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排序方式: 共有242条查询结果,搜索用时 15 毫秒
1.
Aqueous dispersions of single-wall and multiwall carbon nanotubes with designed amphiphilic polycations 总被引:1,自引:0,他引:1
Sinani VA Gheith MK Yaroslavov AA Rakhnyanskaya AA Sun K Mamedov AA Wicksted JP Kotov NA 《Journal of the American Chemical Society》2005,127(10):3463-3472
Poor solubility of single-walled and multiwalled carbon nanotubes (NTs) in water and organic solvents presents a considerable challenge for their purification and applications. Macromolecules can be convenient solubilizing agents for NTs and a structural element of composite materials for them. Several block copolymers with different chemical functionalities of the side groups were tested for the preparation of aqueous NT dispersions. Poly(N-cetyl-4-vinylpyridinium bromide-co-N-ethyl-4-vinylpyridinium bromide-co-4-vinylpyridine) was found to form exceptionally stable NT dispersions. It is suggested that the efficiency of macromolecular dispersion agents for NT solubilization correlates with the topological and electronic similarity of polymer-NT and NT-NT interactions in the nanotube bundles. Raman spectroscopy and atomic force and transmission electron microcopies data indicate that the polycations are wrapped around NTs forming a uniform coating 1.0-1.5 nm thick. The ability to wind around the NT originates in the hydrophobic attraction of the polymer backbone to the graphene surface and topological matching. Tetraalkylammonium functional groups in the side chains of the macromolecule create a cloud of positive charge around NTs, which makes them hydrophilic. The prepared dispersions could facilitate the processing of the nanotubes into composites with high nanotube loading for electronic materials and sensing. Positive charge on their surface is particularly important for biological and biomedical applications because it strengthens interactions with negatively charged cell membranes. A high degree of spontaneous bundle separation afforded by the polymer coating can also be beneficial for NT sorting. 相似文献
2.
Ornithine methyl ester reacts with aromatic aldehydes to generate bis-Schiff bases, which depending on the structure of the aromatic aldehyde, further undergo an intramolecular cycloaddition through the transient formation of a reactive 1,3-dipole. 相似文献
3.
This study is attempted to develop a green corrosion inhibitor from a waste material of Jack fruit (Artocarpus heterophyllus). This method is therefore quite valuable to health, environment, and economic point of view. Pectin is isolated from the jackfruit peel waste using 0.05 ?N oxalic acid and used as an inhibitor for mild steel corrosion in acidic environment as it is highly water soluble. 250–1000 ?ppm of pectin was used in this study at a temperature range of 303–323 ?K. The protection efficiency of jack fruit pectin (JP) in 0.5 ?M HCl was evaluated by conventional weight loss and electrochemical techniques. The potentiodynamic polarization results revealed that JP could effectively reduce the corrosion of mild steel in acidic medium at 1000 ?ppm concentration with an inhibition efficiency of 89.75% and corrosion rate of 2.392 mpy. The mixed type behavior of the inhibitor is identified from Tafel polarization studies. Electrochemical impedance spectroscopy (EIS) measurements suggest that the corrosion inhibition process is kinetically controlled. adsorption and kinetic behavior of the inhibitor also have been studied. Surface manifestations were followed using FESEM and AFM techniques. DFT calculations and Monte Carlo simulations were also carried out to corroborate the experimental results with theoretical outputs and succeeded to a great extent. 相似文献
4.
