排序方式: 共有33条查询结果,搜索用时 15 毫秒
11.
Tuhina Banerjee 《Thermochimica Acta》2004,411(2):195-201
A differential scanning calorimetry study on the thermal denaturation of concanavalin A at pH 5.2 where it exists in the dimeric form was carried out. The calorimetric transitions were observed to be irreversible and the transition temperature of the protein increased with increasing scan rate, indicating that the thermal denaturation process is under kinetic control. The thermal unfolding, and its scan rate dependence could be explained according to the kinetic scheme with k as first-order kinetic constant whose change with temperature is given by the Arrhenius equation. Using this model, rate constant as a function of temperature and activation energy of the process have been calculated. The average activation energy of the kinetic process using different approaches is 129±10 kJ mol−1. The differential scanning calorimetric results on transition temperatures and calorimetric enthalpies supported by intrinsic fluorescence indicate that the irreversibility in the calorimetric transitions of concanavalin A includes a combination of post-transition aggregation, chain separation and loss of cofactor. 相似文献
12.
Manirul Islam Paramita Mondal Anupam Singha Roy Kazi Tuhina 《Transition Metal Chemistry》2010,35(4):491-499
A poly(3,6-dibenzaldimino N-vinyl carbazole) Pd(II) complex has been synthesized and characterized by physicochemical and
spectroscopic techniques. The complex was found to be highly active toward hydrogenation reactions of various organic substrates
under atmospheric pressure at ambient temperature. A tentative reaction mechanism is proposed on the basis of kinetic studies
and isolation of reactive intermediates. The catalyst shows good conversion rates, thermal stability and recyclability. 相似文献
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14.
Sk.Manirul Islam Sanchita Mondal Paramita Mondal Anupam Singha Roy K. Tuhina Noor Salam Manir Mobarak 《Journal of organometallic chemistry》2012,696(26):4264-4274
A simple and industrially viable protocol for C–N and C–O coupling was reported here. The polymer supported heterogeneous copper catalyst was prepared from chloromethyl polystyrene using a simple procedure. O-Arylation of substituted phenols with various aryl halides was achieved using this copper catalyst in DMSO medium. This heterogeneous copper catalyst, also efficiently works for the N-arylation of N–H heterocycles with aryboronic acids in methanol. This catalyst was also effective in amination reaction of primary amines with aryl halides as well as arylboronic acids in DMSO medium. The effects of solvent, base and temperature for the O-Arylation and amination reactions were reported. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused up to several times without sufficient loss of its catalytic activity. 相似文献
15.
A novel polystyrene-supported palladium(II) complex, an excellent and recyclable catalyst, was synthesized for Sonogashira reactions. The present complex shows high catalytic activity for Sonogashira cross-coupling reaction of aryl halides with phenylacetylene under phosphine-free and copper-free reaction conditions in aqueous (DMF–H2O) medium. The catalyst could be reused for at least six reaction cycles with almost unchanged catalytic properties.
16.
The effect on the hydrogen storage attributes of magnesium hydride (MgH2) of the substitution of Mg by varying fractions of Al and Si is investigated by an ab initio plane‐wave pseuodopotential method based on density functional theory. Three supercells, namely, 2×2×2, 3×1×1 and 5×1×1 are used for generating configurations with varying amounts (fractions x=0.0625, 0.1, and 0.167) of impurities. The analyses of band structure and density of states (DOS) show that, when a Mg atom is replaced by Al, the band gap vanishes as the extra electron occupies the conduction band minimum. In the case of Si‐substitution, additional states are generated within the band gap of pure MgH2—significantly reducing the gap in the process. The reduced band gaps cause the Mg? H bond to become more susceptible to dissociation. For all the fractions, the calculated reaction energies for the stepwise removal of H2 molecules from Al‐ and Si‐substituted MgH2 are much lower than for H2 removal from pure MgH2. The reduced stability is also reflected in the comparatively smaller heats of formation (ΔHf) of the substituted MgH2 systems. Si causes greater destabilization of MgH2 than Al for each x. For fractions x=0.167 of Al, x=0.1, 0.167 of Si (FCC) and x=0.0625, 0.1 of Si (diamond), ΔHf is much less than that of MgH2 substituted by a fraction x=0.2 of Ti (Y. Song, Z. X. Guo, R. Yang, Mat. Sc. & Eng. A 2004 , 365, 73). Hence, we suggest the use of Al or Si instead of Ti as an agent for decreasing the dehydrogenation reaction and energy, consequently, the dehydrogenation temperature of MgH2, thereby improving its potential as a hydrogen storage material. 相似文献
17.
