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121.
Lisa N. Yee Casimir C. Akoh Robert S. Phillips 《Journal of the American Oil Chemists' Society》1997,74(3):255-260
Pseudomonas sp. lipase PS was immobilized by adsorption and tested for its ability to catalyze the synthesis of citronellyl butyrate
and geranyl caproate by transesterification in n-hexane. The reaction parameters investigated were: enzyme load, effect of substrate concentration, added water, temperature,
time course, organic solvent, pH memory, and enzyme reuse. Yields as high as 96 and 99% were obtained for citronellyl butyrate
and geranyl caproate, respectively, with 300 units (approx. 15% w/w of reactants) of lipase PS. Increasing amounts of terpene
alcohol inhibited lipase activity, while excess acyl donor (triacylglycerol) concentration enhanced ester production. Optimal
yields were obtained at temperatures from 30–50°C after 24-h incubation time. Yields of 90 and 99% were obtained for citronellyl
and geranyl esters, respectively, with 2% added water. Solvents with log P values ≥ 2.5 showed the highest conversion yields. pH 7 and 6–8 seemed to be ideal for citronellyl butyrate and geraniol
caproate, respectively. The lipase remained active after reusing 12 times. 相似文献
122.
Narrowly distributed nanoparticles of poly (n‐butyl methacrylate‐co‐vinyl pyrrolidone) were prepared through microemulsion polymerization with a nonionic surfactant of Tween‐80 as emulsifier (6 wt % of the latex) and n‐butanol as coemulsifier. The polymerizations were initiated with benzoylperoxide (BPO), potassium persulfate (KPS), KPS/ferric sulfate (FeSO4), and BPO/FeSO4, respectively, where the initiation in the case of BPO/FeSO4 took place mainly at the interphase between the oil phase and the reaction media. Namely, this interfacial‐initiated microemulsion polymerization resulted in larger particles with relatively narrower particle size distribution as well as higher limiting monomer conversion but lower polymerization rate compared with the polymerization initiated with KPS/FeSO4. In this article, the influences of initiation method, monomer ratio, and addition of water‐soluble components on microemulsion polymerization and latex particle size were studied to discuss the mechanism of interfacial‐initiated microemulsion polymerization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2334–2340, 2004 相似文献
123.
A series of well‐defined and property‐controlled polystyrene (PS)‐b‐poly(ethylene oxide) (PEO)‐b‐polystyrene (PS) triblock copolymers were synthesized by atom‐transfer radical polymerization, using 2‐bromo‐propionate‐end‐group PEO 2000 as macroinitiatators. The structure of triblock copolymers was confirmed by 1H‐NMR and GPC. The relationship between some properties and molecular weight of copolymers was studied. It was found that glass‐transition temperature (Tg) of copolymers gradually rose and crystallinity of copolymers regularly dropped when molecular weight of copolymers increased. The copolymers showed to be amphiphilic. Stable emulsions could form in water layer of copolymer–toluene–water system and the emulsifying abilities of copolymers slightly decreased when molecular weight of copolymers increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 727–730, 2006 相似文献
124.
Al_2O_3负载TiO_2光催化氧化剂的制备与性能试验 总被引:1,自引:2,他引:1
以钛酸四丁酯为钛源、Al2O3为载体,采用浸渍法制备了一系列TiO2/Al2O3复合氧化物光催化剂。以光催化降解甲醛为探针反应,考察了催化剂的光催化活性。并采用XRD、SEM技术对催化剂进行了表征。考察了催化剂的焙烧温度、钛含量、反应温度等因素对甲醛光催化降解率的影响。结果表明:400℃是制备TiO2/Al2O3光催化剂的最佳焙烧温度;在TiO2负载质量为5.0%的复合氧化物光催化剂催化效果最好,甲醛的降解率达到58.4%。随着反应温度的升高,复合氧化物光催化剂的催化性能下降,由25℃时的58.4%的甲醛降解率下降到50℃时的4.8%。 相似文献
125.
