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在许多不对称合成中,手性试剂能催化反应,因此手性试剂可称之为手性催化剂,不过许多手性催化剂往往用其化学计算量。近年来已发现有许多手性试剂可用催化量级,并已有效地用于许多不对称合成之中,产物的对映选择性很高。Corey及其合作者认为催化量的手性试剂可称之为化学酶(Chemical Enzyme,Chemzyme)。化学酶是可溶性有机小 相似文献
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综述了前列腺素的关键手性中间体———Corey lactone的制备方法,重点阐述了Corey lactone的外消旋体拆分法,不对称合成法及手性源原料法的最新研究进展。参考文献28篇。 相似文献
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Corey化学酶与不对称合成 总被引:1,自引:0,他引:1
本文从立体化学和反应机理方面综述了Corey化学酶的催化作用及其在有机不对称合成中的应用, 指出了Corey化学酶与酶的相同点和不同点, 对于关键的反应过程态均以空间关系更为清楚的构象式表示。 相似文献
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手性冠醚被用作不对称合成的手性试剂, 是具有构型识别能力的立体。本文用廉价易得的手性胺作为合成γ, 合成了一个新的手性含氮冠醚, 并将该冠醚的醋酸铜络合物催化剂与铜粉催化剂, 以及手性苯乙胺的水杨醛席夫碱的铜络合物催化剂的催化性能进行了比较。 相似文献
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评述了目前半导体光催化在国内外的研究概况,并对存在的问题和未来的发展动向进行简要分析.列举了近30年来关于光催化研究的部分成果,内容涉及光催化剂的制备(包括新催化剂的开发, TiO2、 ZnO、 CdS等光催化剂的各种改性或修饰)、光催化作用机理研究、光催化技术的工程化、光催化技术的各种应用研究和产品开发等等从基础到应用研究的各个方面.总体上来看,半导体光催化基本上是一个没有选择性的化学过程,所以再进行大量的不同反应物的光催化活性的评价研究意义已不是很显著,认为未来的半导体光催化研究应该集中在机理的深刻认识、光响应范围宽和量子效率高的催化剂制备、半导体光催化技术工程化及新型光催化产品开发方面. 相似文献
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Effect of solvents on electro-spinnability of polystyrene solutions and morphological appearance of resulting electrospun polystyrene fibers 总被引:2,自引:0,他引:2
Teeradech Jarusuwannapoom Sujinda Jitjaicham Manit Nithitanakul Piyawit Koombhongse Pitt Supaphol 《European Polymer Journal》2005,41(3):409-421
The effects of solvents and their properties on electro-spinnability of the as-prepared polystyrene (PS) solutions and the morphological appearance of the as-spun PS fibers were investigated qualitatively by means of a scanning electron microscope (SEM). The eighteen solvents used were benzene, t-butylacetate, carbontetrachloride, chlorobenzene, chloroform, cyclohexane, decahydronaphthalene (decalin), 1,2-dichloroethane, dimethylformamide (DMF), 1,4-dioxane, ethylacetate, ethylbenzene, hexane, methylethylketone (MEK), nitrobenzene, tetrahydrofuran (THF), 1,2,3,4-tetrahydronaphthalene (tetralin), and toluene. The PS solutions in 1,2-dichloroethane, DMF, ethylacetate, MEK, and THF could produce fibers with high enough productivity, while the PS solutions in benzene, cyclohexane, decalin, ethylbenzene, nitrobenzene, and tetralin were not spinnable. Qualitative observation of the results obtained suggested that the important factors determining the electro-spinnability of the as-prepared PS solutions are high enough values of both the dipole moment of the solvent and the conductivity of both the solvent and the resulting solutions, high enough boiling point of the solvent, not-so-high values of both the viscosity and the surface tension of the resulting solutions. 相似文献
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建立了电感耦合等离子体原子发射光谱法(ICP–AES)测定稀土硅铁球化剂和孕育剂中Ca,Mg,Al,Mn,La,Ce等元素含量的方法。通过基体匹配消除了铁基体的干扰,Ca,Mg,Al,Mn,La,Ce的分析谱线分别为317.933,279.553,394.401,257.610,333.749,456.236 nm。各元素标准曲线的线性相关系数均在0.999以上,检出限在0.000 1%~0.000 4%之间。方法的加标回收率为99.4%~102.8%,测定结果的相对标准偏差均小于3%(n=11)。用该方法测定标准样品,测定结果与认证值相吻合。该法适用于稀土硅铁球化剂和孕育剂中钙、镁、铝、锰、镧、铈的测定。 相似文献
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Liquid marbles (LMs) are liquid droplets coated with a layer of lyophobic particles at the air-liquid interface. Since the pioneering work by Aussillous et al. in 2001, LMs have attracted significant attention owing to their facile fabrication, flexibility in the choice of the constituent particles and liquids, intriguing properties such as non-wetting and non-adhesive nature, satisfactory elasticity and stability, as well as promising applications in microfluidics, sensors, controlled release, and microreactors. The classical strategy for the preparation of LMs involves rolling a small volume of a droplet on a lyophobic powder bed for complete encapsulation of the liquid by the particles. In addition, various innovative methods, including electrostatic and coalescent approaches, have been developed for preparing special LMs with a complicated structure or morphology. Diverse materials such as water, surfactant solutions, liquid metals, reagents, blood, and even viscous adhesives have been employed as the internal liquid for the fabrication of LMs. Theoretically, any particulates such as lycopodium, polytetrafluoroethylene, Fe3O4, SiO2, and graphite grains can be employed as the outer coating, but they are usually required to be lyophobic with sizes of less than hundreds of microns. The unique structure of the particle-covered droplet and the