Masters Degrees (Chemistry)

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The structure and synthesis of metabolites from virgilia oroboides and chlorophora excelsa (Iroko)
(1989) Swinny, Ewald Eugene.; Malan, E.
In the present study the acetone extract of the heartwood of two trees, Virgilia oroboides and Chlorophora excelsa, were investigated. The heartwood of Virgilia oroboides afforded a variety of known flavonoids, as well as a new pterocarpene and a new α-hydroxydihydrochalcone, viz.; 3-hydroxy-8, 9-methylenedioxy-6a,11a-dihydropterocarpan (αS), 2' ,4'-trihydroxy-4-methoxydihydrochalcone. A series comprising substituted hydroxygeranylstilbenes, substituted benzenoid compounds and quercitin-type flavones were isolated from the acetone extract of the heartwood of Chlorophora excelsa. The new compounds isolated from this tree are: 3,5-dihydroxy-4-geranylbenzaldehyde; 3' ,4,5'-trihydroxy-4'-geranylstilbene; 2'-methoxy-3, 4',7-tri-O-methylquercitin. A combination of solvent extraction, Craig countercurrent, column (LH 20 and silica gel) and thin layer chromatography procedures were used to isolate and purify the compounds mentioned. Structures were elucidated by high resolution (300 MHz) ¹HNMR spectroscopy (including NOE and spin-spin decoupling experiments) and mass spectrometry. The proposed structural assignments of the following compounds were confirmed by synthesis: 3, 5-dihydroxy-4-geranylbenzaldehyde; 3' ,4 ,5'-trihydroxy-4' -geranylstilbene; 2 ,3' ,4 ,5'-tetrahydroxy-4' -geranylstilbene (chlorophorin). The modified Wittig reation was used to synthesize 3' ,4 ,5' trihydroxystilbene. U.V. irradiation experiments were performed on chlorophorin in an attempt to synthesize the cis-isomer and a phenanthrene-type compound. Biosynthetic pathways showing the structural relationships of the identified compounds in Virgilia oroboides and Chlorophora excelsa were proposed. An attempt to synthesize (+)-catechin lignoid involved the coupling of (+)-catechin to sinapyl alcohol, with the latter synthesized from 2 ,6-dimethoxyphenol via vinyl quinone methide. Further investigations on lignoid currently in progress.
Toxic compounds in cycads.
(1990) Nair, Jerald James.; Osborne, Roy.
The present-day cycads comprise the diverse, modified, remnants of a much larger group of gymnosperms which flourished in the Mezozoic era. The systematic position that the cycads occupy in the botanical hierarchy is significant in that they represent relatively unchanged survivors from prehistory. The present global complement of 182 species occur in tropical and mild temperate regions in both hemispheres. Despite the density of proliferation of species, about one-half of the extant taxa are considered endangered, vulnerable or rare. Apart from characteristic features such as differences in growth forms, variation in reproductive structures and anatomical details, cycads are distinguished from all other plant groups by the unique phytotoxins, azoxyglycosides, which they possess. The toxicity of cycads is well-documented in cases which refer to both man and animals. Cycasin, which together with macrozamin represent the major azoxyglycosides occurring in cycads, has been reported to elicit responses similar to those that have been observed during carcinogenicity, mutagenicity and neurotoxicity assays. It has become apparent that the mechanism by which azoxyglycosides manifest their toxicity involves deglucosylation, by enzyme systems, which releases the aglycone, methylazoxymethanol (MAM), and sugar moieties. Metabolic activation of MAM succeeds deglucosylation to generate methylene carbene units (: CH2) which are capable of methylating macromolecules including DNA, RNA and protein. During this investigation, macrozamin was extracted from seed kernels of Encephalartos transvenosus and cycasin was tentatively identified in seed kernels of Cycas thouarsii . The hexa-acetate derivative of macrozamin was prepared whereas the tetra-acetate derivative of cycasin was not secured in a pure form. The spectroscopic techniques employed for identification include DV-absorption, infra-red and nuclear magnetic resonance spectroscopy, all of which are useful for detecting signals which arise as a result of the azoxy function. A kinetic study was carried out to determine the rate of hydrolysis of macrozamin with 4M sulphuric acid, and to allow calculation of the activation energy for the process. A comparison of the kinetic parameters determined for the above process with those derived for the hydrolysis of cycasin and methylazoxymethanol under similar conditions followed. The rates of hydrolysis increase in the order macrozamin, cycasin, methylazoxymethanol since the molecules contain two, one and zero glycosidic linkages respectively. Additional glycosidic bonds are observed to decrease the rate of reaction. Consequently, activation energies for hydrolysis of the above molecules decrease in the above-stated order. Macrozamin and cycasin were quantified in cycad material by high performance liquid chromatography (HPLC), gas-liquid chromatography (GLC) and by the chromotropic acid assay. The results of the quantitative analysis has highlighted certain limitations of the methods of detection, and has been found to be applicable to a taxonomic evaluation and a proposal for the biosynthesis of the azoxyglycosides.
