Highly efficient glucosylation of flavonoids

Abstract  

A highly efficient procedure for glucosylation of flavonoids by acetobromoglucose is described. Glucosylation is carried out in a two-phase system CHCl₃/H₂O over 96 h using tetrabutylammonium bromide as phase-transfer catalyst. A purification procedure can be performed without column chromatography, and the yields of the glucosylated flavonoids are mostly quantitative. Acetylated glucosides were deprotected with sodium methanolate to afford the desired glucosides of flavonoids.     

Nonlinear vibration analysis of laminated shallow shells with clamped cutouts by the R-functions method

In present work, an effective method to research geometrically nonlinear free vibrations of elements of thin-walled constructions that can be modeled as laminated shallow shells with complex planform is applied. The proposed method is numerical–analytical. It is based on joint use of the R-functions theory, variational methods, Bubnov–Galerkin procedure and Runge–Kutta method. The mathematical formulation of the problem is performed in a framework of the refined first-order shallow shells theory. To implement the developed method, appropriate software was developed. New problems of linear and nonlinear vibrations of laminated shallow shells with clamped cutouts are solved. To confirm reliability of the obtained results, their comparison with the ones known in the literature is provided. Effect of boundary conditions is studied.     

Prospects of Development of Radiation Technologies in Russia

The present review article describes the role of radiation technologies in various realms of human activities, including fundamental science, industry, agriculture, and medicine. The development of radiation technologies in the world and in Russia is compared. The total number of ionizing-radiation sources in the world is approximately 11 million units, most of them being radioactive sources (about six to seven million units) and x-ray facilities (about four million units). The number of high-technology facilities (such as accelerators and tomography units of various types) that employ ionizing radiation does not exceed 200 thousand units. In Russia, there are more than 153 thousand units of such instruments and facilities. They include about 64700 units employing x-ray radiation; about 79700 radioisotope devices and setups, reactors, and radioactive-waste storage facilities; and 471 accelerators. The most promising lines of development of radiation technologies in Russia are analyzed from the strategic and economic points of view.

     

Hypersatellites at <Superscript>109</Superscript>Ag, <Superscript>123</Superscript>Te,and <Superscript>147</Superscript>Pm autoionization during internal electron conversion

The formation of hypersatellites during internal electron conversion in ¹⁰⁹Ag, ¹²³Te, and ¹⁴⁷Pm nuclei has been investigated on multidimensional-coincidence spectrometers with Ge-Si(Li), Ge-Ge, and NaI(Tl) detectors. The probability of double ionization of the K shell in these nuclei is determined and hypersatellite energy shift is measured.     

An alternative approach to the synthesis of [1,2,4]triazolo[1,5-a]pyridine-8-carbonitriles,their crystal structure,and DFT calculations

New representatives of [1,2,4]triazolo[1,5-a]pyridine-8-carbonitriles were synthesized via the condensation of β-diketones or β-dialdehydes and characterized using MS spectrometry, ¹H, ¹³C and, ¹⁹F NMR and IR spectroscopy. Crystal structures of two compounds were established using X-ray analysis and showed that title compounds are prone to the formation of planar molecules. The absence of band responsible for CN stretching vibration in trifluoromethyl-containing compounds was explained using the DFT calculations method, which also showed a significant influence of fluorines introducing on the energy gap between HOMO and LUMO.     

Effect of absorption of low-molecular-weight compounds by some polymer flocculants

The sorption properties of the intramolecular complex - poly(acrylamide) to poly(vinyl alcohol) grafted copolymer (PVA-PAA_N) in block state were investigated with respect to a number of compounds. The relatively small molecules of phenol, phenylalanine in water solution as well as nitrobenzene in hexane are strongly absorbed by PVA-PAA_N films. The large humine acid molecules (sizes are larger by more than ≈ 10 times) are absorbed by PVA-PAA_N very weakly. It was determined the absorption influence on the character of polymer film solution. In a number of cases the oscillation of the dilution and sorption were observed when determining the critical concentrations of guest molecules in the upper layer of polymer films were achieved. The possible mechanisms of absorption were discussed.     

The peculiarities of sorbtion mechanism of phenole molecules by films of PVA‐PAAN interpolymer complex

The peculiarities of sorbtion mechanism of phenole molecules by poly(vinylalcohol) and poly(acrylamide) (PVA‐PAA_N) films are examined. An analytical model of absorbtion process based on diffusive character of penetration of phenole molecules in polymer film with the following spontaneous capturing by selftuning traps is proposed. The analytical results can be easy compared with experimental data obtained by spectrophotometry method. The comparison of theory and experiment gives the average value of resulting diffusion lenght of phenole molecule during «free» life‐time <l>∼10⁻⁶ cm.     

Reversible structure destruction of intramolecular polycomplexes formed by poly(acrylamide) and poly(vinyl alcohol), under hydrodynamic shear flow

A set of rheologic and thermodynamic researches of diluted and semi‐diluted aqueous solutions of poly(acrylamide) to poly(vinyl alcohol) grafted copolymers (PVA‐PAA_N) forming intramolecular polycomplexes (Intra PC) by the methods of static light scattering, interferometry and rheology (for gradients of shear rate j≤1312 s⁻¹) was carried out. It is established, that the thermodynamic water quality towards the copolymers improves, when the quantity N of grafts increases, but on the whole it remains close to θ‐solvent. In PVA‐PAA_N solutions under action of a hydrodynamic shear field two level of reversible structure destruction are shown. The first level is destruction of network of pinnings and the second one is destruction of Intra PC structure together with destroying of primary associates of copolymer macromolecules. It is shown, that the character of destruction (gradual or uneven) and its depth depend on intensity of the hydrodynamic shear field action, concentration of solution and also copolymer structure. Possible reason of reversibility of PVA‐PAA_N structure destruction in strong hydrodynamic fields is pointed out.     

Properties of poly(vinyl alcohol)-graft-polyacrylamide copolymers depending on the graft length. 2. Thermal properties in the bulk state

Thermal behavior of poly(vinyl alcohol)-graft-polyacrylamide copolymers (PVA-g-PAA), so-called intramolecular polymer-polymer complexes (intraPC), with variable M̄ _vPAA and constant average number N of grafts is considered in this report. Complete compatibility of PVA and PAA through hydrogen bonding is realized in the range of the graft lengths not exceeding some critical value. The content of adsorbed and trapped water in graft copolymers reflects some features of PVA-g-PAA_N structure depending on the graft lengths. The first thermal decomposition region in air for copolymers begins at higher temperatures with growing M̄ _vPAA, but the total destruction interval reduces. Formal kinetic decomposition parameters of the first decomposition stage appear to be the largest for the PVA-g-PAA with the largest quantity of H-bonds between the main and graft chains. Chemical transformations in graft copolymers, PVA and PAA during thermal decomposition are discussed.     

Polyacrylamide-Grafted Silica as Special Type of Polymer-Colloid Complex

Structure and properties of polyacrylamide-grafted silica have been investigated with the help of thermal analysis methods, NMR spectroscopy and by measuring the ability solubilization in benzene when compared with homopolymer polyacrylamide (PAA). More homogeneous structure, low rigidity and density of packing have been revealed for the polymer shell. PAA form a dense polymer shell, which interact with silica surface through H-bonds. ¹H NMR spectroscopy suggests no influence of silica particles on PAA stereoregularity. PAA-grafted silica considered as a special type of polymer-colloid complex where polymer chains are covalently bound to silica with one end and polymer segments along the chain are hydrogen bound to the particle surface.