排序方式: 共有116条查询结果,搜索用时 343 毫秒
41.
Samson Rwawiire Blanka Tomkova Jiri Militky Bandu Madhukar Kale Petr Prucha 《International Journal of Polymer Analysis and Characterization》2015,20(2):160-171
The quest for sustainable materials as a consequence of a global drive to mitigate climate change has led to a focus on natural fiber–reinforced composite materials. In this study, skillful ply angle arrangement of bark cloth–reinforced laminar epoxy composites was carried out for the first time using vacuum-assisted resin transfer molding, and the composites fabricated were characterized for the effect of the layering pattern on their static and dynamic mechanical properties. Tensile strength and flexural strength were shown to be dependent on the ply angle arrangement. Dynamic mechanical analysis of the composites showed a glass transition temperature of 70°C, and the storage modulus and mechanical damping properties showed that the developed composites can withstand considerable loads and have excellent fiber-to-matrix adhesion. 相似文献
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Mads H. Rnnest Morten T. Nielsen Blanka Leber Uffe H. Mortensen Alwin Krmer Mads H. Clausen Thomas O. Larsen Pernille Harris 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(3):o125-o128
The fungal metabolite (+)‐geodin [systematic name: (2R)‐methyl 5,7‐dichloro‐4‐hydroxy‐6′‐methoxy‐6‐methyl‐3,4′‐dioxospiro[benzofuran‐2,1′‐cyclohexa‐2′,5′‐diene]‐2′‐carboxylate], C17H12Cl2O7, was isolated from Aspergillus terreus. The crystal structure contains two independent molecules in the asymmetric unit. Molecules denoted 1 interact through O—H...O hydrogen bonds creating chains of molecules parallel to the crystallographic 21 screw axis. Molecules denoted 2 interact through an O...Cl halogen bond, also creating chains of molecules parallel to the crystallographic 21 screw axis. Molecules 1 and 2 interact through another O...Cl halogen bond. The two molecules are similar but molecules 2 have a slightly more planar cyclohexadiene ring than molecules 1. The absolute structure of (+)‐geodin has been unequivocally assigned with the spiro centre having the R configuration in both molecules. The structurally related (+)‐griseofulvin has an S configuration at the spiro centre, a difference of potential biological and biosynthetic relevance. 相似文献
43.
Aleš Marek Mahadeo R. Patil Blanka Klepetářová Ladislav Kohout Tomáš Elbert 《Tetrahedron letters》2012,53(16):2048-2050
A new and efficient procedure for the preparation of brassinosteroids labeled with hydrogen isotopes was developed. A four-step reaction sequence started with the selective oxidation of a 2,3-diol group to an α-hydroxy ketone, which was converted stereospecifically into a chlorocarbonate by reaction with triphosgene. A subsequent Pd-catalyzed reductive dechlorination with deuterium gas yielded deuterium-labeled brassinosteroid 2,3-carbonates. The reaction sequence was completed by base-catalyzed hydrolysis of the cyclic carbonate. 相似文献
44.
Didem Ketenoglu Georg Spiekermann Manuel Harder Erdinc Oz Cevriye Koz Mehmet C. Yagci Eda Yilmaz Zhong Yin Christoph J. Sahle Blanka Detlefs Hasan Yavaş 《Journal of synchrotron radiation》2018,25(2):537-542
The effects of varying LiPF6 salt concentration and the presence of lithium bis(oxalate)borate additive on the electronic structure of commonly used lithium‐ion battery electrolyte solvents (ethylene carbonate–dimethyl carbonate and propylene carbonate) have been investigated. X‐ray Raman scattering spectroscopy (a non‐resonant inelastic X‐ray scattering method) was utilized together with a closed‐circle flow cell. Carbon and oxygen K‐edges provide characteristic information on the electronic structure of the electrolyte solutions, which are sensitive to local chemistry. Higher Li+ ion concentration in the solvent manifests itself as a blue‐shift of both the π* feature in the carbon edge and the carbonyl π* feature in the oxygen edge. While these oxygen K‐edge results agree with previous soft X‐ray absorption studies on LiBF4 salt concentration in propylene carbonate, carbon K‐edge spectra reveal a shift in energy, which can be explained with differing ionic conductivities of the electrolyte solutions. 相似文献
45.
Richard Tykva Zdenêk Wimmer Blanka Bennettov Vêra Vlaskov 《Helvetica chimica acta》1998,81(1):163-173
The fate of an insect juvenile hormone analog applied to the insect body of the flesh fly (Sarcophaga bullata) or the tsetse fly (Glossina palpalis), respectively, was studied using three different radiolabeled positions in the parent biologically active compound 1 . Several metabolites were found and analyzed. A mechanism of degradation of the applied molecule was designed using a combination of several radioanalytical methods. A unique monitoring of the applied compound and its metabolites was provided, based on the different radiolabeling of the structure (cf. 1a – 1c ), and established their fate in an insect body during a 10-day experiment. A 14C and 3H radiolabeling, respectively, was employed to synthesize three different radiolabeled forms 1a – 1c derived from the parent non-labeled 1 . A combination of three different ways of radiolabeling resulted in an advantage in tracing the metabolic pathway of degradation of the employed compound 1 in its radiolabeled forms 1a – 1c . 相似文献
46.
