Showing papers by "Indian Association for the Cultivation of Science published in 2010"

Facile Synthesis of Water-Soluble Fluorescent Silver Nanoclusters and HgII Sensing

Abstract: A single step facile synthesis of highly emissive, water-soluble, fluorescent Ag nanoclusters has been reported using a small molecule, dihydrolipoic acid. These clusters were characterized using ultraviolet/visible (UV/vis) spectroscopy, photoluminescence spectroscopy, Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS), and X-ray diffraction (XRD) studies. Mass spectrometric analysis shows the presence of a few atoms in nanoclusters containing only Ag4 and Ag5. The reported fluorescent Ag nanoclusters show excellent optical properties, including narrow emission profile, larger Stokes shift (more than 200 nm), and good photostability. Interestingly, these nanoclusters also exhibit semiconducting property. Moreover, as-prepared fluorescent Ag nanoclusters have been utilized as an indicator for selective and ultrasensitive detection of highly toxic HgII ions in water, even at subnanomolar concentrations.

Functional and multifunctional nanoparticles for bioimaging and biosensing.

Abstract: Herein, we describe the synthesis of functional and multifunctional nanoparticles (NPs), derived from our recent work, for bioimaging and biosensing applications. The functionalized NPs involve quantum dots (QDs), magnetic particles (MPs) and noble metal NPs for the aforementioned applications. A diverse silica coating approaches (reverse microemulsion and thin silanization) are delineated for the design of water-soluble NPs. We also review the synthesis of silica-coated bifunctional NPs consisting of MPs and QDs for live cell imaging of human liver cancer cells (HepG2) and mouse fibroblast cells (NIH-3T3). Using silica coated NPs, various NPs that are functionalized with antibody, oligonucleotide, biotin and dextran are efficiently used for protein detection.

Ascorbate-assisted growth of hierarchical ZnO nanostructures: sphere, spindle, and flower and their catalytic properties.

Abstract: A simple solution-based method to prepare mainly flowerlike zinc oxide (ZnO) nanostructures using the ascorbate ion as a shape-directing/capping agent at relatively low temperature (ca. 30 and 60 °C) was described. However, we observed that different shapes of hierarchical ZnO nanostructures such as flowerlike, spindlelike, and spherical could be obtained with an increase in the synthesis temperature from 60 to 90 °C. The effects of other organic capping agents on the shape of hierarchical ZnO nanostructures were also studied. FTIR, FESEM, and XRD characterization were performed on the formed ZnO nanostructures to understand the role of ascorbate in the growth of flowerlike morphology. The nucleation and growth process can regulate by changing the metal precursor and ascorbate ion concentrations. We were able to identify intermediate nanostructures such as spherical/quasi-spherical and spindle that are very much on the pathway of formation of large, flowerlike ZnO nanostructures. Electron microscopy resul...

Study of the Properties of Microcrystalline Cellulose Particles from Different Renewable Resources by XRD, FTIR, Nanoindentation, TGA and SEM

Abstract: The main objective of this work was to extract microcrystalline cellulose (MCC) particles from different cellulosic resources like cotton, jute, newsprint, filter paper and investigate their suitability as green reinforcing material in biocomposites. The MCC particles were extracted by acid hydrolysis with 64% sulphuric acid. The processing parameters like acid concentration, temperature, time and mechanical force were kept constant. The MCC particles were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), particle size analysis, Fourier transform infrared spectroscopy and thermogravimetric analysis. The viscoelastic properties of the MCC particles were investigated with the help of nanoindentation technique for the first time. The acid hydrolysis changed the %crystallinity and crystallite sizes of the MCC particles compared to their source materials. The modulus and hardness of the MCC particles varied significantly depending on their precursors. The presence of non-cellulosic constituents controlled the deformation behaviour of the MCC particles. The thermal stability of the MCC particles was correlated with the tangling effect of the flexible cellulose chains.

