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51.
Miroslav Rievaj Eva Culkov Damina andorov Zuzana Luk
ov-Chomistekov Renata Bellov Jaroslav Durdiak Peter Tom
ík 《Molecules (Basel, Switzerland)》2021,26(6)
This short review deals with the properties and significance of the determination of selenium, which is in trace amounts an essential element for animals and humans, but toxic at high concentrations. It may cause oxidative stress in cells, which leads to the chronic disease called selenosis. Several analytical techniques have been developed for its detection, but electroanalytical methods are advantageous due to simple sample preparation, speed of analysis and high sensitivity of measurements, especially in the case of stripping voltammetry very low detection limits even in picomoles per liter can be reached. A variety of working electrodes based on mercury, carbon, silver, platinum and gold materials were applied to the analysis of selenium in various samples. Only selenium in oxidation state + IV is electroactive therefore the most of voltammetric determinations are devoted to it. However, it is possible to detect also other forms of selenium by indirect electrochemistry approach. 相似文献
52.
José J. Garrido-González Irene Boya del Teso Dr. Ángel L. Fuentes de Arriba Dr. Francisca Sanz Dr. Eva M. Martín del Valle Dr. Joaquín R. Morán Dr. Victoria Alcázar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(59):14605-14609
Cleft type receptors showing the oxyanion hole motif have been prepared in a straightforward synthesis starting from the commercial 3,7-dihidroxy-2-naphthoic acid. The double H-bond donor pattern is achieved by the introduction of a sulfonamide group in the C-8 position of naphthalene and a carboxamide at the C-2 position. This cleft, for which the geometry resembles that of an oxyanion hole, is able to adjust to different guests, as shown by the analysis of the X-ray crystal structures of associates with methanol or acetic acid. Combination of hydrogen bonds and charge-transfer interactions led to further stabilization of the complexes, in which the electron-rich aromatic ring of the receptor was close in space to the electron-deficient dinitroaromatic guests. Modelling studies and bidimensional NMR experiments have been carried out to provide additional information. 相似文献
53.
Dr. Eva González-Freire Dr. Federica Novelli Antonio Pérez-Estévez Prof. Dr. Rafael Seoane Dr. Manuel Amorín Prof. Dr. Juan R. Granja 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(9):3029-3038
A new class of amphipathic cyclic peptides, which assemble in bacteria membranes to form polymeric supramolecular nanotubes giving them antimicrobial properties, is described. The method is based on the use of two orthogonal clickable transformations to incorporate different hydrophobic or hydrophilic moieties in a simple, regioselective, and divergent manner. The resulting cationic amphipathic cyclic peptides described in this article exhibit strong antimicrobial properties with a broad therapeutic window. Our studies suggest that the active form is the nanotube resulted from the parallel stacking of the cyclic peptide precursors. Several techniques, CD, FTIR, fluorescence, and STEM, among others, confirm the nanotube formation. 相似文献
54.
G. Buogo P. Meduri W. Lintzel Eva Herring W. P. Golmow und F. Hillig 《Fresenius' Journal of Analytical Chemistry》1943,125(7-8):309-310
Ohne Zusammenfassung 相似文献
55.
Mats Johansson Eva Malmstrm Anders Hult 《Journal of polymer science. Part A, Polymer chemistry》1993,31(3):619-624
A model two-step synthesis of a saturated hyperbranched hydroxyl-terminated ester has been developed to show a synthesis route. Three different series of hyperbranched esters with different terminations have been synthesized to relate some of their properties to their structures. This route has then been used to synthesize three different allyl ethermaleate functional hyperbranched ester resins in a two-step procedure. The resins have been characterized with respect to rheology, structure, and properties, and the differences are discussed. The allyl ether-maleate functional resins have also been studied with respect to curing performance and final film properties. © 1993 John Wiley & Sons, Inc. 相似文献
56.
Petr Brázda Eva Večerníková Eva Pližingrová Adriana Lančok Daniel Nižňanský 《Journal of Thermal Analysis and Calorimetry》2014,117(1):85-91
Thermal behavior of highly crystalline ε-Fe2O3 nanoparticles of different apparent crystallite sizes was characterized using thermogravimetry, differential thermal analysis, and analysis of evolved gas by mass spectrometry. Phase composition of the samples was monitored ex situ by X-ray powder diffraction. The results show that the thermal stability of this metastable iron oxide polymorph decreases with increasing particle size. For the particle diameter of 19(2) nm, the transformation temperature was equal to 794(5) °C, while for 28(2) nm only 755(10) °C. Surface of the nanoparticles contained adsorbed water and carbon dioxide. Elimination of these species proceeds in two steps. Water is removed at temperatures below 200 °C and CO2 in the temperature range between 200 and 450 °C. 相似文献
57.
