Theoretical Investigation of Molecular and Electronic Structures of Buckminsterfullerene-Silicon Quantum Dot Systems.

Density functional theory (DFT) and density functional tight binding (DFTB) molecular dynamics (DFTB/MD) simulations of embedding and relaxation of buckminsterfullerene C60 molecules chemisorbed on (001) and (111) surfaces and inside bulk silicon lattice were performed. DFT calculations of chemisorbed fullerenes on both surfaces show that the C60 molecule deformation was very small and the C60 binding energies were roughly ∼4 eV. The charge analysis shows that the C60 molecule charges on (001) and (111) surfaces were between -2 and -3.5 electrons, respectively, that correlates well with the number of C-Si bonds linking the fullerene molecule and the silicon surface. DFT calculations of the C60 molecule inside bulk silicon confirm that the C60 molecule remains stable with the deformation energy values of between 11 and 15 eV for geometries with different C60 configurations. The formation of some C-Si bonds causes local silicon amorphization and corresponding electronic charge uptake on the embedded fullerene cages. Charge analysis confirms that a single C60 molecule can accept up to 20 excessive electrons that can be used in practice, wherein the main charge contribution is located on the fullerene's carbon atoms bonded to silicon atoms. These DFT calculations correlate well with DFTB/MD simulations of the embedding process. In this process, the C60 molecule was placed on the top of the Si(111) surface, and it was further exposed by a stream of silicon dimers, resulting in subsequent overgrowth by silicon.

The electronic structure and spin states of 2D graphene/VX2 (X = S, Se) heterostructures.

The structural, magnetic and electronic properties of 2D VX2 (X = S, Se) monolayers and graphene/VX2 heterostructures were studied using a DFT+U approach. It was found that the stability of the 1T phases of VX2 monolayers is linked to strong electron correlation effects. The study of vertical junctions comprising of graphene and VX2 monolayers demonstrated that interlayer interactions lead to the formation of strong spin polarization of both graphene and VX2 fragments while preserving the linear dispersion of graphene-originated bands. It was found that the insertion of Mo atoms between the layers leads to n-doping of graphene with a selective transformation of graphene bands keeping the spin-down Dirac cone intact.

Electronic structure of α-SrB4O7: experiment and theory.

The investigation of valence band structure and electronic parameters of constituent element core levels of α-SrB(4)O(7) has been carried out with x-ray photoemission spectroscopy. Optical-quality crystal α-SrB(4)O(7) has been grown by the Czochralski method. Detailed photoemission spectra of the element core levels have been recorded from the powder sample under excitation by nonmonochromatic Al Kα radiation (1486.6 eV). The band structure of α-SrB(4)O(7) has been calculated by ab initio methods and compared to XPS measurements. It has been found that the band structure of α-SrB(4)O(7) is weakly dependent on the Sr-related states.

Relative isomer abundance of fullerenes and carbon nanotubes correlates with kinetic stability.

A methodology to evaluate the kinetic stability of carbon nanostructures is presented based on the assumption of the independent and random nature of thermal vibrations. The kinetic stability is directly correlated to the cleavage probability for the weakest bond of a given nanostructure. The application of the presented method to fullerenes and carbon nanotubes yields clear correlation to their experimentally observed relative isomer abundances. The general and simple formulation of the method ensures its applicability to other nanostructures for which formation is controlled by kinetic factors.

[Stability of lepidopterous pheromone molecules of forest insects to environmental factors].

The interactions of the pheromones of some representatives of the Lepidoptera order with each other and with materials contained in the forest air, as well as the effect of electromagnetic radiation on pheromone have been studied. It was found that the reactions of pheromones with substances contained in the forest air are irreversible and proceed with the liberation of heat. Electromagnetic radiation affects very strongly the structure of pheromones. In this case, a pheromone molecule is activated and can readily enter into reaction.

[Modification of the surface of bioresorbed polymer matrices by laser treatment].

