Radical intermediates in the oxidation of octaethylheme to octaethylverdoheme.
Iron(III) oxyoctaethylporphyrin was isolated and purified as a dimer. The addition of tosylmethyl isocyanide to a solution of the dimer produced a monomer species, which was isolated and identified as bis(tosylmethyl isocyanide)iron(II) 5-oxyoctaethylporphyrin pi-neutral radical. The product of dissociation of the dimer by imidazole was bis(imidazole)iron(III) 5-oxyoctaethylporphyrin. The spectral properties of the product of dissociation of the dimer by pyridine and published data on bis(pyridine)oxymesoheme and bis(pyridine)oxyprotoheme were consistent with its identification as bis(pyridine)iron(II) 5-oxyoctaethylporphyrin pi-neutral radical. When this product was exposed to oxygen, a weak radical signal appeared in its electron spin resonance spectrum, which was attributed to the displacement of one of its pyridine ligands by O2 to form (pyridine)(dioxygen)iron(II) 5-oxyoctaethylporphyrin pi-neutral radical. The pyridine oxygen radical converted spontaneously to octaethylverdohemochrome, which was purified and identified as bis-(tosylmethyl isocyanide)iron(II) octaethylverdohemochrome hydroxide. The yield of verdohemochrome from iron oxyporphyrin was increased by the addition of phenylhydrazine or ascorbate. A scheme for the oxidation of iron(III) oxyporphyrin to iron(II) verdoheme by O2 that proposes a mechanism for the expulsion of CO and the replacement of a methene bridge of the porphyrin ring by an oxa bridge is presented.
Masuoka
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N
Department of Pathology, University of California, San Diego, La Jolla 92093.
Itano
H A
HA
D001654:Bile Pigments / Q000138:chemical synthesis*; D055598:Chemical Phenomena; D002621:Chemistry; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000031:analogs & derivatives*; D007202:Indicators and Reagents; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D013053:Spectrophotometry; D013329:Structure-Activity Relationship
D001654:Bile Pigments; D007202:Indicators and Reagents; C044987:octaethylverdohemochrome; D006418:Heme; C016626:octaethylheme