Biswajit Maiti

Banaras Hindu University, Vārānasi, Uttar Pradesh, India

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Publications (14)39.74 Total impact

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    ABSTRACT: Nanohybrids have been synthesized by incorporating organically modified layered silicate in poly(vinylidene fluoride) (PVDF) matrix. Molecular level phenomena have been explored after exposing electron beam at varying doses to PVDF and its nanohybrid. Electron beam interact with polymer chains and thereby generates different free radicals whose extent is quite high in nanohybrid as compared to pure PVDF. The stability of free radicals has been confirmed through density function theory (DFT) energy minimization, predicting stable β − phase free radicals in nanohybrid. Quantitative analysis of chain scission, crosslinking and double bond formations are reported and compared after irradiation both for PVDF and its nanohybrid using UV–vis, FTIR, sol–gel analyses and gel permeation chromatography revealing both chain scission and crosslinking phenomena in irradiated PVDF and its nanohybrids, but at higher dose (>90 Mrad), crosslinking dominates in nanohybrid due to more number of free radicals and proximity of radical chains on top of templated system in nanohybrid as compared to pure PVDF. The enhanced crosslinking alter the nanostructure causing disappearance of peak at 2θ ~ 3°. Moreover, electron beam induces significant piezoelectric β − phase in nanohybrids against only α − phase in pure PVDF at similar dose and has raises the possibility to use electron irradiated nanohybrid as electromechanical devices. β-phase formation is also supported through solid state NMR, SEM and DSC studies. The thermal properties in terms of heat of fusion and degradation temperature have been verified indicating steady decrease of melting point and heat of fusion for pure PVDF while considerably less effect is observed in nanohybrids. The combined effect of chain session and crosslinking make both PVDF and nanohybrid brittle but higher stiffness with respect to unirradiated specimen.
    Polymer International 06/2014; · 2.13 Impact Factor
  • Karunamoy Rajak, Biswajit Maiti
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    ABSTRACT: Intersystem crossing (ISC) dynamics plays an important role in determining the product branching in the O(3P) + C2H2 reaction despite the necessarily small spin-orbit coupling constant values. In this study we investigate the effect of collision energy on the extent of the contribution of a spin non-conserving route through ISC dynamics to the product distributions at the initial collision energies 8.2, 9.5, and 13.1 kcal/mol. A direct dynamics trajectory surface hopping method is employed with potential energy surfaces generated at the unrestricted B3LYP/6-31G(d,p) level of theory to perform nonadiabatic dynamics. To make our calculation simpler, nonadibatic transitions were only considered at the triplet-singlet intersections. At the crossing points, Landau-Zener transition probabilities were calculated using spin-orbit coupling constant values computed at the same geometry. The Landau-Zener model for the title reaction is validated against a more rigorous Tully's fewest switches method and found to be working reasonably well as expected because of weak spin-orbit coupling. We have compared our results with the recent crossed molecular beam experiments and observed a very good agreement with respect to the primary product branching ratios. Our calculation revealed that there is no noticeable effect of the initial collision energy on the overall product distributions that corroborates the recent experimental findings. Our calculation indicates, however, that the extent of intersystem crossing contributions varies significantly with collision energy, needed to be verified, experimentally.
    The Journal of Chemical Physics 01/2014; 140(4):044314. · 3.12 Impact Factor
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    ABSTRACT: Novel polyurethanes have been synthesized using an aliphatic diisocyanate and aliphatic chain extenders with varying chain length. Nanocomposites of polyurethanes have been prepared by dispersing two-dimensional nanoclay in poly-ol followed by prepolymerization and subsequent chain extension using various chain extenders. Systematic improvement in toughness and adequate enhancement in stiffness in the presence of nanoclay has been observed for PUs with larger length of chain extender exhibiting no trade-off for these new classes of nanocomposites. Bottom-up self-assembly starting from molecular level to micron scale crystallite has been revealed through electronic structure calculation, X-ray diffraction, small angle neutron scattering, atomic force microscopy and optical images. The role of hydrogen bonding has been uncovered for this type of supramolecular assembly which further aggravated in the presence of organically modified nanoclay by making bigger clusters for nanocomposites. Controlled biodegradation of PU and its nanocomposites has been investigated in enzymatic media. Biocompatibility of these novel nanocomposites has been well verified through platelet adhesion, aggregation and hemolysis assay. Biocompatible pristine PU and its nanocomposites in the sustained drug delivery has been demonstrated either by controlling the crystallite size of the polyurethane through alteration of the aliphatic chain length of the extender or by incorporating disc-like nanoclay by making tortuous path rendering delayed diffusion. Hence, the developed nanohybrids illustrate potential biomaterials for tissue engineering and drug delivery.
