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排序方式: 共有2100条查询结果,搜索用时 31 毫秒
911.
Biswanath Das Joydeep Banerjee Anjoy Majhi Gurram Mahender 《Tetrahedron letters》2004,45(50):9225-9227
A convenient and facile stereoselective synthesis of (E)- and (Z)-trisubstituted alkenes has been achieved by treatment of unactivated Baylis-Hillman adducts with NaBH4 in the presence of CuCl2·2H2O at room temperature for 15 min. 相似文献
912.
Arun Kashinath Salunke Mukesh Kumar Madhra Mamta Sharma Susanta Banerjee 《Journal of polymer science. Part A, Polymer chemistry》2002,40(1):55-69
A series of poly(arylene ether)s were successfully prepared by aromatic, nucleophilic substitution reactions with various perfluoroalkyl‐activated bisfluoromonomers with 4,4′‐bishydroxybiphenyl and 4,4′‐bishydroxyterphenyl. 4,4′‐Bishydroxyterphenyl was synthesized through the Grignard coupling reaction of magnesium salt of 4‐bromoanisole with dibromobenzene followed by demethylation with pyridine–hydrochloride. The products obtained by the displacement of fluorine atoms exhibited good inherent viscosity, up to 0.77 dL/g, and number‐average molecular weights up to 69,300. These poly(arylene ether)s showed very good thermal stability, up to 548 °C for 5% weight loss according to thermogravimetric analysis under synthetic air, and high glass‐transition temperatures, up to 259 °C according to differential scanning calorimetry, depending on the exact repeat unit structure. These polymers were soluble in a wide range of organic solvents, such as N‐methylpyrrolidone, dimethylformamide, tetrahydrofuran, toluene, and CHCl3, and were insoluble in dimethyl sulfoxide and acetone. Thin films of these poly(arylene ether)s showed good transparency and exhibited tensile strengths up to 132 MPa, moduli up to 3.34 GPa, and elongations at break up to 84%, depending on their exact repeating unit structures. These values are comparable to those of high‐performance thermoplastic materials such as poly(ether ether ketone) (PEEK) and Ultem poly(ether imide) (PEI). These poly(arylene ether)s exhibited low dielectric constants. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 55–69, 2002 相似文献
913.
Banerjee S Bhattacharya S Basu S 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(6):1039-1044
The extraction behaviour of Pr(III) from aqueous nitric acid medium employing benzoylacetone has been studied in presence of two crown ethers, viz., 15-crown-5 and benzo-15-crown-5 in chloroform medium using UV-vis absorption spectroscopy. The binary equilibrium constant (logk(ex)) for the complex [Pr(benzoylacetonate)(NO3(-))2(H(2)O)] in organic phase was found to be 1.170. The overall equilibrium constants (logK) for the ternary species [Pr(benzoylacetonate)(crown ether)(NO3(-))(2)] were estimated to be 4.01 and 4.41 for 15-crown-5 and benzo-15-crown-5, respectively. The trend in the equilibrium constant values were very much in accordance with the nature of substitution of the donor moiety. The extraction of Pr(III) by the benzoylacetone-crown ether combination was maximum at pH 3.0 and extraction decreases with increase in pH. It has been found that the extent of extraction of Pr(III) in organic phase as the binary as well as ternary complex [Pr(benzoylacetonate)(NO3(-))(2)(H(2)O)] and [Pr(benzoylacetonate)(crown ether)(NO3(-))(2)] increases with increase in concentration of the ligand. Similar trend is observed in the extraction by only donors. Enthalpies and entropies of formation for the ternary extraction process have been estimated. In addition, the effect of NaNO(3) as foreign salt was also studied and it was observed that with increase in ionic strength, percentage extraction increases. 相似文献
914.
Banerjee AL Swanson M Roy BC Jia X Haldar MK Mallik S Srivastava DK 《Journal of the American Chemical Society》2004,126(35):10875-10883
We elaborate on a novel strategy for enhancing the binding affinity of an active-site directed inhibitor by attaching a tether group, designed to interact with the surface-exposed histidine residue(s) of enzymes. In this approach, we have utilized the recombinant form of human carbonic anhydrase-II (hCA-II) as the enzyme source and benzenesulfonamide and its derivatives as inhibitors. The steady-state kinetic and the ligand binding data revealed that the attachment of iminodiacetate (IDA)-Cu(2+) to benzenesulfonamide (via a triethylene glycol spacer) enhanced its binding affinity for hCA-II by about 40-fold. No energetic contribution of either IDA or triethylene glycol spacer was found (at least in the ground state of the enzyme-inhibitor complex) when Cu(2+) was stripped off from the tether group-conjugated sulfonamide derivative. Arguments are presented that the overall strategy of enhancing the binding affinities of known inhibitors by attaching the IDA-Cu(2+) groups to interact with the surface-exposed histidine residues will find a general application in designing the isozyme-specific inhibitors as potential drugs. 相似文献
915.
