表面修饰多壁碳纳米管负载二氧化钛的制备及催化碳酸二甲酯与苯酚酯交换反应的性能

制备了表面修饰多壁碳纳米管负载TiO₂的催化剂,并将其应用于碳酸二甲酯与苯酚的酯交换反应. 采用X射线电子能谱、透射电子显微镜、低温N₂吸附-脱附和X射线衍射等对催化剂进行了表征. 结果表明,以低浓度的氨水（0.4%）代替去离子水作为沉淀剂时,制备的催化剂显示出更好的催化活性、分离性与重复使用性. 考察了TiO₂负载量、催化剂用量及反应时间对反应性能的影响. 在最佳反应条件下,苯酚转化率为42.5%,碳酸甲苯酯与碳酸二苯酯的总选择性达到99.9%以上. 经过4次重复使用后,催化剂的活性略有下降.     

G-四链体DNA稳定剂的研究进展

人体端粒由富含鸟嘌呤(G)的DNA重复序列组成,该序列在一定的条件下可以形成G-四链体DNA的结构.小分子化合物诱导该结构的形成并使之稳定,不但可以抑制端粒酶的活性或降低癌基因的转录表达而达到抗肿瘤的目的,还可以作为G-四链体DNA的探针,辅助G-四链体DNA生物功能的研究及与之相关疾病的诊断.因此,G-四链体DNA稳定剂的设计是近年来化学生物学的重要前沿领域之一.到目前为止,G-四链体DNA稳定剂主要可分为有机小分子化合物和金属配合物.本文重点综述这两方面特别是后者的最新研究进展.     

Oxidative Cross‐Coupling of Allenyl Ketones and Organoboronic Acids: Expeditious Synthesis of Highly Substituted Furans

Allenyl ketones are employed as coupling partners in palladium‐catalyzed oxidative cross‐coupling reactions with organoboronic acids. This reaction constitutes an efficient methodology for the synthesis of highly substituted furan derivatives. Palladium‐carbene migratory insertion is proposed as the key step in this transformation.     

Bioactive Trichothecenes Produced by the Myrothecium sp. QB‐1

Three new simple trichothecenes, 15‐acetyltrichoverrol B ( 3 ), 13′‐acetyltrichoverrin B ( 5 ), and 6′‐dehydroxytrichoverrin B ( 6 ), along with five known trichothecenes trichodermadienediol B ( 1 ), trichoverrol B ( 2 ), trichoverrin B ( 4 ), and roridins A ( 7 ) and D ( 8 ), have been isolated from the liquid culture of Myrothecium roridum (strain no. QB‐1). The structures of the new compounds were established by comprehensive analysis of 1D‐ and 2D‐NMR data. All the compounds were evaluated for antifungal activity, only compounds 7 and 8 showed significant antifungal activity against the tested fungi (MIC ranged from 10 to 5 μg/ml).     

Frontal polymerization synthesis of starch-grafted hydrogels: Effect of temperature and tube size on propagating front and properties of hydrogels

The frontal polymerization process was used to produce superabsorbent hydrogels based on acrylic acid monomers grafted onto starch. Using a simple test tube which was nonadiabatic and permitted contact with air, the effects of initial temperature and tube size on the propagating front of grafting copolymerization and the properties of hydrogels were explored. The unrestricted access of the reaction mixture to oxygen delayed the formation of self-propagating polymerization front. The ignition time was markedly lengthened with the increasing of tube size attributed to the formation of large amounts of peroxy radicals. The front velocity dependence on initial temperature could be fit to an Arrhenius function with the average apparent activation energy of 24 kJ mol(-1), and on tube size to a function of higher order. The increase of the initial temperature increased the front temperature, which lead to more soluble oligomers and higher degree of crosslinking. The interplay of two opposite effects of oligomer and crosslinking determined the sol and gel content. An increase in tube size had two effects on the propagating front. One was to reduce heat loss. The other effect was to increase the number of escaping gas bubbles. The combined action of the two effects resulted in a maximum value of front temperature, an increase in sol content and a reduction in gel content with tube size. The highest swelling capacity of hydrogels was obtained when the initial temperature or tube size favored a formation of porous microstructure of hydrogels.     