The effect of laser irradiation on the properties of the surface of film matrices obtained from the bioresorbed polymer polyhydroxybuturate has been studied. To determine the spectral region of the polymer optimal for the effective action of radiation on electron molecular bonds, theoretical investigations have been performed, which have shown that, for modifying the surface of matrices obtained from polyhydroxybuturate, it is expedient to use a vacuum laser at a wavelength of 160 nm. Using the laser regime of irradiation of matrices at a radiation power from 3.0 to 30 Wt, a series of films with modified surface, from roughnesses to perforations, have been obtained. The microstructure and properties of the film surface depending on the mode of irradiation have been examined, and conditions have been found under which the contact marginal angles of moistening of films with water can be decreased to 50 degrees (compared with 76-80 degrees in starting products). Thus, the conditions of laser treatment of polyhydroxybuturate matrices have been theoretically substantiated and experimentally realized that provide a beneficial effect on the properties of the surface without destroying the structure of the material.

[Role of histidine in ligand binding ability of hemoglobin gene]. / Rol' gistidina v ligandsviazyvaiushchei sposobnosti gena gemoglobina.

The atomic and electronic structures of heme complexes with His, Gly, and Cys residues (Heme-His, Heme-Gly, and Heme-Cys) in the fifth coordination position of the Fe atom and with oxygen and nitrogen oxide molecules in the sixth Fe position were studied by the semiempirical quantum-chemical method PM3. A comparative analysis of internuclear distances showed that the strength of chemical bonding between the ligand molecules (oxygen and nitrogen oxide) is greater for Heme-Cys than for Heme-His and Heme-Gly complexes. Consequently, the strengthening of the chemical bond of the oxygen (or nitrogen oxide) molecule with Heme-Cys substantially weakens the chemical bond in the ligand molecule. The Mulliken population analysis showed that the electronic density of ligand (oxygen or nitrogen oxide) p-orbitals is transferred to the d-orbitals of the Fe atom, whose charge, calculated according to the Mulliken analysis, formally becomes negative. In the Heme-His complex with oxygen, this charge is substantially greater than in the complex with NO, and the oxygen molecule becomes polarized. No oxygen polarization is observed in the Heme-Cys complex, and the electron density (judging from the change in the Fe charge) is transferred to the coordinated sulfur atom. This is also characteristic of Heme-Cys complexes with nitrogen oxide. An analysis of charges on the atoms indicates that the character of chemical bonding of the oxygen molecule in Heme-Cys and Heme-Gly complexes is similar and basically differs from that in the case of the Heme-His complex. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 2; see also http://www.maik.ru.

[Structure and electronic properties of heme complexes with various ligands]. / Struktura i élektronnye svoistva kompleksov gema s rzalichnymi ligandami.

The electronic and atomic structures, and the molecular dynamics of the atomic structure at 310 K of a set of heme complexes with His and Gly amino acids in the 5th coordination position and some ligands (O2, NO) in the 6th position were studied by ab initio (3-21G basis set) and semiempirical (PM3) quantum chemistry methods and the method of molecular dynamics. It was shown that the type of coordination of the imidazole ring influences the constant of chemical bonding of molecular oxygen of the complexes. On the other hand, NO and O2 molecules have different transinfluence on the ligand in the 5th coordination position. It was shown that temperature affects profoundly the atomic and electronic structures of the complexes, the tightness of chemical bonding and their reactivity.

DNA-methyltransferase SsoII interaction with own promoter region binding site.

The investigation of Sso II DNA-methyltransferase (M.Sso II) interaction with the intergenic region of Sso II restriction-modification system was carried out. Seven guanine residues protected by M. Sso II from methylation with dimethylsulfate and thus probably involved in enzyme-DNA recognition were identified. Six of them are located symmetrically within the 15 bp inverted repeat inside the Sso II promoter region. The crosslinking of Sso II methyltransferase with DNA duplexes containing 5-bromo-2'-deoxyuridine (br5dU) instead of thymidine was performed. The crosslinked products were obtained in all cases, thus proving that tested thymines were in proximity with enzyme. The ability to produce the crosslinked products in one case was 2-5-fold higher than in other ones. This allowed us to imply that thymine residue in this position of the inverted repeat could be in contact with M. Sso II. Based on the experimental data, two symmetrical 4 bp clusters (GGAC), which could be involved in the interaction with M. Sso II in the DNA-protein complex, were identified. The model of M. Sso II interaction with its own promoter region was proposed.