Theses and dissertations (Applied Sciences)
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Item Hollow fibre liquid phase microextraction of pharmaceuticals in water and Eichhornia crassipes(2019) Mlunguza, Nomchenge Yamkelani; Madikizela, Lawrence Mzukisi; Chimuka, Luke; Mahlambi, Precious N.This work describes a simple and rapid method for the simultaneous isolation, enrichment, and quantitation of selected pharmaceuticals in aqueous environmental samples and Eichhornia crassipes. This was achieved by developing a hollow fiber liquid phase microextraction (HF-LPME) technique coupled with ultra-high-pressure liquid chromatography-high resolution mass spectrometry for the simultaneous extraction, pre- concentration and quantitation of four non-steroidal anti-inflammatory drugs (NSAIDs) and three antiretroviral drugs (ARVDs) from aqueous matrices and different segments of water hyacinth plant species. The target compounds for NSAIDs were naproxen (NAP), fenoprofen (FENO), diclofenac (DICLO) and ibuprofen (IBU) whereas the selected ARVDs included emtricitabine (FTC), tenofovir disoproxil (TD) and efavirenz (EFV). A multivariate approach by means of a half-fractional factorial design was used to optimize the HF-LPME technique focusing on six factors; donor phase (DP) pH, acceptor phase (AP) pH, extraction time, stirring rate, supported liquid membrane carrier composition (SLM carrier comp.) and salt content. Four of these factors (DP pH, AP pH, stirring rate and extraction time) were identified as vital for an enhanced enrichment of each of the selected NSAIDs and four of the previously mentioned vital factors including the SLM carrier composition were classified as significant for the selected ARVDs from aqueous samples into the hollow fiber. These essential factors were further paired according to their level of significance. The paired significant factors were then optimized using central composite designs (CCD) where empirical quadratic response models were used to visualize the response surface through contour plots, surface plots and optimization plots of the response outputs. The optimized factors for individual analytes belonging to each class were then altered to universal conditions for their simultaneous extraction from same sample solution. The acceptability of the universal conditions was defined using desirability studies. A composite desirability value of 0.7144 was obtained when the optimum factors of the three ARVDs were applied for their simultaneous extraction while a simultaneous extraction of NSAIDs had a desirability value of 0.7735. This implied that the set conditions were ideal for a combined extraction of the target compounds from the donor phase into the acceptor phase across a supported liquid membrane impregnated with a carrier molecule. For the simultaneous extraction of ARVDs, the universal optimum HF- LPME conditions were found to be DP pH of 4, AP HCl conc. of 200 mM (pH = 0.4) with SLM carrier comp. set at 4.5 (%w/w) and stirring at 1000 rpm. Under optimum conditions, the enrichment factors (EF) for ARVDs from aqueous phase were 78 (FTC), 111 (TD) and 24 (EFV). These conditions yielded recoveries in the range of 96 to 111%. The sensitivity of the analytical method through limits of quantification (LOQ) for the selected ARVDs in wastewater samples were 0.033 μg L-1 (FTC), 0.10 μg L-1 (TD) and 0.53 μg L-1 (EFV). The LOQ values were computed for surface water samples using the same target ARVDs were 0.169 μg L-1 (FTC), 0.018 μg L-1 (TD) and 0.113 μg L-1 (EFV). For NSAIDs, the overall conditions were DP pH of 10, AP pH of 3 at an extraction time of 60 min with stirring rate at 1000 rpm. The recoveries yielded under these optimum conditions for the target compounds ranged from 86 to 116%. The EF for the target NSAIDs from aqueous media were 49 (NAP), 126 (FENO), 93 (DICLO) and 156 (IBU). The LOQ values for each target NSAID in wastewater samples were 0.47 μg L-1 (NAP), 0.09 μg L-1 (FENO), 0.59 μg L-1 (DICLO) and 0.49 μg L-1 (IBU). The specific universal conditions were then used in the analysis of ARVDs in wastewater and surface water whereas for NSAIDs analysis, only wastewater samples were analysed. The surface water samples were obtained from North of Johannesburg in Hartbeespoort dam and the wastewater samples were collected from various wastewater treatment plants located in Durban, KwaZulu-Natal. The technique was also applied in the analysis of the target compounds in plant samples obtained from Hartbeespoort dam in North of Johannesburg, Umgeni river located in Springfield (Durban in KwaZulu-Natal) and