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  • Title: Significant change in electronic structures of heme upon reduction by strong Coulomb repulsion between Fe d electrons.
    Author: Kamiya K, Yamamoto S, Shiraishi K, Oshiyama A.
    Journal: J Phys Chem B; 2009 May 14; 113(19):6866-72. PubMed ID: 19371055.
    Abstract:
    We report total-energy electronic-structure calculations based on the density functional theory performed on a low-spin heme. We have found that the high-lying occupied and low-lying unoccupied states having Fe d and/or porphyrin pi orbital character are significantly rearranged upon the reduction of the heme. An analysis of these states shows that the remarkable elevation of the Fe d levels takes place due to the strong Coulombic repulsion between accommodated d electrons. Due to a peculiarity of the heme, this elevation could be controlled by lower-lying empty porphyrin pi states, leading to electron transfer from Fe d orbitals to the porphyrin pi ones in order to reduce the Coulomb-energy cost. This self-limiting mechanism provides a natural explanation not only for the present calculated results, but also for general electron delocalization appearing under various physiological conditions, regardless of the types of the hemes.
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