Isotopic oxygen exchange between aqueous vanadyl ions and solvent water

Abstract

The 180 isotopic oxygen exchange of the oxo (yl) oxygens of dr-V02+(aq) is too rapid to measure by static methods. Studies using the rapid formation of [V02(C204)2]3", followed by [Co(en)3]3+ precipitation, revealed complete oxygen exchange during the conversions. Studies on the yl-oxygen exchange of c/r-[V02(C204)2]3' found the rate to be less and the rate equation to be rate = fc0[VO2(C2O4)2]3" + fch[H+][V02(C204)2]3", where A:0 = 0.31 ± 0.1 s"1 and *h = (4.7 ± 1) X 103 s"1 M"1 at 0 °C and a pH <6. Above this pH a chemical modification occurs and the observed rate increases with pH.An impurity, presumably V(IV), also increases the rate. It can be removed with traces of H4I06", which oxidizes it to V(V). V02+(aq) is rapidly reduced and complexed by excess NCS" to VCKNCSls3", which exchanges its yl oxygen slowly.Competition between lsO-solvent exchange and NCS" reduction allows an estimation of the intrinsic exchange rate of V02+(aq). At 0 °C the r1/2 of 0.15 s was estimated (A: = 4.7 s"1).

Aqueous Ferryl(IV) Ion: Kinetics of Oxygen Atom Transfer To Substrates and Oxo Exchange with Solvent Water

“…21 Although there are a number of reports on oxygen exchange between a metal-oxo group and water, quantitative kinetics data for such reactions are rare. [22][23][24][25][26][27][28][29] From the few rate constants that have been measured, it is obvious that these values are a function of the metal, its oxidation state, and the ligand environment, which makes a direct comparison to Fe IV aq O 2+ rather difficult to make. The closest example in the literature is the exchange between traces of water in acetonitrile and the iron(IV)-oxo complex of tetramethylcyclam, for which the rate constant of 5.4 ( 0.6 M -1 s -1 was reported.…”

17O ESEEM Evidence for Exchange of the Axial Oxo Ligand in the Molybdenum Center of the High pH Form of Sulfite Oxidase

“…Another possible pathway for introducing the axial 17 O ligand is via the reduced Mo(V) form (Figure ). Mo−OH and Mo−OH 2 species exchange rapidly with water, and proton transfer between these groups and an adjacent MoO group has been shown to facilitate exchange of oxo ligands in coordination compounds. − However, a resonance Raman study of the molybdenum domain of recombinant human SO that had been redox cycled in H 2 18 O indicated that only one oxo group exchanged with 18 O at pH 8 …”

“…Mo-OH and Mo-OH 2 species exchange rapidly with water, and proton transfer between these groups and an adjacent ModO group has been shown to facilitate exchange of oxo ligands in coordination compounds. [22][23][24] However, a resonance Raman study of the molybdenum domain of recombinant human SO that had been redox cycled in H 2 18 O indicated that only one oxo group exchanged with 18 O at pH 8. 25 On the other hand, the higher pH (9.7) and different reduction process in our study might facilitate exchange of the axial oxygen of hpH SO during the ∼1 min reaction with sulfite.…”