Spectroscopic and Computational Characterization of Diethylenetriaminepentaacetic Acid/Transplutonium Chelates: Evidencing Heterogeneity in the Heavy Actinide(III) Series

Abstract

The chemistry of trivalent transplutonium ions (Am , Cm , Bk , Cf , Es …) is usually perceived as monotonic and paralleling that of the trivalent lanthanide series. Herein, we present the first extended X-ray absorption fine structure (EXAFS) study performed on a series of aqueous heavy actinide chelates, extending past Cm. The results obtained on diethylenetriaminepentaacetic acid (DTPA) complexes of trivalent Am, Cm, Bk, and Cf show a break to much shorter metal-oxygen nearest-neighbor bond lengths in the case of Cf . Corroborating those results, density functional theory calculations, extended to Es , suggest that the shorter Cf-O and Es-O bonds could arise from the departure of the coordinated water molecule and contraction of the ligand around the metal relative to the other [M DTPA(H O)] (M=Am, Cm, Bk) complexes. Taken together, these experimental and theoretical results demonstrate inhomogeneity within the trivalent transplutonium series that has been insinuated and debated in recent years, and that may also be leveraged for future nuclear waste reprocessing technologies.

Contemporary Chemistry of Berkelium and Californium

“…The ligand, which is the only approved drug treatment for internal contamination with actinides, provides coordination through nitrogen and oxygen donors as shown in Figure . As found in the simpler aforementioned systems, there is a drop in coordination number through loss of a water molecule, and the observation of contracted Cf−O bonds versus other cations complexed by DTPA . These data led the researchers to conclude that Er III provided a better bond length match for Cf III than larger Ln III cations.…”

“…[56] versus other cationsc omplexed by DTPA. [58] These data led the researchers to conclude that Er III provided ab etter bond length match for Cf III than larger Ln III cations.…”

Synthesis and Photochemical Studies on Gallium and Indium Complexes of DTPA-PEG3-ArN3 for Radiolabeling Antibodies

“…22,23 The DTPA chelate has been wildly used in nuclear chemistry due to the fact that it forms stable coordination compounds with various metal ions including, indium 24 25 (log b = 22.46). 22,23,[26][27][28][29][30][31][32] Several 111 In-radiolabelled antibodies that incorporated the DTPA chelate have received clinical approval for SPECT imaging. These include 111 In-satumomab pendetide for the diagnosis of colorectal and ovarian carcinomas 33 , and 111 In-capromab pendetide for prostate cancer therapy.…”

Ultra-selective ligand-driven separation of strategic actinides

“…Bk and Cf are produced via prolonged neutron irradiation of Am/Cm targets, yielding mixtures of actinides from Am to Fm and some fission products 5 . These transplutonium elements have traditionally displayed very similar chemistries as they exhibit the +III oxidation state in solution and have almost identical ionic radii 44 . To separate Cf 3+ from Bk 3+ , Bk 3+ can eventually be oxidized to Bk 4+ under harsh conditions (heating combined with excess NaBrO 3 in 8 M HNO 3 ) but it is unstable, which adds another level of complications to the eventual separation scheme.…”

“…Finally, the separation method was tested at the mCi level. Legacy samples of 249 Bk/ 249 Cf used in previous studies 44,47 were gathered, evaporated, incinerated and reconstituted in 3 M HNO 3 solutions containing multiple mCi of 249 Bk with a Cf/Bk ratio of ~3.4 mol/mol. The solution was split in five, 343HOPO was added, and an extraction step was performed using TODGA.…”