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用量子化学理论方法研究了硅杂环丙烯单重态的异构化反应。结果表明:该异构化反应的过渡态为三元环结构,该反应为氢迁移反应;反应的势垒高度为276.67kJ·mol^-^1[MP2/6-31G(d)]。通过内禀反应坐标(IRC)计算,获得了沿反应途径的势能剖面。 相似文献
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L1 β-Lactamase催化反应机理研究 总被引:1,自引:0,他引:1
用混合量子力学和分子力学(QM/MM)方法和密度泛函理论讨论了L1 β-Lactamase催化Nitrocefin水解的过程, 研究结果表明, 反应为多步反应: 第一步亲核进攻反应为反应的决速步骤, 并且伴随着酰胺键的断裂, 第二步反应为质子迁移反应. 同时讨论了金属锌在反应中的作用. 相似文献
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以2-氯烟酸和2-氯-3-氨基-4-甲基吡啶为起始原料合成中间体I;然后通过氨化和环化反应,在微通道反应器中连续化合成奈韦拉平中间体II和奈韦拉平;在合成中间体II的反应中考察反应温度、反应物料摩尔比和气体流速对反应的影响;合成奈韦拉平的反应中重点考察反应温度对反应的影响。结果表明: 合成中间体II的最佳工艺条件为反应温度为90℃,物料摩尔比n(中间体I)/n(环丙胺)=1/1.2,氮气流速为25mL/min为最佳;合成奈韦拉平的最佳工艺条件是反应温度为110℃。在最佳工艺条件下,中间体II的转化达到率为 99.5%以上,选择性为 99%以上。
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以甘氨酸和金属钙盐为原料,采用水体系合成法制备甘氨酸钙螯合物,探讨不同反应温度、反应时问、反应体系pH等对产品产率的影响,从而确定反应的最佳条件,并对甘氨酸钙螯合物采用傅里叶红外光谱FT-IR进行表征。实验结果表明,合成甘氨酸钙螯合物的最适反应条件是,反应体系pH为5~6,反应时间为2~3h,反应温度为70~80℃。 相似文献
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研究了松香(Rosin)与甲基丙烯酸缩水甘油酯(GMA)在甲苯溶液中进行的酯化反应,探讨了催化剂种类及用量、原料配比、反应温度、反应时间对酯化反应的影响,并对酯化反应动力学进行了研究。结果表明,反应的优化条件为三乙胺作催化剂,用量为松香质量的0.5%,反应物配比n(rosin)∶n(GMA)=1.0∶1.0,反应温度120℃,反应时间7 h。红外(FT-IR)及1H-NMR分析表明已成功制备了松香与GMA的酯化物,动力学分析表明酯化反应为一级反应,反应活化能为57.81 KJ·mol-1。 相似文献
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The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula. 相似文献
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氢气在炭狭缝微孔内吸附的预测 总被引:1,自引:0,他引:1
通过边界的平均场近似,推导二平板狭缝孔格子理论Ono-Kondo吸附等温方程.利用格子气模型特性和微观物理学理论,计算氢分子在石墨平面的最大吸附容量.比较由氢分子在石墨平面二典型聚集状态标定的Ono-Kondo方程,并用预测精度较高的方程计算了与文献相同条件下的吸附等温线.在比较了计算结果、试验结果和GCMC分子模拟结果后,对Ono-Kondo吸附等温方程的特点、理论基础作了分析,指出了方程的适用范围. 相似文献
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利用元胞动力学方法在二维情况下对浓度、取向序参量的含时Ginzberg-Landau方程进行数值求解,研究了液晶聚合物/柔性链聚合物共混体系的相分离动力学,考察了浓度、取向有序过程的耦合对相分离形态的影响.结果表明,此耦合作用对相分离的时间进程以及相分离图样的空间排布都有影响.液晶聚合物的取向有序相当于增加了两组分间的不相容性而促进两相分离;两个序参量在热力学方面的耦合使液晶聚合物趋向于沿着界面方向取向,而动力学方面的耦合使液晶聚合物分子沿着其取向方向扩散,相分离图样的空间排布由这两种效应共同决定通过极化率张量的定义用数值方法模拟得到了相分离体系的小角光散射图样,结果表明,散射强度分布具有方位角依赖性,它是由浓度、取向序参量的空间变化共同决定的. 相似文献
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Melt extrusion was used to prepare binary nanocomposites of ethylene copolymers and organoclay and trinary nanocomposites of low-density polyethylene (LDPE), ethylene copolymer and organoclay. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to analyze the structure of the clay phase and the morphology of the nanocomposites. Influences of the comonomer in the copolymer and the content of the copolymer on the morphology of the resulting nanocomposites were discussed. The binary and the trinary composites may form intercalated or exfoliated structures depending on the interaction between the copolymer and the clay layers and the content of the copolymer. 相似文献
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Yakov I. Estrin 《Central European Journal of Chemistry》2004,2(1):52-81
Bimodal molecular mass distribution (MWD) of polymers, obtained upon polymerization of hydrocarbon monomers in the nonpolar
media under the action of dilithium initiators, is the consequence of separation of the reaction mixture into two phases.
