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Modification of Tetraphenylporphyrin Ring in Manganese(III) Complexes - Theoretical Description of the Influence on Their Physicochemical Properties

Szaleniec M., Tokarz-Sobieraj R., Witko M.

Polish Journal of Chemistry

2008

Vol. 82, nr 9

1853-1863

Metalloporphyrins are known to be efficient catalysts in oxidation of hydrocarbons. To understand a mechanism of oxidation processes de tailed knowledge of the electronic and structural parameters of these systems is required. Here, atomic parameters calculated by means of DFT method for the selected manganese porphyrins are correlated with experimental redox potential. The results of calculations carried out for systems with modification in phenyl substituents showed that charge of porphyrin ring and charge of axial ligand are good theoretical descriptors of effect introduced by the substituent. These descriptors correlate (R2 = 0.97) with experimental value of redox potential of the MnIII/MnII system.

Quantum Chemical Modelling of the Oxidation of Myoglobin

Ilkowska E., Witko M., Tokarz-Sobieraj R., Stochel G.

Polish Journal of Chemistry

2004

Vol. 78 / nr 10

1907-1924

The electronic structure (charge distribution, bond indices) and the geometry (bond distances and angles) of the deoxyheme and the oxyheme with coordinated proximal histidine in their reduced and oxidized form were determined by the INDO method. The effect of the distal histidine (in the case of the oxyheme) and a water molecule (in the case of the metheme) on the geometry, charge distribution and stability of the systems was investigated. The method was adopted to model the oxidation of myoglobin in biological systems. The results revealed that both deoxy- and oxymyoglobin could spontaneously undergo one-electron oxidation. The mechanistic considerations based on the charge distribution and energetic effects led to the conclusion, that in oxymyoglobin's case the electron transfer are followed by dissociation of a dioxygen molecule and addition of a water molecule, where both processes proceed in parallel.