Approximately 70% of the western world's known nickel reserves are contained in laterite ores, but only 30% of the world's nickel production comes from these ores. This is due to the lack of economically viable technology to extract the nickel from these ores. However, recent advances in pressure acid leaching technology have resulted in new commercial attempts to extract nickel and its valuable by-product, cobalt, from laterite ores. The commissioning of three nickel laterite projects in Western Australia in the late 1990s represents the first of these new generation nickel operations, with several other projects; in Australia and overseas, in various stages of development. Unfortunately, several technical issues have hindered full production in these new refineries. Some of these problems are directly attributable to the mixer-settler contactors used in the solvent extraction process. This has highlighted a need to develop alternative contactors for industrial use. Electrostatic Pseudo Liquid Membrane (ESPLIM) is an alternative, novel technique to conduct the solvent extraction process. It combines the basic principles of solvent extraction, liquid membrane and electrostatic dispersion into a simple, compact reactor that utilises many advantages of each technique. The aim of this study w as to develop a method of extracting and separating cobalt from an acidic nickel laterite leach solution using ESPLIM. Bench scale tests using synthetic and actual leach solutions have shown that: the design and construction materials of the baffle plate and electrodes have a significant effect on the performance of the reactor; an AC power supply provided better droplet dispersion than a DC power supply; an increase in the applied electric field strength above a critical value resulted in a decrease in the aqueous droplet size and an increase in residence tune. / These effects increased the extraction efficiency and the concentration of the loaded strip solution. However, further increases in applied electric field strength decreased efficiency due to excessive levels of swelling and leakage; the known extraction isotherms for cobalt and nickel apply in the ESPLIM technique; salts of soluble organic acids influence extraction efficiency by changing the aqueous pH and interfacial tension; the use of ammonia was found to be effective as a replacement for salts of soluble organic acids; the ESPLIM reactor can cope with large changes in the flow rates of both feed and strip solutions. However, an increase in the feed flow rate should be accompanied by a relative increase in the ship flow rate to maintain high extraction efficiencies; the baffle design has a significant impact on the levels of swelling and leakage; provided the electrostatic field strength is maintained and flow rates are increased proportionately to the size of the reactor, no significant scale-up issues were observed, indicating that the data generated in bench scale studies could be applied to plant scale contactors. The optimum conditions, devised as a result of this investigation, to extract cobalt from an acidic nickel laterite leach solution using the ESPLIM technique are as follows: an applied electric field strength of 5.5 kV/cm. a raffinate pH of 5.5, a solvent containing 10% Cyanex 272 with 5% TBP in Solvent HF diluent, a feed to strip flow ratio of approximately 5 and a 1 M H[subscript]2S0[subscript]4 strip solution. At these conditions, almost complete cobalt extraction is achieved after only two extraction stages. A comparable extraction using conventional mixer-settlers could only be achieved after five stages.

