Tuning Amidoximate to Enhance Uranyl Binding: A Density Functional Theory Study

Amidoxime functionalized sorbents have shown great promise in extracting uranium from seawater, though the rationale for this affinity is not apparent. To enhance binding by amidoxime and to develop more selective sorbents, a detailed understanding of the electronic structure is necessary. This study investigates the electronic effects of amidoximate ligands bound to the uranyl cation, UO22+. Density functional theory calculations have been performed on a series of uranyl-amidoximate derivatives to investigate their structural, electronic, and thermochemical properties. The computational findings are in good agreement with available experimental data, with average error in bond length below 0.07 angstrom for all systems. Binding strength was observed to be directly related to electron donation, as evidenced by the plot of log(K/K-0) vs the Hammett constant (sigma(para)) of the substituent adjacent to the oximate function. From this observation, we propose and investigate two new imidazole-derived oximes, both of which possess greater binding strength than amidoximate derivatives.