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991.
Alireza Ghiasvand Farzaneh Zarghami Mohammad Beiranvand 《Journal of the Iranian Chemical Society》2018,15(5):1051-1059
A pressure-controlled headspace solid-phase microextraction (PC-HS-SPME) setup was developed, by reconsidering the strengths and weaknesses points of the similar reported systems. The new setup was coupled with gas chromatography–flame ionization detection (GC–FID) for direct analysis of benzene, toluene, ethylbenzene and xylene (BTEX) in contaminated soils, without any sample preparation step. The important experimental factors, affecting the performance of the method, including volumes of extraction and vacuum vials, type of SPME fiber, extraction time and temperature, moisture content of the sample, and sonication time were studied and optimized. Under the optimal conditions, good linearity of the calibration curves (R2 > 0.997) was obtained in the concentration range of 0.1–20,000 ng g?1. The limits of detections were found to be 0.001–0.08 ng g?1. The relative standard deviations, for six repetitive analyses of 100 ng g?1 BTEX, were obtained to be 5.7–12.3%. The PC-HS-SPME–GC–FID procedure was successfully applied for the extraction and determination of BTEX in the polluted soil samples. 相似文献
992.
A fast and simple ultrasound-assisted dispersive liquid–liquid microextraction method for determination of Sodium Closantel has been developed. High-performance liquid chromatography with ultraviolet detector has been used for the determination of Sodium Closantel. The effect of influencing parameters such as type and volume of extraction and disperser solvents, pH of sample solution, extraction time and amount of salt was also investigated. Optimization of method was performed using Plackett–Burman experimental design and surface response methodology. Under the optimal conditions, the linear dynamic range of Sodium Closantel was from 10 to 3000 µg L?1 with a correlation coefficient of 0.997 and a detection limit of 1.0 µg L?1. The relative standard deviation was less than 3.5% (n = 5). The method has been successfully applied for determination of Sodium Closantel in real samples. The enrichment factor was 48 under optimal conditions. 相似文献
993.
Abbasi A Lindqvist-Reis P Eriksson L Sandström D Lidin S Persson I Sandström M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(14):4065-4077
Trivalent lanthanide-like metal ions coordinate nine water oxygen atoms, which form a tricapped trigonal prism in a large number of crystalline hydrates. Water deficiency, randomly distributed over the capping positions, was found for the smallest metal ions in the isomorphous nonahydrated trifluoromethanesulfonates, [M(H2O)n](CF3SO3)3, in which M = Sc(III), Lu(III), Yb(III), Tm(III) or Er(III). The hydration number n increases (n = 8.0(1), 8.4(1), 8.7(1), 8.8(1) and 8.96(5), respectively) with increasing ionic size. Deuterium (2H) solid-state NMR spectroscopy revealed fast positional exchange between the coordinated capping and prism water molecules; this exchange started at temperatures higher than about 280 K for lutetium(III) and below 268 K for scandium(III). Similar positional exchange for the fully nonahydrated yttrium(III) and lanthanum(III) compounds started at higher temperatures, over about 330 and 360 K, respectively. An exchange mechanism is proposed that can exchange equatorial and capping water molecules within the restrictions of the crystal lattice, even for fully hydrated lanthanoid(III) ions. Phase transitions occurred for all the water-deficient compounds at approximately 185 K. The hydrated scandium(III) trifluoromethanesulfonate transforms reversibly (DeltaH degrees = -0.80(1) kJ mol(-1) on cooling) to a trigonal unit cell that is almost nine times larger, with the scandium ion surrounded by seven fully occupied and two partly occupied oxygen atom positions in a distorted capped trigonal prism. The hydrogen bonding to the trifluoromethanesulfonate anions stabilises the trigonal prism of water ligands, even for the crowded hydration sphere of the smallest metal ions in the series. Implications for the Lewis acid catalytic activity of the hydrated scandium(III) and lanthanoid(III) trifluoromethanesulfonates for organic syntheses performed in aqueous media are discussed. 相似文献
994.
Alireza Hoorfar W. David Ollis J. Fraser Stoddart David J. Williams 《Tetrahedron letters》1980,21(43):4211-4214
The tetra-anthranilide derivatives ()–() have been synthesised. X-Ray crystallography shows that ,′,″-trimethyltetra-anthranilide () adopts a conformation with three - and one -amide linkages in the solid state. Dynamic 1H n.m.r. spectroscopy indicates that -benzyl-′,″,′″-trimethyltetra-anthranilide () exists as an interconverting ternary mixture of chiral non-planar conformational diastereoisomers in solution. 相似文献
995.