    Acta biomaterialia 12/2013; · 5.68 Impact Factor
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    ABSTRACT: A new simple organic scaffold based on acenaphthene 4 was designed and synthesized. The chromogenic and fluorogenic properties of 4 toward different metal ions and anions were investigated in H2O/MeCN (8:2, v/v) solution. The probe 4 in the presence of Cu2+ exhibited strong static excimer emission at 507 nm along with a decrease in monomer emission at ∼400 nm ratiometrically, attributed to a complexation through aldimine and amide groups of 4. Additionally, 4 upon interaction with different anions illustrated significant fluorescence enhancement with cyanide. However, interaction of complex, 4-Cu2+ with CN− revealed fluorescence quenching attributed to formation of stable [Cu(CN)x]1−x species in the medium. A naked-eye sensitive fluorescent green color of solution was changed to blue. The mechanism of interaction between 4 and Cu2+ and sensing of cyanide through Cu2+ displacement approach was confirmed by the change in optical behaviors and 1H NMR and ESI-MS spectral data analysis.
    Tetrahedron. 11/2012; 68(44):9076–9084.
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    ABSTRACT: Six heteroleptic dipyrrinato complexes [Ni(fcdpm)(dedtc)] (1), [Ni(fcdpm)(dipdtc)] (2), [Ni(fcdpm)(dbdtc)] (3), [Pd(fcdpm)(dedtc)] (4), [Pd(fcdpm)(dipdtc)] (5), and [Pd(fcdpm)(dbdtc)] (6) (fcdpm = 5-ferrocenyldipyrromethene; dedtc = diethyldithiocarbamate; dipdtc = diisopropyldithiocarbamate; dbdtc = dibutyldithiocarbamate) have been synthesized and characterized by elemental analyses and spectral (ESI-MS, IR, (1)H, (13)C NMR, UV-vis) and electrochemical studies. Crystal structures of 1, 2, 4, and 5 have been authenticated by X-ray single-crystal analyses. Nickel-based complexes 1-3 display selective chromogenic and redox sensing for Hg(2+) and Pb(2+) ions, while palladium complexes 4-6 display selective chromogenic and redox sensing only for Hg(2+). Electronic absorption, ESI-MS, and electrochemical studies indicated that sensing arises from interaction between 1-3 and Hg(2+)/Pb(2+) through sulfur of the coordinated dithiocarbamates, while it arises from the pyrrolic nitrogen of fcdpm and dithiocarbamate sulfur from 4-6 and Hg(2+). Different modes of binding between Ni and Pd complexes have further been supported by theoretical studies. The receptor-cation binding constants (K(a)) and stoichiometry between probes and Hg(2+)/Pb(2+) have been estimated by the Benesi-Hildebrand method and Job's plot analysis. Detection limits for 1-3 toward Hg(2+)/Pb(2+) and 4-6 for Hg(2+) have been found to be reasonably high.
