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71.
Koushik Mazumder Swarbhanu Sarkar Asish Kumar Sen 《Journal of carbohydrate chemistry》2013,32(9):673-685
The terminal disaccharide of the O-antigenic polysaccharide of Vibrio cholerae O37, 4-O-methyl-α-D-QuiNAc-(1→4)-α-d-QuiNAc, was synthesized as methyl glycoside involving glycosylation between glycosyl donor ethyl 2-azido-3-O-benzyl-2,6-dideoxy-4-O-methyl-6-iodo-1-thio-α-d-glucopyranoside and glycosyl acceptor methyl 2-azido-3-O-benzyl-2,6-dideoxy-6-iodo-α-d-glucopyranoside. Dehalogenation, global deprotection, and reduction of the azide to amine were effected in one step by catalytic hydrogenation. It was followed by selective N-acetylation to give the desired deprotected disaccharide. 相似文献
72.
Nairwita Mazumder Ritabrata Biswas Subenoy Chakraborty 《General Relativity and Gravitation》2011,43(5):1337-1345
The work deals with the thermodynamics of the universe bounded by the event horizon. The matter in the universe has three
constituents namely dark energy, dark matter and radiation in nature and interaction between then is assumed. The variation
of entropy of the surface of the horizon is obtained from unified first law while matter entropy variation is calculated from
the Gibbss’ law. Finally, validity of the generalized second law of thermodynamics is examined and conclusions are written
point wise. 相似文献
73.
Manisha Samanta Koushik Pal Umesh V. Waghmare Kanishka Biswas 《Angewandte Chemie (International ed. in English)》2020,59(12):4822-4829
A challenge in thermoelectrics is to achieve intrinsically low thermal conductivity in crystalline solids while maintaining a high carrier mobility (μ). Topological quantum materials, such as the topological insulator (TI) or topological crystalline insulator (TCI) can exhibit high μ. Weak topological insulators (WTI) are of interest because of their layered hetero‐structural nature which has a low lattice thermal conductivity (κlat). BiTe, a unique member of the (Bi2)m(Bi2Te3)n homologous series (m:n=1:2), has both the quantum states, TCI and WTI, which is distinct from the conventional strong TI, Bi2Te3 (where m:n=0:1). Herein, we report intrinsically low κlat of 0.47–0.8 W m?1 K?1 in the 300–650 K range in BiTe resulting from low energy optical phonon branches which originate primarily from the localized vibrations of Bi bilayer. It has high μ≈516 cm2 V?1 s?1 and 707 cm2 V?1 s?1 along parallel and perpendicular to the spark plasma sintering (SPS) directions, respectively, at room temperature. 相似文献
74.
Md. Hasan Zahir K. Alhooshani Mohammad A. Jafar Mazumder Toshio Suzuki 《Kinetics and Catalysis》2013,54(5):578-585
The Ga2O3-Al2O3-ZnO (GAZ) multi-component spinel powders with incorporated Cu2+, Co2+, Fe2+, Ni2+, Mn2+ and In2+ metal cations were synthesized by co-precipitation method from a mixed solution of nitrate salts. Spinel crystal structure of each composition was confirmed by XRD measurements. The multi-component oxide powders were tested in the reduction of nitrogen oxide (NO) under lean conditions. Among the catalysts tested, In2O3-containing GAZ with a pure spinel phase structure showed promising catalytic activity in the NO reduction in the presence of 10% H2O vapor. In addition, the effect of H2O vapor and SO2 on the selective reduction of NO over In2O3-GAZ/cordierite and In2O3-GAZ/metal honeycombs catalysts has been investigated. 相似文献
75.
Ghosh K Yang HB Northrop BH Lyndon MM Zheng YR Muddiman DC Stang PJ 《Journal of the American Chemical Society》2008,130(15):5320-5334
The synthesis of a new 120 degree diplatinum(II) acceptor unit and the self-assembly of a series of two-dimensional metallacyclic polypseudorotaxanes that utilize both metal-ligand and crown ether-dialkylammonium noncovalent interactions are described. Judiciously combining complementary diplatinum(II) acceptors with bispyridyl donor building blocks, with an acceptor and/or donor possessing a pendant dibenzo[24]crown-8 (DB24C8) moiety, allows for the formation of three new rhomboidal bis-DB24C8, one new hexagonal tris-DB24C8, and four new hexakis-DB24C8 metallacyclic polygons in quantitative yields. The size and shape of each assembly, as well as the location and stoichiometry of the DB24C8 macrocycle, can be precisely controlled. Each polygon is able to complex two, three, or six dibenzylammonium ions without disrupting the underlying metallacyclic polygons, thus producing eight different poly[2]pseudorotaxanes and demonstrating the utility and scope of this orthogonal self-assembly technique. The assemblies are characterized with one-dimensional multinuclear ((1)H and (31)P) and two-dimensional ((1)H-(1)H COSY and NOESY) NMR spectroscopy as well as mass spectrometry (ESI-MS). Further analysis of the size and shape of each assembly is obtained through molecular force-field simulations. (1)H NMR titration experiments are used to establish thermodynamic binding constants and poly[2]pseudorotaxane/dibenzylammonium stoichiometries. Factors influencing the efficiency of poly[2]pseudorotaxane formation are discussed. 相似文献
76.
