NHC-catalyzed [12+2] reaction of polycyclic arylaldehydes for access to indole derivatives.

An N-heterocyclic carbene (NHC) catalyzed enantio- and diastereoselective [12+2] cycloaddition is disclosed to rapidly construct sophisticated molecules bearing a tricyclic core and morpholine moiety. The success of our reaction relies on the NHC-catalyzed remote sp3 (C-H) bond activation of a 5H-benzo[a]pyrrolizine-3-carbaldehyde under oxidative conditions. Preliminary studies revealed that our products exhibit superior in vitro bioactivities against two plant pathogens to commercial Bismerthiazol (BT) and Thiodiazole Copper (TC).

Exploring Molecular Complexity by N-Heterocyclic Carbene Organocatalysis: New Activation and Reaction Diversity.

The development of catalytic synthetic approaches towards molecular complexity from simple materials continues to be an ultimate goal in synthetic chemistry. Over the past decades, N-heterocyclic carbene (NHC) organocatalysis has been extensively investigated to provide opportunities for a vast number of novel chemical transformations. Various activation modes and reactive intermediates enabled by NHC small-molecule catalysts, such as Breslow intermediates, (homo)enolates, acyl azoliums and their derived unsaturated azoliums exhibit great potential in the construction of complicated skeletons. This personal account will summarize our group's recent work in the exploration of new activation modes of NHC catalysis towards molecular complexity with a focus on the development and applications of NHC to achieve diversity and enantioselectivity in the preparation of functional molecules.

Sustainable alginate lyases catalyzed degradation of bio-based carbohydrates.

Alginate is a water-soluble and acidic polysaccharide derived from the cell wall and intercellular substance of brown algae. It is widely distributed in brown algae, such as Laminaria, Sargassum, and Macrocystis, etc. Alginate lyase can catalytically degrade alginate in a ß-eliminating manner, and its degradation product-alginate oligosaccharide (AOS) has been widely used in agriculture, medicine, cosmetics and other fields due to its wide range of biological activities. This article is mainly to make a brief introduction to the classification, source and application of alginate lyase. We hope this minireview can provide some inspirations for its development and utilization.

An Efficient Propagation System through Root Cuttings of an Ecological and Economic Value Plant-Broussonetia papyrifera (L.) L'Hér. ex Vent.

Broussonetia papyrifera (L.) L'Hér. ex Vent. has considerable economic and ecological value and a long history of use in China. In this paper, root cuttings were used as the material to establish an efficient vegetative propagation of B. papyrifera. The results revealed that root segments with a diameter of 1.5~2.0 cm and a length of 20~30 cm were most suitable for shoot regeneration, as these segments had the highest adventitious shoot induction rates (93.3%), strongest adventitious shoots, and highest multiplication coefficients (7.07). With regard to the methods used for root burial, a horizontal burial at a depth of 1~3 cm yielded the best results, in this case, the adventitious shoot induction rate can reach 86.7%. The best substrate combination was perlite: peat: coconut chaff = 1:1:1 (v/v/v), wherein the adventitious shoot induction rate can reach 75.6%. The best sterilization method was mixing soil with carbendazim and soaking the root sections in carbendazim for 30 min, wherein the adventitious shoot induction rate can reach 77.8%. Adding 0.2 mg/L naphthaleneacetic acid (NAA) to 1/4 Hoagland nutrient solution significantly improved the rooting rate of adventitious shoots to 82.2%, and the survival rate of the acclimatized plants was more than 90.0%.

Carbene-Catalyzed Enantioselective Aldol Reaction: Post-Aldol Stereochemistry Control and Formation of Quaternary Stereogenic Centers.

The dominated approaches for asymmetric aldol reactions have primarily focused on the aldol carbon-carbon bond-forming events. Here we postulate and develop a new catalytic strategy that seeks to modulate the reaction thermodynamics and control the product enantioselectivities via post-aldol processes. Specifically, an NHC catalyst is used to activate a masked enolate substrate (vinyl carbonate) to promote the aldol reaction in a non-enantioselective manner. This reversible aldol event is subsequently followed by an enantioselective acylative kinetic resolution that is mediated by the same (chiral) NHC catalyst without introducing any additional substance. This post-aldol process takes care of the enantioselectivity issues and drives the otherwise reversible aldol reaction toward a complete conversion. The acylated aldol products bearing quaternary/tetrasubstituted carbon stereogenic centers are formed in good yields and high optical purities.

Observer-based H∞ control for cyber-physical systems encountering DoS jamming attacks: An attack-tolerant approach.

