>Magister Scientiae - MSc / The emergence of multiple drug resistant microorganisms poses a major threat to human life. These microorganisms have made the currently used antibiotics ineffective and therefore continue to thrive. Therefore, there is a need for development of new, broad-secptrum antibiotics which is effective against almost every infectious microorganism. These antibiotics should ensure high effectiveness against the infectious pathogens while it is less detrimental to human health. Thus the search is channelled in nanoscience and nanotechnology in order to develop antibiotics that can kill infectious microorganisms effectively and hindering the development of drug resistance by these microorganisms. Nanoscience is the study of properties of a material when reduced to it smallest size (below 100 nm). It is a newly developing field of science which includes chemistry, physics and biology and has made it easy to synthesise nanomaterials for applications in many sectors of life including in medicine. The synthesis of nanoparticles can be achieved by physical and chemical methods. However, these methods are energy and capital intensive. Additionally, chemical method of synthesis uses chemicals that may be toxic which restrict the use of resultant nanoparticles in medicine. Therefore, there is a need for the use of eco-friendly methods of nanoparticle synthesis. The synthesis of silver and gold nanoparticles in this study was carried out by a green synthesis method, at room temperature, using an aqueous extract from the endemic brown alga Sargassum incisifolium. For comparison, commercially available brown algal fucoidans were also used to synthesise these nanoparticle, in addition to conventional methods of synthesis. The formation of nanoparticles was followed by the use of UV-Vis spectrophotometry. The characterization of the nanoparticles was done by TEM, XRD, DLZ and FT-IR. The rate of nanoparticle formation varied with specific reducing agent used. The faster reaction rate was recorded with S. incisifolium aqueous extracts pretreated with organic solvents while extracts obtained without this pretreatment produced slightly slower reaction rates. However, the commercially available fucoidans were less effective and required elevated temperatures for nanoparticle formation. Sodium borohydride reduction of silver nitrate was faster than the biological methods while the reduction of auric chloride by the S. incisifolium extracts and sodium citrate proceeded at similar rates. The nanoparticles synthesised with the help of the untreated aqueous extract were bigger than those synthesised from pre-treated extracts with both giving irregular shaped of nanoparticles. Also the nanoparticles formed from commercially available fucoidans were not of the same size, with bigger sizes recorded with Macrocystis fucoidan and smaller sizes with Fucus fucoidan. The shapes of nanoparticles from these fucoidans were spherical. From the conventional method, the nanoparticle sizes were smaller compared to the green synthesised nanoparticles and were predominantly spherical. The silver nanoparticles synthesised from the Sargassum aqueous extracts showed excellent antimicrobial activity against five pathogenic microorganisms including A. baumannii, K. pneumoniae, E. faecalis, S. aureus, and C. albicans. The gold nanoparticles were much less effective. To adequately assess the antimicrobial activities of the nanoparticles, it is or paramount importance to also asses their cytotoxicity activity. Three cell lines were used in this study namely, MCF-7, HT-29 and MCF-12a. The silver nanoparticles were found to be toxic to HT-29 and MCF-7 cell lines, exhibiting sligtly less toxicity against MCF-12a cells. The gold nanoparticles showed lower toxicity but a similar trend was observed.

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There is an increased interest in understanding the toxicity and rational design of gold nanoparticles (GNPs) for biomedical applications in recent years. Such efforts warrant reliable, viable, and biofriendly synthetic methodology for GNPs with homogeneous sizes and shapes, particularly sizes above 30 nm, which is currently challenging. In the present study, an environmentally benign, biofriendly, singlestep/ single-phase synthetic method using dextrose as a reducing and capping agent in a buffered aqueous solution at moderate temperature is introduced. The resulting GNPs are near-spherical, stable, catalytically active, place exchangeable, and water-soluble within the size range of 10-120 nm. The added advantage of the biologically friendly reaction medium employed in this new synthetic approach provides a method for the direct embedment/integration of GNPs into biological systems such as the E. coli bacterium without additional capping ligand or surface modification processes.

