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151.
Ruby Chauhan Ashavani Kumar Ram Pal Chaudhary 《Journal of Sol-Gel Science and Technology》2012,61(3):585-591
Undoped and zinc-doped TiO2 nanoparticles (Ti1−xZnxO2 where x = 0.00–0.10) were synthesized by a sol–gel method. The synthesized products were characterized by X-ray diffraction
(XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and UV–VIS spectrometer. XRD pattern confirmed
the tetragonal structure of synthesized samples. Average grain size was determined from X-ray line broadening using the Debye–Scherrer
relation. The crystallite size was varied from 10 to 40 nm as the calcination temperature was increased from 350 to 800 °C.
The incorporation of 3–5 mol% Zn2+ in place of the Ti4+ provoked a slight decrease in the size of nanocrystals as compared to undoped TiO2. The SEM and TEM micrographs revealed the agglomerated spherical-like morphology with a diameter of about 10–30 nm and length
of several nanometers, which is in agreement with XRD results. Optical absorption measurements indicated a blue shift in the
absorption band edge upon 3–5 mol% zinc doping. Direct allowed band gap of undoped and Zn-doped TiO2 nanoparticles measured by UV–VIS spectrometer were 2.95 and 3.00 eV at 550 °C, respectively. 相似文献
152.
Tyagi V Khan S Bajpai V Gauniyal HM Kumar B Chauhan PM 《The Journal of organic chemistry》2012,77(3):1414-1421
Several diversity-oriented syntheses of N-fused polycyclic heterocycles have been demonstrated but most of them are based on point diversity within the same library and usually involve time-consuming sequential multistep syntheses, which also suffer from low yields and/or poor precursor scopes. We have developed a new strategy for the syntheses of skeletal diverse N-fused polycyclic compounds via an Ugi-type MCR followed by a CuI-catalyzed coupling reaction or tandem Pictet-Spengler reaction. This two-step sequence provides eight distinct skeleton of fused {6-5-5-6}, {5-5-5-6}, {6-5-6-6}, and {5-5-6-6} ring systems that have applications in medicinal chemistry and chemical genetics too. 相似文献
153.
The in situ synthesis is reported of noble metal nanoparticles via 3-glycidoxypropyltrimethoxysilane mediated reduction of 3-aminopropyltrimethoxysilane treated metal salts during sol-gel processing. The method described involves the synthesis of uniform spherical nanoparticles of gold, silver and palladium with controlled size that can be directly utilized for thin film preparation. A detailed study of the synthesis and application of gold nanoparticles to the electrochemical detection of hydrogen peroxide was carried out and reveals that the amplification of hydrogen peroxide sensing is size-dependent. In addition, these nanoparticles exhibit excellent compatibility towards composite preparation. As an example, a nanocomposite with Prussian Blue (PB) is synthesized and found to be useful for the fabrication of chemically modified electrodes (CME). The resulting CME shows dramatic improvement in the electrochemistry of PB with gradual enhancement in electrocatalytic efficiency towards hydrogen peroxide sensing. The nanocomposite is used to study the direct and horseradish peroxidase (HRP)-catalyzed reduction of hydrogen peroxide. The results recorded for hydrogen peroxide analysis show an improvement in sensitivity and limit of detection on decreasing the size of gold nanoparticles in all cases. 相似文献
154.
Rajendra S. Chauhan Mohan C. Nautiyal Aldo Tava Mariella Mella 《Helvetica chimica acta》2012,95(5):780-787
The essential oil from the underground parts of Selinum tenuifolium Wall. (Apiaceae) was extracted by hydrodistillation using a Clevenger‐type apparatus, and analyzed by GC/FID and GC/MS. Nine constituents, representing 97.7% of the total oil, were identified, five of which belong to the class of polyacetylenes. The structures of the compounds 1 – 5 were elucidated by using IR, MS, and 1H‐ and 13C‐NMR data after purification by column chromatography. The major constituent detected was nona‐3,5‐diyne ( 1 ; 85.6% of the total volatiles), followed by nona‐3,5‐diyn‐2‐one ( 2 ), nona‐4,6‐diyn‐3‐one ( 3 ), nona‐3,5‐diyn‐2‐ol ( 4 ), and nona‐4,6‐diyn‐3‐ol ( 5 ), accounting for 3.0, 2.5, 2.2, and 3.1% of the total volatiles, respectively. The latter four polyacetylenes, 2 – 5 , were never reported in plants so far, and, therefore should be regarded as novel compounds. 相似文献
155.
The chemical composition of the volatile extract (yield ≈ 0.13%, v/w) from the bark of Quercus leucotrichophora (Fagaceae) was analysed for the first time by GC-MS. Twenty-three constituents, amounting to 93.0% of the total detected contents of the volatile extract, were identified. The volatile extract contained approximately 86.36% monoterpenoids, 6.53% sesquiterpenoids and 0.11% aliphatic aldehydes. 1,8-Cineol (40.359%) followed by γ-terpinene (16.369%) were the major monoterpene constituents of the volatile extract. The residue of volatile extract (0.00025-250 μg mL(-1)) exhibited a potent antimicrobial activity against Streptococcus pyogenes ATCC 19615. This study concludes that residues of the volatile extract of Q. leucotrichophora could serve as an important bioresource for the extraction and isolation of monoterpenoids exhibiting antimicrobial activity, and thus has good potential for use in the pharmaceutical industry. 相似文献
156.
157.
Tulika Chakraborty Satyaveer S. Chauhan Bibhas C. Giri 《Applied Mathematical Modelling》2013,37(10-11):6593-6608
In this article we develop an economic manufacturing quantity (EMQ) model subject to stochastic machine breakdown, repair and stock threshold level (STL). Instead of constant production rate, in this model production rate is considered as a decision variable. Since, the stress of the machine depends on the production rate, failure rate of the machine will be a function of the production rate. Again, in this article consideration of safety stock in all existing literature is replaced by the concept of stock threshold level (STL). Further, extra capacity of the machine is considered to buffer against the possible uncertainties of the production process where machine capacity is predetermined. The basic model is developed under general failure and general repair time distributions. Since, the assumption of variable production rate makes the objective function quite complex, so main emphasis is given on computational methodology to solve the present problem. We suggest two computational algorithms for the determination of production rate and stock threshold level which minimize the expected cost rate in the steady state. Finally, through numerical examples we illustrate the key insights of our model from managerial point of view. 相似文献
158.
A. Bagaria S. Ramakumar M. Gupta V. S. Chauhan 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(3):o174-o176
The title compound (systematic name: 3‐benzylidene‐6‐isobutylpiperazine‐2,5‐dione), C15H18N2O2, an α,β‐dehydrophenylalanine containing diketopiperazine, crystallizes in the space group P1 with two molecules in the asymmetric unit arranged antiparallel to one another. The α,β‐dehydrophenylalanine (ΔPhe) residue in this cyclic peptide retains its planarity but deviates from the standard conformations observed in its linear analogues. Each type of molecule forms a linear chain with molecules of the same type via pairwise N—H⋯O hydrogen bonds, while weaker C—H⋯O interactions link the chains together to form a three‐dimensional network. 相似文献
159.
160.