The bulk of the world's known nickel reserves are contained in laterite ores but sulphidic ores remain the main source of the Western world's nickel production. With the continuing increase in nickel consumption and the depletion of sulphidic ores, the traditional source of nickel, the extraction of nickel from lateritic ores has been the subject of research interest worldwide. Advances in pressure acid leaching (PAL) technology have resulted in significant commercial attempts to extract nickel from these ores. Leaching the ore with sulphuric acid at elevated temperatures and pressures allows almost complete dissolution of the nickel and cobalt, a valuable byproduct of these ores, but yields highly contaminated pregnant leach solutions. Separating and purifying the nickel and cobalt from these solutions remains a hindrance to full commercial production. Several purifying techniques have been commercialised but all suffer from continuing technical problems. Among them, however, the direct solvent extraction (DSX) technique offers several advantages. Direct solvent extraction involves the separation of the nickel and cobalt directly from the partially neutralised pregnant liquor stream (PLS) by solvent extraction with Cyanex(R) 272 as the extractant. However certain contaminants adversely affect the solvent extraction process. Among them is chromium and little is known about the solvent extraction behaviour of this metal. The present work investigated the solvent extraction of chromium with Cyanex(R) 272. It was found that the solvent extraction behaviour of chromium(III) and chromium(VI), both of which could be found in PAL-generated PLS, are distinctly different. / For chromium(III), solvent extraction tests showed that (a) it is extracted in the pH range 4-7; (b) the extraction is partly influenced by diffusion; (c) the apparent equilibration time is significantly longer than most transition metals; (d) increases in temperature from 22 to 40 C resulted in increases in the extraction; (e) the pH0.5 increases in the order nitrate < chloride < sulphate in the presence of these anions; (f) the presence of acetate depresses extraction of chromium(III) when the solution is allowed to stand before extraction; (g) in the PLS, chromium(III) precipitated at lower pH than that predicted by the solubility product principle; and (h) the pH0.5 decreases as the Cyanex(R) 272 concentration increases. Chromium(III) is initially extracted by solvation of its inner sphere complex, which then undergoes further reaction in the organic phase leading to the formation of a much more stable species that is difficult to strip. A reaction scheme together with a description of both the initially extracted and resulting stable species is proposed. Extraction of chromium(VI), on the other hand, (a) occurs at pH less than 2 by solvation of chromic acid; (b) is independent of the aqueous phase composition; (c) does not occur in the pH range (3-6) used in the separation of nickel and cobalt. The latter is irrespective of temperature up to 40 C, the use of industrial PLS as the aqueous phase or the presence of an anti-oxidant in the organic phase. The stripping of chromium(III) from a loaded organic phase can be achieved using 1-4 mol L-1 mineral acids provided the stable organic species have not formed making industrial scale stripping of chromium(III) from Cyanex(R) 272 difficult. The exact composition of the aqueous phase during extraction affects the stripping efficiency.

Thesis (LL.M. (Estate Law))--North-West University, Potchefstroom Campus, 2007.

Thesis (Ph.D. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2009.

Understanding structure and folding of a protein is the key to understanding its biological function and potential role in diseases. Despite the importance of protein folding, a molecular level understanding of this process is still lacking. Solution-state nuclear magnetic resonance (NMR) is a powerful technique to investigate protein structure, dynamics, and folding mechanisms, since it provides residue-specific information. One of the major contributions that govern protein structure appears to be the interaction with the solvent. The importance of these interactions is particularly apparent in membrane proteins, which exist in an amphiphilic environment. Here, individual peptide fragments taken from the disulfide bond forming protein B (DsbB) were investigated in various solvents. The alpha-helical structures that were obtained, suggest that DsbB follows the two-stage model for folding. However, side chains of polar residues showed different conformations compared to the X-ray structure of fulllength protein, implying that polar side-chains may re-orient upon helix packing in order to form the necessary tertiary interactions that stabilize the global fold of DsbB. Model peptides in general represent attractive systems for the investigation of non-covalent interactions important for protein folding, including those with the solvent. NMR structures of the water soluble peptide, BBA5, were obtained in the presence an organic co-solvent, methanol. These structures indicate that the addition of methanol stabilizes an alpha-helix segment, but disrupts a hydrophobic cluster forming a beta-hairpin. Since dynamic effects reduce the ability for experimental observation of individual, bound solvent molecules, results were compared with molecular dynamics simulations. This comparison indicates that the observed effects of NMR structures are due to preferred binding of methanol and reduction of peptide-water hydrogen bonding. NMR structures, such as those determined here, represent a distribution of conformations under equilibrium. The dynamic process of protein unfolding can nevertheless be accessed through denaturation. A method was developed to probe thermal denaturation by measuring the temperature dependence of NOE intensity. Applied to a model peptide, trpzip4, it was confirmed that the beta-hairpin structure of this peptide is stabilized by the hydrophobic cluster formed by tryptophan residues. Together, the peptides investigated here illustrate the important roles that solvent-peptide interactions and side chain-side chain hydrophobic interactions play in forming stable secondary and tertiary structures.

