Browsing by Author "Antunes, Edith"

Now showing 1 - 7 of 7
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    Antimicrobial activity of the secondary metabolites isolated from a South African red seaweed, laurencia corymbosa
    (MDPI, 2023) Fakee, Jameel; Bolton, John J.; Antunes, Edith
    South Africa’s highly diverse marine biota includes several endemic marine red algae of the Laurencia genus. Cryptic species and morphological variability make the taxonomy of Laurencia plant challenging, and a record of the secondary metabolites isolated from South African Laurencia spp. can be used to assess their chemotaxonomic significance. In addition, the rapid development of resistance against antibiotics, coupled with the inherent ability of seaweeds to resist pathogenic infection, supported this first phycochemical investigation of Laurencia corymbosa J. Agardh.
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    The antimicrobial activity of zinc oxide nanoparticles synthesized with plant extracts against Staphylococcus aureus
    (University of the Western Cape, 2019) Kriek, Gisela; Antunes, Edith
    Nanoparticles using a green synthesis production method is of increasing interest for biomedical applications. Zinc oxide is currently used in medicinal and cosmetic formulations, and zinc oxide nanoparticles have potential in biomedical applications. Antibiotic-resistant bacterial infections are of growing concern globally, and novel antimicrobial agents are drastically needed. In this work, zinc oxide nanoparticles were synthesized using Calendula officinalis flowers aqueous extract and zinc nitrate hexahydrate using a single-pot green synthesis approach. The synthesized particles were calcined and characterised using UV-Vis spectrophotometry, Dynamic Light Scattering (DLS), X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), Fourier-Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance Imaging (NMR). Quasi-spherical, hexagonal phase zinc oxide nanoparticles with core size <10nm according to TEM and average size of ~53nm according to XRD were successfully synthesized. The particles tended towards agglomeration. Antioxidant assays were run to determine the reducing power, antioxidant activity, and presence of polyphenols in the final products. The final product possessed antioxidant activity, polyphenols and had reducing power, confirming the constituents from Calendula officinalis playing a role in the reduction of the zinc ions and capping of the zinc oxide nanoparticles. Minimum inhibitory concentration of the samples by tube dilution was conducted to determine potential of the samples as antimicrobial agent against methicillin-resistant Staphylococcus aureus, using Clindamycin as control. Results of antimicrobial studies indicate the need for investigation of MIC using a variety of concentrations of the samples, and a variety of solvents, in order to determine exact MIC values. Further work is needed to improve the methodology to obtain particles that have a narrow size distribution, that are well dispersed, and are of higher concentration to be considered for antimicrobial use in the biomedical field.
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    Carbon-carbon coupling reactions catalysed by palladium nanoparticles supported on the green alga Ulva armoricana
    (University of Western Cape, 2018) De Bruin, Franklin Quelain; Antunes, Edith
    The synthesis of nanomaterials, especially metallic nanoparticles, has attracted an enormous amount of interest over the past decade. They exhibit unique properties that allow the multiple applications in a variety of fields in science and technology. Their applications are limited by the efficiency and control of their synthesis to produce nanoparticles of certain size and shape. With ever mounting concern for the environment, a great amount of research has recently been extended to synthetic procedures that are carried out with limited or no toxicity to human health and the environment. One method involves the use of biological (or biogenic) materials for nanoparticle synthesis. This method is particularly attractive due to the fact that it is a relatively cheap, simple and environmentally friendly method compared to that of conventional chemical methods of synthesis.
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    Green Synthesis and characterization of gold Nanoparticles using Green Alga Ulva Lactuca and evaluation of their Catalytric Role
    (University of the Western Cape, 2016) Mukhoro, Ofhani Christopher; Antunes, Edith
    Nanoparticles synthesized using typical chemical procedures have associated environmental risks because of the use of hazardous chemicals. With the ever-increasing potential application for nanomaterials, there is a growing need to develop new synthetic procedures for nanomaterials which are non-toxic and eco-friendly. This study presents, as a first step, the screening of the aqueous extracts of several seaweeds in order to assess their ability to produce gold nanoparticles (AuNPs). Eleven aqueous extracts were screened for the synthesis of AuNPs and where AuNPs were formed, these were further characterized using UV-vis spectroscopy and HRTEM primarily. Three of the eleven aqueous extracts shown to produce AuNPs were extracts obtained from brown algae. The total antioxidant and total reducing power contents, as well as the DPPH radical scavenging abilities for these extracts were determined and related to their ability to produce the NPs. The AuNPs were found to be of various shapes and sizes including spheres, rods and triangles, with sizes ranging from 20 nm to 200 nm.
