Hierarchical and helical self-assembly of ADP-ribosyl cyclase into large-scale protein microtubes

Proteins are macromolecules with characteristic structures and biological functions. It is extremely challenging to obtain protein microtube structures through self-assembly as proteins are very complex and flexible. Here we present a strategy showing how a specific protein, ADP-ribosyl cyclase, helically self-assembles from monomers into hexagonal nanochains and further to highly ordered crystalline microtubes. The structures of protein nanochains and consequently self-assembled superlattice were determined by X-ray crystallography at 4.5 A resolution and imaged by scanning electron microscopy. The protein initially forms into dimers that have a fixed size of 5.6 nm, and then, helically self-assembles into 35.6 nm long hexagonal nanochains. One such nanochain consists of six dimers (12 monomers) that stack in order by a pseudo P6(1) screw axis. Seven nanochains produce a series of large-scale assemblies, nanorods, forming the building blocks for microrods. A proposed aging process of microrods results in the formation of hollow microstructures. Synthesis and characterization of large scale self-assembled protein microtubes may pave a new pathway, capable of not only understanding the self-assembly dynamics of biological materials, but also directing design and fabrication of multifunctional nanobuilding blocks with particular applications in biomedical engineering.     

Sacrificial templating synthesis of hematite nanochains from [Fe18S25](TETAH)14 nanoribbons: their magnetic, electrochemical, and photocatalytic properties

Unique hematite nanochains self-assembled from α-Fe(2)O(3) nanoparticles can be synthesized by thermal decomposition of [Fe(18)S(25)](TETAH)(14) as an appropriate nanoribbon precursor (TETAH = protonated triethylenetetramine). Magnetic studies have revealed greatly enhanced coercivity of the 1D hematite nanochains compared with that of dispersed α-Fe(2)O(3) nanoparticles at low temperature, which may be attributed to their increased shape anisotropy and magnetocrystalline anisotropy. The photocatalytic properties of the hematite nanochains have been studied, as well as their electrochemical properties as cathode materials of lithium-ion batteries. The results have shown that both properties are dependent on the BET specific surface areas of the 1D hematite nanochains.     

Self-assembled silver nanochains for surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) integrates high levels of sensitivity with spectroscopic precision and has tremendous potential for chemical and biomolecular sensing. The key to the wider application of Raman spectroscopy using roughened metallic surfaces is the development of highly enhancing substrates for analytical purposes. Here, we demonstrate a simple strategy for self-assembling silver nanochains on glass substrates for sensitive SERS substrates. The chain length of short Ag nanochains can be controlled by adjusting the concentration of cetyltrimethylammonium bromide (CTAB) and 11-mercaptoundecanoic acid (MUA). CTAB with appropriate concentration serves as the "glue" that can link the {100} facets of two neighboring Ag nanoparticles. MUA is found to be effective in "freezing up" the aggregation of Ag short chains and preventing them from further aggregating into a long chainlike network structure. The surface plasmon bands can be tuned over an extended wavelength range by controlling the length of the nanochains. The Ag monolayer, mainly composed of four-particle nanochains, exhibited the maximum SERS enhancement factor of around 2.6 x 108, indicating that a stronger SERS enhancement can be obtained in these interstitial sites of chainlike aggregated Ag nanoparticles.     

Selective and Sensitive Nitrite Sensor Based on Glassy Carbon Electrode Modified by Silver Nanochains

Herein, we report a facile method for the synthesis of silver nanochains (Ag nanochains) using pyridine as growth directing agent and citrate ions as capping agents in alkaline medium. The characterization of the synthesized high aspect ratio Ag nanochains was accomplished with the help of Transmission Electron Microscopy (TEM) and High Resolution Transmission Electron Microscopy (HRTEM) which demonstrates the thickness below 100 nm. Crystalline nature of the synthesized Ag nanochains was investigated using X‐ray diffractrometry. A sensitive electrochemical nitrite sensor was assembled using synthesized Ag nanochains as electrode modifier. An improved cyclic voltammetric response for the oxidation of nitrite ions was witnessed at the modified GCE surface in comparison to bare GCE in Britton Robinson (BR) buffer (pH 4). The influence of pH on the oxidation peak current of nitrite ions was also examined using cyclic voltammetry. The electrocatalytic oxidation currents attained through amperometric measurements at Ag nanochains modified GCE were linearly dependent on the concentration of nitrite ions in the two ranges of 0.5–7.5 µM, 5–480 µM. Linear calibration plots of Ip vs. concentration of nitrite were also constructed at the proposed sensor using square wave voltammetry and differential pulse voltammetry. The proposed sensing strategy was successfully employed for the determination of nitrite in water samples with excellent recoveries.     