>Magister Scientiae - MSc / Recently researchers reported that nanoparticles functionalised through chemical methods possess risks to the environment and to the human health since they use hazardous chemicals and produce toxic waste. The increasing demand of nanomaterials for application in the field of science require an alternative method for synthesis of nanomaterials that are environmentally friendly, eco-friendly and non-toxic. The present study describes the green synthesis method for functionalisation of nanomaterials. Green synthesis methods are considered as a novel approach for functionalisation of nanoparticles using biological sources. / 2022

Magister Chirurgiae Dentium (MChD) / The rate at which the population is ageing is much faster than in the past. An increase in age results in an increase in oral diseases. One of the most common types of oral diseases in the elderly are fungal infections caused by Candida albicans. It has been noted that drug resistance to fungal pathogens is developing into a serious threat to public health and healthcare systems worldwide. This has consequently led to the need to develop effective and innocuous treatment modalities. The purpose of this study was to explore the antimicrobial and cytotoxic potential of silver nanoparticles (AgNPs) synthesised from Berzelia lanuginose, Helichrysum cymosum, and Searsia crenata.

>Magister Scientiae - MSc / Currently, non-renewable sources are mostly used to meet the ever-growing demand for energy. However, these sources are not sustainable. In addition to these energy sources being not sustainable, they are bad for the environment although the energy supply sectors highly depend on them. To address such issues the use of renewable energy sources has been proven to be beneficial for the supply of energy for the global population and its energy needs. Advantageous over non-renewable sources, renewable energy plays a crucial role in minimizing the use of fossil fuel and reduces greenhouse gases. Minimizing use of fossil fuels and greenhouse gases is important, because it helps in the fight against climate change. The use of renewable energy sources can also lead to less air pollution and improved air quality. Although solar energy is the most abundant source of renewable energy that can be converted into electrical energy using various techniques, there are some limitations. Among these techniques are photovoltaic cells which are challenged by low efficiencies and high costs of material fabrication. Hence, current research and innovations are sought towards the reduction of costs and increasing the efficiency of the renewable energy conversion devices.

The antimicrobial properties of dextrose encapsulated gold nanoparticles (dGNPs) with average diameters of 25 nm, 60 nm, and 120 nm (± 5 nm) synthesized by green chemistry principles were investigated against both Gram-negative and Gram-positive bacteria. Studies were performed involving the effect of the dGNPs on the growth, morphology and the ultrastructural properties of bacteria. dGNPs were found to have significant dose dependent antibacterial activity which was directly proportional to their size and also their concentration. The microbial assays revealed the dGNPs to be bacteriostatic as well as bactericidal. The dGNPs exhibited their bactericidal action through the disruption of the bacterial cell membrane causing leakage of cytoplasmic content. The overall outcomes of this study suggest that dGNPs hold promise as a potent antimicrobial agent against a wide range of disease causing bacteria and can control and prevent possible infections or diseases.

