Antibacterial activity and action mechanism of flavonoids against phytopathogenic bacteria.

As the most difficult to control in plant disease, phytopathogenic bacteria cause huge losses to agricultural products and economy worldwide. However, the commercially available bactericides are few and enhance pathogen resistance. To alleviate this situation, 50 flavonoids were evaluated for their antibacterial activities and mechanism of action against two intractable plant bacterial pathogens. The results of bioassays showed that most of the flavonoids exhibited moderate inhibitory effects against Xanthomonas oryzae (Xo) and Xanthomonas axonopodis pv citri (Xac). Remarkably, kaempferol showed excellent antibacterial activity against Xo in vitro (EC50 = 15.91 µg/mL) and quercetin showed the best antibacterial activity against Xac in vitro (EC50 = 14.83 µg/mL), which was better than thiodiazole copper (EC50 values against Xo and Xac were 16.79 µg/mL, 59.13 µg/mL, respectively). Subsequently, in vivo antibacterial activity assay further demonstrated kaempferol exhibited a stronger control effect on bacterial infections than thiodiazole copper. Then, the preliminary antibacterial mechanism of kaempferol was investigated by ultrastructural observations, transcriptomic, qRT-PCR analysis and biochemical index determination. These results showed that kaempferol mainly exerted bacteriostatic effects at the molecular level by affecting bacterial energy metabolism, reducing pathogenicity, and leading to disruption of cellular integrity, leakage of contents and cell death eventually.

Atomically thin half-van der Waals metals enabled by confinement heteroepitaxy.

Atomically thin two-dimensional (2D) metals may be key ingredients in next-generation quantum and optoelectronic devices. However, 2D metals must be stabilized against environmental degradation and integrated into heterostructure devices at the wafer scale. The high-energy interface between silicon carbide and epitaxial graphene provides an intriguing framework for stabilizing a diverse range of 2D metals. Here we demonstrate large-area, environmentally stable, single-crystal 2D gallium, indium and tin that are stabilized at the interface of epitaxial graphene and silicon carbide. The 2D metals are covalently bonded to SiC below but present a non-bonded interface to the graphene overlayer; that is, they are 'half van der Waals' metals with strong internal gradients in bonding character. These non-centrosymmetric 2D metals offer compelling opportunities for superconducting devices, topological phenomena and advanced optoelectronic properties. For example, the reported 2D Ga is a superconductor that combines six strongly coupled Ga-derived electron pockets with a large nearly free-electron Fermi surface that closely approaches the Dirac points of the graphene overlayer.

Antifungal Activity and Action Mechanism Study of Coumarins from Cnidium monnieri Fruit and Structurally Related Compounds.

The increasing resistance of plant diseases caused by phytopathogenic fungi highlights the need for highly effective and environmentally benign agents. The antifungal activities of Cnidium monnieri fruit extracts and five isolated compounds as well as structurally related coumarins against five plant pathogenic fungi were evaluated. The acetone extract, which contained the highest amount of five coumarins, showed strongest antifungal activity. Among the coumarin compounds, we found that 4-methoxycoumarin exhibited stronger and broader antifungal activity against five phytopathogenic fungi, and was more potent than osthol. Especially, it could significantly inhibit the growth of Rhizoctonia solani mycelium with an EC50 value of 21 µg mL-1 . Further studies showed that 4-methoxycoumarin affected the structure and function of peroxisomes, inhibited the ß-oxidation of fatty acids, decreased the production of ATP and acetyl coenzyme A, and then accumulated ROS by damaging MMP and the mitochondrial function to cause the cell death of R. solani mycelia. 4-Methoxycoumarin presented antifungal efficacy in a concentration- dependent manner in vivo and could be used to prevent the potato black scurf. This study laid the foundation for the future development of 4-methoxycournamin as an alternative and friendly biofungicide.

Spin-Dependent Thermoelectric Power of Nanoislands.

The Seebeck effect explains the generation of electric voltage as a result of a temperature gradient. Its efficiency, defined as the ratio of the generated electric voltage to the temperature difference, is sensitive to local inhomogeneities that alter the scattering rate and the density of the conduction electrons. Spin-polarized Seebeck tunneling generates a distinct thermovoltage in spin-up and spin-down charge transport channels, which, as a key to spin caloritronics, focuses on transport phenomena related to spin and heat. Here, we report spatially resolved measurement of the spin-dependent thermovoltage in a tunneling junction formed by ferromagnetic Co nanoislands and a Ni tip using spin-dependent scanning tunneling thermovoltage microscopy (SP-STVthM). We resolve the nanoscale thermoelectric powers with respect to spin polarization, nanoisland size, stacking order of Co layers on a Cu substrate, and local sample heterogeneities. The observed thermally generated spin voltages are supported by first-principles and model calculations.

