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The f-element coordination by ethylenediamine-N,N′-di(acetylglycine)-N,N′-diacetic acid (EDDAG-DA) was investigated using potentiometric and spectroscopic techniques. Collected thermodynamic constants for the complexation of trivalent americium and lanthanides demonstrated that EDDAG-DA (a member of the aminopolycarboxylate class of complexants) may be utilized to differentiate the trivalent 4f and 5f groups. The metal-coordination studies revealed a similar coordination chemistry to ethylenediamine-N,N,N′,N′-tetraacetic acid (EDTA) but relatively lower strength of complexation.
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 (Ka) 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.
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