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351.
Solid-phase extraction (SPE) of phenol and chlorophenols, their derivatization to methyl ethers, headspace single-drop microextraction (HS-SDME) of methyl ethers using 1-butanol as extraction solvent, and direct transfer of the drop into the injector for high performance liquid chromatography with diode array detection (HPLC-DAD) have been reported. A flanged-end polytetrafluoroethylene sleeve, 3 mm × 0.5 mm, placed at the tip of the syringe needle, allowed the use of 10 μL solvent drop for extraction. The procedure has been optimized for variables involved in SPE and HS-SDME. A rectilinear relationship was obtained between the amount of chlorophenols and peak area ratio of their methyl ethers/internal standard (4-methoxyacetophenone) in the range 0.01-10 mg L−1, correlation coefficient in the range 0.9956-0.9996, and limit of detection in the range 1.5-3.9 μg L−1 when HS-SDME alone was used for sample preparation. When using coupled SPE and HS-SDME, the linear range obtained was 0.1-500 μg L−1, correlation coefficient in the range 0.9974-0.9998, and the limit of detection in the range 0.04-0.08 μg L−1. Spiked real samples have been analyzed with adequate accuracy, and application of the method has been demonstrated for the analysis of chlorophenols formed upon bamboo pulp bleaching. 相似文献
352.
Aakash D. Nidhankar Goudappagouda Divya S. Mohana Kumari Shailendra Kumar Chaubey Rashmi Nayak Rajesh G. Gonnade G. V. Pavan Kumar Retheesh Krishnan Sukumaran Santhosh Babu 《Angewandte Chemie (International ed. in English)》2020,59(31):13079-13085
Room‐temperature phosphorescence of metal and heavy atom‐free organic molecules has emerged as an area of great potential in recent years. A rational design played a critical role in controlling the molecular ordering to impart efficient intersystem crossing and stabilize the triplet state to achieve room‐temperature ultralong phosphorescence. However, in most cases, the strategies to strengthen phosphorescence efficiency have resulted in a reduced lifetime, and the available nearly degenerate singlet‐triplet energy levels impart a natural competition between delayed fluorescence and phosphorescence, with the former one having the advantage. Herein, an organic helical assembly supports the exhibition of an ultralong phosphorescence lifetime. In contrary to other molecules, 3,6‐phenylmethanone functionalized 9‐hexylcarbazole exhibits a remarkable improvement in phosphorescence lifetime (>4.1 s) and quantum yield (11 %) owing to an efficient molecular packing in the crystal state. A right‐handed helical molecular array act as a trap and exhibits triplet exciton migration to support the exceptionally longer phosphorescence lifetime. 相似文献
353.
354.
Sumit Sood Poonam Kumari Ajar Nath Yadav Anil Kumar Karan Singh 《Journal of heterocyclic chemistry》2020,57(7):2936-2944
An efficient microwave-assisted method of synthesis of pyrazole-4-carbonitriles has been developed. Condensation of pyrazole-4-carbaldehydes with hydroxylamine hydrochloride followed by reaction of the resulting oximes with the Vilsmeier-Haack reagent pre-formed from phthaloyl dichloride and dimethylformamide under microwave irradiation afforded the corresponding pyrazole-4-carbonitriles in 73% to 91% yield. The operational simplicity, avoidance of toxic reagents such as POCl3, shorter reaction time, higher yield compared to the classical version, easy work up, and the use of the by-product in the regeneration of phthaloyl dichloride are the advantages of this methodology. All the target compounds were tested for antimicrobial activity against Gram-positive bacteria Bacillus cereus and Staphylococcus aureus; Gram-negative bacteria Escherichia coli and Yersinia enterocolitica, and the fungal species Candida albicans. 相似文献
355.
Porous chitosan scaffolds with possible tissue engineering applications were synthesized by using lyophilization and supercritical carbon dioxide (sc.CO2) drying technique. 1% Chitosan (CS) solution in aq. acetic acid was treated with 37% formaldehyde solution; the resulting hydrogels were subjected to solvent-exchange prior to the final treatment procedures. Their morphology, pore structure, and physical properties were characterized by Fourier transform infrared spectroscopy (FTIR), thermal analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the specific surface areas and porosities of scaffolds were determined by using N2 adsorption. The sc.CO2 treated scaffolds showed a much greater surface area in comparison to the lyophilized one. Hence, sc.CO2 treated scaffolds is better for cell proliferation. We further investigated the bioactivity of sc.CO2 treated scaffolds using simulated body fluid (SBF). The sc.CO2 assisted chitosan scaffold prepared by using green chemistry approach is highly pure and from a hygienic point of view, it is an ideal material for tissue engineering applications. 相似文献
356.
