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Showing papers by "Indian Association for the Cultivation of Science published in 2000"




Journal ArticleDOI
TL;DR: In this article, the bimodal response of confined water is studied, with one bulk water-like subpicosecond component and a much slower component in a time scale of hundreds or thousands of picoseconds.
Abstract: Although water is often hailed as the lubricant of life, a detailed understanding of its role in many chemical and biological processes still eludes us. In many natural systems, water is confined in an environment where its free movement is restricted and its three-dimensional hydrogen-bonded network is disrupted. Very recently, several groups applied ultrafast laser spectroscopy to study the dynamics of the constrained water molecules. It is observed that the dynamic behavior of the confined water molecules is markedly different from that of the ordinary water molecules. The most striking result is the bimodal response of confined water, with one bulk water-like subpicosecond component and a much slower component in a time scale of hundreds or thousands of picoseconds. This slow second component constitutes 10−30% of the total response and is crucial in the understanding of the role of water in complex chemical and biological processes. The origin of the slow component has been a subject of intense recen...

357 citations


Journal ArticleDOI
TL;DR: It is observed that the hopping frequency can be used as the scaling frequency in the absence of well-defined dielectric loss peaks, and a universality of the scaling of the conductivity can be obtained for compositions with a similar structure.
Abstract: A scaling approach in the conductivity formalism is applied to lithium tellurite glasses of different compositions. We observe that the hopping frequency can be used as the scaling frequency in the absence of well-defined dielectric loss peaks, and a universality of the scaling of the conductivity can be obtained for compositions with a similar structure. Further, the reasons behind the inapplicability of the scaling approach reported recently are elucidated in terms of structure of the glasses.

318 citations


Journal ArticleDOI
TL;DR: In this article, a miscible homopolymer-copolymer pair viz., poly(ethyl methacrylate) (PEMA) and poly(styrene-co-butyl acrylate), was reported.
Abstract: A miscible homopolymer–copolymer pair viz., poly(ethyl methacrylate) (PEMA)–poly(styrene-co-butyl acrylate) (SBA) is reported. The miscibility has been studied using differential scanning calorimetry. While 1 : 1 (w/w) blends with SBA containing 23 and 34 wt % styrene (ST) become miscible only above 225 and 185 °C respectively indicating existence of UCST, those with SBA containing 63 wt % ST is miscible at the lowest mixing temperature (i.e., Tg's) but become immiscible when heated at ca 250 °C indicating the existence of LCST. Miscibility for blends with SBA of still higher ST content could not be determined by this method because of the closeness of the Tg's of the components. The miscibility window at 230 °C refers to the two copolymer compositions of which one with the lower ST content is near the UCST, while the other with the higher ST content is near the LCST. Using these compositions and the mean field theory binary interaction parameters between the monomer residues have been calculated. The values are χST-BA = 0.087 and χEMA-BA = 0.013 at 230 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 369–375, 2000

230 citations


Journal ArticleDOI
TL;DR: A review of the applications of indium metal and indium(III) halides in organic synthesis with particular reference to regio-, stereo-, and chemoselectivity is given in this paper.

190 citations


Journal ArticleDOI
TL;DR: In this paper, a highly regio-and stereoselective method for the synthesis of (Z)-3-aryl(alkyl)idene isoindolin-1-ones through palladium-copper catalysis is described.

161 citations


Journal ArticleDOI
TL;DR: In this paper, the role of different components in the glass formation has been explored from the density and thermal measurements, and a wide transmitting window having sharp cut-off in both ultraviolet-visible (UV-VIS) and infrared (IR) regions for almost all compositions of these glasses has been observed, making them an appealing candidate for different spectral devices.
Abstract: New glasses with high Li2O content have been obtained in the system Li2O–Bi2O3–PbO. The role of the different components in the glass formation has been explored from the density and thermal measurements. A wide transmitting window having sharp cut-off in both ultraviolet–visible (UV–VIS) and infrared (IR) regions for almost all compositions of these glasses has been observed, making them an appealing candidate for different spectral devices.

