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Structural and Functional Model of the Rieske Dioxygenases

Professor Larry Que and his research group:

The initial step in remediation of aromatic compounds in the environment involves the cis-dihydroxylation of an arene double bond. This unusual reaction is catalyzed by the Rieske dioxygenases, bacterial enzymes that have mononuclear iron active sites with a 2-His-1-carboxylate facial triad. In an article to appear in Angew. Chem. Int. Ed., graduate student Paul Oldenburg and postdoctoral associates Chun-Yen Ke and A. Alex Tipton in the group of Professor Larry Que report the structure and characterization of [Fe(L1)(Cl)], a complex that serves as the first structural and functional model of the Rieske dioxygenases. The polydentate L1 ligand provides two pyridine donors and a bidentate carboxylate, closely mimicking the iron environment in the Rieske dioxygenase active site. [Fe(L1)(Cl)] promotes olefin epoxidation with H2O2 as oxidant but effects instead, after dechlorination by treatment with AgOTf, the desired cis-dihydroxylation of olefins. This contrasting behavior emphasizes the requirement for two available cis sites for dihydroxylation. Isotopic labeling studies suggest that the activation of H2O2 at the iron center involves formation of a cis HO-Fe(V)=O oxidant.

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