DNA attraction in monovalent and divalent electrolytes

The dependence of the effective force on the distance between two DNA molecules was directly computed from a set of extensive all-atom molecular dynamics simulations. The simulations revealed that in a monovalent electrolyte the effective force is repulsive at short and long distances but can be attractive in the intermediate range. This attractive force is, however, too weak (approximately 5 pN per turn of a DNA helix) to induce DNA condensation in the presence of thermal fluctuations. In divalent electrolytes, DNA molecules were observed to form a bound state, where Mg(2+) ions bridged minor groves of DNA. The effective force in divalent electrolytes was predominantly attractive, reaching a maximum of 42 pN per one turn of a DNA helix.     

Revealing Active Sites and Reaction Pathways in Methane Non-Oxidative Coupling over Iron-Containing Zeolites

Non-oxidative coupling of methane is a promising route to obtain ethylene directly from natural gas. We synthesized siliceous [Fe]zeolites with MFI and CHA topologies and found that they display high selectivity (>90 % for MFI and >99 % for CHA) to ethylene and ethane among gas-phase products. Deactivated [Fe]zeolites can be regenerated by burning coke in air. In situ X-ray absorption spectroscopy demonstrates that the isolated Fe³⁺ centers in zeolite framework of fresh catalysts are reduced during the reaction to the active sites, including Fe²⁺ species and Fe (oxy)carbides dispersed in zeolite pores. Photoelectron photoion coincidence spectroscopy results show that methyl radicals are the reaction intermediates formed upon methane activation. Ethane is formed by methyl radical coupling, followed by its dehydrogenation to ethylene. Based on the observation of intermediates including allene, vinylacetylene, 1,3-butadiene, 2-butyne, and cyclopentadiene over [Fe]MFI, a reaction network is proposed leading to polyaromatic species. Such reaction intermediates are not observed over the small-pore [Fe]CHA, where ethylene and ethane are the only gas-phase products.     

Microextraction-Colorimetric Determination of Quaternary Ammonium Compounds in Medicines and Disinfectants

Moscow University Chemistry Bulletin - We propose a method for the determination of quaternary ammonium compounds (QACs) in medicines and disinfectants, based on dispersive liquid–liquid...     

Slow viscous flow near a superhydrophobic surface with trapped gas bubbles

The Boundary Element Method (BEM) is used to solve the problem of Stokes flow of a viscous fluid over a periodic striped texture of a superhydrophobic surface (SHS), partially filled with frictionless gas bubbles. The shape of the bubble surfaces and the position of the meniscus pinning points relative to the cavity walls are taken into account in the study. Two kinds of flows important for practical applications are considered: a pressure-driven flow in a thin channel with a bottom superhydrophobic wall and a shear-driven flow over a periodic texture. We study the flow pattern in the fluid over a single cavity containing a bubble with a curved phase interface shifted into the cavity. A parametric numerical study of the averaged slip length of the SHS is performed as a function of the geometric parameters of the texture. It is shown that the curvature of the phase interface and/or its shift into the cavity both result in the decrease in the average slip length. It is demonstrated that the BEM can be an efficient tool for studying Stokes flows over textured superhydrophobic surfaces with different geometries of microcavities and phase interfaces. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Raman response function of atmospheric air

A model of the full Raman response function of a gas mixture including rotational and vibrational motions of molecules is presented and is applied to examine the properties of the retarded optical nonlinearity of atmospheric air. For few-cycle laser pulses, broadband field waveforms, and/or high gas temperatures, both rotational and vibrational motions can significantly contribute to the Raman response of atmospheric air, with the ratio of the rotational and vibrational parts of the Raman response function controlled by the gas temperature and the temporal shape of the laser field.     

Use of polyanions for alkylation of hydrazine derivatives

Alkylation of hydrazine and its derivatives still remains a quite complicated task. The novel method utilizing the polyanion strategy is reported. Formation and use of trianion for alkylation of hydrazine derivatives is first reported. Described method provides fast and convenient access to multialkylated derivatives. Scope and limitations of new method are also investigated.