<i>N</i>-heterocyclic carbenes (NHC) have widely been used as spectator ligands in organometallic chemistry. Chelating bidentate di-<i>N-</i>heterocyclic carbenes (diNHC) provide additional entropic stability to their complexes relative to monodentate analogues. The steric and electronic environment around the metal centre can be fine-tuned by varying the substituents on the nitrogen atoms of the diNHC ligand. Synthesis and characterization of air and moisture stable bis(diimidazolylidene)nickel(II) complexes, [(diNHC)2Ni]2+, and their corresponding silver(I) and palladium(II) analogues are described.<p> Investigations into the catalytic potential of diNHC complexes of nickel as an alternative to palladium systems in carbon-carbon coupling reactions are discussed. In the Suzuki-Miyaura coupling reaction, the [(diNHC)2Ni]2+ complex was active for the coupling of aryl chlorides as well as aryl fluorides. The analogously synthesized Pd(II) complexes resulted in formation of (diNHC)PdCl2 species which were not active for the coupling of aryl fluorides. Transition-metal free coupling reactions were investigated and the results indicated that in the Mizoroki-Heck reaction, aryl iodides could be activated in the absence of nickel or palladium precatalysts when using Na2CO3 or NEt3 as base, while in the Suzuki-Miyaura reaction, aryl iodides and aryl bromides could be activated without any precatalyst when K3PO4 was used as base.<p> A general route into the synthesis of non-symmetrically substituted ligand precursors has been developed. Synthesis and characterization of non-symmetrically substituted ligand precursors, and their corresponding silver(I), palladium(II) and nickel(II) complexes are described. The activity of one of the non-symmetrically substituted (diNHC)Pd(II) complexes in the Suzuki-Miyaura coupling reaction of bulky substrates has been investigated. Non-symmetrically substituted diNHC ligand precursors with a hemi-labile pyridine arm have been synthesized and their corresponding Ni(II) and Pd(II) complexes are described.<p> Attempts to synthesize three-coordinate Pd(II) complexes using bulky â-diketiminato ligands are also discussed.

Helicobacter pylori (H. pylori) is a gram-negative pathogenic bacterium that infects half of the world’s population. It resides in the human stomach, where it survives extremely acidic conditions. Efficient colonization by H. pylori requires urease and hydrogenase enzymes, both of which utilize nickel as a cofactor. The intracellular level of nickel in H. pylori is strictly maintained by a nickel-responsive transcription factor, HpNikR, which acts as a master regulator to control both activation of the urease genes and repression of a variety of other genes including its own. In addition to its role in nickel homeostasis, HpNikR has been implicated in the adaptive response of H. pylori to acidic environmental conditions. In this work, two representative genes, ureA and nikR, are confirmed to be regulated by HpNikR directly in response to changes in nickel concentration, with HpNikR binding to the promoter region of each gene. The binding sequences on the two promoters are distinct from each other and no consensus sequence could be identified from them. The binding affinity of HpNikR to the ureA promoter is much tighter than to the nikR promoter. Another signal that can activate the DNA-binding activity of HpNikR is a change in pH. Once HpNikR is activated by proton binding, it binds to the ureA promoter independently of nickel concentration, but still binds to the nikR promoter in a nickel-dependent manner. Several amino acids at the N-terminus of HpNikR, including Asp7, Asp8 and Lys6, are critical for the specific response of HpNikR to pH changes. In addition, the binding of HpNikR to distinct DNA sequences induces different degrees of DNA bending, which provides another possible means of gene regulation by HpNikR. The ability of HpNikR to differentially regulate distinct genes in response to several signals allows a graduated level of control of gene expression by HpNikR. In vivo studies to evaluate the physiological relevance of the above in vitro results have been initiated. Given the relatively low abundance of transcription factors in H. pylori, information about the effects of nickel and pH on HpNikR in vivo is important for understanding the multifaceted roles of HpNikR in fine-tuning the physiology of this organism. Ultimately this study may provide us with a better idea of how to control H. pylori-caused diseases.

