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排序方式: 共有465条查询结果,搜索用时 46 毫秒
111.
A two-step protocol based on tandem Wessely oxidation/intramolecular Diels-Alder reaction to provide general access to the 3-prenyl-4-oxa-tricyclo[4.3.1.03,7]dec-8-en-2-one core present in the caged Garcinia xanthonoids is demonstrated. These readily accessible tricyclic scaffolds also provide ready entry into a variety of substituted γ-lactones through a photochemical 1,3-acyl shift and decarbonylation. 相似文献
112.
Rauth Goutam K. Maity Subrata Sinha Chittaranjan Mahapatra Ambikesh 《Transition Metal Chemistry》2003,28(5):518-524
Nucleophilic substitutions of Pd(N,N)Cl2[(N,N = 1-methyl-2-(arylazo)imidazole (RaaiMe), p-RC6H4N=NC3H2NN-1-Me; 2-(arylazo)pyridine (Raap), p-RC6H4N=NC5H4N; 2-(arylazo)pyrimidine (Raapm), p-RC6H4N=NC4H3N2 where R = H (a), Me (b), Cl (c)] with 8-quinolinol (HQ) have been examined by spectrophotometry at 298 K in MeCN solution. The product, Pd(Q)2, has also been confirmed by independent synthesis from Na2[PdCl4] and HQ in EtOH. The kinetics of the reaction have been studied under pseudo-first-order conditions and the analyses support a nucleophilic association path. A single phase reaction has been observed and follows the rate law, rate = a + k [Pd(N,N)Cl2] [HQ]2. Thus, the reaction is first order in [Pd(N,N)Cl2] and second order in [HQ]. External addition of Cl–(LiCl) suppresses the rate. The rate increases as follows: Pd(RaaiMe)Cl2 < Pd(Raap)Cl2 < Pd(Raapm)Cl2. 相似文献
113.
Rajesh Belgamwar Ayan Maity Tisita Das Sudip Chakraborty Chathakudath P. Vinod Vivek Polshettiwar 《Chemical science》2021,12(13):4825
An excessive amount of CO2 is the leading cause of climate change, and hence, its reduction in the Earth''s atmosphere is critical to stop further degradation of the environment. Although a large body of work has been carried out for post-combustion low-temperature CO2 capture, there are very few high temperature pre-combustion CO2 capture processes. Lithium silicate (Li4SiO4), one of the best known high-temperature CO2 capture sorbents, has two main challenges, moderate capture kinetics and poor sorbent stability. In this work, we have designed and synthesized lithium silicate nanosheets (LSNs), which showed high CO2 capture capacity (35.3 wt% CO2 capture using 60% CO2 feed gas, close to the theoretical value) with ultra-fast kinetics and enhanced stability at 650 °C. Due to the nanosheet morphology of the LSNs, they provided a good external surface for CO2 adsorption at every Li-site, yielding excellent CO2 capture capacity. The nanosheet morphology of the LSNs allowed efficient CO2 diffusion to ensure reaction with the entire sheet as well as providing extremely fast CO2 capture kinetics (0.22 g g−1 min−1). Conventional lithium silicates are known to rapidly lose their capture capacity and kinetics within the first few cycles due to thick carbonate shell formation and also due to the sintering of sorbent particles; however, the LSNs were stable for at least 200 cycles without any loss in their capture capacity or kinetics. The LSNs neither formed a carbonate shell nor underwent sintering, allowing efficient adsorption–desorption cycling. We also proposed a new mechanism, a mixed-phase model, to explain the unique CO2 capture behavior of the LSNs, using detailed (i) kinetics experiments for both adsorption and desorption steps, (ii) in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy measurements, (iii) depth-profiling X-ray photoelectron spectroscopy (XPS) of the sorbent after CO2 capture and (iv) theoretical investigation through systematic electronic structure calculations within the framework of density functional theory (DFT) formalism.Capturing CO2 before its release. Lithium silicate nanosheets showed high CO2 capture capacity (35.3 wt%) with ultra-fast kinetics (0.22 g g−1 min−1) and enhanced stability at 650 °C for at least 200 cycles, due to mixed-phase-model of CO2 capture. 相似文献
114.
Kevin C. Seavey Indrajit Ghosh Richard M. Davis Wolfgang G. Glasser 《Cellulose (London, England)》2001,8(2):149-159
Thermoplastic fiber composites were prepared using high modulus lyocell (regenerated cellulose) fibers for reinforcement and cellulose acetate butyrate (CAB) as matrix. Choices were made with regard to fiber options (fabric versus continuous tow) and method of matrix deposition (prepregging by powder coating, film stacking, or solution impregnating). The results suggest that solution-prepregged fiber tow consolidated at circa 200°C produced unidirectional consolidated panels with tensile strength, modulus, and strain at failure values of approximately 250MPa,>20GPa and 3–4%, respectively, at fiber volume contents of approximately 60%. Modulus and ultimate tensile strength increased with fiber content, and modulus followed rule-of-mixture behavior. Adequate surface wetting and matrix-fiber adhesion were found with solution-prepregged composites. The unexpectedly low strain at failure (2 to <4%) was attributed to brittle matrix failure, and failure surfaces revealed that the fibers, for the most part, remained intact after the matrix had failed. 相似文献
115.
