Radiolysis Study of the Alloxan-Dialuric Acid Couple: I. The Reduction of Alloxan by e aq - and ⋅COO - Radicals

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Abstract
Reduction of alloxan (A) [a cytotoxic substance] to dialuric acid (AH2) by eaq- [hydrated electron] and .COO- was studied by .gamma. and pulse radiolysis. By .gamma. radiolysis, the G-value for dialuric acid formation is equal to G(AH2) = 4.7 .+-. 0.25 eq/100 eV = GH + Geaq- + GOH - 2GH2O2, dialuric acid being oxidized by H2O2. Pulse radiolysis gives evidence for an intermediate .AH formation which should be of a semiquinone type, and whose absorption spectrum has been characterized. Its production rate constants by reactions of eaq- and .COO- with alloxan were measured: k(eaq- + A) = (1.7 .+-. 0.02) .times. 1010 M-1 s-1; k(.COO- + A) = (3.7 .+-. 1.1) .times. 107 M-1 s-1. .AH disappears by disproportionation with a rate constant 2k = (1.6 .+-. 0.03) .times. 108 M-1 s-1.

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