    Inorganic Chemistry 08/2012; 51(16):8916-30. · 4.59 Impact Factor
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    ABSTRACT: The synthesis and characterization of ferrocene (Fc) derivatives 4-[2,5-diferrocenyl-4-(4-pyridyl)imidazolidin-1-ylmethyl]pyridine (1), ferrocenylmethylenepyridin-3-ylmethylamine (2), N,N'-bis(ferrocenylmethylene)-2,4,6-trimethylbenzene-1,3-diamine (3), and 6-ferrocenyl-5,6-dihydro[4,5]imidazo[1,2-c]quinazoline (4) have been described. Structures of 1, 2, and 4 have been determined by single-crystal X-ray diffraction analyses. At 25 °C, 1-3 are nonfluorescent, while 4 displays moderate fluorescence and chromogenic, fluorogenic, and electrochemical sensing selectively toward Hg(2+) and Pb(2+) ions. Association constants (K(a)) for Hg(2+) and Pb(2+) have been determined by the Benesi-Hildebrand method. Job's plot analysis supported 1:1 and 1:2 stoichiometries for Hg(2+) and Pb(2+) ions. Cyclic voltammograms of 1-4 exhibited reversible waves corresponding to a ferrocene/ferrocenium couple. The wave associated with 4 (+0.0263 V) exhibited positive (ΔE(pa) = 0.136 V) and negative (ΔE(pa) = 0.025 V) shifts in the presence of Hg(2+) and Pb(2+) ions, respectively. The mode of interaction between metal ions and 4 has been supported by (1)H NMR spectroscopy and mass spectrometry studies and verified by theoretical studies. It presents the first report dealing with ferrocene-substituted quinazoline as a multichannel chemosensor for Hg(2+)/Pb(2+) ions.
    Inorganic Chemistry 11/2011; 51(1):298-311. · 4.59 Impact Factor
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    ABSTRACT: A series of polyurethane (PU) ionomers with different degree of sulfonation (DS) have been synthesized and successfully used as corrosion inhibitor for mild steel (MS) in acidic medium. Nuclear magnetic resonance (NMR) and Fourier transform infra red (FTIR) spectra of the sulfonated PUs confirmed the sulfonation on the >NH group of the urethane linkage and DS increases with the increase in the ratio of the sulfonating agent and PU. More than 90% inhibition efficiency (IE) of sulfonated polyurethanes (SPU) has been reported using only 20 ppm of the ionomers. These ionomers inhibited the corrosion of MS through adsorption following the Langmuir adsorption isotherm. Surface coverage has been scaled using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effect of sulfonation on the electronic and chemical structure of PU molecules has also been investigated. Electronic structure calculations have been performed to predict the adsorption behavior of ionomers on the metal surface, and thereby, the relative inhibition has been quantitatively correlated with DS.
    RSC Advances 08/2011; 1(2):199-210. · 3.71 Impact Factor
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    ABSTRACT: A series of high molecular weight poly(N-isopropylacrylamide) (PNIPAM)s with low polydispersity (Mn = 7.0 × 104 to 10.2× 104 g mol–1, PDI = 1.23–1.35) having different isotacticity [meso diad (m) = 47–88%]] was successfully synthesized using the reversible addition–fragmentation chain transfer (RAFT) polymerization method in the presence of different concentrations of Y(OTf)3 Lewis acid. Measurement of the glass transition temperature (Tg) of this high molecular weight isotactic PNIPAM series and the low molecular weight PNIPAM series (Mn = 3.5 × 104 to 4.0 × 104 g mol–1, PDI = 1.2–1.3) having different isotacticity [meso diad (m) = 45–72%)] reported earlier by us (Ray et al. Polym. J. 2005, 37, 234) showed that Tg of PNIPAM decreases with increase in its meso diad content (m %) and decrease in its molecular weight.
    Macromolecules. 06/2011; 44(14).
