Over the past decade, advances in ethylene oligomerization have witnessed explosive growth of interest from both commercial and academic standpoint, with chromium metal invariably being the metal of preference. A common feature in this literature was the extended long debate regarding the mechanism, metal oxidation states responsible for selectivity and the role of the ligand. This thesis work embarked on the isolation and characterization of new active intermediates called “single component catalysts” (or self activating) to address two important questions: (1) how the catalyst precursors re-arrange upon activation and (2) the real oxidation state of the activated species. Four different ligands systems have been examined for this purpose. The first part is a study on the NPIIIN ligand which can be described as a dynamic and non-spectator ligand. Upon aluminum alkyl activation, a series of single component chromium catalysts for selective ethylene oligomerization and polymerization have been isolated, fully characterized and tested. New selective single component chromium(I) catalysts have also been isolated and tested positively for ethylene trimerization. The second part includes a new series of chromium complexes based on the NPVN ligand. This ligands enabled to obtain the first polymer-free extremely active catalytic system. In both NPN ligand systems, a new activation pathway was discovered by using vinyl Grignard reagent [(CH2=CH)MgCl] as activator and/or reducing agent. The third part explores new modified pyrrole-chromium complexes which were found to be highly active and selective ethylene trimerization catalysts. This part was a continuation of previous work from our lab to complete the mechanistic picture of this highly successful pyrrole-chromium catalyst independently commercialized by Phillips-Chevron and Mitsubishi. Interestingly upon aluminum alkyl treatment, the first example of a Schrock-type chromium ethylidene complex has been isolated and characterized and found to be a potent catalyst for selective ethylene trimerization. Finally, the other ligands introduced in this thesis are new systems called pyridine-SNS and Si-SNS that introduce some modification to the known commercial SNS catalyst (Sasol technology). The introduction of a pyridine ring or a silyl unit in the ligand scaffold has allowed to understand the mechanism of action of this remarkable system.

Silicalite-1 crystals and hollow tube structures were synthesized and functionalized with amine and sulfur containing groups. The adsorption behavior of metal ions (Pb2+, CrO4-) in aqueous solution was investigated on nanocrystalline zeolites functionalized with amines and thiols. Nanocrystalline zeolites with a diameter of 30-50 nm and external surface areas around 100 m2/g were functionalized with 3-aminopropyltriethoxysilane (3-APTES) and 3-mercaptopropyltrimethoxysilane (3-MPTMS). The materials were characterized by 29Si magic angle spinning nuclear magnetic resonance spectroscopy and x-ray diffraction. The adsorption of metal ions from aqueous solutions of Pb (NO3)2 and Na2Cr2O7 was measured by inductively coupled plasma-atomic emission spectroscopy. The effects of various conditions such as pH and concentration were studied to optimize adsorption. Adsorption on functionalized mesoporous silica (MS) was conducted for comparison to the functionalized zeolites. Magnetic zeolite/iron composites were prepared using nanoscale and commercial faujasite zeolites. The composites were functionalized with amine groups to facilitate chromate adsorption under acidic conditions. The materials were characterized using nitrogen adsorption, scanning electron microscopy, thermogravametric analysis, FTIR spectroscopy, and Mossbauer spectroscopy. The adsorption of chromium was evaluated using inductively coupled plasma-optical emission spectroscopy (ICP/OES) to monitor solution chromium quantitatively. The removal of the composites with a magnet was demonstrated. The materials were then evaluated for the adsorption of Cr6+ using ICP-OES to detect chromium. Iron containing zeolite composites were prepared using nanoscale faujasite zeolites. The composites were functionalized with amine groups and Fe ions to facilitate arsenate(As V) adsorption under a variety of pH conditions. The materials were characterized using nitrogen adsorption, X-ray diffraction, thermogravametric analysis and FTIR spectroscopy, and Mossbauer spectroscopy. The adsorption of arsenic was evaluated using inductively coupled plasma-optical emission spectroscopy (ICP/OES) to monitor solution concentration quantitatively. The removal of the composites with a magnet was demonstrated. Kinetics and pH dependence of the adsorption were studied.

