The H2 role in the synergistic phenomenon in selective NO x reduction by propane over a mechanical mixture of oxide catalysts

The synergistic phenomenon observed in NO _x selective reduction by propane over the mechanical mixture of commercial NTK and Ni-Cr-oxide catalysts is explained by the distinctions in the reaction mechanism over the individual mixture components. Hydrogen formed over Ni-Cr-oxide catalyst in propane oxidation significantly increases the rate of interaction between surface nitrate and acetate complexes. Besides, there is an additional input made by the route of NO _x reduction over NTK in the presence of H₂.     

Microcrystals of antimony compounds in lead–potassium and lead glass and their effect on glass corrosion: a study of historical glass beads using electron microscopy

Crystalline inclusions of antimony compounds in lead glass of the nineteenth century have been investigated by means of transmission electron microscopy, scanning electron microscopy, X-ray microanalysis, electron backscatter diffraction and microcathodoluminescence. Microcrystallites of orthorhombic \(\hbox {KSbOSiO}_4\) (KSS) with the sizes ranging from about 200 nm to several micrometers have been detected in lead–potassium glass of turquoise seed beads prone to a glass disease causing the irrecoverable deterioration of beaded articles kept in museums. The KSS crystals have high number density and tend to form large colonies. Crystallites of cubic \(\hbox {Pb}_2\hbox {Fe}_{0.5}\hbox {Sb}_{1.5}\hbox {O}_{6.5}\) have been detected in stable yellow lead glass beads. Their number density and sizes are much less than those of the KSS particles observed in turquoise glass; they do not form large clusters. We have come to conclusion that KSS precipitates are responsible for the internal strain-induced corrosion of turquoise lead–potassium glass eventually resulting in crumbling of beads to sand particles. The following scenario explains this phenomenon: \(\hbox {K}^+\) and \(\hbox {Sb}^{5+}\) used for glass doping form KSS crystallites during glass melting; tensile strain arising in the glass matrix during cooling because of difference in temperature coefficients of linear expansion of glass and KSS crystals gives rise to crack formation and in course of time results in glass falling apart to heterogeneous pieces. Small crystallites of \(\hbox {Pb}_2\hbox {Fe}_{0.5}\hbox {Sb}_{1.5}\hbox {O}_{6.5}\) cannot induce a sufficient strain to break yellow lead glass, and internal cracks do not arise in this glass during its cooling. This may explain the stability of yellow lead glass.     

Effect of growth conditions on advantages of hup− strain for H2 photoproduction by Rubrivivax gelatinosus

H₂ photoproduction by growing cultures of hup^? mutant and parental strain RL2 of Rubrivivax gelatinosus was compared. We checked the influence of different substrates, presence of air and N₂, culture shaking, inoculum concentrations. At low inoculum concentration, hup^? strain demonstrated significant advantage over the parental strain in microaerobic conditions, while under N₂–Ar atmosphere it was lower and vanished in anaerobic conditions (Ar only). This advantage was evident when using substrates with low degree of reduction (malate and succinate). Culture shaking under microaerobic conditions and in presence of N₂ completely prevented H₂ production by both strains. The high inoculum concentration inhibited H₂ production under microaerobic conditions and in presence of N₂, unlike to anaerobic conditions. With inoculum concentration increase, H₂ production decreased not gradually but stepwise which means some metabolic shift. H₂ production by hup^? strain seems to be more tolerant to air traces than by parental strain.     

Effect of grinding on the fractional composition of polymineral laminated bituminous shales

The effects of size reduction on oil shales from the Yaregskoye oil field were conducted. These shales are characterized by lamination and by high degree of schistosity and expressed zones of pyritization and bituminization. The influence of the level of crushing on the distribution and composition functions was studied. Size separation as a method for the preconcentration of this material at the ore preparation stage was substantiated. The results obtained using predictive formulas showed the possibility of obtaining a product with an increased TiO₂ content at the ore preparation stage and a reduced amount of material requiring processing.     

New method for controlled synthesis of polylactide block copolymers: organoborane/p-quinone system and reversible-deactivation radical polymerization

We developed a new approach to obtain polylactide hybrid block copolymers with vinyl monomers (styrene, methyl methacrylate, methyl acrylate) through the realization of a reaction sequence using triethylborane and various p-quinones. The method offered includes two stages. In the first stage, a chain-transfer agent was obtained by borylation of the terminal hydroxyl groups of polylactide. The second stage was vinyl monomer radical polymerization in the presence of p-quinone accompanied by S_H2-substitution at the boron atom.1,4-Naphthoquinone, 2,3-dimethyl-1,4-benzoquinone, duroquinone and 2,5-di-tert-butyl-1,4-benzoquinone were used as synthetic polymer chain growth mediators. It is shown that 1,4-naphthoquinone and 2,3-dimethyl-1,4-benzoquinone, similar in their characteristics, are effective agents providing the realization of reversible-deactivation radical polymerization. Realization of reversible-deactivation radical polymerization was proved with the analysis of the kinetics of block copolymerization, molecular weight characteristics and compositional homogeneity of block copolymers as well as its further capability to elongate the polymer chain. Synthesized block copolymers have a high thermal stability compared to the initial borylated polylactide. © 2021 Society of Industrial Chemistry.     

Redesigning the Active Site of Transaldolase TalB from Escherichia coli: New Variants with Improved Affinity towards Nonphosphorylated Substrates

Recently, we reported on a transaldolase B variant (TalB F178Y) that is able to use dihydroxyacetone (DHA) as donor in aldol reactions. In a second round of protein engineering, we aimed at improving the affinity of this variant towards nonphosphorylated acceptor aldehydes, that is, glyceraldehyde (GA). The anion binding site was identified in the X‐ray structure of TalB F178Y where a sulfate ion from the buffer was bound in the active site. Therefore, we performed site‐directed saturation mutagenesis at three residues forming the putative phosphate binding site, Arg181, Ser226 and Arg228. The focused libraries were screened for the formation of D ‐fructose from DHA and d,l ‐GA by using an adjusted colour assay. The best results with respect to the synthesis of D ‐fructose were achieved with the TalB F178Y/R181E variant, which exhibited an at least fivefold increase in affinity towards d,l ‐GA (K_M=24 mM ). We demonstrated that this double mutant can use D ‐GA, glycolaldehyde and the L ‐isomer, L ‐GA, as acceptor substrates. This resulted in preparative synthesis of D ‐fructose, D ‐xylulose and L ‐sorbose when DHA was used as donor. Hence, we engineered a DHA‐dependent aldolase that can synthesise the formation of polyhydroxylated compounds from simple and cheap substrates at preparative scale.