A Method of Deducing L-Polyhedra for n-Lattices

We suggest a method for selecting an L-simplex in an L-polyhedron of an n-lattice in Euclidean space. By taking into account the specific form of the condition that a simplex in the lattice is an L-simplex and by considering a simplex selected from an L-polyhedron, we present a new method for describing all types of L-polyhedra in lattices of given dimension n. We apply the method to deduce all types of L-polyhedra in n-dimensional lattices for n=2,3,4, which are already known from previous results.     

Aggregation of 1,3,7-trimethylxanthine with methylene blue in aqueous solution

We have studied self-association of aromatic molecules of the thiazine dye methylene blue in aqueous solution, using a dimer model. We have determined the dimerization equilibrium constant for the dye molecules K_D = 3900 ± 800 M⁻¹ at T = 293 K. We have decomposed the experimental spectrum into dimer and monomer components. Using the ratio of the molar absorption coefficients for two absorption bands of the dimer spectrum, we obtained the “average” value of the angle between the electronic transition moments of the molecules in the dimers, α = 48°. We have studied heteroassociation of methylene blue (MB) and 1,3,7-trimethylxanthine (caffeine) molecules in aqueous solution. We have calculated the heteroassociation constant as 200 ± 34 M⁻¹. We conclude that heteroassociation of methylene blue and caffeine molecules leads to a lower effective dye concentration in solution, which hypothetically may affect its biological activity. We have determined the values of the Gibbs free energy, the enthalpy, and the entropy for dimerization of methylene blue molecules: ΔG₂₉₃ = −(20 ± 3) kJ/mol, ΔH = −(25 ± 9) kJ/mol, Δ S₂₉₃ = −(17 ± 6) J/mol·K; and for methylene blue-caffeine heteroassociation: ΔG₂₉₃ = −(13 ± 3) kJ/mol, ΔH = −(14 ± 10) kJ/mol, ΔS₂₉₃ = −(2.4 ± 0.2) J/mol·K, respectively. We have shown that the methylene blue aggregates and the heteroassociates with caffeine are predominantly stabilized by dispersion interactions between the chromophore molecules in the associates. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 158–163, March–April, 2006.     

Theoretical basis for the quantitative characterization of impurities in n-type III–V compound semiconductors by photoelectromagnetic spectroscopy

Theoretical results are described for the quantitative characterization of impurities by photoelectromagnetic spectroscopy. The diagnostics is based on a study of profiles of spectral lines. Line broadening is caused mainly by the influence of electric fields of charged impurities on neutral donors, in which optical transitions occur. The profile of the spectral line for the intradonor transition between 1s and 2p₀ states is calculated taking into account Coulomb correlations in the distribution of charged impurities in space at low temperatures. Calculations were carried out by computer simulation of the impurity system over a wide range of compensation degrees. This parameter can be found by a study of line profile evolution with an increase of temperature. The concentration of donors can then be found by a comparison of the experimental curve with the theoretical line profile for the corresponding degree of compensation. For low compensations an analytical theory is developed for the evolution of line profile with temperature.     

Association of riboflavin,caffeine, and sodium salicylate in aqueous solution

We have used UV and visible spectrophotometry to study self-association of aromatic riboflavin molecules (RFN, vitamin B₂, 7,8-dimethyl-10-N-(1′-D-ribityl)isoalloxazine) in aqueous solution (pH 6.86) at T = 298 K, using a dimer model. We have determined the equilibrium dimerization constant for riboflavin, K_dB = 125 ± 40 M⁻¹. We have studied heteroassociation in the system of molecules of 7,8-dimethyl-10-ribitylisoalloxazine with 1,3,7-trimethylxanthine (caffeine) and sodium salicylate (NAS) in aqueous solution (pH 6.86; T = 298 K). We have determined the heteroassociation constants for RFN-NAS and RFN-caffeine molecules in the absence and in the presence of urea in solutions using a modified Benesi-Hildebrand equation: 25 ± 4, 17 ± 3, and 74 ± 11, 53 ± 7 M⁻¹ respectively. We have determined the dimerization constants for NAS (2.7 ± 0.5 M⁻¹) and caffeine (17.0 ± 1.5 M⁻¹). We conclude that heteroassociation of the aromatic molecules leads to a lower effective riboflavin concentration in solution, and the presence of urea in mixed solutions leads to an decrease in the complexation constants for the RFN-NAS and RFN-caffeine systems. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 188–194, March–April, 2007.     

Temperature dependence of the thermophysical properties of a Teflon — Bronze antifriction material

The effect of temperature and the concentration of the dispersed metallic filler on the thermophysical properties of a Teflon-based composition have been experimentally investigated. The results of the measurements of the thermophysical characteristics of the filled and unfilled Teflon are evaluated with allowance for the thermal conductivity of the components, their physicochemical interaction, and the change in the structure of the heterogeneous systems investigated.Deceased.A. M. Gor'kii Kiev State Pedagogical Institute; Institute of Colloidal Chemistry and the Chemistry of Water, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 6, pp. 1053–1056, November–December, 1971.     

Synthesis and structure of 3-methoxy-5′,6′-dihydro-4′<Emphasis Type="Italic">H</Emphasis>-1′,2′-oxazine-[5′,6′: 14β,15β]-estra-1, 3,5(10),16-tethraen-17-yl acetate

At the radical reduction of the bridging nitrosteroid (I) with tributyltin hydride oxazine (III) was obtained. The crystal and molecular structure of this compound was investigated by XRD analysis.