Chemical displacements at solid interfaces. Easy cathodic reduction of alkyl bromides in the presence of iodide ions at palladized surfaces

Solid electrodes such as glassy carbon and platinum modified by “palladization” (galvanostatic deposits from acidic solutions of Pd²⁺) may exhibit exceptional catalytic capabilities, especially in the cathodic cleavage of alkyl bromides when achieved in the presence of traces of iodide ions. The use of such chemically modified surfaces leads to important potential shifts compared to the use of glassy carbon or smooth palladium in the absence of iodide. The catalytic behaviour is assigned to a nucleophilic-like displacement at the adsorbed state, between the organic bromide and iodide ion. Thus palladium surfaces can be successfully employed for cleaving carbon–halogen bonds at very moderate negative potentials. Preliminarily results have revealed that all palladized electrodes give an adsorption-like peak assigned to the corresponding alkyl iodide adsorbed on (or reacting with) the surface. The influence of different parameters like the organic substrate and the iodide concentration, the thickness of the palladium deposit, and the stand-by time before reduction are preliminarily presented. Such processes were found to be one-electron. However, electrodes were shown to readily age, presumably by strong adsorption of generated alkyl radicals.     

Voltammetric study on the complex of thiram-copper(II) and its application

Based on the formation of tetramethylthiuram disulfide (thiram)-copper(II) complex by square-wave voltammetry on a glassy carbon electrode, a new method is proposed for determination of thiram. There is a good linear relationship between peak current and concentration of thiram in the range of  mol l⁻¹ (r=0.999). The method is applied to the determination of thiram residue in plant with satisfactory results, compared with results achieved by using HPLC. Two oxidation peaks and two reduction peaks are obtained by cyclic voltammetry on a glassy carbon electrode in 0.2 mol l⁻¹ HAc-NaAc (pH 4.0) solution containing thiram-copper(II) complex. The electrode reaction process is quasi-reversible with adsorptive characteristics. The mechanism of electrode reaction is discussed.     

Cloud point extraction and determination of trace trichlorfon by high performance liquid chromatography with ultraviolet-detection based on its catalytic effect on benzidine oxidizing

4-Amino-4′-nitrobiphenyl, which is formed by catalytic effect of trichlorfon on sodium perborate oxidizing benzidine, is extracted with a cloud point extraction method and then detected using a high performance liquid chromatography with ultraviolet detection (HPLC-UV). Under the optimum experimental conditions, there was a linear relationship between trichlorfon in the concentration range of 0.01-0.2 mg L⁻¹ and the peak areas of 4-amino-4′-nitrobiphenyl (r = 0.996). Limit of detection was 2.0 μg L⁻¹, recoveries of spiked water and cabbage samples ranged between 95.4-103 and 85.2-91.2%, respectively. It was proved that the cloud point extraction (CPE) method was simple, cheap, and environment friendly than extraction with organic solvents and had more effective extraction yield.     

Reusability of immobilized β-glucosidase on sodium alginate-coated magnetic nanoparticles and high productivity applications

The purpose of this study is to detect the impact of the covalent immobilization of β-glucosidase (β-Glu) from Thermatoga maritima on sodium alginate-based magnetically recyclable iron nanoparticles (SA-Fe₃O₄ MNPs) for boosting robustness, facile retrieval, and recycling of enzyme. We developed a novel green method to amend the transformation of lactose to galacto-oligosaccharides (GOS). The interaction of the Immobilized β-Glu and SA-Fe₃O₄ MNPs were characterized by SDS-PAGE, Transmission electron microscope (TEM) and FT-IR spectroscopy. After immobilization, the ideal pH maintained 7.0, the optimum temperature (temp.) increased to 85 °C and deceptive K_m and V_max raised by 65 and 41%, respectively. Immobilization provided low activation energy and enhanced pH and heat stability. The SA-Fe₃O₄ MNPs maintained the effectiveness of enzyme by 39.52% up to the 6th cycle of reuse and the hydrolysis power exceed 28.13% of lactose to GOS. Conclusively, thermal stability, improved pH, and excellent reusability over β-Glu make SA-Fe₃O₄ MNPs a viable option for long-term GOS production as well as other industrial uses.     

Urban dynamics and multiple-objective programming: A case study of Beijing

This study serves as a primary application of the integrated system dynamics and multiple-objective programming (ISDMOP) model for strategic planning of Beijing city, which is here divided into six subsystems as population, resources, energy, economy, environment and ecosystem, with the planning horizon spanning from 2003 to 2020. Comparison between the original system dynamics (ORSD) model based on the existing economic structure of Beijing and the optimized system dynamics (OPSD) model adjusted according to the solutions of the multiple-objective programming (MOP) are conducted. The developing trend of each subsystem is simulated and illuminated, based on which constructive suggestions are provided for urban strategic planning of Beijing. The ISDMOP model is proved effective for investigating urban dynamics and realizing the multiple-objective programming.     

固相萃取-液相色谱质谱法测定稻米中乙虫腈对映体残留

在3种不同的纤维素手性柱上,对亚砜类手性杀虫剂乙虫腈对映体进行了反相高效液相色谱拆分研究,通过优化手性色谱柱和流动相,实现了乙虫腈对映体基线分离,结合液相色谱-圆二色检测器分析,柱流出顺序为(+)-、(-)-对映体,并在此基础上建立了稻米中乙虫腈对映异构体残留量的高效液相色谱-串联质谱分析方法.稻米样品加水浸润,乙腈高速匀浆、盐析,上清液旋转浓缩后经氨基固相萃取柱净化,洗脱液经氮气吹干后定容.采用纤维素-三(3-氯-4-甲基苯基氨基甲酸酯)(Lux Cellulose-2)手性色谱柱,以甲醇-水(60∶40,V/V)为流动相,液相色谱-串联质谱电喷雾负离子扫描进行分析,外标法定量.以精米和糙米为基质进行3个添加水平和5次重复性实验,结果表明:添加浓度为0.01～0.2 mg/kg,样品中乙虫腈单一对映体平均添加回收率为87.4％～97.8％,相对标准偏差(RSD,n=5)为3.1％～9.3％,方法检出限(LOD)为0.001 mg/kg,定量限(LOQ)为0.003 mg/kg.     

菠菜和苏州青类囊体溶液的光谱特性

通过分析不同波长光激发下菠菜(Spinach)和苏州青(Suzhou Green)类囊体溶液的发射光谱和荧光光谱,以及同一波长下磁场处理前后类囊体溶液的光谱变化,探讨了低强度稳恒磁场对类囊体溶液的作用机理.结果表明,类囊体溶液中形成了大量的氢键,磁场处理前菠菜和苏州青的氢键喇曼散射峰为531nm和533.2nm,两者光系统II(PSII)荧光分别在689.8nm和686nm;磁场处理后两者的喇曼散射峰变为532.8nm和532.4nm,PSII荧光变为686.8nm和685.4nm.磁场改变了两样品中氢键键能,使其趋于相等.     

Branching optical signals by fractional vortex dipoles

We study the evolution and interaction of semi-infinite dark beams carrying phase dislocations, where step- and screw-like phase profiles are combined. Similar to dark beams with a finite length, semi-infinite dark beams tend to move in transversal direction with respect to their background beam. In addition, they develop a snake-like instability and optical vortices detach from their bending ends. We are looking for appropriate conditions to control the process of concatenating and crossing the ends of several such semi-infinite dark beams in a way suitable for probe-beam branching and routing in self-defocusing Kerr nonlinear media. Colinear and perpendicular probe beam propagations in the optically-induced guiding structures are modeled and analyzed with respect to the branching efficiency to respective virtual output channels.