Influence of Pre-organized N-Donor Group on the Coordination of Trivalent Actinides and Lanthanides by Aminopolycarboxylate Complexant.

Thermodynamic influence of a pre-organized N-donor group on the coordination of trivalent actinides and lanthanides by an aminopolycarboxylate aqueous complexant was investigated. The synthesized reagent N-2-methylpicolinate-ethylenediamine-N,N',N'-triacetic acid, EDTA-Mpic, resembles ethylenediamine-N,N,N',N'-tetraacetic acid, EDTA, with a single acetate pendant arm replaced for a 6-carboxypyridin-2-yl-methyl group. The rigidified N-donor picolinate functionality shows a profound impact on ligand protonation and trivalent f-element complexation equilibria as demonstrated using potentiometric, spectroscopic, liquid-liquid metal partitioning studies and molecular dynamics calculations. Relative to DTPA, the ability to preferentially bind trivalent actinides over trivalent lanthanides was moderately lowered due to the presence of N-2-methylpicolinate substitutent. The structural modification substantially amplifies the total ligand acidity of EDTA-Mpic. As a result the complexant sustains the metal complexation, and efficient An3+/Ln3+ differentiation in aqueous mixtures of unprecedented acidity for this class of reagents.