Facile Size-Selective Defect Sealing in Large-Area Atomically Thin Graphene Membranes for Sub-Nanometer Scale Separations.

Atomically thin graphene with a high-density of precise subnanometer pores represents the ideal membrane for ionic and molecular separations. However, a single large-nanopore can severely compromise membrane performance and differential etching between pre-existing defects/grain boundaries in graphene and pristine regions presents fundamental limitations. Here, we show for the first time that size-selective interfacial polymerization after high-density nanopore formation in graphene not only seals larger defects (>0.5 nm) and macroscopic tears but also successfully preserves the smaller subnanometer pores. Low-temperature growth followed by mild UV/ozone oxidation allows for facile and scalable formation of high-density (4-5.5 × 1012 cm-2) useful subnanometer pores in the graphene lattice. We demonstrate scalable synthesis of fully functional centimeter-scale nanoporous atomically thin membranes (NATMs) with water (∼0.28 nm) permeance ∼23× higher than commercially available membranes and excellent rejection to salt ions (∼0.66 nm, >97% rejection) as well as small organic molecules (∼0.7-1.5 nm, ∼100% rejection) under forward osmosis.

Exceptional ballistic transport in epitaxial graphene nanoribbons.

Graphene nanoribbons will be essential components in future graphene nanoelectronics. However, in typical nanoribbons produced from lithographically patterned exfoliated graphene, the charge carriers travel only about ten nanometres between scattering events, resulting in minimum sheet resistances of about one kilohm per square. Here we show that 40-nanometre-wide graphene nanoribbons epitaxially grown on silicon carbide are single-channel room-temperature ballistic conductors on a length scale greater than ten micrometres, which is similar to the performance of metallic carbon nanotubes. This is equivalent to sheet resistances below 1 ohm per square, surpassing theoretical predictions for perfect graphene by at least an order of magnitude. In neutral graphene ribbons, we show that transport is dominated by two modes. One is ballistic and temperature independent; the other is thermally activated. Transport is protected from back-scattering, possibly reflecting ground-state properties of neutral graphene. At room temperature, the resistance of both modes is found to increase abruptly at a particular length--the ballistic mode at 16 micrometres and the other at 160 nanometres. Our epitaxial graphene nanoribbons will be important not only in fundamental science, but also--because they can be readily produced in thousands--in advanced nanoelectronics, which can make use of their room-temperature ballistic transport properties.

Tuning Magnetic Soliton Phase via Dimensional Confinement in Exfoliated 2D Cr1/3NbS2 Thin Flakes.

Thin flakes of Cr1/3NbS2 are fabricated successfully via microexfoliation techniques. Temperature-dependent and field-dependent magnetizations of thin flakes with various thicknesses are investigated. When the thickness of the flake is around several hundred nanometers, the softening and eventual disappearance of the bulk soliton peak is accompanied by the appearance of other magnetic peaks at lower magnetic fields. The emergence and annihilation of the soliton peaks are explained and simulated theoretically by the change in spin spiral number inside the soliton lattice due to dimensional confinement. Compared to the conventional magnetic states in nanoscale materials, the stability and thickness tunability of quantified spin spirals make Cr1/3NbS2 a potential candidate for spintronics nanodevices beyond Moore's law.

[Determination of forbidden and restricted pesticides in Angelicae Sinensis Radix].

The present study is to establish a method for simultaneous determination of 50 kinds of pesticides in Angelicae Sinensis Radix by using liquid chromatography tandem mass spectrometry. The forbidden,restricted and customary pesticides were picked out as detecting indexes according to the principals of risk management. The factors affecting the extraction,purification,and detection were optimized,and the final condition was established as follows: the samples were extracted with acetonitrile. The separation of target compounds were performed by liquid column,and quantitative analysis was carried out by LC-MS/MS with MRM model. The calibration curves were linear in the range of 1-100 µg·L~(-1) with correction coefficients of greater than 0. 990. The recoveries of more than 93. 9%pesticides were ranged from 60% to 140% at three spiked levels. The detecting indexes in the method cover most forbidden and restricted pesticides,which is meaningful for the safety supervision of the Angelicae Sinensis Radix. With the advantage of rapidness and accuracy,this method can be used for routine determination of multi-pesticides in Angelicae Sinensis Radix.