Many heavy metals are essential for biological functions; however some of these metals, especially at high concentrations, can have serious adverse effects on humans. The main sources of heavy metal exposure are through agriculture, transport, mining and related operations. South Africa has a thriving mining industry and is known for its rich mineral resources, but due to the incorrect method of disposal of the waste from these mines, substances, including heavy metals, get into the water and air supply, affecting the people living in close proximity to these mines. Exposure is through inhalation of contaminated air and consumption of contaminated food and water. The most vulnerable to heavy metals are the developing fetus, because of the high rate of cell division and differentiation. In the current study, two heavy metals cadmium (Cd) and chromium (Cr) were chosen based on the possibility of being exposed to them in South Africa. Thus, the aim of this study was to investigate the possible cellular effects of the heavy metals Cd and Cr alone and in combination, at different concentrations, on brain, liver and kidney tissue by using a chick embryo model. This model was successfully implemented over a 14 day period after which the embryos were terminated and the brains, livers and kidneys removed and processed for light- and transmission electron microscopy (with energy dispersive spectroscopy and electron energyloss spectroscopy). In addition, the effect of Cd and Cr alone and in combination on DNA structure and micronuclei formation was evaluated. The levels of the major antioxidant component, glutathione was determined in the brains of the chick embryos. At low concentration of Cd and Cr alone and in combination, a hormesis effect was observed in the survival rates and weights of the chick embryos, while at x1000 physiological dose (PD) Cr and Cd alone and in combination the effects were toxic. The majority of viable embryos did not have any macro-anatomy abnormalities. Morphological evaluation of the brain, liver and kidney samples revealed that Cd caused severe alterations at its highest concentration with minor alterations at the lower concentrations. Cr and the metal combination groups on the other hand, only caused minimal alterations throughout the concentration ranges evaluated. The presence of Cd and Cr alone and in combination in the liver tissue was confirmed with the electron energy-loss spectroscopy analysis that detected these metals in the nuclei, mitochondria and Golgi complexes of the hepatocytes. This might contribute to the ultrastructural changes observed in this organ. The genotoxicity testing on the red blood cells revealed no substantial differences, as only a few micronuclei were present. Although heavy metals cause DNA damage through an indirect mechanism of oxidative damage, the presence of Cd and Cr in the nucleus and mitochondria indicates that these metals may have a direct effect on DNA structure. With DNA agarose gel electrophoresis it was found that Cd and Cr alone and in combination caused DNA fragmentation. In the brain, GSH levels were normal; however changes may be the result of Cd and Cr causing the depletion of other antioxidant elements such as glutathione reductase, glutathione peroxidase, superoxide dismutase and catalase. In conclusion, this study indicates that Cd and Cr alone and in combination are toxic to the chick embryo. Cd is more toxic than Cr, and both metals accumulate in the nuclei and mitochondria where they induce damage either through oxidative and/or other mechanisms associated directly with DNA damage. / Dissertation (MSc)--University of Pretoria, 2014. / tm2015 / Anatomy / MSc / Unrestricted

<p>Tetraazamacrocycles, such as cyclam (1,4,8,11-tetraazacyclotetradecane), are useful ancillary ligands in the formation of organometallic complexes. Coordination of a 3d metal can lead to the formation of square planar complexes, such as with Ni^II and Cu^II, or octahedral complexes upon coordination of additional ligands, such as with Co^II/III and Cr^II/III. Notably with Cr, a mixture of <i>cis-</i> and <i>trans-</i>octahedral complexes are formed, and the isomerism can be influenced through <i>C</i>-substitution of the cyclam macrocycle. Herein, Cr^III complexes featuring <i>C</i>-substituted cyclam derivatives and either redox-active ligands or alkynyl ligands are reported.</p> <p>Chapter 1 features an introduction to the photophysical processes of Cr(III), an overview of cyclam and its derivatives, and a brief review of Cr^III(cyclam/cyclam’) bis-alkynyl complexes for various applications. Chapter 2 discusses the structural, optical, electronic, and magnetic characterizations of <i>cis</i>-[Cr(HMC)catecholate]⁺ and <i>cis</i>-[Cr(HMC)semiquinonate]²⁺ complexes, which feature redox-active catecholate and semiquinonate ligands. Chapter 3 highlights a series of <i>trans</i>-[Cr(HMC)(C₂Ar)Cl]⁺ complexes, which expands upon prior research on bis-alkynyl complexes. Chapter 4 discusses how a different <i>C</i>-substituted cyclam derivative, MPC, is used to produce <i>trans</i>-[Cr(MPC)Cl₂]⁺ starting material in higher quantity than the HMC derivative. This allows for higher amounts of <i>trans</i>-[Cr(MPC)(C₂Ar)₂]⁺ complexes to be synthesized, making it a more practical macrocycle for the future pursuit of dissymmetric bis-alkynyl complexes.</p>

In order to identify hexavalent chromium (Cr6) sources, behavior, and treatability, this thesis has profiled Cr6 in seven full-scale drinking water treatment plants and six distribution systems. Bench-scale jar tests assessed the treatment efficacy of coagulation and developed strategies to remove ultra-low level (0.01- 1.0 ~tg/L) Cr6. All water sources measured in this project contained dissolved Cr6 greater than or equal to the California Public Health Goal (0.02 ~g/L Cr6). The investigated coagulation plants did not remove Cr6; in fact, four of the seven treatment plants inadvertently added Cr6 to the treated waters. Thirteen types of drinking water treatment chemicals were evaluated as a potential non-water source of chromium. Amongst these, only iron-based coagulants contained trace levels of chromium sufficient to account for the observed increases at the full-scale plants. Other discussed non-water sources include leaching of chromium-bearing infrastructure or oxidation of Cr3. One of the treatment systems showed chlorine oxidized Cr3 to Cr6 and raised the finished concentration, in less than seven hours. One suggested improvement strategy was to use ferrous iron to reduce and remove Cr6 during coagulation. Bench-scale tests showed ferrous iron and a cationic polymer improved removal of both Cr6 and Total Cr. Chlorine interfered with that reduction. The full-scale test of this reduction-coupled coagulation treatment successfully decreased the finished Cr6 concentration when 40% ferrous iron was used and the point of chlorination was moved downstream from the coagulation process.

