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Complexation of Uranium(VI) by Gluconate in Acidic Solutions: a Thermodynamic Study with Structural Analysis

Zhicheng ZhangChemistry Department and Center for NMR Spectroscopy, Washington State University, Pullman, Washington 99164, Lawrence Berkeley National Laboratory, Berkeley, California 94720, and Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, 35131, Padova, ItalyGregory L. HelmsLawrence Berkeley National LaboratorySue B. ClarkLawrence Berkeley National LaboratoryGuoxin TianLawrence Berkeley National LaboratoryP. ZanonatoLawrence Berkeley National LaboratoryLinfeng RaoLawrence Berkeley National Laboratory

2009en

ABI

Annotatsiya

Within the pC(H) range of 2.5 to 4.2, gluconate forms three uranyl complexes UO(2)(GH(4))(+), UO(2)(GH(3))(aq), and UO(2)(GH(3))(GH(4))(-), through the following reactions: (1) UO(2)(2+) + GH(4)(-) = UO(2)(GH(4))(+), (2) UO(2)(2+) + GH(4)(-) = UO(2)(GH(3))(aq) + H(+), and (3) UO(2)(2+) + 2GH(4)(-) = UO(2)(GH(3))(GH(4))(-) + H(+). Complexes were inferred from potentiometric, calorimetric, NMR, and EXAFS studies. Correspondingly, the stability constants and enthalpies were determined to be log beta(1) = 2.2 +/- 0.3 and DeltaH(1) = 7.5 +/- 1.3 kJ mol(-1) for reaction (1), log beta(2) = -(0.38 +/- 0.05) and DeltaH(2) = 15.4 +/- 0.3 kJ mol(-1) for reaction (2), and log beta(3) = 1.3 +/- 0.2 and DeltaH(3) = 14.6 +/- 0.3 kJ mol(-1) for reaction (3), at I = 1.0 M NaClO(4) and t = 25 degrees C. The UO(2)(GH(4))(+) complex forms through the bidentate carboxylate binding to U(VI). In the UO(2)(GH(3))(aq) complex, hydroxyl-deprotonated gluconate (GH(3)(2-)) coordinates to U(VI) through the five-membered ring chelation. For the UO(2)(GH(3))(GH(4))(-) complex, multiple coordination modes are suggested. These results are discussed in the context of trivalent and pentavalent actinide complexation by gluconate.

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DOI: 10.1021/ic8018925

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