Supramolecular Materials: Self-Organized Nanostructures

Miniaturized triblock copolymers have been found to self-assemble into nanostructures that are highly regular in size and shape. Mushroom-shaped supramolecular structures of about 200 kilodaltons form by crystallization of the chemically identical blocks and self-organize into films containing 100 or more layers stacked in a polar arrangement. The polar supramolecular material exhibits spontaneous second-harmonic generation from infrared to green photons and has an adhesive tape-like character with nonadhesive-hydrophobic and hydrophilic-sticky opposite surfaces. The films also have reasonable shear strength and adhere tenaciously to glass surfaces on one side only. The regular and finite size of the supramolecular units is believed to be mediated by repulsive forces among some of the segments in the triblock molecules. A large diversity of multifunctional materials could be formed from regular supramolecular units weighing hundreds of kilodaltons.     

Curving and frustrating flatland

Two polymer chains that occupy equal volumes when covalently linked together at one end self-assemble into an alternating lamellar morphology that has a characteristic period dictated by the molecular weight. When such copolymers are confined within alumina membranes that have cylindrical pores with diameters comparable to the repeat period, the interaction of the blocks with the confining walls and the imposed curvature induces a morphological transformation to relieve the constraints. Here, we show a lamella-to-toroid transition, captured through the dissolution of the surrounding membrane.     

Atomic-level models of the bacterial carboxysome shell

The carboxysome is a bacterial microcompartment that functions as a simple organelle by sequestering enzymes involved in carbon fixation. The carboxysome shell is roughly 800 to 1400 angstroms in diameter and is assembled from several thousand protein subunits. Previous studies have revealed the three-dimensional structures of hexameric carboxysome shell proteins, which self-assemble into molecular layers that most likely constitute the facets of the polyhedral shell. Here, we report the three-dimensional structures of two proteins of previously unknown function, CcmL and OrfA (or CsoS4A), from the two known classes of carboxysomes, at resolutions of 2.4 and 2.15 angstroms. Both proteins assemble to form pentameric structures whose size and shape are compatible with formation of vertices in an icosahedral shell. Combining these pentamers with the hexamers previously elucidated gives two plausible, preliminary atomic models for the carboxysome shell.     

机构连接点的分类及速度分析

对单自由度系统和两个自由度系统连接点进行分类分析两构件在连接点上的速度，第一类连接点是两构件以铰链相连，这类连接点，两构件在连接点上具有相同的速度，第二类连接点，两构件不是以铰链相连，连接点随构件的运动而变化，此类连接点，两构件在连接点具有不同的速度。     

Laser Rapid Prototyping of Photonic Band-Gap Microstructures

Three-dimensional periodic microstructures of aluminum oxide, which are important for creating photonic band-gap structures (PBGs), were fabricated by laser rapid prototyping by means of laser-induced direct-write deposition from the gas phase. The structures consisted of layers of parallel rods forming a face-centered tetragonal lattice with lattice constants of 66 and 133 micrometers. These structures showed transmission minima centered around 4 terahertz (75 micrometers) and 2 terahertz (150 micrometers), respectively. PBGs will allow precise control of the optical properties of materials, including lasers without threshold.     

卷烟滤嘴中三醋酸甘油酯向主流烟气的转移研究

[目的]探索卷烟滤嘴中三醋酸甘油酯向卷烟主流烟气的转移情况。[方法]将4种施加了不同含量的三醋酸甘油酯滤棒切成4份作为滤嘴卷制卷烟,考察卷烟滤嘴中三醋酸甘油酯的含量与其卷烟制品主流烟气中的三醋酸甘油酯含量的关系。[结果]随着滤棒的三醋酸甘油酯施加比例从3.06%增加到10.35%,三醋酸甘油酯转移到烟气中的量也随之提高,但转移率却由10.41%下降到4.43%。[结论]该研究为了解滤嘴中三醋酸甘油酯在卷烟主流烟气中的转移情况提供了依据。     

Polymer vesicles

Vesicles are microscopic sacs that enclose a volume with a molecularly thin membrane. The membranes are generally self-directed assemblies of amphiphilic molecules with a dual hydrophilic-hydrophobic character. Biological amphiphiles form vesicles central to cell function and are principally lipids of molecular weight less than 1 kilodalton. Block copolymers that mimic lipid amphiphilicity can also self-assemble into vesicles in dilute solution, but polymer molecular weights can be orders of magnitude greater than those of lipids. Structural features of vesicles, as well as properties including stability, fluidity, and intermembrane dynamics, are greatly influenced by characteristics of the polymers. Future applications of polymer vesicles will rely on exploiting unique property-performance relations, but results to date already underscore the fact that biologically derived vesicles are but a small subset of what is physically and chemically possible.     

