No description available.

No description available.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The work presented in this thesis throws light on the supramolecular approach in exploration of bi-porphyrin nanorods system wherein self-assembly plays an important role. Porphyrin based nanorods were synthesized via self-assembly of meso-tetrakis (4-phenylsulfonicacid) porphyrin dihydrochloride and Sn (IV) tetrakis (4-pyridyl) porphyrin. Understanding the sizes and growth mechanism of the porphyrin nanorods by self-assembly and molecular recognition is essential for their successful implementation in nanodevices. Spectroscopic and microscopic studies were carried out to investigate the effect that time, concentration and solvents have on the fabrication of the porphyrin nanorods by ionic self- assembly. This study demonstrated that aggregates of the di- acid form of meso-tetrakis (4-phenylsulfonic acid) porphyrin dihydrochloride and Sn (IV) tetrakis (4-pyridyl) porphyrin resulted in porphyrin nanorods with diameters between 20 nm and 60 nm, and μm in lengths. Enhanced optical properties illustrated the potential for slightly modifying the method of synthesis to influence the physical and optical properties of porphyrin nanorods. The porphyrin nanorods reflectance data demonstrated that these structures are good absorbers of light and therefore could potentially be used to harvest light. The nonlinear optical (NLO) properties of the porphyrin nanorods were investigated for the first time in this study by second and third harmonic generation techniques. Such study was influenced by the fact that porphyrins have great thermal stability and extended -conjugated macro cyclic ring which give them large nonlinear optical effects. The NLO results showed that the porphyrin nanorods may have many potential uses in photonic applications due to larger third order nonlinear susceptibility. Single molecule spectroscopy was also used to investigate the dynamics of intermolecular and intramolecular processes. Porphyrin nanorods were incorporated into polymer matrices to achieve an arrangement where they can be directly used as a device. The assembly of porphyrin nanorods on track-etched membranes was achieved through altering the surface charge of the respective membranes. Porphyrin nanorods-polymer composites were produced using latex technology and electrospinning techniques. The fibres were characterized with respect to morphology and optical properties. / AFRIKAANSE OPSOMMING: Die werk wat in hierdie tesis beskryf word werp lig op die supramolekulêre benadering in die ondersoek van bi-porfirien nano-silinders waarin self-versameling ‘n belangrike rol speel. Porifirien nano-silinders was voorberei via self-versameling van meso-tetrakis(4-feniel sulfoonsuur) porfirien dihidrochloried en Sn (IV) terakis (4-piridiel) porfirien. Dit is belangrik om die meganismes wat verband hou met die groei en grootte van die nano-silinder struktuur te ondersoek. Dit het ‘n invloed op die self-versameling asook die uiteindelike toepassing. Spectroskopiese en mikroskopiese studies was uitgevoer om die effek van tyd, konsentrasie en oplosmiddel op die selfversamelling te bestudeer. Die studie dui daarop dat bondels van die disuur vorm van meso-tetrakis(4-feniel sulfoonsuur) porfirien dihidrochloried en Sn (IV) terakis (4-piridiel) porfirien het gelei tot porfirien nano-silinders met lengtes tussen 20 nm en 60 nm asook in die mikro meter skaal. Verhoogde optiese eienskappe het die potensiaal om effense veranderinge in die metode om die nano-silinders voor te berei om sodoende ‘n groter invloed op die fisiese en optiese einskappe te hê. Die reflektansie data wys dat hierdie strukture goeie absorbsies van lig toon en daarom geskik sal wees om lig te stoor. Die nie-liniêre optisie (NLO) eienskappe van die profirien nano-silinders was vir die eerste keer ondersoek deur middel van tweed en derde hormoniese generasie tegnieke. Hierdie studie was beïnvloed deur die feit dat porfiriene goeie stabiliteit by hoë temperatuur en ‘n verlengde -gekonjugeerde makro-sikliese ring bevat wat dan groot nie-liniêre optiese effekte gee. Die NLO resultate wys dat die profirien nano-silinders groot potensiaal het in die gebruik van fotoniese toepassings as gevolg van derde orde nie-liniêre vatbaarheid. Enkel molekuul spektroskopie was ook gebruik om die dinamika van intermolekulêre en intramolekulêre prosesse te ondersoek. Porfirien nano-silinders was geïnkorporeer in polimeer matrikse om ‘n eweredige verspreiding te verkry en om direk as ‘n toestel te gebruik. Die versameling van porfirien nano-silinders op baan-ingeëtse membrane was bereik deur die verandering in oppervlak lading van die membrane. Porfirien nano-silinder / polimeer samestellings was verkry deur lateks tegnologie en elektrospin tegnieke. Die vesels was gekarakteriseer in terme van morfologie en optiese eienskappe.

For trace elements, such as copper (Cu) and zinc (Zn), the bioavailability of these elements, Cu and Zn, in biosolids is important because both are essential elements and both are potential contaminants when biosolids are land applied. A greenhouse study was conducted in factorial experiment based on a completely randomized design (CRD) with four replications on a soil treated with four rates of Cu (0, 50, 100, and 150 mg/kg) and four rates of Zn (0, 150, 300, and 450 mg/kg) on celery plants to investigate the distribution and mobility of these elements as well as growth and antioxidant changes of celery. The results of antioxidant changes were inconclusive due to irregular changes with Zn and Cu applications. However, generally the results show that Cu did not affect superoxide dismutase (SOD) or peroxidase (POD) activities in most of the treatments. On the other hand, Zn stimulated SOD and POD activities in most of the treatments. The photosynthesis rate decreased with the applications of Cu and Zn at the rates above 100 and 300 mg/kg and increased in low Cu concentration (50 mg/kg) compared to S (soil without biosolid).

