Individual bottle brush molecules in dense 2D layers restoring high degree of extension after collapse-decollapse cycle: Directly measured scaling exponent

We prepared dense films of adsorbed brush-like macromolecules on mica substrate by transfer of compressed Langmuir monolayers from water subphase. The main macromolecular contours in the dense films were clearly resolved by SFM. The films were subjected to successive treatments by ethanol and water vapours. In accordance with previous results for isolated macromolecules, the films underwent collapse and subsequent decollapse morphological transformations in the changing vapour environment. Statistical analysis of the macromolecular dimensions in the films allowed us to measure the values of the scaling exponent determining the correlation between mean lateral and linear dimensions of the macromolecules. The analysis showed that the macromolecular conformations in the film as transferred were similar to the previously described conformations of the same macromolecules deposited directly on mica as isolated chains at much lower surface densities. The determined was close to the 0.75 value corresponding to the 2D SAW statistics. We assumed that the molecules retained the high degree of extension during the compression step due to suppressed reorganisation of the side chains. Differently from previous observations for isolated macromolecules, the restored conformations in the dense films after collapse-decollapse cycle were more extended with the of about 0.73 value. A theoretical explanation of the high degree of re-extension is proposed.     

Intermolecular interactions in heteromolecular crystals of tetrazine derivatives with azoles

Heteromolecular crystal structures formed by symmetrically and unsymmetrically 3,6-disubstituted tetrazine derivatives with NH donor azoles are investigated. The main crystal motifs and the intermolecular interactions responsible for their formation are identified.     

Interface between ionic and nonionic liquids: theoretical study

We use a Flory-Huggins type approach to calculate the structure and the surface tension coefficient of the boundary between ionic and nonionic liquids. The mixture of ionic and nonionic liquids is treated as a "three-component" system including anions, cations, and neutral molecules. We show that if the affinities of the cations and the anions to the neutral molecules are different, the interface comprises an electric double layer. The presence of this layer (uncompensated electric field) stabilizes the interface: the field inhibits the ions segregation at the interface and increases the surface tension. On the other hand, the short-range volume interactions promote the segregation and decrease the surface tension. Furthermore, the surface tension coefficient can be negative, if the difference of the affinities is high enough. It implies a possibility of microphase separation of the system.     

[4+2]-Cycloaddition of 3,6-bis(3,5-dimethyl-4-R-pyrazol-1-yl)-1,2,4,5-tetrazines with alkenes

A number of 1,4-dihydropyridazines and pyridazines were prepared by the Diels-Alder reaction with an inverse electron demand from cyclic heterodiene systems, 3,6-bis(3,5-dimethyl-4-R-pyrazol-1-yl)-1,2,4,5-tetrazines, and some enamines as well as from 4-vinylpyridine, butyl vinyl ether, phenylacetylene, and acrylamide. The reaction of 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2,4,5-tetrazine with styrene afforded 4,5-dihydropyridazine, which was readily oxidized by atmospheric oxygen to form the corresponding pyridazine. Electron-withdrawing substituents (Br or Cl) in the pyrazole rings accelerate [4+2]-cycloaddition. When heated, 1,4-dihydropyridazines, which were synthesized from tetrazines and enamines, eliminated amine to give pyridazines. The reactivities of tetrazines were evaluated by quantum-chemical methods. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 354–360, February, 2000.     

Synthesis of Polyampholyte Janus‐like Microgels by Coacervation of Reactive Precursors in Precipitation Polymerization

Controlling the distribution of ionizable groups of opposite charge in microgels is an extremely challenging task, which could open new pathways to design a new generation of stimuli‐responsive colloids. Herein, we report a straightforward approach for the synthesis of polyampholyte Janus‐like microgels, where ionizable groups of opposite charge are located on different sides of the colloidal network. This synthesis approach is based on the controlled self‐assembly of growing polyelectrolyte microgel precursors during the precipitation polymerization process. We confirmed the morphology of polyampholyte Janus‐like microgels and demonstrate that they are capable of responding quickly to changes in both pH and temperature in aqueous solutions.     

