ESR characterization of Thallium (III)-mediated nitrones oxidation

VERSTRAETEN S.,; LUCANGIOLI S.,; GALLEANO M.

INORGANICA CHIMICA ACTA

Elsevier

Lugar: Amsterdan, The Netherlands; Año: 2009 vol. 362 p. 2305 - 2310

0020-1693

We characterized the reactions between Tl (III) and the usual nitrone spin traps (DMPO, POBN, and PBN). 2424 The ESR signal obtained with DMPO corresponded to DMPOX which was avoided neither by the enzymes 2525 superoxide dismutase or catalase, nor by the hydroxyl radical scavengers’ mannitol, ethanol, or methanol. 2626 Only when methanol concentration rose to 90% (v/v), a significant decrease in DMPOX formation was 2727 observed while no detectable DMPOX signal was present at 100% methanol solution. POBN rendered 2828 an unexpected adduct, while no oxidation products were obtained with PBN. Together, the experimental 2929 evidence demonstrates that Tl(III)-supported DMPO oxidation is not mediated by oxygen reactive spe- 3030 cies. Instead, we propose that Tl(III) interacts with the probe, favoring the addition of water. The inter- 3131 mediate is susceptible to be further oxidized by Tl(III) yielding a keto group. Kinetic studies showed 3232 that Tl(III) disappearance rate was higher (1.6 times) than DMPOX formation rate, and equal to Tl(I) for- 33Tl(I) for- 33 mation rate, suggesting a stoichiometry 1.5:1 for Tl(III):DMPOX and 1:1 for Tl(III):Tl(I). The process, an 3434 example of the Forrester–Hepburn’s mechanism, was demonstrated for DMPO while the reactions of 35Forrester–Hepburn’s mechanism, was demonstrated for DMPO while the reactions of 35 Tl(III) with POBN and PBN are still under elucidation.