Tetragonal Array Research Articles

Assisted Self-Assembly of Nanoporous Ices via Carbon Nanomaterial Templates.

Self-assembly is a widely used synthetic method in nanoscience to assemble well-organized structures. Self-assembly processes usually occur in a water solvent environment. However, the self-assembly of water molecules is rarely studied. Herein, we show a strategy to fabricate porous ice via carbon nanomaterial-assisted self-assembly. Diverse frameworks of nanoporous ice are formed by using orthorhombic and tetragonal arrays of carbon nanotubes or carbon-atom chains as templates. In contrast to many bulk ices discovered in nature, nanoporous ices are shown to be stable only under negative pressure. Hence, nanoporous ices cannot be produced through the direct nucleation of water at negative pressure. The template-assisted self-assembly method is shown to be the most effective method to fabricate nanoporous ice in quantity. Several key factors for the self-assembly of nanoporous ices are identified, including proper gap spacings in the carbon nanomaterial template and suitable interactions between water and the carbon nanomaterials.

Two-Dimensional Mixed-Ligand Metal–Organic Framework Constructed from Bridging Bidentate V-Shaped Ligands

A two-dimensional and bifunctional pillar-layered metal–organic framework (MOF)—with the molecular formula [Zn(cba)(bpdb)]·DMF (2DTMU-1), H2cba = 4,4′-methylenedibenzoic acid, bpdb = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene—was obtained via the reaction of zinc(II) nitrate with H2cba as the carboxylate linker and bpdb as the N-donor pillar. 2DTMU-1 is based on a binuclear paddlewheel Zn(II) unit complexed by four bridging bidentate (dicarboxylate) V-shaped ligands, which combine to from H2cba; this tetragonal array, which is connected by bpdb with a bridging azine group, presents a pore size of 18 × 12 Å2.

Voltage controlled shutter regulates channel size and motion direction of protein aperture as durable nano-electric rectifier-----An opinion in biomimetic nanoaperture

In optical devices such as camera or microscope, an aperture is used to regulate light intensity for imaging. Here we report the discovery and construction of a durable bio-aperture at nanometerscale that can regulate current at the pico-ampere scale. The nano-aperture is made of 12 identical protein subunits that form a 3.6-nm channel with a shutter and “one-way traffic” property. This shutter responds to electrical potential differences across the aperture and can be turned off for double stranded DNA translocation. This voltage enables directional control, and three-step regulation for opening and closing. The nano-aperture was constructed in vitro and purified into homogeneity. The aperture was stable at pH2-12, and a temperature of −85C–60C. When an electrical potential was held, three reproducible discrete steps of current flowing through the channel were recorded. Each step reduced 32% of the channel dimension evident by the reduction of the measured current flowing through the aperture. The current change is due to the change of the resistance of aperture size. The transition between these three distinct steps and the direction of the current was controlled via the polarity of the voltage applied across the aperture. When the C-terminal of the aperture was fused to an antigen, the antibody and antigen interaction resulted in a 32% reduction of the channel size. This phenomenon was used for disease diagnosis since the incubation of the antigen-nano-aperture with a specific cancer antibody resulted in a change of 32% of current. The purified truncated cone-shape aperture automatically self-assembled efficiently into a sheet of the tetragonal array via head-to-tail self-interaction. The nano-aperture discovery with a controllable shutter, discrete-step current regulation, formation of tetragonal sheet, and one-way current traffic provides a nanoscale electrical circuit rectifier for nanodevices and disease diagnosis.

Expanding Alternating Spherical and Cylindrical Regions by Tailoring Binary Symmetric ABC/ABC Blends

The self-assembly of a binary blend composed of two different symmetric ABC triblock copolymers has been investigated using self-consistent field theory in the grand canonical ensemble, aiming to expand the phase regions of alternating spherical and cylindrical phases by tailoring the molecular parameters. Our study confirms that the region of the spherical phase is expanded by the effect of bidispersity in which the long and short A-blocks (or C-blocks) form a core–shell distribution within the spherical domain to increase the spontaneous curvature. The bidispersity effect also expands the phase region of the alternating cylinders. In contrast to the spherical phase, the cylindrical region can be expanded by another effect of bidisperse B-blocks to release the high packing frustration of the low-coordinated tetragonal array of alternating A/C cylinders. With optimized parameters, the regions of both the spherical and cylindrical phases are tremendously expanded to such large volume fractions that the spheres and cylinders are remarkably deformed. Our work not only deepens the understanding on the self-assembly mechanism of ABC/ABC blends but also provides a valuable guide for the fabrication of alternating spherical and cylindrical morphologies with large volume fractions.