In this paper, considering two typical attack strategies of a DoS jammer, a new kind of H∞ control problem is studied for Cyber-Physical Systems (CPSs) with different transmission mechanism encountering DoS jamming attacks. By defining a concept of working subcycle, the concrete attack strategies of a DoS jammer can be generated by choosing different reasonable value combinations in a unified framework according to the DoS jammer's energy efficiency and stealthiness. Then, for two different transmission mechanisms, namely the time-triggered mechanism (TTM) and the event-triggered mechanism (ETM), in which CPSs can employ in its wireless channels, two DoS jammers employ different attack strategies and launch SINR-based DoS jamming attacks to decrease the quality of wireless communication. Considering the case that the CPSs do not know the DoS jammers' attack strategies, the corresponding H∞ observer-based controllers are designed by using an attack-tolerant mechanism to achieve the desired H∞ disturbance attenuation level, and the controller design problems are transformed to auxiliary convex optimization problems. Finally, numerical simulations are presented to demonstrate the effectiveness of the proposed H∞ control methods and the varying of system performance under different interference power chosen by the DoS jammers.

Carbene-Catalyzed Enantioselective Aromatic N-Nucleophilic Addition of Heteroarenes to Ketones.

The aromatic nitrogen atoms of heteroarylaldehydes are activated by carbene catalysts to react with ketone electrophiles. Multi-functionalized cyclic N,O-acetal products are afforded in good to excellent yields and optical purities. Our reaction involves the formation of an unprecedented aza-fulvene-type acylazolium intermediate. A broad range of N-heteroaromatic aldehydes and electron-deficient ketone substrates works effectively in this transformation. Several of the chiral N,O-acetal products afforded through this protocol exhibit excellent antibacterial activities against Ralstonia solanacearum (Rs) and are valuable in the development of novel agrichemicals for plant protection.

[Antagonism against Beauveria bassiana by lipopeptide metabolites produced by entophyte Bacillus amyloliquefaciens strain SWB16].

OBJECTIVE: We screened bacterial strains that have strong antagonism against Beauveria bassiana, an important pathogen of silkworm industry, and detected the antagonistic activity of lipopeptide metabolites. METHODS: We identified bacterium SWB16 by morphological observation, physiological and biochemical experiments, 16SrRNA, and gyrA gene sequence analysis, tested antagonistic activity of strain SWB16 against Beauveria bassiana by measuring the inhibition zone diameter using filter paper diffusion method (Kirby-Bauer method), obtained lipopeptide metabolites of the strain using methanol extraction and observed the antagonism of strain SWB16 lipopeptide extracts against the conidia and hyphae of Beauveria bassiana, detected main ingredients and genes of lipopeptide metabolites by high-performance liquid chromatography-mass spectrometry and PCR amplification. RESULTS: SWB16 isolated from tissue of plant Dioscorea zingiberensis C. H. Wright belongs to Bacillus amyloliquefaciens and showed high antagonistic activity to Beauveria bassiana, and the lipopeptide extracts of isolate SWB16 exhibited significant inhibition to conidial germination and mycelial growth of Beauveria bassiana. The result of mass spectrometric detection indicated main component of the lipopeptide metabolites were fengcin and iturin, and genes fenB, ituA involved in the synthesis of them were amplified in the genome. CONCLUSION: Bacillus amyloliquefaciens strain SWB16 could produce lipopeptide antibiotics with strong antagonism to the entomopathogenic fungus Beauveria bassiana, and the results suggested that strain SWB16 has potential application value for controlling white muscardine of economic insects including silkworm.

Diversity analysis of Beauveria bassiana isolated from infected silkworm in southwest China based on molecular data and morphological features of colony.

Beauveria bassiana is an important entomopathogenic fungus that not only often causes infection and epidemics of wild insects but some strains also show pathogenicity to the silkworm, Bombyx mori. The present study is about diversity of B. bassiana isolated from the silkworm in southwest China. Five strains of B. bassiana were isolated from infected silkworm. Two isolates, GXtr1009 and GXtr1010, were isolated from infected silkworms treated with two kinds of biological pesticides applied in Guangxi province, and three isolates, SCsk1006, YNsk1106 and GXsk1011, were collected from naturally infected silkworms from different geographical locations in Yunnan and Sichuan. All of the isolates showed highly similar conidia and conidial fructification, but the colony characteristics demonstrated great differences among the isolates. The ITS and 18S rDNA sequence analysis was sufficient to identify all five isolates as B. bassiana. However, the dendrogram, based on the ISSR data, produced two large genetic groups. GXtr1009 and GXtr1010 comprised one group, and SCsk1006, YNsk1106 and GXsk1011 converged in a different large group. The results suggested that, although all of these five B. bassiana strains were pathogenic to silkworms, strains of biological pesticides could be differentiated from strains of naturally infected silkworm via ISSR analysis.

Effects of the transparent cathode on the performance of a relativistic magnetron with axial radiation.