The isothermal and nonisothermal cure behaviors of a novel nitrogen‐containing epoxy resin (XT resin) were studied by differential scanning calorimetry (DSC). Various kinetic parameters and details of cure process were obtained based on the Avrami theory. The results indicated that Avrami method is suitable for calculating the kinetic parameters up to the gel point at least. The apparent activation energy (Ea) for isothermal cure process was in agreement with that for nonisothermal cure process. Ea value in the early stage (78.5–81.0 KJ mol?1) was about three times than that in the later stage (23.3–26.5 KJ mol?1). The kinetic results from Avrami theory may present a combined effect of all factors, and which is helpful to understand the cure technique for XT–DDS system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3483–3489, 2006 相似文献
126.
Allemann C Gordillo R Clemente FR Cheong PH Houk KN 《Accounts of chemical research》2004,37(8):558-569
Computational studies have led to models to understand some classic and contemporary asymmetric reactions involving organocatalysts. The Hajos-Parrish-Eder-Sauer-Wiechert reaction and intermolecular aldol reactions as well as Mannich reactions and oxyaminations catalyzed by proline and other amino acids, and Diels-Alder reactions catalyzed by MacMillan's chiral amine organocatalysts have been studied with density functional theory. Quantitative predictions for several new catalysts and reactions are provided. 相似文献
127.
Four oil absorbents based on styrene–butadiene (SBR)—pure SBR (PS), 4‐tert‐butylstyrene–SBR (PBS), EPDM–SBR network (PES), and 4‐tert‐butylstyrene‐EPDM‐SBR (PBES)—were produced from crosslinking polymerization of uncured styrene–butadiene rubber (SBR), 4‐tert‐butylstyrene (tBS), and ethylene–propylene–diene terpolymer (EPDM). The reaction took place in toluene using benzoyl peroxide (BPO) as an initiator. Uncured SBR was used as both a prepolymer and a crosslink agent in this work, and the crosslinked polymer was identified by IR spectroscopy. The oil absorbency of the crosslinked polymer was evaluated with ASTM method F726‐81. The order of maximum oil absorbency was PBES > PBS > PES > PS. The maximum values of oil absorbency of PBES and PBS were 74.0 and 69.5 g/g, respectively. Gel fractions and swelling kinetic constants, however, had opposite sequences. The swelling kinetic constant of PS evaluated by an experimental equation was 49.97 × 10?2 h?1. The gel strength parameter, S, the relaxation exponent, n, and the fractal dimension, df, of the crosslinked polymer at the pseudo‐critical gel state were determined from oscillatory shear measurements by a dynamic rheometer. The morphologies and light resistance properties of the crosslinked polymers were observed, respectively, with a scanning electron microscope (SEM) and a color difference meter. 相似文献
128.
梅丽 《重庆科技学院学报(社会科学版)》2010,(8):186-188
探讨语类理论指导下的大学英语教学模式,提出了该教学模式的五个阶段:判断语篇归类,输入语境知识,形成语类结构范式,独立创作语篇和评价学生语篇。这五个阶段循环往复,能够把阅读和写作教学有效地结合起来,使两者相互促进。 相似文献
129.
高校法律基础教学研究 总被引:1,自引:0,他引:1
彭美 《重庆科技学院学报(社会科学版)》2010,(19)
分析了我国高校的法律基础教学目前存在的问题和不足.认为高校法律基础教学的目标重点是培养大学生的法治信仰.高校应加强法律基础教学师资队伍建设,提高师资队伍专业化水平.教学过程中应该实行理论教学与实践教学相结合、教师讲授与学生自学相结合、学校与家庭和社会相结合,切实提高教学实效. 相似文献
130.
目前,自然语言处理系统由于缺乏语义信息及知识理解和推理能力,因此存在很多缺陷,在自动问答领域中很难分清用户表达的真正意图,并给出用户满意的答案.本文就此给出基于句法语义的问句分析方法,采用本体构建技术构建答案库,在此基础上进行领域知识语义推理,实现智能问答.本研究以黄山旅游为限定领域建立问答系统,试验结果表明多策略的方法是有效的. 相似文献