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排序方式: 共有227条查询结果,搜索用时 15 毫秒
51.
Mohammad Reza Hadjmohammadi S. Saman S. J. Nazari 《Journal of separation science》2010,33(20):3144-3151
The chemometrics approach was applied for the separation optimization of flavonoid markers (quercetin, hesperetin and chrysin) in honey using micellar liquid chromatography (MLC). The investigated method combines SPE of flavonoids from honey using C18 cartridge and their separation and quantification by micellar liquid chromatography. A two level full factorial design was carried out to evaluate the effect of four experimental factors including concentration of SDS, alkyl chain length of the alcohol used as the organic modifier (N), volume percentage of the organic modifier (Vm) and volume percentage of acetic acid (AcOH) in mobile phase on analytes retention times. Experiments for analytes retention times modeling and optimization of separation were performed according to central composite design. Multiple linear regression method was used for the construction of the best model based on experimental retention times. Pareto optimal method was used to find suitable compatibility between resolution and analysis time of analytes in honey. The optimum mobile phase composition for separation and determination of analytes in honey were [SDS]=0.124 mol/L; 7.8% v/v ethanol and 5.0% v/v AcOH. Limits of detection and linear range of flavonoid markers were 0.0079–0.0126, 0.05–50.0 mg/L, respectively. 相似文献
52.
Ozone water reaction including a complex was studied at the MP2/6-311++G(d,p) and CCSD/6-311++G(2df,2p)//MP2/6-311++G(d,p) levels of theory. The interaction between water oxygen and central oxygen of ozone produces stable H2O-O3 complex with no barrier. With decomposition of this complex through H-abstraction by O3 and O-abstraction by H2O, three possible product channels were found. Intrinsic reaction coordinate, topological analyses of atom in molecule, and vibrational frequency calculation have been used to confirm the preferred mechanism. Thermodynamic data at T = 298.15 K and atmospheric pressure have been calculated. The results show that the production of hydrogen peroxide is the main reaction channel with ΔG = ?21.112 kJ mol-1. 相似文献
53.
Morad Alizadeh Fazlollah Lak Mahdi Rasekhi Thiago G. Ramires Haitham M. Yousof Emrah Altun 《Computational Statistics》2018,33(3):1217-1244
We introduce a new class of distributions and provide a comprehensive treatment of its mathematical properties. The maximum likelihood method is discussed to estimate the parameters of the new model by means of Monte-Carlo simulation study. The heteroscedastic regression models with long-term survival are introduced to model data sets with the non homogeneity of the error variances in the presence of cured individuals. The potentiality of the proposed models is illustrated by means of four real data sets. 相似文献
54.
55.
In this paper, for a given set of numbers with special conditions, we construct a nonnegative matrix such that the given set is its spectrum. 相似文献
56.
Bogdan M. Benin Dr. Kyle M. McCall Dr. Michael Wörle Viktoriia Morad Marcel Aebli Dr. Sergii Yakunin Dr. Yevhen Shynkarenko Prof. Dr. Maksym V. Kovalenko 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(34):14598-14605
Low-dimensional ns2-metal halide compounds have received immense attention for applications in solid-state lighting, optical thermometry and thermography, and scintillation. However, these are based primarily on the combination of organic cations with toxic Pb2+ or unstable Sn2+, and a stable inorganic luminescent material has yet to be found. Here, the zero-dimensional Rb7Sb3Cl16 phase, comprised of isolated [SbCl6]3− octahedra and edge-sharing [Sb2Cl10]4− dimers, shows room-temperature photoluminescence (RT PL) centered at 560 nm with a quantum yield of 3.8±0.2 % at 296 K (99.4 % at 77 K). The temperature-dependent PL lifetime rivals that of previous low-dimensional materials with a specific temperature sensitivity above 0.06 K−1 at RT, making it an excellent thermometric material. Utilizing both DFT and chemical substitution with Bi3+ in the Rb7Bi3−3xSb3xCl16 (x≤1) family, we present the edge-shared [Sb2Cl10]4− dimer as a design principle for Sb-based luminescent materials. 相似文献
57.