Mbokodweni river located in south of Durban city, KwaZulu-Natal. The plant samples were first cut and separated into different segments (roots, stems and leaves) and the target analytes then extracted into 20 mL water using an optimized microwave assisted extraction technique (MAE). The HF-LPME technique initially optimized for water samples was then applied for pre-concentration of the target pharmaceuticals from the MAE water extract. Factors that were optimized for MAE technique were irradiation time and temperature for ARVDs whereas irradiation time and solvent volume were optimized for the extraction of NSAIDs. For extraction of both ARVDs and NSAIDs, the optimum irradiation time was 20 min while the irradiation temperature was set at 90 ̊C during the extraction of ARVDs and 100 ̊C for NSAIDs. Generally, the studied ARVDs were all detected in most samples with concentrations for FTC (0.11 – 3.10), TD (0.10 – 0.25) and EFV (1.09 up to 37.3) μg L-1 recorded in wastewater samples. EFV had the highest concentration of 37.3 μg L-1 in the wastewater effluent. The concentration of ARVDs in the roots of the water hyacinth ranged from 7.4 to 29.6 μg kg-1, 0.97 to 11.42 μg kg-1 in the stem and 0.98 to 9.98 μg kg-1 in the leaves of the aquatic plant. Roots of the water hyacinth plant had higher concentrations of the investigated ARVDs. Lastly, the NSAIDs were also detected in various wastewater samples with concentration for NAP (1.15 to 3.30) μg L-1, FENO (Item Development of a third-generation electrochemical enzyme-based biosensor for a scalable detection of oxygen in power generation cells(2019-12) Jiyane, Sphumelele Nomnontho; Bisetty, Krishna; Sabela, M. I.; Kanchi, S.Pencil graphite electrodes (PGEs) are another form of carbon electrodes with good mechanical strength and comparable electrical properties. Moreover. their low cost makes them an excellent alternative to more conventional electrodes. especially in disposable applications. In this study. the PGEs were constructed with a 2 mm diameter pencil graphite with hardness 4H. HB. and 4B. The electrodes were cleaned and modified with 1 mg/ml of graphene oxide (GO) to enhance the surface area of the electrodes. The PGE-GO was further reduced electrochemically using Na2S2O4 from -1.2 V to 0.8 V at 50 mV/s for 50 cyclic voltammetry scans in the presence of oxygen. using K3Fe(CN)6 / K4Fe(CN)6 as a redox couple. The performance of the PGE was evaluated with multi-walled carbon nanotubes and nanomaterials with various linking agents. A further evaluation was conducted with multi-copper oxidase (MCO) enzymes (Bilirubin oxidase (BOx) and Laccase oxidase) applied for the bio-catalytic reduction of oxygen. The outcome of this study showed that the modification with GO revealed redox peaks 3.6 times higher than the bare PGE. The immobilization of MCO was confirmed by cyclic voltammetry in the presence of a phosphate buffer. Furthermore. the amperometric measurements of O2 at a reducing potential of +0.34 V. showed linearity up to 0.36 mM and sensitivity of 520 μA/(mM.cm2) to O2. Furthermore. computational adsorption studies were performed for the layer-by-layer electrode modification steps. The adsorption simulations revealed a lowering of the energy favored between the designed electrode layers. suggesting a most favorable interaction for the GO/MWCNTs/PBSE/BOx layer. Overall the computational data correlated well with experimental work. Notably. the layer-by-layer adsorption of the GO/MWCNTs/PBSE/BOx showed excellent affinity 11.4 M−1 between PBSE and the enzyme interaction. The direct electron transfer (DET) of the enzymatic reaction integrated with nanotechnology. has led to a small. portable and renewable power generating device. Thus this study addresses the demand for implantable medical devices. in the absence of an external power source.Item Fabrication of a colorimetric paper-based microfluidic sensor for residual poly-dadmac detection in water treatment(2019) Magubane, Sibongile Elizabeth; Mdluli, Phumlani Selby; Mlambo, MbusoPoly– diallyldimethylammonium chloride (poly-DADMAC) is an established coagulant in the treatment of drinking water. Reports have indicated that poly-DADMAC can degrade into a suspected carcinogenic form which is N-nitrosodimethylamine (NDMA). Consequently, water treatment plant operators are required to know the residual concentration of polyelectrolytes at various stages in the treatment process and the eventual quality of the treated water. Historical research has proven that, over the years, a number of methods such as extraction-spectrophotometry, fluorometry and