[NiFe] hydrogenases are found in a variety of microorganisms and catalyze the reversible oxidation of hydrogen gas to protons and electrons. This enzyme has generated intense interest due to its contribution to pathogenicity in certain organisms as well as its application in bioremediation and the production of hydrogen as an alternative fuel source. The biosynthesis of the dinuclear active site requires a number of accessory proteins to chaperone and insert the metal cofactors to the awaiting large subunit of hydrogenase. The proteins responsible for nickel delivery to Escherichia coli hydrogenase 3 are HypA, HypB, and SlyD, however the mechanism by which this is accomplished is unclear. The goal of this work was to analyze the metal-binding abilities and protein interactions of these nickel insertion proteins to enhance our understanding of their roles. Isolated N-terminal peptide of HypB has similar high-affinity metal-binding to the full-length protein. This peptide binds nickel in a square planar site with three cysteinyl and a fourth N-terminal amine ligand. Additionally, studies with SlyD and HypA reveal protein interactions that occur during hydrogenase maturation. Pull-down experiments of a tagged variant of hydrogenase revealed multi-protein complexes with HypA, HypB, and SlyD. A complex between SlyD and hydrogenase forms prior to both nickel and iron insertion, supporting chaperone activity of SlyD during hydrogenase maturation. HypA can interact with hydrogenase in the absence of HypB and SlyD, and a possible role as the bridging protein during the nickel insertion event is proposed. In addition, fluorescent imaging of E. coli cells using a fluorescently labeled streptavidin conjugate revealed localization of both Strep-tagged II hydrogenase and HypA at or near the cell membrane, suggesting that enzyme maturation occurs proximal to metal transporters. This work provided a deeper understanding of the role that each of these proteins play in [NiFe] hydrogenase assembly and is helpful for any future applications of this enzyme.

Fluorocarbons (FCs) and their derivatives (FCDs) are heavily relied on due to their wide range of uses (e.g. solvents, surfactants, refrigerants, and pharmaceuticals). Currently, FCs and FCDs are produced on an industrial scale via energy-intensive processes, using hazardous materials. Hence, new catalytic chemical technologies are required to provide cleaner and greener synthetic routes to partially fluorinated materials. The exploration of fundamental organofluorometallic chemistry of base metals, such as nickel, has potential to advance the development of novel catalytic processes towards this end. It has been established previously that zero-valent nickel complexes have the ability to efficiently catalyze the hydrodimerization of polyfluoroalkenes. The reactivity of the intermediate polyfluoronickelacycles was found to be influenced by modifications in the ligand sphere. Furthermore, an increase in oxidation state of the central metal atom was proposed as an additional strategy to increase the reactivity of the M-RF bond. In this thesis, through variation of the ligand environment and oxidation state of nickel, we have further developed the chemistry of high-valent polyfluoronickelacycles. Synthesis and characterization (NMR, EPR, UV/Vis, IR spectroscopy and electrochemistry) of new trivalent polyfluoronickelacycles are described as well as attempts to generate the corresponding tetravalent cations. Attempts to induce nucleophilic insertion of acetonitrile into the Ni-RF bond were also investigated herein. Challenges were encountered with the isolation of the tetravalent cations due to decomposition to the corresponding divalent nickelacycle.

The principal methylglyoxal (MG)-detoxifying system in most living organisms is the two metalloenzyme Glyoxalase system. Glyoxalase I (GlxI) initially converts the non-enzymatically formed MG-GSH hemithioacetal to the thioester S,D-lactoylglutathione. The hydrolase, Glyoxalase II(GlxII) regenerates GSH and liberates the product D-lactate. Ni2+/Co2+- and Zn2+-activated GlxI enzymes exist in nature. The Ni2+/Co2+-activated GlxI are not active as Zn2+-holoenzymes in spite of the structural similarities to the Zn2+-dependent enzymes. The Zn2+-GlxI enzymes have been investigated heavily relative to the Ni2+/Co2+-activated enzymes, which have been isolated more recently. As part of this study the three GlxI homologs isolated from Pseudomonas aeruginosa were characterized. The homologous genes encode GlxI enzymes of both metal activation type. The Zn2+-activated P. aeruginosa GlxI is difficult to de-metallate compared to the Ni2+/Co2+-activated enzymesreflecting a difference in metal-binding/insertion between the two types of GlxI. The E. coli GlxII was isolated and characterized to determine whether Ni2+/Co2+-activation is a characteristic of the Glx system as a whole in this organism. Inductively coupled plasma mass spectrometry on purified E. coli GlxII confirms that the active protein is a binuclear Zn2+-metalloenzyme. The results to date indicate a detectable isotope effect for the Cd2+-holoenzyme but not the Ni2+-reconstituted enzyme. Chemical crosslinking experiments indicate that the SlyD Ni2+ metallochaperone does not form a complex with E.coli GlxI. This indicates that the E. coli active site is not metallated in vivo by this accessory protein. The principal biophysical experiment in this project was determining of Ni2+-binding stoichiometry for E. coli GlxI by 1H-15N heteronuclear single quantum coherence (HSQC) NMR. The GlxI dimer reorganization ceases when the metal:dimer stoichiometry reaches 0.5 during apoenzyme titration. This finding supports previous studies that indicate half-of-the-sites metal binding in this enzyme.

