[en] A class of sequestering agents has been designed and synthesized for the specific role of complexing plutonium and other actinide (IV) ions. The chemical properties of Pu(IV) and Fe(III) are similar in many respects and this similarity extends to the biological transport and distribution properties of Pu(IV). The design of specific sequestering agents for FE(III) was solved by microbes a few billion years ago with the production of low molecular-weight chelating agents (siderophores) that incorporate chelating groups such as hydroxamic acids and catechol. Synthetic macrochelates have been designed such that the chelating groups can form a cavity that gives eight-coordination about the metal and the dodecahedral geometry observed in the unconstrained actinide complexes composed of monomeric ligands. The most promising actinide sequestering agents yet prepared are the sulfonated catechoylamide derivatives of linear tetraamines. These compounds appear to strongly bind tetravalent actinides, while only weak complexation has been observed for trivalent and divalent metals. A derivative of the natural product spermine, 3,4,3-LICAMS, is more effective in plutonium removal at low dosages than any other sequestering agent tested to date