The destabilising effects of various cations on a surfactant derivative of poly iso-butenyl succinic anhydride.
(1990) Rutherford, Christine Elizabeth.; Salter, Leo F.
The interfacial behaviour of two amphiphillic poly iso-butenyl succinic anhydride (PIBSA)-derived surfactants and the effect of their interaction with various nitrate salts on the stability of a water-in-oil type emulsion has been investigated. The adsorption of the esterification product of PIBSA and coco-diethanolamide (PICDEA) and of Experse-70 (E-70) at the equilibrated aqueous-fuel oil interface was investigated via the measurement of interfacial tension using the ring detachment method.The interfacial pressure of PICDEA decreased in the presence of excess unreacted coco-diethanolamide (CDE) and for both PICDEA and E-70 interfacial pressure decreased with an increase in the length of the poly iso-butenyl (PIB) hydrocarbon tail. Interfacial tension-concentration curves and the Gibbs Equation were used to determine surfactant surface excess concentration and the packing efficiency of the surfactant in the interphase. The double hydrocarbon PICDEA molecule was found to occupy a larger interfacial area than the single hydrocarbon E-70 molecule. The pH of the aqueous phase effects the interfacial activity and nature of, PICDEA and E-70 at the interface. PICDEA is protonated at pH values less than 4.6 and deprotonated at higher pH values. E-70 is neutral at low pH and deprotonated at pH values greater than approximately 2.The effect of sodium, calcium and ferric nitrate salts on the interfacial free energy of the surfactant saturated interface was also determined. The interfacial tension at the E-70 aqueous nitrate interface was dependent on ionic strength alone with a general decrease in interfacial free energy as nitrate concentration was increased. In the case of PICDEA, however, a surfactant-cation orientation effect was observed. The divalent Ca2+ cation attracts two adjacent PICDEA anions resulting in the adverse interaction of hydrocarbon tails in the interphase. This produces an interface with a higher than expected interfacial free energy. The Na+ cation produces an interface with a more energetically stable orientation. PICDEA in the presence of a ferric nitrate solution (pH 1 to 2) is protonated and therefore the univalent nitrate anion forms the counterion layer at the positively charged surfactant interface. Stability studies were carried out on aqueous nitrate salt in diesel emulsions using PICDEA as the stabilizing surfactant. Droplet coalescence rates were determined from droplet size distribution data in the presence of varying concentrations of sodium, calcium and ferric nitrate salts. Droplets were sized microscopically at progressive time intervals and the rate of coalescence determined from the change in droplet concentration with time. Coalescence was found to follow two or more consecutive first order reactions. After an initial period of rapid droplet coalescence, involving small droplets with diameters of 5~m and less, a droplet distribution is attained conducive to a more stable emulsion which then undergoes a slower rate of coalescence involving larger droplets. The effect of the nitrate salt type on the initial droplet coalescence rate (in order of increasing rate) is as follows: Ca2+< Na+< Fe3+. The opposite trend was observed for the slower long term rate of coalescence, i.e. Fe3+< Na+< Ca2+. These trends are explained in terms of the surfactant cation orientation effect, the effect of the droplet's radius of curvature on the potential energy barrier against coalescence and the effect of the droplet distribution of the emulsion system.
Extractives from the Meliaceae and Icacinaceae.
(1990) Akerman, Leigh-Anne.; Mulholland, Dulcie Aca.; Pegel, Karl H.
The wood, leaf and seed extracts of Apodytes dimidiata, Turraea floribunda and Turraea obtusifolia were examined. Two new limonoids belonging to the Toonafolin group were isolated from the seeds, two known havanensin-type limonoids were isolated from the leaves and both stigmasterol and sitosterol were isolated from the wood of Turraeafloribunda. Sitosterol as well as a limonoid which could not be characterised were isolated from the seeds, phytol, melianone and a protolimonoid similar to sapelin-F were isolated from the leaves and three protolimonoids: melianodiol, melianotriol and 7,8-dihydroturraeanthin 3-acetate were isolated from the wood of Turraea obtusifolia. An ester was isolated from the seeds of Apodytes dimidiata. Appropriate reactions were performed, where possible, on the compounds isolated.
Complexes formed by zinc and cyanide ions at elevated pH.
(1990) Monberg, Christian.; Marsicano, Fabrizzio.
