title: Thermodynamic, Spectroscopic, and Computational Studies of f-Element Complexation by N-Hydroxyethyl-diethylenetriamine-N,N',N″,N″-tetraacetic Acid.
abstract: Potentiometric and spectroscopic techniques were combined with DFT calculations to probe the coordination environment and determine thermodynamic features of trivalent f-element complexation by N-hydroxyethyl-diethylenetriamine-N,N',N″,N″-tetraacetic acid, HEDTTA. Ligand protonation constants and lanthanide stability constants were determined using potentiometry. Five protonation constants were accessible in I = 2.0 M (H+/Na+)ClO4. UV-vis spectroscopy was used to determine stability constants for Nd3+and Am3+complexation with HEDTTA. Luminescence spectroscopy indicates two water molecules in the inner coordination sphere of the Eu/HEDTTA complex, suggesting HEDTTA is heptadentate. Luminescence data was supported by DFT calculations, which demonstrate that substitution of the acetate pendant arm by a N-hydroxyethyl group weakens the metal-nitrogen bond. This bond elongation is reflected in HEDTTA's ability to differentiate trivalent actinides from trivalent lanthanides. The trans-lanthanide Ln/HEDTTA complex stability trend is analogous to Ln/DTPA complexation; however, the loss of one chelate ring resulting from structural substitution weakens the complexation by ∼3 orders of magnitude. Successful separation of trivalent americium from trivalent lanthanides was demonstrated when HEDTTA was utilized as aqueous holdback complexant in a liquid-liquid system. Time-dependent extraction studies for HEDTTA were compared to diethylenetriamine-N,N,N',N″,N″-pentaacetic acid (DTPA) and N-hydroxyethyl-ethylenediamine-N,N',N'-triacetic acid (HEDTA). The results indicate substantially enhanced phase-transfer kinetic rates for mixtures containing HEDTTA.
authors.affiliation: Aqueous Separations and Radiochemistry, Idaho National Laboratory , Idaho Falls, Idaho, 83415, United States.
authors.forename: Travis S
authors.identifier: http://orcid.org/0000-0003-2751-0492
authors.initials: TS
authors.lastname: Grimes
authors.affiliation: Aqueous Separations and Radiochemistry, Idaho National Laboratory , Idaho Falls, Idaho, 83415, United States.
authors.forename: Colt R
authors.initials: CR
authors.lastname: Heathman
authors.affiliation: Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Santa
authors.initials: S
authors.lastname: Jansone-Popova
authors.affiliation: Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Vyacheslav S
authors.identifier: http://orcid.org/0000-0002-6501-6594
authors.initials: VS
authors.lastname: Bryantsev
authors.affiliation: Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Sriram
authors.initials: S
authors.lastname: Goverapet Srinivasan
authors.affiliation: Actinide Chemistry Group, Japan Atomic Energy Agency, Material Science Research Center , 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo-pref 679-5148 Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Nakase
authors.affiliation: Aqueous Separations and Radiochemistry, Idaho National Laboratory , Idaho Falls, Idaho, 83415, United States.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Zalupski