Generation of New Complestatin Analogues by Heterologous Expression of the Complestatin Biosynthetic Gene Cluster from Streptomyces chartreusis AN1542.

The heterologous expression of the biosynthetic gene cluster (BGC) of natural products enables the production of complex metabolites in a well-characterized host, and facilitates the generation of novel analogues by the manipulation of the genes. However, the BGCs of glycopeptides such as vancomycin, teicoplanin, and complestatin are usually too large to be directly cloned into a single cosmid. Here, we describe the heterologous expression of the complestatin BGC. The 54.5 kb cluster was fully reconstituted from two overlapping cosmids into one cosmid by λ-RED recombination-mediated assembly. Heterologous expression of the assembled gene cluster in Streptomyces lividans TK24 resulted in the production of complestatin. Deletion of cytochrome P450 monooxygenase genes (open reading frames 10 and 11) and heterologous expression of the modified clusters led to the production of two new monocyclic and linear derivatives, complestatins M55 and S56.

Effects of nitrogen doping from pyrolyzed ionic liquid in carbon nanotube fibers: enhanced mechanical and electrical properties.

Nitrogen doping in carbon nanotube (CNT) fibers using pyrolyzed ionic liquid induced interfacial hydrogen bonding between individual CNTs, enhancing mechanical properties and electrical conductivity simultaneously. In particular, the nitrogen doped CNT fiber using the ionic liquid BMI-I exhibited about 104%, 714%, and 38% increased tensile strength (0.65 N/tex), elastic modulus (83 N/tex), and electrical conductivity (1350 S cm(-1)), respectively, compared to pristine CNT fiber.

Synthesis and mechanistic study of in situ halogen/nitrogen dual-doping in graphene tailored by stepwise pyrolysis of ionic liquids.

New halogen/nitrogen dual-doped graphenes (X/N-G) with thermally tunable doping levels are synthesized via the thermal reduction of graphite oxide (GO) with stepwise-pyrolyzed ionic liquids. The doping process of halogen and nitrogen into the graphene lattice proceeds via substitutional or covalent bonding through the physisorption or chemisorption of in situ pyrolyzed dopant precursors. The doping process is performed by heating to 300-400 °C of ionic liquid, and the chemically assisted reduction of GO is facilitated by ionic iodine, resulting in I/N-G materials possessing about three and two orders of magnitude higher conductivity (∼22,200 S m(-1)) and charge carrier density (∼10(21) cm(-3)), compared to those of thermally reduced GO. The thermally tunable doping levels of halogen in X/N-G significantly increase the conductivity of doped graphene to ∼27,800 S m(-1).

A putative role of Drep1 in apoptotic DNA fragmentation system in fly is mediated by direct interaction with Drep2 and Drep4.

DNA fragmentation is common phenomenon for apoptotic cell death. DNA fragmentation factor, called DFF40 (CAD: mouse homologue), is a main nuclease for apoptotic DNA fragmentation. Nuclease activity of DFF40 is normally inhibited by DFF45 by tight interaction via CIDE domain without apoptotic stimuli. Once effector caspase is activated during apoptosis signaling, it cleave DFF45, allowing DFF40 to enter the nucleus and cleave chromosomal DNA. Unlike mammalian system, apoptotic DNA fragmentation in the fly might be controlled by four DFF-related proteins, known as Drep1, Drep2, Drep3 and Drep4. Although the function of Drep1 and Drep4 is well known as DFF45 and DFF40 homologues, respectively, the function of Drep2 and Drep3 is still unclear. DFF-related proteins contain a conserved CIDE domain of ~90 amino acid residues that is involved in protein-protein interaction. Here, we showed that Drep1 directly bind to Drep2 as well as Drep4 via CIDE domain. In addition, we found that the interaction of Drep2 and Drep4 to Drep1 was not competitive indicating that Drep2 and Drep4 bind different place of Drep1. All together, we suggest that Drep1 might be involved in apoptotic DNA fragmentation of fly system by direct interaction with Drep2 as well as Drep4.

Defect healing of reduced graphene oxide via intramolecular cross-dehydrogenative coupling.