dual solid-liquid characteristics endow LMs with some unique and interesting properties, especially the non-wetting and non-adhesive nature. As the lyophobic coating particles restrain the internal liquid from contacting the substrate, LMs can move easily across either solid or liquid surfaces, neither wetting the substrate nor contaminating the internal liquid. An equally fascinating property of LMs is their satisfactory stability, which is necessary for most of their applications. The high stability of LMs stems from the protection of the coating powders and is embodied in both good mechanical stability (remaining intact after being released from a certain height or under a certain compression) and long lifetime (greatly suppressing the evaporation of the internal liquid). These extraordinary properties make LMs promising candidates for use in multitudinous fields, especially droplet microfluidics and microreactors. The potential application of LMs in microfluidics is ascribed to their non-wetting, non-adhesive nature and other features such as an ability to float on a liquid surface, coalescence, split, a small force of rolling friction, and response to external forces. Notably, LMs hold great promise for applications in microreactions, because they can create a confined reaction microenvironment, minimize reagent usage, facilitate unhindered gas exchange between the internal liquid medium and the surrounding environment, and allow the entry/exit of the reactants/products. We herein review the recent advances in LMs, such as manufacturing techniques, formation mechanisms, physical properties, and emerging applications. In particular, much attention is paid to the factors affecting the stability of LMs and the potential strategies to increase their stability. Moreover, this review discusses the challenges in the future development of LMs, suggests several possible ways of addressing these challenges, and forecasts the future development directions. We believe that this review can help researchers gain a better understanding of LMs and promote their further advances. 相似文献
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张晨 《中国无机分析化学》2020,10(6):18-22
针对银精矿样品复杂,难消解的特点,研究了不同酸溶法和碱熔法对样品的消解情况,建立了硝酸,盐酸,氢氟酸,高氯酸消解银精矿的方法。根据元素灵敏度和抗干扰性,选定各元素的测定波长。通过酸溶样和碱熔样测定结果比对,验证了方法准确性。建立了四酸消解-电感耦合等离子体光谱法测定银精矿中铜、铅、锌、砷、镉、钙、镁、锰含量的方法,元素的线性相关系数均在0.9999以上。通过共存元素干扰实验,确定了银精矿中高含量元素(铜、铅、锌、铁、锑、铋等)对测定元素结果没有影响。方法检出限:Cu 0.0063 mg/L, Pb 0.0159 mg/L ,Zn 0.0090 mg/L,As 0.0192 mg/L, Cd 0.0093 mg/L ,Ca 0.0084 mg/L, Mg 0.0075 mg/L, Mn 0.0081 mg/L。测定下限:Cu 0.0105mg/L,Pb 0.0265 mg/L, Zn 0.0150 mg/L, As 0.0320 mg/L, Cd 0.0155 mg/L, Ca 0.0140 mg/L, Mg 0.0125 mg/L,Mn 0.0135 mg/L。3个样品的相对标准偏差在0.87%~3.56%之间,加标回收率在95.00%~103.56%之间。方法流程短,操作简单,快速,灵敏度和再现性高,结果准确可靠,可以满足银精矿中铜、铅、锌、砷、镉、钙、镁、锰含量的测定。 相似文献
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纳米沉淀法是目前制备纳米药物的主要途径, 是指通过向药物的良溶剂中引入不良溶剂产生过饱和体系, 进而形成纳米尺度药物颗粒的方法. 该方法操控灵活, 能够大范围地选择药物分子、 溶剂、 载体、 表面活性剂及其它赋形剂, 实现对纳米药物成核及生长过程的调控. π-π堆积和疏水相互作用等分子间弱相互作用能够主导纳米药物成核, 从而用于制备高生物安全性的无载体纳米药物(CFNs). 目前超分子自组装在成核过程中的具体作用、 协同效应及调控方法尚缺少归纳总结. 根据纳米沉淀法的成核理论, 本文对超分子相互作用在成核过程中的重要贡献进行了诠释; 基于目前单药自组装CFNs的进展, 对多药共组装CFNs的优势进行了强调; 并将超分子相互作用主导成核的概念拓展到通过金属离子螯合形成的CFNs. 从理论上阐明了超分子相互作用在纳米药物成核过程中的主导作用, 将极大促进以高生物安全、 多功能及以联合治疗为标志的下一代CFNs的发展. 相似文献
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EFFECT OF STRESS-INDUCED REACTIONS ON MORPHOLOGICAL STRUCTURE AND PROCESSABILITY OF PVC DURING PAN-MILLING 总被引:1,自引:0,他引:1
Hua-weiZou WenXu Qing-fenFeng XiXu 《高分子科学》2005,(2):227-234
The effect of pan-milling on morphological structure, processability and properties of PVC was studied through SEM, FTIR, granulometer, GPC and mechanical properties test in the hope of gaining ease in operation, needless of plasticizers, a clean and efficient route for improving the processability of PVC through stress-induced reactions,fulfilling the idea of “plasticizing PVC by itself”. The experimental results show that during pan-milling at ambient temperature, within 2-3 min, the microcrystalline structure of PVC becomes indistinct, the grain size of PVC is reducedfrom 130-160 μm to 1-50 μm the molecular weight of PVC is slightly decreased, the variation of molecular weight distribution is indistinct, the plasticizing time and torque at balance drop a great deal from 71-132 s to 31-33 s and from 18.2-22.1 Nm to 14.7-18.4 Nm, respectively, the processability of PVC is markedly improved, and the mechanical properties get enhanced too. 相似文献
