Showing papers in "Doklady Chemistry in 2015"

Magnesium-vapor reduction of niobium oxide compounds

Abstract: The effect of precursor composition and reduction conditions on the characteristics of niobium powders obtained by magnesium reduction were studied. The hypothesis of the possible increase in the specific surface area of the powders by a large factor by using complex oxides as precursors was confirmed. With magnesium niobate Mg4Nb2O9 as the precursor, mesoporous powders, unprecedented in the world, with a specific surface area of up to150 m2 g–1 and an average pore size of 4.6 nm were produced.

Determination of stability constants of inclusion complexes of betulin derivatives with β-cyclodextrin by capillary electrophoresis

Abstract: 67 Betulin and its derivatives relating to pentacyclic triterpenoids of lupan series exhibit pharmacological activity including human immunodeficiency virus inhibition, as well as antibacterial, antimalarial, anti inflammatory, antioxidant, and anticancer activity [1–3]. However, their medical application is rather limited because of their low solubility in water, which hampers the preparation of formulation for injection in humans.

Kinetics of the release of antibiotics from chitosan-based biodegradable biopolymer membranes

Abstract: A process for manufacture of chitosan-based biodegradable biopolymer membranes suitable for medical applications was developed. A technology for inclusion of broad spectrum antibiotics into the chitosan membranes was elaborated. The effects of pH of the solution surrounding the membranes and the initial solvent chosen for chitosan on the kinetics of release of antibiotics from the membranes were studied. It was demonstrated that the kinetics of drug release from the chitosan-based biodegradable biopolymer membranes depends on the properties of substance immobilized in the membrane, the membrane manufacture process, and extraction conditions.

Methane in the surface waters of Northern Eurasian marginal seas

Abstract: More than 12 000 measurements of the dissolved methane (CH4) concentrations in the surface waters of Northern Eurasian marginal seas (Barents, Kara, Laptev, Chukchi, and Bering Seas, Sea of Okhotsk, and Sea of Japan) during two marine expeditions (September–October 2011 and 2012) show that all seas are CH4 source to the atmosphere, but the Laptev and East Siberian seas demonstrate the strongest signal.

CaZrO3 synthesis in combustion reactions with glycine

Abstract: One of the methods for its production is the synthe sis in combustion reactions, known internationally as solution combustion synthesis (SCS). In this synthe sis, to an aqueous solution of metal nitrates, a water soluble organic fuel is added, and the obtained mixture is heated until a xerogel forms, which self ignites once a certain temperature is reached. The combustion reactions yield powders of metal oxides [1]. As a fuel in the CaZrO3 synthesis by the SCS method, β alanine [2], citric acid with urea [3], citric acid [4, 5], and gly cine [6, 7] are used.

A phosphorylated ketone, 5-(diphenylphosphoryl)hexan-3-one, as a new effective extractant for the recovery and separation of lanthanides in the eudialyte processing

Abstract: The increased consumption of rare earth elements (REEs) requires processing of new lowprofitable mineral raw materials such as ores with low REE con� tents and industrygenerated wastes of various origin (chemical plant wastes, spent nuclear fuel and so on) Eudialyte containing up to 25% lanthanide impurities is a highly promising "nontraditional" mineral for the recovery of lanthanides (1) The elemental composi� tion of lanthanides in eudialyte is characterized by high (up to 50% of the lanthanide sum) contents of heavy lanthanides, which makes eudialyte a valuable mineral raw material for the recovery of rare earth elements This distinguishes eudialyte from other known minerals such as apatite or loparite, in which the content of most expensive yttrium group lan� thanides is much lower (2) Eudialyte is readily digested with acids without preliminary activation, which markedly facilitates the industrial processing of the mineral (3) Since eudialyte contains consider� able amounts of some other valuable components (zirconium, scandium), apart from lanthanides, a topical task is to develop an integrated processing technology for this mineral The traditional ore processing flow charts include leaching with concentrated mineral acids and recovery of rare earth elements by multistep liquid extraction (3-6) In the processing of raw materials with low contents of valuable components (eudialyte, apatite, or fluoroapatite ores), it is especially important to choose an appropriate extractant, because the known neutral organophosphorus extractants (NOPCs) have rather low distribution ratios and separation levels for lanthanides and extract actinides at almost the same level Therefore, the search for new effective, synthet� ically accessible, and commercially attractive extract� ants for the recovery and separation of rare earth ele� ments remains topical

Redox mediators of hydrogen sulfide oxidation in reactions with cycloalkanes

Abstract: An indirect electrochemical method for thiolation of cycloalkanes C5–C7 has been suggested. The method is based on a new approach to activation of hydrogen sulfide by redox mediators.

Control of the dimension of nanopores and the structure of layers of nanoporous silicon during its electrolytic etching in hydrofluoric acid solutions

Abstract: 109 Nanoporous silicon is a promising nanomaterial for devices of various functional purposes. Such sili con has a specific electron subsystem, developed inter nal surface, high adsorption capacity, and biocompat ibility. Nanoporous silicon is used for producing cur rent microsupplies, matrices for various sensors, and also in medicine and biology as a safe container for targeted and controlled drug delivery [1–4]. For each of the areas of practical application of nanoporous sil icon, nanomaterials differing in structure, layer thick ness, and radial and axial pore sizes are required.

