Polymerization of methyl methacrylate in the presence of iron(II) complex with tetradentate nitrogen ligands under conditions of atom transfer radical polymerization

Four tetradentate nitrogen ligands, viz. dichloro{[N,N^′-diphenyl-N,N^′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (1), {[N,N^′-dioctyl-N,N^′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (2), {[N,N^′-dibenzyl-N,N^′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (3), and (1R,2R)-(−)-N,N^′-di(quinoline-2-methyl) di-iminocyclohexane (4), were investigated as novel complexing ligands in iron-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate where ethyl-2-bromoisobutyrate was the initiator in o-xylene at 90 °C. With ligands 1 and 2 the experimental molecular weights increased gradually with monomer conversion. High to moderate conversions (87%, 43%) were obtained in relatively short times (90 min for 1 and 30 min for 2), which indicates an efficient catalyst system, but after these times a dramatic increase in viscosity of the polymerization medium led to loss of control. It is noteworthy that polymerization proceeded in a controlled manner with ligand 1, which has two rather bulky substituents on the N-atom. Such bulky ligands did not work for a copper-based system, where they led to excessive terminations or other side reactions. When the bulkiness of the substituents was significantly increased, as in ligand 3, a decrease in polymerization rate and loss of control occurred. Ligand 4 was less efficient than the other ligands, probably because the ethylene bridge was replaced by cyclohexane bridge.     

Evaluation of a synergetic effect between Rh as permanent chemical modifier and acetylacetone as complexing agent in Sc determination in sediment slurry samples by ETAAS

In the present work, scandium was determined in sediment slurry samples (from three different rivers) by electrothermal atomic absorption spectrometry (ETAAS). Slurries were prepared by weighting 100 mg of dry sediment samples (≤53 μm particle sizes) and adding 6 ml of HCl:HNO₃:HF (3:1:2, v/v). Accurate results were only possible due to the synergetic effect between Rh as permanent chemical modifier and acetylacetone (Acac) as complexing agent. The same platform was used for 400 heating cycles. The performance of the chemical modification was evaluated by using scanning electron microscopy (SEM), synchrotron radiation X-ray fluorescence (SRXRF) and some figures of merit (precision and detectability). The best analytical conditions were attained using 1500 and 2550 °C as pyrolysis and atomization temperatures. The scandium content in the liquid phase of the slurries ranged from 61 to 73%, thus indicating, in this study, that both liquid and solid phases play an important role in slurry analyses. An amount of 5.0–20.0 μg l⁻¹ Sc linear range as well as LOD and LOQ of 0.19 and 0.62 μg l⁻¹, respectively, were obtained under these conditions. The accuracy was checked by using microwave-assisted decomposition, and the results compared to those obtained with the proposed methodology (slurry analysis). By checking both sets of the results, there is no statistical difference at the 95% confidence levels.     

1—取代苯基—1,4—二氢—6—甲基—4—哒嗪酮—3—酰胺的合成

用杂交方法培育新作物品种是农业增产的重要措施。与常规杂交育种方法相比,采用化学杀雄法(Chemical induction lf male sterility)育种具有程序简单,节省劳力,时间缩短等优点,可以诱导产生非遗传性的雄性不育母本,与另一品种的文本杂交而得优化组合的良种,国外在小麦上已试验成功但在水稻上尚在探索,美国Rohm and Haas公司曾报道一些哒嗪酮类     

β微管蛋白中紫杉醇(Taxol)结合腔的性质分析

采用多拷贝同时搜寻法(MCSS), 并结合现有微管抑制剂的SAR及3D-QSAR对β微管蛋白中Taxol(紫杉醇)结合腔的性质进行了分析. 结构研究结果表明, Taxol结合腔以疏水性质为主, 并指出官能团分布的具体位置: 在Phe270上方(Leu361-Pro272-Leu273-Leu228之间)的弧形区域、Asp26羧基下方及其与Glu22羧基之间、M-loop的中部, 以及Asp224内侧且靠近Arg276的胍基的位置. 而Asp224的内侧又是新提出的结合位点. 研究结果符合现有微管抑制剂的SAR, 为现有抗肿瘤药物的结构改造以及小分子微管抑制剂设计提供了理论依据.     

