NaBF4对锂离子电池石墨负极性能的影响

利用恒流充放电、循环伏安、交流阻抗、SEM、EDS等测试技术研究了在锂离子电池石墨负极和浆过程中加入NaBF₄对其电化学性能的影响。结果表明:NaBF₄的最佳添加量为2%,可明显提高石墨电极的首次放电比容量和充放电效率;电极的自放电性能和循环稳定性得到明显改善。室温条件下,添加了2% NaBF₄的电极以放电容量计算的自放电率为0.87%·d^-1,比未添加时降低了15%;循环伏安、EDS以及SEM测试结果表明,四氟硼酸钠参与了石墨电极的成膜过程,改变了SEI膜的组分和形貌。     

Simultaneous derivatization and air-assisted liquid–liquid microextraction of some aliphatic amines in different aqueous samples followed by gas chromatography-flame ionization detection

The paper presents a new method based on simultaneous derivatization and air-assisted liquid–liquid microextraction (AALLME) for the extraction and preconcentration of some aliphatic amines prior to gas chromatography-flame ionization detection (GC-FID). Primary aliphatic amines are derivatized and extracted simultaneously by a fast reaction with butylchloroformate (derivatization agent/extraction solvent) under mild conditions. The mixture of butylchloroformate and aqueous sample solution is rapidly sucked into a 10-mL glass syringe and then is injected into a test tube with conical bottom and the procedure is repeated seven times. After centrifuging the resulted cloudy solution, the derivatized analytes in the sedimented phase are determined by GC-FID. The influence of main factors on the efficiency of derivatization/extraction procedure is studied. Under the optimal conditions, the enrichment factors (EFs) for aliphatic amines are obtained in the range of 248–360 and limits of detection (LODs) are between 0.30 and 2.6 μg L⁻¹. The obtained extraction recoveries ranged from 50 to 72% and the relative standard deviation (RSD) was less than 4.8% for intra-day (n = 6) and inter-days (n = 4) precision. The method is successfully applied to determine some aliphatic amines in environmental water samples.     

具有固定时滞的经济周期模型的动态分析

在经济活动中,投资行为和资本存量存在一定的时滞效应,这会影响经济周期模型的动态行为,进而使得投资政策对经济的稳定调整复杂化.考虑到资本存量的预期时间以及投资时滞对经济活动的影响,采用Hopf分岔理论,研究具有固定时滞的经济周期模型的均衡点的稳定性以及形成经济周期的条件.研究发现,投资过程中的投资时滞,以及投资决策中对于资本存量的预测时间构成经济周期产生的诱因;同时可通过政府投资政策调整达到预期均衡目标,这对保持经济周期稳定及经济政策制定有一定的指导作用.     

关于具有二次相关性收获率的捕食与被捕食系统极限环的存在性分析

讨论了一类两种群具有二次相关性收获率的捕食与被捕食系统,利用常微分定性方法和分支理论,得到了系统平衡点处的性态和极限环的存在性条件,并用Matlab软件对其进行数值模拟,推广了相关文献中两种群捕食模型定性分析的相应结论.     

Consequences of weak Allee effect on prey in the May–Holling–Tanner predator–prey model

In this work, a modified Holling–Tanner predator–prey model is analyzed, considering important aspects describing the interaction such as the predator growth function is of a logistic type; a weak Allee effect acting in the prey growth function, and the functional response is of hyperbolic type. Making a change of variables and time rescaling, we obtain a polynomial differential equations system topologically equivalent to the original one in which the non‐hyperbolic equilibrium point (0,0) is an attractor for all parameter values. An important consequence of this property is the existence of a separatrix curve dividing the behavior of trajectories in the phase plane, and the system exhibits the bistability phenomenon, because the trajectories can have different ω ? limit sets; as example, the origin (0,0) or a stable limit cycle surrounding an unstable positive equilibrium point. We show that, under certain parameter conditions, a positive equilibrium may undergo saddle‐node, Hopf, and Bogdanov–Takens bifurcations; the existence of a homoclinic curve on the phase plane is also proved, which breaks in an unstable limit cycle. Some simulations to reinforce our results are also shown. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,characterization and applications of schiff base chemosensor for determination of Cu2+ ions

