Chemistry

Synthesis and characterization of phosphate Geopolymers of pumice and medical waste incinerator fly ash fractions: methylene blue adsorption and recyclability studies.

2025-01-01T00:00:00Z

Synthesis and characterization of phosphate Geopolymers of pumice and medical waste incinerator fly ash fractions: methylene blue adsorption and recyclability studies. ONYANGO, Collins Odongo Methylene blue (MB) is a toxic dye used mainly in the textile industry as a fabric colourant. Medical waste incinerator fly ash (MWI-FA) is a toxic waste with unresolved disposal challenges. The general objective of this study was to synthesize composite geopolymers of pumice with fractions of MWI-FA, and to evaluate the effect of the fractions on the physicochemical and adsorptive properties of the geopolymers for the abatement of MB from water. Four composites, GP-0, GP-10, GP-20 and GP-30 were synthesized from pumice, substituted with fractions of 0, 10, 20 and 30% w/w of MWI-FA respectively, followed by a phosphoric acid activation. The adsorptive performance of the geo-composites was evaluated for the abatement of MB, assessing the effect of the MWI-FA fractions on this performance. Material characterization revealed the formation of new functional groups such as –Si-O-P-O-T- and -Si-O-P- bonds, confirming geopolymer formation, and the evolution of new mineral phases tobermorite and heulandite, attributable to the incorporation of MWI-FA. Some physicochemical dissimilarities resulting from the incorporation of the fractions of the adjuvant were also observed. Furthermore, geopolymerization with 10% MWI-FA increased the specific surface area (SSA) of the precursors, but this diminished proportionately with increased MWI-FA fractions. The adsorption kinetics was best described by the pseudo-second order kinetic model, with the rate constant, (K2), increasing linearly with the rate of incorporation of MWI-FA. Thermodynamically, the results show that the adsorption process was enthalpy-driven, exothermic (negative ΔH values) and a physisorption process (ǀΔHǀ and Ea < 40 kJmol-1). Gibbs free energy, ΔG < 0, suggested a spontaneous and feasible adsorption process, with the adsorption spontaneity increasing linearly with temperature. The equilibrium data was best described by the Sips isotherm model. The maximum adsorption capacities of the geopolymers, ~31 mg/g, were indistinguishable despite the decline in SSA with increase in MWI-FA. MWI-FA provided new energetically favorable adsorption sites compensating the diminished SSA. Hot water showed good potential to regenerate the spent geopolymers twice, with up to 76.9% recovery. The adsorption of MB diminished considerably under saline conditions. The composite geopolymers provide an acceptable strategy for stabilization of up to 30% MWI-FA without compromising their chemical stability or adsorptive properties. The study recommends the incorporation of up to 30% MWI-FA, with sufficient aluminosilicate composition, in the pumice-based phosphate geopolymers for the sequestration of MB as a dual waste management strategy. Masters's Thesis

Temperature and composition effects on charge transport in pbdb-t-2cl: ieico-4f solar blends for next-generation organic photovoltaics

