Showing papers by "National Chemical Laboratory published in 2001"

Fungus-mediated synthesis of silver nanoparticles and their immobilization in the mycelial matrix: a novel biological approach to nanoparticle synthesis

Abstract: A novel biological method for the synthesis of silver nanoparticles using the fungus Verticillium is reported. Exposure of the fungal biomass to aqueous Ag+ ions resulted in the intracellular reduction of the metal ions and formation of silver nanoparticles of dimensions 25 ± 12 nm. Electron microscopy analysis of thin sections of the fungal cells indicated that the silver particles were formed below the cell wall surface, possibly due to reduction of the metal ions by enzymes present in the cell wall membrane. The metal ions were not toxic to the fungal cells and the cells continued to multiply after biosynthesis of the silver nanoparticles.

Bioreduction of aucl4− ions by the fungus, verticillium sp. and surface trapping of the gold nanoparticles formed

Abstract: Fungi make piles of gold! A green-chemistry route, based on the bioreduction of AuCl 4 - ions by the fungus Verticillium sp., for the formation of gold nanoparticles is demonstrated. The TEM micrograph shows a single Verticillium cell after reaction with gold ions and entrapment of gold nanoparticles on the cell wall and cytoplasmic membrane.

A rheological study on the kinetics of hybrid formation in polypropylene nanocomposites

Abstract: We present an experimental investigation on the creep behavior of molten polypropylene organically modified clay nanocomposites. The nanocomposite hybrids were prepared by melt intercalation in an extruder in the presence or absence of a compatibilizer. They were subsequently annealed and simultaneously characterized using high-temperature wide-angle X-ray diffraction and controlled stress rheometry. The creep resistance of compatibilized hybrids was significantly higher than that of uncompatibilized hybrids and also increased with annealing time. The microstructure of the nanocomposites as investigated by TEM and high-temperature WAXD showed the presence of clay crystallites dispersed within the polymer matrix. The creep data together with the microstructural investigation are probably indicative of a small amount of exfoliation from the edges of the clay crystallites during extrusion and annealing. The zero shear viscosity of the compatibilized nanocomposites containing greater than 3 wt % clay was at l...

Pepsin-gold colloid conjugates: preparation, characterization, and enzymatic activity

Abstract: Pepsin−colloidal gold conjugates were prepared by a simple protein-friendly process and the enzymatic activity of the bioconjugates is reported. The pepsin−gold conjugates are obtained by mixing colloidal gold and protein solutions at pH = 3 and, thereafter, centrifugation, washing, and redispersion of the pepsin−gold conjugate material in water. The bioconjugates in solution were characterized by UV−vis spectroscopy, fluorescence spectroscopy, and biocatalytic activity measurements while films of the bioconjugate material obtained by solvent evaporation on suitable substrates were further analyzed by scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX), transmission electron spectroscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). While TEM and SEM measurements showed aggregates of the enzyme/colloidal gold conjugates, the intactness of secondary and tertiary structures of the enzyme, as determined by FTIR and fluorescence s...

Differential Distribution of Simple Sequence Repeats in Eukaryotic Genome Sequences

Abstract: Complete chromosome/genome sequences available from humans, Drosophila melanogaster, Caenorhabditis elegans, Arabidopsis thaliana, and Saccharomyces cerevisiae were analyzed for the occurrence of mono-, di-, tri-, and tetranucleotide repeats. In all of the genomes studied, dinucleotide repeat stretches tended to be longer than other repeats. Additionally, tetranucleotide repeats in humans and trinucleotide repeats in Drosophila also seemed to be longer. Although the trends for different repeats are similar between different chromosomes within a genome, the density of repeats may vary between different chromosomes of the same species. The abundance or rarity of various di- and trinucleotide repeats in different genomes cannot be explained by nucleotide composition of a sequence or potential of repeated motifs to form alternative DNA structures. This suggests that in addition to nucleotide composition of repeat motifs, characteristic DNA replication/repair/recombination machinery might play an important role in the genesis of repeats. Moreover, analysis of complete genome coding DNA sequences of Drosophila, C. elegans, and yeast indicated that expansions of codon repeats corresponding to small hydrophilic amino acids are tolerated more, while strong selection pressures probably eliminate codon repeats encoding hydrophobic and basic amino acids. The locations and sequences of all of the repeat loci detected in genome sequences and coding DNA sequences are available at http://www.ncl-india.org/ssr and could be useful for further studies.

