No description available.

Kinetic studies of a number of interesting and significant reactions involving activation of hydrogen, olefins, oxygen and carbon monoxide by solutions of rhodium complexes containing sulphur and/or chloride ligands are described. The cis 1,2,3-trichlorotris(diethylsulphide)rhodium (III) complex, RhCl(EtS₃and the corresponding dibenzyl sulphide complex, RhCl₃(Bz₂S)₃in N,N -dimethylacetamide (DMA) solution were found to be effective catalysts for the homogeneous hydrogenation of maleic, fumaric and trans-cinnamic acids. The kinetic data are consistent with a dissociation of a sulphur ligand prior to the hydrogen reduction of rhodium (III) to rhodium (I). The rhodium (I) is stablized in solution by rapid complexing with the olefin to produce a Rh¹(olefin)(Ln) complex (L = auxiliary ligands) which then reacts with H₂ in a rate determining step to produce the saturated paraffin and rhodium (I). In some instances, more complex kinetics resulted when one of the auxiliary ligands in the Rh¹ (olefin)(Ln) complex dissociates prior to reaction with H(2); a unique apparent zero order in catalyst concentration has been observed. Isomerization was observed in the RhCl(EtS)₃catalyzed hydrogenation of fumaric acid and a mechanism involving rhodium (III) alkyl intermediate seems likely. The cyclooctene complex, [Rh(C8H14)₂C1], in DMA was found to be a convenient source for preparing rhodium (I) complexes "in situ" by adding the desired ligands, for example, chloride or diethyl sulphide. Kinetic data obtained using such solutions are in good agreement with the hydrogenation data obtained by starting from the corresponding rhodium (III) complexes. This result confirms that rhodium (I) intermediates are involved in the catalytic hydrogenation starting from rhodium (III) complexes. During studies to investigate the effect of solvent on catalytic hydrogenation of olefins by rhodium (III) complexes, dimethyl sulphoxide (DMSO) was found to be catalytically reduced by hydrogen to dimethyl sulphide and water in the presence of RhCl(EtS)₃ and RhCl‧3H2O. The kinetics were consistent with a rate determining heterolytic splitting of H₂ by Rh(III)(DMSO) to produce Rh[III](DMSO)H¯ which then decomposes to the products in a fast step. RhCl₃‧3H₂O also catalyzed the oxidation of DMSO to dimethyl sulphone using a mixture of oxygen and hydrogen. The solution of [Rh(C8H14)₂C1]₂ in DMA containing LiCl was found to be a versatile catalyst, for besides the activation of hydrogen and olefins, oxygen and carbon monoxide could also be activated. The formation of a rhodium (I) molecular oxygen complex, Rh(I)(O2) and a subsequent catalyzed oxidation of the DMA solvent and cyclooctene were studied in detail. The formation of the Rh(I)(O2) complex appears to be irreversible. An E.S.R. signal, possibly due to species such as Rh(II)(O2¯) was also observed. The kinetics of the oxidation suggest the equilibrium formation of the Rh(I)(O2) complex followed by a rate determining step to give the products. A free radical mechanism seems likely. Solutions of [Rh(C8H14)₂C1]₂ in LiCl/DMA readily reacted with carbon monoxide to form a Rh(I)(CO)₂ species. A solution of the oxygen complex was converted more slowly to the Rh(I)(CO)₂ species in a reaction whose observed rate was determined by the dissociation of the coordinated oxygen. Preliminary studies indicated that a mixture of CO and O₂ is converted catalytically to CO₂ by a solution of [Rh(C8H14)₂C1]₂ in LiCl/DMA. / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

Cart Lake, located 1.6 km south of the town of Cobalt, ON, contains elevated concentrations of As (0.95 to 18.05 mg/L Ast) resulting from uncontained mine tailings deposited during a silver mining boom from 1910 to 1983. Aqueous geochemical and investigations indicate tailings are sulfate-affected but subject to extensive carbonate buffering, with pH ranging from 6.7 to 8.6, Eh ranging from 46 to 210 mV, and alkalinity ranging from 32 to 201 mg/L HCO3-. The dominant cation species are Ca (4.9 to 192.0 mg/L), K (1.1 to 13.5 mg/L), Mg (1.2 to 8.7 mg/L), and Na (2.1 to 16.9 mg/L) and the dominant anionic species are alkalinity, As (0.003 to 18.1 mg/L), Cl- (0.3 to 16.8 mg/L), PO4 (0.04. to 9.6 mg/L), and SO42- (6.8 to 456.1 mg/L). Concentrations of minor and trace cations such as Fe, Co, and Ni are present at the g/L scale. Mineralogical investigations suggest As is mobilized from primary reactive sulfide and arsenide minerals such as arsenopyrite, skutterudite, and safflorite/löllingite/ rammelsbergite solid solutions. Primary mineral alteration products including Ca-Fe arsenates and erythrite are found in these tailings, resulting from direct alteration from primary minerals and precipitation from solution respectively. Secondary Ca-Fe arsenates and Co-Arsenates attenuate As, Co, and Fe by absorption and coprecipitation throughout the tailings profile, influenced by the presence of alteration rims around reactive mineral grains in the vadose zone. Field analysis of cation speciation and geochemical modelling of elemental equilibrium concentrations with weathering primary mineral surfaces would further inform conclusions regarding the relative contributions of each mineral to total As attenuation.

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Glaucoma is the leading cause of irreversible blindness worldwide with the most prevalent form, primary open-angle glaucoma (POAG), accounting for the vast majority of glaucoma cases. The main risk-factor for POAG is an elevated intraocular pressure (IOP), and is due to an increased resistance to aqueous humor outflow in the conventional outflow pathway at the juxtacanalicular region of the trabecular meshwork (TM) and the inner wall of Schlemm’s canal (SC). Reducing elevated IOP is the most effective method to prevent further loss of vision in glaucoma; therefore, it is important to understand how outflow resistance is regulated in the conventional outflow pathway in order to find effective methods to reduce ocular hypertension. Sphingosine-1-phosphate (S1P) is an endogenous lipid that reduces outflow facility in porcine eyes, thereby increasing resistance. S1P plays a major role in affecting cell migration, endothelial permeability, and junctional formation, processes that are intimately linked and regulated by cytoskeletal dynamics. Due to S1P’s known effect of decreasing endothelial permeability in vascular endothelial cells, the overall hypothesis of this dissertation is that the S1P-induced decrease in outflow facility occurs through a mechanism that involves S1P receptor activation in SC cells. The results from the studies within this dissertation demonstrate the expression of the S1P₁₋₃ receptor subtypes in SC and TM cells and a decrease of outflow facility by S1P in perfused human eyes. Additionally, S1P promotes F-actin formation and myosin light chain (MLC) phosphorylation at the SC cell cortex. The S1P-promoted MLC phosphorylation in both SC and TM cells, in addition to the S1P-induced decrease of outflow facility in porcine and human eyes, were blocked by the S1P₂ antagonist JTE-013. Results from these studies demonstrate S1P to actively regulate actomyosin dynamics in the cells of the outflow pathway through the S1P₂ receptor. S1P₂ also mediates the S1P-induced increase in outflow resistance. Therefore, S1P₂ is a novel pharmacological target in the conventional outflow pathway to reduce elevated IOP in glaucoma patients.