The experimental work described in this thesis is aimed primarily towards elucidation of the speciation of zinc-cyanide systems at elevated pH. In this study the formation and stability of H+-eN-, binary Zn2+-eN- and ternary Zn2+-CN--QH- complexes were studied by glass electrode potentiometry in aqueous solutions at 25.0°0 and in a medium of ionic strength of 0.1 mol dm-3. The solution pH was varied to cover the range 4 to 11. The study was undertaken with a view to establishing whether and under what conditions soluble binary zinc-cyanide complexes and ternary zinc-cyanide-hydroxide complexes form, and to determine formation constants for any such species that are found. This information would be useful in defining more precisely the speciation of solutions containing zinc and cyanide ions at elevated pH values. A titration method was used, in which hydrogen ion concentration was monitored by means of a glass indicating electrode. The cell was calibrated to allow measurements of hydrogen ion concentration rather than hydrogen ion activity. Owing to precipitation difficulties, the reagents were used at sub-millimolar concentration levels. The potentiometric data was interpreted with the aid of various formation function plots together with the use of various computer programs, such as HALTAFALL and ESTA. The results show that the ternary complex Zn(ON)3(OH)2- is formed in significant amounts in solutions of pH > 8.5. Some evidence was also obtained for the existence of the five coordinated species Zn(CN)3(OH)~- and Zn(CN)~- in these solutions, but existence of the latter two species cannot yet be regarded as firmly established. No polynuclear complexes were detected at the sub-millimolar concentrations used. Formation constants are reported for H+-eN- and both binary Zn2+-eN- and ternary Zn2+-eN--QH- species.
The liquid-liquid extraction of Germaniun with the 7-alkylated 8- hydroxyquinoline derivative - KELEX 100.
(1990) Pellow-Jarman, Martin Vincent.; Salter, Leo F.
Germanium can be extracted from aqueous solutions by KELEX 100 dissolved in an appropriate diluent. KELEX 100 is a commercially available chelating extractant containing the active constituent 7-(4ethyl-l-methyloctyl)-8-hydroxyquinoline. Previous work in the solvent extraction of germanium with this reagent has shown that germanium is extracted most efficiently at low pH. When the germanium is present in sulphuric acid solutions at pH less than 2, the extracted complex is GeL3+HS04-,however at pH 3 to 8, the metal is extracted as GeL2(OH)2 (where HL = KELEX 100). In this work, the extraction kinetics and equilibrium extraction of germanium in the GeKELEX 100 solvent extraction system is examined by AKUFVE and shaking assemblies, which both employ rapid mixing of the organic and aqueous phases, and by a quiescent interface Lewis Cell. The AKUFVE is a Swedish designed apparatus for solvent extraction, its performance and suitability for solvent extraction studies is evaluated using the extraction experiments carried out on the GeKELEX 100 solvent extraction system. Experiments conducted using an experimental set-up with a large interfacial area to phase volume ratio reveal that the extraction of germanium occurs in two distinct kinetic regimes. The first regime occurs in the first few minutes of an extraction experiment and is fast relative to the second kinetic regime which follows this fast initial extraction period and occurs until the extraction of germanium attains the equilibrium value. In this work an extraction mechanism involving interfacial reaction of germanium and extractant is proposed to explain this kinetic behaviour. An increase in ionic strength is shown to reduce the rate of germanium extraction in the Ge-KELEX 100 solvent extraction system. Modifiers, such as organic alcohols, are shown to greatly improve extraction kinetics.
The determination of activity coefficients at infinite dilution using gas liquid chromatography.
(1991) Moollan, Warren Charles.; Letcher, Trevor M.
The aim of this investigation was to develop and test a theory that allowed for the calculation of the activity coefficients at infinite dilutions (l' ~ 3) from G.L.C. measurements using moderately volatile solvents. The solvents chosen for study were straight chained (Cs to C7) and cyclic (Cs, C6 and benzene) liquid hydrocarbons using cis- and trans-decahydronaphthalene (decalin) as the stationary liquid phase (solvent). The systems were studied at two different temperatures, 283.15 K and 298.15 K. The solutes were n-pentane~ n-hexane, n-heptane, cyclopentane, cyclohexane and benzene. This method for the determination of activity coefficients has the advantage of being able to work at infinite dilution, whereas in other techniques, extrapolation to infinite dilution of finite-concentration data is necessary. In addition solutes are separated from impurities when chromatographed so that only very small quantities of moderately pure material need be· used. However the technique is also limited since the solute studied (injected reagent) needs to be volatile, while the solvent (liquid stationary phase) should be involatile. The solvents chosen in this experiment (cis- and transdecalin) are moderately volatile which introduces many limitations since the theory developed for the determination of activity coefficients at infinite dilution is restricted to involatile solvents. However a novel method for working with moderately volatile solvents is developed by relating the loss of solvent to its partial pressure and modifying the existing theory. In the past the use of precolumns and/or saturators, coarse packing, small pressure gradients, and internal standards were used when working with volatile solvents. However employing this new method excludes the use of precolumns, saturators, or internal standards, and allows any type of packing and pressure gradient to be used. The calculated activity coefficients are compared with literature values, where the wor~ers employed G.L.C. techniques, and with predicted values. The activity coefficients calculated at both temperatures are used in the calculation of excess partial molar enthalpies. These results are compared with values obtained from finite concentration data by other workers.
