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991.
992.
A novel type of phosphated puerarin derivatives were synthesized through a simplified Atheron‐Todd reaction for the first time. The structure of these compounds were elucidated by IR, ESI‐MS and NMR. Moreover, the reason the dialkylphophite reagent had different chemselectivities toward different hydroxys on the puerarin was discussed. 相似文献
993.
Jing?Zhou Yuqi?Liu Liming?Tang Xinchen?Teng Ning?Tang Zhongxian?HuangEmail author 《中国科学B辑(英文版)》2003,46(1):64-74
Two mutants of the zinc finger protein, ZNF191 (243–368) I323W and R327W, are successfully obtained by site-directed mutagenesis.
The fluorescence spectrum is used to study the interaction between these two mutants and the oligonucleotides. The influence
of the mutation on the interaction has been studied using ethidium bromide (EB) as the fluorescence probe. The binding constants
of the I323W-DNA and R327W-DNA have been calculated and the possible binding models have been discussed. 相似文献
994.
Wang GC Zhou YH Morikawa Y Nakamura J Cai ZS Zhao XZ 《The journal of physical chemistry. B》2005,109(25):12431-12442
The decomposition of methanol on the Ni(111) surface has been studied with the pseudopotential method of density functional theory-generalized gradient approximation (DFT-GGA) and with the repeated slab models. The adsorption energies of possible species and the activation energy barriers of the possible elementary reactions involved are obtained in the present work. The major reaction path on Ni surfaces involves the O-H bond breaking in CH(3)OH and the further decomposition of the resulting methoxy species to CO and H via stepwise hydrogen abstractions from CH(3)O. The abstraction of hydrogen from methoxy itself is the rate-limiting step. We also confirm that the C-O and C-H bond-breaking paths, which lead to the formation of surface methyl and hydroxyl and hydroxymethyl and atom hydrogen, respectively, have higher energy barriers. Therefore, the final products are the adsorbed CO and H atom. 相似文献
995.
利用分子束技术改变甲烷的平动能E_k来研究E_k及其法向分量E_n对甲烷在Ni表面及La薄膜上激活解离吸附的影响。对CH_4/Ni及CH_4/La系统, 当甲烷的平动能E_k分别低于58.5 kJ·mol~(-1)及52.3 kJ·mol~(-1)时, 没观察到甲烷的解离吸附。当甲烷的平动能超过此阈值时, 即对CH_4/Ni系统, 当Ek=58.5增至63.8 kJ·mol~(-1)时, 初始沾着几率s_0由0至0.54线性增加; 对CH_4/La系统, 当E_k=52.3增至63.8 kJ·mol~(-1)时, S_0由0至0.49线性增加。这些结果表明, 两个系统的化学吸附是不经过前趋态的直接化学吸附。最后求出CH_4/Ni, CH_4/La系统的表观活化能分别为46.8 kJ·mol~(-1)和38.1 kJ·mol~(-1)。 相似文献
996.
Lifang Yang Haifeng He Hongqing Cao Xinhua Wan Qi-feng Zhou Department of Polymer Science & Engineering College of Chemistry & Molecular Engineering Peking University Beijing China 《高分子科学》2002,(5):401-407
Four new rod-coil diblock molecules, which had well-defined para-phenylene oligomers (PPP, from biphenyl toquinquephenyl) as rigid segments and poly(ethylene oxide) (PEO, M_w ca. 750) as flexible segments, were synhesized. Thechemical structure and the number of repeating unit in PEO coil and PPP rod were characterized by ~1H-NMR and MALDI-TOF mass spectromeny. The diblock oligomers showed good solubility in common organic solvents and aggregated in wateras characterized by a blue shift in UV-vis absorption spectra, a red shift in emission spectra, quenching of the fluorescenceand formation of the microfibrilla and fractal-like structures. The formation of different supramolecular structures meant thatthis effort might lead to commercial important highly organized functional materials. 相似文献
997.
Titanate nanoribbons were prepared via a hydrothermal treatment of rutile-type TiO2 powders in a 10 M NaOH solution at 200 °C for 48 h. The as-prepared titanate nanoribbons were then hydrothermally post-treated at 150 °C for 12-36 h. The titanate nanoribbons before and after hydrothermal post-treatment were characterized with FESEM, XRD, TEM, UV-VIS and nitrogen adsorption-desorption isotherms. The results showed that the hydrothermal post-treatment not only promoted the phase transformation from titanate to anatase TiO2, but also was beneficial to the removal of Na+ ions remained in the titanate nanoribbons. After hydrothermal post-treatment, the TiO2 samples retained the one-dimensional structure feature of the titanate nanoribbons and showed an obvious increase in the specific surface area and the pore volume. 相似文献
998.
Two polyether bridged dihydroxamic acids and their mono-and binuclear manganese(Ⅱ), zinc(Ⅱ) complexes have been synthesized and employed as models to mimic hydrolase in catalytic hydrolysis of p-nitrophenyl picolinate (PNPP). The reaction kinetics and the mechanism of hydrolysis of PNPP have been investigated. The kinetic mathematical model for PNPP cleaved by the complexes has been proposed. The effects of the different central metal ion, mono-and binuclear metal, the pseudo-macrocyclic polyether constructed by polyethoxy group of the complexes, and reactive temperature on the rate for catalytic hydrolysis of PNPP have been examined. The results showed that the transition metal dthydroxamates exhibited high catalytic activity to the hydrolysis of PNPP, the catalytic activity of binuclear complexes was higher than that of mononuclear ones, and the pseudo-macrocyclic polyether might synergetically activate H20 coordinated to metal ion with central metal ion together and promote the catalytic hydrolysis of PNPP. 相似文献
999.
An on-line coupled continuous flow liquid membrane extraction (CFLME) and C18 precolumn system was developed for sample preconcentration in liquid chromatography determination. After preconcentration by CFLME, which is based on the combination of continuous flow liquid–liquid extraction and supported liquid membrane, bisphenol A (BPA) was enriched in 960 μl of 1 mol l−1 NaOH used as acceptor. This acceptor was on-line neutralized and transported onto the C18 precolumn where analytes were absorbed and focused. Then the focused analytes were injected onto a C18 analytical column for separation and detected at 220 nm with a diode array detector. CFLME related parameters such as flow rates, pH of donor and acceptor, and enrichment time were optimized. The proposed method presents a detection limit of 0.03 μg l−1 (S/N=3) when 60 ml samples was enriched with an enrichment time of 30 min. Compared with C18 based column-switching procedure, this proposed procedure presents similar sample throughput and lower detection limits. The proposed method was successfully applied to determine BPA in tap water, river water, and municipal sewage effluent samples. 相似文献
1000.
Hui Chao Yi-Xian Yuan Feng Zhou Liang-Nian Ji Jian Zhang 《Transition Metal Chemistry》2006,31(4):465-469
A novel dinuclear ruthenium(II) complex [(phen)2Ru(mbpibH2)Ru(phen)2]4+ [phen = 1,10-phenanthroline; mbpibH2 = 1,3-bis(1,10-phenanthroline[5,6-d]imidazol-2-yl)-benzene] has been synthesized and characterized. The DNA-binding behavior
of this complex has been studied by spectroscopic and viscosity measurements. Results suggest that the dinuclear ruthenium(II)
complex intercalates into DNA base pairs via its bridging moiety. It has also been found that the dinuclear ruthenium(II) complex displays the enantiopreferential DNA-binding
after equilibrium dialysis. 相似文献