2025-11-12T00:00:00Z

Temperature and composition effects on charge transport in pbdb-t-2cl: ieico-4f solar blends for next-generation organic photovoltaics AKINYI, Elizabeth Odunga Organic photovoltaics (OPVs) based on non-fullerene acceptors (NFAs) have achieved ~18 % power-conversion efficiency, benefitting from superior thermal stability and broader absorption compared to fullerene acceptors (FAs). Despite these advances, the performance and stability of OPVs remain strongly influenced by blend composition and temperature, which affect charge transport and recombination. The main objective of this study is to investigate the influence of blend composition on optical, morphological, electrical properties and the effect of temperature variation on photoluminescence properties of PBDB-T-2CL: IEICO-4F for organic photovoltaics application and the specific objectives are; To investigate the optical and morphological of pristine PBDB-T-2CL and IEICO-4F thin films, to analyze the effect of IEICO-4F dopant on optical, morphological, and electrical properties of PBDB-T-2CL: IEICO-4F thin films and to evaluate the effect of temperature variation on photoluminescence properties of PBDB-T-2CL: IEICO-4F thin films. Specifically, the bulk heterojunction (BHJ) structure formed by donor-acceptor blend was analyzed using temperature-dependent PL to evaluate charge transfer dynamics across different blend ratios. Spin coated thin films were characterized using ultraviolet-visible (UV-Vis) spectroscopy, atomic force microscopy (AFM), PL spectroscopy and four-point probe measurements. Data analysis was performed using Origin software. The UV-Vis spectra revealed that PBDB-T-2CL exhibited a primary absorption peak near 620 nm, while IEICO-4F showed complementary absorption at ~ 860 nm and the blends forms four characteristic peaks at 568 nm, 620 nm, 817 nm and 833 nm effectively broadening the spectra and enhance photo harvesting. Temperature – dependent PL analysis showed suppressed radiative recombination and enhanced charge transfer with increasing annealing temperature, particularly in the blends. AFM measurements indicated strong morphology dependence: pristine PBDB-T-2CL film were smooth (root mean square ≈2.28 nm), IEICO-4F film were rougher (root mean square ≈5.18 nm), while the optimized 70:30 blend exhibited the finest morphology (root mean square ≈1.398 nm ). These morphology features translated into distinct device characteristics. The 50% IEICO-4F composition achieved the highest PCE of 2.12 %, with a short circuit current density (Jsc) of 9.6 mA/cm2, open circuit voltage (Voc) of 0.60 V, and fill factor (FF) of 36 %. In contrast donor-acceptor blends showed reduced efficiencies (≤1.70 %), correlating with roughness and recombination losses. In conclusion, the study demonstrates that broad optical absorption, efficient charge transfer, favorable nanoscale morphology, and stable photovoltaic response are the key thin film properties supporting high efficiency bulk heterojunction and flexible thin film OPV devices. These finding proved experimental evidence that fine donor-acceptor morphology is crucial to balance charge generation and transport, offering insights for the design of next generation OPVs. Master's Thesis

Surveillance and influence of application rates and post-application harvest durations on imidacloprid residue levels in Solanum lycopersicum fruits of Kimira-Oluch, Kenya

2025-11-12T00:00:00Z

Surveillance and influence of application rates and post-application harvest durations on imidacloprid residue levels in Solanum lycopersicum fruits of Kimira-Oluch, Kenya ACHIENG, Roselyne Omondi Tomato, (Solamun lycoperscicum) is a widely grown and consumed fruit-vegetable. It is susceptible to pest infestations that is usually controlled by pesticides use, especially imidacloprid (IMI), whose residues negatively impacts the environment and human health. Despite its low toxicity to humans, IMI bioaccumulation causes human health issues. Although widely used in Kenya, IMI use was banned by EU since it contributed to bee population decline. Even though exported agricultural products are often screened to meet international market limits, it is not practiced for locally consumed produce, this may lead to consumer exposure and subsequent poisoning. There is a need to compare IMI residue levels in local produce with EU/Codex-MRL to ensure safety and conformation to required standards. Kimira-Oluch Smallholder Farm Improvement Project (KOSFIP) is an irrigation scheme producing tomatoes in Homa Bay County. Farm gate tomatoes from KOSFIP have not been evaluated for safety and/or if they meet the EU/Codex-MRLs. It is not documented if KOSFIP farmers observe Good Agricultural Practices (GAPs) or IMI residue levels at farm-gates meet EU/Codex-MRL. Sometimes farmers use higher IMI concentrations and/or fail to observe minimum pesticide post application period (PAP). IMI recommended rate and PAP used at KOSFIP were developed in different environments. It is not known whether they suit the KOSFIP environment and/or influence residual IMI. This study assessed IMI residue levels in tomatoes at farm-gates and compared the levels with EU/Codex limits; determined influence of application rate and PAP on residue levels in KOSFIP tomatoes. Cross-sectional survey using random sampling method was used to sample tomato farmers applying imidacloprid. A 4x5 split-plot design in RCBD layout replicated thrice was used to determine effects of rates (0, 2.5, 5, 7.5 g/20L) and PAP (0, 2, 4,7,10 days) on IMI levels. Samples were prepared by QuEChERS method, residues analysed using LCMS/MS and data subjected to ANOVA using GenStat program. Results were compared with EU (0.3 mg/kg and Codex (0.5 mg/kg) limits. Approximately 62.9% of farm-gate samples had residues below EU-MRL and 92.9% below Codex-MRL, demonstrating most farmers were observing GAPs. Imidacloprid residues increased (p≤0.05) with high application rates and short PAP. Rates higher than the recommended had residue levels above EU-MRL. Recommended rate of application (5 g/20L) and PAP (3 days) are suitable for use in KOSFIP. Continued use of IMI at KOSFIP should be done according to GAPs and regular monitoring of GAPs implementation be prioritized. Master's Thesis

