Preparation of polydivinylbenzene microspheres in supercritical carbon dioxide using acetone as cosolvent

Monodisperse polydivinylbenzene (PDVB) microspheres with clean surface were prepared by precipitation polymerization without stabilizer in supercritical carbon dioxide using acetone as cosolvent. Effects of the cosolvent, reaction time and pressure, and monomer concentration on the polymerization were studied. It was found that the conversions in all polymerization systems were above 95%. Examination by scanning electron microscopy showed that reaction pressure, divinylbenzene concentration, and level of the cosolvent had pronounced effects on the morphology of the microspheres. When 6?～?7 ml of acetone was used in a reactor of 50 ml, monodisperse PDVB microspheres of around 2.1 μm in diameter were obtained. Thermal gravimetrical analysis showed the products were of good thermostability up to about 400 °C.     

Two New Chromeno[3,2-c]Pyridine Derivatives from the Whole Plants of Thalictrum finetii and Their Antirotavirus Activity

Chemistry of Natural Compounds - Two new chromeno[3,2-c]pyridin derivatives, 8-acetyl-3-(hydroxymethyl)-7-methoxy-10H-chromeno[3,2-c]pyridin-10-one (1) and...     

A Two-Dimensional Semiconductive Metal-Organic Framework for Highly Efficient Microwave Absorption

Advanced microwave absorbing materials(MAMs)are urgently required to eliminate and attenuate microwaves to address the ubiq-uitous microwave radiations and inte...     

铌-二溴茜素紫-硫酸根-十六烷基三甲基溴化铵多元络合物测定铌

文献[1]提到二溴茜素紫(DBG)测定铌的可能性,但尚未见详细报导。至于DBG与铌组成四元混配络合物的研究迄今未见介绍。本文研究了DBG、CTMAB、SO₄^2-与铌组成四元混配络合物测定铌的新方法,并初步探讨了络合物的组成。     

表面活性剂对碳纳米管分散性及其湿法纺丝纤维性能的影响

碳纳米管(CNT)纤维因具有低密度、高强度以及高电导率等特性受到广泛关注。在湿法纺丝技术制备CNT纤维的工艺中,探究纺丝分散液和纺丝条件对CNT纤维性能的影响具有重要意义。本文研究了十二烷基硫酸钠(SDS)、十六烷基三甲基溴化铵(CTAB)、胆酸钠(SC)、牛磺脱氧胆酸钠(STDC)等表面活性剂对CNT纤维制备及性能的影响。通过拉曼光谱、紫外可见光谱、偏光显微镜、旋转流变仪、扫描电镜等方法对材料进行表征,以拉伸测试和“四探针”法对材料性能进行测试。结果表明,单壁碳纳米管(SWNTs)在表面活性剂的2(wt)%水溶液中的分散能力顺序依次为STDC> SC> CTAB> SDS;SDS或CTAB修饰的SWNTs分散液无法纺制纤维,SC和STDC修饰的SWNTs分散液具有良好的可纺性。其中以STDC作表面活性剂制备的CNT纤维性能最好,其断裂强度为160MPa,杨氏模量为12.3GPa,电导率为2300S/cm。     

Chelate synthesis of 2,2′-bipyridin-4-one

A method for the synthesis of 2,2′-bipyridin-4-one from 4-amino-4-(2-pyridyl)-but-3-en-2-onevia its diphenylboron, chelates was proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2071–2073, November, 1997.     

Photo-Controlled Macroscopic Self-Assembly Based on Photo-Switchable Hetero-Complementary Quadruple Hydrogen Bonds

A photo-switchable hetero-complementary quadruple H-bonding array, which consists of an azobenzene-derived ureidopyrimidinone (UPy) module ( Azo-UPy ) and a nonphotoactive diamidonaphthyridine (DAN) derivative ( Napy-1 ), is constructed based on a reversible photo-locking approach. Upon UV (390 nm)/Vis (460 nm) light irradiations, photo-switchable quadruple H-bonded dimerization between Azo-UPy and Napy-1 can be achieved with exhibiting 4.8×10⁴-fold differences in binding strength (ON/OFF ratios). Furthermore, smart polymeric gels with unique photo-controlled macroscopic self-assembly behavior can be fabricated by introducing such quadruple H-bonding array as photo-regulable noncovalent interfacial connections.     

