(IV) ions and removes many other physiologically important metals ions, such as calcium and zinc. The goal has been the rational synthesis of sequestering agents specific for plutonium, utilizing its similarity to ferric iron to prepare octadentate ligands that can completely encapsulate the large plutonium(IV) ion, most commonly found in an 8-coordinate environment. Such octadentate ligands were initially based on the incorporation of 4 catechol moieties. Subsequent ligand designs have included the incorporation of hydroxamate, terephthalamide and hydroxypyridone functional groups, in several combinations. The more recently synthesized ligands are described and their biological properties and efficacy of plutonium removal (from mice as test animals) are described. Following the animal test protocol, 90% of the plutonium remains in the control (untreated) mouse. Only 10--15% of the plutonium remains after one administration of the most effective sequestering agents