Effect of curing temperature on geopolymers from solid waste incinerator fly ash for removal of bromocresol green dye from water: synthesis, kinetics and thermodyanimics

2024-01-01T00:00:00Z

Effect of curing temperature on geopolymers from solid waste incinerator fly ash for removal of bromocresol green dye from water: synthesis, kinetics and thermodyanimics OWINO, Eugene Kevin Bromocresol green (BCG) dye is extensively used in the textile and medical fields. However, the excessive and uncontrollable usage of this dye has resulted in contamination of water sources, endangering both aquatic life and human beings, hence the need for an urgent remedy. Geopolymers have been proposed as suitable adsorbents for removing various water pollutants due to their excellent adsorption capabilities compared to conventional treatment methods. The adsorption rates and capacities of geopolymers have been shown to depend on their structural, morphological, and compositional characteristics, which can be controlled by preparation conditions. Nonetheless, there is no available data on the influence of curing temperature on the structural, morphological and composition of solid waste incinerator fly ash (SWI-FA) based geopolymer adsorbents. Furthermore, although SWI-FA geopolymer-based adsorbent has been used in the removal of cationic, methylene blue dye from water, no study has reported on its interaction with an anionic dye. Thus, the aim of this work was to determine the suitability of SWI-FA for geopolymer production, and the effect of curing temperature on the composition, structural, morphological, and adsorption characteristics of SWI-FA based geopolymers for the removal of bromocresol green (BCG), an anionic dye from water. Alkali-activated SWI-FA geopolymer samples (GP30, GP50, GP70 and GP90) were prepared at curing temperature of 30 ° C, 50 ° C, 70 ° C, and 90 ° C, respectively. The SWI-FA and the geopolymers were characterized for morphology, elemental composition, functional groups, crystalline phases, and pH of point of zero charge (pHPZC). The effect of adsorption parameters namely initial dye concentration, pH, contact time, and temperature were examined. The EDS analysis results indicated presences of C, O, Al, Si, and Ca elements in SWI-FA, GP30, GP50, GP70, and GP90, and a variation in Si/Al ratio in the geopolymers as curing temperature was increased. The SEM results revealed morphological changes with curing temperature. The FT-IR analysis revealed a shift in the main band at 991 cm-1 due to asymmetric vibrations of Si-O-T (T=Al/Si) in SWI-FA to lower wavenumber in the geopolymers. The XRD analysis confirmed changes in crystalline phases of the geopolymers while the pHPZC of the geopolymers remained unchanged at 6.8. The kinetic data were best described by the pseudo-second order model (R2>0.99) while Langmuir isotherm model presented the best fit to the equilibrium data. From Langmuir isotherm model the maximum adsorption capacity for BCG dye uptake increased with curing temperature from 41.70 mg/g to 515.5 mg/g for GP30 and GP90, respectively. The thermodynamic parameters; namely enthalpy (ΔH ), Gibbs free energy (ΔG ), entropy (ΔS ) and activation energy (Ea) indicated that BCG adsorption processes is spontaneous, exothermic, physical (Ea kJ/mol and ΔH kJ/mol) and enthalpy-driven. The adsorption mechanisms controlling BCG adsorption onto the geopolymers included hydrogen bonding and strong electrostatic interactions. The results of this present study highlighted the opportunity of recycling SWI-FA and the potential of the synthesized SWI-FA based geopolymer adsorbents in effectively treating BCG dye-contaminated water. Master's Thesis

