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421.
Kateřina Macounová Jakub Jirkovský Marina V. Makarova Jiří Franc Petr Krtil 《Journal of Solid State Electrochemistry》2009,13(6):959-965
Nanocrystalline Ru1 − x
Ni
x
O2 − y
with 0.02 < x < 0.30 were prepared by a sol–gel approach at temperatures between 300 and 600 °C. XRD patterns of the prepared materials
indicate a single-phase character conforming to a tetragonal syngony. All prepared materials are sufficiently stable in acid
media and show activity towards oxygen evolution. The activity towards oxygen evolution reaction of the materials with constant
chemical composition decreases with increasing particle size. The increasing Ni content enhances the electrocatalytic activity
in a stepwise manner with abrupt changes for materials containing approximately 5% or 15% of the cationic sites substituted
by Ni. 相似文献
422.
Petr Vítek Jan Jehli?ka Howell G. M. Edwards Kate?ina Osterrothová 《Analytical and bioanalytical chemistry》2009,393(8):1967-1975
Since evaporitic rocks on the Martian surface could (or still can) serve as potential habitats for microbial life on Mars,
there is a reasonable possibility that these rocks may sustain molecular remnants as evidence for the presence of extinct
or extant living organisms on Mars and that β-carotene could be a suitable biomarker. In this paper, Raman microspectrometry
was tested as a nondestructive method of determining the lowest detectable β-carotene content in experimentally prepared evaporitic
matrices—namely, gypsum, halite and epsomite. Two excitation wavelengths were compared—514.5 nm, because of the resonance
Raman enhancement in the carotenoid analysis, and 785 nm, as a more universal wavelength now much used in the detection of
biomolecules terrestrially. Mixtures were measured directly as well as with a laser beam penetrating the crystals of gypsum
and epsomite. We have obtained β-carotene signals at the 0.1 to 10 mg kg−1 level—the number of registered β-carotene Raman bands differed depending on the particular mineral matrix and the excitation
wavelength. Concentrations of β-carotene of about one order of magnitude higher were identified when analysed through single
crystals of gypsum and epsomite, respectively. 相似文献
423.
Kovaříková P Stariat J Klimeš J Hrušková K Vávrová K 《Journal of chromatography. A》2011,1218(3):416-426
This paper presents a systematic study of the retention behavior of a model bisdioxopiperazine drug, dexrazoxane (DEX) and its three polar metabolites (two single open-ring intermediates-B and C and an EDTA-like active compound ADR-925) on different stationary phases intended for hydrophilic interaction liquid chromatography (HILIC). The main aim was to estimate advantages and limitations of HILIC in the simultaneous analysis of a moderately lipophilic parent drug and its highly polar metabolites, including positional isomers, under MS compatible conditions. The study involved two bare silica columns (Ascentic Express HILIC, Atlantis HILIC) and two stationary phases with distinct zwitterionic properties (Obelisc N and ZIC HILIC). The chromatographic conditions (mobile phase strength and pH, column temperature) were systematically modified to assess their impact on retention and separation of the studied compounds. It was found that the bare silica phases were unable to separate the positional isomers (intermediates B and C), whereas both columns with zwitterionic properties (Obelisc N and ZIC HILIC) were able to separate these structurally very similar compounds. However, only ZIC HILIC phase allowed appropriate separation of DEX and all its metabolites to a base line within a single run. A mobile phase composed of a mixture of ammonium formate (0.5 mM) and acetonitrile (25:75, v/v) was suggested as optimal for the simultaneous analysis of DEX and its metabolites on ZIC HILIC. Thereafter, HILIC-LC-MS analysis of DEX and all its metabolites was performed for the first time to obtain basic data about the applicability of the suggested chromatographic conditions. Hence, this study demonstrates that HILIC could be a viable solution for the challenging analysis of moderately polar parent drug along with its highly polar metabolites including the ability to separate structurally very similar compounds, such as positional isomers. 相似文献
424.
Apples are the most frequently consumed fruit and about 90 % of apple production is stored. Fatty acids and lipids are important constituents of plant cells. Disturbances in the lipid composition of fruit may lead to various stress processes, resulting in some storage disorders. This work is focused on an analysis of surface lipids of different varieties of apples stored in a normal atmosphere and a modified atmosphere with ultra-low oxygen content, for 4 months and 6 months. The major fatty acids in apple surface layers are palmitic acid, stearic acid, linoleic acid, and oleic acid. During the 6-months storage period, a variety-specific decrease in the total fatty acids content and an increase in saturation degree was observed in all the varieties tested, when compared with the 4-months storage. The greatest differences in saturation degree were observed in the Golden Delicious variety, in which the highest content of unsaturated fatty acids was also found. Microbial contamination of apple surfaces increased gradually over the storage process. Higher fungi levels were found in apples stored in the regular atmosphere than in the modified atmosphere, which can be attributed to changes observed in the total lipid content and saturation degree of the surface fatty acids and also to the sensitivity of microorganisms to the oxygen content in the storage room. 相似文献
425.