This thesis is an experimental investigation on the binding of self-assembling peptides to oligodeoxynucleotides (ODNs) and the characterization of the resulting peptide-ODN complexes/aggregates, the first key step in the development of a peptide-based gene delivery system. Effects of pH, charge distribution along the peptide backbone, and oligonucleotide sequences on the peptide-ODN binding were investigated by a series of physicochemical methods. UV-Vis absorption and fluorescence anisotropy experiments demonstrate that aggregates are formed after mixing the peptide and ODN in aqueous solution. The aggregates in solution can be centrifuged out. Based on this property, the fraction of ODNs incorporated in the peptide-ODN aggregates can be obtained by comparing the UV-Vis absorption of the solution before and after centrifugation. Binding isotherms are generated by a binding density function analysis of the UV absorbance results. The binding parameters are extracted from the analysis of the binding isotherms based on the McGhee and von Hippel model. Equilibrium binding parameter studies show that the binding of two self-assembling peptides, EAK16-II and EAK 16-IV, to model single and double-stranded ODNs at pH 4 is stronger than at pH 7, and that no binding occurs at pH 11. These results demonstrate that electrostatic interactions play an important role in the EAK-ODN binding because EAKs are more positively charged at low pH. EAKs bind more strongly to dG16 than to the other ODN sequences dC16 and dGC16. This demonstrates that the hydrogen bond might be involved because they promote the binding of the lysine residues of the peptide to dG16 to a greater extent than to dC16. The charge distribution along the peptides is found to have an effect on the binding. EAK16-IV, whose positively charged residues are clustered at one end of the peptide, binds to the ODNs more strongly than EAK16-II, whose positively charged residues are distributed throughout the peptide chain, at the same pH. The binding process of EAKs to the ODNs was investigated by fluorescence anisotropy and static light scattering experiments. The results show that individual EAK and ODN molecules complex first, followed by the aggregation of these complexes into large aggregates. The nature of the resulting peptide-ODN complexes/aggregates is examined by UV-Vis absorption, fluorescence anisotropy, and PAGE experiments. The results demonstrate that free EAK, free ODNs, and small EAK-ODN complexes, which can not be centrifuged out, exist in the supernatant, and that large aggregates are collected in the pellets after centrifugation of the solution. The size of the resulting EAK-ODN complexes/aggregates measured by AFM and DLS is around a few hundreds of nanometers at low EAK concentrations. The accessibility of the ODNs to the quencher in the solution is reduced by 40 % and 60 % after binding to EAK16-II and EAK16-IV, respectively, as determined by fluorescence quenching experiments on EAK-ODN mixture solutions. An ODN protection from Exonuclease 1 degradation is provided by the EAK16-II or EAK16-IV matrix when they are mixed with the ODNs at pH 4. However, the ODNs are protected to a much lower degree when the EAK-ODN aggregates are prepared at pH 7. The EAK-ODN aggregates prepared at pH 7 are found to dissociate more easily than those prepared at pH 4 when they are incubated with exonuclease I solution at pH 9.5. These results suggest that the ODN protection afforded by the EAK-ODN aggregates is correlated with their structural stability after being incubated with the nuclease solution. The stability of the EAK-ODN aggregates after dilution is determined by UV-Vis absorption. No detectable dissociation of the aggregates is observed over 20 hrs after a 5- and 10-fold dilution of the solution in the same buffer used for their preparation. The EAK-ODN aggregates remain stable after the solutions are centrifuged, and re-dissolved in fresh buffer solutions. The ability of an EAK matix to protect ODNs from nuclease degradation together with its biocompatibility and low-toxicity suggests that EAK self-assembling peptides could be used as carriers for gene delivery.

No description available.

Triazenes, compounds containing a diazoamino moiety (–N(1)=N(2)–N(3)<), are known for their reversible cis-trans isomerization character and hence, have the potential to be used in photoswitchable devices and photostorage media. However, little is known about their cis-trans isomerization mechanism. In this thesis, kinetic studies on the thermal cis-to-trans isomerization of N-(phenylazo)-substituted nitrogen heterocycles are presented. It is shown that the isomerization rate constant increases as the size and electron-donating character of the cyclic amine increases, as the electron-withdrawing character of the para substituent group on the phenyl ring increases, and as the polarity of the solvent increases. All these trends are interpreted in terms of a rotational isomerization mechanism involving a dipolar transition state. In addition, photolytic cleavage of the N(2)–N(3) bond of target substrates is shown to be affected as well by the size and electronic character of the cyclic amine, the electronic character of the phenyl ring substituent, and the polarity of the solvent, with the result that the photolysis yield increases as the isomerization rate decreases. Theoretical calculations on target substrates both in the gas phase and various solvents were also performed based on DFT-B3LYP/6-31+G* method. Overall, the cis-to-trans isomerization is predicted to take place through rotation around the N(1)=N(2) bond. Furthermore, the calculated energy barriers are found to be influenced by the size and electronic character of the cyclic amine, the electronic character of the phenyl ring substituent, and the polarity of the solvent, consistent with the effects obtained experimentally from the kinetic studies.