Piyali Bhar Farook Rahaman Tuhina Manna Ayan Banerjee 《The European Physical Journal C - Particles and Fields》2016,76(12):708
In this article, we study the possibility of sustaining static and spherically symmetric traversable wormhole geometries admitting conformal motion in Einstein gravity, which presents a more systematic approach to search a relation between matter and geometry. In wormhole physics, the presence of exotic matter is a fundamental ingredient and we show that this exotic source can be dark energy type which support the existence of wormhole spacetimes. In this work we model a wormhole supported by dark energy which admits conformal motion. We also discuss the possibility of the detection of wormholes in the outer regions of galactic halos by means of gravitational lensing. Studies of the total gravitational energy for the exotic matter inside a static wormhole configuration are also performed. 相似文献
18.
Dr. Tanveer Hussain Dr. Tuhina Adit Maark Dr. Sudip Chakraborty Prof. Rajeev Ahuja 《Chemphyschem》2015,16(12):2557-2561
A thorough study of the structural, electronic, and hydrogen‐desorption properties of β‐ and γ‐MgH2 phases substituted by selected transition metals (TMs) is performed through first‐principles calculations based on density functional theory (DFT). The TMs considered herein include Sc, V, Fe, Co, Ni, Cu, Y, Zr, and Nb, which substitute for Mg at a doping concentration of 3.125 % in both the hydrides. This insertion of TMs causes a variation in the cell volumes of β‐ and γ‐MgH2. The majority of the TM dopants decrease the lattice constants, with Ni resulting in the largest reduction. From the formation‐energy calculations, it is predicted that except for Cu and Ni, the mixing of all the selected TM dopants with the MgH2 phases is exothermic. The selected TMs also influence the stability of both β‐ and γ‐MgH2 and cause destabilization by weakening the Mg?H bonds. Our results show that doping with certain TMs can facilitate desorption of hydrogen from β‐ and γ‐MgH2 at much lower temperatures than from their pure forms. The hydrogen adsorption strengths are also studied by density‐of‐states analysis. 相似文献
19.
Amalesh Roy Kazi Tuhina Bidyut Biswas Ramanathapuram V. Venkateswaran 《Tetrahedron》2012,68(32):6575-6580
A novel radical induced fragmentation in a benzoxocane ring system has been employed for a synthesis of elvirol 8 and an advanced intermediate in the synthesis of 7,8-dihydroxycalamenene 20. The coumarins 9, 22 were taken through a sequence of reactions to the benzoxocanols 16, 30, which when subjected to Barton’s deoxygenation conditions involving conversion to the corresponding thionocarbonates 17, 31 followed by exposure to tri-n-butyltin hydride, underwent a radical induced fragmentation to furnish elvirol 8 and the curcuphenol derivative 32, which was converted to the dimethoxy compound 33. This had served as an advanced intermediate in a previous synthesis of dihydroxycalamenene. 相似文献
20.
Tiwari Tuhina Chauhan Jagdish Kumar Yadav Madhavi Kumar Manindra Srivastava Neelam 《Ionics》2017,23(10):2809-2815
Ionics - Energy devices are the lifeline of today’s society, and hence, they are produced in large number resulting in tremendous increase of chemical garbage. Hence, the scientific community... 相似文献