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Studies pre-edge features of iron complexes using X-ray absorption spectroscopy. Types of ligating atoms; Relative intensities of electric quadrupole transitions; Characterization of iron active sites.

Investigates the geometric structure of the catalytically relevant ferrous active site of phenylalanine hydroxylase (PAH). Observation of the low ligand field strength; Use of the magnetic circular dichroism and X-ray absorption; Effects of the substrate-induced allosteric activation on the structure of iron site.

Presents the background and theoretical description of the GNXAS, an integrated approach to the analysis of extended X-ray absorption fine structure method. Comparison of Fe(acac)3 GNXAS distance and angle fitting results to crystallographic values; Molecular structure of Fe(acac); Angle dependence of the Fe-C-N multiple scattering contribution in K3Fe(CN)6.

Probes the oxidation and spin state of the iron in activated bleomycin using X-ray absorption spectroscopy. Determination of the presence of a short iron-oxo bond; Pre-edge and edge regions of the Fe K-edge spectra; Bond distances.

Characterizes extended X-ray absorption fine structure (EXAFS) data on a series of {FeNO}7 model compounds using a theoretical data analysis package GNXAS. GNXAS fits; Angle determination; Models.

Chemical reduction of the mononuclear ferric active site in the bacterial intradiol cleaving catecholic dioxygenase protocatechuate 3,4-dioxygenase (3,4-PCD, Brevibacterium fuscum) produces a high-spin ferrous center. We have applied circular dichroism (CD), magnetic circular dichroism (MCD), variable-temperature-variable-field (VTVH) MCD, X-ray absorption (XAS) pre-edge, and extended X-ray absorption fine structure (EXAFS) spectroscopies to investigate the geometric and electronic structure of the reduced iron center. Excited-state ligand field CD and MCD data indicate that the site is six-coordinate where the (5)E(g) excited-state splitting is 2033 cm(-)(1). VTVH MCD analysis of the ground state indicates that the site has negative zero-field splitting with a small rhombic splitting of the lowest doublet (delta = 1.6 +/- 0.3 cm(-)(1)). XAS pre-edge analysis also indicates a six-coordinate site while EXAFS analysis provides accurate bond lengths. Since previous spectroscopic analysis and the crystal structure of oxidized 3,4-PCD indicate a five-coordinate ferric active site, the results presented here show that the coordination number increases upon reduction. This is attributed to the coordination of a second solvent ligand. The coordination number increase relative to the oxidized site also appears to be associated with a large decrease in the ligand donor strength in the reduced enzyme due to protonation of the original hydroxide ligand.