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31.
Pawel Mierczynski Waldemar Maniukiewicz Tomasz P. Maniecki 《Central European Journal of Chemistry》2013,11(6):912-919
The activity of monometallic Pd, Ru, Ni and Cu catalysts supported on spinel ZnAl2O4 for water gas shift reaction (WGS) was investigated. The physicochemical properties of each catalyst was studied by XRD, TPR, BET and chemisorption methods. The highest activity was obtained for Cu/ZnAl2O4 among the catalysts tested. The activation process carried out in a reducing atmosphere 5%H2-95%Ar in the case of Cu/ZnAl2O4 system lead to the catalytic activity improvement. In the case of copper catalysts, the water gas shift reaction proceeded by the redox surface mechanism between Cu0/Cu+. The PdZn alloy formation after reduction at 350°C was shown. 相似文献
32.
33.
Tomasz Chmiel Dionna Abogado Waldemar Wardencki 《Analytical and bioanalytical chemistry》2014,406(20):4965-4986
A reliable and repeatable isotachophoretic method for the simultaneous determination of K+, Na+, Ca2+, Mg2+, and ammonium in berries of different blue honeysuckle cultivars was developed. The usefulness of the complex-forming equilibria in determining the cations mentioned above was studied. The addition of 7.5 mM 18-crown-6 and 2 mM α-hydroxyisobutyric acid to sulfuric acid enhanced the separation capacity of the leading electrolyte. The terminating electrolyte of 10 mM TRIS buffered to pH 4.30 was chosen as most appropriate for these studies. An ultrasound-assisted procedure for the extraction of macroelements from dried fruit of Lonicera caerulea L. was investigated using response surface methodology. The Box-Behnken experimental design showed the optimal extraction conditions as follows: temperature of 36 °C, extraction time of 42.3 min and solid-to-liquid ratio of 1:800 v/w. Detection limits for the method ranged from 0.030 to 0.097 mg/l with precision expressed by RSD ranging from 1.4 % for Mg to 4.4 % for Na. The results showed that blue honeysuckle berries are a good source of potassium, from 199 to 402 mg/100 g FW, especially ‘Zielona’ and ‘Zojka’ cultivars. The average content of other analytes in these berries was 5.2 mg Na, 24.8 mg Ca, 7.5 mg Mg and 52.0 mg ammonium per 100 g FW. The berry products contained lower amounts of minerals especially Mg and K. However, a glass of freshly squeezed juice can provide almost 20 % of the RDI of potassium. The results obtained using both the developed isotachophoretic method and ion chromatographic procedure did not differ significantly. Figure
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34.
Paweł Mierczynski Piotr Kaczorowski Agnieszka Ura Waldemar Maniukiewicz Marcin Zaborowski Radoslaw Ciesielski Adam Kedziora Tomasz P. Maniecki 《Central European Journal of Chemistry》2014,12(2):206-212
Ternary CuO-ZrO2-Al2O3 catalysts promoted by palladium or gold were prepared and tested in CO hydrogenation reaction at 260°C under elevated pressure (4.8 MPa). The promotion effect of palladium or gold addition on the physicochemical and catalytical properties of CuO-ZrO2-Al2O3 catalysts in methanol synthesis (MS) was studied. The catalysts were characterized by BET, XRD, TPR-H2, TPD-NH3 methods. The BET results showed that the ternary system CuO-ZrO2-Al2O3 had the largest specific surface area, cumulative pore volume and average pore size in comparison with the promoted catalysts. The yield of methanol can be given through the following sequence: 5%Pd/CuO-ZrO2-Al2O3 > CuO-ZrO2-Al2O3 > 2%Au/CuO-ZrO2-Al2O3. We also found that the presence of gold or palladium on catalyst surface has strong influence on the reaction selectivity. The high selectivity of gold doped ternary catalyst is explained by the gold-oxide interface sites created on the catalyst surface and the acidity of those systems. The higher selectivity to methanol in the case of the palladium catalyst is explained by the spillover effect between Pd and CuO. 相似文献
35.
Vladimir M. Gun’ko Waldemar Tomaszewski Tetyana V. Krupska Konstantin V. Turov Roman Leboda Vladimir V. Turov 《Central European Journal of Chemistry》2014,12(4):509-518
To prepare nitrocellulose (NC), microcrystalline cellulose was treated in a mixture of nitric and sulfuric acids. Prepared NC containing a small amount of acids was studied at a different hydration degree (h = 10–1000 mg g?1) in different dispersion media (chloroform-d, acetone-d6 or their mixtures) using low-temperature 1H NMR spectroscopy. The hydration degree and the presence of residual acids affected the temperature dependence of the chemical shifts of proton resonance of water bound to NC. The Gibbs free energy of bound water became less negative with increasing hydration rate. The chloroform and acetone media affect the behavior of bound-to-NC water unfrozen at T<273 K differently. Quantum chemical calculations were performed using ab initio (HF/6-31G(d,p)), DFT (B3LYP/6-31G(d,p)) and semiempirical PM7 methods to analyze the interfacial behavior of water interacting with NC containing residual amounts of nitric and sulfuric acids. 相似文献
36.
