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用MMX分子力学程序公及分子图形学方法对α-氨基磷酸酯与N-氯乙酰基甘氨酸乙酯反应机理进行了探讨,结果表明,此类反应热力学因素不起主要作用,动力学因素起主要作用,取代基突效应是影响反应历程的重要因素。 相似文献
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强调反应分子中某些特殊轨道起主要作用的普遍化的微扰理论(Generalized Perturba-tion Theory,简称GPT)是六十年代中期发展起来的讨论有机化学反应性的重要理论模型之 相似文献
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用微量热法研究漆酶和过氧化氢的反应 总被引:6,自引:0,他引:6
漆树酶是含铜酶。在酶系统中属于一种选择性较差的氧化酶,它能与许多还原底物作用,同时亦能还原分子氧生成水。在这些反应中漆酶中的三个不同的氧化还原活性中心和其作用途径常常是研究中的主要对象。在无氧条件下,漆酶被底物还原后,可用氧再氧化,实验表明,酶分子中的Cu2~+—Cu~(1+)循环是催化机理的一部分。1970年Farver等人在研究漆树酶与过氧化氢之间的反应时发现,漆树酶与过氧化氢有一种特殊作用,二者会生成一种稳定的具有高亲合力的复合物,该复合物不会被氧再氧化,其反应可用下式表示:式中L-Cu(Ⅱ)表示含二价铜的漆酶分子,二价铜在此反应中起活性中心的作用。本工作中,用微量热法测量了漆树酶与过氧化氢反应的一些热动力学性质。 相似文献
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本文首先介绍了Thorpe-Ingold效应及其相关理论和实验研究进展,然后综述了近年来Thorpe-Ingold效应在形成三、四、五和六元环产物的环化反应中的应用。Thorpe-Ingold效应可以有效地促进分子内和分子间环化,提高环化的产率和速率。该效应主要通过空间效应、电子效应或者两者协同起作用,在某些情况下,该效应还会受催化剂和溶剂等影响。利用该效应可以促使一些难以发生的环化反应顺利进行,并能获得较好的产率。 相似文献
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香草醛系列化合物分子印迹聚合物膜的渗透特性 总被引:1,自引:0,他引:1
以香草醛(Van)或邻香草醛(o-Van)为模板分子, 用紫外光引发原位聚合, 分别制备了以尼龙和聚偏氟乙烯微孔滤膜为支撑材料的分子印迹复合膜, 并用紫外分光光度法研究了模板分子与功能单体之间的相互作用. 模板分子及竞争物的混合溶液渗透实验结果表明, 支撑材料对膜选择性传输趋势基本没有影响, 但选用合适的支撑材料会得到更理想的分离效果; 当竞争物尺寸小于模板分子时, 尺寸效应起主要作用, 竞争物优先传输; 当模板分子与竞争物尺寸相近时, 尺寸效应不起作用, 模板分子的选择性识别位点及与其相匹配的孔穴起主要作用, 模板分子优先传输; 当竞争物尺寸大于模板分子时, 则尺寸效应和模板分子的选择性识别位点及与其相匹配的孔穴同时起作用, 故模板分子优先传输. 相似文献
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采用第一性原理方法研究了乙炔分子在Ge(001)表面的吸附反应.通过系统考察0.5和1.0ML覆盖度时形成di-σ和end-bridge构型的反应路径,研究在表面形成di-σ和paired-end-bridge构型的反应几率.除了表面反应以外,本文还涉及了亚表层Ge原子参与的吸附反应,乙炔在亚表层原子上吸附形成的亚稳态结构sub-di-σ,是形成end-bridge结构的第二条途径,此反应机理对于表面吸附结构的形成起重要的作用.与乙炔分子不同的是,表面以下原子参与时乙烯分子的吸附反应为吸热反应.综合热力学和动力学的分析表明,paired-end-bridge构型是乙炔分子吸附的主要构型,此结论解释了乙炔分子在Ge(001)表面吸附构型的实验结果.对于乙烯和乙炔两分子在Ge(001)表面吸附的分析比较揭示了导致两者之间差异的原因. 相似文献
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Abstract The leaving groups of organophosphorus compounds and carbo-xylic esters are differently located in the active centers of cholinesterases that is connected with the stereochemi-cal regularities of the nucleophilic displacement reactions occurring at the carboxyl and phosphoryl groups of these reagents. This different spatial location of quasisubstrates in the enzyme active center also reveals in the mechanism of the bond-breaking steps leading to the formation of the covalent enzymereagent intermediate. In the present coinmunication the mechanism of these reaction steps is discussed with the implication of the putative structures of the transition states. The analysis is based on the results of QSAR for the leaving group effects of ester substrates and organophosphorus quasisubstrates in their reactions with acetylcholinesterase and butyrylcholinesterase. It has been found that the sensitivity of the enzyme phosphorylat-ion rate against the inductive effect of the quasisubstrate leaving group was remarkably nigh pointing to the complete separation of charges in the transition state. On the other hand, the transition state of the butyrylcholinesterase acylation reaction has been found to be similar to the structure of the appropriate acyl-enzyme. aesides these two enzymes the reactions of ester substrates and organophosphorus quasisubstrates have been studied with a covalently modified derivative of acetylcholinesterase, synthesized by affinity labelling of the native enzyme with N,N-dimethyl-2-phenylaziridinium ions, The data obtained allow to discuss the role of the putative “anionic point” of acetylcholinesterase in the enzyme reactions with organophosphorus quasisubstrates and ester substrates. 相似文献