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    ABSTRACT: Thermoreversible gelation of a copolymer, poly(vinylidene fluoride-co-chlorotrifluoroethylene), has been studied in a series of aromatic diesters (phthalates) with varying aliphatic chain length, n. The gelation rate gradually increases with increasing n, but no gelation occurs in dioctyl phthalate (n = 8), giving rise to a solvent dependency. Structures of gels and dried gels have been studied through X-ray diffraction and FTIR studies. Fibrillar morphology is evident for the series of solvents, but its dimension (both lateral and diameter) systematically changes with n. Solvent retention power of gels has gradually been increased with increasing n while the thermal degradation of copolymer occurs at same temperature, reflecting varying interactions between copolymer and various aliphatic chain length phthalates in gels. Phase diagrams of the gels exhibit the formation of two kinds of polymer−solvent complexes and have been predicted theoretically through electronic structure calculation. Both the small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) have been performed to elucidate the structure of fibril indicating gradual changes in lamellar organization. The experimental data have been fitted with different models and power law to check their validity. Molecular modeling has been carried out to understand the nature of interaction between copolymer and the solvent through energy minimization program and found a typical n = 6 value of lowest dipolar distance, indicating strongest interaction. The magic number of six has further been explored through quantum chemical calculations.
    Macromolecules. 03/2011;
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    Karunamoy Rajak, Biswajit Maiti
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    ABSTRACT: The importance of intersystem crossing dynamics for the O((3)P)+C(2)H(2) reaction is demonstrated in this work. A direct dynamics trajectory surface hopping method has been employed to study the intersystem crossing effects. Our study reveals that there is a significant contribution from the spin nonconserving route to the chemical dynamics of the O((3)P)+C(2)H(2) reaction, despite small spin-orbit coupling constant values (<70 cm(-1)).
    The Journal of Chemical Physics 07/2010; 133(1):011101. · 3.12 Impact Factor
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    ABSTRACT: First examples of heteroleptic arene ruthenium complexes containing dipyrrin ligands with the general formulations [(eta(6)-arene)RuCl(L)] [(arene = C(6)H(6), C(10)H(14); L = 5-(4-cyanophenyl)-dipyrromethene, cydpm; 5-(4-nitrophenyl)-dipyrromethene, ndpm and 5-(4-benzyloxyphenyl)-dipyrromethene, bdpm] have been synthesized. The complexes [(eta(6)-C(10)H(14))RuCl(L)] (L = ndpm and cydpm) reacted with NaN(3) and NH(4)SCN to afford neutral mononuclear complexes [(eta(6)-C(10)H(14))Ru(N(3))(L)] and [(eta(6)-C(10)H(14))Ru(SCN)(L)]. Their reactions with EPh(3) (E = P, As) and exobidentate ditopic P-P and N-N donor ligands, namely, bis-(diphenylphosphino)methane (dppm) and 4,4'-bipyridine (bpy) in the presence of AgSO(3)CF(3) afforded cationic mono- and binuclear complexes [(eta(6)-C(10)H(14))Ru(L)(EPh(3))]SO(3)CF(3), [{(eta(6)-C(10)H(14))Ru(L)}(2)(mu-dppm)](SO(3)CF(3))(2), and [{(eta(6)-C(10)H(14))Ru(L)}(2)(mu-bpy)](SO(3)CF(3))(2), respectively. The reaction products have been characterized by analytical and spectral studies. Molecular structures of the representative complexes [(eta(6)-C(10)H(14))RuCl(cydpm)], [(eta(6)-C(6)H(6))RuCl(cydpm)], [(eta(6)-C(10)H(14))RuCl(ndpm)], [(eta(6)-C(10)H(14))Ru(N(3))(ndpm)], and [(eta(6)-C(10)H(14))Ru(PPh(3))(ndpm)]SO(3)CF(3) have been determined crystallographically. Redox behavior of the complexes has been investigated by electrochemical studies. Emission spectral studies at room temperature suggested that the complexes under study are non-emissive.
