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Radiometals are increasingly used in nuclear medicine for both diagnostic and therapeutic purposes. The DOTA ligand (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) is widely used as a chelating agent for various radionuclides, including 89Zr, with high thermodynamic stability constants and great in vivo stability. However, in contact with radioisotopes, chelating molecules are subjected to the effects of radiation, which can lead to structural degradation and induce alteration of their complexing properties. For the first time, the radiolytic stability of the Zr–DOTA complex in aqueous solution was studied and compared to the stability of the DOTA ligand. The identification of the major degradation products allows us to propose two different degradation schemes for the DOTA ligand and Zr–DOTA complex. DOTA is degraded preferentially by decarboxylation and cleavage of an acetate arm CH2–COOH, whereas in Zr–DOTA, DOTA tends to oxidize by the addition of the OH group in its structure. In addition, the degradation of the ligand, when involved in a Zr complex, is significantly less than when the ligand is free in solution, indicating that the metal protects the ligand from degradation. DFT calculations were performed to supplement the experimental data and give an improved understanding of the behaviour of DOTA and Zr–DOTA solutions after irradiation: the increase in stability upon complexation is attributed to the strengthening of the bonds in the presence of metal cations, which become less vulnerable to radical attack. Bond dissociation energies and Fukui indices are shown to be useful descriptors to estimate the most vulnerable sites of the ligand and to predict the protective effect of the complexation. [ABSTRACT FROM AUTHOR]

Two new aqueous UIV complexes were synthesized by the interaction between the tetravalent uranium cation and the (1,4,7,10‐Tetraazacyclododecane‐1,4,7,10‐tetra(methylene phosphonic acid) (DOTP) macrocyclic ligand. Two distinct homonuclear complexes were identified; the first was characterized by X‐ray crystallography as a unique "out‐of‐cage", [U(DOTPH6)2] complex, in which the UIV cation is octa‐coordinated to 4 phosphonic arms from each ligand in a square anti‐prism geometry, with a C4 symmetry. The second is the "in‐cage" [U(DOTPH4)] complex, in which the tetravalent cation is located between the macrocycle O4 and N4 planes. With the help of UV‐Vis absorption, 1H/31P NMR, ATR‐IR, and MALDI‐TOFMS analytical techniques, the chemical interchange between both species is presented. It is shown that the one‐way transition is governed by the formation of a multiple number of soluble oligomeric species consisting of varied stoichiometric ratios of both characterized homonuclear complexes. [ABSTRACT FROM AUTHOR]

Actinide +VI complexes (AnVI =UVI , NpVI and PuVI) with dipicolinic acid derivatives were synthesized and characterized by powder XRD, SQUID magnetometry and NMR spectroscopy. In addition, NpVI and PuVI complexes were described by first principles CAS based and two‐component spin‐restricted DFT methods. The analysis of the 1H paramagnetic NMR chemical shifts for all protons of the ligands according to the X‐rays structures shows that the Fermi contact contribution is negligible in agreement with spin density determined by unrestricted DFT. The magnetic susceptibility tensor is determined by combining SQUID, pNMR shifts and Evans' method. The SO‐RASPT2 results fit well the experimental magnetic susceptibility and pNMR chemical shifts. The role of the counterions in the solid phase is pointed out; their presence impacts the magnetic properties of the NpVI complex. The temperature dependence of the pNMR chemical shifts has a strong 1/T contribution, contrarily to Bleaney's theory for lanthanide complexes. The fitting of the temperature dependence of the pNMR chemical shifts and SQUID magnetic susceptibility by a two‐Kramers‐doublet model for the NpVI complex and a non‐Kramers‐doublet model for the PuVI complex allows for the experimental evaluation of energy gaps and magnetic moments of the paramagnetic center. [ABSTRACT FROM AUTHOR]

The [AnIV(DPA)3]2− series with An = Th, U, Np, Pu has been synthesized and characterized using SC-XRD and vibrational spectroscopy. First principles calculations were performed, the total electron density is analyzed using the Quantum Theory of Atoms in Molecules. Crystal field parameters and strength parameters are deduced following a previous work on the LnIII analog series e.g. [J. Jung et al., Chem. – Eur. J., 2019, 25, 15112]. The trends in the parameters along the series are compared to the LnIII complexes. They evidence larger covalent interactions and larger J mixing. [ABSTRACT FROM AUTHOR]

