Characteristic Features of Magnetization Reversal of Exchange Coupled Tb–Co/FeNi Film Structures in a Temperature Range Including the Compensation Point of the Ferrimagnetic Layer

Physics of the Solid State - The results of the study of the magnetic properties of exchange coupled Tb–Co/FeNi film structures obtained by magnetron sputtering in a wide range of...     

Palladium-catalyzed asymmetric benzylation of 3-aryl oxindoles

Herein we report palladium-catalyzed asymmetric benzylic alkylation with 3-aryl oxindoles as prochiral nucleophiles. Proceeding analogously to asymmetric allylic alkylation, asymmetric benzylation occurs in high yield and enantioselectivity for a variety of unprotected 3-aryl oxindoles and benzylic methyl carbonates using chiral bisphosphine ligands. This methodology represents a novel asymmetric carbon-carbon bond formation between a benzyl group and a prochiral nucleophile to generate a quaternary center.     

Screening and Production Study of Microbial Xylanase Producers from Brazilian Cerrado

Hemicelluloses are polysaccharides of low molecular weight containing 100 to 200 glycosidic residues. In plants, the xylans or the hemicelluloses are situated between the lignin and the collection of cellulose fibers underneath. The xylan is the most common hemicellulosic polysaccharide in cell walls of land plants, comprising a backbone of xylose residues linked by β-1,4-glycosidic bonds. So, xylanolytic enzymes from microorganism have attracted a great deal of attention in the last decade, particularly because of their biotechnological characteristics in various industrial processes, related to food, feed, ethanol, pulp, and paper industries. A microbial screening of xylanase producer was carried out in Brazilian Cerrado area in Selviria city, Mato Grosso do Sul State, Brazil. About 50 bacterial strains and 15 fungal strains were isolated from soil sample at 35 °C. Between these isolated microorganisms, a bacterium Lysinibacillus sp. and a fungus Neosartorya spinosa as good xylanase producers were identified. Based on identification processes, Lysinibacillus sp. is a new species and the xylanase production by this bacterial genus was not reported yet. Similarly, it has not reported about xylanase production from N. spinosa. The bacterial strain P5B1 identified as Lysinibacillus sp. was cultivated on submerged fermentation using as substrate xylan, wheat bran, corn straw, corncob, and sugar cane bagasse. Corn straw and wheat bran show a good xylanase activity after 72 h of fermentation. A fungus identified as N. spinosa (strain P2D16) was cultivated on solid-state fermentation using as substrate source wheat bran, wheat bran plus sawdust, corn straw, corncob, cassava bran, and sugar cane bagasse. Wheat bran and corncobs show the better xylanase production after 72 h of fermentation. Both crude xylanases were characterized and a bacterial xylanase shows optimum pH for enzyme activity at 6.0, whereas a fungal xylanase has optimum pH at 5.0–5.5. They were stable in the pH range 5.0–10.0 and 5.5–8.5 for bacterial and fungal xylanase, respectively. The optimum temperatures were 55C and 60 °C for bacterial and fungal xylanase, respectively, and they were thermally stable up to 50 °C.     

Entanglement cost in practical scenarios

We quantify the one-shot entanglement cost of an arbitrary bipartite state, that is, the minimum number of singlets needed by two distant parties to create a single copy of the state up to a finite accuracy, by using local operations and classical communication only. This analysis, in contrast to the traditional one, pertains to scenarios of practical relevance, in which resources are finite and transformations can be achieved only approximately. Moreover, it unveils a fundamental relation between two well-known entanglement measures, namely, the Schmidt number and the entanglement of formation. Using this relation, we are able to recover the usual expression of the entanglement cost as a special case.     

On the Effect of the Aglycon Structure of Three Aryl β-D-Galactosides on the Yield and the Regioselectivity of the Transglycolytic Synthesis of N-Acetyllactosamine

ABSTRACT

We examined the effect as donors of three aryl β-D-galactosides (i.e. p-nitrophenyl β-D-galactopyranoside, o-nitrophenyl β-D-galactopyranoside and phenyl β-D-galacto-pyranoside) on the regioselectivity and the yield of the synthesis of N-acetyllactosamine obtained from the transglycosylation reaction catalyzed by a crude preparation of β-D-galactosidase from Bacillus circulans at 25 °C, 37 °C and 55 °C, respectively. Using p-nitrophenyl β-D-galactopyranoside the reaction results were fully regiospecific at all the temperatures considered: the maximum molar yield (74%) was obtained at an incubation temperature of 55 °C. Using o-nitrophenyl β-D-galactopyranoside as the donor the reaction was still highly regioselective and the maximum molar yield (50%) was achieved at an incubation temperature also of 55 °C. Using phenyl β-D-galactopyranoside transglycolytic products appear only at an incubation temperature of 55 °C but at very low molar yield (about 14%) and lower regioselectivity.     

(2‐Hydroxy isobutyric) acid containing poly(glycolic acid): Structure–properties relationship

Poly(glycolic acid) (PGA) and a series of novel random copolymers of PGA containing 2‐hydroxyisobutyrric acid (PGAPHIB) (HIB unit content from 1.5 to 7.4 mol %) were synthesized and characterized in terms of chemical structure and molecular weight. Afterward, the polyesters were examined by thermogravimetric analysis, differential scanning calorimetry, and X‐ray diffraction techniques. The copolymers, which displayed a better thermal stability than PGA, at room temperature appeared as semicrystalline materials: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of the melting temperature with respect to homopolymer PGA. Baur's equation described well the T_m‐composition data. X‐ray diffraction measurements allowed the identification of the PGA crystalline structure in all cases. After melt quenching, semicrystalline samples were obtained with the exception of PGAPHIB7.4 copolymer. The introduction of HIB units decreased the crystallization rate compared with pure PGA. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1901–1910, 2010     

Photoinduced molecular rearrangements. Some comments on the ring‐photoisomerization of 1,2,4‐oxadiazoles into 1,3,4‐oxadiazoles

The ring‐photoisomerization of 3‐amino‐ and 3‐methylamino‐5‐phenyl‐1,2,4‐oxadiazoles into the corresponding 2‐amino‐ and 2‐methylamino‐5‐phenyl‐1,3,4‐oxadiazoles has been reinvestigated by examining the effect of a base on the photoreaction. On irradiating at λ = 254 nm in methanol, yields of the ring‐photoisomers were found to be significantly enhanced by the addition of triethylamine (TEA) in the photoreaction medium. By contrast, irradiation of the 3‐amino‐5‐phenyloxadiazole in acetonitrile containing TEA gave an almost complete photoreduction into benzoylguanidine, while few percent of the ring photoisomer were detected. Furthermore, the pyrene‐sensitized photolysis of 3‐amino‐5‐phenyloxadiazole in acetonitrile containing triethylamine also gave benzoylguanidine but no traces of the ring photoisomer.     

The Direction of Time: From the Global Arrow to the Local Arrow

In this paper we discuss the traditional approaches to the problem of the arrow of time. On the basis of this discussion we adopt a global and nonentropic approach, according to which the arrow of time has a global origin and is an intrinsic, geometrical feature of space-time. Finally, we show how the global arrow is translated into local terms as a local time-asymmetric flux of energy.     

Superdeformation in142Eu

A rotational band with 15 transitions has been observed in¹⁴²Eu in an experiment with the GASP Ge detector array by the¹¹⁰Pd(³⁷Cl,5_n) reaction. The average energy spacing between the neighbouring transitions is 60 keV, which is similar to the energy spacings in the superdeformed bands in the mass 140 region. The band has a constant dynamic moment of inertia as suggested by Cranked Shell Model calculations.