Alloxan-dialuric acid cycling: a complex redox mechanism.
Time-resolved kinetic studies involving the reactions of alloxan (A.H(2)O) 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.H(2)O + [image omitted] ) < 10(5) m ( -1 ) s(-1), k(A.H(2)O + O(2) (-))=(3.4+/-0.5)x10(6) m ( -1 ) s(-1), k(HA(-)+[image omitted] )=(8+/-1)x10(7) m ( -1 ) s(-1) and k(AH(.)+AH(.))=(1.7+/-0.8)x10(8) m ( -1 ) s(-1). From these values, the redox potentials E degrees (A.H(2)O,H(+)/AH(.))=(-290+/-20) mV, E degrees (AH(.)/HA(-))=(277+/-20) mV and E degrees (A.H(2)O,H(+)/HA(-))=(-15+/-20) mV, were obtained.
Rosso
Janina A
JA
Instituto de Investigaciones Fisicoquimicas Teoricas y Aplicadas, Departamento de Quimica, Universidad Nacional de La Plata, La Plata, Argentina. janina@inifta.unlp.edu.ar
Astorga
Marcos A
MA
Martire
Daniel O
DO
Gonzalez
Mónica C
MC
D000496:Alloxan / Q000737:chemistry*; D001463:Barbiturates / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D005978:Glutathione / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000737:chemistry; D007700:Kinetics; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D010782:Photolysis; D013431:Sulfates / Q000737:chemistry
D001463:Barbiturates; D005609:Free Radicals; D013431:Sulfates; C069025:sulfate radical; C004718:dialuric acid; D000496:Alloxan; D006861:Hydrogen Peroxide; D005978:Glutathione; D010100:Oxygen