Asymmetric synthesis of rubiginones A(2) and C(2) and their 11-methoxy regioisomers

Convergent enantioselective syntheses of angucyclinone-type natural products rubiginones A(2) (2) and C(2) (1) and their 11-methoxy regioisomers 3 a and 3 b have been achieved by using two domino processes from a common enantiomerically pure 1-vinylcyclohexene 4. Key steps in the synthesis of this diene were the stereoselective conjugate addition of AlMe(3) on (SS)-[(p-tolylsulfinyl)methyl]-p-quinol (9) and the elimination of the beta-hydroxy sulfoxide fragment, after oxidation to sulfone, to recover a carbonyl group. The first domino sequence comprised Diels-Alder reaction with a sulfinyl naphthoquinone followed by sulfoxide elimination. An efficient opposite regioselection in the cycloaddition step was achieved in the convergent construction of the tetracyclic skeleton using a sulfoxide at C-2 or C-3 of the dienophiles 5 or 6, derived from 5-methoxy-1,4-naphthoquinone. The second domino process, triggered by oxygen and sunlight, allowed the transformation of the initial tetracyclic adducts into the final products after B ring aromatization, silyl deprotection and C-1 oxidation.     

Ion trap mass spectrometry on a comet nucleus: the Ptolemy instrument and the Rosetta space mission

In May 2014, the Rosetta spacecraft is scheduled to rendezvous with the comet Churyumov-Gerasimenko ('67P'). One of the instruments on board the 'Lander' which will descend on to the surface of the comet is a miniaturised GC/MS system that incorporates an ion trap mass spectrometer, specially developed for isotope ratio analysis. This article describes the development and optimisation of the ion trap for this unique application, and presents a summary of the range of pre-programmed experiments that will contribute to the characterisation of the solid and volatile cometary materials.     

Cathode of a fuel cell with a solid polymer electrolyte: Calculating overall currents in the presence of a gas-diffusion layer

Mathematical apparatus, which makes it possible to perform calculations of the current-voltage characteristics of cathodes of fuel cells with a solid polymer electrolyte in conditions where there are present extraneous diffusion restrictions is proposed. In so doing, the partial pressure of oxygen and the absolute pressure of gas in the gas chamber may assume any values. First of all presented are the results of calculations of the current-voltage characteristics intrinsic to active layers of the air and oxygen cathodes, which are performed under the assumption that the extraneous diffusion restrictions are absent altogether. Thereafter, in the same conditions (at the same parameters that characterize the active layer of a cathode), obtained are results of a calculation of the current-voltage characteristics inherent in the air and oxygen cathodes in the presence of extraneous diffusion restrictions. Afterward there is performed an analysis of the way a gas-diffusion layer restricts the process of generation of current in a cathode and of what measures should be taken in order for the extraneous diffusion restrictions to become less significant.     

Comparative methods in the determination of wax content and pour points of crude oils

In this research, differential scanning calorimetry (DSC) and gas chromatography is used to determine the wax content of fourteen crude oils of different sources. Different empirical equations were applied to compare the wax content of crude oils. For the fourteen crude oil samples with the wax content ranging from 7.5 to 43.8 mass%, it was observed that the results of empirical equations were in good agreement with those determined by DSC and GC. Accordingly, a correlation between ASTM pour point and the temperature at which 2 mass% of wax has precipitated out from crude oil is developed.     

Effects of Oxygen and Water Vapor on Volatile Organic Compounds Decomposition Using Gliding Arc Gas Discharge

The combined effects of oxygen and water vapor on three typical volatile organic compounds, i.e. tetrachloromethane, n-butane and toluene, decomposition efficiency under gliding arc gas discharge conditions are studied. The electron density and the density of the reactive radicals such as O and OH are modified by addition of oxygen and water vapor. Consequently, the decomposition process can be enhanced or suppressed, depending on the involved chemical structures and reaction channels. The addition of oxygen and water vapor suppresses the tetrachloromethane decomposition which indicates that this process is mainly controlled by the electron dissociation reactions. By contrast, the n-butane and toluene decompositions are enhanced, which shows that they can be mainly ascribed to the radical induced reactions. Especially, in a moist atmosphere the OH radicals are supposed to play the most important role in the n-butane decomposition process.     

