Four-component stereoselective synthesis of tetracyano-substituted piperidines

Research on Chemical Intermediates - A novel four-component stereoselective synthesis of polysubstituted piperidines is reported. The Knoevenagel–Michael–Mannich cascade of two...     

Phase transitions in molecular crystals of the paraffin series: Heneicosane and docosane

Comparative analysis of phase transition in normal paraffins, heneicosane (C₂₁H₄₄) and docosane (C₂₂H₄₆), was performed using differential scanning calorimetry. Elimination of methodical inaccuracies allowed obtaining proper values of the thermodynamic parameters of the phase transitions and revealing their nature. Quantitative analysis of the heat capacity steps was made based on the theory of blurred first-order phase transitions and Landau’s theory for second-order phase transitions.

     

Study of palladium nanoparticles synthesized in alkali borosilicate glass pores by the X-ray line shift method

Metallic Pd synthesized in porous glass with an average pore diameter of 7 ± 2 nm has been studied using the X-ray diffraction and X-ray line shift methods for the first time. The irregular dependence of the reflection width in X-ray patterns on the diffraction angle has been revealed. This can be caused by crystallite growth mostly in the [111] direction or by tetrahedral distortions of the fcc lattice. The shift (difference in energy) of K _α1 lines (ΔE _α1 = 19 ± 2 meV) for nanostructured Pd in comparison with the bulk material is first detected. The detected effect is considered within the assumption of the palladium electron redistribution between Pd 5s- and 4d-bands.     

Isotope effects in Raman spectra of crystalline sulfur α-S8

The Raman spectra of ³²S, ³³S, and ³⁴S powders, as well as ^naturS powder with the natural isotopic composition, have been measured in the temperature range of 5–300 K. The isotope mass dependences of the vibrational frequencies have been obtained. It has been shown that such a dependence in the region of mixed translational-librational modes differs from the dependences known for monatomic inorganic crystals. The role of zero-point vibrations for low- and high-frequency modes has been revealed throughout the entire temperature range.     

Products of tetramethyllead dealkylation with bromine

Products of tetramethyllead dealkylation with bromine in the temperature interval from ?20 to 20°C were analyzed by X-ray diffraction, IR spectroscopy, and spectrophotometry. Specific features of their thermal behavior were studied by differential thermal analysis and mass spectrometry.     

Radiation of a Resonant Medium Excited by a Periodically Phase-Modulated Laser in the Regime of Strong Coupling between the Field and the Matter

Optics and Spectroscopy - The radiation of a two-level resonant medium that is placed into a cavity and is excited by a periodically phase modulated laser pulse is studied theoretically. The...     

Synthesis of Substituted Bis-Semicarbazides by Reaction of Hexamethylene Diisocyanate with Hydrazine Derivatives

Russian Journal of General Chemistry - New bis-semicarbazides were obtained by the reaction of hexamethylene diisocyanate with aliphatic and aromatic acids hydrazides, as well as semicarbazide,...     

Phase transitions in crystals of protein amino acids with trapped drops of water solutions

It has been shown that the phase transitions observed at temperatures of about 250 K in crystals of protein amino acids and of their compounds grown from water solutions are related to drops of these solutions trapped by crystals in their growth.     

Modelling of sensitivity of plasmon sensory elements based on silver nanoparticles obtained by laser evaporation and ablation

A comparison of the sensitivity of the spectral position of plasmon resonance calculated by numerical methods to a change in the refractive index of the environment for ellipsoidal and spherical silver nanoparticles with a dielectric shell synthesized by laser ablation has been performed. It has been shown that sensitivity is higher for nanoparticles with the shape of a prolate ellipsoid than for spherical nanoparticles. The modeling has shown that the optimal thickness of the dielectric shell should be 10–12 nm and its refractive index should be 1.6. With this, a sensitivity of the plasmon sensor of 32 nm/RIU (RIU is refractive index unit) may be provided.