Inhibition of α-amylase and α-glucosidase by alkaloids and phenolics from stem bark of Zanthoxylum chalybeum and Zanthoxylum gilletii

2024-01-01T00:00:00Z

Inhibition of α-amylase and α-glucosidase by alkaloids and phenolics from stem bark of Zanthoxylum chalybeum and Zanthoxylum gilletii OTIENO, Kevin Yamo Diabetes prevalence is on the rise with conventional drugs either being unaffordable, unavailable or having undesirable side effects. The plants Zanthoxylum chalybeum (ZC) and Zanthoxylum giletii (ZG) are reported for management of diabetes by local communities. Root bark and stem bark extract from two plants has shown in vivo anti-diabetic activity against alloxan streptozotocin–induced diabetic rats. Two benzophenanthridine alkaloids and a phenolic were established to inhibit the α-amylase and α-glucosidase activities. Based on the molecular variations of benzophenanthridine alkaloids and phenolics, the inhibitory effects of only three compounds were not predictive enough for the trends of inhibition against α-amylase and α-glucosidase. Molecular structural requirement including enzymatic inhibitory modes of alkaloids and phenolics from Zanthoxylum plants was also unknown. Further research to establish the structural characteristics exhibiting the enzymatic inhibition of these compounds is thus necessary to provide insight into their potential in hyperglycemic management. Therefore, the study intends to determine the structures of these compounds, their relative α-amylase and α-glucosidase inhibitory activities, and kinetic modes of inhibition of the active molecule. The stem bark of ZC was collected from Homa Hills, Kenya and stem bark of ZG from Kakamega forest, Kenya. Both the samples were air dried, ground into fine powder followed by acid-base alkaloid extraction comprising of 25% v/v of aq.NH4OH: ethyl acetate-petroleum ether: 2% v/v H2SO4; chloroform fractionation into alkaloid and non-alkaloids extracts. The fractions were subjected to chromatographic separations then characterization of the pure isolates using mass spectrometry, NMR, and UV-vis spectroscopic techniques. Eleven compounds were isolated: six alkaloids {Norchelerythrine (9), Phenanthridine A (42), chalybemide A (39), chalybemide B (40), chalybemide C (41) and skimmianine (21); two phenolics {2,3-epoxy-6,7-methylenedioxy coniferyl alcohol (10) and sesamine(46})} from Z. chalybeum. Whereas Z. gilettii yielded six compounds: four alkaloids {9, 42, Zanthocapensine (43), Zanthoamide D (45)}; and two phenolics {Zanthocapensol (44) and sesamine (46)}. Ten compounds showed inhibitory activities against α-amylase and α-glycosidase in the range of IC50 = 43.22-49.36 μM which had no significant difference (P > 0.05) relative to acarbose (IC50 = 42.67, 44.88) following in vitro bioassay by Worthington Enzyme assay protocols except sesamine (IC50 = 54.67, 54.77) which showed lower activity. The kinetic analysis based on Lineweaver-Burk plots {1/velocity vs 1/[Substrate] at constant [Inhibitor] (sample compounds)} established modes of inhibition and on each kinetic mode, Dixon plots {1/velocity vs [Inhibitor] at constant [Substrate]} were used to establish the respective enzymatic dissociation constants (Ki). Compound 10 showed competitive inhibition with Ki of 5.54 and 17.21 µM as acarbose (Ki = 6.14 and 22.40 µM) against α-amylase and α-glucosidase, respectively. Alkaloids 9, 21, 42, and 43 showed mixed modes of inhibitions (Ki ranges 2.74-3.10 µM and 4.73-9.17 µM) in α-amylase and α-glucosidase enzymes, respectively. Compounds with amides functionality 39, 40, 41, 45 showed non-competitive inhibition (Ki = 11.05-26.69 and 17.56-44.58) against α-amylase and α-glucosidase, respectively, except compound 40 which showed uncompetitive inhibition (Ki = 44.58 µM) against α-glucosidase same as 44 (Ki = 26.28 and 20.62 µM). Compounds showing competitive inhibition similarly exhibited stronger binding (lower Ki values) to the enzymes followed by mixed inhibitors and noncompetitive modes while uncompetitive inhibitors showed the highest Ki. Compounds 10, 9, 21, 42 and 43 exhibited good activity against α-amylase and α-glucosidase thus were considered as lead compounds for management of hyperglycemia. The study offers guidance for future investigations into drug discovery using these kinds of molecular templates. Master's Thesis