A three‐factor mixture design and response surface methodology were employed to find the optimal weight ratio of graphite powder, n‐dodecylpyridinium hexafluorophosphate and paraffin for the fabrication of a copper hexacyanoferrate modified carbon ionic liquid paste electrode (CuHCFe‐CILPE). The fabricated sensor showed electrocatalytic activity towards oxidation and reduction of hydrogen peroxide. It also was observed that the electrocatalytic activity for hydrogen peroxide oxidation was much higher than the electrocatalytic activity for hydrogen peroxide reduction. Glucose oxidase was then successfully immobilized on the surface of the proposed sensor to examine the possibility of using CuHCFe‐CILPE for the biosensor fabrication. 相似文献
58.
Radineh Motamedi Majid M. Heravi Zahra Nazari Fatemeh F. Bamoharram 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1672-1675
2-Substituted [1,2,4]triazolo[5,1-b][1,3]thiazin-7-ones 3 were synthesized via regioselective cyclization of 4H-[1,2,4]triazol-3-ylsulfanyl-acrylic acids 2 in the presence of catalytic amounts of heteropolyacids at room temperature in very good yields and rates. 相似文献
59.
A.A. Moosavi-Movahedi F. Semsarha H. Heli K. Nazari H. Ghourchian J. Hong G.H. Hakimelahi A.A. Saboury Y. Sefidbakht 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,320(1-3):213-221
The UV–vis spectrophotometry and cyclic voltammetry were employed to investigate the incorporation of hematin into histidine (His) in a micellar environment of sodium dodecyl sulfate (SDS). Histidine undergoes a reduction process on silver electrode, while, hematin and sodium dodecyl sulfate are not electroreactive species on this electrode. Electrochemistry of twine-by-twine mixture of His, hematin and SDS on silver electrode shows that the peak potential of His in the presence of SDS or hematin shifts negatively which indicates the interaction of SDS and hematin with His. The interaction of SDS and hematin with His was also confirmed using spectrophotometric measurements. However, the peak potential of His on silver electrode shifts positively in the presence of both SDS and hematin which indicates that in a triple-component solution of His–hematin–SDS a unique species is formed and is electroreactive on silver electrode. In this context, this triple-component solution represents unique absorption band in UV–vis spectra, which is related to the formation of a unique structure of a hemoprotein-like biomimetic catalyst. The catalytic activity of this artificial enzyme formed in triple-component solution was examined with respect to hydrogen peroxide and the apparent Michaelis–Menten (Km) and catalytic rate (kcat) constants were evaluated to be 3.31 μM and 0.043 s−1, respectively. 相似文献
60.
Z. Taheri K. Nazari A.A. Safekordi N. Seyed-Matin R. Ahmadi N. Esmaeili A. Tofigh 《Journal of molecular catalysis. A, Chemical》2008,286(1-2):79-86
A dense membrane of La0.6Sr0.4Co0.8Fe0.2O3−δ (LSCF) perovskite was prepared by a new chelating agent, ethylene diamine N,N,N′,N′-tetra N-acetyl diamine (EDTNAD). As a potent ligand, EDTNAD provided a facile one-step method to form complexes of the four metal ions, simultaneously. The oxygen permeation flux through the pure perovskite LSCF dense membrane was measured over temperature range of 1073–1223 K, thickness of 0.7–1.0 mm and oxygen partial pressure of 0.1–1.0 bar. Oxidative coupling of methane (OCM) reaction using LSCF disk in the atmospheric membrane reactor and over the temperature range of 1073–1173 K showed a C2 selectivity of 100% and C2 yield of 5.01% at 1153 K. Furthermore, OCM reaction data of the membrane reactor were discussed and compared with those of the fixed bed using the same perovskite powder as the catalyst. 相似文献