Jana Holubová Zdeněk Černošek Eva Černošková 《Journal of Thermal Analysis and Calorimetry》2014,116(2):699-702
Thermal properties and structure of bulk glasses of (As2S3)1?x(Sb4S4)x system (x varies from 0 to 60 mol%) were studied by differential scanning calorimetry and Raman spectroscopy. It was found that with increasing Sb content the glasses can be sorted out to the three groups. The structure of glasses with x ≤ 10 is build-up mainly from AsS3/2 pyramidal units and the well-known crystallization resistance of As2S3 can explain the reluctance of these undercooled liquids against crystallization. In glasses with a higher content of antimony, i.e., 10 < x ≤ 30 mol%, the vibration characteristics of As4S4 clusters appear. Undercooled melts of these glasses crystallize forming both β-As4S4 and high-temperature phases of Sb2S3. Structure of glasses with the highest antimony content (x > 30 mol%) is based on SbS3/2 structural units significantly lowering stability of their undercooled melts from which only Sb2S3 crystallizes. 相似文献
58.
Eva Kuzielová Matúš Žemlička Jiří Másilko Martin T. Palou 《Journal of Thermal Analysis and Calorimetry》2018,133(1):63-76
Stability of Dyckerhoff cement Class G partially substituted (15 mass%) by metakaolin (MK), silica fume (SF) and ground granulated blast-furnace slag (BFS) was investigated after 7 days of curing under standard and two different autoclaving conditions. Mercury intrusion porosimetry, X-ray diffraction analysis and combined thermogravimetric–differential scanning calorimetry were used to evaluate pore structure development, compressive strength and their dependence on the type of additives in relation to the particular phase composition. Hydrothermal curing led to the formation of α-C2SH and jaffeite, mostly in the case of referential samples and compositions with addition of slowly reacting BFS. Whilst modest hydrothermal curing (0.6 MPa, 165 °C) favoured formation of α-C2SH, larger amounts of jaffeite were determined after curing at the highest used pressure and temperature (2.0 MPa, 220 °C). Undesired transformation of primary hydration products was prevented especially by addition of highly reactive and very fine SF. Particular composition attained the best pore structure characteristics and compressive strength after curing at 0.6 MPa and 165 °C. Formation of more stable phases with C/S ratio close to 1 was proved by wollastonite formation during DSC analyses. More severe conditions of curing, however, led to the significant deterioration of microstructure and strength of corresponding sample, probably due to the formation of trabzonite, killalaite and zoisite. Considering the values of hydraulic permeability coefficient and compressive strength, replacement of cement by MK improved significantly the properties of cement when compared with the referential as well as with other blended compositions under the mentioned curing conditions. 相似文献
59.
Edi?Bralatei Karolina?Nekrosiute Jenny?Ronan Andrea?Raab Evin?McGovern Dagmar?B.?Stengel Eva?M.?Krupp Joerg?FeldmannEmail authorView authors OrcID profile 《Mikrochimica acta》2017,184(6):1701-1709
Inorganic arsenic (iAs) in 13 store-bought edible seaweed samples and 34 dried kelp (Laminaria digitata) samples was determined by a newly developed, field-deployable method (FDM) with the aid of a field test kit for arsenic in water. Results from the FDM were compared to results from speciation analysis achieved by using high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The FDM consisted of a simple extraction method using diluted HNO3 to quantitatively extract iAs without decomposing the organoarsenicals to iAs followed by the selective volatilisation of iAs as arsine (AsH3) and subsequent chemo-trapping on a filter paper soaked in mercury bromide (HgBr2) solution. Method optimization with a sub-set of samples showed 80–94% iAs recovery with the FDM with no matrix effect from organo-arsenic species in the form of dimethylarsinic acid (DMA) on the iAs concentration. The method displayed good reproducibility with an average error of ±19% and validation by HPLC-ICP-MS showed that the results from the FDM were comparable (slope = 1.03, R2 = 0.70) to those from speciation analysis with no bias. The FDM can be conducted within an hour and the observed limit of quantification was around 0.05 mg kg?1 (dry weight). This method is well suited for on-site monitoring of iAs in seaweed before it is harvested and can thus be recommended for use as a screening method for iAs in seaweed. 相似文献
60.