Carbon nanomaterials doped with heteroatoms, in particular, nitrogen atoms, are of great interest for electrochemical power engineering as nonmetallic catalysts or carriers of catalytically active ...metal nanoparticles. A nanostructured, reduced graphene oxide modified with nitrogen in a gas discharge plasma in a vacuum chamber of a magnetron-ion sputtering facility is considered. It is shown that plasma treatment of reduced graphene oxide does not cause undesirable morphological changes in the structure of carbon nanomaterial, but it leads to the incorporation of nitrogen atoms into the structure of reduced graphene oxide with the formation of pyridine-, pyrrole-, and graphite-like configurations. The application of pulsed negative bias voltages of various magnitudes to the substrate with the sample increases the concentration of nitrogen atoms to 2.6 at % and also promotes an increase in the proportion of nitrogen atoms in the pyridine form and a slight decrease in the proportion of atoms in the pyrrole form. The results allow for considering the obtained carbon nanomaterials for use as components of electrochemical devices, for example, fuel cells, in the future.
We study apricot pomace extract as a novel ecologically friendly inhibitor of the corrosion of steel in neutral aqueous solutions. It is shown that the efficiency of corrosion protection of steel ...with the help of apricot pomace extract in a 0.5 M NaCl solution increases with its concentration and the duration of holding. The data of gravimetric and electrochemical measurements demonstrate that a film is gradually formed on the steel surface with time (~ 48 h) and its thickness exceeds 800 nm. The morphology of the protective film is studied by the methods of scanning-electron microscopy and atomic-force microscopy. The chemical composition of the protective film is investigated by the method of FT-IR spectroscopy.
The large-scale commercialization of polymer electrolyte membrane (PEM) water electrolyzers is still constrained by their high capital cost, which is largely associated with the use of noble ...metal-based electrocatalysts. There is an urgent need to reduce their loading in the composition of electrocatalytic layers. In the present work, an approach of the microporous sublayer made of titanium nitride (TiNx) and formed over the anode surface by magnetron sputtering is proposed. It contributes to an increase in the anode electrocatalyst utilization, opening up wide possibilities to reduce its loading.
A comparative study of the possibilities of using ribokinase → phosphopentomutase → nucleoside phosphorylase cascades in the synthesis of modified nucleosides was carried out. Recombinant ...phosphopentomutase from
HB27 was obtained for the first time: a strain producing a soluble form of the enzyme was created, and a method for its isolation and chromatographic purification was developed. It was shown that cascade syntheses of modified nucleosides can be carried out both by the mesophilic and thermophilic routes from D-pentoses: ribose, 2-deoxyribose, arabinose, xylose, and 2-deoxy-2-fluoroarabinose. The efficiency of 2-chloradenine nucleoside synthesis decreases in the following order: Rib (92), dRib (74), Ara (66), F-Ara (8), and Xyl (2%) in 30 min for mesophilic enzymes. For thermophilic enzymes: Rib (76), dRib (62), Ara (32), F-Ara (<1), and Xyl (2%) in 30 min. Upon incubation of the reaction mixtures for a day, the amounts of 2-chloroadenine riboside (thermophilic cascade), 2-deoxyribosides (both cascades), and arabinoside (mesophilic cascade) decreased roughly by half. The conversion of the base to 2-fluoroarabinosides and xylosides continued to increase in both cases and reached 20-40%. Four nucleosides were quantitatively produced by a cascade of enzymes from D-ribose and D-arabinose. The ribosides of 8-azaguanine (thermophilic cascade) and allopurinol (mesophilic cascade) were synthesized. For the first time, D-arabinosides of 2-chloro-6-methoxypurine and 2-fluoro-6-methoxypurine were synthesized using the mesophilic cascade. Despite the relatively small difference in temperatures when performing the cascade reactions (50 and 80 °C), the rate of product formation in the reactions with
enzymes was significantly higher.
enzymes also provided a higher content of the target products in the reaction mixture. Therefore, they are more appropriate for use in the polyenzymatic synthesis of modified nucleosides.
Flow coefficients vn of the orders n = 1 – 6 are measured with the High-Acceptance Spectrometer (HADES) at GSI for protons, deuterons, and tritons as a function of centrality, transverse momentum, ...and rapidity in Au + Au collisions at √sNN = 2.4 GeV. Combining the information from the flow coefficients of all orders allows us to construct for the first time, at collision energies of a few GeV, a multidifferential picture of the angular emission pattern of these particles. It reflects the complicated interplay between the effect of the central fireball pressure on the emission of particles and their subsequent interaction with spectator matter. The high precision information on higher order flow coefficients is a major step forward in constraining the equation of state of dense baryonic matter.