Seven chromium-containing complexes were tested for effects on blood glucose regulation, serum cholesterol levels, serum triglyceride levels, and body composition. The compounds included Cr picolinate, Cr chelidonate, chromate, Cr chelidamate, Cr arginate, nichrome, and Cr chloride. The study was divided into two major sections, a rat study and a chicken study. In the rat study all seven chromium-containing complexes were tested. They were administered to the rats in four different testing periods at 1 ppm, 5 ppm, and 25 ppm of chromium. Methods of administration varied for each testing period. After the chromium compounds were administered, a glucose tolerance test (GTT) was conducted on the rats in each of the four experiments. No consistent, significant findings were observed in blood glucose or insulin levels or in blood glucose or insulin change during the GTI. Tissue and blood samples were collected at the end of the study. Liver tissue weights were significantly reduced as the level of chromium supplementation increased. A similar trend was noted in the epididymal fat pad weight, but was not statistically significant. In the chicken study the partitioning effects of Cr picolinate, chromate, Cr chelidamate, Cr arginate, nichrome, and Cr chloride were more closely examined. The chickens were supplemented at 3, 15, and 75 ppm for 8 weeks. No beneficial effects from the supplementation were noted in feed efficiency, total intake, fasting blood glucose and insulin levels, HDL and total cholesterol levels, or serum triglycerides. At the end of 3 weeks the birds supplemented at 3 ppm were heavier than the other treatment birds. At the end of the 8 weeks the birds were sectioned into primal cuts and weighed. No beneficial effects of chromium supplementation were noted in any of the cuts when expressed as a raw weight, percent of dressed weight, or percent of live bird weight. Kidney chromium levels were significantly increased as the level of chromium supplementation increased in the picolinate-, arginate-, and chelidamate-treated groups. Chromium chloride-, picolinate-, arginate-, and chelidamate-treated groups all showed significant increases in liver chromium levels as the level of chromium supplementation increased.

Pure chromium oxide trifluoride was prepared for the first time by reaction of CrO3 and ClF with subsequent multiple fluorine treatments at 120°c. On the basis of its infrared spectrum, the purple CrOF3 was assigned as a fluorine-bridged polymer with terminal oxygen groups. Chromium oxide trifluoride was found to be stable to 300°c, where it decomposes with the loss of oxygen to CrF3.

Indiana University-Purdue University Indianapolis (IUPUI) / Insulin resistance, a hallmark of type 2 diabetes (T2D), is associated with accompanying derangements such as hyperinsulinemia that promote the progression of insulin resistance, yet a mechanism(s) is imperfectly understood. Data have demonstrated that hyperinsulinemia promotes insulin resistance as evidenced by diminished ability of insulin to mobilize glucose transporter GLUT4 to the plasma membrane (PM). We found that loss of PM phosphatidylinositol 4,5-bisphosphate (PIP2)-regulated filamentous actin (F-actin) structure contributes to hyperinsulinemia-induced insulin resistance. We tested if increased glucose flux through hexosamine biosynthesis pathway (HBP) causes dysregulation of PM components necessary for GLUT4 translocation. Increased HBP activity was detected in 3T3-L1 adipocytes cultured in hyperinsulinemia (5 nM Ins; 12 h) and also 2 mM glucosamine (GlcN), a distal HBP activator, inducing losses of PM PIP2 and F-actin. In accordance with HBP flux directly weakening PIP2/F-actin structure, inhibition of the rate-limiting HBP enzyme (glutamine:fructose-6-phosphate amidotransferase) restored F-actin and insulin responsiveness. Furthermore, less invasive challenges with glucose led to PIP2/F-actin dysregulation. New findings support a negative correlation between PM cholesterol accrual, PIP2/F-actin structure and GLUT4 regulation. These data stemmed from parallel study aimed at understanding the antidiabetic mechanism of the nutrient chromium (Cr3+). We found that chromium picolinate (CrPic) enhanced insulin-stimulated GLUT4 trafficking via reduction in PM cholesterol. In line with glucose/cholesterol toxicity findings, we demonstrated that therapeutic effects of CrPic occurred solely in adipocytes with increased HBP activity and a concomitant elevation in PM cholesterol. Mechanistically, data are consistent with a role of AMP-activated protein kinase (AMPK) in CrPic action. These data show that CrPic increases AMPK activity and perhaps suppresses cholesterol synthesis via distal phosphorylation and inactivation of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR), a rate-limiting enzyme in cholesterol synthesis. Continued study of the consequence of increased HBP activity revealed alterations in cholesterogenic transcription factors – Sp1, SREBP-1, and NFY – with Sp1 showing a significant increase in O-linked glycosylation. Consistent with Sp1 modification eliciting maximal transcriptional activation of SREBP-1, Hmgr mRNA was significantly enhanced. In conclusion, these data are consistent with a central role of PM cholesterol in glucose transport and suggest perturbations in this lipid have a contributory role in developing insulin resistance.

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