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Biswas C.,University of Calcutta | Biswas C.,Sarojini Naidu College for Women | Drew M.G.B.,University of Reading | Figuerola A.,Italian Institute of Technology | And 4 more authors.
Inorganica Chimica Acta | Year: 2010

Three new trinuclear copper(II) complexes, [(CuL1)3(μ3-OH)](ClO4) 2·3.75H2O (1), [(CuL2)3(μ3-OH)](ClO4) [(CuL3)3(μ3-OH)](BF4) 2·0.5CH3CN (3) have been synthesized from three tridentate Schiff bases HL1, HL2, and HL3 (HL1 = 2-[(2-amino-ethylimino)-methyl]-phenol, HL2 = 2-[(2-methylamino-ethylimino)-methyl]-phenol and HL3 = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol). The complexes are characterized by single-crystal X-ray diffraction analyses, IR, UV-vis and EPR spectroscopy, and variable-temperature magnetic measurements. All the compounds contain a partial cubane [Cu3O4] core consisting of the trinuclear unit [(CuL)3(μ3-OH)]2+ together with perchlorate or fluoroborate anions. In each of the complexes, the three copper atoms are five-coordinated with a distorted square-pyramidal geometry except in complex 1, in which one of the CuII ions of the trinuclear unit is six-coordinate being in addition weakly coordinated to one of the perchlorate anions. Variable-temperature magnetic measurements and EPR spectra indicate an antiferromagnetic exchange coupling between the CuII ions of complexes 1 and 2, while this turned out to be ferromagnetic for complex 3. Experimental values have been fitted according to an isotropic exchange Hamiltonian. Calculations based on Density Functional Theory have also been performed in order to estimate the exchange coupling constants in these three complexes. Both sets of values indicate similar trends and specially calculated J values establish a magneto-structural correlation between them and the Cu-O-Cu bond angle, in that the coupling is more ferromagnetic for smaller bond angle values. © 2010 Elsevier B.V. All rights reserved.

Naiya S.,University of Calcutta | Biswas C.,University of Calcutta | Biswas C.,Sarojini Naidu College for Women | Drew M.G.B.,University of Reading | And 3 more authors.
Inorganic Chemistry | Year: 2010

Four new Cu(II)-azido complexes of formula [CuL(N3)] (1), [CuL(N3)]2 (2), [Cu7L2(N 3)12]n (3), and [Cu2L(dmen)(N 3)3]n (4) (dmen = N,N-dimethylethylenediamine) have been synthesized using the same tridentate Schiff base ligand HL (2-[1-(2-dimethylaminoethylimino)ethyl]phenol, the condensation product of dmen and 2-hydroxyacetophenone). The four compounds have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Complex 1 is mononuclear, whereas 2 is a single μ-1,1 azido-bridged dinuclear compound. The polymeric compound 3 possesses a 2D structure in which the Cu(II) ions are linked by phenoxo oxygen atoms and two different azide bridges (μ-1,1 and μ-1,1,3). The structure of complex 4 is a double helix in which twoμ-1,3-azido-bridged alternating one-dimensional helical chains of CuL(N3) and Cu(dmen)(N3)2 are joined together by weakμ-1,1 azido bridges and H-bonds. The complexes interconvert in solution and can be obtained in pure form by carefully controlling the conditions. The magnetic properties of compounds 1 and 2 show the presence of very weak antiferromagnetic exchange interactions mediated by a ligand π overlap (J = -1.77) and by an asymmetric 1, 1-N3 bridge (J= -1.97 cm-1), respectively. Compound 3 presents, from the magnetic point of view, a decorated chain structure with both ferro- and antiferromagnetic interactions. Compound 4 is an alternating helicoidal chain with two weak antiferromagnetic exchange interactions (J= -1.35 and -2.64 cm-1). © 2010 American Chemical Society.