Features of gold nanoparticle formation in matrices of humic substances of different origin

Abstract: One of environmentally friendly methods of prep aration of biocompatible metal nanoparticles consists in the reduction of their precursors in aqueous medium in the presence of a reagent that simulta neously behaves as both a reducing agent and a stabi lizer for resultant nanoparticles [3–6]. Such promising materials for the synthesis of metal nanoparticles are humic substances (HSs), which are a set of com pounds of polyaromatic, polysaccharide, and other biopolymer nature [7].

Catalytic properties of diblock copolymers of N-vinylcaprolactam and N-vinylimidazole

Abstract: Thermoresponsive diblock copolymers of N-vinylcaprolactam (VCL) with N-vinylimidazole (NVI) have been synthesized for the first time through two-stage controlled reversible addition–fragmentation chain transfer (RAFT) polymerization. The resulting diblock copolymers exhibit the same catalytic activity toward p-nitrophenyl propionate (NPP) hydrolysis as “protein-like” copolymers of VCL and NVI. The catalytic activity of the diblock copolymers is likely caused by their structure favorable for the manifestation of catalytic properties, namely, by micelle-like chain conformations with a relatively dense core formed by the more hydrophobic PVCL block and a periphery formed by the hydrophilic poly-N-vinylimidazole (PNVI).

Isothermal diagrams of the Li2O–MnO–MnO2 system

Abstract: The isothermal diagrams of the Li2O–MnO–MnO2 system at an oxygen pressure up to 100 kPa were constructed, which allow to consistently represent phase transformations involving stable ternary phases: low-temperature spinel, cubic spinel c-LiMn2O4, tetragonal phase t-LiMn2O4, orthorhombic phase LiMnO2, monoclinic solid solution Li x MnO2 (0.33 ≤ x < 0.5), spinel-structure solid solution Li x Mn3–x O4, and solid solution Mn(Li)O.

Complexation of N-vinylpyrrolidone–N-allylamine copolymer with perrhenate ion in aqueous solutions

Abstract: The most common method of metal binding is the introduction of a bifunctional chelating site into natural macromolecules [8]. The direct incorporation of manga nese group metals (technetium 99m, rhenium 188) in the permetallate form into monoclonal antibodies and large proteins has also been reported [9, 10]. This method is accompanied by partial cleavage of the dis ulfide bonds in large proteins, which also leads to loss of their properties.

Synthesis and structure of 3-(tert-butyl)-10,10-dimethyl-10H-indolo[1,2-a]indoline-1,4-dione

Abstract: 33 The structure of products resulting from reaction of 2 methylated azaheterocyclic compounds with 1,2 ben zoquinones depends on the nature of both heterocycle and 1,2 benzoquinone [1–3]. In the series of 2 methyl quinolines [3], 2 methylquinoxalines [4], 2 methyl quinazolinones [5], and 2 methylbenzoxa(thia)zoles [6, 7], the reaction with spatially hindered 1,2 benzo quinone and 3,4,5,6 tetrachloro 1,2 benzoquinone proceeds with expansion of the o quinone ring to give 2 hetaryl substituted 1,3 tropolones. When donor substituent (morpholine or piperidine) is present in the 4 position of 2 methylquinoline, the reaction with 4,6 di tert butyl 3 nitro 1,2 benzoquinone may pro ceed through another route to give derivatives of 2 (quinolin 2 yl) N oxide 2 azabicyclo[3.3.0]octa 2,7 diene 4,6 diones [1, 2]. At the same time, the reaction of 3,5 di (tert butyl) 1,2 benzoquinone 2 with 2 meth ylbenzimidazoles leads to formation of polycyclic iso quinoline derivatives [8], while the reaction of quinone 2 with 1,2,3 trimethylbenzimidazolium salt affords spirane derivative of spatially hindered pyro catechol [9].

Isomerization [ trans -B 20 H 18 ] 2– → [ iso -B 20 H 18 ] 2– during silver(I) complexation with triphenylphosphine

Abstract: The trans–iso isomerization of the dimeric borohydride cluster anion [B20H18]2– in the course of the silver(I) complexation reaction with triphenylphosphine has been described for the first time. The isomeric complexes [Ag2(Ph3P)6[trans-B20H18]] and [Ag2(Ph3P)6[iso-B20H18]] have been isolated and characterized by physicochemical methods. The structures of the compounds have been determined by X-ray crystallography.

Tubular structure of J-aggregates of cyanine dye

Abstract: 1 A heightened interest in certain supramolecular organic structures is associated with their unusual optical and electronic properties. These structures include J aggregates of cyanine dyes that represent a variation of micro and nanosized molecular crystals with strong and narrow absorption band (J band) in the visible range shifted toward longer wavelengths as compared with the spectrum of monomers [1, 2]. Owing to high electron–hole conductivity and special spectral properties caused by excitation of delocalized Frenkel excitons, J aggregates are promising organic systems for application in different optoelectronic devices [3–7].

First complexes of diphenylphosphorylalkanones with titanium tetrafluoride

Abstract: The reaction of TiF4 with a twofold excess of Ph2P(O)CH2C(O)Me (L) (one of the simplest and, very likely, most practically interesting representatives of a new class of organophosphorus ligands—diorganylphosphorylalkanones) in CH2Cl2 has been studied.