996.
Mehdi Amirnasr Amir H. Mahmoudkhani Alireza Gorji Saeed Dehghanpour Hamid Reza Bijanzadeh 《Polyhedron》2002,21(27-28)
A series of complexes of the type M(Phca2en)X2, where Phca2en=N,N′-bis(β-phenyl-cinnamaldehyde)-1,2-diiminoethane, M(II)=Co, Ni or Zn and X=Cl, Br, I or NCS have been synthesized and characterized. The crystal and molecular structures of Co(Phca2en)Cl2 (2), Ni(Phca2en)Br2 (5) and Zn(Phca2en)Cl2 (6) were determined by X-ray crystallography from single-crystal data. Complexes 2 and 5 are isomorph and isostructure, in which the coordination polyhedron about the central metal ion is distorted tetrahedron with Cl---Co---Cl, 110.17(6)°; N---Co---N, 84.16(13)° and Cl---Zn---Cl, 112.02(6)°; N---Zn---N, 83.45(16)°. The complex 5 crystallizes in triclinic system with two molecules per asymmetric unit, both having nickel ion in distorted tetrahedral geometry, Br---Ni---Br, 122.645(18)° and 125.729(18)°; N---Ni---N, 84.63(9)° and 85.08(9)°. These structures consist of intermolecular hydrogen bonds of the type C---HX. The formation of the C---HM weak intramolecular hydrogen bonds due to the trapping of C---H bonds in the vicinity of the metal atoms are reported for 2, 5 and 6. A 1H NMR study of Zn complexes gives further evidence for the presence of such interactions and their significance. The spectral properties of the above complexes are also discussed. 相似文献
997.
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
998.
Aqueous ferrofluid of magnetite nanoparticles: Fluorescence labeling and magnetophoretic control 总被引:6,自引:0,他引:6
Sahoo Y Goodarzi A Swihart MT Ohulchanskyy TY Kaur N Furlani EP Prasad PN 《The journal of physical chemistry. B》2005,109(9):3879-3885
A method is presented for the preparation of a biocompatible ferrofluid containing dye-functionalized magnetite nanoparticles that can serve as fluorescent markers. This method entails the surface functionalization of magnetite nanoparticles using citric acid to produce a stable aqueous dispersion and the subsequent binding of fluorescent dyes to the surface of the particles. Several ferrofluid samples were prepared and characterized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), BET surface area analysis, transmission electron microscopy (TEM), and SQUID magnetometry. In addition, confocal fluorescence microscopy was used to study the response of the fluorescent nanoparticles to an applied magnetic field and their uptake by cells in vitro. Results are presented on the distribution of particle sizes, the fluorescent and magnetic properties of the nanoparticles, and the nature of their surface bonds. Biocompatible ferrofluids with fluorescent nanoparticles enable optical tracking of basic processes at the cellular level combined with magnetophoretic manipulation and should be of substantial value to researchers engaged in both fundamental and applied biomedical research. 相似文献
999.
Dabbagh HA Teimouri A Chermahini AN Shahraki M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,69(2):449-459
We present a detailed analysis of the structural, infrared spectra and visible spectra of a series of azo dyes preparation of salicylic acid and 2,4-dihydroxy benzoic acid derivatives as the coupling component. The preparation of these azo dyes with salicylic acid and 2,4-dihydroxy benzoic acid derivatives (salicylic acid, methyl salicylate, ethyl salicylate, butyl salicylate, methyl 2,4-dihydroxy benzoate, ethyl 2,4-dihydroxy benzoate, salicylaldehyde, salicylamide, 2,4-dihydroxy benzamide, salicylaldoxime) have been investigated theoretically by performing HF and DFT levels of theory using the standard 6-31G* basis set. The optimized geometries and calculated vibrational frequencies are evaluated via comparison with experimental values. The vibrational spectral data obtained from solid phase FT-IR spectra are assigned modes based on the results of the theoretical calculations. The observed spectra are found to be in good agreement with the calculations. 相似文献
1000.
A reversible crystal-to-crystal transformation of a 3D lead(ii) coordination polymer with the ligand 4-pyridinecarboxylic acid (4-Hpyc), from [Pb(4-pyc)(2)(H(2)O)](n) () to [Pb(4-pyc)(2)](n) () by de- and re-hydration, has been observed and the structures of and were determined by single-crystal X-ray diffraction. The thermal stabilities of compounds and were studied by thermal, gravimetric and differential thermal analyses. Powder X-ray diffraction experiments showed that the phase transitions observed for the single crystals also occur in the batch powder samples and lead to mono phasic products. 相似文献