Axial ligand effects on iron and manganese porphyrins: extended Hueckel calculations of Cyt P450 analogs and of O/sub 2/ binding to iron and manganese

Journal Article · Mon Jan 01 04:00:00 EST 1979 · Int. J. Quant. Chem., Quant. Biol. Symp.; (United States)

DOI:https://doi.org/10.1002/qua.560160705· OSTI ID:6572867

Hanson, L K

Certain axial ligand-metal interactions can perturb the electronic structure of metallorporphrins in ways that significantly alter their optical and magnetic spectra. Two classes of such interactions, the origin of the anomalous optical spectra of the hydroxylating enzyme cytochrome P450 and the nature of molecular oxygen binding to Fe(II) and Mn(II) porphyrins, have been examined by charge iterative extended Hueckel calculations. (1) Calculations performed on various low-spin ferrous and ferric porphin RS/sup -/ (mercaptide) and RSH (mercaptan) complexes support the hypothesis that the anomalous spectra of cyt P450 complexes are due to mercaptide sulfur p ..-->.. porphin ..pi..* charge transfer transitions which mix with the porphin ..pi.. ..-->.. ..pi..* transitions. (2) Oxy Fe and Mn porphins were calculated with O/sub 2/ bound in the Pauling (end on, bent) and Griffith (edge on, parallel to the porphin ring) modes. On the basis of optical spectra, the Fe calculations cannot distinguish between the two possible modes of O/sub 2/ binding. In the Mn case, however, all the experimental optical and magnetic data can be explained in terms of the Griffith model but not the Pauling model. The anomalous optical spectra of oxy Mn porphrns are ascribed to porphin ..pi.. ..-->.. d/sub ..pi../ + O/sub 2/..pi../sub g/ charge transfer transitions which mix with the porphin ..pi.. ..-->.. ..pi..* transitions.

• Research Organization: Brookhaven National Lab., Upton, NY
• DOE Contract Number: EY-76-C-02-0016
• OSTI ID: 6572867
• Journal Information: Int. J. Quant. Chem., Quant. Biol. Symp.; (United States), Journal Name: Int. J. Quant. Chem., Quant. Biol. Symp.; (United States) Vol. 6; ISSN IJQBD
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ANGULAR MOMENTUM
CARBOXYLIC ACIDS
COMPLEXES
CYTOCHROMES
ELECTRONIC STRUCTURE
ELEMENTS
ENERGY LEVELS
EXCITED STATES
GROUND STATES
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
IRON COMPLEXES
LIGANDS
MANGANESE COMPLEXES
MOLECULAR STRUCTURE
NONMETALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXYGEN
OXYGEN COMPLEXES
PARTICLE PROPERTIES
PIGMENTS
PORPHYRINS
SPECTRA
SPIN
TRANSITION ELEMENT COMPLEXES