Showing papers by "Indian Association for the Cultivation of Science published in 2005"

Adsorption of a model anionic dye, eosin Y, from aqueous solution by chitosan hydrobeads.

Abstract: The process of sorption is being increasingly used for ecofriendly and economic remediation of textile dye effluents. The present model study deals with the adsorption of a model anionic dye, eosin Y, from wastewater using conditioned chitosan hydrobeads. Conditioning reduced the pH sensitivity and maintained the maximum sorption capacity of the beads near pH 8. To understand the chemicophysical characteristics of the adsorption process we studied, the kinetics and isotherm behavior of the system. It was observed that temperature played a significant role in the process. The Langmuir model was found to be most appropriate for the description of the adsorption process. The kinetic results followed a second-order equation. It was observed that 1 g of chitosan adsorbed ∼ 76 mg of eosin Y. The dye was desorbed from the beads by changing the pH of the solution, and the conditioned chitosan beads were reused five times without any loss of mechanical and chemical efficacy.

Controlled synthesis and photoluminescence properties of ZnS nanowires and nanoribbons.

Abstract: Rapid synthesis of wurtzite ZnS nanowires and nanoribbons has been achieved by a simple thermal evaporation of ZnS powder onto Si substrate in the presence of Au catalyst. A vapor−liquid−solid process is proposed for the formation of the ZnS nanostructures. The flow rate of the inert carrier Ar gas along with the temperature play an important role in defining the morphology of the ZnS nanostructures. The morphological change of the ZnS nanostructures and their growth sequence were studied through scanning electron microscopy. Room-temperature photoluminescence measurements showed intense blue emission at ∼398 nm from both the nanowires and the nanoribbons.

Optical and magnetic properties of manganese-incorporated zinc sulfide nanorods synthesized by a solvothermal process.

Abstract: Manganese-incorporated ZnS (MnxZn1-xS) nanorods were synthesized by a simple solvothermal process. Synthesized nanorods were single crystalline. Manganese incorporation in the ZnS lattice induces a phase transformation from hexagonal wurtzite to cubic zinc blende structure. The diameter of the nanorods increased with the increase of Mn concentration. Intense orange luminescence at ∼585 nm was observed for the nanorods. Six-line hyperfine splitting was observed in the EPR spectra for lower Mn concentrations, whereas broad Lorentzian-shaped EPR spectra were obtained for higher Mn concentrations because of the Mn−Mn cluster formation at higher Mn concentrations.

Synthesis of copper sulfides of varying morphologies and stoichiometries controlled by chelating and nonchelating solvents in a solvothermal process

Abstract: Different morphological patterns of copper sulfide crystals, e.g., flowers, distorted rods (rice, grainlike morphology), and spaghetti-like and spherical microparticles have been successfully synthesized using different organic solvents, namely, ethylenediamine, ethyleneglycol, and ethanol, by a solvothermal process. From the experimental results, it has been revealed that the solvents played an important role to control the morphology and composition of copper sulfide crystals.

Vickers microhardness studies on solution-grown single crystals of magnesium sulphate hepta-hydrate

Abstract: A Vickers microhardness study has been carried out on (1 0 0) and (0 1 0) faces of solution-grown single crystals of magnesium sulphate hepta-hydrate (MgSO 4 ·7H 2 O) over a load range of 10–80 g. The Vickers hardness numbers ( H v ) are found to decrease initially with increase in load and then appear to level-off. The (1 0 0) face is the softest one. The Meyer index ‘ n ’ of the two faces is less than 2 as expected theoretically if the particular crystal system belongs to the soft material category. Neither Kick's law nor Hays and Kendall's law can fully explain the nonlinear variation of microhardness with load. Instead, preference is given to Li and Bradt's proportional specimen resistance (PSR) model. The elastic stiffness coefficient, c 11 , has also been calculated using Wooster's empirical relation from the hardness data and it shows reasonable agreement with a reported value. A hardness anisotropy for both planes has been observed in accordance with the orientation of the crystallographic planes.

Catalysis by ionic liquid. A green protocol for the stereoselective debromination of vicinal-dibromides by [pmIm]BF4 under microwave irradiation.

Abstract: An easily accessible ionic liquid, 1-methyl-3-pentylimidazolium fluoroborate, [pmIm]BF4, has been demonstrated to be an efficient catalyst as well as reaction medium for the stereoselective debromination of a variety of structurally diverse vicinal-dibromides to the corresponding (E)-alkenes in high yields under microwave irradiation. This reaction does not require any organic solvent and any metal or any conventional reducing agent, and the ionic liquid is recycled without any appreciable loss of its catalytic efficiency.

