Magnesium Acetate Used as an Effective Catalyst for Synthesizing Aliphatic Polycarbonates via Melt Transesterification Process

High-molecular-weight aliphatic polycarbonates(APCs) were synthesized through a two-step transesterification process under solvent-free conditions. Oligomers with equal numbers of hydroxyl and phenyl carbonate terminal groups could be easily controlled by using equimolar amounts of diphenyl carbonate(DPC) and aliphatic diols as feedstocks in the first step. In the second step, the high-molecular-weight APCs can be obtained by connecting -OH with -OC(O)OC₆H₅ end-group upon removing the generated phenol at reduced pressure. Mg(OAc)₂ was found to be the best catalyst for this process among the screened catalysts, which gave the poly(1,4-butylene carbonate)(PBC) a weight-average molecular weight(M_w) of 148600 and a yield of 84.8% under its suitable reaction conditions. In addition, based on the results of X-ray diffraction(XRD), scanning electron microscopy(SEM) and fourier transform infrared spectroscopy(FTIR), a possible reaction mechanism over Mg(OAc)₂ was proposed for APCs synthesis.     

液-液-液微萃取/高效液相色谱法测定人血浆中的西地那非和伐地那非

建立了液-液-液微萃取与高效液相色谱联用同时测定血浆中西地那非和伐地那非的方法。考察了萃取溶剂、溶剂体积、接受相液滴大小、搅拌速度和萃取时间等因素对富集因子的影响,得到了萃取溶剂为300 μL 甲苯、接受相为2 μL 0.2 mol/L HCl、搅拌速度为600 r/min和萃取时间为40 min的最佳实验条件。在该条件下,获得了较高的富集因子。两种组分的线性范围均为5 μg/L~1.0 mg/L,加标回收率高于87%,其相对标准偏差小于5%。以信噪比为3计,西地那非的检测限为1 μg/L,伐地那非为0.5 μg/L。该方法能有效地去除复杂基体的干扰,有机溶剂消耗少,萃取效率高,是一种有效的、灵敏的样品前处理方法,适用于血浆中微量西地那非和伐地那非的测定。     

Selective O-Methylation of Phenol with Dimethyl Carbonate over Catalysts Supported on CaO

Kinetics and Catalysis - In this work CaO-based catalysts were found to be efficient heterogeneous catalysts for the methylation of phenol with dimethyl carbonate (DMC) in a closed high pressure...     

Second Order Asymptotics for Infinite-Time Ruin Probability in a Compound Renewal Risk Model

Consider a compound renewal risk model, in which a single accident may cause more than one claim. Under the condition that the common distribution of the individual claims is second order subexponential, we establish a second order asymptotic formula for the infinite-time ruin probability. Compared with the traditional ones, our second order asymptotic result is more precise and effective, which can be demonstrated by the numerical studies.

     

An optimization and fast load-oriented control for current-based solid oxide fuel cell system

Journal of Solid State Electrochemistry - One of the key problems for a solid oxide fuel cell (SOFC), which is a high-temperature power-generation plant, is the cooperative control of safe...     

Role of Melatonin in Plant Tolerance to Soil Stressors: Salinity,pH and Heavy Metals

Melatonin (MT) is a pleiotropic molecule with diverse and numerous actions both in plants and animals. In plants, MT acts as an excellent promotor of tolerance against abiotic stress situations such as drought, cold, heat, salinity, and chemical pollutants. In all these situations, MT has a stimulating effect on plants, fomenting many changes in biochemical processes and stress-related gene expression. Melatonin plays vital roles as an antioxidant and can work as a free radical scavenger to protect plants from oxidative stress by stabilization cell redox status; however, MT can alleviate the toxic oxygen and nitrogen species. Beyond this, MT stimulates the antioxidant enzymes and augments antioxidants, as well as activates the ascorbate–glutathione (AsA–GSH) cycle to scavenge excess reactive oxygen species (ROS). In this review, we examine the recent data on the capacity of MT to alleviate the effects of common abiotic soil stressors, such as salinity, alkalinity, acidity, and the presence of heavy metals, reinforcing the general metabolism of plants and counteracting harmful agents. An exhaustive analysis of the latest advances in this regard is presented, and possible future applications of MT are discussed.     

毛细管高效液相色谱-毛细管电泳二维分离接口的优化

对毛细管高效液相色谱－毛细管电泳二维分离的动态脉冲接触式接口系统进行了最优化研究。讨论了它的设计原理,优化了操作条件,并对其性能进行了评价。利用这种接口,使样品在第二维的进样浓度达到第一维流出浓度的８１％,１００次连续进样峰高及迁移时间的ＲＳＤ平均值分别为３．０％、１．８％,进样时间也得以缩短,并对甘草的水提取物实现了高效二维分离。,     

金属有机框架材料的制备及在吸附分离CO2中的应用

金属有机框架（MOFs）材料是当今的研究热点之一,是一类颇有潜力成为适用于CO₂吸附和分离的重要材料。本文从MOFs的发展及其所具有的特点、MOFs用于CO₂的吸附与分离所取得的突破性进展以及MOFs的传统合成及绿色制备方法三个方面展开论述。主要论述了MOFs适用于CO₂吸附的原理,及其相对于传统的CO₂吸附材料所具有的特点和优势,亦阐述了MOFs修饰与调变的方法。列出了MOFs用于单组分CO₂吸附及CO₂/CH₄、CO₂/N₂吸附分离的结果。同时,针对传统MOFs制备方法不适宜大规模CO₂捕集材料的生产,特别论述了机械化学合成法和新兴的潮湿矿物风化法,其均具有绿色化、无溶剂、低能耗和简单等特点,是一类较有研究价值和应用潜力的技术。随着温室效应和不可再生石化燃料的消耗等环境和能源问题的日趋严峻,研究及开发适用于CO₂捕集与封存技术的MOFs新材料迫在眉睫,且任重而道远。     

丁腈羟增韧环氧树脂固化反应

丁腈羟增韧环氧树脂固化反应李绍英＊＊韩孝族＊刘振海张庆余（中国科学院长春应用化学研究所长春１３００２２）关键词丁腈羟，增韧环氧树脂，固化反应动力学，ＤＳＣ１９９６－０５－０４收稿，１９９６－０９－１７修回＊＊现在河北轻化工学院化工设计研究所工作环氧树...     

Comparison of the characteristic behavior of two azo dyes on temperature dependent microstructure changes in micelles and vesicles

The new hydrophobic azo dye 4-(N-phenyl-N-decylamino)-4'-nitroazobenzene (AzoC10) has been synthesized. It is compared with 4-(N-phenylamino)-4'-nitroazobenzene (Azo) in terms of reactivity (k(iso) of the thermal cis-->trans isomerization, microsecond flash photolysis) and of the solvatochromic behavior (lambda(max) of the trans-isomer, UV/vis absorption), respectively, within membrane mimeting amphiphile microstructures in aqueous solutions of poly(ethylene oxide)(m)-poly(propylene oxide)(n)-poly(ethylene oxide)(m) micelles and of extruded vesicles. The temperature-induced micelle formation and phase transitions in bilayers of vesicles, respectively, caused characteristic discontinuous changes of k(iso) and lambda(max) with temperature. They differ between the two dyes due to their different solubilization sites and different impact on their microenvironment.