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排序方式: 共有106条查询结果,搜索用时 31 毫秒
81.
Chaitanya Das Pemmaraju Thomas ArcherRuairi Hanafin Stefano Sanvito 《Journal of magnetism and magnetic materials》2007
We investigate using density functional theory (DFT) the electronic structure of (∼3%) Co-doped ZnO in the presence of native n-type donor defects such as VO and ZnI. In particular, we apply a pseudopotential-based self-interaction correction (pseudo-SIC) scheme as an improvement to the local spin-density approximation (LSDA). This overcomes major short comings of the LSDA in describing Co-doped ZnO. Donor+dopant pair complexes such as Co–VO and Co–ZnI are studied as relevant magnetic centres for long-range magnetic interactions at low-dopant concentrations. We find that complex formation is energetically favourable but the inter-complex magnetic coupling is too weak to account for room temperature ferromagnetism in ZnO:Co 相似文献
82.
Anil K. Bhatnagar B. Bhanu Prasad N. Ravi R. Jagannathan T.R. Anantharaman 《Solid State Communications》1982,44(6):905-909
Amorphous Fe40Ni40B20 (VITROVAC 0040) alloy has been investigated using 57Fe Mössbauer Spectroscopy. The Curie temperature Tc is found to be well defined and is 695 ± 1 K. The quadrupole splitting just above Tc is 0.64 mm sec?1. The crystallization temperature is 698 ± 2 K, close to but definitely above Tc. The average hyperfine field Heff(T) of the glassy state shows a temperature dependence of indicative of the existence of spin wave excitations. The values of and are found to be 0.40 and 0.06, respectively, for T/Tc ? 0.72. At temperatures close to Tc, Heff(T) varies as (1 ? T/Tc)β where β is one of the critical exponents and its value is found to be 0.29 ± 0.02. 相似文献
83.
Formation of chunks of various sizes ranging between 2 and 6 mm was achieved using high-energy ball milling in Al–1at.%Pb–1at.%W alloy system at room temperature during milling itself, aiding in in situ consolidation. X-ray diffraction and transmission electron microscopy (TEM) studies indicate the formation of multi-phase structure with nanocrystalline structural features. From TEM data, an average grain size of 23 nm was obtained for Al matrix and the second-phase particles were around 5 nm. A high strain rate sensitivity (SRS) of 0.071 ± 0.004 and an activation volume of 4.71b3 were measured using nanoindentation. Modulus mapping studies were carried out using Berkovich tip in dynamic mechanical analysis mode coupled with in situ scanning probe microscopy imaging. The salient feature of this investigation is highlighting the role of different phases, their crystal structures and the resultant interfaces on the overall SRS and activation volume of a multi-phase nc material. 相似文献
84.
T. N. Srinivasan P. B. Sattur K. Rama Rao A. S. Bhanu Prasad E. D. Jemmis 《Journal of heterocyclic chemistry》1989,26(3):553-555
A study of the cycloaddition behaviour of substituted pyridazin-3-ones with arylnitrile oxides has been carried out, Nitrile oxides udergo site and regioselective 1, 3-dipolar cycloaddition to 4, 5-double bond of pyridazinone to afford 3a, 7a-dihydroisoxazolo[4, 5-d]pyridazin-4-ones. The reactions follow frontier orbital predictions. Nitrile oxide HOMO-pyridazinone LUMO combination is dominant. 相似文献
85.
Odedra A Wu CJ Pratap TB Huang CW Ran YF Liu RS 《Journal of the American Chemical Society》2005,127(10):3406-3412
TpRu(PPh3)(CH3CN)2 PF6 (10 mol %) catalyst effected the nucleophilic addition of water, alcohols, aniline, acetylacetone, pyrroles, and dimethyl malonate to unfunctionalized enediynes under suitable conditions (100 degrees C, 12-24 h) and gave functionalized benzene products in good yields. In this novel cyclization, nucleophiles very regioselectively attack the internal C1' alkyne carbon of enediynes to give benzene derivatives as a single regioisomer. Experiments with methoxy substituents exclude the possible involvement of naphthyl cations as reaction intermediates in the cyclization of (o-ethynylphenyl) alkynes. Deuterium-labeling experiments indicate that the catalytically active species is ruthenium-pi-alkyne rather than ruthenium-vinylidene species. This hypothesis is further confirmed by the aromatization of o-(2'-iodoethynyl)phenyl alkynes with alcohols. We propose a nucleophilic addition/insertion mechanism for this nucleophilic aromatization on the basis of a series of experiments. 相似文献
86.
Sarvjeet Kaur Bhanu Sharma E. S. Lin M. M. Lee Gulshan Kumar V. Chandrasekhar Shih-Sheng Sun Ashutosh S. Singh 《中国化学会会志》2023,70(11):2016-2021
Mutual induced-fit is well known process in biological system and playing crucial role in enzymatic catalysis, peptide-bond synthesis, protein synthesis, etc…, proceeds by mutual interactions of two or more than two components. However, in an artificial system, to mimic such process is challenging, especially by purely organic components. In this report, we have shown importance of mutual induced-fit in signal amplification of hydrogen-bonded capsule formation. Two different types of highly flexible ligands (one N-bridged and another triazine-bridged) are used. N-bridged tripodal ligand acting as clip over the adduct obtained from triazine-bridged ligand, bringing the resultant adduct in the cone-shape conformation. The resulting cone-shape conformation undergo solvent polarity dependent hydrogen-bonded capsule formation as a sole product. In absence of N-bridged tripodal ligand, only 50% capsule formation is observed through 1H NMR at 100 mM concentration. However, in the presence of N-bridged tripodal ligand, organic components undergo mutual interactions to opt the cone-shape conformation and 100% capsule is formed (independent of concentration). The complete process is characterized by IR-spectra, 1H and 13C NMR spectra, concentration dependent 1H NMR titration spectra, 1H-1H COSY, 1H-1H NOESY, DOSY NMR, high resolution ESI mass spectra, and also by energy-minimized structure. 相似文献
87.