Reflections on size-extensivity, size-consistency and generalized extensivity in many-body theory

Abstract: An overview is presented of the notions of size-extensivity and size-consistency, which play an important role in the discussion of many-body methods in physics and chemistry. We also introduce the concept of generalized extensivity, which has been used before implicitly in the literature, and provide an operational definition, which can be tested numerically in a similar way as size-consistency. A numerical example illustrates the concept of generalized extensivity as applied to the EOM-CCSD, STEOM-CCSD and extended-STEOM-CCSD electronic structure methods for excited states. In another line of thought it is argued that algebraic proofs are often more easily constructed than diagrammatic proofs to demonstrate proper separation into non-interacting fragments. The algebraic line of reasoning is illustrated for single reference methods and applied to discuss separability properties for a variety of Hilbert space multi-reference coupled cluster methods.

Ionic liquid as reagent. A green procedure for the regioselective conversion of epoxides to vicinal-halohydrins using [AcMIm]X under catalyst- and solvent-free conditions.

Abstract: A variety of structurally diverse epoxides undergo facile cleavages by ionic liquid, [AcMIm]X without any catalyst and solvent to produce the corresponding vicinal halohydrins in high yields. The cleavages are considerably fast and highly regioselective.

Dinuclear zinc(II) complexes of tetraiminodiphenol macrocycles and their interactions with carboxylate anions and amino acids. Photoluminescence, equilibria, and structure.

Abstract: The reaction equilibria [H4L]2+ + Zn(OAc)2 ⇌ [Zn(H2L)]2+ + 2HOAc (K1) and [Zn(H2L)]2+ + Zn(OAc)2 ⇌ [Zn2L]2+ + 2HOAc (K2), involving zinc acetate and the perchlorate salts of the tetraiminodiphenol macrocycles [H4L1-3](ClO4)2, the lateral (CH2)n chains of which vary between n = 2 and n = 4, have been studied by spectrophotometric and spectrofluorimetric titrations in acetonitrile. The photoluminescence behavior of the complexes [Zn2L1](ClO4)2, [Zn2L2(H2O)2](ClO4)2, [Zn2L2(μ-O2CR)](ClO4) (R = CH3, C6H5, p-CH3C6H4, p-OCH3C6H4, p-ClC6H4, p-NO2C6H4), and [Zn2L3(μ-OAc)](ClO4) have been investigated. The X-ray crystal structures of the complexes [Zn2L2(H2O)2](ClO4)2, [Zn2L3(μ-OAc)](ClO4), and [Zn2L2(μ-OBz)(OBz)(H3O)](ClO4) have been determined. The complex [Zn2L2(μ-OBz)(OBz)(H3O)](ClO4) in which the coordinated water molecule is present as the hydronium ion (H3O+) on deprotonation gives rise to the neutral dibenzoate-bridged compound [Zn2L2(μ-OBz)2]·H2O. The equilibrium constants (K) for the reaction [Zn2L2(H2O)...

Rare azido-bridged manganese(II) systems: syntheses, crystal structures, and magnetic properties.

Abstract: Two new polymeric azido-bridged manganese complexes of formulas [Mn(N3)2(bpee)]n (1) and {[Mn(N3)(dpyo)Cl(H2O)2](H2O)}n (2) [bpee, trans-1,2-bis(4-pyridyl)ethylene; dpyo, 4,4‘-dipyridyl N,N‘-dioxide] have been synthesized and characterized by single-crystal X-ray diffraction analysis and low-temperature magnetic study. Both the complexes 1 and 2 crystallize in the triclinic system, space group P1, with a = 8.877(3) A, b = 11.036(3) A, c = 11.584(4) A, α = 72.62(2)°, β = 71.06(2)°, γ = 87.98(3)°, and Z = 1 and a = 7.060(3) A, b = 10.345(3) A, c = 11.697(4) A, α = 106.86(2)°, β = 113.33(2)°, γ = 96.39(3)°, and Z = 2, respectively. Complex 1 exhibits a 2D structure of [−Mn(N3)2−]n chains, connected by bpee ligands, whose pyridine rings undergo π−π and C−H···π interactions. This facilitates the rare arrangement of doubly bridged azide ligands with one end-on and two end-to-end (EO-EE-EE) sequence. Complex 2 is a neutral 1D polymer built up by [Mn(N3)(dpyo)Cl(H2O)2] units and lattice water molecules. The meta...

