UWCScholar :: Browsing by Author "Green, Ivan R."

Browsing by Author "Green, Ivan R."

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Chemical and biological investigation into some selected African indigenous medicinal plants
(University of the Western Cape, 2009) Babajide, Jelili Olalekan; Mabusela, Wilfred Thozamile; Green, Ivan R.; Dept. of Chemistry; Faculty of Science
African medicinal plants are commonly used throughout Africa to treat a variety of ailments including wounds and ulcers, cough and chest complaints, gingivitis, fever and gonorrhoea, indication all related to infection and inflammation. In screening several plant species from an inventory of common medicinal plants from both South and West Africa for diverse medicinal purposes, 6 plants were selected because of their interesting and useful ethnomedicinal values.
The extraction, purification and evaluation of compounds from the leaves of Leonotis Leonorus for anticonvulsant activity
(University of the Western Cape, 2002) Muhizi, Theoneste; Green, Ivan R.; Amabeoku, George J.; Dept. of Chemistry; Faculty of Science
The aim of this study is to isolate and evaluate the anticonvulsant components from the leaves of Leonotis leonorus (L) R.aR. and to see if there is any change in activity with the origin of the plant material and I or the season in which plant material is collected. Therefore, in this study, two sites were chosen for collection of plant material and the collection was made in summer and in winter. Chemical, physical and pharmacological methods were used to isolate, identify and to evaluate compounds isolated from the leaves of Leonotis leonorus for anticonvulsant activity.
The Isolation and Electrochemical Studies of Flavanoids from Galenia africana and Elytropapus rhinocerotis from the North Western Cape
(University of the Western Cape, 2010) Maiko, Khumo Gwendoline; Green, Ivan R.; Iwuoha, Emmanuel; Dept. of Chemistry; Faculty of Science
In this study two medicinal plant species, namely Galenia africana and Elytropapus rhinocerotis, the former belonging to the family Aizoceae and the latter belonging to the family Asteraceae, have been investigated and different compounds isolated and characterized. Both species are important plants used in traditional medicine in Africa and particularly in South Africa. Flavanoids are secondary metabolites found in plants. They have a protective function against UV radiation and have a defence against invading illnesses due to their important antioxidant activity. Much of the food we eat and some beverages we drink contain flavonoids. The aim of this study was to investigate the electrochemistry of flavanoids isolated from these species.
Pharmacological evaluation of some central nervous system effects of Cotyledon Orbiculata
(University of the Western Cape, 2005) Kabatende, Joseph; Amabeoku, George J.; Green, Ivan R.; School of Pharmacy; Faculty of Science
The use of traditional medicine through the use of medicinal plants in Africa and especially in South Africa has long been considered an important characteristic of people's daily lives and socio-cultural heritage. Cotyledon Orbiculata is among the medicinal plants that are used by South African traditional practitioners for the treatment of epilepsy and painful conditions such as corns, warts, toothache, earache, boils and various other ailments. However, the claim of therapeutic successes of medicinal plants by traditional medicine practitioners are hardly subjected to scientific scrutiny. This study therefore, investigated the anti-epileptic property of Cotyledon Orbiculata by studying the effects of the methanol extract of the plant against chemically induced seizures by pentylenetetrazole, picrotoxin, bicuculline and N-methyl-DL-aspartic acid in mice. The study also investigated the analgestic effects of Cotyledon Orbiculata by studying the effect of the plant extract on pain induced by acetic acid and hot plate thermal stimulation.