In this review, we present an assessment of recent advances in alkyne functionalization reactions, classified according to different classes of recyclable catalysts. In this work, we have incorporated and reviewed the activity and selectivity of recyclable catalytic systems such as polysiloxane-encapsulated novel metal nanoparticle-based catalysts, silica–copper-supported nanocatalysts, graphitic carbon-supported nanocatalysts, metal organic framework (MOF) catalysts, porous organic framework (POP) catalysts, bio-material-supported catalysts, and metal/solvent free recyclable catalysts. In addition, several alkyne functionalization reactions have been elucidated to demonstrate the success and efficiency of recyclable catalysts. In addition, this review also provides the fundamental knowledge required for utilization of green catalysts, which can combine the advantageous features of both homogeneous (catalyst modulation) and heterogeneous (catalyst recycling) catalysis. 相似文献
88.
Shibaji Ghosh Nellore Bhanu Chandar Kalyanashis Jana Bishwajit Ganguly 《Journal of computer-aided molecular design》2017,31(8):729-742
Inhibition of acetylcholinesterase (AChE) with organophosphorus compounds has a detrimental effect on human life. Oxime K203 seems to be one of the promising reactivators for tabun-inhibited AChE than (K027, K127, and K628). These reactivators differ only in the linker units between the two pyridinium rings. The conformational analyses performed with quantum chemical RHF/6-31G* level for K027, K127, K203 and K628 showed that the minimum energy conformers have different orientations of the active and peripheral pyridinium rings for these reactivator molecules. K203 with (–CH2–CH=CH–CH2–) linker unit possesses more open conformation compared to the other reactivators. Such orientation of K203 experiences favorable interaction with the surrounding residues of catalytic anionic site (CAS) and peripheral anionic site (PAS) of tabun-inhibited AChE. From the steered molecular dynamics simulations, it has been observed that the oxygen atom of the oxime group of K203 reactivator approaches nearest to the P-atom of the SUN203 (3.75 Å) at lower time scales (less than ~1000 ps) as compared to the other reactivators. K203 experiences less number of hydrophobic interaction with the PAS residues which is suggested to be an important factor for the efficient reactivation process. In addition, K203 crates large number of H-bonding with CAS residues SUN203, Phe295, Tyr337, Phe338 and His447. K203 barely changes its conformation during the SMD simulation process and hence the energy penalty to adopt any other conformation is minimal in this case as compared to the other reactivators. The molecular mechanics and Poisson–Boltzmann surface area binding energies obtained for the interaction of K203 inside the gorge of tabun inhibited AChE is substantially higher (?290.2 kcal/mol) than the corresponding K628 reactivator (?260.4 kcal/mol), which also possess unsaturated aromatic linker unit. 相似文献
89.
Tirtha Raj Acharya Pradeep Lamichhane Rizwan Wahab Dinesh Kumar Chaudhary Bhanu Shrestha Leela Pradhan Joshi Nagendra Kumar Kaushik Eun Ha Choi 《Molecules (Basel, Switzerland)》2021,26(24)
This paper compared the effects of A. indica plant proteins over chemical methods in the morphology of zinc oxide nanoparticles (ZnO NPs) prepared by a co-precipitation method, and ethanol sensing performance of prepared thin films deposited over a fluorene-doped tin oxide (FTO) bind glass substrate using spray pyrolysis technique. The average crystallite sizes and diameters of the grain-sized cluster ZnO NPs were 25 and (701.79 ± 176.21) nm for an undoped sample and 20 and (489.99 ± 112.96) nm for A. india dye-doped sample. The fourier transform infrared spectroscopy (FTIR) analysis confirmed the formation of the Zn–O bond at 450 cm−1, and also showed the presence of plant proteins due to A. indica dye extracts. ZnO NPs films exhibited good response (up to 51 and 72% for without and with A. indica dye-doped extracts, respectively) toward ethanol vapors with quick response-recovery characteristics at a temperature of 250 °C for undoped and 225 °C for A. indica dye-doped ZnO thin films. The interaction of A. indica dye extracts helps to decrease the operating temperature and increased the response and recovery rates of the sensor, which may be due to an increase in the specific surface area, resulting in adsorption of more oxygen and hence high response results. 相似文献
90.
Amar Singh Singha Bhanu Priya 《International Journal of Polymer Analysis and Characterization》2015,20(4):357-366
In the present study, biocomposite films of starch/poly(vinyl alcohol) (St/PVA) reinforced with delignified Grewia optiva fiber and methyl methacrylate (MMA) grafted fibers were prepared using citric acid as a plasticizer and glutaraldehyde as the cross-linker. The biocomposite films were subjected to evaluation of mechanical properties, biodegradability, and antibacterial properties. The biocomposite films were characterized by using Fourier transform-infrared (FT-IR) spectrophotometry, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA/DTA/DTG). SEM showed good adhesion between St/PVA blend matrix and fibers. The antimicrobial activity of biocomposite films against pathogenic bacteria such as Staphylococcus aureus and Escherichia coli was also explored. The results confirmed that the biocomposite films may be used for food packaging. 相似文献