Axial coordination in nickel and vanadium porphyrins: Transient and difference raman spectroscopy
Nickel and vanadium tetrapyrroles occurring in coal and petroleum are of biological origin and their present day molecular structures provide a valuable chemical fossil marker of the diagenesis of the deposits. Both Ni- and V-porphyrins add axial ligands at the metal site. The authors have investigated the equilibrium properties and nanosecond dynamics of axial ligation in Ni(II)- and V(IV)-porphyrin complexes, Ni-porphyrin-reconstituted heme proteins, and Ni-porphyrin polymers using resonance Raman spectroscopy. The state of axial coordination is recognized by characteristic frequencies of Raman oxidation-state and core-size marker lines arising from the vibrations of the porphyrin ring, and the frequencies distinguish between 4-, 5-, and 6-coordination. For the Ni-porphyrins, 4- and 6-coordinate species are observed in coordinating solvents, while 5-coordinate Ni occurs only in the protein matrix. The axial ligand-Ni stretching mode frequency is influenced by the conformation of the protein matrix. Ligand affinity is affected by porphyrin structure, ligand basicity, and the porphyrin's environment. The authors also investigated photoinduced ligand-release and ligand binding kinetics using transient Raman spectroscopy. The protein matrix has a strong influence on the kinetics of ligand rebinding. For vanadium porphyrins, similar shifts in the marker lines characterize 5- and 6-coordinate forms.
- Research Organization:
- Sandia National Labs., Albuquerque, NM 87185
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 5399740
- Report Number(s):
- CONF-860425-
- Journal Information:
- Am. Chem. Soc., Div. Pet. Chem., Prepr.; (United States), Journal Name: Am. Chem. Soc., Div. Pet. Chem., Prepr.; (United States) Vol. 31:2; ISSN ACPCA
- Country of Publication:
- United States
- Language:
- English
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Axial coordination in nickel porphyrins and nickel-reconstituted heme proteins investigated by Raman-difference and transient-Raman spectroscopy
Axial coordination in nickel porphyrins and nickel-reconstituted heme proteins investigated by Raman-difference and transient-Raman spectroscopy
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400104 -- Spectral Procedures-- (-1987)
CARBONACEOUS MATERIALS
CARBOXYLIC ACIDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COAL
COMPLEXES
ENERGY SOURCES
FOSSIL FUELS
FUELS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
KINETICS
LASER SPECTROSCOPY
LIGANDS
MATERIALS
MOLECULAR STRUCTURE
NICKEL COMPLEXES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDATION
PETROLEUM
PORPHYRINS
RAMAN SPECTRA
RAMAN SPECTROSCOPY
REACTION KINETICS
SPECTRA
SPECTROSCOPY
STRUCTURAL CHEMICAL ANALYSIS
TRANSITION ELEMENT COMPLEXES
VANADIUM COMPLEXES