Controlling the Reduction of Chelated Uranyl to Stable Tetravalent Uranium Coordination Complexes in Aqueous Solution

The solution-state interactions between octadentate hydroxypyridinone (HOPO) and catecholamide (CAM) chelating ligands and uranium were investigated and characterized by UV-visible spectrophotometry and X-ray absorption spectroscopy (XAS), as well as electrochemically via spectroelectrochemistry (SEC) and cyclic voltammetry (CV) measurements. Depending on the selected chelator, we demonstrate the controlled ability to bind and stabilize U-IV, generating with 3,4,3-LI(1,2-HOPO), a tetravalent uranium complex that is practically inert toward oxidation or hydrolysis in acidic, aqueous solution. At physiological pH values, we are also able to bind and stabilize U-IV to a lesser extent, as evidenced by the mix of U-IV and U-VI complexes observed via XAS. CV and SEC measurements confirmed that the U-IV complex formed with 3,4,3-LI(1,2-HOPO) is redox inert in acidic media, and U-VI ions can be reduced, likely proceeding via a two-electron reduction process.

Automated summary

The study investigated the interactions between octadentate hydroxypyridinone (HOPO) and catecholamide (CAM) chelating ligands and uranium through various spectroscopic and electrochemical techniques. Results showed controlled binding and stabilization of U-IV with different chelators, with the 3,4,3-LI(1,2-HOPO) forming a tetravalent uranium complex inert to oxidation in acidic solution. Additionally, U-IV was found to be less extensively stabilized at physiological pH, with a mix of U-IV and U-VI complexes observed.