Hydrogen Peroxide Decomposition by a Non-Heme Iron(III) Catalase Mimic: A DFT Study

✍ Scribed by Willi Sicking; Hans-Gert Korth; Georg Jansen; Herbert de Groot; Reiner Sustmann

• Book ID: 102794546
• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 874 KB
• Volume: 13
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200601209

✦ Synopsis

Abstract

Non‐heme iron(III) complexes of 14‐membered tetraaza macrocycles have previously been found to catalytically decompose hydrogen peroxide to water and molecular oxygen, like the native enzyme catalase. Here the mechanism of this reaction is theoretically investigated by DFT calculations at the (U)B3LYP/6‐31G* level, with focus on the reactivity of the possible spin states of the Fe^III^ complexes. The computations suggest that H~2~O~2~ decomposition follows a homolytic route with intermediate formation of an iron(IV) oxo radical cation species (L^.+^Fe^IV^O) that resembles Compound I of natural iron porphyrin systems. Along the whole catalytic cycle, no significant energetic differences were found for the reaction proceeding on the doublet (S=1/2) or on the quartet (S=3/2) hypersurface, with the single exception of the rate‐determining OO bond cleavage of the first associated hydrogen peroxide molecule, for which reaction via the doublet state is preferred. The sextet (S=5/2) state of the Fe^III^ complexes appears to be unreactive in catalase‐like reactions.