Cross-Module Enoylreduction in the Azalomycin F Polyketide Synthase

The colinearity of canonical modular polyketide synthases, which creates a direct link between multienzyme structure and the chemical structure of the biosynthetic end-product, has become a cornerstone of knowledge-based genome mining. Herein, we report genetic and enzymatic evidence for the remarkable role of an enoylreductase in the polyketide synthase for azalomycin F biosynthesis. This internal enoylreductase domain, previously identified as acting only in the second of two chain extension cycles on an initial iterative module, is shown to also catalyze enoylreduction in trans within the next module. The mechanism for this rare deviation from colinearity appears to involve direct cross-modular interaction of the reductase with the longer acyl chain, rather than back transfer of the substrate into the iterative module, suggesting an additional and surprising plasticity in natural PKS assembly-line catalysis.     

基于偶氮苯衍生物的三阶非线性光开关性能的调控

偶氮苯衍生物因其具有特殊的共轭体系常用作光开关特性的三阶非线性光学（NLO）开关材料,但有部分带有特殊基团的偶氮类分子在一般条件下无法显示其性能.然而,这类分子在被调节之后能展示出优异的光控的NLO开关性能.以无光控的NLO开关性能的5-（N-4-偶氮苯基）氨甲基间苯二甲酸为研究对象,并对其潜在的光控NLO开关性能进行调控.经过调节后的这类分子在光照条件下能顺利地经历可逆的顺反异构化反应,且产生三阶非线性性能的转换.其Z-扫描实验结果显示处于反式构型的材料展示出反饱和吸收和自散焦特性;在光照之后,这类材料转化为顺式构型并展现出饱和吸收和自聚焦行为.三阶NLO性能的转换是由于材料的结构发生转变其内部电子产生重排,使得它们在激光刺激下产生不同的响应机制.     

Synthesis and Herbicidal Activity of Muti‐Substituted Pyrido[4,3‐d]pyrimidin‐4‐ones

A series of novel muti‐substituted pyrido[4,3‐d]pyrimidin‐4‐one derivatives 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j , 5k , 5l were designed and synthesized by the muti‐step reaction. N,S‐acetal 1 reacted with acetyl acetamide in the presence of zinc nitrate to obtain muti‐substituted pyridine 2 , which reacted with triethyl orthoformate to give 8‐cyano‐5‐methyl‐7‐methylthio‐pyrido[4,3‐d]pyrimidin‐4‐one 3 ; the target compounds 5 were obtained in good yields by the oxidation of 3 with H₂O₂ in a catalytic amount of sodium tungstate then by the substitution with various substituted phenols. Their structures were confirmed by IR, ¹H NMR, EI‐MS, and elemental analyses. The preliminary bioassay indicated that some of them displayed moderate herbicidal activity against dicotyledonous weed Brassica campestris L. at the concentration of 100 mg/L. For example, compounds 5a , 5f , and 5g possessed 76.0%, 62.7%, and 60.2% inhibition against B. campestris at the concentration of 100 mg/L. Moreover, 5a exhibited 58.2% inhibition against B. campestris at the concentration of 10 mg/L.     

Transport properties and magnetoresistance in La0.8Te0.2MnO3/ZrO2 composites

The transport properties and magnetoresistance of electron-doped manganate / insulator composites (La_0.8Te_0.2MnO₃)_{1 - x}/(ZrO₂)_x (x=0, 0.3, and 0.5) are investigated. It is found that the metal-insulator transition temperature of this system shifts to a lower value as the ZrO₂ content increases. The introduction of ZrO₂ enhances both the domain scattering and electron relative scattering in the metal transport region. In the adiabatic small polaron hopping transport region, the thermal activation energy seems invariable regardless of the ZrO₂ content. The application of a magnetic field promotes the charge transportation capabilities of the composites, and the magnetoresistance is enhanced with an increase of the ZrO₂ content. This could be attributed to the more remarkable modification effect of magnetic field on ordering degree in the composites than in pure La_0.8Te_0.2MnO₃.     

