Bairatisal, India

North Bengal University

www.nbu.ac.in
Bairatisal, India

University of North Bengal is a state university, situated at Raja Rammohanpur near Siliguri in Darjeeling district in the Indian state of West Bengal. While the second campus of the university is situated at Danguajhar, Jalpaiguri in Jalpaiguri district in the Indian state of West Bengal. The university was established in 1962 with a goal to disseminate knowledge to fulfill growing socio-economic and technical manpower needs in the six North Bengal districts and the neighbouring state of Sikkim. Currently, colleges from Alipurduar, Cooch Behar, Jalpaiguri and Darjeeling districts are affiliated to this university. North Bengal University offers degrees in undergraduate, post graduate, M. Phil and doctorate programs. Wikipedia.

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Mandal B.,Surya Sen College | Basu B.,North Bengal University
RSC Advances | Year: 2014

Organic compounds possessing S-S bonds, often called disulfides or more specifically disulfanes, have been widely applied in various fields ranging from biochemistry to different industrially important polymers, used as synthetic intermediates in other fine chemicals such as catenanes, rotaxanes, micelles, and also in areas like peptidomimetics, self-assembled monolayers (SAMs) etc. Such versatile applications have steered the development of several new methods for the preparation of organic disulfides. The present review has attempted to comprehensively summarize recent advances in the process of S-S bond formation, highlighting plausible mechanistic considerations, scope and limitations. © 2014 The Royal Society of Chemistry.


Precise measurements on electrical conductance (λ) of solutions of an ionic liquid (IL) tetrabutylphosphonium tetrafluoroborate in acetonitrile (ACN), tetrahydrofuran (THF), and 1,3-dioxolane (1,3-DO) and their binary mixtures have been reported at 298.15 K. The conductance data have been analyzed by the Fuoss conductance equation (1978) in terms of the limiting molar conductance (λo), the association constant (KA), and the association diameter (R) for ion-pair formation. The Walden product is obtained and discussed. However, the deviation of the conductometric curves (λ versus √c) from linearity for the electrolyte in THF and 1,3-DO and their binary mixtures indicated triple-ion formation and therefore the corresponding conductance data have been analyzed by the Fuoss-Kraus theory of triple ions. The limiting ionic conductances (λo ±) have been estimated from the appropriate division of the limiting molar conductivity value of tetrabutylammonium tetraphenylborate [Bu4NBPh4] as the "reference electrolyte" method along with a numerical evaluation of ion-pair and triple-ion formation constants (KP ≈ KA and KT). The results have been discussed in terms of solvent properties and configurational theory. Ionic association in the limiting molar conductances as well as the single-ion conductivity values have been determined for the electrolyte in the solvent media. © 2012 American Chemical Society.


Paul S.,North Bengal University | Basu B.,North Bengal University
Tetrahedron Letters | Year: 2011

A facile and expeditious solid-phase synthesis of libraries of quinoxalines promoted on KF-alumina surface via tandem oxidation-condensation or condensation reactions is reported. The reaction protocol is operationally simple and mild. Moreover, solvent-free reaction condition makes the reaction procedure eco-friendly and economically viable. © 2011 Elsevier Ltd. All rights reserved.


Nandi K.K.,North Bengal University | Bhadra A.,North Bengal University
Physical Review Letters | Year: 2012

A Comment on the Letter by P.D. Mannheim and J.G. O'Brien, Phys. Rev. Lett.PRLTAO0031-9007 106, 121101 (2011). © 2012 American Physical Society.


Paul B.C.,North Bengal University | Ghose S.,North Bengal University
General Relativity and Gravitation | Year: 2010

We obtain cosmological solutions which admit emergent universe (EU) scenario in the framework of Einstein Gauss-Bonnet (GB) gravity coupled with a dilaton field in 4-dimensions. The coupling parameter of the GB terms and the dilaton in the theory are determined for obtaining an EU scenario. The corresponding dilaton potential which admits such scenario is determined. It is found that the GB terms coupled with a dilaton field plays an important role in describing the dynamics of the evolution of the early as well as the late universe. We note an interesting case where the GB term dominates initially in the asymptotic past regime, subsequently it decreases and thereafter its contribution in determining the dynamics of the evolution dominates once again. We note that the Einstein's static universe solution permitted here is unstable which the asymptotic EU might follow. We also compare our EU model with supernova data. © Springer Science+Business Media, LLC 2009.


