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991.
The regioselective ring‐opening reactions of some epoxides with ammonium thiocyanate in the presence of a series of new 9H‐thioxanthen‐9‐one‐fused azacrown ethers, i.e., 7 – 11 (Scheme 1), and also of dibenzo[18]crown‐6 ( 12 ), Kryptofix® 22 ( 13 ), and benzo[15]crown‐5 ( 14 ) were studied (Tables 1 and 2). The epoxides were subjected to cleavage by NH4SCN in the presence of these catalysts under mild conditions in various aprotic solvents. Reagents and conditions were identified for the synthesis of individual β‐hydroxy thiocyanates in high yield and with more than 90% regioselectivity. The results can be discussed in terms of a four‐step mechanism (Scheme 2): 1) formation of a complex between catalyst and NH4SCN, 2) release of SCN? from the complex, 3) reaction of the released SCN? at the sterically less hindered site of the epoxide, and 4) regeneration of the catalyst. The major advantages of this method are the high regioselectivity, the simple regeneration of the catalyst, the reuse of it through several cycles without a decrease of activity, and the ease of workup of the reaction mixtures. 相似文献
992.
Thermal analysis study on the simultaneous grain refinement and modification of 380.3 aluminum alloy
Mehdi Malekan Davood Dayani Alireza Mir 《Journal of Thermal Analysis and Calorimetry》2014,115(1):393-399
In this research, effect of integrated Al–10Sr–1Ti–2B master alloy has been studied on the microstructure and solidification characteristics of 380.3 aluminum alloy. Thermal Analysis has been used as a technique to study the cooling curves and first derivative curves during solidification of the alloy. Effect of integrated grain refiner and modifier on solidification parameters such as α-Al dendrite growth temperature (T G,α), α-Al dendrite recalescence undercooling (?T R,α), aluminum–silicon eutectic growth temperature (T G,E), and eutectic recalescence undercooling (?T R,E) has been determined. By increasing master alloy content, T G,α and ?T R,E have been increased, but, ?T R,E has been decreased, and T G,E increases first and then decreases. Aluminum–silicon eutectic depression temperature ( $ \Updelta T_{\text{G,E}}^{{{\text{Al}} - {\text{Si}}}} $ ) can be used as a parameter to control the modification of eutectic silicon. The results of this research indicate that the optimum level of Al–10Sr–1Ti–2B master alloy for the simultaneous grain refinement and modification of 380.3 alloy is about 0.5 mass%. 相似文献
993.
Alireza Talaei Faramarz Afshar Taromi Ahmad Arefazar Saeid Ahmadjo Omid Moini Jazani 《高分子科学》2014,32(2):137-142
Ethylene polymerization was carried out by immobilization of rac-ethylenebis(1-indenyl)zirconium dichloride(Et(Ind)2 ZrCl2) and rac-dimethylsilylbis(1-indenyl)zirconium dichloride(Me2 Si(Ind)2 ZrCl2) preactivated with methylaluminoxane(MAO) on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2 Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 °C and 70 °C for Me2 Si(Ind)2 ZrCl2 /MAO and Et(Ind)2 ZrCl2 /MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 °C for both catalysts systems. The melting points of the produced polyethylene were about 130 °C, which could be attributed to the linear structure of HDPE. 相似文献
994.
Efficient One‐Pot Solvent‐Free Synthesis of 1H‐Pyrazolo[1,2‐b]phthalazine‐5,10‐diones Catalyzed by Sulfonic Acid Functionalized Nanoporous Silica (SBA‐Pr‐SO3H) 下载免费PDF全文
Ghodsi Mohammadi Ziarani Nina Hosseini Mohtasham Alireza Badiei Negar Lashgari 《中国化学会会志》2014,61(9):990-994
A green protocol has been developed for the synthesis of 1H‐pyrazolo[1,2‐b]phthalazine‐5,10‐diones by one‐pot cyclocondensation reaction of phthalhydrazide, aromatic aldehydes, and malononitrile or ethyl cyanoacetate using sulfonic acid functionalized SBA‐15 (SBA‐Pr‐SO3H) as a heterogeneous solid acid catalyst under solvent‐free conditions. 相似文献
995.
Dr. Alireza Mashaghi Samaneh Mashaghi Prof. Dr. Ir. Sander J. Tans 《Angewandte Chemie (International ed. in English)》2014,53(39):10390-10393
The folding of complex proteins can be dramatically affected by misfolding transitions. Directly observing misfolding and distinguishing it from aggregation is challenging. Experiments with optical tweezers revealed transitions between the folded states of a single protein in the absence of mechanical tension. Nonfolded chains of the multidomain protein luciferase folded within seconds to different partially folded states, one of which was stable over several minutes and was more resistant to forced unfolding than other partially folded states. Luciferase monomers can thus adopt a stable misfolded state and can do so without interacting with aggregation partners. This result supports the notion that luciferase misfolding is the cause of the low refolding yields and aggregation observed with this protein. This approach could be used to study misfolding transitions in other large proteins, as well as the factors that affect misfolding. 相似文献
996.