Bifunctional /living/ oligomers produce the insoluble sediment due to tetrameric association of the lithium active sites (the
swollen gel-fraction). Part of the active site remains in the solution (the solfraction). Difference in the concentrations
of the active sites into the phases leads to difference between the propagation rates of the /living/ chains and, as a result,
to Bimodal MWD. The mathematical model of polymerization in the two-phase system is proposed. Satisfactory agreement between
the calculations and the experiments is shown for butadiene polymerization in heptane under the action of 1,4-dilithiumpentane.
Regulation of MWD up to the complete elimination of bimodality is possible via the programmed dosage of monomer and solvent
into the reactor. 相似文献
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The applicability of the method of Giese to the measurement of the influence of monomer reactivity is examined. The reaction of alkyl mercuric salts with sodium borohydride permits the production of alkyl (cyclohexyl and butyl) radicals. Since hydrogen radicals are present in high concentration, the addition of alkenes to the reaction mixture leads to radicals from the alkenes. Further addition of alkene (polymerization) can be nearly completely excluded in this way. The composition of the reaction products is determined by gas chromatography. The addition rate of the alkenes relative to styrene allows correlation with the e value of the Q-e scheme of Alfrey and Price. The method answers the question of how far addition of the monomer complex occurs in one step or as separate addition of both monomers during copolymerization in the presence of charge-transfer (CT) complexes of the monomers. The investigations are performed by using the styrene/acrylonitrile/ZnCl2system, and it is demonstrated that the reactivity of the complexed 相似文献
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The micellar properties of aqueous binary mixed solutions of sodium glycocholate, NaGC, and octa-oxyethylene glycol mono-n-decyl ether, C10E8, have been studied on the basis of surface tensions, the mean aggregation number and the polarity of the interior of the micelles. The mean aggregation number, measured by steady state quenching method, decreased with the increase of the mole fraction of NaGC in the mixed system. The polarity of the interior, estimated by the ratio of first and third vibronic peak in a monomeric pyrene fluorescence emission spectrum, suggested that the hydrophobicity of intramicelles increased with the increase of the mole fraction of NaGC in the mixed system. These are considered to be caused by the differences in the chemical structure and the hydrophobic nature between NaGC and C10E8. The mean aggregation number and the polarity of the interior for each micelle near the CMC in lower total concentration of surfactants showed the tendency approaching those of pure micelle of the nonionic surfactant. This suggests that the ratio of NaGC in the initial micelles in the range of lower total concentration near the CMC is lower than that of the corresponding prepared mole fraction in the mixed system. This lower value was confirmed also from theoretical calculation of the ratio of NaGC at the CMC in the mixed micelle by regular solution treatment of Rubingh in the solution. 相似文献
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When drugs are poorly soluble then, instead of the potentiometric determination of dissociation constants, pH-spectrophotometric
titration can be used along with nonlinear regression of the absorbance response surface data. Generally, regression models
are extremely useful for extracting the essential features from a multiwavelength set of data. Regression diagnostics represent
procedures for examining the regression triplet (data, model, method) in order to check (a) the data quality for a proposed model; (b) the model quality for a given set of data; and (c) that
all of the assumptions used for least squares hold. In the interactive, PC-assisted diagnosis of data, models and estimation
methods, the examination of data quality involves the detection of influential points, outliers and high leverages, that cause many problems when regression fitting the absorbance response hyperplane. All graphically
oriented techniques are suitable for the rapid estimation of influential points. The reliability of the dissociation constants
for the acid drug silybin may be proven with goodness-of-fit tests of the multiwavelength spectrophotometric pH-titration
data. The uncertainty in the measurement of the pK
a of a weak acid obtained by the least squares nonlinear regression analysis of absorption spectra is calculated. The procedure
takes into account the drift in pH measurement, the drift in spectral measurement, and all of the drifts in analytical operations,
as well as the relative importance of each source of uncertainty. The most important source of uncertainty in the experimental
set-up for the example is the uncertainty in the pH measurement. The influences of various sources of uncertainty on the accuracy
and precision are discussed using the example of the mixed dissociation constants of silybin, obtained using the SQUAD(84)
and SPECFIT/32 regression programs. 相似文献
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S. Havriliak Jr 《Colloid and polymer science》1990,268(5):426-439
The dielectric relaxation data of Ishida et al. on a number of acrylic polymers are represented in terms of the relaxation function proposed by Havriliak and Negami using the multi-response techniques developed by Havriliak and Watts. Two of the parameters of this function are interpreted in terms of a temperature dependent distribution of relaxation times. In this method of interpretation the breadth of the distribution function is temperature-dependent while the skewness is not. The temperature dependence of the breadth of the distribution function is similar for most of these acrylic polymers.The parameters of the relaxation function are also interpreted in terms of Mansfield's model which represents intra- and inter-molecular interactions in terms of springs and dash pots. Briefly, increasing the side chain length for the methacrylate series increases the inter-molecular relaxation time which may be due to an increase in the entropy of activation for the orientation process. The difference between the one acrylate in this study and the four methacrylates of the series is a reduction in the intra-molecular relaxation time, apparently due to the lack of the alpha methyl group. 相似文献