Binuclear Cobalt Paddlewheel-Type Complexes: Relating Metal-Metal Bond Lengths to Formal Bond Orders.

Paddlewheel-type complexes are prominent among experimentally known binuclear cobalt complexes and incorporate substituted formamidinate, guanidinate, and carboxylate ligands in digonal, trigonal, and tetragonal arrays around the bimetallic core. Such complexes are modeled here by density functional theory using unsubstituted ligands, extending the whole set to incorporate a variety of metal oxidation states and spin multiplicities. The DFT results for ground state cobalt-cobalt bond lengths and ground state spin multiplicity of the model complexes are often quite close to the experimental results for the corresponding substituted complexes. The three series of complexes often exhibit parallel trends with regard to effects of change in the metal oxidation state and spin multiplicity. The formamidinate and guanidinate series show marked resemblances. The lowered symmetry in many model trigonal complexes implies that such deviations in the experimentally known congeners arise from the inherent electronic structure. For ground state species, the DFT results provide Co-Co bond orders (BOs) from MO occupancy considerations. Further, using a revised electron bookkeeping method, Co-Co formal bond order (fBO) values from 0.0 to 2.0 are assigned to all of the 85 complexes studied. The computed Co-Co bond lengths fall into distinct ranges according to the formal bond order values (from 0.5 to 2).

Tetragonal Superlattice of Elongated Rhombic Dodecahedra for Sensitive SERS Determination of Pesticide Residues in Fruit.

The self-assembly of plasmonic nanoparticles into highly ordered superlattices could pave the way toward novel nanomaterials for surface-enhanced Raman scattering (SERS). Here, we propose the formation of large-area superlattices of elongated rhombic dodecahedra in a vertical orientation via a controlled droplet evaporation process. Expectedly, the constant humidity of the experimental condition could control the evaporation speed of droplets and this procedure promotes the balance between driven depletion attraction and electrostatic repulsion in the system, leading to the generation of well-organized three-dimensional (3D) superlattices. The unique geometry of elongated rhombic dodecahedra could establish the tetragonal superlattices, which breaks the conventional hexagonal symmetry of gold nanorods. Specifically, the influence of the type and concentration of surfactants, the concentration of nanoparticles, and the amount of droplets on the preparation results were systematically investigated to find the optimal assembly parameters. Remarkably, such close-packed tetragonal arrays of vertically aligned elongated rhombic dodecahedra exhibit more excellent SERS performance compared with the traditional hexagonal superstructure of gold nanorods. Benefiting from the high sensitivity and reproducibility of elongated rhombic dodecahedron superlattices, their applications in the determination of pesticide residues in apple and grape peels were successfully demonstrated. As a result, this study may advance the production of innovative plasmonic nanomaterials for a broad range of fields.

Ordered arrays of Ag nanodendrite clusters as effective surface-enhanced Raman scattering substrates

Large-area ordered Ag nanodendrite cluster tetragonal arrays have been achieved on a Zn plate via galvanic replacement reaction.

Unravelling the structure of the C60 and p-But-calix[8]arene complex

The structure of the C60 and p-Bu(t)-calix[8]arene complex has been reinvestigated, showing an unprecedented continuous layered tetragonal array of fullerenes encapsulated by calixarenes. Electron diffraction data revealed the tetragonal symmetry, with a stepped structure observed by AFM and SEM, and the thickness of the basal plane was measured by XRD, as 2 nm. The molecular simulated arrangement of fullerenes accounts for the ability to take up to ca. 11% of fullerenes C70 in place of the smaller fullerene.

Bioinspired Multifunctional Hetero-Hierarchical Micro/Nanostructure Tetragonal Array with Self-Cleaning, Anticorrosion, and Concentrators for the SERS Detection

Heterohierarchical micro/nanostructure tetragonal array consisted of engineering materials of microprotrusion-like Cu and secondary nanostructured dendrite Ag have been fabricated via a primary cell-induced deposition and a facile galvanic displacement reaction combined with photolithography technique on Cu foil. Confined by the circle microwell tetragonal array of the photoresist template, regular microprotrusion-like Cu with the tunable size of diameter can be easily deposited on the surface of Cu foil. Then, the secondary dendritic Ag nanostructures in situ grow on the surface of microprotrusion via a galvanic displacement reaction, leading to the formation of heterohierarchical micro/nanostructure tetragonal array, which is similar to the surface microstructure of the lotus leaf. Inspired by this novel surface structure of imitating lotus leaf, its wettability has been systematically investigated. The results indicate that the fabricated heterohierarchical micro/nanostructure regular array after the surface fluoration presents a remarkable superhydrophobic performance. Initiated from its superhydrophobicity, an excellent self-cleaning property has also been demonstrated. In addition, the durability of the superhydrophobic surfaces is examined in the wide pH range of corrosive liquids. Notably, the fabricated superhydrophobic surface can be potentially used as concentrators, which presents a great perspective in the field of analysis through employing the SERS detection as an example.

