Green synthesis of biopolymer-silver nanoparticle nanocomposite: An optical sensor for ammonia detection

Biopolymer used for the production of nanoparticles (NPs) has attracted increasing attention. In the presence article we use aqueous solution of polysaccharide Cyamopsis tetragonaloba commonly known as guar gum (GG), from plants. GG acts as reductive preparation of silver nanoparticles which are found to be <10. nm in size. The uniformity of the NPs size was measured by the SEM and TEM, while a face centered cubic structure of crystalline silver nanoparticles was characterized using powder X-ray diffraction technique. Aqueous ammonia sensing study of polymer/silver nanoparticles nanocomposite (GG/AgNPs NC) was performed by optical method based on surface plasmon resonance (SPR). The performances of optical sensor were investigated which provide the excellent result. The response time of 2-3. s and the detection limit of ammonia solution, 1. ppm were found at room temperature. Thus, in future this room temperature optical ammonia sensor can be used for clinical and medical diagnosis for detecting low ammonia level in biological fluids, such as plasma, sweat, saliva, cerebrospinal liquid or biological samples in general for various biomedical applications in human. © 2012 Elsevier B.V.

Functional Analysis of the Genes Encoding Diaminopropionate Ammonia Lyase in Escherichia coli and Salmonella enterica Serovar Typhimurium

Diaminopropionate ammonia lyase (DAPAL) is a pyridoxal-5'phosphate (PLP)-dependent enzyme that catalyzes the conversion of diaminopropionate (DAP) to pyruvate and ammonia and plays an important role in cell metabolism. We have investigated the role of the ygeX gene of Escherichia coli K-12 and its ortholog, STM1002, in Salmonella enterica serovar Typhimurium LT2, presumed to encode DAPAL, in the growth kinetics of the bacteria. While Salmonella Typhimurium LT2 could grow on DL-DAP as a sole carbon source, the wild-type E. coli K-12 strain exhibited only marginal growth on DL-DAP, suggesting that DAPAL is functional in S. Typhimurium. The expression of ygeX in E. coli was low as detected by reverse transcriptase PCR (RT-PCR), consistent with the poor growth of E. coli on DL-DAP. Strains of S. Typhimurium and E. coli with STM1002 and ygeX, respectively, deleted showed loss of growth on DL-DAP, confirming that STM1002 (ygeX) is the locus encoding DAPAL. Interestingly, the presence of DL-DAP caused a growth inhibition of the wild-type E. coli strain as well as the knockout strains of S. Typhimurium and E. coli in minimal glucose/glycerol medium. Inhibition by DL-DAP was rescued by transforming the strains with plasmids containing the STM1002 (ygeX) gene encoding DAPAL or supplementing the medium with Casamino Acids. Growth restoration studies using media lacking specific amino acid supplements suggested that growth inhibition by DL-DAP in the absence of DAPAL is associated with auxotrophy related to the inhibition of the enzymes involved in the biosynthetic pathways of pyruvate and aspartate and the amino acids derived from them.

Green synthesis of polysaccharide/gold nanoparticle nanocomposite: An efficient ammonia sensor

A low cost eco-friendly method for the synthesis of gold nanoparticles (AuNPs) using guar gum (GG) as a reducing agent is reported. The nanoparticles obtained are characterized by UV-vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Based on these results, a potential mechanism for this method of AuNPs synthesis is discussed. GG/AuNPs nanocomposite (GG/AuNPs NC) was exploited for optical sensor for detection of aqueous ammonia based on surface plasmon resonance (SPR). It was found to have good reproducibility, response times of similar to 10 s and excellent sensitivity with a detection limit of 1 ppb (parts-per-billion). This system allows the rapid production of an ultra-low-cost GG/AuNPs NC-based aqueous ammonia sensor.

Role of substrate temperature on the properties of Na-doped ZnO thin film nanorods and performance of ammonia gas sensors using nebulizer spray pyrolysis technique

Sodium doped zinc oxide (Na:ZnO) thin films were deposited on glass substrates at substrate temperatures 300,400 and 500 degrees C by a novel nebulizer spray method. X-ray diffraction shows that all the films are polycrystalline in nature having hexagonal structure with high preferential orientation along (0 0 2) plane. High resolution SEM studies reveal the formation of Na-doped ZnO films having uniformly distributed nano-rods over the entire surface of the substrates at 400 degrees C. The complex impedance of the ZnO nano-rods shows two distinguished semicircles and the diameter of the arcs got decreased in diameter as the temperature increases from 170 to 270 degrees C and thereafter slightly increased. (c) 2013 Elsevier B.V. All rights reserved.