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研究了具有较高酯合成活性的华根霉膜相关脂肪酶及其沉淀酶蛋白的重折叠处理过程, 发现膜成分及表面活性剂可能是影响其活性的关键因素. 进一步考察了影响异源表达的可溶性华根霉脂肪酶r27RCL酯合成活性重塑的关键因子及作用阶段. 研究结果表明, 表面活性剂对脂肪酶的酯合成活性具有关键影响, 直接添加表面活性剂可使酯合成活性显著提高. 在7种不同表面活性剂中, 两性离子表面活性剂LPC14将r27RCL的酯合成活性提高了5.75倍. 分子动力学模拟结果表明, 在有机相反应中, 表面活性剂的添加使脂肪酶催化三联体之间的氢键作用力得到加强, 从而提高了脂肪酶的有机相酯合成能力. 相似文献
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Experimental data on the molecular decomposition of esters with various structures into an olefin and the corresponding acid
in the gas phase are analyzed in terms of the intersecting parabolas method. Enthalpies and kinetic parameters characterizing
this decomposition have been calculated for 33 reactions. Ester decomposition is a concerted two-center reaction characterized
by a very high classical potential barrier of thermoneutral reaction (148–206 kJ/mol). The totality of reactions examined
is divided into eight classes. Activation energies and rate constants have been calculated for 38 reactions using the kinetic
parameters obtained. The activation energies and rate constants of the reverse bimolecular reaction of acid addition to olefins
have been calculated by the intersecting parabolas method. Factors in the activation energy of ester decomposition and formation
reactions are discussed. 相似文献
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Kotel'nikov S. A. Sukhinin V. S. Ermilov A. S. 《Russian Journal of Applied Chemistry》2002,75(3):477-479
Kinetic parameters of formation of P-9AD oligoether urethane allyl ester with terminal double bonds and of its curing with dinitrile oxide were determined. The dependence of the rate constant on the allyl alcohol concentration and temperature was studied. The mechanism of reaction of P-9A prepolymer with allyl alcohol was proposed. The kinetic and thermodynamic parameters of curing of oligoether urethane allyl ester with dinitrile oxide were determined. The mechanism of reaction of P-9AD oligoether urethane allyl ester with dinitrile oxide was proposed. 相似文献
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This paper investigates the hydrolysis kinetics of levodopa methyl ester in 0.05–1.5 M HCl between 37 and 75°C. An isocratic
HPLC assay was developed for simultaneous determination of levodopa methyl ester and levodopa in the hydrolysate of levodopa
methyl ester. A series of hydrolysis rate constants were obtained and the effects of hydrogen ion concentration and temperature
on the reaction were evaluated. It was found that pH was a key factor at low temperature, but that when the temperature was
raised, temperature became in turn the most influent factor on the hydrolysis. From the measured pseudo-first order reaction
rate constants, the activation energy for levodopa methyl ester hydrolysis in 0.5, 1.0 and 1.5 M HCl were calculated to be
71.24, 74.32 and 76.57 kJ mol−1, respectively.
Revised: 24 May and 15 August 2005 相似文献
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以氯化血红素(Ⅰ)为原料,经过溴化氢-冰醋酸加成反应、羟基亲核取代反应和无水氯化氢催化酯化反应制得3,8-双-(1-羟基乙基)次卟啉二甲酯(Ⅲ),然后通过琼斯试剂氧化反应制备了3,8-双乙酰基次卟啉二甲酯(Ⅳ)。 考察了血红素与溴化氢-冰醋酸饱和溶液反应过程中温度和时间对3,8-双-(1-羟基乙基)次卟啉二甲酯(Ⅲ)产率的影响;改进了酯化反应的实验条件;选用了廉价易得、选择性较好的羟基选择性氧化剂。 实验结果表明,当反应温度为35 ℃、反应时间为25 h时,血卟啉(Ⅱ)的产率最高,为98.5%;当催化剂为无水氯化氢时产物(Ⅲ)的产率最高,为72.1%;使用琼斯试剂做氧化剂使实验成本大大降低。 通过1H NMR、MS和IR测试技术对产物结构进行了表征。 相似文献