应用高分子铂络合物催化合成硅烷偶联剂

以二氧化硅为载体的侧链上含有配位基团和-COOH的聚硅氧烷(1-5)分别与氯铂酸反应制备了五种聚硅氧烷-铂络合物(“St-Pt-l”—“St-Pt-5”).这些高分子铂络合物,用于催化环氧丙基烯丙基醚与三甲及基氢硅烷反应具有很高的催化活性,在温和的条件下(80℃,30min),反应以72—98％的产率生成了硅烷偶联剂γ-(2,3-环氧丙氧基)丙基三甲氧基硅烷.通过对含,配位基的高分子铂络合物“Si-Pt-1”的稳定性研究,发现它可以重复使用多次而不降低其催化活性.     

Rewiring cellular metabolism for heterologous biosynthesis of Taxol

Abstract

Taxol is one of the anticancer drugs synthesized naturally in the evergreen Taxus brevifolia forest tree belonging to the yew family (Taxaceae) growing on the Pacific. There are reportedly evidence for treating ovarian, breast and lung cancers through this drug given its unique structural and functional features. Extraction of this drug from yew trees bark is one of the most common ways of producing this drug, but 3000 trees are needed to obtain a kilogram of Taxol. Hence, further attention has recently been attracted to the metabolic engineering strategies, including, engineering cellular metabolism of microorganisms and their optimization. Accordingly, the present paper article was aimed to review recent advances in elevating the production and commercialization of Taxol through metabolic engineering techniques.     

纳米级TiO2粉体的制备研究——Ⅱ.絮凝剂及其浓度的影响

采用溶胶-凝胶-超临界流体干燥(SCFD)法制备纳米级TiO₂超细粉，详细考察了不同絮凝剂及其浓度对TiO₂织构和结构性质的影响。结果表明，利用强碱溶液作为絮凝剂，浓度为5 mol·L^-1是制备大孔高比表面TiO₂超细粉较为适宜的条件。     

核磁共振法研究CH2=CHSi（OET）3的水化反应

高强水泥的生产近年来巳成为许多国家发展水泥生产的一个主要方向。在水泥中加入有机单体可以改善混凝土的质量,如加重量比为3％的有机硅烷偶联剂乙烯基三乙氧基硅烷CH_2=CHSi(OEt)_3(简称VTES)于水泥中,即可在较大程度上增加水泥石的强度。     

Synthesis and anticholinesterase activity of some new fluorogenic analogues of organophosphorus nerve agents

Eighteen new fluorogenic analogues of organophosphorus nerve agents were synthesised and characterised. They included analogues of tabun, sarin, cyclosarin, soman, VX, and Russian VX, with the 7-oxy-4-methylcoumarin or 7-oxy-4-(trifluoromethyl)coumarin leaving group. These analogues inhibited acetylcholinesterase (AChE) effectively in vitro and therefore have potential as tools for the identification of novel organophosphatases in biological systems. Analogues of VX and Russian VX with the 7-amino-4-methylcoumarin group, although poor AChE inhibitors, may have utility for screening enzyme libraries for phosphoramidases capable of cleaving P-N bonds.     

Immobilization,characterization, and laboratory-scale application of bovine liver arginase

Arginase isolated from beef liver was covalently attached to a polyacrylamide bead support bearing carboxylic groups activated by a water-soluble carbodiimide. The most favorable carbodiimide wasN-cyclohexyl-Nt’-(methyl-2-p-nitrophenyl-2-oxoethyl) aminopropyl carbodiimide methyl bromide, but for practical purposes,N-cyclohexyl-Nt’-morpholinoethyl carbodiimide methyl tosylate was used. The optimal conditions for the coupling procedure were determined. The catalytic activity of the immobilized arginase was 290–340 U/g solid or 2.9–3.4 U/mL wet gel. The pH optimum for the catalytic activity was pH 9.5, the apparent temperature maximum was at 60°C and K_mapp was calculated to be 0.37M L-arginine. Immobilization markedly improved the conformational stability of arginase. At 60°C, the pH for maximal stability was found to be 8.0. The immobilized arginase was used for the production of L-ornithine and D-arginine.