Physical determinants of the shape of the psychophysical curve relating tactile roughness to raised-dot spacing: implications for neuronal coding of roughness

There are conflicting reports as to whether the shape of the psychometric relation between perceived roughness and tactile element spacing [spatial period (SP)] follows an inverted U-shape or a monotonic linear increase. This is a critical issue because the former result has been used to assess neuronal codes for roughness. We tested the hypothesis that the relation's shape is critically dependent on tactile element height (raised dots). Subjects rated the roughness of low (0.36 mm)- and high (1.8 mm)-raised-dot surfaces displaced under their fingertip. Inverted U-shaped curves were obtained as the SP of low-dot surfaces was increased (1.3-6.2 mm, tetragonal arrays); a monotonic increase was observed for high-dot surfaces. We hypothesized that roughness is not a single sensory continuum across the tested SPs of low-dot surfaces, predicting that roughness discrimination would show deviations from the invariant relation between threshold (ΔS) and the value of the standard (S) surface (Weber fraction, ΔS/S) expected for a single continuum. The results showed that Weber fractions were increased for SPs on the descending limb of the inverted U-shaped curve. There was also an increase in the Weber fraction for high-dot surfaces but only at the peak (3 mm), corresponding to the SP at which the slope of the psychometric function showed a modest decline. Together the results indicate that tactile roughness is not a continuum across low-dot SPs of 1.3-6.2 mm. These findings suggest that correlating the inverted U-shaped function with neuronal codes is of questionable validity. A simple intensive code may well contribute to tactile roughness.

The diamond and other non-conventional morphologies in two-scale multiblock AB copolymers

We revisit the idea of the existence of the ordered block copolymer phase possessing diamond symmetry Fdm (space group No. 227), which was first put forward within the framework of the strong segregation approach. For this purpose we study the order–disorder and order–order transitions in molten two-scale multiblock copolymers AmN/2(BN/2AN/2)nBmN/2via the pseudo-spectral numerical procedure of the self-consistent field theory (SCFT). The phase diagram in the plane (fC, ), where fC = n/(m + n) and = χ N(m + n) is the effective energetic Flory–Huggins parameter, is built and some accompanying quantities are analyzed. Near the order–disorder transition line the phase diagram contains the regions where the lamellar, alternating gyroid, diamond and simple cubic phase, respectively, exist. With an increase of the degree of segregation, the diamond phase is replaced by a tetragonal array of cylinders (simple square) phase, which agrees with the preceding results obtained within the Leibler-like weak segregation theory, and with the SCFT calculations for a physically similar melt of linear ABC triblock copolymers with a non-selective middle block. Thus, the diamond morphology in the system under study is shown to exist as an essentially weak or moderately (not strongly) segregated phase. The ways to visualize the patterns of ordering in such morphologies are discussed. A new quantity (topological permeability) to characterize the transport properties in 3D bicontinuous morphologies is introduced and first calculated for real block copolymer ordered morphologies. Some implications of the results obtained for the design of the block copolymer thin films with improved permeability are discussed.

Cover Picture: A Tetragonal 2D Array of Single-Molecule Magnets with Modulated Collective Behavior (Chem. Eur. J. 10/2011)

Cover Picture: A Tetragonal 2D Array of Single-Molecule Magnets with Modulated Collective Behavior (Chem. Eur. J. 10/2011)

Anatomy of a Red Copper Center: Spectroscopic Identification and Reactivity of the Copper Centers of Bacillus subtilis Sco and Its Cys-to-Ala Variants

