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排序方式: 共有372条查询结果,搜索用时 15 毫秒
91.
B. Harihara Venkatraman Piyali D. Chaudhuri Serkan Yurt D. Venkataraman 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(12):983-985
In this paper, we show a common strategy to synthesize tetraalkenylmethanes, a cross-linker series for building three-dimensional hydrocarbon networks. To demonstrate the feasibility of this method, we have synthesized tetrapentenylmethane. Attempts to synthesize this cross-linker from pentaerythrityl tetrabromide using substitution reactions resulted in the formation of a spiro compound due to intramolecular cyclization. We also show that the difficulty in reactions at the neopentyl carbon site is due to the neopentyl carbanion stability, not the sterics. 相似文献
92.
We have measured electron transport in small bundles of identical conducting molybdenum selenide nanowires where the number of weakly interacting one-dimensional chains ranges from 1 to 300. The linear conductance and current in these nanowires exhibit a power-law dependence on temperature and bias voltage, respectively. The exponents governing these power laws decrease as the number of conducting channels increase. These exponents can be related to the electron-electron interaction parameter for transport in multichannel 1D systems with a few defects. 相似文献
93.
A series of bridged triarylamines, which constitute a new class of heterohelicenes, have been synthesized using a simple three-step procedure. These compounds are shown to be highly luminescent chromophores and are capable of being oxidized. The solid-state structures of these helicenes show a tendency for pi-stacking interactions into an overall zigzag motif. 相似文献
94.
Pendergrass JA Srinivasan V Kumar KS Jackson WE Seed TM 《Journal of AOAC International》2002,85(3):551-554
A liquid chromatographic method using electrochemical detection is presented for measuring the thiol WR-1065 12-(3-aminopropylamino) ethanethiol] and its symmetrical disulfide WR-33278 [NH2(CH2)3NHCH2CH2S]2. WR- 1065 is the active, radioprotective drug derived from the phosphorothioate pro-drug WR-2721 (amifostine). External standard curves for both compounds were linear over the range of 40-200 pmol injected (r2 = 0.999 and 0.996 for the thiol and disulfide, respectively). The detection and quantitation limits for WR-1065 were 9 and 18 pmol, respectively, whereas the corresponding values for WR-33278 were 30 and 59 pmol, respectively. Within- and between-day determinations of measurement Vision and accuracy for both compounds validated the suitability of this assay method. 相似文献
95.
Venkataraman Narasimhan Robert Y. M. Huang Charles M. Burns 《Journal of polymer science. Part A, Polymer chemistry》1984,22(12):3895-3904
The average molecular weights and the molecular weight distributions of polystyrene (PS) in the conjugate incompatible phases of the ternary system of PS and polybutadiene with toluene as solvent were studied at 23°C. Gelpermeation chromatography, with ultraviolet and differential refractive index detectors, was used for analyzing the compositions of the conjugate phases and for obtaining the molecular weight averages of PS in the phases. Both narrow and broad molecular weight distribution (MWD) polymer samples were used. The effect of broad MWD polymers is seen as one of narrowing the shape of the binodal, thus effectively increasing the compatible region. The molecular weight averages of PS in the two conjugate phases do not vary significantly in the case of the narrow MWD PS sample while for broad MWD samples the average molecular weight of PS is found to be higher in the PS-rich phase than in the polybutadiene-rich phase for tie lines closer to the plait point indicating a partitioning or redistribution of the molecular weight species of PS between the incompatible phases. 相似文献
96.
The substitution reactions by bulky tricyclohexylphosphine (PCy3) ligands on W6S8L6 (L = 4-tert-butylpyridine or n-butylamine) clusters were investigated to prepare clusters with mixed axial ligands for low-dimensional cluster linking. When 4-6 equiv of PCy3 are used to react with W6S8(4-tert-butylpyridine)6 (4) in THF, cis-W6S8(PCy3)4(4-tert-butylpyridine)2 (1) is preferentially formed. But when starting with W6S8(n-butylamine)6 (2), only W6S8(PCy3)6 (3) is produced with 6 equiv of PCy3. Other conditions with fewer equivalents of PCy3 led to mixtures of partially substituted complexes in the W6S8L6-n(PCy3)n (0 < or = n < or = 6, L = 4-tert-butylpyridine or n-butylamine) series. A significantly distorted structure for 1 helps to explain its preferential formation. 1H NMR spectra were collected for clusters 1 and 2 and 31P NMR spectra for 1 and W6S8(4-tert-butylpyridine)6-n(PCy3)n complexes. P-P coupling through P-W-W-P is reported for the first time in octahedral metal clusters and shown to be very useful in identifying nearly all the W6S8L6-n(PR3)n complexes and their stereoisomers in the mixtures even before individual species are isolated. 相似文献
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100.
Ranjan Das Balu Venkataraman Vinod R Bhagat Ajit S Ghangrekar Thomas Kuruvilla B K Chaturvedi G S Isola B M Marwaha P G Nair R S Parolia B K Sarkar 《Pramana》1986,27(5):661-677
A computer-controlled X-band time domain electron paramagnetic resonance (EPR) spectrometer, with a time resolution of the
order of 0.5μsec, has been constructed with many of the crucial microwave components designed and fabricated by the Microwave Engineering
Group of TIFR. The spectrometer operates either in a microwave power pulsed mode for determination of spin-lattice relaxation
times by the saturation recovery technique or in the kinetic mode for determination of the time dependence of EPR signal after
laser excitation. It has an automatic frequency control, an automatic phase control and, most importantly, a field-frequency
lock which ensures good stability of the EPR line positions enabling signal averaging for extended periods. The constructional
details of the spectrometer and its performance in both the modes are described here by reporting results on certain typical
systems. 相似文献