Anu Kumari Najam A. Shakil Braj B. Singh Arthur C. Watterson 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):417-424
Sixteen amphiphilic polymers were synthesized using poly(ethylene glycols) (PEGs) of different molecular weights, viz. 1000, 1500, 2000 and 4000 as hydrophilic block and linkers namely azelaic acid, suberic acid, terephthalic acid and glycolic acid as hydrophobic block in the presence of catalyst conc. H2SO4 out of which four with glycolic acid as linker are new. Synthesized polymers were characterized by using 1H-NMR, 13C-NMR and IR spectroscopy. Micellar sizes of the polymers were determined using Dynamic Light Scattering (DLS) technique which ranged from 32.1–262.0 nm and confirmed by Transmission Electron Microscope (TEM) analysis. Molecular weights were determined using HORIBA SZ-100 scientific and varied from 6.5?×?102 to 6.5?×?103 Kilo Daltons(kDa) by Debye plot. Critical Micelle Concentrations (CMC) of the synthesized polymers was determined using electrical conductivity meter and it ranged from 105 to 125 milligrams per litre (mg L?1). 相似文献
357.
Ellis Bagga Sunita Kumari Rajesh Kumar Rakesh Kumar R. P. Bajpai Lalit M. Bharadwaj 《Pramana》2005,65(5):967-972
The present study reports the covalent immobilization of myosin on glass surface andin-vitro motility of actin-myosin biomolecular motor. Myosin was immobilized on poly-L-lysine coated glass using heterobifunctional
cross linker EDC and characterized by AFM. Thein-vitro motility of actin was carried out on the immobilized myosin. It was observed that velocity of actin over myosin increases
with increasing actin concentration (0.4–1.0 mg/ml) and was found in the range of 0.40–3.25 μm/s. The motility of actinmyosin
motor on artificial surfaces is of immense importance for developing nanodevices for healthcare and engineering applications 相似文献
358.
Devulapalli Venu Gopal Basavaraju Srinivas Mangalampalli Venkata Phanikrishna Sharma Lipsa Panda Pullur Anil Kumar Machiraju Subrahmanyam Valluri Durga Kumari 《Reaction Kinetics and Catalysis Letters》2004,83(1):63-70
The vapor phase hydrogenation of acetophenone at atmospheric pressure is carried out for the synthesis of 1-phenylethanol
in a fixed bed reactor using Cu-Zn-Al-O (LTS-1) and LTS-2, Zn-Cr-Al-O (HTS-1) and Zn-Cu-Cr-Al-O (HTS-2) metal oxide catalysts.
Our studies clearly indicate that a catalyst of low temperature hydrogenation activity, when modified for its acidity with
magnesium oxide, shows maximum selectivity of 1-phenylethanol.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
359.
The problem of combined convection from vertical surfaces in a porous medium saturated with a power-law type non-Newtonian fluid is investigated. The transformed conservation laws are solved numerically for the case of variable surface heat flux conditions. Results for the details of the velocity and temperature fields as well as the Nusselt number have been presented. The viscosity index ranged from 0.5 to 2.0. 相似文献
360.
The boundary layer in free convection above a uniformly heated semi-infinite flat plate, which is inclined at a small angle to the horizontal in porous media is discussed. For positive inclinations of the plate, series solutions, one valid near the leading edge and the other at large distances from it, are obtained. When the inclination is negative, a series solution valid near the leading edge is again obtained. A step-by-step numerical technique, based on a scheme by Keller, is used to complete the solution in the region where neither series is adequate. For the negative inclinations of the plate, the boundary layer separates and a region of reverse flow develops.Hier wird die Grenzschicht bei freier Konvektion in einem porösem Medium oberhalb einer gleichmäßig beheizten, halbunendlichen flachen Platte, die mit einem kleinen Winkel gegen die Horizontale geneigt ist, untersucht. Für positive Neigungen der Platte sind zwei Reihenlösungen, eine gültig für den Anlaufbereich und die andere für einen großen Abstand davon, emittelt worden. Eine gültige Reihenlösung für eine negative Neigung in der Nähe des Anlaufbereiches ist ebenfalls bestimmt worden.Es ist ein schrittweises numerisches Verfahren, das auf der Methode von Keller basiert, benützt worden, um das Ergebnis im Bereich, in welchem keine Reihenansätze existieren, zu vervollständigen. Für negative Neigungen der Platte zerteilt sich die Grenzschicht und es entwickelt sich ein Bereich von Rückströmung. 相似文献