Synthesis and Characterization of Iron(II) Complexes Modeling the Active Site Structure of Nonheme Iron Dioxygenases
Date of Award
Master of Science (MS)
Fiedler, Adam T.
The aerobic degradation of polycyclic aromatic compounds, which are widespread contaminants in soils and groundwaters, is carried-out in large part by various Fe-containing dioxygenases that perform the cis-dihydroxylation and oxidative cleavage of aromatic rings. Recently, a new Fe dioxygenase family emerged that catalyzes a remarkable set of transformations; the distinguishing feature of these enzymes is that their monoiron(II) centers are coordinated by three histidines residues (i.e., imidazole ligands) in a facial geometry - a departure from the "canonical" 2-histidine-1-carboxylate facial triad that is dominant among nonheme monoiron enzymes. Members of the "3His family" are capable of oxidatively cleaving C-C bonds in substrates that are generally resistant to degradation, including β-diketones and monohydroxylated aromatics (e.g., salicylic acid). This thesis describes the design, synthesis, and characterization of novel transition-metal complexes with polyimidazole ligands that serve as faithful structural and functional models of these important metalloenzymes. Specifically, high-spin iron(II) β-diketonato complexes were synthesized with the PhTIP (tris(2-phenylimidazol-4-yl)phosphine), and tBuTIP ((tris-2-tert-butylimidazol-4-yl)phosphine) ligands. The complexes were analyzed with a combination of experimental and computational methods including X-ray crystallography, cyclic voltammetry, UV-vis absorption, 1H nuclear magnetic resonance, and density functional theory (DFT). The resulting geometric- and electronic-structure descriptions were compared with those obtained for analagous models with the anionic Me2Tp (hydrotris(3,5-dimethylpyrazol-1-yl)borate) and Ph2Tp (hydrotris(3,5-diphenylpyrazol-1-yl)borate) ligands. A similar biomimetic approach was employed in the synthesis and characterization of models of the enzyme salicylate 1,2-dioxygenase.