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    Green synthesis: the use of brown algae in the synthesis of palladium nanoparticles and applications in carbon – carbon bond formation reactions
    (University of the Western Cape, 2020) Damon, Eldon Pierre; Antunes, Edith
    Due to the negative impact on the environment and the associated biological risks on human and animal life, the need for eco-friendly synthetic protocols is critical. With the rapid advancement in nanotechnology, this extends to the synthesis of nanomaterials. Eco-friendly nanoparticle synthesis protocols have led to the use of fungi, plants and other biological substances, due to their remarkable ability in reducing metal ions. This led to the formation of very efficient hybrid catalysts, which are partially organic/inorganic composites. Palladium nanoparticles have drawn much interest due to its potential in catalytic applications and in photovoltaic cell development. In this study, the brown marine algae, Ecklonia radiata, was employed as a putative palladium nanoparticle bioreactor. Aqueous extracts of the algae were used as a supporting matrix for the synthesis of palladium nanoparticle (AE-PdNPs) catalysts according to the principles of green chemistry. The catalysts were then assessed for their capability in various carbon-carbon coupling reactions such as Suzuki-Miyaura, Sonogashira, and Heck coupling reactions. Selectivity studies were also performed. The PdNPs were compared to “model” polyvinylpyrrolidone palladium nanoparticles (PVP-PdNPs), synthesized according to literature methods. A variety of spectroscopic techniques were used to characterize the nanoparticles and the organic reaction products, including HRTEM, EDX, NMR, FTIR, DLS, TGA, UV-Vis, ICP-AES, GC-MS and XRD spectroscopy. qNMR was used to determine the product % yields. The aqueous extracts were characterised using NMR and a variety of assays, including total antioxidant potential, total reducing power and radical scavenging ability) to assess its ability to reduce the Pd metal salt. 2D NMR revealed polysaccharides and polyphenols to be the major and minor components, respectively, present in the extract. HRTEM images revealed the average size of the AE-PdNPs and PVP-PdNPs to be 12 nm and 8 nm, respectively. The images also showed the shapes of the NPs to be cubic for the AE-PdNPs and cubic or triangular for the PVP-PdNPs. SAED and XRD spectroscopy revealed the face-centred cubic phase and polycrystalline nature of the AE-PdNPs. No reliable data, other than the HRTEM images was obtained for the PVP-PdNPs. Zeta potential and DLS measurements confirmed the negative charge present on the surface of the nanoparticles, while the hydrodynamic radii were found to be 65 nm and 99 nm for the AE- and PVP-PdNPs, respectively, substantiating the presence of the capping agents. ICP-AES analysis revealed the Pd content of the NPs to be 48.8 and 28.9 ppm for the AE- and PVP-PdNPs. Following characterization, the PdNPs were assessed as potential catalysts in the Suzuki-Miyaura, Heck and Sonogashira carbon-carbon coupling reactions. Bromo and iodo substrates were employed, together with sterically hindered substrates, with a nitro moiety in the ortho or para positions. For the Suzuki-Miyaura reactions, both sets of PdNPs revealed slightly higher yields for the products synthesized using the bromo substrate (>90%), while low yields (40 – 55% yields) were obtained for the ortho substituted substrate in comparison to the para substrate (>90% yields). The Heck coupling reactions with butyl acrylate and 4-iodoacetphenone were successful (~70% yields), while reactions with 4-bromoacetophenone failed. However, the Sonogashira couplings did not proceed at all. With the series of reactions NPs showed some selectivity, with the AE-PdNPs consistently producing higher yields for the products obtained. This may be due to overall nature of the NPs, or due to the higher platinum loading content for the AE-PdNPs.
