Toward model compounds for the resting cytochrome c oxidase active site

[摘要] Part I. An unusual appended-tail porphyrin, UroTPPH$sb2$, which possesses a site of unsaturation in the tail (lending rigidity) and a terminal imidazole moiety joined at the C-4 rather than N-1, has been examined. Zinc(II) and iron(III) derivatives of the photosensitive (UroTPP)$sp{2-}$ have been prepared and characterized to explore the potential for (and mode of chelation) of the imidazole-containing tail. The metalloporphyrin compounds are of special interest, with both neutral imidazole and charged imidazolate tail forms being possible. Characterization of these compounds have included physical measurements utilizing NMR, IR, EPR, $sp{57}$Fe Mossbauer, and MCD spectroscopies and magnetic susceptibility studies. This study is one of the first in-depth studies of chloro and trifluoroacetate derivatives of appended-tail iron(III) porphyrin systems. After deprotonation of the imidazole moiety of the appended-tail, both high- and low-spin forms of the iron(III) derivatives have been observed. The predominant form of these high- and low-spin iron(III) derivatives in the solid state is probably best described as a dimer form, while a high-spin form predominates in solution at room temperature. These (Fe$sp{m III}$(UroTPP)X) compounds with X = Cl$sp{-}$ and CF$sb3$CO$sb{2-}$ have been investigated as potential precursors to bimetallic $mu$-X synthetic analogs of derivatized active-site structures of cytochrome c oxidase. Part II. Imidazolate-bridged, mixed-metal binuclear porphyrin compounds have been reinvestigated to model the proposed imidazolate-bridged (cytochrome $asb3sp{3+}$(imid)Cu$sp{2+}$) active-site structure of resting cytochrome c oxidase. The model compounds have been derived from (M$sp{m II}$(TPP)) (M = Co or Mn) and (M$sp{m II}$(imidH)$sb2$DAP) $sp{2+}$ (M = Zn or Cu) to form binuclear compounds with (M(imid)M$sp{primeprime}$) centers. A reevaluation of the manganese compounds has been necessary to clarify the oxidation state of the manganese porphyrin center and to reevaluate the magnetic properties reported for the (Mn(imid)Cu) compound. Also, the previously presumed deoxygenated forms of the binuclear cobalt(II) compounds have been actually found to be oxygenated forms of cobalt(III). New deoxygenated forms of the cobalt(II) compounds have been synthesized and characterized in this work. Characterization of the compounds have included physical measurements utilizing IR, uv-visible, and EPR spectroscopies, and magnetic susceptibility studies.

[发布机构] Rice University