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61.
Synthesis and utilization of a simple copper on iron catalyst in the coupling of aryl halides with thiols through disulfide intermediate is reported. The iron support of copper catalyst ensures reductive media for the coupling, allows easy removal of the metals by outer magnetic field and enables the recycling of the catalyst. 相似文献
62.
The enantiomers of imperanene, a novel polyphenolic compound of Imperata cylindrica (L.), were separated via cyclodextrin-modified capillary electrophoresis. The anionic form of the analyte at pH 9.0 was subject to complexation and enantioseparation CE studies with neutral and charged cyclodextrins. As chiral selectors 27 CDs were applied differing in cavity size, sidechain, degree of substitution (DS) and charge. Three hydroxypropylated and three sulfoalkylated CD preparations provided enantioseparation and the migration order was successfully interpreted in each case in terms of complex mobilities and stability constants. The best enantioresolution (R(S) =?1.26) was achieved using sulfobutyl-ether-γ-CD (DS ~4), but it could be enhanced by extensive investigations on dual selector systems. After optimization (CD concentrations and pH) R(S) =?4.47 was achieved using a 12.5 mM sulfobutyl-ether-γ-CD and 10 mM 6-monodeoxy-6-mono-(3-hydroxy)-propylamino-β-cyclodextrin dual system. The average stoichiometry of the complex was determined with Job's method using NMR-titration and resulted in a 1:1 complex for both (2-hydroxy)propyl-β- and sulfobutyl-ether-γ-CD. Further NMR experiments suggest that the coniferyl moiety of imperanene is involved in the host-guest interaction. 相似文献
63.
ABSTRACT Two diamond-bearing meteorites (ALH-77257 and ALH-78113) were investigated by petrographic microscope and micro-Raman spectroscopy. The meteoritic diamonds can be found in fractures or veins cross-cutting the original minerals (olivine, pyroxene, feldspar) and inside the host minerals. The micro-Raman spectral features of microdiamonds in two studied meteorites are very similar to each other. The diamond peak was found at 1329 in ALH-77257 and 1332 cm?1 in ALH-78113. Hexagonal diamond was not present. However, we observed the D and G bands of graphite or amorphous carbon at 1322 and 1582 cm?1 wavenumbers, indicating an origin of the meteoritic microdiamonds by magmatic processes. 相似文献
64.
The effect of static external field is studied on the isotropic–nematic phase transition of a system of hard non-spherical particles (rods or platelets) with negative anisotropic polarizability (susceptabilities). On the basis of Onsager theory, the phase coexistence curve is calculated numerically without any approximation. It is found that a weakly ordered nematic phase (uniaxial planar) is in coexistence with a highly ordered biaxial nematic phase which ends at a tricritical point. In the limit of infinite field strength, the orientations of the particles are confined in a plane perpendicular to the field and continuous isotropic–nematic phase transition takes place. 相似文献
65.
Marosi A Szalay Z Béni S Szakács Z Gáti T Rácz Á Noszál B Demeter Á 《Analytical and bioanalytical chemistry》2012,402(4):1653-1666
Multinuclear one (1D-) and two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopic investigations of famotidine,
the most potent and widely used histamine H2-receptor antagonist, were carried out in dimethyl sulfoxide-d6 (DMSO-d6) and water. Previous NMR assignments were either incomplete or full assignment was based only on 1D spectra and quantum-chemical
calculations. Our work revealed several literature misassignments of the 1H, 13C, and 15N NMR signals and clarified the acid–base properties of the compound at the site-specific level. The erroneous assignment
of Baranska et al. (J. Mol. Struct. 2001, 563) probably originates from an incorrect hypothesis about the major conformation of famotidine in DMSO-d6. A folded conformation similar to that observed in the solid-state was also assumed in solution, stabilized by an intramolecular
hydrogen bond involving one of the sulphonamide NH2 protons and the thiazole nitrogen. Our detailed 1D and 2D NMR experiments enabled complete ab initio
1H, 13C, and 15N assignments and disproved the existence of the sulphonamide NH hydrogen bond in the major conformer. Rather, the molecule
is predominantly present in an extended conformation in DMSO-d6. The aqueous acid–base properties of famotidine were studied by 1D 1H- and 2D 1H/13C heteronuclear multiple-bond correlation (HMBC) NMR-pH titrations. The experiments identified its basic centers including
a new protonation step at highly acidic conditions, which was also confirmed by titrations and quantum-chemical calculations
on a model compound, 2-[4-(sulfanylmethyl)-1,3-thiazol-2-yl]guanidine. Famotidine is now proved to have four protonation steps
in the following basicity order: the sulfonamidate anion protonates at pH = 11.3, followed by the protonation of the guanidine
group at pH = 6.8, whereas, in strong acidic solutions, two overlapping protonation processes occur involving the amidine
and thiazole moieties. 相似文献
66.