Muddaser Shah Waheed Murad Najeeb Ur Rehman Sobia Ahsan Halim Manzoor Ahmed Hazir Rehman Muhammed Zahoor Sidra Mubin Ajmal Khan Mohamed A. Nassan Gaber El-Saber Batiha Ahmed Al-Harrasi 《Molecules (Basel, Switzerland)》2021,26(12)
In the current study, in vitro antimicrobial and antioxidant activities and in vivo anti-inflammatory and analgesic activities of Scutellaria edelbergii Rech. f. (crude extract and subfractions, i.e., n-hexane, ethyl acetate (EtOAc), chloroform, n-butanol (n-BuOH) and aqueous) were explored. Initially, extraction and fractionation of the selected medicinal plant were carried out, followed by phytochemical qualitative tests, which were mostly positive for all the extracts. EtOAc fraction possessed a significant amount of phenolic (79.2 ± 0.30 mg GAE/g) and flavonoid (84.0 ± 0.39 mg QE/g) content. The EtOAc fraction of S. edelbergii exhibited appreciable antibacterial activity against Gram-negative (Escherichia coli and Klebsiella pneumoniae) strains and significant zones of inhibition were observed against Gram-positive bacterial strains (Bacillus subtilis and Staphylococcus aureus). However, it was found inactive against Candida Albicans and Fusarium oxysporum fungal strains. The chloroform fraction was the most effective with an IC50 value of 172 and 74 µg/mL against DPPH (1,1-Diphenyl-2-picryl-hydrazyl) and ABTS assays, in comparison with standard ascorbic acid 59 and 63 µg/mL, respectively. Moreover, the EtOAc fraction displayed significant in vivo anti-inflammatory activity (54%) using carrageenan-induced assay and significant (55%) in vivo analgesic activity using acetic acid-induced writing assay. In addition, nine known compounds, ursolic acid (UA), ovaul (OV), oleanolic acid (OA), β-sitosterol (BS), micromeric acid (MA), taraxasterol acetate (TA), 5,3′,4′-trihydroxy-7-methoxy flavone (FL-1), 5,7,4′-trihydroxy-6,3′-dimiethoxyflavone (FL-2) and 7-methoxy catechin (FL-3), were isolated from methanolic extract of S. edelbergii. These constituents have never been obtained from this source. The structures of all the isolated constituents were elucidated by spectroscopic means. In conclusion, the EtOAc fraction and all other fractions of S. edelbergii, in general, displayed a significant role as antibacterial, free radical scavenger, anti-inflammatory and analgesic agents which may be due to the presence of these constituents and other flavonoids. 相似文献
5.
Sushant G. Ghosh Muhammed Amir 《The European Physical Journal C - Particles and Fields》2015,75(11):553
We investigate the horizon structure and ergosphere in a rotating Bardeen regular black hole, which has an additional parameter (g) due to the magnetic charge, apart from the mass (M) and the rotation parameter (a). Interestingly, for each value of the parameter g, there exists a critical rotation parameter (\(a=a_{E}\)), which corresponds to an extremal black hole with degenerate horizons, while for \(a<a_{E}\) it describes a non-extremal black hole with two horizons, and no black hole for \(a>a_{E}\). We find that the extremal value \(a_E\) is also influenced by the parameter g, and so is the ergosphere. While the value of \(a_E\) remarkably decreases when compared with the Kerr black hole, the ergosphere becomes thicker with the increase in g. We also study the collision of two equal mass particles near the horizon of this black hole, and explicitly show the effect of the parameter g. The center-of-mass energy (\(E_\mathrm{CM}\)) not only depend on the rotation parameter a, but also on the parameter g. It is demonstrated that the \(E_\mathrm{CM}\) could be arbitrarily high in the extremal cases when one of the colliding particles has a critical angular momentum, thereby suggesting that the rotating Bardeen regular black hole can act as a particle accelerator. 相似文献
6.
Muhammed Mizher Radhi 《Research on Chemical Intermediates》2014,40(5):1975-1987
A grafted polymer reference electrode (GPRE) (polystyrene grafted with acrylonitrile as a monomer using gamma irradiation) was fabricated as a reference electrode using cyclic voltammetry (CV). The redox process of K3Fe(CN)6 during CV was studied. It was found that the redox current peaks of Fe(II)/Fe(III) in 0.1 M of KCl as supporting electrolyte is given the same oxidation–reduction current as in the Ag/AgCl reference electrode, indicating a good result of GPRE and, hence, it can be used for voltammetric analysis technique. The physical properties of GPRE include good hardness, insoluble in non-aqueous electrolytes (except dimethyl formamide and chloroform), and good stability at different solvents. In addition, the sensitivity under conditions of CV is significantly dependent on the scan rate (SR) and variation in concentration. At different SRs, redox peaks of K3Fe(CN)6 were observed in a reversible process: Fe(II)/Fe(III). Interestingly, the redox reaction of Fe(II)/Fe(III) solution using GCE versus GPRE remains constant even after 15 cyclings. It is therefore evident that the GPRE possesses some degree of stability. Also, the new reference electrode GPRE has improved the properties of electroanalysis of CV on the working electrode GCE in reliability with the relative standard deviation. 相似文献
7.