Fabrication of one-dimensional Fe3O4/P(GMA-DVB) nanochains by magnetic-field-induced precipitation polymerization

One-dimensional (1D) magnetic Fe(3)O(4)/P(GMA-DVB) peapod-like nanochains have been successfully synthesized by magnetic-field-induced precipitation polymerization using Fe(3)O(4) as building blocks and P(GMA-DVB) as linker. The Fe(3)O(4) microspheres without surface modification can be arranged with the direction of the external magnetic field in a line via the dipolar interaction between Fe(3)O(4) microspheres and linked permanently via P(GMA-DVB) coating during precipitation polymerization. The length of peapod-like nanochains can be controlled by magnetic field intensity, and the thickness of polymer shell can be tuned by the amount of monomers. Magnetic measurement revealed that these 1D peapod-like nanochains showed highly magnetic sensitivity. In the presence of magnetic field, 1D magnetic Fe(3)O(4)/P(GMA-DVB) peapod-like nanochains can be oriented and aligned along the direction of external magnetic field.     

Highly ordered superlattices from polydisperse Ag nanoparticles: a comparative study of fractionation and self-correction

We have examined two different routes to construct highly ordered two- or three-dimensional (2D or 3D) superlattice structures from hydrophilic polydisperse mercaptosuccinic acid (MSA)-modified Ag nanoparticles of the average size of 2.5 nm. First, polydisperse particles were fractionized by the polyacrylamide gel electrophoresis (PAGE) method. Due to the size-dependent migration under the electric field, the particles were isolated into a series of gel bands and each band contained particles with significantly narrow size distribution. Subsequent to phase transfer into chloroform by cationic surfactant, long-range 2D superlattices were simultaneously formed on the substrate upon evaporation of chloroform. Second, 3D superlattices were directly grown at an air-water interface from the polydisperse bulk dispersion by diffusion of HCl vapor without any pretreatment for the size narrowing. The influence of diffusion rate of HCl was also studied. The achievement of 3D superlattices via this route was ascribed as a long-time self-correction process. Furthermore, it was revealed that the superlattice structures obtained by the above two procedures exhibited distinct features though the starting material was the same MSA-Ag nanoparticles. The surface distance of core between component particles, the orientation of particles inside the superlattice, and the process of superlattice formation were comprehensively studied. We confirmed that each growth process depended on a corresponding self-assembly mechanism.     

Gold nanoparticle multilayer films based on surfactant films as a template: preparation, characterization, and application

Highly ordered gold nanoparticle multilayer films were achieved conveniently using didodecyldimethylammonium bromide (DDAB) films as a template. The template was produced by casting DDAB chloroform solution onto the surface of a (3-aminopropyl)trimethoxysilane-modified indium tin oxide substrate and then evaporating the organic solvent. Gold nanoparticle multilayer films were prepared by soaking the template in 2.6 nm colloidal gold solution for 120 min. The well-ordered superlattice structure of the DDAB template and the gold nanoparticle multilayer films was identified by x-ray diffraction. The characterizations of the gold nanoparticle multilayer films by UV-vis spectroscopy, atomic force microscopy, and cyclic voltammerty were described in detail. The application of the as-prepared gold nanoparticle multilayer films in surface-enhanced Raman spectroscopy (SERS) was investigated by using Rhodamine 6G as a probe molecule. It was found that the colloidal gold nanoparticle multilayer films exhibit remarkable enhancement ability and can be used as SERS substrates.     

Melting and Sintering of a Body-Centered Cubic Superlattice of PbSe Nanocrystals Followed by Small Angle X-ray Scattering

The structural evolution of a body-centered cubic (bcc) superlattice of 6.6 nm diameter organic ligand-coated PbSe nanocrystals was studied in situ by small angle X-ray scattering (SAXS) as it was heated in air from room temperature to 350°C. As it was heated above room temperature, the superlattice contracted slightly, but maintained bcc structure up to 110°C. Once the temperature rose above 110°C, the superlattice began to disorder, by first losing long-range translational order and then local positional order. At temperatures exceeding 168°C, the nanocrystals sintered and oxidized, transforming into PbSeO(3) nanorods.     

