[en] The 1,4,7,10‐tetrazacyclodecane‐1,4,7,10‐tetraacetic acid (DOTA) aqueous complex of U with HO, OH, and F as axial ligands was studied by using UV/Vis spectrophotometry, ESI‐MS, NMR spectroscopy, X‐ray crystallography, and electrochemistry. The U-DOTA complex with either water or fluoride as axial ligands was found to be inert to oxidation by molecular oxygen, whereas the complex with hydroxide as an axial ligand slowly hydrolyzed and was oxidized by dioxygen to a diuranate precipitate. The combined data set acquired shows that, although axial substitution of fluoride and hydroxide ligands instead of water does not seem to significantly change the aqueous DOTA complex structure, it has an important effect on the electronic configuration of the complex. The U/U redox couple was found to be quasi‐reversible for the complex with both axially bonded HO and hydroxide, but irreversible for the complex with axially bonded fluoride. Intriguingly, binding of the axial fluoride renders the irreversible one‐electron U/U oxidation of the [U(DOTA)(HO)] complex quasi‐reversible, which suggests the formation of the short‐lived pentavalent form of the complex, an aqueous non‐uranyl chelated UV cation. (© 2020 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Journal
Chemistry (Weinheim. Internet); ISSN 1521-3765; 
; v. 26(15); p. 3390-3403
; v. 26(15); p. 3390-3403
[en] The complexation of 1,4,7,10-tetraaza-cyclodecane-1,4,7,10- tetraacetic acid (DOTA) ligand with two trivalent actinides (Am3+ and Pu3+) was investigated by UV-visible spectrophotometry, NMR spectroscopy, and extended X-ray absorption fine structure 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 place in different steps and ends 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 to complete the coordination sphere. 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 showed 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. (authors)
Journal
Inorganic Chemistry; ISSN 0020-1669; ; v. 56; p. 12248-12259
; v. 56; p. 12248-12259
[en] Targeted α therapy holds tremendous potential as a cancer treatment: it offers the possibility of delivering a highly cytotoxic dose to targeted cells while minimizing damage to surrounding healthy tissue. The metallic α-generating radioisotopes 225Ac and 227Th are promising radionuclides for therapeutic use, provided adequate chelation and targeting. In this work, we demonstrate a new chelating platform composed of a multidentate high-affinity oxygen-donating ligand 3,4,3-LI(CAM) bound to the mammalian protein siderocalin. Respective stability constants log β110= 29.65 ± 0.65, 57.26 ± 0.20, and 47.71 ± 0.08, determined for the EuIII(a lanthanide surrogate for AcIII), ZrIV, and ThIVcomplexes of 3,4,3-LI(CAM) through spectrophotometric titrations, reveal this ligand to be one of the most powerful chelators for both trivalent and tetravalent metal ions at physiological pH. The resulting metal-ligand complexes are also recognized with extremely high affinity by the siderophore-binding protein siderocalin, with dissociation constants below 40 nM and tight electrostatic interactions, as evidenced by X-ray structures of the protein:ligand:metal adducts with ZrIV and ThIV. Finally, differences in biodistribution profiles between free and siderocalin-bound 238PuIV-3,4,3-LI(CAM) complexes confirm in vivo stability of the protein construct. The siderocalin:3,4,3-LI(CAM) assembly can therefore serve as a lock to consolidate binding to the therapeutic 225Ac and 227Th isotopes or to the positron emission tomography emitter 89Zr, independent of metal valence state.
Journal
Inorganic Chemistry; ISSN 0020-1669; ; v. 55(22); p. 11930-11936
; v. 55(22); p. 11930-11936
[en] Since the past few years, Pu(V) has gained much attention due to its potential contribution to the environmental migration of actinides. However, the preparation of concentrated (up to mM) and pure Pu(V) solutions is quite difficult and often hindered by its great instability towards disproportionation, thus limiting the accessibility to physical and chemical property data. This work describes the rapid and facile sonochemical preparation of relatively stable Pu(V) solutions in the millimolar range free from the admixtures of the other oxidation states of plutonium. The mechanism deals with the sonochemical reduction of Pu(VI) in weakly acidic perchloric solutions by using the in situ generated H2O2, where the kinetics can be dramatically enhanced under high frequency ultrasound and an Ar/O2 atmosphere. The quasi-exclusive presence of the Pu(V) aqua ion in solution was evidenced by UV-vis absorption spectroscopy. The prepared solutions were found to be stable for more than one month which allowed the accurate XAFS and NMR investigations of Pu(V). EXAFS spectra revealed the presence of two trans dioxo Pu-O double bonds at 1.81 angstrom and 4-6 equatorial Pu-Oeq interactions at 2.47 angstrom characteristic of coordinated water molecules. The exact number of water molecules (N[Oeq(H2O) (= 4) was determined by simulating the EXAFS spectra of the PuO2+ aqua complexes using DFT calculations (geometry and the Debye-Waller factor) and comparing them with experimental signals. For the first time, the magnetic susceptibility of the pentavalent state of plutonium in aqueous solutions was also determined (χM' = 16.3 x 10(-9) m(3) mol(-1) at 25 degrees C) and the related Curie constant was estimated (C = 6.896 x 10-6 m3 K mol-1). (authors)
Journal
Inorganic Chemistry Frontiers (Online); ISSN 2052-1553; ; v. 5(no.1); p. 100-111
; v. 5(no.1); p. 100-111
[en] Na3.16(2)UV,VI0.84(2)O4 is obtained from the reaction of sodium with uranium dioxide under oxygen potential conditions typical of a sodium-cooled fast nuclear reactor. In the event of a breach of the steel cladding, it would be the dominant reaction product forming at the rim of the mixed (U,Pu)O2 fuel pellets. High-temperature X-ray diffraction measurements show that a distortion of the uranium environment in Na3.16(2)UV,VI0.84(2)O4 results in a strongly anisotropic thermal expansion. A comparison with several related sodium metallates Nan-2Mn+On-1 - including Na3SbO4 and Na3TaO4, whose crystal structures are reported for the first time - has allowed us to assess the role played in the lattice expansion by the Mn+ cation radius and the Na/M ratio. On this basis, the thermomechanical behavior of the title compound is discussed, along with those of several related double oxides of sodium and actinide elements, surrogate elements, or fission products. - Highlights: •Thermal expansion and structural mechanism of Na3(U0.84(2),Na0.16(2))O4, main product of the reaction of sodium with nuclear fuel. •Thermomechanical behavior of sodium uranate suggests possible strains on the fuel cladding and risks of de-cohesion with the fuel pin. •Effect of homo- and aliovalent cation substitutions allows to predict the thermomechanical behavior of sodium metallates involving fission products or minor actinide elements. •Crystal structure of new compounds Na3SbO4 and Na3TaO4.
Journal