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Regional distributions of manganese,iron, copper,and zinc in the brains of 6-hydroxydopamine-induced parkinsonian rats 总被引:1,自引:0,他引:1
Tarohda T Ishida Y Kawai K Yamamoto M Amano R 《Analytical and bioanalytical chemistry》2005,383(2):224-234
Time courses of changes in manganese, iron, copper, and zinc concentrations were examined in regions of the brain of a 6-hydroxydopamine
(6-OHDA)-induced rat model of Parkinson’s disease using inductively coupled plasma mass spectrometry (ICP-MS). The concentrations
were simultaneously determined in brain section at the level of the substantia nigra 1, 3, 7, 10, 14, and 21 days after the
6-OHDA treatment and compared with those of control rats. The distributions of these elements were obtained for 18 regions
of the sagittal section (1-mm thick). The ICP-MS results indicated that Mn, Fe, Cu, and Zn levels of the 6-OHDA-induced parkinsonian
brain were observed to increase in all regions that lay along the dopaminergic pathway. In the substantia nigra, the increase
in Mn level occurred rapidly from 3 to 7 days and preceded those in the other elements, reaching a plateau in the 6-OHDA brain.
Iron and Zn levels increased gradually until 7 days and then increased rapidly from 7 to 10 days. The increase in the copper
level was slightly delayed. In other regions, such as the globus pallidus, putamen, and amygdala, the levels of Mn, Fe, Cu,
and Zn increased with time after 6-OHDA treatment, although the time courses of their changes were region-specific. These
findings contribute to our understanding of the roles of Mn and Fe in the induction of neurological symptoms and progressive
loss of dopaminergic neurons in the development of Parkinson’s disease. Manganese may hold the key to disturbing cellular
Fe homeostasis and accelerating Fe levels, which play the most important role in the development of Parkinson’s disease. 相似文献
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Hans-Peter Baldus Martin Jansen 《Angewandte Chemie (International ed. in English)》1997,36(4):328-343
Materials research is an interdisciplinary field in which engineers and physical scientists work together. Since the major binary oxides, nitrides, and carbides, which are currently used as high-performance ceramics, were discovered in the last century, the role of chemistry in the development of materials has become barely noticeable. This has changed only in the recent past as, for example, purity and defined morphology of starting powders were recognized as crucial parameters for enhancing the reliability of ceramic workpieces. While the application of chemical methods led to gradual–though significant–improvements, the true potential of chemistry lies rather in the exploitation of new chemical systems and the development of new preparative routes to already known materials. Such an approach is the preparation of ceramics from molecular or polymeric precursors. Herein we survey the most important contributions to those preparative routes starting from the pioneering work in the 1960s and the 1970s; a certain emphasis is placed on the concepts that we have applied to the preparation of multinary, nonoxide materials and amorphous inorganic networks. The name “amorphous high-performance ceramics” is in fact a contradiction in terms. Such materials are thermodynamically unstable with respect to the transformation or decomposition to crystalline phases, thus excluding their application in sensitive areas at high temperatures. However, the selection of element combinations for which the binding energies are derived from strong, local covalent bonds and which are therefore less dependent on a long-range crystalline order, can yield amorphous materials of remarkable thermal and mechanical durability. This is exemplified by novel quaternary ceramics in the Si/B/N/C system, for which an efficient synthesis, starting from raw materials suitable for industrial production, has been developed. For instance, a material of the composition SiBN3C remains amorphous up to 1900°C, which is unique, and, with respect to oxidation, is the most stable nonoxide ceramic known to date. Another advantage of this in several respects unsurpassed material is the simple way, in which the viscosity of the polymeric precursors can be adjusted to various methods of shaping. So far infiltrations and coatings have been realized. Most developed is the preparation of fibers, which in terms of their performance characteristics are significantly better than those currently available. 相似文献