Arya Vidyapeeth College

Guwāhāti, India

Arya Vidyapeeth College

Guwāhāti, India

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Bhattacharyya P.K.,Arya Vidyapeeth College
New Journal of Chemistry | Year: 2017

The stabilization energy of benzene-borazine sandwich and multidecker complexes bridged via B2H6 have been estimated using density functional theory. The gas and solvent phase calculations showed that the stabilization energy increases with the size of the complexes; in contrast, trifling reduction in the average stabilization energy is observed with increasing size of the complexes. The values of reactivity parameters, namely the energy of the HOMO, global hardness and chemical potential, suggest that the benzene complexes are more stable as compared to the borazine complexes. The complexes with as many as six aromatic rings containing B-Hb⋯π interactions are studied and are predicted to be stable (in terms of stabilization energy). The effect of solvents on the stability of the complexes is not so pronounced. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Dutta B.J.,Arya Vidyapeeth College | Bhattacharyya P.K.,Arya Vidyapeeth College
International Journal of Quantum Chemistry | Year: 2015

Effect of external electric field on interaction energy as well as stability of the hydrogen-bonding, stacking, and O-H π-bonded systems are analyzed in the light of density functional theory (DFT) and conceptual DFT. Interaction energy and stability measured in terms of global hardness and highest occupied molecular orbital energy of the considered systems are observed to be sensitive toward the strength and direction of the applied external electric field. The curvature of the potential energy surfaces gets changed in presence of an external electric field. © 2015 Wiley Periodicals, Inc.

Existence of both compressive and rarefactive solitons are found to exists in a magnetized plasma model consisting of ions, electrons and positive ion beams using the Korteweg-de Vries (KdV) equation. Both fast and slow modes are found to exist due to the presence of ion temperature in the plasma. Moreover, the amplitude of the soliton decreases with an increase in temperature for Q′ (=m b/m i, beam-ion mass to warm-ion mass ratio) >2 and the amplitude becomes maximum when the wave propagates parallel with the direction of the magnetic field. The investigation further revealed that though both compressive and rarefactive solitons exist for slow mode, only compressive soliton exist for the fast mode. © 2012 Springer Science+Business Media B.V.

Singh D.,Indian Institute of Technology Guwahati | Bhattacharyya P.K.,Arya Vidyapeeth College | Baruah J.B.,Indian Institute of Technology Guwahati
Crystal Growth and Design | Year: 2010

Structures of eight solvates of cyclic imide tethered carboxylic acids and aromatic tetra carboxylic acids with pyridine (solvate I-VI) and quinoline (VII-VIII) are determined. Different types of hydrogen bond motifs (discrete or cyclic) in these solvates are identified. Solvates I and II possess discrete O-H⋯N interactions, solvates III and VIII possess combinations of cyclic interactions arising from O-H-⋯ -N and C-H- • -O interactions, solvates IV, V, and VII have both the above namely discrete and cyclic types of interactions, whereas, solvate VI is an exception which possesses discrete O-H⋯N as well as fl 2 2(8) types of interactions and provides a model system for incomplete cleavage of dimeric assembly of carboxylic acid moiety. On the basis of the results of various hydrogen bond motifs, density functional theory calculations (DFT) on similar motifs generated from formic acid and its interaction with pyridine and quinoline are carried out. In the case of a pyridine formic acid system, DFT calculations show that the energy difference between the cyclic R 2 2(7) motif and the discrete motif is ∼0.6 kcal/mol. Such a small difference accounts for the formation of both types of structural patterns in solvates I-V depending on the steric requirements. The observed motif of VI is established by comparison of theoretical energies between a dimeric carboxylic acid moiety generated from two formic acids interactions and a trimeric moiety that exhibits two formic acids and pyridine interactions. The energy of different types of hydrogen bond motifs formed by the interactions between quinoline and formic acid is also calculated. Calculations based on DFT show that the salt formation between formic acid and pyridine is not a favorable process, but it may occur in the case of quinoline. © 2009 American Chemical Society.

Deka B.C.,Arya Vidyapeeth College | Bhattacharyya P.K.,Arya Vidyapeeth College
Computational and Theoretical Chemistry | Year: 2015

We described density functional study carried out in order to delve into the interaction between chitosan, a gene carrier and nucleobases. Our study asserts the pivotal role played by hydrogen bonding in chitosan-nucleobase adduct formation. Incorporation of aqueous medium is found to bring about a significant impact on the interaction between the two. Thermochemical analysis suggests the presence of strong thermodynamic driving force for adduct formation in gas phase while no such driving force is observed in aqueous phase. Moreover, except adenine, aromaticity of nucleobases is enhanced by adduct formation with chitosan. Protonation of the nucleobases leads to dissociation of the two constituents of the adducts. © 2014 Elsevier B.V.

