Dynamic pH junction-sweeping for on-line focusing of dipeptides in capillary electrophoresis with laser-induced fluorescence detection

In this paper, we developed a simple and effective on-line focusing technique combining dynamic pH junction and sweeping by capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection. Dynamic pH junction-sweeping is defined when the sample has a different buffer pH (dynamic pH junction condition) and is devoid of micelles (sweeping condition) relative to the background electrolyte (BGE). This hyphenated focusing mode was applied to the sensitive and selective focusing of four dipeptides: Tyr-Phe, Tyr-Leu, Trp-Gly, and Ala-Gln. Picomolar detectability of these dipeptides by CE-LIF detection was demonstrated through effective focusing of large sample volumes (up to 39% capillary length) using the dual pH junction-sweeping focusing mode. 25 mmol L(-1) sodium dihydrogen phosphate, pH 2.5 was used as the sample matrix, and 100 mmol L(-1) borate, 21 mmol L(-1) sodium dodecylsulfate (SDS), 16 mmol L(-1) Brij35, pH 9.0 as the background solution (BGS). The concentration detection limits (S/N = 3) of the four dipeptides were in the range of 1.0-5.0 pmol L(-1). The developed method has been successfully used for the determination of dipeptides in human serum samples.     

Nitrate enhanced electrochemiluminescence determination of tris(2,3-dibromopropyl) isocyanurate with a gold nanoparticles-modified gold electrode

Tris(2,3-dibromopropyl) isocyanurate (TBC) is a heterocyclic hexabrominated flame retardant, which cannot be degraded even over a long time and may be a potential environmental pollutant. In this paper, TBC is for the first time as far as we know determined by silver nitrate-enhanced electrochemiluminescence (ECL) using a gold nanoparticles (AuNPs)-modified gold electrode. In our experiments, TBC was found to have the characteristics of increasing the ECL intensity of Ru(bpy)(3)(2+), and the ECL signal was proportional to the concentration of TBC. Based on this, we have successfully developed a novel, fast and sensitive method for the analysis of TBC. The main influencing factors including the volume ratio of acetonitrile and water, and the concentration of Ru(bpy)(3)(2+) were investigated in detail. Compared with using a bare gold electrode in MeCN without AgNO(3), the limit of detection is remarkably lowered by 20 times and the linear range is expanded by 5 times by using the AuNPs-modified gold electrode and AgNO(3). Under the optimal conditions, a limit of detection of 5.0 × 10(-8) M (S/N = 3) is achieved with a linear range of 1.0 × 10(-7) to 5.0 × 10(-5) M. The mechanism of the ECL enhancement of the system is also investigated.     

1H NMR研究溶质浓度对三碳多元醇水溶液氢键作用以及玻璃化的影响

为考察溶质浓度对三碳多元醇水溶液氢键作用以及不同物质玻璃态形成能力的影响,采用¹H NMR外标法研究不同浓度的1-丙醇（NPA）,2-丙醇（IPA）,1,2-丙二醇（PG）,1,3-丙二醇（PD）和丙三醇（glycerol）的水溶液在室温常压下质子化学位移.结果表明:具有CH₃CH（OH）一基团的PG烷基质子的化学位移变化趋势与其他几种醇相比有较大差异.醇羟基质子与水分子的氧形成较强O-H…O氢键.相同摩尔分数下,羟基数的增加导致水质子和羟基质子的化学位移降低,而且羟基位置不同也会导致水质子和羟基质子化学位移差异.这几种三碳多元醇碱性强弱的顺序和降低冰的均相成核温度能力的顺序一致,即glycerol>PG>PD>IPA>NPA,¹H NMR技术表明glycerol和PG更适合用作低温保护剂.     

