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排序方式: 共有455条查询结果,搜索用时 15 毫秒
311.
A new series of β-ketoanilides, in which the keto group attached to an olefinic linkage, have been synthesized by the reaction of acetoacetanilide with p-substituted benzaldehydes (4-methoxybenzaldehyde, 4-ethoxybenzaldehyde, 4-dimethylaminobenzaldehyde and 4-nitrobenzaldehyde) under specified conditions. The existence of these β-ketoanilides predominantly in the intramolecularly hydrogen bonded enol forms has been well demonstrated from their IR, 1H NMR and mass spectral data. Details on the formation of [ML2] complexes of these compounds with Ni(II), Cu(II) and Zn(II) and their nature of bonding were discussed on the basis of analytical, IR, 1H NMR and mass spectral data. 相似文献
312.
When male strains of Escherichia coli are irradiated with 254 nm ultraviolet (UV) light and mated with suitable females, DNA is transferred at almost the normal frequency (Howard-Flanders et al. , 1968). Cole (1971) observed that an episome damaged by UV irradiation of the male parent could be transferred to a recipient and restored to activity by administering photoreactivating light. He therefore deduced that UV lesions are transferred to the recipients during bacterial conjugation. The object of this Research Note is to report experiments providing direct evidence of the transfer of pyrimidine dimers -the main lesions of UV irradiation. 相似文献
313.
Hongyin Gao Qing‐Long Xu Muhammed Yousufuddin Daniel H. Ess Lszl Kürti 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(10):2739-2743
We disclose an efficient and operationally simple protocol for the preparation of fused N‐heterocycles starting from readily available 2‐nitrobiaryls and PhMgBr under mild conditions. More than two dozen N‐heterocycles, including two bioactive natural products, have been synthesized using this method. A stepwise electrophilic aromatic cyclization mechanism was proposed by DFT calculations. 相似文献
314.
Miah Muhammed Yusuf Hiroaki Imai Hiroshi Hirashima 《Journal of Sol-Gel Science and Technology》2000,19(1-3):599-601
SrBi2Ta2O9 (SBT) has potential application in FERAM. Some problems in the sol-gel processing of SBT, such as the solubility of metal alkoxides, chemical modification with a chelating reagent and crystallization behavior of the gels, are investigated.The starting solutions were prepared with Sr(OC4H9)2, Bi(OC3H7)3, and Ta(OC2H5)5. Ethoxyethanol and acetylacetone (ACAC) were used as solvent and chelating reagent, respectively. Ta- and Bi-alkoxide are chemically modified with ACAC, but Sr-alkoxide was not. The SBT solution was stabilized with ACAC for ca. 3 months. After hydrolysis of the SBT solution with the addition of ACAC, a monolithic and transparent gel was obtained at room temperature in 100 days. The X-ray diffraction peaks of SBT and very weak peaks of SrTa2O6 (ST) and SrBi2O4 (SB) were found after calcination at 700°C for both of the gels obtained with and without addition of ACAC. In contrast, the stronger peaks of ST and SB were observed for the powder mixture of SrCO3, Bi2O3, and Ta2O5 after calcination at 800°C. These results show the better homogeneity of the gels. 相似文献
315.
Safacan Kolemen Yusuf Cakmak Tugba Ozdemir Sule Erten-Ela Muhammed Buyuktemiz Yavuz Dede Engin U. Akkaya 《Tetrahedron》2014
Two electron rich Bodipy dyes with strong absorptivities in the visible region were designed and synthesized as potential electron donors in bulk heterojunction photovoltaic constructs. Overall efficiency is above 1%, with impressive responsiveness at both UV and near-IR ends of the visible spectrum. Computational studies reveal an unexpected effect of meso-substituents on the electron transfer efficiency. 相似文献
316.
Modeling the controller of the railway network, having resource sharing based on mutual exclusion constraints, is an important problem. This paper firstly addresses the specification of safety properties for the model of a complex railway crossing. The operations, i.e., occupied, free and block, are formalized to describe the safety properties along railway crossing. Second, to develop the control model of the crossing system we construct the subnet representing the train flow along the tracks in the crossing region and the set of monitors or supervisors are also modeled as subnets. Arc-constant colored Petri net (ac-CPN) is used to construct the train flow subnet while the monitors are modeled using the place/transition-net. Arc-constant colored Petri net enforces the specification of not to shift the train from a track to another one. Bottom-up approach is adopted to model the control for railway crossing as a synchronous synthesis of the subnets is applied to build the final model. Finally, to verify the safety properties in the developed controller, the coverability tree method is used for the analysis of the final model. 相似文献
317.