Biswas C.,University of Calcutta | Biswas C.,Sarojini Naidu College for Women | Drew M.G.B.,University of Reading | Ruiz E.,University of Barcelona | And 3 more authors.
Dalton Transactions | Year: 2010

Three novel mixed bridged trinuclear and one tetranuclear copper(ii) complexes of tridentate NNO donor Schiff base ligands [Cu3(L 1)2(μ1,1-N3)2(CH 3OH)2(BF4)2] (1), [Cu 3(L1)2(μ1,1-N3) 2(μ-NO3-1κO:2κO′)2] (2), [Cu3(L2)2(μ1,1-N 3)2(μ-NO3-1κO:2κO′) 2] (3) and [Cu4(L3)2(μ 1,1-N3)4(μ-CH3COO-1κO: 2κO′)2] (4) have been synthesized by reaction of the respective tridentate ligands (L1 = 2-[1-(2-dimethylamino-ethylimino) -ethyl]-phenol, L2 = 2-[1-(2-diethylamino-ethylimino)-ethyl]-phenol, L3 = 2-[1-(2-dimethylamino-ethylimino)-methyl]-phenol) with the corresponding copper(ii) salts in the presence of NaN3. The complexes are characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. Complex 1 is composed of two terminal [Cu(L1)(μ1,1-N3)] units connected by a central [Cu(BF4)2] unit through nitrogen atoms of end-on azido ligands and a phenoxo oxygen atom of the tridentate ligand. The structures of 2 and 3 are very similar; the only difference is that the central unit is [Cu(NO3)2] and the nitrate group forms an additional μ-NO3-1κO:2κO′ bridge between the terminal and central copper atoms. In complex 4, the central unit is a di-μ1,1-N3 bridged dicopper entity, [Cu 2(μ1,1-N3)2(CH 3COO)2] that connects two terminal [Cu(L 3)(μ1,1-N3)] units through end-on azido, phenoxo oxygen and μ-CH3COO-1κO:2κO′ triple bridges to result in a tetranuclear unit. Analyses of variable-temperature magnetic susceptibility data indicates that there is a global weak antiferromagnetic interaction between the copper(ii) ions in complexes 1-3, with the exchange parameter J of -9.86, -11.6 and -19.98 cm-1 for 1-3, respectively. In complex 4 theoretical calculations show the presence of an antiferromagnetic coupling in the triple bridging ligands (acetato, phenoxo and azido) while the interaction through the double end-on azido bridging ligand is strongly ferromagnetic. © 2010 The Royal Society of Chemistry.

Biswas C.,University of Calcutta | Biswas C.,Sarojini Naidu College for Women | Drew M.G.B.,University of Reading | Asthana S.,CNRS Laboratory of Condensed Matter Chemistry, Bordeaux | And 2 more authors.
Journal of Molecular Structure | Year: 2010

Two new mono-aqua-bridged dinuclear Cu(II) complexes of tridentate NNO Schiff bases, [Cu2(μ-H2O)L1 2 (H2O)2](BF4)2·2H2O (1) and [Cu2(μ-H2O)L2 2 (H2O)2](BF4)2·2H2O (2) where HL1 = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol and HL2 = 2-[(2-dimethylamino-ethylimino)-methyl]-phenol were synthesized. Both the complexes were characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. For both the complexes each Cu(II) ion is in a square-pyramidal environment being bonded to three atoms from the tridentate NNO Schiff base and a terminal H2O molecule in the equatorial plane; a second H2O ligand acts as a bridge between the two Cu(II) centres through the axial positions. Hydrogen bonds between the terminal H2O ligand and the Schiff base of the adjacent centre complete the intra-dimer linkages. Variable-temperature (4-300 K) magnetic susceptibility measurement shows the presence of significant antiferromagnetic coupling for both the complexes (J = -12.2 and -12.5 cm-1, respectively, for 1 and 2), mediated mainly through the intra-dimer H-bonds. © 2009 Elsevier B.V. All rights reserved.

