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排序方式: 共有1365条查询结果,搜索用时 15 毫秒
111.
Anna Śmiechowska Witold Przychodzeń Jarosław Chojnacki Piotr Bruździak Jacek Namieśnik Agnieszka Bartoszek 《Structural chemistry》2010,21(5):955-964
Adducts of natural allyl, phenethyl, and benzyl isothiocyanates and 2-amino-1-methylbenzimidazole were synthesized. After
optimization of the reaction conditions, the target 2-benzimidazolylthioureas were obtained in reasonable yields. The detailed
molecular and crystal structures of these compounds were characterized by spectroscopic and X-ray methods. Spectral analysis
demonstrated that N-(1-methylbenzimidazolyl)-N′-allylthiourea, N-(1-methylbenzimidazolyl)-N′-benzylthiourea, and N-(1-methylbenzimidazolyl)-N′-phenethylthiourea exist in solution in an unprecedented three tautomeric forms, whose structures were corroborated unambiguously. 相似文献
112.
Jeong SD Nowak-Król A Kim Y Kim SJ Gryko DT Lee CH 《Chemical communications (Cambridge, England)》2010,46(46):8737-8739
meso-Alkylidene (m-benzi)pentaphyrin containing exocyclic C=C double bonds at two meso-positions is synthesized and fully characterized for the first time. The single crystal X-ray crystallographic analysis shows a concave conformation with two pyrrole rings inverted. The first protonation occurs exclusively at core nitrogen. The synthesized compound displays concentration dependent chromogenic responses for fluoride anion in organic solvent. 相似文献
113.
Agnieszka Czapik Maria Gdaniec 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(7):o356-o360
2,3,5,6‐Tetrafluorobenzene‐1,4‐diol easily forms cocrystals with heteroaromatic bases containing the pyrazine unit. In the 1:1 complexes with pyrazine, C6H2F4O2·C4H4N2, (I), and quinoxaline, C6H2F4O2·C8H6N2, (II), the crystal components are linked via O—H...N hydrogen bonds into one‐dimensional chains. With the largest base, phenazine, the 1:2 benzenediol–phenazine complex, C6H2F4O2·2C12H8N2, (III), was obtained, with the molecules linked via O—H...N interactions into a discrete heterotrimer. In all three cocrystals, the two types of molecules are organized into layers via softer C—H...O and C—H...F interactions and π–π stacking interactions, with stronger hydrogen bonds linking molecules of adjacent layers. In (II) and (III), molecules are arranged into heterostacks, whereas in (I) separate stacks are formed by the heterocyclic base and the benzenediol molecule. 相似文献
114.
Fic E Kedracka-Krok S Jankowska U Pirog A Dziedzicka-Wasylewska M 《Electrophoresis》2010,31(21):3573-3579
Sample preparation is a fundamental step in proteomic methodologies. The quality of the results from a proteomic experiment is dependent on the nature of the sample and the properties of the proteins. In this study, various pre-treatment methods were compared by proteomic analysis; we analysed various rat brain structures after chloroform/methanol, acetone, TCA/acetone and TCA protein precipitation procedures. The protein content of the supernatant was also examined by 2-DE. We found that for four of the rat brain structures, precipitation with chloroform/methanol and acetone delivered the highest protein recovery for top-down proteomic analysis; however, TCA precipitation resulted in good protein separation and the highest number of protein spots in 2-DE. Moreover, TCA precipitation also gave high efficiency of protein recovery if prior sonication procedure was performed. 相似文献
115.
Agnieszka Zgoła-Grześkowiak 《Journal of chromatography. A》2010,1217(11):1761-1766
Dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography with fluorescence detector was applied for the determination of alkylphenols and their short-chained ethoxylates in water samples. Development of DLLME procedure included optimisation of some important parameters such as kind and volume of extracting and dispersing solvents. Under optimised conditions 50 μL of trichloroethylene in 1.5 mL of acetone were rapidly injected into 5 mL of a water sample. After centrifuging the organic phase containing the analytes was taken for evaporation with a gentle nitrogen purge and reconstituted to 50 μL of acetonitrile. The aliquot of this solution was analysed with the use of HPLC. For octylphenol (OP) and octylphenol ethoxylates (OPEOs) linearity was satisfactory in the range 8–1000 μg L−1 and for nonylphenol (NP) and nonylphenol ethoxylates (NPEOs) linearity was in the range from 50 to about 3000 μg L−1. Limit of quantitation was 0.1 μg L−1 for OP and OPEOs and 0.3 μg L−1 for NP and NPEOs. Satisfactory recoveries between 66 and 79% were obtained for environmental samples. The results showed that DLLME is a simple, rapid and sensitive analytical method for the preconcentration of trace amounts of alkylphenols and their ethoxylates in environmental water samples. 相似文献
116.
We consider problems of the calculus of variations on unbounded time scales. We prove the validity of the Euler–Lagrange equation
on time scales for infinite horizon problems, and a new transversality condition. 相似文献
117.
Piotr Gwiazda Agnieszka Świerczewska-Gwiazda Petra Wittbold Aleksandra Zimmermann 《Journal of Functional Analysis》2014
We consider scalar balance laws with a dissipative source term. The flux function may be discontinuous with respect to both the space variable x and the unknown quantity u. We formulate the definition of entropy weak solutions and provide existence and uniqueness to the considered problem. The problem is formulated in the framework of multi-valued mappings. The notion of entropy measure-valued solutions is used to prove the so-called contraction principle and comparison principle. 相似文献
118.
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120.
Maria Chrzanowska Agnieszka Grajewska Zofia Meissner Maria Rozwadowska Iwona Wiatrowska 《Tetrahedron》2012,68(14):3092-3097
A sequence of two reactions: the Petasis reaction, in which an aminoacetaldehyde acetal was used as the amine component, followed by Pomeranz–Fritsch–Bobbitt cyclization, has been shown to be a convenient and simple method for the synthesis of tetrahydroisoquinoline-1-carboxylic acids. Using this method several acids have been prepared in good to excellent yields and characterized as hydrochloride salts. 相似文献