Alloxan-dialuric acid cycling: A complex redox mechanism

Abstract

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 + ) < 10⁵m⁻¹ s⁻¹, k(A.H₂O + O₂⁻)=(3.4±0.5)×10⁶m⁻¹ s⁻¹, k(HA⁻+)=(8±1)×10⁷m⁻¹ s⁻¹ and k(AH.+AH.)=(1.7±0.8)×10⁸m⁻¹ s⁻¹. From these values, the redox potentials E°(A.H₂O,H⁺/AH.)=(−290±20) mV, E°(AH./HA⁻)=(277±20) mV and E°(A.H₂O,H⁺/HA⁻)=(−15±20) mV, were obtained.

• Alloxan
• dialuric acid
• superoxide radical ions
• sulphate radicals