Magnesium hydroxide, a stable flame retardant, can be obtained by mining or by the hydration of magnesium oxide. In this study, the effect of different hydrating agents on the pH of the hydrating solution, rate of hydration of MgO to Mg(OH)2 and product surface area were studied as a function of the temperature of hydration. Ammonium chloride, magnesium acetate, magnesium nitrate, nitric acid, acetic acid, water, magnesium chloride, sodium acetate and hydrochloric acid were used as hydrating agents. The hydration experiments were carried out in a water bath between 30 - 80 oC for 30 minutes. Dried MgO samples were introduced to the hydrating solution and the slurry was stirred at a constant speed. At the end of each experiment, the slurry was vacuum filtered, washed with water, dried at 200 oC and hand ground. The products were then characterized by TGA, XRF, XRD and BET surface area analyses. There was not a significant difference in the hydration behaviour of the hydrating agents up to 50 oC, where less than 10 % of magnesium hydroxide was formed. When compared to the hydration in water, all the hydrating agents with the exception of sodium acetate showed a significant increase in the degree of hydration. Sodium acetate formed the lowest amount of magnesium hydroxide, ranging between 1.2 and 12.2 % magnesium hydroxide. Hydrations performed in hydrochloric acid and magnesium nitrate formed the largest percentage (11.8 %) of magnesium hydroxide at 60 oC. Magnesium acetate, magnesium nitrate, magnesium chloride and hydrochloric acid seemed to be the most effective hydrating agents at 70 oC with the percentage magnesium hydroxide being formed ranging between 20.0 and 23.9 %. The amount of hydroxide formed doubled at 80 oC, with the largest percentage (56.7 %) formed from the hydration in magnesium acetate. The hydration reaction seemed to be dependent upon the presence of Mg2+ and acetate ions. It seemed that magnesium oxide hydration is a dissolution-precipitation process controlled by the dissolution of magnesium oxide. The results have also indicated that the pH and temperature of the hydrating solution strongly influence the degree of hydration. / Chemistry / M.Sc. (Chemistry)

Enzymes are becoming an effective tool in industrial processes, from crude applications such as bioremediation to fine processes such as chirally selective biocatalysis. The ligninolytic enzymes have recently received considerable attention for industrial application due to both their broad substrate range and their ability to degrade the most recalcitrant natural polymer, lignin. This group of enzymes was therefore identified as the target group for this study. Improved enzyme properties are constantly being sought to enhance the range of applications for enzymes. Biodiversity provides a wide variety of enzymes. Several researchers have concentrated on extremophiles as their primary source of superior enzymes, consequently neglecting temperate environments in their search for these enzymes. The relatively neglected fungal biodiversity of South Africa provided an opportunity to test the hypothesis that potentially important industrial enzymes with unusual properties could be isolated from mesophilic basidiomycetous fungi. Subsequent screening of Eastern Cape biodiversity for thermostable ligninolytic enzymes from basidiomycetes resulted in the isolation of a novel laccase enzyme from a basidiomycetous species. This fungus was identified as Peniophora sp. UD4 by phylogenetic analysis of rDNA ITS sequences. Initial studies indicated a superior optimum temperature of 70°C and thermostability, indicated by no loss in activity at 60°C over nine hours. Further characterization of the laccase revealed a broader than usual substrate range through its unusual ability to oxidatively couple DMAB and MBTH. The laccase also exhibited a broad pH oxidation range for ABTS (pH 2 – 6.8), and a relatively high affinity (K_m_ = 0.0123 mM) and catalytic efficiency (63 252 mM^(-1)^s^(-1)^) for ABTS as a substrate. The laccase activity from Peniophora sp. UD4 was shown to be comprised of three isozymes with a molecular weight of 62 kDa and pI’s of 6.33, 6.45 and 6.50. Investigation of the nutrient and physical factors affecting ligninolytic enzyme production and growth of Peniophora sp. UD4 indicated that the wild-type organism was unsuitable for large scale production of the thermostable laccase due to the low levels of laccase production. The thermostable laccase was applied to defouling of ultrafiltration membranes, bioremediation of industrial waste streams, biocatalysis, and biosensor technology as potential applications. Application of the Peniophora sp. UD4 laccase to defouling of membranes used for ultrafiltration of brown water showed large flux recoveries of 31, 21 and 21% after the first three defouling recycles respectively, compared to 3% for the control without immobilized enzyme. The novel laccase showed potential for the bioremediation of industrial waste streams, the most successful being that of bleach plant effluent, where a reduction of 66% of the phenolic load was achieved. Application of the novel laccase to biocatalytic oxidation of ferulic acid and (±)-α-pinene showed higher product yield as compared to oxidation of these compounds by Trametes versicolor laccase in mediated and non-mediated systems. The major products of (±)-α-pinene oxidation were identified as verbenol and trans-sorberol. The Peniophora sp. UD4 laccase was successfully applied to biosensor technology, which benchmarked significantly better than Trametes versicolor laccase for the detection of 4-chlorophenol. The biosensor developed with laccase from UD4 by covalent binding to a glassy carbon electrode exhibited the best combination of sensitivity and stability. This thesis shows that a laccase with superior properties was obtained from a mesophilic South African basidiomycete. The catalytic properties displayed by the novel laccase from Peniophora sp. UD4 all contribute to the increased industrial applicability of laccases, and may be the most industrially feasible enzyme of its class isolated to date.

