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Structural characterization of Am(III) and Pu(III)-DOTA complexes

Audras, M.; Berthon, L.; Berthon, C.; Guillaumont, D.; Dumas, T.; Illy, M. C.; Martin, N.; Zilbermann, I.; Ben-Eliyahu, Y.; Moissev, Y.; Bettelheim, A.; Camelli, S.; Hennig, C.; Moisy, P.

The complexation of DOTA ligand (1,4,7,10-tetrazacyclodecane-1,4,7,10-tetraacetic acid) with two trivalent actinides (Am3+ and Pu3+) was investigated by UV-visible spectrophotometry, Nuclear Magnetic Resonance (NMR) spectroscopy and extended X-ray absorption fine structure (EXAFS) in conjunction with computational methods. The complexation process of these two cations is similar to what has been previously observed with lanthanides(III) of similar ionic radius. The complexation takes places in different steps and ends up with the formation of a (1:1) complex [(An(III)DOTA)(H2O)]- where the cation is bonded to the nitrogen atoms of the ring, the four carboxylate arms and a water molecule is completing the coordination sphere. Nevertheless, the formation of An(III)-DOTA complexes is faster than the Ln(III)-DOTA systems of equivalent ionic radius. Furthermore, it is found that An-N distances are slightly shorter than Ln-N distances. Theoretical calculations have shown that the slightly higher affinity of DOTA toward Am over Nd is correlated with slightly enhanced Ligand-to-metal charge donation arising from oxygen and nitrogen atoms.

Keywords: DOTA; UV-visible spectrophotometry; NMR; EXAFS; DFT calculations; Americium; Plutonium; lanthanides

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Publ.-Id: 25773