Preliminary investigation of the natural contamination of agricultural crops with selected mycotoxins in northern rural South Africa (Limpopo and Mpumalanga Provinces)
(University of Western Cape, 2013) Mngqawa, Pamella; Green, Ivan R.; Shephard, Gordon; Katerere, David
Subsistence farmers may contribute significantly to food production, food security, and employment in South Africa. However poor storage practices and contamination with mycotoxins, particularly fumonisins and aflatoxins impacts adversely on production, food safety and food security. Mycotoxins are toxic natural food-borne compounds which frequently contaminate agricultural produce worldwide. They are hazardous to humans and animals and result in significant production losses for farmers. This study focused on former Bantustans in Northern South Africa, namely Vhembe District Municipality (Limpopo) and Gert Sibande District Municipality (Mpumalanga). The aim was to assess mycological and mycotoxin contamination of crops grown by subsistence farmers. A semi-structured questionnaire was administered to randomly thirty-nine households. Data on demographics, storage practices and production during period of 2011 and 2012 cropping seasons were collected. One hundred and fifteen (115) crop samples (maize, beans and peanuts) were collected for analysis. Standard mycological methods and validated mycotoxin analysis methods (HPLC and LC- MS/MS) were used. It was found that maize was the staple food in both provinces, with a significant difference (p = 0.0184) in its production between the two districts; Vhembe produced 0.6 tonnes compared to 2.4 tonnes in Gert Sibande. The majority of the farmers for storage used traditional open wooden cribs (15/20) and steel tanks (5/20) while VDM farmers used sealed store houses 5/19 and 15/19 used polystyrene sacks. Aflatoxin occurrence was low with <1% of GSDM samples contaminated compared to 11% of VDM samples. No significant difference (p > 0.05) was observed in the aflatoxin contamination in VDM samples between the year 2011 and 2012. Samples from VDM households had higher Aspergillus fungal infection (maximum incidence 69%) compared to GSDM (27%) over both seasons. The most frequently isolated Fusarium species in VDM samples was F. verticillioides (92%; 93%), and F. subglutinans (97%; 80%) in GSDM samples over seasons 2011 and 2012, respectively. Highest levels of fumonisins (FB1+ FB2) ranged between 1010 μg/kg and 12168 μg/kg with less than 30% extremely contaminated above the regulated limit in 91% of samples from Limpopo over both seasons (2011 and 2012). Fumonisin levels between the two seasons in VDM showed no significant difference (p>0.05). Only three (less than 5%) from 68% GSDM contaminated maize samples were above the FB1 and FB2 limit. In 2011, there were two highly contaminated maize samples (1762 μg/kg and 4598 μg/kg) with the other samples less than 600 μg/kg, whereas in season two (2012) all samples were below 200 μg/kg, except one highly contaminated sample (26115 μg/kg). None of the beans and peanuts from Mpumalanga was contaminated with mycotoxins above the recommended limit, but from Limpopo 1/5 peanuts was found contaminated with aflatoxin G1 (41 μg/kg). Natural occurrence and contamination of both fumonisin and aflatoxin in stored home-grown maize from VDM was significantly (p < 0.0001) higher than GSDM over both seasons. In general, Limpopo farmers’ experience lower harvests and greater mycotoxin contamination of agricultural produce. This may be attributed in part to poor storage practices and environmental and climatic conditions in that agro-ecological zone.
Role of the methoxy group in product formation via TiCl4 promoted 4-phenyldioxolane isomerizations
(ARKAT USA INC, 2010) Green, Ivan R.; October, Natasha
The product distribution obtained from the TiCl4 initiated intramolecular isomerizations of 4- methoxyphenyl- and trimethoxyphenyldioxolanes at -78 oC, -30 oC and 0 oC provided insights into the important regiochemical role played by these groups in such Mukaiyama- type rearrangements through their resonance effects on the aryl ring of the dioxolanes.Our interest in naphthopyranquinones as potential antimicrobial and antibiotic agents has extended over two decades1-6 as a result of their well documented importance.7,8 Additionally, the synthesis of benzopyrans as model systems has received attention by ourselves6,9-13 and others.14- 16 Of particular interest to us was our earlier discovery of a TiCl4 - induced intramolecular isomerization in which phenyl- and naphthyldioxolanes were stereoselectively transformed into their corresponding benzo- and naphthopyrans.17
Synthesis and characterization of pt-sn/c cathode catalysts via polyol reduction method for use in direct methanol fuel cell
(2013) Martin, Lynwill Garth; Green, Ivan R.; Pollet, Bruno G.