A novel thiazole-based Schiffbase chemosensor SB1 with N- and O- donor atoms was synthesized and characterized by different techniques (UV–vis, ¹³C NMR, ¹H NMR, and FT-IR analysis). The chemosensor SB1 was used for the determination of Cu²⁺ ions in various samples. The significant spectral changes in absorption spectra of chemosensor SB1 at 220 and 416 nm and the color change from light yellow to yellowish-brown indicate high selectivity and sensitivity towards Cu²⁺ ions as compared to other cations (Na⁺, K⁺, Ag⁺, Zn²⁺, Ni²⁺, Pb²⁺, Mn²⁺, Mg²⁺, Co²⁺, Cd²⁺, Sn²⁺, Hg²⁺, Cr³⁺, Fe^3+, and Al³⁺). The sensing mechanism of SB1 was investigated through various techniques such as FT-IR, UV–vis and ¹H NMR titration experiment and further confirmed by DFT computational studies. The 2:1 binding mode between SB1 and Cu²⁺ ions was confirmed by Job‘s plot using UV–vis spectrophotometry. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.015 and 0.0471 µg mL^?1, respectively. The percent recovery of Cu²⁺ from various environmental samples was found to be 95.00–103.33% at various levels. These obtained results demonstrate that chemosensor SB1 is a cost-effective, facile, selective, sensitive, and colorimetric sensing platform to detect trace amounts of Cu²⁺ ions in variousenvironmental and agricultural samples.     

Design,synthesis and docking studies of new hydrazinyl-thiazole derivatives as anticancer and antimicrobial agents

Increase in the number of infections caused by pathogenic microbes in cancer patients has prompted the searcher to invest in the development of agents having dual anticancer and antimicrobial properties. The present study is concerned with synthesis and screening for anticancer and antimicrobial activity of a series of 5-hydrazinyl-2-(2-(1-(thien-2-yl)ethylidene)hydrazinyl)thiazole derivatives. The structure elucidation of the synthesized hydrazinyl thiazole derivatives was illustrated by spectroscopic and elemental analysis. All the newly synthesized compounds 5a-p were evaluated for in-vitro cytotoxic activity against breast carcinoma (MCF-7 cell line), hepatocellular carcinoma (HePG-2) and colorectal cancer (HCT-116) cell lines using MTT assay method. Compounds 5 g, 5h showed broad spectrum activity against three cancer cell lines with IC₅₀ ranged from 3.81 to 11.34 µM in compared to the reference drug Roscovitine (IC₅₀ = 9.32 to 13.82 µM), while compounds 5 l and 5 m were found to be more selective against HePG-2 and HCT-116 cell line (IC₅₀ = 9.29 and 8.93 µM respectively) and compound 5j was more selective against HePG-2 and MCF-7 cell lines (IC₅₀ = 6.73 and 10.87 µM respectively). The inhibitory activity of the most promising compounds was tested against the EGFR and ARO enzymes and were further tested for apoptosis and Annexin V/PI staining. The results of enzyme-based tests revealed that the tested compound 5j has a dual inhibitory effect on the EGFR and ARO enzymes with IC₅₀ = 82.8 and 98.6 nM respectively in compared to the reference drugs Erlotinib and Letrozole (IC₅₀ = 62.4 and 79 nM respectively). Furthermore, the majority of the tested hydrazinyl thiazole derivatives exhibited significant antimicrobial activity against the used pathogenic microbes species. Compounds 4b, 5h, 5j and 5 m exerted a good antibacterial and antifungal activity against all tested pathogenic microbes. Therefore, it was concluded that compounds 5 h, 5j and 5 m proved to possess dual anticancer and antimicrobial agent and may serves as a useful lead compounds in search for further modification or derivatization to give more potent and selective agents.     

