Structure‐controlled synthesis of novel soluble and thermally stable poly (aryl ether nitrile ether ketone ketone)/poly (aryl ether nitrile ether ketone biphenyl ketone) copolymers by electrophilic polycondensation

One new synthesis route was first designed to synthesize the biphenyl acid chloride (BPACl), and then a series of novel poly (aryl ether nitrile ether ketone ketone) (PENEKK)/poly (aryl ether nitrile ether ketone biphenyl ketone) (PENEKBK) copolymers with different controlled structure compositions were synthesized by electrophilic polycondensation and varying the molar ratio of BPACl to terephthaloyl chloride (TPC). The obtained PENEKK/PENEKBK copolymers were characterized by different physical and chemical techniques. The results showed, the copolymers with 10–50% molar contents of biphenyl moities exhibited good thermal properties with glass transition temperatures (T_gs) of 184–196°C, decomposition temperatures (T_ds) of 498–515°C, and good solubility in organic solvents (N‐Methyl‐2‐pyrrolidone (NMP), N,N‐dimethylformamide (DMF), and DMSO), indicating that they would have good potential for solvent processing. The thin films of the polymers had tensile strengths of 93.6–101.5 MPa, Young's moduli of 3.03–3.32 GPa, elongations at break of 9–14%, indicating they were strong materials. The densities of the obtained polymers were 1.31–1.40 g/cm^?3, which were far lower than those of some main inorganic materials (such as Fe, nearly 7.8 g/cm^?3), indicating that they would have possible potential for substituting some inorganic materials used as high temperature materials in some areas due to the merits of lightweight. Thus, the copolymers with 10–50% molar contents of biphenyl moities were promising polymer materials. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrochemical detection of anticancer drug topotecan using nano-acetylene black film

Topotecan, a novel anticancer drug, has been widely used in the treatment of ovarian and cervical cancers. Herein, acetylene black (AB) nanoparticles were used to modify the electrode surface, and the electrochemical behavior of topotecan was examined. At the AB film surface, an irreversible oxidation peak was observed for topotecan, and the response signal greatly increased. The influences of pH value, amount of AB, accumulation potential and time were investigated. As a result, a novel electrochemical method with high sensitivity and rapid response was developed for the detection of topotecan. The linear range is from 2 μg L(-1) to 0.4 mg L(-1), and the limit of detection is 1.45 μg L(-1) (or 3.17×10(-9) M). The method was successfully used to detect topotecan in blood serum, and the results consisted with the values that obtained by high performance liquid chromatography.     

Controlled synthesis of novel reactive cationic copolymers of 3-chloro-2-hydroxypropylmethyldiallylammonium chloride and dimethyldiallylammonium chloride [P(CMDA-DMDAAC)s]: designed as useful polycationic dye-fixatives on cotton fabric

A series of novel reactive cationic copolymers [P(CMDA-DMDAAC)s] of 3-chloro-2-hydroxypropylmethyldiallylammonium chloride (CMDA) and dimethyldiallylammonium chloride (DMDAAC), were designed as useful polycationic dye-fixatives on cotton fabric. The structures of obtained P(CMDA-DMDAAC)s could be controlled by varying molar ratios of raw materials of CMDA to DMDAAC during polymerization, and their molecular weights were possibly controlled by adjusting different polymerization conditions. The results showed that under the same conditions when the polymerization temperatures were kept at 60 °C for 6 h and then heated to 70 °C for 2 h, when the initial monomer concentrations (w/w) were increased from 23 to 40 % and the initiator amounts were gradually decreased from 7 to 6 %, a series of novel products P(CMDA-DMDAAC)s with 2–20 % molar contents of reactive units (CMDA units) in main chains and controlled intrinsic viscosities of 0.15–0.76 dL/g were successfully synthesized, which were as designed and could be expected as novel useful reactive polycationic dye-fixatives on cotton fabric.     

Electrochemical sensing chemical oxygen demand based on the catalytic activity of cobalt oxide film

Cobalt oxide sensing film was in situ prepared on glassy carbon electrode surface via constant potential oxidation. Controlling at 0.8 V in NaOH solution, the high-valence cobalt catalytically oxidized the reduced compounds, decreasing its surface amount and current signal. The current decline was used as the response signal of chemical oxygen demand (COD) because COD represents the summation of reduced compounds in water. The surface morphology and electrocatalytic activity of cobalt oxide were readily tuned by variation of deposition potential, time, medium and Co²⁺ concentration. As confirmed from the atomic force microscopy measurements, the cobalt oxide film, that prepared at 1.3 V for 40 s in pH 4.6 acetate buffer containing 10 mM Co(NO₃)₂, possesses large surface roughness and numerous three-dimensional structures. Electrochemical tests indicated that the prepared cobalt oxide exhibited high electrocatalytic activity to the reduced compounds, accompanied with strong COD signal enhancement. As a result, a novel electrochemical sensor with high sensitivity, rapid response and operational simplicity was developed for COD. The detection limit was as low as 1.1 mg L⁻¹. The analytical application was studied using a large number of lake water samples, and the accuracy was tested by standard method.     