Two recombinant purine nucleoside phosphorylases from thermophilic bacterium Thermus thermophilus HB27 encoded by genes TT_C1070 (TthPNPI) and TT_C0194 (TthPNPII) were purified and characterized. The ...comparative analysis of their sequences, molecular weight, enzymes specificity and kinetics of the catalyzed reaction were realized. As a result, it was determined that the TthPNPI is specific to guanosine while the TthPNPII to adenosine. According to the results of the size exclusion chromatography and SAXS study both enzymes are hexameric molecules. Based on the sequence alignment with homologous purine nucleoside phosphorylases (PNPs), Asn was identified as a purine base recognizing residue in the active site of TthPNPI and Asp in TthPNPII. The three-dimensional structure of TthPNPII was solved at 2.5 Å resolution by molecular replacement method using crystals grown in microgravity. Position of phosphate in the active site cavity is located. The possible arrangement of adenosine and guanosine in TthPNPII active site cavity is considered using superposition with the structures of homologous trimeric and hexameric PNPs complexed with corresponding substrates. The peculiarities of oligomeric structure of TthPNPII in comparison with homologous PNPs are described. It is shown that two trimeric molecules of TthPNPII in the asymmetric part of the unit cell are connected by three two-fold axis into a hexamer with 32-point symmetry. This type of hexameric structure of PNP is found for the first time. The interface area between the subunits in trimeric molecule and between the trimers in TthPNPII hexamer is described.
Communicated by Ramaswamy H. Sarma.
IR investigations of lithium graphite intercalation compounds with different lithium in-plane density (LiC
6, LiC
4, LiC
2) were carried out. The spectra interpretation was done on the basis of ...normal coordinate analysis for model structures. LiC
2 and LiC
4 spectra exhibit the bands corresponding to a complex skeleton stretching in Li
7 or LiC
6 clusters including equilateral triangles of metal atoms at short distances which shows that covalence exists between Li atoms in the intercalated layer and that LiC
2 decomposition proceeds keeping these clusters in LiC
x
structure for
x < 4 at least.
During the preparative synthesis of 2-fluorocordycepin from 2-fluoroadenosine and 3'-deoxyinosine catalyzed by
purine nucleoside phosphorylase, a slowdown of the reaction and decrease of yield down ...to 5% were encountered. An unknown nucleoside was found in the reaction mixture and its structure was established. This nucleoside is formed from the admixture of 2',3'-anhydroinosine, a byproduct in the preparation of 3-'deoxyinosine. Moreover, 2',3'-anhydroinosine forms during radical dehalogenation of 9-(2',5'-di-
-acetyl-3'-bromo- -3'-deoxyxylofuranosyl)hypoxanthine, a precursor of 3'-deoxyinosine in chemical synthesis. The products of 2',3'-anhydroinosine hydrolysis inhibit the formation of 1-phospho-3-deoxyribose during the synthesis of 2-fluorocordycepin. The progress of 2',3'-anhydroinosine hydrolysis was investigated. The reactions were performed in D
O instead of H
O; this allowed accumulating intermediate substances in sufficient quantities. Two intermediates were isolated and their structures were confirmed by mass and NMR spectroscopy. A mechanism of 2',3'-anhydroinosine hydrolysis in D
O is fully determined for the first time.
Time Projection Chamber (TPC) is the main tracker of the Multi-Purpose Detector (MPD). The detector will operate at one of the beam interaction points of collider NICA (Nuclotron-based Ion Collider ...fAcility) 1 and it is optimized to investigate heavy-ion collisions in the energy range from 4 to 11 GeV/nuclon. At the average luminosity of 1027 cm−2⋅s−1 for gold collisions at 9 GeV/nuclon the event rate will reach up to 7 kHz. The emphasis of this paper is made on the TPC front end electronics based on novel ASIC chips, other systems of the TPC are shortly described.
A highly effective producer strain
Escherichia coli
C3030/pET23d
+
-
Ec
HGPRT, allowing production of recombinant hypoxanthine‒guanine phosphoribosyltransferase from
E. coli
(
Ec
HGPRT) in a soluble ...form, has been created. A method for isolating and purifying the recombinant protein has been developed. The specific activity against the natural substrate and pyrazine-2-carboxamide derivatives has been determined. Crystals of the
Ec
HGPRT complexes with 3-hydroxypyrazine-2-carboxamide (T-1105) and 6-fluoro-3-hydroxypyrazine-2-carboxamide (T-705), suitable for X-ray diffraction analysis, have been grown by capillary counter diffusion. X-ray diffraction sets with a resolution of up to 2.4 and 2.5 Å have been collected at the ESRF synchrotron (France, station ID23-1) at a temperature of 100 K. The crystals belong to the sp. gr.
P
3(1)21; the independent part of the cell contains two enzyme molecules.
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