Accessing the Intrinsic Spin Transport in a Topological Insulator by Controlling the Crossover of Bulk-to-Surface Conductance.

We report a method to control contributions of bulk and surface states in the topological insulator Bi_{2}Te_{2}Se that allows accessing the spin-polarized transport endowed by topological surface states. An intrinsic surface dominant transport is established when cooling the sample to low temperature or reducing the conduction channel length, both achieved in situ in the transport measurements with a four-probe scanning tunneling microscope without the need of further tailoring the sample. The topological surface states show characteristic transport behaviors with mobility about an order of magnitude higher than reported before, and a spin polarization approaching the theoretically predicted value. Our result demonstrates accessibility to the intrinsic high mobility spin transport of topological surface states, which paves a way to realizing topological spintronic devices.

3D Imaging and Manipulation of Subsurface Selenium Vacancies in PdSe_{2}.

Two-dimensional materials such as layered transition-metal dichalcogenides (TMDs) are ideal platforms for studying defect behaviors, an essential step towards defect engineering for novel material functions. Here, we image the 3D lattice locations of selenium-vacancy V_{Se} defects and manipulate them using a scanning tunneling microscope (STM) near the surface of PdSe_{2}, a recently discovered pentagonal layered TMD. The V_{Se} show a characterisitc charging ring in a spatially resolved conductance map, based on which we can determine its subsurface lattice location precisely. Using the STM tip, not only can we reversibly switch the defect states between charge neutral and charge negative, but also trigger migrations of V_{Se} defects. This allows a demonstration of direct "writing" and "erasing" of atomic defects and tracing the diffusion pathways. First-principles calculations reveal a small diffusion barrier of V_{Se} in PdSe_{2}, which is much lower than S vacancy in MoS_{2} or an O vacancy in TiO_{2}. This finding opens an opportunity of defect engineering in PdSe_{2} for such as controlled phase transformations and resistive-switching memory device application.

Surface Magnetism of Cobalt Nanoislands Controlled by Atomic Hydrogen.

Controlling the spin states of the surface and interface is key to spintronic applications of magnetic materials. Here, we report the evolution of surface magnetism of Co nanoislands on Cu(111) upon hydrogen adsorption and desorption with the hope of realizing reversible control of spin-dependent tunneling. Spin-polarized scanning tunneling microscopy reveals three types of hydrogen-induced surface superstructures, 1H-(2 × 2), 2H-(2 × 2), and 6H-(3 × 3), with increasing H coverage. The prominent magnetic surface states of Co, while being preserved at low H coverage, become suppressed as the H coverage level increases, which can then be recovered by H desorption. First-principles calculations reveal the origin of the observed magnetic surface states by capturing the asymmetry between the spin-polarized surface states and identify the role of hydrogen in controlling the magnetic states. Our study offers new insights into the chemical control of magnetism in low-dimensional systems.

Seamless Staircase Electrical Contact to Semiconducting Graphene Nanoribbons.

Electrical contact to low-dimensional (low-D) materials is a key to their electronic applications. Traditional metal contacts to low-D semiconductors typically create gap states that can pin the Fermi level (EF). However, low-D metals possessing a limited density of states at EF can enable gate-tunable work functions and contact barriers. Moreover, a seamless contact with native bonds at the interface, without localized interfacial states, can serve as an optimal electrode. To realize such a seamless contact, one needs to develop atomically precise heterojunctions from the atom up. Here, we demonstrate an all-carbon staircase contact to ultranarrow armchair graphene nanoribbons (aGNRs). The coherent heterostructures of width-variable aGNRs, consisting of 7, 14, 21, and up to 56 carbon atoms across the width, are synthesized by a surface-assisted self-assembly process with a single molecular precursor. The aGNRs exhibit characteristic vibrational modes in Raman spectroscopy. A combined scanning tunneling microscopy and density functional theory study reveals the native covalent-bond nature and quasi-metallic contact characteristics of the interfaces. Our electronic measurements of such seamless GNR staircase constitute a promising first step toward making low resistance contacts.

