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

Abstract

The chemistry of trivalent transplutonium ions (Am3+, Cm3+, Bk3+, Cf3+, Es3+…) 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 Cf3+. Corroborating those results, density functional theory calculations, extended to Es3+, 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 [MIIIDTPA(H2O)]2− (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.

Electrochemical Studies of Selected Lanthanide and Californium Cryptates

“…This likely has broader consequences in terms of addressing Cf II chemistry. It is now known that Cf−L bonds are shorter than expected, 29,90 and rather than possessing an effective ionic radius similar to that of Gd III as originally predicted, it now appears that the effective radius parallels smaller lanthanides like Er 3+ . 90 The ionic radius of Cf II remains unknown, and it appears that extrapolating from the size of Ln II cations is unwise.…”

“…It is now known that Cf−L bonds are shorter than expected, 29,90 and rather than possessing an effective ionic radius similar to that of Gd III as originally predicted, it now appears that the effective radius parallels smaller lanthanides like Er 3+ . 90 The ionic radius of Cf II remains unknown, and it appears that extrapolating from the size of Ln II cations is unwise. Thus, it is apparent that, if cryptands are to be employed to stabilize Cf II , they will likely need to be smaller than 2.2.2-cryptand.…”

Uncovering Heavy Actinide Covalency: Implications for Minor Actinide Partitioning

“…52,53 From previous experimental and theoretical reports, it is likely that covalency driven preferential bonding to actinides over lanthanides by certain ligands is a key marker in choosing extractants for minor actinide partitioning. Though a considerable amount of work has been done on the separation of minor actinides (Am, Cm) from lanthanides, there are only few reports [11][12][13]18,46 in the literature involving complexation of heavy actinides, particularly, Bk and Cf, because of their radiological toxicity and close chemical similarities with heavy lanthanides.…”

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

“…It bears three tertiary amines and five sterically unconstrained carboxylic acids that can coordinate metal ions or be used as functionalization handles. 22,23 The DTPA chelate has been widely used in nuclear chemistry due to the fact that it forms stable coordination compounds with various metal ions including indium 24 (formation constant log β = 29.0−29.5), yttrium 24 (log β = 21.2−22.5), gallium 24 (log β = 25.5), and lanthanides like gadolinium 25 (log β = 22.46). 22,23,[26][27][28][29][30][31][32] Inradiolabeled antibodies that incorporated the DTPA chelate have received clinical approval for SPECT imaging.…”

“…22,23 The DTPA chelate has been widely used in nuclear chemistry due to the fact that it forms stable coordination compounds with various metal ions including indium 24 (formation constant log β = 29.0−29.5), yttrium 24 (log β = 21.2−22.5), gallium 24 (log β = 25.5), and lanthanides like gadolinium 25 (log β = 22.46). 22,23,[26][27][28][29][30][31][32] Inradiolabeled 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.…”