NanopartÃculas de prata à um tÃpico de destaque dentre os materiais nanoestruturados, por exibirem propriedades Ãpticas e eletromagnÃticas diferente das observadas no metal agregado, alÃm de uma excelente atividade bactericida, sendo essa propriedade uma das mais investigadas. A sÃntese e a estabilizaÃÃo verdes de nanopartÃculas de prata (NPAg) visa a reduÃÃo ou a substituiÃÃo de reagentes usados nos processos convencionais, minimizando assim o efeito nocivo dos mesmos ao meio ambiente. O uso de polissacarÃdeos à uma alternativa verde, tanto no perspectiva de redutor ou como estabilizante. A proposta deste trabalho foi sintetizar nanopartÃculas de prata utilizando galactomanana da fava danta (Dimorphandra gardneriana) (GFD) como estabilizante e redutor. Para isso, as sÃnteses foram realizadas atravÃs de dois mÃtodos diferentes: 1) SÃntese parcialmente verde: a galactomanana como estabilizante e boroidreto de sÃdio (NaBH4) como redutor; 2) SÃntese verde: a galactomanana atuando como agente redutor e estabilizante, utilizando aumento da temperatura e variaÃÃo do pH como recursos auxiliares na sÃntese. Foram realizadas sÃnteses com razÃo molar fixa de 1:1 de NaBH4/AgNO3. A razÃo molar de unidades monossacarÃdicas de GFD e Ãons Ag+ (proporÃÃo GFD:Ag) variou de 1:1 a 100:1. Para a sÃntese verde, foi escolhida a proporÃÃo GFD:Ag 10:1, o pH das soluÃÃes foi ajustado para 3, 7, 10 e 12, e os sistemas mantidos à temperatura constante de 50, 70 e 90 ÂC, com tempo de reaÃÃo de 30 min e 3h. Todos os coloides sintetizados foram analisados por espectroscopia de absorÃÃo na regiÃo do UV-Vis, confirmando a formaÃÃo de NPAg pelo aparecimento da banda de ressonÃncia de plasmon de superfÃcie (SPR) na regiÃo de 400 nm. A estabilidade dos coloides foi acompanhada tambÃm por UV-Vis e esses ainda mostraram-se estÃveis mesmo apÃs um ano da sÃntese. Para a sÃntese verde, apenas as soluÃÃes em pH 12 a 70 e 90 ÂC (FDAg12/70 e FDAg12/90) mostraram bandas de SPR no espectro de UV-Vis com 30 min de reaÃÃo, com intensidades semelhantes ao da banda do coloide obtido com NaBH4 (FDAgBH). Os coloides FDAgBH, FDAg12/70 e FDAg12/90 apresentaram potencial zeta negativo, com baixos valores, indicando que a estabilidade deve-se ao impedimento estÃrico devido Ãs cadeias do polissacarÃdeo. Tais coloides mostraram-se estÃveis mesmo apÃs a secagem e a redispersÃo em Ãgua. Os espectros de infravermelho indicam que a estabilizaÃÃo das NPAg ocorre principalmente pelas hidroxilas da cadeia da GFD. Por aumentar a condutividade da amostra, a presenÃa da prata diminui a estabilidade tÃrmica da GFD. A galactomanana da fava danta mostrou-se um bom estabilizante de coloides de NPAg sintetizados com NaBH4 e um bom agente redutor e estabilizante para sÃntese verde. Os coloides de NPAg e galactomanana da fava danta mostraram efeito bactericida, dependente da concentraÃÃo de prata inicial, contra a bactÃria Gram-positiva Staphylococcus aureus. / Silver nanoparticles is a topic prominent among nanostructured materials for exhibit optical and electromagnetic properties different from those observed in the bulk metal, but its bactericidal activity, one of their most investigated property. Green synthesis and stabilization of silver nanoparticles green (NPAG) aims to reduce or substitution of reagents used in conventional processes thereby minimizing the harmful effect to the environment. The use of polysaccharides is an green alternative as a reducing and stabilizing agent. The purpose of this study was to synthesize silver nanoparticles using galactomannan of fava danta (Dimorphandra gardneriana) (GFD) as stabilizer and reducing agent. Therefore, syntheses were carried out by two different methods: 1) Galactomannan as a stabilizer and sodium borohydride (NaBH4) as a reducing agent, 2) Green Synthesis: galactomannan acting as a reducing agent and stabilizer, using increased temperature and pH variation as auxiliary resources. Syntheses were perfomed with fixed molar ratio of 1:1 NaBH4/AgNO3. The molar ratio of monosaccharide units of GFD /Ag+ (GFD ratio Ag) varying from 1:1 to 100:1. For green synthesis GFD:Ag 10:1 ration was chosen, the pH was adjusted to 3, 7, 10 and 12, and the systems kept at constant temperature of 50, 70 and 90 ÂC, with 30 min and 3 h of reaction. All colloid synthesized were analyzed by absorption spectroscopy in the UV-Vis confirming the formation of the band NPAG the appearance of surface plasmon resonance (SPR) in the region of 400 nm. The stability of colloids was also monitored by UV-Vis and even these were stable even after a year of synthesis. For green synthesis, only the solutions in pH 12 at 70 and 90  C (FDAg12/70 and FDAg12/90) SPR showed bands in the spectrum of UV-Vis with 30 min of reaction, with similar intensities to those given for colloid obtained with NaBH4 (FDAgBH). FDAgBH, FDAg12/70 and FDAg12/90 colloids showed a negative and low zeta potential, indicating that stability is due to the steric hindrance from polysaccharide chains. The colloids were stable even after drying and redispersion in water. Infrared spectra indicate that the stabilization of NPAg occurs mainly by the hydroxyl groups from GFD. The conductivity of the sample increase with the presence of silver nanoparticles decreasing the thermal stability of the GFD. The galactomannan of fava danta acts as a good stabilizing agent for NPAg colloids synthesized with NaBH4 and a good reducing and stabilizing agent for green synthesis. The colloids obtained from this polysaccharides showed bactericidal effect against gram positive Staphylococcus aureus with increasing of the initial concentration of silver ions.