Sco is a mononuclear red copper protein involved in the assembly of cytochrome c oxidase. It is spectroscopically similar to red copper nitrosocyanin, but unlike the latter, which has one copper cysteine thiolate, the former has two. In addition to the two cysteine ligands (C45 and C49), the wild-type (WT) protein from Bacillus subtilis (hereafter named BSco) has a histidine (H135) and an unknown endogenous protein oxygen ligand in a distorted tetragonal array. We have compared the properties of the WT protein to variants in which each of the two coordinating Cys residues has been individually mutated to Ala, using UV/visible, Cu and S K-edge X-ray absorption, electron paramagnetic resonance, and resonance Raman spectroscopies. Unlike the Cu(II) form of native Sco, the Cu(II) complexes of the Cys variants are unstable. The copper center of C49A undergoes autoreduction to the Cu(I) form, which is shown by extended X-ray absorption fine structure to be composed of a novel two-coordinate center with one Cys and one His ligand. C45A rearranges to a new stable Cu(II) species coordinated by C49, H135 and a second His ligand recruited from a previously uncoordinated protein side chain. The different chemistry exhibited by the Cys variants can be rationalized by whether a stable Cu(I) species can be formed by autoredox chemistry. For C49A, the remaining Cys and His residues are trans, which facilitates the formation of the highly stable two-coordinate Cu(I) species, while for C45A such a configuration cannot be attained. Resonance Raman spectroscopy of the WT protein indicates a net weak Cu-S bond strength at approximately 2.24 A corresponding to the two thiolate-copper bonds, whereas the single variant C45A shows a moderately strong Cu-S bond at approximately 2.16 A. S K-edge data give a total covalency of 28% for both Cu-S bonds in the WT protein. These data suggest an average covalency per Cu-S bond lower than that observed for nitrosocyanin and close to that expected for type-2 Cu(II)-thiolate systems. The data are discussed relative to the unique Cu-S characteristics of cupredoxins, from which it is concluded that Sco does not contain highly covalent Cu-S bonds of the type expected for long-range electron-transfer reactivity.

Barium Titanate Tetragonal Prism Arrays: Preparation and Characterization

Sub-micrometer barium titanate (BaTiO 3 ) pillar arrays were prepared by nanoparticle electrophoretic deposition and characterized with scanning electron microscopy and atomic force microscopy. Well dispersed BaTiO 3 nanoparticle suspension in a mixed solvent of 2-methoxyethonal and acetylacetone were prepared by ultrasonication dispersion. By using nanoparticle electrophoretic deposition, BaTiO 3 tetragonal prism arrays with controlled crystal structures and architectures were deposited on Pt/Ti/SiO 2 /Si substrates from the BaTiO 3 suspension. A strain hysteresis loop of an isolated micropillar was observed with a scanning probe microscopy (SPM) and a ferroelectric measuring system.

Fabrication of Massive Sheets of Single Layer Patterned Arrays Using Lipid Directed Reengineered Phi29 Motor Dodecamer

The bottom-up assembly of patterned arrays is an exciting and important area in current nanotechnology. Arrays can be engineered to serve as components in chips for a virtually inexhaustible list of applications ranging from disease diagnosis to ultra-high-density data storage. Phi29 motor dodecamer has been reported to form elegant multilayer tetragonal arrays. However, multilayer protein arrays are of limited use for nanotechnological applications which demand nanoreplica or coating technologies. The ability to produce a single layer array of biological structures with high replication fidelity represents a significant advance in the area of nanomimetics. In this paper, we report on the assembly of single layer sheets of reengineered phi29 motor dodecamer. A thin lipid monolayer was used to direct the assembly of massive sheets of single layer patterned arrays of the reengineered motor dodecamer. Uniform, clean and highly ordered arrays were constructed as shown by both transmission electron microscopy and atomic force microscopy imaging.

(C4H12N)2][Zn3(HPO3)4]: An Open‐Framework Zinc Phosphite Containing Extra‐Large 24‐Ring Channels

Hydrothermal reaction of Zn(OAc)2⋅2 H2O and H3PO3 in the presence of n-butylamine gives the title compound, which contains extra-large 24-ring channels (see framework representation). Each channel is enclosed by a tetragonal array of four 8-ring channels interconnected by corner-sharing 4-ring chains through Zn-O-P linkages.

Oxidation of Structured Silicon Thin Films for Inverse Silicon Square Spiral Photonic Crystal Fabrication

