Spiral Assembly Research Articles

1,4]Ditellurino[2,3-b:5,6-b']di-pyrazine.

[1,4]Ditellurino[2,3-b:5,6-b']di-pyrazine represents the first reported [1,4]chalcogena[2,3-b:5,6-b']di-pyrazine containing a heavy chalcogens The asymmetric unit consists of three mol-ecules. In contrast to its sulfur analog, which is planar [Lynch et al. (1994 ▸) Cryst. Struct. Commun. 50,1470-1472], C8H4N4Te2 is folded along the Te⋯Te axis to accommodate the larger chalcogenide atoms. The dihedral angle between the two Te2C2 rings of the central ring is 57.9° (mean of three). C-Te bond lengths range from 2.1105 (16) Å to 2.1381 (17) Å, in good agreement with those predicted by their covalent radii. All Te atoms are involved in inter-molecular Te⋯N contacts, with distances in the range 2.894 (2) to 2.963 (2) Å. These result in a spiral supra-molecular assembly, forming helical columns.

Analysis of Archimedean Spiral Slot Antennas in Infinite Ground Planes Using the Theory of Characteristic Modes

The analysis of Archimedean spiral slots using the theory of characteristic modes is presented in this article. Purely magnetic characteristic modes are used to study the behavior of a spiral slot etched in an infinite ground plane. The effect of the spiral geometry parameters (slot width, separation between spiral slot arms, number of spiral turns, and inner spiral spacing) on the characteristic modes are investigated using the theory of characteristic modes. Based on the results of the characteristic mode analysis, guidelines are presented for selecting the appropriate slot dimensions for realizing a compact spiral slot assembly (miniaturization), multimode behavior and for improving the bandwidth of the purely magnetic characteristic modes. Additionally, analytical equations are presented for accurately predicting the resonant frequencies of the purely magnetic characteristic mode of the spiral slot antenna.

Morphological and Orientational Controls of Self-Assembly of Gold Nanorods Directed by Evaporative Microflows.

Evaporative self-assembly of noble metal nanoparticles into ordered structures holds great promise for fabricating optical and plasmonic devices by virtue of its low cost, high efficiency, and ease of operation. However, poor control of Marangoni flows is one of the challenges accounting for realizing a well-defined assembly. Herein, based on the theoretical analysis of the influence of evaporative intensity on the assembly, two simple but reliable flow-field-confinement platforms are designed to control the evaporative microflows and to work concurrently with depletion forces to enable the regulated self-assembly of gold nanorods. Orientationally ordered assemblies are realized by the designed strong unidirectional microflow in a capillary, and a device-scale assembly of monolayer membrane is obtained by the created weak convection in homemade glass cells. Morphologically diversified superstructure assemblies, such as spherulite-like, boundary-twisted, chiral spiral assemblies, and merging membranes with a π-twisted domain wall, are obtained due to the spontaneous symmetry breaking or in the presence of defects, such as surface steps and screw dislocations. Optical anisotropy and polarization-dependent behaviors of these assemblies are further revealed, implying the potential applications in plasmonic coupling devices and optoelectronic components. An understanding of the entropy-driven assembly behaviors and control of evaporative microflows to guide the self-assembly of gold nanorods provides insights into the general bottom-up approach that is helpful for constructing complex yet robust nanosuperstructures.

Postpartum ovulation and early pregnancy in the menstruating spiny mouse, Acomys cahirinus

Egyptian spiny mice are the only known species to have human-like menstruation and a postpartum ovulation. Unfortunately, no endocrine or morphological evidence has been provided for a postpartum ovulation in spiny mice, and while later stages of pregnancy have been well studied, early events including embryo implantation and spiral artery remodelling have not been reported. This study compared the sex steroid endocrinology and reproductive tract morphology of dams at eight timepoints (n = 40) postpartum to determine the timing of ovulation and the timing and invasiveness of embryo implantation in A. cahirinus. Reproductive tracts were fixed and stained for histology and immunohistochemistry, and plasma was prepared for enzyme-linked immunosorbent assay. Ovarian histology and estradiol-17B concentrations indicate ovulation within 48 h of parturition and then immediate resumption of follicular growth. Uterine histology and immunohistochemistry revealed progressive epithelial repair, endometrial growth and spiral artery assembly and remodelling in dams postpartum. Blastocysts were seen in the uterine lumen at day 4–5 postpartum and embryos had implanted superficially with minimal stromal invasion by day 5–6. This study provides further evidence for the unique, humanesque reproductive biology of spiny mice and for a postpartum ovulation using endocrine and morphological changes observed during early pregnancy. Taken together, our data suggest that spiny mice may act as appropriate models of human pregnancy disorders such as implantation failure or pre-eclampsia.

