Ligand design and model complexes of (nitrogen,sulfur)M(II) metalloenzymes

This thesis describes the synthesis, structural, and spectroscopic characterization of new NxSy ligands and their zinc(II) and iron(II) complexes as models of the active sites of the non-heme iron enzymes peptide deformylase (PDF) and superoxide reductase (SOR). These two enzymes share the common structural features of a single iron center bound in the active site by a mixed N/S donor set from His/Cys ligands. The two N2S(thiolate) ligands PATH and LIm2SH were used to prepare zinc(II) and iron(II) models of PDF, while an N 3S(thiolate) ligand was used in work aimed at modeling features of both PDF and SOR.; Chapter 1 reviews the current knowledge regarding the enzymes PDF and SOR. The discussion involves the structure of the active sites, and the role of the metal ion in the catalytic mechanism of these enzymes. Other related metalloenzymes e.g. carbonic anhydrase (CAII), and nitrite hydratase (NHase) are discussed briefly for background information.; In Chapter 2, we discuss the synthesis and spectroscopic characterization of a rare tripodal, N2S ligand, LIm2SH. The reactions of this ligand with various zinc(II) and iron(II) starting materials to give metal complexes (LIm2S)ZnCH3, [(LIm2S)2Zn], [(LIm2S )2Zn2. (OH)(CH3CN)2](BF 4)3, [(LIm2S)2Zn 2Br2], and (LIm2S)2Fe are discussed in detail. The characterization of these metal complexes suggests that the ligand LIm2SH can bind in a tripodal N 2S fashion, however, bidentate N,S coordination mode is the preferred bonding mode.; Chapter 3 describes the synthesis of a monomeric complex, (PATH)ZnNCS, of the linear ligand PATH. The lability of the open site in this complex was determined by VT-NMR experiments involving (PATH)ZnNCS and (PATH)ZnBr. (PATH)ZnBr was also converted into the new species [(PATH)ZnOH] by titration with NaOH in MeOH, which was monitored by 1H NMR spectroscopy. Through these experiments we have demonstrated that a linear ligand can also form model complexes with similar structural properties as that of the enzyme.; In Chapter 4, we present a series of zinc(II) and iron(II) formate complexes of the tetradentate N3S ligand Py2SH. The bonding modes of the formate ligand in these complexes have been studied to insight into the bonding mode in the catalytic cycle of Zn(II)-PDF and Fe(II)-PDF. This work combined with theoretical calculations (DFT) has led to the formation of hypothesis regarding the differences in reactivity of zinc(II) and iron(II) PDF.; The focus of chapter 5 is on the synthesis of model complexes of SOR. The reactions of KO2 and H2O2 with (Py 2S)FeCl are described, and the intermediate formed in the reaction is characterized by UV-vis and EPR spectroscopies. The data indicates that the intermediate formed is possibly an iron(III)-hydroxide complex, [(Py 2S)FeOH]+, although iron(III)-peroxo intermediate ([(Py 2S)FeOOH]+) cannot be ruled out.