排序方式: 共有144条查询结果,搜索用时 31 毫秒
91.
Françoise Fenouillot Françoise Méchin Fernande Boisson Pierre Alcouffe Tomasz Pokropski Tasnim Kallel Mahdi Mnif 《European Polymer Journal》2012,48(2):284-295
The reaction in bulk at high temperature of α,ω-aminopropyl oligodimethylsiloxane and thermoplastic polyurethane (TPU) allowed observing interesting behavior. Mixing at 200 °C first involved dissociation of urethanes and splitting of polyurethane chains followed by reaction of the released isocyanates with amino end-groups of the oligosiloxane. At this stage, a copolymer was formed which morphology consisted of a very fine dispersion of the polysiloxane domains at the nanoscale (20 nm) with a narrow size dispersity. The polymer blend was perfectly transparent. Increasing the reaction time resulted in a significant coarsening of the morphology and a consequent loss of transparency. The reason for such a morphology evolution has been elucidated. The progressive formation of alkyl–alkyl urea linkages at the expense of aryl–alkyl bonds obtained earlier in the process caused an increase in the average number of successive polydimethylsiloxane (PDMS) blocks that organized in larger domains. The average number of consecutive polysiloxane segments was found to evolve from ~1.5 in the first 10–15 min to a value of 3–5 at the end of the reactive process. 相似文献
92.
Dr. Colin C. Seaton Prof. Nicholas Blagden Dr. Tasnim Munshi Prof. Ian J. Scowen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(32):10663-10671
Four new ternary crystalline molecular complexes have been synthesised from a common 3,5‐dinitrobenzoic acid (3,5‐dnda) and 4,4′‐bipyridine (bipy) pairing with a series of amino‐substituted aromatic compounds (4‐aminobenzoic acid (4‐aba), 4‐(N,N‐dimethylamino)benzoic acid (4‐dmaba), 4‐aminosalicylic acid (4‐asa) and sulfanilamide (saa)). The ternary crystals were created through the application of complementary charge transfer and hydrogen‐bonding interactions. For these systems a dimer was created through a charge‐transfer interaction between two of the components, while hydrogen bonding between the third molecule and this dimer completed the construction of the ternary co‐crystal. All resulting structures display the same acid ??? pyridine interaction between 3,5‐dnba and bipy. However, changing the third component causes the proton of this bond to shift from neutral OH ??? N to a salt form, O? ??? HN+, as the nature of the group hydrogen bonding to the carboxylic acid was changed. This highlights the role of the crystal environment on the level of proton transfer and the utility of ternary systems for the study of this process. 相似文献
93.
Qaiser Mahmood Adeel Afzal Humaira M. Siddiqi Amir Habib 《Journal of Sol-Gel Science and Technology》2013,67(3):670-674
In this letter, we present a facile route to produce metastable tetragonal zirconia (ZrO2) nanoparticles via pH-controlled precipitation of dilute zirconyl nitrate dihydrate [ZrO(NO3)2·2H2O] solution in liquid NH3 under ambient conditions and calcination at 500 °C for 2 h. The phase pure tetragonal ZrO2 nanoparticles are obtained at pH 9. The effect of pH on metastable phase stabilization in precipitated ZrO2 nanoparticles is demonstrated with the help of XRD, SEM/EDX, and X-ray photoelectron spectroscopy techniques. The stability of tetragonal ZrO2 phase is attributed to the smaller crystallite size and greater oxygen deficiency in phase-pure tetragonal ZrO2. 相似文献
94.
Syeda Sara Hassan Yuping Liu Sirajuddin Amber Rehana Solangi Alan M. Bond Jie Zhang 《Analytica chimica acta》2013
Phosphomolybdate, H3PMo12O40, (PMo12)-doped-poly(3,4-ethylenedioxythiophene) (PEDOT) coated gold nanoparticles have been synthesized in aqueous solution by reduction of AuCl4− using hydroxymethyl EDOT as a reducing agent in the presence of polystyrene sulfonate and PMo12. The resulting PMo12-doped-PEDOT stabilized Au nanoparticles are water soluble and have been characterized by UV–visible spectroscopy, scanning electron microscopy and electrochemistry. Glassy carbon electrodes modified with these Au nanoparticles show excellent stability and catalytic activity towards the reduction of bromate in an aqueous electrolyte solution containing 10 mM H2SO4 and 0.1 M Na2SO4. 相似文献
95.
