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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

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2008

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Vol. 82, nr 9

1853-1863

EN

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.

2

Quantum Chemical Modelling of the Oxidation of Myoglobin

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

Polish Journal of Chemistry

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2004

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Vol. 78 / nr 10

1907-1924

EN

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.

3

Cluster model studies on catalytic properties of vanadium pentoxide

Witko M., Tokarz R., Hermann K.

Polish Journal of Chemistry

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1998

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Vol. 72, nr 7S

1565-1583

EN

ZINDO cluster model calculation are performed to study the electronic structure and chemical reactivity of the V2O5(010) surface. Inter-atomic binding in vanadium pentoxide is determined to be of a mixed ionic and covalent character. The calculations reveal the difference in the catalytic propertoes between structurally inequivalent surface oxygen centers and show the increased local reactivity of bridging oxygens with respect to the electrophilic adparticles. Convergence of the electronic properties with respect to the cluster size is achieved for cluster as large as V10O31H12. The effect of the second substrate layer on the surface electronic properties is found to be negligile. Further, rather similar electronic parameters of the V10O31H12 cluster in its idealized, bulk and optimized geometry are obtained. The H/H(+) species adsorb at the V2O5(010) surface, always at oxygen sites, forming very stable surface hydroxyl groups. The strongest binding occurs with the oxygen O(c) bridging two bare vanadium atoms. These O(c) oxygens become quite mobile in presence of the H/H(+) adparticle. Allowing the surface oxygen to ralax during adsorption of H/H(+) leads to different adsorption scenarios depending on the surface oxygen site. At the vanadyl oxygen site a very stable and rigid hydroxyl group O(A)H is formed above the vanadium center. At the doubly coordinated oxygen site O(b) the adsorbate penetrates between two vanadyl groups to form a local O(b)H group, while at the O(c) site an O(c)H group is created (slightly above the surface O(c) position), where O-H binding is strongest. Weak initial interaction, between triply coordinated oxygen O(d,e) and the incoming H/H(+) species, leads to stabilizaton of the adsorbate near the closest vanadyl site resulting in a tilted O(a)H group instead of O(d) H or O(e)H.