A methodology for monitoring low level of caffeine in aqueous samples via gas chromatography coupled with an ion-trap tandem
mass spectrometry detection system (IT-MS/MS) was developed. Four IT-MS/MS operating parameters, including the collision-induced
dissociation (CID) voltage, the excitation time (ET), the isolation time (IT) and the maximum ionization time (MIT) were optimized
in order to maximize the sensitivity of the IT-MS/MS technique towards the analyte and its isotope-labeled standard. After
optimization, a limit of detection of 500 fg μl−1 with S/N = 3 was achieved. Taking into account blank values and the matrix background, a method detection limit of 1.0–2.0 ng l−1 was derived and applied to all of the samples analyzed in the study. Various mass spectrometric conditions have been applied
to caffeine and its trimethyl-13C-labeled standard to elucidate fragmentation pathways for new and commonly occurring product ions observed in the collision-induced
dissociation (CID) spectra produced by the ion trap. Ion structures and fragmentation pathway mechanisms have been proposed
and compared with previously published data. An isotope dilution method using 13C-labeled caffeine as a surrogate internal standard was employed to determine and correct the recovery of native caffeine
in water samples. The developed methodology has been applied for the determination of caffeine in surface marine and freshwater
samples collected on the west coast of Vancouver Island in British Columbia, Canada. The results obtained for the marine water
samples indicated a wide variation in the level of caffeine, ranging from 4.5 to 149 ng l−1, depending on the location of the sampling site within the inlet. The concentrations of caffeine in samples from lakes associated
with various residential densities ranged from ND to 6.5, 1.8 to 10.4 and 6.1 to 21.7 ng l−1 for low, moderate and high residential densities, respectively. 相似文献
77.
A supramolecular gel results from the immobilization of solvent molecules on a 3D network of gelator molecules stabilized by various supramolecular interactions that include hydrogen bonding, π–π stacking, van der Waals interactions, and halogen bonding. In a metallogel, a metal is a part of the gel network as a coordinated metal ion (in a discrete coordination complex), as a cross‐linking metal node with a multitopic ligand (in coordination polymer), and as metal nanoparticles adhered to the gel network. Although the field is relatively new, research into metallogels has experienced a considerable upsurge owing to its fundamental importance in supramolecular chemistry and various potential applications. This focus review aims to provide an insight into the development of designing metallogelators. Because of the limited scope, discussions are confined to examples pertaining to metallogelators derived from discrete coordination complexes, organometallic gelators, and coordination polymers. This review is expected to enlighten readers on the current development of designing metallogelators of the abovementioned class of molecules. 相似文献
78.
Umme Solaem Akond Koushik Barman Abhinandan Mahanta Sk. Jasimuddin 《Electroanalysis》2021,33(4):900-908
p-Nitrophenol (p−NP) is a high priority toxic pollutant and that has harmful effects on human, animals and plants. Thus, the detection and determination of p−NP present in the environment is an urgent as well as highly important requisite. The present article, therefore focused on the construction of a novel electrochemical sensor based on NiO nanoparticles/α-cyclodextrin functionalized reduced graphene oxide modified glassy carbon electrode (NiO−NPs-α-CD-rGO-GCE) for the selective and sensitive detection of p−NP. UV-vis, high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction pattern (SAED) and X-ray diffraction (XRD) analysis confirms the formation of highly pure NiO nanoparticles. Field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), and cyclic voltammetry (CV) were used to characterize the step-wise electrode modification process. DPV was carried out to quantify p−NP within the concentration range of 1−10 μM and found the detection limit of 0.12 nM on the basis of the signal-to-noise ratio S/N=3. The electrode can able to detect different isomers of nitrophenols. Interferences of other pollutants such as phenol, p-aminophenol, o- and m- nitrophenol, 4-chlorophenol, 2,6-dichlorophenol and ions like K+, Cd2+, Cl−, SO42− did not affect the sensing of p−NP. The newly developed sensor exhibited diffusion controlled kinetics and had excellent sensitivity, selectivity and reproducibility for the detection of p−NP. The electrode showed good recoveries in real sample analysis. 相似文献
79.
[reaction: see text] Self-recognition in the coordination-driven self-assembly of three-dimensional (3-D) polyhedra is described. Multiple discrete 3-D polyhedra were formed in one vessel through the self-recognition of a mixture of subunits. The dynamic self-recognition process is determined by the information stored within the geometry and directionality of multiple rigid building blocks as well as the thermodynamic stability of the discrete products. 相似文献
80.
Ayre GN Uchino T Mazumder B Hector AL Hutchison JL Smith DC Ashburn P de Groot CH 《J Phys Condens Matter》2011,23(39):394201
This work examines the recent developments in non-traditional catalyst-assisted chemical vapour deposition of carbon nanotubes (CNTs) with a view to determining the essential role of the catalyst in nanotube growth. A brief overview of the techniques reliant on the structural reorganization of carbon to form CNTs is provided. Additionally, CNT synthesis methods based upon ceramic, noble metal, and semiconducting nanoparticle catalysts are presented. Experimental evidence is provided for CNT growth using noble metal and semiconducting nanoparticle catalysts. A model for CNT growth consistent with the experimental results is proposed, in which the structural reorganization of carbon to form CNTs is paramount. 相似文献