Lipid tubule self-assembly: length dependence on cooling rate through a first-order phase transition

The formation kinetics and self-assembly of multilamellar tubules of the diacetylenic phospholipid 1,2-bis(tricosa-10,12-diynoyl)-sn-glycerol-3-phosphocholine formed under controlled cooling rates were studied by x-ray diffraction and optical, atomic force, and scanning electron microscopy. Tubule formation was driven by a reversible first-order phase transition from an intralamellar, chain-melted L(alpha) phase to a chain-frozen L(beta), phase. These observations are the basis of a highly efficient method of tubule production in which tubule lengths can be controlled, between 1 and 100 micrometers, by varying the cooling rate. These tubules can be made in suspensions with 10 percent lipid by mass, far exceeding the lipid solubility limit.     

Supramolecular self-assembly of lipid derivatives on carbon nanotubes

Images of the assembly of surfactants and synthetic lipids on the surface of carbon nanotubes were obtained by transmission electron microscopy. Above the critical micellar concentration, sodium dodecyl sulfate (SDS) forms supramolecular structures made of rolled-up half-cylinders on the nanotube surface. Depending on the symmetry and the diameter of the carbon nanotube, we observed rings, helices, or double helices. Similar self-assemblies were also obtained with several synthetic single-chain lipids designed for the immobilization of histidine-tagged proteins. At the nanotube-water interface, permanent assemblies were produced from mixed micelles of SDS and different water-insoluble double-chain lipids after dialysis of the surfactant. Such arrangements could be further exploited for the development of new biosensors and bioelectronic nanomaterials.     

Hierarchical organization of modularity in metabolic networks

Spatially or chemically isolated functional modules composed of several cellular components and carrying discrete functions are considered fundamental building blocks of cellular organization, but their presence in highly integrated biochemical networks lacks quantitative support. Here, we show that the metabolic networks of 43 distinct organisms are organized into many small, highly connected topologic modules that combine in a hierarchical manner into larger, less cohesive units, with their number and degree of clustering following a power law. Within Escherichia coli, the uncovered hierarchical modularity closely overlaps with known metabolic functions. The identified network architecture may be generic to system-level cellular organization.     

Action of anionic and cationic nerve-blocking agents: experiment and interpretation

Barbiturates and anesthetics similar to procaine bind to phospholipids in vitro. The former increase the binding of calciumn to the phospholipids; the latter decrease it. The data can be correlated with the effects of these drugs Otl peripheral nerve. The nonpolar portion of the narcotic agents may lie between the lipid chains of the membrane, with the charged region in close approximation to the polar heads of the phospholipids.     

Direct redox regulation of F-actin assembly and disassembly by Mical

Different types of cell behavior, including growth, motility, and navigation, require actin proteins to assemble into filaments. Here, we describe a biochemical process that was able to disassemble actin filaments and limit their reassembly. Actin was a specific substrate of the multidomain oxidation-reduction enzyme, Mical, a poorly understood actin disassembly factor that directly responds to Semaphorin/Plexin extracellular repulsive cues. Actin filament subunits were directly modified by Mical on their conserved pointed-end, which is critical for filament assembly. Mical posttranslationally oxidized the methionine 44 residue within the D-loop of actin, simultaneously severing filaments and decreasing polymerization. This mechanism underlying actin cytoskeletal collapse may have broad physiological and pathological ramifications.     

Molecular self-assembly and nanochemistry: a chemical strategy for the synthesis of nanostructures

Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.     

DNA-templated self-assembly of protein arrays and highly conductive nanowires

A DNA nanostructure consisting of four four-arm junctions oriented with a square aspect ratio was designed and constructed. Programmable self-assembly of 4 x 4 tiles resulted in two distinct lattice morphologies: uniform-width nanoribbons and two-dimensional nanogrids, which both display periodic square cavities. Periodic protein arrays were achieved by templated self-assembly of streptavidin onto the DNA nanogrids containing biotinylated oligonucleotides. On the basis of a two-step metallization procedure, the 4 x 4 nanoribbons acted as an excellent scaffold for the production of highly conductive, uniform-width, silver nanowires.     

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.     

Synthesis of macrocyclic copolymer brushes and their self-assembly into supramolecular tubes

We report on an efficient route to design large macrocyclic polymers of controlled molar mass and narrow dispersity. The strategy is based on the synthesis of a triblock copolymer ABC, in which the long central block B is extended by two short A and C sequences bearing reactive antagonist functions. When reacted under highly dilute conditions, this precursor produces the corresponding macrocycle by intramolecular coupling of the A and C blocks. Chloroethyl vinyl ether was selected as the monomer for the central block B, because it can be readily derivatized into brushlike polymers by a grafting process. The corresponding macrocyclic brushes were decorated with polystyrene or randomly distributed polystyrene and polyisoprene branches. In a selective solvent for the polyisoprene branches, the macrocyclic brushes self-assemble into cylindrical tubes of up to 700 nanometers.     

