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121.
Niranjan Karak Buddhadeb Roy Brigitte Voit 《Journal of polymer science. Part A, Polymer chemistry》2010,48(18):3994-4004
A series of s‐triazine‐based hyperbranched polyethers (HBPE) have been synthesized to obtain thermostability but flexible polymers by an interfacial polycondensation of different diols as A2 and cyanuric chloride as B3 monomers using A2 + B3 approach in the presence of a phase transfer catalyst. The polymerization reaction parameters are optimized, and the results indicate that the optimum conditions for the interfacial polycondensation are a 2:3 mole ratio of cyanuric chloride to diol using butanediol, benzyldimethylhexadecyl ammonium chloride as the catalyst, dichloromethane as the organic solvent, and a three‐step procedure with keeping the reaction mixture at different low temperatures for 2h/2h/5h. Other techniques such as high‐temperature solution, one‐step polycondensation, and transesterification were also carried out to synthesize the HBPE but proved to be not suitable due to large number of side reactions. The synthesized polymers were characterized by FTIR, 1H NMR, and 13C NMR spectroscopy, hydroxyl number determination, solution viscosity measurements, and GPC analysis. The thermal behavior of the hyperbranched polymer was investigated by thermogravimetric analysis and differential scanning calorimetry. All the results were compared with those from an analogous linear polyether, obtained from 2‐methoxy‐4,6‐dichloro‐s‐triazine and butanediol by using the same polymerization technique. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3994–4004, 2010 相似文献
122.
<正>A brominated hyperbranched polyether has been synthesized from cyanuric chloride and sodium salt of tetrabromobisphenol-A by an A_2+B_3 approach.The synthesized polyether was characterized by ~1H-NMR,~(13)C-NMR,UV, FTIR spectroscopy and X-ray diffraction studies,measurements of solution viscosity,molecular weight and solubility and elemental and thermogravimetric analyses.The flame retardancy of the synthesized polyether and its blends with commercially available plasticized poly(vinyl chloride)(PVC) and low density polyethylene(LDPE) was investigated by measurements of limiting oxygen index(LOI) value and thermogravimetric analysis.The properties are compared with a non-halogenated similar type of bisphenol-A based aromatic polyether after blending at different dose levels with the same base polymers.The LOI values of these blends indicated that these hyperbranched polyethers acted as flame retardant additives,and antimony trioxide had prominent synergistic effect with the bromo hyperbranched polyether for the above base polymers,and an increment of 4 to 6 units in LOI values was observed. 相似文献
123.
Venugopal N McCurdy B Al Mehairi S Alamri A Sandhu GS Sivalingam S Drachenberg D Ryner L 《Magnetic resonance imaging》2012,30(2):195-204
Visualization of short echo time (TE) metabolites in prostate magnetic resonance spectroscopic imaging is difficult due to lipid contamination and pulse timing constraints. In this work, we present a modified pulse sequence to permit short echo time (TE=40ms) acquisitions with reduced lipid contamination for the detection of short TE metabolites. The modified pulse sequence employs the conformal voxel MRS (CV-MRS) technique, which automatically optimizes the placement of spatial saturation planes to adapt the excitation volume to the shape of the prostate, thus reducing lipid contamination in prostate magnetic resonance spectroscopic imaging (MRSI). Metabolites were measured and assessed using a modified version of LCModel for analysis of in vivo prostate spectra. We demonstrate the feasibility of acquiring high quality spectra at short TEs, and show the measurement of short TE metabolites, myo-inositol, scyllo-inositol, taurine and glutamine/glutamate for both single and multi-voxel acquisitions. In single voxels experiments, the reduction in TE resulted in 57% improvement in the signal-to-noise ratio (SNR). Additional 3D MRSI experiments comparing short (TE=40 ms), and long (TE=130 ms) TE acquisitions revealed a 35% improvement in the number of adequately fitted metabolite peaks (775 voxels over all subjects). This resulted in a 42 ± 24% relative improvement in the number of voxels with detectable citrate that were well-fitted using LCmodel. In this study, we demonstrate that high quality prostate spectra can be obtained by reducing the TE to 40 ms to detect short T2 metabolites, while maintaining positive signal intensity of the spin-coupled citrate multiplet and managing lipid suppression. 相似文献
124.
Eco-friendly heterogeneous solid acids as novel and recyclable catalysts in ionic medium for tetrahydropyranols 总被引:1,自引:0,他引:1
J. S. Yadav B. V. S. Reddy M. Sridhar Reddy N. Niranjan 《Journal of molecular catalysis. A, Chemical》2004,210(1-2):99-103
A variety of aldehydes and homoallylic alcohols undergo smoothly Prins-cyclization on the surface of solid acids such as H-ZSM-5 zeolite or Amberlyst-15® ion-exchange resin in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid to afford the corresponding tetrahydropyranols in high yields with cis-diastereoselectivity. The recovered ionic liquid containing solid acid was recycled in subsequent runs without loss of activity. 相似文献
125.