Short‐Peptide‐Based Hydrogel: A Template for the In Situ Synthesis of Fluorescent Silver Nanoclusters by Using Sunlight

Abstract: N-terminally Fmoc-protected dipeptide, Fmoc-Val-Asp-OH, forms a transparent, stable hydrogel with a minimum gelation concentration of 0.2 % w/v. The gelation property of the hydrogel was investigated by using methods such as transmission electron microscopy, field-emission scanning electron microscopy, atomic force microscopy and Fourier transform infrared spectroscopy. The silver-ion-encapsulating hydrogel can efficiently and spontaneously produce fluorescent silver nanoclusters under sunlight at physiological pH (7.46) by using a green chemistry approach. Interestingly, in the absence of any conventional reducing agent but in the presence of sunlight, silver ions were reduced by the carboxylate group of a gelator peptide that contains an aspartic acid residue. These clusters were investigated by using UV/Vis spectroscopy, photoluminescence spectroscopy, high-resolution transmission electron microscopy (HR-TEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) studies. Mass spectrometric analysis shows the presence of a few atoms in nanoclusters containing only Ag2. The reported fluorescent Ag nanoclusters show excellent optical properties, including a very narrow emission profile and large Stokes shift (>100 nm). The reported fluorescent Ag nanoclusters within hydrogel are very stable even after 6 months storage in the dark at 4 °C. The as-prepared hydrogel–nanocluster conjugate could have applications in antibacterial preparations, bioimaging and other purposes.

Photoluminescence and Photoconductivity of ZnS-Coated ZnO Nanowires

Abstract: ZnO nanowires (NWs) with a ZnS coating are synthesized in order to modify the surface without changing the diameter of the NWs. They have the wurtzite ZnO at the core and a cubic ZnS at the outer layer. The NWs show a sharp ultraviolet and a broad visible emission of the photoluminescence spectra. Surface modification has led to a change in the position of the maxima of the visible emission in ZnO-ZnS NWs. The photocarrier relaxation under steady UV illumination occurs in ZnO NW arrays but is absent in ZnO-ZnS NW arrays. The dark current value for both type of NWs are similar, whereas the photocurrent value is much higher in the surface-modified NWs. Higher photocurrent value indicates a transport of the photogenerated carriers from the ZnS layer to ZnO during UV illumination. The carrier transport mechanism is proposed through a model.

Self-assembled TiO2 nanoparticles: mesoporosity, optical and catalytic properties

Abstract: Herein, we explore the idea of self-assembly of nearly monodisperse nanoparticles as uniform building blocks to design highly crystalline mesoporous TiO2 nanoparticles, through evaporation-induced self-assembly (EISA) and hydrothermal methods by using non-ionic Pluronic F127 and anionic surfactant SDS, respectively as structure directing agents. The small- and wide-angle powder X-ray diffraction and transmission electron microscopy (TEM) are used to characterize the mesophases. N2 adsorption–desorption studies and high-resolution TEM results further reveal that mesopores are formed by the arrangement of the nanoparticles of size ca. 4.0–5.0 nm for SDS-templated and 8.0–9.0 nm for F127-templated TiO2 nanoparticles with broad interparticle pore size distribution. Optical properties of these nanomaterials are studied by UV-visible diffuse-reflectance spectroscopy, photoluminescence (PL) and time-resolved fluorescence (TCSPC). These nanostructured titania exhibited excellent catalytic activity in the photodegradation of ecologically abundant dyes Methylene blue and Rose Bengal under UV-visible light irradiation.

Transition-Metal Decoration Enhanced Room-Temperature Hydrogen Storage in a Defect-Modulated Graphene Sheet

Abstract: Using first-principles density functional calculations, we show that a transition-metal (TM)-doped defected graphene sheet with periodic repetition of a C atom vacancy (Vc) can be used as a promising system for hydrogen storage. The TM atoms adsorbed above and below the defected site are found to have a strong bonding to the graphene sheet, thereby circumventing the problem of TM clustering, which is the main impediment for efficient hydrogen storage in nanostructure systems. The results reveal that, when the vacancy-modulated graphene sheet is decorated on both sides by a combination of less than half-filled (TM1) and more than half-filled (TM2) elements, it results in the adsorption of molecular hydrogen with a binding energy lying in the desirable energy window. Among all the different TM1−TM2 combinations at a C vacancy site, Fe−Ti turns out to be the best choice where five H2 molecules get attached on each pair. To underscore the stability of these hydrogenated systems, we have performed an ab initio...

