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排序方式: 共有8939条查询结果,搜索用时 46 毫秒
91.
Dong Cao Huogao Huang Ming Hu Lin Cui Fanglan Geng Ziyu Rao Hongyun Niu Yaqi Cai Yuehui Kang 《Analytica chimica acta》2015
Natural organic matter (NOM) is a complex and non-uniform mixture of organic compounds which plays an important role in environmental processes. Due to the complexity, it is challenging to obtain fully detailed structural information about NOM. Although Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) has been demonstrated to be a powerful tool for providing molecular information about NOM, multiple ionization methods are needed for comprehensive characterization of NOM at the molecular level considering the ionizing selectivity of different ionization methods. This paper reports the first use of matrix assisted laser desorption/ionization (MALDI) method coupled with FT-ICR-MS for molecular characterization of NOM within a mass range of 200–800 Da. The mass spectral data obtained by MALDI were systematically compared with data generated by electrospray ionization (ESI). It showed that complementary molecular information about NOM which could not be detected by ESI, were provided by MALDI. More unsaturated and aromatic constituents of NOM with lower O/C ratio (O/C ratio < 0.5) were preferentially ionized in MALDI negative mode, whereas more polar constituents of NOM with higher O/C ratio were preferentially ionized in ESI negative mode. Molecular anions of NOM appearing at even m/z in MALDI negative ion mode were detected. The results show that NOM molecules with aromatic structures, moderate O/C ratio (0.7 > O/C ratio > 0.25) and lower H/C ratio were liable to form molecular anions at even m/z, whereas those with higher H/C ratio are more likely to form deprotonated ions at odd m/z. It is speculated that almost half of the NOM molecules identified by MALDI may be aromatic or condensed aromatic compounds with special groups which are liable to absorb electron from other molecules to generate free radical anions during MALDI ionization. 相似文献
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Won Se Suh Ki Hyun Kim Ho Kyung Kim Sang Un Choi Kang Ro Lee 《Helvetica chimica acta》2015,98(8):1087-1094
Two new aryl‐tetralin lignan glycosides, linderanosides A and B ( 1 and 2 , resp.), and a new dihydrobenzofuran neolignan glycoside, linderanoside C ( 3 ), together with five known lignan derivatives ( 4 – 8 ) were isolated from the trunk of Lindera glauca. The structures of these new compounds were determined through spectroscopic analyses, including extensive 2D‐NMR data and acid hydrolysis. The absolute configurations of the compounds were clarified by circular dichroism (CD) spectroscopic studies. Compounds 1 – 8 were evaluated for their cytotoxicity against A549 (non‐small cell lung adenocarcinoma), SK‐OV‐3 (ovarian cancer cells), A498 (human kidney epithelial cells), and HCT‐15 (colon cancer cells) human tumor cell lines using sulforhodamine B assays in vitro. 相似文献
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Four Metal Complexes Based on Bulky Imidazole Ligands: Solvothermal Syntheses,Crystal Structures,and Fluorescence Properties 下载免费PDF全文
Xue Zhang Sai Li Yue‐Jiao He Tong Han Xiao‐Ling Wang Bang Chen Kang‐Yu Zou Zuo‐Xi Li 《无机化学与普通化学杂志》2015,641(11):1874-1880
In order to explore the influences of (de‐)protonation of the imidazole ring on the structural diversity of the resulting complexes, the imidazole‐based ligands 4, 5‐diphenylimidazole (Hdpi) and 1H‐phenanthro[9, 10‐d]imidazole (Hpi) were utilized as bulky building blocks to construct four complexes by solvothermal reactions, i.e. [Ag(Hdpi)2](NO3) · (H2O) ( 1 ), [Cu(dpi)]∞ ( 2 ), [Cu(Hpi)(NO3)]∞ ( 3 ), and [(H2pi)(NO3)] · H2O ( 4 ). In complex 1 , two Hdpi ligands adopt a monodentate pattern and coordinate with one AgI ion to form a mononuclear unit, which is further connected by hydrogen bonds into a 1D supramolecular helix. The deprotonated dpi ligand of 2 acts in bidentate mode, and bridges CuI ions to afford a 1D chain. In 3 , the NO3– ion, acts as a monodentate bridging ligand and joins CuI ions to generate a 1D chain. The Hpi ligand employs a monodentate mode to bond with CuI ions of the 1D chain. 4 is protonated and two H2pi nitrogen atoms are free of coordination. Interestingly, hydrogen bonds among the NO3– ion, the H2pi ligand, and the water molecule yield a macro ring R44(14). The resulting structural diversity reveals that the (de‐)protonation of imidazole ring directly steers the coordination number of ligand, and thus causes a significant effect on the structure, especially the dimensionality. Furthermore, the solid‐state fluorescence properties of the free ligands and compounds 1 – 4 were studied at room temperature. 相似文献
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Plasma Chemistry and Plasma Processing - Two dielectric barrier discharge reactors, based on L-shaped electrodes, were designed and fabricated for in-line surface treatment of polyimide (PI)... 相似文献
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