Goud TV Srinivasulu M Reddy VL Reddy AV Rao TP Kumar DS Murty US Venkateswarlu Y 《Chemical & pharmaceutical bulletin》2003,51(8):990-993
Two new bromotyrosine-derived metabolites (1, 2) have been isolated along with the known compounds 3,5-dibromo-4-methoxyphenylacetonitrile, 3-bromo-4-methoxyphenylacetonitrile, 3-bromo-4-hydroxyphenylacetonitrile, 1-hydroxyuracil, 1-methoxyhemibastadin 2, purpuramine H and a steroid 5alpha,8alpha-epidioxycholest-6-en-3beta-ol from the sponge Psammaplysilla purpurea. Compounds 1 and 2 were characterized by interpretation of their spectral data. The antibacterial activity of these compounds is summarized. 相似文献
126.
Two novel triterpenoid saponins, mimusopin ( 3-O-β-D-glucopyranosyl-2β, 3β, 6β, 23-tetrahydroxyolean-12-en-28-oic acid 28-O--L-rhamnopyranosyl-(1→3)-β-D-xylopyranosyl-(1→4)[a-L-rhamnopyranosyl-(1→ 3)]--L-rhamnopyranosyl-(1→2)--L-arabinopyranoside)(1) and mimusopsin 3-O-[β-D-glucopyranosyl-(1→3)β-D-gluco-pyranosyl]-2β, 3β, 6β, 23-tetrahydroxyolean-12-en-28-oic acid 28-O--L-rhamnopyranosyl-(1→3)-β-D-xylopyranosyl-(1→4)--L-rhamnopyranosyl-(1→2)--L-arabinopyranoside (2) were isolated from the seeds of Mimusops elengi. Their structures were elucidated by a combination of 2D-NMR (COSY, HOHAHA, HETCOR, HMBC and NOESY), FAB-MS/MS and strategic chemical degradation. In addition, molecular mechanics and dynamics studies showed that the lack of a 13C glycosylation shift at the C-4 of the inner rhamnose in 1 could be correlated with distortion in the corresponding torsion angles. 相似文献
127.
Alain Connes Matilde Marcolli Niranjan Ramachandran 《Selecta Mathematica, New Series》2005,11(3-4):325-347
We construct a quantum statistical mechanical system which generalizes the Bost–Connes system to imaginary quadratic fields
K of arbitrary class number and fully incorporates the explicit class field theory for such fields. This system admits the
Dedekind zeta function as partition function and the idèle class group as group of symmetries. The extremal KMS states at
zero temperature intertwine this symmetry with the Galois action on the values of the states on the arithmetic subalgebra.
The geometric notion underlying the construction is that of commensurability of K-lattices. 相似文献
128.
Niranjan Kumar Shrestha Toshiaki Kamachi Ichiro Okura 《Reaction Kinetics and Catalysis Letters》2000,70(2):287-292
Hydrogen evolution system from L-lactate and L-malate consisting of lactate dehydrogenase or malate dehydrogenase and hydrogenase from cell free extracts of Alcaligenes eutrophus H16 was established. When the solution containing L-lactate, lactate dehydrogenase, NAD and hydrogenase was incubated at 30°C hydrogen evolution was observed. Similarly, the hydrogen evolution was also observed from the L-malate incubated at 30°C. 相似文献
129.
We investigated the feasibility of using a silica microsphere sensor for detection of small molecules. Using the silica molecules (60 Da) at the sphere's surface as a model system, we measured the spectral shifts in the whispering-gallery modes (WGMs) when the sphere size was decreased by a hydrofluoric acid (HF) solution. The results demonstrate that our sensor is capable of detecting a 4 pm (or 0.01 layer of silica) decrease in sphere radius, corresponding to a change of 0.4 fmol silica molecule. These results suggest that small molecules can be detected in trace quantities at the surface of an optical microsphere sensor. 相似文献
130.
Niranjan Deo R. Karl Dieter Bharat Lagu William T. Pennington 《Journal of chemical crystallography》1997,27(12):689-694
The structures of two diastereomers ((1R,2R) and (1R,2S)) of the title compound have been determined. The molecular conformation of the (1R,2R) isomer is heavily influenced by strong intramolecular hydrogen bonding between the secondary and tertiary amine groups (N(1)…N(2) 2.629(8) Å; N(4)…N(5) 2.628(8) Å). In the (1R,2S) isomer no intramolecular interaction is observed, but somewhat weaker intermolecular hydrogen bonding does occur between the secondary amine and the carbonyl group of a neighboring molecule (N(1)…O(1) 2.960(6) Å) related by a 21 screw operation along thea-axis (x1/40). No close intermolecular contacts are observed for the (1R,2R) isomer. Crystal data for (1R,2R); monoclinic,P21 (No. 4),a=18.588(5),b=16.743(4),c=6.062(1) Å, β=97.26(2)o,V=1871.5(8) A3, Z=4,D cale=1.16 g/cm3. Crystal data for (1R,2S): orthorhombic,P212121 (No. 19),a=8.008(2),b=9.985(3),c=23.458(5)Å,V=1875.8(6) Å3, Z=4,D cale=1.15 g/cm3. 相似文献