Surfaces and interfaces in short-period GaAs/AlAs superlattices

Photoelectron spectroscopy, in particular the angular resolved photoemission excited by ultraviolet radiation (ARUPS), provides the most direct experimental information about the electron structure of crystals, both of the bulk and of the low-index surfaces. The sensitivity of the method, as well as its difficulties, when applied to GaAs/AlAs superlattices are described. The new periodicity of these man-made crystals in the direction of their growth (e.g., in the layer-by-layer growth in molecular beam epitaxy), is responsible for opening of the new energy gaps (so-called minigaps) in the electron energy bands of crystals forming the superlattice. In addition to the well-known confinement of electrons at the valence and conduction band edges in long-period superlattices, the electron confinement to the interfaces has also been found in the vicinity of minigaps in short-period superlattices. The role of this confinement in the intensities of electrons photoemitted from superlattice surfaces is discussed. Superlattices with different thicknesses in the topmost layers represent systems with a simple change of the surface atomic structure. The predictions of one-dimensional models about a change of the surface-state energy within the band gap with a change of crystal potential termination are tested for the ideally terminated (1 0 0) surface of a very thin superlattice (GaAs)₂(AlAs)₂. The results of the energy distributions of photoemitted electrons, calculated in the one-step model of photoemission, show that the ARUPS experimental observation of surface-state shifts should be possible, at least in larger minigaps. The results indicate the possibility of a straightforward tuning of the electronic structure of the superlattice surface by geometrical means.     

Novel 1D Ni–Ag composition nanostructure: Synthesis,properties and antioxygenation improvement

Nickel nanochains assembled with submicrometer-sized flowers were synthesized through a mild hydrothermal method without any template and surfactant. Subsequently, nickel–silver metal composition nanostructures were also prepared by taking advantage of reducing property of nickel metal. The resulting chains superstructures were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and the thermogravimetric analysis (TGA) measurements. This synthesis of such hierarchical structures implies a simple and inexpensive way to prepare bimetallic composite superstructures on a large scale. Furthermore, antioxygenation properties of these bimetallic composites could be improved drastically.     

Displacement Plating of a Mesoporous Pt Skin onto Co Nanochains in a Low‐Concentration Surfactant Solution

Mesoporous Pt skins on Co nanochains are successfully synthesized by a displacement reaction between Pt species and a Co support with the assistance of surfactant micelles. The assembly of surfactant micelles on Co nanochains plays a key role in the formation of mesoporous Pt layers. The evolution of the mesoporous Pt layers is carefully studied at different time intervals. As the reaction time increases, the mesoporous Pt layers become thicker, and well‐defined mesoporous structures gradually develop. The obtained mesoporous Pt skin exhibits high activity and superior CO tolerance in the electro‐oxidation reaction of methanol. The mesoporous Pt skin also shows very high durability, and only a 20.2 % loss of the Pt electrochemical surface area is found even after a harsh durability test.     

Tamm surface states in semiconductor superlattices

A short review is presented of some theoretical investigations of the occurrence, position and localization properties of a single electronic state (Tamm surface state) appearing inside mini-gaps and being localized near the superlattice/substrate interface (i.e., at the superlattice internal surface). The article is restricted to the gallium-arsenide-type superlattices, represented by a terminated Kronig-Penney-type model, and studied via the direct-matching procedure. Special attention is paid to the effect of the location of the superlattice surface.     

磁场诱导沉淀聚合制备一维Fe3O4/P（MAA-DVB）纳米链

采用溶剂热法制备了单分散Fe3O4纳米粒子,以甲基丙烯酸（MAA）和二乙烯基苯（DVB）为聚合单体,在沉淀聚合过程中通过磁场诱导自组装制备了一维高磁响应性永久连接的Fe3O4/P（MAA-DVB）纳米链.采用扫描电镜（SEM）,透射电镜（TEM）,X射线衍射仪（XRD）,热重分析（TGA）及振动样品磁强计（VSM）等对其形貌、磁含量和磁响应性等进行了分析表征.结果表明,该法制备的一维Fe3O4/P（MAA-DVB）纳米链的磁含量为91%时,其比饱和磁化强度为72emu/g.在外磁场存在条件下,一维Fe3O4/P（MAA-DVB）纳米链将按外界磁场的方向取向.此外,每个豆荚内的Fe3O4纳米粒子规则的排列在一条线上,并通过P（MAA-DVB）聚合物使其均匀分布.     

Effect of halo substitution on the geometry of arenethiol films on Cu(111)

Incomplete coverages of p-fluorothiophenol, p-chlorothiophenol, and p-bromothiophenol form ordered islands on a Cu(111) surface even at low temperatures. The complexity of the molecular patterns increases from a simple (3 x 4) superlattice to a honeycomb (8 x 8)R19 degrees structure with increasing substituent electronegativity. We propose a model based on quadrupolar intermolecular interactions to account for this observation.     

Template ordered open-grid arrays of paired endohedral fullerenes

Developing useful molecular systems, such as planar networks for novel molecular electronics, requires the ability to control the way molecules assemble at surfaces. Here we report how an oxide crystal surface can be used as a template to controllably order endohedral fullerenes, Er3N@C80, into two-dimensional (2D) open-grid arrays. The crystal surface is made of highly ordered oxide nanostructures which self-assemble on the surface of SrTiO3(001). This method of molecular ordering can be applied to other fullerenes and has the potential to provide a basis for developing a wide range of molecular architectures.     

