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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Thermodynamic and Kinetic Investigation of Reactions of Low-Valent Group 6 Complexes with N-Donor Ligands

Fortman, George Charles 06 March 2009 (has links)
The reactivities of several electron rich, low-valent group 6 complexes with a series of N-donor ligands were explored in order to gain information about the nature of M-N binding. Reactions of trimethylsilyl diazomethane (N=N=CHSiMe3) and 1-adamntyl azide (N=N=N-Ad) with the organometallic complexes [Cr(CO)3(C5R5)]2 (R = H, Me) and HMo(CO)3(C5R5) (R = H, CH3) were studied from both a kinetic and thermodynamic aspect. Ultimately, this information was used to propose plausible mechanisms by which the reactions take place. Furthermore, reactions of M(PiPr3)2(CO)3 (M = Mo, W; iPr = isopropyl) with N2, trimethylsilyl diazomethane, 1-adamantyl azide, a series of nitriles, and a choice group of N-heterocyclic compounds were studied. The use of the coordinatively unsaturated but sterically hindered M(PiPr3)2(CO)3 complex was used to evaluate the importance of sigma and pi bonding in these complexes.
32

Metalated Nitriles: Ligand Exchange and Copper-Catalyzed Reactions

Nath, Dinesh 17 April 2015 (has links)
This thesis describes new methods of carbon-carbon bond formation using metalated nitriles generated via metal exchange reactions. Sulfinylnitriles undergo a sulfinyl-metal exchange to yield lithiated, magnesiated and zincated nitriles, which can trap a range of electrophiles. The sulfinyl-metal exchange is effective with vinylic, quaternary and tertiary substitution patterns and addresses the long-standing problem of alkylating secondary nitriles. This method was then further extended to other oxidation states of sulfur, namely sulfonyl-metal exchange and relatively unknown sulfide-metal exchange. The sulfide metal exchange overcomes the problem related to the propensity of highly substituted sulfinylnitriles to eliminate. Sulfide-metal exchange is synthetically attractive because of the numerous methods for generating arylsulfides and the high tolerance of arylsulfides to numerous reagents. <br>A copper-catalyzed arylation reaction of aryl iodides and metalated nitriles was developed using catalytic Cu (I) and an amine ligand. A proof of principle has been established, providing a sound basis for developing the reaction. A new strategy has been developed for alkylation of alkenenitrile using LDA as base in presence of catalytic CuCN. Subsequent trapping with an electrophile, affords alkylated alkenenitriles in which the olefin is no longer in conjugation with the nitrile. <br>The distinct structural differences between N- & C-metalated nitriles have been harnessed in a series of chemoselective alkylations. Lithiated nitriles are found to be particularly reactive toward alkyl halides whereas magnesiated nitriles react selectively with oxygenated electrophiles. Using this strategy allows chemoselective alkylation of metalated nitriles. / Bayer School of Natural and Environmental Sciences; / Chemistry and Biochemistry / PhD; / Dissertation;
33

Enhanced Stabilization of Nitrile Hydratase Enzyme From Rhodococcus Sp. DAP 96253 and Rhodococcus

Ganguly, Sangeeta 12 January 2007 (has links)
Treatment of industrial wastewaters contaminated with toxic and hazardous organics can be a costly process. In the case of acrylonitrile production, due to highly volatile and toxic nature of the contaminant organics, production wastewaters are currently disposed by deepwell injection without treatment. Under the terms granting deepwell injection of the waste, alternative treatments must be investigated, and an effective treatment identified. Cells of two Gram-positive bacteria, Rhodococcus sp. DAP 96253 and R. rhodochrous DAP 96622 were evaluated for their potential as biocatalysts for detoxification of acrylonitrile production wastewaters. Rhodococcus sp. DAP 96253 and R. rhodochrous DAP 96622 when multiply induced, are capable of utilizing the hazardous nitrile and amide components present in the wastewater as sole carbon and/or nitrogen sources, employing a 2-step enzymatic system involving nitrile hydratase (NHase) and amidase enzymes. There is a significant potential for overproduction of NHase upon multiple induction. However, high-level multiple induction required the presence of highly toxic nitriles and/or amides in the growth medium. Asparagine and glutamine were identified as potent inducers with overexpression at 40% of total soluble cellular protein as NHase. In native form (either cell free enzymes or whole cells) the desired NHase is very labile. In order to develop a practical catalyst to detoxify acrylonitrile production wastewaters, it is necessary to significantly improve and enhance the stability of NHase. Stabilization of desired NHase activity was achieved over a broad range of thermal and pH conditions using simultaneous immobilization and chemical stabilization. Previously where 100% of NHase activity was lost in 24 hours in the non-stabilized cells, retention of 20% of initial activity was retained over 260 days when maintained at 50-55 C, and for over 570 days for selected catalyst formulations maintained at proposed temperature of the biodetoxification process. In addition, NHase and amidase enzymes from Rhodococcus sp. DAP 96253 were purified. Cell free NHase was characterized for its substrate range and effect of common enzyme inhibitors and was compared to available information for NHase from other organisms. As a result of this research a practical alternative to the deepwell injection of acrylonitrile production wastewaters is closer to reality.
34

