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961.
Gholam Hossein Rounaghi Mohammad Hossein Arbab Zavvar Fatemeh Boosaeedi Razieh Sanavi Khoshnood 《Journal of inclusion phenomena and macrocyclic chemistry》2003,47(3-4):101-107
The complexation reactions betweenT1+, Hg2+ andAg+ metal cations with 18-Crown-6 (18C6)were studied in acetonitrile (AN)-methanol (MeOH) andbenzonitrile (BN)-methanol (MeOH) binary mixtures at differenttemperatures using the conductometric method. The conductance datashow that the stoichiometry of the complexes in most cases is1 : 1 (ML), but in the case of theTl+ cation, in addition to a1 : 1 complex, a 1 : 2 (ML2)complex is formed in solutions. A non-linear behaviourwas observed for the variation of log Kfof the complexes vs the composition of the binary mixed solvents. The stability of 18C6 complexes with T1+, Hg2+ and Ag+ cations is sensitive to solvent composition and in some cases, the stability order is changed with changingthe composition of the mixed solvents. The values of the thermodynamic parameters (Δ Hc°, Δ Sc°) for formation of 18C6-T1+, 18C6-Hg+2 and the 18C6-Ag+ complexes were obtained from the temperature dependence of the stability constants and the results show that the thermodynamics of the complexationreactions is affected by the nature and composition of the mixed solvents and in most cases, the complexes are enthalpy destabilized but entropy stabilized. 相似文献
962.
Amir Abdolmaleki 《Polymer Degradation and Stability》2007,92(2):292-298
A series of new poly(amide-hydrazide)s were obtained by the direct polycondensation of 5-amino 5′-carbohydrazido-2,2′-bipyridine with commercially available diacids by means of triphenyl phosphite and pyridine in the N-methyl-2-pyrrolidone (NMP) solutions containing dissolved LiCl. The resulting hydrazide containing polymers exhibited inherent viscosities in the 0.42-0.64 dL/g range. All copolymers were soluble in polar solvents such as NMP and dimethyl sulfoxide (DMSO). Most of the amorphous hydrazide copolymers formed flexible and tough films by solvent casting. The poly(amide-hydrazide)s had glass-transition temperatures (Tg) between 178 and 206 °C. All hydrazide copolymers could be thermally converted into the corresponding poly(amide-oxadiazole) approximately in the region of 300-400 °C, as evidenced by the DSC thermograms. The oxadiazole polymers and copolymers showed a dramatically decreased solubility and higher Tg when compared to their respective hydrazide prepolymers. They exhibited Tgs of 197-248 °C and were stable up to 450 °C in air or nitrogen. 相似文献
963.
Two lithium sulfenamides were prepared by reaction of (CH(3))(3)C-N(H)-S-C(6)H(4)CH(3)-4 (1) and 4-CH(3)C(6)H(4)-N(H)-S-C(6)H(4)CH(3)-4 (2) with an alkyllithium. The unsolvated sulfenamide Li[(CH(3))(3)C-NS-C(6)H(4)CH(3)-4] (3) was soluble enough for variable-temperature (VT) (7)Li NMR to provide evidence of a dynamic exchange of oligomers in solution. The crystal structures of the solvated sulfenamides of [Li(2)(eta(2)-(CH(3))(3)C-NS-C(6)H(4)CH(3)-4)(2)(THF)(2)] (4) and of [Li(2)(eta(1)-4-CH(3)C(6)H(4)-NS-C(6)H(4)CH(3)-4)(2)(THF)(4)] (6) consisted of dimers in which the anions display different hapticities. The VT (7)Li NMR spectra of 4 suggest that the two different structures exist in equilibrium in toluene-THF mixtures. These compounds are easily oxidized to the neutral thioaminyl radicals as identified by EPR spectroscopy. 相似文献
964.
An efficient and highly enantioselective (up to 95% ee) Cu-catalyzed method for asymmetric conjugate addition (ACA) of alkylzinc reagents to acyclic disubstituted nitroalkenes is presented. Reactions are typically effected at ambient temperature in the presence of 2 mol % chiral dipeptide phosphine and 1 mol % (CuOTf)(2).C(6)H(6). Nitroalkenes bearing aromatic as well as aliphatic substituents readily undergo asymmetric additions. [reaction: see text] 相似文献
965.