The molecular characterization based on multi‐technique approach has led to major highlights on revealing the coordination of americium with citric acid. The structure of the different complexes at pH 1 and 3 are described. These characterizations are made possible by the comparison of the americium‐citric acid system with the americium‐tricarballylic acid (one analogue of the citric acid without the alpha‐hydroxo group). The structural analyses (Vis spectrophotometry, NMR, EXAFS, TRLFS and capillary electrophoresis) were carried out after the establishment of the speciation distribution diagrams, allowing to take into account the species repartition for structural analysis data treatment. For the 1:1 complex the hydroxo group is counter intuitively deprotonated and coordinated to the Am(III) at pH 1 as well as two carboxylate functions, whereas at pH 3 the hydroxo is not coordinated and stays protonated allowing the three carboxylate functions to coordinate the metallic cation. Therefore, the hydroxo group affects the Am complexation differently depending on the pHs: by inductive effect at pH 3, and by direct coordination at pH 1. [ABSTRACT FROM AUTHOR]

The 1,4,7,10‐tetrazacyclodecane‐1,4,7,10‐tetraacetic acid (DOTA) aqueous complex of UIV with H2O, OH−, and F− as axial ligands was studied by using UV/Vis spectrophotometry, ESI‐MS, NMR spectroscopy, X‐ray crystallography, and electrochemistry. The UIV–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 UIV/UIII redox couple was found to be quasi‐reversible for the complex with both axially bonded H2O and hydroxide, but irreversible for the complex with axially bonded fluoride. Intriguingly, binding of the axial fluoride renders the irreversible one‐electron UV/UIV oxidation of the [UIV(DOTA)(H2O)] complex quasi‐reversible, which suggests the formation of the short‐lived pentavalent form of the complex, an aqueous non‐uranyl chelated UV cation. [ABSTRACT FROM AUTHOR]

Two series of lanthanide complexes have been chosen to analyze trends in the magnetic properties and crystal field parameters (CFPs) along the two series: The highly symmetric LnZn16(picHA)16 series (Ln=Tb, Dy, Ho, Er, Yb; picHA=picolinohydroxamic acid) and the [Ln(dpa)3](C3H5N2)3⋅3H2O series (Ln=Ce–Yb; dpa=2,6‐dipicolinic acid) with approximate three‐fold symmetry. The first series presents a compressed coordination sphere of eight oxygen atoms whereas in the second series, the coordination sphere consists of an elongated coordination sphere formed of six oxygen atoms. The CFPs have been deduced from ab initio calculations using two methods: The AILFT (ab initio ligand field theory) method, in which the parameters are determined at the orbital level, and the ITO (irreducible tensor operator) decomposition, in which the problems are treated at the many‐electron level. It has been found that the CFPs are transferable from one derivative to another, within a given series, as a first approximation. The sign of the second‐order parameter B02 differs in the two series, reflecting the different environments. It has been found that the use of the strength parameter S allows for an easy comparison between complexes. Furthermore, in both series, the parameters have been found to decrease in magnitude along the series, and this decrease is attributed to covalent effects. [ABSTRACT FROM AUTHOR]

The magnetic properties of LnIII and AnIII complexes formed with dipicolinate ligands have been studied by NMR spectroscopy. To know precisely the geometries of these complexes, a crystallographic study by single‐crystal X‐ray diffraction (XRD) and extended X‐ray absorption fine structure (EXAFS) in solution was performed. Several methods to separate the paramagnetic shifts observed in the NMR spectra were applied to these complexes. Methods using a number of nuclei of the dipicolinate ligands revealed an abrupt change in the geometries of the complexes and a metal–ligand interaction in the middle of the lanthanide series. A study of the variation of the paramagnetic shifts with temperature demonstrated that higher‐order terms of the dipolar and contact contributions are required, especially for the lightest LnIII and almost all the studied AnIII. Bleaney's parameters a and CaD relating to the contact and dipolar terms, respectively, were deduced from experimental data and compared with the results of ab initio calculations. Quite a good agreement was found for the temperature dependencies of a and CaD. However, the CaD values obtained from cation magnetic anisotropy calculations showed some discrepancies with the values derived from Bleaney's equation defined for LnIII. Other parameters, such as the crystal field parameter and the hyperfine constants Fi obtained from the experimental data of the [An(ethyl‐dpa)3]3− complexes (ethyl‐dpa=4‐ethyl‐2,6‐dipicolinic acid), are at odds with the assumptions underlying Bleaney's theory. Valid for Ln, but for An? Is Bleaney's equation for paramagnetic NMR shifts of LnIII valid for AnIII complexes? (see figure) Several methods have been applied to separate the paramagnetic shifts observed in the NMR spectra of LnIII and AnIII complexes formed with dipicolinate ligands. Discrepancies with Bleaney's equation have been found for the AnIII complexes, and some parameters are at odds with the assumptions underlying Bleaney's theory. [ABSTRACT FROM AUTHOR]

