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991.
(Z)-3-丁烯基苯酞和它的衍生物广泛地存在于微形科植物,如当归、川芎等,这些植物有些是重要的中药材。(Z)-3-丁烯基-4,5-二羟基苯酞是(Z)-3-丁烯基苯酞的类似物;它对前列腺素F2α具有抑制作用。本文以3,4-二甲氧基苯甲醇(2)或价廉易得的胡椒醇(6)为起始原料,分别经四步反应顺利地合成了(Z)-3-丁烯基-4,5羟基苯酞(1)。和一步是本方法的关键,即利用杂原子诱导的区域选择性的芳环 相似文献
992.
利用紫外-可见吸收和荧光发射光谱, 结合非线性最小二乘法拟合曲线以及分子力学(MM2)模拟系统地研究了手性分子N-[4-(1-芘基)]丁酰-D/L-苯丙氨酸(PDP和PLP, 总称PPs)与β-环糊精(β-CD)、 2-位硒桥联双β-CD(2-SeCD)和2-位碲桥联双β-CD(2-TeCD)的包结能力大小及这3个环糊精对PPs手性识别能力的差异和识别机理. 研究结果表明, PPs不能与单疏水空腔的β-CD形成很好的包结复合物, 与具有较长桥联链的2-TeCD结合能力最强. 2-TeCD与PDP和PLP的结合常数分别为2.33×104和6.07×103 L/mol, 对PPs的手性识别比达到KD/KL=3.84, 高于2-SeCD(KD/KL=2.61). 用MM2模拟得出了PPs与这两个双环糊精形成复合物的三维结构: PPs的绝大部分位于双环糊精两个空腔之间, 但是在这两个复合物中, 苯环与芘环所成的二面角不同. 此外, PPs与这两个双环糊精作用时均存在明显的氢键相互作用, 且2-TeCD强于2-SeCD. 相似文献
993.
Static second-order nonlinear optical effects of amino acid zinc(Ⅱ) porphyrins 1, 2,3 and 4 were calculated by the TDHF/PM3 method based on the molecular structures optim.zed at the semiempirical PM3 quantum chemistry level, showing due to the cancellation of symmetric center, these amino acid zinc(H) porphyrins exhibit second order nonlinear optical response. The analysis of β components indicated that these amino acid zinc(Ⅱ) porphyrins are of multipolarizabilities, and they may be ascribed as the “mixture” of octupolar and dipoar molecules with ||βJ=3||/||βJ=1||≈5. It is found that there are no significant differences between the static β values of non-chiral and chiral amino acid zinc(Ⅱ) porphyrins. However, the βxyz component, which is quite important to quadratic macroscopic X^(2) susceptibility of chiral material, is increased significantly with the increase of side chain group of amino acids. 相似文献
994.
A series of poly [2-(dimethylamino)ethyl methacrylate (DMA)-sodium acrylate (SA)] diblock copolymers were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymerization exhibits controlled characters: well-controlled molecular weight, narrow molecular weight distribution, molecular weight increasing with polymerization time. The zwitterionic diblock copolymers show rich solution behaviors. Dynamic light scattering (DLS) indicated the formation of micelles and reverse micelles of copolymers is affected by net charge density of copolymers. Microcalorimetry studies showed that the lower critical solution temperature (LCST) increases with incorporation of hydrophilic segments in buffer. 相似文献
995.
996.
环氧合酶-2抑制剂的三维定量构效关系研究 总被引:2,自引:0,他引:2
建立三环系COX-1和COX-2抑制剂结构与活性的三维定量构效关系模型,为设 计新型的具有选择性的COX-2抑制剂提供线索。通过与酶的对接并优化,确定化合 物在受体结合腔中的构象,利用比较分子力场分析方法建立三维定量构效关系模型 。模型1R_(cv)~2=0.685,最佳主成分数为6,传统相关系数为R~2=0.988, F-726. 2,标准偏差S = 0.080;模型2 R_(cv)~2 = 0.573,最佳主成分数为6,传统相关 系数为R~2=0.996, F = 1147.6,标准偏差S = 0.034。所得的模型不仅解释了化合 物的构效关系,而且对预测集中的化合物有很好的预测能力;比较不同模型的系数 相关图,分析了结构与活性、结构与选择性的关系,得到的结果可以指导新化合物 的设计与合成。 相似文献
997.
