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排序方式: 共有167条查询结果,搜索用时 15 毫秒
91.
V. K. Thakur M. K. Thakur A. S. Singha 《International Journal of Polymer Analysis and Characterization》2013,18(6):430-438
Surface modification of a natural cellulosic polymer system is required to improve the physicochemical properties of the fibers to be used as reinforcement for green composite applications. Surface modification through graft copolymerization improves the existing properties of the cellulosic fibers for a number of applications. Therefore, in the present study, an attempt was made to synthesize butyl acrylate (BA)-g-Saccaharum cilliare fibers using a redox initiator. Graft copolymers were characterized through FT-IR/SEM/TGA/DTA/DTG techniques, and the effect of grafting percentage on the water absorption properties of raw as well as grafted fibers was also investigated. 相似文献
92.
Manirul Islam Sanchita Mondal Paramita Mondal Anupam Singha Roy Kazi Tuhina Noor Salam Sumantra Paul Dildar Hossain Manir Mobarok 《Transition Metal Chemistry》2011,36(4):447-458
Immobilization of copper onto polystyrene provided a polymer-supported copper(II) catalyst, which was effective in cross-coupling
reactions between N-containing substrates and arylboronic acids using methanol as a solvent in air under base-free conditions. This catalyst
was also effective in N-arylation of imidazole with aryl halides in DMSO using K2CO3 as a base under nitrogen atmosphere. The catalyst was characterized by physico-chemical and spectroscopic techniques. The
product N-arylimidazoles and N-arylbenzimidazoles were isolated in good to excellent yields. This copper catalyst was air stable and could be recycled with
minimal loss of activity. 相似文献
93.
S. Das R. K. Singha S. Manna S. Gangopadhyay A. Dhar S. K. Ray 《Journal of nanoparticle research》2011,13(2):587-595
We have grown Ge nanocrystals (NCs) (4.0–9.0 nm in diameter) embedded in high-k HfO2 matrix for applications in floating gate memory devices. X-ray photoelectron spectroscopy has been used to probe the local
chemical bonding of Ge NCs. The analysis of Ge–Ge phonon vibration using Raman spectroscopy has shown the formation of compressively
stressed Ge NCs in HfO2 matrix. Frequency dependent electrical properties of HfO2/Ge-NCs in HfO2/HfO2 sandwich structures have been studied. An anticlockwise hysteresis in the capacitance–voltage characteristics suggests electron
injection and trapping in embedded Ge NCs. The role of interface states and deep traps in the devices has been thoroughly
examined and has been shown to be negligible on the overall device performance. 相似文献
94.
Sk Manirul Islam Manir Mobarok Paramita Mondal Anupam Singha Roy Noor Salam Dildar Hossain Sanchita Mondal 《Transition Metal Chemistry》2012,37(1):97-107
A tetradentate Schiff base (teta), obtained from triethylenetetramine and salicylaldehyde, has been covalently bonded to divinylbenzene
cross-linked chloromethylated polystyrene. This chelating ligand, abbreviated as PS-teta (PS = polymeric support), reacts
with metal chlorides (Cu2+, Co2+, and Ni2+) in methanol to give polymer-bound transition metal complexes, PS-Cu(II)teta/(Cat-1), PS-Ni(II)teta/(Cat-2), and PS-Co(II)teta/(Cat-3),
formation of which has been established by various physiochemical methods and spectroscopic techniques. The catalytic potential
of these materials has been tested for the oxidation of various alkenes, alkanes, alcohols, and thioethers in the presence
of 30% H2O2 as an oxidant. At the same time, these catalysts are very stable and could be reused in oxidation reactions for more than
five times without noticeable loss of their catalytic activity. 相似文献
95.
Priya Singh Dipanjan Mukherjee Subhankar Singha Ranjan Das Samir Kumar Pal 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(41):9728-9736
Enzyme-mediated catalysis is attributed to enzyme–substrate interactions, with models such as “induced fit” and “conformational selection” emphasizing the role of protein conformational transitions. The dynamic nature of the protein structure, thus, plays a crucial role in molecular recognition and substrate binding. As large-scale protein motions are coupled to water motions, hydration dynamics play a key role in protein dynamics, and hence, in enzyme catalysis. Here, microfluidic techniques and time-dependent fluorescence Stokes shift (TDFSS) measurements are employed to elucidate the role of nanoscopic water dynamics in the interaction of an enzyme, α-Chymotrypsin (CHT), with a substrate, Ala-Ala-Phe-7-amido-4-methylcoumarin (AMC) in the cationic reverse micelles of benzylhexadecyldimethylammonium chloride (BHDC/benzene) and anionic reverse micelles of sodium bis(2-ethylhexyl)sulfosuccinate (AOT/benzene). The kinetic pathways unraveled from the microfluidic setup are consistent with the “conformational selection” fit for the interaction of CHT with AMC in the cationic reverse micelles, whereas an “induced fit” mechanism is indicated for the anionic reverse micelles. In the cationic reverse micelles of BHDC, faster hydration dynamics (≈550 ps) aid the pathway of “conformational selection”, whereas in the anionic reverse micelles of AOT, the significantly slower dynamics of hydration (≈1600 ps) facilitate an “induced fit” mechanism for the formation of the final enzyme–substrate complex. The role of water dynamics in dictating the mechanism of enzyme–substrate interaction becomes further manifest in the neutral reverse micelles of Brij-30 and Triton X-100. In the former, the faster water dynamics aid the “conformational selection” pathway, whereas the significantly slower dynamics of water molecules in the latter are conducive to the “induced fit” mechanism in the enzyme–substrate interaction. Thus, nanoscopic water dynamics act as a switch in modulating the pathway of recognition of an enzyme (CHT) by the substrate (AMC) in reverse micelles. 相似文献
96.
