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931.
Tianle Zhu Jiming Hao Lixin Fu Junhua Li Zhiming Liu 《Reaction Kinetics and Catalysis Letters》2005,84(1):61-67
Summary The cooperation effect of reducing species for selective reduction of NO over Ag/Al2O3 has been investigated in the presence of excess oxygen. When the combinations of propene or propane and ethanol or methanol were used as reducing agents, NO reduction took place over a wider temperature range, compared with a single hydrocarbon as reducing agent. 相似文献
932.
The sequence-specific recognitions between DNA and proteins are playing important roles in many biological functions. The double-stranded DNA microarrays (dsDNA microarrays) can be used to study the sequence-specific recognitions between DNAs and proteins in highly parallel way. In this paper, two different elongation processes in forming dsDNA from the immobilized oligonucleotides have been compared in order to optimize the fabrication of dsDNA microarrays: (1) elongation from the hairpins formed by the self-hybridized oligonucleatides spotted on a glass; (2) elongation from the complementary primers hybridized on the spotted oligonucleatides. The results suggested that the dsDNA probes density produced by the hybridized-primer extension was about four times lower than those by the self-hybridized hairpins. Meanwhile, in order to reduce the cost of dsDNA microarrays, we have replaced the Klenow DNA polymerase with Taq DNA polymerase, and optimized the reaction conditions of on-chip elongation. Our experiements showed that the elongation temperature of 50 °C and the Mg2+ concentration of 2.5 mM are the optimized conditions in elongation with Taq DNA polymerase. A dsDNA microarray has been successfully constructed with the above method to detect NF-kB protein. 相似文献
933.
A coal tar pitch and a petroleum vacuum residue have been separated by TLC using pyridine, acetonitrile, toluene and pentane to develop the chromatograms. The bands of material detected were recovered in 1-methyl-2-pyrrolidinone (NMP) solvent and examined by size-exclusion chromatography (SEC) in NMP eluent. The relation between elution time in SEC and mobility on the TLC plate indicated that molecular size increased steadily with increasing immobility on the plate. This relation was reinforced by UV fluorescence spectroscopy in that the fluorescence moved to longer wavelengths with increasing immobility. The molecular size of the material excluded from the porosity of the SEC column remains undefined; some excluded material was found in all of the fractions from both samples. The valley of zero intensity separating the retained material from the excluded material may suggest a change of structure from near-planar in the retained region to three-dimensional in the excluded region. 相似文献
934.
Laure Gouriou Štěpán Vysko?il Pavel Ko?ovský 《Journal of organometallic chemistry》2003,687(2):525-537
The reaction of iso-cinnamyl acetate with NaC(Me)(CO2Me)2, catalysed by Pd-‘MOP’ (MOP=2-methoxy-2′-diphenylphosphino-1,1′-binaphthalene) is known to proceed with a regiochemical memory effect that results in the predominant generation of the branched alkylation product. The analogous reaction employing ‘MAP’ as ligand (MAP=2-N,N-dimethylamino-2′-diphenylphosphino-1,1′-binaphthalene) proceeds with ‘normal’ regioselectivity to generate predominantly the linear isomer of product. A 2H-NMR based analysis, employing quadrupolar coupling in a chiral liquid crystal matrix, has been developed to facilitate the simultaneous study of the regiochemical and stereochemical outcome of the reaction of both enantiomers of iso-cinnamyl ester substrates in 2H-labelled but racemic samples. The analysis allows the comparison of relative rates of two competing isomerisation processes occurring in the π-allyl intermediates in the Pd-catalysed reaction, one of which facilitates asymmetric induction, the other resulting in loss of regiochemical memory. It is demonstrated that the two processes are partially coupled and that this then limits the attainment of high global enantiomeric excess in the branched product to reactions that proceed with low regiochemical retention. A key factor for the observation of high regiochemical memory is found to be the nucleophilicity of the malonate anion and the electrophilicity of the Pd-π-allyl intermediate with reduction in the reactivity of either partner resulting in the onset of substantial loss of memory. 相似文献
935.