No description available.

Although it has long been recognized that physiological acclimation of photosynthesis and respiration can occur in plants exposed to changing environmental conditions (e.g. light, temperature or stress), the extent of acclimation in different tissues (i.e. pre-existing and new foliage) however, has not received much attention until recently. Furthermore, few studies have investigated the extent of photosynthetic and respiratory acclimation under natural conditions, where air temperatures vary diurnally and seasonally. In this study, the effects of variations in temperature on respiratory CO2 loss and photosynthetic carbon assimilation were examined under both controlled and natural environments. The purpose of the investigations described in this thesis was to identify the effects acclimation would have on two key metabolic processes in plants exposed to temperature change, with emphasis also placed on the role of nutrition (nitrogen) and respiratory enzymatic characteristics on the potential for acclimation in two contrasting tree species, Pinus radiata and Populus deltoides. Controlled-environment studies (Chapter 2 and 3) established that rates of foliar respiration are sensitive to short-term changes in temperature (increasing exponentially with temperature) but in the longer-term (days to weeks), foliar respiration acclimates to temperature change. As a result, rates of dark respiration measured at any given temperature are higher in cold-acclimated and lower in warm-acclimated plants than would be predicted from an instantaneous response. Acclimation in new foliage (formed under the new temperature environment) was found to result in respiratory homeostasis (i.e. constant rates of foliar respiration following long-term changes in temperature, when respiration is measured at the prevailing growth temperature). Available evidence suggests that substantial adjustments in foliar respiration tend to be developmentally dependent. This may in part explain why respiratory homeostasis was only observed in new but not in pre-existing tissues. Step changes in temperature (cold and warm transfers) resulted in significant changes in photosynthetic capacity. However, in stark contrast to the findings of respiration, there was little evidence for photosynthetic acclimation to temperature change. The results obtained from field studies (Chapter 4) show that in the long-term over a full year, dark respiration rates in both tree species were insensitive to temperature but photosynthesis retained its sensitivity, increasing with increasing temperature. Respiration in both species showed a significant downregulation during spring and summer and increases in respiratory capacity were observed in autumn and winter. Thermal acclimation of respiration was associated with a change in the concentration of soluble sugars. Hence, acclimation of dark respiration under a naturally changing environment is characterized by changes in the temperature sensitivity and apparent capacity of the respiratory apparatus. The results from controlled and natural-environment studies were used to drive a leaflevel model (which accounted for dark respiratory acclimation) with the aim of forecasting the overall impact of responses of photosynthesis and respiration in the long term (Chapter 5). Modellers utilise the temperature responses of photosynthesis and respiration to parameterize carbon exchange models but often ignore acclimation and use only instantaneous responses to drive such models. The studies here have shown that this can result in erroneous estimates of carbon exchange as strong respiratory acclimation occurs over longer periods of temperature change. For example, it was found here that the failure to factor for dark respiratory acclimation resulted in the underestimation of carbon losses by foliar respiration during cooler months and an overestimation during warmer months - such discrepancies are likely to have an important impact on determinations of the carbon economy of forests and ecosystems. The overall results substantiate the conclusion that understanding the effect of variations in temperature on rates of carbon loss by plant respiration is a prerequisite for predicting estimates of atmospheric CO2 release in a changing global environment. It has been shown here that within a moderate range of temperatures, rate of carbon uptake by photosynthesis exceeds the rate of carbon loss by plant respiration in response to warming as a result of strong respiratory acclimation to temperature change. This has strong implications for models which fail to account for acclimation of respiration. At present, respiration is assumed to increase with increasing temperatures. This erroneous assumption supports conclusions linking warming to the reinforcement of the greenhouse effect.

Most plants produce leaves with stomata on either both surfaces (amphistomatous) or on the lower surface only (hypostomatous). The importance of stomata to plant survival suggests that these two stomatal distribution patterns may be adaptive, and this problem is explored. It is concluded that amphistomaty is an adaptation to produce a high conductance to CO₂ diffusion into the leaf. As such it is advantageous to plants with high photosynthetic capacity leaves in high light environments, experiencing rapidly fluctuating or continuously available soil water. Plants meeting these criteria are found to be almost exclusively amphistomatous; those not meeting the criteria are mostly hypostomatous. Also investigated is the adaptive significance of differences in stomatal conductances and conductance responses to environmental factors between the two surfaces of amphistomatous leaves. Although differences in stomatal conductance are found between the two surfaces in sunflower, differences in conductance response to light intensity and water vapor pressure difference across the stomatal pore were neglible. Water stress relieved one day prior to experiments caused upper stomatal conductance to be reduced more than lower, but responses to light and water vapor pressure difference remained essentially parallel for the two surfaces. For these differences in conductance to be adaptive differences in photosynthetic characteristics between the two surfaces. In addition, estimation of the resistance to diffusion of CO₂ across the mesophyll yields values low enough to preclude steep gradients in CO₂ partial pressure in the mesophyll. In the absence of CO₂ gradients within the leaf, differences in photosynthetic characteristics between the two surfaces cannot exist. It is concluded that differences in stomatal conductance between the two surfaces of amphistomatous leaves are not adaptations to differences in CO₂ uptake characteristics.

No description available.

No description available.

No description available.