Optimizing bio-ethanol production from sweet sorghum stalk juice using Saccharomyces cerevisiae, finger millet malt and sorghum malt by taguchi method

2024-01-01T00:00:00Z

Optimizing bio-ethanol production from sweet sorghum stalk juice using Saccharomyces cerevisiae, finger millet malt and sorghum malt by taguchi method OKOTH, Dolphene Adhiambo Bio-ethanol is a viable alternative source of energy because it is renewable and environmentally friendly. However, the cost of its production remains prohibitive due to the high cost of feedstock, more so, food insecurity is caused if food crops are used. Studies on the use of sweet sorghum stalk juice for bio-ethanol production are ongoing due to its adaptability to different climatic and environmental conditions coupled with its high ability to accumulate high concentration of fermentable sugars within its stalk. Most of these fermentations are carried out using Saccharomyces cerevisiae as the main yeast which is obtained industrially. However, due to high cost of producing industrial yeast for bio-ethanol production, there is need to establish an alternative source of yeast that would be of low cost but of good quality and efficient in bio-ethanol production. The use of fossil fuels causes environmental pollution, adverse human health effects and high cost of production therefore there is an urgent need to produce bio-ethanol which is a cleaner alternative source of fuel. The objectives of this study were to find: the best sweet sorghum variety with the highest °Brix, optimum bio-ethanol production temperature, pH, yeast to substrate ratio and reaction time, compare the effectiveness of Saccharomyces cerevisiae, finger millet malt and sorghum malt as sources of enzyme for bio-ethanol production and finally characterize the bio-ethanol produced in terms of calorific value, pH, density and flame test. Five sweet sorghum varieties namely: IESV 92001 DL (V1), NTJ (V2), 15233 IESV (V3), 92008 DJ (V4) and IESV 92028 DL (V5) were planted at Jaramogi Oginga Odinga University of Science and Technology experimental farm. °Brix content of their stalk juice was determined using a digital refractometer (Model MA871, Milwaukee Co. Ltd., Romania) at the 11th to 16th week after sowing. The highest °Brix for all the genotypes, indicated by ANOVA, was registered at the 15th week where V1 had the highest °Brix of 22.07 (P≤𝟎.𝟎𝟓). It was then harvested for bio-ethanol production. Fermentation factors were optimized using L16 (44) Taguchi approach. The optimal conditions were temperature of 30 ℃, 36 hours, pH 5 and yeast to substrate ratio of 5 g/L using Saccharomyces cerevisiae while optimal conditions of pH 5, temperature of 35 ℃, 48 hours and yeast to substrate ratio of 5 g/L on using sorghum malt finally with finger millet malt the optimal conditions were yeast to substrate ratio of 5 g/L, pH 5, 48 hours and temperature of 30 ℃. Kinetics of the fermentation reaction for Vmax and Km were 0.35 g/L/h and 12.56 g/L respectively using finger millet malt, while a Vmax and Km of 0.34 g/L/h and 14.09 g/L obtained for sorghum malt and a Vmax and Km of 0.69 g/L/h and 13.96 g/L with Saccharomyces cerevisiae. Fermentation of sweet sorghum stalk juice with the 3 sources of enzyme followed Michaelis Menten model. Both the optimized and kinetic parameters were within reported literature values and therefore results show that finger millet malt has a greater potential, as a substitute yeast source in application in bio-ethanol production industries. In terms of characterization of the bio-ethanol produced the calorific value, pH, density and flame test were found to be 8740±29 kcal/kg, 6.3±0.2, 0.895±0.076 g/cm3 and a blue flame produced respectively. The bio-ethanol produced burnt with a hot blue flame hence a viable alternative fuel for domestic cooking. This information is important to policy makers in designing ways that can help implement it as a clean source of cooking fuel and at the same time create employment to the people living in the rural areas. Master's Thesis