Direct methanol fuel cells (DMFCs) are attractive power sources as they offer high conversion efficiencies with low or no pollution. One of the major advantages DMFCs has over PEMFCs is that methanol is a liquid and can be easily stored where in the case for PEMFCs storing hydrogen requires high pressures and low temperatures. However, several challenging factors especially the sluggish oxygen reduction reaction (ORR) and the high cost of Pt catalysts, prolong their commercialization. With the aim to search for more active, less expensive more active ORR catalysts and methanol tolerant catalysts than pure Pt, this dissertation focuses on the development of low loading Pt electrocatalyst and the understanding of their physical and electrochemical properties. Pt-Sn/C electrocatalsyts have been synthesized by a modified polyol reduction method. The effect of temperature, pH, water, sonication and addition of carbon form were studied before a standard polyol method was established. From XRD patterns, the Pt-Sn/C peaks shifted slightly to lower 2Ө angles when compared with commercial Pt/C catalyst, suggesting that Sn is alloying with Pt. Based on HRTEM data, the Pt-Sn/C nanoparticles showed small particle sizes well-dispersed onto the carbon support with a narrow particle distribution. The particle sizes of the different as-prepared catalysts were found to be between 2-5 nm. The Pt-Sn/C HA Slurry pH3 catalysts was found to be the best asprepared catalyst and was subjected to heat-treatment in a reducing atmosphere at 250-600 °C which led to agglomeration yielding nanoparticles of between 5-10 nm. The Methanol Oxidation Reaction (MOR) on the as-prepared Pt-Sn/C HA Slurry pH3 catalyst appeared at lower currents (+7.11 mA at 860 mV vs. NHE) compared to the commercial Pt/C (+8.25 mA at +860 mV vs. NHE) suggesting that the Pt-Sn/C catalyst has „methanol tolerance capabilities‟. Pt-Sn/C HA Slurry pH3 and Pt-Sn/C 250 °C catalysts showed better activity towards the ORR than commercial Pt/C with specific and mass activities higher than Pt/C at +0.85 V vs NHE. The Tafel slopes of Pt-Sn/C HA Slurry pH3 catalyst was -62 and -122 mV dec-1 for the low and high current regions respectively and suggests that the ORR mechanism is similar to that of commercial Pt/C indicating that the ORR kinetics was not negatively influenced by the addition of tin. It was found that the electrochemical oxidation reduction reaction follows first order kinetics of a multi-electronic (n=4ē) charge transfer process producing water. All the Pt-Sn/C catalysts showed resistance towards MOR and it was found for the heat-treated catalysts that an increase in temperature resulted in an increase in methanol tolerance. The synthesized Pt-Sn/C HA Slurry pH3 catalysts were also tested in a fuel cell environment. Electrodes were prepared by either spraying on Toray carbon paper with the Asymtek machine or by VI spraying directly on the membrane with a hand spray gun the catalysts coated membrane (CCM) technique. Polarization curves obtained in DMFC with CCM showed superior performance than electrode prepared by spraying on the carbon paper with the machine. In our study, the Pt-Sn/C catalyst appears to be a promising methanol tolerant catalyst with activity towards the ORR in the DMFC.
The synthesis and evaluation of potential anti-Mycobacterium tuberculosis and apoptotic agents
(University of the Western Cape, 2007) Sagar, Sunil.; Green, Ivan R.; Ameer, F.; Dept. of Chemistry; Faculty of Science
Tuberculosis (TB) and Cancer are among the most devastating and therapeutically challenging diseases that need to be addressed in South Africa today. The development of muti-drug resistance in TB causing bacteria, Mycobacterium tuberculosis and cancerous cells has prompted the search for effective novel compounds. The present study focused on the synthesis and the evaluation of different analogues of diospyrin, a proven anti-TB and anti-cancer agent.
The synthesis of analogues of the Anti-TB (agent: Diospyrin)
(University of the Western Cape, 2005) Sitoza, Mluleki; Green, Ivan R.
Diospyrin, a bisnaphthyl quinone molecule with proven anti-TB activity can be retrosynthetically formulated into two halves. In this work, the analogue chosen to be synthesized was similarly retrosynthesized into two halves. The one half, 2-bromo-5- methoxy-1 ,4-naphthoquinone was synthesized successfully starting from 1,5- diacetoxynaphthalene which was oxidized and brominated with N-bromosuccimide to the corresponding 5-acetoxy-2-bromo-1,4-naphthoquin one. Hydrolysis of the acetoxy group was effected with methanolic potassium hydroxide followed by methylation of the phenolic group by methyl iodide and silver (II) oxide. The second half of the analogue, 7-bromo-1,4,6-trimethoxynaphthalene was attempted to be synthesized in the following way. Condensation between benzoquinone and Danishefsky's diene afforded an adduct which after much investigation was converted into 1,4,6-triacetoxynaphthalene. Through the process of transformations viz., oxidation, hydrolysis and phenol protection, the triacetoxynaphthalene was converted into 6- hydroxy-1,4-dimethoxynaphthalene. Attempts to brominate both this latter phenol as well as the original Diels-Alder adduct at C-7 proved to be problematic but gave some interesting results. Finally, by converting the 6-hydroxy-1,4-dimethoxyna phthalene into the corresponding carbamate, it could be transformed into the C-7 boronic acid albeit in low yield. Intwo reference Suzuki coupling experiments, the boronic acid derived from the carbamate of phenol was condensed with 2-bromo-1,4-dimethoxybenzen e and 6- methoxynaphthyl-2-boronic acid was coupled with 2-bromo-5-methoxy- 1,4- naphthoquinone. Finally, Suzuki coupling between 2-bromo-5-methoxy-1,4-naphthoquino ne and C-7 boronic acid of 6-(N,N-diethylcarbamyloxy) -1,4-dimethoxynaphthalene proved to be problematic with a very low yield of biaryl product being detected.