158 citations


Journal ArticleDOI
TL;DR: In this article, a simple and efficient procedure for the synthesis of 4-alkylquinolines by a one-pot reaction of anilines with alkyl vinyl ketones on the surface of silica gel impregnated with indium(III) chloride under microwave irradiation without any solvent.

115 citations


Journal ArticleDOI
TL;DR: A novel 1-D chain of Cu(II) with alternate single end-on andsingle end-to-end azido bridge having a very high Cu−N3(1,1)−Cu bond angle has been synthesized and characterized, which shows an intrachain antiferromagnetic interaction.
Abstract: A novel 1-D chain of Cu(II) with alternate single end-on and single end-to-end azido bridge having a very high Cu−N3(1,1)−Cu bond angle (129.98°) has been synthesized and characterized, which shows an intrachain antiferromagnetic interaction (J = −11.5 cm-1 for end-on bridge and −2.7 cm-1 for end-to-end bridge).

104 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the solvation dynamics of 4-(dicyanomethylene)-2-methyl-6(p-dimethylaminostyryl)-4H-pyran (DCM) in DMPC vesicles in water by using the Stokes shift technique.
Abstract: Solvation dynamics of 4-(dicyanomethylene)-2-methyl-6(p-dimethylaminostyryl)-4H-pyran (DCM) in dimyristoylphosphatidylcholine (DMPC) vesicles in water is studied by using the picosecond time-resolved Stokes shift technique In unilamellar DMPC vesicles, DCM exhibits wavelength-dependent fluorescence decays with a fast decay at the blue end and a slow decay preceded by a distinct growth at the red end of the emission spectrum The solvation dynamics of DCM in DMPC vesicles is found to be biexponential with two components 230 ps (40%) and 16 ns (60%) and is attributed to the relaxation of the water molecules inside the water pool of DMPC vesicles

Journal ArticleDOI
TL;DR: Estimated enhancement factor of the principal SERS bands indicate that the molecule is adsorbed on the silver surface through both the nitrogen atoms with the molecular plane almost perpendicular to the surface.

Journal ArticleDOI
TL;DR: In a moisture-free environment 6 is indefinitely stable in the solid state, but in CH2Cl2-MeCN solution 6a is rapidly oxidized by air, affording [Os(pap)(Br)(CO)(PPh3)2]+, 6a+, which has been isolated as the diamagnetic PF6- salt; 6b+PF6- has been similarly prepared.
Abstract: The reaction of [Os(H)(Br)(CO)(PPh3)3], 5, with 2-(phenylazo)pyridine (pap) in boiling dry heptane has afforded the azo anion radical complex [Os(pap•-)(Br)(CO)(PPh3)2], 6a, as the major product and [Os(pap)(H)(CO)(PPh3)2]Br, 7, as a minor byproduct. Upon replacing pap by the better π-acceptor azo-2,2‘-bipyridine (abp) in the above synthesis, the radical complex [Os(abp•-)(Br)(CO)(PPh3)2], 6b, becomes the sole product. It is proposed that 6 is formed via homolytic cleavage of the Os−H bond in 5; in the formation of 7, the Os−Br bond of 5 is heterolytically cleaved. The X-ray structures of 6b and 7·CH2Cl2 have been determined. In 6b, the N−N length is 1.35(2) A, consistent with the anion radical description; in 7·CH2Cl2 the length is 1.27(1) A. The spin-bearing extended Huckel HOMO in a model of 6 is found to be ∼70% azo-π* in character associated with a small metal contribution. An electronic band observed in the range 600−700 nm in solutions of 6 is assigned to the HOMO → LUMO transition, the LUMO being ...

Journal ArticleDOI
TL;DR: In this article, the variation of magnetization as a function of temperature has been analyzed using the Bloch equation and the results show a trend different from that predicted theoretically, which is attributed to an exchange interaction of the iron core with a ferrimagnetic oxide (either Fe 3 O 4 or γ-Fe 2 O 3 ) shell.

Journal ArticleDOI
14 Mar 2000-Langmuir
TL;DR: Polyaniline (PANI) forms thermoreversible gels in four different sulfonic acids, e.g., Dinonylnaphthalene sulfonic acid (DNNSA), dinonylnapthalene disulfonic acid(DNNDSA), ±camphor-10-sulfonic aci...
Abstract: Polyaniline (PANI) forms thermoreversible gels in four different sulfonic acids, e.g., dinonylnaphthalene sulfonic acid (DNNSA), dinonylnapthalene disulfonic acid (DNNDSA), ±camphor-10-sulfonic aci...

