Solution Chemistry of Uranyl Ion with Iminodiacetate and Oxydiacetate:  A Combined NMR/EXAFS and Potentiometry/Calorimetry Study

Abstract

The solution chemistry of uranyl ion with iminodiacetate (IDA) and oxydiacetate (ODA) was investigated using NMR and EXAFS spectroscopies, potentiometry, and calorimetry. From the NMR and EXAFS data and depending on stoichiometry and pH, three types of metal:ligand complex were identified in solution in the pH range 3-7: 1:1 and 1:2 monomers; a 2:2 dimer. From NMR and EXAFS data for the IDA system and previous studies, we propose the three complex types are [UO(2)(IDA)(H(2)O)(2)], [UO(2)(IDA)(2)](2)(-), and [(UO(2))(2)(IDA)(2)(mu-OH)(2)](2)(-). From EXAFS spectroscopy, similar 1:1, 2:2, and 1:2 complexes are found for the ODA system, although (13)C NMR spectroscopy was not a useful probe in this system. For the 1:1 and 1:2 complexes in solution, EXAFS spectroscopy is ambiguous because the data can be fitted with either a long U-N/O(ether) value (ca. 2.9 A) suggesting 1,7-coordination of the ligand or a U-C interaction at a similar distance, consistent with terminal bidentate coordination. However, the NMR data of the IDA system suggest that 1,7-coordination is the more likely. The stability constants of the three complexes were determined by potentiometric titrations; the log beta values are 9.90 +/-, 16.42 +/-, and 10.80 +/- for the 1:1, 1:2, and 2:2 uranyl-IDA complexes, respectively, and 5.77 +/-, 7.84 +/-, and 4.29 +/- for the 1:1, 1:2, and 2:2 uranyl-ODA complexes, respectively. The thermodynamic constants for the complexes were calculated from calorimetric titrations; the enthalpy changes (kJ mol(-)(1)) and entropy changes (J K(-)(1) mol(-)(1)) of complexation for the 1:1, 1:2, and 2:2 complexes respectively are the following. IDA: 12 +/- 2, 230 +/- 8; 8 +/- 2, 151 +/- 9; -33 +/- 3, -283 +/- 11. ODA: 26 +/- 2, 198 +/- 12; 20 +/- 2, 106 +/- 8; -24 +/- 2; -219 +/- 8.

Binary and ternary complexation of NpO2 + with carboxylate and aminocarboxylate ligands

“…The complexation enthalpies for Eu(ODA) + are weakly exothermic (Δ 101 = −3 kJ/mol), while the corresponding values for UO 2 -ODA are substantially endothermic (Δ 101 = +17 kJ/mol for = 0.1 M) [42]. [35]), in agreement with the conclusions based on the correlation of log 101 vs. pK a . Figure 5 shows the variation of complexation entropy for the Ox, ODA, IDA and TDA for the actinides cations.…”

“…The stability constants of values measured are listed in Table 3. The literature stability constant values of these ligands at lower ionic strengths are also listed in Table 3 [35,36]. In addition, crystal structures of both 5 and Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 6/1/15 1:05 PM 6-coordinated dioxouranium (VI) complexes with two ODA molecules have been reported.…”

“…The EXAFS spectroscopy of UO 2 -IDA/ODA, although ambiguous in determining the structure of the 1 : 1 complex[35],suggests interaction of U with N and O atoms and the presence of a chelate ring. Furthermore, the stability constant of NpO 2 + -ODA is larger than the stability constant value of NpO 2 + -Mal which is known to have a bidentate coordination.…”

Modulating Uranium Binding Affinity in Engineered Calmodulin EF-Hand Peptides: Effect of Phosphorylation

“…Indeed, IDA has been demonstrated to be a uranyl ligand and the stability constants of its uranyl complexes have been measured by potentiometry at 25°C with a ionic strength of 0.1 M (KNO 3 ) [38].…”

“…Therefore, the conditional stability constants of the three uranyl complexes formed with IDA (UO 2 IDA, [UO 2 (IDA) 2 ] 2− and [(UO 2 ) 2 (IDA) 2 (OH) 2 ] 2− ) were calculated at pH 6 and pH 7 from the pK a s of IDA and the stability constants of these complexes [38]. Their values were fixed in the analysis of the titrations of the peptides with uranyl done in presence of 10 equivalents of IDA.…”