Photoluminescent Semiconducting Graphene Nanoribbons via Longitudinally Unzipping Single-Walled Carbon Nanotubes.

The lack of a sizeable band gap has so far prevented graphene from building effective electronic and optoelectronic devices despite its numerous exceptional properties. Intensive theoretical research reveals that a band gap larger than 1 eV can only be achieved in sub-3 nm wide graphene nanoribbons (GNRs), but real fabrication of such ultranarrow GNRs still remains a critical challenge. Herein, we demonstrate an approach for the synthesis of ultranarrow and photoluminescent semiconducting GNRs by longitudinally unzipping single-walled carbon nanotubes. Atomic force microscopy reveals the unzipping process, and the resulting 2.2 nm wide GNRs are found to emit strong and sharp photoluminescence at ∼685 nm, demonstrating a very desirable semiconducting nature. This band gap of 1.8 eV is further confirmed by follow-up photoconductivity measurements, where a considerable photocurrent is generated, as the excitation wavelength becomes shorter than 700 nm. More importantly, our fabricated GNR field-effect transistors (FETs), by employing the hexagonal boron nitride-encapsulated heterostructure to achieve edge-bonded contacts, demonstrate a high current on/off ratio beyond 105 and carrier mobility of 840 cm2/V s, approaching the theoretical scattering limit in semiconducting GNRs at room temperature. Especially, highly aligned GNR bundles with lengths up to a millimeter are also achieved by prepatterning a template, and the fabricated GNR bundle FETs show a high on/off ratio reaching 105, well-defined saturation currents, and strong light-emitting properties. Therefore, GNRs produced by this method open a door for promising applications in graphene-based electronics and optoelectronics.

High speed chalcogenide glass electrochemical metallization cells with various active metals.

We fabricated electrochemical metallization cells using a GaLaSO solid electrolyte, an InSnO inactive electrode and active electrodes consisting of various metals (Cu, Ag, Fe, Cu, Mo, Al). Devices with Ag and Cu active metals showed consistent and repeatable resistive switching behaviour, and had a retention of 3 and >43 days, respectively; both had switching speeds of <5 ns. Devices with Cr and Fe active metals displayed incomplete or intermittent resistive switching, and devices with Mo and Al active electrodes displayed no resistive switching ability. Deeper penetration of the active metal into the GaLaSO layer resulted in greater resistive switching ability of the cell. The off-state resistivity was greater for more reactive active metals which may be due to a thicker intermediate layer.

Differential expression of a cysteine proteinase and cystatin pair as side­by­side fusion forms in Escherichia coli.

As a basic study, the fusion expressions of two functionally related proteins were described. The side by side fusion construction, expression, purification and functional characterization of Arabidopsis papain-like cysteine proteinase (CP) and cysteine proteinase inhibitor (CPI) were successfully carried out by using an Escherichia coli expression system without affecting the recombinant bacterial growth. The purification products of two different fused constructs designated as «R1: H2N-maltose binding protein-CPI-CP-COOH and R2: H2N-maltose binding protein-CP-CPI-COOH¼ showed inverse enzymatic/inhibitory activities, in vitro. Analysis of the constructs by using computational tools revealed that the arrangement of CP/CPI pair in fusion forms might be the important criteria for proper tertiary organization, structural folding and functional property. The overall results showed that the C-terminally located molecule could be the active folded structure in each fusion construct. The achievements of the present work may be utilized in a specific protein engineering application such as manufacturing the novel switchable expression systems in the future.

The possible involvement of D-amino acids or their metabolites in Arabidopsis cysteine proteinase/cystatin N-dependent proteolytic pathway.

Cysteine proteinases and their inhibitors 'cystatins' play essential roles in plant growth and development. They are involved in various signaling pathways and in the response to wide ranges of biotic and abiotic environmental stresses. To investigate their possible influence from D-amino acids or their metabolism in vivo, Arabidopsis seedlings were allowed to grow under four physicochemically different D-amino acids including D-aspartate, D-serine, D-alanine and D-phenylalanine containing media. The reverse transcription polymerase chain reaction (R T-PCR) analysis of cysteine proteinase and cystatin gene expressions showed that the addition of D-amino acid to the plant growth media considerably induce the expression of proteinase transcript while decrease the expression level of inhibitor gene in the leaf and root tissues of the test plant in overall. Based on the obtained results the potential impact of D-amino acids or their metabolism on the activity of cysteine proteinase/cystatin-dependent proteolytic apparatus as well as their possible cooperation were predicted and discussed in the plant system.

Maltose-binding protein switches programmed cell death in Nicotiana glutinosa leaf cells.

Maltose-binding protein (MBP) is a part of the complex regulatory and transport maltose system of Escherichia coli that is responsible for the uptake and efficient catabolism of maltodextrins through the transmembrane signaling at the expense of ATP. In the present work, this bacterial periplasmic protein was identified as a cell death inducer in Nicotiana glutinosa plant. Upon exogenous application at the concentrations more than 50 microg/ml, purified MBP protein induced wilting and localized cell death on the leaves of test plant. DNA fragmentation assay and antioxidant enzymes activity test showed that the induced cell death might be programmed. It was predicted that maltose-binding protein signals programmed cell death (PCD) upstream of reactive oxygen species (ROS) and DNA fragmentation processes in the test plant leaves. However, it needs to be clarified that how MBP switches and signals PCD in plant tissues.