A way of establishing quality of measurements in gas analysis—national and international aspects

Standardising quality of measurements at both the national and international level results in a unity in measurement that may be regarded a synonym of traceability. In gas analysis, the key issue in achieving this aim is production of gaseous reference materials. Establishing a network of secondary measurement standards at gaseous CRM producers’ sites in Ukraine might be interesting for those involved in gas analysis activities. Inevitably, problems concerning the recognition of measuring capabilities of both national metrological institutes and local CRM producers are now an international issue. Thus, the problems of national adoption of international standards, as well as harmonisation between different international documents are currently relevant, and Ukrainian experience may be useful to others in this field. Presented at the 3rd International Conference on Metrology, November 2006, Tel Aviv, Israel.     

Natural-abundance 15N--13C correlation spectra of vitamin B-12

Two-dimensional nitrogen-carbon NMR correlation spectra have been derived by a new reconstruction technique based on standard two-dimensional HMQC and HMBC spectra, and operating with natural 15N and 13C isotopic abundances. Compared with conventional three-dimensional spectroscopy in which 15N and 13C spins must be present in the same molecule, the reconstruction method offers two orders of magnitude improvement in sensitivity. Vitamin B-12 serves as an illustrative example.     

Hydrogen analysis in solid samples by utilizing He metastable atoms induced by TEA CO2 laser plasma in He gas at 1 atm

A TEA CO₂ laser (350 mJ–1.5 J, 10.6 μm, 200 ns, 10 Hz) was focused onto a metal sub-target under He as host gas at 1 atmospheric pressure with a small amount of impurity gas, such as water and ethanol vapors. It was found that the TEA CO₂ laser with the help of the metal sub-target is favorable for generating a strong, large volume helium gas breakdown plasma at 1 atmospheric pressure, in which the helium metastable-excited state was then produced overwhelmingly. While the metal sub-target itself was never ablated. The helium metastable-excited state produced after the strong helium gas breakdown plasma was considered to play an important role in exciting the atoms. This was confirmed by the specific characteristics of the detected H emission, namely the strong intensity with low background, narrow spectral width, and the long lifetime. This technique can be used for gas and solid samples analysis. For nonmetal solid analysis, a metal mesh was introduced in front of the nonmetal sample surface to help initiation of the helium gas breakdown plasma. For metal sample, analysis can be carried out by combining the TEA CO₂ laser and an Nd–YAG laser where the Nd–YAG laser is used to ablate the metal sample. The ablated atoms from the metal sample are then sent into the region of helium gas breakdown plasma induced by the TEA CO₂ laser to be excited through the helium metastable-excited state. This technique can be extended to the analysis of other elements, not limited only to hydrogen, such as halogens.     

多维气相色谱法提高丙烯腈色谱分析速度的方法

采用多维气相色谱法,既可提高丙烯醛、丙酮、乙腈、丙烯腈相邻两组分的分离度,又可提高分析速度。按GDX-502与402的体积比为85∶15比例混装长4.5m、内径3mm的色谱柱;氢气作为载气,流速为65mL/min;柱箱初温140℃保持15min,以15℃/min的速率升至180℃保持12min。丙烯腈样品中7种组分即可全部出峰,总分析时间为30min,比原国标推荐的方法缩短了近50min。     

气相色谱法分析生产过程中的邻甲基苯胺

气相色谱法测定工业生产过程中邻甲基苯胺及其杂质邻硝基甲苯、间甲基苯胺、对甲基苯胺的含量。4种物质的浓度与色谱峰面积呈良好的线性关系,测定结果与标准值基本一致。邻甲基苯胺、邻硝基甲苯、间甲基苯胺、对甲基苯胺的RSD分别为0.0025%、1.4081%、0.9929%、1.1365%,检出限分别为0.065、0.044、0.062、0.056mg/L。