Make conjugation simple: a facile approach to integrated nanostructures

We report a facile approach to the conjugation of protein-encapsulated gold fluorescent nanoclusters to the iron oxide nanoparticles through catechol reaction. This method eliminates the use of chemical linkers and can be readily extended to the conjugation of biological molecules and other nanomaterials onto nanoparticle surfaces. The key to the success was producing water-soluble iron oxide nanoparticles with active catechol groups. Further, advanced electron microscopy analysis of the integrated gold nanoclusters and iron oxide nanoparticles provided direct evidence of the presence of a single fluorescent nanocluster per protein template. Interestingly, the integrated nanoparticles exhibited enhanced fluorescent emission in biological media. These studies will provide significantly practical value in chemical conjugation, the development of multifunctional nanostructures, and exploration of multifunctional nanoparticles for biological applications.     

Formation of different gold nanocrystal core-resin shell structures through the control of the core assembly and shell polymerization

The formation of different Au nanocrystal core-resin shell structures through the control of the nanocrystal assembly and shell polymerization is investigated. 4-Mercaptophenol is employed together with formaldehyde as the resin monomers. 4-Mercaptophenol molecules bond to the surface of Au nanocrystals so that the resultant phenolic resin can intimately encapsulate Au nanocrystals. The morphologies of the obtained structures are determined by the nanocrystal assembly and the monomer polymerization behaviors, which are controlled by the solution pH as well as the monomer amounts. At pH = 8-9, Au nanorods are assembled and fused together under hydrothermal conditions in a preferential end-to-end manner. The fused structures are coated with a layer of resin, with the thickness controlled by the supplied amounts of the monomers. At pH = ～10, Au nanorods are coated with resin of controllable thicknesses and separated from each other. The resin-coated Au nanorods are stable in both aqueous and nonaqueous solutions. At pH = ～12, Au nanorods are coated with a thin layer of resin and assembled together in a side-by-side manner. A similar assembly and resin coating behavior is also observed with Au nanopolyhedrons. Moreover, plasmonic-fluorescent bifunctional structures are readily produced by incorporating CdTe nanocrystals in the resin shell that is coated on Au nanocrystals, owing to the presence of a number of thiol groups in the resin shell.     

In situ solid-state NMR for heterogeneous catalysis: a joint experimental and theoretical approach

In situ solid-state NMR is a well-established tool for investigations of the structures of the adsorbed reactants, intermediates and products on the surface of solid catalysts. The techniques allow identifications of both the active sites such as acidic sites and reaction processes after introduction of adsorbates and reactants inside an NMR rotor under magic angle spinning (MAS). The in situ solid-state NMR studies of the reactions can be achieved in two ways, i.e. under batch-like or continuous-flow conditions. The former technique is low cost and accessible to the commercial instrument while the latter one is close to the real catalytic reactions on the solids. This critical review describes the research progress on the in situ solid-state NMR techniques and the applications in heterogeneous catalysis under batch-like and continuous-flow conditions in recent years. Some typical probe molecules are summarized here to detect the Br?nsted and Lewis acidic sites by MAS NMR. The catalytic reactions discussed in this review include methane aromatization, olefin selective oxidation and olefin metathesis on the metal oxide-containing zeolites. With combining the in situ MAS NMR spectroscopy and the density functional theoretical (DFT) calculations, the intermediates on the catalyst can be identified, and the reaction mechanism is revealed. Reaction kinetic analysis in the nanospace instead of in the bulk state can also be performed by employing laser-enhanced MAS NMR techniques in the in situ flow mode (163 references).     