Quest for mode of binding of 2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide with calf thymus DNA.

Abstract: The mode of binding of 2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide (DASPMI) with calf thymus DNA as revealed from different steady state and time-resolved emission spectroscopic measurements has been reported in this paper. Fluorescence enhancement of DASPMI and its quenching by potassium iodide (KI) points to groove binding of dye with ct-DNA, rather than intercalation in the ct-DNA helix. An increase in steady state anisotropy and fluorescence lifetime hints at binding with ct-DNA. The value of binding constant from emission and association constant from circular dichroic spectrum also indicates weak binding. The strong dependence on ionic strength or salt in controlling the binding of DASPMI with ct-DNA by electrostatic interaction confirms groove binding. The high semicone angle of DASPMI in ct-DNA certainly rules out the possibility of intercalated bonding. A theoretical modeling shows that the probe is bound to ct-DNA as a crescent with a curvature of 11.35 A, which is the previously known curvature of probe in the minor groove.

Hydrogelation through self-assembly of fmoc-peptide functionalized cationic amphiphiles: potent antibacterial agent.

Abstract: The present work reports a new class of antibacterial hydrogelators based on anti-inflammatory N-fluorenyl-9-methoxycarbonyl (Fmoc) amino acid/peptides functionalized cationic amphiphiles These positively charged hydrogelators were rationally designed and developed by the incorporation of a pyridinium moiety at the C-terminal of Fmoc amino acid/peptides, because the pyridinium-based amphiphiles are a known antibacterial agent due to their cell membrane penetration properties The Fmoc amino acid/peptide-based cationic amphiphiles efficiently gelate (minimum gelation concentration ∼06−22%, w/v) water at room temperature Judicious variation of amino acid and their sequences revealed the architectural dependence of the molecules on their gelation ability Several microscopic techniques like field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) were used to obtain the visual insight of the morphology of the gel network A number of spectroscopic techniques like circular dic

A new functionalized mesoporous matrix supported Pd(II)-Schiff base complex: an efficient catalyst for the Suzuki–Miyaura coupling reaction

Abstract: A new Pd(II) bounded 2D-hexagonally ordered functionalized MCM-41 type material (IV) has been synthesized. Functionalization was carried out by the anchoring of 3-aminopropyltriethoxysilane in the MCM-41 type mesoporous material, followed by grafting with 2,6-diacetylpyridine (DAP) to give a N3-type Schiff base chelating attachment for the Pd(II) species. Fourier transform infrared (FTIR), powder X-ray diffraction (PXRD) and high resolution transmission electron microscopy (HRTEM) studies have been used to characterize the material. Material IV behaves as a highly active catalyst towards Suzuki–Miyaura cross-coupling reaction for the synthesis of biaryl organics. In addition, IV acts as a true heterogeneous catalyst in coupling reaction. It was found that this catalyst is highly efficient and recyclable towards Suzuki–Miyaura reaction with high turn over frequencies. X-Ray photoelectron spectroscopic (XPS) analysis was employed to understand the oxidation state of the palladium atom in the catalyst (IV) and its loading in the material.

Microbial synthesis of multishaped gold nanostructures.