Bania K.K.,Tezpur University | Guha A.K.,Dibrugarh University | Bhattacharyya P.K.,Arya Vidyapeeth College | Sinha S.,Arya Vidyapeeth College
Dalton Transactions | Year: 2014

A DFT and ab initio quantum chemical study has been carried out at different theoretical levels to delve into the role of the cation-π interaction within the main group metal cations (Li+, Na+ and K+), substituted benzene and borazine. The effects of electron withdrawing and electron donating groups on these non-covalent forces of interaction were also studied. The excellent correlation between Hammett constants and binding energy values indicates that the cation-π interaction is influenced by both inductive and resonance effects. Electron donating groups (EDG) such as -CH3 and -NH2 attached to benzene at the 1, 3 and 5 position and the three boron atoms of borazine were found to strengthen these interactions, while electron withdrawing groups (EWG) such as -NO 2 did the reverse. These results were further substantiated by topological analysis using the quantum theory of atoms in molecules (QTAIM). The polarized continuum model (PCM) and the discrete solvation model were used to elucidate the effect of solvation on the cation-π interaction. The size of the cations and the nature of the substituents were found to influence the enthalpy and binding energy of the systems (or complex). In the gas phase, the cation-π interaction was found to be exothermic, whereas in the presence of a polar solvent the interaction was highly endothermic. Thermochemical analysis predicts the presence of thermodynamic driving forces for borazine and benzene substituted with EDG. DFT based reactivity descriptors, such as global hardness (η), chemical potential (μ) and the electrophilicity index (ω) were used to elucidate the effect of the substituent on the reactivity of the cation-π complexes. This journal is © The Royal Society of Chemistry.

Bujarborua D.,Pragjyoti Eye Care and Research Center | Nagpal P.N.,Retina Foundation | Deka M.,Arya Vidyapeeth College
Graefe's Archive for Clinical and Experimental Ophthalmology | Year: 2010

Background: To study the demography, various morphological patterns and fluid dynamics of the smokestack leak by fluorescein angiography (FA) in central serous chorioretinopathy (CSC). Methods: Part I (clinical): review of the medical records and angiographic documents of 69 consecutive cases of CSC with smokestack leak. Part II (experimental): documentation of the movement of various concentrations of fluorescein dye due to convection currents in a laboratory model that roughly represents a closed chamber similar to that of CSC in human eyes. Results: The clinical study (Part I) revealed that 14.40% of 479 consecutive cases had smokestack leak, of which 70% occurred in first acute episode (p-value: <0.001), 27.14% in acute recurrent episodes (50% fresh leak) and 2.85% in chronic stage. Patients were predominantly male (84.05%) with a median age of 34.00±8.14 years. The median symptom duration excluding the chronic cases was 15±34.28 days. This type of leak was mostly (48.57%) seen in medium-sized CSC, and the majority were in the parafoveal superonasal quadrant (31.42%). The ascending type of leak was predominant (94.28%). In four eyes, an atypical pattern and in two eyes more than one smokestack leak were seen within the same detached area. The experimental study (Part II) demonstrated that fluid containing a low concentration of fluorescein ascended due to convection currents, whereas highly concentrated dye descended. Conclusions: The clinical study revealed smokestack leaks to be significantly more common in a primary acute episode, and they usually develop in the early part of the acute phase of the disease (average duration 15±34.28 days). Rarely, this type of leak can occur in the chronic stage, and multiple leaks may develop in the same detached space. The various patterns of dye movement due to convection currents in the experimental model resembled the dye movement in certain cases of CSC of the present series. The experimental study also hinted at the probability of drainage of unbound fluorescein molecules along with protein-laden heavy fluid in downward spread of the leak. © 2009 Springer-Verlag.

Bhattacharyya P.K.,Arya Vidyapeeth College
Computational and Theoretical Chemistry | Year: 2016

Reactivity, aromaticity and absorption spectra of Perylo[1,12-b,c,d] thiophene tetraester doped with B, N, O Se and BN have been discussed in the light of Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT). Doping with electron rich and electron deficient centres affects the reactivity and aromaticity of the thiophene tetraesters. A significant shift in the absorption spectra is observed in case of B and BN doped species. Aromaticity of the species is gauged by nucleus independent chemical shift (NICS). Results show that the doped species vary in their reactivity and aromaticity. N, O or Se doped species exhibit almost comparable excitation energies and absorption peaks. © 2016.

Dutta B.J.,Arya Vidyapeeth College | Bhattacharyya P.K.,Arya Vidyapeeth College
Journal of Physical Chemistry B | Year: 2014

Reactivity and aromaticity of DNA and RNA bases toward an external electric field are analyzed using density functional theory (DFT) and density functional reactivity theory (DFRT). Reactivity of the nucleobases is measured in terms of the DFT-based reactivity descriptor, such as energy of the HOMO, global hardness, electrophilicity, etc. and is observed to be sensitive toward the strength as well as direction of the applied external electric field. In addition, the reactivity pattern follows the maximum hardness and minimum electrophilicity principles. Further, aromaticity of the species is observed to be effected by the presence of an external electric field. © 2014 American Chemical Society.

Purkayastha J.,Arya Vidyapeeth College | Matsui M.,Kyoto University
Asian Herpetological Research | Year: 2012

A new Dicroglossid species is described from Mawphlang, Meghalaya, northeastern India. The new species differs from all the congeners occurring in this region in body size and call characteristics. It is larger than Fejervarya syhadrensis and F. nepalensis, but smaller than F. teraiensis. It overlaps F. pierrei in snout-vent length, but clearly differs from it in advertisement call, with much shorter note duration, much longer inter note interval, and much lower dominant frequency. Paucity of genetic information and underestimation of species diversity in this region are discussed.

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