Browsing by Author "Naicker, Thirusha."

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Activation of n-hexane using vanadium-exchanged zeolites.
(2010) Naicker, Thirusha.; Friedrich, Holger Bernhard.
The influence of the form of the ZSM-5 zeolite, vanadium content and the elimination of the exterior surface acidity on the activity and selectivity of n-hexane oxidation was studied using a fixed bed reactor. Blank reactor studies (carborundum packed reactor) showed no conversion below 450°C with the highest conversion (8%) at 500°C. The dominant products were found to be carbon oxides (Sel./% = 90) with minor selectivities to the hexene isomers (7%) and the remainder being cracked products, THF and benzene. H-ZSM-5 with different SiO2/Al2O3 ratios (100 and 320) and Na-ZSM-5 (SiO2/Al2O3 ratio of 100) were tested under non-oxidative and oxidative conditions. Under oxidative conditions as the ratio of the SiO2/Al2O3 increased, the aluminium content decreased and so too did the cracking ability of the zeolite (i.e. yield of cracked products dropped from 36% to 8%). However, the use of the Na- form of ZSM-5 completely eliminated acid cracking. Under oxidative conditions H-ZSM-5 (100) was found to be more active and resulted in higher formation of cyclic and aromatic compounds. With increasing time on-stream and higher temperatures the catalyst was found to deactivate. Evidence of this was seen by a decrease in surface area and pore volumes of the spent catalyst. The Na-ZSM-5 (100) showed lower activity, but deactivation was shown to be lower. These findings led to the investigation of vanadium ion-exchanged Na-ZSM-5 catalyst for n-hexane activation. Catalysts with different vanadium loadings were prepared using the solid state ion-exchange method. Catalysts were characterised using various methods. These techniques showed that vanadium was successful loaded onto the catalyst and that the highest vanadium loading that could be achieved was 2.5%. The lower loadings were not found to alter the catalyst structure while the highest loading of 2.5% was found to show some pore blockage and to possibly alter the structural environment of the zeolite. Time on stream experiments were conducted and temperature (350, 400 and 450°C), contact time (0.5, 0.8, 1.1 and 1.5 s) and fuel-air ratios (0.7, 1.3 and 2) were varied. The optimum conditions (Conv./% = 39) for terminally activated products were found using the Na-V-ZSM-5 (0.9%) at a temperature of 400°C, a contact time of 1.1 s and fuel-air ratio of 1.3. With the lower fuel-air ratio of 0.7 (oxygen rich conditions), hexanal formation was favoured. The Na-V-ZSM-5 catalyst could be regenerated with initial activity and selectivity being regained. Silanisation was found to be possible, however, the extent and degree of silanisation was difficult to control. Pore blockage was possibly responsible for the lower activity and selectivity obtained using the silanised Na-V-ZSM-5.
The role of immunoglobulin isotypes (IgG1-IgG4, IgA AND IgM) in HIV preeclamptics on highly active anti-retroviral therapy, in South Africa.
(2018) Moodley, Mikaila.; Naicker, Thirusha.
Background: The epicentre of a successful pregnancy lies within the placenta and is nurtured by suppressed immune responses. However, the fragile balance between maternal inflammatory responses and the regulation of maternal immunoglobulins is distorted by HIV and Preeclampsia (PE). Preeclampsia and co-morbid diseases such as HIV infections are major contributors to maternal morbidity and mortality, worldwide. Furthermore, the effects of Highly Active Antiretroviral therapy (HAART) on the reconstitution of immunity in HIV preeclamptics remain obscure. Therefore, the current study aims to investigate the role of immunoglobulins in HIV infected preeclamptics and elucidate the effects of HAART on immunoglobulin levels in HIV infected PE. Method: Ethical clearance was granted by the Biomedical Research Ethics Committee (BREC). Serum samples of 38 normotensive and 38 preeclamptic pregnancies were collected at a regional hospital and further categorized based on HIV status. The serum samples were then subjected to the analysis of immunoglobulin (IgG1-IgG4, IgA and IgM) concentration (ng/dl). The Bio-Plex immunoassay technique of analysis was used to investigate the concentration of immunoglobulin isotypes in the sample population. Immunoglobulin concentrations were considered significant when p < 0.05. Results: Immunoglobulin concentration was evaluated in pregnancy type irrespective of HIV status. A non-significant down-regulated trend of IgG1, IgG3 and IgG4 was observed, whilst IgG2 and IgM showed a non-significant up-regulation. On the contrary, IgA levels presented a significant increase in preeclamptics irrespective of HIV status. However, in HIV infected pregnancies irrespective of pregnancy type IgG1 presented a non-significant up-regulated trend, whilst IgG3 and IgG4 showed non-significant down-regulatory trends. Nonetheless, IgG2, IgA and IgM demonstrated a significant down-regulation in HIV infected pregnancies, irrespective of pregnancy type. Furthermore, IgG1, IgG3, IgG4 and IgM showed a non-significant difference when analysed according to pregnancy type and HIV status. However, IgG2 and IgA presented a significant up-regulation in HIV negative PE. Conclusion: This study highlights the importance of the maternal-fetal transfer of immunoglobulins (IgG subclass) in pregnancy. We report a significant up-regulation of IgG2, indicating its role in activating the classical complement pathway thereby, exacerbating the inflammatory response in PE. The up-regulation of IgA is an ingenerate anti-inflammatory response, which inhibits the exacerbated inflammatory cascade via classical complement activation in PE. In HIV infection the down-regulation of IgG2, IgA and IgM maybe due to HAART. In addition, IgA showed an up-regulation in HIV associated PE, suggesting that the reconstitution of HAART is insufficient in neutralizing the exaggerated inflammatory response in PE. To further understand the role of IgG2 and IgA in HIV associated PE, larger studies are warranted.