A chemical defect healing of reduced graphene oxide (RGO) was carried out via intramolecular cross-dehydrogenative coupling (ICDC) with FeCl3 at room temperature. The Raman intensity ratio of the G-band to the D-band, the IG/ID ratio, of the RGO was increased from 0.77 to 1.64 after the ICDC reaction. From XPS measurements, the AC=C/AC-C ratio, where the peak intensities from the C=C and C-C bonds are abbreviated as AC=C and AC-C, of the RGO was increased from 2.88 to 3.79. These results demonstrate that the relative amount of sp(2)-hybridized carbon atoms is increased by the ICDC reaction. It is of great interest that after the ICDC reaction the electrical conductivity of the RGO was improved to 71 S cm(-1), which is 14 times higher than that of as-prepared RGO (5 S cm(-1)).

In situ synthesis of thermochemically reduced graphene oxide conducting nanocomposites.

Highly conductive reduced graphene oxide (GO) polymer nanocomposites are synthesized by a well-organized in situ thermochemical synthesis technique. The surface functionalization of GO was carried out with aryl diazonium salt including 4-iodoaniline to form phenyl functionalized GO (I-Ph-GO). The thermochemically developed reduced GO (R-I-Ph-GO) has five times higher electrical conductivity (42,000 S/m) than typical reduced GO (R-GO). We also demonstrate a R-I-Ph-GO/polyimide (PI) composites having more than 10(4) times higher conductivity (~1 S/m) compared to a R-GO/PI composites. The electrical resistances of PI composites with R-I-Ph-GO were dramatically dropped under ~3% tensile strain. The R-I-Ph-GO/PI composites with electrically sensitive response caused by mechanical strain are expected to have broad implications for nanoelectromechanical systems.

Single-step fabrication of surface morphology tuned iron oxide anchored highly porous carbon nanotube hybrid foam for a highly stable supercapacitor electrode.

The pseudocapacitive metal oxide anchored nanocarbon-based three-dimensional (3D) materials are considered attractive electrode materials for high-performance supercapacitor applications. However, the complex multistep synthesis approaches raise production costs and act as a major barrier to the practical real-world field. To overcome this limitation, in this study, an easily scalable and effective fabrication approach for the development of iron oxide (Fe3O4) anchored highly porous carbon nanotube hybrid foam (f-Fe3O4/O-CNTF) with micro/mesoporous structure was suggested to improve the durability and energy storage performance. The surface morphology-tuned f-Fe3O4/O-CNTF (f-Fe3O4/O-CNTF(M)) was fabricated through electromagnetic interaction between the anchored magnetic Fe3O4 on the CNT surface and the applied magnetic field. The obtained results clearly demonstrated that the changed surface morphology of the f-Fe3O4/O-CNTF(M) strongly affected the meso- and micropore structure, electrochemical performance, and durability. Consequently, the f-Fe3O4/O-CNTF(M) showed an almost 120% enhanced specific surface area and nearly 1.9 times increased specific capacitance compared to that of the f-Fe3O4/O-CNTF. Furthermore, the changed surface morphology successfully prevented the re-aggregation of the initial structure and significantly improved durability. As a result, f-Fe3O4/O-CNTF(M) showed outstanding cycling stability, maintaining almost 100% capacitance retention after 14,000 cycles. Consequently, the assembled symmetric supercapacitor device delivered an energy density of 20.1 Wh·kg-1 at a power density of 0.37 kW·kg-1 with good cycling stability. These results suggest that the f-Fe3O4/O-CNTF(M) can potentially be used as an electrode for supercapacitors with good durability.

MoS2 -Carbon Nanotube Porous 3 D Network for Enhanced Oxygen Reduction Reaction.