Waldemar Hoffmann Johanna Hofmann Kevin Pagel 《Journal of the American Society for Mass Spectrometry》2014,25(3):471-479
Recent works using ion mobility-mass spectrometry (IM-MS) have highlighted the power of this instrumental configuration to tackle one of the greatest challenges in glycomics and glycoproteomics: the existence of isobaric isomers. For a successful separation of species with identical mass but different structure via IM-MS, it is crucial to have sufficient IM resolution. In commercially available IM-MS instruments, however, this resolution is limited by the design of the instrument and usually cannot be increased at-will without extensive modifications. Here, we present a systematic approach to improve the resolving capability of IM-MS instruments using so-called energy-resolved ion mobility-mass spectrometry. The technique utilizes the fact that individual components in an isobaric mixture fragment at considerably different energies when activated in the gas phase via collision-induced dissociation (CID). As a result, certain components can be suppressed selectively at increased CID activation energy. Using a mixture of four isobaric carbohydrates, we show that each of the individual sugars can be resolved and unambiguously identified even when their drift times differ by as little as 3 %. However, the presented results also indicate that a certain difference in the gas-phase stability of the individual components is crucial for a successful separation via energy-resolved IM-MS. Figure
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37.
Ewa esawska Izabela Korona-Gowniak Wojciech Nitek Waldemar Tejchman 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(4):359-366
Derivatives of pyrimidine‐2(1H)‐selenone are a group of compounds with very strong antimicrobial activity. In order to study the effect of the position of the methoxy substituent on biological activity, molecular geometry and intermolecular interactions in the crystal, three derivatives were prepared and evaluated with respect to their antimicrobial activities, and their crystal structures were determined by X‐ray diffraction. The investigated compounds, namely, 1‐(X‐methoxyphenyl)‐4‐methyl‐6‐phenylpyrimidine‐2(1H)‐selenones (X = 2, 3 and 4 for 1 , 2 and 3 , respectively), C18H16N2OSe, showed very strong activity against selected strains of Gram‐positive bacteria and fungi. Two compounds, 1 and 2 , crystallize in the monoclinic space group P21/c, while 3 crystallizes in the space group P21/n; 1 has two molecules in the asymmetric unit and the other two ( 2 and 3 ) have one molecule. The geometries of the investigated compounds differ slightly in the mutual orientations of the aromatic and pyrimidineselenone rings. The O atom in 1 stabilizes the conformation of the molecules via intramolecular C—H…O hydrogen bonding. The packing of molecules is determined by weak C—H…N and C—H…Se intermolecular interactions and additionally in 1 and 2 by C—H…O intermolecular interactions. The introduction of the methoxy substituent results in greater selectivity of the investigated compounds. 相似文献
38.
39.
Adam W Bargon RM Bosio SG Schenk WA Stalke D 《The Journal of organic chemistry》2002,67(20):7037-7041
The direct molybdenum-catalyzed sulfuration of a variety of isonitriles with elemental sulfur or propene sulfide as sulfur donors affords the corresponding isothiocyanates in good yields and under mild reaction conditions. A catalytic cycle is suggested, in which the molybdenum oxo disulfur complex operates as the active sulfur-transferring species. A novel adduct between the isonitrile and the molybdenum complex has been characterized by X-ray analysis and its association constant determined by UV-vis spectroscopy, but this adduct appears not to be involved in the sulfur-transfer process. 相似文献
40.
Adam W García H Diedering M Martí V Olivucci M Palomares E 《Journal of the American Chemical Society》2002,124(41):12192-12199
The photochemical denitrogenation of the cyclopentene-annelated DBH-type azoalkanes 1 has been examined in solution as a function of bridgehead substitution and temperature. For all derivatives, namely, the unsubstituted 1a(H/H), monomethyl 1b(Me/H) dimethyl 1c(Me/Me), monophenyl 1d(Ph/H), and diphenyl 1e(Ph/Ph), the temperature-dependent ratio of syn and anti housanes 2 provides experimental support for a competition between the singlet (high temperature) and triplet (low temperature) reaction channels in the direct photolysis. The syn/anti ratio of the housanes 2 depends on the extent and type of bridgehead substitution; the amount of the anti diastereomer (retention) follows the order Ph > Me > H, and double substitution is more effective than single. This stereochemical memory is interpreted in terms of the mass effect (inertia) of the substituents and steric interaction (size) between the substituents at the bridgehead and the methylene bridge during the deazetation step of the transient diazenyl diradical conformations (1)DZ (exo-ax) and (1)DZ (exo-eq). These conformers are impulsively generated upon decay of the (1)(n,pi)-excited azoalkane, a trajectory assessed through computational work. The new mechanistic feature disclosed by the unprecedented anti stereoselectivity (retention) is the intervention of a puckered 1,3-cyclopentanediyl singlet diradical (1)DR as product bifurcation step, whose conformational relaxation to the planar species (loss of stereochemical memory) is encumbered by bridgehead substitution. 相似文献