Department of Chemistry
http://hdl.handle.net/11394/33
2024-03-28T12:48:23ZPolyphenolic, tannin and chemical compositional changes in leaves of sub-tropical grasses and fynbos shrubs at elevated atmospheric CO2 concentrations
http://hdl.handle.net/11394/10662
Polyphenolic, tannin and chemical compositional changes in leaves of sub-tropical grasses and fynbos shrubs at elevated atmospheric CO2 concentrations
Hattas, Dawood
The effects of elevated atmospheric CO2 concentrations on plant polyphenolic concentration, tannin concentration and chemical composition were investigated in leaves of sub-tropical grass species and fynbos shrubs. The working hypothesis was based on predictions that carbon based secondary compounds (polyphenolics and tannins) would increase when carbon in excess of growth requirements accumulate in plant leaves under nutrient imbalanced conditions. This imbalance would arise due to an increase in atmospheric CO2 level. Furthermore, empirical evidence suggests that nutrient paucity would enhance carbon-based secondary compound production.
This hypothesis was tested in two different systems involving plants with differential photosynthetic mechanisms and growth strategies. Polyphenolics, tannins and chemical composition (N, P, C and TNC) were quantified in grass species from a natural, C4 dominated, sub-tropical grassland in KwaZulu/Natal. Three plots were subjected to different freeĀair CO2 enrichment treatments, i.e. elevated (550-800 ppm), intermediate no more than 400 ppm) and ambient CO2 (currently at 365 ppm). One of the seven grass species, Alloteropsis semialata, had C3 photosynthetic mechanism. Polyphenolics, tannins and chemical composition (N, P, C and TNC) were quantified in three fynbos species grown in open-top chambers under controlled greenhouse conditions. The plants were grown under ambient (360 ppm) and ambient+ 350 ppm CO2 in typical low nutrient acid sands of the fynbos biome.
This study shows that despite some of the grasses having the capacity to produce tannin-like substances, polyphenolics and tannins do not increase in the grass species studied. Polyphenolic and tannin concentrations were increased only in Leucadendron laureolum amongst the fynbos species. Its sister species Leucadendron xanthoconus did not show any change in phenolic or tannin concentrations.
Chemical composition in grasses were largely unaffected by elevated CO2, however, some species-specific responses were observed. The C3 A. semialata showed a decrease in P concentration and a consequent increase in C:P ratio at elevated CO2. Only L. laureolum showed a response in chemical composition at elevated CO2, whereas its sister species did not show any response except a decrease in N concentration. In conclusion, fast growing grass species invest extra carbon into growth rather than polyphenolics and tannins and show small species-specific chemical changes at elevated atmospheric CO2 concentrations. Increased investment into phenolics and tannins as well as changes in chemical composition in fynbos species were species-specific even within plants from the same genus. Thus generalizations about plant responses to elevated CO2 based on theoretical principles cannot be directly applied. This is especially true in complex natural environments where ecophysiological processes may dictate phytochemical responses.
>Magister Scientiae - MSc
2002-01-01T00:00:00ZElectrochemical evaluation of chemically Modified microelectrodes
http://hdl.handle.net/11394/10630
Electrochemical evaluation of chemically Modified microelectrodes
Moeletsi, JM
Aniline and N-alkylated substituted anilines have been polymerized by chemical and electrochemical methods. The chemically synthesized polymers indicated that N-alkylation improves solubility remarkably in common organic solvents. The compounds were characterized by FTIR, 1H NMR, TGA and also studied by cyclic voltammetry on glassy carbon macroelectrodes for comparison with electrochemical synthesized polymers.
Magister Artium - MA
2001-01-01T00:00:00ZInvestigation of ternary catalysts as anode catalysts for direct methanol fuel cell
http://hdl.handle.net/11394/10488
Investigation of ternary catalysts as anode catalysts for direct methanol fuel cell
Adebare, Nurudeen Adewunmi
This chapter reports on various catalyst synthesis methods (impregnation, polyol, modified polyol and microwave-assisted modified polyol methods) to determine which method would result in the most electrochemically active platinumāruthenium (PtRu) electrocatalyst supported on multi-walled carbon nanotubes (MWCNTs) for methanol oxidation reaction in an acidic medium. Different techniques were used to characterise the synthesised catalysts, including the high-resolution transmission electron microscope used for morphology and
calculating particle sizes, and X-ray diffraction for determining crystalline sizes while Energy dispersive analysis Spectroscopy, EDS was used to determine elemental compositions. The electroactive catalyst surface area, ECSA of the electrocatalysts was determined using cyclic voltammetry (CV), while the electroactivity, electron kinetics and stability of the electrocatalysts towards methanol oxidation were evaluated using CV, electrochemical impedance spectroscopy and chronoamperometry, respectively. The microwave-assisted modified polyol method produced the PtRu/MWCNT electrocatalyst with the most enhanced electrocatalytic activity compared to other PtRu/MWCNT catalysts produced by the impregnation, polyol and modified polyol methods.
>Magister Scientiae - MSc
2023-01-01T00:00:00ZGreen synthesis of silver nanoparticles using honey from the meliponinae stingless bee species and antibacterial studies.
http://hdl.handle.net/11394/10407
Green synthesis of silver nanoparticles using honey from the meliponinae stingless bee species and antibacterial studies.
Leteba, Semphete
Green synthesis of silver nanoparticles (AgNPs) is an environmentally friendly approach for preparing nanoparticles using biological sources as the reducing agent. Apart from using plant extracts, honey, that is used in this study affords to act as a reducing and capping agent. Silver nanoparticles have been reported to show good antibacterial and anti-inflammatory properties and can be potentially applied as antibacterial agents. Additionally, to their attractive characteristics, they are biocompatible which makes them safe for therapeutic applications. Similarly, stingless bees honey has been reported to have anti-inflammatory properties and have been historically used to heal wounds.
>Magister Scientiae - MSc
2023-01-01T00:00:00Z