A generalized quantum chemical approach for electron transport in molecular devices is developed. It allows to treat the devices where the metal electrodes and the molecule are either chemically or physically bonded on equal footing. Effects of molecular length and hydrogen bonding on the current-voltage (I-V) characteristics of molecular devices are discussed. An extension to include the vibration motions of the molecule has been derived and implemented. It provides the inelastic electron tunneling spectroscopy (IETS) of molecular devices with unprecedented accuracy, and reveals important information about the molecular structures that are not accessible in the experiment. The IETS is shown to be a powerful characterization tool for molecular devices. An effective elongation method has been developed to study the electron transport in nanoand bio-electronic devices at hybrid density functional theory level. It enables to study electronic structures and transportation properties of a 40 nm long self-assembled conjugated polymer junction, a 21 nm long single-walled carbon nanotubes (SWCNT), and a 60 basepairs DNA molecule. It is the first time that systems consisting of more than 10,000 electrons have been described at such a sophisticated level. The calculations have shown that the electron transport in sub-22 nm long SWCNT and short DNA molecules is dominated by the coherent scattering through the delocalized unoccupied states. The derived length dependence of coherent electron transport in these nanostructured systems will be useful for the future experiments. Moreover, some unexpected behaviors of these devices have been discovered. / QC 20101203

A research report submitted to the Faculty of Science in partial fulfilment of the requirements for the degree of Master of Science. Johannesburg March 2015 / This research was motivated by the necessity for Biotechnology education in the General Education and Training (GET) phase as biotechnology influences our daily lives in almost every way. Our human population is continually increasing and there is a need for increased food security to sustain the larger population. Hence technological advancement in the medical, agricultural and commercial sectors are taking place every day. Therefore, biotechnology education is necessary at an early age in order for learners to make an informed decision about the different products that are available in the market. This qualitative study aimed to identify the knowledge of and attitude towards biotechnology among grade 9 learners. This study was conducted in two South African schools in the Gauteng province. A total of 360 learners participated in the study and 25 learners from each school were selected as the sample for the study. Data was gathered using a questionnaire which consisted of closed ended and open ended questions based on knowledge and attitudes. The data analysis was essentially qualitative as it involved interpretation of the learners’ response in order to gain further understanding and insight. However, part of the questionnaire i.e. question 2 was quantitative. The data analysis revealed that grade 9 learners do indeed have knowledge about biotechnology. However, some of the knowledge they have, has many misconceptions i.e. in terms of genetic modification, inserting or removing genes and this largely due to a lack of formal teaching, as it is not a requirement in the grade 9 Natural Science curriculum. This information is useful for teachers teaching Natural Science and for teachers teaching Life Sciences to grade 10, 11 and 12, as well as curriculum developers.

The unicellular yeast, Pichia pastoris has currently emerged as one of the most popular host systems for heterologous proteins due to its relatively cheap cost, easy genetic manipulability, ability to perform post-translational modifications on proteins, and respiratory growth capabilities which allow it to be cultured in very high concentrations. Over 700 foreign proteins have been recombinantly expressed using P. pastoris. Although P. pastoris appears to be an ideal host system, its main drawback is its inability to efficiently export some heterologous proteins into the extracellular medium. The incorporation of S. cerevisiae's MATα pre-pro signal leader (MATα) has led to increased protein secretion in most cases. MATα is thus used in the production of 90% of all proteins secreted in P. pastoris. However secretion efficiency still remains a problem. It has been suspected that low secretion may be attributed to improper extracellular targeting (a function of MATα). In order to address these issues there has been a precedent for performing limited mutagenesis of a signal leader peptide (like MATα) to increase protein secretion. In one study the insertion of a 10 amino-acid residue into MATα resulted in a 5-fold increase in secretion of bacterial phytase, an important industrial enzyme. Despite this success there have been no systematic mutagenesis processes which would help elucidate the reason behind this case of increased secretion. In our study, we performed a series of mutagenesis events, both random and site directed, with the intent of illuminating the mechanisms of MATα that contribute to secretion. As a result were able to create a novel secretion signal (pLL3) with enhanced secretion levels of our reporter protein HRP.

The recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic arose due to its ease of spreading, exacerbated by its ability to reproduce in asymptomatic carriers. Symptomatic patients of coronavirus disease 2019 (COVID-19) risk severe respiratory illness that can be fatal. Novel methods must be implemented to inhibit the proliferation of SARS-CoV-2 and similar pathogens. By coating face masks and face shields (commonly known as PPEs) with engineered nanoparticles embedded in a polyelectrolyte thin film, the PPEs can be imbued with antimicrobial properties and offer improved protection from pathogens. The Layer by layer (LBL) technique was performed to coat PPEs with antimicrobial polyelectrolyte thin films embedded with nanoparticles smaller than 15nm. The coatings were confirmed by physical studies, including XPS and SEM, to evaluate the morphology and chemistry of the composite films. E. coli was used as a model microbe for antimicrobial studies where it was cultured on coated PPEs. Significant inhibition was observed. Based on these results, PPE coated with this material shows promise for bacterial and possibly viral protection of healthcare workers.

