Modeling the 2-his-1-carboxylate Facial Triad: Iron-catecholato Complexes As Structural and Functional Models of the Extradiol Cleaving Dioxygenases.
From: Organic Chemistry and Catalysis Group, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
Journal of the American Chemical Society
- Publish Date: Feb 2007
- ISSN: 0002-7863
- Volume: 129
- Issue: 8
- Pages: 2275-86
- Medium: Print
- Language: English
- Citation (JAMA): Bruijnincx Pieter C A, Lutz Martin, Spek Anthony L, et al. Modeling the 2-his-1-carboxylate Facial Triad: Iron-catecholato Complexes As Structural and Functional Models of the Extradiol Cleaving Dioxygenases.. J. Am. Chem. Soc. Feb 2007;129:2275-86
Abstract
Mononuclear iron(II)- and iron(III)-catecholato complexes with three members of a new 3,3-bis(1-alkylimidazol-2-yl)propionate ligand family have been synthesized as models of the active sites of the extradiol cleaving catechol dioxygenases. These enzymes are part of the superfamily of dioxygen-activating mononuclear non-heme iron enzymes that feature the so-called 2-His-1-carboxylate facial triad. The tridentate, tripodal, and monoanionic ligands used in this study include the biologically relevant carboxylate and imidazole donor groups. The structure of the mononuclear iron(III)-tetrachlorocatecholato complex [Fe(L3)(tcc)(H2O)] was determined by single-crystal X-ray diffraction, which shows a facial N,N,O capping mode of the ligand. For the first time, a mononuclear iron complex has been synthesized, which is facially capped by a ligand offering a tridentate Nim,Nim,Ocarb donor set, identical to the endogenous ligands of the 2-His-1-carboxylate facial triad. The iron complexes are five-coordinate in noncoordinating media, and the vacant coordination site is accessible for Lewis bases, e.g., pyridine, or small molecules such as dioxygen. The iron(II)-catecholato complexes react with dioxygen in two steps. In the first reaction the iron(II)-catecholato complexes rapidly convert to the corresponding iron(III) complexes, which then, in a second slow reaction, exhibit both oxidative cleavage and auto-oxidation of the substrate. Extradiol and intradiol cleavage are observed in noncoordinating solvents. The addition of a proton donor results in an increase in extradiol cleavage. The complexes add a new example to the small group of synthetic iron complexes capable of eliciting extradiol-type cleavage and provide more insight into the factors determining the regioselectivity of the enzymes.
Mesh Headings (Keywords): Binding Sites, Carboxylic Acids, Catalysis, Catechols, Crystallography, X-Ray, Dioxygenases, Ferric Compounds, Hydrogen Bonding, Ligands, Models, Molecular, Molecular Structure, Oxygen
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