Humaira Farooqui Amena Mahmood Deeba S. Jairajpuri Faizan Ahmad Shakir Ali 《Journal of Thermal Analysis and Calorimetry》2011,104(1):339-342
Transition temperature and thermal stability of proteins were studied in the presence and absence of boron. The observed midpoint
of thermal denaturation (T
m) of cytochrome c (Cyt c) at pH 9.2 was 68.8 °C, which in the presence of boron increased to 71.0 °C. For metmyoglobin, T
m increased from 79.7 °C in the absence of boron to 83.5 °C in the presence of boron. Boron caused an increase of 10% in the
reversibility of thermal denaturation of cytochrome c when compared with control. Activity measurements of the heat treated proteins and T
m suggest an increased thermal stability toward inactivation and denaturation of heme proteins in the presence of boron. 相似文献
96.
Muhammad Ali Hashmi Umar Farooq Syeda Sidra Bibi Sadia Naz Hong-Guang Xu Basim H. Asghar Yahia Nasser Mabkhot Abdulrahman Alsayari Abdullatif Bin Muhsinah Ayesha Khan 《中国化学会会志》2020,67(4):558-566
A comprehensive theoretical model was designed for two new flavanols that have been reported from Glycosmis pentaphylla, differing in the placement of α-pyrone ring. The density functional theory (DFT) approach was utilized for computing different properties of these compounds to validate the experimental findings and stereochemical assignments. Electronic properties, geometric parameters, frontier molecular orbitals (FMOs), molecular electrostatic potential (MESP), and natural bond orbital analysis were performed for the first time at the PBE0-D3BJ/def2-TZVP level of theory for the compounds under study. The simulated vibrational frequencies for compounds 1 and 2 were computed and compared with the experimental results. nuclear magnetic resonance (NMR) (1H and 13C) chemical shift values were computed at the PBE0-D3BJ/def2-TZVP/SMDDMSO level of theory and showed a very good agreement with the experimental results for both the compounds. The electronic circular dichroism (ECD) and ultraviolet–visible (UV) spectra for both the compounds were obtained using time-dependent DFT in methanol, whose results exhibited excellent correlation with experimental data. The intermolecular interaction effect on geometric parameters, vibrational frequencies, and electronic properties were studied for the first time. 相似文献
97.
Sandeep Kumar Marvadi Devendra Nagineni Syeda Safoora Vagolu Siva Krishna Dharmarajan Sriram Srinivas Kantevari 《Monatshefte für Chemie / Chemical Monthly》2020,151(3):405-415
A series of novel 5-chloro-2-(thiophen-2-yl)-7,8-dihydroquinoline-6-carboxamides was designed, synthesized, and evaluated for antitubercular activity. The required 5-chloro-2-(thiophen-2-yl)-7,8-dihydroquinoline-6-carboxylic acid intermediate was prepared by oxidizing the respective aldehyde with sodium chlorite and 30% H2O2. Further, the acid was coupled with various aryl, alkyl, and heterocyclic amines using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and hydroxybenzotriazole to give the desired 5-chloro-2-(thiophen-2-yl)-7,8-dihydroquinoline-6-carboxamides in excellent yields. All the new compounds were characterized by their NMR and mass spectral analysis. Screening of all new compounds for in vitro antimycobacterial activity against M. tuberculosis H37Rv (Mtb) resulted in five analogs with MIC 3.12 µg/cm3 as promising antitubercular agents with lower cytotoxicity profiles. 相似文献
98.