tannic acid have been developed and implemented for the analysis of polymers in drinking water. However, they produced poor linearity, sensitivity and precision, high detection limits or produced false positives due to matrix effects. The laboratory method that has proven to be simple, affordable and accurate is the colloidal titration method. However, this method cannot be used at the plant for quick and accurate monitoring of poly-DADMAC. In this study, the aim was to fabricate a Lovibond portable colorimetric comparator device based on gold nanoparticles for colorimetric quantification and detection of poly-DADMAC in raw and treated potable water. The colorimetric disk and comparator was fabricated from 14 nm gold nanoparticles with the concentration of poly-DADMAC varying from 1 to 10 mg L-1. The addition of higher concentrations of poly-DADMAC resulted in the aggregation of gold nanoparticles with the colour changing from red to blue. The gold nanoparticles were prepared via the citrate reduction method. Characterisation of the gold nanoparticles was done by ultraviolet- visible (UV/VIS) spectrophotometry and transmission electron microscopy (TEM). The Lovibond comparator was fabricated with a colour filter disk for the screening of residual poly-DADMAC in raw and potable water. The colorimetric disk was printed on the plastic slide and inserted in the plastic compartment of the comparator. The Lovibond comparator was verified with raw and potable water samples from different sampling points in and around the Mhlathuze river area located in the province of KwaZulu-Natal, South Africa. Preliminary results showed that the developed colorimetric comparator device can visually detect poly-DADMAC concentrations lower than 1 mg L-1. The colour development was first developed on normal paper and then optimised by UV/VIS spectrophotometry. The method developed has a linear range from zero to 10 mg L-1 with the correlation coefficient of R=0.9954. The effectiveness of the device was investigated by doing a recovery study on a potable water sample. Potable water is water that is suitable for drinking. In this research, potable water refers to tap water. The potable water sample was spiked with 1 mg L-1 poly-DADMAC. This exercise was done three times. The acceptance criterion for recovery is 80 to 120%. The 3 recoveries that were obtained are 107.95, 91.26 and 100.3%. The average recovery was 99.84%. This shows that the proposed method can detect poly-DADMAC with the acceptable level of accuracy. One of the important parameters that a quality method must have is selectivity. This parameter shows that the method can accurately detect the analyte of interest in the midst of different matrices. This was done by analysing the raw water samples together with their treated samples. Physical-chemical parameters were also analysed to show the broader state of the samples. The poly-DADMAC results obtained from the UV/VIS spectrophotometer compared quite well with those obtained from using the Lovibond colorimetric filter. The limited observation of colours using our eyes is a major contributor of systematic errors during the application of colorimetric devices. Thus, such a limitation can be reduced by using CIELAB system. A gold nanoparticle-based colorimetric CIELAB system for detection of poly-DADMAC in potable and raw water was also demonstrated. The method is based on the application of a paper-based analytical device which is printed on the normal A4 white printing paper. Fully enclosed 6 X 9 hydrophobic wells were fabricated on this paper. This work provides a clear evidence of the application of CIELAB colour system, and thus, replacing the conventional spectrophotometric technique to quantify polymers. Results of this work showed that the intensity of the fabricated well is proportional to the concentration of the detected polymer. The change in colour (ΔE) was calculated for each fabricated well and clear evidence of the colour change was observed upon the variation of the polymer. Moreover to the application of ΔE, the chromaticity using CIEYxy was used to verify colour change, it was observed that they followed the expected shift from red to blue, symbolising aggregation due to Van Der Waal inter-particle attractions as a result of the addition of poly-DADMAC. The results of this experiment were validated using the spectrophotometric technique which further emphasised the appearance of the new surface Plasmon resonance peak formed at 610nm symbolising aggregation. Importantly, the intensity of the new Surface Plasmon Resonance (SPR) peak at 610 