Chemo-enzymatic synthesis of 4-methylumbelliferyl beta-(1-->4)-D-xylooligosides: new substrates for beta-D-xylanase assays

Transglycosylation catalyzed by a beta-D-xylosidase from Aspergillus sp. was used to synthesize a set of 4-methylumbelliferyl (MU) beta-1-->4-D-xylooligosides having the common structure [beta-D-Xyl-(1-->4)]2-5-beta-D-Xyl-MU. MU xylobioside synthesized chemically by the condensation of protected MU beta-D-xylopyranoside with ethyl 2,3,4-tri-O-acetyl-1-thio-beta-D-xylopyranoside was used as a substrate for transglycosylation with the beta-D-xylosidase from Aspergillus sp. to produce higher MU xylooligosides. The structures of oligosaccharides obtained were established by 1H and 13C NMR spectroscopy and electrospray tandem mass spectrometry. MU beta-D-xylooligosides synthesized were tested as fluorogenic substrates for the GH-10 family beta-D-xylanase from Aspergillus orizae and the GH-11 family beta-D-xylanase I from Trichoderma reesei. Both xylanases released the aglycone from MU xylobioside and the corresponding trioside. With substrates having d.p. 4 and 5, the enzymes manifested endolytic activities, splitting off MU, MUX, and MUX2 primarily.     

The Impact of SF<Subscript>6</Subscript> Plasma on the Properties of Graphene Oxide

The paper considers the effect of SF₆ plasma-chemical treatment on the processes of defect formation and the electrical properties of graphene oxide partially reduced by heat treatment. The fluorine content on the graphene oxide surface is shown to increase as a result of SF₆ plasma treatment, depending on the plasma power and the duration of the treatment. The measured electrical parameters testify increased resistance of graphene oxide films as a result of plasma treatment. The rate of resistance change depends on the thickness of the films and is minimal for thin structures (～10 nm). Further heating of graphene oxide decreases its resistance, but the content of surface fluorine changes insignificantly. Thin films (10-15 nm) exhibit the smallest change of their resistance as a result of annealing. The highest rate of resistance change is observed for non-fluorinated samples. The obtained data indicate that only several nanometers of nearsurface layers are subject to SF₆ plasma fluorination. The results testify the possibility of using SF₆ plasma treatment as an effective tool for selective fluorination of graphene oxide surface layers and controlled modification of its properties without changing the bulk properties of the material.     

Nucleophilic Functionalization of Tropylium Salts with Aromatic Amines

Russian Journal of Organic Chemistry - The mini-review systematizes recently published data on nucleophilic N- and C-amination of electron-deficient tropylium salts with aromatic amines.     

Irradiation Creep Behavior of Steels 08Х18Н10Т and 07Х16Н12М3Т Irradiated in the BOR-60 Reactor in a Temperature Range of 330 to 350°С

Physics of Atomic Nuclei - The paper describes the results of post-irradiation examinations for pressurized specimens that varied in design and were made of austenitic steels...     

Status of the Yakutsk Air Shower Array and Future Plans

Physics of Atomic Nuclei - The Yakutsk Extensive Air Shower Array has been continuously operating for more than 50 years (since 1970) and up until recently it has been one of world’s largest...     

Advantages of anhysteretic magnetooptic films in nondestructive testing

The potentialities provided by bismuth-containing garnet ferrite films with uniaxial anisotropy and easy-plane anisotropy for the visualization of spatially nonuniform magnetic fields in magnetooptic nondestructive testing are compared.     

Search for sterile neutrinos in the neutrino-4 experiment

An experimental search for sterile neutrinos has been carried out at a neutrino facility based on the SM-3 nuclear reactor in Dimitrovgrad, Russia. The movable detector with passive shielding against the external radiation may be positioned at a distance varying between 6 and 12 m from the center of the reactor. The antineutrino flux has for the first time been measured using a movable detector placed close to the antineutrino source. The accuracy of the measurements is largely restricted by the cosmic background. The results of the measurements performed at small and large distances are analyzed in terms of the sterile-neutrino model parameters Δm ₁₄ ² and sin²2θ₁₄.     

Products of Quasi-Involutions in Unitary Groups

Given a regular ^–-hermitian form on an n-dimensional vector space V over a commutative field K of characteristic 2 ( ). Call an element of the unitary group a quasi-involution if is a product of commuting quasi-symmetries (a quasi-symmetry is a unitary transformation with a regular (n–1)-dimensional fixed space). In the special case of an orthogonal group every quasi-involution is an involution. Result: every unitary element is a product of five quasi-involutions. If K is algebraically closed then three quasi-involutions suffice.     

Experiment for search for sterile neutrino at SM-3 reactor

In connection with the question of possible existence of sterile neutrino the laboratory on the basis of SM-3 reactor was created to search for oscillations of reactor antineutrino. A prototype of a neutrino detector with scintillator volume of 400 l can be moved at the distance of 6–11 m from the reactor core. The measurements of background conditions have been made. It is shown that the main experimental problem is associated with cosmic radiation background. Test measurements of dependence of a reactor antineutrino flux on the distance from a reactor core have been made. The prospects of search for oscillations of reactor antineutrino at short distances are discussed.     

Reversible-adsorption-induced variation of domain width in iron garnet films

It has been found using the Faraday-effect magneto-optic method that the width of magnetic domains of the labyrinth domain structure in bismuth-containing iron garnet films with perpendicular anisotropy changes considerably after the adsorption of methanol molecules. A maximum change in domain width of 50% has been observed in methanol saturated vapor. This effect is reversible. A decrease in domain width under adsorption has been attributed to a decrease in the effective constant of the perpendicular magnetic anisotropy of the film caused by the adsorption of methanol molecules.