Extractives from the Meliaceae.
(1991) Monkhe, Thabo Vincent.; Mulholland, Dulcie Aca.
No abstract available.
An investigation of the complexes of zinc and germanium with 8-hydroxyquinoline.
(1991) Maharaj, Vanitha.; Martincigh, Bice Susan.; Salter, Leo F.
The experimental work described in this thesis is aimed at the elucidation of the speciation of the zinc and germanium 8-hydroxyquinoline systems. A knowledge of this speciation could aid in modelling the kinetics of solvent extraction of zinc and germanium with 7alkyl derivatives of 8-hydroxyquinoline. In this study the stability constants of the ligand 8hydroxyquinoline with the ions H+, Zn2+ and Ge4+ have been investigated by potentiometry at 25°C in a partially aqueous medium. A titration technique was used in which the hydrogen ion concentration was monitored using a glass indicating electrode. The partially aqueous medium comprised of O. 1 mol dm- 3 NaCl04 in 60% (v/v) dioxane and the concentration levels of the reagents were at least millimolar. The analysis of the potentiometric data was carried out with the aid of the computer programs HALTAFALL, ESTA and STATGRAPHICS. The results obtained for the systems involving the H+ and Zn2+ ions compare with those reported in the literature. The stability constant of a protonated species in the zinc-8-hydroxyquinoline system (ZnLH) was established for the first time. Precipitates obtained from the Zn2+ titrations were identified as zinc 8-hydroxyquinolate dihydrate. The germanium 8-hydroxyquinoline system has not been studied previously via potentiometry techniques. The complex hydrolysed species of germanium in aqueous solutions and the unusual features displayed in the formation curves increased the complexity of species selection. Although a suitable model of the species present could not be determined some evidence suggests the presence of protonated species. Hence, a prerequisite for resolving the germanium-8hydroxyquinoline system could be a more complete understanding of the hydrolysis of germanium in the partially aqueous medium used.
Immunological studies of thymine dimer quantitation.
(1992) Kriste, Angela Gayle.; Salter, Leo F.
Ultraviolet irradiation of DNA induces the formation of a number of mutagenic lesions. The most prolific of these is the cis-syn thymine dimer (formed maximally at 260 nm) and this has been implicated in the reaction pathways that lead to ultraviolet-induced carcinogenesis. In order that the molecular events underlying these neoplastic events be understood, it is imperative that the thymine dimers formed in ultraviolet-irradiated thymine containing systems be quantitated. In this laboratory, dimer quantitation is performed using reverse phase high performance liquid chromatography (HPLC) with ultraviolet (DV) detection and the data obtained has allowed a kinetic mechanism for lesion formation to be proposed. Such studies have used in vitro thymine containing substrates (aqueous thymine, thymidine, thymidylyl-3',5'thymidine, calf thymus DNA and pUC19 plasmid DNA) to generate the thymine dimer using DV irradiation. with the planned extension of this research to in vivo cellular systems (where DNA and hence thymine concentrations are intrinsically less than those of in vitro systems), a more sensitive technique for thymine dimer quantitation is required. An immunological approach to providing this technique was chosen. Here, DV-irradiated DNA was injected into rabbits whose immune system mounted a ' response (i.e. antibody production) to the DV-DNA antigen. Blood was drawn from the rabbits at regular intervals to obtain the antibodies. The technique of immunoblotting was chosen and developed to allow detection of the thymine dimer antigen. This involved the reaction between the UV-DNA antigen, the primary antibody (generated by the rabbit) and a secondary antibody conjugated to an enzyme, all of which were immobilized on a commercially available membrane system. Detection and quantitation of the immune complex immobilized on the membrane was performed using the technique of enhanced chemiluminescence. Upon addition of a chemiluminescent substrate (luminol) to the immune complex, the horseradish peroxidase enzyme catalysed the reaction of luminol, with one of the products being light of 425 nm to 430 nm. This light impinged on a luminescence film which was developed and printed using standard photographic techniques. The use of dilutions of the primary antibody in the immunoblotting protocol with enhanced chemiluminescent detection, allowed correlations of antibody dilutions with UV-DNA antigen to be made. This immunoblotting technique with enhanced chemiluminescent detection has been used successfully in detecting thymine dimer lesion formation at levels currently above the detection limit of the HPLC. It has also been used successfully in detecting and quantitating thymine dimers at levels undetectable by the HPLC. To this end it has proved to be 4000 to 8000 times more sensitive than the chromatographic technique. Any immunological technique requires that the antibody of interest be purified and characterized. Here, purification of the crude serum was performed using the classical technique of ammonium sulphate precipitation of proteins. As an alternative technique, affinity chromatography was performed on the crude serum using a Memsep 1000 affinity chromatography cartridge attached to a preparative HPLC system. Chromatographic data illustrating this purification are given. Characterization of the DV-DNA antigen was performed by considering the specificity of the antibody response in the laboratory animal. Support for the kinetic mechanisms previously proposed for pyrimidine dimer formation in DNA is also given in this work. Calf thymus DNA was irradiated and dimer yields obtained by immunoblotting. These were used in the computer programme CAKE together with the previously determined rate constants to determine simulated dimer yields. A good agreement between experimental and simulated data indicated the validity of the mechanism at a DNA concentration of 0.025 mg/ml.