Abstract: The development of methodologies for the synthesis of nanoparticles of well-defined size and shape is a challenging one and constitutes an important area of research in nanotechnology. This Full Paper describes the controlled synthesis of multishaped gold nanoparticles at room temperature utilizing a simple, green chemical method by the interaction of chloroauric acid (HAuCl4 x 3H20) and cell-free extract of the fungal strain Rhizopus oryzae. The cell-free extract functions as a reducing, shape-directing, as well as stabilizing, agent. Different shapes of gold nanocrystals, for example, triangular, hexagonal, pentagonal, spherical, spheroidal, urchinlike, two-dimensional nanowires, and nanorods, are generated by manipulating key growth parameters, such as gold ion concentration, solution pH, and reaction time. The synthesized nanostructures are characterized by UV/Vis and Fourier-transform infrared spectroscopy, transmission electron microscopy, and energy dispersive X-ray analysis studies. Electron diffraction patterns reveal the crystalline nature of the nanoparticles and a probable mechanism is proposed for the formation of the different structural entities.

Preparation and Characterization of Cross-Linked Starch/Poly(vinyl alcohol) Green Films with Low Moisture Absorption

Abstract: The effects of incorporating different cross-linking agents into starch/poly(vinyl alcohol) (PVA) blend were examined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), mec...

Full implementation and benchmark studies of Mukherjee's state-specific multireference coupled-cluster ansatz

Abstract: The state-specific multireference coupled-cluster (SS-MRCC) ansatz developed by Mukherjee and co-workers [J. Chem. Phys. 110, 6171 (1999)] has been implemented by means of string-based techniques. The implementation is general and allows for using arbitrary complete active spaces of any spin multiplicity and arbitrarily high excitations in the cluster operators. Several test calculations have been performed for single- and multiple-bond dissociations of molecular systems. Our experience shows that convergence problems are encountered when solving the working equations of the SS-MRCC in the case the weight of one or more reference functions tends to take on very small values. This is system specific and cannot yet be handled in a black-box fashion. The problem can be obviated by either dropping all the cluster amplitudes from the corresponding model functions with coefficients below a threshold or by a regularization procedure suggested by Tikhonov or a combination of both. In the current formulation the S...

Hemoglobin−Silver Interaction and Bioconjugate Formation: A Spectroscopic Study

Abstract: In this article, we report the results of the extent of interaction as well as the formation of a bioconjugate of human hemoglobin (Hb) with silver (Ag). The complexation process and conformational changes are characterized using different spectroscopic and microscopic techniques. The UV−vis study demonstrates the perturbation of the soret/heme band and generates conformational heterogeneity within the heme group in the presence of silver. A fluorescence study suggests that the Tryptophan (Trp) residues of Hb are in a more polar environment after conjugation. Initial fluorescence enhancement with addition of silver is due to metal-enhanced fluorescence. Moreover, the fluorescence quenching after the formation of the Hb−Ag bioconjugate follows the modified Stern−Volmer (S−V) plot. The S−V plot along with the time-resolved fluorescence study indicates the presence of both static and dynamic types of quenching. In addition, the reduction potential values of the entities (Hb−heme, Ag+, and Trp) indicate the p...

Synthesis, Characterization, Photophysical, and Anion-Binding Studies of Luminescent Heteroleptic Bis-Tridentate Ruthenium(II) Complexes Based on 2,6-Bis(Benzimidazole-2-yl)Pyridine and 4′-Substituted 2,2′:6′,2′′ Terpyridine Derivatives

Abstract: A series of heteroleptic tridentate ruthenium(II) complexes of composition [(H2pbbzim)Ru(tpy-X)](PF6)2 (1−7), where H2pbbzim = 2,6-bis(benzimidazole-2-yl)pyridine and tpy-X = 4′-substituted terpyridine ligands with X = H, p-methyl phenyl (PhCH3), p-bromomethylphenyl (PhCH2Br), p-dibromomethylphenyl (PhCHBr2), p-cyanomethylphenyl (PhCH2CN), p-triphenylphosphonium methylphenyl bromide (PhCH2PPh3Br), and 4′-phenylformyl (PhCHO) groups, has been synthesized and characterized by using standard analytical and spectroscopic techniques. These compounds were designed to increase the excited-state lifetime of ruthenium(II) bisterpyridine-type complexes. The X-ray crystal structure of a representative compound 2, which crystallized with monoclinic space group P2(1)/c, has been determined. The absorption spectra, redox behavior, and luminescence properties of the ruthenium(II) complexes have been thoroughly investigated. All of the complexes display moderately strong luminescence at room temperature with lifetimes in...

