Iron(III)-catecholato complexes as structural and functional models of the intradiol-cleaving catechol dioxygenases.
The structural and spectroscopic characterization of mononuclear iron(III)-catecholato complexes of ligand L4 (methyl bis(1-methylimidazol-2-yl)(2-hydroxyphenyl)methyl ether, HL4) are described, which closely mimic the enzyme-substrate complex of the intradiol-cleaving catechol dioxygenases. The tridentate, tripodal monoanionic ligand framework of L4 incorporates one phenolato and two imidazole donor groups and thus well reproduces the His2Tyr endogenous donor set. In fact, regarding the structural features of [FeIII(L4)(tcc)(H2O)] (5.H2O, tcc = tetrachlorocatechol) in the solid state, the complex constitutes the closest structural model reported to date. The iron(III)-catecholato complexes mimic both the structural features of the active site and its spectroscopic characteristics. As part of its spectroscopic characterization, the electron paramagnetic resonance (EPR) spectra were successfully simulated using a simple model that accounts for D strain. The simulation procedure showed that the observed g = 4.3 line is an intrinsic part of the EPR envelope of the studied complexes and should not necessarily be attributed to a highly rhombic impurity. [FeIII(L4)(dtbc)(H2O)] (dtbc = 3,5-di-tert-butylcatechol) was studied with respect to its dioxygen reactivity, and oxidative cleavage of the substrate was observed. Intradiol- and extradiol-type cleavage products were found in roughly equal amounts. This shows that an accurate structural model of the first-coordination sphere of the active site is not sufficient for obtaining regioselectivity.
Bruijnincx
Pieter C A
PC
Chemical Biology & Organic Chemistry, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
Lutz
Martin
M
Spek
Anthony L
AL
Hagen
Wilfred R
WR
van Koten
Gerard
G
Gebbink
Robertus J M Klein
RJ
D050548:Catechol 1,2-Dioxygenase / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry*; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D013056:Spectrophotometry, Ultraviolet
D005290:Ferric Compounds; D050548:Catechol 1,2-Dioxygenase