Hydrocarbon Hydroxylations Catalyzed by AaeAPO: Evidence of Radical Intermediates and Kinetic Isotope EffectsOpen image in new window
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Recently, a new heme-thiolate peroxygenase enzyme from the fungus Agrocybe aegerita, was identified and found to be capable of catalyzing hydrocarbon hydroxylation by using H2O2 as co-substrate with high efficiency and selectivity. It not only shows potential for practical biocatalytic application but also might provide some inspiration for designing biomimetic catalysts. In order to investigate the reaction mechanism, several radical clocks were used in this chapter. Products indicative of radical intermediates were all detected during the oxidation of norcarane, bicycle[2.1.0]pentane and 1,1,2,2-tetremethylcycloprotane with lifetimes ranging from 3.0 to 132 ps. At the same time, a large intramolecular deuterium isotope effect was measured with the hydroxylation of 1,1,1,2,2,3,3-d 7-n-hexane and methyl partially deuterated toluenes. Taken together, a mechanism involving hydrogen atom abstraction and rebound is suggested. More interestingly, small intramolecular KIEs probed by (R)-1-ethylbenzene were also observed. We thought these suppressions were caused by steric hindrance in the active site of enzyme. These isotope masking effects can give us some information about the dynamics of substrates and map the active site environment of enzyme.
KeywordsIsotope Effect Mandelic Acid Kinetic Isotope Effect Hydrogen Atom Abstraction Desaturation Product
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