Synthesis of magnetite (Fe3O4) nanoparticles under oxidizing environment by precipitation from aqueous media is not straightforward because Fe2+ gets oxidized to Fe3+ and thus the ratio of Fe3+:Fe2+=2:1 is not maintained during the precipitation. A molar ratio of Fe3+:Fe2+ smaller than 2:1 has been used by many to compensate for the oxidation of Fe2+ during the preparation. In this work, we have prepared iron oxide nanoparticles in air environment by the precipitation technique using initial molar ratios Fe3+:Fe2+?2:1. The phases of the resulting powders have been determined by several techniques. It is found that the particles consist mainly of maghemite with little or no magnetite phase. The particles have been suspended in non-aqueous and aqueous media by coating the particles with a single layer and a bilayer of oleic acid, respectively. The particle sizes, morphology and the magnetic properties of the particles and the ferrofulids prepared from these particles are reported. The average particle sizes obtained from the TEM micrographs are 14, 10 and 9 nm for the water, kerosene and dodecane-based ferrofluids, respectively, indicating a better dispersion in the non-aqueous media. The specific saturation magnetization (σs) value of the oleic-acid-coated particles (∼53 emu/g) is found to be lower than that for the uncoated particles (∼63 emu/g). Magnetization σs of the dodecane-based ferrofluid is found to be 10.1 emu/g for a volume fraction of particles ?=0.019. Zero coercivity and zero remanance on the magnetization curves indicate that the particles are superparamagnetic (SPM) in nature. 相似文献
116.
S.P. Das A. Datta M. Guchait M. Maity S. Mukherjee 《The European Physical Journal C - Particles and Fields》2008,54(4):645-653
The estimation of the backgrounds for gluino signals in focus point supersymmetry is extended by including the backgrounds
from the production of four third generation quarks in the analysis. We find that these backgrounds are negligible if one
uses the strong selection criteria proposed in the literature (including this analysis) for heavy gluino searches. Softer
selection criteria often recommended for lighter gluino searches yield backgrounds that are small but numerically significant.
We have also repeated the more conventional background calculations and compared our results with the other groups. We find
that the size of the total residual background estimated by different groups using different event generators and hard kinematical
cuts agree approximately. In view of the theoretical uncertainties in the leading order signal and background cross sections
mainly due to the choice of the QCD scale, the gluino mass reach at the LHC cannot be pinpointed. However, requiring a signal
with ≥3 tagged b-jets (instead of the standard choice of ≥2) it is shown that gluino masses close to 2 TeV can be probed at
the LHC for a range of reasonable choices of the QCD scale for an integrated luminosity of 300 fb-1.
PACS 11.30.Pb; 12.60.Jv; 14.80.Ly; 95.35.+d 相似文献
117.
K. Bhattacharjee S. Maity G. C. Das K. K. Chattopadhyay 《Colloid and polymer science》2013,291(11):2589-2597
Partial filling of mixed ferrite (Ni0.5Zn0.5Fe2O4; NZFO) nanoparticles into the amorphous carbon nanotubes (aCNTs) cavity is achieved by simple mixing of the aqueous dispersions of the two (aCNTs and NZFO) at room temperature. The process of incorporation of the nanoparticles into the aCNT cavity is solely mediated by the capillary action of the liquid. NZFO nanoparticles were homogeneously dispersed in the aqueous solution but after mixing they are sparsely distributed into the aCNT channel as a result of the capillary action. The encapsulation of the nanoparticles into the aCNTs amorphous shield was established by means of X-ray diffraction, transmission electron microscopy, Fourier transformed infrared spectroscopy, and Raman spectroscopic analysis. Such entrapment of the nanoparticles causes the composite nanotubes superparamagnetic in nature with blocking temperature (T B) at 15 K. However, compared to the powder NZFO nanoparticles, T B appears more sharply and at relatively lower temperature. Low filling density and the spatial confinement of the nanoparticles lessen the inter-particle interactions and the polydispersity within the NZFO nanoparticles which are manifested in their altered magnetic behavior. 相似文献
118.
Synthetic studies directed towards allo-cedrane based, tashironin sibling natural products, involving some deft functional group manipulations on a preformed tetracyclic scaffold, are delineated. 相似文献
119.
Nonlinear Dynamics - Middle East Respiratory Syndrome Coronavirus (MERS-CoV) can cause mild to severe acute respiratory illness with a high mortality rate. As of January 2020, more than 2500 cases... 相似文献
120.
Tushar Debnath Jayanta Dana Partha Maity Dr. Hyacintha Lobo Prof. Ganapati S. Shankarling Prof. Hirendra N. Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5704-5708
To understand the photophysical properties of intramolecular charge transfer (ICT) and twisted intramolecular charge transfer (TICT) states on a gold nanoparticle (Au NP) surface, we have designed and synthesized a new coumarin molecule (C3) that exists both as ICT and TICT states in its excited state in a polar environment. On a Au NP surface, an excited C3 molecule only exists as an ICT state owing to restricted molecular rotation of a diethylamino group; as a result, no conversion from the ICT to TICT state was observed. Selection of the preferential state of a molecule with dual emitting states can be helpful for selected biological applications. 相似文献