Simona Zlá Bed?ich Smetana Monika ?aludová Jana Dobrovská Vlastimil Vodárek Kate?ina Kone?ná Vlastimil Matějka Hana Francová 《Journal of Thermal Analysis and Calorimetry》2012,110(1):211-219
The presented paper deals with the study of thermophysical properties of cast and complex alloyed nickel based on superalloy Inconel 713LC (IN713LC). In this work, the technique of Differential Thermal Analysis was selected for determination of the phase transformation temperatures and for the study of the effect of varying heating/cooling rate at these temperatures. The samples taken from as-received state of superalloy were analysed at heating and cooling rates of 1, 5, 10, 20 and 50?°C?min?1 with the help of the experimental system Setaram SETSYS 18TM. Moreover, the transformation temperatures at zero heating/cooling rate were calculated. The recommended values for IN713LC after correcting to a zero heating rate, are 1,205?°C (T ?á?,solvus), 1,250?°C (solidus) and 1,349?°C (liquidus). Influence of heating/cooling rate on shift of almost all temperatures of phase transformations was established from the DTA curves. Undercooling was observed at the cooling process. The samples before and after DTA analysis were also subjected to the phase analysis by scanning electron microscopy using the microscope JEOL JSM-6490LV equipped with an energy dispersive analyser EDAX (EDS INCA x-act). Documentation of the microstructure was made in the mode of secondary (SEI) and backscattered (BEI) electron imaging. On the basis of DTA analysis and phase analysis it may be stated that development of phase transformations of the alloy IN713LC will probably correspond to the following scheme: melting?????? phase; melting???????+?MC; melting????eutectics ??/?á?; melting???????+?minority phases (e.g. borides); and matrix ???????á?. 相似文献
426.
Mikšík I Lacinová K Zmatlíková Z Sedláková P Král V Sýkora D Rezanka P Kašička V 《Journal of separation science》2012,35(8):994-1002
In this work, open-tubular capillary electrochromatography (OT-CEC) method with bare gold nanoparticles (GNPs)-based stationary phase has been developed and applied for separation of tryptic peptide fragments of native and glycated proteins, bovine serum albumin (BSA), and human transferrin (HTF). The GNPs-based stationary phase was prepared by immobilization of bare GNPs, freshly reduced from tetrachloroaurate(III) ions by citrate reduction, on the sol-gel pretreated inner wall of the fused silica capillary. The separation efficiency, peak capacity, and peptide recovery of this open-tubular capillary column were investigated by varying the experimental parameters such as type and concentration of the buffering constituent and pH of the background electrolyte (BGE), temperature, and separation voltage. The best separations of the above tryptic peptides were achieved in the BGE composed of aqueous 100 mmol/L sodium phosphate buffer, pH 2.5, at separation voltage 10 kV per 47-cm long, 50 μm inside diameter capillary thermostated at 25°C. OT-CEC with bare GNPs stationary phase is shown to be a suitable technique for separation of complex peptide mixtures arising from tryptic digestion of native and glycated BSA and HTF, and for investigation of glycation (nonenzymatic glycosylation) of these proteins. 相似文献
427.
428.
Making a comeback: The inefficient condensation of sulfinic acid and aryl nitroso compounds has been transformed into a chemoselective process that converts sulfinic acid into stable cyclic sulfonamide analogues (see scheme). This ligation proceeds rapidly under aqueous conditions in high yield, and lays the groundwork for the development of sulfinic acid detection methods in biological systems. 相似文献
429.
KM Clapham T Rennison G Jones F Craven J Bardos BT Golding RJ Griffin K Haggerty IR Hardcastle P Thommes A Ting C Cano 《Organic & biomolecular chemistry》2012,10(33):6747-6757
Substitution at the 7-position of the chromen-4-one pharmacophore of 8-(dibenzo[b,d]thiophen-4-yl)-2-morpholino-4H-chromen-4-one NU7441, a potent and selective DNA-dependent protein kinase (DNA-PK) inhibitor, with allyl, n-propyl or methyl enabled the resolution by chiral HPLC of atropisomers. Biological evaluation against DNA-PK of each pair of atropisomers showed a marked difference in potency, with biological activity residing exclusively in the laevorotatory enantiomer. 相似文献
430.
AK Swenson KE Higgins MG Brewer WW Brennessel MG Coleman 《Organic & biomolecular chemistry》2012,10(37):7483-7486
A convenient Cu(i)-catalyzed cycloaddition of electron rich internal aryl alkynes and diazoacetates was discovered for the chemoselective and regioselective synthesis of tetra-substituted furans and cyclopropenes in moderate isolated yields (18-67%), and alkyne conversion (29-73%). 相似文献