Thesis (Ph.D.)--Murdoch University, 2008. / Thesis submitted to the Faculty of Sustainability, Environmental and Life Sciences. Includes bibliographical references (p. 156-202)

The chemistry of the tantalum dinitrogen complex ([NPN]Ta)₂ (μ-H)₂ (μ-η¹:η²-N₂ )Ta-[NPN], 1, (where [NPN] represents the acyclic tridentate ligand [(PhNSiMe₂ CH₂ )₂ -PPh]² -), with primary alkenes, group IV and V metallocene complexes, and GaCp* is explored. The reaction of 1 with 1-pentene and 1-hexene occurs via olefin-insertion into the metal-hydride bond to give two new complexes, ([NPN]Ta(CH₂)₄CH₃)₂ (μ-η¹:η¹-N₂ ), 10, and ([NPN]Ta(CH₂ )₅CH₃)₂ (μ-η¹:η¹-N₂ ), 11, which were characterized using NMR spectroscopy. The solid-state structure of 11 was established and revealed that N₂ has been transformed into a bridging end-on mode. In contrast to its G symmetry in solution, the solid-state structure of 11 is C, symmetric; a VT-NMR study was performed and showed that 11 exists as an equilibrium between two isomers in solution: a C, symmetric isomer 11A,which is the predominant isomer at room temperature, and a C, symmetric isomer 11B,which is the minor isomer. The reactivity of 1 with group IV and V metallocenes was investigated. The reaction of 1 with Cp₂ Hf(PMe₃)(η²-Me₃SiCCSiMe₃) produces [N(μ-P=N)N]Ta(μ-H)₂(μ-N(Hf-Cp₂ ))Ta[NPN], 14, in which N₂ is cleaved and new Hf-N and P=N bonds have formed. The reaction of 1 with group V metallocene hydrides Cp₂ MH₃ (M Nb, Ta) was also attempted however these complexes do not react with 1. The reaction of 1 with GaCp* produces a new complex, [NPN]Ta(μ-N(GaCp*))Ta(=NPμ)[NPIA,-N], 18, which was characterized using NMR spectroscopy. Complex 18 decomposes over several days in solution, and one product of decomposition that was isolated was [(PhNH)(NPμ-N)Ta]₂ , 19. The solid-state structure of 19 showed that the [NPN] ligand was cleaved at the N-Si bond, similar to that observed for the reaction of 1 with 9-BBN and HB(C₆H₅)₂ . A mechanism for the formation of complexes 18 and 19 is proposed. / Science, Faculty of / Chemistry, Department of / Graduate

Soybeans are able to obtain nitrogen from two different sources, nitrogen found in the soil (e.g. from fertilizers) and biologically fixed nitrogen (from symbiotic bacteria called rhizobia). Nitrogen source and degree of reliance on N-fixation can impact plant nitrogen dynamics, which has the potential to impact above-ground herbivore performance. We examined the impact of nitrogen availability and rhizobial association on soybean aphid biology and reproduction in a series of greenhouse and field experiments. Aphid establishment on plants was not significantly affected in any experiment. However, aphid reproduction was significantly affected by rate of nitrogen fertilization, rhizobial inoculation, and type of rhizobial seed inoculant. In general, aphid densities were not correlated with plant parameters associated with plant nitrogen or N-fixation. Producers commonly use fertilizers and rhizobial seed inoculants, thus it is important to continue exploring the mechanisms underlying how plant nitrogen dynamics impact soybean insect pests.

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No description available.

Investigations of the nitrogen fixing (nif) genes in the cyanobacterium Nostoc commune UTEX 584 revealed a gene encoding a hemoprotein, named cyanoglobin. The cyanoglobin gene was isolated and subcloned into Escherichia coli previously. Cyanoglobin possesses a high oxygen affinity. The study presented here investigated the functional role of cyanoglobin, and encompassed the determination of the kinetic basis for the high oxygen affinity of cyanoglobin through kinetic studies utilizing stopped-flow spectrophotometry and flash photolysis. In addition, studies of cyanoglobin, in the presence of a variety of ligands, employed as structural probes of the distal pocket architecture, are presented. These data are interpreted in terms of structural models of cyanoglobin produced by homology modelling and hemoglobins with known crystal structures. Cyanoglobin coordinated oxygen and a variety of ligands with high rates of association, which explained the high oxygen affinity of cyanoglobin. Cyanoglobin possessed high rates of autoxidation and hemin loss. The ligand binding behavior of cyanoglobin was more similar to leghemoglobin than to sperm whale myoglobin. The ligand binding behavior of cyanoglobin is explained in terms of a highly reactive, and solvent exposed, heme-iron. The 5' region of glbN interacted with NtcA, the global regulator of nitrogen metabolism in cyanobacteria, which may provide an indication of the nitrogen deprivation signal required for cyanoglobin expression in vivo. Finally, the isolation and N-terminal sequencing of a potential cyanoglobin homolog in Anabaena sp. strain PCC 7120 is presented. Collectively, the data obtained in this study may support the model of cyanoglobin function described by Hill, et al., that cyanoglobin sequesters oxygen, and presents it to, or is a part of, a terminal cytochrome oxidase complex in Nostoc commune UTEX 584 under microaerobic conditions, when nitrogen fixation, and thus ATP demand, is maximal. / Ph. D.

This investigation has determined the presence of biological nitrogen fixation in two reservoirs in the southwestern United States: Lake Arlington and Lake Ray Hubbard. Subsequent tests have gathered baseline data on the effects of various biological, chemical, and physical parameters on in situ nitrogen fixation in these reservoirs. Of specific importance is the relationship between nitrogen fixation arid occasional blooms of blue-green algae which produce such problems as testes and odors in these water-supply impoundments.

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves [90]-114).

The thermophilic bacterium designated NT-7 was shown to reduce acetylene to ethylene at 35 C. It was found that the organism does not reduce acetylene when it is grown in Burk's medium with 0.3 per cent (w/v) NH4 N0 3 . Reduction of acetylene at 55 C could not be demonstrated due to insolubility of acetylene in Burk's medium at this temperature. It was shown that the bacterium NT-7 can not grow in the absence of atmospheric nitrogen at 55 C when combined nitrogen is not supplied with the nutrient medium. All these characteristics were used to prove that NT-7 is a nitrogen fixing bacterium. Identification procedures confirmed a previous finding that the organisms are rod shaped cells possessing endoepores. Further tests showed that NT-7 is obligately aerobic and motile.

Call number: LD2668 .T4 1933 B72