Aftab Aslam Parwaz Khan Abdullah M. Asiri Anish Khan Naved Azum Malik Abdul Rub Mohammed M. Rahman Sher Bahadar Khan 《Research on Chemical Intermediates》2013,39(6):2379-2389
The effect of anionic surfactant sodium dodecyl sulfate (SDS) on the rate of oxidation of levothyroxine (LVT) by hexacyanoferrate(III) in alkaline medium has been investigated spectrophotometrically at different temperatures. The reaction follows a complex kinetics showing first order dependence of rate with respect to both alkali and LVT. The effect of SDS on the rate of reaction has been observed at the critical miceller concentration of the surfactant. indicating binding of the substrate with the surfactant micelle. The binding parameters have also been evaluated using the Menger and Portnoy model. 相似文献
318.
Uheida A Iglesias M Fontàs C Hidalgo M Salvadó V Zhang Y Muhammed M 《Journal of colloid and interface science》2006,301(2):402-408
The adsorption of palladium(II), rhodium(III), and platinum(IV) from diluted hydrochloric acid solutions onto Fe(3)O(4) nanoparticles has been investigated. The parameters studied include the contact time and the concentrations of metals and other solutes such as H(+) and chloride. The equilibrium time was reached in less than 20 min for all metals. The maximum loading capacity of Fe(3)O(4) nanoparticles for Pd(II), Rh(III), and Pt(IV) was determined to be 0.103, 0.149, and 0.068 mmol g(-1), respectively. A sorption mechanism for Pd(II), Rh(III), and Pt(IV) has been proposed and their conditional adsorption equilibrium constants have been determined to be logK=1.72, 1.69, and 1.84, respectively. Different compositions of eluting solution were tested for the recovery of Pt(IV), Pd(II), and Rh(III) from Fe(3)O(4) nanoparticles. It was found that 0.5 mol L(-1) HNO(3) can elute all of the metal ions simultaneously, while 1 mol L(-1) NaHSO(3) was an effective eluting solution for Rh(III), and 0.5 mol L(-1) NaClO(4) for Pt(IV). In competitive adsorption, the nanoparticles showed stronger affinity for Rh(III) than for Pd(II) and Pt(IV). 相似文献
319.
Perveen S Khan SB Malik A Tareen RB Nawaz SA Choudhary MI 《Natural product research》2006,20(4):347-353
Perovskoate, an isorinic acid derivative (1) and perovskoside, the catechol derivative (2) have been isolated from the ethyl acetate soluble fraction of the whole plant of Perovskia atriplicifolia and assigned the structure 3(7-hydroxyphenyl)-2-hydroxy propanoic acid; (R)-form, 2-O-(6',7'-dihydroxy-E-cinnamoyl) (1) and 2-methoxy-4-(undecyl-4'-O-beta-D-glucopyranosyl) phenol (2). In addition, caffeic acid (3) and ferulic acid (4) have been reported for the first time from this species. The structures of these compounds were assigned on the basis of 1D and 2D NMR techniques. The compound 1 showed significant inhibitory activity against lipoxygenase and weak to moderate activity against cholinesterases. 相似文献
320.
Carmen Vogt Muhammet S. Toprak Mamoun Muhammed Sophie Laurent Jean-Luc Bridot Robert N. Müller 《Journal of nanoparticle research》2010,12(4):1137-1147
Obtaining small (<50 nm), monodispersed, well-separated, single iron oxide core–silica (SiO2) shell nanoparticles for biomedical applications is still a challenge. Preferably, they are synthesised by inverse microemulsion
method. However, substantial amount of aggregated and multicore core–shell nanoparticles is the undesired outcome of the method.
In this study, we report on the production of less than 50 nm overall size, monodispersed, free of necking, single core iron
oxide–SiO2 shell nanoparticles with tuneable shell thickness by a carefully optimized inverse microemulsion method. The high degree
of control over the process is achieved by understanding the mechanism of core–shell nanoparticles formation. By varying the
reaction time and precursor concentration, the thickness of silica layer on the core nanoparticles can be finely adjusted
from 5 to 13 nm. Residual reactions during the workup were inhibited by a combination of pH control with shock freezing and
ultracentrifuging. These high-quality tuneable core–shell nanocomposite particles exhibit superparamagnetic character and
sufficiently high magnetization with great potential for biomedical applications (e.g. MRI, cell separation and magnetically
driven drug delivery systems) either as-prepared or by additional surface modification for improved biocompatibility. 相似文献