The chemical fixation of CO2 with mono-substituted terminal epoxides or cyclohexene oxide to form cyclic carbonates under the ZnCl2/[BMIm]Br catalyst system without using additional organic solvents was achieved in excellent selectivity (>98%) and TOF (5410 h−1) and the catalyst could be used six times almost without losing its catalytic activity and selectivity. Besides, the pure cis-cyclic carbonate of cyclohexene oxide was obtained in this catalyst system. 相似文献
936.
在纳米尺度下构建有序的磁性模板和图形是当前的研究热点之一 [1,2 ] .这种模板在生物样品的分离[1] 、磁电子学研究和信息存储 [2 ] 等领域具有重要意义 .目前 ,光刻 [3] 、微触点印刷 [4 ] 和自组装 [5] 等多项技术已被用来构建各种纳米模板 .1 999年 ,美国西北大学 Mirkin小组 [6 ]发明的 Dip- pen纳米刻蚀技术 (简称 DPN技术 )更在可控组装方面显示出巨大优越性 .这项技术是在一定驱动力作用下 ,使吸附在原子力显微镜 ( AFM)针尖上的分子“墨水”逐渐转移到基底表面上 ,实现纳米模板的可控构建 .与传统技术相比 ,DPN技术可在纳米尺… 相似文献
937.
采用两种分子场分析方法即比较分子场分析法(CoMFA)和比较分子相似因子分析法(CoMSIA)进行了37个褪黑激素受体拮抗剂的构效关系研究.计算结果表明,两种方法得到的构效关系模型都具有较好的预测能力.在计算中,还考察了不同格点距离和电荷计算方法对构效关系模型的影响.通过分析分子场等值面图在空间的分布,可以观察到叠合分子周围分子场特征对化合物活性的影响,为设计新的褪黑激素拮抗剂提供了一些理论依据. 相似文献
938.
F U Erko? S Ozsar B Güven G Kalkandelen E U?rar 《Journal of chromatographic science》1989,27(2):86-90
In the present work, a practical, rapid, reliable and isocratic reversed-phase high-performance liquid chromatographic (HPLC) method is described for the qualitative and quantitative analysis of estriol, estradiol-17 beta, estrone, testosterone, and progesterone. Chromatographic separation is complete in 16 min using a mobile phase of 50% acetonitrile (v/v) in water. The order of elution is estriol, testosterone, estradiol-17 beta, estrone, and progesterone; retention times are 2.5, 5.5, 5.6, 6.9, 16.3 min, respectively. Absorbance maxima of individual steroids is the limiting factor in quantitative determination. The recommended wavelengths for UV monitoring are E3 214, E2 280, T 254, E1 214, and P4 254 nm. 相似文献
939.
用TEA CO_2激光将C_2H_4分子激发到高振动激发态,高振动激发态的C_2H_4分子与基态的K原子碰撞发生振动态→电子态(V→E)传能过程,根据提出的能级组模型,对测得的时间分辨原子荧光信号进行处理,获得温度在453-663 K范围内,C_2H_4-K体系中V→E传能速率的数量级为10~(-10)/cm~3·molecule~(-1)·s~(-1),对应的碰撞传能截面约为0.30~0.80 nm.随着反应温度升高,V→E传能截面减小.上述实验结果表明碰撞体间吸引相互作用在这种非共振的V→E传能过程中起主要作用.利用多极相互作用势下的碰撞络合物模型对实验结果进行了讨论. 相似文献
940.
石墨炉原子吸收光谱无标样分析法的研究:Ⅰ.消除基体干扰 总被引:1,自引:0,他引:1
实现石墨炉原子吸收光谱绝对分析必须消除基体干扰,本研究采用有机基体改进剂,管壁原子化、热解涂层石墨管,峰面积积分吸收信号,D2灯或Zeeman效应扣除背景,有效地控制和消除了海水基体对As,Cd,Co,Cr,Cu,Mn,Ni,Pb和V等元素的干扰,实现了无干扰测定。 相似文献