Alloxan-dialuric acid cycling: a complex redox mechanism

JANINA A. ROSSO; MARCOS A. ASTORGA; DANIEL O. MÁRTIRE; MÓNICA C. GONZALEZ

FREE RADICAL RESEARCH

Imforma Healthcare,Taylor and Francis

Lugar: London; Año: 2008 vol. 43 p. 93 - 99

1071-5762

Time-resolved kinetic studies involving the reactions of alloxan (A.H2O) with the reducing species superoxide and carbon dioxide radical anions and the reaction of dialuric acid (HA.) with sulphate radicals showed that the same radical (AH+) was formed either by the one-electron reduction of alloxan or by the one-electron oxidation of dialuric acid. A mechanism including several reversible reactions was proposed and validated. A detailed kinetic analysis yields the following bimolecular rate constants: k(A.H2O+SO4.-)< 105 M-1 s-1, k(A.H2O+O2-) = (3.4+/-0.5)x106 M-1 s-1, k(HA+SO4.-) = (8+/-1)x107 M-1 s-1 and k(AH.+AH.) = (1.7+/-0.8)x108 M-1 s-1. From these values, the redox potentials Eo(A.H2O,H+/AH+) = (-290+/-20) mV, Eo(AH+/HA.) = (277+/-20) mV and Eo(A.H2O,H+/HA-) = (-15+/-20) mV, were obtained.