Models for extradiol cleaving catechol dioxygenases: syntheses, structures, and reactivities of iron(II)-monoanionic...

Area of Science:

• Bioinorganic Chemistry
• Coordination Chemistry
• Enzyme Mimicry

Background:

• Extradiol cleaving catechol dioxygenases are crucial enzymes in microbial metabolism.
• Enzyme-substrate complexes feature an iron(II) center and a monoanionic catecholate.
• Understanding these complexes aids in designing biomimetic catalysts.

Purpose of the Study:

• To synthesize and characterize iron(II)-monoanionic catecholate complexes as models for enzyme-substrate complexes.
• To investigate the reactivity of these model complexes with O(2) and NO.
• To elucidate the factors influencing catechol cleavage pathways.

Main Methods:

• Synthesis of iron(II)-catecholate complexes with varying ligands (TPA, bpmcn) and catecholates (CatH, DBCH).
• X-ray crystallography to determine complex structures.
• Spectroscopic studies (UV-vis, EPR) to characterize reaction intermediates and products.
• Reactivity studies with O(2) and NO, followed by product analysis.

Main Results:

• Synthesized and structurally characterized four iron(II)-catecholate complexes.
• Observed conversion to iron(III)-catecholate dianion complexes upon reaction with O(2) or NO.
• Identified ligand epimerization (syn/anti configurations) affecting reactivity and spectroscopic properties.
• Demonstrated that catechol cleavage occurs primarily via intradiol pathways, with minor extradiol cleavage.
• Found that the syn configuration of iron(III)-catecholate complexes inhibits O(2) reaction.

Conclusions:

• The synthesized iron(II)-catecholate complexes effectively model key features of catechol dioxygenase active sites.
• Ligand configuration plays a critical role in the reactivity and catechol cleavage mechanisms of these iron complexes.
• These findings provide insights into the structure-activity relationships governing catechol dioxygenase function.