Real-Time Monitoring of the Energy Deposition under the Tight Focusing of Femtosecond Laser Radiation into a Bulk Transparent Dielectric Based on Third Harmonic Signal

It has been found that the third harmonic generated under the tight focusing of a near-infrared (1.24-μm) femtosecond laser pulse indicates the energy deposition into the bulk transparent dielectric and can be used as a feedback system in the process of microstructuring. A third harmonic signal is sensitive to a change in both the size of a laser-induced microplasma and the free-electron density, which allows the detection of the microplasma with submicron longitudinal sizes. It has been shown that the method based on the third harmonic is universal and can be applied in both single-pulse and two-color microstructuring.     

On the noncompactness of classes of mappings with restrictions on dilation in measure

We establish that the classes of mappings with restrictions in measure cannot be compact except for certain degenerate cases. In particular, this implies that any David class ΓI is noncompact. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 50, No. 11, pp. 1522–1531, November, 1998.     

X-ray and quantum-topological studies of intermolecular interactions in partially fluorinated quinoline crystals

An X-ray study of the crystals of bicyclic compounds containing fluorinated aromatic and nonfluorinated heteroaromatic rings, 5,6,7,8-tetrafluoroquinoline, 5,6,8-trifluoroquinoline, 5,7-difluoroquinoline, 5,7,8-trifluoro-2-phenylquinoline, and 5,7,8-trifluoro-6-trifluoromethylquinoline, was carried out. The basic supramolecular motifs and the underlying intermolecular interactions that control the lattice structure of these compounds were investigated. B3LYP DFT quantum-chemical calculations (6-311G(d,p) basis set) and the topological analysis of the electron density distribution in terms of Bader’s QTAIM theory were performed for the compounds. It is shown that the intermolecular interactions in question, traditionally regarded as nonvalent interactions, are related, to a definite extent, to the formation of very weak covalent chemical bonds in the intermolecular space due to the overlap of the “tails” of the molecular wave functions.     

Gas-phase carbonylation of dimethoxymethane to methyl methoxyacetate over the Cs<Subscript>2.5</Subscript>H<Subscript>0.5</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript> catalyst

It has been shown that cesium hydrogen phosphotungstate Cs_2.5H_0.5PW₁₂O₄₀ is a promising catalyst of the gas-phase carbonylation of dimethoxymethane (DMM) to methyl methoxyacetate (MMA). This catalyst provided the MMA selectivity and yield of 54% and 40%, respectively, under mild experimental conditions: T = 110°C, P = 10 bar, and GHSV = 6000 h^–1 for DMM/CO/Ar = 4/76/20 mol/mol/mol. The carbonylation of DMM to MMA is accompanied by side reactions of DMM disproportionation into dimethyl ether (DME) and methyl formate (MF), as well as by secondary side reactions of MF decomposition into methanol and CO and methanol dehydration into DME.     

Compressibility of Gas Hydrates

Experimental data on the pressure dependence of unit cell parameters for the gas hydrates of ethane (cubic structure I, pressure range 0–2 GPa), xenon (cubic structure I, pressure range 0–1.5 GPa) and the double hydrate of tetrahydrofuran+xenon (cubic structure II, pressure range 0–3 GPa) are presented. Approximation of the data using the cubic Birch–Murnaghan equation, P=1.5B₀[(V₀/V)^7/3?(V₀/V)^5/3], gave the following results: for ethane hydrate V₀=1781 ų, B₀=11.2 GPa; for xenon hydrate V₀=1726 ų, B₀=9.3 GPa; for the double hydrate of tetrahydrofuran+xenon V₀=5323 ų, B₀=8.8 GPa. In the last case, the approximation was performed within the pressure range 0–1.5 GPa; it is impossible to describe the results within a broader pressure range using the cubic Birch–Murnaghan equation. At the maximum pressure of the existence of the double hydrate of tetrahydrofuran+xenon (3.1 GPa), the unit cell volume was 86 % of the unit cell volume at zero pressure. Analysis of the experimental data obtained by us and data available from the literature showed that 1) the bulk modulus of gas hydrates with classical polyhedral structures, in most cases, are close to each other and 2) the bulk modulus is mainly determined by the elasticity of the hydrogen‐bonded water framework. Variable filling of the cavities with guest molecules also has a substantial effect on the bulk modulus. On the basis of the obtained results, we concluded that the bulk modulus of gas hydrates with classical polyhedral structures and existing at pressures up to 1.5 GPa was equal to (9±2) GPa. In cases when data on the equations of state for the hydrates were unavailable, the indicated values may be recommended as the most probable ones.