Macroscopic hierarchical surface patterning of porphyrin trimers via self-assembly and dewetting

The use of bottom-up approaches to construct patterned surfaces for technological applications is appealing, but to date is applicable to only relatively small areas (approximately 10 square micrometers). We constructed highly periodic patterns at macroscopic length scales, in the range of square millimeters, by combining self-assembly of disk-like porphyrin dyes with physical dewetting phenomena. The patterns consisted of equidistant 5-nanometer-wide lines spaced 0.5 to 1 micrometers apart, forming single porphyrin stacks containing millions of molecules, and were formed spontaneously upon drop-casting a solution of the molecules onto a mica surface. On glass, thicker lines are formed, which can be used to align liquid crystals in large domains of square millimeter size.     

高速公路改扩建中的递阶智能控制

将递阶结构应用于高速公路多匝道的协调控制,建立了反应高速公路动态变化的数学模型,提出了多匝道的协调控制方法.通过佛开高速的交通调研,建立了佛开高速主线和匝道控制的仿真模拟系统.仿真结果表明,该方法能有效消除交通拥堵,改善交通状况.     

Immunoassay of androgen binding protein in blood: a new approach for study of the seminiferous tubule

Androgen binding protein, a secretory product of seminiferous tubules, was isolated by means of affinity chromatography. A radioimmunoassay was developed and used to identify androgen binding protein in rat plasma. The ability to measure a testicular protein in blood provides a new method for investigation of seminiferous tubular physiology.     

蜂胶对高脂血症大鼠血液和肝脏脂质的影响

测定和比较蜂胶水提液、醇提液对实验性高脂血症SD大鼠血液和肝脏脂质的影响. 结果表明:蜂胶醇提液和水提液均能有效抑制高脂血症SD大鼠血清中的甘油三酯(TG)、总胆固醇(TC)、低密度脂蛋白(LDL-C)、谷丙转氨酶(GPT)、谷草转氨酶(GOT)的升高,并且能有效抑制肝脏组织中的TC、TG、MDA的升高,但对血清中的高密度脂蛋白(HDL-C)、超氧化物歧化酶(SOD)、丙二醛(MDA)、一氧化氮(NO)的影响不明显;蜂胶醇提液能有效降低高脂血症SD大鼠的体重、肝重及肝指数,蜂胶水提液对体重、肝重及肝指数的影响则不显著. 表明蜂胶能够改善高脂血症大鼠的脂质代谢,并具有一定的抗氧化作用.     

Oxygen-carrying iridium complexes: kinetics, mechanism, and thermodynamics

The rates of oxygenation and deoxygenation of a series of iridium complexes increase and decrease, respectively, with increasing electron-releasing tendency of the anionic ligands (A) attached to the metal atom in the oxygencarrying compounds, [IrA(CO)(Ph(3)P)(2)]. Calculated heats of oxygenation (-DeltaH(2)(0)), related to Ir-O(2) bond energies, are proportional to the previously reported O-O bond lengths in the oxygen adducts, [O(2)IrA(CO)(Ph(3)P)(2)].     

农田水利投资的增收效应——基于层级收入与地区差异的分析

农村公共投资作为财政支农改革的重要内容,近年来在促进农业发展和农民增收方面的作用愈加凸显。基于2003—2016年的相关数据,实证研究了农田水利专项投资对农民收入的影响。结果表明:(1)在控制相关影响因素条件下,农田水利投资的增收效应主要体现在农民家庭经营性收入的增长,而难以成为拉动农民整体收入水平的有利因素。(2)农田水利建设投资在一定程度上挤出了财政对农民的补贴性或转移性支出,产生了收入“替代效应”。(3)异质性分析结果表明,农田水利专项投资的农业生产增收效应具有收入递增性和地区差异性。一方面,增收表现出边际递增态势,农民家庭经营性收入越高,农田水利投资的增收效果越强。另一方面,更依赖农业收入的地区,农田水利投资的增收效应越显著。依据本文得出结论,农田水利投资的增收效应还未趋于饱和,继续加大投资力度并优化农田水利支农资金结构,有助于深化财政支农改革,促进各地区农村均衡发展。