Synthèse asymétrique de 2-isoxazolines en vue de la synthèse totale de la négamycine

Juneau, Sylvie January 2008 (has links) (PDF)
La (+)-négamicyne est un antibiotique présentant une activité inhibitrice contre plusieurs bactéries hautement résistantes telles Staphylococcus aureus, Escherichia coli, Salmonella typhi, en plus d'une très faible toxicité. L'emploi de la négamycine s'est également avéré prometteur pour le traitement de maladies congénitales telles que la dystrophie musculaire. La synthèse de cette molécule, qui possède deux centres stéréogéniques ainsi qu'un lien hydrazido peptidique, s'avère donc d'un grand intérêt. L'approche proposée dans le cadre de ce projet implique d'abord la formation d'un intermédiaire 2-isoxazoline par une cycloaddition 1,3-dipolaire asymétrique entre une oléfine portant un auxiliaire chiral N-tosylperhydrobenzoxazine et un oxyde de nitrile généré in situ. Une optimisation de la préparation de l'oléfine chirale fut d'abord menée et la procédure élaborée s'avéra reproductible et efficace pour fournir sélectivement l'isomère chaise-bateau. Suite à l'échec des nombreux protocoles tentés pour la préparation de précurseurs oximes et nitros de l'oxyde de nitrile, une procédure d'estérification quasi quantitative de l'acide 3-nitropropanoïque fut développée. Une optimisation de la cycloaddition 1,3-dipolaire a donc pu être menée en employant l'oléfine chiral et le 3-nitropropanoate de méthyle, activé in situ en oxyde de nitrile par une déshydratation avec le 1,4-phénylènediisocyanate. Un ratio diastéréomérique de 80 :20 en faveur de la 2-isoxazoline 5' R et un rendement isolé de 78 % du mélange épimérique furent obtenus dans les conditions réactionnelles optimales. Une méthode de séparation efficace des deux diastéréoisomères fut élaborée et la configuration R au centre C5' a pu être confirmée par spectroscopie nOe pour l'isomère majoritaire. Cette induction asymétrique permet donc de générer le premier centre stéréogénique C5 de la (+)-négamycine. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Cycloaddition 1,3-dipolaire, 2-isoxazoline, (+)-négamycine, 8-N-tosylaminomenthol, Perhydrobenzoxazine, Oxyde de nitrile.
35

Proteomic analysis of nitrile-induced proteins in Klebsiella oxytoca

Chou, Shu-min 06 September 2006 (has links)
The cyanide-degradation bacteria Klebsiella oxytoca SYSU-110 was isolated from the waste water of a metal-plating plant in southern Taiwan. K. oxytoca can utilize many nitrile compounds [including acetonitrile (100 mM), benzonitrile (1 mM), butyronitrile (100 mM), glutaronitrile (50 mM), methacrylnitrile (100 mM), phenylacetonitrile (1 mM), propionitrile (25 mM), succinonitrile (25 mM) and valeronitrile (50 mM)] as its sole nitrogen source. In this study, we found out that K. oxytoca was capable of degrading acetonitrile and propionitrile. Frome GC analysis, we recognized amide was an intermediate compound, while the carboxylic acid and ammonia were the final end-products. Therefore, we presume that K. oxytoca biodegraded nitrile compounds by two enzymes, the nitrile hydratase and amidase. We also analyzed the total cell proteins by 2-D polyacrylamide gel electrophoresis after the cells were cultured in medium containing 25mM succinonitrile. There were 23 proteins could be induced or overexpressed by nitrile and we had identified 11 by Mascot Peptide mass Fingerprint and Blast. Six proteins that can protect the cells from oxidative damage are: superoxide dismutase, glutathione s-transferase, dyp-type peroxidase, metal binding protein PsaA (that can transport metal ions into the cells), LraI, and FepA (used to transport inorganic ions into the cells). Three enzymes glutamine synthetase, methylenetetrahydrofolate reductase,¡@and dihydroxyacid dehydratase were used to synthesize amino acids. One protein was identified as ribosomal protein L9. The last identified protein is nucleoside triphosphates kinase which can convert nucleoside diphosphates to nucleoside triphosphates non-specifically. From the activity analysis, superoxide dismutase and glutathione S-transferase activities were escalated when the cells were cultured in 25mM succinonitrile, and the concentration of ROS has rise. These results suggested that succinonitrile could cause oxidative damage to the cells and induce some anti-oxidative damage proteins to protect them.
36

Catalysis via Induced Intramolecularity: Carbonyl-catalyzed Hydration of α-Amino Nitriles

