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151.
Two new uncommon nitrogenous sesquiterpenes, 11‐ethoxy‐3‐formamidotheonellin ( 1 ) and 7‐ethoxy‐3‐formamidobisabolane‐8,10‐diene ( 2 ), together with two known related sesquiterpenes, 3‐formamidotheonellin (=theonellin formamide; 3 ) and theonellin isothiocyanate ( 4 ), were isolated from the Hainan sponge Axinyssa aff. variabilis. Their structures were determined on the basis of extensive spectroscopic analysis and by comparison of their NMR data with those of known compounds. 相似文献
152.
When DNA is mixed with the cationic polyelectrolyte poly(diallyldimethyl ammonium chloride) (PDDA), the DNA/PDDA complex is formed instantaneously at room temperature. This complex is much more efficient in enhancing the fluorescence of Hoechst 33258 (H 33258) than DNA alone. Based on the interaction of H 33258 with the DNA/PDDA complex, a new fluorescence assay for DNA is described. At pH 7.3 in Tris-HCl buffered solution, the DNA/PDDA complex causes a sharp enhancement in fluorescence intensity of H 33258. Simultanously, the emission maximum wavelength of H 33258 blueshifts from 490nm to 450nm, while the excitation redshifts from 345 to 350nm. The calibration graphs for calf thymus DNA (ctDNA) and herring sperm DNA (hsDNA) are both linear up to 5.0µgmL–1 when the concentration of H 33258 and PDDA are fixed at 1.5×10–6 and 1.6×10–5molL–1, respectively. The method is specific for native DNA. The 3 detection limits for ctDNA and hsDNA are 1.8 and 5.6ngmL–1, respectively, i.e. much lower than in the presence of H 33258 alone. Four synthetic samples were determined satisfactorily. This method can also be developed to investigate the formation and the nature of the complexes between DNA and polycations, which have recently been widely applied in some fields such as genetic engineering and gene therapy. 相似文献
153.
We report synthesis of temperature- and redox-responsive multiblock copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization. Well-defined α,ω-bis(dithioester)-functionalized poly(N-isopropylacrylamide) (PNIPAM) and poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) were prepared using 1,4-bis(thiobenzoylthiomethyl)benzene and 1,4-bis(2-(thiobenzoylthio)prop-2-yl)benzene as RAFT agents, respectively. Dually responsive multiblock copolymers were synthesized in a single aminolysis/oxidation step from the α,ω-bis(dithioester)-terminated PNIPAM and PDMAEMA. The copolymers and their stimulus-responsive behavior were characterized by size exclusion chromatography, NMR, light scattering and atomic force microscopy. Due to the presence of redox-sensitive disulfide bonds between the blocks, the copolymers were readily reduced to the starting polymer blocks. The presence of temperature-responsive PNIPAM blocks provided the copolymers with the ability to assemble into core-shell nanostructures with hydrophobic PNIPAM as a core and cationic PDMAEMA as stabilizing shell when above the phase transition temperatures of PNIPAM. The temperature-induced assembly of the copolymers also showed substantial pH sensitivity. The phase transition temperature increased with decreasing pH, while molecular weight of the assemblies decreased. 相似文献
154.
化学位移估算研究ATP构象随溶液pH值的变化 总被引:2,自引:0,他引:2
利用Johnson和Bovey的理论和方法计算了不同扭曲角χ(O4′-C1′-N9-C4)的ATP(5′-三磷酸腺苷)分子中糖环质子H1′和H2′由于环流效应引起的化学位移.H1′的化学位移与扭曲角χ有较强的依赖关系,反映了ATP在溶液中细微的构象变化.将计算结果与实验结果比较,证明在本文讨论的pH值范围(1~10)内,Mg2+加入后,ATP的扭曲角χ在230~360°范围内变化.随溶液的pH值减小,ATP分子的构象由trans 构象通过-gauche构象转变为cis构象. 从而证明在酸性条件下, ATP倾向于以cis构象存在,而在碱性条件下trans构象更为稳定,从另一方面支持了在酸性条件下N1参与配位而在碱性条件下N7参与配位的结论.在讨论中也考虑了由pH变化所引起的环流强度的变化. 相似文献
155.
156.
Feng-Ling Qing Min JiRonghua Lu Kelu YanZhiping Mao 《Journal of fluorine chemistry》2002,113(1):139-141
A new kind of perfluoroalkyl-containing multifunctional groups compound was designed. Treatment of 1H,1H,2H,2H-perfluorooctyltrichlorosilane (4) with allylmagnesium bromide provided key intermediate 1H,1H,2H,2H-perfluorooctyltriallylsilane (2). Hydroboration followed by oxidation, epoxidation and dihydroxylation of 2 gave perfluoroalkyl-containing multifunctional groups compound 1a, 1b and 1c, respectively. 相似文献
157.
Matthieu Baudelet Myriam Boueri Jin Yu Samuel S. Mao Vincent Piscitelli Xianglei Mao Richard E. Russo 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007,62(12):1329-1334
Ultraviolet pulses (266 nm) delivered by a quadrupled Nd:YAG laser were used to analyze organic samples with laser-induced breakdown spectroscopy (LIBS). We present characteristics of the spectra obtained from organic samples with special attentions on the emissions of organic elements, O and N, and molecular bonds CN. The choice of these atomic or molecular species is justified on one hand, by the importance of these species to specify organic or biological materials; and on the other hand by the possible interferences with ambient air when laser ablation takes place in the atmosphere. Time-resolved LIBS was used to determine the time-evolution of line intensity emitted from these species. We demonstrate different kinetic behaviors corresponding to different origins of emitters: native atomic or molecular species directly vaporized from the sample or those generated through dissociation or recombination due to interaction between laser-induced plasma and air molecules. Our results show the ability of time-resolved UV-LIBS for detection and identification of native atomic or molecular species from an organic sample. 相似文献
158.
微波辐射下LaNaY沸石的水热交换反应 总被引:8,自引:0,他引:8
报道微波辐射应用于NaY沸石与La(NO_3)_3溶液的离子交换反应,结果表明微波辐射可提高La ̄+的交换度,缩短交换时间。 相似文献
159.
160.
用溴化钾-溴酸钾滴定法测定双键含量,元素分析法测定共聚物组成。讨论了HEMA-NVP-St三元共聚体系在不同反应程度时共聚物组成的变化,以及在此三元共聚体系中引入均化剂后,少量均化剂对共聚体系组成均一性的影响。发现在HEMA-NVP-St三元共聚体系中加入均化剂,对共聚反应的反应动力学影响不大,但对共聚物的组成均一性有较大影响。它的加入使三元共聚物中的链节比分布(即不同反应程度时,产物的累积平均组成)向较均一的方向发展。结合红外光谱、电子显微镜等实验证据,从微观结构上探讨了约化剂的作用。阐明均化剂改善了反应体系的相容性,从而得到组成分布较为均一的共聚产物。 相似文献