nm increased by increasing the concentration of poly-DADMAC. Comparison of the Lovibond and UV/VIS results showed that there was no significant difference between the two methods. This proved that the fabricated Lovibond colour comparator is capable of the detection of residual poly-DADMAC in water treatment. This therefore implies that plant operators can be able to detect poly-DADMAC at any stage during the water treatment process by using a rapid, user-friendly portable device.Item Comparison of lignin yield from sugarcane bagasse pellets using liquid hot water and ionic liquid pretreatment methods(2019) Gnana, Gueh Charles; Deenadayalu, NirmalaIn this research work, lignin yield from sugarcane bagasse pellets (SBP) was investigated after treatment of sugar cane bagasse with liquid hot water (LHW) and enzymatic hydrolysis followed by ionic liquids (ILs) and only ionic liquids pretreatment methods. In the LHW and ionic liquid methods, the SBP were first treated with LHW at 200 °C, for 30 minutes in a suitable reactor, for removal of hemicellulose. The complex cellulignin residue was treated separately with either of two ionic liquids namely: 1-ethyl-3- methylimidazolium acetate ([Emim][OAc]) or 1-butyl-3- methylimidazolium hydrogen sulphate ([Bmim][HSO4]), using microwave digestion at varying time intervals. Theionicliquidmethodinvolvedthepretreatmentofsugarcanebagasse pelletswith either 1-ethyl-3-methylimidazolium acetate or 1-butyl-3-methylimidazolium hydrogen sulphate followed by microwave digestion at varying time intervals. Ultraviolet (UV) spectroscopy at a wavelength of 280 nm was used as a tool for quantification of lignin. The different functional groups of the extracted lignin were confirmed using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Thermogravimetric analysis (TGA) provided information on thermal characteristics of the extracted lignin. In addition to material characterization, mixed factorial ANOVA was performed to compare the extracted lignin yield using the LHW and IL and the ionic liquid pretreatment methods. High performance liquid chromatography (HPLC) was used to identify the C5 sugars in the hydrolysate after LHW pretreatment. X-ray diffraction (XRD) was used to identify cellulose peaks of cellulignin and SBP and ILs treated samples. The results indicated that the lignin yield from sugarcane bagasse pellets after liquid hot water treatment and enzymatic hydrolysis was 37.8 % (m/v). The highest percentage yield of lignin extracted from the complex cellulignin (LHW and IL) was found to be 68.00 % (m/v) and 32.04 % (m/v) for [Emim][OAc] and [Bmim][HSO4], respectively for the optimized reaction time of 10 minutes. However, 67.25 % (m/v) and 48.94 % (m/v) of the extracted lignin were obtained for the pretreated SBP with [Emim][OAc] and [Bmim][HSO4], respectively for a reaction time of 20 minutes. This comparative study revealed that, there is no significant difference between the yield of lignin extracted from the complex cellulignin (68.00%) and sugarcane bagasse pellets (67.25 %).The sugarcane bagasse pellets is the preferred method since it doesn’t require high energy input.Item Development of electrochemical immunosensors for detection of Tau protein : computational and experimental studies(2019-11) Harilal, Calvin Carl; Bisetty, Krishna; Kanchi, SuvardhanTau protein is a microtubule-associated protein (MAP) found in neuronal cells of the central nervous system. In recent years it has become an important biomarker for neurodegeneration and pathologies of the nervous system, thereby necessitating novel approaches for its detection. This study involves the development of two immunosensors for the detection of tau protein. The study makes use of nanomaterials and antibody transducers as signal enhancing strategies. Both sensors rely on indirect detection of tau protein as a copper(II) complex using a Cu(II)/Cu (I) redox probe. The electrochemical immunoassay is based on the immobilisation of anti-tau antibodies onto a gold working electrode that has been modified with nanomaterials using N- Hydroxysuccinimide (NHS) binder. The first sensor makes use of gold nanoparticles (AuNPs) and the second utilises a nanocomposite of graphene oxide (GO) decorated with silver nanoparticles (AgNPs). Cyclic voltammetry (CV) was used to optimise the electrochemical signal of the tau protein, while quantitative analyses were achieved by differential pulse voltammetry (DPV) and square wave voltammetry (SWV) under the established optimised conditions. Results for the quantitative experimental studies revealed relatively low