The staining efficiency of cyanine dyes for single‐stranded DNA is enormously dependent on nucleotide composition

The staining of nucleic acids with fluorescent dyes is one of the most fundamental technologies in relevant areas of science. For reliable and quantitative analysis, the staining efficiency of the dyes should not be very dependent on the sequences of the specimens. However, this assumption has not necessarily been confirmed by experimental results, especially in the staining of ssDNA (and RNA). In this study, we found that both SYBR Green II and SYBR Gold did not stain either homopyrimidines or ssDNA composed of only adenine (A) and cytosine (C). However, these two dyes emit strong fluorescence when the ssDNA contains both guanine (G) and C (and/or both A and thymine (T)) and form potential Watson‐Crick base pairs. Interestingly, SYBR Gold, but not SYBR Green II, strongly stains ssDNA consisting of G and A (or G and T). Additionally, we found that the secondary structure of ssDNA may play an important role in DNA staining. To obtain reliable results for practical applications, sufficient care must be paid to the composition and sequence of ssDNA.     

蛋品中苏丹红残留的液相色谱串联质谱测定法研究

采用液相色谱-串联质谱法（LC-MS/MS）测定了蛋品中苏丹红I、II、III、Ⅳ号染料的残留。制样后,装柱,应用基质固相分散技术,用氯仿、乙腈混合溶液（体积比为90：10）淋洗,浓缩定容后经ZORBAX SB-C18柱分离,采用电喷雾正离子,多反应监控（MRM）模式检测。外标曲线定量,苏丹红I、II、III、Ⅳ的线性范围分别为0.5～100ng/g,5.0～100ng/g,1.0～100ng/g和2.0～100ng/g,线性方程的相关系数都大于0.99,添加样品回收率在87.3～113％之间,相对标准偏差均小于9.1％。针对四种苏丹红染料,该方法的检测低限分别可达0.1μg/kg,2.0μg/kg,0.2μg/kg,0.4μg/kg,可以满足国内外蛋品中苏丹红监控要求。     

Controlled‐synthesis of Slightly Crosslinked Poly(dimethyldiallylammonium chloride)s Used as Useful Polycationic Dye‐fixatives on Cotton Fabric

A series of slightly crosslinked poly (dimethyldiallylammonium chloride) s (PDMs) as useful polycationic dye‐fixatives on cotton fabric were synthesized by copolymerization of triallylmethylammonium chloride (TAMAC) and dimethyldiallylammonium chloride (DM). The structures of slightly crosslinked PDMs could be controlled by varying molar ratio of TAMAC to DM during polymerization, and their molecular weights were possibly controlled by adjusting different polymerization conditions. The results showed, under the same conditions that the polymerization temperatures were kept at 65 °C for 6 h and then heated to 80 °C for 2 h, when the initial monomer concentrations (w/w) were increased from 37% to 50%, the initiator amount were gradually decreased from 9% to 5%, a series of slightly crosslinked PDMs with controlled structures of 1%‐5% TAMAC molar contents and controlled intrinsic viscosities of 0.18～0.65 dL/g were successfully synthesized, which were as designed and could be expected as novel useful polycationic dye‐fixatives on cotton fabric.     

Diastereoselective control of intramolecular aza-Michael reactions using achiral catalysts

An intramolecular aza-Michael reaction with a Cbz carbamate and an enone is reported to result in 3,5-disubstituted nitrogen-containing heterocycles. Either cis or trans isomers were obtained selectively using chiral substrates and an achiral Pd(II) complex or strong Br?nsted acid catalysis. A range of substrates undergoes these selective transformations. Functionalization of the resulting products yielding bicyclic heterocycles is also demonstrated.     

Control of olefin geometry in macrocyclic ring-closing metathesis using a removable silyl group

Introducing a silyl group at one of the internal olefin positions in diolefinic substrates results in E-selective olefin formation in macrocyclic ring-forming metathesis. The application of this method to a range of macrocyclic (E)-alkenylsiloxanes is described. Protodesilylation of alkenylsiloxane products yields novel Z-configured macrocycles.     

群对称桁架振动设计的半正定模型与降维问题(英)

桁架振动优化设计可描述为：在给定振动系统最低频率的约束条件下,设计用材最省的桁架结构. 本文针对具有某种结构对称性的桁架,利用有限群描述这一特性,在已有桁架设计的半正定规划模型基 础上,运用最近提出的矩阵代数方法对半正定规划问题的决策变量和数据进行降维,给出了构造有限群 表示的两个充分条件,并实现了一类群对称桁架振动优化设计的半正定模型降维.基于问题的实际背景, 我们又考虑了一个具有八根弹性棒的桁架设计实例,进一步说明在实际问题中根据群对称构造群表示以 及对应不可约表示的具体方法.