Symmetry breaking and structural polymorphism in a bacterial microcompartment shell protein for choline utilization.

Bacterial microcompartments are protein-based organelles that carry out specialized metabolic functions in diverse bacteria. Their outer shells are built from several thousand protein subunits. Some of the architectural principles of bacterial microcompartments have been articulated, with lateral packing of flat hexameric BMC proteins providing the basic foundation for assembly. Nonetheless, a complete understanding has been elusive, partly owing to polymorphic mechanisms of assembly exhibited by most microcompartment types. An earlier study of one homologous BMC shell protein subfamily, EutS/PduU, revealed a profoundly bent, rather than flat, hexameric structure. The possibility of a specialized architectural role was hypothesized, but artifactual effects of crystallization could not be ruled out. Here we report a series of crystal structures of an orthologous protein, CutR, from a glycyl-radical type choline-utilizing microcompartment from the bacterium Streptococcus intermedius. Depending on crystal form, expression construct, and minor mutations, a range of novel quaternary architectures was observed, including two spiral hexagonal assemblies. A new graphical approach helps illuminate the variations in BMC hexameric structure, with results substantiating the idea that the EutS/PduU/CutR subfamily of BMC proteins may endow microcompartment shells with flexible modes of assembly.

Microfluidics-Assisted Assembly of Injectable Photonic Hydrogels toward Reflective Cooling.

Development of fast curing and easy modeling of colloidal photonic crystals is highly desirable for various applications. Here, a novel type of injectable photonic hydrogel (IPH) is proposed to achieve self-healable structural color by integrating microfluidics-derived photonic supraballs with supramolecular hydrogels. The supramolecular hydrogel is engineered via incorporating β-cyclodextrin/poly(2-hydroxypropyl acrylate-co-N-vinylimidazole) (CD/poly(HPA-co-VI)) with methacrylated gelatin (GelMA), and serves as a scaffold for colloidal crystal arrays. The photonic supraballs derived from the microfluidics techniques, exhibit excellent compatibility with the hydrogel scaffolds, leading to enhanced assembly efficiency. By virtue of hydrogen bonds and host-guest interactions, a series of self-healable photonic hydrogels (linear, planar, and spiral assemblies) can be facilely assembled. It is demonstrated that the spherical symmetry of the photonic supraballs endows them with identical optical responses independent of viewing angles. In addition, by taking the advantage of angle independent spectrum characteristics, the IPH presents beneficial effects in reflective cooling, which can achieve up to 17.4 °C in passive solar reflective cooling. The strategy represents an easy-to-perform platform for the construction of IPH, providing novel insights into macroscopic self-assembly toward thermal management applications.

Trefoiled Propeller-Shaped Spiral Terpyridyl Metal-Organic Architectures.

Constructing exquisite and intricate molecular architectures is always the pursuit of chemists. In this report, the propeller-shaped trefoil structures S1 and S2 were successfully prepared by the stepwise self-assembly of predesigned tripodal metal-organic ligands, which consist of bis(terpyridine)s-Ru2+-tris(terpyridine)s connectivities for the following complexation with Fe2+. The complexes can be described as racemic spiral assemblies with three-fold spiralism. These unique discrete metal-organic architectures were fully characterized by 1H NMR, 2D NMR spectroscopy (COSY and NOESY), diffusion-ordered NMR spectroscopy (DOSY), ESI-MS, TWIM-MS, and TEM, and their photophysical and electrochemical properties were also investigated. Further, hybrid trefoiled structure [Fe3L1L2] was detected by taking advantage of the flexibility of metal-organic ligands.

Systematic probing into periodic lamellar assembly via induced cracks in crystallized polyesters

Using poly(3-hydroxybutyrate) (PHB) of two molecular weights and various other polymeric or blend systems, this study has shed a critical clue that cracks are inclined to be guided by interior lamellae via interior inter-lamellae discontinuity and interfaces that exist between the successive ring bands or radial/tangential lamellae. Advanced interior dissection analysis on the aggregated spherulites of several polymers further proves that the cracks occur at the interface between the valley and ridge bands of the ringed spherulites, where interfaces with discontinuous lamellae exist with either impingement or intersection. Propagation of the cracks follows the spiral or circular lamellae assembly into similarly spiral or circular concentric patterns, Such updated views via interior lamellae dissection and analysis on PHB's or other polymers' banded spherulites provide avenues for cracks to develop upon cooling contraction. The mechanism of spiral/circular cracks' formation is well proven in this work, which is related to the inner arrangement/assembly of the periodic spiral lamellae into banded types; by contrast, without such lamellae periodicity, cracks tends to be randomly irregular.