DNA nanostructure-based nucleic acid probes: construction and biological applications

In recent years, DNA has been widely noted as a kind of material that can be used to construct building blocks for biosensing, in vivo imaging, drug development, and disease therapy because of its advantages of good biocompatibility and programmable properties. However, traditional DNA-based sensing processes are mostly achieved by random diffusion of free DNA probes, which were restricted by limited dynamics and relatively low efficiency. Moreover, in the application of biosystems, single-stranded DNA probes face challenges such as being difficult to internalize into cells and being easily decomposed in the cellular microenvironment. To overcome the above limitations, DNA nanostructure-based probes have attracted intense attention. This kind of probe showed a series of advantages compared to the conventional ones, including increased biostability, enhanced cell internalization efficiency, accelerated reaction rate, and amplified signal output, and thus improved in vitro and in vivo applications. Therefore, reviewing and summarizing the important roles of DNA nanostructures in improving biosensor design is very necessary for the development of DNA nanotechnology and its applications in biology and pharmacology. In this perspective, DNA nanostructure-based probes are reviewed and summarized from several aspects: probe classification according to the dimensions of DNA nanostructures (one, two, and three-dimensional nanostructures), the common connection modes between nucleic acid probes and DNA nanostructures, and the most important advantages of DNA self-assembled nanostructures in the applications of biosensing, imaging analysis, cell assembly, cell capture, and theranostics. Finally, the challenges and prospects for the future development of DNA nanostructure-based nucleic acid probes are also discussed.

In recent years, DNA has been widely noted as a kind of material that can be used to construct building blocks for biosensing, in vivo imaging, drug development, and disease therapy because of its advantages of good biocompatibility and programmable properties.     

Bacteria and cancer cell pearl chain under dielectrophoresis

In this work, we aim to observe and study the physics of bacteria and cancer cells pearl chain formation under dielectrophoresis (DEP). Experimentally, we visualized the formation of Bacillus subtilis bacterial pearl chain and human breast cancer cell (MCF-7) chain under positive and negative dielectrophoretic force, respectively. Through a simple simulation with creeping flow, AC/DC electric fields, and particle tracing modules in COMSOL, we examined the mechanism by which bacteria self-organize into a pearl chain across the gap between two electrodes via DEP. Our simulation results reveal that the region of greatest positive DEP force shifts from the electrode edge to the leading edge of the pearl chain, thus guiding the trajectories of free-flowing particles toward the leading edge via positive DEP. Our findings additionally highlight the mechanism why the free-flowing particles are more likely to join the existing pearl chain rather than starting a new pearl chain. This phenomenon is primarily due to the increase in magnitude of electric field gradient, and hence DEP force exerted, with the shortening gap between the pearl chain leading edge and the adjacent electrode. The findings shed light on the observed behavior of preferential pearl chain formation across electrode gaps.     

Rate sensitivity and deformation mechanism of semi-crystalline polymers during instrumented indentation

Instrumented indentation tests using both constant loading rate (CLR) and continuous stiffness measurement (CSM) operation modes were performed to investigate the deformation mechanism and their sensitivity to the deformation rate in semi-crystalline polymers through the quantitative analysis of load-depth loading and unloading curves. The strain rate was constant during the CSM tests, while the strain rate decreased with the increasing of loading time in CLR tests. The mechanical response mechanism of the semi-crystalline polymers to these tests was very complicated because of the combined effects of strain-hardening in the crystal phase and strain-softening in the amorphous phase. Results show that the loading index m reflects the strain-hardening or strain-softening response during indentation. When m > 2, the mechanical response was due to the strain-hardening, and when m < 2, the response was due to strain-softening. A method based on the measured contact hardness was proposed to obtain the unloading stiffness, and the other mechanical parameters could then be determined according to the unloading stiffness.