DMPOX formation through a non-radical process

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

Montevideo, Uruguay

Congreso; V Reunión de la Sociedad de Radicales Libres en Biología y Medicina, Grupo Sudamericano y V Conferencia Internacional de Peroxinitrito y Especies Reactivas del Nitrógeno; 2007

Sociedad de Radicales Libres en Biología y Medicina, Grupo Sudamericano

DMPOX (5,5-dimethyl-1-pyrrolidone-2-oxyl) is an oxidation product of the spin probe DMPO (5,5-dimethyl-1-pyrroline N-oxide). We characterized DMPOX formation in the reaction between DMPO (10 mM) and thallium (III) (Tl(III): 5-100 M). DMPOX was determined by ESR at room temperature using a Bruker ECS 106 with an ER 4102ST cavity. The obtained spectrum in water solution was a primary nitrogen triplet with each line split into triplets with a 1:2:1 pattern, aN(1) = 7.3 ± 0.1 G and aH(2) = 3.9 ± 0.1 G. Superoxide dismutase (SOD, 100 mU), catalase (CAT, 100 mU), mannitol (50 mM), ethanol or methanol (50%) did not affect the intensity of DMPOX signal, suggesting that oxygen free radicals are not involved in this process. However, DMPOX signal intensity decreased 82 % (P < 0.01) in 90 % (v/v) methanol, and no signal was detected in 100 % (v/v) methanol, indicating that water is necessary for this reaction. Tl(III) and Tl (I) concentrations were determined by the reaction with trifluoperazine dihydrochloride, and by capillary electrophoresis with UV detection at 214 nm, respectively. In these conditions, Tl(III) disappearance rate was 1.6- times higher than DMPOX formation rate, and equal to Tl (I) formation rate, suggesting a stoichiometry 1.5:1 for Tl(III):DMPOX and 1:1 for Tl(III):Tl(I). Additionally, Tl(III) did not oxidize the aliphatic nitrones PBN and POBN. In conclusion, we propose that the reaction between Tl(III) and DMPO is a non-radical mediated process, and that it could proceed through a Forrester-Hepburn mechanism where Tl (III) caused a nucleophilic attack to the 2-position of DMPO ring, forming the intermediate DMPO-OH. Next, Tl(III) mediates the two-electron oxidation of DMPO-OH to a keto group, rendering DMPOX and Tl (I). Supported by UBA (B802, B072) and CONICET, Argentina.