Journal ArticleDOI
TL;DR: In this article, the solvation dynamics of 4-(dicyanomethylene)-2-methyl-6(p-dimethylaminostyryl) 4H-pyran (DCM) have been studied in neutral (Triton X-100, TX), cationic (cetyl trimethyl ammonium bromide, CTAB) and anionic (sodium dodecyl sulfate, SDS) micelles using Stokes shift.

Journal ArticleDOI
15 Nov 2000-EPL
TL;DR: In this paper, the optical absorption of these particles was found to be characterized by excitons with corresponding energies varying from 2.6 to 2.25 eV in the particle size range mentioned above.
Abstract: Cuprous oxide (Cu2O) particles coated with polyacrylamide having diameters in the range from 4.8 to 8.6 nm were prepared by a chemical method. The optical absorption of these particles was found to be characterized by excitons with corresponding energies varying from 2.6 to 2.25 eV in the particle size range mentioned above. A second optical-absorption maximum signifying surface states within the band gap is exhibited by the specimens with relevant energies varying from 2.6 to 1.77 eV in this particle size range.

Journal ArticleDOI
TL;DR: Ring-closing metathesis has been applied to a series of glucose derivatives to produce cyclopentene derivatives 5a and 5b, cyclohexene derivatives 8 and 9, cycleheptene 12, and cyclooctene 14, and a range of fused oxepine derivatives 29a-c and one oxo-cyclononene 31.
Abstract: Ring-closing metathesis has been applied to a series of glucose derivatives to produce cyclopentene derivatives 5a and 5b, cyclohexene derivatives 8 and 9, cycloheptene 12, and cyclooctene 14. Spirocyclic dihydrofurans 19, 26a, and 26b, along with dihydropyran 22, were also produced. A range of fused oxepine derivatives 29a-c and one oxo-cyclononene 31 were also prepared. Cyclopentene 5b was subjected to a sequence of hydrogenation, NBS bromination, and treatment with powdered zinc to furnish the ring-expanded product 35. No such ring expansion occurred when the cyclohexaannulated compound 8 was treated with NBS followed by powdered zinc, leading to aldehyde 39. The spiro dihydrofuran derivative 19 was converted to the aldehyde 42 via the same reaction sequence used to fragment cyclopentene derivative 5b.

Journal ArticleDOI
TL;DR: In this article, two new tridentate ligands of the type NH4C5NNC6H4N(H)C 6H4(R) (R = H (HL1) or CH3 (HL2)) have been synthesized by the cobalt mediated direct phenyl ring amination of co-ordinated NH4c5NNc6H5.
Abstract: Two new tridentate ligands of the type NH4C5NNC6H4N(H)C6H4(R) (R = H (HL1) or CH3 (HL2)) have been synthesized by the cobalt mediated direct phenyl ring amination of co-ordinated NH4C5NNC6H5. These bind to metal ions as monoanionic N,N,N-donors (L−), affording [MnIIL2] and [CoIIIL2]ClO4 complexes in very high yields. The compounds have low-spin electronic configurations. While the manganese complexes are paramagnetic with one unpaired electron (1.65–1.70 μB) the cobalt complexes are diamagnetic. Crystal structure determination of [Mn(L1)2] has revealed the presence of a distorted octahedral MnN6 co-ordination sphere. The two aza nitrogens of the anionic tridentate ligands approach the metal centre closest with Mn–N(aza) ca. 1.89 A. The other two Mn–N distances are: Mn–N(py), 2.00; Mn–N(amido), 1.95 A. There is a significant degree of ligand backbone conjugation in the co-ordinated ligands which has resulted in shortening of the C–N bond distances and also in lengthening of the diaza (N=N) distances. In fluid solution, [MnL2] species exhibit six line EPR spectra with low hyperfine constant (A = 75 G). In frozen dichloromethane–toluene (77 K), rhombic EPR spectra are observed, consisting of an isolated signal g3 (ca. 1.91) and two relatively close signals g1 and g2 (ca. 2.06 and 2.03 respectively). Both manganese as well as cobalt complexes display multiple redox responses. The manganese complexes show MnII ⇌ MnIII oxidation at ca. 0.38 V and the cobalt analogues display reversible CoIII ⇌ CoII reduction at −0.40 V. Electrogenerated [MnIIIL2]+ shows transitions in the near IR region.

