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981.
Metabolomics method based on ultra high performance liquid chromatography with time‐of‐flight mass spectrometry to analyze toxins in fresh and dried toad venom 下载免费PDF全文
Hongyue Ma Huixia Niu Qin Cao Jing Zhou Yan Gong Zhenhua Zhu Xiang Lv Liuqing Di Dawei Qian Qinan Wu Jin'ao Duan 《Journal of separation science》2016,39(24):4681-4687
Drying is a critical step to prolong the storage time in natural medicine processing but it changes the chemical characteristics of the product. In this study, research was performed to characterize the metabolomic changes in toad venom induced by vacuum‐drying at 60°C and air‐drying at room temperature by ultra high performance liquid chromatography coupled with pattern recognition approaches. In total 52 metabolites, down‐regulated or up‐regulated, were identified as potential chemical markers. Compared with fresh toad venom, vacuum‐drying at 60°C succeeded in raising the conjugated‐type bufadienolide content significantly, while the content of free‐type bufadienolides were slightly reduced. On the other hand, toad venom air‐dried at room temperature presented a relatively low amount of bufadienolides compared with fresh venom. For example, the content of several known anti‐tumor components (gamabufotalin, bufotalin, cinobufagin, etc.) were significantly reduced. The 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide bioassay further showed that venom air‐dried at room temperature had weaker anti‐tumor activity on human hepatocellular carcinoma SMMC‐7721 proliferation in vitro than samples vacuum‐dried at 60°C. These results showed that the great metabolomic changes of toad venom occurred during the drying process, suggesting that a proper drying procedure is important for sustaining the chemical quality of natural medicines. 相似文献
982.
Morphology evolution and crystalline structure of controlled‐rheology polypropylene in micro‐injection molding 下载免费PDF全文
Mengjue Li Yang Qi Zhongguo Zhao Zhang Xiang Xia Liao Yanhua Niu Miqiu Kong 《先进技术聚合物》2016,27(4):494-503
In this paper, the microstructural evolution of controlled‐rheology polypropylene (CRPP) with different melt viscoelasticities was investigated by polarized optical microscopy, scanning electronic microscopy, differential scanning calorimeter, and wide‐angle X‐ray diffraction. It is found that a typical “skin‐core” structure formed in CRPP microparts and the thickness of oriented layer of CRPP microparts decreases notably with the addition of peroxide. The thickness of oriented layer and the distribution of different layers strongly depend on the melt flow properties and the corresponding relaxation time (λ). Furthermore, the mechanisms of the suppressed formation of oriented layers during the micro‐injection molding process are discussed mainly from the viewpoint of rheology and thermodynamics. It is revealed that the shear‐induced orientation is one of the key factors for the formation of oriented molecular structure (row nuclei). The final thickness of the oriented layer is the result of the competition between the orientation behavior and the disorientation behavior. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
983.
High yield synthesis of biodegradable poly(propylene carbonate) from carbon dioxide and propylene oxide 下载免费PDF全文
A novel SalenCoIII (2,4‐dinitrophenoxy) (Salen = N,N'‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamino) and 1,10‐phenanthroline monohydrate catalyst system was designed and employed for the copolymerization of CO2 and propylene oxide (PO). The perfectly alternating copolymerization of CO2 and PO proceeds effectively under middle temperature and pressure to yield poly(propylene carbonate) with a high yield and a high number average molecular weight of polymer. The structure of polymer was characterized by the IR and NMR measurements. The perfectly alternating copolymer was confirmed. The MALDI‐TOF spectrum insinuates that the copolymerization of CO2 and PO was initiated by H2O. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
984.
Five inorganic–organic hybrid vanadates based on tetravanadate cores, transition metals and N-donor ligands have been designed and synthesized under hydrothermal conditions, namely, [Zn(eIM)_3]_2V_4O_(12)(1), [Zn(pIM)_3]_2V_4O_(12)H_2O(2), [Zn(ipIM)_3]_2V_4O_(12)(3), [Co(e IM)_3]_2V_4O_(12)H_2O(4), [Cu(eIM)_2(H+2O)]_2V_4O_(12)(_5)(eIM = 1-ethylimidazole, p IM = 1-propylimidazole, ip IM = isopropylimidazole). All compounds were fully characterized by single-crystal XRD, powder XRD, elemental analysis, TGA, and FT-IR spectroscopy.The hybrid zinc vanadates(1–3) and cobalt vanadate(4) exhibit interesting 2D folded structures and the hybrid copper vanadate(5) presents a 1D chain configuration. All compounds can catalyze olefin epoxidation reactions when using TBHP(TBHP = tert-butyl hydroperoxide) as an oxidant in acetonitrile.The introduction of transition metal ions into tetravanadate cores not only improved the catalytic activity but also fulfilled the heterogeneous catalytic behavior. 1–5 all exhibit extraordinary efficiency in converting olefins to the corresponding epoxides with high conversion and selectivity(particularly,conv. up to 97.1%, sele. up to 100% for 1). Leaching test was also carried out to prove the heterogeneous behavior. 相似文献
985.
