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411.
Nahid Mashkouri Najafi Shahram SeidiReza Alizadeh Hamed Tavakoli 《Spectrochimica Acta Part B: Atomic Spectroscopy》2010
Speciation analyses are of increasing interest in the environmental, toxicological and analytical fields, because the toxicity and reactivity of trace elements depend strongly on the chemical forms in which they are present. A simple electrodeposition–electrothermal atomic absorption spectrometry method for speciation analysis of some organic and inorganic selenium species in typical environmental water and agricultural soil samples has been developed. The method is based on the selective reduction of water-soluble Se(IV) and selenocystine (Se–Cys) species by an uncontrolled applied potential (1.8 V) on a mercury-coated electrode. In acidic media (1.0 M HCl solution) the only inorganic selenium species electrodeposited was Se(IV), and, of the water-soluble organic selenium species Se–Cys and Se–Met only Se–Cys was electrodeposited onto the mercury electrode surface. The proposed methodology was successfully applied to the speciation and determination of selenium in a few environmental samples. The spiked recovery value varied between 91% and 99%. The suggested method has been shown to have a characteristic mass (m0) of 25 pg, a limit of detection (LOD) of 1.0 μg L− 1 and a relative standard deviation (RSD%) of 3.5% for 6 measurements at a concentration of 100 μg L− 1 Se(VI). 相似文献
412.
Stable derivatives of 2,5-dihydro-1,2-oxaphospholes were obtained in excellent yields from the reaction between electron-deficient acetylenic compounds, and ethyl 3-bromopyruvate or methyl 4-chloroacetoacetate in the presence of triphenylphosphine in dry ether. 相似文献
413.
Issa Yavari Abdolali AlizadehMohammad Anary-Abbasinejad Hamid R Bijanzadeh 《Tetrahedron》2003,59(32):6083-6086
Protonation of the highly reactive 1:1 intermediates produced in the reaction between alkyl isocyanides and dibenzoylacetylene by saccharin, phthalimide, or 4-methyl-5-nitroimidazole, leads to vinylnitrilium cations, which undergo carbon-centered Michael type addition with the conjugate base of the NH-acid to produce highly functionalized aminofuran derivatives. 相似文献
414.
In this study, the synthesis of bis-(2-ethylhexyl) terephthalate, via the transesterification reaction of dimethyl terephthalate (DMT) by 2-ethylhexanol in the presence of different heterogeneous catalysts, such as Pb(OAc)2·3H2O, Cd(OAc)2·2H2O, Zn(OAc)2·2H2O, Hg(OAc)2·Ca(OAc)2·H2O, Cu(OAc)2·H2O, NaOAc, CaCO3, CaO, ZnSO4·7H2O, and sulfated zirconia, has been investigated. The reactivity of the catalysts in the reaction progress has been studied and compared. It was found that, hydrated cadmium acetate and sulfated zirconia were reactive catalysts to this reaction. The extent of transesterification of methyl ester groups reached up to 93% and 85.6% using these catalysts, respectively. 相似文献
415.
Abdolali Alizadeh Hassan Masrouri Sadegh Rostamnia Farnaz Movahedi 《Helvetica chimica acta》2006,89(5):923-926
The reactive 1 : 1 adducts in the reaction between Ph3P and dialkyl acetylenedicarboxylates have been trapped with ‘tosylmethyl isocyanide’ (TsMIC ; 1 ) to yield dialkyl 2‐[(4‐methylphenyl)sulfonyl]‐1H‐pyrrole‐3,4‐dicarboxylates 3 (Scheme 1). The structures of the highly functionalized compounds 3 were corroborated spectroscopically (IR, 1H‐ and 13C‐NMR, and EI‐MS) and by elemental analyses. A plausible mechanism for this type of cyclization is proposed (Scheme 2). 相似文献
416.
Abolghasem Moghimi Robabeh Alizadeh M. Carla Aragoni Vito Lippolis Hossein Aghabozorg Parviz Norouzi Francesco Isaia Shabnam Sheshmani 《无机化学与普通化学杂志》2005,631(10):1941-1946
The novel 1,10‐phenanthroline‐2,9‐dicarboxylate containing Chromium(III) complex, (pydaH)[Cr(phendc)2] · 5H2O, was synthesized using proton‐transfer compound LH2, (pydaH2)2+(phendc)2?, (pyda: 2,6‐pyridinediamine; phendcH2: 1,10‐phenanthroline‐2,9‐dicarboxylic acid) and thoroughly characterized by elemental analysis, IR spectroscopy, X‐ray crystallography and cyclic voltammetry. The complex crystallizes in the monoclinic space group P21/n with four formula units in the unit cell. The unit cell dimensions are: a = 13.962(3) Å, b = 14.529(3) Å, c = 16.381(3) Å and β = 106.691(4)°. In this complex, 1,10‐phenanthroline‐2,9‐dicarboxylate acts as a tridentate ligand and the lattice is composed of anionic hexacoordinated complex, [Cr(phendc)2]?, 2,6‐pyridiniumdiamine counter ion, (pydaH)+, and five lattice water molecules. Crystallographic characterization revealed that the resulting supramolecular structure is strongly stabilized by complicated network of hydrogen bonds between the crystallization water molecules, counter ion and both coordinated and uncoordinated carboxylate groups. There is no relevant π‐π interaction for this anionic complex between pyda or phendc moieties. The electrochemical studies indicated over potential for both the cathodic and anodic peaks of the complex with respect to the free Cr3+ ion, as a consequence of the energy requirement for rearrangement of the ligand at electrode surface. 相似文献
417.