Szabolcs Harnos György Onyestyák Róbert Barthos Magdalena Štolcová Alexander Kaszonyi József Valyon 《Central European Journal of Chemistry》2012,10(6):1954-1962
This work relates to the consecutive reduction of short chain carboxylic acids (volatile fatty acids, VFAs) to alcohols as main products. Acetic acid (AA) was used as a reactant to model the VFAs that can be produced by either thermochemical or biological biomass degradation. The amorphised zeolite supported copper catalysts (Cu/SiAl), especially the In-modified CuIn/SiAl catalysts, showed high hydroconversion activity and selectivity for alcohol, ester and aldehyde. Catalysts containing dispersed copper particles in amorphous aluminosilicate were obtained by dehydrating and H2-reducing Cu-forms of low-silica synthetic zeolites (A, X, P). The activity of the highly destructed Cu-aluminosilicates was found to depend on the structure of the zeolite precursor. The formation of ethyl acetate could be suppressed by adding water to the AA feed and by modifying the catalyst, e.g. by In2O3 additive. In the catalysts modified by In2O3 additive formation of copper-indium alloy phase (Cu2In intermetallic compound) was detected resulting in a different selectivity than the one recorded for the Cu/SiAl. 相似文献
67.
Szabolcs Fekete Jenő Fekete Imre Molnár Katalin Ganzler 《Journal of chromatography. A》2009,1216(45):7816-7823
Many different strategies of reversed phase high performance liquid chromatographic (RP-HPLC) method development are used today. This paper describes a strategy for the systematic development of ultrahigh-pressure liquid chromatographic (UHPLC or UPLC) methods using 5 cm × 2.1 mm columns packed with sub-2 μm particles and computer simulation (DryLab® package). Data for the accuracy of computer modeling in the Design Space under ultrahigh-pressure conditions are reported. An acceptable accuracy for these predictions of the computer models is presented. This work illustrates a method development strategy, focusing on time reduction up to a factor 3–5, compared to the conventional HPLC method development and exhibits parts of the Design Space elaboration as requested by the FDA and ICH Q8R1. Furthermore this paper demonstrates the accuracy of retention time prediction at elevated pressure (enhanced flow-rate) and shows that the computer-assisted simulation can be applied with sufficient precision for UHPLC applications (p > 400 bar). Examples of fast and effective method development in pharmaceutical analysis, both for gradient and isocratic separations are presented. 相似文献
68.
Zoltán Siklósy Attila Demény Torsten W. Vennemann Sebastien Pilet Jan Kramers Szabolcs Leél‐Őssy Mária Bondár Chuan‐Chou Shen Ernst Hegner 《Rapid communications in mass spectrometry : RCM》2009,23(6):801-808
Stable isotope analyses of speleothems (carbonate deposits formed in caves) have been widely used to reconstruct paleoenvironmental conditions. Recent improvements in geochemical techniques have enabled us to analyze climate‐influenced deposits at high temporal resolution so that hitherto unrecognized environmental conditions may be identified. Stable H, C and O isotope analyses on carbonate and inclusion water have been combined with multicollector inductively coupled plasma mass spectrometry (MC‐ICP‐MS) age dating and laser‐ablation ICP‐MS trace element analyses on a stalagmite from southern Hungary. The study reveals significant changes in chemical and isotopic compositions of the speleothem between approx. 3800 and 3500 years BP (‘Before Present’) indicating coupled changes in the temperature and precipitation regime under which the speleothem formed. Stable isotopic and trace element correlations within this time period correlate with similar studies of stalagmites of comparable age from the Alpine‐Mediterranean region. Our studies suggest that traces of deposition of volcanic dust, possibly related to the Thera eruption of Santorini (Greece) ca. 1650 BC (~3650 BP), and environmental changes can be detected at a distance of several thousand kilometers. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
69.
Korhammer Kathrin Mihály Judith Bálint Szabolcs Trif László Vass Ádám Tompos András Tálas Emília 《Journal of Thermal Analysis and Calorimetry》2019,137(1):11-23
Journal of Thermal Analysis and Calorimetry - The influence of temperature and magnesia content on the formation of phases and their transformation kinetics in stoichiometric and non-stoichiometric... 相似文献
70.
Attila Lengyel Gyula Tolnai Zoltán Klencsár Vijayendra Kumar Garg Aderbal Carlos de Oliveira L. Herojit Singh Zoltán Homonnay Roland Szalay Péter Németh Bálint Szabolcs Mira Ristic Svetozar Music Ernő Kuzmann 《Journal of nanoparticle research》2018,20(5):137
57Fe Mössbauer spectroscopy, XRD, and TEM were used to investigate the effect of mandelic- and salicylic acid coatings on the iron oxide nanoparticles. These two carboxylic acids have similar molecules size and stoichiometry, but different structure and acidity. Significant differences were observed between the Mössbauer spectra of samples coated with mandelic acid and salicylic acid. These results indicate that the occurrence of iron microenvironments in the mandelic- and salicylic acid-coated iron oxide nanoparticles is different. The results can be interpreted in terms of the influence of the acidity of carboxylic acids on the formation, core/shell structure, and oxidation of coated iron oxide nanocomposites. 相似文献