Syed Tasqeeruddin Yahya I. Asiri Syeda Shaheen 《Journal of heterocyclic chemistry》2021,58(2):630-635
An efficient, a hitherto unreported, sustainable, and environmentally friendly microwave-assisted synthesis of 2,3-disubstituted quinolines by reductive cyclization of 2-nitrobenzaldehydes and various active methylene compounds via tandem Knoevenagel condensation promoted by an efficient eco-friendly, chemoselective reducing catalyst ammonium chloride (NH4Cl) and zinc powder was developed. This present methodology is a mild, green, efficient, and environmentally benign process as it eliminates the harsh reaction conditions, non-volatile solvents, relatively expensive reagents, high catalyst loading, and also provides a number of other benefits like fast synthesis, simple reaction set-up, and good to the excellent yield of the products. 相似文献
99.
New route to ABCD-porphyrins via bilanes 总被引:1,自引:0,他引:1
Dogutan DK Zaidi SH Thamyongkit P Lindsey JS 《The Journal of organic chemistry》2007,72(20):7701-7714
A new strategy for preparing porphyrins that bear up to four different meso-substituents (ABCD-porphyrins) relies on two key reactions. One key reaction entails a directed synthesis of a 1-protected 19-acylbilane by acid-catalyzed condensation at high concentration (0.5 M) of a 1-acyldipyrromethane and a 9-protected dipyrromethane-1-carbinol (derived from a 9-protected 1-acyldipyrromethane). Three protecting groups (X) were examined, including thiocyanato, ethylthio, and bromo, of which bromo proved most effective. The bilanes were obtained in 72-80% yield, fully characterized, and examined by 15N NMR spectroscopy. The second key reaction entails a one-flask transformation of the 1-protected 19-acylbilane under basic, metal-templating conditions to give the corresponding metalloporphyrin. The reaction parameters investigated for cyclization of the bilane include solvent, metal salt, base, concentration, temperature, atmosphere, and time. The best conditions entailed the 1-bromo-19-acylbilane at 100 mM in toluene containing DBU (10 mol equiv) and MgBr2 (3 mol equiv) at 115 degrees C exposed to air for 2 h, which afforded the magnesium porphyrin in 65% yield. The magnesium porphyrin is readily demetalated to give the free base porphyrin. A stepwise procedure (which entailed treatment of the 1-(ethylthio)-19-acylbilane to oxidation, metal complexation, desulfurization, carbonyl reduction, and acid-catalyzed condensation) was developed but was much less efficient than the one-flask process. The new route to ABCD-porphyrins retains the desirable features of the existing "2 + 2" (dipyrromethane + dipyrromethane-1,9-dicarbinol) method, such as absence of scrambling, yet has significant advantages. The advantages include the absence of acid in the porphyrin-forming step, the use of a metal template for cyclization, the ability to carry out the reaction at high concentration, the lack of a quinone oxidant, avoidance of use of dichloromethane, and the increased yield of macrocycle formation to give the target ABCD-metalloporphyrin. 相似文献
100.
Blends of ethylene‐glycidyl methacrylate copolymer (PE‐GMA) and polyamide 6 (PA6) were prepared in a corotating twin screw extruder. Two processing temperatures were used in order to disperse PA6 in two forms: at high temperature in the molten state in molted PE‐GMA Matrix (emulsion type mixture) and at lower temperature as fillers in molted PEGMA matrix (suspension type mixture). Processed blends were analyzed by scanning electron microscopy and dynamic mechanical experiments to probe the reactivity in the extruder and the compatibilization phenomena. The dependence of the morphology and the rheological properties of PE‐GMA/PA6 blends on blend composition and screw rotational speed was also investigated and is discussed in the paper. The results show that dispersion of the two polymers in the molten state leads to a higher level of interfacial reaction. They also show that whatever the screw rotational speed and the temperature of extrusion are, the rate of interfacial reaction in PE‐GMA/PA6 blends is higher for 50/50 PE‐GMA/PA blends than for 70/30 PE‐GMA/PA blends. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献