Journal ArticleDOI
TL;DR: In this article, the authors studied the solvation dynamics of Coumarin 480 in a tetraethyl orthosilicate (TEOS) sol−gel matrix using time-resolved emission spectroscopy.
Abstract: Solvation dynamics of Coumarin 480 (C-480) in a tetraethyl orthosilicate (TEOS) sol−gel matrix has been studied using time-resolved emission spectroscopy. In the macroscopically solid TEOS matrix the solvation dynamics of C-480 is described by a major (85%) component of 120 ± 20 ps and a minor (15%) component of 800 ± 100 ps. These components are substantially slower than the solvation dynamics in bulk water. The rotational relaxation time of C-480 in this matrix is found to be very short (<80 ps).

Journal ArticleDOI
TL;DR: In this article, the authors synthesize CuInS2 films by sulphurization of In/Cu stacked elemental layers (SEL) deposited onto glass and Mo-coated glass substrates by graphite box annealing at temperatures of 620-880 K. The properties of these films were characterized by measuring electrical, optical, microstructural and photoluminescence properties.

Journal ArticleDOI
TL;DR: In this paper, the frequency dependent ultrasonic velocities (both longitudinal and shear) and attenuation in BaTiO 3 doped (80V 2 O 5 -20PbO + x BaTi O 3 ) oxide (VPB) glasses (for x = 0, 1, 5, 10, and 15 wt% of the base glass) were measured using pulse echo overlap method at room temperature.
Abstract: The frequency dependent ultrasonic velocities (both longitudinal and shear) and attenuation in BaTiO 3 doped (80V 2 O 5 -20PbO + x BaTiO 3 ) oxide (VPB) glasses (for x = 0, 1, 5, 10, and 15 wt% of the base glass) have been measured using pulse echo overlap method at room temperature. From the measured velocity, density and attenuation, various parameters namely longitudinal, shear, bulk, and Young's moduli, Debye temperature, Poisson's ratio, acoustic impedance and microhardness of the VPB glasses were determined. All these parameters of the glasses increase with addition of BaTiO 3 content. On the other hand, attenuation decreases with addition of BaTiO 3 The variation of these parameters with the addition of BaTiO 3 content was discussed in terms of the change in structure of the glass network. The study reveals that ultrasonic velocity and attenuation measurements have been effectively used as a tool to explore the structural changes and mechanical properties on addition of BaTiO 3 in vanadate lead glasses.

Journal ArticleDOI
TL;DR: Metal-mediated magnetic interaction makes the EPR-silent diradical 4 strongly antiferromagnetic with J = -299 cm-1 and the monoradicals 4+, 5, and 6 uniformly display a strong EPR signal near g = 2.00.
Abstract: The reaction of the dihydride [RuII(H)2(CO)(PPh3)3], 3, with excess azo-2,2‘-bipyridine (abp) in boiling dry benzene has afforded the diradical bischelate [RuII(abp•-)2(CO)(PPh3)], 4, and the hydridic monochelate monoradical [RuII(abp•-)(H)(CO)(PPh3)2], 5. A similar reaction between 3 and 2-(p-chlorophenylazo)pyridine (Clpap) did not yield a bischelate, but the hydridic monoradical [RuII(Clpap•-)(H)(CO)(PPh3)2], 6, has been isolated. Upon treatment of 4−6 with NH4PF6 in a wet dichloromethane−acetonitrile medium, the one-electron-oxidized salts 4+PF6-, 5+PF6-, and 6+PF6- are isolated, H+ being the oxidizing agent. The X-ray structures of 4+PF6-·CH2Cl2, 5+PF6-·H2O, and 6+PF6- have been determined. In the monoradical 4+ the azo N−N bond lengths in the two chelate rings are 1.284(6) and 1.336(6) A, showing that the radical electron is localized in the latter ring. The half-filled extended Huckel HOMO is indeed found to be so localized, and it has a large azo character. Complexes 4−6 display radical redox coup...