硅钨杂多酸在中孔全硅分子筛HMS上的固载及其催化性能

用十二烷基胺代替传统的季铵盐合成了中孔全硅分子筛ＨＭＳ，并将硅钨杂多酸浸渍固载在ＨＭＳ上，用ＸＲＤ，ＦＴ－ＩＲ以及ＮＨ３－ＴＰＤ等手段对ＨＭＳ及不同负载量的焙烧温度的负载论剂进行了表征，即使在固载量为５０％的ＳｉＷ１２／ＨＭＳ中，ＳｉＷ１２仍保持其Ｋｅｇｇｉｎ结构产均匀分布在载体表面上，没有ＳｉＷ１２晶相生成，同时，在气－固相反应体系中研究了固载在ＨＭＳ上的ＳｉＷ１２在合成乙酸丁酯中的催化性能，实     

Orientational ordering of the second layer of C60 molecules on Au(111)

We have studied the orientational ordering of the second layer of C(60) molecules on Au(111) using scanning tunnelling microscopy (STM) at 77 K. The orientation of individual molecules within the second layer follows a regular pattern, giving rise to a 2 × 2 superlattice. The long-range order of the 2 × 2 lattice depends on the structure of the first molecular layer with the best ordering found inside the R14° domain. The second layer formed on top of the contrast-disordered R30° domain consists of patches of bright and dim molecules. The contrast between bright and dim patches shows a clear dependence on the sample bias. This bias-dependent contrast is explained by considering the contributions to tunnel current from HOMO and LUMO mediated electron transfer processes. Scanning tunnelling spectroscopic measurement reveals the narrowing of the HOMO-LUMO gap for the layer of molecules in direct contact with the Au(111) substrate.     

Electronic structure of some mesoscopic systems: I. Semiconductor superlattices

As an example of a mesoscopic system, a Kronig-Penney-type model of a semi-infinite GaAs/Ga_1−xAl_xAs superlattice is considered. The effect of the superlattice termination on the formation of a surface state as well as on the density-of-states distributions is discussed. Varying the position of the superlattice surface (i.e., superlattice/substrate interface) within a superlattice period influences strongly the appearance and position of surface states. They occur in particular minigaps for some ranges of the outermost layer thickness only.     

Spacer effect of novel bifunctional organophosphorus monomers in metal-imprinted polymers prepared by surface template polymerization

The interfacial activity and the molecular structure of functional monomers are critical factors that determine the success of synthesizing metal-imprinted polymers by surface template polymerization. From this point of view, first we prepared three distinct novel bifunctional organophosphorus monomers that are interspaced, in each case, by an alkyl spacer having a specific length. Each monomer carries two phosphonic acid groups and two aromatic groups in its molecular structures. Further, by using the synthesized bifunctional monomers, we prepared highly selective Zn(II)-imprinted polymers by the surface template polymerization initiated from a water-in-oil emulsion. To evaluate the template effect, we conducted diagnostic adsorption studies on Zn(II)-imprinted and unimprinted polymers with zinc ions. A high interfacial activity was found to be required for the functional monomers to create the predominant template effect. It became clear that Zn(II)-imprinted polymers having bifuctional monomers with 12-length alkyl chains (1,12-dodecanediol-O, O′-diphenyl phosphonic acid: DDDPA) yielded the best results. Moreover, analysis results of adsorption behavior supported a high-performance of the Zn(II)-imprinted polymers with DDDPA. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2727–2734, 1998     

Crystal growth of para-sexiphenyl on clean and oxygen reconstructed Cu(110) surfaces

The formation of crystalline para-sexiphenyl (6P) films on Cu(110) and Cu(110)-(2 × 1)O (Cu-O) has been studied by low energy electron diffraction, X-ray absorption spectroscopy and both in situ and ex situ X-ray diffraction methods to elucidate the transition from the initial monolayers to crystalline thin films. It is found that, for Cu-O, a single and, for Cu(110), a double wetting layer is formed which then acts as a template for the subsequent 3D crystal growth. For both substrates the orientation of the long molecular axes of the 6P molecules in the first layers is conserved for the molecules in the bulk crystals growing on them. The main difference between both systems is that on Cu-O the first monolayer assembles in a form close to that of a 6P bulk plane which can be easily continued by crystallites grown upon them, while on the Cu(110) surface the 6P mono- and bi-layers differ substantially from the bulk structure. The bi-layer forms a complex periodically striped phase. Thin 6P films grow with the 6P(203) crystal plane parallel to the Cu-O substrate surface. For this orientation, the 6P molecules are stacked in layers and the molecules demonstrate only one tilt of the mean molecular plane with respect to the sample surface. On clean Cu(110), a more complex 6P(629) plane is parallel to the substrate surface and this orientation is likely a consequence of the super-molecular long-range periodicity of the second molecular layer striped phase.