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91.
92.
Bartosz Mozgawa Dr. Filip Zasada Dr. Monika Fedyna Prof. Kinga Góra-Marek Dr. Edyta Tabor Dr. Kinga Mlekodaj Dr. Jiří Dědeček Prof. Zhen Zhao Dr. Piotr Pietrzyk Prof. Zbigniew Sojka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(68):17159-17180
NH3 temperature-programmed desorption (NH3-TPD) is frequently used for probing the nature of the active sites in CuSSZ-13 zeolite for selective catalytic reduction (SCR) of NOx. Herein, we propose an interpretation of NH3-TPD results, which takes into account the temperature-induced dynamics of NH3 interaction with the active centers. It is based on a comprehensive DFT/GGA+D and first-principles thermodynamic (FPT) modeling of NH3 adsorption on single Cu2+, Cu+, [CuOH]+ centers, dimeric [Cu-O-Cu]2+, [Cu-O22−-Cu]2 species, segregated CuO nanocrystals and Brønsted acid sites (BAS). Theoretical TPD profiles are compared with the experimental data measured for samples of various Si/Al ratios and distribution of Al within the zeolite framework. Copper reduction, its relocation, followed by the intrazeolite olation/oxolation processes, which are concomitant with NH3 desorption, were revealed by electron paramagnetic resonance (EPR) and IR. DFT/FPT results show that the peaks in the desorption profiles cannot be assigned univocally to the particular Cu and BAS centers, since the observed low-, medium- and high-temperature desorption bands have contributions coming from several species, which dynamically change their speciation and redox states during NH3-TPD experiment. Thus, a rigorous interpretation of the NH3-TPD profiles of CuSSZ-13 in terms of the strength and concentration of the active centers of a particular type is problematic. Nonetheless, useful connections for molecular interpretation of TPD profiles can be established between the individual component peaks and the corresponding ensembles of the adsorption centers. 相似文献
93.
94.
The dependence of tumor on essential nutrients is known to be crucial for its evolution and has become one of the targets for medical therapies. Based on this fact a reaction–diffusion system with chemotaxis term and nutrient-based growth of tumors is presented. The formulation of the model considers also an influence of tumor and pharmacological factors on nutrient concentration. In the paper, convergence of solutions to constant, stationary states in the one-dimensional case for small perturbation of the equilibria is investigated. The nonlinear stability results are obtained by means of the classical symmetrization method and energy Sobolev estimates. 相似文献
95.
Determination of catechin and epicatechin in the peel of apple varieties resistant and non-resistant to apple scab 总被引:1,自引:0,他引:1
Marek Gołębiowski Edmund Maliński Małgorzata Szankin Mariusz Marszeniuk Monika Paszkiewicz Piotr Stepnowski 《Chemical Papers》2010,64(6):729-733
Catechin and epicatechin were analysed in the peel of six apple cultivars (three resistant and three non-resistant to apple
scab). Two methods of analytical sample preparation following extraction were tested: solid phase extraction and column separation
with Sephadex LH-20 coupled to a differential refractometric detector. Prior to GC and GC-MS analyses, these compounds were
silylized. This permitted co-injection with standards and the comparison of retention values and mass spectra with those recorded
for standards. The content of catechin and epicatechin in apple peel is discussed in relation to the resistance of apple trees
to scab. 相似文献
96.
97.
Sajewicz Mieczysław Wojtal Łukasz Hajnos Michał Waksmundzka-Hajnos Monika Kowalska Teresa 《平面色谱法杂志一现代薄层色谱法》2010,23(4):270-276
JPC – Journal of Planar Chromatography – Modern TLC - In a previous paper we discussed the possibility of fractionating the essential oils of different sage species by low-temperature... 相似文献
98.
99.
Monika Michel Luke Chimuka Tomasz Kowalkowski Ewa M. Cukrowska Bogusław Buszewski 《Journal of separation science》2013,36(5):986-991
An artificial neural network model of supported liquid membrane extraction process with a stagnant acceptor phase is proposed. Triazine herbicides and phenolic compounds were used as model compounds. The model is able to predict the compound extraction efficiency within the same family based on the octanol–water partition coefficient, water solubility, molecular mass and ionisation constant of the compound. The network uses the back‐propagation algorithm for evaluating the connection strengths representing the correlations between inputs (octanol–water partition coefficients logP, acid dissociation constant pKa, water solubility and molecular weight) and outputs (extraction efficiency in dihexyl ether and undecane as organic solvents). The model predicted results in good agreement with the experimental data and the average deviations for all the cases are found to be smaller than ±3%. Moreover, standard statistical methods were applied for exploration of relationships between studied parameters. 相似文献
100.
Timo Stark Sandra Marxen Andrea Rütschle Genia Lücking Siegfried Scherer Monika Ehling-Schulz Thomas Hofmann 《Analytical and bioanalytical chemistry》2013,405(1):191-201
A fast and robust high-throughput ultra-performance liquid chromatography/time-of-flight mass spectrometry (UPLC–TOF MS) profiling method was developed and successfully applied to discriminate a total of 78 Bacillus cereus strains into no/low, medium and high producers of the emetic toxin cereulide. The data obtained by UPLC–TOF MS profiling were confirmed by absolute quantitation of cereulide in selected samples by means of high-performance liquid chromatography with tandem mass spectrometry (HPLC–MS/MS) and stable isotope dilution assay (SIDA). Interestingly, the B. cereus strains isolated from four vomit samples and five faeces samples from patients showing symptoms of intoxication were among the group of medium or high producers. Comparison of HEp-2 bioassay data with those determined by means of mass spectrometry showed differences, most likely because the HEp-2 bioassay is based on the toxic action of cereulide towards mitochondria of eukaryotic cells rather than on a direct measurement of the toxin. In conclusion, the UPLC–electrospray ionization (ESI)–TOF MS and the HPLC–ESI–MS/MS–SIDA analyses seem to be promising tools for the robust high-throughput analysis of cereulide in B. cereus cultures, foods and other biological samples. Figure
Score plot (comp[1] vs. comp[2]) of UPLC‐TOF MS full scan analysis (50–1,300 Da) of 78 B. cereus strains with color‐coded signal intensity of the accurate mass of pseudo molecular ion of cereulide (m/z 1175.6608, [M+Na]+), from group 1 with the lowest up to group 5 with the highest signal intensity 相似文献