Resonance Raman studies on oxidation products of iron(II) and ruthenium(II) porphyrins

Insook Rhee Paeng, Marquette University

Abstract

The elucidation of the molecular mechanism of dioxygen binding and its biological activation by heme proteins has been the focus of sustained attention. The main objective of this research was to obtain structural and bonding information about the metal centers (active sites) of hemoproteins through resonance Raman (RR) spectroscopic studies on model system by detecting intermediates. The major accomplishments of this research were summarized as follows: (1) The RR spectra (406.7 nm excitation) of PFe-O-O-FeP and O=FeP (P = TMP, TPP, OEP and other porphyrins) which are formed in the oxidation process of these FeP were measured. These newly observed bridged species have been postulated as intermediates in the oxidation of FeP. The assignment is supported by previous NMR and UV spectral studies and vibrational assignments obtained for the FePO$\sb{2}$ and PFe-O-FeP. (2) The dioxo ruthenium porphyrin, RuP(O)$\sb{2}$ were prepared by the oxidation of RuP(CO) with m-chloroperoxybenzoic acid (mCPBA). The RR and IR spectra of RuP(O)$\sb{2}$ were measured, and their O=Ru=O vibrations assigned by normal coordinate calculations (NCA). A reaction scheme involving two successive O-O bond cleavage of mCPBA was proposed based on the observed intensity patterns of O=Ru=O vibrations. (3) When a toluene solution of RuP(P=TPP) was saturated with O$\sb{2}$ at $-$80$\sp\circ$C, the $\nu\sb{s}$ (RU-O) of PRu-O-O-RuP, $\nu$(RuO) of O=RuP and $\nu\sb{s}$(O=Ru=O) of Ru(TPP)(O)$\sb{2}$ was observed upon raising the temperature. (4) The RR spectra of dioxygen adducts of FeP in O$\sb{2}$ matrices at 30 K were measured. The $\nu$(O-O), $\nu$(Fe-O)$\sb{2}$ and $\delta$(FeOO) of "end-on" adducts and $\nu$(O-O) and $\delta$(FeOO) of "side-on" adducts were detected and former bands were conformed by $\sp{56}$Fe/$\sp{54}$ substitution as well as NCA. During RR measurements, two isomeric ferryl species are formed as result of the O-O bond cleavage by laser irradiation.

Recommended Citation

Insook Rhee Paeng, "Resonance Raman studies on oxidation products of iron(II) and ruthenium(II) porphyrins" (January 1, 1989). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. Paper AAI9014058.
http://epublications.marquette.edu/dissertations/AAI9014058

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