Detection of the Spin-Chemical Potential in Topological Insulators Using Spin-Polarized Four-Probe STM.

We demonstrate a new method for the detection of the spin-chemical potential in topological insulators using spin-polarized four-probe scanning tunneling microscopy on in situ cleaved Bi_{2}Te_{2}Se surfaces. Two-dimensional (2D) surface and 3D bulk conductions are separated quantitatively via variable probe-spacing measurements, enabling the isolation of the nonvanishing spin-dependent electrochemical potential from the Ohmic contribution. This component is identified as the spin-chemical potential arising from the 2D charge current through the spin momentum locked topological surface states (TSS). This method provides a direct measurement of spin current generation efficiency and opens a new avenue to access the intrinsic spin transport associated with pristine TSS.

Differentiation of Surface and Bulk Conductivities in Topological Insulators via Four-Probe Spectroscopy.

We show a new method to differentiate conductivities from the surface states and the coexisting bulk states in topological insulators using a four-probe transport spectroscopy in a multiprobe scanning tunneling microscopy system. We derive a scaling relation of measured resistance with respect to varying interprobe spacing for two interconnected conduction channels to allow quantitative determination of conductivities from both channels. Using this method, we demonstrate the separation of 2D and 3D conduction in topological insulators by comparing the conductance scaling of Bi2Se3, Bi2Te2Se, and Sb-doped Bi2Se3 against a pure 2D conductance of graphene on SiC substrate. We also quantitatively show the effect of surface doping carriers on the 2D conductance enhancement in topological insulators. The method offers a means to understanding not just the topological insulators but also the 2D to 3D crossover of conductance in other complex systems.

[Thinking on development of Shanxi Astragali Radix industry].

Shanxi, a traditional production area to produce genuine Astragali Radix of high quality, has experienced major changes in the pattern of resources. This area once accounted for half of Astragali Radix industry, but now only serves as the largest supply area of traditional wild Astragali Radix. Furthermore, the strategic position of Shanxi Astragali Radix industry will become more prominent and more important to economic and social development in face of the diversity of market demands, especially for the strong demands of high-end Astragali Radix. In addition, Astragalus industry involves the simultaneous development of the first, second and tertiary industries in many areas, and it is typical and representative in the traditional Chinese medicine industry development. However, the application and industrial development of Shanxi Astragali Radix have been restricted due to the problems such as blind promotion of transplanting cultivation technology, and lack of science and technology including efficacy investigation, safety evaluation, standardization and controllability studies. Therefore, we would analyze the production history, resource structure, the current situation and progress of industry development, scientific research foundation and existing problem in this paper, and put forward countermeasures for development and technical innovation in order to make Astragali Radix industry bigger and stronger through innovation-driven and make benefits for demos. This thought provides a reference for the exploratory development of other large varieties of Chinese medicinal materials.

[Evaluation analysis of alkaloids in seed of Sophora flavescens from Shanxi province and exploration of its utilization value].

According to the research strategy of resource chemistry of Chinese medicinal materials and Chinese medicinal resources recycling utilization, this study intends to explore the potential resource-oriented utilization value of the seed of Sophora flavescens by contrasting with its kindred plant S. alopecuroides. This study established a rapid UPLC-Q-TOF-MS/MS and UPLC-TQ-MS/MS method to determine the alkaloids in the seed of S. flavescens. Results of UPLC-Q-TOF-MS/MS analysis showed that the alkaloids in the seed of S. flavescens were highly similar with S. alopecuroides.In the determination of 7 kinds of alkaloids, the total content was 11.203 and 15.506 mg•g⁻¹ in the seed of S. flavescens and S. alopecuroides, respectively. The content of oxymatrine, oxysophocarpine and sophoridine is high in the seed of S. flavescens. The results indicated that the seeds of S. flavescens. could be an important material resource to obtain alkaloids.

[Analysis and evaluation of alkaloids and flavonoids in flower of Sophora flavescens from Shanxi province].