Microwave-assisted Synthesis of Pyrazolo[4,3-f]quinolin-7-one Derivatives via Multi-component Reactions

A series of new pyrazolo[4,3‐f]quinolin‐7‐one derivatives were synthesized by multi‐component reactions of equimolar amount of aromatic aldehydes with 2,2‐dimethyl‐1,3‐dioxane‐4,6‐dione and 1H‐indazol‐5‐amine in ethylene glycol without catalyst under microwave irradiation. This one‐pot protocol has the advantage of good yields, simple workup procedure and shorter reaction time.     

Durable Mesenchymal Stem Cell Labelling by Using Polyhedral Superparamagnetic Iron Oxide Nanoparticles

Small polyhedral superparamagnetic iron oxide (SPIO) nanoparticles (<10 nm) coated with a thin layer of silica were prepared (SPIO@SiO₂ and SPIO@SiO₂‐NH₂). Surface modification of the small polyhedral silica‐coated SPIO nanoparticles with amines led to substantially higher mesenchymal stem cell (MSC) labelling efficiency without the use of additional transfecting agents. Therefore, amine surface‐modified nanoparticles (SPIO@ SiO₂‐NH₂) appeared to be the preferred candidate for MSC labelling. In vitro studies demonstrated that controlled labelling of SPIO@SiO₂ and SPIO@SiO₂‐NH₂ did not cause MSC death or proliferation inhibition. MSCs labelled with SPIO@SiO₂‐NH₂ nanoparticles retained differentiation potential and showed osteogenic, adipogenic and chondrogenic differentiations. The noncytotoxic polyhedral SPIO@SiO₂‐NH₂ nanoparticle‐labelled MSCs were successfully implanted in rabbit brain and erector spinae muscle, and demonstrated long‐lasting, durable MRI labelling efficacy after 8–12 weeks.     

Simultaneous determination of 18alpha- and 18beta-glycyrrhetic acid in human plasma by LC-ESI-MS and its application to pharmacokinetics

A highly sensitive and selective LC-ESI-MS was developed, validated for the simultaneous determination of 18alpha-glycyrrhetic acid (alpha-GA) and 18beta-glycyrrhetic acid (beta-GA) for pharmacokinetic studies in healthy subjects. Sample preparation was performed by liquid-liquid extraction with ethyl acetate and the separations were achieved using a C(18) column with the mobile phase composed of 10 mmol/L ammonium acetate solution-methanol-acetonitrile (40:36:24, v/v/v) at a flow rate of 1 mL/min. The internal standard was honokiol and the epimers were quantified using a single quadrupole mass spectrometer employing ESI in the negative ion mode. The separation factor, alpha, was 1.512 for alpha- and beta-GA. The standard curves were linear for both epimers with coefficients of determination (r >or= 0.9998) over the concentration range of 1-150 ng/mL. The precision and accuracy were 相似文献   

Highly selective molecular recognition and high throughput detection of melamine based on molecularly imprinted sol-gel film

Multimode reader has been generally applied in immunoassay, and in the proposed paper, the 96 well micro-plate was modified with molecularly imprinted melamine sol-gel film, based on which the highly selective and high throughput detection of melamine was achieved. Melamine was imprinted into silica sol-gel films directly using phenyltrimethoxysilane and methyltrimethoxysilane as functionalized organosilicon precursors. The binding characteristic of the imprinted film to melamine was evaluated by equilibrium binding experiments and the morphology was studied by scanning electronic microscope (SEM). Scatchard analysis was carried out to estimate the binding parameters of the imprinted film. The proposed method exhibited excellent selectivity because of specific recognition of MM by molecularly imprinted film. Under the optimum conditions, the chemiluminescence (CL) intensity had a linear relationship against the concentration of melamine over the range of 0.1-50 μg mL⁻¹ with a lower detection limit of 0.02 μg mL⁻¹.