Quantum chemical calculations of the molecular structure of diphenylguanidine and experimental studies of its tautomerism in solution

MNDO-PM3 and AMI quantum chemical calculations of the molecular structure of N,N’-diphenylguanidine (DPG) prove that the molecule preferably exists as an asymmetric tautomer with a basic center C=N-. IR and UV spectral data, dipole moments, and average molecular weights of DPG solutions in nonpolar and low-polar solvents confirm the results of calculations, indicating formation of hydrogenbonded cyclic self-associates of DPG in solution. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 4, pp. 618–625, July–August, 1998.     

Vibrational moments of fundamental transitions in low-temperature molecular liquids: Determination from the band shape of vibrations in the overtone spectral range

It is shown that the integrated absorption coefficients of strong fundamental bands of some gaseous substances can be determined with an accuracy of 5–10% using experimental data on the spectral moments of bands in the overtone spectral range of these substances in the liquid phase near the melting point. The absorption coefficients are calculated within the framework of the cell model of the liquid state from the contributions of the resonance dipole-dipole interaction to the second spectral moment. The combination and overtone absorption bands of the SF₆, CF₄, SiF₄, NF₃, CHF₃, CC1F₃, CBrF₃, OCS, N₂O, and CO₂ molecules in the liquid state and in solutions in liquefied Xe, Kr, and O₂ are recorded. The data in the literature on the intensity of strong IR bands in the gas phase are analyzed. Using an improved experimental technique, additional measurements are performed. It is found that the absorption coefficients determined from the spectral characteristics of the liquids agree well with the coefficients measured in the gas phase.     

Effect of screening on the emissivity of field electron emitters based on carbon nanotubes

The effect of screening on the emissivity of a field cathode built around a carbon nanotube array is analyzed. A numerical method of solving the Laplace equation for intricate-shape cathodes is developed that makes it possible to relate the amplification factor to the nanotube spacing in arrays containing as many as 225 emitters. Mutual screening of the tubes, which shows up in the dependence of the field amplification factor on the average emitter spacing, is studied numerically. The optimal spacing between the tubes that provides an emission current maximum density at a given applied voltage is determined. The role of edge effects in carbon nanotube screening is established.     

Preparation of the recombinant НU-proteins from <Emphasis Type="Italic">S. melliferum</Emphasis> and <Emphasis Type="Italic">M. gallisepticum</Emphasis> and of their complexes with DS-DNA for structural NMR experiments

We created a high-performance system for expression of ¹³C, ¹⁵N-double-labeled recombinant НU-proteins from mycoplasms S. melliferum (HUSpm) and M. gallisepticum (HUMgal), and a purification protocol that yields protein samples suitable for structure studies by high-resolution NMR. Using these proteins we optimized the conditions of NMR experiments and obtained two-dimensional heteronuclear ¹H/¹⁵N-HSQC and ¹H/¹³С-HSQC-CT NMR spectra of free НU-proteins (HUSpm and HUMGal), and 1H/15N-HSQC spectrum of a complex between HUSpm and a double-stranded DNA (ds-DNA). The techniques we created are applicable in the studies of НU-proteins from other organisms. They allow analyzing structure and dynamics of free proteins and of their conformational changes induced by binding of various ds-DNAs or of DNA binding inhibitors.     

Molding loose metal particles into briquettes with the use of short pulses of high density current

Theoretical estimates and experimental investigations were carried out on the process of molding a mixture of metal particles and a dielectric (air) into briquettes with the use of short pulses of high density current. Four groups of specimens were studied consisting of metal fragments and the dielectric in various proportions. In the experiments and the current and voltage oscillograms, the electrical resistance and the temperature of the specimens before and after passing the current were measured and their ultimate strength was determined. It has been found that the processes affecting the distribution of the current over the specimen cross section and the specimen inductance during the current pulse play an important role in molding briquettes of sufficient strength for transportation and processing.     

Thermally stable polymers based on bis-acenaphthyls

The thermal stability of poly-bis-acenaphthylenyls was studied by dynamic and isothermal TG methods.All these polymers demonstrate high thermal stabilities; increasing length of the dicarboxylic acid leads to an enhancement of the thermal properties of the polymers.

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Zusammenfassung Mittels dynamischen und isothermischen TG-Methoden wurde die thermische StabilitÄt von Poly-bis-acenaphthylenen untersucht. Jeder dieser Polymere zeigt eine hohe thermische StabilitÄt; lÄngere DicarbonsÄuren führen zu einer Verbesserung der thermischen Eigenschaften der Polymere.

     

Spectroscopic evidence for hydrogen diffusion through a several-nanometers-thick titanium carbonitride layer on silicon

Multiple internal reflection Fourier transform infrared spectroscopy, together with other analytical techniques, was used to follow the diffusion of atomic hydrogen through a 10-nm-thick titanium carbonitride layer deposited onto a Si(100)-2x1 surface from tetrakis(dimethylamino)titanium as a chemical vapor deposition precursor. The recombinative desorption of hydrogen from the TiCN/Si interface was shown to coincide with the temperature range where most Ti-based diffusion barriers break down.     

Parametric analysis of eigenvalues of matrices corresponding to linear one-route catalytic reaction mechanism

The parametric analysis of accepted eigenvalues of matrices observed in chemical kinetics and corresponding to the linear n-stage one-route mechanisms with irreversible stages has been conducted. Relaxation times with varying one of the rate constants are given. The possibility of nonmonotonic change of relaxation times with growing rate constants is shown.

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Rival approaches to mathematical modelling in immunology

In order to formulate quantitatively correct mathematical models of the immune system, one requires an understanding of immune processes and familiarity with a range of mathematical techniques. Selection of an appropriate model requires a number of decisions to be made, including a choice of the modelling objectives, strategies and techniques and the types of model considered as candidate models. The authors adopt a multidisciplinary perspective.