title: On the mechanism of oxygen exchange between uranyl(VI) oxygen and water in strongly alkaline solution as studied by (17)O NMR magnetization transfer.
abstract: The mechanism, rate constant, and activation parameters for the exchange between uranyl(VI) oxygen and water oxygen in tetramethyl ammonium hydroxide solution, TMA-OH, have been determined using (17)O NMR magnetization transfer technique. In the concentration range investigated, the predominant complex is UO(2)(OH)(4)(2-). The experimental rate equation, rate = k(ex)[TMA-OH](free)[U(VI)](2)(total) indicates that the exchange takes place via a binuclear complex or transition state with the stoichiometry [(UO(2)(OH)(4)(2-))(UO(2)(OH)(5)(3-)]. The rate-determining step most likely takes place between the axial "yl" oxygens and the equatorial hydroxides. The experimental Gibbs energy of activation, DeltaG(++) = 60.8 +/- 2.4 kJ/mol is in good agreement with the value, DeltaA(++) approximately DeltaG(++) = 52.3 +/- 5.4 kJ/mol, found by Buhl and Schreckenbach in a recent Car-Parrinello molecular dynamics study, indicating that their proposed "shuttle" mechanism may be applicable also on the proposed binuclear transition state.
authors.affiliation: School of Chemical Science and Engineering, Department of Chemistry, Royal Institute of Technology (KTH), S-10044 Stockholm, Sweden. zoltan@kth.se
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Szabó
authors.forename: Ingmar
authors.initials: I
authors.lastname: Grenthe
mesh_terms: D000468:Alkalies / Q000737:chemistry*; D007554:Isotopes; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D010100:Oxygen / Q000737:chemistry*; D012996:Solutions; D014501:Uranium / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D000468:Alkalies; D007554:Isotopes; D012996:Solutions; D014867:Water; D014501:Uranium; D010100:Oxygen