A novel sensitive and simple method for rapid and selective extraction, preconcentration and determination of iron (as its
bathophenanthroline complex) and copper (as its neocuproine complex) using octadecyl silica cartridges and dual wavelength
spectrophotometry is presented. The dual wavelength method (533 nm for the iron-bathophenanthroline and 454 nm for the copper-neocuproine
as the analytical wavelength) is used to eliminate spectral interferences. Extraction efficiency and the influence of flow
rates of sample solution and eluent, pH, amount of neocuproine, bathophenanthroline and hydroxylamine hydrochloride, type
and least amount of eluent for elution of iron and copper complexes from cartridge, break-through volume and limit of detection
are evaluated. The effects of various cationic and anionic interferences on percent recovery of iron and copper are also studied.
Extraction efficiencies >95% are obtained by elution of cartridges with minimal amount of organic solvent. Iron and copper
were determined in the range of 3–100 ng mL−1. The limits of detection are 0.98 and 1.13 ng mL−1 for iron and copper, respectively. The proposed method is applied successfully to the determination of both analytes in river,
tap and well water samples.
Author for correspondence. E-mail: yyamini@modares.ac.ir
Received September 18, 2002; accepted December 12, 2002
Published online May 5, 2003 相似文献
998.
A vinyl monomer having an electron-donating moiety, p-(N,N-dimethylamino)styrenc (DMAS),was synthesized. It was combined with benzoyl peroxide (BPO) to form a redox initiation system to initiatethe polymerization of methyl methacrylate (MMA). UV spectra measurements show that DMAS enters thePMMA chain as well. Both DMAS and its polymer P(DMAS) display strong fluorescence, and thefluorescence can be quenched by electron-deficient compounds such as methacrylonitrile, fumaronitrile andmethyl methacrylate etc. Moreover, DMAS can also form charge transfer complex (CTC) with strongelectron acceptors such as tetracyanoethylene (TCNE). The difference between the photochemical propertiesof DMAS and P(DMAS) were explained in terms of molecular structure change and polymer conformationeffect in solution. In addition, the CTC and exciplex formation of DMAS or P(DMAS) with C_(60) were alsostudied. 相似文献
999.
Cheanyeh Cheng 《中国化学会会志》1998,45(5):679-688
The activity of cellulase has traditionally been described by pH and temperature; however, the buffering medium is also an important factor, Taking plain water as a reference medium, three kinds of buffer including KH2PO4/K5HPO4, citric acid/sodium citrate, and acetic acid/sodium acetate were adopted to survey their effects on the activity of cellulase. Chromatographic assays indicated that xylose, glucose, and cellobiose were the major products and that minor products such as cellotriose and cellotetraose were present in some cases. The activities of cellulase based on glucose production showed that the phosphate buffer acted as a deactivator for cellulase and each of the two organic acid buffers acted as activators for cellulase. The concentration of activation buffer should be high to reach a high cellulase activity; however, this effect would be compensated for by the product inhibition of cellulase. The highest activity obtained was 4.16 ± 0.08 (× 10?3) IU mg?1 for the citric acid/sodium citrate buffer under pH 4.80, 40 °C and an agitation speed of 150 rpm. 相似文献
1000.
二氧化碳和氧气的快速电化学方法联合测定 总被引:4,自引:0,他引:4
根据O2和CO2在二甲亚砜(DMSO)介质中Pt电极上的伏安特性,采用微电极并结构计算机控制的电位调制技术,建立了快速联合测定CO2和O2的调制电位脉冲库仑法和调制电位脉冲电流法,取得了满意的结果。一次测量时间快达40ms。CO2检测范围0 ̄10%(体积百分比);O2检测范围不受限制。通过编程设计特定的调制电位-时间波形,可保持连续检测的长期稳定性。 相似文献