Characterization of superoxide-metalloporphyrin reaction products: effective use of deuterium NMR spectroscopy
Nuclear magnetic resonance spectroscopy has been utilized to define the solution electronic structures of complexes generated from combination of superoxide ion with iron(II) and manganese(II) porphyrins. Very large proton NMR line widths for the iron porphyrin product dictated the use of deuterium NMR for selectively deuterated synthetic porphyrins. On the basis of the pyrrole deuterium signal at 60 ppm (Me/sub 2/SO solvent, 28/sup 0/C, Me/sub 4/Si reference) and a solution magnetic moment of greater than or equal to5.6 ..mu../sub B/, a peroxoiron(III) porphyrin structure consistent with an earlier formulation is favored. A corresponding manganese porphyrin signal at 32 ppm and a solution magnetic moment of 5.0 ..mu../sub B/ are indicative of a superoxomanganese(II) porphyrin configuration with spin coupling between the superoxide ligand and the manganese center. This species provides an excellent model for what has been described as superoxide coupling to a low-spin iron(III) center in the oxyhemoglobin molecule. The peroxoiron porphyrin complex is likely coordinated in the second axial position by a solvent molecule. The axial ligand combination leaves the iron center in a high-spin state, but the peroxo ligand serves to reduce the zero-field-splitting value and indirectly induce large NMR line widths. Variable-temperature NMR Curie law behavior is consistent with monomeric structures. Absence of splitting in the pyrrole signals suggests no attack of porphyrin nitrogen atoms by peroxide or superoxide species.
- Research Organization:
- Univ. of Iowa, Iowa City
- OSTI ID:
- 5485877
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 104:23; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
CARBOXYLIC ACIDS
CHALCOGENIDES
COMPLEXES
DEUTERIUM
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN ISOTOPES
IRON COMPLEXES
ISOTOPES
LABELLING
LIGHT NUCLEI
MANGANESE COMPLEXES
NMR SPECTRA
NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PORPHYRINS
SPECTRA
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES