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排序方式: 共有212条查询结果,搜索用时 15 毫秒
161.
Dibyajyoti Haldar Dwaipayan Sen Kalyan Gayen 《Applied biochemistry and biotechnology》2017,181(4):1416-1434
Present study is a critical analysis and subsequent development of an analytical tool to measure the total sugar concentration in a carbohydrate mixture comprising both hexose and pentose. For this purpose, individual sugars were measured and standardized with anthrone reagent prepared in an ice-cold 98 % sulphuric acid followed by 3 min of boiling. Furthermore, regression analysis was performed after mathematical manipulation with the individual standards to formulate a linear relation between the absorbance of the mixture and its concentration, which satisfies Beer’s law. It was found that the correlation coefficient for the equation is 0.973, when confidence interval was set at 0.95. The validation was done with a synthetic mixture of concentrations at 0.17 and 0.22 g/L (as range was ensured between 0.1 and 0.3 g/L) and also with the carbohydrate mixture as the prehydrolyzate obtained after the pretreatment of banana stem, which showed around 94.1 % accuracy and higher sensitivity with the cellulose present in the mixture. Thus, the method is evident to quantify the total sugars accurately obtained from hydrolyzed lignocellulosic biomass. 相似文献
162.
Dr. Stefan M. Marschner Dr. Ritesh Haldar Dr. Olaf Fuhr Prof. Dr. Christof Wöll Prof. Dr. Stefan Bräse 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(4):1390-1401
Differently functionalized porphyrin linkers represent the key compounds for the syntheses of new porphyrin-based metal–organic frameworks (MOFs), which have gathered great interest within the last two decades. Herein we report the synthesis of a large range of 5,15-bis(4-ethoxycarbonylphenyl)porphyrin derivatives, through Suzuki and Sonogashira cross-coupling reactions of an easily accessible corresponding meso-dibrominated trans-A2B2-porphyrin with commercially available boronic acids or terminal alkynes. The resulting porphyrins were fully characterized through NMR, MS, and IR spectroscopy and systematically investigated through UV/Vis absorption. Finally, selected structures were saponified to the corresponding carboxylic acids and subsequently proven to be suitable for the synthesis of surface-anchored MOF thin films. 相似文献
163.
Flexible and Rigid Amine‐Functionalized Microporous Frameworks Based on Different Secondary Building Units: Supramolecular Isomerism,Selective CO2 Capture,and Catalysis
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Ritesh Haldar Dr. Sandeep K. Reddy Venkata M. Suresh Dr. Sudip Mohapatra Prof. Sundaram Balasubramanian Prof. Tapas Kumar Maji 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(15):4347-4356
We report the synthesis, structural characterization, and porous properties of two isomeric supramolecular complexes of ([Cd(NH2?bdc)(bphz)0.5]?DMF?H2O}n (NH2?bdc=2‐aminobenzenedicarboxylic acid, bphz=1,2‐bis(4‐pyridylmethylene)hydrazine) composed of a mixed‐ligand system. The first isomer, with a paddle‐wheel‐type Cd2(COO)4 secondary building unit (SBU), is flexible in nature, whereas the other isomer has a rigid framework based on a μ‐oxo‐bridged Cd2(μ‐OCO)2 SBU. Both frameworks are two‐fold interpenetrated and the pore surface is decorated with pendant ?NH2 and ?N?N? functional groups. Both the frameworks are nonporous to N2, revealed by the type II adsorption profiles. However, at 195 K, the first isomer shows an unusual double‐step hysteretic CO2 adsorption profile, whereas the second isomer shows a typical type I CO2 profile. Moreover, at 195 K, both frameworks show excellent selectivity for CO2 among other gases (N2, O2, H2, and Ar), which has been correlated to the specific interaction of CO2 with the ?NH2 and ?N?N? functionalized pore surface. DFT calculations for the oxo‐bridged isomer unveiled that the ?NH2 group is the primary binding site for CO2. The high heat of CO2 adsorption (ΔHads=37.7 kJ mol?1) in the oxo‐bridged isomer is realized by NH2???CO2/aromatic π???CO2 and cooperative CO2???CO2 interactions. Further, postsynthetic modification of the ?NH2 group into ?NHCOCH3 in the second isomer leads to a reduced CO2 uptake with lower binding energy, which establishes the critical role of the ?NH2 group for CO2 capture. The presence of basic ?NH2 sites in the oxo‐bridged isomer was further exploited for efficient catalytic activity in a Knoevenagel condensation reaction. 相似文献
164.
Regio‐ and Diastereoselective and Enantiospecific Metal‐Free C(sp3)H Arylation: Facile Access to Optically Active 5‐Aryl 2,5‐Disubstituted Pyrrolidines
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Surajit Haldar Subhra Kanti Roy Bholanath Maity Prof. Dr. Debasis Koley Prof. Dr. Chandan K. Jana 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(43):15290-15298
Optically active 5‐aryl 2,5‐disubstituted pyrrolidines are the principal structural moiety of many bioactive compounds including natural products and catalysts for asymmetric synthesis. A highly regio‐ and diastereoselective and enantiospecific method for direct C?H arylation of aliphatic amine has been developed. Structurally diverse enantiopure arylated pyrrolidines were synthesized from commercially available starting materials, through a single‐step three‐component reaction under metal‐ and oxidant‐free conditions. Furthermore, the complex analogous structure of CCK antagonist RP 66803 and angiotensin‐converting enzyme inhibitors was easily constructed using the synthesized arylated pyrrolidine derivative. Detailed theoretical calculations (M06‐2X/TZVPP/SMD//M06‐2X/6‐31+G(d,p) level) were also carried to investigate the mechanism and high level of stereocontrol involved in this direct sp3 C?H arylation reaction. Preference for a given regio‐ and stereoselectivity in the arylated product can be explained through elucidation of the mechanism for dehydration, generating azomethine ylide, and for the final re‐aromatization step. The calculated energies reveals that the re‐aromatization step is essentially rate determining, accompanying an activation barrier of Δ≠${G{{{\rm S}\hfill \atop {\rm L}\hfill}}}$ =25.6 kcal mol?1. 相似文献
165.
