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991.
Brian D. McGarvey Hui Liao Keyi Ding Xiaoling Wang 《Journal of mass spectrometry : JMS》2012,47(6):687-693
In the search for novel natural products in plants, particularly those with potential bioactivity, it is important to efficiently distinguish novel compounds from previously isolated, known compounds, a process known as dereplication. In this study, electrospray ionization‐multiple stage tandem mass spectrometry (ESI‐MSn) was used to study the behaviour of 12 pregnane glycosides and genins previously isolated from Marsdenia tenacissima, a traditional Chinese medicinal plant, as a basis for dereplication of compounds in a plant extract. In addition to [M + Na]+ and [M + NH4]+ ions, a characteristic [M‐glycosyl + H]+ ion was observed in full‐scan mode with in‐source fragmentation. Sequential in‐trap collision‐induced dissociation of [M + Na]+ ions from 11,12‐diesters revealed consistent preferred losses of substituents first from C‐12, then from C‐11, followed by losses of monosaccharide fragments from the C‐3 tri‐ and tetrasaccharide substituents. A crude methanol extract of M. tenacissima stems was analysed using high‐performance liquid chromatography coupled to ESI‐MS. Several previously isolated pregnane glycosides were dereplicated, and the presence of an additional nine novel pregnane glycosides is predicted on the basis of the primary and fragment ions observed, including two with a previously unreported C4H7O C‐11/C‐12 substituent of pregnane glycosides. This study is the first report of prediction of the structures of novel pregnane glycosides in a crude plant extract by a combination of in‐source fragmentation and in‐trap collision‐induced dissociation and supports the usefulness of LC‐ESI‐MSn not only for dereplication of active compounds in extracts of medicinal plants but also for detecting the presence of novel related compounds. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
992.
Kuo PC Chen YH Leu YL Huang CH Liao YR Lee EJ Yang ML Wu TS 《Chemical & pharmaceutical bulletin》2012,60(4):557-561
A new and efficient synthetic pathway employed the aldol condensation between the acetophenone (3) and vanillin derivative (4) resulted in the precursor chalcone intermediate (14). The target compound viscolin (1) could be afforded through the hydrogenation of the chalcone and followed by deprotection. The present strategy described the development of a more efficient procedure that allowed large-scale production of viscolin for the further research of biological activity both in vitro and in vivo. 相似文献
993.
Maoxin Liao Xianhua TangChangjin Xu 《Communications in Nonlinear Science & Numerical Simulation》2012,17(1):183-194
In this paper, a three-species predator-prey system with two delays is investigated. By choosing the sum τ of two delays as a bifurcation parameter, we first show that Hopf bifurcation at the positive equilibrium of the system can occur as τ crosses some critical values. Second, we obtain the formulae determining the direction of the Hopf bifurcations and the stability of the bifurcating periodic solutions by using the normal form theory and center manifold theorem. Finally, numerical simulations supporting our theoretical results are also included. 相似文献
994.
Fei Chen Xiaofeng Liao Kwok-wo Wong Qi Han Yang Li 《Communications in Nonlinear Science & Numerical Simulation》2012,17(10):3848-3856
This paper discusses period properties of some linear maps which are employed in various applications such as image encryption, public key cryptography and watermarking. Conditions for the bijectiveness of such maps and the existence of a period are presented. Period structure is also given. Then, the recurrence equation theory is adopted to address the period distribution problem. Finally, a framework to solve the problem is proposed with a demonstration of its effectiveness and efficiency into some applications. 相似文献
995.
廖世俊 《应用数学和力学(英文版)》2008,29(2):223-228
A new modification of false position method for solving nonlinear equations is presented by applying homotopy analysis method (HAM). Some numerical illustrations are given to show the efficiency of algorithm. 相似文献
996.
997.
This paper investigates the dynamics of a TCP system described by a first- order nonlinear delay differential equation. By analyzing the associated characteristic transcendental equation, it is shown that a Hopf bifurcation sequence occurs at the pos- itive equilibrium as the delay passes through a sequence of critical values. The explicit algorithms for determining the Hopf bifurcation direction and the stability of the bifur- cating periodic solutions are derived with the normal form theory and the center manifold theory. The global existence of periodic solutions is also established with the method of Wu (Wu, J. H. Symmetric functional differential equations and neural networks with memory. Transactions of the American Mathematical Society 350(12), 4799-4838 (1998)). 相似文献
998.
We report on the microstructure formation in Foturan glass, induced by 1~kHz, 120 femtosecond laser irradiation. It is found that the line-shaped filamentation, not void array tends to be formed in this glass. This is different from our previous experimental results in fused silica and BK7 glasses. A possible mechanism Ag$^+$ captures the free electrons generated by laser, is proposed to explain the observed phenomena. 相似文献
999.
为获得尤文肉瘤EWS-FLI1融合蛋白有效的HLA-A2.1限制性CTL表位, 综合运用BIMAS, SYFPEITHI, Predep和IEDB方案对EWS-FLI1进行CTL表位的预测, 得出8个CTL表位9肽序列; 应用多项式方案、量化基序方案对8个表位9肽进一步进行筛选, 获得其中4个9肽序列, 并进一步运用分子模拟方法初步模拟了4个表位肽与HLA-A2.1分子间的相互结合作用; 应用标准Fmoc方案合成CTL表位肽, RP-HPLC与MS分别鉴定合成肽的纯度与分子量; 通过亲和力实验验证了表位肽QIQLWQFLL(EWS-FLI1 304)与HLA-A2.1有较强的结合力, 从而为表位肽的后继免疫学特性研究提供了基础. 本研究提供了一个合理高效的表位筛选方法. 相似文献
1000.
Sudden death and revival of entanglement of two qubits coupled collectively to a thermal reservoir 下载免费PDF全文
In this paper, we investigate the entanglement of two qubits coupled collectively to a common thermal environment and find that the the collective decay can lead to a revival of the entanglement that has already been destroyed. We also show that the ability of the system to revival entanglement relies on the mean photon number of the thermal environment and the degree of entanglement of the initial state. 相似文献