Predicting Stability Constants for Uranyl Complexes Using Density Functional Theory

The ability to predict the equilibrium constants for the formation of 1:1 uranyl/ligand complexes (log K₁ values) provides the essential foundation for the rational design of ligands with enhanced uranyl affinity and selectivity. We use density functional theory (B3LYP) and the integral equation formalism polarizable continuum model (IEF-PCM) to compute aqueous stability constants for UO₂²⁺ complexes with 18 donor ligands. Theoretical calculations permit reasonably good estimates of relative binding strengths, while the absolute log K₁ values are significantly overestimated. Accurate predictions of the absolute log K₁ values (root-mean-square deviation from experiment <1.0 for log K₁ values ranging from 0 to 16.8) can be obtained by fitting the experimental data for two groups of mono- and divalent negative oxygen donor ligands. The utility of correlations is demonstrated for amidoxime and imide dioxime ligands, providing a useful means of screening for new ligands with strong chelating capability to uranyl.