Participation of Hydroxyl Radical in the Formation of Verdoheme-type Compound in the Reaction of a Ferric Porphyrin with Hydrogen Peroxide

Abstract

A verdoheme-type compound was formed in the reaction of met-hemoCD2, an inclusion complex of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphinatoiron(III) (FeIIITPPS) with a per-O-methylated β-cyclodextrin dimer (Py2CD) having an OCH2PyCH2O (Py: pyridine-3,5-diyl) linker, with hydrogen peroxide (H2O2) in aqueous solution in the presence of 2-methoxyphenol (guaiacol). In the absence of guaiacol, met-hemoCD2 rapidly reacted with H2O2 to form a radical pair composed of an oxoferryl compound and a hydroxyl radical, which further reacted to yield unknown compounds. However, in the presence of guaiacol, one-electron reduction of the oxoferrylporphyrin afforded the original met-hemoCD2, which reacted with the hydroxyl radical remaining in the cyclodextrin cage to yield the verdoheme-type compound.