97.
Joydeb Chanda Pulok K. Mukherjee Amit Kar Prasanta Kr. Maitra Seha Singha Pallab Kanti Halder Rahul Gajbhiye Ravichandiran Vishnuvardh 《Biomedical chromatography : BMC》2020,34(12):e4950
Coccinia grandis is an important food crop of the Cucurbitaceae family, widely used for culinary purposes in India. It is reported to possess hypoglycemic, hypolipidemic and antioxidant activities. The current study was aimed to explore the inhibition kinetics as well as major constituents of the active fraction of C. grandis against α-glucosidase. The kinetic study was performed through spectrophotometric assay, with p-nitrophenyl-α-d -glucopyranoside as a substrate with varying concentrations. An in vitro antioxidant study was performed by DPPH assay. In addition, UPLC–QTOF–MS analysis was carried out for metabolite profiling of the bioactive fraction of C. grandis. The results showed that the difference between the α-glucosidase inhibitory activity of the ethyl acetate fraction of C. grandis (EFCG) (IC50 2.43 ± 0.27 mg/ml), and standard inhibitor, acarbose (2.08 ± 0.19 mg/ml), was not statistically significant at a P-value of 0.05. The enzyme kinetics confirmed the inhibition mode in a mixed manner. The EFCG also showed the highest antioxidant activity (101.74 ± 1.95 μg/ml) among all of the fractions. A significant correlation between antioxidant and α-glucosidase inhibitory activity of EFCG was observed. The LC–QTOF–MS study of the EFCG putatively identified 35 metabolites, which may be responsible for its antioxidant and α-glucosidase inhibitory properties. Thus, C. grandis fruits can serve as a functional food to address diabetes-related disorders associated with α-glucosidase. 相似文献
98.
Tufan Singha Mahapatra Ananta Dey Harwinder Singh Sk Saddam Hossain Amal Kumar Mandal Amitava Das 《Chemical science》2020,11(4):1032
Despite the recent surge of interest in two-dimensional (2D) inorganic nanosheets derived from photoactive coordination polymers of lanthanide ions having interesting optical properties, research in this area is still in its infancy. Luminescent lanthanide ions, Eu(iii) or/and Tb(iii), as well as a bis-terpyridine ligand (L), were used in this study as the building blocks for the synthesis of the archetypical layered structure of coordination polymers (CPs) (L·Eu/L·Tb). 2D-nanosheets were obtained through exfoliation of the layered precursor of CPs in a suitable solvent system following a sonication-assisted strategy. These nanosheets exhibit lateral sizes on the micrometer scale (0.3–1 μm) and an ultrathin thickness of 2–6.5 nm. 1,1-Diamino-2,2-dinitroethene or FOX-7 is an insensitive high explosive; in a binder mixture, it exhibits a slightly superior detonation velocity of 8870 m s−1 in comparison to RDX. The insensitive nature of FOX-7 makes it a key component for the development of low vulnerable high explosive compositions for further application in weaponry. The growing demand for FOX-7, for use as a suitable replacement of conventional explosives, is of serious concern to human security. Achieving rapid and efficient detection of this unexplored explosive is a challenging task. In the present study, the developed luminescent nanosheets were used for the first time for micromolar level detection of FOX-7 both in solution and in the solid state. A visually distinct color change of the nanosheets from red (L·Eu) and green (L·Tb) to colorless was witnessed upon UV light irradiation during the detection process. Notably, the solid-state detection technique could be exploited for developing a commercial spray kit for quick onsite screening of this important explosive.A new class of luminescent lanthanide 2D nanosheets for detection of FOX-7. 相似文献
99.
Kaushik Sarkar Sovan K. Singha Shital K. Chattopadhyay 《Tetrahedron: Asymmetry》2009,20(15):1719-1721
A general route to α-, β- and γ-pyrrole-branched α-amino acid derivatives has been developed, which featured a one-pot ring-closing metathesis and aromatization reaction as the key step. 相似文献
100.
Polyvinyl alcohol (PVOH) membrane, was modified both physically and chemically by incorporation of inorganic filler, sodium aluminosilicate and chemical crosslinking with maleic acid and glutaraldehyde. The change of morphology and crystallinity of PVOH by this physical and chemical modification was studied by FTIR, DSC, TGA, SEM and XRD. These membranes were evaluated in terms of its potential for dehydration of dioxane by preferential sorption and permeation using pervaporation (PV) technique. These membranes were cast in the laboratory by solution casting from the polymer and other additives. The performance of the unfilled (containing no filler) glutaraldehyde (GA) crosslinked PVOH-1 and maleic acid (MA) crosslinked PVOH-2 membranes were compared with filled (containing aluminosilicate filler) but GA crosslinked PVOH-3 and filled but MA crosslinked PVOH-4 membranes. The filled membranes were found to show higher flux and water selectivity. Among all the four used membranes, the MA crosslinked filled PVOH-4 membrane was found to show best results in terms of both water selectivity and flux. 相似文献