Red top-emitting organic light-emitting device with improved efficiency and saturated color

In this work, characteristics of microcavity top-emitting red organic light-emitting device (TEROLED) having metallic electrodes had been examined. The TEOLED shows the higher efficiency in comparison with that of the bottom OLED. However, color variation with the increasing view angles is also observed. For the purpose of diminishing the blue-shift of resonant wavelength (RW) in the device with increasing view angle, the effect of out-coupling layer on the emission properties of the TEOLED is discussed in detail. Finally, the out-coupling layer was introduced in theory without sacrificing the efficiency through precise optical simulation.     

Superwetting Patterned Membranes with an Anisotropy/Isotropy Transition: Towards Signal Expression and Liquid Permeation

Superwetting membranes with responsive properties have attracted heightened attention because of their fine‐tunable surface wettability. However, their functional diversity is severely limited by the “black‐or‐white” wettability transition. Herein, we describe a coating strategy to fabricate multifunctional responsive superwetting membranes with SiO₂/octadecylamine patterns. The adjustable patterns in the responsive region are the key factor for functional diversity. Specifically, the coated part of the membrane displayed a superhydrophobicity/superhydrophilicity transition at different pH values, whereas the uncoated part exhibited invariant superhydrophilicity. On the basis of this anisotropy/isotropy transition, the membranes can serve as either responsive permeable membranes or signal‐expression membranes, thus enabling the responsive separation and permeation of liquids with satisfactory separation efficiency (>99.90 %) and flux (ca. 60 L m^?2 h), as well as real‐time liquid signal expression with alterable signals.     

Beam controller using nonlinear embedded optical transformation

Flexible and adjustable beam splitters, expanders/compressors and the cloak are presented based on a universal two-dimensional transformation formula for the embedded transformation optics. Nonlinear transformation results by the suggested formula under different conditions reveal several interesting phenomena and potential applications. All beam controllers are achieved by the nonlinear coordinate transformation.     

Phase-change behavior in Si/Sb80Te20 nanocomposite multilayer films

Phase-change behavior in Si/Sb₈₀Te₂₀ nanocomposite multilayer films were investigated by utilizing in situ resistance measurements. It was found that the crystallization temperature increased firstly with increasing Si layer thickness within the multilayer films, and then remained almost unchanged at 170°C. The multilayer films have the merits of both good thermal stability and fast phase-change speed. An increase in crystallization temperature by around 95°C was observed for the multilayer films when the Sb₈₀Te₂₀ layer thickness was reduced to 3 nm. Cross-sectional transmission electron microscopy (TEM) observations revealed that Si/Sb₈₀Te₂₀ nanocomposite multilayer films had layered structures with clear interfaces. The reversible phase change between set and reset states was verified in phase-change random access memory (PCRAM) cell based on [Si (1 nm)/Sb₈₀Te₂₀ (5 nm)]₁₇ multilayer film.     

Magnetic characterization of dual phase FeZrB soft magnetic alloy

The magnetic properties and the annealing process of Fe₇₈Zr₇B₁₅ amorphous ribbons are investigated by X-ray diffraction (XRD), differential scanning calorimetry, and vibrating sample magnetometer. The fully amorphous structure of the as-quenched ribbons is confirmed by the XRD pattern. The Curie temperature and the saturation magnetization M_s of the ribbons are 305 °C and 124.3 emu/g, respectively. Annealing at 550 °C can result in an increase in M_s with annealing time due to the increasing crystallized volume fraction of α-Fe phase. The optimized annealing process is established at 550 °C for 20-30 min with maximum M_s of 146.6 emu/g. The morphology of the ribbons annealed at 550 °C is observed by scanning electron microscopy, showing that nanocrystalline α-Fe grains are dispersed in an amorphous matrix.     

The electronic transport properties in C60 molecular devices with different contact distances

By applying non-equilibrium Green?s functions in combination with the density-functional theory, we investigate the transport behavior of molecular devices composed by metal electrode-C₆₀ molecule-metal electrode. Our results show that the electronic transport properties are affected obviously by the different contact distances between the electrodes, and the tunneling current decreases approximately exponentially at a certain bias with the increasing of contact distances. The negative differential resistance is observed and the peak-to-valley ratio can be tuned by different contact distances. The mechanisms of the contact distance effect and the negative differential resistance behavior are proposed.