Brassinin inhibits proliferation and induces cell cycle arrest and apoptosis in nasopharyngeal cancer C666-1 cells

BackgroundNasopharyngeal cancer is a tumor that occurs in the mucous epithelium of the nasopharynx. Due to its rapid growth and early metastatic nature, the successful treatment of nasopharyngeal cancer is highly challenging.ObjectiveHere, we intended to assess the in vitro anticancer property of brassinin against the nasopharyngeal cancer C666-1 cells.MethodologyThe in vitro free radical scavenging property of the brassinin was assessed by various free radical scavenging activities such as FRAP, DPPH, chemiluminescence (CL), and ORAC assays. The cytotoxic level of the brassinin (1–50 µM) against the nasopharyngeal cancer C666-1 cells and normal Vero cells were assessed by the MTT cytotoxicity assay. The levels of TBARS, GSH, and the SOD activity was assessed using kits. The level of ROS generation, MMP, and apoptosis were investigated by the respective fluorescent staining techniques. The flow cytometry analysis was done to scrutinize the cell cycle arrest. The Bax/Bcl-2 level and caspase activities were examined using respective kits.ResultsThe brassinin treatment effectively scavenged the free radicals, which are assessed by the FRAP, DPPH, chemiluminescence (CL), and ORAC assays. The proliferation of brassinin treated C666-1 cells were decreased remarkably, while the same concentration of brassinin did not disturbed the Vero cell viability. The 30 µM of brassinin effectively increased the ROS production, depleted the MMP, and stimulated the apoptosis in the C666-1 cells. The brassinin increased the TBARS and depleted the GSH and SOD in the C666-1 cells. The flow cytometry analysis revealed that the brassinin administration improved the G0/G1 ratio and decreased the proportion of cells with ‘S’ and ‘G2/M’ phase. The Bax, caspase-3 and ?9 were elevated and Bcl-2 level was decreased in the brassinin administered C666-1 cells.ConclusionOur findings discovered that the brassinin has the capacity to prevent the proliferation and stimulate the apoptotic cell death C666‐1 cells via blocking cell cycle and increasing oxidative stress and apoptotic markers. Hence, it can be a talented therapeutic agent to treat the nasopharyngeal cancer in the future.     

Design,Synthesis and Anticancer Activity of a New Series of N-aryl-N′-[4-(pyridin-2-ylmethoxy)benzyl]urea Derivatives

The development of cancer treatments requires continuous exploration and improvement, in which the discovery of new drugs for the treatment of cancer is still an important pathway. In this study, based on the molecular hybridization strategy, a new structural framework with an N-aryl-N’-arylmethylurea scaffold was designed, and 16 new target compounds were synthesized and evaluated for their antiproliferative activities against four different cancer cell lines A549, MCF7, HCT116, PC3, and human liver normal cell line HL7702. The results have shown seven compounds with 1-methylpiperidin-4-yl groups having excellent activities against all four cancer cell lines, and they exhibited scarcely any activities against HL7702. Among them, compound 9b and 9d showed greatly excellent activity against the four kinds of cells, and the IC₅₀ for MCF7 and PC3 cell lines were even less than 3 μM.     

Limit Cycles Bifurcating from a k-dimensional Isochronous Center Contained in ?n with k ? n

The goal of this paper is double. First, we illustrate a method for studying the bifurcation of limit cycles from the continuum periodic orbits of a k-dimensional isochronous center contained in ℝ ⁿ with n ⩾ k, when we perturb it in a class of differential systems. The method is based in the averaging theory. Second, we consider a particular polynomial differential system in the plane having a center and a non-rational first integral. Then we study the bifurcation of limit cycles from the periodic orbits of this center when we perturb it in the class of all polynomial differential systems of a given degree. As far as we know this is one of the first examples that this study can be made for a polynomial differential system having a center and a non-rational first integral. The first and third authors are partially supported by a MCYT/FEDER grant MTM2005-06098-C01, and by a CIRIT grant number 2005SGR-00550. The second author is partially supported by a FAPESP–BRAZIL grant 10246-2. The first two authors are also supported by the joint project CAPES–MECD grant HBP2003-0017.