Shu Rong Ban Cong Wei Niu Wen Bin Chen Zhi Hong Yu Si Wu Chen Wang Zhen Xi State-Key Laboratory of Elemento-Organic Chemistry Department of Chemical Biology Nankai University Tianjin China School of Pharmaceutical Science Shanxi Medical University Taiyuan China 《中国化学快报》2007,18(2)
Some new sulfonylureas and their hydroxylation products had been synthesized from 2-amino-4-methylpyrimidine. Their bioactivities against E. coli AHAS II in vitro were tested and the results indicated that the hydroxylation decreased the inhibition activities of sulfonylureas significantly. Subsequently herbicidal tests against stem-growth of barnyard grass and root-growth of rape confirmed the above conclusion. The preliminary molecular docking studies were also carried out to investigate the binding modes of non-hydroxylated and hydroxylated sulfonylureas with AHAS. 相似文献
986.
987.
在不同pH值的条件下,多氧霉素B的吸收光谱会发生变化。为此选择无干扰的吸收波长,优化测定条件,建立液相色谱—二极管阵列检测器定量及定性检测多氧霉素B的方法。本方法快速简便,准确可靠。 相似文献
988.
Jia-Xiao Niu Qi Zhang Xi-Lang Zhou Zhi-Yong Shan 《International Journal of Infrared and Millimeter Waves》2008,29(5):519-526
A compact two-dimension (2-D) finite-difference frequency-domain (FDFD) method is used to analyze the dispersion characteristics
of single and double trapezoidal-ridge waveguides. The general 2-D FDFD formulation under orthogonal curvilinear coordinate
system is derived from the difference form of Maxwell’s equations, and modified difference formulas at the trapezoidal-ridge
section are built. After implementing the boundary conditions, the 2-D FDFD formulation is concluded as an eigen equation
and then constructed by a highly sparse matrix. By solving the matrix-eigen equation, the dispersion characteristics of the
ridged waveguides can be obtained. Computed results are in good agreements with the previously published and simulated ones,
which prove the correctness of the method. 相似文献
989.
Yang‐Yao Niu 《国际流体数值方法杂志》2001,36(3):351-371
In this study, the advection upwinding splitting method (AUSM) is modified for the resolution of two‐phase mixtures with interfaces. The compressible two‐fluid model proposed by Saurel and Abgrall is chosen as the model equations. Dense and dilute phases are described in terms of the volume fraction and equations of state to represent multi‐phase mixtures. Test cases involving an air–water shock tube, water faucet, and dilute particulate turbulent flows through a 90° bend are used to verify the current work. It is shown that the AUSM based on flux differences (AUSMD) contains the mechanism to correctly capture the contact discontinuity and interfaces between phases. In addition, a successful application to dilute particulate turbulence flows by the AUSMD is demonstrated. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
990.
In this study the stability of the NO spin-trapping complex, (dithiocarbamate)2Fe2+NO and its interaction with rat peritoneal macrophages was investigated. The stability experiments showed that DTCS (dithiocarboxy sarcosine) trapping complex was more stable than that of MGD (N-methyl-D-glucamine-dithiocarbamate) in macrophages activated by PMA (phorbol-1,2-myristate-1,3-acetate) and L-arginine. Free radical species, O2
- and NO, generated in macrophages respiratory burst were causative for the instability of the NO trapping complex. Addition of more dithiocarbamate and ferrous salt could increase the stability of the trapping complex in the system. Dithiocarbamate and ferrous salt did not impair the oxygen consumption of macrophages. The increasing effects of dithiocarbamate derivatives and ferrous salt on the stability of the trapping complex may be due to their scavenging effects on the free radicals generated by macrophages and their ability to inhibit the oxidation of ferrous ion in the (dithiocarbamate)2Fe2+NO complex. 相似文献