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991.
Shiva Agarwal M. Teresa A. Reis M. Rosinda C. Ismael Jorge M. R. Carvalho 《Chemical Papers》2015,69(5):679-689
The extraction of copper from sulphuric/sulphate solutions using a hollow fibre module as contactor was studied. The aldoxime Acorga M5640 was used as an extractant. The effects on the extraction rate of the flow-rates, the concentrations of copper and extractant, pH, and the presence of Na2SO4 in the feed phase were investigated. The overall mass transfer coefficient for copper extraction was calculated from the experimental data and was compared with the value evaluated by the resistance in the series model. The extraction process was found to be governed by the diffusion in the boundary aqueous layer and also by the chemical reaction. The kinetic data obtained were used to simulate the extraction of copper with the pseudo-emulsion-based hollow fibre with strip dispersion technique. The accordance between the results thus calculated and the experimental data was found to be satisfactory, particularly for dilute feed solutions. 相似文献
992.
Polymeric Micelle Assembly with Inorganic Nanosheets for Construction of Mesoporous Architectures with Crystallized Walls 下载免费PDF全文
Dr. Bishnu Prasad Bastakoti Yunqi Li Dr. Masataka Imura Prof. Nobuyoshi Miyamoto Prof. Teruyuki Nakato Prof. Takayoshi Sasaki Prof. Yusuke Yamauchi 《Angewandte Chemie (International ed. in English)》2015,54(14):4222-4225
Here we propose a novel way to construct mesoporous architectures through evaporation‐induced assembly of polymeric micelles with crystalline nanosheets. As a model study, we used niobate nanosheets exfoliated by the direct reaction of K4Nb6O17?3 H2O crystals with an aqueous solution of propylamine. The electrostatic interaction between negatively charged nanosheets and positively charged polymeric micelles enable us to form composite micelles with the nanosheets. Removal of the micelles by calcination results in robust mesoporous oxides with the original crystalline structure. 相似文献
993.
Reversible Carbene Formation in the Ionic Liquid 1‐Ethyl‐3‐Methylimidazolium Acetate by Vaporization and Condensation 下载免费PDF全文
The role of N‐heterocyclic carbenes in the chemistry of ionic liquids based on imidazolium salts has long been discussed. Here, we present experimental evidence that 1‐ethyl‐3‐methylimidazolium‐2‐ylidene (EMIm) can coexist with its protonated imidazolium cation (EMImH+) at low temperatures. If the vapor of the ionic liquid [EMImH+][AcO?] is trapped in solid argon or nitrogen at 9 K, only acetic acid (AcOH) and the carbene, but no ionic species, are found by IR spectroscopy. This indicates that during the evaporation of [EMImH+][AcO?] proton transfer occurs to form the neutral species. If the vapor of [EMImH+][AcO?] is trapped at 9 K as film in the absence of a host matrix, a solid consisting of EMImH+, EMIm, AcO?, and AcOH is formed. During warming to room temperature the proton transfer in the solid to form back the IL [EMImH+][AcO?] can be monitored by IR spectroscopy. This clearly demonstrates that evaporation and condensation of the IL [EMImH+][AcO?] results in a double proton transfer, and the carbene EMIm is only metastable even at low temperatures. 相似文献
994.
Fei Cong Khem Raj Joshi Hari Prasad Devkota Takashi Watanabe 《Natural product research》2015,29(15):1442-1448
A new flavonoid, dhasingreoside (1) and seven known compounds, quercetin 3-O-β-d-galacturonopyranoside (2), quercetin 3-O-β-d-galactopyranoside (3), quercetin 3-O-β-d-glucuronopyranoside (4), quercetin 3-O-α-l-rhamnopyranoside (5), (–)-epicatechin (6), salicylic acid (7) and gaultherin (8), have been isolated from the shade-dried stems and leaves of Gaultheria fragrantissima, commonly known as ‘Dhasingre’ in Nepal. The structures were elucidated on the basis of physical, chemical and spectroscopic methods. Among known compounds, five compounds (3–6 and 8) were isolated for the first time from G. fragrantissima. In vitro antioxidant activity of all the isolated compounds was evaluated by 1,1-diphenyl-2-picrylhydrazyl free radical-scavenging assay. Dhasingreoside (1) and other compounds (2–6) showed significant free radical-scavenging activity. 相似文献
995.
Tanno A. Schmidt Dr. Benjamin Ciszek Prasad Kathe Prof. Dr. Ivana Fleischer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(16):3641-3646
Herein, we describe the acid/Pd-tandem-catalyzed transformation of glycol derivatives into terminal formic esters. Mechanistic investigations show that the substrate undergoes rearrangement to an aldehyde under [1,2] hydrogen migration and cleavage of an oxygen-based leaving group. The leaving group is trapped as its formic ester, and the aldehyde is reduced and subsequently esterified to a formate. Whereas the rearrangement to the aldehyde is catalyzed by sulfonic acids, the reduction step requires a unique catalyst system comprising a PdII or Pd0 precursor in loadings as low as 0.75 mol % and α,α′-bis(di-tert-butylphosphino)-o-xylene as ligand. The reduction step makes use of formic acid as an easy-to-handle transfer reductant. The substrate scope of the transformation encompasses both aromatic and aliphatic substrates and a variety of leaving groups. 相似文献
996.
