Complexation Study of Pu(III)–Isosaccharinate Using Absorption Spectroscopy and Density Functional Theory Calculations

Plutonium displays intricate chemical behavior due to its various oxidation states, interacting with diverse inorganic and organic ligands under aqueous conditions. Isosaccharinic acid, a product of cellulose degradation in alkaline conditions, is recognized for forming stable complexes with radionuclides, including actinides, potentially enhancing their mobility in environments for radioactive waste disposal. This work focused on determining the formation constant of the PuISA²⁺ species through absorption spectroscopy and principal component analysis. Absorption spectra of Pu(III)-isosaccharinate (ISA) complexes were recorded in a 1 M NaClO₄ solution at pH 5. Derivative spectroscopy was employed to eliminate interference from the high background absorption induced by the ISA species. Under these conditions, the formation constant of the PuISA²⁺ was determined to be log β₁' = 2.38 ± 0.07. Furthermore, the tridentate coordination structure of PuISA²⁺, which involves one carboxyl group and two hydroxyl groups, was explored using density functional theory calculations. The investigation delved into the formation constant, spectral characteristics, and optimized structure of PuISA²⁺ to enhance our comprehension of the chemical behavior of Pu in a radioactive waste disposal system.