Spin-polarized tunneling in a ferromagnetic graphene junction: Interplay between the exchange interaction and the orbital effect of the magnetic field

The influence of magnetic vector potential barrier (MVPB) on the spin-polarized transport of massless Dirac particles in ferromagnetic graphene is studied theoretically. The phenomenon of Klein tunneling of relativistic particles across a rectangular potential barrier prevents any of the massless fermions from being confined but they can be electrically confined by quantum dots with integrable dynamics (Bardarson et al., 2009) [36]. Utilization of only the in-plane exchange splitting in the ferromagnetic graphene cannot produce 100% spin polarization. This tunneling can be confined using the magnetic vector potential barrier, which leads to high degree of spin polarization. By combining the orbital effect and the Zeeman interaction in graphene junction, it is found that the junction mimics behavior of half-metallic tunneling junction, in which it acts as a metal to particles of one spin orientation but as an insulator or a semiconductor to those of the opposite orientation. The idea of the half-metallic tunneling junction can provide a source of ∼100% spin-polarized current, which is potentially very useful. Adjustment of the position of the Fermi level in ferromagnetic layer by placing a gate voltage on top of the ferromagnetic layer shows that reverse of the orientation of the completely spin-polarized current passing through the junction is controlled by adjusting the gate voltage. These interesting characteristics should lead to a practical gate voltage controlled spin filtering and spin-polarized switching devices as a perfect spin-polarized electron source for graphene-based spintronics.     

Chemical constituents and biological activities from branches of Colubrina asiatica

Sixteen compounds were isolated from a Thai medicinal plant, Colubrina asiatica. The isolated compounds were elucidated on the basis of spectroscopic methods (IR, 1D and 2D NMR) as six triterpene acids (1–6), five steroids (7–11), one benzoic acid derivative (12), two peptides (13 and 14), one sesquiterpenoid (15) and one jujubogenin (16). Compounds 3 and 10 showed antimalarial activity against Plasmodium falciparum. Compound 5 showed antimycobacterial activity. Moreover, compounds 3, 5, 6, 10 and 14 exhibited weak cytotoxicity against cancer cell lines. Compounds 1–15 have been isolated for the first time from this plant.     

Two new bioactive triterpenoids from the roots of Colubrina asiatica

Abstract

Two new ceanothane triterpenes, 3,7-O,O-dibenzoyl ceanothic acid methylester (1) and 3-O-acetyl-7-O-benzoyl ceanothic acid methylester (2), along with nine known compounds (3–11), were isolated from the roots of Colubrina asiatica. The isolated compounds were identified by spectroscopic evidence. Compounds 1 and 2 showed antimalarial activity against Plasmodium falciparum with IC₅₀ values of 4.67 and 3.07?µg/mL, respectively. Compound 2 also showed antimycobacterial activity against Mycobacterium tuberculosis (MIC 6.25?µg/mL). In addition, compounds 1, 2, 10 and 11 showed cytotoxicity against three cancer cell lines (KB, NCI-H187 and MCF-7) with IC₅₀ values ranging from 8.32 to 46.72?µg/mL.     

New p-terphenyl and benzoquinone metabolites from the bioluminescent mushroom Neonothopanus nambi

Abstract

Two new p-terphenyls, neonambiterphenyls A and B (1–2), a new benzoquinone, neonambiquinone A (3), together with six known sesquiterpenes (4–9), were isolated from the bioluminescent mushroom Neonothopanus nambi PW3. The isolated compounds were identified by mass, IR and spectroscopic analyses (1D and 2D NMR). Compounds 1–3 and 5–7 showed cytotoxicity against cancer cell lines such as KB, NCI-H187 and MCF-7 with IC₅₀ values ranging from 1.45 to 49.31?µg/mL. In addition, compounds 1 and 5 showed cytotoxicity against Vero cells with IC₅₀ values of 38.72 and 32.90?µg/mL, respectively.     

浅水海豚三维空间定位与发声源级测量

详细阐述了单水听器和水听器阵列进行海豚定距定位的几何模型,以及利用不同接收通道间的时延差计算空间坐标的方法,结合实验数据计算了海豚在水中的三维空间坐标和回声定位信号的声源级,并开展了海豚运动轨迹追踪分析。结果表明,相对于单水听器,水听器阵列对测量环境和海豚行为的限制较少,但对采集设备的同步性和硬件连接有较高要求。误差分析表明水听器阵列在大于3 m的距离,定位误差可降低到5%以下。研究结果为精确计算海豚发声源级及海豚的声呐性能及行为研究提供了技术支撑。      

Hydride Transfer Enables the Nickel-Catalyzed ipso-Borylation and Silylation of Aldehydes

Nickel-catalyzed ipso-borylations and silylations of aldehydes are described for the first time. The new functional-group interconversion protocol is characterized by its scalability, functional-group tolerance and wide substrate scope, including examples of late-stage functionalization of complex molecules. The key for the successful reaction outcome is the use of a ketone as a hydride acceptor that intercepts the nickel hydride to undergo a reductive pathway, thus allowing formation of the desired C−B and C−Si bonds.     

Preparation of anti-CD4 monoclonal antibody-conjugated magnetic poly(glycidyl methacrylate) particles and their application on CD4+ lymphocyte separation

Novel immunomagnetic particles have been prepared for separation of CD4⁺ lymphocytes. The magnetic nanoparticles with a diameter of approximately 5-6 nm were first synthesized by co-precipitation from ferrous and ferric iron solutions and subsequently encapsulated with poly(glycidyl methacrylate) (PGMA) by precipitation polymerization. Monoclonal antibody specific to CD4 molecules expressed on CD4⁺ lymphocytes was conjugated to the surface of magnetic PGMA particles through covalent bonding between epoxide functional groups on the particle surface and primary amine groups of the antibodies. The generated immunomagnetic particles have successfully separated CD4⁺ lymphocytes from whole blood with over 95% purity. The results indicated that these particles can be employed for cell separation and provide a strong potential to be applied in various biomedical applications including diagnosis, and monitoring of human diseases.     

Dispersive magnetic solid phase extraction using octadecyl coated silica magnetite nanoparticles for the extraction of tetracyclines in water samples

Magnetite nanoparticles coated with silica and hydrophobic octadecyl layers were successfully synthesized and used in magnetic solid phase extraction of tetracyclines from water samples. The magnetite nanoparticles facilitated a convenient magnetic separation of sorbent from an aqueous sample, the octadecyl layer helped to enhance the adsorption ability and the silica layer helped to prevent the aggregation of the magnetite nanoparticles. The effect of various parameters on the extraction efficiency were optimized including the amount of sorbent, sample pH, stirring rate, extraction time and desorption conditions. Under the optimum conditions, the recoveries were in the range of 82 to 88%, the calibration curves were linear over the concentration range of 0.002 to 1.0 μg/mL for oxytetracycline and 0.01 to 1.0 μg/mL for tetracycline and chlortetracycline, respectively. The developed method had several advantages such as simplicity, convenience, cost-effectiveness and high extraction efficiency.     

A new tocotrienol from the roots and branches of Allophylus cobbe (L.) Raeusch (Sapindaceae)

Abstract

A new tocotrienol, 5-hydroxy-8-methyltocotrienol (1) was isolated from the roots and branches of A. cobbe (L.) Raeusch, together with seventeen known compounds (2–18). Their structures were elucidated by analysis of spectroscopic data and by comparison of ¹H and ¹³C NMR data with previous literature reports. This is the first phytochemical investigation of the roots and branches of Allophylus cobbe (L.) Raeusch.