Browsing by Author "Vuai Said A. H."

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    Cation–P Interactions Drive Hydrophobic Self Assembly and Aggregation of Niclosamide in Water†
    (Royal Society of Chemistry, 2021-09-13) Vuai Said A. H.; Sahini, Mtabazi G.; Onoka, Isaac.; Kirurib, Lucy W.; Shadrack, Daniel M.
    The beneficial medicinal effects of niclosamide have been reported to be hampered by poor aqueous solubility and so a higher concentration dosage is required. In this work, we have studied the aggregation properties of niclosamide in water by varying the number of monomers. We have employed all-atom classical molecular dynamics simulation in order to explore such properties. The equilibrium structure exists in an aggregated state with structural rearrangements of the stacking units. Niclosamide monomers tend to form clusters in an orderly manner and tend to aggregate in parallel and antiparallel orientations of the phenyl rings as the monomers are increased in number from 4 to 9. Upon increasing the size from 9 to 14, and from 49 to 150, a considerable dominance of the metastable parallel arrangement is observed, resulting in the formation of a closely packed cluster with hydrophobic contacts. The metastable conformation self-arranges to a T-shape before forming a stable planar antiparallel displaced conformation. The aggregated p–p parallel and cation–p antiparallel clusters in water exist in a b-conformer. We further observed that formation of a stable cluster aggregate entails the formation of an intermediate metastable cluster that disperses in solution forming a large stable cluster. We also discovered that movement of the water is faster in less aggregated clusters and as the cluster size increases, the mobility rate becomes much slower.
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    Periodic Flooding and Land Use Effects on Soil Properties in Lake Victoria Basin
    (Academic Journals, 2011-09-19) Nancy Mungai W.; Njue A. M.; Abaya Samuel G.; Vuai Said A. H.; Ibembe John D.
    Frequent periodic flooding and land use changes taking place in the Lake Victoria basin (LVB) in east Africa may cause soil deterioration and further exacerbating food insecurity. Surface (0 to 20 cm) soil samples were collected at three locations along Sondu Miriu (Kenya) and Simiyu-Duma (Tanzania) rivers. Samples were collected from fields that were periodically flooded (1-28 d) and those that never flood, either under grass or crops. Samples were analysed for soil texture, organic carbon (OC), total nitrogen (TN), pH, extractable phosphorus (P), exchangeable potassium (K) and -glucosidase activities. -glucosidase activities, clay and P contents were higher in some of the soils that flood, while OC, exchangeable K and sand contents were lower at P< 0.05 in flooded soils. Observed differences account for 11% of comparisons in the two river basins. Soils under grass had higher -glucosidase activities and silt content but lower sand content than cultivated soils in 6% of samples in the two basins. However, conversion of natural ecosystems to grassland or cropped lands resulted in a 17 to 113% reduction in OC, TN, and exchangeable K in Sondu, and a 129% decline in TN in Simiyu. Soil properties exhibited clear but different patterns from upstream to downstream in the two basins. OC, TN, clay and -glucosidase activities were higher in Sondu upstream, while OC, TN, extractable P and exchangeable K were lower in Simiyu upstream. Observed difference across each basin underscore the importance of inherent soil characteristics in influencing soil properties compared to short-term flooding or short duration changes in land use.