Electrochemical recognition for tryptophan enantiomers based on 3, 4, 9, 10-perylenetetracarboxylic acid–chitosan composite film

A novel and simple chiral sensing platform had been successfully fabricated by means of amidation reaction between 3, 4, 9, 10-perylenetetracarboxylic acid (PTCA) and chitosan (CS) to form 3, 4, 9, 10-perylenetetracarboxylic acid–chitosan (PTCA–CS) composite film. Since CS has chiral center and PTCA has excellent electrical conductivity, the PTCA–CS composite modified glassy carbon electrode (PTCA–CS/GCE) could be treated as an effective electrochemical chiral sensor and applied for chiral discrimination of tryptophan (Trp) enantiomers theoretically. PTCA–CS composite was characterized by Fourier transform infrared (FTIR) spectroscopy and cyclic voltammetry (CV). When the prepared chiral sensing interface interacted with tryptophan isomers, a higher selectivity was received from D-Trp by differential pulse voltammetry (DPV). It indicated that the PTCA–CS/GCE can be treated as an electrochemical chiral sensor for the discrimination of Trp enantiomers. Further study demonstrated that the peak currents were linearly increased with the increasing percentage of L-Trp of Trp racemic mixture. Furthermore, the enantioselective interaction of the PTCA–CS/GCE was systematically studied by other experimental factors, such as the incubation time and acidity.     

用超临界二氧化碳重结晶分离菲蒽混合物

建立了一套以超临界二氧化碳及其改性流体为重结晶溶剂的等压温差超临界流 重结晶实验装置。用色谱保留值法评价了ＳＦＲ分离菲蒽的试验条件。研究了该实验装置影响重结晶的因素，并对同分异构体型菲蒽模型混合物进行了ＳＦＲ分离纯化。     

Prediction of financial distress: An empirical study of listed Chinese companies using data mining

The deterioration in profitability of listed companies not only threatens the interests of the enterprise and internal staff, but also makes investors face significant financial loss. It is important to establish an effective early warning system for prediction of financial crisis for better corporate governance. This paper studies the phenomenon of financial distress for 107 Chinese companies that received the label ‘special treatment’ from 2001 to 2008 by the Shanghai Stock Exchange and the Shenzhen Stock Exchange. We use data mining techniques to build financial distress warning models based on 31 financial indicators and three different time windows by comparing these 107 firms to a control group of firms. We observe that the performance of neural networks is more accurate than other classifiers, such as decision trees and support vector machines, as well as an ensemble of multiple classifiers combined using majority voting. An important contribution of the paper is to discover that financial indicators, such as net profit margin of total assets, return on total assets, earnings per share, and cash flow per share, play an important role in prediction of deterioration in profitability. This paper provides a suitable method for prediction of financial distress for listed companies in China.     

High-quality alloyed CdSxSe1-x whiskers as waveguides with tunable stimulated emission

High-quality ultra-long alloyed CdS(x)Se(1)(-)(x) (0 < or = x < or = 1) whiskers were obtained by a simple thermal evaporation route. The near band-edge emission in these whiskers can be effectively guided at the sub-millimeter scale under continuous-wave laser excitation. As good optical waveguide cavities, the whiskers exhibit stimulated emissions under pulsed light excitation at room temperature for all compositions 0 < or = x < or = 1. The spectral positions of the sharp emission lines of the whiskers were tuned by their compositions, covering the spectral range from green to red.     

Synthesis,crystal structure and magnetic properties of [Mn(LH)2(H2O)2] n with a two-dimensional layered structure and three-dimensional hydrogen bonding network

A new manganese polymer [Mn(LH)₂(H₂O)₂] _n (LH₂ = iminodiacetic acid) (1) has been prepared and structurally and magnetically characterized. The polymer has a two-dimensional (2D) layered structure with the unique Mn atom on an inversion center, surrounded by six oxygen atoms. In each layer, all iminodiacetic acid entities are coordinated to Mn atoms in a bridging/bidentate mode, thus linking the [Mn(LH)₂(H₂O)₂] monomeric units together to form a 2D layered polymer. Hydrogen bonding is responsible for an extended three-dimensional network. Analysis of variable-temperature magnetic susceptibility data (2–300) K shows that the polymer displays weak antiferromagnetic exchange interaction with a coupling constant, J = –0.28 cm^–1.     