Future generation power requirement triggers the increasing search for electrocatalysts towards oxygen reduction, which is the pivotal part to enhance the activity of metal-air batteries and fuel cells. The present article reports a novel 3 D composite structure weaving 1 D carbon nanotubes (CNT) and 2 D MoS2 nanosheets. The MoS2 -CNT composite exhibits excellent electrocatalytic activity for the oxygen reduction reaction (ORR) in alkaline environment. Measurements show better methanol immunity and higher durability than Pt/C, which is considered the state-of-the-art catalyst for ORR. Experimental results suggest that the hybridization of 1 D functionalized multiwalled CNTs (MWCNTs) and exfoliated 2 D MoS2 nanosheet results significant synergistic effect, which greatly promotes the ORR activity. This work presents a new avenue to rationally design a 3 D porous composite out of 1 D and 2 D interlaced components and demonstrate appreciable electrochemical performance of the materials towards ORR activity for fuel cells as well as metal-air batteries.

Magnetic field controlled graphene oxide-based origami with enhanced surface area and mechanical properties.

One can utilize the folding of paper to build fascinating 3D origami architectures with extraordinary mechanical properties and surface area. Inspired by the same, the morphology of 2D graphene can be tuned by addition of magnetite (Fe3O4) nanoparticles in the presence of a magnetic field. The innovative 3D architecture with enhanced mechanical properties also shows a high surface area (∼2500 m2 g-1) which is utilized for oil absorption. Detailed microscopy and spectroscopy reveal rolling of graphene oxide (GO) sheets due to the magnetic field driven action of magnetite particles, which is further supported by molecular dynamics (MD) simulations. The macroscopic and local deformation resulting from in situ mechanical loading inside a scanning electron microscope reveals a change in the mechanical response due to a change internal morphology, which is further supported by MD simulation.

Role of Atomic Layer Functionalization in Building Scalable Bottom-Up Assembly of Ultra-Low Density Multifunctional Three-Dimensional Nanostructures.

Building three-dimensional (3D) structures from their constituent zero-, one-, and two-dimensional nanoscale building blocks in a bottom-up assembly is considered the holey grail of nanotechnology. However, fabricating such 3D nanostructures at ambient conditions still remains a challenge. Here, we demonstrate an easily scalable facile method to fabricate 3D nanostructures made up of entirely zero-dimensional silicon dioxide (SiO2) nanoparticles. By combining functional groups and vacuum filtration, we fabricate lightweight and highly structural stable 3D SiO2 materials. Further synergistic effect of material is shown by addition of a 2D material, graphene oxide (GO) as reinforcement which results in 15-fold increase in stiffness. Molecular dynamics (MD) simulations are used to understand the interaction between silane functional groups (3-aminopropyl triethoxysilane) and SiO2 nanoparticles thus confirming the reinforcement capability of GO. In addition, the material is stable under high temperature and offers a cost-effective alternative to both fire-retardant and oil absorption materials.

Lightweight Hexagonal Boron Nitride Foam for CO2 Absorption.

Weak van der Waals forces between inert hexagonal boron nitride (h-BN) nanosheets make it easy for them to slide over each other, resulting in an unstable structure in macroscopic dimensions. Creating interconnections between these inert nanosheets can remarkably enhance their mechanical properties. However, controlled design of such interconnections remains a fundamental problem for many applications of h-BN foams. In this work, a scalable in situ freeze-drying synthesis of low-density, lightweight 3D macroscopic structures made of h-BN nanosheets chemically connected by poly(vinyl alcohol) (PVA) molecules via chemical cross-link is demonstrated. Unlike pristine h-BN foam which disintegrates upon handling after freeze-drying, h-BN/PVA foams exhibit stable mechanical integrity in addition to high porosity and large surface area. Fully atomistic simulations are used to understand the interactions between h-BN nanosheets and PVA molecules. In addition, the h-BN/PVA foam is investigated as a possible CO2 absorption and as laser irradiation protection material.

N-heterocyclic carbene-silver complex as a novel reference electrode in electrochemical applications.

We demonstrate a novel reference electrode material namely an organometallic silver complex e.g., silver (I) tetramethylbis(benzimidazolium) diiodide [1a] for both acid and alkaline electrolysis. The potential usage of the silver complex as a reference electrode with at least equal electrochemical capabilities compared to those of the conventional electrode materials (e.g., Hg/HgO in alkaline media and Ag/AgCl in acidic media) are also demonstrated using cyclic voltammetry. In addition, the well dispersed surface morphology and fine crystalinity of the silver complex is investigated using field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD).