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1. Structural Changes to the Gd‐DTPA Complex at Varying Ligand Protonation State

   https://doi.org/10.1002/ejic.202300507  

   Summers, Thomas J.; O'Brien, Ravi D.; Sobrinho, Josiane A.; de Bettencourt‐Dias, Ana; Cantu, David C. (November 2023, European Journal of Inorganic Chemistry)

   Abstract Diethylenetriaminepentaacetic acid (DTPA) is a chelating agent whose complex with the Gd³⁺ion is used in medical imaging. DTPA is also used in lanthanide‐actinide separation processes. As protonation of the DTPA ligand can facilitate dissociation of the Gd³⁺ion from the Gd‐DTPA complex, this work investigates the coordination structures of the aqueous Gd³⁺ion and its environment when chelated by DTPA in eight different DTPA protonation states. Both classical and ab initio molecular dynamics (MD) simulations are conducted to model the solvated complexes. Extended X‐ray absorption fine structure (EXAFS) measurements of the Gd³⁺aqua ion, and the Gd‐DTPA complex at pH 1 and 11, are compared to EXAFS spectra predicted from the MD simulations to verify the accuracy of the MD structures. The findings of this work provide atomic‐level details into the fluctuating Gd‐DTPA complex environment as the DTPA ligand gradually detaches from the Gd³⁺ion with increased protonation. 

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2. The solution structures and relative stability constants of lanthanide–EDTA complexes predicted from computation

   https://doi.org/10.1039/D2CP01081J  

   O’Brien, Ravi D.; Summers, Thomas J.; Kaliakin, Danil S.; Cantu, David C. (May 2022, Physical Chemistry Chemical Physics)

   Ligand selectivity to specific lanthanide (Ln) ions is key to the separation of rare earth elements from each other. Ligand selectivity can be quantified with relative stability constants (measured experimentally) or relative binding energies (calculated computationally). The relative stability constants of EDTA (ethylenediaminetetraacetic acid) with La 3+ , Eu 3+ , Gd 3+ , and Lu 3+ were predicted from relative binding energies, which were quantified using electronic structure calculations with relativistic effects and based on the molecular structures of Ln–EDTA complexes in solution from density functional theory molecular dynamics simulations. The protonation state of an EDTA amine group was varied to study pH ∼7 and ∼11 conditions. Further, simulations at 25 °C and 90 °C were performed to elucidate how structures of Ln–EDTA complexes varying with temperature are related to complex stabilities at different pH conditions. Relative stability trends are predicted from computation for varying Ln 3+ ions (La, Eu, Gd, Lu) with a single ligand (EDTA at pH ∼11), as well as for a single Ln 3+ ion (La) with varying ligands (EDTA at pH ∼7 and ∼11). Changing the protonation state of an EDTA amine site significantly changes the solution structure of the Ln–EDTA complex resulting in a reduction of the complex stability. Increased Ln–ligand complex stability is correlated to reduced structural variations in solution upon an increase in temperature. 

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3. Solution structure of a europium–nicotianamine complex supports that phytosiderophores bind lanthanides

   https://doi.org/10.1039/D0CP06150F  

   Kaliakin, Danil S.; Sobrinho, Josiane A.; Monteiro, Jorge H.; de Bettencourt-Dias, Ana; Cantu, David C. (February 2021, Physical Chemistry Chemical Physics)

   null (Ed.)

   We report the solution structure of a europium-nicotianamine complex predicted from ab initio molecular dynamics simulations with density functional theory. Emission and excitation spectroscopy show that the Eu 3+ coordination environment changes in the presence of nicotianamine, suggesting complex formation, such as what is seen for the Eu 3+ –nicotianamine complex structure predicted from computation. We modeled Eu 3+ –ligand complexes with explicit water molecules in periodic boxes, effectively simulating the solution phase. Our simulations consider possible chemical events ( e.g. coordination bond formation, protonation state changes, charge transfers), as well as ligand flexibility and solvent rearrangements. Our computational approach correctly predicts the solution structure of a Eu 3+ –ethylenediaminetetraacetic acid complex within 0.05 Å of experimentally measured values, backing the fidelity of the predicted solution structure of the Eu 3+ –nicotianamine complex. Emission and excitation spectroscopy measurements were also performed on the well-known Eu 3+ –ethylenediaminetetraacetic acid complex to validate our experimental methods. The electronic structure of the Eu 3+ –nicotianamine complex is analyzed to describe the complexes in greater detail. Nicotianamine is a metabolic precursor of, and structurally very similar to, phytosiderophores, which are responsible for the uptake of metals in plants. Although knowledge that nicotianamine binds europium does not determine how plants uptake rare earths from the environment, it strongly supports that phytosiderophores bind lanthanides. 

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4. Two Beta-Phosphorylamide Compounds as Ligands for Sm3+, Eu3+, and Tb3+: X-ray Crystallography and Luminescence Properties

   https://doi.org/10.3390/molecules25132971  

   Lear, Alan R.; Lenters, Jonah; Patterson, Michael G.; Staples, Richard J.; Werner, Eric J.; Biros, Shannon M. (July 2020, Molecules)

   null (Ed.)

   This paper describes the synthesis of two beta-phosphorylamide ligands and their coordination chemistry with the Ln ions Tb3+, Eu3+, and Sm3+. Both the ligands and Ln complexes were characterized by IR, NMR, MS, and X-ray crystallography. The luminescence properties of the Tb3+ and Eu3+ complexes were also characterized, including the acquisition of lifetime decay curves. In the solid state, the Tb3+ and Sm3+ ligand complexes were found to have a 2:2 stoichiometry when analyzed by X-ray diffraction. In these structures, the Ln ion was bound by both oxygen atoms of each beta-phosphorylamide moiety of the ligands. The Tb3+ and Eu3+ complexes were modestly emissive as solutions in acetonitrile, with lifetime values that fell within typical ranges. 

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5. Parametrized ion-distribution model for extended x-ray absorption fine-structure analysis at high-energy-density conditions

   https://doi.org/10.1063/5.0191549  

   Chin, D_A; Nilson, P_M; Ruby, J_J; Bunker, G.; Ghosh, M.; Signor, M_E; Bishel, D_T; Smith, E_A; Coppari, F.; Ping, Y.; et al (April 2024, Physics of Plasmas)

   Experiments today can compress solids near isentropically to pressures approaching 100 × 106 atmospheres; however, determining the temperature of such matter remains a major challenge. Extended x-ray absorption fine-structure (EXAFS) spectroscopy is one of the few techniques sensitive to the bulk temperature of highly compressed solid matter, and the validity of this temperature measurement relies on constraining the local ion structure from the EXAFS spectrum. At high-energy-density (HED) conditions, the local ion structure often becomes distorted, which must be accounted for during the EXAFS analysis. Described here is a technique, using a parametrized ion-distribution model to directly analyze EXAFS spectra that provides a better constraint on the local structure than traditional second- or third-order cumulant expansion techniques at HED conditions. The parametrized ion-distribution model is benchmarked by analyzing EXAFS spectra from nickel molecular-dynamics simulations at ∼100 GPa and shown to provide a 10%–20% improvement in constraining the cumulants of the true ion distribution. 

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