Spectroelectrochemical determination of the antioxidant properties of carpobrotus mellei and carpobrotus quadrifidus natural products

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dc.contributor.advisorMabusela, W. T.
dc.contributor.authorMaoela, Manki Sarah
dc.date.accessioned2021-09-07T09:23:34Z
dc.date.accessioned2024-05-13T12:40:34Z
dc.date.available2021-09-07T09:23:34Z
dc.date.available2024-05-13T12:40:34Z
dc.date.issued2009
dc.descriptionPhilosophiae Doctor - PhDen_US
dc.description.abstractSouth African Carpobrotus species have been found to contain hydrolysable tannins, various tlavonoids e.g. rutin and hyperoside, phytosterols and aromatic acids which have a diverse range of pharmacological properties including antimicrobial and, antioxidant activities. The main aim of the thesis was to determine the natural products in C. mellei and C. quadrifidus using chromatographic techniques and electrochemical analysis. The antioxidant activity of both Carpobrotus species was determined by using a superoxide dismutase (SOD) biosensor. ESI-LC-MS was used to separate and determine tlavonoids in C. mellei and C. quadrifidus. 8 tlavonoid compounds: catechin, epicatechin, epicatechin-epicatechin, coumarylquinic acid, isorhamnetin, quercetin-hexose (hyperoside), rutin and myricetin-deoxyhexose were identified. Cyclic and square wave voltammetry were used to detect tlavonoids from C. mellei and C. quadrifidus. Catechin was detected in the ethyl acetate extract of C. mellei and C. quadrifidus. The oxidation potential of the plant extracts were observed at +150.6 mV to +1072.6 mV. The oxidation mechanism proceeds in sequential steps, related to the catechol moiety, -OH groups in C ring and the resorcinol group. The oxidation process of the catechol moiety involves a two electron - two proton reversible reaction and forms o-quinone. This occurs first at low potential and is a reversible reaction. The hydroxyl group in the C ring and resorcinol group oxidise there after and undergo an irreversible reaction. UV-vis and FTIR spectroscopy were used to confirm the presence of catechin in the ethyl acetate extract of both plants. UV -visible spectroelectrochemistry confirmed the oxidation process of catechin at constant potential. Since C. mellei and C. quadrifidus were confirmed to contain flavonoids by ESI-LC-MS and electrochemical analysis, the antioxidant activity was further investigated using a SOD biosensor. The superoxide dismutase (SOD) enzyme was immobilised with 1% Nafion on a platinum electrode. Detection limit and sensitivity of the SOD biosensor were found to be 0.03918 umol L-' and 1.44 !lA (umol i.'):', respectively. The results showed that C. mellei and C. quadrifidus have antioxidant activity, with relative antioxidant capacity (RAC) of 24% and 42%, respectively.en_US
dc.identifier.urihttps://hdl.handle.net/10566/14702
dc.language.isoenen_US
dc.publisherUniversity of the Western Capeen_US
dc.rights.holderUniversity of the Western Capeen_US
dc.subjectAntioxidantsen_US
dc.subjectCarpobrotus speciesen_US
dc.subjectCyclic Voltammetryen_US
dc.subjectElectrochemical analysisen_US
dc.subjectESI-LC-MSen_US
dc.subjectFlavonoidsen_US
dc.subjectSpectroelectrochemical analysisen_US
dc.subjectSquare Wave Voltammetryen_US
dc.subjectSuperoxide Disrnutase (SOD) Biosensoren_US
dc.titleSpectroelectrochemical determination of the antioxidant properties of carpobrotus mellei and carpobrotus quadrifidus natural productsen_US

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Philosophiae Doctor - PhD (Chemistry)