The principal methylglyoxal (MG)-detoxifying system in most living organisms is the two metalloenzyme Glyoxalase system. Glyoxalase I (GlxI) initially converts the non-enzymatically formed MG-GSH hemithioacetal to the thioester S,D-lactoylglutathione. The hydrolase, Glyoxalase II(GlxII) regenerates GSH and liberates the product D-lactate. Ni2+/Co2+- and Zn2+-activated GlxI enzymes exist in nature. The Ni2+/Co2+-activated GlxI are not active as Zn2+-holoenzymes in spite of the structural similarities to the Zn2+-dependent enzymes. The Zn2+-GlxI enzymes have been investigated heavily relative to the Ni2+/Co2+-activated enzymes, which have been isolated more recently. As part of this study the three GlxI homologs isolated from Pseudomonas aeruginosa were characterized. The homologous genes encode GlxI enzymes of both metal activation type. The Zn2+-activated P. aeruginosa GlxI is difficult to de-metallate compared to the Ni2+/Co2+-activated enzymesreflecting a difference in metal-binding/insertion between the two types of GlxI. The E. coli GlxII was isolated and characterized to determine whether Ni2+/Co2+-activation is a characteristic of the Glx system as a whole in this organism. Inductively coupled plasma mass spectrometry on purified E. coli GlxII confirms that the active protein is a binuclear Zn2+-metalloenzyme. The results to date indicate a detectable isotope effect for the Cd2+-holoenzyme but not the Ni2+-reconstituted enzyme. Chemical crosslinking experiments indicate that the SlyD Ni2+ metallochaperone does not form a complex with E.coli GlxI. This indicates that the E. coli active site is not metallated in vivo by this accessory protein. The principal biophysical experiment in this project was determining of Ni2+-binding stoichiometry for E. coli GlxI by 1H-15N heteronuclear single quantum coherence (HSQC) NMR. The GlxI dimer reorganization ceases when the metal:dimer stoichiometry reaches 0.5 during apoenzyme titration. This finding supports previous studies that indicate half-of-the-sites metal binding in this enzyme.

<p>The purpose of this work was to design and to develop a high performance catalyst for the production of hydrogen from reforming of crude ethanol and also, to develop the kinetics and reactor model of crude ethanol reforming process. Crude ethanol reforming is an endothermic reaction of ethanol and other oxygenated hydrocarbons such as (lactic acid, glycerol and maltose) with water present in fermentation broth to produce hydrogen (H2) and carbon dioxide (CO2). Ni/Al2O3 catalysts were prepared using different preparation methods such as coprecipitation, precipitation and impregnation methods with different Ni loadings of 10 25 wt.%, 10-20 wt.%, and 10-20 wt.% respectively.</p><p>All catalysts were characterised by thermogravimetric/differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), (including X-ray line broadening), temperature programmed reduction (TPR), BET surface area measurements, pore volume and pore size distribution analysis. TG/DSC analyses for the uncalcined catalysts showed the catalyst were stable up from 600oC. XRD analyses showed the presence of NiO, NiAl2O4 and Al2O3 species on the calcined catalysts whereas Ni, NiAl2O4, and Al2O3 were present on reduced catalysts. BET surface area decreased and average pore diameter reached a maximum and then decreased as the Ni loading increased. The temperature programmed reduction profiles showed peaks corresponding to the reduction of NiO between 400-600oC and reduction of NiAl2O4 between 700-800oC. Catalyst screening was performed in a micro reactor with calcination temperature, reaction temperature and the ratio of catalyst weight to crude ethanol flow rate (W/Fcrude-C2H5OH) of 600 oC, 400oC and 0.59 h respectively. Maximum crude-ethanol conversion of 85 mol% was observed for catalyst with 15wt% Ni loading prepared by precipitation method (PT15), while maximum hydrogen yield (= 4.33 moles H2 / mol crude-ethanol feed) was observed for catalyst with 15wt% Ni loading prepared by coprecipitation (CP15). </p><p>Performance tests were carried out on (CP15) in which variables such as space velocity (WHSV) 1.68h-1to 4.68h-1, reduction temperature 400 to 600oC and reaction temperature 320 to 520 oC, were changed for optimum performance evaluation of the selected catalyst. The catalyst deactivated over first three hours of 11 hours time-on-stream (TOS) before it stabilized, the reaction conditions resulted in a drop of ethanol conversion from 80 to 70mol%.</p><p>The compounds identified in the liqiud products in all cases were ethanoic acid, butanoic acid, butanal, propanone, propanoic acid, propylene glycol and butanedioic acid. The kinetic analysis was carried out for the rate data obtained for the reforming of crude ethanol reaction that produced only hydrogen and carbon dioxide. These data were fitted to the power law model and Eldey Rideal models for the entire temperature range of 320-520 oC. The activation energy found were 4405 and 4428 kJ/kmol respectively. Also the simulation of reactor model showed that irrespective of the operating temperature, the benefit of an increase in reactor length is limited. It also showed that by neglecting the axial dispersion term in the model the crude ethanol conversion is under predicted. In addition the beneficial effects of W/FAO start to diminish as its value increases (i.e. at lower flow rates).

