MECHANISM OF OXYGEN ACTIVATION BY IRON-CHLORIN COMPLEXES AND THEIR REACTIVITIES.

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Preparation and characterization of reaction intermediates observed or proposed in the catalytic cycle chlorin-containing heme enzymes. Catalases in Escherichia coli and Neurospora crassa possess iron chlorin prosthetic groups and catalyze dismutation of hydrogen peroxide. While a high-valent iron chlorin complex (chlorin compound I) is postulated to be a reaction intermediate in the catalytic cycle of these catalases, the high-valent chlorins have not been prepared and thus the details of chlorin compound I are still obscure. Thus, we have prepared the chlorin compound I by employing a sterically hindered chlorin model complex. The oxo-iron (IV) chlorin pi-cation radical has been successfully prepared.Models of oxo-iron (IV) chlorin complexes have been prepared and characterized in detail to elucidate the unusual properties of the intermediate of cytochrome d. The six-coordinated oxo-ferrylchorin complex exhibited an unusual splitting of the hyperfine-shifted pyrroline proton resonances in its NMR spectrum, suggestive of deformation of the pyrroline ring of the chlorin complex.The model complexes of the putative reaction intermediate, peroxo-Fe (III), have been synthesized. The peroxo complexes have electronics structures similar to those of the corresponding porphyrin complexes. However, unusual features have been observed in their deuterium NMR spectra, rationalized by large deformation of the pyrroline ring of the peroxo complexes.