Differential fusion expression and purification of a cystatin in two different bacterial strains.

To date, the identification of the novel multifunctional properties of cysteine proteinase inhibitors "known as cystatins" is the great of interests for molecular biologists. The efficient production, purification and correctly folded form of these proteins are the most important requirements for their any basic research. To the best of our knowledge, maltose-binding protein (MBP) fusion tags are being used to overcome the impediment to their heterologous recombinant expression in Escherichia coli as insoluble and bio-inactive inclusion bodies. In the present work, to evaluate the expression efficiency of a cystatin molecule in E. coli cells by using MBP tags, the expression of Celosia cystatin was studied in two different strains of this bacterium. The quantitative analysis results based on the one-step purification yield of the fused product showed the excellency of the E. coli TB1 strain in comparison to E. coli DH5alpha for the high-level production of active product.

Comparative fusion expression of maize SINAT5 in two different strains of Escherichia coli.

SINAT5 is a plant E3 ligase that regulates auxin signaling and root morphogenesis by ubiquitination of the NAC1 protein. Consequently, it may be a putative regulator of aspects of plant development cycles that are controlled by auxin. Efficient production, purification and correctly folded form of this protein are important requirements for functional studies. We produced and quantitatively compared fusion expression of the "maltose binding protein (mbp)-maize sinat5" construct in two different strains of Escherichia coli. One-step purification of fused products gave about 33 mg protein/L bacterial cell culture for E. coli TB1 cells and approximately 18 mg protein/L bacterial cell culture for E. coli DH5α cells. Continuous expression of the fused product and similarity of growth patterns were observed in both cultures.

Over-expression, purification and functional characterization of Celosia ClpS as a fused protein in Escherichia coli.

A ClpS homologue from Celosia cristata was expressed as maltose-binding fusion protein under the control of strong inducible tac promoter of pMALc2X vector in TB 1 strain of Escherichia coli. SDS-PAGE analysis showed that fused ClpS is produced as about 63 kDa protein in recombinant bacteria. Expressed product was purified to homogeneity with a yield of about 31 mg/l of bacterial culture. The results indicated that heterologous expression of Celosia ClpS does not affect bacterial growth under different induced conditions. Total cellular antioxidant assessment results revealed that the induction of ClpS activates the bacterial antioxidative system. Since, the purified ClpS did not exhibit antioxidant activity in vitro, we speculated a functional corelation between bacterial protelolytic apparatus and its anti-oxidative system. This prediction may contribute to our better understanding of functional relationship between proteolytic and antioxidative systems in biological worlds in the future investigations.

Early detection of immunization: a study based on an animal model using 1H nuclear magnetic resonance spectroscopy.

Vaccines require a period of at least three months for clinical trials, hence a method that can identify elicitation of immune response a few days after the first dose is a necessity. Evolutionary variable selections are modeling approaches for proper manipulation of available data which were used to set up an animal model for classification of time dependent 1HNMR metabolomic profiles and pattern recognition of fluctuations of metabolites in two groups of male rabbits. One group of rabbits was immunized with human red blood cells and the other used as control. Blood was obtained every 48 h from each rabbit for a period of six weeks and the serum monitored for antibodies and metabolites by 1HNMR spectra. Evaluation of data was carried out using orthogonal signal correction followed by principal component analysis and partial least square. A neural network was also set up to predict immunization profiles. A distinct separation in patterns of significant metabolites was obtained between the two groups, just a few days after the first and the second dose. These metabolites were used as targets of neural networks where each sample was used as test, validation and training and their quantitative influence predicted by regression. This model could be used for prediction of immunization in rabbits a few days after the first dose with 96% accuracy. Similar animals and human vaccine trials would assist greatly in reaching early conclusions in advance of the usual two month immunization schedule; resulting in an appreciable saving of cost and time.

Genome wide cloning of maize meiotic recombinase Dmc1 and its functional structure through molecular phylogeny.

The development of meiotic division and associated genetic recombination paved the way for evolutionary changes. However, the secondary and tertiary structure and functional domains of many of the proteins involved in genetic recombination have not been studied in detail. We used the human Dmc1 gene product along with secondary and tertiary domain structures of Escherichia coli RecA protein to help determine the molecular structure and function of maize Dmc1, which is required for synaptonemal complex formation and cell cycle progression. The maize recombinase Dmc1 gene was cloned and characterized, using rice Dmc1 cDNA as an orthologue. The deduced amino acid sequence was used for elaborating its 3-D structure, and functional analysis was made with the CDD software, showing significant identity of the Dmc1 gene product in Zea mays with that of Homo sapiens. Based on these results, the domains and motives of WalkerA and WalkerB as ATP binding sites, a multimer site (BRC) interface, the putative ssDNA binding L1 and L2 loops, the putative dsDNA binding helix-hairpin-helix, a polymerization motif, the subunit rotation motif, and a small N-terminal domain were proposed for maize recombinase Dmc1.