Resolving ESCRT-III Spirals at the Intercellular Bridge of Dividing Cells Using 3D STORM

The ESCRT machinery mediates membrane fission in a variety of processes in cells. According to current models, ESCRT-III proteins drive membrane fission by assembling into helical filaments on membranes. Here, we used 3D STORM imaging of endogenous ESCRT-III component IST1 to reveal the evolution of the structural organization of ESCRT-III in mammalian cytokinetic abscission. Using this approach, ESCRT-III ring and spiral assemblies were resolved and characterized at different stages of abscission. Visualization of IST1 structures in cells lacking the microtubule-severing enzyme spastin and in cells depleted of specific ESCRT-III components or the ATPase VPS4 demonstrated the contribution of these components to the organization and function of ESCRTs in cells. This work provides direct evidence that ESCRT-III proteins form helical filaments to mediate their function in cells and raises new mechanistic scenarios for ESCRT-driven cytokinetic abscission.

A location- and sharpness-specific tactile electronic skin based on staircase-like nanowire patches.

Human skin can sense an external object in a location-specific manner, simultaneously recognizing whether it is sharp or blunt. Such tactile capability can be achieved in both natural and stretched states. It is impractical to mimic this tactile function of human skin by designing pixelated sensor arrays across our whole curvilinear human body. Here, we report a new tactile electronic skin sensor based on staircase-like vertically aligned gold nanowires (V-AuNWs). With a back-to-back linear or spiral assembly of two staircase structures into a single sensor, we are able to recognize pressure in a highly location-specific manner for both non-stretched and stretched states (up to 50% strain); with a concentric design on the fingertip, we can identify the sharpness of an external object. We believe that our strategy opens up a new route to highly specific second-skin-like tactile sensors for electronic skin (E-skin) applications.

Novel Motorized Spiral Enteroscopy: First Clinical Case

A novel reusable endoscope (Olympus Corp.) with an integral motor was developed for rotating a disposable short spiral overtube mounted on the insertion tube portion. The drive motor located in the endoscope handle is activated via foot pedals and controls the direction and speed of rotation of a coupler located in the middle of the endoscope’s insertion tube. The rotation coupler is the only portion of the endoscope that rotates; the distal and proximal portions of the insertion tube do not rotate. Other than the presence of the drive motor and the rotation coupler, the endoscope design is the same as that of conventional flexible endoscopes. The single-use spiral assembly is comprised of corrugated tubing with an atraumatic plastic spiral bonded to its exterior. It relies on rotation of the spiral component to “pleat” or “unpleat” the bowel either on or off the insertion tube as the spiral thread rotates in a clockwise or counter-clockwise direction, respectively. The operator can monitor how much torque is being applied to the small bowel by observing the system’s “visual force gauge”. This display provides the operator with a visual indication of the direction of rotation and the force of rotation throughout the examination. The clinical case represents the first use of this device in humans. Enteroscopy was indicated for treatment of angiodysplasias in the jejunum identified by small bowel capsule endoscopy in a 48 year old patient with iron deficiency anaemia. The novel motorized enteroscope could be smoothly inserted approximately 250 cm distal of the ligament of Treitz within 20 minutes. The technique allowed controlled movement of the tip of the endoscope and it provided an excellent visualization of the intubated small bowel. An angiodysplasia was detected and treated with argon plasma coagulation. Careful removal of the endoscope with counter-clockwise rotation of the spiral revealed no iatrogenic mucosal trauma. No adverse events were registered.

Spiral assembly of amphiphilic cytarabine prodrug assisted by probe sonication: Enhanced therapy index for leukemia

In order to overcome the drawbacks of cytarabine (Ara-C), such as low lipophilicity as well as short plasma half-life and rapid inactivation, a new derivative of Ara-C was designed by incorporation into the non-toxic material, oleic acid (OA), obtaining an amphiphilic small molecular weight prodrug (OA-Ara). By a simple amidation reaction, OA-Ara was synthesized successfully with a yield up to 61.32%. It was for the first time to see that the novel prodrug molecules could assemble into the unexpectedly spiral assembly under probe ultrasonication in aqueous solution. The oil/water partition coefficient (Ko/w) and the permeability of cell membrane of the prodrug were significantly increased compared with Ara-C molecules. In addition, OA-Ara molecules were stable in various pH solutions and artificial digestives, which indicated that it could be administrated orally. Cell viability assay showed that the prodrug displayed much higher antiproliferative effect against K562 and HL60 cells due to its improvement of the lipophilicity and penetrability of cell membrane. These findings demonstrate the feasibility of utilizing structural modification to broaden the clinic application of Ara-C and thus provide an effective new therapeutic alternative for leukemia.