Nag S.,Sarojini Naidu College for Women | Acharya S.,Ramakrishna Mission Vidyamandira | Ray A.K.,Jaypee University of Engineering & Technology | Das T.K.,Harish Chandra Research Institute | Das T.K.,Academia Sinica, Taiwan
New Astronomy | Year: 2012

Using mathematical formalism borrowed from dynamical systems theory, a complete analytical investigation of the critical behaviour of stationary flows in low angular momentum axisymmetric black hole accretion, provides significant insight about the nature of the phase trajectories corresponding to transonic accretion in the steady state, without taking recourse to any explicit numerical method commonly reported in the literature on multi-transonic black hole accretion discs and related astrophysical phenomena. Investigation of an accretion process around a non-rotating black hole, forming different geometrical configurations of the flow structure under the influence of various pseudo-Schwarzschild potentials, reveals that the general profile of the parameter space divisions describing multi-critical accretion, is roughly equivalent for various flow geometries. However, a mere variation of the polytropic index of the flow cannot map a critical solution from one flow geometry to another, since the numerical domain of the parameter space responsible for producing multi-critical accretion does not undergo a continuous transformation in multi-dimensional parameter space. The stationary configuration used to demonstrate the aforementioned findings is shown to be stable under time-dependent linearised perturbations for all kinds of flow geometries, driven by any pseudo-Schwarzschild potential, and using a standard equation of state. Finally, the structure of the acoustic metric corresponding to the propagation of the linear perturbation is discussed for various flow geometries used. © 2011 Elsevier B.V. All rights reserved.

Banerjee S.,CSIR - Central Electrochemical Research Institute | Saraswat G.,CSIR - Central Electrochemical Research Institute | Bandyopadhyay S.A.,CSIR - Central Electrochemical Research Institute | Bandyopadhyay S.A.,Sarojini Naidu College for Women | Kabir S.N.,CSIR - Central Electrochemical Research Institute
PLoS ONE | Year: 2014

The ovary receives a finite pool of follicles during fetal life. Atresia remains the major form of follicular expenditure at all stages since development of ovary. The follicular reserve, however, declines at an exponential rate leading to accelerated rate of decay during the years preceding menopause. We examined if diminished follicle reserve that characterizes ovarian aging impacts the attrition rate. Premature ovarian aging was induced in rats by intra-embryonic injection of galactosyltransferase-antibody on embryonic day 10. On post-natal day 35 of the female litters, either a wedge of fat (sham control) or a wild type ovary collected from 25-day old control rats, was transplanted under the ovarian bursa in both sides. Follicular growth and atresia, and ovarian microenvironment were evaluated in the follicle-deficient host ovary and transplanted ovary by real time RT-PCR analysis of growth differentiation factor-9, bone morphogenetic protein 15, and kit ligand, biochemical evaluation of ovarian lipid peroxidation, superoxide dismutase (SOD) and catalase activity, and western blot analysis of ovarian pro- and anti-apoptotic factors including p53, bax, bcl2, and caspase 3. Results demonstrated that the rate of follicular atresia, which was highly preponderant in the follicle-deficient ovary of the sham-operated group, was significantly prevented in the presence of the transplanted ovary. As against the follicle-deficient ovary of the sham-operated group, the follicle-deficient host ovary as well as the transplanted ovary in the ovary-transplanted group exhibited stimulated follicle growth with increased expression of anti-apoptotic factors and down regulation of pro-apoptotic factors. Both the host and transplanted ovaries also had significantly lower rate of lipid peroxidation with increased SOD and catalase activity. We conclude that the declining follicular reserve is perhaps the immediate thrust that increases the rate of follicle depletion during the final phase of ovarian life when the follicle reserve wanes below certain threshold size. © 2014 Banerjee et al.

Das A.,Acharya Prafulla Chandra College | Bhadra S.,Acharya Prafulla Chandra College | Saha S.,Sarojini Naidu College for Women
Quantum Information Processing | Year: 2015

Quantum phase transition in dimerised antiferromagnetic Heisenberg spin chain has been studied. A staircase structure in the variation of concurrence within strongly coupled pairs with that of external magnetic field has been observed indicating multiple critical (or critical like) points. Emergence of entanglement due to external magnetic field or magnetic entanglement is observed for weakly coupled spin pairs too in the same dimer chain. Though closed dimerised isotropic XXX Heisenberg chains with different dimer strengths were mainly explored, analogous studies on open chains as well as closed anisotropic (XX interaction) chains with tilted external magnetic field have also been studied. © 2015, Springer Science+Business Media New York.