Habib Bagheri Alireza Akbarinejad Ali Aghakhani 《Analytical and bioanalytical chemistry》2014,406(8):2141-2149
A high-temperature-resistant solid-phase microextraction (SPME) fiber was prepared based on polyetherimide (PEI) by the electrospinning method. The PEI polymeric solution was converted to nanofibers using high voltages and directly coated on a stainless steel SPME needle. The scanning electron microscopy images of PEI coating showed fibers with diameter range of 500–650 nm with a homogeneous and smooth surface morphology. The SPME nanofibers coating was optimized for PEI percentage, electrospinning voltage, and time. The extraction efficiency of the coating was investigated for headspace SPME of some environmentally important polycyclic aromatic hydrocarbons from aqueous samples followed by gas chromatography–mass spectrometry measurement. In addition, the important extraction parameters including extraction temperature, extraction time, ionic strength, as well as desorption temperature and time were investigated and optimized. The detection limits of the method under optimized conditions ranged from 1 to 5 ng L?1 using time-scheduled selected ion monitoring mode. The relative standard deviations of the method were between 1.1 and 7.1 %, at a concentration level of 500 ng L?1. The calibration curves of polycyclic aromatic hydrocarbons showed linearity in the range of 5–1000 ng L?1. The developed method was successfully applied to real water samples and the relative recovery percentages obtained from the spiked water samples were from 84 to 98 % for all the selected analytes except for acenaphthene which was from 75 to 106 %. 相似文献
997.
Zarrin Es’haghi Shakiba Taghizade Alireza Mazloomi-Bajestani 《Journal of the Iranian Chemical Society》2014,11(5):1421-1428
In the present work, hollow fiber solid-phase microextraction coupled with hydride generation–atomic fluorescence spectroscopy was employed in the extraction and determination of Arsenic(III), in water samples including acid mine drainage, gold mine wastewater and spring water of Iran. In this technique, an innovative solid sorbent containing mixture of nano TiO2 and a composite microporous compound was developed by the sol–gel method via the reaction of tetraethylorthosilicate and methyltrimethoxysilane. Sol–gel processing was done under acidic catalyst condition. The stated sol was held in the lumen of a porous polypropylene hollow fiber segment for in situ gelation procedure. The experimental setup is very simple and highly affordable. The hollow fiber is disposable, so single use of the fiber reduces the risk of cross-contamination and carry-over problems. The main factors influencing the pre-concentration and extraction of As(III) have been examined in detail. The optimized conditions were obtained and the relationship between the atomic fluorescence signal versus As(III) concentration was linear over the range of 0.01–30 μg L?1 for As(III). The limits of detection and quantification were 0.003 and 0.01 μg L?1, respectively. Under the adjusted conditions, the enrichment factor was 501.4. 相似文献
998.
In this paper, an analytical approach based on ballistic current transport is presented to investigate the electrical characteristics
of the coaxial nanowire field effect transistor (CNWFET). The potential distribution along the nanowire is derived analytically
by applying Laplace equation. In addition to application of WKB approximation and ballistic transport, tunneling process and
quantum state of energy are implemented to determine the amount of electron transport along the nanowire from the source to
the drain terminals. To consider the tunneling phenomena, WKB approximation is used and the transmission coefficients on both
sides of the channel are obtained separately. In ballistic regime, an expression for channel current in terms of the bias
voltages and Schottky barrier height (SBH) is derived. The results confirm a close correlation between the current equation
of this work and the results presented via other approaches. 相似文献
999.
Through a study of torsion functors of local cohomology modules we improve some non-finiteness results on the top non-zero
local cohomology modules with respect to an ideal. 相似文献
1000.
Alireza Badiei Hassan GoldoozGhodsi Mohammadi Ziarani 《Applied Surface Science》2011,257(11):4912-4918
8-Hydroxyquinoline (8-HQ) was attached to mesoporous silica by sulfonamide bond formation between 8-hydroxyquinoline-5-sulfonyl chloride (8-HQ-SO2Cl) and aminopropyl functionalized SBA-15 (designated as SBA-SPS-Q) and then aluminum complexes of 8-HQ was covalently bonded to SBA-SPS-Q using coordinating ability of grafted 8-HQ.The prepared materials were characterized by powder X-ray diffraction (XRD), nitrogen adsorption-desorption, Fourier transform infrared (FT-IR), thermal analysis (TGA-DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental analysis and fluorescence spectra. The environmental effects on the emission spectra of grafted 8-HQ and its complexes were studied and discussed in details. 相似文献