胶束电动色谱-激光诱导荧光检测法测定肌松弛药巴氯芬

以4-氯-7-硝基苯并-2-氧杂-1,3-二唑(NBD-Cl)为柱前衍生试剂,建立了胶束电动色谱-激光诱导荧光检测法测定肌松弛药巴氯芬(BAL)的新方法。经过实验条件的优化,采用15 mmol/L硼砂、20 mmol/L十二烷基硫酸钠、10%(v/v)乙腈、pH 9.75的缓冲体系,在分离电压为17.5 kV、柱温为25 ℃的条件下,压力进样3.45 kPa(0.5 psi)×3 s,巴氯芬及其内标物的衍生产物在7 min内实现较好的基线分离,线性范围为0.025～25 mg/L,相关系数为0.9999,检出限(S/N=3)和定量限(S/N=10)分别为0.90 μg/L和6.25 μg/L。该方法被应用于巴氯芬制剂及加入巴氯芬对照品的尿液样品分析,回收率范围分别为101.6%～107.9%和107.0%～109.6%。该方法有望应用于巴氯芬药物制剂的质量监控以及为巴氯芬药物代谢的研究提供辅助手段。     

Efficient Synthesis of Functionalized Benzimidazoles and Perimidines: Ytterbium Chloride Catalyzed C?C Bond Cleavage

An efficient method is developed for the synthesis of functionalized benzimidazoles and perimidines by the condensation of aryl diamines with β‐carbonyl compounds catalyzed by ytterbium chloride. The reactions give good yields under mild conditions. A mechanism involving a lanthanide activated C C bond cleavage is proposed.     

Effect of Structural Parameters of TiO2 Nanotube Arrays upon Their Photocatalytic/Photoelectrocatalytic Performance

The effect of structural parameters of TiO₂ nanotube arrays (TNAs) upon their photocatalytic/photoelectro‐catalytic performance is studied by comparing the morphological characteristics and physicochemical properties with different tube lengths prepared from three kinds of electrolytes. The results show that the UV‐Vis absorption edge of TNAs red‐shifted with the increment of tube length and the short TNAs possess higher bandgap energy. The variation tendency of electrochemical window of TNAs is DMSO (5.5 V)>Cit (3.2 V)>HF (1.8 V). The long TNAs possess higher photocatalytic (PC) reactivity suggesting the surface roughness factor is the main determinant of PC efficiency, although, there is obvious recombination effects for the long TNAs. Evidenced by the positive correlation between tube length and photoelectrocatalytic (PEC) efficiency for TNAs from the same electrolyte, the enhancement of the tube length could lead to better PEC reactivity, but when the tube length is over a certain value, the PEC degradation rate no longer increases but decreases. The long TNAs with large surface roughness factor prepared from Cit and DMSO electrolytes exhibit comparative or even lower PEC performance compared with the short TNAs prepared from HF electrolyte, indicating that the PEC performance of TNAs was dominated by charge separation and photoelectron transfer properties rather than surface roughness coefficient and the tube length.     

Palladium-catalyzed Coupling between Aryl Halides and Trimethylsilylacetylene Assisted by Dimethylaminotrimethyltin

Palladium‐catalyzed coupling between aryl halides, especially less reactive ones or N‐heteroaryls, and trimethylsilylacetylene in the presence of dimethylaminotrimethyltin generated the coupled products in high yields. The reaction does not need CuI and base as auxiliary agents.     

Synthesis of 1‐Aryl‐1H‐indazoles via a Ligand‐Free Copper‐ Catalyzed Intramolecular Amination Reaction

A general synthesis of 1‐aryl‐1‐H‐indazoles from o‐halogenated aryl aldehydes or ketones and aryl hydrazines was described. This protocol included an intermolecular condensation and a ligand‐free copper‐catalyzed intramolecular Ullmann‐type coupling reaction. This method was applied to a wide range of substrates to produce the indazole products in good yields.     

Dielectric analysis on phase transition and micelle shape of polyoxyethylene trisiloxane surfactant in dilute aqueous solution

The cloudy Silwet L-77 aqueous solution on the concentration range from 0.5%to 50%was investigated by dielectric relaxation spectroscopy.The concentration dependence of phase microstructure was confirmed by means of analyzing the dielectric parameters of bulk solution.The relaxation behavior was assigned to the interfacial polarization between the micelle and the medium,and the relaxation distribution parameter was used to figure the shape transition from sphere to ellipsoid with the concentration increasing.The synchronous reduction of permittivity and conductivity indicated the formation of the lamellar phase. As compensation,the quantity of the surfactant liquid phase gradually decreased,whose shape constantly kept ellipsoidal.