Thorium and zirconium are determined in the presence of rare earths, alkaline earths and magnesium, when precipitated from weakly acid solution with 5:6-benzoquinaldinic acid. Thorium is completely precipitated at pH 3.0 as Th(C14H8O2N)4, but though zirconium is precipitated at the lower pH of 1.8, its composition is not stoichiometric and hence is ignited to the oxide before weighing. Co-precipitation of magnesium and alkaline earths is prevented by the addition of ammonium chloride. 相似文献
916.
[reaction: see text] A reagent combination of beta-SnO and catalytic [Rh(COD)Cl](2) in THF-H(2)O promotes the reaction of propargyl bromides and aldehydes and directs the regioselectivity toward the formation of either allenic alcohols or homopropargylic alcohols. This highly regioselective either/or transformation proceeds via a transmetalation from rhodium to tin, in which metallotropic rearrangement between a propargylmetal and allenylmetal is arrested. 相似文献
917.
Roy BC Banerjee AL Swanson M Jia XG Haldar MK Mallik S Srivastava DK 《Journal of the American Chemical Society》2004,126(41):13206-13207
The enzyme inhibitors are usually designed by taking into consideration the overall dimensions of the enzyme's active site pockets. This conventional approach often fails to produce desirable affinities of inhibitors for their cognate enzymes. To circumvent such constraints, we contemplated enhancing the binding affinities of inhibitors by attaching tether groups, which would interact with the surface exposed amino acid residues. This strategy has been tested for the inhibition of human carbonic anhydrase II. Benzenesulfonamide serves as a weak inhibitor for the enzyme, but when it is conjugated to iminodiacetate-Cu2+ (which interacts with the surface-exposed His residues) via a spacer group, its binding affinity is enhanced by about 2 orders of magnitude. This "two-prong" approach is expected to serve as a general strategy for converting weak inhibitors of enzymes into tight-binding inhibitors. 相似文献
918.
Chen YF Banerjee IA Yu L Djalali R Matsui H 《Langmuir : the ACS journal of surfaces and colloids》2004,20(20):8409-8413
Ferrocene nanotubes were fabricated by binding carboxylic acid-derivatized ferrocenes onto template peptide nanotubes via hydrogen bonding. When these ferrocene-functionalized nanotubes were incubated with beta-cyclodextrin (beta-CD) self-assembled monolayers (SAMs) coated on patterned Au substrates in solution, the ferrocene nanotubes recognized and attached onto the beta-CD SAMs via host-guest molecular recognition. The ferrocene nanotubes were also observed to recognize the certain cavity size of CD. The attachment/detachment of nanotubes on the beta-CD SAMs was controlled electrochemically by tuning the redox states of ferrocene nanotubes. This electric field-responsive building block may be applied to build nanometer-sized switching components in electronics and sensors. 相似文献
919.
A thermal investigation of M(N2H5)2(SO4)2, where M = Mn(II) or Co(II), has been carried out. On heating, the complexes become MSO4 via an intermediate compound, M(N2H4)0·5(HSO4)(SO4)0·5. The intermediate compound has been isolated and characterised by elemental analyses, IR spectra, diffuse reflectance spectra, magnetic and conductance data. The intermediate compound seems to possess pseudo-tetrahedral coordination where one SO4 group is tetradentate and bonded with four different metal ions which are surrounded by HSO4 groups and hydrazines bridging two metal ions. The X-ray powder diffraction pattern of the intermediate derived from the cobalt(II) complex has been obtained and the d-values are reported. Activation energies (E*) and enthalpy changes (ΔH) for each decomposition step have also been calculated. The probable mechanisms of decompositions are discussed. 相似文献
920.
A. Banerjee S. B. Duttachoudhury Abhik Kumar Sanyal 《General Relativity and Gravitation》1986,18(5):461-477
A spatially homogeneous and locally rotationally symmetric Bianchi type-II cosmological model under the influence of both shear and bulk viscosity has been studied. Exact solutions are obtained with a barotropic equation of state (p=) and considering the linear relationships between, 2, and 2, which represent the fluid density, the expansion, and the shear scalars, respectively. Special cases with vanishing bulk viscosity coefficients and with the perfect fluid in the absence of viscosity have also been studied. The formal appearance of the solutions is the same for both the viscous as well as the perfect fluids. The difference is only in choosing a constant parameter which appears in the solutions. In the cases of either a fluid with bulk viscosity alone or a perfect fluid, the barotropic equation of state is no longer an additional assumption to be imposed; rather it follows directly from the field equations. 相似文献