A thesis submitted in fulfillment of the requirement for the Degree Master of Technology: Biotechnology, M.L. Sultan technikon, 2000. / The ever-increasing demand for a wide variety of paper products has led to the pulp and paper industry becoming one of the largest industries in the world. In 1988 the United States alone produced almost 71 million metric tonnes of paper and pulp board (Jeffries, 1992). South Africa has also become one of the major international producers of pulp and paper products. Since 1970, the production of paper and board by the South African industry achieved an average growth rate of 5.2% per annum, and in 1997 South Africa was the twelfth largest producer of pulp and 24th biggest supplier of paper and board in the world (Molony, 1999 / M

The adsorption and separation of Pd(II) from Pt(IV), Ir(IV) and Rh(III) by silica microparticles functionalized with triethylenetetramine (TETA), 2-(2-aminoethylthio)ethanamine (NSN) and 2-(2-(2-aminoethyl)ethylthio)ethanamine (NSSN) in 1 M hydrochloric acid medium was investigated by continuous column studies. The functionalized sorbent materials were characterized by microanalysis, SEM-EDS and FT-IR. Palladium selectivity of the sorbent materials was achieved by stripping of rhodium, iridium and platinum chlorido species with 0.5 M of NaClO4 in 1 M HCl while [PdCl4]2 was eluted with 3% w/v thiourea. The desorption efficiency of thiourea was confirmed by the SEM-EDS analysis of the materials after Pd(II) elution. Palladium loading capacity of the sorbents were in the order S-NSSN (23.85 mg/g) > S-NSN (12.70 mg/g) > S-TETA (4.97 mg/g). The extraction patterns on the sorbent materials were explained by considering the coordination chemistry of the ligand with [PdCl4]2ˉ and ionic interactions of [PtCl6]2ˉ and [IrCl5(H2O]ˉ. The square planar complexes, [Pd(HNSSNH)Cl2]Cl2 and [Pd(NSNH)Cl2][PdCl4]2, were isolated, analyzed by spectroscopy and single crystal X-ray, whereas evidence of the fraction of Pd(II)-TETA complex was obtained by HPLC studies. This provided proof of the inner sphere coordination mechanism as the mode of interaction of these ligands with [PdCl4]2ˉ. Trace amounts of Brˉ anions in ligands resulted in the inadvertent isolation of bromide coordinated Pd(II) NSN and NSSN complexes. The ion-pair salts of [TETAH4]4+ with [PtCl6]2ˉ, [IrCl6]3ˉ and [RhCl6]3ˉ were also isolated and characterized by microanalysis and IR to further explain the extraction patterns.

