Specific Sequestering Agents for the Actinides: 4. Removal of 238 Pu(IV) from Mice by Sulfonated Tetrameric Catechoyl Amides

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Abstract
The similar chemical properties of Fe3+ and Pu4+, small ionic size, high charge and high acidity, and the great stability of the complexes of Fe3+ with ligands secreted by microorganisms, specifically those containing the catechoyl (o-dihydroxybenzoic acid) functional group, imply tetracatechoyl ligands would be efficient in vivo sequestering agents for Pu4+. Cyclic (CY) and linear (LI) tetracatechoyl amides (CAM) connected by ethylene, propylene and/or butylene bridges were synthesized and administered i.p. to mice (20-30 .mu.mol/kg) 1 h after injection of about 1.5 .mu.Ci/kg of 238Pu4+ citrate. The mice were killed 24 h after the 238Pu injection and the 238Pu in tissues and excreta was measured by using the L X-rays. The prototype CAM ligand, 3,3,3,3-CYCAM, bound circulating 238Pu4+, but the complex could not be excreted. Sulfonation of the benzene rings produced ligands (CAMS) that were soluble in water and stable to air oxidation. The linear 3,3,3-LICAMS was more efficient than its cyclic analog, 3,3,3,3-CYCAMS; 238Pu excretions were 44 and 35% of the injected dose, respectively. Lengthening the intergroup bridges to expand the metal coordination cavity (4,4,4-LICAMS or 3,4,3-LICAMS) increased 238Pu excretion to 65%; an equimolar amount of CaNa3DTPA [diethyltriaminepentaacetate, calcium trisodium salt] promoted 63% 238Pu excretion. The advantages of the CAMS ligands are low reactivity at pH 7 with divalent metals, their depletion is the cause of DTPA toxicity; moderate toxicity, all CAM ligands except 4,4,4-LICAMS were tolerated by mice at the dosage administered; and removal of some 238Pu already deposited in the skeleton, 3,4,3-LICAMS reduced skeletal 238Pu to 0.29 of the 1 h control value compared to a reduction to 0.56 by CaNa3DTPA.