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Calculated optical spectrum of model oxyheme complex
Author(s) -
Loew Gilda H.,
Herman Zelek S.,
Zerner Michael C.
Publication year - 1980
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.560180218
Subject(s) - delocalized electron , chemistry , absorption spectroscopy , spectral line , crystal (programming language) , porphyrin , molecular physics , molecular orbital , atomic physics , crystallography , physics , photochemistry , molecule , optics , quantum mechanics , organic chemistry , computer science , programming language
The optical spectrum of a model oxyheme complex has been calculated using a new intermediate neglect of differential overlap ( INDO‐SCF‐CI ) method that allows for the inclusion of configuration interaction and transition metals. In addition to the porphyrin π→π* transitions common to all heme proteins, four weak x , y polarized transitions observed only in oxyheme complexes have been calculated and assigned to excitations involving the lowest‐empty highly delocalized (Oπ, d π) orbital. Two broad z ‐polarized bands observed in the single‐crystal polarized absorption spectra of oxymyoglobin and hemoglobin have also been calculated. Controversy exists over the assignment of these transitions and, in particular, over the extent of involvement of the oxygen ligand. Our calculations assign the weaker near‐ IR visible band mainly to the d σ d π→ d π* excitations and the more intense UV band mainly to a 2 u → d σ* excitations. While significant participation (25%) of the highly delocalized (Oπ, d π) virtual orbital is also found, these z ‐polarized transitions need not be totally unique to oxyheme complexes, in keeping with experimental observation.