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51.
Catalytic asymmetric Reformatsky reactions of benzaldehyde with optically active menthyl bromoacetates in the presence of Zn-Cu couple were performed using 0.25 equiv. of (1R,2S) or (1S,2R)-dimethyl-2-amino-1,2-diphenyl ethanol as chiral ligand to obtain β - hydroxy esters with enantioselectivities up to 60.2%. The obvious double chiral induction effect was observed while chiral ligands matched with optically active substrates. 相似文献
52.
53.
Qianping Ran Ponisseril Somasundaran Changwen Miao Jiaping Liu Shishan Wu Jian Shen 《Journal of Dispersion Science and Technology》2013,34(6):790-798
Comb polymers are commonly used as dispersants to stabilize highly concentrated cement suspensions. The effectiveness of such polymeric additives to stabilize these suspensions is determined to a large extent by the amount adsorbed. In this study we investigated the adsorption characteristics of various comb dispersant containing different graft densities on surfaces of cement particle. The effect of inorganic salts on their adsorption was also examined in order to elucidate their adsorption mechanism. The results show that the adsorption of comb polymer dispersants on cement surface conforms approximately to Langmuir's adsorption isotherm and the characteristic plateau A s and adsorption free energy ΔGads are largely dependent on the anionic group content of the comb polymers. The A s and ΔGads increase with increasing anionic group content. This information suggests that the adsorption of comb polymers on cement surfaces is dominated by electrostatic interaction between COO-groups on the comb polymers and the positive surface of the cement. This conclusion is supported by effects of inorganics such as calcium and sulfate ions, and diffuse reflectance FTIR spectroscopy. The implication of results for tuning polymers for the required performance in cement manufacture should be noted. 相似文献
54.
利用溶胶凝胶法制备出一种三角形Au@TiO2核壳材料。经过水热晶化,该材料膨胀至300 nm,壳层TiO2晶化为介孔锐钛矿相,但核心三角形Au颗粒的形貌保持不变。采用粉末X射线衍射(PXRD)、ζ电位、高分辨透射电子显微镜(HRTEM)、热重分析(TGA)、光致发光(PL)光谱、光电流(i-t)以及光催化降解技术,对样品的结构和性能进行了系统、详细的检测与分析。经过晶化处理的Au@TiO2在可见光波段的光降解亚甲蓝性能比未晶化时有了显著的提升, 1 mg·mL-1 Au@c-TiO2可以在可见光照射1 h后实现对60 mg·L-1亚甲蓝全降解。电子顺磁共振(EPR)测试表明·O2-和·OH两种自由基对光降解起到了很大作用。通过综合分析实验结果和时域有限差分(FDTD)分析,探究了催化反应的机理。 相似文献
55.
A new simple receptor 1 based on aminosalicylimine was prepared. It exhibited an ‘off–on fluorescence type’ mode with high sensitivity in the presence of Zn2+. In particular, this chemosensor could clearly distinguish Zn2+ from Cd2+. Also, it could be a reusable chemosensor because the addition of EDTA quenched the fluorescence of the Zn2+-2·1 complex. Furthermore, receptor 1 had a sufficiently low detection limit (68 nM) in aqueous solutions, which implies that 1 could sense the nanomolar concentration of Zn2+. Therefore, this sensor has the ability to be a practical system for the monitoring of Zn2+ concentrations in aqueous samples. 相似文献
56.
Shao‐Bo Mi 《Surface and interface analysis : SIA》2014,46(2):102-105
Structural properties of YBa2Cu3O7‐δ/PrBa2Cu3O7‐δ heterointerfaces have been investigated by aberration‐corrected electron microscopy. Experimental evidence shows that c‐axis‐oriented YBa2Cu3O7‐δ/PrBa2Cu3O7‐δ heterostructures with atomically sharp interface epitaxially grow on SrTiO3(001) substrates. In terms of the contrast analysis, no apparent interdiffusion between YBa2Cu3O7‐δ and PrBa2Cu3O7‐δ occurs at the interface. In addition, stand‐off misfit dislocations and planar faults appear within PrBa2Cu3O7‐δ layer near the interface. Both misfit dislocations and interfacial dislocations resulting from the termination of planar faults contribute to misfit relaxation at the YBa2Cu3O7‐δ/PrBa2Cu3O7‐δ interface. The defect configuration of planar faults and stand‐off misfit dislocations is explored. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
57.
Cancer is a global issue and a serious threat to human health, one approach to treatment is starvation therapy. Recently, three-dimensional (3D) bioprinted tumor tissue models have been developed; however, whether 3D bioprinted models are good for in vitro study of starvation therapy is unclear. In this study, we studied the state of cells with serum-free medium in both 3D bioprinted scaffold and 2D cell cultures and found that 3D bioprinted cancer cells (3D cells) were more tolerant to serum starvation than 2D cells in terms of cell viability, cell proliferation, and M2 macrophage polarization. Moreover, the ratio of LC3II/I, an index of autophagy, increased much more in 3D cells, and 3D cells showed more autophagosomes than 2D cells after serum starvation, which indicated that the autophagy levels were higher in 3D cells. These results suggested that 3D cells are more tolerant to serum starvation than 2D cells, and autophagy may play an important role in this process. 相似文献
58.