Synthesis and characterization of municipal waste incinerator fly ash based Geopolymers for the removal of Endosulfan from water: kinetics, isotherms, and thermodynamics

2023-01-01T00:00:00Z

Synthesis and characterization of municipal waste incinerator fly ash based Geopolymers for the removal of Endosulfan from water: kinetics, isotherms, and thermodynamics LUTTAH, Isaac Endosulfan is a broad spectrum organochlorine insecticide which acts as a contact poison for controlling a wide variety of insects. However, extensive and uncontrolled use of insecticides leads to water pollution. Conventionally, adsorption onto activated carbon is used to remove water pollutants from influent wastewater. A suitable adsorbent must be cheap, possess high adsorption capacity, fast adsorption kinetics and recyclable among other properties. Geopolymers are emerging low-cost and efficient adsorbents for removal of various contaminants from water. The performance of the geopolymers varies with both sorption conditions and adsorbent structural and textural characteristics, which are controlled by several factors such as; the precursor material and the preparation conditions. While silicate to NaOH ratios affect mechanical properties of geopolymers for construction purposes, the impact of silicate to NaOH ratios on the adsorptive performance of geopolymers is unknown. Furthermore, although research has been done on remediation of pesticides from water using various adsorbents, no article has reported the use of solid waste incinerator fly ash MWFA-based geopolymers especially on their synthesis and/or application as adsorbent for endosulfan removal from water. The present work investigated the adsorption of endosulfan on alkaline activated geopolymers, synthesized from MWFA. Since there is no reported theory for predicting the geopolymer sorption capacity and adsorption rate based on precursor materials and silicate to NaOH ratios conditions, this leaves a clear gap in our understanding of the role of these factors. The objective of this study was to synthesize MWFA-based geopolymers and evaluate the effect of sodium silicate to NaOH ratio of the activator solution on morphology, chemical composition, and adsorptive performance (adsorption capacity and mechanism) in batch-mode. Alkali-activated MWFA-based geopolymers, GPA, GPB, and GPC, were synthesized using 0.17, 0.21 and 0.24 sodium silicate to sodium hydroxide mole ratios, respectively. The geopolymers were applied in the removal of endosulfan from water. The adsorbents were characterized by XRD, SEM-EDX, and FTIR. Variation of sodium silicate to sodium hydroxide mole ratios resulted in morphologically distinguishable geopolymers with different compositions. Adsorption experiments were done at different parameters such as initial endosulfan concentration, contact time, pH, geopolymer dosage and temperature. The adsorption equilibrium data were best described by Langmuir isotherm. The maximum adsorption capacities increased with an increase in sodium silicate to sodium hydroxide mole ratios in the order 1.872, 15.899, 16.970, and 20.010 mg/g for MWFA, GPA, GPB, and GPC, respectively. The kinetic data were best described by the pseudo-first-order model wherein the adsorption rate (k1) was independent of the sodium silicate to sodium hydroxide mole ratio and the geopolymer composition. The thermodynamic parameters, that is enthalpy (∆H > 0), Gibbs free energy (∆G < 0), entropy (∆S > 0), and activation energy (Ea > 0) show that the processes were endothermic, spontaneous, physical (Ea and ∆H < 40 kJ/mol) and entropy-driven. Alkalination was beneficial since the geopolymers had a higher adsorption capacity (~8-10 times) and affinity for endosulfan (~30 times) than the precursor material (MWFA). The adsorption mechanism entailed electrostatic interactions and hydrogen bonding. Increase in sodium silicate to NaOH ratio increases the adsorption capacity of the geopolymers for endosulfan. The MWFA-based geopolymers prepared with high silicate to NaOH ratios are recommended as alternative high adsorbing materials for wastewater treatment and a strategy for the valorization of MWFA. Master's Thesis

Antimicrobial activities of extracts and isolates from Senna didymobotrya flowers.