Rapid excavation with a newly developed retaining system: Spiral assembly steel structure

The spiral assembly steel structure, a newly developed retaining wall for the rapid excavation of small-sized foundation pits in unsaturated soil, is presented. This new type of retaining structure is prefabricated in the factory and is assembled on site in the excavation of a pit. This retaining structure is composed of several prefabricated steel structural units, in which the adjacent steel structural units are joined with connectors. Each steel structural unit has one steel pipe in the radial direction and is welded to a single piece of steel plate. After full installation in situ, the retaining structure becomes a cylindrical steel structure. With the protection afforded by this new type of retaining structure, excavation work can be completed within 24 h to a depth up to 5 m. In order to verify the reliability and effectiveness of this new retaining structure, field construction tests were conducted in Beijing, China. The test construction was monitored. The monitoring program included measuring stress in the structure, lateral earth pressure, and lateral deformation of the surrounding soil. The monitoring data from the field test were compared with the theoretical results. The results show that the proposed new structure is reliable and effective.

New analytical spiral tube assembly for separation of proteins by counter-current chromatography

A new spiral column assembly for analytical separation by counter-current chromatography is described. The column is made from a plastic spiral tube support which has 12 interwoven spiral grooves. The PTFE tubing of 1.6mm ID was first flattened by extruding through a narrow slit and inserted into the grooves to make 5 spiral layers with about 60ml capacity. The performance of the spiral column assembly was tested with separation of three stable protein samples including cytochrome C, myoglobin and lysozyme in a polymer phase system composed of polyethylene glycol 1000 and dibasic potassium phosphate each at 12.5% (w/w) in water. At 2ml/min, three protein samples were well resolved in 1h. The separation time may be further shortened by application of higher revolution speed and flow rate by improving the strength of the spiral tube support in the future.

The 3D structure of Kaposi sarcoma herpesvirus LANA C-terminal domain bound to DNA

Kaposi sarcoma herpesvirus (KSHV) persists as a latent nuclear episome in dividing host cells. This episome is tethered to host chromatin to ensure proper segregation during mitosis. For duplication of the latent genome, the cellular replication machinery is recruited. Both of these functions rely on the constitutively expressed latency-associated nuclear antigen (LANA) of the virus. Here, we report the crystal structure of the KSHV LANA DNA-binding domain (DBD) in complex with its high-affinity viral target DNA, LANA binding site 1 (LBS1), at 2.9 Å resolution. In contrast to homologous proteins such as Epstein-Barr virus nuclear antigen 1 (EBNA-1) of the related γ-herpesvirus Epstein-Barr virus, specific DNA recognition by LANA is highly asymmetric. In addition to solving the crystal structure, we found that apart from the two known LANA binding sites, LBS1 and LBS2, LANA also binds to a novel site, denoted LBS3. All three sites are located in a region of the KSHV terminal repeat subunit previously recognized as a minimal replicator. Moreover, we show that the LANA DBD can coat DNA of arbitrary sequence by virtue of a characteristic lysine patch, which is absent in EBNA-1 of the Epstein-Barr virus. Likely, these higher-order assemblies involve the self-association of LANA into supermolecular spirals. One such spiral assembly was solved as a crystal structure of 3.7 Å resolution in the absence of DNA. On the basis of our data, we propose a model for the controlled nucleation of higher-order LANA oligomers that might contribute to the characteristic subnuclear KSHV microdomains ("LANA speckles"), a hallmark of KSHV latency.