An investigation of acetone-photosensitised DNA kinetics.
(1992) Clemmett, Susan Joy.; Salter, Leo F.
Ultraviolet (UV) radiation is a potent DNA-damaging agent and a known inducer of mutations and skin cancer. The increasing incidence of skin cancer has emphasised the importance of understanding the mechanistic processes involved in the interaction of UV radiation with DNA. One of the most significant photoproducts, induced by UV light, in the DNA molecule is the cis-syn cyclobutane pyrimidine dimer. These dimers, particularly the cytosinecontaining dimers, have been implicated in the mutagenic and carcinogenic effects of sunlight. Dimerisation of contiguous pyrimidine residues in DNA can result from direct irradiation (A = 295-310 nm) or photosensitised irradiation (A > 300 nm) by endogenous photosensitisers. Direct irradiation of DNA produces a wide range of photoproducts, whereas triplet photosensitisation of DNA by acetone produces only thymine, cytosine and cytosinethymine dimers. Thus, acetone photosensitisation of DNA can be used in the elucidation of the mechanistic processes involved in the formation of photoproducts from the direct irradiation of DNA. Calf thymus DNA was irradiated in the presence of acetone at wavelengths greater than 300 nm, using a high pressure mercury lamp. Experimental conditions investigated were irradiation time, acetone concentration and DNA concentration. Irradiated DNA samples were degraded by hot acid hydrolysis to excise the dimers. The yields of thymine and cytosine-thymine dimers were able to be quantitated by reverse phase high performance liquid chromatography with DV detection.Independent kinetic mechanisms were proposed for thymine and cytosine-thymine dimerisation in calf thymus DNA. Rate constants were assigned from experimentally determined values, values cited in literature and values calculated from Stern-Volmer steady state analysis of the proposed mechanisms. Verification of the proposed kinetic mechanisms was achieved by the comparison of experimental dimer yields with those calculated from the computer simulation of the proposed kinetic mechanism. The computer program CAKE (Computer Analysis of Kinetic Equations) was used to obtain the simulated data. Good agreement between the experimental and simulated data was taken as corroboration of the proposed kinetic mechanism. A section of this work was concerned with the application of spectroradiometry to determine the amount of light intensity absorbed by irradiated solutions. The modification, calibration and operation of a Macam SR 9010 spectroradiometer to achieve this aim is discussed.
The design of rhodium and ruthenium catalysts for asymmetric aldol coupling.
(1992) Raab, Conrad Edmund.; Roos, Gregory H. P.; Haines, Raymond John.
Abstract available in PDF.
The polycyclic aromatic hydrocarbon content and mutagenicity of the residue from cane burning and vehicle emissions.
(1992) Godefroy, Susan Jessica.; Salter, Leo F.
