Complexation of uranium(VI) by gluconate in acidic solutions: a thermodynamic study with structural analysis
Zhicheng Zhang1, Gregory Helms, Sue B Clark
1Chemistry Department, Washington State University, Pullman, Washington 99164, USA.
Inorganic Chemistry
|March 27, 2009
Summary
Gluconate forms three uranyl complexes, UO(2)(GH(4))(+), UO(2)(GH(3))(aq), and UO(2)(GH(3))(GH(4))(-), with distinct coordination modes. Stability constants and enthalpies were determined for these uranyl-gluconate complexes.
Area of Science:
- Inorganic Chemistry
- Radiochemistry
- Coordination Chemistry
Background:
- Understanding the complexation behavior of uranyl (UO(2)(2+)) with organic ligands is crucial for nuclear waste management and environmental remediation.
- Gluconate is a biodegradable and abundant organic ligand present in various environmental compartments, influencing the speciation and mobility of metal ions.
Purpose of the Study:
- To investigate the formation and characterization of uranyl-gluconate complexes under varying pC(H) conditions.
- To determine the thermodynamic parameters (stability constants and enthalpies) for the complexation reactions.
- To elucidate the coordination modes of gluconate with uranyl ions.
Main Methods:
- Potentiometric, calorimetric, and nuclear magnetic resonance (NMR) studies were employed to infer complex formation.
- Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy was utilized for structural characterization.
- Complexation was studied in a 1.0 M NaClO(4) ionic medium at 25 degrees C.
Main Results:
- Three uranyl complexes were identified: UO(2)(GH(4))(+), UO(2)(GH(3))(aq), and UO(2)(GH(3))(GH(4))(-), within the pC(H) range of 2.5 to 4.2.
- Stability constants (log beta) and enthalpies (DeltaH) were quantified for each complex formation reaction.
- The UO(2)(GH(4))(+) complex involves bidentate carboxylate binding, while UO(2)(GH(3))(aq) features hydroxyl-deprotonated gluconate coordinating via a five-membered ring chelation.
Conclusions:
- Gluconate forms multiple stable uranyl complexes with distinct coordination geometries.
- The thermodynamic data provide valuable insights into the uranyl-gluconate interaction.
- These findings contribute to understanding the environmental fate and transport of actinides in the presence of organic ligands.
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