title: Thermodynamic and Spectroscopic Studies of Trivalent f-element Complexation with Ethylenediamine-N,N'-di(acetylglycine)-N,N'-diacetic Acid.
abstract: The coordination behavior and thermodynamic features of complexation of trivalent lanthanides and americium by ethylenediamine-N,N'-di(acetylglycine)-N,N'-diacetic acid (EDDAG-DA) (bisamide-substituted-EDTA) were investigated by potentiometric and spectroscopic techniques. Acid dissociation constants (K(a)) and complexation constants (β) of lanthanides (except Pm) were determined by potentiometric analysis. Absorption spectroscopy was used to determine stability constants for the binding of trivalent americium and neodymium by EDDAG-DA under similar conditions. The potentiometry revealed 5 discernible protonation constants and 3 distinct metal-ligand complexes (identified as ML(-), MHL, and MH2L(+)). Time-resolved fluorescence studies of Eu-(EDDAG-DA) solutions (at varying pH) identified a constant inner-sphere hydration number of 3, suggesting that glycine functionalities contained in the amide pendant arms are not involved in metal complexation and are protonated under more acidic conditions. The thermodynamic studies identified that f-element coordination by EDDAG-DA is similar to that observed for ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA). However, coordination via two amidic oxygens of EDDAG-DA lowers its trivalent f-element complex stability by roughly 3 orders of magnitude relative to EDTA.
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: Aqueous Separations and Radiochemistry, Idaho National Laboratory , Idaho Falls, Idaho 83415, United States.
authors.forename: Travis S
authors.initials: TS
authors.lastname: Grimes
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