Phytochemical analysis and biological activity studies of an Eastern Cape medicinal plant, Strychnos Henningsii
- Authors: Mngoma, Mondeli
- Date: 2018
- Subjects: Medicinal plants -- South Africa -- Eastern Cape , Traditional medicine -- South Africa -- Eastern Cape Plants -- South Africa -- Eastern Cape -- Analysis
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/22758 , vital:30074
- Description: This project sees the chemical investigation of an Eastern Cape medicinal plant, Strychnos henningsii. The aim of this project was to investigate the phytoconstituents and activity of organic extracts of S. henningsii as well as isolation and characterization of single compounds. S. henningsii is one of the most widely used tree bark in the Eastern Cape in treating a variety of ailments. Evaluation of the traditional herbal use of the S. henningsii bark was warranted. Both the ethyl acetate and methanol extract proved to possess non-toxic properties and showed cell growth potential at low concentrations. The anti-inflammatory response of both extracts showed appreciable results, and they did not promote inflammatory due to the alkaloidal presence. Although the extracts both showed the presence of phenols, the anti-oxidant capacity by DPPH, FRAP, and ORAC assays was considerately lower than expected. The ethyl acetate extract presented a compound thought to be a terpenoid (4.1). Three compounds were isolated from the methanol extract; two alkaloidal compounds and one acrylate. The alkaloids were isolated from the methanol extract, stryvomicine (4.2) and an isovomicine derivative (4.3). Their structures were deduced from NMR (1D and 2D experiments) and HRMS spectra. This acrylate was found to be 3-(4-methylphenyl)acrylic acid via single-crystal XRD, and this is the first report of it being isolated from the Strychnos genus. Profiling of S. henningsii was performed via Liquid Chromatography–Mass Spectroscopy. Other spectroscopic techniques utilised in the interpretation of isolated compounds included Nuclear Magnetic Resonance, Infrared, single-crystal X-Ray Diffraction and High Resolution Mass spectroscopy.
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- Date Issued: 2018
Hydrogen economy : MEA manufacturing for PEM electrolysers
- Authors: Gojela, Ntombekaya
- Date: 2011
- Subjects: Water -- Electrolysis , Hydrogen
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10380 , http://hdl.handle.net/10948/1483 , Water -- Electrolysis , Hydrogen
- Description: The electrolysis of water was evaluated as a potentially efficient, as a low cost means of hydrogen production. The theoretical energy, voltage, current, and energy efficiencies of water electrolysis were considered by using various catalyst materials used in the fabrication of membrane electrode assemblies used in low temperature water electrolysis systems. Traditionally, iridium based catalysts have shown to be the most suitable material for its use on electrocatalysis of water to form hydrogen. This study showed that a combination of various elements as a binary and or ternary mixture in the base catalyst that was applied to the anode and cathode by using the Adam’s method had shown to give comparatively good results to that of using iridium oxide on its own. These catalysts were characterized by cyclic voltammetry, at different temperatures (30oC-80oC) with a range of catalyst loading of 0.2-0.5 mg.cm-2 noble metals. The study showed that the Ir40Co40 mixture as an anode catalyst was found to show highest hydrogen efficiency of 73 percent with a relatively low over potential of 0.925V at higher temperature of 80oC. The mixture also showed to give the best electrocatalytic activity with a low Tafel slope of 30.1mV.dec-1. Whereas the Ir50Pt50 showed a comparatively lower hydrogen efficiency of 65 percent with a lower over potential of 0.6V at 50oC. Ternary mixed oxide of Ir20Ru40Co40 showed an even lower over potential of 0.5- 0.6V over a large range of temperatures with a low hydrogen efficiency of 44 percent but gave good electrocatalytic activity in terms of the Tafel slope analysis. On the other hand, mixtures with relatively cheaper material such as Nickel in binary mixture systems such as Pt50Ni50 as cathode catalyst was found to show promising performance of a relatively low over potential that was less than 1.4 V with a low hydrogen efficiency of 62.1 percent Ternary cathode catalyst materials such as Pt33Ni33Co33 exhibited good performance with higher hydrogen efficiency of 65.2 percent at lower over potential of 1.2 V and a higher Tafel slope of 133.9 mV.dec-1 at 80 0C.
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- Date Issued: 2011