纳米二氧化钛催化苯乙烯环氧化反应的研究(Ⅰ)

通过烯烃的环氧化反应可制得一系列活泼的有机中间体--环氧化物,再通过选择性开环或功能团转化可方便地合成多种有价值的化合物.含钛催化剂对烯烃环氧化催化效果较好,如Ti-ZSM-5、Ti-ZSM-11、α-和β-[SiW₉Ti₃O₄₀]^10-.     

酞菁亚铁/亚碘酰苯催化3-(1′,3′-二氧戊环)-5(10),9(11)-雌甾二烯-17-α-(1-丙炔)-17-β-醇的选择环氧化

目前, 对酞菁过渡金属配合物的研究已引起人们广泛的重视. 酞菁过渡金属催化烯烃的环氧化反应, 可以看作是对自然界生物体内许多酶催化氧化反应的模拟[1]. 其反应条件温和, 环氧化产物具有较高的区域选择性和立体选择性, 可应用于合成特定构型的环氧化物, 特别是用于合成药物中间体.     

光学活性环氧化物的酶催化合成

光学活性环氧化物的酶催化合成①夏仕文尉迟力沈润南李树本②（中国科学院兰州化学物理研究所羰基合成与选择氧化国家重点实验室，兰州７３００００）关键词光学活性环氧化物酶催化不对称合成动力学拆分１前言光学活性环氧化物含有两个手性碳，通过选择性开环和官能团转换...     

1.6-缩水-2,4-二-氧-苄基-β-D-吡喃葡萄糖合成、开环及立体选择性成苷反应研究

以较好产率合成了3-位具有不同保护基的1,6-缩水-2,4-二-氧-苄基-β-D-吡喃葡萄糖,并对其开环反应以及成苷反应的立体选择性进行了研究.     

理论与计算化学在基础化学课程中的应用：1,2-环氧化物开环反应

1,2-环氧化物开环反应是化学类各专业有机化学课程中的重要教学内容，教材中的描述缺少定量、直观信息，学生通常采用机械记忆方式予以学习，不能完全理解相关的反应机制。本文设计了一个用理论化学方法研究化学反应的典型案例，通过量子化学计算探讨了酸、碱催化1,2-环氧化物开环反应的分子机制，揭示了反应的热力学和动力学性质，描绘了反应过程的直观物理图像，给出了理解反应区域选择性的定量信息。论文将计算量子化学与有机化学教学内容有机融合，不仅有助于学生加深对化学基本概念和基础理论的理解，而且有助于学生开阔视野、拓展思路，使学生充分认识到理论计算是开展化学研究的重要手段。     

环氧水解酶在不对称合成中的应用

环氧水解酶是一种普遍存在于生物体内的酶,它能选择性水解环氧生成相应的手性二醇。这种酶在催化反应中通常显示出十分高的对映立体选择性,生成高光学活性的环氧和二醇。近年来国际上采用微生物来源的环氧水解酶对环氧底物进行不对称水解,然后再通过酸处理未开环的环氧化物“一锅法”高产率、高选择性的生成单一构型的手性二醇。这一新发展为这种酶在精细合成工业上的运用开辟了广阔的前景。     

双氮席夫碱配体对甲基三氧化铼催化烯烃环氧化反应的影响

 利用 2-吡啶甲醛、6-甲基-2-吡啶甲醛或 6-异丙基-2-吡啶甲醛与对甲基苯胺缩合制得双氮席夫碱配体, 考察了席夫碱配体以及溶剂和温度对甲基三氧化铼 (MTO) 催化不同结构烯烃环氧化反应的影响. 结果表明, 这些席夫碱配体与 MTO 构成的催化剂体系在甲醇溶剂中的催化性能最好, 双氮配体能显著提高环氧化反应的选择性. 当以甲醇为溶剂, 环己烯为底物, 在 –10 oC 反应 12 h 时, 环己烯转化率和环氧化物选择性均可达 100%. 席夫碱的配位能力越强, 越有利于提高环氧化物选择性, 而其配位能力取决于吡啶环中 6-位取代基的电子和立体结构. 给电子能力较强和空间位阻较小的烷基对应的配体的配位能力较强.     

