Volume profile analysis for the reversible binding of superoxide to form iron(II)-superoxo/Iron(III)-peroxo porphyrin complexes.
The one-electron reduced iron(II)-dioxygen adduct, {Fe(II)-O(2)}(-), is known to be an important intermediate in the catalytic cycle of heme (mono)oxygenases. The same type of species, considered as Fe(III)-peroxo, can be formed in a direct reaction between a Fe(II) center and superoxide. In a unique high-pressure study of the reaction between superoxide and the Fe(II) complex of a crown ether porphyrin conjugate in dimethylsulfoxide (DMSO), the overall Fe(II)-superoxide interaction mechanism could be visualized and the nature of all species that occur along the reaction coordinate could be clarified. The equilibrium between the low-spin and high-spin forms of the starting Fe(II) complex was quantified, which turns out to be the actual activation step toward substitution and subsequent inner-sphere electron transfer reactions. The constructed reaction volume profile demonstrates that the reaction product consists of Fe(III)-peroxo and Fe(II)-superoxo species that exist in equilibrium, which can better account for the versatile reactivity of {Fe(II)-O(2)}(-) adducts toward different substrates.
Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany.
Katharina
K
Dürr
Norbert
N
Jux
Achim
A
Zahl
Rudi
R
van Eldik
Ivana
I
Ivanović-Burmazović
D043844:Crown Ethers / Q000737:chemistry; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011166:Porphyrins / Q000737:chemistry*; D011312:Pressure; D013481:Superoxides / Q000737:chemistry*; D013696:Temperature
D043844:Crown Ethers; D005290:Ferric Compounds; D005296:Ferrous Compounds; D011166:Porphyrins; D013481:Superoxides; D004121:Dimethyl Sulfoxide