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排序方式: 共有218条查询结果,搜索用时 15 毫秒
71.
M. H. Soorgi G. H. Rounaghi M. S. Kazemi 《Russian Journal of General Chemistry》2008,78(10):1866-1871
The complex formation between Na+, K+, Cs+, Rb+ and Tl+ metal cations with macrocyclic ligand, dicyclohexyl-18-crown-6 (DCH18C6) was studied in acetonitrile-water (AN-H2O) binary systems at different temperatures using conductometric method. DCH18C6 forms 1:1 complexes with these metal cations.
The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program
Genplot. The results show that the selectivity order of DCH18C6 for the metal cations in acetonitrile-water mixtures (AN =
25.3 and 50.4 mol %) is: Tl+ > K+ > Rb+ > Cs+ > Na+. A non-linear behaviour was observed between the log K
f of the complexes versus the composition of the mixed solvent which it related to changes of acidity, basicity, polarity and
also polarizability of AN-H2O mixtures with the composition of this binary solution. The values of standard enthalpy changes (ΔH
s0) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in the standard entropy
(ΔS
s0) were calculated from the relationship: ΔG
s,298.150 = ΔH
s0 − 298.15ΔS
s0. The obtained results show that in most cases, the complexes are enthalpy stabilized but entropy destabilized.
Original Russian Text ? M.H. Soorgi, G.H. Rounaghi, M.S. Kazemi, 2008, published in Zhurnal Obshchei Khimii, 2008, vol. 78,
No. 10, pp. 1627–1632. 相似文献
72.
Elham Memarian Saied Saeed Hosseiny DavaraniSaeed Nojavan Siyavash Kazemi Movahed 《Analytica chimica acta》2016
In this work, a new solid-phase microextraction fiber was prepared based on nitrogen-doped graphene (N-doped G). Moreover, a new strategy was proposed to solve problems dealt in direct coating of N-doped G. For this purpose, first, Graphene oxide (GO) was coated on Pt wire by electrophoretic deposition method. Then, chemical reduction of coated GO to N-doped G was accomplished by hydrazine and NH3. The prepared fiber showed good mechanical and thermal stabilities. The obtained fiber was used in two different modes (conventional headspace solid-phase microextraction and cold-fiber headspace solid-phase microextraction (CF-HS-SPME)). Both modes were optimized and applied for the extraction of benzene and xylenes from different aqueous samples. All effective parameters including extraction time, salt content, stirring rate, and desorption time were optimized. The optimized CF-HS-SPME combined with GC-FID showed good limit of detections (LODs) (0.3–2.3 μg/L), limit of quantifications (LOQs) (1.0–7.0 μg/L) and linear ranges (1.0–5000 μg/L). The developed method was applied for the analysis of benzene and xylenes in rainwater and some wastewater samples. 相似文献
73.
A new tetranuclear cubane-like complex, [Ni4(L)4Cl4(H2O)3(EtOH)]·(H2O), has been synthesized from the reaction of a metal salt with the bidentate ligand 2-hydroxymethylpyridine (LH), and its crystal structure, spectroscopic and chromotropic properties have been studied. The complex has a [Ni4O4] core comprising a distorted cubane arrangement, of which four nickel(II) ions were bridged by μ3-alkoxo moieties. Each nickel(II) was coordinated to three μ3-alkoxo oxygens, one pyridine nitrogen and one chloride. The peripheral ligation was completed by an oxygen atom of water or ethanol ligand, which participated in intramolecular hydrogen bonding. Chromotropism properties of the complex including solvato-, thermo-, and ionochromism were investigated. The complex displayed strong ionochromism and shows high-sensitive and selective activity toward CN? and SCN? anions in the presence of other halides and pseudo-halides. The solvatochromic property of the complex was analyzed by a multi-parametric equation using SPSS/PC software. The stepwise multiple linear regression method demonstrated that the acceptor power of the solvent plays the most important role in the observed negative solvatochromism of the compound. It shows reversible thermochromism in solution due to loss of the weakly coordinated water and ethanol from the nickel(II) units. 相似文献
74.
Lotfi Shiri Mosstafa Kazemi 《Phosphorus, sulfur, and silicon and the related elements》2017,192(11):1171-1176
We report a new strategy to immobilize a bromine source on the surface of magnetic Fe3O4 nanoparticles (Fe3O4 MNPs-DETA/Benzyl-Br3) leading to a magnetically recoverable catalyst, which exhibits high catalytic efficiency in oxidative coupling of thiols to the disulfides (89–98%). The Fe3O4 MNPs-DETA/Benzyl-Br3 catalyst was fabricated by anchoring 3-chloropropyltrimethoxysilane (CPTMS) on magnetic Fe3O4 nanoparticles, followed with N-benzylation and reaction with bromine in tetrachloridecarbon. The resulting nanocomposite was analyzed by a series of characterization techniques such as FT-IR, SEM, TGA, VSM and XRD. The catalyst could be recovered via magnetic attraction and could be recycled at least 5 times without appreciable decrease in activity. 相似文献
75.