Journal ArticleDOI
TL;DR: In this article, structural studies of strontium vanadate glasses of compositions xV2O5-SrO are reported, where the network structure for the glass compositions with 90 and 80 mol% vanadium oxide content is built up of the VO5 polyhedra.
Abstract: Structural studies of the strontium vanadate glasses of compositions xV2O5–(100 − x)SrO are reported. X-ray diffractograms, density, and oxygen molar volume, etc., of the glasses show that single-phase and homogeneous glasses were obtained in the composition domain x = 50 to 90 mol%. The network structure for the glass compositions with 90 and 80 mol% V2O5 is built up of the VO5 polyhedra, while the other glass compositions consist of the VO4 polyhedra. Density and glass transition temperature are observed to decrease with an increase in the V2O5 content. The magnetic susceptibility of the glasses shows an increase of concentration of the reduced V4+ ion with the increase of vanadium oxide content in the compositions. The well-resolved electron spin resonance structure observed for the glass composition with 50 mol% V2O5 gradually becomes poor and reduces to a single component line, which has been attributed to the increase of the hopping rate of charge carriers with the increase of the V2O5 content in the compositions.

Journal ArticleDOI
29 Jan 2000-Langmuir
TL;DR: In this paper, the authors studied the course of dispersion polymerization of aniline using ammonium peroxodisulfate (APS) as initiator oxidant and poly(vinyl alcohol) as stabilizer in different media, viz., water (1 M HCl), water (pH = 2.41, [aniline] ≡ [HCl]), and aqueous ethanol (1M HCl) was followed spectrophotometrically.
Abstract: The course of dispersion polymerization of aniline using ammonium peroxodisulfate (APS) as initiator oxidant and poly(vinyl alcohol) as stabilizer in different media, viz., water (1 M HCl), water (pH = 2.41, [aniline] ≡ [HCl]), and aqueous ethanol (1 M HCl), was followed spectrophotometrically. It was found that the absorption peak positions for the pernigraniline salt change markedly with change in acidity and [APS]/[aniline] ratio. The spectral shape also changes greatly when water is replaced by aqueous ethanol. The evolution of the spectra with time was used to generate rate curves which reveal the autocatalytic nature of the reaction. The activation energies of the reaction in the various media were evaluated for both the induction period and the polymerization period using the inverse of the times of these periods as representing average rates for the periods, respectively. The activation energies increase with decrease in medium polarity and/or acidity. These variations have been discussed.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the relaxation dynamics of lithium ions in lead bismuthate glasses in the frequency range from 10 Hz to 2 MHz and in the temperature range from 303--553 K.
Abstract: We have investigated relaxation dynamics of lithium ions in lead bismuthate glasses in the frequency range from 10 Hz to 2 MHz and in the temperature range from 303--553 K. Using the Anderson-Stuart model, we have calculated the activation energy, which is observed to be lower than that of the dc conductivity. We have studied the relaxation mechanism of these glasses in the framework of the electric modulus and conductivity formalisms. The microscopic parameters obtained from these formalisms have been compared. We have also calculated the decoupling index and correlated them with the stretched exponential relaxation parameter and the dc conductivity.

Journal ArticleDOI
TL;DR: In this article, the physical properties of polyvinylidene fluoride (PVF2) gels were studied by variation of the number of intermittent carbon atoms (n = 0−7) of the diesters.
Abstract: Poly(vinylidene fluoride) (PVF2) produces thermoreversible gels in diesters. By variation of the number of intermittent carbon atoms (n = 0−7) of the diesters, the physical properties of the gels are studied. The morphology of the PVF2/diethyl oxalate (DEO) gel is spheroidal, but the morphology of PVF2−diethyl malonate (DEM) gel is a mixture of both spheroidal and fibrillar. The PVF2/diethyl succinate (DES), PVF2/diethyl gluterate (DEG), PVF2/diethyl pimelate (DEP), and PVF2/diethyl azelate (DEAZ) gels are “fibrillar-like” as evidenced from scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The X-ray and solvent subtracted FT-IR spectra indicate the presence of α-polymorph PVF2 in all the gels. The enthalpy of gel formation and the enthalpy of gel fusion, measured from differential scanning calorimetry (DSC), show linear plot with PVF2 concentration for PVF2−DEO gels but others exhibit positive deviation from linearity. From the deviation vs PVF2 weight fraction (WPVF2) plot, t...

