| Abstract: | Nickel is an essential metal in biological systems and numerous studies have investigated the import, regulation, utilization, and export in cells and the proteins involved. Coordination complexes of nickel have been aimed at providing background information on exchange of nickel from N-rich binding sites used for import and storage to S-rich sites of the active enzymes. The model compounds were used to investigate a range of metal exchange reactions that are plausible during nickel homeostasis in cells. A comprehensive review has examined the MN2S2 complexes that have been synthesized-to-date and their structural aggregation properties when two to four metals bind to the available lone pair on the thiolate in MN₂S₂ complexes. The review summarized a wide range of modifications that are possible for MN₂S₂ complexes ranging from the metal used to the organic linker between the N and S donor atoms. The aggregation modes are largely determined by the coordination number preferences of the secondary metal(s). Another project attempted to quantify the electron donor properties and steric requirements of such MN₂S₂ metalloligands. Electronic donor properties were measured using the IR stretches in metal carbonyl reporter units. Attempts to quantify the spacial requirements of MN₂S₂ metalloligands were challenging due to the asymmetry of such ligands and several approaches were utilized such as the ligand cone angles (related to the famous Tolman cone angle) for monodentate binding, wedge angles for bidentate binding, or percent buried volume computations for both cases. A series of MN₂S₂O₂ complexes was synthesized and metal exchange properties examined. The complexes could be obtained from S-modification of MN₂S₂ compounds of from the free N₂S₂ ligand followed by metallation. The study showed the hierarchy of metal exchange followed the Irving-Williams series of stability for first row transition metals: Fe²⁺ < Co²⁺ < Ni²⁺ < Cu²⁺ > Zn²⁺. The mechanism of exchange appears to occur through a ligand unwrapping/wrapping process similar to the previously investigated M(EDTA) systems by Margerum in the 1960's. A wide range of biomimetic and inorganic compounds structures were solved using X-ray diffraction methods and figures for the finalized structures are presented. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155443 |
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