Hussain, Bashir 11 June 2014 (has links)
In the last decade, there has been a surge of interest from the chemistry community in developing synthetic catalysts that emulate the remarkable rate accelerations observed for enzymatic reactions. One approach utilized by enzymes involves preorganization of substrate(s) using a favourable binding event to orient the substrate(s) in a reactive arrangement. Although the “induced intramolecularity” is entropically unfavourable, it is facilitated by the enzymes and utilized to accelerate the subsequent chemical transformation. Chemists have often used a conceptually related stepwise approach in which temporary tethers are assembled to induce a temporary intramolecularity. This preorganization often enables difficult intermolecular reactions, and typically leads to increased regio-, chemo-, and stereoselectivity in chemical reactions. Seeking to develop a catalytic approach, we focused our efforts in developing a mild, carbonyl-catalyzed hydration protocol for - and -amino nitriles to give the corresponding - and -amino amide and acid. This work highlights the value of employing induced intramolecularity in accessing structurally important chemical motifs that otherwise require harsh reaction conditions. Additionally, this thesis presents the background material, design process, optimization and scope of this reactivity.
37

From early to late transition metal complexes syntheses, structures and electrochemical properties = Von frühen zu späten Übergansmetallverbindungen : Darstellung, Strukturen und elektrochemische Eigenschaften /

Köcher, Stefan, January 2008 (has links)
Chemnitz, Techn. Univ., Diss., 2008.
38

1,3,5-Triazapenta-1,3-diene Darstellung, Strukturen, Reaktionen /

Heße, Nadine. Unknown Date (has links) (PDF)
Universiẗat, Diss., 2003--Münster (Westfalen).
39

Investigations into the Oxidative Desulfurization Activity in a Film-Shear Reactor, the Source of Enhanced Reactivity, and Other Potential Applications

Fox, Brandy R., 1981- 06 1900 (has links)
xviii, 242 p. : ill. (some col.) / Fuel purification is an extremely active area of research in today's green world. Specifically, desulfurization of fuels is an important area of research for two reasons. First, any sulfur present in fuels generates SOx pollutants that are hazardous to human health and also contribute to acid rain. Secondly, even trace sulfur contaminants prohibit the use of fuel streams in fuel cells. However, achieving near-zero sulfur levels with existing technology is impractical. The work in this thesis investigates a new process for the removal of sulfur from fuel streams using a film-shear reactor (based on a process known as oxidative desulfurization), and goes on to investigate the mode of activation for the process within the reactor through a study of the reactor conditions. Additionally, other applications of the film-shear reactor, including mechanical activation of molecules and controlled nanoparticle synthesis are explored. Chapter I outlines the current status of oxidative desulfurization research, highlighting the strengths of the method, innovative approaches and drawbacks to the various approaches. Chapters II and III go on to discuss the enhancement of the process in the film-shear reactor using model fuels and a variety of substrates. This method was found to significantly enhance the oxidative desulfurization process, reducing both the time and temperature required to achieve considerable sulfur removal. Levels of desulfurization that require hours at elevated temperatures by conventional stirring methods were obtainable on the scale of seconds at or below room temperature. Chapter IV offers investigations into the conditions within the film-shear reactor, and also presents studies of the ability of the high shear rates obtained in the reactor to mechanically activate molecules. Chapter V extends the applicability of the film-shear reactor to nanoparticle synthesis through investigation of two titania synthesis methods utilizing the film-shear reactor. Appendices A and B offer supplementary information to enhance the studies presented in Chapters II and III, while Appendices C, D, and E highlight work done investigating the ability of platinum complexes to hydrate nitriles and cyanohydrins. This dissertation includes previously published and unpublished co-authored material. / Committee in charge: Victoria J. DeRose, Chairperson; David R. Tyler, Advisor; Kenneth M. Doxsee, Member; Catherine J. Page, Member; Mark H. Reed, Outside Member
40

Catalysis via Induced Intramolecularity: Carbonyl-catalyzed Hydration of α-Amino Nitriles

Hussain, Bashir January 2014 (has links)
In the last decade, there has been a surge of interest from the chemistry community in developing synthetic catalysts that emulate the remarkable rate accelerations observed for enzymatic reactions. One approach utilized by enzymes involves preorganization of substrate(s) using a favourable binding event to orient the substrate(s) in a reactive arrangement. Although the “induced intramolecularity” is entropically unfavourable, it is facilitated by the enzymes and utilized to accelerate the subsequent chemical transformation. Chemists have often used a conceptually related stepwise approach in which temporary tethers are assembled to induce a temporary intramolecularity. This preorganization often enables difficult intermolecular reactions, and typically leads to increased regio-, chemo-, and stereoselectivity in chemical reactions. Seeking to develop a catalytic approach, we focused our efforts in developing a mild, carbonyl-catalyzed hydration protocol for - and -amino nitriles to give the corresponding - and -amino amide and acid. This work highlights the value of employing induced intramolecularity in accessing structurally important chemical motifs that otherwise require harsh reaction conditions. Additionally, this thesis presents the background material, design process, optimization and scope of this reactivity.

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