    Inorganic Chemistry 08/2009; 48(16):7593-603. · 4.59 Impact Factor
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    ABSTRACT: First examples of heteroleptic arene ruthenium complexes containing dipyrrin ligands with the general formulations [(η6-arene)RuCl(L)] [(arene = C6H6, C10H14; L = 5-(4-cyanophenyl)-dipyrromethene, cydpm; 5-(4-nitrophenyl)-dipyrromethene, ndpm and 5-(4-benzyloxyphenyl)-dipyrromethene, bdpm] have been synthesized. The complexes [(η6-C10H14)RuCl(L)] (L = ndpm and cydpm) reacted with NaN3 and NH4SCN to afford neutral mononuclear complexes [(η6-C10H14)Ru(N3)(L)] and [(η6-C10H14)Ru(SCN)(L)]. Their reactions with EPh3 (E = P, As) and exobidentate ditopic P−P and N−N donor ligands, namely, bis-(diphenylphosphino)methane (dppm) and 4,4′-bipyridine (bpy) in the presence of AgSO3CF3 afforded cationic mono- and binuclear complexes [(η6-C10H14)Ru(L)(EPh3)]SO3CF3, [{(η6-C10H14)Ru(L)}2(μ-dppm)](SO3CF3)2, and [{(η6-C10H14)Ru(L)}2(μ-bpy)](SO3CF3)2, respectively. The reaction products have been characterized by analytical and spectral studies. Molecular structures of the representative complexes [(η6-C10H14)RuCl(cydpm)], [(η6-C6H6)RuCl(cydpm)], [(η6-C10H14)RuCl(ndpm)], [(η6-C10H14)Ru(N3)(ndpm)], and [(η6-C10H14)Ru(PPh3)(ndpm)]SO3CF3 have been determined crystallographically. Redox behavior of the complexes has been investigated by electrochemical studies. Emission spectral studies at room temperature suggested that the complexes under study are non-emissive.
    Inorganic Chemistry 07/2009; 2009(48):7593–7603. · 4.59 Impact Factor
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    ABSTRACT: Thermoreversible gelation of poly(vinylidene fluoride) (PVDF) has been studied in a new series of solvents (phthalates), for example, dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), and dihexyl phthalate (DHP) as a function of temperature and polymer concentration, both by test tube tilting and dynamic light scattering (DLS) method. The effect of aliphatic chain length (n) of diesters on the gelation kinetics, structure/microstructure and morphology of PVDF gels has been examined. Gelation rate was found to increase with increasing aliphatic chain length of diester. DLS results indicate that the sol-gel transformation proceeds via two-steps: first, microgel domains were formed, and then the infinite three-dimensional (3D) network is established by connecting microgels through polymer chains. The crystallites are responsible for 3D network for gelation in phthalates, and alpha-polymorph is formed during gelation producing higher amount of crystallinity with increasing aliphatic chain length of diester. Morphology of the networks of dried gels in different phthalates showed that fibril thickness and lateral dimensions decrease with higher homologues of phthalates. The scattering intensity is fitted with Debye-Bueche model in small-angle neutron scattering and suggested that both the correlation length and interlamellar spacing increases with n. A model has been proposed, based on electronic structure calculations, to explain the conformation of PVDF chain in presence of various phthalates and their complexes, which offer the cause of higher gelation rate for longer aliphatic chain length.
    The Journal of Physical Chemistry B 05/2008; 112(15):4594-603. · 3.61 Impact Factor
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    ABSTRACT: A ruthenium(II) complex of type [Ru(bpy)2(L′H)]·PF61 (L′H = 5-Nitroso-pyrimidine-2,4,6-trione, is prepared by the reaction of [1,5-dihydro-5-[5-pyrimidine-2,4(1H,3H)-dionyl]-2H-chromeno[2,3-d] pyrimidine-2,4(3H)-dione)]) LH4 with [Ru(bpy)2(NO3)2] (prepared in situ). It is characterized using elemental analyses, spectroscopic and single crystal X-ray diffraction techniques. This complex is converted in another complex of type [Ru(bpy)2(L′)] 2 by the addition of an aqueous solution of NaOH. The complex 2 turns back to complex 1 after its neutralization by the addition of an aqueous solution of HCl. The reversible conversion of complexes 1 and 2 in each other is monitored using their UV–Vis and luminescence spectra. Quantum chemical calculations using density functional theory (DFT) method corroborates transfer of electron density from nitrosobarbiturate to metal ion leading the formation of complex 2.
    Inorganica Chimica Acta. 404:123–130.