Mai Lê Anh Dr. Martin Kaiser Dr. Madhav Prasad Ghimire Dr. Manuel Richter Dr. Klaus Koepernik Markus Gruschwitz Prof. Dr. Christoph Tegenkamp Prof. Dr. Thomas Doert Prof. Dr. Michael Ruck 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(67):15549-15557
Topological insulators (TIs) gained high interest due to their protected electronic surface states that allow dissipation-free electron and information transport. In consequence, TIs are recommended as materials for spintronics and quantum computing. Yet, the number of well-characterized TIs is rather limited. To contribute to this field of research, we focused on new bismuth-based subiodides and recently succeeded in synthesizing a new compound Bi12Rh3Sn3I9, which is structurally closely related to Bi14Rh3I9 – a stable, layered material. In fact, Bi14Rh3I9 is the first experimentally supported weak 3D TI. Both structures are composed of well-defined intermetallic layers of ∞2[(Bi4Rh)3I]2+ with topologically protected electronic edge-states. The fundamental difference between Bi14Rh3I9 and Bi12Rh3Sn3I9 lies in the composition and the arrangement of the anionic spacer. While the intermetallic 2D TI layers in Bi14Rh3I9 are isolated by ∞1[Bi2I8]2− chains, the isoelectronic substitution of bismuth(III) with tin(II) leads to ∞2[Sn3I8]2− layers as anionic spacers. First transport experiments support the 2D character of this material class and revealed metallic conductivity. 相似文献
997.
Saúl J. C. Salazar Humberto G. Laguna Vinod Prasad Robin P. Sagar 《International journal of quantum chemistry》2020,120(11):e26188
The appearance of critical points in the Shannon entropy sum as a function of confinement radius, in ground and excited state confined hydrogenic systems, is discussed. We illustrate that the Coulomb potential in tandem with the hard sphere confinement are responsible for these points. The positions of these points are observed to vary with the intensity of the potential. The effects of the Coulomb potential on the system are further probed, by examining the differences between the densities of the confined atom and those of the particle confined in a spherical box, for the same confinement radius. These differences are quantified by using Kullback-Leibler and cumulative residual Kullback-Leibler distance measures from information theory. These measures detect that the effects of the Coulomb potential are squeezed out of the system as the confinement radius decreases. That is, the confined atom densities resemble the particle in a box ones, for smaller confinement radii. Furthermore, the critical points in the entropy sum lie in the same regions where there are changes in the distance measures, as the atom behaves more particle in a spherical box-like. The analysis is further complemented by examination of the derivative of the entropy sum with respect to confinement radius. This study illustrates the inhomogeneity in the magnitudes of the derivatives of the entropy sum components and their dependence on the Coulomb potential. A link between the derivative and the entropic force is also illustrated and discussed. Similar behaviors are observed when the virial ratio is compared to the entropic power one, as a function of confinement radius. 相似文献
998.
Pradip Roul Kiran Thula VMK Prasad Goura 《Mathematical Methods in the Applied Sciences》2019,42(8):2613-2630
This paper is concerned with the numerical solutions of Bratu‐type and Lane‐Emden–type boundary value problems, which describe various physical phenomena in applied science and technology. We present an optimal collocation method based on quartic B‐spine basis functions to solve such problems. This method is constructed by perturbing the original problem and on a uniform mesh. The method has been tested by four nonlinear examples. In order to show the advantage of the new method, numerical results are compared with those obtained by some of the existing methods, such as normal quartic B‐spline collocation method and the finite difference method (FDM). It has been observed that the order of convergence of the proposed method is six, which is two orders of magnitude larger than the normal quartic B‐spline collocation method. Moreover, our method gives highly accurate results than the FDM. 相似文献
999.
Madavalam Sreeman Sheshshayee Hanumantha Rao Bindumadhava Rengaswamy Ramesh Trichy Ganesh Prasad Makarla Udayakumar 《Isotopes in environmental and health studies》2013,49(1):122-129
Models that explain the oxygen isotope enrichment in leaf water (and biomass) treat the relationship between the kinetic fractionation that occurs during evapotranspiration and the stomatal conductance in an empirical way. Consequently, the isotopic enrichment is always predicted to decrease with increasing stomatal conductance, regardless of the experimental evidence to the contrary. We explain why and suggest an alternative method to reconcile theory and experiment. We support this with our experimental data on rice and groundnut plants. 相似文献
1000.
Ararimeh Aiyejina Dhurjati Prasad Chakrabarti Angelus Pilgrim M.K.S. Sastry 《International Journal of Multiphase Flow》2011
The gelling of waxy crudes and the deposition of wax on the inner walls of subsea crude oil pipelines present a costly problem in the production and transportation of oil. The timely removal of deposited wax is required to address the reduction in flow rate that it causes, as well as to avoid the eventual loss of a pipeline in the event that it becomes completely clogged. In order to understand this problem and address it, significant research has been done on the mechanisms governing wax deposition in pipelines in order to model the process. Furthermore, methods of inhibiting the formation of wax on pipeline walls and of removing accumulated wax have been studied to find the most efficient and cost-effective means of maintaining pipelines prone to wax deposition. This paper seeks to review the current state of research into these areas, highlighting what is so far understood about the mechanisms guiding this wax deposition, and how this knowledge can be applied to modelling and providing solutions to this problem. 相似文献