Structural and thermodynamic investigation of AnIVLI(O)HOPO

Abstract

For the first time, capillary electrophoresis coupled with inductively coupled plasma mass spectrometry has been used to determine the stability constants of Pu^IV with the multidentate hydroxypyridinonate chelating agents 3,4,3-LI(1,2-HOPO) and 5-LIO(Me-3,2-HOPO) in 0.1 M NaNO₃ solution, p_cH = 1.395 at 25 °C through competition with the NTA ligand. The limiting electrophoretic mobility was found to be zero for An^IV[5-LIO(Me-3,2-HOPO)] and slightly positive for An^IV[3,4,3-LI(1,2-HOPO)] (An^IV = Th, Pu). They were respectively assigned to the formation of the 1 : 2 neutral species An[5-LIO(Me-3,2-HOPO)]₂ and a mixture of the neutral species An^IV[3,4,3-LI(1,2-HOPO)] and its protonated form An^IVH[3,4,3-LI(1,2-HOPO)]⁺. The corresponding stability constants of Th^IV with both chelators were evaluated through the same experiments for the sake of comparison. The stability of both Pu^IV–HOPOs was about ten orders of magnitude better than that of the equivalent Th^IV complexes. To complement these thermodynamic data, structural parameters of Pu[3,4,3-LI(1,2-HOPO)] and Th[3,4,3-LI(1,2-HOPO)] complexes in solution have been derived from EXAFS experiments and compared to previously reported crystallographic structures.