Ki Cheol Hwang Hyun Young Shin Woo Jung Kim Mi Suk Seo Hoon Kim 《Molecules (Basel, Switzerland)》2021,26(6)
Persimmon (Diospyros kaki), a familiar and widespread fruit worldwide, is known to exhibit several physiological effects because of the presence of pharmacologically active compounds called phytochemicals. However, its high-molecular-weight compounds, particularly polysaccharides, have not been extensively studied. In this study, D. kaki extract (DK) was fractionated into low- and high-molecular-weight fractions (DK-L and DK-H, respectively) through ethanol fractionation, and their effects on antioxidant, anti-inflammatory, and antiwrinkle activities were investigated by an in vitro system. DK-H contained significantly higher contents of neutral sugar, uronic acid, and polyphenols compared to DK and DK-L. Furthermore, DK-H exhibited significantly improved pharmacological activities, such as antioxidant, anti-inflammatory, and antiwrinkle properties, compared to those of DK and DK-L, demonstrating that DK-H may play an important role in mediating the beneficial effects of persimmon. Sugar composition analysis and molecular characterization indicated that DK-H consisted of a galacturonic acid (GalA)-rich polysaccharide with a molecular weight of >345 kDa that mainly comprised GalA and small amounts of neutral sugar and polyphenol residues. These results suggest that the bioactive fraction DK-H is likely to be a GalA-rich pectic polysaccharide containing a small number of polyphenol residues, which may be a novel candidate in the pharmaceutical and cosmeceutical industries. 相似文献
59.
随着全球人为温室气体排放量(主要是甲烷和二氧化碳)的增加,全球变暖的趋势逐渐增加,因此,迫切需要通过各种技术来捕获和利用这些温室气体.甲烷干气重整反应(DRM)可以有效地将甲烷和二氧化碳这两种资源丰富、价格低廉的温室气体转化为高附加值化学品,减少它们向大气排放.尽管DRM工艺的应用具有许多优势,但是反应期间碳沉积和活性组分的烧结是阻碍其工业应用的两个主要原因.这些碳沉积物可能覆盖活性中心或阻塞催化剂的孔道,从而导致催化剂活性降低.镍基催化剂因其价格低廉、初始活性高和资源丰富而得到广泛的应用.但应用于DRM反应的Ni基催化剂在反应中容易烧结和积碳,导致催化剂迅速失活.为解决上述问题,本文从三功能策略角度出发,即SiO2壳层的限域作用和Ni-Ce之间的协同作用以及CeO2的消除积碳作用,采用原位一锅法设计合成了一种限域型Ni-CeO2核壳结构催化剂(Ni-CeO2@SiO2).通过X射线衍射、透射电子显微镜、能量色散X射线光谱、N2吸附/脱附、氢气程序升温还原和脱附、氧气程序升温脱附、拉曼光谱、热重分析和原位漫反射红外傅里叶变换光谱测试对催化剂进行了系统的表征,来揭示催化剂的理化性质和反应机理.催化剂应用于甲烷干气重整反应结果表明,在温度区间为550~800℃时,与传统浸渍法合成的催化剂相比,Ni-CeO2@SiO2催化剂具有更高的活性.高温800℃下的稳定性测试结果显示,传统浸渍法合成的催化剂在反应20 h后就出现了大量的积碳且活性下降明显;而Ni-CeO2@SiO2催化剂在800℃下反应100 h后未检测到积碳,并且催化剂中的Ni纳米颗粒的平均粒径从5.01 nm仅增长到5.77 nm,表现出很好的高温抗积碳和耐烧结性能.值得注意的是,Ni-CeO2@SiO2催化剂在低温600℃(形成碳沉积的最可能温度区域)下反应20h后也未检测到积碳的形成,表现出催化剂良好的低温稳定性和抗积碳性能.这可能归因于对Ni-CeO2@SiO2催化剂的三功能作用,即多孔二氧化硅壳层的限域作用、Ni与CeO2之间强的金属-金属氧化物相互作用以及具有丰富活性氧物种CeO2的消除积碳的作用.通过原位漫反射红外傅里叶变换光谱测试来探究反应机理.结果 表明,DRM反应在Ni-CeO2@SiO2催化剂上遵循L-H机理,添加CeO2可以消除碳沉积并促进CO2活化.该三功能策略为设计其他应用于DRM的高性能催化剂提供了指导,有望加快该工艺的工业化. 相似文献
60.
We report a 1.8 μm two-section distributed Bragg reflector laser using butt-jointed In Ga As P bulk material as the waveguide core layer. The threshold current is 17 m A and the output power is 8 m W on average. The threshold current, output power, and emitting wavelength dependences on temperature are measured. The obtained wavelength tuning range is 10 nm. This device has potential applications in simultaneous multiple-gas detection. 相似文献