Thermodynamic properties of an alternating copolymer of bicyclo[2.2.1]hepta-2,5-diene and carbon monoxide in a region from <Emphasis Type="Italic">T</Emphasis> → 0 to 550 K

The temperature dependence of the heat capacity of an alternating copolymer of bicyclo[2.2.1]hepta-2,5-diene and carbon monoxide in the temperature range 6–550 K (with an error of 0.2–0.5% at 6–350 K and 0.5–1.5% at 330–550 K) was studied by the adiabatic vacuum and dynamic calorimetry. Physical transformations of the copolymer in the studied temperature region were identified, and their thermodynamic characteristics were determined. The combustion energy of the copolymer at 298.15 K was measured in a calorimeter with a static bomb and isothermal jacket. The thermodynamic functions for a region of 0–550 K, enthalpy of combustion, and thermodynamic parameters of copolymer formation from simple substances at T = 298.15 K and p = 101.325 kPa were calculated from the obtained experimental data. The new results and earlier published data were used for the calculation of the thermodynamic characteristics of the alternate copolymerization of bicyclo[2.2.1]hepta-2,5-diene and CO under standard pressure for a region of 0–350 K for the bulk reaction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1483–1487, June, 2005.     

Fragmentation of biotinylated cyclic peptides

Electrospray ionization coupled with tandem mass spectrometry (MS/MS) was used to determine the preferred binding site(s) of biotin NHS ester with a series of cyclic peptides with antibiotic properties. The peptides investigated are polymyxins, cyclic peptides produced by Bacillus polymyxa. In spite of the 1:1 stoichiometry used in the labeling reaction, multiple biotin molecules were incorporated into intact polymyxin peptides. Given the amine specificity of the activated biotin and the large number of amino acids with primary amines in the polymyxins, it was not clear by inspection which binding sites were more reactive than others. MS/MS was used to characterize the structure of the biotinylated peptides. MS/MS spectra of cyclic peptides often lead to ambiguous structure determinations due to the potential for multiple ring openings which result in the generation of multiple ion series. The MS/MS spectra of polymyxin peptides are especially difficult to characterize due to the lack of variety in their amino acids; however, the added complexity of the biotin aided the elucidation of the fragmentation pathways. MS/MS spectra of the species with biotin additions were used to rationalize the preferential binding sites of these molecules.     

Optimization of Tabersonine Methoxylation to Increase Vindoline Precursor Synthesis in Yeast Cell Factories

Plant specialized metabolites are widely used in the pharmaceutical industry, including the monoterpene indole alkaloids (MIAs) vinblastine and vincristine, which both display anticancer activity. Both compounds can be obtained through the chemical condensation of their precursors vindoline and catharanthine extracted from leaves of the Madagascar periwinkle. However, the extensive use of these molecules in chemotherapy increases precursor demand and results in recurrent shortages, explaining why the development of alternative production approaches, such microbial cell factories, is mandatory. In this context, the precursor-directed biosynthesis of vindoline from tabersonine in yeast-expressing heterologous biosynthetic genes is of particular interest but has not reached high production scales to date. To circumvent production bottlenecks, the metabolic flux was channeled towards the MIA of interest by modulating the copy number of the first two genes of the vindoline biosynthetic pathway, namely tabersonine 16-hydroxylase and tabersonine-16-O-methyltransferase. Increasing gene copies resulted in an optimized methoxylation of tabersonine and overcame the competition for tabersonine access with the third enzyme of the pathway, tabersonine 3-oxygenase, which exhibits a high substrate promiscuity. Through this approach, we successfully created a yeast strain that produces the fourth biosynthetic intermediate of vindoline without accumulation of other intermediates or undesired side-products. This optimization will probably pave the way towards the future development of yeast cell factories to produce vindoline at an industrial scale.     

The Influence of Technological Regimes of Synthesizing a Solar Furnace on the Phase Composition of TiO<Subscript>2</Subscript>-CuO Cermets and the Optical Properties of Coatings on Their Basis

We present the results of studying the effect of technological synthesis regimes of a solar furnace using the method of a partial metal reduction of one of the oxides on the phase formation of cermet composite materials of the TiO₂-CuO system. It has been established that the phase composition of the synthesized cermet composite materials depends on the carbon concentration, melting temperature and cooling rate. The dependence of the spectral-optical properties of selectively absorbing coatings on the production technology and properties of synthesized composite materials has been presented. It has been found that the coatings fabricated by melting in air with overheating at a melt cooling rate of about 105–106°C/s have the highest values of the integral absorption coefficient, α _s = 91.0–94.5%.     

Nonlinear Bleaching of InAs Nanowires in the Visible Range

Optics and Spectroscopy - Spectral and nonlinear optical properties of InAs nanowires synthesized via molecular beam epitaxy suspended in isopropanol are studied in this work at room temperature....     

Evolution of Dislocation Substructure in Deformed Ordered and Disordered Pd3Fe Alloys in Low-Stability State

Russian Physics Journal - The paper presents the results of the transmission electron microscopy of the evolution of the dislocation substructure (DSS) of the polycrystalline ordered and disordered...     

Lasing in microdisks with an active region based on lattice-matched InP/AlInAs nanostructures

The emissivity of unstrained quantum-dimensional InP/AlInAs nanostructures and their lasing properties in microdisk cavities prepared by wet etching have been studied. For as-prepared structures, it has been found that they radiate owing to quantum-dimensional InP islands 50–300 nm in diameter. At temperatures below 160 K, whispering gallery modes have been observed in the microdisks. Experimental data on the PL intensity for microcavity modes versus the pump power, which were obtained at liquid helium temperature, have made it possible to find the lasing threshold, 50 W/cm². The half-width of the laser line at above-threshold powers equals 0.06 nm, which corresponds to a Q factor of 15 000.     

Nitrolysis of 2,6,8,12-tetraacetyl-4,10-dibenzyl-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.03,11.05,9]dodecane

Russian Chemical Bulletin - Nitrolysis of 2,6,8,12-tetraacetyl-4,10-dibenzyl-2,4,6,8,10,12-hexaazatetracyclo-[5.5.0.03,11.05,9]dodecane results in the substitution of benzyl groups by the nitro...