Syftet med detta examensarbete var att utveckla en GC-metod för analys av etylenglykoler i förorenade vattenprover, exempelvis industriavloppsvatten. Detta skulle åstadkommas med en GC-FID och MMI (Multimode Inlet), samt helst utan provupparbetning. Ett annat av målen var att kunna kvantifiera inom området 1 ppm till 100 ppm, och att metoden skulle vara tillräckligt stabil för att kunna ackreditera den.Ett flertal kolonner testades, där en HP-5 med dimensionerna 30 m*0,53 mm*0,88 μm från Agilent var den som gav bäst resultat. Även två olika liners provades, dels en med glasull och dels en 2 mm dimpled liner, där dimpled linern gav bäst resultat, och minst ”carry-over” mellan analyserna. Bland de parametrar som gav störst effekt utmärker sig trycket i injektorn, och tiderna som de olika flödena är igång. För fullständiga inställningar, se bilaga 2.En metod redo för ackreditering hann ej tas fram, det finns ett flertal parametrar som bör undersökas för en effektivare och stabilare analys. Men metoden som är framtagen är redo för omfattande repeterbarhetstest. / The purpose of this bachelor’s thesis was to develop a GC method for analysis of ethylene glycols in polluted water samples, for example industrial sewage water. This was meant to be accomplished with a GC FID and MMI (Multimode Inlet), preferably without sample preparation. One of the goals was to be able to quantify between 1 ppm and 100 ppm, and that the method was stable enough for accreditation.A number of columns were tested, from where a HP-5 with the dimensions 30 m*0,53 mm*0,88 μm from Agilent gave the best results. Also, two different liners were tested, one with glass wool and one 2 mm dimpled liner, where the dimpled liner gave the best results and the least carry-over between samples. Amongst the parameters which gave the biggest effect, the inlet pressure and the different flow times stands out. For a full set of settings, see Bilaga 2.A method ready for accreditation was not developed due to short of time. There are still a number of parameters which should be investigated for a more efficient and stabile analysis. But the method developed is ready for extensive repeatability tests.

Triazenes, compounds containing a diazoamino moiety (–N(1)=N(2)–N(3)<), are known for their reversible cis-trans isomerization character and hence, have the potential to be used in photoswitchable devices and photostorage media. However, little is known about their cis-trans isomerization mechanism. In this thesis, kinetic studies on the thermal cis-to-trans isomerization of N-(phenylazo)-substituted nitrogen heterocycles are presented. It is shown that the isomerization rate constant increases as the size and electron-donating character of the cyclic amine increases, as the electron-withdrawing character of the para substituent group on the phenyl ring increases, and as the polarity of the solvent increases. All these trends are interpreted in terms of a rotational isomerization mechanism involving a dipolar transition state. In addition, photolytic cleavage of the N(2)–N(3) bond of target substrates is shown to be affected as well by the size and electronic character of the cyclic amine, the electronic character of the phenyl ring substituent, and the polarity of the solvent, with the result that the photolysis yield increases as the isomerization rate decreases. Theoretical calculations on target substrates both in the gas phase and various solvents were also performed based on DFT-B3LYP/6-31+G* method. Overall, the cis-to-trans isomerization is predicted to take place through rotation around the N(1)=N(2) bond. Furthermore, the calculated energy barriers are found to be influenced by the size and electronic character of the cyclic amine, the electronic character of the phenyl ring substituent, and the polarity of the solvent, consistent with the effects obtained experimentally from the kinetic studies.