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排序方式: 共有6658条查询结果,搜索用时 15 毫秒
1.
Kento Nishikibe Keisuke Nishikawa Momochika Kumagai Matsumi Doe Yoshiki Morimoto 《化学:亚洲杂志》2022,17(1):e202101137
There are marine cytotoxic bromotriterpenoids, named the thyrsiferol family that are structurally characterized by some tetrahydropyran (THP) and tetrahydrofuran (THF) rings. The thyrsiferol family belongs to natural products that are often difficult to determine their stereostructures even by the current, highly advanced spectroscopic methods, especially in acyclic systems including stereogenic tetrasubstituted carbon centers. In such cases, it is effective to predict and synthesize the possible stereostructures. Herein, to elucidate ambiguous stereostructures and unassigned absolute configurations of aplysiol B, laurenmariannol, and saiyacenol A, members of the thyrsiferol family, we carried out their asymmetric chemical syntheses featuring 6-exo and 5-exo oxacyclizations of epoxy alcohol precursors and 6-endo bromoetherification of a bishomoallylic alcohol. In this paper, we report total assignments of their stereostructures through their asymmetric chemical syntheses and also their preliminary cytotoxic activities against some tumor cells. These results could not have been achieved without depending on asymmetric total synthesis. 相似文献
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3.
Lubomír Havlk Jan Fbry Margarida Henriques Michal Duek 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(7):623-630
The title structures of KScS2 (potassium scandium sulfide), RbScS2 (rubidium scandium sulfide) and KLnS2 [Ln = Nd (potassium neodymium sufide), Sm (potassium samarium sulfide), Tb (potassium terbium sulfide), Dy (potassium dysprosium sulfide), Ho (potassium holmium sulfide), Er (potassium erbium sulfide), Tm (potassium thulium sulfide) and Yb (potassium ytterbium sulfide)] are either newly determined (KScS2, RbScS2 and KTbS2) or redetermined. All of them belong to the α‐NaFeO2 structure type in agreement with the ratio of the ionic radii r3+/r+. KScS2, the member of this structural family with the smallest trivalent cation, is an extreme representative of these structures with rare earth trivalent cations. The title structures are compared with isostructural alkali rare earth sulfides in plots showing the dependence of several relevant parameters on the trivalent cation crystal radius; the parameters thus compared are c, a and c/a, the thicknesses of the S—S layers which contain the respective constituent cations, the sulfur fractional coordinates z(S2−) and the bond‐valence sums. 相似文献
4.
Leila Torkian Mostafa M. Amini Tayebeh Gorji Omid Sadeghi 《Arabian Journal of Chemistry》2019,12(7):1315-1321
In this study, multiwalled carbon nanotube (MWCNT) was modified by the pyridine group using a silane agent and characterized by infrared spectroscopy (IR), thermal analysis (TG/DTA), and elemental analysis (CHN) and scanning electron microscopy (SEM). The application of this sorbent was investigated in determination of lead ions in aqueous samples, using flame atomic absorption spectrometry (FAAS). Through this study, different parameters such as pH and sample flow rate on adsorption process and eluent concentration, volume and flow rate were optimized. The limit of detection (LOD), the relative standard deviation and the recovery of the method were 2 ng mL?1, 1.3% and 99.7%, respectively. Two standard reference materials (NIST 1571 and NIST 1572) were used to verify accuracy of this method. Finally, the sorbent was successfully applied for extraction and determination of low levels of Pb(II) ions in aqueous samples. 相似文献
5.
Natalia L. Calvo Sebastian O. SimonettiRubén M. Maggio Teodoro S. Kaufman 《Analytica chimica acta》2015
Exposure of cimetidine (CIM) to dry heat (160–180 °C) afforded, upon cooling, a glassy solid containing new and hitherto unknown products. The kinetics of this process was studied by a second order chemometrics-assisted multi-spectroscopic approach. Proton and carbon-13 nuclear magnetic resonance (NMR), as well as ultraviolet and infrared spectroscopic data were jointly used, whereas multivariate curve resolution with alternating least squares (MCR-ALS) was employed as the chemometrics method to extract process information. It was established that drug degradation follows a first order kinetics. 相似文献
6.
M. M. Moustafa 《Journal of Thermal Analysis and Calorimetry》1997,50(3):463-471
The oxime and Schiff's base of N-furoylphenylhydroxylamine form complexes with Co2+, Cu2+, Zn2+ and Fe3+. These complexes were studied by means of the UV — Vis. spectra of nujol mulls, electron spin resonance (ESR) spectra and magnetic susceptibility to determine their stereochemistry. The complexes were characterized via elemental analyses, molar conductivities and thermogravimetric analyses. Organic reagents were used for the gravimetric determination of Co2+, Cu2+ and Fe3+ through the precipitation of their complexes. The compounds were also used for separation of a binary mixture of Cu2+ and Cu2+. Interferences were studied. 相似文献
7.
车前子中多糖含量的测定 总被引:12,自引:1,他引:11
采用蒽酮-硫酸法比色测定,用精制车前子多糖测得车前子多糖对葡萄糖的换算因子,对我国同属不同品种的车前子不同采集时间及炮制前后其多糖含量进行了比较研究。结果表明:此测定方法简便可行。供试液在8h内显色稳定,重现性较好,平均回收率为97.8%,RSD=1.41%(n=5)。江西吉安产大粒车前子生品多糖含量在9.15%~9.83%之间,炮制后其多糖含量在6.29%~6.81%之间;南昌新祺周车前GAP标准基地的大粒车前子生品多糖含量为7.85%~8.38%,炮制后其多糖含量为6.01%~6.64%;东北产的小粒车前子生品多糖含量为6.61%,炮制后其多糖含量为6.45%。 相似文献
8.
N. U. Aldiyarov K. K. Kadyrzhanov E. M. Yakushev V. S. Zhdanov 《Hyperfine Interactions》2005,164(1-4):67-72
The conditions for achievement of high resolving power of depth selective conversion electron Mössbauer spectroscopy method at a combined installation ‘electron spectrometer–nuclear gamma-resonance spectrometer’ have been obtained. There has been made a considerable step in development of the method at its realization at a magnetic sector electron spectrometer with double focusing, equipped with electron source (a sample under investigation) of large-area and position-sensitive detector. The paper presents a prospective symmetrical version of a magnetic sector electron spectrometer that allows realizing more completely possibilities of the method. It is noted that the proposed method is particularly valuable for investigations of nanosystems, nanostrutures that contain Mössbauer nuclei. 相似文献
9.
横向放大率法确定复合光学系统的基点 总被引:2,自引:0,他引:2
介绍了应用测量横向放大率确定两薄透镜组成的复合光学系统基点的方法。由于采用线阵光电耦合器件(CCD)测量物经光学系统成像的横向放大率,提高了测量精度。 相似文献
10.
描述了简并V型三能级原子与单模相干态光场的Raman相互作用,获得了处于激发态单态的原子与相干态光场相互作用的结果.利用探测原子与光场的相互作用将原子和光场制备成最大缠结态,并注入待测原子,通过原子与腔模构成的Bell基矢演化,对腔场进行选择性探测,获得探测原子相互作用后可能的量子状态,然后对待测原子与腔场进行联合探测,接着对探测原子的量子状态实施幺正变换,就将探测原子制备到待测原子的初始量子态上,从而实现未知原子态的隐形传送. 相似文献