共查询到20条相似文献,搜索用时 31 毫秒
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Three series of dealuminated Y zeolites have been prepared by chemical extraction ofhydrothermally dealuminated Y zeolite(USY)with H_2Na_2EDTA,HCl and H_4EDTA.The unitcell constant,mesopore distribution,acidity and extraframework aluminum(EFAL)of thezeolites were studied with XRD,chemical analyses,adsorption,IR and NH_3-TPD techniques.It was shown that H_2Na_2EDTA only removed EFAL species deposited in the pores of USY,by contrast,HCl and H_4EDTA extract both extraframework and framework aluminum,andmake the zeolite framework further dealuminated.Adsorption tests gave evidence that a second-ary pore system exists in these dealuminated zeolites.H_2Na_2EDTA extraction increased bothmicropore and mesopore volumes,but after HCl and H_4EDTA treatments,new mesopores formedand the micropore volume was decreased.The pyridine-IR and NH_3-TPD measurements demon-strated that EFAL had no evident contribution to the zeolite acidity. 相似文献
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When driven far from equilibrium,nonlinear chemical reactions often show a variety of self-organization behavior,including chemical oscillations,waves,chaos and patterns[1].Recently,the study of such nonlinear phenomena in‘complex’systems,such as the li… 相似文献
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MINDO/3 method has been used to study the mechanism of the consecutive addition ofHCN to aminoacetonitrile.The results obtained for the first three steps show that the reaction isexothermic,and step I is the rate determining step. 相似文献
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LI Yong-Hong HONG San-GuoDepartment of Chemistry Jiangxi Normal University Nanchang Jiangxi China 《中国化学》1996,14(2):105-108
MINDO/3 molecular orbital theory has been used to study the thermal rearrangements of HNCRCR'CO.The results obtained show that the activation energy of this rearrangement depends on the migrating group R and the group R'. 相似文献
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HONG San-Guo WANG Sheng Department of Chemistry Jiangxi Normal University Nanchang Jiangxi China 《中国化学》1994,12(6):490-494
MINDO/3 MO method has been used to study the mechanism of the consecutive addition of HCN to propionitrile. The results obtained for the first five steps show that the reaction is exothermic, and step 1 is the rate determining step. 相似文献
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WU Xiong-Wu SHI JunDepartment of Chemical Engineering Nanjing Institute of Chemical Technology Nanjing Jiangsu ChinaWANG Wen-ChuanDepartment of Chemical Engineering Beijing Institute of Chemical Technology Beijing China 《中国化学》1994,12(2):105-112
A new approach to the computation of the chemical potential of fluids is presented. In this method the particle-insertion operation in the conventional test particle method is replaced by the growth of a specific particle. Application of the new technique to hard sphere and Lennard-Jones fluids shows that it is capable of providing reliable estimates of the chemical potential, even at high density where the conventional test particle methods are difficult to apply. 相似文献
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One-carbon unit transfer reaction of folate cofactor model compound, 1-acetyl-2-methyl-imidazolinium, with 1,2-diaminobenzene has been studied theoretically with ONIOM method. The result shows that there are two pathways to complete this reaction because the imidazolinium ring has two breaking patterns. Both the two pathways have six steps. They are combination of two reactants, proton migration, break of five-membered ring, formation of benzimidazole derivate, another proton migration, and formation of final products. In each of the above pathways, the two proton migration steps have higher energy, which illuminate that the reaction is catalyzed by general acid-base. This fact agrees with the experimental results of enzymatic one-carbon unit transfer at oxidation level of formate. 相似文献
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The geometries,heats of formation and electronic structures of 15 azido-derivatives of 1,2,3-TNB (Ⅰ),1,2,4-TNB (Ⅱ) and 1,3,5-TNB (Ⅲ) have been studied using quantum chemical AMI method at HF level.The effect of azido substitution on the structures and properties of TNBs has been discussed and the relative stability of the title compounds has been established.The processes of the decomposition of the title compounds by breaking C-NO2,C-N3 and CN-N2 bonds are investigated at UHF-AM1 level.It is shown that the decomposition of the title compounds may be initiated by the cleavage of both C-NO2 and N-N2 bonds. 相似文献
