X-ray absorption spectroscopic studies of binuclear iron proteins and transition metal synthetic complexes

X-ray absorption spectroscopy (XAS) has been used to investigate several biologically or catalytically relevant transition-metal containing systems. An XAS spectrum provides local electronic and geometric structural information through analysis of the edge, pre-edge, and extended X-ray absorption fine structure (EXAFS) regions. An overview of XAS is given in Chapter 1. Studies on the Fe-containing enzyme system of soluble methane monooxygenase (sMMO) are presented in Chapters 2, 3, and 4. An EXAFS fitting methodology is described and applied to the oxidized form of the hydroxylase of MMO (MMOHox) alone and in the presence of MMOD, a protein in the sMMO system of unknown function. The methodology is also applied to the oxidized hydroxylase of another bacterial multicomponent monooxygenase, toluene/o-xylene monooxygenase (ToMOHox), with and without its coupling protein, ToMOD. A further study on the reduced forms of MMOH and ToMOH, and the effect of their respective coupling proteins, MMOB and ToMOD, is presented in Chapter 3, while Chapter 4 focuses on the investigation of the structure of the [2Fe-2S] cluster in the reductase protein, MMOR, from sMMO. The characterizations of a series of (side-on-peroxo)dicopper(II) complexes with different counterions and three intermediates in the reaction of one such complex with sodium 2,4-di- tert-butyl-phenolate are presented in Chapter 5. The XAS analysis of equilibrium mixtures of (bis-mu2-oxo)dicopper(III) and (side-on-peroxo)dicopper(II) complexes and the effect that backbone ligand and counterion have on the position of the equilibrium position of the two isomers is given in Chapter 6. A series of mononuclear copper complexes is presented in Chapter 7, with a focus on the oxidation state of the Cu centers. Ferrous complexes that undergo ligand and temperature dependent spin-transitions are discussed in Chapter 8. XAS data are correlated to magnetic susceptibility, UV/vis, and crystallography measurements. A zinc complex that catalyses the carbon-carbon bond forming aldol reaction is presented in Chapter 9. XAS is used to determine the zinc nuclearity. While these studies represent a wide range of interests in inorganic, biological, and catalysis chemistry, their structures and functions are better understood through XAS investigations.