共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
The electronic and molecular structures of the monomer and dimer of trimethylalu-minium have been studied using density functional theory and ab initio MP2 method. The optimized geometry of the monomer Al(CH3)3 is of C3h symmetry, whereas that of the dimer [A1(CH3)3]2 contains a carbon-bridged four-membered ring structure with C2h symmetry. The hydrogen-bridged six-membered ring structure is found to be unstable. The calculated dimerization energy for the four-membered ring structure is 78 kJ/mol, in close proximity to the experimental value of 85.27 kJ/mol. 相似文献
3.
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
4.
Yuyan Liu Yuanqing Guo Hongping Liu Xiaoyong Liu Jieli Lin Guangming Huang Jinrui Li Fengyan Li 《中国科学B辑(英文版)》2000,43(3):261-267
From the theories of the nuclear hyperfine structure (HFS) and Λ doubling of diatomic molecules, several brief algebraic equations
for interpretation of HFS and Λ doubling of transitions of diatomic molecule have been developed. A few important parameters
of HFS and Λ doubling of15N16O have been efficiently and accurately obtained from the analysis of the high resolution spectra of15N16O (X2∏) observed in our experiments with these equations. This method can provide an effective approach to obtain important hyperfine
parameters of novel radicals from their high resolution laser magnetic resonance spectra.
Liu Yu-yan, Guo Yuan-qing, Assignments of FIR-LMR spectra of CF X2∏(υ= 1) and MIR-LMR spectra of NO X2∏ (υ =1←0), Spectroscopy and Spectral Analysis (in press). 相似文献
5.
Farid I. El-Dossoki 《Journal of solution chemistry》2010,39(9):1311-1326
The effect of the charge and the nature of both the cations and the anions of some electrolytic salts: sodium fluoride (NaF),
potassium fluoride (KF), sodium bromide (NaBr), potassium bromide (KBr), sodium iodide (NaI), potassium iodide (KI), sodium
sulfate (Na2SO4), potassium sulfate (K2SO4), calcium chloride (CaCl2), and barium chloride (BaCl2), on the solubility of zwitterionic amino acids (glycine, DL-alanine, DL-valine, and DL-serine) in aqueous solutions at 298.15 K
are studied and discussed. A salting-in effect is observed for all amino acids under investigation with all electrolytes used
in the present study, except for DL-alanine and DL-valine in aqueous solutions containing sodium fluoride where a salting-out
effect was observed. The orders of the effect of the nature and the charge of both the anions and the cations are: F- < Cl- < Br- < I- < NO3- < SO42-\mathrm{F}^{-}<{}\mathrm{Cl}^{-}<{}\mathrm{Br}^{-}<{}\mathrm{I}^{-}<\mathrm{NO}_{3}^{-}<{}\mathrm{SO}_{4}^{2-} with both sodium and potassium cations; Na+<K+<Ca2+<Ba2+ with chloride anion. 相似文献
6.
(4R,5S)-2,2-Dimethyl-4-(1',2'-dimethylpropyl)-5-(1'-bromoethyl)--1,3-dioxolane(15) with the side chain of brassinolide and (4R, 5S)--2, 2-dimethyl-4-(l'-methylene-2'-methylpropyl)-5-(1'-bromoethyl) 1,3-dioxolane(14) with the side chain of dolicholide were first synthesized through 11 and 10 stepes from D-mannitol respectively. All of the intermediates 7-13 were first synthesized too. 相似文献
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8.
M. Yu. Kolobov Yu. Yu. Morzherin V. A. Bakulev V. S. Mokrushin 《Chemistry of Heterocyclic Compounds》1991,27(11):1228-1233
The reaction of unsymmetrical N,N-disubstituted malonamides with benzenesulfonyl azide in the presence of sodium ethoxide gives individual sodium 1,2,3-triazol-5-olates or mixtures of their isomers, from the relative amounts of which the effect of substituents in the amido groups on the cyclization pathways and reactivities of -diazoimidolates was ascertained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1521–1527, November, 1991. 相似文献
9.