2023-01-01T00:00:00Z

Antimicrobial activities of extracts and isolates from Senna didymobotrya flowers. ATIENO, Hellen Onyango The emerging trends in pathogenic microorganisms becoming resistant to available antibiotics coupled with the evolution of new strains of pathogens causing diseases, is a major concern to the global health community and this requires urgent remedy. Prolonged treatment with conventional antimicrobial drugs has led to their toxicities among patients and therefore, for effective treatment of diseases caused by pathogenic microbes, search for new pharmaceuticals or some potential sources of novel drugs are necessary. Medicinal plants commonly used by various communities could be potential sources for bioprospection to help in the fight against this menace. This study focused on evaluating the antimicrobial activity of Senna didymobotrya flowers (Caesalpiniaceae), a plant widely used in Kenyan folklore medicine to manage bacterial and fungal infections. In parts of Kisumu, the flowers of the plant are used to manage diarrhoea and itching of the skin. Although the flowers are traditionally used by herbalists to manage microbial infections, very little work has been done to evaluate the efficacy of the extracts against pathogenic microbes. In addition, compounds responsible for the antimicrobial activity in the flowers have not been isolated and characterized. The objectives of this study were to evaluate the extracts and isolated compounds from flowers for antifungal and antibacterial activities. The dry and pulverized flowers of the plant were sequentially extracted with n-hexane, ethyl acetate and methanol. The methanol extract significantly (P≤0.05) inhibited M. gypseum (MIC 3.9µg/ml), T. mentagrophyte (MIC 7.8µg/ml), K. pneumoniae and C. albicans (MIC value 31.3 µg/ml each). This was followed by ethylacetate extract which gave moderate results against M. gypseum (MIC 15.6µg/ml), S. faecalis, B. anthracais, C. albicans and T. mentagrophyte (MIC value 62.5 µg/ml each). n-Hexane extract afforded MIC values ranging between 125 µg/ml to over 250 µg/ml. Fractionation of the various extracts led to the isolation of twelve compounds whose structures were determined using physical and spectroscopic methods as well as comparison with literature data. The compounds were: chrysophanol (7), physcion (9), emodin (10), quercetin (253), β-sitosterol (302), stigmasterol (303), lupeol (323), betulinic acid (324), oleanolic acid (335), 4’, 5-dihydroxystilbene-3-O-glucoside (336), 5-hydroxyflavone (337) and 7-hydroxyflavone (338). All the isolated compounds were screened for antimicrobial activities.The most active metabolite was emodin which gave a MIC in the range 15.6-250 µg/ml against all the microorganisms tested except E. coli (MIC >250 µg/ml). 7-Hydroxyflavone also afforded good results by displaying MIC values in the range 31.3-250 µg/ml against all microorganisms that were tested. The least active metabolites were β-sitosterol and stigmasterol which were observed to show mild activities against S. aureus (MIC 250 µg/ml). Activities of the three extracts and isolated compounds against the tested pathogenic microbes were significantly (P≤0.05) lower compared to the activities exhibited by kanamycin and fluconazole which were used as standards against bacteria and fungi, respectively. This study has authenticated the traditional use of S.didymobotrya flowers in the management of bacterial and fungal infections. It has also identified the individual compounds responsible for the activities. Compounds that exhibited high antimicrobial activities such as emodin, and 7-hydroxyflavone may be developed into formulations to be used as antimicrobials. Master's Thesis

Phytochemical evaluation of Ocimum kilimandscharicum GUERKE, Gnidia subcordata MEISN AND Annona mucosa jacq leaves for secondary metabolites and their insecticidal activities against Sitophilus zeamais and Prostephanus truncatus.