Submitted in complete fulfillment for the Degree of Master of Technology: Biotechnology, Durban University of Technology, Durban, South Africa, 2014. / Global warming is a major concern to the world’s population. It is caused by greenhouse gases that result from the burning of fossil fuel. The fossil fuel reserves are rapidly depleting as the needs and wants of man in the world increases. Biodiesel is one of the solutions proposed to remedy this environmental crisis facing the world today. The aim of this study was to characterise the biodiesel that can be produced from the oil of Litsea glutinosa by transesterification. Biodiesel can be used in a diesel engine without modification and be produced from many different natural renewable oil sources such as algae, plants and kitchen waste material. Jatropha curcas has been identified as a potential producer of oil for biodiesel. The biodiesel properties of Jatropha curcas meet the required American Society for Testing and Materials (ASTM) standards. The fruit of Jatropha curcas contains 40.0% lipids. The oil has a saponification number of 202.6 and an iodine value of 93.0. However Jatropha curcas cannot be grown in South Africa because it is a highly invasive plant. Cetane number is the most important parameter of biodiesel. The higher the cetane value, the better the quality of the biodiesel. Oil from Jatropha curcas has a cetane number of 57.1. An alternative is the oil from Litsea glutinosa, which is found as a naturalised free forest along the South African coastline, and is also found in many Asian countries. It has many medicinal properties, however, it is not edible and hence its use for biodiesel does not add to the debate of fuel versus food production. The cetane number of oil from Litsea glutinosa is 64.79, which is ideal for ignition, and the fruit with 61.29% lipids can yield valuable quantities of biodiesel. Thus, the aim of the research was to determine the potential of Litsea glutinosa as a source of biodiesel. Furthermore, to maintain a sustainable source, Litsea glutinosa was micropropagated, and transformation of Litsea glutinosa was attempted for hairy root cultures. The Clevenger apparatus was used to extract fatty acids from dried crushed fruit of Litsea glutinosa. Fatty acids were converted to fatty acid methyl esters by transesterification. Transesterification was conducted in the presence of nitrogen and the reaction was catalysed with a mixture of methanol and sodium hydroxide (NaOH). The ratio 1 : 3 of oil to catalyst mixture was used for optimum transesterification to ensure a forward reaction and it was transferred to a separating funnel to allow the glycerol and fatty acid methyl esters to separate. GC-MS was used to determine the fatty acids. The iodine number, saponification number, acid value, viscosity, kinematic viscosity, density, specific gravity, thermostability, distillation point and sulphur content were determined. The seeds of Litsea glutinosa were germinated and tissue culture callus was produced from the seeds and leaves. The leaves and stems were used to produce hairy root cultures by inoculating them with Agrobacterium rhizogenes. Litsea glutinosa yielded 61% oil, which included 47 fatty acids in the fruit and 24 fatty acids in the seeds. The fatty acid profile of the oils indicated that the predominant fatty acids present were those that are essential for good quality biodiesel. The dominant fatty acids found in the fruit were 65.4% 9-octadecenoic acid and 13.6% hexadecanoic acid. The dominating fatty acids found in the seeds contained 36.3% 9-octadecenoic acid, 13.9%, hexadecanoic acid and 39.1%, dodecanoic acid. The iodine value was 6.3. The saponification value was 274. The acid value was 0.45 mg KOH. g-1. The viscosity was 22.48 mm2. s-1 and the kinematic viscosity was 23.84 mm2. s-1. The density was 942.69 kg. m-3 and the specific gravity was found to be 0.9 g. cm-3. The distillation temperature ranged between 52.2°C to 610.2°C. The sulphur content was found to be 383 µg. ml-1. These characteristics indicate that Litsea glutinosa can be used as a source of biodiesel, because the properties meet the required ASTM standards. However, the production of biodiesel from Litsea glutinosa has not been commercialised because the production of fuel is dependent on the fruit of the plant, which is seasonal. To overcome this, a part of this study investigated micropragation of Litsea glutinosa and transformation of Litsea glutinosa by Agrobacterium rhizogenes into hairy roots and attempts where made to determine whether fatty acid could be produced by these techniques. Callus cultures were grown on MS media and McCowns woody plant media supplemented with 1 ml BAP and 1 ml 2,4-D per 1 L of media. Callus cultures were obtained in the light. However, Litsea glutinosa resisted transformation by Agrobacterium rhizogenes.

A vector, called pWreckl, was constructed for the direct DNA transformation of N. tabacum protoplasts. This vector was shown to confer kanamycin resistance to transformed callus. Using derivatives of this plasmid containing various reporter genes, a protocol for direct DNA transformation by PEG-mediated uptake was established. However, all attempts to obtain transformed callus by electroporation were unsuccessful. The CAB6 gene from N. tabacum was identified as a suitable candidate for gene targeting and was further manipulated to produce constructs in pWreckl which were used in gene targeting experiments. Using a derivative of pWreckl, called BinsupF, transformed tobacco plants were generated and used as a model system for the rescue of integrated sequences by supF selection. This system was found to be capable of rescuing integrated pWreckl sequences, but at an efficiency below that which would be required for the rescue of rare gene targeting events. Therefore a second protocol was developed which used the technique of polymerase chain amplification to amplify specific integration events. Following direct DNA transformation with a pWreckl.CAB6 construct, a number of possible gene targeting events were identified and subcloned into pUC13. Partial sequencing of these clones revealed that they were not the result of homologous recombination, but arose through a combination of plasmid degradation and rearrangement which appeared to precede the actual integration event.

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