This study intends to explore the potential resource-orientedutilization value of the flower of Sophora flavescents by analyzing alkaloids and flavonoids in the flower of S. flavescens from Shanxi province. This study established a rapid UPLC-TQ-MS/MS method that is used for determination of seven alkaloids and seven flavonoids in the flower of S.flavescens. The different florescences all have the seven detected alkaloids such as cytisine, oxy-matrine, oxy-sophocarpine, sophoridine, N-methylcytisine, matrine, sophocarpine.The total contents of detected alkaloids are as follows: flower buds 1.47%, primal flowers 1.34%, full bloomed flowers 1.17%, faded flowers 1.01%. The top three contents of alkaloids are N-methylcytisine , oxy-sophocarpine and oxymatrine, accounting for about 83% of the total amount of detected alkaloids. All the samples in different florescences have the seven detected flavonoids such as rutin, luteolin, quercetin, isoquercitrin, trifolirhizin, kurarinone, and kushenol I. The total contents of detected alkaloids are as follows: flower buds 495.2 µg•g⁻¹, primal flowers 313.7 µg•g⁻¹, faded flowers 224.2 µg•g⁻¹, full bloomed flowers 193.0 µg•g⁻¹. The content of luteolinis relatively higher than other detected flavonoids, accounting for about 89%-94% of the total amount of detected flavonoids. The results indicated that the flower of S.flavescens could be an important material resource to obtain the resourceful alkaloids. This result can provide scientific basis for resource-oriented utilization and industrial development of the flower of S. flavescens.

Anti-tumor activities of active ingredients in Compound Kushen Injection.

Kushen (Radix Sophorae Flavescentis) has a long history of use for the treatment of tumors, inflammation and other diseases in traditional Chinese medicine. Compound Kushen Injection (CKI) is a mixture of natural compounds extracted from Kushen and Baituling (Rhizoma Smilacis Glabrae). The main principles of CKI are matrine (MT) and oxymatrine (OMT) that exhibit a variety of pharmacological activities, including anti-inflammatory, anti-allergic, anti-viral, anti-fibrotic and cardiovascular protective effects. Recent evidence shows that these compounds also produce anti-cancer actions, such as inhibiting cancer cell proliferation, inducing cell cycle arrest, accelerating apoptosis, restraining angiogenesis, inducing cell differentiation, inhibiting cancer metastasis and invasion, reversing multidrug resistance, and preventing or reducing chemotherapy- and/or radiotherapy-induced toxicity when combined with chemotherapeutic drugs. In this review, we summarize recent progress in studying the anti-cancer activities of MT, OMT and CKI and their potential molecular targets, which provide clues and references for further study.

Atomic-scale mapping of thermoelectric power on graphene: role of defects and boundaries.

The spatially resolved thermoelectric power is studied on epitaxial graphene on SiC with direct correspondence to graphene atomic structures by a scanning tunneling microscopy (STM) method. A thermovoltage arises from a temperature gradient between the STM tip and the sample, and variations of thermovoltage are distinguished at defects and boundaries with atomic resolution. The epitaxial graphene has a high thermoelectric power of 42 µV/K with a big change (9.6 µV/K) at the monolayer-bilayer boundary. Long-wavelength oscillations are revealed in thermopower maps which correspond to the Friedel oscillations of electronic density of states associated with the intravalley scattering in graphene. On the same terrace of a graphene layer, thermopower distributions show domain structures that can be attributed to the modifications of local electronic structures induced by microscopic distortions (wrinkles) of graphene sheet on the SiC substrate. The thermoelectric power, the electronic structure, the carrier concentration, and their interplay are analyzed on the level of individual defects and boundaries in graphene.

Polaronic transport and current blockades in epitaxial silicide nanowires and nanowire arrays.

Crystalline micrometer-long YSi2 nanowires with cross sections as small as 1 × 0.5 nm(2) can be grown on the Si(001) surface. Their extreme aspect ratios make electron conduction within these nanowires almost ideally one-dimensional, while their compatibility with the silicon platform suggests application as metallic interconnect in Si-based nanoelectronic devices. Here we combine bottom-up epitaxial wire synthesis in ultrahigh vacuum with top-down miniaturization of the electrical measurement probes to elucidate the electronic conduction mechanism of both individual wires and arrays of nanowires. Temperature-dependent transport through individual nanowires is indicative of thermally assisted tunneling of small polarons between atomic-scale defect centers. In-depth analysis of complex wire networks emphasize significant electronic crosstalk between the nanowires due to the long-range Coulomb fields associated with polaronic charge fluctuations. This work establishes a semiquantitative correlation between the density and distributions of atomic-scale defects and resulting current-voltage characteristics of nanoscale network devices.