detection limits for both sensors. The lowest of these detection limits were obtained for DPV analysis of using sensor 1 which produced an LOD of 3.31 nM and an LOQ of 11.04 nM. For sensor 2 the SWV analysis produced the lowest LOD and LOQ of 1.73 nM and 5.76 nM respectively. Computational chemistry methods implemented at the DFT level were used to support the developed electrochemical sensor. The molecular docking results showed relatively good binding affinity of -4.72 kcal/mol between the NHS and the antibody. A 100 ns MD simulation showed a good free binding energy value of -20.51 kcal/mol at pH 7, in accordance with the optimum pH implemented in the experimental work. Furthermore, adsorption studies were performed between the citrate coated nanoparticles on the Au electrode and NHS/anti-tau antibody/tau complex. The energy adsorption simulations revealed the energy favoured interaction between the designed layers with the stabilizing energy changes from -- 23.74 to -142.96 kcal/mol for sensor 1 and for sensor 2 it changed from -7.6 to -127.82 kcal/mol. Overall the computational data correlated well with experimental work. The two novel immunosensors developed in this work, give new insights into electrochemical and computational methods for the detection of proteins, and could lead to the fabrication of a device for point-of-applications in early diagnosis of neurodegenerative disorders.Item Characterisation and application of bambara protein-polysaccharide complex coacervates in encapsulation of bioactive compounds(2019) Busu, Nyasha M.; Amonsou, Eric OscarBambara groundnut (Vigna subterranea) is a leguminous crop that is indigenous to Africa. In South Africa, the legume is cultivated in KZN, Limpopo and Mpumalanga where it is considered a traditional food. Bambara groundnut is a good source of protein (15 – 28 %) and contains substantial amounts of starch. The legume thrives well in areas of low agricultural input. Despite its good protein content, bambara groundnut is mostly cultivated in rural areas for by subsistence farmers. In recent years, there has been increased interest in bambara groundnut protein as an alternative protein source. The purpose of this study is to investigate the complexation behavior of bambara protein with gum Arabic and test the application of the formed complexes in encapsulation and delivery of bioactive compounds. In the first part of this study, four protein fractions extracted at different pH including the salt-solubilisation method were complexed with gum Arabic. The protein content as well as physicochemical properties (SDS-PAGE, FTIR, Zeta potential, SEM) of the protein fractions and resulting bambara protein-gum Arabic (BPI-GA) complexes were then investigated. In subsequent parts of the study, bambara protein extracted by the salt-solubilisation method was complexed with gum Arabic. The influence of ionic strength and biopolymer mixing ratio on complex formation was investigated. Subsequently, the emulsification properties, foaming properties, encapsulation efficiency and release properties of the formed complexes were also investigated under simulated gastric and intestinal pH conditions. The salt-soluble fraction showed the highest protein content (82%) whilst the lowest protein content (76%) was recorded at pH 2. The FTIR analyses revealed an increase in β-sheet content with decrease in pH of extraction. Complexation of the protein fractions with GA resulted in the optimal pHs of interaction shifting towards acidic regions (pHopt: 4.8 to 2.9) as pH of protein extraction became more acidic. Upon complexation, protein fractions produced coacervate yields ranging between 41 - 68%, with the pH 2 fraction recording the lowest (41%) yield. Further, addition of gum arabic seemed to broaden the turbidity profiles. When assessed by SEM, the particles appeared as spherical and aggregated structures between 100-200 nm.Item Food hygiene and safety practices of food handlers in tuckshops at secondary schools in Umlazi(2019) Dlomo, Kaite Nokuthula; Napier, Carin E.; Ijabadeniyi, Oluwatosin Ademola; Vermeer, S. I.Objective: To determine the food safety and hygiene practices of the food handlers at secondary school tuck shops in Umlazi, Durban, South Africa in order to assess the risk of exposure to harmful bacteria that may cause food poisoning by conducting knowledge questionnaires and microbial tests from food handlers’ hands, counter surfaces and kitchen cloths. Research Methods: A total of 18 secondary schools, 48 food handlers and 24 managers were included in the study. The observational, descriptive and