Devipriya Balu Kumaradhas Poomani Kalyanam Nagabushanam Sridhar Balasubramanium Rajendran Ramanujam Majeed Muhammed 《Journal of chemical crystallography》2011,41(5):697-702
Abstract
5-Lipoxygenase inhibitor 3-O-acetyl-9,11-dehydro-β-boswellic acid was detected in the extract of Boswellia serrata gum resulting from unstable 11-hydroxy precursor. It was reported more potent than other Boswellic acids in its inhibition of 5-Lipoxygenase. Here, we report the method of conversion of 3-acetoxy-β-boswellic acid to 3-O-acetyl-9,11-dehydro-β-boswellic acid, and the crystal structure of later. This compound crystallizes in orthorhombic space group P212121 with cell parameters of a = 12.726(1) ?, b = 16.597(1) ?, c = 27.332(2) ?, α = β = γ = 90°, V = 5772.7(5) ?3, D c = 1.143 Mg/m3, and Z = 8. The X-ray structure investigation indicates that the rings A, B, D and E are exhibit chair and the ring C adopts a distorted half chair conformation. The conformational difference of the two structures in the arrangement is due to crystal packing of 3-O-acetyl-9,11-dehydro-β-boswellic acid. The molecular packing is stabilized by C–H···O and O–H···O types of hydrogen bonding interactions. 相似文献8.
Anwar M Bailey JH Dickinson LC Edwards HJ Goswami R Moloney MG 《Organic & biomolecular chemistry》2003,1(13):2364-2376
Alkylation reactions using alpha-halolactams or lactam enolates derived from bicyclic lactam templates can proceed with high endo- or exo- diastereoselectivity respectively. In the latter case, stereochemical correction by means of enolate generation and hindered phenol quench is possible with moderate efficiency. This protocol has been applied to the synthesis of protected penmacric acid and its analogues. 相似文献
9.
Z. Iqbal Y. Zhang H. Grebel S. Vijayalakshmi A. Lahamer G. Benedek M. Bernasconi J. Cariboni I. Spagnolatti R. Sharma F.J. Owens M.E. Kozlov K.V. Rao M. Muhammed 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):509-515
Evidence is presented for the formation of a solid phase based on the smallest fullerene, C20, in thin diamond-like carbon films deposited by ultraviolet laser ablation from diamond onto nickel substrates at room temperature
in the presence of 10-4 torr of cyclohexane or benzene. Laser desorption mass spectrometry from the films shows the presence of C20, C21 and C22 species, while micro-Raman spectroscopy and electron diffraction from selected particles together with first principle density-functional
calculations, indicate a cubic solid with dodecahedral C20 cages as building blocks. Unlike solid C60 and fully protonated C20, which are bound by van der Waals forces, the proposed structure is stabilized by linking of the C20 dodecahedra with bridging carbon atoms at interstitial tetrahedral sites to form a face-centered-cubic lattice with 22 carbon
atoms per unit cell.
Received 10 October 2002 / Received in final form 24 December 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: zafar.iqbal@njit.edu 相似文献
10.
Shanghua Li Zeming He Muhammet S. Toprak Christian Stiewe Eckhard Müller Mamoun Muhammed 《固体物理学:研究快报》2007,1(6):259-261
Maize‐like CoSb3 powders were obtained via the chemical alloying method. After the consolidation of the nanopowder using hot press, the CoSb3 compact shows a higher Seebeck coefficient and lower thermal conductivity. For the investigated CoSb3, a ZT of 0.15 at 673 K is shown. Though the achieved ZT does not reach the optimal value (0.17 to 0.18) for pure CoSb3, due to its lower electrical conductivity, the novel structure fabrication provides an interesting and promising approach to enhancing the thermoelectric performance. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献