ABSTRACTPhotonic Band Gap (PBG) crystals are artificially engineered structures of periodically alternating dielectric materials that enable manipulation of light in unique ways. As proposed by O. Toader and S. John, large bandwidth PBG crystals based on the diamond lattice can be constructed by fabricating a two-dimensional periodic array of silicon square spirals. Furthermore, an improved photonic crystal can be constructed by fabricating the inverse of this structure, such that void square spirals are situated in a silicon backfill. This structure yields a theoretical maximum PBG of 24%, while the direct silicon square spiral structure yields a theoretical maximum of 16%. [1]The direct silicon square spiral structure has previously been successfully fabricated using the glancing angle deposition (GLAD) process [2]. The GLAD fabrication process uses advanced substrate motion and oblique incidence deposition to engineer precise nanostructures such as helices, chevrons, or polygonal spirals. These nanostructures are grown with lateral and longitudinal periodicity using a pre-patterned substrate consisting of a tetragonal array of relief structures.Upon successful fabrication of the direct silicon square spiral structure, it was proposed that fabrication of the inverse structure could be completed using a backfill process with a silica template [2]. A periodic array of silica square spirals would be fabricated using the GLAD technique. The template would then be filled with amorphous silicon using low-pressure chemical vapour deposition (LPCVD). To reveal the inverse silicon structure, the silica template would be removed by means of chemical etching with an isotropic chemical etchant. Creation of a suitable template for the inversion of silicon square spirals is an important step in the realization of the inverse silicon square spiral PBG crystal. However, we have seen empirically that silica square spiral films grown directly via the GLAD technique are structurally inferior to silicon films. We present an intermediate step for the fabrication of a suitable template, whereby a silicon structure is fabricated with appropriate geometries and subsequently oxidized. The procedure has been optimized to ensure a thorough oxidization of the silicon posts, while minimally distorting the structure of the square spiral template.

Morphology of periodic nanostructures for photonic crystals grown by glancing angle deposition

An enhancement of the glancing angle deposition (GLAD) technique called PhiSweep was used to grow slanted columns of silicon and titanium dioxide onto patterned substrates. The PhiSweep technique involves periodically rotating the substrate back and forth during the deposition process, which reduces column fanning caused by anisotropy in the shadowing conditions. The patterned substrates consisted of a tetragonal array of hillocks with 100, 200, and 300 nm periodicities and were fabricated using electron beam lithography. The PhiSweep method alters the tilt angle of the slanted columns compared with those grown using traditional GLAD. We present a derivation of the tilt angle of the slanted columns as a function of the parameters of the PhiSweep technique. The tilt angles of the silicon and titanium dioxide films were measured and agree with the predicted values. The films fabricated using the PhiSweep method are compared with similar films grown using traditional GLAD. The PhiSweep technique produced films with substantially less column fanning than those grown by traditional GLAD. This reduction in column fanning has extended the size range over which periodic GLAD structures, such as square spiral photonic crystals, can be grown.

Construction and 3-D Computer Modeling of Connector Arrays with Tetragonal to Decagonal Transition Induced by pRNA of phi29 DNA-Packaging Motor

The bottom-up assembly of patterned arrays is an exciting and important area in current nanotechnology. Arrays can be engineered to serve as components in chips for a virtually inexhaustible list of applications ranging from disease diagnosis to ultrahigh-density data storage. In attempting to achieve this goal, a number of methods to facilitate array design and production have been developed. Cloning and expression of the gene coding for the connector of the bacterial virus phi29 DNA-packaging motor, overproduction of the gene products, and the in vitro construction of large-scale carpet-like arrays composed of connector are described in this report. The stability of the arrays under various conditions, including varied pH, temperature and ionic strength, was tested. The addition of packaging RNA (pRNA) into the array caused a dramatic shift in array structure, and resulted in the conversion of tetragonal arrays into larger decagonal structures comprised of both protein and RNA. RNase digestion confirmed that the conformational shift was caused by pRNA, and that RNA was present in the decagons. As has been demonstrated in biomotors, conformational shift of motor components can generate force for motor motion. The conformational shift reported here can be utilized as a potential force-generating mechanism for the construction of nanomachines. Three-dimensional computer models of the constructed arrays were also produced using a variety of connector building blocks with or without the N- or C-terminal sequence, which is absent from the current published crystal structures. Both the connector array and the decagon are ideal candidates to be used as templates to build patterned suprastructures in nanotechnology.

Structure and Magnetic Properties of a Giant Cu44II Aggregate Which Packs with a Zeotypic Superstructure

Reaction of Cu(II) and the aminopolycarboxylate nitrilotripropionic acid (H(3)ntp) in water leads to the formation of [Cu(44)(mu(8)-Br)(2)(mu(3)-OH)(36)(mu-OH)(4)(ntp)(12)Br(8)(OH(2))(28)]Br(2).81H(2)O. The Cu(44) aggregates have a central inorganic core corresponding to [Cu(24)(mu(8)-Br)(2)(mu(3)-OH)(24)(mu-OH)(8)](14+) anchored on two bromide anions, and this is encased in a shell of Cu(II)/ligand units. The aggregates pack into a distorted tetragonal array with a very open structure containing large amounts of water of crystallization. The magnetic properties have been studied and, while complicated by the presence of low-lying excited states, indicate that the individual clusters have nonzero spin ground states.