碳素基体固相微萃取吸附质的研制

研制了石墨型碳素基体固相微萃取吸附质,并以该新型固相微萃取装置联用气相色谱 电子捕获检测器分析水体中的有机农药。考察了吸附萃取时间及离子强度对分析结果的影响,并与商品装置进行了对比,结果表明其具有很好的应用前景。     

Good Laboratory Practice for optimization research

Good Laboratory Practice has been a part of non-clinical research for over 40 years. Optimization Research, despite having many papers discussing standards being published over the same period of time, has yet to embrace standards that underpin its research. In this paper we argue the need to adopt standards in optimization research. Building on previous papers, many of which have suggested that the optimization research community should adopt certain standards, we suggest a concrete set of recommendations that the community should adopt. We also discuss how the proposals in this paper could be progressed.     

Simultaneous determination of oleanolic acid,ursolic acid,quercetin and apigenin in Swertia mussotii Franch by capillary zone electrophoresis with running buffer modifier

The method of capillary zone electrophoresis (CZE) with direct UV detection was developed for the determination of oleanolic acid, ursolic acid, quercetin and apigenin. and then for the first time successfully applied to the analysis of four analytes in Swertia mussotii Franch and its preparations. Various factors affecting the CZE procedure were investigated and optimized, and the optimal conditions were: 50 × 10^?3 mol/L borate‐phosphate buffer (pH 9.5) with 5.0 × 10^?3 mol/L β‐cyclodextrin, 15 kV separation voltage, 20 °C column temperature, 250 nm detection wavelength and 5 s electrokinetic injection time (voltage 20 psi). Under the conditions, oleanolic acid, ursolic acid, quercetin and apigenin could be determined within the test ranges with a good correlation coefficient (r² > 0.9991). The limits of detection for conditions, oleanolic acid, ursolic acid, quercetin and apigenin were 0.3415, 0.2003, 0.0062 and 0.2538 µg/mL, respectively, and the intra‐ and inter‐day relative standard deviations were no more than 4.72%. This procedure provided a convenient, sensitive and accurate method for simultaneous determination of oleanolic acid, ursolic acid, quercetin and apigenin in S. mussotii Franch. Copyright © 2014 John Wiley & Sons, Ltd.     

新固相微萃取—气相色谱法分析大气中芳烃物质

用石墨吸附质棒固相微萃取装置吸附、富集大气芳烃污染物，于气相以谱中解吸并分析。实验表明此法具有无溶剂、快速、简便、灵敏等优点，具有很大的实用性。     

In situ growth and phenyl functionalization of titania nanoparticles coating for solid-phase microextraction of ultraviolet filters in environmental water samples followed by high performance liquid chromatography–UV detection

Based on TiO₂-nanoparticles coating fabricated by a one-step anodization method on titanium wire substrate, a novel phenyl functionalized solid-phase microextraction (SPME) fiber coating was prepared by simple and rapid in situ chemical assembling technique between the fiber surface titanol groups and trichlorophenylsilane reaction. The as-fabricated fiber exhibited good extraction capability for some UV filters and was employed to determine the ultraviolet (UV) filters in combination with high performance liquid chromatography–UV detection (HPLC–UV). The main parameters affecting extraction performance were investigated and optimized. Under the optimized conditions, the developed method was applied to detect several UV filters at trace concentration levels with only 8 mL of sample volume. They were determined in the range from 0.005 to 25 μg L⁻¹ with detection limits (S/N = 3) from 0.1 to 50 ng L⁻¹. The relative standard deviations (RSDs) for single fiber repeatability varied from 4.6 to 6.5% (n = 5) and fiber-to-fiber reproducibility (n = 5) ranged from 5.5 to 9.1%. The linear ranges spanned two-four magnitudes with correlation coefficients above 0.9990. Five real water samples including four Yellow River water samples and one rain water sample were determined sensitively with good recoveries ranging from 86.2 to 105.5%. The functionalized fiber coating performed good reproducible manner, high mechanical strength, good stability and long service life. Moreover, this study proposed an efficient sample pretreatment method for the determination of UV filters from environmental water samples.