Polycyclic (or polynuclear) aromatic hydrocarbons (PAHs) are environmental pollutants produced during the incomplete combustion of organic matter. Since many of these compounds have been shown to be mutagenic and/or carcinogenic, an investigation was initiated into determining the PAH content and mutagenicity of the ash that remains after sugar cane crop burning, and the soot deposited on toll booths by vehicle exhaust emissions. Due to the large amount of sugar cane farming in the Natal coastal region and that the favoured method of disposing unwanted leafy trash is crop burning, concern was expressed as to the nature of the residue that is formed. PAHs have been identified in the residues from combusted wood and straw and, due to their intrinsic similarity to sugar cane, it was considered that the burning of sugar cane could generate PAHs. It is well documented that vehicle exhaust emissions exhibit mutagenic properties and PAHs have been identified as the major contributors of this observed mutagenicity. Since a toll plaza is an area of high traffic density, it was considered to be an ideal location for an investigation into the build-up of particles emitted by the passing vehicles, and to study to what extent the operators are exposed to harmful compounds. In addition, this sample acted as a control, since the detection of PAHs and mutagenic activity in the soot would be an indication that the correct experimental techniques were being employed. Samples were collected on site. The sugar cane ash was collected off a field immediately after burning had taken place, and the soot was collected either by scraping the toll booth walls and surrounding areas or by wiping the surfaces with cotton wool swabs. The organic portion of the samples was separated from the inorganic and carbonaceous substances by extraction into a suitable solvent; the use of both acetone and dichloromethane was investigated. The extracts were divided into two portions - one was used for the analysis of PAHs and the other for determining mutagenic activity. Analysis for PAHs involved subjecting the extracts to a sample clean-up routine and the use of a number of analytical techniques to characterise the components. The mutagenic properties of the samples were investigated by means of two bacterial mutagenicity tests: the Salmonella typhimurium assay (the Ames test) and a new commercially available test kit, the SOS Chromotest. A number of PARs were identified in the extracts by means of reverse phase high performance liquid chromatography (HPLC) with both ultraviolet and fluorescence detection, the latter being the more sensitive method. Mutagenic activity was detected for both samples in the Ames test and for the toll booth soot in the SOS Chromotest, and this observed mutagenicity was attributed to the presence of the PAHs.
The thermodynamics of liquid mixtures : an investigation into the low temperature bleaching of a cotton non- woven fabric using hydrogen peroxide.
(1993) Govender, Ursula Penelope.; Letcher, Trevor M.
This thesis is presented in two parts. In part one, the excess molar volumes and the excess molar enthalpies have been determined for several binary systems at 298.15 K using an LKB flow microcalorimeter and/or a 2277 Thermal Activity Monitor and an Anton Paar Digital Densitometer. The excess molar volumes and excess molar enthalpies, V; and H; , have been determined for systems involving an alkanol (I-propanol, 2-propanol) mixed with a hydrocarbon (1hexene, I-heptene, l-octene, I-hexyne, I-heptyne, l-octyne). The results show trends relating to the degree of unsaturation of the hydrocarbon to the position of the hydroxyl group on the alkanol. The excess molar volumes and excess molar enthalpies, V; and H; of di-n-butylamine + diethyl ether or dipropyl ether or di-l-methylethyl ether or dibutyl ether or 1,1 dimethylethyl methyl ether or 1,1 dimethylpropyl methyl ether or tetrahydrofuran or tetrahydropyran or 1,4 dioxane have been measured over the whole composition range at the temperature 298.15 K in order to investigate di-n-butylamine - ether interactions. The V; values for each of the systems studied are negative with the exception of the mixtures of (di-n-butylamine + dibutyl ether or tetrahydrofuran or tetrahydropyran or 1,4 dioxane. The H; results over the whole mole fraction range are formed endothermically. Measurements were also made on mixtures involving (a cycloalkane + a pseudocycloalkane). The congruency theory was tested for the (cycloalkane + pseudo-cycloalkane) mixture. The cycloalkane mixtures studied here did not satisfy the null test of the congruency principle. In the second part of this thesis the main aim of the investigation was to apply ambient temperature hydrogen peroxide bleaching techniques to a novel non-woven fabric and to optimize the treatment conditions for this technique. Five cold-pad batch bleaching formulas were applied to the non-woven and the sample fabrics were analyzed for the following properties a) fluidity (measure of degree of degradation of the cotton fibre as a result of the bleaching process) b) wettability (absorbency) c) whiteness (using instrumental techniques) d) inherent fibre surface properties (SEM) A method was elucidated for the cold batch bleaching of the non-woven which produced a fabric with minimum fibre damage, an acceptable degree of whiteness and excellent absorbency properties. The treatment parameters of time (Xl), temperature(x2) and hydrogen peroxide concentration (x3) for this method were optimised using a multiple regression analysis for three variables and response surface plots.
Chemistry of ruthenium derivatives of the 2-diphenylphosphinoquinoline ligand.
(1993) Schauerte, Werner Karl.; Haines, Raymond John.; Field, John Stainer.
Abstract available in PDF.
Investigations into the reactions of imines and enamines.
(1993) Mahomed, Hamdani Ahmed.; Hickmott, Peter W.
Recent work in our laboratory has led to a new synthesis of the 2-oxo-a8'&-hexahydroquinoline ring system. This involved the condensation of B-alkylaminopropanoates with 2-methylcyclohexanone. Further reactions of B-aminopropanoates with other cyclic ketones and acyclic ketones have been investigated and are now reported. These reactions are found to be sensitive to steric effects, the stability of the ketone and the presence of molecular sieves and have led not only to the synthesis of the quinolone ring system but also to the inden-7-one and pyridone ring systems. A new one pot synthesis of the bicyclo[2.2.2]octan-5-one ring system from acyclic precursors has recently been reported. Reaction of" two equivalents of phenyl vinyl ketone with one equivalent of N-2-butylidenebenzylamine has lead to the synthesis of 2-benzoyl-4-methyl-l-phenylbicyclo[2.2.2]octan-5one as a mixture of two isomers. This reaction has now been extended to N-2-(4-phenylbutylidene)propylamine and ethyl N-propyl-4-iminopentanoate and our findings are reported.