analytical study consisted of quantitative data collection methods. Quantitative data was obtained through a food hygiene and safety questionnaire designed for food handlers and tuck shop owners/managers, an observational checklist and microbial swab tests from food handlers’ hands, counter surfaces and kitchen cloths for analysis of microbial presence before preparation, during preparation and after preparation of food. The microbes tested for were Staphylococcus aureus, Escherichia coli, Salmonella, Listeria monocytogene, Aerobic spore formers and anaerobic spore formers. Data was captured in Excel and analyzed using a statistical package for social sciences (SPSS) version 24 for descriptive statisticsItem Production and characterization of polyhydroxyalkanoates (PHA) from corn silage using Thermus thermophilus HB8(2019-08-08) Zondo, Sandisiwe Gladness; Deenadayalu, Nirmala; Permaul, KugenIn this study, a biodegradable copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was produced from an agricultural by-product namely corn silage through a fermentation process using Thermus thermophilus HB8. Two types of corn silage pre-treatment processes viz. deionized water treatment (unhydrolysed) and acid hydrolysis were carried out at different loadings of corn silage (6%, 12%, 24% and 48% m/v), at 70°C for 50 h. Both pre-treatments were able to produce biopolymer where 6%, 12%, 24% and 48% unhydrolyse pre-treatment yielded 12%, 20.44%, 28.42% and 18.65% PHA, respectively; 6%, 12%, 24% and 48% acidic pre-treatment yielded 42.23%, 49.53%, 56,41% and 61.32% PHA, respectively. The extracted polymer was characterized by Fourier transform infrared spectroscopy (FT-IR) and ultraviolet-visible spectroscopy (UV-Vis) to study the characteristic bands; gas chromatography was used to identify the PHA monomers of the extracted methyl esters; scanning electron microscopy (SEM) was used to study the morphology of the bioplastic products; tensile testing was used to study the tensile properties of the bioplastics.Item Characterisation of Opuntia phenolic extracts and enzymatic modification of selected compunds(2019) Aruwa, Christiana Eleojo; Kudanga, Tukayi; Amoo, Stephen O.Opuntia species are utilised as local medicinal interventions for chronic diseases and as food sources. The phytochemical profile varies within and across Opuntia species and has been related to differences in cultivar and geographical location. Macromolecular antioxidant (MA) fractions are also largely ignored from most conventional extractive processes compared to the well-known extractable polyphenol fractions. This study characterised subtropical spineless cladode, fruit pulp and peel extracts and selected phenolic compounds for enzymatic modification using a laccase from Trametes pubescens. MA extracts were also characterised in comparison with extractable fractions. The effects of drying methods and extraction solvent on extract yields and bioactivities were also studied. Extracts were assayed for phenolic content and antioxidant activities were determined using standard 2,2’-diphenyl-1-picrylhydrazyl (DPPH), 2,2,-azinobis3-ethylbenzthiazoline-6-sulfonic acid (ABTS) and ferric reducing antioxidant power (FRAP) assays. Antimicrobial activities and mode of antibacterial action were assessed against type-bacterial cultures. Minimum inhibitory concentration (MIC) values were recorded for the extracts and compounds. Compound profiling was achieved using liquid chromatography-time of flight-mass spectrometry (LC-TOF/MS) in negative ionisation mode. Antibacterial and antioxidant activities were higher in MA, hydrolysed and hydroalcoholic cladode and fruit extracts than in aqueous fractions. Ethanolic, methanolic and hexane extracts of freeze-dried Opuntia cladode, MA and peel samples showed higher total phenolic content, and in vitro antioxidant and antimicrobial activities than the oven-dried extracts. Cladode extracts inhibited growth of both Gram-positive and Gram-negative microorganisms (MIC range of 25 to 250 mg/mL). Likewise, fruit extracts inhibited both Gram-positive and Gram- negative microorganisms (MIC range of 2.5 to 18.75 mg/mL). Cladode and fruit extract profiles showed the presence of mainly phenolic acids and flavonoid derivatives. Isovitexin 7-O- xyloside-2"-O-glucoside, polyhydroxypregnane glycoside and neohancoside C in Opuntia cladode, and pinellic acid in Opuntia fruit were identified for the first time in this study. Some compounds, however, remained unidentified. Thereafter, selected Opuntia cladode and fruit phenolic compounds (isorhamnetin and luteolin) were used for