Premium
Axial ligand effects on iron and manganese porphyrins: Extended hückel calculations of cyt p450 analogs and of O 2 binding to iron and manganese
Author(s) -
Hanson Louise Karle
Publication year - 2009
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560160705
Subject(s) - porphin , chemistry , manganese , ligand (biochemistry) , spectral line , ferric , crystallography , photochemistry , computational chemistry , inorganic chemistry , porphyrin , organic chemistry , biochemistry , receptor , physics , astronomy
Certain axial ligand‐metal interactions can perturb the electronic structure of metalloporphyrins 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 Hückel calculations (1) Calculations performed on various low‐spin ferrous and ferric porphin RS − (mercaptide) and RSH (mercaptan) complexes support the hypothesis that the anomalous spectra of cyt P450 complexes are due to mercaptide sulfur p → porphin π* charge transfer transitions which mix with the porphin π → π* transitions. (2) Oxy Fe and Mn porphins were calculated with O 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 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 porphyrins are ascribed to porphin π → d π + O 2 π g charge transfer transitions which mix with ihe porphin π → π* transitions.