Influence of porphyrin radical type on V double bond O bond strength in vanadyl porphyrin cation radicals: Implications for heme protein intermediates

Journal Article · Wed May 16 04:00:00 EDT 1990 · Inorganic Chemistry; (USA)

DOI:https://doi.org/10.1021/ic00335a044· OSTI ID:6664256

Macor, K A ^[1]; Czernuszewicz, R S; Spiro, T G ^[2]

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1. Univ. of Notre Dame, IN (USA)
2. Princeton Univ., NJ (USA)

Resonance Raman spectra have been analyzed for vanadyl porphyrin cation radicals of octaethylporphyrin (OEP), meso-tetra-phenylporphyrin (TPP), and meso-tetrametisylporphyrin (TMP). The strength of the metal-oxo bond in these cation radicals is demonstrated to be a function of radical type, a{sub 1u} or a{sub 2u}. Porphyrin ring mode {nu}{sub 2}, which has previously been shown to be a marker for the radical type was used to identify the radicals. The a{sub 1u} OV(OEP) radical exhibited an upshift in the V{double bond}O stretching frequency resulting from the increased positive charge on the porphyrin, which reduces the porphyrin {yields} vanadium electron donation and increases the O {yields} vanadium donation. {nu}(V{double bond}O) frequency decreases were observed for the a{sub 2u} OV(TPP) and OV(TMP) radicals. These can be explained on the basis of mixing of the porphyrin {pi} a{sub 2u} orbital with the vanadium d{sub z{sup 2}} and oxygen p{sub z} orbitals, which is allowed in C{sub 4v} symmetry. This interaction decreases the bond strength in a {sub 2u} cation radicals, since an electron is removed from an orbital with partial V-O {sigma}-bonding character. Mixing of the porphyrin a{sub 1u} {pi} orbital with metal or oxygen orbitals is forbidden. These results imply that porphyrin radical type is an important determinant of the Fe{double bond}O bond strength in heme protein cation-radical intermediates. 34 refs., 5 figs.

• DOE Contract Number: AC02-81ER10861
• OSTI ID: 6664256
• Journal Information: Inorganic Chemistry; (USA), Journal Name: Inorganic Chemistry; (USA) Vol. 29:10; ISSN 0020-1669; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
CARBOXYLIC ACIDS
CHEMICAL BONDS
COMPLEXES
DATA
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PORPHYRINS
RAMAN SPECTRA
SPECTRA
TRANSITION ELEMENT COMPLEXES
VANADIUM COMPLEXES