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    Nanoparticles for use in imaging, catalysis and phthalocyanine synthesis
    (University of the Western Cape, 2018) Samsodien, Mogammad Luqmaan; Antunes, Edith
    Nanoscience and nanotechnology are known to be interdisciplinary, crossing and combining various fields and disciplines in pursuit of desirable outcomes. This has brought about applications of nanoscience and nanotechnology in multitudes of industries, spanning from the health, pharmaceutical to industrial industry. Within the health industry, the medical field has seen much advancement through nanoscience and nanotechnology. The importance of finding cures to diseases is top priorities within the medical field, along with advancements in understanding and diagnosing diseases. Due to these outcomes, we see the emergence of imaging techniques playing a crucial role. The work covered in this thesis looks at a prospective luminescent agent applicable in the medical field for bio-imaging, but also at a possible phthalocyanine sensitizer for treatment of cancer through photodynamic therapy. Another area where nanoscience and nanotechnology are found is in industry, where nanoparticles are utilised as catalysts in many synthetic reactions. Highly desirable catalysts in industry are those involved in oxidative reactions where we explore a metal nanoparticle catalyst within this work.
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    Polyacrylic acid and polyvinylpyrrolidone stabilised ternary nanoalloys of platinum group metals for the electrochemical production of hydrogen from ammonia
    (University of the Western Cape, 2016) Molefe, Lerato Yvonne; Iwuoha, Emmanuel; Jahed, Nazeem; Antunes, Edith
    The electrochemical oxidation of ammonia has attracted much attention as an efficient green method for application in direct ammonia fuel cells (DAFCs) and the production of high purity hydrogen. However, the insufficient performance and high costs of platinum has hindered the large scale application of ammonia (NH₃) electro-oxidation technologies. Therefore, there is a need for the fabrication of efficient electrocatalysts for NH₃ electrooxidation with improved activity and lower Pt loading. Owing to their unique catalytic properties, nanoalloys of platinum group metals (PGMs) are being designated as possible electrocatalysts for NH₃ oxidation. This study presents for the first time a chemical synthesis of unsupported ternary PGM based nanoalloys such as Cu@Pt@Ir with multi-shell structures and Cu-Pt-Ir mixed nanoalloys for electro-catalysis of NH3 oxidation. The nanoalloys were stabilised with polyvinylpyrrolidone (PVP) as the capping agent. The structural properties of the nanoalloys were studied using ultraviolet-visible (UV-Vis) and fourier transform infra-red (FTIR) spectroscopic techniques. The elemental composition, average particle size and morphology of the materials were evaluated by high resolution transmission electron microscopy (HRTEM) coupled to energy dispersive X-ray (EDX) spectroscopy. High resolution scanning electron microscopy (HRSEM) was used for morphological characterisation. Additionally, scanning auger nanoprobe microscopy (NanoSAM) was employed to provide high performance auger (AES) spectral analysis and auger imaging of complex multi-layered Cu@Pt@Ir nanoalloy surface. X-ray diffraction (XRD) spectroscopy was used to investigate the crystallinity of the nanoalloys. The electrochemistry of the nanoalloy materials was interrogated with cyclic voltammetry (CV) and square wave voltammetry (SWV). The electrocatalytic activity of novel Cu-Pt-Ir trimetallic nanoalloys for the oxidation of ammonia was tested using CV. UV-Vis spectroscopy confirmed the complete reduction of the metal precursors to the respective nanoparticles. FTIR spectroscopy confirmed the presence of the PVP polymer as well as formation of a bond between the polymer (PVP) chains and the metal surface for all nanoparticles (NPs). Furthermore, HRTEM confirmed that the small irregular interconnected PVP stabilised Cu@Pt@Ir NPs were about 5 nm in size. The elemental composition of the alloy nanoparticles measured using EDX also confirmed the presence of Cu, Pt and Ir. Cyclic voltammetry indicated that both the GCE|Cu-Pt-Ir NPs and GCE|Cu@Pt@Ir NPs are active electrocatalysts for NH3 oxidation as witnessed by the formation of a well-defined anodic peak around -0.298 V (vs. Ag/AgCl). Thus the GCE|Cu-Pt-Ir NPs was found to be a suitable electrocatalyst that enhances the kinetics of oxidation of ammonia at reduced overpotential and high peak current in comparison with GCE|Cu@Pt@Ir NPs, GCE|Pt NPs, GCE|Ir NPs and GCE|Cu NPs electrocatalysts. The presence of the crystalline phases in each sample was confirmed by XRD analysis. The surface analysis of Cu@Pt@Ir nanoalloy with AES surveys revealed the presence of Pt, Ir and Cu elements in all probed spots suggesting some mixing between the layers of the nanoalloy. Yet, analysis of nanoalloys by CV and XRD confirmed the presence of Cu-Pt and Pt-Ir solid solutions in the Cu-Pt-Ir and Cu@Pt@Ir nanoalloys respectively.