Reaction of hydrogen peroxide with low molecular weight iron complexes

Fe(II) complexed with trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) reacts with hydrogen peroxide in neutral aqueous solution at room temperature to yield reactive species which are not scavenged by t-butanol, under conditions where > 90% of hydroxyl radical would be scavenged. Further, the ratio of the rate constants for the reaction of the reactive species with Fe(II)CDTA and H2O2 is 6.2, in contrast to a ratio of 200 which would result if the species were the hydroxyl radical. Thus, it is concluded that the reactive species produced is not the hydroxyl radical, but an iron-oxo species such as the ferryl ion. The reactive species is formed in an apparent first order reaction, when either hydrogen peroxide or Fe(II)CDTA is in kinetic excess. The bimolecular reaction rate constant is (1.26 ± 0.19) x 103 M-1 s-1. In experiments where H2O2 was in kinetic excess, a chain decomposition of H2O2 was observed in which the initially produced iron-oxo intermediate exhibits hydroperoxidase activity. (author)