The transpassive behaviour of the anodic film on Fe-Cr alloys.
(1993) Tonkinson, Charles Henry Llewelyn.; Brookes, H. C.
This work was undertaken to investigate the transpassive behaviour of the anodic film on two Fe-Cr alloys, namely Fe18Cr and Fe18Cr2Mo in acidic aqueous media in the pH range 0.5 to 3.8. Two electrochemical techniques were used, namely cyclic voltammetry and chronoamperometry. The two primary experimental variables in the cyclic voltammetric experiments were pH and sweep rate (2 - 800 mV/s). The main variables in the chronoamperometric experiments were the size of the potential step, the number of potential steps and the starting and ending potentials. Secondary experimental variables were temperature (25, 90°C), rotation rate (0, 150 rad/s), and the artificial addition of cations (Fe2+, Fe3+ and Cr3+) to some of the solutions. A voltammetric anodic peak, referred to as peak A, occurs in the transpassive region of the above Fe-Cr alloys, followed by a region of secondary passivity and then oxygen evolution. It was this peak that was investigated by cyclic voltammetric methods. The peak A current response was independent of rotation rate at pH 3.8 but was dependent on rotation rate at pH 0.5 with solutions of intermediate pH showing a gradual change in rotation rate dependence. This indicated a predominantly solid state process in less acidic solutions (pH 2.4 & 3.8) whereas in strongly acidic solutions (pH 0.5) the action of ions in solution must contribute significantly towards peak A processes. A method was developed to correct the peak A current response for the current due to oxygen evolution. The results of this method indirectly confirmed the hypothesis that more than one oxidation process contributes to the peak A current response. A diagnostic plot for diffusion control was applied to the peak height of peak A. The diagnostic involves plotting the peak height over the square root of the sweep rate versus the square root of the sweep rate. A process under diffusion control would give a horizontal line for this diagnostic plot. At pH 0.5 and at slow sweep rates (less than or equal to 60 mV/s) the diagnostic plot gave a positive deviation from the horizontal and this deviation was enhanced as the temperature was increased. As the pH was increased (towards pH 3.8), the deviation from the horizontal at slow sweep rates gradually became negative and this deviation was again enhanced when the temperature was increased. This phenomenon is explained in terms of the role of the hydronium ion. From the addition of Fe2+, Fe3+, and Cr3+ to pH 0.5 and pH 3.8 solutions it was noted that ferrous ions increased the peak A current response more than chromic ions of the same concentration. Ferric ions slightly decreased the peak A current response. Based on these results, reports in the literature, and the apparent role of the hydronium ion, a partial scheme was proposed in order to explain the role of Fe and Cr, from the alloy substrate, in the anodic film in the transpassive region. In chronoamperometric experiments, stepping to the transpassive region confirmed the phenomenon of the rising transient. A quantitative nucleation model - which was based on previous models from the literature - was generated. The model was successfully fitted to two rising transients, one from the pH 3.8, and the other from the pH 0.5 solution. The model also allows for the presence of a pre-existent laver at the starting potential of a chronoamperometric experiment after the electrochemical cleaning procedure. The model incorporates both diffusion controlled and charge transfer controlled steps. A key concept in the model is that of nucleation and "slow death" of corrosion pits growing into the electrode. "Death" of a pit occurs when it is covered by a nucleating and or growing passivating film. The rising transients were only obtained on Fe-Cr alloys (with one exception) when stepping to the transpassive region and also only in solutions where peak A was obtained in a cyclic voltammetric experiment. The exception to this was that in the pH 0.5 solution and at 90°C, rising transients were obtained when stepping to the passive region. This did not occur at 25°C. Rising transients were also obtained on pure iron when stepping to the passive region. In addition to the rising transient, a reverse rising transient was discovered. This reverse rising transient (which generated a cathodic current) was obtained when stepping the potential cathodically from the transpassive region. It was shown that the occurrence of the reverse rising transient was dependent on the presence of a stable, transpassive anodic film before the potential step. One indirect result from the discovery of the reverse rising transient was that it indicates that secondary passivity exists at least 200 mV into the oxygen evolution region.
Influence of alkali metal promotion on the properties of co-precipitated Cu/Zn/Cr higher alcohol synthesis.
(1994) Maboka, Maboka Sydney.; Haines, Raymond John.; Sofianos, Alkeos.
Abstract available in PDF.
