Theory of electron-vibrational and electron-conformational interactions in chemistry,
biochemistry, biological and molecular physics; protein structure and dynamics; quantum
chemistry; theoretical spectroscopy (optical absorption, resonance Raman scattering, nuclear
magnetic resonance, Mössbauer effect); catalytic activity of transition metal complexes and
metalloenzymes, especially of metalloporphyrins and heme proteins.
Main Results
Theoretical approach to understanding and prediction of structural and dynamic features of
metalloporphyrins and heme proteins based on the Jahn-Teller and pseudo Jahn-Teller effects
was developed. In particular
1.
Influence of axial ligand coordination to 3dn metalloporphyrins on the
metal position in respect to the porphyrin plane. The developed theory
explained all the known experimental data and allowed to predict
configuration of new complexes. Application of the developed theory to the
heme structure of different heme proteins explained change in the iron atom
position caused by coordination of different axial ligands and weak
dependence of the heme structure of cytochrome c on the iron oxidation state.
The developed theory also predicted specific change in the heme geometry
upon Soret excitation, this result was proved experimentally lately.
2.
Influence of the iron displacement out of the porphyrin plane on the
resonance Raman and optical absorption spectra of deoxyheme proteins.
It was obtained that position of the resonance Raman iron-histidine band and
intensity of the optical absorption band III are controlled by the heme doming.
This result allowed to explain the experimentally obtained temperature and
pressure dependences of the shapes of both the bands. Also it was shown that
temporal dependence of the resonance Raman iron-histidine band and optical
absorption band III after the photolysis of the heme protein complexes allows
to study separately heme and protein globule relaxations.
3.
The differences in the coordination geometries of carbon monoxide, nitric
oxide and dioxygen to different 3dn metalloporphyrins was shown to be a
manifestation of pseudo Jahn-Teller effect. The same theory explained
difference between yields of photolysis of these compounds and predicted
essential population of high rotational states of photodissoated ligands, this
prediction was supported experimentally lately.
4.
The specific relationship between the splitting of the visible and Soret
optical absorption bands of different porphyrins in a low-symmetry
environment was shown to be controlled by the Jahn-Teller and pseudo JahnTeller interactions with low symmetry porphyrin vibrations.
A method for investigation of activation of different molecules by metallocomplexes based
on the vibronic theory of chemical activation and quantum chemical calculations of electron
density metal→ligand transfer, was developed. This method was used to study activation of
different diatomic ligands by iron porphyrin complexes, modeling active centers of different
heme proteins. In particular
1.
The stretching vibration of carbon monoxide, dioxygen and cyanide
coordinated by different heme complexes in dependence on the
coordination geometry and heme electrostatic environment. It was
obtained that this frequency is strongly affected by the electric field, this result
explained variation of the carbon monoxide band position in different heme
proteins and their mutants. It was concluded that the shape of the carbon
monoxide infrared absorption band must be sensitive to the dynamics of the
heme environment, this conclusion was supported experimentally lately.
2.
The experimental results on the temperature dependence of the carbon
monoxide infrared absorption band of the corresponding complexes of
different heme proteins in different solvents were interpreted using the
theory of molecular absorption and taking into account the effect of the
dynamics of the of amino acids forming the heme pocket and water molecules
located in this pocket. It was shown that this dynamics is sensitive to the state
of the protein environment, glassy matrix or solvent.
3.
Electronic structures of thiolate and imidazolate iron porphyrin complexes
(models of active centers of cytochrome P450 and horseradish peroxidase,
respectively) with carbon monoxide and dioxygen were studied by using heme
quantum chemical calculations. It was shown that deprotonation of the
proximal iron ligand essentially affects the catalytic activities of these heme
proteins and their optical absorption spectra.
4.
Development of a theoretical model in frameworks of which experimental data
on optical absorption, resonance Raman and Mössbauer spectroscopies, and
magnetic susceptibility will be explained. Such a model is necessary to
provide reliable interpretation of numerous spectroscopic data on the heme
protein structure and dynamics.