The Synthesis of Biaxial Naphthoquinones and an Initial Investigation regarding their Potential as anti- Mycobacterium tuberculosis and Apoptotic Agents
(University of the Western Cape, 2009) Swigelaar, Wendell Peter; Green, Ivan R.
Tuberculosis and cancer are amongst the most devastating diseases affecting the world today, especially Africa and other less developed countries. Both diseases have the ability to develop resistance against drugs being used as treatment regimes and therefore the search for effective novel drugs remains an ongoing challenge. Diospyrin and its monomer 7-methyljuglone, both naturally occurring quinones, and their synthetic derivatives have been shown to exhibit significant antimycobacterial and anti-tumour activity. The present study focuses on the synthesis of new compounds of similar structures to that of the lead compounds diospyrin and 7-methyljuglone, and their evaluation as potential antimycobacterial and anti-cancer agents via apoptosis. Three methoxynaphthoquinones were synthesized and coupled to several commercially available boronic acids using the Suzuki methodology. Eight compounds were evaluated against a drug susceptible strain, H37Rv of Mycobacterium tuberculosis, using the BACTEC method. Results indicate that the presence of an hydroxyl group peri to the quinone carbonyl moiety is crucial for these quinonoidal compounds to be effective as anti-TB agents, since their methyl ether analogues had little effect on the growth rate of the bacteria. Substituents, capable of donating electrons through a resonance electron effect to the carbonyl group, peri to the methoxy group, also enhance activity of these molecules. Several of the synthesized compounds were screened for their ability to induce apoptosis in five human cancer cell lines viz.,Hl57,Hek239T, HeLa, Jurkat, MCF-7 and two non cancerous cell lines viz., CHO (animal) and KMST-6 (human). The methods employed to assess the pro-apoptotic potential of the compounds were APOPercentagerM and DNA fragmentation. The APOPercentagerM assay showed that the activity of the compounds is concentration dependent and also revealed that in addition to the redox ability of the quinone carbonyl groups, the peri methoxy or hydroxyl group also plays a role in the apoptotic activity. An independent evaluation, the DNA fragmentation test, confirmed both a degree of selectivity viz, being not too active against non-cancerous cell lines on the one hand whereas on the other having a high apoptotic potential against all five of the cancer cell lines evaluated.
The synthesis of prodrugs and novel analogues of Beta-sympathomimetic bronchodilators
(University of the Western Cape, 1998) Adams, Mortimer Hilary; Ameer, Farouk; Green, Ivan R.
Prodrugs are reversible derivatives of active drugs destined to undergo chemical or enzymatic transformation to the active drug after administration in order that the active drug may subsequently elicit the desired pharmacological response . In synthesizing a prodrug, the physico chemical properties of a drug are altered by suitable functionalisation of an appropriate appendage of the drug molecule such that some barrier or problem may be circumvented or obviated in totality. Prodrugs of bronchodilators have been prod used with the aim of reducing enzymatic degradation, improving their bio-availability and, displaying a marked separation between their desirable bronchodilator and undesirable cardiovascular activities. Chlorphentermine (II), a lung accurnulating arnine, was used as a carrier molecule in novel prodrugs which potentially possess these attributes. Model prodrugs viz. CPE (20) and CPETA (t4), consisting of chlorpltentennine (ll) connected through a propionic ester link to ethanol and etafedrine (13), respectively, were synthesized by reacting the alcohols with acryloyl chloride and the resultant acrylates subsequently reacted with chlorphentennine (II). CPA (21), the prodmg hydrolysis product of CPE (20), was also synthesized. Closely related analoEres of CPETA (t4) narnely PETA (15) and CPAP' (16) were then synthesized. PETA (15) was synthesized by the condensation of methylamino- I -phenylpropane (phentenrtine) and etaf-edrine ( I 3).

Browsing by Author "Green, Ivan R."

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