Molecular Structure,Thermodynamic and Spectral Characteristics of Metal-Free and Nickel Complex of Tetrakis(1,2,5-thiadiazolo)porphyrazine

The Knudsen effusion method with mass spectrometric control of the vapor composition was used to study the possibility of a congruent transition to the gas phase and to estimate the enthalpy of sublimation of metal-free tetrakis(1,2,5-thiadiazolo)porphyrazine and its nickel complex (H₂TTDPz and NiTTDPz, respectively). The geometrical and electronic structure of H₂TTDPz and NiTTDPz in ground and low-lying excited electronic states were determined by DFT calculations. The electronic structure of NiTTDPz was studied by the complete active space (CASSCF) method, following accounting dynamic correlation by multiconfigurational quasi-degenerate second-order perturbation theory (MCQDPT2). A geometrical structure of D_2h and D_4h symmetry was obtained for H₂TTDPz and NiTTDPz, respectively. According to data obtained by the MCQDPT2 method, the nickel complex possesses the ground state ¹A_1g, and the wave function of the ground state has the form of a single determinant. Electronic absorption and vibrational (IR and resonance Raman) spectra of H₂TTDPz and NiTTDPz were studied experimentally and simulated theoretically.     

The behavior of benzene confined in a single wall carbon nanotube

We present the molecular dynamics study of benzene molecules confined into the single wall carbon nanotube. The local structure and orientational ordering of benzene molecules are investigated. It is found that the molecules mostly group in the middle distance from the axis of the tube to the wall. The molecules located in the vicinity of the wall demonstrate some deviation from planar shape. There is a tilted orientational ordering of the molecules which depends on the location of the molecule. It is shown that the diffusion coefficient of the benzene molecules is very small at the conditions we report here. © 2015 Wiley Periodicals, Inc.     

Effect of the near-lying level on the kinetics of the field of superradiance of a thin layer

The effect of the local field on the competition of transitions in the superradiance of an incompletely excited thin layer of three-level atoms (Λ-diagram of working transitions) is studied. Analysis is made for the conditions when one of the sublevels of the lower doublet is initially unpopulated. For an initially unpopulated upper sublevel of the lower doublet, a new superradiance regime is found.     

Effect of the near-lying level on the kinetics of populations in the superradiance of a thin layer: Local-field regime

The effect of the local field on the competition of transitions in the superradiance of an incompletely excited thin layer of three-level atoms Λ-diagram of working transitions) is studied. The analysis made proves that the upper sublevel of the lower doublet is initially unpopulated. It is shown that the Raman transition, in the local-field regime, is ahead of the development of the superradiance pulse and causes the transfer of populations between sublevels of the lower doublet.     

Calculation of the properties of a self magnetic insulation wave in a vacuum transmission line on the basis of conservation laws

On the basis of the conservation laws for the energy and the z component of the momentum in a self magnetic insulation wave propagating in a vacuum transmission line, the relativistic factor γ_m corresponding to the voltage at the outer boundary of the electron sheath is found under the assumption that all electrons incident to the anode have identical energies and identical angles of incidence. The effect of energy losses in the precursor wave on basic properties of the self magnetic insulation wave is investigated.     

Suppression of unstable oscillations in a boundary layer

The study considers emission of Tollmien—Schlichting waves by a vibrator mounted on a plate with a viscous incompressible fluid flowing round it. It is shown that by changing the shape of a membrane working at a supercritical frequency, it is possible not only to reduce greatly the amplitude of the forced oscillations, but also to achieve their complete degeneration. This possibility opens the door to the suppression of an already formed Tollmien—Schlichting wave by a vibrator with specially chosen parameters. This type of equipment makes it possible to suppress perturbations in a laminar boundary layer and delay its transition to the turbulent state.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 20–26, March–April, 1987.The authors are grateful to the referee V. A. Buchin for a useful observation expressed in the course of preparation of the article for the press.     

Post-translational modification in the gas phase: mechanism of cysteine S-nitrosylation via ion-molecule reactions

The gas-phase mechanism of S-nitrosylation of thiols was studied in a quadrupole ion trap mass spectrometer. This was done via ion-molecule reactions of protonated cysteine and many of its derivatives and other thiol ions with neutral tert-butyl nitrite or nitrous acid. Our results showed that the presence of the carboxylic acid functional group, -COOH, in the vicinity of the thiol group is essential for the gas-phase nitrosylation of thiols. When the carboxyl proton is replaced by a methyl group (cysteine methyl ester) no nitrosylation was observed. Other thiols lacking a carboxylic acid functional group displayed no S-nitrosylation, strongly suggesting that the carboxyl hydrogen plays a key role in the nitrosylation process. These results are in excellent agreement with a solution-phase mechanism proposed by Stamler et al. (J. S. Stamler, E. J. Toone, S. A. Lipton, N. J. Sucher. Neuron 1997, 18, 691-696) who suggested a catalytic role for the carboxylic acid group adjacent to cysteine residues and with later additions by Ascenzi et al. (P. Ascenzi, M. Colasanti, T. Persichini, M. Muolo, F. Polticelli, G. Venturini, D. Bordo, M. Bolognesi. Biol. Chem. 2000, 381, 623-627) who postulated that the presence of the carboxyl in the cysteine microenvironment in proteins is crucial for S-nitrosylation. A concerted mechanism for the gas-phase S-nitrosylation was proposed based on our results and was further studied using theoretical calculations. Our calculations showed that this proposed pathway is exothermic by 44.0 kJ mol(-1). This is one of the few recent examples when a gas-phase mechanism matches one in solution.     

Core-softened system with attraction: trajectory dependence of anomalous behavior

In the present article we carry out a molecular dynamics study of the core-softened system and show that the existence of the water-like anomalies in this system depends on the trajectory in P-ρ-T space along which the behavior of the system is studied. For example, diffusion and structural anomalies are visible along isotherms as a function of density, but disappears along the isochores and isobars as a function of temperature. On the other hand, the diffusion anomaly may be seen along adiabats as a function of temperature, density, and pressure. It should be noted that it may be no signature of a particular anomaly along a particular trajectory, but the anomalous region for that particular anomaly can be defined when all possible trajectories in the same space are examined (for example, signature of diffusion anomaly is evident through the crossing of different isochors. However, there is no signature of diffusion anomaly along a particular isochor). We also analyze the applicability of the Rosenfeld entropy scaling relations to this system in the regions with the water-like anomalies. It is shown that the validity of the Rosenfeld scaling relation for the diffusion coefficient also depends on the trajectory in the P-ρ-T space along which the kinetic coefficients and the excess entropy are calculated.     

Convective transport of combustion products in the atmosphere above large fires

A nonstationary axisymmetric model of the development of a turbulent convective combustion product column above a fire in a stratified atmosphere is proposed. The model takes into account the compressibility of the gas and the diffusion of the aerosol particles and makes it possible to predict the dynamics of ascent of the convective column, the height of the cloud and the distribution of the aerosol in the atmosphere. The numerical and experimental data are compared.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 47–52, July–August, 1990.