共查询到20条相似文献,搜索用时 31 毫秒
1.
《European Polymer Journal》1986,22(10):769-773
Effects of the concentrations and ratio of reacting components and of temperature on the kinetics of reaction of N-propionyllactam (I) with potassium salt of lactam (KL) were studied for derivatives of ϵ-caprolactam, 8-octanelactam and 12-dodecanelactam. For ϵ-caprolactam, the initial rates of propagation, acylation of open-chain amide groups and condensation of growth centres were estimated. At the ratio of the starting components [I]0/[KL]0 = 0.5-3, the participation of the polymerization reaction is constant, amounting to ca 45% of the overall consumption of 1. The condensation reaction is 14–36% of the total consumption of I; its initial rate passes through a maximum at [I]0/[KL]0 = 2. With increasing permittivity of the medium, the total rate of consumption of I increases; in two media with the same bulk permittivity, however, the rates may differ by as much as one order of magnitude. 相似文献
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Construction of the Skeleton of Phthalascidin, Mechanism of the Formation of the Key Tricyclic Lactam Intermediate 总被引:1,自引:0,他引:1
Zhan Zhu LIU Ye WANG Shi Zhi CHEN* Institute of Materia Medica Chinese Academy of Medical Sciences& Peking Union Medical College Beijing 《中国化学快报》2002,13(8)
Phthalascidin is a structurally simplified version of Et-743, which is a potent anti-tumor marine natural product isolated from Ecteinascidia turbinata. Its antiproliferative activity is greater than that of the agents taxol, camptothecin, adriamycin, mitomycin C, cisplatin, bleomycin, and etoposide by 1-3 orders of magnitude. An elegant synthesis of Et-743 and phthalascidin has been reported by E. J. Corey and co-workers1,2. As part of our continuing program, we have also engaged in dev… 相似文献
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Using the method of solid-phase peptide synthesis, two peptides have been synthesized, one of which corresponds to the central ring structure of -bungarotoxin (-BTX), while the second has in position 28 a Gly residue in place of the Trp in the first peptide, and their interrelationship with antitoxin antibodies has been investigated. It has been shown that the amino acid residue Trp-28 of -BTX, which is the contact residue in binding with the acetylcholine receptor, also participates directly in binding with the active centers of antibodies to -BTX.Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 628–631, July–August, 1997. 相似文献
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ZHU Chuan-Zheng YANG Bao-Lin ZHAO Hong GU Wen-Xiu AI Shi-YunDepartment of Chemistry East China Normal University Shanghai China 《中国化学》1997,15(1):68-75
The dissociation constant of each step for TB-chlorosulphophenol has been determined by potentiometric method, and the thermodynamic constants, △G°, △H° and △S°, of the dissociation process have been calculated. The protonation constants were measured by the spectrophotometric method. The pH values of various forms of anions of the chromogenic reagent at their concentrations were also calculated. 相似文献
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Juhász P. Varga J. Belina K. Marand H. 《Journal of Thermal Analysis and Calorimetry》2002,69(2):561-574
The melting behavior of the -form of isotactic polypropylene (-iPP) was investigated as a function of crystallization time and temperature. Calcium suberate, a selective -nucleating agent was used to produce samples that consist entirely of -form i-PP. The experimental melting points were recorded at different crystallization times and were extrapolated to the start of the crystallization process in order to eliminate the effect of lamellar thickening. Using the non-linear Hoffman—Weeks approach to correlate these extrapolated experimental melting temperatures with the corresponding crystallization temperatures, an equilibrium melting point of 209°C was obtained for -iPP. The equilibrium melting point estimated through the non-linear Hoffman—Weeks analysis is about 30°C higher than that (T
m
0=177°C) obtained on the basis of the linear extrapolation. These results are consistent with earlier claims that a linear extrapolation of T
m–T
c data leads to an underestimation of the equilibrium melting point. The results obtained for -iPP exemplify the importance of accounting for both the isothermal lamellar thickening effects and the non-linearity in the T
m–T
c correlation, when the determination of an equilibrium melting point is carried out using a procedure based on the predictions of the Lauritzen—Hoffman secondary nucleation theory.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
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The straight-line method of Asmus was originally developed for the determination of n in mononuclear complexes of the general form ABn (n≧ 1). In the present investigation it is demonstrated that the method also can be used for determining the value of n in polynuclear complexes of the form A[mBn (m > 1). The method as suggested by Asmus, is, however, not capable of distinguishing between mono- and polynuclear species. It is further shown, that the straight-line method can be applied for the determination of the value of m. 相似文献