Journal ArticleDOI
29 Nov 2000-Langmuir
TL;DR: In this article, the properties of binary and ternary surfactant combinations of sodium dodecyl benzene sulfonate, polyoxyethylene sorbitan monolaurate, and polyoxy methylene lauryl ether have been investigated in detail by employing tensiometric, fluorometric, and conductometric techniques in aqueous medium.
Abstract: Micellar properties of the binary and ternary surfactant combinations of sodium dodecyl benzene sulfonate, polyoxyethylene sorbitan monolaurate, and polyoxyethylene lauryl ether have been investigated in detail by employing tensiometric, fluorometric, and conductometric techniques in aqueous medium. The critical micelle concentrations, counterion binding, interfacial adsorption, energetics of micellization as well as adsorption, micropolarity, aggregation number, composition of the micellar species, and molecular interaction parameters in the mixed micelles have been evaluated. The physicochemical properties of the systems are observed to depend on the solution composition. We have estimated the characteristics of the micellar aggregates such as composition, activity coefficients, critical micelle concentration, and synergism of the binary and ternary surfactant systems following the treatments of Clint, Rubingh, Motomura, et al. and Rubingh and Holland.

Journal ArticleDOI
15 Aug 2000
TL;DR: The apparent enhancement factor calculations of the principal Raman bands indicate that in the surface-adsorbed state, an HQ molecule is oriented neither flat nor vertical to the silver surface but is tilted, which supports the evidence of a charge transfer interaction.
Abstract: Surface-enhanced Raman scattering (SERS) of 8-hydroxy quinoline (HQ) adsorbed on silver hydrosols are compared with the FTIR and normal Raman spectrum in the bulk and in solution. Definite evidence of the charge transfer interaction to the overall contribution in the SER enhancement has been reported. The excitation profile study also supports the evidence of a charge transfer interaction. The effect of pH variation on the SER band intensity is explained in terms of chemisorption of the molecule on bare and chlorinated silver surfaces. The apparent enhancement factor calculations of the principal Raman bands indicate that in the surface-adsorbed state, an HQ molecule is oriented neither flat nor vertical to the silver surface but is tilted.

Journal ArticleDOI
TL;DR: The significantly higher metal reduction potentials of the azopyridine compared to pyridine-2-aldimine complexes is ascribed to the superior pi-acidity and electron-withdrawing character of the azo function relative to the aldimine function.
Abstract: The concerned azo ligands are 2-(phenylazo)pyridine (HL) and 2-((p-chlorophenyl)azo)pyridine (ClL). The reaction of KReO4 with HL in hot concentrated HCl is attended with metal reduction and ligand chlorination affording the oxo complex ReVOCl3(ClL), 2, which furnishes ReIII(OPPh3)Cl3(ClL), 3, upon treatment with PPh3. Aromatic amines, ArNH2, convert 2 to the imido complex ReV(NAr)Cl3(ClL), 5, and the unusual oxo−imido dimer (ClL)Cl2(O)ReVOReV(NAr)Cl2(ClL), 7. The complex ReIII(OPPh3)Cl3(HL), 4, has been generated from ReVOCl3(PPh3)2 and HL. Reaction of 4 with HL has yielded ReV(NPh)Cl3(HL), 6, via azo splitting. The complexes have been characterized with the help spectral, magnetic, and X-ray structural data (2, 3, 5c (Ar = pClC6H4) and 7·CH2Cl2 (Ar = pMeC6H4)). In 2, 3, and 5c the ReCl3 fragment is meridionally disposed, and in 7 the ReCl2 fragments have a trans configuration. The Re−O(oxo) bond, 1.663(6) A, in 2 and Re−N(imido) bond, 1.719(5) A, in 5c are triple bonds. The corresponding bonds are sligh...