The widely used antibiotics tetracyclines have been effectively used for ailing heart attack, ulcer cure and gene therapy. The actual mechanism of their activity has been proposed to link with the complexes with many metal ions.However, the sites at which complex formation takes place are not well established. In the present work, the deprotonation sequence of tetracycline (TC) and oxytetracycline (OTC), and their specific group used to bind europium ion were investigated by examining the character of fluorescence of TC and OTC as well as that of their complexes.It was concluded that the site of complexation is coordinated with the deprotonation sequence changing with the acidity/basicity of the solution. And it was inferred that five hydrogens in TC and OTC could be dissociated. The deprotonation sequence is as follows: C(3) hydroxy, C(10) phenol, C(4) dimethylamine, C(12) hydroxy and C(12a) hydroxy. The corresponding complexation site changed with pH increase in solution as follows: C(2) acylamino and C(3) hydroxy moiety, C(10)-C(11) ketophenol moiety, C(4) dimethylamine and C(3) hydroxy moiety,C(11)-C(12)β-diketone moiety, C(12) hydroxy and C(12a) hydroxy moiety, and C(12) hydroxy and C(1) ketonemoiety respectively. 相似文献
10.
11.
Journal of Solution Chemistry - The T???x phase diagram of a binary system of tetradecane?+?hexadecane is calculated using the Landau phenomenological model.... 相似文献
12.
Patricia H. Risso Domingo Mariano Borraccetti César Araujo María Eugenia Hidalgo Carlos A. Gatti 《Colloid and polymer science》2008,286(12):1369-1378
κ-Casein (κ-CN) aggregation by heating has been studied at pH 7.2 and 5.2 using UV-visible spectrophotometry, sodium dodecyl
sulfate polyacrylamide gel electrophoresis, spectrofluorometric study of the 1–8 aniline naphtalene sulfonate (ANS)–κ-CN binding
and circular dichroism (CD) spectroscopy. The aggregation process to form aggregates like micelles or submicelles and the
structural characteristics of these aggregates were pH dependent. Far-UV CD showed that the aggregates obtained by heating
presented changes in the κ-CN secondary structure. Near-UV CD spectra showed a certain degree of tertiary organization in
the Tyr environment for the protein heated or unheated, only at pH 5.2. ANS binding at both pH was quite different and depends
on the self-association process. Heating produced exposition of hydrophobic binding sites only at pH 7.2, including those
in the neighborhood of the κ-CN Trp residue. 相似文献
13.
Khalid M. Tawarah Hakam M. Abu-Shamleh 《Journal of inclusion phenomena and macrocyclic chemistry》1991,11(1):29-40
The color fading caused by the addition of-cyclodextrin or-cyclodextrin to an aqueous solution of a tautomeric mixture of methyl orange or methyl yellow is studied spectrophotometrically at pH 1.1 and 25.0°C. A model involving 1 : 1 stoichiometry has been used to analyze the spectrophotometric data. The addition of a cyclodextrin shifts the tautomeric mixture towards the side of the ammonium tautomer. An expression allowing the calculation of the tautomeric equilibrium constant of the inclusion complexes is derived. The formation constants of the inclusion complexes of the individual tautomers are determined. Both- and-cyclodextrins bind the ammonium tautomer stronger than the azonium tautomer. The inclusion complexes of-cyclodextrin are more stable than the corresponding ones of-cyclodextrin. 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
16.
Janca J. Kuzmin S. Maximov A. Titova J. Czernichowski A. 《Plasma Chemistry and Plasma Processing》1999,19(1):53-67
The plasma–solution interaction processes for gliding and point arcs between the aqueous solution surface and the metal electrode in the gas phase are studied. The plasma, liquid, and surface zones are taken into consideration. The electric field strength is measured, and the gas and electron temperatures and ion composition are estimated for the plasma zone. The cathode fall, water vaporization rate, and active species current yield due to the radiation chemistry mechanism are determined for the surface zone. The efficiency of oxidation of iodine ions and organic dyes by different types of discharge in the liquid zone are investigated. The difference in action of the various discharge types may be connected with various influences of the plasma and surface zone on the oxidation processes. 相似文献
17.