Collider signatures for the heavy lepton triplet in the type I+III seesaw mechanism

Abstract: The minimal SU(5) theory augmented by the fermionic adjoint representation restores the coupling constant unification and gives realistic neutrino masses and mixing through the hybrid Type I and Type III seesaw. The crucial prediction of the theory is an SU(2) lepton triplet with the mass below TeV. We study the signature of these heavy leptons at the hadron and lepton colliders. The smoking gun evidence of the theory, as in general seesaw mechanisms, is $\ensuremath{\Delta}L=2$ lepton-number violation through events of a pair of like-sign leptons plus four jets without significant missing energy at hadron colliders. We find that via this unique channel the heavy lepton can be searched for up to a mass of 200 GeV at the Tevatron with $8\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, and up to 450 (700) GeV at the LHC of 14 TeV C.M. energy with $10(100)\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$. The 7 TeV LHC run of $1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ is expected to probe a mass window of 110--200 GeV. We also comment on how to distinguish this theory from other models with similar heavy leptons. Finally, we compare the production rates and angular distributions of heavy leptons in ${e}^{+}{e}^{\ensuremath{-}}$ collisions for various models.

Monometallic and Bimetallic Ruthenium(II) Complexes Derived from 4,5-Bis(benzimidazol-2-yl)imidazole (H3Imbzim) and 2,2′-Bipyridine as Colorimetric Sensors for Anions: Synthesis, Characterization, and Binding Studies

Abstract: Mixed-ligand monometallic and bimetallic ruthenium(II) complexes of compositions [(bpy)2Ru(H3Imbzim)](ClO4)2·2H2O (1) and [(bpy)2Ru(H2Imbzim)Ru(bpy)2](ClO4)3·CH2Cl2 (2), where H3Imbzim = 4,5-bis(benzimidazol-2-yl)imidazole and bpy = 2,2′-bipyridine, have been synthesized and characterized using standard analytical and spectroscopic techniques. The X-ray crystal structures of both compounds have been determined and showed that 1 crystallized in the triclinic form with space group P1 and 2 is in the monoclinic form with space group P2(1)/m. The anion binding properties of complexes 1 and 2, as well as those of the parent H3Imbzim, were thoroughly investigated in an acetonitrile solution using absorption, emission, and 1H NMR spectral studies, which revealed that both of the metalloreceptors act as sensors for F−, for AcO−, and, to some extent, for H2PO4−. At a relatively lower concentration of anions, a 1:1 hydrogen-bonded adduct was formed; however, in the presence of an excess of anions, stepwise deproto...

Radiative contribution to neutrino masses and mixing in μνSSM

Abstract: In an extension of the minimal supersymmetric standard model (popularly known as the μνSSM), three right handed neutrino superfields are introduced to solve the μ-problem and to accommodate the non-vanishing neutrino masses and mixing. Neutrino masses at the tree level are generated through R−parity violation and seesaw mechanism. We have analyzed the full effect of one-loop contributions to the neutrino mass matrix. We show that the current three flavour global neutrino data can be accommodated in the μνSSM, for both the tree level and one-loop corrected analyses. We find that it is relatively easier to accommodate the normal hierarchical mass pattern compared to the inverted hierarchical or quasi-degenerate case, when one-loop corrections are included.

Advances in Coating Chemistry in Deriving Soluble Functional Nanoparticle

Abstract: Nanoparticle-based probes are emerging as alternatives to molecular probes with several advantages. A variety of water-soluble functional nanoparticles and nanobioconjugates need to be prepared and tested for this research. Development of appropriate coating chemistries is the key in deriving such functional nanoparticles. Herein we summarize different coating approaches those we have developed and compared them in the context of currently available coating methods, for the synthesis of soluble functional nanoparticles. We have focused on conventional ligand exchange, interdigited bilayer strategy, silica coating, polyacrylate coating, and imidazole based polymer coating and found that cross-linked coating, specifically by polyacrylate, provides a superior colloidal stability of nanoparticles. The robust coating provides the opportunity to explore various conjugation chemistries involving nanoparticle and to derive different soluble nanobioconjugates. A library of functional nanoprobes with hydrodynamic d...