Sm(Ⅲ)催化的三级环氧醇高度非对映选择性重排还原 反应-1, 3-二醇单酯的新 合成方法

本文报道了一个α-羟基环氧化物被Sm(Ⅲ)催化的新颖的串联反应。此反应一步完成了两个连续反应,高度非对映选择性地构筑了三个连续的立体中心。它可以成为一种高度非对映选择性地构筑2-季碳-1,3-二醇结构的一般方法。该反应的条件和机理在文中也作了详细的讨论。     

酞菁亚铁／亚碘酰苯催化3—（1‘，3 ’—二氧戊环）—5（10），9（11）—雌甾二烯—17—α—（1—丙炔）—17—β—醇的选择环氧化

目前 ,对酞菁过渡金属配合物的研究已引起人们广泛的重视 .酞菁过渡金属催化烯烃的环氧化反应 ,可以看作是对自然界生物体内许多酶催化氧化反应的模拟[1] .其反应条件温和 ,环氧化产物具有较高的区域选择性和立体选择性 ,可应用于合成特定构型的环氧化物 ,特别是用于合成药物中间体 .用 F3CCOCF3/H2 O2 作环氧化剂对药物中间体 3 -(1′,3′-二氧戊环 ) - 5 (1 0 ) ,9(1 1 ) -雌甾二烯 - 1 7- α- (1 -丙炔基 ) - 1 7-β-醇 (1 )的环氧化反应 ,已有文献报道 [2 ,3] ,5 α、 1 0 α-环氧化物 (2 )与 5 β、 1 0 β-环氧化物(3 )的摩尔比为…     

镁对3-氯-2-烃基四氢呋喃的开环反应

本文首次报道镁对3-氯-2-烃基四氢呋喃(1)的开环反应,制得一系列4-烃基-3-丁烯-1-醇(2)。反应平稳、安全、产率高,立体选择性亦较强。反式1开环时,所得反式2的纯度达99.9%;顺式1开环时,所得顺式2的纯     

Alteration in photosystem II photochemistry of thylakoids isolated from senescing leaves of wheat seedlings

Wheat seedlings, grown for 7 days in the light, were allowed to senesce in the light or dark, and the change in the photosystem II (PS II) photochemistry of chloroplasts isolated from the primary leaves of these seedlings was investigated. The decrease in oxygen evolution and the fast fluorescence results indicated that the impairment of PS II in the leaves of seedlings senescing in the light was different from that in the leaves of seedlings senescing in the dark. Thermoluminescence studies showed a structural modification in the Q_B protein of chloroplasts isolated from leaves senescing in the light and an alteration in the S state transition of chloroplasts isolated from leaves senescing in the dark.     

Determination of Penicillins in Milk by a Dual-Optrode Biosensor

Penicillins are the most frequently found antibiotic residues in milk, as they are commonly used for the treatment of bacterial infections in cows. In the present study, we introduce a method for the rapid detection of penicillin residues in raw milk based on the determination of glucose concentration in milk with a dual flow-through biosensor. The molar concentration of glucose in milk is typically over 500 times lower than the concentration of lactose and is highly dependent on the rate of lactose hydrolysis, which is catalyzed by β-galactosidase. Glucose concentrations in milk change with variation in the β-galactosidase activity. β-Galactosidase is an enzyme produced in the microbiota in milk and its activity is inhibited by benzylpenicillin. Spiking milk with benzylpenicillin lowers glucose concentrations in comparison to high-quality milk after short storage intervals. The presence of penicillin in the milk of treated animals resulted in decreased glucose concentrations in comparison with high-quality milk that contained no antibiotics. The glucose concentration in milk samples was followed by the system enabling the elimination of the effects of bacterial respiration in the output with reliable results in less than 1?min.     

