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The kinetics of the reaction of superoxide radical with Fe(III) complexes of EDTA, DETAPAC and HEDTA

Authors
Journal
FEBS Letters
0014-5793
Publisher
Wiley Blackwell (John Wiley & Sons)
Publication Date
Volume
158
Issue
1
Identifiers
DOI: 10.1016/0014-5793(83)80695-4
Keywords
  • Superoxide
  • Fenton Reaction
  • Hydroxyl Radical
  • Haber—Weiss Reaction
  • Iron Complex
  • Pulse Radiolysis
  • Spin Trapping

Abstract

Abstract To gain an understanding of the mechanism by which the hydroxyl free radical can arise in superoxide generating systems and learn how different chelaters of iron can inhibit this reaction, a pulse radiolysis kinetic study of the reaction of O − 2 with Fe(III)EDTA, Fe(III)HEDTA and Fe(III)DETAPAC (or DTPA) was undertaken. Superoxide reacts readily with Fe(III)EDTA and Fe(III)HEDTA with a pH-dependent second-order rate constant having values of 1.9 × 10 6 M −1.s −1 and 7.6 × 10 5 M −1.s −1 at pH 7, respectively. However, the rate constant for the reaction of O − 2 with Fe(III)DETAPAC was found to be much slower, the upper limit for the rate constant being 10 4 M −1.s −1. These results in conjunction with spin-trapping experiments with Fe(II)EDTA, Fe(II)HEDTA, Fe(II)DETAPAC and H 2O 2 suggests that DETAPAC inhibits the formation of OH by slowing the reduction of Fe(III) to Fe(II) and not by inhibiting the Fenton reaction.

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