Paul S.,North Bengal University | Misra A.,North Bengal University
Inorganic Chemistry | Year: 2011

All-metal aromatic molecules are the latest inclusion in the family of aromatic systems. Two different classes of all-metal aromatic clusters are primarily identified: one is aromatic only in the low spin state, and the other shows aromaticity even in high-spin situations. This observation prompts us to investigate the effect of spin multiplicity on aromaticity, taking Al 4 2-, Te 2As 2 2-, and their copper complexes as reference systems. Among these clusters, it has been found that the molecules that are aromatic only in their singlet state manifest antiaromaticity in their triplet state. The aromaticity in the singlet state is characterized by the diatropic ring current circulated through the bonds, which are cleaved to generate excess spin density on the atoms in the antiaromatic triplet state. Hence, in such systems, an antagonistic relationship between aromaticity and high-spin situations emerges. On the other hand, in the case of triplet aromatic molecules, the magnetic orbitals and the orbitals maintaining aromaticity are different; hence, aromaticity is not depleted in the high-spin state. The nonlinear optical (NLO) behavior of the same set of clusters in different spin states has also been addressed. We correlate the second hyperpolarizability and spin density in order to judge the effect of spin multiplicity on thirdórder NLO response. This correlation reveals a high degree of NLO behavior in systems with excess spin density. The variance of aromaticity and NLO response with spin multiplicity is found to stem from a single aspect, the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), and eventually the interplay among aromaticity, magnetism, and NLO response in such materials is established. Hence, the HOMO-LUMO energy gap becomes the cornerstone for tuning the interplay. This correlation among the said properties is not system-specific and thus can be envisaged even beyond the periphery of all-metal aromatic clusters. Such interplay is of crucial importance in tailoring novel paradigm of multifunctional materials. © 2011 American Chemical Society. © 2011 American Chemical Society. © 2011 American Chemical Society.


Mali P.,North Bengal University | Mukhopadhyay A.,North Bengal University
Physica A: Statistical Mechanics and its Applications | Year: 2014

The multifractal detrended fluctuation analysis technique is employed to analyze the time series of gold consumer price index (CPI) and the market trend of three world's highest gold consuming countries, namely China, India and Turkey for the period: 1993-July 2013. Various multifractal variables, such as the generalized Hurst exponent, the multifractal exponent and the singularity spectrum, are calculated and the results are fitted to the generalized binomial multifractal (GBM) series that consists of only two parameters. Special emphasis is given to identify the possible source(s) of multifractality in these series. Our analysis shows that the CPI series and all three market series are of multifractal nature. The origin of multifractality for the CPI time series and Indian market series is found due to a long-range time correlation, whereas it is mostly due to the fat-tailed probability distributions of the values for the Chinese and Turkey markets. The GBM model series more or less describes all the time series analyzed here. © 2014 Elsevier B.V. All rights reserved.


Paul S.,North Bengal University | Misra A.,North Bengal University
Journal of Chemical Theory and Computation | Year: 2012

This work develops a formalism to quantify the interaction among unpaired spins from the ground state spin topology. Magnetic systems where the spins are coupled through direct exchange and superexchange are chosen as references. Starting from a general Hamiltonian, an effective Hamiltonian is obtained in terms of spin density which is utilized to compute exchange coupling constants in magnetic systems executing direct exchange. The high-spin-low-spin energy gap, required to extract the coupling constant, is obtained through the broken symmetry approach within the framework of density functional theory. On the other hand, a perturbative approach is adopted to address the superexchange process. Spin transfer in between the sites in the exchange pathway is found to govern the magnetic nature of a molecule executing superexchange. The metal-ligand magnetic interaction is estimated using the second order perturbation energy for ligand to metal charge transfer and spin densities on the concerned sites. Using the present formalism, the total coupling constant in a superexchange process is also partitioned into the contributions from metal-ligand and metal-metal interactions. Sign and magnitude of the exchange coupling constants, derived through the present formalism, are found to be in parity with those obtained using the well-known spin projection technique. Moreover, in all of the cases, the ground state spin topology is found to complement the sign of coupling constants. Thus, the spin topology turns into a simple and logical means to interpret the nature of exchange interaction. The spin density representation in the present case resembles McConnell's spin density Hamiltonian and in turn validates it. © 2012 American Chemical Society.


Basu B.,North Bengal University | Paul S.,North Bengal University
Applied Organometallic Chemistry | Year: 2013

An improved and eco-friendly procedure has been developed to generate mesoporous silica-supported palladium nanoparticles (SiO2@PdNP) that could be used as a sustainable heterogeneous Pd catalyst for phosphine-free Suzuki-Miyaura and Heck coupling reactions with excellent turnover number and turnover frequency. The presence of Pd on the silica surface was detected by X-ray diffraction and the structural morphology of SiO2@PdNP was obtained by transmission electron microscopy. The heterogeneous catalytic system is recyclable and leaching of the metal after the reaction is not apparently observed. Copyright © 2013 John Wiley & Sons, Ltd.


Paul S.,North Bengal University | Basu B.,North Bengal University
Tetrahedron Letters | Year: 2012

An efficient and highly selective synthesis of functionalized 1,2-benzimidazoles has been developed under solvent-free conditions at ambient temperature using eco-friendly ferric sulfate soaked with silica [iron(III)sulfate-silica]. Recycling of the solid support up to six runs was investigated with appreciable yield and selectivity of the product. © 2012 Elsevier Ltd. All rights reserved.

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