Stability Series for the Complexation of Six Key Siderophore Functional Groups with Uranyl Using Density Functional Theory

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 124; no. 12; pp. 2460 - 2472
• Main Authors: Kirby, Matthew Edward, Sonnenberg, Jason Louis, Simperler, Alexandra, Weiss, Dominik Jakob
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 26.03.2020
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.9b10649

Determining stability constants of uranyl complexes with the principal functional groups in siderophores and identifying stability series is of great importance to predict which siderophore classes preferentially bind to UVI and, hence, impact uranium speciation in the environment. It also helps to develop resins for scavenging UVI from aqueous solutions. Here, we apply a recently developed computational approach to calculate log β values for a set of geochemically relevant uranium organometallic complexes using Density Functional Theory (DFT). We determined the stability series for catecholate, hydroxamate, α-hydroxycarboxylate, α-aminocarboxylate, hydroxy-phenyloxazolonate, and α-hydroxyimidazole with the uranyl cation. In this work, the stability constants (log β110) of α-hydroxyimidazolate and hydroxy-phenyloxazolonate are calculated for the first time. Our approach employed the B3LYP density functional approximation, aug-cc-pVDZ basis set for ligand atoms, MDF60 ECP for UVI, and the IEFPCM solvation model. DFT calculated log β110 were corrected using a previously established fitting equation. We find that the siderophore functional groups stability decreases in the order: α-hydroxycarboxylate bound via the α-hydroxy and carboxylate groups (log β110 = 17.08), α-hydroxyimidazolate (log β110 = 16.55), catecholate (log β110 = 16.43), hydroxamate (log β110 = 9.00), hydroxy-phenyloxazolonate (log β110 = 8.43), α-hydroxycarboxylate bound via the carboxylate group (log β110 = 7.51) and α-aminocarboxylate (log β110 = 4.73). We confirm that the stability for the binding mode of the functional groups decrease in the order: bidentate, monodentate via ligand O atoms, and monodentate via ligand N atoms. The stability series strongly suggests that α-hydroxyimidazolate is an important functional group that needs to be included when assessing uranyl mobility and removal from aqueous solutions.