Cloning of Thermostable Cellulase Genes of <Emphasis Type="Italic">Clostridium thermocellum</Emphasis> and Their Secretive Expression in <Emphasis Type="Italic">Bacillus subtilis</Emphasis>

Screening for the powerful cellulase genes with improved activities remains a challenge for the biorefinery research. In this study, five cellobiohydrolase genes and one endoglucanase gene sourced from Clostridium thermocellum DSM 1237, cbhA, celK, celO, cel48Y, cel48S, and celA were cloned into a newly established tool vector pP43JM2 and expressed in two Bacillus subtilis strains, B. subtilis WB600 and B. subtilis WB800, respectively. Most of the cellulases produced in the B. subtilis recombinants were efficiently secreted into the culture medium. These secreted soluble proteins showed distinct cellulase activities using phosphoric acid swollen cellulose (PASC) as the substrate and they also demonstrated strong synergistic effects for PASC, Avicel cellulose, and the dilute acid pretreated corn stover. The current work provided a quick secretive cloning method for screening cellulase genes and may provide a host strain for constructing a consolidated bioprocessing platform with the capacity of secretive expression of multiple cellulases.     

Maximum Saccharification of Cellulose Complex by an Enzyme Cocktail Supplemented with Cellulase from Newly Isolated <Emphasis Type="BoldItalic">Aspergillus fumigatus</Emphasis> ECU0811

Either the natural biodegradation process or the industrial hydrolytic process requires synergistic interactions between various cellulases. However, it is sometimes impeded by low hydrolytic rate of existing cellulases and the lack of accessory enzymes. Herein, the ability of a commercial cellulase (Spezyme CP, from Genencor) to degrade steam explosion-pretreated corn stover was significantly improved. Firstly, a fungal cellulase producer, Aspergillus fumigatus ECU0811, was isolated from hundreds of soil samples. A 96-deep-well microscale-based platform was developed here to reduce the labor-intensive screening work and proved to be consistent with macroscale screening work. After optimization of fermentation, 3% corn cob could induce A. fumigatus ECU0811 to yield the highest cellulase production. Based on the high activities of β-glucosidase and xylanase by A. fumigatus ECU0811, 0.91 and 125 U/mg protein, respectively, an enzyme cocktail was composed with a fixed dosage of Spezyme CP (CPCel) at 14.2 filter paper units (FPU)/g glucan and varied dosages of A. fumigatus cellulase (AFCel). Consequently, the glucan-to-glucose conversion of corn stover was increased from 25.6% in the presence of CPCel at a dosage of 14.2 FPU/g glucan to 99.5% in the presence of the enzyme cocktail (14.2 FPU CPCel plus 1.21 FPU AFCel per gram of glucan). On the other side, it reduced the total protein amount of CPCel by as much as tenfold, which extremely improved the hydrolytic rate of Spezyme CP and reduced its dosage.     

Deformation-induced morphology evolution during uniaxial stretching of isotactic polypropylene: effect of temperature

The effects of draw temperature on the deformation-induced morphology evolution of isotactic polypropylene in terms of crystal orientation, degree of crystallinity, crystal size in the direction normal to chain axis, long spacing, and the deformation behavior at the crystal lattice and lamellae scale were investigated using differential scanning calorimetry, two-dimensional wide-angle X-ray diffraction, and small-angle X-ray scattering, respectively. The results revealed that the thermal behaviors are associated with the deformation-induced morphology evolution, and the morphology evolution is strongly temperature dependent. At low strain, crystal fragmentation takes place at all the draw temperature range studied; at high strain, after crystal fragmentation the draw temperature shows different effects on the morphology evolution: at low temperature (25 °C), fragmentation of the crystal blocks continues; at medium temperatures (80 and 110 °C), the broken crystal blocks remain stable and the unfolded chains and disentangled chains in amorphous region crystallize into crystal blocks with crystal size almost identical to that of the original broken ones; at high temperatures (130 and 140 °C), not only the unfolded chains and disentangled chains in amorphous region crystallize into crystal blocks, but also these small broken crystal blocks melt and recrystallize and the new crystal blocks formed possess larger crystal size than those of the original broken ones.     

叠层荧光集光太阳能光伏器件的性能模拟和优化

荧光集光太阳能光伏器件可以减少太阳能电池的用量,有效降低光伏发电的成本.相对于单层荧光 集光太阳能光伏器件,叠层荧光集光太阳能光伏器件能分波段充分利用太阳光谱,提高荧光集光太阳能光伏 器件的效率,进一步降低光伏发电的成本.但是,叠层荧光集光太阳能光伏器件涉及较多的参量,难以通过实验 优化.本文分析了从单层到叠层荧光集光太阳能光伏器件的全部物理过程,建立了数学模型,并相应编制了 计算机模拟软件.运用上述软件,系统研究了器件尺寸、太阳能电池的带隙对光电转换效率的影响.     