In a previous paper, the influence of radioactive decay (α and β−) on magnetic susceptibility measurements by the Evans method has been demonstrated by the study of two americium isotopes. To characterize more accurately this phenomenon and particularly its influence on the Curie law, a new study has been performed on two uranium isotopes (238U and 233U) and on tritiated water (3H2O). The results on the influence of α emissions have established a relationship between changes in the temperature dependence and the radioactivity in solution. Regarding the β− emissions, less influence was observed while no temperature dependence linked to this kind of radioactive emission could be identified. Once magnetic susceptibility measurements of actinide(iii) cations were corrected from radioactivity effects, methods of quantum chemistry have been used on free ions and aquo complexes to calculate the electronic structure explaining the magnetic properties of Pu(iii), Am(iii) and Cm(iii). The ligand field effect on the magnetic behavior (the Curie constant and temperature-independent susceptibilities) was analyzed by considering different solvation environments. [ABSTRACT FROM AUTHOR]

Several hydrometallurgical processes studied in France for lanthanide/minor actinide separation use a combination of DMDOHEMA and HDEHP as extractants. Although these processes have proved to be reliable, the modeling of their extraction properties remains a difficult task due to a lack of knowledge about the behavior of the mixed DMDOHEMA-HDEHP organic phase. In the present work, it was found that the solvent extraction of Ln(III) ions by a mixture of these extractants exhibits a complex behavior involving a synergistic effect at either 1 M HNO3or high metal concentration, and an antagonistic effect on extraction of metal traces at higher pH (> 2). To understand these effects, Ln(III) complexes formed after extraction by DMDOHEMA and/or HDEHP were characterized by several spectroscopic techniques (FT-IR, UV-Vis, ESI-MS, TRLIFS). Results suggested formation of DMDOHEMA-HDEHP adducts and ternary mixed complexes involving both extractants and possibly a nitrate ion. [ABSTRACT FROM PUBLISHER]

In order to explain the higher magnetic susceptibility of some aquo actinide ions than predicted by Hund's rules, the molar magnetic susceptibilities of two americium isotopes (241Am and 243Am) were measured using the Evans method. The results obtained show a growing change in the magnetic susceptibility with α and also a β− activity increase in solution. β− particle effects appear to be stronger than radicals formed by α particles on the experimental values. The temperature dependence of Am(iii) magnetic susceptibility has been observed but from experiments carried out here, it appears to be difficult to prove whether this effect arises from radicals or β−. Finally, magnetic susceptibilities of americium recorded in different media (HClO4, HCl, and HNO3) have been compared to alpha and beta emissions' impact. [ABSTRACT FROM AUTHOR]

Although there is a tremendous volume of data available on the interaction of actinides with living organisms as plants, nearly all the studies are limited to macroscopic or physiological measurements with no specific information at the molecular level. Peptides allow the study of complex coordination chemistry, as that involving actinide(iv) and proteins, without the intricacy of tertiary structure properties. For that purpose, a linear pentapeptide, acetyl–diaspartyl–prolyl–diaspartyl–amide (Ac–Asp–Asp–Pro–Asp–Asp–NH2, denoted PP1 in this report), was synthesized and investigated as a potential chelating ligand of thorium(iv), neptunium(iv) and/or plutonium(iv) cations. Comparison with the biological relevant iron(iii) cation is also provided. Noteworthy, PP1 was able to prevent Np(iv) from hydrolysis into an insoluble precipitate. Spectrophotometry, 13C NMR and EXAFS at the iron K edge and actinide L3edges were used to probe the cation coordination sphere and better describe the cation–peptide interaction. The complexes were found to be polynuclear with oxo or hydroxo bridged cations, Fe(iii) forming a binuclear complex, Th(iv), Np(iv) or Pu(iv) forming a polynuclear complex with higher nuclearities. [ABSTRACT FROM AUTHOR]