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Hydrogen Peroxide Decomposition by a Non‐Heme Iron(III) Catalase Mimic: A DFT Study
Author(s) -
Sicking Willi,
Korth HansGert,
Jansen Georg,
de Groot Herbert,
Sustmann Reiner
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200601209
Subject(s) - chemistry , hydrogen peroxide , homolysis , bond cleavage , heme , catalase , photochemistry , reactivity (psychology) , peroxide , catalysis , porphyrin , catalytic cycle , medicinal chemistry , reaction mechanism , radical , stereochemistry , organic chemistry , enzyme , medicine , alternative medicine , pathology
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 OO 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.