Ionic Liquid as Catalyst and Reaction Medium: A Simple, Convenient and Green Procedure for the Synthesis of Thioethers, Thioesters and Dithianes using an Inexpensive Ionic Liquid, [pmIm]Br

Abstract: An easily accessible and inexpensive room temperature ionic liquid, 1-pentyl-3-methylimidazolium bromide, [pmIm]Br efficiently catalyzes the reaction of alkyl halides or acyl halides with thiols without any solvent at room temperature leading to the synthesis of thioethers and thioesters in high yields. This reaction has also been extended for the preparation of dithianes and transthioetherification. The ionic liquid is recovered and recycled for subsequent runs.

Synthesis and optical properties of CdS nanoribbons.

Abstract: Rapid production of single crystalline CdS nanoribbons with hexagonal wurtzite phase has been achieved by thermal evaporation of CdS powder on Si wafers. The flow rate of the carrier (Ar) gas along with the synthesis temperature plays an important role in defining the size and shape of the CdS nanoribbons. Scanning electron and transmission electron microscopic observations revealed the nanoribbons to have a flat end as well as side surfaces which will make it ideal for optoelectronic devices such as nanolasers and light emitting diodes based on individual nanoribbons. The nanoribbons have widths within 200−400 nm and lengths approximately a few hundred micrometers. Room-temperature photoluminescence measurements show green emission centered at ∼525 nm which may be ascribed to the near band edge emission. The Raman spectra of the CdS nanoribbons show peaks around 304, 609, 915, and 1220 cm-1 corresponding to the first-, second-, third-, and fourth-order longitudinal optical phonon modes, respectively.

Fluorescence anisotropy decay and solvation dynamics in a nanocavity : Coumarin 153 in methyl β-cyclodextrins

Abstract: Fluorescence anisotropy decay and solvation dynamics of coumarin 153 (C153) are studied in dimethyl β-cyclodextrin (DIMEB) and trimethyl β-cyclodextrin (TRIMEB) nanocavity in water. C153 binds to DIMEB and TRIMEB to form both 1:1 and 1:2 (C153:cyclodextrin) complexes. The anisotropy decays of C153 in DIMEB and TRIMEB are found to be biexponential. The fast component of anisotropy decay (∼1000 ps) is attributed to the 1:1 complex and the slower one (∼2500 ps) to the 1:2 complex. From the components of the anisotropy decay, the length of the 1:1 and 1:2 complexes are estimated. Solvation dynamics of C153 in DIMEB exhibits a very fast (2.4 ps) component (41%) and two slower components of 50 ps (29%) and 1450 ps (30%). Solvation dynamics in TRIMEB is described by three slow components of 10.3 ps (24%), 240 ps (45%), and 2450 ps (31%). Possible origins of the ultraslow components are discussed.

Occurrence of ribbons of cyclic water pentamers in a metallo-organic framework formed by spontaneous fixation of CO2

Abstract: In the reaction of equimolar amounts of copper(II) acetate with 2,2′-dipyridylamine (DPA) in aqueous tetrahydrofuran, in presence of KOH, aerial CO2 is spontaneously fixed to the carbonate anion yielding [Cu(DPA)(CO3)]·3H2O (1). X-ray crystallography shows the presence of zigzag ribbons of cyclic water pentamers in the channels of a chain-like metallo-organic framework. The water ribbons are stabilised by hydrogen bonds to the metallo-organic backbone. Each (H2O)5 pentamer is approximately planar.

Mesoporous Cr-MCM-41: An efficient catalyst for selective oxidation of cycloalkanes

Abstract: Highly ordered mesoporous Cr-MCM-41 materials with different Si:Cr mole ratios have been synthesized by using the hydrothermal method and avoiding co-precipitation of chromium oxides during synthesis. Detailed characterizations of these two-dimensional hexagonal mesoporous Cr-MCM-41 materials were carried out using powder XRD, TEM, SEM-EDS, N 2 sorption, FT-IR and UV–vis diffuse reflectance measurements. Cr-MCM-41 materials showed excellent catalytic activity and high selectivity in the direct oxidation of cycloalkanes viz. cyclohexane and cyclooctane to cyclohexanone and cyclooctanone, respectively, using dilute aqueous H 2 O 2 or tert -butyl hydroperoxide (TBHP) as oxidant under mild liquid phase reaction conditions.