Lizbeth Laureano-Perez Farzaneh Teymouri Hasan Alizadeh Bruce E. Dale 《Applied biochemistry and biotechnology》2005,124(1-3):1081-1099
Spectroscopic characterization of both untreated and treated material is being performed in order to determine changes in
the biomass and the effects of pretreatment on crystallinity, lignin content, selected chemical bonds, and depolymerization
of hemicellulose and lignin. The methods used are X-ray diffraction for determination of cellulose crystallinity (CrI); diffusive
reflectance infrared (DRIFT) for changes in C-C and C-O bonds; and fluorescence to determine lignin content. Changes in spectral
characteristics and crystallinity are statistically correlated with enzymatic hydrolysis results to identify and better understand
the fundamental features of biomass that govern its enzymatic conversion to monomeric sugars. Models of the hydrolysis initial
rate and 72 h extent of conversion were developed and evaluated. Results show that the hydrolysis initial rate is most influenced
by the cellulose crystallinity, while lignin content most influences the extent of hydrolysis at 72 h. However, it should
be noted that in this study only crystallinity, lignin, and selected chemical bonds were used as inputs to the models. The
incorporation of additional parameters that affect the hydrolysis, like pore volume and size and surface area accessibility,
would improve the predictive capability of the models. 相似文献
418.
A membrane electrode selective to hexadecylpyridinium bromide was used to study the micellization of the surfactant in the presence of varying concentrations of crown ethers 15-crown-5, dicyclohexyl-18-crown-6 and dicyclohexyl-24-crown-8 at 27°C. The critical micelle concentration of surfactant was largely influenced by the crown ethers used, indicating their participation in the structure of the resulting micelle. The degree of attachment of crown ethers to the surfactant in the micellar structure was found to be 1. An estimation of the Kf for the 1:1 surfactant-crown interaction in the micellar region is reported. The degree of counter ion dissociation was found to increase with the crown ether concentration, and with the nature of macrocyclic ligands in the order 15-crown-5 < dicyclohexyl- l8-crown-6 < dicyclohexyl-24-crown-8. There was also some evidences for a rather strong interaction between dicyclohexyl-24-crown-8 and the surfactant in the submicellar concentration ranges in solution. 相似文献
419.
An effective route to hydantoins is described, based on the 2 : 1 : 1 addition of arylsulfonyl isocyanates, dialkyl acetylenedicarboxylates, and dialkyl trialkylsilyl phosphites. The resulting tetrasubstituted, stable hydantoins 4 / 4′ (Table) were obtained in excellent yields, and their structures were corroborated spectroscopically (IR, 1H‐, 13C‐, 31P‐NMR, EI‐MS) and by elemental analyses. A plausible mechanism for this type of cyclization is proposed (Scheme 2). 相似文献
420.
Ion Pairing,H‐bonding,and π‐π Interactions in Cobalt(II) Compound Containing Guanidinium Counter Ion
Shabnam Sheshmani Hossein Aghabozorg Fahimeh Mohammad Panah Robabeh Alizadeh Guido Kickelbick Bahar Nakhjavan Abolghasem Moghimi Farshid Ramezanipour Hamid Reza Aghabozorg 《无机化学与普通化学杂志》2006,632(3):469-474
A novel proton transfer compound, (GH)2(phendc), ( 1 ), was synthesized from the reaction of 1,10‐phenanthroline‐2,9‐dicarboxylic acid, phendcH2, and guanidine hydrochloride, (GH)(Cl), (G: guanidine). The characterization was performed using IR, 1H and 13C NMR spectroscopy. The cobalt(II) compounds were synthesized using proton transfer compounds containing guanidinium counter ion. These proton transfer compounds are (GH)2(phendc), and (GH)2(pydc) (pydcH2: 2,6‐pyridinedicarboxylic acid). The chemical formulae and space groups are (GH)2[Co(phendc)2]·4H2O, (2) , and (GH)2[Co(H2O)6][Co(pydc)2]2, P21/n (3) . Non‐covalent interactions such as ionpairing, hydrogen bonding and π‐π stacking are discussed. 相似文献