To model the mononuclear FeIII-OOH species identified in the catalytic cycle of the anticancer drug bleomycin, the iron chemistry of the pentadentate ligand N-[bis(2-pyridylmethyl)aminoethyl]pyridine-2-carboxamide (H-PaPy3) has been investigated. The complex [Fe III(PaPy3)OCH3](ClO4) was reacted with H2O2 to form a red species (λ max=480 nm, ε=1800 M-1 cm-1) with an S=1/ 2 EPR signal at g=2.25, 2.17, and 1.95. This species has been identified by electrospray ionization mass spectrometry as [FeIII(PaPy 3)OOH](ClO4) and further characterized by resonance Raman and EXAFS analysis. The decomposition of this intermediate leads to the modification of the ligand, as revealed by 1H NMR. One hydrogen atom is substituted by a solvent-derived methoxy group. The substitution at this site is a result of the two-electron oxidation of the ligand following the heterolytic cleavage of the O-O bond of the FeIII-OOH species. This is a plausible mechanism to rationalize related ligand modifications that have been proposed in the decay of activated bleomycin.
- Iron-hydroperoxo intermediate
- Ligand modification