A chemical investigation of a KwaZulu-Natal medicinal plant, Momordica foetida Schum. & Sond.
(1994) Sewram, Vikash.; Osborne, Roy.; Mulholland, Dulcie Aca.
Momordica foetida Schum. & Sond. (Cucurbitaceae), locally known as iNtshungu, is widely used by the Zulu people of Natal-KwaZulu for the treatment of a variety of ailments. The dried leaves leaves and stems of this plant was subjected to soxhlet extraction by refluxing with hexane, chloroform and methanol successively. Thin layer chromatography of the chloroform extract of the leaves revealed a multiplicity of compounds. The chloroform extract was further partitioned with sodium hydroxide resulting in an organic and aqueous phase. The organic phase, containing extract A, afforded two compounds, viz. compounds 1 and 2. The basic aqueous fraction was neutralised and re-extracted with chloroform to give extract B, affording five compounds, viz. compounds 3,4,5,6 and 7. Structural elucidation was accomplished by techniques such as IH and 13C NMR spectroscopy, HETCOR, COSY, FTIR and High Resolution Mass Spectrometry. Compounds 1 and 2 were identified as cucurbitane triterpenoids known as momordicines which had been previously discovered in the related species of this plant, Momordica charantia L. The remaining five compounds were identified as novel compounds, although natural derivatives of compounds 6 and 7 had been isolated previously from Momordica charantia L. Compounds 3-7 were each isolated as an epimeric mixture but it was possible to select the resonances corresponding to the major epimer. These five epimers were respectively identified as 5, 19-epoxy-19(R)-hydroxy-25-methoxy-5β- cucurbita-6,23-diene-3β-ol [102], 5,19-epoxy-19(R),25-dihydroxy-5β-cucurbita- 6,23-diene-3β-ol [103], 5,19-epoxy-19(R)-methoxy-25-hydroxy-5β-cucrbita- 6,23-diene-3β-ol [104], 5,19-epoxy-25-methoxy-5β-cucurbita-6,23diene- 3β-ol [105] and 5,19-epoxy-19(R),25-dimethoxy-5β-cucurbita-6,23diene- 3β-ol [106]. Appropriate reactions were performed, where possible, on the compounds isolated in order to confirm their identity.
Antioxidant activity of Maillard reaction products.
(1994) Devchand, Kamlashkumar.; de Muelenaere, H. J. H.
The use of natural antioxidants to improve the oxidative stability of food lipids has received special attention because of the worldwide trend to avoid the use of synthetic food additives. A wide range of natural sources has been shown to contain antioxidant properties, these include plant extracts, herbs and spices, citrus fruits, oilseeds and legumes. Some antioxidants have been found to be fonned during the heat processing of foods, including the Maillard reaction products that are formed by the reaction of amino acids, peptides and proteins with reducing carbohydrates. A study was undertaken to investigate the antioxidant activity of Maillard reaction products fonned during extrusion of soyabeans. A preliminary oxidation study carried out to identify a suitable substrate revealed that sunflower oil stripped of antioxidants was a suitable substrate with a low induction period of 15 minutes via the Rancimat Method and 4.5 hours via the method of Ross and de Muelenaere. Methyllinoleate was found to be sensitive to oxidation, but not readily available and costly. Storage test of antioxidant stripped sunflower oil under various headspace conditions showed that the substrate stability was best at 4°C under nitrogen or vacuum. Under such conditions the product could be stored for a period of 136 days. Nitrogen was chosen as the most suitable for this exercise as it was not easy to remove all residual air from the samples by vacuum. Furthermore with nitrogen headspace residual 02 could be measured based on Ni02 ratio changes. Hexane solvent was found to be able to remove all lipids from soyabeans. Under the experimental conditions practised it was found that the induction periods for extruded and unextruded soya flour hexane extracted lipids were very similar. Addition of glucose or fructose to the extrusion mixture increased induction period of hexane extracted lipids by 37.5% and 1.5% respectively as measured by the Ross and de Muelenaere method and by 50% and 6.5% respectively as measured by the Rancimat Method. Available lysine of glucose containing extrudate was reduced by 69% while that of the fructose containing extrudate was reduced by 23%. Residual glucose and fructose analysis of extrudates showed that 66% of glucose was utilized in the formation of the Maillard reaction products while only 21% of fructose was utilized during extrusion processing. Comparison of induction periods of soya glucose and soya fructose extrudates to induction period of TBHQ antioxidants (200ppm) in antioxidant stripped sunflower oil gave antioxidant activity of 86ppm and 9ppm for soya glucose extrudates and soya fructose extrudates respectively. The observed antioxidant activity of Maillard reaction products could be utilized with success in different types of processed foods without the need for extensive testing as required for synthetic antioxidants but supplementation of lysine may be required to maintain nutritional balance.

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