MnII/CoII-Terephthalate Frameworks Containing Dipyridine Coligands: Syntheses, Crystal Structures, Magnetic Behaviors, and Thermal Studies

Abstract: Three new metal–organic hybrid polymeric networks of CoII and MnII with the molecular formulae [Co(bpp)(tp)(H2O)2] (1), [Mn(bpds)(tp)(H2O)2]·(bpds) (2), and [Mn(4,4′-bipy)(H2O)4]·(tp) (3) (bpp = 4,4′-trimethylenedipyridine; bpds = 4,4′-bipyridyl disulfide; 4,4′-bipy = 4,4′-dipyridyl; tp = terephthalate) have been synthesized and characterized by single-crystal X-ray diffraction studies, low temperature (300–2 K) magnetic measurements, and thermal behaviors The structure determination of complexes 1 and 2 reveals a parallel interpenetrated structure of 2D layers with (4,4) topology, with metal ions at the nodes connected through tp and N,N-donor coligands The octahedral N2O4 chromophore surrounding the metal ion results from trans located tp oxygens, two water molecules, and two nitrogen donors of the co-ligands in the cis position The presence of uncoordinated bpds between the interpenetrated layers leads to the formation of a wafer-like structure for 2 In complex 3, however, manganese(II) ions bridged by 4,4′-bipy and coordinated by four water molecules give rise to a 1D polymeric chain The adjoining chains encapsulate terephthalate anions (tp) to give a 3D structure through H-bonding Low-temperature magnetic data indicate weak antiferromagnetic coupling in complexes 1 and 2 (© Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2005)

Peptide-assisted synthesis of gold nanoparticles and their self-assembly.

Abstract: A novel gold nanoparticle-tripeptide (GNP-tripeptide) conjugate was prepared by peptide in-situ redox technique at ambient temperatureusing a newly designed tripeptide. This new tripeptide was nso designed that it has a C-terminus tyrosine residue, which reduced Au+3 to Au, and the terminally located free amino group was bound to the gold nanoparticle (GNP) surface resulting in highly stable Au colloids. The average diameter of the tripeptide-stabilized GNP is 8.7 +/- 2.3 nm. Tripeptide bound gold nanoparticles formed three-dimensional assemblies in the presence of an excess of similar or disimilar tripeptides. The aggregation of GNPs results in a red shift in the surface plasmon resonance from lambda max = 527 to 556 nm. The effect of the solvent, concentration, and nature of the tripeptides on the assembly process were investigated by TEM and UV-visible spectroscopy.

Slow solvation dynamics at the active site of an enzyme: implications for catalysis.

Abstract: Solvation dynamics at the active site of an enzyme, glutaminyl-tRNA synthetase (GlnRS), was studied using a fluorescence probe, acrylodan, site-specifically attached at cysteine residue C229, near the active site. The picosecond time-dependent fluorescence Stokes shift indicates slow solvation dynamics at the active site of the enzyme, in the absence of any substrate. The solvation dynamics becomes still slower when the substrate (glutamine or tRNAGln) binds to the enzyme. A mutant Y211H-GlnRS was constructed in which the glutamine binding site is disrupted. The mutant Y211H-GlnRS labeled at C229 with acrylodan exhibited significantly different solvent relaxation, thus demonstrating that the slow dynamics is indeed associated with the active site. Implications for catalysis and specificity have been discussed.

Comparison of low-order multireference many-body perturbation theories

Abstract: Tests have been made to benchmark and assess the relative accuracies of low-order multireference perturbation theories as compared to coupled cluster (CC) and full configuration interaction (FCI) methods. Test calculations include the ground and some excited states of the Be, H2,BeH2,CH2, and SiH2 systems. Comparisons with FCI and CC calculations show that in most cases the effective valence shell Hamiltonian (Hv) method is more accurate than other low-order multireference perturbation theories, although none of the perturbative methods is as accurate as the CC approximations. We also briefly discuss some of the basic differences among the multireference perturbation theories considered in this work.