Agarwal S.,Banaras Hindu University | Das T.K.,Harish Chandra Research Institute | Dey R.,Harish Chandra Research Institute | Nag S.,Sarojini Naidu College for Women
General Relativity and Gravitation | Year: 2012

We apply the theory of algebraic polynomials to analytically study the transonic properties of general relativistic hydrodynamic axisymmetric accretion onto non-rotating astrophysical black holes. For such accretion phenomena, the conserved specific energy of the flow, which turns out to be one of the two first integrals of motion in the system studied, can be expressed as a 8th degree polynomial of the critical point of the flow configuration. We then construct the corresponding Sturm's chain algorithm to calculate the number of real roots lying within the astrophysically relevant domain of ℝ. This allows, for the first time in literature, to analytically find out the maximum number of physically acceptable solution an accretion flow with certain geometric configuration, space-time metric, and equation of state can have, and thus to investigate its multi-critical properties completely analytically, for accretion flow in which the location of the critical points can not be computed without taking recourse to the numerical scheme. This work can further be generalized to analytically calculate the maximal number of equilibrium points certain autonomous dynamical system can have in general. We also demonstrate how the transition from a mono-critical to multi-critical (or vice versa) flow configuration can be realized through the saddle-centre bifurcation phenomena using certain techniques of the catastrophe theory. © 2012 Springer Science+Business Media, LLC.

Bilic N.,Ruder Boskovic Institute | Choudhary A.,University of Lucknow | Das T.K.,Harish Chandra Research Institute | Nag S.,Sarojini Naidu College for Women
Classical and Quantum Gravity | Year: 2014

We investigate the salient features of the acoustic geometry corresponding to the axially symmetric accretion of dissipationless inhomogeneous fluid onto a non-rotating astrophysical black hole under the influence of a generalized pseudo-Schwarzschild gravitational potential. For a few chosen flow configurations, we determine the location of the acoustic horizon and calculate analytically the corresponding analogue surface gravity κ and the associated analogue Hawking temperature TAH. We study the dependence of κ on various boundary conditions and geometry governing the dynamic and thermodynamic properties of the background flow. © 2014 IOP Publishing Ltd.

Saha S.,Sarojini Naidu College for Women
Proceedings of the Indian National Science Academy | Year: 2015

Generally a centrally located accreting super massive (∼ 108M⊙) black hole is thought to be playing the role of the gravitational powerhouse of gigantic scale in AGN. The accretion process for such a black hole may be studied using general relativistic as well as post Newtonian scheme for various possible flow geometries with different equation of states of the accreted matter. For the sake of simplicity, hydro-dynamical flow models are generally adopted to get an analytical estimate for those accretion process. In our work, accretion process over a region far beyond the dimension of a single galaxy by a much more massive object (∼ 1018M⊙, a cluster of galaxies or a possible super-giant black hole) has been studied where the large scale feature of the space-time structure of the Universe may be relevant. In the non-rotating limit of the accreting black-hole with accelerated expansion of the Universe, Schwarzschild-de Sitter (SdS) space is chosen to be a suitable one. Pseudo-Newtonian potential describing the gravitational field of static and spherically symmetric black holes in the Universe with a repulsive cosmological constant, i.e. for SdS space, has been recently introduced by Stuchlik and Kovar. Using this potential, here we have studied the phase topology of the flow and also the possibility of formation of stationary shocks both in adiabatic and isothermal limits in accretion discs. In AGN, the existence of stationary shock is believed to be a plausible explanation of the extremely hot annular region there. In our study, in adiabatic (and in isothermal) cases, a significant region of parameter space allow shock formation and those regions shift in comparison with the same for Schwarzschild case due to the effect of cosmological constant in SdS space. © Printed in India.

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