F. N. Tomilin

Fluorescence of calcium-discharged obelin: The structure and molecular mechanism of emitter formation

279 The systems named “preliminary charged” occupy a special place among numerous bioluminescence systems. The most well-known and studied representatives of such bioluminescence systems are Ca 2+ -regulated photoproteins, which are mainly responsible for the luminescence of marine coelenterates [1]. The photoprotein molecule is a stable enzyme–substrate complex composed of a monosubunit polypeptide and an oxygen-preactivated substrate, 2-hydroperoxycoelenterazine, which is stably but noncovalently bound to the protein. Bioluminescence is initiated by calcium ions and emerges due to oxidative decarboxylation of the substrate bound to the protein. This causes formation of the reaction product, coelenteramide (CLM), in an excited state, and ëé 2 . The transition of CLM from the excited to ground state is accompanied by light emission. The bioluminescence of photoproteins is independent of é 2 , because oxygen is already bound to the protein as a 2-hydroperoxy derivative of coelenterazine. The independence of oxygen is among the main distinctions of photoprotein reactions from the other bioluminescence reactions catalyzed by luciferases. The bioluminescence of photoproteins is observed in the range of 465–495 nm and depends on the particular organism from which the photoprotein is isolated. The photoproteins bound to 2-hydroperoxycoelenterazine do not fluoresce but display a bright fluorescence immediately after the reaction, when bound to CLM.

Theoretical study of the magnetic properties of ordered vacancies in 2D hexagonal structures: Graphene, 2D-SiC, and h-BN

The magnetic properties of vacancies in 2D hexagonal structures—graphene and 2D-SiC and h-BN monolayers—have been studied. It has been found that a local magnetic moment exists in all listed systems in the presence of vacancies. However, in 2D hexagonal silicon carbide, the local magnetic moment appears only in the presence of silicon vacancy. In addition, the effect of the distance between vacancies in a monolayer on transitions between the ferromagnetic and antiferromagnetic states has been revealed.

Theoretical study of vacancies and adatoms in white graphene

The stability of the B and N atomic vacancies and divacancies in an h-BN monolayer deformed by 2 and 4% along one of the axes has been investigated. It has been established that the N atomic vacancies are most stable; their concentration is insignificant and does not affect the properties of white graphene. The number of vacancies depends on the mobility of N and B atoms on the layer surface; therefore, the probability of recombination with the vacancies has been estimated. It has been revealed that the energy barrier for the migration of the B and N adatoms is about 0.23 and 1.23 eV, respectively. In view of such a low barrier for the B adatom, this type of adatoms will quite rapidly move over the surface and recombine with vacancies, in contrast to the N adatoms. Therefore, only nitrogen atom vacancies can exist in the h-BN monolayer grown by the methods, where the adatoms could possibly appear on the surface.

The effect of halogen substitution on the structure and electronic spectra of fluorone dyes

By means of the B3LYP density functional method with the use of the polarized continuum model PCM, we have performed quantum-chemical computations of the electronic absorption and fluorescence spectra of fluorone dianions: fluorescein, dibromofluorescein, eosin, erythrosine, and Rose Bengal in vacuum and methanol. We have revealed conformational features of the structure of fluorone dianions (charge redistribution, changes in the bond lengths and angles between bonds) second by the halogen substitution, the transition from the ground state to an excited state, and the change of the solvent (vacuum-methanol). Absorption and fluorescence wavelengths, constant dipole moments, transition dipole moments, and oscillator strengths have been calculated. We have showed that, upon halogenation of fluorones, the absorption spectra are redshifted and the Stokes shift decreases, which is qualitatively consistent with experimental results.

Theoretical study of the influence of vacancies on the electronic structure of a hexagonal boron nitride monolayer

The influence of boron and nitrogen vacancies and divacancies on the electronic structure of a hexagonal boron nitride h-BN monolayer is studied. In the presence of vacancies in the structure, the introduced states appear in the forbidden band. The position of an introduced state with respect to the upper occupied level and the lower vacant level depends on deformation. Calculations show that, depending on the defect type and the magnitude of the applied deformation, the introduced state can be both localized and not localized on atoms surrounding the defect. When the state is localized in the system, the inhomogeneous distribution of the spin density is observed, resulting in the appearance of the magnetic moment in the system.

Possible scheme of synthesis-assembling of fullerenes

A new scheme of fullerene formation is proposed on the basis of the similarity between the experimentally detected carbon structures. According to experimental data, the microclusters of C2 and C10 are synthesized first and then either an intermediate nucleus cluster or an obtainable lower fullerene is assembled from them. A high-symmetry fullerene can be assembled with a high probability from a nucleus cluster with a “good” symmetry. The atomic and electronic structures of molecules such as C36, C60, C70, and C76 are analyzed. For C36, the NMR spectra are calculated and compared with the experimental data.

Correlation of the chemical properties of carbon nanotubes with their atomic and electronic structures

The nature of chemical bonding in carbon nanoclusters is investigated by the PM3 semiempirical quantum-chemical method. The influence of the atomic structure on the electronic characteristics and chemical properties of nanoclusters is analyzed. A σ-π model is proposed for the chemical bonding in nanotubes. It is shown that, in the framework of the proposed model, nanotubes are objects characterized by a small contribution of π states to the valence band top.

Possibility of a 2D SiC Monolayer Formation on Mg(0001) and MgO(111) Substrates

The geometrical characteristics of a 2D SiC monolayer on Mg(0001) and MgO(111) plates regarded as potential materials for growing two-dimensional silicon carbide were studied. The most favorable positions of the atoms of 2D SiC on the substrates were determined. In the 2D SiC/Mg(0001) system, unlike in 2D SiC/MgO(111), the deviation of the carbon atom from the silicon carbide monolayer was insignificant (0.08 Å). Consequently, magnesium can be used as a substrate for growing two-dimensional silicon carbide. The use of MgO(111) is not recommended because of a significant distortion of the 2D SiC surface.

Stability of forest lepidopteran pheromones against environmental factors

A quantum-chemical study has been made of the interactions of pheromones of some lepidopteran forest pests (Siberian moth Dendrolimus superans sibiricus Tschetv and gypsy moth Limantria dispar L.) with components of the ambient air, as well as the effect of electromagnetic radiation on the pheromones. It is found that the reactions of pheromones with substances contained in the forest air are irreversible and proceed with liberation of heat. Electromagnetic radiation quite strongly affects the structure of pheromones, whereby the pheromone molecule is activated and can readily enter into reactions.

Action of the atomic and electronic structure of pheromone molecules on the effectiveness of communication in xylophagous insects

The B3LYР/6-31(p,d) density functional method is applied to pheromones of the forest xylophagous insects Ips typographus L., Monochamus urussovi Fisch., and Monochamus galloprovincialis Oliv. to calculate the absorption spectra and find excited states. The calculated results are used to assess the possible activity of the molecules when they are affected by solar radiation.