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排序方式: 共有178条查询结果,搜索用时 171 毫秒
41.
Yasemin Ö. Çiftci Kemal Çolakoğlu Sefa Kazanç SonerÖzgen 《Central European Journal of Physics》2006,4(4):472-480
This paper describes the effect of pressure on some the mechanical properties of transition metals Cu, Ag, and Au, such as
elastic constants and bulk modulus. Using molecular dynamics (MD) simulation, the present study was carried out using the
modified many-body Morse potential function expression in the framework of the Embedded Atom Method (EAM). The effect of pressure
on equilibrium volume, elastic constants, and bulk modulus were determined, and found to be in agreement with other theoretical
calculations and experimental data. 相似文献
42.
Osman Yilmaz Ali Usanmaz Kemal Alyürük 《Journal of polymer science. Part A, Polymer chemistry》1993,31(13):3205-3211
n-Butyl isocyanate (nBIC) was polymerized in bulk by the Pruitt–Baggett adduct (PBA) at ?23, 0.0, and 25.0°C. Polymerization was accompanied by trimerization to the cyclicisocyanurates at all temperatures. Spectroscopic evidences supported the nylon-1 structure for both trimer and polymer. The polymer/trimer ratio and the molecular weight of produced polymers were found to increase with decreasing temperature. The Pruitt–Baggett catalyst (PBC), which is the reaction product of (PBA + H2O) system, also polymerized nBIC, but with a relatively slower rate. In aromatic and etheric solutions, nBIC was only trimerized by PBA. Copolymerization of nBIC with propylene oxide by PBA and PBC failed. Some selected monoisocyanates were also polymerized by PBA. © 1993 John Wiley & Sons, Inc. 相似文献
43.
3-Aminoquinazolinone–phosphine proligands (5a–e) and their Ru(II) complexes (6a–e) were prepared and characterized by NMR (1H, 13C, 31P{1H}), FTIR and microanalysis. The 3-aminoquinazolinone–phosphine ligands were found to coordinate with the Ru(II) center via their phosphorus and nitrogen atoms. The Ru(II) complexes were applied as catalysts for the hydrogenation and transfer hydrogenation of prochiral ketones. The results showed that these complexes are efficient transfer hydrogenation catalysts. 相似文献
44.
Rainer Kahner Benedikt Waerder Hasan Kemal Arslan Heinz Rehage 《Colloid and polymer science》2010,288(4):461-468
In this publication we describe a new self-association process, which leads to the formation of ultra-thin alginate layers
at the interface between oil and water. The water phase contains a highly dilute solution of sodium alginate. These macromolecules
are negatively charged and they are not surface active. The oil phase contains a small concentration of positively charged
surfactants. At the interface between oil and water, the cationic surfactants tend to form complexes with the negatively charged
alginate polyelectrolytes in the aqueous solutions. This leads to striking adsorption processes of the solved polysaccharide
molecules at the oil-water interface. Upon the addition of calcium ions, a cross-linking process sets in and one obtains the
thin viscoelastic membranes, which are anchored at the interface between oil and water. The thickness of these membranes is
of the order of 0.2 mm. Similar structures can also be formed by solving positively charged Gemini surfactants in the oil
phase. In this case, the cationic surfactant molecules induce the adsorption processes of alginate macromolecules, and they
also act as cross-linking compounds. In a series of experiments, we measured the surface rheological properties of these ultra-thin
alginate membranes. The results of these investigations point to the presence of electrostatically stabilized membranes. Special
interest was given to the influence of the guluronate content of the alginates, which is important for the cross-linking mechanism
according to the egg-box model. Finally, this article finishes with the discussion of the proposed building mechanisms of
these membranes. 相似文献
45.
Hasan Tanak Yavuz Köysal Yasemin Ünver Metin Yavuz Şamil Işık Kemal Sancak 《Structural chemistry》2009,20(3):409-416
The Imidazole compound, Ethyl N′-3-(1H-imidazol-1-yl) propylcarbamoyl benzohydrazonate monohydrate, has been synthesized and
characterized by IR, NMR, electronic spectroscopy, and X-ray single-crystal determination. Molecular geometry from X-ray experiment
of the title compound in the ground state has been compared using the density functional method (B3LYP) with 6-31G+(d) basis
set. To determine conformational flexibility, molecular energy profile of the title compound was obtained by DFT calculations
with respect to two selected degrees of torsional freedom, which were varied from −180° to +180° in steps of 10°. Besides,
molecular electrostatic potential (MEP), natural bond orbitals (NBO), frontier molecular orbitals (FMO), and thermodynamic
properties were performed at B3LYP/6-31G+(d) level of theory. 相似文献
46.
