title: Oxidation Kinetics of the Potent Insulin Mimetic Agent Bis(maltolato)oxovanadium(IV) (BMOV) in Water and in Methanol.
abstract: The kinetics of oxidation of bis(maltolato)oxovanadium(IV), BMOV or VO(ma)(2), by dioxygen have been studied by UV-vis spectroscopy in both MeOH and H(2)O media. The VO(ma)(2):O(2) stoichiometry was 4:1. In aqueous solution, the pH-dependent rate of the VO(ma)(2)/O(2) reaction to generate cis-[VO(2)(ma)(2)](-) is attributed to the deprotonation of coordinated H(2)O, the deprotonated species [VO(ma)(2)(OH)](-) being more easily oxidized (k(OH) = 0.39 M(-)(1) s(-)(1), 25 degrees C) than the neutral form VO(ma)(2)(H(2)O) (k(H)()2(O) = 0.08 M(-)(1) s(-)(1), 25 degrees C). The activation parameters for the two second-order reactions in aqueous solution were deduced from variable temperature kinetic measurements. In MeOH, VO(ma)(2) was oxidized by dioxygen to cis-VO(OMe)(ma)(2), whose structure was characterized by single-crystal X-ray diffraction; the crystals were monoclinic, C2/c, with a = 28.103(1) Å, b = 7.721(2) Å, c = 13.443(2) Å, beta = 94.290(7) degrees, and Z = 8. The structure was solved by Patterson methods and was refined by full-matrix least-squares procedures to R = 0.043 for 1855 reflections with I >/= 3sigma(I). The kinetic results are consistent with a mechanism involving an attack of O(2) at the V(IV) center, followed by the formation of radicals and H(2)O(2) as transient intermediates.
authors.affiliation: Medicinal Inorganic Chemistry Group, Department of Chemistry, University of British Columbia, Vancouver, BC, Canada V6T 1Z1.
authors.forename: Yan
authors.initials: Y
authors.lastname: Sun
authors.forename: Brian R.
authors.initials: BR
authors.lastname: James
authors.forename: Steven J.
authors.initials: SJ
authors.lastname: Rettig
authors.forename: Chris
authors.initials: C
authors.lastname: Orvig