Theoretical study of the structure and stability of oxo heme derivatives

The geometric and electronic structures, energy stability, and normal mode frequencies of molecules and ions of oxo heme derivatives Heme=O^0,±, Heme-O-Heme^0,±, Heme-OO^0,±, and Heme-OO-Heme^0,± (Heme=FeC₃₄H₃₂N₄O₄) in the states of different multiplicity have been calculated by the density functional theory B3LYP method with several basis sets. Energetically preferred states have been determined, and the energies of different channels of their decomposition with dissociation of the Fe-O and O-O bonds have been estimated. The relative energies of superoxide and peroxide isomers of the dioxygenyl complexes Heme-OO^0,± and Heme-OO-Heme^0,± have been estimated. For the double-decker Heme-OO-Heme^0,± complexes, local minima (intermediates) have been found, which correspond to the structures containing rhombic Fe(μ-O)₂Fe moieties with the iron atoms linked by two covalent oxygen bridges Fe-O-Fe. The trends in the behavior of the equilibrium geometric parameters, vibrational frequencies, and spin density distribution between the Fe and O atoms and the porphyrin ring of oxohemes have been analyzed as a function of the electronic state multiplicity and the external charge of the complex.