Tabanca N Demirci B Turner JL Pounders C Demirci F Başer KH Wedge DE 《Natural product communications》2010,5(9):1421-1426
Volatile compounds from seven Salvia species and one interspecific hybrid growing at the Dallas Arboretum and Botanical Garden, Texas, US. Salvia coccinea, S. farinacea, S. greggii, S. leucantha, S. longispicata x farinacea, S. madrensis, S. roemeriana and S. splendens were investigated for their chemical compositions using a microdistillation technique. Volatiles were analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS). One hundred and twenty seven compounds were identified representing 94.3-99.7% of the oils. The major components in each of the seven species were as follows: S. coccinea (Z)-3-hexenal (31%), viridiflorol (19%); S. farinacea 1-octen-3-ol (30%) and (Z)-3-hexenal (23%); S. greggii 1,8-cineole (22%), borneol (17%), camphene (11%) and alpha-pinene (10%); S. leucantha limonene (35%) and alpha-pinene (17%); S. longispicata x farinacea 1-octen-3-ol (50%) and (Z)-3-hexenal (24%); S. madrensis (Z)-3-hexenal (53%); S. roemeriana limonene (49%) and alpha-pinene (20%); and S. splendens (Z)-3-hexenal (36%), 2,5-dimethoxy-p-cymene (19%) and linalool (11%). The microdistillation method was fast, practical and a useful technique that enabled the isolation of the volatiles in samples when only limited quantities were available. 相似文献
47.
Serbetçi T Demirci B Güzel CB Kültür S Ergüven M Başer KH 《Natural product communications》2010,5(9):1369-1374
The chemical compositions of the water-distilled essential oil of Stachys cretica ssp. lesbiaca Rech. fil. and S. cretica ssp. trapezuntica Rech. fil. were determined by GC and GC-MS. Altogether 63 compounds were identified. The sesquiterpene hydrocarbon, germacrene D (20.3% and 12.9% respectively) was the main component identified in both oils. Furthermore, ethanol, light petroleum, dichloromethane, ethyl acetate and n-butanol extracts prepared from the aerial parts of the plants were tested for their antimicrobial activities against six bacterial strains and the yeast Candida albicans. The extracts exhibited no antibacterial activity, but the light petroleum and n-butanolic fractions showed low antifungal activities. Crude ethanolic extracts of the two subspecies were tested for their ability to inhibit the growth of HL-60 and Ishikawa human tumor cell lines. The IC50 values were 100 microg/mL for the HL-60 cell line and 200 microg/mL for the Ishikawa cell line. 相似文献
48.
The proposed polar nucleophilic mechanism of MAO was investigated using quantum chemical calculations employing the semi-empirical PM3 method. In order to mimic the reaction at the enzyme's active site, the reactions between the flavin and the p-substituted benzylamine substrate analogs were modeled. Activation energies and rate constants of all the reactions were calculated and compared with the published experimental data. The results showed that electron-withdrawing groups at the para position of benzylamine increase the reaction rate. A good correlation between the log of the calculated rate constants and the electronic parameter (sigma) of the substituent was obtained. These results agree with the previous kinetic experiments on the effect of p-substituents on the reduction of MAO-A by benzylamine analogs. In addition, the calculated rate constants showed a correlation with the rate of reduction of the flavin in MAO-A. In order to verify the results obtained from the PM3 method single-point B3LYP/6-31G*//PM3 calculations were performed. These results demonstrated a strong reduction in the activation energy for the reaction of benzylamine derivatives having electron-withdrawing substituents, which is in agreement with the PM3 calculations and the previous experimental QSAR study. PM3 and B3LYP/6-31G* energy surfaces were obtained for the overall reaction of benzylamine with flavin. Results suggest that PM3 is a reasonable method for studying this kind of reaction. These theoretical findings support the proposed polar nucleophilic mechanism for MAO-A. 相似文献
49.
Ismail Akgun Markus Ganzera Canan Gur Serdar Senol Kemal Korkmaz Erdal Bedir 《Chromatographia》2009,70(5-6):963-967
As part of our ongoing studies, a new and validated method for analysis of isohexenyl-naphthazarines in Turkish Alkanna species was developed. By using reversed phase material (Synergi MAX RP) it was possible to determine four known isohexenylnaphthazarin-derivatives, namely alkannin, acetylalkannin, deoxyalkannin, and β,β-dimethylacrylalkannin within 25 min in n-hexane extracts of the roots. The quantification of these compounds in 16 Anatolian Alkanna species is described for the first time. In order to assure peak identity LC-MS experiments were performed. Quantitative results revealed that the most dominant compound in the extracts was β,β-dimethylacrylalkannin. 相似文献
50.