Self-sorted assembly in a mixture of donor and acceptor chromophores.

Abstract: A simple and novel supramolecular approach for orthogonal self-assembly of donor and acceptor chromophores has been demonstrated. Suitably designed 1,5-dialkoxynaphthalene (DAN) and naphthalene tetracarboxylic acid diimide (NDI) derivatives were used as the donor and acceptor systems, respectively. The molecular design for self-sorting relies upon the precise control over the placement of the self-complementary hydrogen-bonding units (amide functionality) with respect to the individual chromophore. By design, the distances between the two amide groups in the donor and acceptor chromophores are not identical, and consequently the effect of the hydrogen-bonding interaction cannot be maximised in the case of alternate donor-acceptor-type pi-stacking. Thus a relatively weak charge-transfer interaction is expected to be sacrificed, and segregated assembly among the individual chromophores should be enforced by virtue of the much stronger effects of hydrogen bonding and pi-pi stacking. Detailed spectroscopic studies were carried out to probe the mode of self-assembly in various derivatives of the DAN-NDI donor-acceptor pairs to establish the utility of the molecular design as a generalised one for orthogonal self-assembly.

Palladium Nanoparticle Catalyzed Hiyama Coupling Reaction of Benzyl Halides

Abstract: An efficient Hiyama coupling reaction between benzylic halide and aryltrialkoxysilane using Pd nanoparticles has been developed. This procedure accommodates various functional groups to yield a diverse range of diarylmethanes which are ubiquitous units of natural products and pharmaceuticals.

Energy transfer study between Ce3+ and Tb3+ ions in doped and core-shell sodium yttrium fluoride nanocrystals.

Abstract: Here, we report the preparation of Ce3+ and Tb3+ co-doped sodium yttrium fluoride nanorods and NaYF4:Ce3+/Tb3+ core-shell nanoparticles by the emulsion method. The core-shell nanoparticles are confirmed by X-ray diffraction study and transmission electron microscopy (TEM) analysis. The hexagonal crystal phase of Ce3+-doped sodium yttrium fluoride nanocrystals is converted to the cubic polymorph after surface coating by TbF3. Cell volume, cell parameters and lattice strain have been modified due to core-shell structure. The decay times are found to be 8.4 ms and 5.4 ms for doped nanorods and core-shell nanoparticles, respectively, which reveals that non-radiative decay is higher in the case of core-shell nanoparticles than doped nanorods. Energy transfer efficiencies from Ce3+ to Tb3+are 65% and 45% for doped Na(Y1.5Na 0.5)F6:Ce:Tb material and NaYF4:Ce/Tb core-shell materials, respectively. Quantum yields are found to be 75% and 42% for doped and core-shell samples, respectively.

Template-Free Synthesis of Mesoporous CuO Dandelion Structures For Optoelectronic Applications

Abstract: A simple template-free hydrothermal route was used for the synthesis of novel mesoporous CuO dandelion structures formed by self-organized CuO nanorods. A very high surface area ∼325 m2/g and remarkably enhanced photoconductivity under white light irradiation of the CuO dandelions were observed compared to the nanocrystals. The extremely high photoconductivity is attributed to the presence of oxygen related hole-trap states at the large surface area of the dandelions. The fast response (τ = 24 s) of the photocurrent holds promise for the fast photo-sensing device applications.

Metal Conjugated Semiconductor Hybrid Nanoparticle-Based Fluorescence Resonance Energy Transfer

Abstract: In the present study, we demonstrate a pronounced effect on the photoluminescence (PL) quenching and shortening of decay time of CdSe quantum dots (QDs) during interaction with Au nanoparticles in ...