Effect of Pb Volatilization on Dielectric Properties of 0.77PbMg1/3(Nb0.9Ta0.1)2/3O3-0.23PbTiO3

Lead magnesium niobate-lead titanate (PMN-PT) is an intriguing candidate for applications in many electronic devices such as multi-layer capacitors, electro-mechanical transducers etc. because of its high dielectric constant, low dielectric loss and high strain near the Curie temperature. As an extension of our previous work on Ta-doped PMNT-PT aimed at optimizing the performance and reducing the cost, this paper focuses on the effect of Pb volatilization on the dielectric properties of 0.77Pb(Mg1/3(Nb0.9Ta0.1)2/3)O3-0.23PbTiO3. The dielectric constant and loss of the samples are measured at different frequencies and different temperatures. The phase purity of this compound is determined by X-ray diffraction pattern. It is found that the volatilization during sintering does influence the phase formation and dielectric properties. The best condition is sintering with 0.5 g extra PbO around a 4 g PMNT-PT sample.

Catalytic conversion of nitrogen to ammonia by an iron model complex

Threefold symmetric Fe phosphine complexes have been used to model the structural and functional aspects of biological N₂ fixation by nitrogenases. Low-valent bridging Fe-S-Fe complexes in the formal oxidation states Fe(II)Fe(II), Fe(II)/Fe(I), and Fe(I)/Fe(I) have been synthesized which display rich spectroscopic and magnetic behavior. A series of cationic tris-phosphine borane (TPB) ligated Fe complexes have been synthesized and been shown to bind a variety of nitrogenous ligands including N₂H₄, NH₃, and NH₂-. These complexes are all high spin S = 3/2 and display EPR and magnetic characteristics typical of this spin state. Furthermore, a sequential protonation and reduction sequence of a terminal amide results in loss of NH₃ and uptake of N₂. These stoichiometric transformations represent the final steps in potential N₂ fixation schemes.

Treatment of an anionic FeN₂ complex with excess acid also results in the formation of some NH₃, suggesting the possibility of a catalytic cycle for the conversion of N₂ to NH₃ mediated by Fe. Indeed, use of excess acid and reductant results in the formation of seven equivalents of NH₃ per Fe center, demonstrating Fe mediated catalytic N₂ fixation with acids and protons for the first time. Numerous control experiments indicate that this catalysis is likely being mediated by a molecular species.

A number of other phosphine ligated Fe complexes have also been tested for catalysis and suggest that a hemi-labile Fe-B interaction may be critical for catalysis. Additionally, various conditions for the catalysis have been investigated. These studies further support the assignment of a molecular species and delineate some of the conditions required for catalysis.

Finally, combined spectroscopic studies have been performed on a putative intermediate for catalysis. These studies converge on an assignment of this new species as a hydrazido(2-) complex. Such species have been known on group 6 metals for some time, but this represents the first characterization of this ligand on Fe. Further spectroscopic studies suggest that this species is present in catalytic mixtures, which suggests that the first steps of a distal mechanism for N₂ fixation are feasible in this system.

Influence of formulated diets with varying protein levels on growth and ammonia excretion in the fry of Indian major carp, Cirrhina mrigala

The influence of formulated isocaloric diets of different protein levels (30, 35, 40, 45 and 50%) on the growth and ammonia excretion of the Indian major carp Cirrhina mrigala fry was studied for a rearing period of four weeks in the laboratory. Fishmeal, groundnut oilcake and silkworm pupae formed the source of protein in all the diets. As the dietary protein level increased from 30 to 40%, the growth and conversion efficiency increased significantly. Further increase in the protein level resulted in decrease in growth and conversion efficiency. Growth rate, weight gain (%), and gross and net feed conversion efficiencies were maximum at 40% dietary protein level. Ammonia excretion was directly proportional to the level of protein in the diet.