High-Temperature X-ray Diffraction Studies on the Crystalline Transitions in the α- and γ-Forms of Nylon-6

Abstract: The crystallization of nylon-6 from the melt was monitored in situ by X-ray diffraction. The nylon-6 was found to crystallize into a high-temperature α‘-phase as indicated by the two-peak nature of the diffractogram. On cooling from the crystallization temperature to room temperature, nylon-6 retained the two-peak nature. However, data analysis indicates a change from high-temperature (HT) α‘-phase to low-temperature α-phase at ∼180 °C. On heating, the α-phase transformed into the α‘-phase at about 190 °C and melted in the α‘-phase. The transition took place over a temperature range where both phases coexisted. However, samples crystallized from the melt at temperatures 140 and 180 °C showed the α-phase at room temperature, but on heating the α-phase first transformed into a pseudohexagonal phase and before melting the pseudohexagonal phase further transformed into the α‘-phase. The α-phase was transformed into the γ-phase, by potassium iodide−iodine treatment, and the behavior of the γ-phase with tempera...

Linear Superclusters of Colloidal Gold Particles by Electrostatic Assembly on DNA Templates

Abstract: The organization of nanoparticles into superstructures of predefined geometry is an important challenge in the area of nanoscale architecture. Attractive Coulombic interaction between positively charged amine groups on gold particle surfaces and negatively charged phosphate backbones of DNA molecules drives the self-assembly of gold nanoparticles into linear supercluster structures.

Nonhazardous Direct Oxidation of Hydrogen to Hydrogen Peroxide Using a Novel Membrane Catalyst.

Abstract: Nonhazardous and highly selective H2O2production! An H 2 -permselective membrane (2) has been developed which consists of thin films of Pd–Ag alloy (2b) and oxidized Pd (2c), and a hydrophobic polymer membrane (2d) supported on a tubular membrane (2a) within a reactor wall (1). Hydrogen atoms permeate through the membrane and react with molecular OH 2 in a liquid medium (LM; 2 M HH 2 SOH 4 ).

PP/clay nanocomposites: Effect of clay treatment on morphology and dynamic mechanical properties

Abstract: The morphology and properties of polypropylene (PP)/clay nanocomposites are described. The melt intercalation of organophilic clay was carried out with a single-screw extruder. The effects of two kinds of treatments of clay are discussed. Maleic anhydride (MAH)-grafted PP was used as a compatibilizer. The expansion of the intergallery distance of the clay was governed by the interaction between the clay treatment and the compatibilizer. In one case, the composites exhibited significantly reduced intensities of diffraction peaks, suggesting partial exfoliation of the clay layers, whereas for the second clay sample, expansion of the gallery height was noted. The mechanical properties of the PP/clay composites showed significant enhancement in their mechanical and thermal properties. About a 35% increase in the tensile modulus and about a 10% increase in the tensile strength were observed. The thermal degradation temperature increased from 270 to about 400°C as a result of the incorporation of clay, and the extent depended on the dispersion of clay in the composite. The most interesting outcome of this study was the changes in morphology for PP/clay composites, which are reported here for the first time. An optical microscopic study revealed that the PP/clay composites could be crystallized at higher temperatures than pure PP and that the morphology was remarkably altered because of the presence of layers of clay. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1786–1792, 2001

Identification of inter simple sequence repeat (ISSR) markers associated with seed size in wheat

Abstract: The feasibility of identifying inter-simple sequence repeat markers associated with seed weight in hexaploid wheat was tested using 113 recombinant inbred lines developed by the single-seed descent method, from a cross between Rye selection111, an Indian genetic stock obtained through the introgression of genes for bold seed size from rye, and Chinese Spring having small seed size. Three markers were associated with low seed size with gene effects of 14.8%, 9.5%, and 6%, while four markers with contributions of 8%, 4.66%, 2.92% and 2.61% were found to be linked to high seed size, together contributing 31% of the phenotypic variance in seed size. Nulli-tetrasomic and di-telosomic analysis revealed the presence of three low seed size QTL-associated markers on three chromosomes, 6BL, 2DL, and 1DS respectively. This study clearly demonstrates that ISSRs are highly useful for finding markers associated with major and minor genes controlling agronomically important traits in wheat.

Investigations in the Transition Metal Catalyzed Aziridination of Olefins, Amination, and Other Insertion Reactions with Bromamine-T as the Source of Nitrene†

Abstract: Investigations into the transition metal catalyzed aziridination of olefins with Bromamine-T as a new source of nitrene is presented in this account. Comparison of Chloramine-T and Bromamine-T in this reaction indicates that the latter is superior as the source of nitrene. Systematic study with several transition metal based catalysts suggests that Cu-halides are the best catalysts. A first report of aziridination under microwave and ultrasound irradiation conditions is also presented. Copper-catalyzed aziridination of methyl cinnamate with Bromamine-T did not proceed at ambient temperature but was effected smoothly under ultrasound irradiation to furnish trans-aziridine selectively, while under microwave irradiation, a mixture of cis and trans isomers, was obtained. It has been demonstrated that aziridination of olefins proceeds smoothly with inexpensive bleaching powder. Preliminary results of Rh-catalyzed benzylic insertion reactions with Bromamine-T are included in this account.

