Characterization of a Hexanuclear Plutonium(IV) Nanostructure in an Acetate Solution via Visible-Near Infrared Absorption Spectroscopy, Extended X-ray Absorption Fine Structure Spectroscopy, and Density Functional Theory

Chronicles of plutonium peroxides: spectroscopic characterization of a new peroxo compound of Pu(IV)

Although hydrogen peroxide (H2O2) has been highly used in nuclear chemistry for more than 75 years, the preparation and literature description of tetravalent actinide peroxides remain surprisingly scarce. A new insight is given in this topic through the synthesis and thorough structural characterization of a new peroxo compound of Pu(IV).

Investigation of the Plutonium(IV) Interactions with Two Variants of the EF-Hand Ca-Binding Site I of Calmodulin

Due to its presence in the nuclear industry and its strong radiotoxicity, plutonium is an actinide of major interest in the event of internal contamination. To improve the understanding of its mechanisms of transport and accumulation in the body, the complexation of Pu(IV) to the most common protein calcium-binding motif found in cells, the EF-hand motif of calmodulin, was investigated. Visible and X-ray absorption spectroscopies (XAS) in solution made it possible to investigate the speciation of plutonium at physiological pH (pH 7.4) and pH 6 in two variants of the calmodulin Ca-binding site I and using Pu(IV) in different media: carbonate, chloride, or nitrate solutions. Three different species of Pu were identified in the samples, with formation of 1:1 Pu(IV):calmodulin peptide complexes, Pu(IV) reduction, and formation of peptide-mediated Pu(IV) hexanuclear cluster.

Crystal Structures of Ce(IV) Nitrates with Bis(2-pyrrolidone) Linker Molecules Deposited from Aqueous Solutions with Different HNO3 Concentrations

We investigated the molecular and crystal structures of Ce(IV) compounds deposited under different [HNO₃] with bis(2-pyrrolidone) linker molecules having a trans-1,4-cyclohexyl bridging moiety (L). As a result, we found that, after loading L, Ce(IV) in HNO₃(aq) exclusively provides one of different crystalline phases, (HL)₂[Ce(NO₃)₆] or [Ce₂(μ-O)-(NO₃)₆(L)₂]_n 2D MOF, depending on [HNO₃]. The former has been obtained at [HNO₃] = 4.70-9.00 M and is isomorphous with the analogous (HL)₂[An(NO₃)₆] we reported previously. In contrast, the deposition of the latter phase at the lower [HNO₃] conditions (1.00-4.30 M) demonstrates that hydrolysis and oxolation of Ce⁴⁺ proceed even below pH 0 to provide a [Ce-O-Ce]⁶⁺ unit included in this compound. These different Ce(IV) phases are exchangeable with each other under soaking in HNO₃(aq), implying that chemical equilibria of dissolution/deposition of these crystalline phases and hydrolysis and oxolation of Ce⁴⁺ and its complexation with NO₃^- occur in parallel. Indeed, such coordination chemistry of Ce(IV) in HNO₃(aq) was well corroborated by ¹⁷O NMR, Raman, and IR spectroscopy.