基于离子液体的单滴液相微萃取-高效液相色谱法测定水中杀螨隆农药残留

建立了基于1-辛基-3-甲基咪唑六氟磷酸盐离子液体的单滴液相微萃取-高效液相色谱测定水中的杀螨隆农药残留的新方法.考察了萃取剂种类、萃取剂体积、液滴大小、萃取时间、搅拌速度、温度、盐度等对萃取效率的影响.在最佳条件下,该方法的线性范围为0.05～5 mg/L,r2=0.9994,RSD为2.1%(n=6),检出限为0....     

疏水高分子单链在疏水表面上吸附和扩散过程的分子动力学模拟

采用分子动力学模拟方法研究不同聚合度(N)的聚乙烯(PE)单链在Si(111)表面上的吸附和扩散行为. 分别设置相对介电常数为1和78模拟无溶剂和不良溶剂环境. PE单链的平衡吸附构象均呈现为二维吸附构象, 但在这两种截然不同的环境中呈现不同的构象和动力学特征, 说明溶剂环境对于疏水高分子单链在疏水表面上的吸附和扩散起到了很大的作用. 吸附能与聚合度呈线性关系, 单位链长的平均吸附能是-0.38 kJ·mol^-1. 另外, 扩散系数(D)与聚合度之间的标度关系是D~N^-3/2.     

全伸展DNA链折叠过程中三种非线性作用的布朗动力学模拟

脱氧核糖核酸(DNA)单分子链从完全拉伸状态折叠到平衡状态的动力学过程是溶液中DNA单分子力学的重要特征之一.通过构建全参数化的珠子-弹簧分子链模型,并运用一种高效平衡的半隐式预测——校验积分算法,系统研究了体积排斥作用、有限伸长弹性作用和涨落流体动力学作用等三种非线性作用对稀溶液中DNA分子链折叠过程相对回旋半径和驰豫时间的影响程度和变化趋势.模拟结果发现:体积排斥作用不影响分子链的折叠驰豫时间,但能显著减小平衡时的相对回旋半径;流体动力学作用不影响分子链的相对回旋半径,但明显缩短折叠过程的驰豫时间;有限伸长弹性作用能明显减小短链的相对回旋半径,能显著延长长链的折叠驰豫时间.模拟数据进一步表明:完全伸展的DNA分子链在折叠过程中的相对回旋半径随时间平滑变化,且折叠驰豫时间随长度的标度指数对上述三种非线性作用都具有两种不同的长度依赖性.     

Characterization of silicone oil emulsions stabilized by TiO2 suspensions pre-adsorbed SDS

To study the effects of pre-adsorbed emulsifier on Pickering emulsion stability, the preparation of silicone oil emulsions by TiO₂ suspensions pre-adsorbed sodium dodecyl sulfate (SDS) at the fixed TiO₂ concentration of 0.15 g was carried out below a fiftieth of critical micelle concentration (cmc) of SDS, where all added amounts of SDS are adsorbed on the TiO₂ particles. The stability of the Pickering emulsions incorporating TiO₂ suspensions pre-adsorbed SDS was investigated by measuring the volume fraction of emulsified silicone oil, adsorbed amounts of TiO₂ suspensions pre-adsorbed SDS, oil droplet size, and some rheological responses such as the stress-strain sweep curve and strain and frequency dependences of dynamic viscoelastic moduli. The silicone oil was almost emulsified by TiO₂ suspensions pre-adsorbed SDS above cmc/10³. Increasing in the adsorbed amount of SDS on the TiO₂ particles leads to an increase in the adsorbed amounts of TiO₂ suspensions pre-adsorbed SDS. Such silicone oil emulsions for the first time showed two yield stresses in the stress-strain sweep curve as well as the oscillatory stress-strain curve. The respective yield stresses also increase with an increase in the adsorbed amounts of TiO₂ suspensions pre-adsorbed SDS. From such characteristic rheological properties and a partial sedimentation of some TiO₂ particles remained in the dispersion medium, we proposed the formation of a three dimensional network of the flocculated TiO₂ particles pre-adsorbed SDS on the silicone oil droplets.     

Single atom doping in 2D layered MoS2 from a periodic table perspective

Molybdenum Disulfide (MoS₂) is a well-known transition metal dichalcogenide with a hexagonal structure arrangement analogous to graphene. Two dimensional (2D) MoS₂ has attracted wide attention in various applications such as energy storage, catalysis, sensing, energy conversion and optoelectronics due to its unique properties including tunable bandgap, substantial carrier mobility, outstanding mechanical strength and dangling-bond free basal surface. Moreover, MoS₂ has shown an excellent capability to be a host for foreign atoms which tune its physicochemical properties. Herein, currently known structural changes in the MoS₂ crystals introduced by various single atom dopants coming from all over the chemical table of elements are reviewed. Accompanying electrical, optical and magnetic properties of such structures are discussed in detail. Potential applications of the doped MoS₂ are introduced briefly as well. The review concentrates on the recent state-of-the-art results obtained mostly by the high resolution scanning transmission electron microscopy (STEM), such as high angle annular dark field (HAADF) imaging as well as scanning probe microscopy (SPM) such as scanning tunneling microscopy (STM). These techniques have been used to decipher dopant positions and other sub-atomic structural changes introduced to the MoS₂ structure by isolated dopants.     