enzymatic (laccase) transformation after preliminary screening reactions. Laccase-catalysed oxidation of luteolin in a monophasic system containing sodium acetate buffer (pH 5.0) and ethanol (50%, v/v) as co- solvent, resulted in the production of a dimer (m/z 569, M=570). Using a similar approach, oxidative coupling of isorhamnetin produced two main products, IP1 which was a dimer (m/z 629, M=630) and IP2 (m/z 457, M=458) which was most likely a result of coupling of an oxidative cleavage product and the isorhamnetin monomer. Dimers showed up to two-fold improvement in antioxidant and antimicrobial activities, compared to their respective substrates. The synthesised products showed a bactericidal mode of action as demonstrated by time-kill and bacterial cell integrity assays. The bactericidal action was further confirmed by scanning electron microscopy (SEM) which showed that treatment of bacterial cells with the synthesised compounds resulted in deformed, pitted, broken or fragmented cells, indicating strong bactericidal action. In conclusion, this study showed that Opuntia fruit pulp, peel and cladode extractable and MA extracts have potential as sources of phenolic compounds with antioxidant and antimicrobial activities. Laccase catalysis has potential to transform the phenolic compounds into coupling products with higher biological activities. The synthesised products have potential for application in the food, nutraceutical and other relevant industries.Item Synthesis, characterization and antimicrobial evaluation of piperazinyl-quinolinyl-a-aminophosphonates(2019) Rajkoomar, Nikisha; Gengan, Robert Moonsamyα-Aminophosphonates (α-APs) is an important motif among heterocycles particularly in medicinal chemistry due to their reduced levels of cytotoxicity and structural resemblance to the corresponding α-amino acids. They are useful intermediates in synthetic organic processes and present with a broad spectrum of biological activities. Hence, there is an ongoing interest in the development of improved synthetic methods for the preparation of these α-APs. The complex molecules were initially synthesized in a step-wise reaction but this method suffered several drawbacks such as long reaction times and resulted in low yields. However, since the development of multi-component reactions (MCRs), three or more substrates can undergo an efficient one-pot reaction which results in higher product yields. The first step in the synthetic aspect of this study involved the preparation of a novel palladium supported strontium titanate (Pd-SrTiO3) material. Herein, an aqueous solution of strontium (II) nitrate was mixed with citric acid followed by reflux in an ethanolic solution of titanium (IV) butoxide. Thereafter, the dried solid was mixed with palladium (II) nitrate and this solution mixture was refluxed, filtered, calcined and subsequently dried. The characterization of Pd- SrTiO3 was undertaken with FT-IR, P-XRD, SEM, BET, SEM-EDX and Raman spectroscopic techniques. The synthesis of a series of novel -αAPs in a MCR system comprising an aldehyde, diethyl phosphate and selected aniline derivatives via the Kabachnik Fields reaction approach in the presence of catalytic amounts of Pd-SrTiO3 was investigated Twenty methyl piperazinyl-quinolinyl α-aminophosphonates (MPQ-α-APs) (4a-4t) were synthesized, purified and characterized by FT-IR, 1H-NMR, 13C-NMR, 31P-NMR, 2D-NMR and high resolution mass spectroscopic techniques. Valuable features of this routine included high yields, extensive substrate range, straight forward procedures and excellent catalytic properties. The cytotoxicity of 4d, 4e, 4f, 4m, 4q, 4r and 4s was evaluated using the Brine shrimp lethality assay. These compounds showed Artemia salina death < 50 % thereby suggesting their potential for other biological evaluation. The antimicrobial evaluation was conducted using the agar disc diffusion assay. The twenty MPQ-α-APs were assessed against Bacillus cereus , Staphylococcus aureus , Klebsiella pneumonia and Micrococcus luteus ; and three yeast cultures Candida albicans, Caraipa utilis and Saccharomyces cerevisiae. Compound 4m showed slight bacterial growth inhibition for the test species Bacillus cereus and Micrococcus luteus while compound 4r was marginally inhibitory to the growth of Staphylococcus aureus. Finally, the MPQ-α-APs were screened for their antioxidant activity by the DPPH assay. Compounds 4f and 4r demonstrated significant free radical scavenging potential of 94.24 % and 67.32 %, respectively. The remaining compounds showed low antioxidant activity within the range of 21 – 42 %.