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161.
Two new spirostanol saponins, namely elephanosides G and H ( 1 and 2 , resp.) were isolated from the leaves of Yucca elephantipes (Agavaceae), together with the two known furostanol saponins 3 and 4 and the six known flavonoid O‐ and C‐glycosides 5 – 10 . The new structures were elucidated as (3β,25S)‐spirost‐5‐en‐3‐yl O‐β‐D ‐glucopyranosyl‐(1→3)‐O‐β‐D ‐glucopyranosyl‐(1→4)‐β‐D ‐galactopyranoside ( 1 ) and (3β,5β,25R)‐3‐[(2‐O‐β‐D ‐glucopyranosyl‐β‐D ‐galactopyranosyl)oxy]spirostan‐12‐one ( 2 ) on the basis of detailed spectroscopic analysis and acidic hydrolysis. 相似文献
162.
Zaesung No Shi Yong Ryu Seong-Kie Kim Jong Woong Ahn Bok Ju Song Keun Jae Kim 《合成通讯》2013,43(5):887-892
Thermal or base-promoted conversion of 5′-O-TBDMS-3′-O-(1H-imidazole-1-thiocarbonyl)thymidine (1) afforded 5′-O-TBDMS-2,3′-anhydro-thymidine (2), a pivotal intermediate for the transformation of the 3′-hydroxy group of 2′-deoxyribonucleosides, in high yield. 相似文献
163.
Yun Khoon Liew Vasanthakumari Neela Rukman Awang Hamat Syafinaz Amin Nordin Pei Pei Chong 《Electrophoresis》2013,34(3):397-400
The typical concentration of protein loaded varies from 0.13 to 1.40 μg/μL for a classical silver staining method in 2DE gel. Here, we present a simple modified classical silver staining method by modifying the silver impregnation and development reaction steps. This modified method detects the protein spots at extremely low loaded concentrations, ranging from 0.0048 to 0.0480 μg/μL. We recommend this modified silver staining as an excellent method for the limited biological samples used for silver‐stained 2DE analysis. Altogether, the protocol takes close to two days from first dimension separation to second dimension separation, followed by silver staining, scanning, and analysis. 相似文献
164.
Jinsoo Kim Jimin Park Young Ju Jung Eun Chol Kim Taek Ahn Jae-Won Ka 《Liquid crystals》2013,40(5):589-599
We have synthesised a series of new reactive mesogens with photopolymerisable di-acrylates and their corresponding non-reactive analogues based on the π-conjugated aromatic core, fluorene (F)-di-[thiophene (T)-benzene (B)], using the Stille and Suzuki coupling reaction. The effect of lateral alkyl chains on the 9-position of the central fluorene moiety as well as α, ω- side alkyl chains attached to the π-conjugated aromatic core on the mesomorphism was investigated by utilising differential scanning calorimetry (DSC) and polarising optical microscopy (POM). A wide angle X-ray scattering (WAXS) study at the various temperatures was also carried out to reveal phase structures. Photopolymerisable di-acrylates connected directly to the rigid aromatic core showed higher phase transition temperatures, probably due to the induced dipole moment in comparison with those of a non-reactive methyl–ether counterpart. 相似文献
165.
166.
Hyungju Ahn Yonghoon Lee Hoyeon Lee Yoonkeun Kim Du Yeol Ryu Byeongdu Lee 《Journal of polymer science. Part A, Polymer chemistry》2013,51(7):567-573
We present an overview of the recent progress on the phase transition in the block copolymer (BCP) films in terms of the interfacial interactions effects of the substrates and the χ (Flory-Huggins segmental interaction parameter) effects between the two blocks. For the BCP films thinner than a critical thickness (Lc) above which the transition is independent of film thickness, the order-to-disorder transition (ODT) increased or decreased with decreasing film thickness depending on the interfacial interaction types. The rapid and slow changes in the ODT were attributed to the relative magnitude of enthalpic contribution to χ between two blocks. Interestingly, a periodic amplification in the block composition for the BCP films suppressed the compositional fluctuation in the film geometry, resulting in the ODT shifts from the bulk ODTs above Lc. This effect of the BCP films was more illustrated by the ODT shift effects depending on the strength of the preferential interactions on the substrates. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 相似文献
167.