Synthesis and characterization of N-heterocyclic carbene palladium complex and its application on direct arylation of benzoxazoles and benzothiazoles with aryl bromides

A mixed-halogen bis(1-(4-tert-butylbenzyl)-3-(2, 4, 6-trimethylbenzyl)-1H-benzo[d]imidazol-2-ylidene) palladium(II) complex, trans-[Pd(Cl_0.7Br_0.3)₂(C₂₈H₃₂N₂)₂], has been synthesized and characterized by elemental analysis, ¹H-NMR, ¹³C-NMR, and IR spectroscopy, and single crystal X-ray diffraction. The palladium in the mononuclear complex is four-coordinate in a square-planar configuration with two carbenes of two benzo[d]imidazole rings and two halides. The two halides are disordered between Br and Cl, with the Cl: Br ratio approximately 0.7 : 0.3. The angles C1–Pd1–Br1, 88.63(11)° and C1ⁱ–Pd1–Br1ⁱ, 91.37(11)° (i: 1?x, 1?y, 1?z) in the coordination sphere are very close to the ideal value of 90°. The Pd–X distance is slightly longer than other carbene derivative Pd–Cl single bond distances and slightly shorter than Pd–Br single bond distances. These results agree with the Cl/Br disorder at the halogen position. The palladium–carbene complex was tested as a catalyst in the direct arylation reaction of benzoxazoles and benzothiazoles with aryl bromides.     

Synthesis,crystal structure,and magnetic properties of a new end-to-end thiocyanato-bridged dicobalt(II) complex CoII(dien)(H2O)(NCS)(μ1,3-NCS)CoII(dien)(NCS)2 (dien = diethylenetriamine)

Synthesis, characterization, crystal structure, and magnetic properties of the first single µ_1,3-thiocyanato-bridged dicobalt(II) compound, [Co^II(dien)(H₂O)(NCS)(µ_1,3-NCS)Co^II(dien)(NCS)₂] (1; dien = diethylenetriamine), are described. In 1, cobalt(II) is six coordinate with distorted-octahedral geometry. The Co(1) ··· Co(2) distance is 5.99 Å. The magnetic properties of 1 have been investigated by variable-temperature magnetic susceptibility measurements. The metal centers are coupled by weak ferromagnetic interaction (J = 1.14 cm^?1). The structure and magnetic properties are compared with related thiocyanate-bridged compounds.     

Linear oxalato- and 4,4′-dipyridyldisulfide-bridged copper(II) coordination polymer involving in situ ligand synthesis

The reaction of 1,3-bis(pyridyl-4-ylthio)propan-2-one with Cu(ClO₄)₂?·?6H₂O gave a new complex {[Cu₂(4PDS)₂(ox)(H₂O)₄](ClO₄)₂} _n (4PDS?=?4,4′-dipyridyldisulfide, ox?=?oxalate), with 4PDS and ox being created by the Cu(II)-assisted oxidation of 1,3-bis(pyridyl-4-ylthio)propan-2-one. The complex determined by X-ray crystallography is a 1D polymer, in which metallacycles formed by two 4PDS and two Cu(II) ions are further bridged through ox anions. It crystallizes in the orthorhombic system, space group Fddd, with lattice parameters a?=?15.106(2), b?=?23.667(4), c?=?27.637(3)?Å and Z?=?8.     

Voltammetric detection of the α-dicarbonyl compound: Methylglyoxal as a flavoring agent in wine and beer

A simple, rapid and highly selective method for the determination of the most abundant α-dicarbonyl compound in wine and beer has been developed for the first time by employing square wave voltammetry. A novel electrochemical sensor, based on the electrodeposition of platinum nanoparticles onto single wall carbon nanotubes that were cast on a glassy carbon electrode (GCE) substrate, is presented in this paper. This modified electrode exhibited excellent catalytic activity in the electroreduction of methylglyoxal, showing much higher peak currents than those measured on an unmodified GCE. The effects of different experimental and instrumental parameters, such as solution pH and square wave frequency, were examined. The reduction peak current showed a linear range of from 0.1 × 10⁻⁶ to 100 × 10⁻⁶ M with a 0.9979 correlation coefficient; and a low detection limit of 2.8 × 10⁻⁹ M was also obtained. The proposed methodology was successfully applied to the quantitative analysis of methylglyoxal in wine and beer samples. The developed sensor possesses advantageous properties such as a high active surface area, stability, and rapid electron transfer rate, which cumulatively demonstrate high performance toward the electrocatalytic reduction and detection of methylglyoxal.     

A scalable approach to diaminopyrazoles using flow chemistry

This Letter reports on how the combination of microwave and continuous flow chemistry facilitated the convenient preparation of aminopyrazoles from commercial aryl halides. The method was applied to a variety of substrates with good to excellent yields and further extended toward the complete flow synthesis of 5,7-dimethyl-3-phenylpyrazolo[1,5-a]pyrimidin-2-amine.