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Bentley PA Flood RW Roberts SM Skidmore J Smith CB Smith JA 《Chemical communications (Cambridge, England)》2001,(17):1616-1617
Epoxidation of chalcone (1), using basic hydrogen peroxide, catalysed by polypeptides with defined primary structures demonstrates that the residues in the chain near to the N-terminus determine the stereochemical outcome of the reaction. 相似文献
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Alexandre Lumbroso Anna Blonska Isabelle Beaudet Slawomir Jarosz Jean-Paul Quintard 《Tetrahedron》2010,66(8):1570-1580
Ethyl glyoxylate was reacted with α-substituted γ-(t-butyldimethylsilyloxy)-allyltributyltin in order to obtain selectively each diastereomer of ethyl 3-(t-butyldimethylsilyloxy)-2-hydroxyhex-4-enoate and subsequently the corresponding diols. Diastereomers syn-E, anti-E and anti-Z were obtained in good yields with good to high selectivities and the obtained results were rationalized by consideration of cyclic or open transition states in agreement with the experimental conditions and with the structure of the starting reagents. 相似文献
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N. V. Chukanov V. V. Zakharov B. L. Korsunskii A. V. Raevskii V. V. Nedel’ko S. A. Vozchikova T. S. Larikova N. I. Golovina S. M. Aldoshin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(1):29-33
The α → γ polymorphic transition in hexanitrohexaazaisowurtzitane was studied by optical microscopy, calorimetry, IR spectroscopy, thermogravimetry, and X-ray diffraction. The thermal effect of the transition was determined. The kinetics of the process is complex because of the relation between structural rearrangement and transition with the removal of water stabilizing the structure of the α polymorph. Depending on the morphological characteristics of the initial sample, the polymorphic transition can follow a frontal-heterogeneous mechanism (single crystal → polycrystalline aggregate) or a quasi-homogeneous mechanism (single crystal → single crystal). 相似文献
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S. Nakashima T. Kitao H. Matsunaga I. Kimura H. Inamura T. Okuda H. Sakai 《Journal of Radioanalytical and Nuclear Chemistry》1999,239(2):279-283
Azaferrocene has two active sites of iron and nitrogen atoms. Drastic change of the oxidation state in iodine oxidation of
azaferrocene is observed by introducing the methyl substituents into the pyrrole ring, while all the N-methylates show a similar
electronic state. It was revealed that an introduction of methyl substituent to the pyrrole ring promotes the oxidation of
nitrogen atom in pyrrole ring more than the central iron atom. 相似文献
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Usacheva T. R. Ledenkov S. F. Sharnin V. A. Gzejdzak A. 《Russian Journal of Coordination Chemistry》2001,27(3):203-207
The effect of a water–dimethyl sulfoxide solvent (X
DMSO= 0–0.97, where X
DMSOis the mole fraction of DMSO) on the thermodynamics of complexation between Ag+and 18-crown-6 and the solvation of all reagents involved in this equilibrium were studied. In aqueous solutions, the complex is stable mainly because of the enthalpy contribution to
r
G°. For X
DMSO> 0.3, the contributions from entropy and enthalpy become comparable in magnitude, but they are opposite in sign. In the binary solvent, the complex is most stable at X
DMSO= 0.2 to 0.3. Analysis of the enthalpy characteristics of reagent solvation showed that this solvent effect was due to the superposition of two opposite solvation contributions occurring with an increase in the DMSO concentration in the binary solvent, namely, the destabilization of the ligand solvate sphere and the formation of stable Ag+complexes with DMSO. 相似文献
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In recent hundred years the annual discharge variations of the Changjiang River (represented by the Yichang station) and the Huanghe River (represented by Shanxian and Tangnaihe, respectively) have closely related to the geographical distribution of the earthquakes coming about in China in the same year, Both the occurrence of the destructive seism or seismic swarm in the river basins and the disappearance of the shocks in the east and south of the basins are the conditions that the Changjiang and Huanghe Rivers are the high flow while that the strong earthquake of magnitude 7 or more occurred in North China is the condition for the Changjiang low flow year and that of 6 or more in the Qilian Mountains area is for the Huanghe River. In the latter part of this paper, a 2-year sample is given to explain that the conditions of the 2 rivers being high flow years are that the north-south seismic belt is active and in the meanwhile no seism occurred in South China, and those of the low flow year are that the 相似文献
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The mechanism of the formation of a key tricyclic lactam intermediate 3 was studied. It was found that the E-form compound 3 was transformed from the Z-form compound 4. The formation of 4 was a kinetically controlled process while the formation of 3 was a thermodynamically favorable one. A possible mechanism was given in this paper. 相似文献
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