This study reports the chemical composition, antimicrobial activity and antioxidant properties of Psammogeton canescens essential oil (EO) and its main compounds. The EO was obtained from the aerial parts of P. canescens by hydrodistillation and analysed by using GC/MS. The main constituent was β-bisabolene (25%), followed by α-pinene (20%), apiole (15.34%), γ-terpinene (7.34%), p-cymene (5.35%), β-pinene (5.41%), camphene (5.12%), dill apiole (5%), myrcene (4.54%), colchicine (0.56), sylvestrene (0.56%), β-caryophyllene (0.45%), caryophyllene oxide (0.43%), (Z)-β-farnesene (0.32%), cembrene (0.21%), folic acid (0.21%), germacrene D (0.14) and β-sesquiphellandrene (0.13). β-Bisabolene exhibited strong antioxidant activity (14 ± 0.8 μg/mL). The EO of P. canescens was particularly active against Candida albicans and Escherichia coli, with the lowest minimum inhibitory concentration and minimum bactericidal/fungicidal concentration values. In conclusion, these results support the use of the EO and its main compounds for their antioxidant properties and antimicrobial activity. 相似文献
76.
M Kazemi Zanjani M Nourelfath D Ait-Kadi 《The Journal of the Operational Research Society》2011,62(7):1334-1343
Motivated by sawmill production planning, this paper investigates multi-period, multi-product (MPMP) production planning in a manufacturing environment with non-homogeneous raw materials, and consequently random process yields. A two-stage stochastic program with recourse is proposed to address the problem. The random yields are modelled as scenarios with stationary probability distributions during the planning horizon. The solution methodology is based on the sample average approximation (SAA) scheme. The stochastic sawmill production planning model is validated through the Monte Carlo simulation. The computational results for a real medium capacity sawmill highlight the significance of using the stochastic model as a viable tool for production planning instead of the mean-value deterministic model, which is a traditional production planning tool in many sawmills. 相似文献
77.
Nanoparticles are usually 1–100 nm in each spatial dimension considered as building blocks of the next generation of optoelectronics,
electronics, and various chemical and biochemical sensors. In the synthesis of nanoparticles use of microorganisms emerges
as an eco-friendly and exciting approach that reduce waste products (ultimately leading to atomically precise molecular manufacturing
with zero waste); the use of nanomaterials as catalysts for greater efficiency in current manufacturing processes by minimizing
or eliminating the use of toxic materials (green chemistry principles); the use of nanomaterials and nanodevices to reduce
pollution (e.g. water and air filters); and the use of nanomaterials for more efficient alternative energy production (e.g.
solar and fuel cells). Fungi have many advantages for nanoparticle synthesis compared with other organisms. In this study,
Geotricum sp. found to successfully produce Ag nanoparticles. Geotricum sp. was grown in SDA (Sabro Dextrose Agar) medium at 25 ± 1 °C for 96 h. The mycelia were used to convert silver nitrate
solution into nano-silver. Silver nanoparticles were synthesized using these fungi (Geotricum sp.) extracellularly. UV–VIS spectroscopy, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy images shows the
nanoparticle formation in the medium. Energy-dispersive X-ray spectroscopy (EDX) also confirmed that silver nanoparticles
in the range of 30–50 nm were synthesized extracellularly. FTIR analyses confirmed the presence of amide (I) and (II) bands
of protein as capping and stabilizing agent on the surface of nanoparticles. 相似文献
78.
In this article, a parametric bootstrap approach for testing the equality of coefficient of variation of $k$ normal populations is proposed. Simulations show that the actual size of our proposed test is close to the nominal level, irrespective of the number of populations and sample sizes, and that this new approach is better than the other existing ones. Also, the power of our approach is satisfactory. An example is proposed for illustrating our new approach. 相似文献
79.
Sayed Yahya Kazemi Seyed Mohammad Abedirad Seyed Hassan Zali Mohadeseh Amiri 《Journal of luminescence》2012,132(5):1226-1231
Hypericin (HYP) molecule is a natural photoactive pigment, which plays a role as an effective photoreceptor in some plants of the Hypericum species (the most common of which is Saint John’s Wort) and some insect species. The present work deals with the first attempt to the study of peroxyoxalate chemiluminescence (POCL) system in the presense of HYP as a natural fluorophore. Reaction of bis (2,4,6-trichlorophenyl) oxalate(TCPO)–H2O2–imidazole can transfer energy to a HYP via formation of dioxetane through the chemically initiated electron exchange luminescence (CIEEL) mechanism and can emits a very intense red light. The effects of HYP, hydrogen peroxide, TCPO and imidazole concentrations on kinetic chemiluminescence parameters were also studied. These parameters including rise and fall rate constant for the chemiluminescence burst, theoretical and experimental maximum intensity, theoretical and experimental time to reach maximum intensity and total light yield emission were evaluated by using a pooled intermediate model for a non-linear least-squares curve fitting program, KINFIT. Moreover, quenching effect of two lipophilic natural antioxidant, Quercetin and β-carotene on it system was also investigated. The measurable concentration range of 7×10?6 M to 7.5×10?5 M of antioxidants were evaluated from the proper Stern–Volmer plots with satisfactory RSD% and corresponding detection limits of 2.2×10?6 and 3.7×10?6 for β-carotene and quercetin respectively. 相似文献
80.
A. Sheykhi K. Karami M. Jamil E. Kazemi M. Haddad 《International Journal of Theoretical Physics》2012,51(6):1663-1673
Considering the power-law corrections to the black hole entropy, which appear in dealing with the entanglement of quantum
fields inside and outside the horizon, the holographic energy density is modified accordingly. In this paper we study the
power-law entropy-corrected holographic dark energy in the framework of Brans-Dicke theory. We investigate the cosmological
implications of this model in detail. We also perform the study for the new agegraphic dark energy model and calculate some
relevant cosmological parameters and their evolution. As a result we find that this model can provide the present cosmic acceleration
and even the equation of state parameter of this model can cross the phantom line w
D
=−1 provided the model parameters are chosen suitably. 相似文献