Nickel contaminated wastewater from plating industries is a major environmental concern. Current treatment methods are often expensive and can also create additional problems. Biosorption is an alternative treatment method that uses inexpensive biomaterials to sequester metals from aqueous solutions. In this study, acid washed barley straw (AWBS) was used for adsorbing nickel ions (Ni2+) from simulated nickel plating wastewater. The adsorption process was rapid and the equilibrium was reached in about an hour. An increase in the initial nickel concentration increased the equilibrium nickel uptake, and the maximum uptake was found to be 8.45 mg/g of AWBS when the initial nickel concentration was1000 mg/L at pH 5. Nickel adsorption was favorable at room temperature than 5oC and 40oC, better adsorption rate and equilibrium uptake was observed at 23oC. Increasing the pH from 3 to 7 increased the equilibrium nickel uptake and the maximum uptake was observed at pH 7, whilst the initial nickel ion concentration was 100 mg/L. The Freundlich isotherm model exhibited better fit with the equilibrium data than the Langmuir equation. Nickel was desorbed using hydrochloric acid solution at pH 2 and the desorption efficiency was 86%. FT-IR studies indicated the participation of hydroxyl, carboxyl and amide groups from cellulose, hemi-cellulose, protein and lignin of barley straw.

<i>N</i>-heterocyclic carbenes (NHC) have widely been used as spectator ligands in organometallic chemistry. Chelating bidentate di-<i>N-</i>heterocyclic carbenes (diNHC) provide additional entropic stability to their complexes relative to monodentate analogues. The steric and electronic environment around the metal centre can be fine-tuned by varying the substituents on the nitrogen atoms of the diNHC ligand. Synthesis and characterization of air and moisture stable bis(diimidazolylidene)nickel(II) complexes, [(diNHC)2Ni]2+, and their corresponding silver(I) and palladium(II) analogues are described.<p> Investigations into the catalytic potential of diNHC complexes of nickel as an alternative to palladium systems in carbon-carbon coupling reactions are discussed. In the Suzuki-Miyaura coupling reaction, the [(diNHC)2Ni]2+ complex was active for the coupling of aryl chlorides as well as aryl fluorides. The analogously synthesized Pd(II) complexes resulted in formation of (diNHC)PdCl2 species which were not active for the coupling of aryl fluorides. Transition-metal free coupling reactions were investigated and the results indicated that in the Mizoroki-Heck reaction, aryl iodides could be activated in the absence of nickel or palladium precatalysts when using Na2CO3 or NEt3 as base, while in the Suzuki-Miyaura reaction, aryl iodides and aryl bromides could be activated without any precatalyst when K3PO4 was used as base.<p> A general route into the synthesis of non-symmetrically substituted ligand precursors has been developed. Synthesis and characterization of non-symmetrically substituted ligand precursors, and their corresponding silver(I), palladium(II) and nickel(II) complexes are described. The activity of one of the non-symmetrically substituted (diNHC)Pd(II) complexes in the Suzuki-Miyaura coupling reaction of bulky substrates has been investigated. Non-symmetrically substituted diNHC ligand precursors with a hemi-labile pyridine arm have been synthesized and their corresponding Ni(II) and Pd(II) complexes are described.<p> Attempts to synthesize three-coordinate Pd(II) complexes using bulky â-diketiminato ligands are also discussed.

No description available.