Degradation of cellulose under alkaline conditions is involved either involuntarily or deliberately in many different cellulose processing steps, such as pulping, bleaching, or aging within the viscose process, and the underlying chemistry has been the topic of numerous studies. When it comes to aging under alkaline conditions—either natural or accelerated (artificial)—the degradation processes are by far less investigated and understood. A prominent example of moderately alkaline cellulosic material is deacidified book paper from libraries which had undergone a mass-deacidification treatment. We studied their aging behavior under accelerated conditions in comparison to non-deacidified duplicates in order to better understand how the alkaline reserve, which was introduced by the deacidification treatment, affects the stability of the books on the long run. GPC analysis of cellulose and determination of carbonyl functionalities were performed, which were critical parameters to achieve a deeper insight into hydrolytic and oxidative changes of cellulose structure upon deacidification treatment and subsequent aging. Also, model book papers impregnated with different amounts of alkaline reserve were used to support the findings from the original book samples. Hydrolytic degradation rates of the original book papers were significantly reduced after mass deacidification compared to the non-deacidified duplicates. The beneficial effect of mass deacidification on cellulose stability was found to be strongly related to the amount of alkaline reserve deposited, independent of varying parameters of book papers. Although some indication of alkali-induced β-elimination was found (a minor decrease of the along-chain carbonyl content in the original deacidified book papers during aging), it did not occur to an extent that significantly influenced the molar mass of cellulose. The beneficial effect of retarded hydrolytic degradation by mass deacidification thus clearly outweighed possible negative alkalinity effects of the deposited alkaline reserve. 相似文献
168.
采用基于密度泛函理论的第一性原理方法和平板模型研究了CH3SH分子在Cu(111)表面的吸附反应.系统地计算了S原子在不同位置以不同方式吸附的一系列构型, 第一次得到未解离的CH3SH分子在Cu(111)表面顶位上的稳定吸附构型,该构型吸附属于弱的化学吸附, 吸附能为0.39 eV. 计算同时发现在热力学上解离结构比未解离结构更加稳定. 解离的CH3S吸附在桥位和中空位之间, 吸附能为0.75-0.77 eV. 计算分析了未解离吸附到解离吸附的两条反应路径, 最小能量路径的能垒为0.57 eV. 计算结果还表明S―H键断裂后的H原子并不是以H2分子的形式从表面解吸附而是以与表面成键的形式存在. 通过比较S原子在独立的CH3SH分子和吸附状态下的局域态密度, 发现S―H键断裂后S原子和表面的键合强于未断裂时S原子和表面的键合. 相似文献
169.
Qiu‐Yan Chen Xian Cheng Tao Wang Zi‐Hao Yu Chong Zhang Shu‐Kun Lin Hao‐Hong Li Zhi‐Rong Chen 《无机化学与普通化学杂志》2014,640(2):439-443
A new low‐dimensional benzyl viologen/iodoargentate hybrid, [(BV)2(Ag5I9)]n ( 1 ) (BV2+ = benzyl viologen) was prepared. In 1 , (Ag6I9)n2– chain exhibits a new type of one‐dimensional chain constructed from vertex‐sharing of Ag5I10 units, and its two‐dimensional layer structure was constructed from C–H ··· I hydrogen bonds. Strong luminescence at 404 nm can be detected in 1 . DFT calculation suggests that 1 displays a reduced bandgap, which is led by a more dispersed LUMO band of BV2+ compared with MV2+ in [MV(Ag2I4)]n. 相似文献
170.
Determination of six polyynes in Oplopanax horridus and Oplopanax elatus using polyethylene glycol modified reversed migration microemulsion electrokinetic chromatography
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Zhong‐mei Yang Jing Zhao Ka‐meng Lao Xiao‐jia Chen Fong Leong Chong‐Zhi Wang Chun‐Su Yuan Shao‐ping Li 《Electrophoresis》2014,35(20):2959-2964
A PEG‐modified reversed migration MEEKC method was developed for simultaneous determination of six polyynes, including oplopandiol, falcarindiol, oplopandiol acetate, (11S, 16S, 9Z)‐9,17‐octadecadiene‐12,14‐diyne‐1,11,16‐triol,1‐acetate, oplopantriol B, and oplopantriol A, in Oplopanax horridus and Oplopanax elatus. The running buffer containing 0.8% v/v ethyl acetate, 3.8% w/v SDS, 6.6% v/v n‐butanol in 20 mM phosphate buffer (pH 2.5), followed by mixing with propan‐2‐ol at 30% v/v and PEG‐1000 at 15% w/v, was applied in the analysis. The proposed method was successfully applied to determine the six polyynes in five samples of Oplopanax horridus and one of O. elatus. The result showed that the types and amounts of polyynes present were obviously different when comparing the two herbs. Besides, the developed PEG‐modified reversed MEEKC method might be suitable for the analysis of hydrophobic analytes in herbal medicines. 相似文献