Rudolf W. Soukup Valentin N. Sapunov Hossein Ateshykashi Roland Schmid 《Monatshefte für Chemie / Chemical Monthly》1982,113(12):1349-1366
The kinetics of the iron(II) reduction of thallium(III) oxinate does not differ essentially from that of the oxinate-transfer from thallium(III)-oxinate to iron(III), described before: formation of a binuclear intermediate, rearrangements within, and subsequent reaction with the excess reactant to the final products. As for the redox process, these intermediates are binuclear Tl(II)-Fe(III) complexes which, with initial reactants, form further complexes in which the second electron is transferred. In the cases of excess Tl(ox)3 and of equimolar reactants, disproportionations are likely involved. 相似文献
966.
Structural and electronic properties of oligomers including dimer, trimer and tetramer of fluoromethylpyrroles (FMPs), NC4H4-CHnF3−n with n = 0, 1, 2, 3, and their radical cations have been studied using DFT-B3LYP method with 6-31G(d, p) basis set. FMPs are proposed in this research as candidate monomers for conducting polymers with modified characteristics compared to polypyrrole and polymethylpyrrole. A preliminary study using a set of ab initio computations (HF) with medium basis set was carried out on di-, tri- and tetramer in order to investigate the stability of configuration of polymer chains for FMPs. The B3LYP/6-31G** optimized geometry and stereochemistry show that the selectivity of branching of the propagating polymer chain is affected by the characteristics of the substitutions of monomer and, therefore, the growth pattern of the polymer chain can be predicted upon characterization of different centers of the monomers. Also, the results of this study, including quinoid coefficients, orbital energy spacing, charge- and spin-density distributions and electric dipole moment vectors show that conducting polymers consisted of trifluoromethyl pyrrole (Py-CF3), compared with the other FMPs, are the most favorable to be used as monomers for conducting polymer structural and electronic properties. 相似文献
967.
Amir Reza Jassbi Pahup Singh Vivek Krishna Pradeep K. Gupta Satoshi Tahara 《Chemistry of Natural Compounds》2004,40(3):250-253
The NMR spectral data including high resolution 1H, 13C and 2D NMR for butrin, 3,4,7-trihydroxyflavanone 3,7-di-O--D-glucopyranoside, isolated from flowers of Butea monosperma, are reported here for the first time. Butrin was hydrolyzed using b-glucosidase to butin in high yield. They were subjected to free radical scavenging test using 2,2-diphenyl-1-picrylhydrazyl (DPPH) spectrophotometric assay. At a dose of 4 × 10-8 mol of tested compounds, the percentage of reduced DPPH for butin was 14.5% while no reduction was observed for butrin (0%). 相似文献
968.
Mohammad Hossein Habibi Morteza Montazerozohori Kazem Barati Ross W. Harrington William Clegg 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(12):m592-m594
The 1:1 adduct of N,N′‐bis(2‐chlorobenzylidene)ethylenediamine (cb2en) with copper(I) chloride proves to be an ionic compound with CuI‐centred cations and anions, [Cu(C16H14Cl2N2)2][CuCl2]·CH3CN. In the cation, the CuI atom has a flattened tetrahedral coordination geometry, with a small bite angle for the chelating ligands, which form a double‐helical arrangement around the metal centre. The anion is almost linear, as expected. The packing of the cations involves intermolecular π–π interactions, which lead to columns of translationally related cations along the shortest unit‐cell axis, with anions and solvent molecules in channels between them. 相似文献
969.
Fungal laccase (Lc) from the basidiomycete Trametes hirsuta was immobilized on top of a carbon ceramic electrode using physical absorption. Direct, unmediated heterogeneous electron transfer between Lc and the carbon ceramic electrode (CCE) under aerobic conditions was shown. The bioelectrocatalytic reduction of oxygen on Lc‐CCE started at about 430 mV vs. Ag|AgCl|KClsat at pH 3.5 and moved with about 57 mV in the cathodic region per pH unit. The Lc‐modified CCE was then used as a biosensing detection element in a single line flow injection system for the amperometric determination of a variety of phenolic substrates of the enzyme. The experimental conditions were studied and optimized for catechol serving as a model compound. Statistical aspects were applied and the sensor characteristics and Michaelis‐Menten constants of the investigated phenolic compounds were calculated and compared with those obtained for solid graphite electrodes modified with Trametes hirsuta laccase. The results showed that the CCE based biosensor in comparison with the solid graphite based biosensor offers a lower detection limit, a wider linear dynamic range, and excellent operational stability with no sensor passivation, indicating that the sol–gel lattice improves the electrochemical behavior of the biosensor. 相似文献
970.
Carbocyclic amines are synthesized efficiently in up to 93% ee by asymmetric ring-closing metathesis (ARCM) with 2-5 mol % chiral Mo complexes. An example is provided where the catalyst is prepared in situ (catalyst isolation not needed) to afford secondary amines that cannot be prepared by alternative methods. [reaction: see text] 相似文献