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Stefanie Mädler Markus Seitz John Robinson Renato Zenobi 《Journal of the American Society for Mass Spectrometry》2010,21(10):1775-1783
Chemical cross-linking in combination with mass spectrometry has emerged as a powerful tool to study noncovalent protein complexes. Nevertheless, there are still many questions to answer. Does the amount of detected cross-linked complex correlate with the amount of protein complex in solution? In which concentration and affinity range is specific cross-linking possible? To answer these questions, we performed systematic cross-linking studies with two complexes, using the N-hydroxysuccinimidyl ester disuccinimidyl suberate (DSS): (1) NCoA-1 and mutants of the interacting peptide STAT6Y, covering a KD range of 30 nM to >25 μM, and (2) α-thrombin and basic pancreatic trypsin inhibitor (BPTI), a system that shows a buffer-dependent KD value between 100 and 320 μM. Samples were analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). For NCoA-1· STAT6Y, a good correlation between the amount of cross-linked species and the calculated fraction of complex present in solution was observed. Thus, chemical cross-linking in combination with MALDI-MS can be used to rank binding affinities. For the mid-affinity range up to about KD ≈ 25 μM, experiments with a nonbinding peptide and studies of the concentration dependence showed that only specific complexes undergo cross-linking with DSS. To study in which affinity range specific cross-linking can be applied, the weak α-thrombin · BPTI complex was investigated. We found that the detected complex is a nonspecifically cross-linked species. Consequently, based on the experimental approach used in this study, chemical cross-linking is not suitable for studying low-affinity complexes with KD ? 25 μM. 相似文献
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Density functional theory (DFT) has been employed to study the geometric and electronic structures, band gap, thermodynamic
properties, density, and performance properties of a series of polynitrotriazoles at the B3LYP/aug-cc-pVDZ level. The detonation
performances were evaluated by the Kamlet–Jacobs semi-empirical equations based on the calculated densities and heats of reaction.
It has been found that the model compounds with the predicted densities of 1.8 g/cm3, detonation velocities of 8.8 km/s, and detonation pressures of 35 GPa may be novel potential candidates of high energy density
materials. The discrepancies in the performance properties, stabilities or sensitivities among isomers are caused by the relative
position of NH2 and NO2 groups. 相似文献
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Kinetics of the single-electron chemical oxidation of rhenium(V) meso-phenyl-β-octaethylporphyrinate
N. G. Bichan E. Yu. Tyulyaeva T. N. Lomova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2014,88(10):1719-1725
The states and reactions of rhenium(V) complexes with meso-monophenyl-β-octaethylporphines containing Cl? and OPh? as axial ligands O=Re(Cl)MPOEP and O=Re(OPh)MPOEP in concentrated sulfuric acid at 298–348 K are studied via spectral and kinetic methods. While stable along M-N bonds, O=Re(Cl)MPOEP is found to undergo slow oxidation after transforming into axial hydrosulfate complex O=Re(HSO4)MPOEP. It is shown that the sole electron oxidizing agent is atmospheric oxygen (with the assistance of highly concentrated protons) and the sites of reduction are aromatic ligands. The reaction product was identified as π-radical cation O=Re(HSO4)MPOEP·+. Forward and inverse chemical kinetics solutions are used to obtain a full kinetic equation and the reaction rate parameters of elementary steps, and to establish the stoichiometric mechanism of the composite oxidation of the complex. Complex O=Re(OPh)MPOEP in the form O=Re(OPh)(O2)MPOEP with coordinated oxygen is shown experimentally to be stable with respect to oxidation. The obtained results are important for identifying intermediates in processes catalyzed by stable metal porphyrins. 相似文献
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Heisenberg’s explanation of how two coupled oscillators exchange energy represented a dramatic success for his new matrix
mechanics. As matrix mechanics transmuted into wave mechanics, resulting in what Heisenberg himself described as “…an extraordinary
broadening and enrichment of the formalism of the quantum theory”, the term resonance also experienced a corresponding evolution.
