Metal Complexes for Structural Modeling of Active Sites of Metalloenzymes Relevant to Gas Catalysis.

摘要

Sulfur rich metal coordinated active sites is a prominent feature of many metalloenzymes (hydrogenase, nitrogenase, carbon monoxide dehydrogenase) involved in catalytically producing and/or absorbing helpful and/or toxic gases. As the mechanism of gas production and/or absorption heavily depends on the structural intricacies, biomimetic modelling of the active sites is of paramount importance to understand the structure--function relationship. It has been established that the small molecule models with steric bulk of the thiols at the ortho- position of derivatized benzenethiols can provide the stability.;Millar and Koch were pioneers in introducing a series of ortho -steric benzene thiols and achieving stabilization of high oxidation state first row transition metal complexes. Fe3+ & Co 3+ complexes and Fe4S4 tertamer with 2,4,6-triisopropyl-benzenethiol are the highlights. Following the idea of increasing the steric bulk, this thesis will present a new compound - 2,4,6-tricyclohexylbenzenethiol, and attempted synthesis and characterization of monomeric and tetrameric metal complexes with it.;Dithiols such as ethanedithiol (edt) and 1,2-benzenedithiol (bdt) have been extensively used for synthesizing models due to their simplicity in structure. While edt lacks the required steric bulk, bdt is a non-innocent ligand influencing electrochemical properties of the complexes. To combat these difficulties, a new class of dithiol was introduced by Michelle Millar and Stephen Koch - norbornanedithiol - a conformationally fixed alkane dithiol. Metal complexes with Fe2+, Co2+, Ni2+ & Pt 2+ will be discussed. Hydrogen bonding of the solvent molecules to the thiolates and the implications of such observation will be presented.;Fe-Ni hydrogenases are responsible for converting H2 gas to H+. This class of enzyme contains a bimetallic active site. In our effort to mimic the structure, we have crystallographically characterized Fe-Ni bimetallic compounds with bridged thiolates and intermetallic distance of ∼3A as found in the wild type from Desulfovibrio gigas. An extensive IR study of the reaction and the compounds will be presented.