Effect of the displacement reaction on the composition of the magnetic layer in electrodeposited layered nanostructures Co-Cu/Cu and Ni-Cu/Cu

Methods of stripping voltammetry, quartz microgravimetry, and x-ray-fluorescence analysis are employed to explore the copper displacement process on thin electrodeposited layers of pure cobalt and nickel and on deposits of these metals with inclusions of copper. The displacement reaction proceeds at a considerable rate on cobalt in the sulfate and sulfosalicylate solutions and virtually does not proceed on nickel in both the sulfate or sulfate-chloride solutions. An estimate of the rate of the copper displacement reaction following a change in the concentration of copper ions in the solution and in the pH of the sulfosalicylate solution is given. A decrease in the contact exchange rate is facilitated by a decrease in the concentration of copper ions in solution and their participation in the formation of complexes.     

Analysis of sequence repeats of proteins in the PDB

Internal repeats in protein sequences play a significant role in the evolution of protein structure and function. Applications of different bioinformatics tools help in the identification and characterization of these repeats. In the present study, we analyzed sequence repeats in a non-redundant set of proteins available in the Protein Data Bank (PDB). We used RADAR for detecting internal repeats in a protein, PDBeFOLD for assessing structural similarity, PDBsum for finding functional involvement and Pfam for domain assignment of the repeats in a protein. Through the analysis of sequence repeats, we found that identity of the sequence repeats falls in the range of 20–40% and, the superimposed structures of the most of the sequence repeats maintain similar overall folding. Analysis sequence repeats at the functional level reveals that most of the sequence repeats are involved in the function of the protein through functionally involved residues in the repeat regions. We also found that sequence repeats in single and two domain proteins often contained conserved sequence motifs for the function of the domain.     

LD-2复合缓蚀剂对海水介质混凝土中钢筋阻锈作用研究

利用电化学检测技术和海水浸泡试验等方法 ,观测和研究了经筛选研制的LD_2复合缓蚀剂对海水介质中钢筋腐蚀电化学行为的影响 ,考察和评价了复合缓蚀剂对钢筋的阻锈作用 .结果表明 ,LD_2复合缓蚀剂主要起阳极型缓蚀剂作用 .在海水中加入 2 5 g·L- 1复合缓蚀剂后 ,钢筋的腐蚀电位提高约 0 .2 2 0V ,腐蚀电流降低至未加缓蚀剂的 1% ,缓蚀效率达 99% .钢筋混凝土试样在海水中浸泡 2年 ,表明混凝土中加入占水泥重量 1.0 %～ 2 .5 %LD_2复合缓蚀剂时 ,能有效阻止混凝土中钢筋的腐蚀     

中国煤中铍的分布赋存特征研究

根据对中国不同矿区1018个煤层煤样和生产煤样铍含量数据的统计结果,分析了中国不同成煤时代、不同聚煤区煤中铍的分布特征。同时,根据对10个不同煤田煤样的实验室浮沉试验、煤岩分析等试验研究,运用Solari方法,计算了煤中各组分中铍的理论含量,讨论了中国煤中铍的赋存特征,尤其是铍在各种煤岩组分中的分布。研究表明,铍在煤中富集程度较高,但相对于世界煤中平均水平来说,中国煤中铍含量总体水平较低。煤中铍主要赋存于惰质组及伊利石粘土矿物中,在镜质组及其它矿物中含量较低。同时,中国大多数煤中铍的有机亲和性指数较高,不利于选煤过程中铍的脱除。     

Calibration methods for microdialysis sampling in vivo: muscle and adipose tissue

Calibration methods for microdialysis sampling were studied in the muscle and adipose tissue of rats. Both the delivery method and the no-net-flux method were used to determine the extraction efficiency (EE) of acetaminophen and caffeine in both tissues. There was no concentration dependence of the EE either in vitro or in vivo for either acetaminophen or caffeine. The EEs determined by the delivery and no-net-flux methods were not different. However, the EEs of both caffeine and acetaminophen determined in vitro were significantly higher than those determined in the muscle and adipose. This indicates that mass transfer in the tissue is the rate-determining factor for the EE in vivo. The relative difference between the EE in vitro and the EE in the muscle was smaller than the difference between the EE in vitro and the EE in the adipose. In addition, the EE in the muscle decreased more than the EE in the adipose after the animal was euthanized. This indicated that exchange between the extracellular fluid and plasma is the rate-determining step in mass transport relative to microdialysis sampling. This has a more significant effect on the EE in the muscle than the EE in the adipose. Both the delivery and no-net-flux methods can be used to calibrate microdialysis probes in the muscle and adipose.     