In this work, we study the competence between the reactions of hydrogen and methyl scission during thermal cracking and combustion of propane, the emergence of the two isomers of the propyl radical, n-propyl and i-propyl, and their subsequent ??-scission reaction to ethene and methyl radical. The purpose of the study was to analyze the accuracy of density functional (DFT) methods as applied on this relatively well-known subset of the reactions implied in the production of propylene oxide from propane and propene. Conventional (B3LYP, B3PW91) and state-of-the-art (PBE0, M06, BMK) DFT methods were employed, and their accuracy checked against experimental data and calculations performed using model chemistries (complete basis set CBS-4M, QB3, and APNO, and G4 methods) and ab initio methods (MP2, CCSD(T) with a large 6-311 ++G(3df,2pd) basis set). The results obtained at the BMK level for the thermodynamics of the reactions are closer to experimental data than those afforded by any other DFT method and very similar actually to CBS or CCSD(T) results, even if a medium size basis set is used. Activation energies determined using two- and three-parameter Arrhenius equations are also very good, but the preexponential factors are incorrect. Tunneling and internal rotation corrections must be applied to obtain semiquantitative results. 相似文献
18.
U. S. Kemelbekov A. Hagenbach D. Lentz Sh. O. Imachova G. M. Pichkhadze Zh. I. Rustembekov K. M. Beketov K. D. Praliev A. Gabdulkhakov A. Guskov W. Saenger 《Journal of inclusion phenomena and macrocyclic chemistry》2010,68(3-4):323-330
The base form of the local anaesthetic kazcaine (BFK, [1-(2-ethoxyethyl)-4-ethynyl-4-benzoyloxypiperidine, C18H23NO3]) and β-cyclodextrin (β-CD) co-crystallized as BFK:β-CD inclusion complex in 1:2 M ratio from a mixture of water and ethanol while the filtered mother liquor yielded crystals of free BFK. X-ray diffraction showed that the crystals of BFK and its inclusion complex with β-CD belong to monoclinic (P21/c) and triclinic (P1) space groups, respectively. The crystals of free BFK are stabilized by pairs of C–H?O, C–H?π and ≡C–H?O type interactions and van der Waals contacts. In the 1:2 BFK:β-CD complex the two β-CD molecules are in hydrogen-bonding contact with their primary hydroxyl groups, the 1-(2-ethoxyethyl)-4-ethynyl-piperidine moiety being located in one and the benzoyloxy group of BFK in the other β-CD. This crystal structure is of the channel-type, the β-CD molecules of the 1:2 BFK:β-CD complex interacting with their secondary hydroxyl groups. The pharmacological activities of the 1:2 BFK/β-CD inclusion complex have been determined in mice, rats, porpoises and rabbits and compare favourably with those of kazcaine, procaine, dicaine, lidocaine and trimecaine. The methods used include terminal (superficial), infiltration, conduction anaesthesia, and acute toxicity. 相似文献
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The traceable and accurate measurement of biogas impurities is essential in order to robustly assess compliance with the specifications for biomethane being developed by CEN/TC408. An essential part of any procedure aiming to determinate the content of impurities is the sampling and the transfer of the sample to the laboratory. Key issues are the suitability of the sample container and minimising the losses of impurities during the sampling and analysis process. In this paper, we review the state-of-the-art in biogas sampling with the focus on trace impurities. Most of the vessel suitability studies reviewed focused on raw biogas. Many parameters need to be studied when assessing the suitability of vessels for sampling and storage, among them, permeation through the walls, leaks through the valves or physical leaks, sorption losses and adsorption effects to the vessel walls, chemical reactions and the expected initial concentration level. The majority of these studies looked at siloxanes, for which sampling bags, canisters, impingers and sorbents have been reported to be fit-for-purpose in most cases, albeit with some limitations. We conclude that the optimum method requires a combination of different vessels to cover the wide range of impurities commonly found in biogas, which have a wide range of boiling points, polarities, water solubilities, and reactivities. The effects from all the parts of the sampling line must be considered and precautions must be undertaken to minimize these effects. More practical suitability tests, preferably using traceable reference gas mixtures, are needed to understand the influence of the containers and the sampling line on sample properties and to reduce the uncertainty of the measurement. 相似文献