Head-group size or hydrophilicity of surfactants: the major regulator of lipase activity in cationic water-in-oil microemulsions

Abstract: To determine the crucial role of surfactant head-group size in micellar enzymology, the activity of Chromobacterium Viscosum (CV) lipase was estimated in cationic water-in-oil (w/o) microemulsions of three different series of surfactants with varied head-group size and hydrophilicity. The different series were prepared by subsequent replacement of three methyl groups of cetyltrimethylammonium bromide (CTAB) with hydroxyethyl (1-3, series I), methoxyethyl (4-6, series II), and n-propyl (7-9, series III) groups. The hydrophilicity at the polar head was gradually reduced from series I to series III. Interestingly, the lipase activity was found to be markedly higher for series II surfactants relative to their more hydrophilic analogues in series I. Moreover, the activity remained almost comparable for complementary analogues of both series I and III, though the hydrophilicity was drastically different. Noticeably, the head-group area per surfactant is almost similar for comparable surfactants of both series I and III, but distinctly higher in case of series II surfactants. Thus the lipase activity was largely regulated by the surfactant head-group size, which plays the dominant role over the hydrophilicity. The increase in head-group size presumably allows the enzyme to attain a flexible conformation as well as increase in the local concentration of enzyme and substrate, leading to the higher efficiency of lipase. The lipase showed its best activity in the microemulsion of 6 probably because of its highest head-group size. Furthermore, the observed activity in 6 is 2-3-fold and 8-fold higher than sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT) and CTAB-based microemulsions, respectively, and in fact highest ever in any w/o microemulsions.

Electrical transport and dielectric relaxation in Fe3O4-polypyrrole hybrid nanocomposites.

Abstract: The polymerization of pyrrole in an aqueous medium in the presence of nanodimensional Fe3O4 using ammonium peroxodisulphate (APS) as oxidant results in the formation of polypyrrole?Fe3O4 nanocomposites. Characterization of the composites was carried out by Fourier transform infrared spectroscopy, x-ray diffraction, scanning and transmission electron microscopy. The magnetization data exhibit a small hysteresis loop at room temperature. The M?ssbauer spectra at room temperature reveal the doublet structure, characteristic of the superparamagnetic phase in magnetite (Fe3O4). The composite samples reveal ordered semiconducting behaviour. Polypyrrole is the dominating component in the transport process of the nanocomposites. A very large dielectric constant of about 11?000 at room temperature has been observed. The interface between polypyrrole and Fe3O4 plays an important role in producing a large dielectric constant in the composite.

Dynamics of Ag + ions in binary tellurite glasses

Abstract: We have reported the ionic relaxation for different compositions of $x{\mathrm{Ag}}_{2}\mathrm{O}\ensuremath{-}(1\ensuremath{-}x)\mathrm{Te}{\mathrm{O}}_{2}$ conducting glasses in wide temperature and frequency ranges. We have explained the composition dependence of the conductivity and the activation energy in terms of composition-dependent network structure of these glasses. We have compared the results for silver tellurite glasses with those for the alkali (Li,Na) tellurite glasses and observed that the migration of ${\mathrm{Ag}}^{+}$ ions in glasses, in general, appears to be anomalous. We have analyzed the frequency-dependent electrical data in the framework of the power-law conductivity formalism. We have explained the decreasing trend of the relaxation time with increasing ${\mathrm{Ag}}_{2}\mathrm{O}$ content in terms of structural transformation of tellurite network. Interestingly, we have observed that the concentration of mobile Ag ions is less than the concentration of total Ag ions and decreases with the increase of silver oxide content in the compositions, while the conductivity increases. We have shown that the scaling of the conductivity spectra is independent of temperature, but depends on composition.

Cobalt doped γ-Fe2O3 nanoparticles: synthesis and magnetic properties

Abstract: We demonstrate here the wet chemical synthesis of cobalt doped γ-Fe2O3 nanoparticles and the subsequent effect on magnetic properties with the variation in dopant concentration. It is observed that cobalt can be homogeneously doped into the γ-Fe2O3 lattice up to 5 mol% without any appreciable change in the particle size ( nm). Further increase in cobalt concentration (10 mol% here) resulted in an increase in particle size ( nm) due to possible adsorption of a cobalt layer on the surface of γ-Fe2O3 nanoparticles rather than complete doping in the iron oxide lattice. The ac susceptibility measurements revealed an increase in blocking temperature (TB) with percentage variation in cobalt doping (2–10%), indicating substitution of Fe3+ ions by Co2+ ions in the γ-Fe2O3 lattice. The dc magnetization measurements showed an increase in saturation magnetization only up to 5%, beyond which it significantly diminished. The reduction in saturation magnetization is attributed to the contribution from surface anisotropy in cobalt coated γ-Fe2O3 nanoparticles.