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L'optimisation de la composition des vitrifiats de REFIOM en les rendant alcali-résistants en vue de leur conférer une bonne durabilité chimique en milieu alcalin pour être ensuite utilisés dans les matrices cimentaires a été étudiée. La méthodologie suivie consiste à étudier le comportement à la lixiviation en mode statique de verres modèles alcali-résistants de type CEMFIL et de vitrifiats de REFIOM auxquels on a rajouté SiO2, Na2O et ZrO2 pour leur conférer un caractère alcali-résistant. Les tests de lixiviation menées à 90°C et à différents temps (de 6 heures à 28 jours) ainsi que les autres techniques d'analyse chimique (ICP-AES, MEB-EDS, SIMS, ERDA, RBS, PIXE) sur ces verres ont montré que ce sont les vitifiats de REFIOM dont la composition a été optimisée qui présentent la meilleure durabilité chimique quelque soit le pH / The main goal of this research work is to optimize the composition of vitrified REFIOM into alkali-resistant glasses in order to enhance their durability and in alkaline media. The expected industrial application deals with the use of these glasses associated with concrete in composite materials. The experimental approach is based on static leaching tests of model alkali-resistant glasses and vitrified REFIOM in witch we have added SiO2, Na2O et ZrO2 in order they become alkali-resistant vitrified REFIOM. The leachates have been analysed by ICP-AES and the solid surfaces characterized by scanning electron microscopy, electron microprobe analysis, secondary ion mass spectrometry depth profiling, and synchrotron radiation spectroscopies. All those analysis showed that alkali-resistant REFIOM are the best durability in every media

L'optimisation de la composition des vitrifiats de REFIOM en les rendant alcali-résistants en vue de leur conférer une bonne durabilité chimique en milieu alcalin pour être ensuite utilisés dans les matrices cimentaires a été étudiée. La méthodologie suivie consiste à étudier le comportement à la lixiviation en mode statique de verres modèles alcali-résistants de type CEMFIL et de vitrifiats de REFIOM auxquels on a rajouté SiO2, Na2O et ZrO2 pour leur conférer un caractère alcali-résistant. Les tests de lixiviation menées à 90°C et à différents temps (de 6 heures à 28 jours) ainsi que les autres techniques d'analyse chimique (ICP-AES, MEB-EDS, SIMS, ERDA, RBS, PIXE) sur ces verres ont montré que ce sont les vitifiats de REFIOM dont la composition a été optimisée qui présentent la meilleure durabilité chimique quelque soit le pH

MSc (Microbiology) / Department of Microbiology / Background: The high on-going incidences of infectious diseases, specifically those caused by multi-drug resistant bacteria in the last decade has made it a necessity to investigate a variety of antimicrobial drug sources, such as plants. Medicinal plants have played a significant role in drug discovery for western pharmaceuticals recently and have also been used successfully by traditional healers and herbalists to treat various infectious diseases for centuries. Currently, a few medicinal plants are commercialized, reason being most medicinal plants phytochemicals have not been studied yet, although they have been traditionally used by healers. Due to the constant development of multi-drug resistance of bacteria to antibiotics, S. africana extracts can provide an opportunity to finding new antibacterial compounds that can be used as the foundation for formulating new antimicrobial drugs. Objectives: The aim of this study was to screen antibacterial activity of the crude extract and fractions of S. africana against multi-drug resistant bacteria and to also evaluate other biological properties. Methods: Preliminary screening of phytochemical constituents of S. africana and fractions was done using standard qualitative and quantitative methods. Antibacterial activity of the extracts was evaluated using the agar well diffusion method and the microdilution assay against MDR bacterial strains. Antioxidant activities of the MCE and its fractions were measured by DPPH and reducing power assays, and the toxicity of the MCE and its fractions was tested on Vero cells using Cell-based high content screening assay. Results: Phytochemical analysis of the MCE and fractions obtained in this study showed the presence of phenolics, flavonoids, alkaloids, steroids, saponins, cardiac glycosides and terpenoids in most of S. african’s test samples. Fraction F1 and F2 both lacked alkaloids and saponins. The micro-plate dilution assay demonstrated that the MCE and all its fractions can inhibit the growth of all selected MDR bacterial strains tested against at different concentrations (0.1mg/ml to >12.5mg/ml), wherein the lowest MIC averages were obtained from fractions F3 and F6, with 0.59 mg/ml and 0.71 mg/ml MIC averages respectively. Contrary to the micro-plate dilution assay, the well diffusion assay demonstrated that MCE and all its fractions were not active against all the selected MDR bacterial strains tested against, as no inhibition was shown against the growth of K. pneumonia by any of S. african’s test samples. For DPPH assay, the IC50 of S. african’s test samples ranged between 0.01 ±0.34 mg/ml to 0.62 ± 0.05 mg/ml, whiles for the reducing power assay, EC50 measured ranged between 0.61 ± 0.01 mg/ml and 11.30 ± 0.04 mg/ml. The MCE and fraction F2 exhibited the highest toxicity to Vero cells. Conclusion: The MCE and fractions of the plant S. africana have antibacterial activity against MDR bacterial strains, beneficial biological properties and contains potential antibacterial compounds that may be valuable in the discovery of new potential drugs for treatment of infectious diseases / NRF