Plastic and moldable metals by self-assembly of sticky nanoparticle aggregates

Deformable, spherical aggregates of metal nanoparticles connected by long-chain dithiol ligands self-assemble into nanostructured materials of macroscopic dimensions. These materials are plastic and moldable against arbitrarily shaped masters and can be thermally hardened into polycrystalline metal structures of controllable porosity. In addition, in both plastic and hardened states, the assemblies are electrically conductive and exhibit Ohmic characteristics down to approximately 20 volts per meter. The self-assembly method leading to such materials is applicable both to pure metals and to bimetallic structures of various elemental compositions.     

Modulation of rod-cone coupling by light

Although electrical coupling between rods and cones in the retina has been assumed to be static, it has now been shown that rod-cone coupling can be strengthened by light. Increment threshold measurements reveal that cone input to rods increases progressively as background light becomes brighter. Current injection into cones produces larger responses in adjacent rods in the presence of background light than in darkness. Weak coupling under dark-adapted conditions facilitates synaptic transmission of small rod signals, and strong coupling under light-adapted conditions enhances transmission of large cone signals.     

Monodisperse FePt nanoparticles and ferromagnetic FePt nanocrystal superlattices

Synthesis of monodisperse iron-platinum (FePt) nanoparticles by reduction of platinum acetylacetonate and decomposition of iron pentacarbonyl in the presence of oleic acid and oleyl amine stabilizers is reported. The FePt particle composition is readily controlled, and the size is tunable from 3- to 10-nanometer diameter with a standard deviation of less than 5%. These nanoparticles self-assemble into three-dimensional superlattices. Thermal annealing converts the internal particle structure from a chemically disordered face-centered cubic phase to the chemically ordered face-centered tetragonal phase and transforms the nanoparticle superlattices into ferromagnetic nanocrystal assemblies. These assemblies are chemically and mechanically robust and can support high-density magnetization reversal transitions.     

How does the toad flip its tongue? Test of two hypotheses

Two conflicting hypotheses purport to explain the mechanism generating the lingual flip in frogs. The first suggests that the intrinsic tongue muscles are stiffened, rotate over the symphysis and catapult the soft tissues; the second suggests that the hyoid suddenly moves forward and transfers its momentum to propel the tongue. High-speed cinematography and synchronized electromyography show that the tongue is rotated over the symphysis by a complex of rods formed from stiffened intrinsic tongue muscles. As the flip occurs even when the hyoid is immobilized, the hyoid momentum hypothesis does not apply. The tongue is then propelled by sets of fibers locked into connective tissues. With activation, these become rigid rods that form a muscular ballista.     

杉木木材/蒙脱土纳米复合材料的结构和表征

该文预先合成水溶性酚醛树脂作为中间介质,通过加压浸渍处理制备了杉木木材/蒙脱土纳米复合材料(WMNC),采用XRD、SEM、FTIR、TG-DTA等分析手段对WMNC的结构特性进行了表征.结果表明:①由于部分蒙脱土剥离片层进入了杉木木材细胞壁,WMNC中杉木木材的结晶度降低.②由于蒙脱土改性、树脂分子对蒙脱土的插层以及木材浸渍处理过程等的差异,蒙脱土在WMNC中的大小、形态和分布具多样性.蒙脱土填充的不均匀性,与杉木木材本身的渗透变异性相关.WMNC中的蒙脱土,部分填充于木材细胞腔等大孔隙,部分附着在木材细胞腔内壁,部分进入了细胞壁.③WMNC的缔合羟基增多,醚键大量增多,蒙脱土与杉木木材可能存在氢键或化学键结合.④WMNC的热分解历程改变,热性能提高,起始分解温度降低,高温区的热解失重显著减少,在一定程度上体现了无机复合组分蒙脱土纳米片层的纳米复合效应.      

Goldfish retina: sign of the rod input in opponent color ganglion cells

After light adaptation, all "on-center" ganglion cells in the dark became "red on-center," and all "off-center" cells turned into "red off-center" cells. On a chance basis, this similitude of effect between the rods and the red cones in opponent color cells was not expected. These findings indicate that in the goldfish there is some similarity between the connections of the rods and of the long-wavelength cones.     

Photoproduction of proton gradients with pi-stacked fluorophore scaffolds in lipid bilayers

Rigid p-octiphenyl rods were used to create helical tetrameric pi-stacks of blue, red-fluorescent naphthalene diimides that can span lipid bilayer membranes. In lipid vesicles containing quinone as electron acceptors and surrounded by ethylenediaminetetraacetic acid as hole acceptors, transmembrane proton gradients arose through quinone reduction upon excitation with visible light. Quantitative ultrafast and relatively long-lived charge separation was confirmed as the origin of photosynthetic activity by femtosecond fluorescence and transient absorption spectroscopy. Supramolecular self-organization was essential in that photoactivity was lost upon rod shortening (from p-octiphenyl to biphenyl) and chromophore expansion (from naphthalene diimide to perylene diimide). Ligand intercalation transformed the photoactive scaffolds into ion channels.     