>Magister Scientiae - MSc / Nature through billions of years of trial and error has produced an immeasurable amount of natural systems like plants, birds and animals. The intelligence of nature is hidden in these natural systems and researchers are turning towards “Nature’s intelligence” to find inspiration and advance novelty in the development of nanomaterials. Gold nanoparticles (AuNPs) have unique optical, electronic and physicochemical features which has gained them popularity and widespread exploitation in various applications. The conventional methods used for AuNPs synthesis employs toxic chemicals which makes these NPs unsafe for biomedical applications. Hence, there is a search for new, ‘green’ and more cost effective methods for AuNPs synthesis. Plant extracts are regarded as a highly desirable system for nanoparticle synthesis due to their tremendous capability to produce a wide range of phytochemicals that can act as reducing agents. The main goal of this study was to synthesize AuNPs in a cost effective manner without the use of toxic chemicals in the synthesis process. Avocado seeds which are an agricultural waste by-product were used for the biosynthesis of AuNPs. The study reports on the synthesis optimization, characterization and activities of the biogenic AuNPs. The avocado seed extract mediated - AuNPs (AvoSE-AuNPs) were optimized by varying reaction parameters and characterized by UV-visible, Dynamic Light Scattering (DLS) and High Resolution Transmission Electron Microscopy (HRTEM), Zetasizer and Fourier Transform Infrared Spectroscopy (FTIR). The formation of AvoSE-AuNPs had an absorption maximum at 534 nm. HRTEM and DLS confirmed that the NPs were polydispersed and present in different shapes. The presence of phytochemical constituents on the AvoSE-AuNPs were confirmed by FTIR. Their potential antibacterial activity was tested on bacterial strains known to exhibit resistance to a number of current antibiotics. The catalytic activity of AvoSE-AuNPs was also assessed as a means to contribute to the development of new methods aimed at alleviating organic pollutants such as nitrophenols in the environment. The AvoSE-AuNPs demonstrated excellent catalytic activity in the reduction of 4-NP by NaBH4 as shown by the rapid decrease in the nitrophenolate absorption band at 400 nm and the appearance of new absorption band at 298 nm, revealing the formation of the 4-aminophenol. Furthermore, the rate constants calculated demonstrated that the reaction occurs faster in the presence AvoSEAuNPs. The AvoSE-AuNPs showed low significant cytotoxicity. Cell cycle analysis was conducted to further investigate the apparent exhibited toxicity of the AvoSE-AuNPs. The results showed that in both cell lines treated with AvoSE-AuNPs and AvoSE there was a ii | P a g e disruption in the regulation of cell cycle. Cell cycle analysis helped improve understanding of the low cytotoxicity observed by the MTT assay results. The results presented in this study clearly demonstrate the feasibility of using AvoSE for the synthesis of AuNPs. This study demonstrated that AvoSE mediated AuNPs synthesis is a greener alternative as it abides by the green chemistry principles. Furthermore, the study outcomes contributed to minimizing environmental pollution by finding use for agricultural waste and thus ultimately adding value to the field.

Metal organic frameworks (MOFs) is a quite recently discovered porous material group which shows potential in many different areas. One of these areas is carbon capture; the framework structure of the porous materials allows gas molecules to adsorb to the surface of the pores. MOFs are conventionally synthesised at high temperatures and with hazardous solvents. The goal of this projectwas to synthesise highly porous MOFs at room temperature with water as the main solvent, using environmentally friendly and non-hazardous precursors. As well as the room temperature synthesis, conventional synthesis methods were used with the same precursors as comparison. The materials were characterised with X-ray diffraction, thermogravimetrical methods and IR-spectroscopy. To assess the porosity of the materials, gas adsorption evaluation was performed with CO2, N2, SF6, and CH4 at 20⁰C. In the end, three novel porous magnesium-based materials and one zirconium-based material were successfully synthesised. One of the magnesium-based materials showed a moderately high CO2 adsorption (2.38mmol/g), and could be synthesised at room temperature. The zirconium-based material showed a remarkably high selectivity (17.7) for SF6 over N2 and a high surface area (550m2/g)