β-Carotene production in sugarcane molasses by a Rhodotorula glutinis mutant

Abstract: Several wild strains and mutants of Rhodotorula spp. were screened for growth, carotenoid production and the proportion of -carotene produced in sugarcane molasses. A better producer, Rhodotorula glutinis mutant 32, was optimized for carotenoid production with respect to total reducing sugar (TRS) concentration and pH. In shake flasks, when molasses was used as the sole nutrient medium with 40 g l−1 TRS, at pH 6, the carotenoid yield was 14 mg l−1 and -carotene accounted for 70% of the total carotenoids. In a 14-l stirred tank fermenter, a 20% increase in torulene content was observed in plain molasses medium. However, by addition of yeast extract, this effect was reversed and a 31% increase in -carotene content was observed. Dissolved oxygen (DO) stat fed-batch cultivation of mutant 32 in plain molasses medium yielded 71 and 185 mg l−1 total carotenoids in double- and triple-strength medium, respectively. When supplemented with yeast extract, the yields were 97 and 183 mg l−1 total carotenoid with a 30% increase in -carotene and a simultaneous 40% decrease in torulene proportion. Higher cell mass was also achieved by double- and triple-strength fed-batch fermentation. Journal of Industrial Microbiology & Biotechnology (2001) 26, 327–332.

Factors affecting in vitro microrhizome production in turmeric

Abstract: In vitro microrhizome production was obtained in turmeric (Curcuma longa Linn.). Freshly sprouted buds with small rhizome portions excised from stored mature rhizomes were cultured on semi-solid culture initiation medium — MS basal medium + 0.88M BAP (6-benzylaminopurine) + 0.92M kinetin + 5% coconut water + 2% sucrose + 0.5% agar — resulting in bud elongation. Multiple shoots were produced from these elongated buds by culturing in liquid shoot multiplication medium — MS basal medium + 2.2 MB AP +0 .92M kinetin + 5% coconut water + 2% sucrose — at 251C and 16-h light (at 11.7mol m 2 s 1 )/8-h dark cycles. Clumps of four to five multiple shoots/single shoots were used in various experiments. Cultures were incubated in the dark at 251C. Half strength MS basal medium supplemented with 80 g l 1 sucrose was found to be optimal for microrhizome production. Cytokinin BAP had an inhibitory effect on microrhizome production. At the highest concentration of BAP tried (35.2M) microrhizome production was totally inhibited. Microrhizome production depended on the size of the multiple shoots used. Microrhizomes produced were of a wide range in size (0.1‐2.0 g) and, readily regenerated when isolated and cultured in vitro on culture initiation medium or shoot multiplication medium. Under in vivo conditions, small (0.1‐0.4 g), medium (0.41‐0.8 g) and big (>0.81 g) microrhizomes regenerated. Plantlets developed from big microrhizomes grew faster.

Production of β-carotene by a mutant of Rhodotorula glutinis

Abstract: Wild strains of Rhodotorula glutinis and R. rubra were investigated concerning their carotenoid production, proportion of β-carotene and cell mass yield. R. glutinis NCIM 3353 produced 2.2 mg carotenoid/l in 72 h; and the amount of β-carotene was 14% (w/w) of the total carotenoid content (17 µg/g cell dry weight). It was subjected to mutagenesis using UV radiation for strain improvement. Out of 2,051 isolates screened, the yellow coloured mutant 32 produced 120-fold more β-carotene (2,048 µg/g cell dry weight) than the parent culture in 36 h, which was 82% (w/w) of the total carotenoid content. Mutant 32 was grown on different carbon and nitrogen sources. The best yield of β-carotene (33±3 mg/l) was obtained when glucose and yeast extract were supplied as carbon and nitrogen sources, respectively. Divalent cation salts further increased the total carotenoid content (66±2 mg/l) with β-carotene as the major component (55±2%, w/w).

A Comparison of Medial and Lateral Temporal Lobe Atrophy in Dementia with Lewy Bodies and Alzheimer’s Disease: Magnetic Resonance Imaging Volumetric Study

Abstract: Objectives: To compare medial and lateral temporal lobe atrophy on magnetic resonance imaging (MRI) in dementia with Lewy bodies (DLB) and Alzheimer’s disease (AD), and to examine t

Modeling nonspherical particles using multisphere discrete elements

Abstract: In this paper axisymmetrical particles are modeled as multisphere discrete elements using a method in which particles are represented by overlapping spheres, fixed rigidly with respect to a local coordinate system. Contact detection is sphere-based and the resultant forces are transformed to the particle centroid to calculate the particle motion using standard discrete element method conventions. The multisphere method was used to model discharge of ellipse-shaped particles through an orifice in a flat-bottomed hopper and the simulations compared with physical experiments at the same scale. There was good agreement between the flow behavior of the simulated and physical particle assemblies for all orifice sizes. The rate of discharge and the vertical velocity profiles in the region of converging flow determined for the simulated and physical flows were in close agreement for flow from the larger orifices. A similar relationship between frequency of arch formation, particle mean diameter, and orifice diameter as for spheres was observed.