Structural analysis and modeling reveals new mechanisms governing ESCRT-III spiral filament assembly

The scission of biological membranes is facilitated by a variety of protein complexes that bind and manipulate lipid bilayers. ESCRT-III (endosomal sorting complex required for transport III) filaments mediate membrane scission during the ostensibly disparate processes of multivesicular endosome biogenesis, cytokinesis, and retroviral budding. However, mechanisms by which ESCRT-III subunits assemble into a polymer remain unknown. Using cryogenic electron microscopy (cryo-EM), we found that the full-length ESCRT-III subunit Vps32/CHMP4B spontaneously forms single-stranded spiral filaments. The resolution afforded by two-dimensional cryo-EM combined with molecular dynamics simulations revealed that individual Vps32/CHMP4B monomers within a filament are flexible and able to accommodate a range of bending angles. In contrast, the interface between monomers is stable and refractory to changes in conformation. We additionally found that the carboxyl terminus of Vps32/CHMP4B plays a key role in restricting the lateral association of filaments. Our findings highlight new mechanisms by which ESCRT-III filaments assemble to generate a unique polymer capable of membrane remodeling in multiple cellular contexts.

A new spiral microelectrode assembly for electroporation and impedance measurements of adherent cell monolayers

In this study, a new microelectrode assembly based on spiral geometry applicable to in situ electroporation of adherent cell monolayers on standard multiwell plates is presented. Furthermore, the structure is specially conceived to perform electrical impedance spectroscopy (EIS) measurements during electroporation. Its performance for cell membrane permeabilization is tested with a fluorescent probe. Gene electrotransfer is also assayed using a plasmid DNA encoding GFP in four different cell lines (CHO, HEK293, 3T3-L1 and FTO2B). Additionally, siRNA α-GFP electrotransfection is tested in GFP gene-expressing CHO cells. Our data show considerable differences between permeabilization and gene transfer results and cell line dependence on gene expression rates. Successful siRNA electro-mediated delivery is also achieved. We demonstrate the applicability of our device for electroporation-mediated gene transfer of adherent cells in standard laboratory conditions. Finally, electrical impedance measurements during electroporation of CHO and 3T3-L1 cells are also given.

Measurement of anisotropic thermophysical properties of cylindrical Li-ion cells

Cylindrical Li-ion cells have demonstrated among the highest power density of all Li-ion cell types and typically employ a spiral electrode assembly. This spiral assembly is expected to cause large anisotropy in thermal conductance between the radial and axial directions due to the large number of interfaces between electrode and electrolyte layers in the radial conduction path, which are absent in the axial direction. This paper describes a novel experimental technique to measure the anisotropic thermal conductivity and heat capacity of Li-ion cells using adiabatic unsteady heating. Analytical modeling of the method is presented and is shown to agree well with finite-element simulation models. Experimental measurements indicate that radial thermal conductivity is two orders of magnitude lower than axial thermal conductivity for cylindrical 26650 and 18650 LiFePO4 cells. Due to the strong influence of temperature on cell performance and behavior, accounting for this strong anisotropy is critical when modeling battery behavior and designing battery cooling systems. This work improves the understanding of thermal transport in Li-ion cells, and presents a simple method for measuring anisotropic thermal transport properties in cylindrical cells.

Tubing Cleaning Nozzle Assembly Structure Improvement and Numerical Simulation

The installation position of nozzle directly affect the efficiency of high pressure water jet cleaning. In order to improve the cleaning efficiency, the paper establish the three-dimensional structure and numerical model of the original nozzle assembly and the spiral nozzle assembly. The numerical simulation results show that, on the same boundary conditions, the effective hit range of the spiral nozzle assembly is greater and more uniform than that of the original nozzle assembly.The effective surge pressure of the spiral nozzle assembly is larger than that of the original nozzle assembly, spiral nozzle assembly can can reduce the blind cleaning area and improve the cleaning efficiency.

Spiral countercurrent chromatography.

For many years, high-speed countercurrent chromatography conducted in open tubing coils has been widely used for the separation of natural and synthetic compounds. In this method, the retention of the stationary phase is solely provided by the Archimedean screw effect by rotating the coiled column in the centrifugal force field. However, the system fails to retain enough of the stationary phase for polar solvent systems such as the aqueous-aqueous polymer phase systems. To address this problem, the geometry of the coiled channel was modified to a spiral configuration so that the system could utilize the radially acting centrifugal force. This successfully improved the retention of the stationary phase. Two different types of spiral columns were fabricated: the spiral disk assembly, made by stacking multiple plastic disks with single or four interwoven spiral channels connected in series, and the spiral tube assembly, made by inserting the tetrafluoroethylene tubing into a spiral frame (spiral tube support). The capabilities of these column assemblies were successfully demonstrated by separations of peptides and proteins with polar two-phase solvent systems whose stationary phases had not been well retained in the earlier multilayer coil separation column for high-speed countercurrent chromatography.