带茎采烤对上部烟叶产质量及采烤成本的影响对比分析

本研究将带茎采烤与上部6片烟叶一次性摘叶编杆烘烤、常规采烤烟叶产质量及采烤成本进行对比分析,结果表明：带茎采烤烟叶各化学指标均处于适宜范围,其烤后烟叶总植物碱显著低于常规采烤,总糖含量显著高于其他两个处理;带茎采烤烤后烟叶的外观质量和感官质量在三个处理中均为最优,带茎采烤烤后烟叶油分、柔软度、颜色和色度以及香气质、香气量均有提升;带茎采烤处理产量低于其他两个处理,但烤后烟叶均价远高于另外两个处理,综合效益比上部6片烟叶一次性摘叶编杆烘烤、常规采烤分别高出1538.95元/房、1089.40元/房。     

Building programmable jigsaw puzzles with RNA

One challenge in supramolecular chemistry is the design of versatile, self-assembling building blocks to attain total control of arrangement of matter at a molecular level. We have achieved reliable prediction and design of the three-dimensional structure of artificial RNA building blocks to generate molecular jigsaw puzzle units called tectosquares. They can be programmed with control over their geometry, topology, directionality, and addressability to algorithmically self-assemble into a variety of complex nanoscopic fabrics with predefined periodic and aperiodic patterns and finite dimensions. This work emphasizes the modular and hierarchical characteristics of RNA by showing that small RNA structural motifs can code the precise topology of large molecular architectures. It demonstrates that fully addressable materials based on RNA can be synthesized and provides insights into self-assembly processes involving large populations of RNA molecules.     

Topology of the outer segment membranes of retinal rods and cones revealed by a fluorescent probe

When N,N'-didansyl cystine binds to the cell membranes of vertebrate rods and cones its fluorescence efficiency increases about 20-fold. The entire outer segments of living cones become brilliantly fluorescent. Stained live rods, as well as most freshly detached outer segments, are only weakly fluorescent, but they become brightly fluorescent within a few seconds if their plasma membranes are osmotically ruptured. The difference in staining of rod and cones suggests that disk membranes of rods are not continuous with the plasma membranes are osmotically ruptured. The difference in staining of rod and cones plasma membrane on outer segments of photoreceptors in electrophysiological and biochemical experiments, and to study the infolding pattern of rod and cone disks.     

新疆玉米产区47个主栽玉米品种抗虫性评价

【目的】筛选评价玉米抗虫(玉米螟)品种,为玉米螟绿色防控及害虫防治提供依据。【方法】对比分析第一代玉米螟和第二代玉米螟的田间百株落卵量、百株幼虫量、百秆为害蛀道长及被害株率等指标,评价新疆47个主栽玉米品种的抗螟性差异。【结果】供试主栽玉米品种抗虫性存在显著差异,其中16W2T118的田间为害最轻、抗虫能力最佳,其百株幼虫量、百株为害蛀道长、被害株率依次为25头/百株、90 cm/百株、20%,其次分别是华美1号、DK517、九圣禾692抗螟性较好,其百株幼虫量、百株为害蛀道长及被害株率依次为40头/百株、265 cm/百株、40%,50头/百株、245 cm/百株、40%,60头/百株、250 cm/百株、45%。五谷310、KWS6333、富友968、宁玉525等品种抗螟性一般。金庆202则为害最为严重、抗虫水平最低,其百株幼虫量、百株为害蛀道长、被害株率依次为195头/百株、875 cm/百株、90%。金庆1号、新玉29号等品种的抗螟性整体较差。【结论】参试的47个品种中16W2T118、DK517、九圣禾692、华美1号等品种抗虫综合表现较优,金庆1号、新玉29号等品种抗虫水平较差,生产上可优先选择种植抗螟较优的品种,避免种植抗螟较差的品种,可较好的实现玉米螟的自然控制。     

Discovery of a Frank-Kasper sigma phase in sphere-forming block copolymer melts

Sphere-forming block copolymers are known to self-assemble into body-centered cubic crystals near the order-disorder transition temperature. Small-angle x-ray scattering and transmission electron microscopy experiments on diblock and tetrablock copolymer melts have revealed an equilibrium phase characterized by a large tetragonal unit cell containing 30 microphase-separated spheres. This structure, referred to as the sigma (σ) phase by Frank and Kasper more than 50 years ago, nucleates and grows from the body-centered cubic phase similar to its occurrence in metal alloys and is a crystal approximant to dodecagonal quasicrystals. Formation of the σ phase in undiluted linear block copolymers (and certain branched dendrimers) appears to be mediated by macromolecular packing frustration, an entropic contribution to the interparticle interactions that control the sphere-packing geometry.     

应用雷达系统遥测低气压层化学成分

应用雷达系统测定污染气体旋转分子光谱共夺频率的超高频范围,从而解决遥测低气压层的化学成分。本对参数和气体污染动力学的测定方法进行了研究。通过综合考虑雷达信息和适合实际情况的吸收线特性来进行测定。对雷达系统的技术潜力做了评估。