Reductive activation of neptunyl and plutonyl oxo species with a hydroxypyridinone chelating ligand

Abstract

Oxo group activation with reduction of neptunyl(vi) and plutonyl(vi) to tetravalent hydroxo species by the hydroxypyridinone siderophore derivative 3,4,3-LI-(1,2-HOPO) was investigated in the gas-phase via electrospray ionization mass spectrometry, in solution via Raman spectroscopy, and computationally via density functional theory. Dissociation of the gas-phase tetravalent complexes resulted in actinide-hydroxo bond cleavage.

Controlling the Reduction of Chelated Uranyl to Stable Tetravalent Uranium Coordination Complexes in Aqueous Solution

“…Multidentate hydroxy­pyridinone (HOPO) and catecholamide (CAM) ligands are known to chelate both actinide (An) and lanthanide (Ln) cations exceptionally well both in vitro and in vivo , ,, and have been shown to be effective decorporation agents of trivalent and tetravalent actinides in multiple animal models. ,, The octadentate 3,4,3-LI­(1,2-HOPO) (Scheme ), denoted 343-HOPO hereafter, was designed for tetravalent plutonium (Pu) chelation, , and has proven exemplary for coordinating a range of tetravalent p-, d-, and f-block metals. − Moreover, it has been shown to significantly increase excretion in vivo of actinyl species such as U VI and Np V , although the mechanism for these latter findings is not well understood. The coordination chemistry and solution thermodynamics of [UO 2 ] 2+ -343-HOPO binding have been investigated in several studies, revealing that 343-HOPO binding with hexavalent uranium is less thermodynamically favorable than that of other targets such as Pu IV . ,, We recently observed 343-HOPO chelation-driven activation and concurrent reduction of the neptunyl­(V) cation to Np IV , , and here we extended these efforts to investigate whether a similar chelation-induced reduction mechanism could occur in uranium systems.…”

“…The coordination chemistry and solution thermodynamics of [UO 2 ] 2+ -343-HOPO binding have been investigated in several studies, revealing that 343-HOPO binding with hexavalent uranium is less thermodynamically favorable than that of other targets such as Pu IV . 10,18,23 We recently observed 343-HOPO chelation-driven activation and concurrent reduction of the neptunyl(V) cation to Np IV , 22,24 and here we extended these efforts to investigate whether a similar chelation-induced reduction mechanism could occur in uranium systems. The chemically-mediated reduction of U, from +VI to +IV, is known in synthetic schemes, 25−27 biological systems, 28 and the environment, 29 yet the reduction is complicated by the known instability of U IV in the presence of molecular oxygen.…”

Structural Snapshots of Cluster Growth from {U6} to {U38} During the Hydrolysis of UCl4

“…The presence of 24 U(IV) ions results in a +96 positive charge balanced by 2 hydroxo, 30 oxo, 4 chloride and 30 benzoate groups. 5, U-µ4O=2.36(6), U-µ3OH=2.37 (5).…”

“…[1c] [3] The chemistry of these species is also important for the understanding of geochemical reactions and for the development of new remediation strategies. [1c, 3c, 4] [5] Notably, discrete clusters have been isolated from hydrolysis and condensation reactions of low valent actinides in aqueous condition in the presence of anionic ligands such as halides or carboxylic acids. [1c, 6] However, the chemistry of uranium oxide clusters remains underdeveloped especially compared to transition metal polyoxometalates.…”

Hydroxypyridinone-Based Metal Chelators towards Ecotoxicity: Remediation and Biological Mechanisms

“…L27 was found to be able to promote oxo group activation via gas-phase chelation with the reduction in hexavalent NpO 2 2+ and PuO 2 2+ to tetravalent bis-hydroxo complexes. In this way, new actinyl complexes can be obtained by gas-phase two-electron actinyl reduction, otherwise not obtainable due to synthetic limitations [ 70 ]. The reduction in the NpO 2 2+ /Np 4+ redox pair (from +6 to +4), upon chelation with L27 or with the bis-catecholamide analogue 3,4,3-LI(CAM) 2 (1,2-HOPO) 2 ( L28 ), was observed to be nearly instantaneous by X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) [ 71 ].…”