Pronounced Fluctuations of Target Fragments in Forward Hemisphere Only in Ultra Relativistic Nuclear Collision
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Dipak Ghosh Argha Dev Samabrata Sarkar Prabir Kumar Haldar 《中国物理快报》2006,23(6):1441-1444
Dynamical fluctuation of target evaporated black particles is investigated in both forward and backward hemispheres within the framework of multi-dimensional factorial moment methodology using the brilliant concept of the Hurst exponent. We analyse the black particles emitted in ^32S-AgBr interactions at 200AGeV and it is evident that the dynamical fluctuation in the backward hemisphere is self-affine. In the forward hemisphere, dynamical fluctuation is self-similar but not self-affine. However, study indicates that the fluctuation in the forward hemisphere is more pronounced than that in backward hemisphere. 相似文献
166.
Dipak Ghosh Argha Deb Prabir Kumar Haldar Sima Guptaroy 《中国物理快报》2006,23(4):815-818
We presents the analysis of ring-like and jet-like events in terms of Scaled Factorial Moments (SFMs) in one dimensional space up to the sixth order of moments for ^32S-AgBr interactions at 200 AGeV energy. The study reveals a power law growth of SFMs with decreasing bin width of the azimuthal distribution in the ^32S- AgBr data at 200 AGeV in both the cases. It is seen that strong intermittent pattern is revealed only in jet-like events. 相似文献
167.
K. Haldar 《Journal of Applied Mathematics and Computing》2003,12(1-2):267-279
The present investigation deals with the application of Adomian's decomposition method to blood flow through a constricted artery in the presence of an external transverse magnetic field which is applied uniformly. The blood flowing through the tube is assumed to be Newtonian in character. The expressions for the two-term approximation to the solution of stream function, axial velocity component and wall shear stress are obtained in this analysis. The numerical solutions of the wall shear stress for different values of Reynold number and Hartmann number are shown graphically. The solution of this theoretical result for a particular Hartmann number is compared with the integral method solution of Morgan and Young [17]. 相似文献
168.
Enhancing Selectivity and Kinetics in Oxidative Photocyclization by Supramolecular Control
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Dr. Ritesh Haldar Dr. Stéphane Diring Dr. Pralok K. Samanta Marius Muth William Clancy Antoine Mazel Dr. Sabine Schlabach Frank Kirschhöfer Dr. Gerald Brenner‐Weiß Prof. Dr. Swapan K. Pati Prof. Dr. Fabrice Odobel Prof. Dr. Christof Wöll 《Angewandte Chemie (International ed. in English)》2018,57(41):13662-13665
Photochemical reactions typically proceed via multiple reaction pathways, yielding a variety of isomers and products. Enhancing the selectivity is challenging. Now, the potential of supramolecular control for oxidative photocyclization of a tetraarylethylene, containing a stereogenic ?C=C? bond, is demonstrated. In solution, this photochemical reaction produces three constitutional isomers (substituted phenanthrenes), with slow kinetics. When the reactant is assembled into a crystalline framework, only one product forms with accelerated kinetics. Key to this selectivity enhancement is the integration into a surface grown metal–organic framework (SURMOF); the dramatic gain in selectivity is ascribed to the hindrance of the rotational freedom of the ?C=C? double bond. The structure of the MOF is key; the corresponding reaction in the solid does not result in such a high increase in selectivity. A striking change of luminescence properties after photocyclization is observed. 相似文献
169.
Usharani Subuddhi Sourav Haldar S. Sankararaman Ashok K. Mishra 《Journal of photochemistry and photobiology. A, Chemistry》2008,200(2-3):381-387
The applicability of 1-(4-N,N-dimethylaminophenylethynyl)pyrene (DMAPEPy), a pyrene derivative showing intramolecular charge transfer, as a prospective probe for lipid bilayer membranes has been evaluated. High sensitivity of DMAPEPy to solvent polarity and viscosity makes it to act both as a polarity-sensitive probe and as a fluorescence anisotropy probe. The molecule shows high partition efficiency towards bilayer membranes in both solid gel as well as in the liquid crystalline phases. The emission spectrum, quenching experiment and lifetime data suggest bimodal distribution of DMAPEPy in the bilayer. Using the solvent polarity scales the polarity parameters of the two locations in lipid bilayer have been estimated. In the bilayer environment it exhibits remarkable spectral changes with temperature. The thermotropic phase change of the bilayer is sensitively monitored by fluorescence intensity as well as fluorescence anisotropy parameters. DMAPEPy is also capable of sensing the changes induced by membrane modifiers like cholesterol. 相似文献
170.
The present study reports the shell thickness dependence fluorescence resonance energy transfer between Rhodamine 6G dye and Au@SnO2 core–shell nanoparticles. There is a pronounced effect on the PL quenching and shortening of the lifetime of the dye in presence of Au@SnO2 core–shell nanoparticles. The calculated energy transfer efficiencies from dye to Au@SnO2 are 64.4% and 78.3% for 1.5 nm and 2.5 nm thickness of shell, respectively. Considering the interactions of single acceptor and multiple donors, the calculated average distances (rn) are 75.8 and 71.5 Å for 1.5 nm and 2.5 nm thick core–shell Au@SnO2 nanoparticles, respectively. 相似文献