Heitler and London’s seminal application of wave mechanics to explain the quantum origins of the covalent bond, combined with
Pauling’s characterization of the effect, introduced resonance into the chemical lexicon. As the Valence Bond approach gave
way to a soon-to-be dominant Molecular Orbital method, our understanding of the term resonance, as it might apply to our understanding
the chemical bond, has also changed. 相似文献
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Miladinović DL Ilić BS Mihajilov-Krstev TM Nikolić ND Miladinović LC Cvetković OG 《Analytical and bioanalytical chemistry》2012,403(4):1007-1018
The antibacterial effects of Thymus vulgaris (Lamiaceae), Lavandula angustifolia (Lamiaceae), and Calamintha nepeta (Lamiaceae) Savi subsp. nepeta var. subisodonda (Borb.) Hayek essential oils on five different bacteria were estimated. Laboratory control strain and clinical isolates from
different pathogenic media were researched by broth microdilution method, with an emphasis on a chemical composition–antibacterial
activity relationship. The main constituents of thyme oil were thymol (59.95%) and p-cymene (18.34%). Linalool acetate (38.23%) and β-linalool (35.01%) were main compounds in lavender oil. C. nepeta essential oil was characterized by a high percentage of piperitone oxide (59.07%) and limonene (9.05%). Essential oils have
been found to have antimicrobial activity against all tested microorganisms. Classification and comparison of essential oils
on the basis of their chemical composition and antibacterial activity were made by utilization of appropriate chemometric
methods. The chemical principal component analysis (PCA) and hierachical cluster analysis (HCA) separated essential oils into
two groups and two sub-groups. Thyme essential oil forms separate chemical HCA group and exhibits highest antibacterial activity,
similar to tetracycline. Essential oils of lavender and C. nepeta in the same chemical HCA group were classified in different groups, within antibacterial PCA and HCA analyses. Lavender oil
exhibits higher antibacterial ability in comparison with C. nepeta essential oil, probably based on the concept of synergistic activity of essential oil components. 相似文献
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MicroRNAs (MiRNAs) have been regarded as clinically important biomarkers and drug discovery targets. In this work, we reported a simple and ultrasensitive electrochemical method for miRNAs detection based on single enzyme amplification and electrochemical–chemical–chemical (ECC) redox cycling. Specifically, upon contact with the target miRNAs, the hairpin structure of biotinylated DNA immobilized on gold electrode was destroyed and the biotin group in DNA was forced away from the electrode surface, allowing for the coupling of streptavidin-conjugated alkaline phosphatase (SA-ALP). Then, ascorbic acid (AA, the enzymatic product of ALP) triggered the ECC redox cycling with ferrocene methanol (FcM) and tris(2-carboxyethyl)phosphine (TCEP) as the redox mediator and the chemical reducing reagent, respectively. The method was more sensitive than that with horseradish peroxidase (HRP) or glucose oxidase (GOx) triggered recycling since one ALP molecule captured by one target miRNA molecule promoted the production of thousands of AA. Analytical merits (e.g., detection limit, dynamic range, specificity, regeneration and reproducibility) were evaluated. The feasibility of the method for analysis of miRNA-21 in human serum has also been demonstrated. 相似文献
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In our group, we work on the surface modification of cellulose nanocrystals. During this work, we have encountered reproducibility
issues when the same reactions were performed on nanocrystals from different hydrolysis batches, indicating a variable surface
composition. Given the inherent purity of the nanoparticles themselves, this issue was believed to be due to the presence
of adsorbed species at the surface of the nanocrystals blocking reactive sites. To investigate this in detail, nanocrystals
from several batches were extracted with different solvents. The effect of these extractions on the surface composition of
the nanowhiskers was investigated, followed by its effect on the Surface-Initiated Ring-Opening Polymerization (SI-ROP) of
ε-caprolactone. The extracted impurities were analysed by NMR (1H and 13C) and MS, showing a variety of adsorbed species which can be removed by solvent extraction. A Soxhlet extraction using ethanol
before the reaction was shown to be the most effective in removing adsorbed low molecular weight organic compounds produced
during the hydrolysis, resulting in improved reproducibility between reactions using nanocrystals from different batches,
as confirmed by FTIR, elemental analysis and XPS. Extraction with ethanol should thus be performed before all reaction as
these adsorbed species can be expected to interfere with all surface modification reactions. 相似文献