Determination of 5-fluorouracil in hospital effluents 总被引:1,自引:0,他引:1
Mahnik SN Rizovski B Fuerhacker M Mader RM 《Analytical and bioanalytical chemistry》2004,380(1):31-35
Cytostatic anticancer drugs are an increasingly important issue in the environmental debate, mainly due to the lack of knowledge about the fate of these toxic substances. Over the last decades, 5-fluorouracil (5-FU) has been one of the most frequently used antineoplastic agents and may, therefore, be regarded as one of the pilot substances for environmental contamination. As a prerequisite for these investigations, a method for the determination of 5-FU in hospital effluents has been developed. Waste water samples were enriched by solid-phase extraction on ENV+ columns (concentration factor 500) and analysed by capillary electrophoresis using a buffer containing 80% 160 mM sodium borate buffer (pH 9.5) and 20% acetonitrile (v/v). This method is applicable within the range 5–500 g 5-FU L–1. The standard curve (correlation coefficient >0.99) was linear with recovery rates from 80 to 96% and an accuracy from 9.0 to 20% (intra-assay standard deviation 0.7–8.9%; inter-assay standard deviation 2.2–9.5%). Based on the consumption of 5-FU in oncologic departments and the detection limit of 1.7 g L–1, this method covers the range necessary to evaluate 5-FU in hospital effluents. The applicability of the method was proven by chemical analysis of real hospital waste water samples. Obtained over a time period of 1 month (range 20–122 g 5-FU L–1), the results were similar to those calculated by an input–output model. The presented method provides an analytical tool necessary to face the monitoring of environmental contamination problems.Abbreviations 5-FU
5-Fluorouracil - OECD
Organization for economic cooperation and development 相似文献
47.
Benová B Adam M Onderková K Královský J Krajícek M 《Journal of separation science》2008,31(13):2404-2409
The roots of three varieties of Polygonum cuspidatum were analyzed for resveratrol and its analogs. The powder of the dried roots was extracted with aqueous ethanol (60% v/v) and the extracts obtained were analyzed using RP HPLC with coulometric detection. A simple HPLC method with a multichannel CoulArray detector was developed for the determination of four stilbenes: resveratrol, its glucoside piceid, piceatannol, and its glucoside astringin. Analyses were carried out on a LiChrospher C18 (125 x 4.6 mm id, particle size 5 microm) column with a mobile phase of ammonium acetate (pH 3) and ACN in gradient mode. Four compounds were monitored by a CoulArray electrochemical detector. Potentials of eight electrochemical cells in series were set in the range of 200-900 mV. Optimization of the mobile phase pH was performed. Calibration curves showed good linearity with correlation coefficients (r(2))--more than 0.9975. 相似文献
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49.
Petr Jansa Ondřej Hradil Ondřej Baszczyňski Martin Dračínský Blanka Klepetářová Antonín Holý Jan Balzarini Zlatko Janeba 《Tetrahedron》2012,68(3):865-871
Polysubstituted pyrimidinylphosphonic and 1,3,5-triazinylphosphonic acids with potential biological properties were prepared in high yields by the microwave-assisted Michaelis–Arbuzov reaction of trialkyl phosphite with the corresponding halopyrimidines and halo-1,3,5-triazines, respectively, followed by the standard deprotection of the phosphonate group using TMSBr in acetonitrile. 4,6-Diamino-5-chloropyrimidin-2-ylphosphonic acid (7a) was found to exhibit a weak to moderate anti-influenza activity (28–50 μM) and may represent a novel hit for further SAR studies and antiviral improvement. 相似文献
50.
Martin Hruby Cestmir Konak Jan Kucka Miroslav Vetrik Sergey K. Filippov David Vetvicka Hana Mackova Goran Karlsson Katarina Edwards Blanka Rihova Karel Ulbrich 《Macromolecular bioscience》2009,9(10):1016-1027
Novel polymer micelles, prepared by self‐assembling thermoresponsive poly(N‐isopropylacrylamide)‐graft‐poly[N‐(2‐hydroxypropyl)methacrylamide] copolymers with hydrolytically degradable N‐glycosylamine groups between the polymer blocks are proposed for delivery of diagnostic and therapeutic radionuclides into solid tumors. The micelles are formed by fast heating of an aqueous solution of the copolymer to 37 °C. They have a hydrodynamic diameter of 128 nm (measured using dynamic light scattering) and slowly degrade during incubation in aqueous buffer at pH = 7.4. Labeling with both 131I and 90Y proceeds with high yields (>85%). The unlabeled polymers are not cytotoxic for any of the tested murine and human cell lines.