Aqueous Complexation of Thorium(IV), Uranium(IV), Neptunium(IV), Plutonium(III/IV), and Cerium(III/IV) with DTPA

Abstract

Aqueous complexation of Th(IV), U(IV), Np(IV), Pu(III/IV), and Ce(III/IV) with DTPA was studied by potentiometry, absorption spectrophotometry, and cyclic voltammetry at 1 M ionic strength and 25 °C. The stability constants for the 1:1 complex of each trivalent and tetravalent metal were calculated. From the potentiometric data, we report stability constant values for Ce(III)DTPA, Ce(III)HDTPA, and Th(IV)DTPA of log β(101) = 20.01 ± 0.02, log β(111) = 22.0 ± 0.2, and log β(101) = 29.6 ± 1, respectively. From the absorption spectrophotometry data, we report stability constant values for U(IV)DTPA, Np(IV)DTPA, and Pu(IV)DTPA of log β(101) = 31.8 ± 0.1, 32.3 ± 0.1, and 33.67 ± 0.02, respectively. From the cyclic voltammetry data, we report stability constant values for Ce(IV) and Pu(III) of log β(101) = 34.04 ± 0.04 and 20.58 ± 0.04, respectively. The values obtained in this work are compared and discussed with respect to the ionic radius of each cationic metal.

Complexation of tetravalent actinides (Th, U, Np, Pu) with 2,6-pyridinedicarboxylic acid in aqueous solutions

“…Taking into account the estimated uncertainty of determining logK i ' (An) , ±0.3 (i = 1, 2), we can conclude that the dependence obtained is close to linear, suggesting [9] mainly electrostatic character of the interaction of An(IV) ions with PDC 2-. It can be noted here for com-parison that the recent data on the stability of the complexes An IV (DTPA) -(An = Th, U, Np, Pu) (DTPA 5-= diethylenetriaminepentaacetate ion) [10] show that logβ increases in this series from 29.6 ± 1 to 33.67 ± 0.02. On the other hand, in the series of PDC 2complexes with trivalent lanthanides from Ce(III) to Gd(III), the overall stability constant of the complexes Ln(PDC) 3 3increases by a factor of 10 3 , from 10 18.67 to 10 21.66 (25°С, ionic strength 0.5) [2].…”

A Macrocyclic Chelator That Selectively Binds Ln4+ over Ln3+ by a Factor of 1029

“…170 This very large Nernstian shift of 1.91 V explains the overwhelming preference of the +4 oxidation state of cerium when it is complexed by L. Unsurprisingly, the potential of CeL 4-is close to that of the Ce(catecholato)4 4-complex (-0.448 V vs. SHE), 166 and smaller Nernstian shifts have been observed with octadentate ligands and Ce 4+ , 152,171 but this is the first measure of the Ce couple with an octadentate catecholate-type ligand.…”

Solution Thermodynamic Stability of Complexes Formed with the Octadentate Hydroxypyridinonate Ligand 3,4,3-LI(1,2-HOPO): A Critical Feature for Efficient Chelation of Lanthanide(IV) and Actinide(IV) Ions

“…An initial titration attempt had been performed at pH 6 in the presence of DTPA (data not shown) to prevent hydrolysis of metal ions and benefit from the known formation constants of [Ce(IV)(DTPA)] − and [Th(IV)(DTPA)] − . 18 However, the presence of Cl − ions favored to reduction of [Ce(IV)(DTPA)] − into [Ce(III)(DTPA)] 2− over the 24h equilibration time precluding the successful determination of thermodynamic constants. Fortunately, Ce(IV) was found indefinitely stable in sulfuric media at pH lower than 2–3, 19 which allowed a direct metal competition titration without additional ligand previously needed to prevent from hydrolysis or reduction of Ce(IV).…”