Homoclinic orbits for first order Hamiltonian systems with some twist conditions

In this paper, we study the nonperiodic first-order Hamiltonian system ù = J L(t)u +J H(t, u), where H ∈ C1(R × R2n). With some assumptions on L, the corresponding Hamiltonian operator has only discrete spectrum. By using the index theory for self-adjoint operator equation,we establish the existence of multiple homoclinic orbits for the asymptotically quadratic nonlinearty satisfying some twist conditions between infinity and origin.     

Total synthesis of Daphnodorin A

A total synthesis of Daphnodorin A, a member of the Daphnodorins, was accomplished. Key features of the synthetic strategy include construction of 2-substituted-3-functionalized benzofuran via intramolecular Heck reaction and a mild Barton–McCombie deoxygenation process mediated by triethylborane. The total synthesis provided Daphnodorin A in 19.7% or 5.6% overall yield over 7 or 15 steps.     

Novel organogelators based on pyrazine-2,5-dicarboxylic acid derivatives and their mesomorphic behaviors

A series of new low molecular organogelators (LMOGs) with thermotropic mesophase were synthesized via the reaction of 3,6-dimethyl-pyrazine-2,5-dicarboxylic acid with p-alkoxyl anilines. These compounds readily formed stable gels in a variety of organic solvents and their self-assembly behavior, structure–property relationship were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), ¹H nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectroscopy (FTIR) and ultra-violet–visible spectroscopy (UV). The results showed a combination of intra-hydrogen bonding, π–π stacking and van der Waals interaction resulted in the aggregation of the organogelators to form three-dimension fibrous networks. The gels formed were multi-responsive to environmental stimuli, such as temperature, fluorinion, and shear stress. More importantly, all the organogelators exhibited thermotropic hexagonal column mesophase as revealed by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and variable temperature XRD studies. A control compound was synthesized and its gelling ability was also checked.     

Fluorescent sensor based on dimesitylborylthiophene derivative for probing fluoride and cyanide

A new D-π-A dimesitylboron derivative with terminal phenothiazine bridged by fluorenevinyl (PFTB) has been synthesized. It was found that PFTB could selectively recognize fluoride and cyanide anions by naked eyes. Upon addition of F⁻ and CN⁻, the color of the solution of PFTB in DCM turned to yellowish-green from yellow and strong green emitting was observed under UV light, while the emission of PFTB in DCM was weak. Moreover, the presence of 10 equiv of tetrabutylammonium salts of other anions, such as Cl⁻, Br⁻, I⁻, AcO⁻, HSO₄⁻, H₂PO₄⁻, could not lead to obvious changes of the UV–vis absorption and the fluorescent emission spectra of PFTB. The detection limits of PFTB towards F⁻ and CN⁻ were 7.52×10⁻⁸ mol/L and 6.12×10⁻⁸ mol/L in DCM, respectively. Therefore, the D-π-A type triarylborane derivatives can be used as ‘turn on’ fluorescent sensors for detecting F⁻ and CN⁻.     

Electrochemical behavior of uranyl in ionic liquid 1-butyl-3-methylimidazolium chloride mixture with water

Electrochemical behaviors of U(VI) in 1-butyl-3-methylimidazolium chloride (C₄MimCl) with various water contents investigated by chronopotentiometry and cyclic voltammetry. The electrochemical reduction of U(VI) was identified to follow two processes: a lower valence intermediate U(V) was initially formed at the potential of ca. ?0.2 V(vs. Ag wire). Then, further deposition of UO₂ was followed at around ?0.8 V. Little amount of water (1–4 wt%) in C₄MimCl, however, has an effect on the U(VI) reduction by changing the current density of the redox reaction and the diffusion coefficient of U(VI) in C₄MimCl. The deposited product by potentiostatic electrolysis on the surface of stainless steel electrode was characterized by the scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) methods. Although the electrodeposited black film was amorphous, the electrochemical reduced product of U(VI) can be still confirmed to be UO₂ by XRD after the crystallization of the amorphous deposits at 1,073 K in nitrogen atmosphere.     

七水合三氯化铈-碘化钠催化氨基苯硫酚与高位阻α,β-不饱和酮的迈克尔加成反应

对七水合三氯化铈-碘化钠(CeCl3·7H2O-NaI)化邻氨基苯硫酚、对氯邻氨基苯硫酚、间氨基苯硫酚、对氨基苯硫酚和对甲基苯硫酚与α,β-不饱和酮(1a~1o)的迈克尔加成反应进行了系统研究.结果表明,CeCl3·7H2O-NaI-SiO2复合催化剂能有效催化邻氨基苯硫酚及对氯邻氨基苯硫酚与α,β-不饱和酮(1a~1o)的迈克尔加成反应.在优化的反应条件下,即n(CeCl3·7H2O)∶n(NaI)∶n(α,β-不饱和酮)=1∶2∶2,m(CeCl3·7H2O)∶m(SiO2)=1∶1.6,三氯甲烷作溶剂,反应温度为回流温度,反应时间为2 h,反应可达到中等产率(43.1%~58.8%).催化剂重复使用4次基本稳定.此外,提出了可能的催化机理.     

氨甲酰基硅烷与酮反应合成α-硅氧基酰胺衍生物

N,N-二甲基氨甲酰基三甲基硅烷与一系列芳基酮、不饱和芳基酮在无水无氧、105℃、甲苯作溶剂的条件下反应,合成了α-三甲基硅氧基酰胺衍生物,收率60%~89%,其结构用元素分析、1H NMR、13C NMR和IR等方法进行了表征.烷基烷基酮、烷基芳基酮、烷基不饱和芳基酮与N,N-二甲基氨甲酰基三甲基硅烷不反应.通过研究反应的影响因素发现,反应底物酮中与羰基相连的芳环上取代基的电子效应是该加成反应的重要影响因素,芳环上取代基的给电子能力越強,反应越慢.     

Fitting formula for the injection volume of a gas chromatograph for radio‐xenon sampling in the lower troposphere

GC is usually used for xenon concentration and radon removal in the International Monitoring System of the Comprehensive Nuclear‐Test‐Ban Treaty. In a gas chromatograph, the injection volume is defined to calculate the column capacity. In this paper, the injection volume was investigated and a fitting formula for the injection volume was derived and discussed subsequently. As a consequence, the xenon injection volume exponentially decreased with the column temperature increased, but exponentially increased as the flow rate increased.     

A wide range optical pH sensor for living cells using Au@Ag nanoparticles functionalized carbon nanotubes based on SERS signals

p-Aminothiophenol (pATP) functionalized multi-walled carbon nanotubes (MWCNTs) have been demonstrated as an efficient pH sensor for living cells. The proposed sensor employs gold/silver core-shell nanoparticles (Au@Ag NPs) functionalized MWCNTs hybrid structure as the surface-enhanced Raman scattering (SERS) substrate and pATP molecules as the SERS reporters, which possess a pH-dependent SERS performance. By using MWCNTs as the substrate to be in a state of aggregation, the pH sensing range could be extended to pH 3.0～14.0, which is much wider than that using unaggregated Au@Ag NPs without MWCNTs. Furthermore, the pH-sensitive performance was well retained in living cells with a low cytotoxicity. The developed SERS-active MWCNTs-based nanocomposite is expected to be an efficient intracellular pH sensor for bio-applications.