Experimental investigation of the transparent cathode used in a relativistic magnetron with axial radiation is reported in this paper. The transparent cathode is composed of six separate stalks with the diameter of 6 mm. Under the working condition of 549 kV and ∼0.38 T, the relativistic magnetron with the transparent cathode experimentally produces a 550 MW microwave. The radiation mode is TE(11) at the frequency of 2.35 GHz. The total efficiency is 16.7%. The variations of the relative positions between the separate stalks and the anode blocks can perform the maximum difference of 4 ns in microwave duration. Compared with the conventional solid cathode, the transparent cathode provides faster startup time of 12 ns, relatively wider pulse duration of 35% and relatively higher efficiency of 10.6%.

Antibacterial effect and cytotoxicity of beta-1,3-1, 4-glucanase from endophytic Bacillus subtilis SWB8.

OBJECTIVE: We studied the antibiotic activity and selective cytotoxicity of beta-1,3-1,4-glucanase from endophytic Bacillus subtilis SWB8. METHODS: Based on gel permeation chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and liquid chromatography-tandem mass spectrometry methods, protein fragments of beta-1,3-1,4-glucanase from endophytic Bacillus subtilis strain SWB8 were purified and identified. Then, beta-1,3-1,4-glucanase was used to evaluate the antimicrobial activity against Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis, Escherichia coli, Salmonella typhi, Salmonella paratyphi A, Shigella dysenteriae, Candida albicans and Cryptococcus neoformans and cytotoxicity against human pulmonary adenocarcinoma cells (A549) and human bone marrow mesenchymal stem cells (MSCs) by using the disc diffusion, methyl thiazolyl tetrazolium and flow cytometry methods, respectively. RESULTS: Bacterial beta-1,3-1,4-glucanase showed broad antimicrobial spectrum against all nine bacterial and fungal strains. Furthermore, beta-1,3-1,4-glucanase possessed significant anticancer activity against A549 cells that the IC50 and IC90 values were 11.5 and 20.1 microg/mL, respectively. The percentage of apoptotic A549 cells treated with different concentrations of beta-1,3-1,4-glucanase was significantly increased from 4.43% of the control to 43.1% of 19.2 microg/mL glucanase in a dose dependent manner. In contrast, these changes could not be observed in human bone marrow mesenchymal stem cells. CONCLUSION: Beta-1,3-1,4-glucanase could be a potential source of desirable antimicrobial agent, or anticancer compounds with higher efficiency and lower toxicity.

Optimal filters with multiple packet losses and its application in wireless sensor networks.

This paper is concerned with the filtering problem for both discrete-time stochastic linear (DTSL) systems and discrete-time stochastic nonlinear (DTSN) systems. In DTSL systems, an linear optimal filter with multiple packet losses is designed based on the orthogonal principle analysis approach over unreliable wireless sensor networks (WSNs), and the experience result verifies feasibility and effectiveness of the proposed linear filter; in DTSN systems, an extended minimum variance filter with multiple packet losses is derived, and the filter is extended to the nonlinear case by the first order Taylor series approximation, which is successfully applied to unreliable WSNs. An application example is given and the corresponding simulation results show that, compared with extended Kalman filter (EKF), the proposed extended minimum variance filter is feasible and effective in WSNs.

Design of a simple annular electron beam source and its operating characteristics in single and repetitive shot modes.

In this work, design and performance of an annular carbon fiber cathode are presented. Measurements on this cathode were performed in a single high-voltage pulse generator (600 kV, 50 ns, and 50 Omega) and a repetitive one (350 kV, <10 ns, 180 Omega, and 100 Hz), respectively. In a single pulse regime, emphasis was placed on the uniformity of electron beam extracted from this cathode. It was found that this cathode could deliver uniform electron beams with current densities exceeding kA/cm(2). Cesium iodide (CsI) coating eliminated hot spots on the cathode surface, significantly improving the uniformity of electron emission. Under repetitively pulsed operation, this cathode exhibited a good shot-to-shot reproducibility at the pressure of 1.5x10(-4) Torr, suggesting an ability of surviving even in poor vacuum. However, once the base pressure rose up to 3.76x10(-4) Torr, the cathode performance gradually degraded as the pulse shot proceeded. Besides, some possible explanations for these experimental results are presented. These results show that given proper diode design, carbon fiber with CsI coating has great promise as electron emitter producing high-current electron beams.

A series of tufted carbon fiber cathodes designed for different high power microwave sources.

We report the fabrication technique of tufted carbon fiber cathodes for different microwave sources. Three carbon fiber cathodes were constructed, including a planar cathode, an annular cathode, and a cylindrical cathode for radial emission. Experimental investigations on these cathodes were performed in a reflex triode virtual cathode oscillator (vircator), a backward wave oscillator (BWO), and a magnetically insulated transmission line oscillator (MILO), respectively. The pulse duration of microwave emission from the reflex triode vircator was lengthened by using the planar carbon fiber cathode. In the BWO with the annular carbon fiber cathode, the uniform electron beam with a kA/cm(2) current density was observed. In addition, carbon fiber has great promise as field emitter for MILOs. These results show that the carbon fiber cathodes can be utilized for electron emission in high power diodes with different structures.