脉冲序列控制电流断续模式Buck变换器的动力学建模与边界碰撞分岔

通过建立一个开关周期内输出电容电荷变化量对应的输出电压变化量, 建立了工作于电感电流断续模式(discontinuous conduction mode, DCM)的脉冲序列(pulse train, PT)控制Buck变换器的近似离散时间模型, 研究了负载电阻及输入电压变化时PT控制DCM Buck变换器的边界碰撞分岔行为. 通过构造相应的迭代映射曲线, 分别分析了不同负载电阻时PT控制DCM Buck变换器的周期1、周期2和周期3运行轨迹的不动点稳定性, 揭示了PT控制DCM Buck变换器在不同周期态时的边界碰撞分岔的形成机理. 研究结果表明, 随参数变化, PT控制DCM Buck变换器始终运行在不同的周期态, 各周期态的切换由边界碰撞分岔引起, 李雅谱诺夫指数始终小于零. 利用PSIM电路仿真软件, 给出了不同负载电阻时的时域波形和相轨图. 实验结果验证了理论分析和仿真结果的正确性, 同时说明了本文动力学建模的可行性.     

Pr1-xCexB6阴极材料的原位反应合成及性能研究

本文以CeH2,PrH2纳米粉和B粉为原料,在无氧环境下采用放电等离子原位反应成功制备了单相多元稀土六硼化物Pr1-xCexB6=（x=0．2—0．8）阴极材料．系统研究了掺杂元素Ce对Pr1-xCexB6的物相组成、力学性能及热电子发射性能的影响．结果表明,当烧结温度为1450℃,烧结压强为50MPa时可制得单相的Pr1-xCexB6多晶块体材料并且该系列样品具有良好的力学性能,维氏硬度和抗弯强度最高值分别达到了24．34GPa和226．02MPa,已达到单晶水平．热电子发射性能结果表明,随着Ce掺杂量的增加Pr1-xCexB6的发射电流密度线性增加．当阴极温度为1973K,外加电压为950V时,Pr0．4Ce0．686最大发射电流密度达到47-3A．cm^-2,该值远高于传统热压烧结法制备的发射电流密度．因此,本文该方法制备的Pr1-xCexB6多晶块体具有良好的力学性能和发射性能,作为热阴极材料将会有很好的应用前景．     

Determination of bakkenolide A in rat plasma using liquid chromatography/tandem mass spectrometry and its application to a pharmacokinetic study

A sensitive rapid analytical method was established and validated to determine the bakkenolide A (BA) in rat plasma. This method was further applied to assess the pharmacokinetics of BA in rats receiving a single dose of BA. Liquid chromatography tandem mass spectrometry in multiple reaction monitoring mode was used in the method, and costundide was used as internal standard. A simple protein precipitation based on methanol was employed. The combination of a simple sample cleanup and short chromatographic running time (2.4?min) increased the throughput of the method substantially. The method was validated over the range of 1-1000?ng/mL with a correlation coefficient?>?0.99. The lower limit of quantification was 1?ng/mL for BA in plasma. Intra- and inter-day accuracies for BA were 93-112% and 103-104%, respectively, and the inter-day precision was less than 15%. After a single oral dose of 20?mg/kg of BA, the mean peak plasma concentration (C(max) ) of BA was 234.7?±?161?ng/mL at 0.25?h. The area under the plasma concentration-time curve (AUC(0-24 h) ) was 535.8?±?223.7?h·ng/mL, and the elimination half-life (T(1/2) ) was 5.0?±?0.36?h. In case of intravenous administration of BA at a dosage of 2?mg/kg, the area under the plasma concentration-time curve (AUC(0-24 h) ) was 342?±?98 h?ng/mL, and the elimination half-life (T(1/2) ) was 5.8?±?0.7?h. Based on the results, the oral bioavailability of BA in rats at 20?mg/kg is 15.7%. Copyright ? 2012 John Wiley & Sons, Ltd.