Stability of a model alkali-soluble associative polymer in the presence of a weak and a strong base

 Hydrophobically modified alkali-soluble emulsion (HASE) polymer is solubilized by the addition of a base. When the pH is increased to greater than 6.5, methacrylic acids on the polymer backbone are neutralized and the carboxylated latex polymer goes into solution causing a large increase in the viscosity due to inter-molecular associations of the hydrophobes. The stability of the viscosity of the polymer solution at pH in the range 9–10 was studied in the presence of a strong (NaOH) and a weak [1-amino-1-methylpropanol (AMP)] base. No change in the viscosity or the moduli was observed for the polymer in AMP. Reduction in the viscous and elastic properties of the polymer solution in NaOH was observed after 4 weeks. Such small changes are detectable using the superposition of oscillation on the steady shear technique. The decrease in the viscoelastic properties is attributed to the hydrolysis reaction of the urethane groups of the macromonomer, which resulted in a decrease in the number of hydrophobes per polymer chain. It is recommended that a weak base be used to neutralise the HASE polymer in order to avoid the possibility of compositional changes in the polymer after neutralisation for more than 6 weeks. Received: 19 May 1998 Accepted in revised form: 26 October 1998     

Effect of pulp composition on the characteristics of residuals in CMC made from such pulps

Four different spruce sulphite pulp samples were used for the preparation of carboxymethylcellulose (CMC). The characteristics of the unreacted fibre and particle residuals obtained in the CMC-preparation were used to establish a correlation between the hemicellulose in the pulp and the intrinsic viscosity, i.e.,␣cellulose chain length and the occurence of unreacted residuals. It was shown that the residual particles in the CMC consisted of fibres, fibre fractions and gel particles of different degrees of substitution. The results suggested that pulps with long cellulose chains, i.e., pulps with high intrinsic viscosities, resulted in particles that were more substituted and more swollen. These pulps also resulted in more substituted hemicelluloses in the CMC and more substituted residuals. It was also suggested that galactoglucomannan in the cellulose pulps is favourable for the swelling which results in more substituted hemicelluloses in the CMC and more swollen residuals. The amount of residuals was influenced mainly by the characteristics of the cellulose in the pulp. It is therefore believed that a combination of high viscosity and a suitable combination of hemicelluloses is the most favourable way of eliminating the occurrence of undissolved residuals in CMC.     

Platinum levels in urban soils from Palermo (Italy); Analytical method using voltammetry

A fast accumulation of platinum in the environmental and biological matrices was observed in the last years and concern arose about potential environmental and health risks.The toxicity of platinum species has been investigated in various studies, some of their, especially the chlorinated ones, are very toxic and allergenic. Information of the acute toxicity of some Pt-chlorinated salts and evidence of DNA damage due to Pt exposure have been observed both in vitro and in vivo.Taking into account what is written above, the development of reliable analytic methods to measure very low Pt concentrations is required. In this work was developed a reliable method for the determination of Pt in soils because of inherent difficulties in using conventional techniques, in particular, the ICP-OES technique. A determination of Pt using ICP-MS, for instance, is problematic, due to interfering signals. Differential pulse voltammetry (DPV/a) was employed by us for the determination of platinum in soils collected in Palermo area. Possible interferences by other environmental metals have been also evaluated.All samples show concentrations of Pt above average upper crust values; concentrations were found in the ranges 0.6–2240 μ/kg d.w. We carried out linear regression analysis between total Pt concentrations in soils obtained in this work and Pt concentrations in leaves of Nerium oleander measured in previous researches. The high correlation coefficient obtained confirms the geographical distribution of the considered pollutant in the Palermo area.