Cellulomonas find was grown on minimal media with casamino acids and yeast extract added. Avicel was found to be the best cellulosic carbon source for the production of cellulase enzymes. The Millipore Ultrafiltration System was found to be the most efficient method of concentrating the enzyme preparations. Unpretreated sawdust samples of four different softwood species were degraded between 12 and 16 percent over a 15-day treatment. Increasing the concentration of substrate lead to a lower percent degradation but a higher overall degradation. Chemical pretreatment did not appreciably increase degradability of the samples. Physical pretreatments decrease the degrada-bility of the sawdust samples. The lotech pretreatment, which is a combination of chemical and physical pretreatment, gives a substrate that is degraded by the Cellulomonas fimi enzyme preparation. The pretreatment makes 50% of the sample water soluble. In 3 days, a further 35% is degraded from large insoluble chunks into insoluble small particles which remain in suspension. There is 6% degraded into soluble state. This leaves only 9% of the initial sample left in the pellet. With longer incubation, one would expect the degradation to continue. / Science, Faculty of / Microbiology and Immunology, Department of / Graduate

This thesis deals with the current methods available for X-ray structure determination and with the crystal and molecular structure determination of five compounds using these methods. The five compounds are 1) [ 2,3-Bis (dimethylarsino)- 1, 1, 1,4, 4, 4-hexaf luorobut-2-ene-As,As]tricarbonyldiiodotungsten(II),Me₂AsC (CF₃):C (CF₃) AsMe₂WI₂(CO)₃ 2) Dimethylammonium trichlorotris(dimethylsulphoxide}-ruthenate(II) , [ ( (CE₃)₂ SQ)₃ RuCl₃ ]⁻ [ (CH₃)₂ NH ₂]+ 3) Dichlorotetrakis{dimethylsulphoxide)ruthenium(II), (Me₂SO)₄fRuCl₂ 4) 1,3,7-Triraethyl-2,6-dioxypuriae hydrochloride dihydrate (caffeine hydrochloride dihydrate), CH₁₁C1N₄0₂-2H₂0 .5) 1-Acetyl-3-benzamido-2-keto-4- (2,3, 4, 6-tetra-O-acetyl-β-D-glucopyranosyloxy)-Δ³-pyrroline, C ₂₇H₃₀N₂O₁₃ The structures of compounds 1), 2), and 3) were determined by Patterson syntheses, compound 4) by centrosymmetric direct methods and compound 5) by non-centrosymmetric direct methods. All structures were then refined using full-matrix least-sguares procedures. The relevant crystal data for all five compounds can be found in Table A In the tungsten compound [1) the tungsten atom is seven-coordinate with a distorted capped octahedral environment, the capping group being a carbonyl. The capped face consists of the two remaining carbonyl groups and one of the arsenic atoms from the bidentate ligand. The uncapped face contains the two iodine atoms and the remaining arsenic. Crystal data for the five compounds examined atom. The structure of the ruthenium compound [ 2) ] consists of two crystallcgraphically non-equivalent anions in the asymmetric unit linked by hydrogen bonding via dimethylammonium cations. The coordination geometry about the structurally similar anions is essentially that of an octahedron with the DHSO ligands being bonded to Ru via the sulphur atoms. The co-ordination geometry about the ruthenium atom for compound 3) is essentially octahedral with cis chlorine atoms; Of the four DMSO ligands three are S-bonded and one is O-bonded, the O-bonded ligand being trans to a S-bonded ligand. For caffeine hydrochloride [ 4) ] the fused ring system is essentially planar and protonated at the 9-positioh. The crystal contains two types of hydrogen bonding involving 0-H...C1 and N-H...0 interactions. The structure of compound 5) consists of a pyranose ring in the chair conformation with the four 0-acetyl substituents in equatorial positions; the pyranose ring is connected to a planar pyrroline ring via a β-oxygen bridge. / Science, Faculty of / Chemistry, Department of / Graduate

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