Graduate Thesis Or Dissertation
 

Synthesis and oxidation of metal-thiolate compounds which mimic the active site function of thiolate dioxygenase enzymes

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  • Part I describes the synthesis of bis(fac-S)((tris)2-aminoethanethiolatoiron( III))iron(III) chloride. The compound was first discovered during an attempt to prepare a ternary complex of iron, thiolate and pi-acid ligand. The compound is a reasonably air-stable iron(III)-thiolate that contains a linear tri-iron cluster with each iron bridged to the adjacent iron by three thiolate sulfurs. The elemental analysis of a microcrystalline sample corresponds to [Fe(Fe(SCH₂CH₂NH₂)₃)₂]Cl₃-3H₂0CH₃0H. Large crystals showed little or no x-ray diffraction. Data collected for one crystal resulted in a structure solution (R = 0.098) for the Fe₃ cluster in one-electron reduced form as a dichloride. UV-visible spectroscopy shows a peak at 490 nm which is due to an Fe[superscript III]-SR charge transfer. The cluster reacts slowly with oxygen when dissolved in solution, causing a decomposition of the compound to iron rust and disulfide. Cyclic voltammetry shows a reversible redox couple between the +3 and +2 charged cluster on a short timescale (-310 mV, -240 mV vs. SCE), followed by dissociation of the reduced cluster after several scans. The infrared spectrum of the cluster has a characteristic pattern in the region between 1800-400 cm⁻¹. Magnetic susceptibility measurements give μ[subscript eff] = 2.6 Bohr Magnetons, which corresponds to each of the three irons being in the low spin ferric state with coupling of spins (S = 1/2). Mossbauer spectroscopy supports this conclusion, giving two major doublets with relative intensity 1.7:1, ΔE[subscript Q] = 1.78, δ = +0.24 and ΔE[subscript Q] = 1.55, δ = +0.34. Oxidation with H₂0₂ and MCPBA did not produce sulfenates; however, added thiolates did react with the cluster. Part II of this work describes the stereochemistry of the products of the H₂0₂ oxidation of potassium trans-N-bis (penicillaminato-N,S,0)cobaltate(III). Two optical isomers were found for the disulfenate (R,S and S,S), while only one isomer (S) was isolated by column chromatography for the monosulfenate. The second isomer (R) was produced in dilute solution and shown to exist by circular dichroism spectroscopy. Differences in the product distribution under light and dark conditions are noted.
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