2023-01-01T00:00:00Z

Phytochemical evaluation of Ocimum kilimandscharicum GUERKE, Gnidia subcordata MEISN AND Annona mucosa jacq leaves for secondary metabolites and their insecticidal activities against Sitophilus zeamais and Prostephanus truncatus. MULIANGA, Albert Makenzi Global food security of which maize is a major component is threatened by food loss due to storage insect pests. Sitophilus zeamais and Prostephanus truncatus cause stored maize losses of 20% world wide and 45% in Africa. Synthetic insecticides though effective in control of insect pests, insect resistance and the adverse side effects associated with the insecticides calls for search of effective and safe botanical insecticides. Ocimum kilimandscharicum, Gnidia subcordata and Annona mucosa leaves have been used traditionally to control insect pests. Efficacy of their crude extracts and active principles occasioning their uses are however not documented. This work evaluated insecticidal activities of the plants’ leaf extracts against S. zeamais and P. truncatus, isolated and characterised pure isolates and evaluated the pure isolates for their insecticidal activity against the two insects. Powdered plant leaves were separately sequentially soaked in n-hexane, ethyl acetate and methanol then filtered, concentrated and subjected to column chromatography fractionation with eluents of differing polarities and then thin layer chromatography. Structural elucidation of isolated compounds was done using physical and spectroscopic methods including NMR, IR, UV-VIS, mass spectrometry and comparison with literature data. Extracts and pure isolates were assayed for toxicity and antifeedant activities against S. zeamais and P. truncatus. Deltamethrine and azadirachtin were used as positive controls. Gnidia subcordata methanol extracts exhibited the highest contact toxicity and antifeedant activities against S. zeamais: LC50 = 27.03 μg/mL, AFI50 = 20.47 μg/mL and P. truncatus: LC50 =22.55 μg/mL, AFI50 = 20.99 μg/mL, which compared favourably with activities of the positive controls. Gnidia subcordata yielded β-amyrin acetate (199), 3β-hydroxy-11-oxoolean-12-ene (200), dihydronitidine (201), dihydrochelerythrine (202), gedunin (203), obacunone (204), nagilactone (205), quercetin (140), kaempferol-3-O-β-galactoside (206) and 4', 5-dihydroxystilbene-3-O-β-glucoside (207). n-Eicosanol (208), friedelin (209), stigmasterol (6), lupeol (49), 2α-hydroxy-3-oxodammar-20, 24-diene (210), 2α, 3β-dihydroxy dammar-20, 24-diene (211), chrysin (212), apigenin (144), fisetin (213), quercetin (140) and apigenin-7-O-neohesperidoside (214) were isolated from Ocimum kilimandscharicum. Annona mucosa yielded; α-amyrin acetate (215), β-sitosterol (96), 3α, 24-diacetoxy-12-oleanene (216),3-oxo-11β-hydroxyurs-12-ene (217), (3R,20S)-3-acetoxy-20-hydroxydammar-24-ene (218), 3β-acetoxy oleanolic acid (219), 3β-acetoxytirucallic acid (220), quercetin (140), oleanolic acid (4), quercetin 3-O-β-D-arabinoside (221) andquercetin-3-O-β-D-glucoside (222).Compounds 210, 211 and 216 are new. Among the isolated compounds, 203 had the highest contact toxicity activities LC50 15.68 and 16.99μg/mL while 222 had the highest antifeedant activities AFI50 14.93and 16.84 μg/mL., against S. zeamais and P. truncatus respectively, which compared well with activities of the positive controls. This study has validated the traditional use of the plants in stored maize protection against insect pests. It has also identified the individual compounds responsible for the activities. These compounds can be developed into formulations individually or as mixtures to control S. zeamais and P. truncatus in maize. PhD Theses

Residual diazinon in brassica oleracea var. Acephala and influence of application conditions on its levels in Kimira-oluch smallholder farmers improvement project, Kenya

2021-01-01T00:00:00Z

Residual diazinon in brassica oleracea var. Acephala and influence of application conditions on its levels in Kimira-oluch smallholder farmers improvement project, Kenya OROMO, George Odoyo Use of pesticides in agriculture often causes residual effects on crops with potential health risks. Diazinon, a synthetic pesticide whose dietary exposures have been associated with human health impacts is popular in the production of Brassica oleracea var. acephala at Kimira-Oluch Smallholder Farmers Improvement Project (KOSFIP), Kenya. Diazinon has relatively long pre-harvest interval (PHI) which farmers may not be observing. Levels of diazinon residues and associated health risks in farm-gate Brassica oleracea var. acephala are unknown. There is no available data on how application conditions influence the residue levels. This study quantified the residual diazinon levels in farm-gate baskets of the vegetable; influence of rate of application on residual levels at PHI; and influence of post-application duration on residual levels at different application rates. Cross-sectional survey based on purposive snowball sampling identified 40 of 45 farms from which samples were collected in triplicate. Randomized complete block design arranged in 5x8 split-plot controlled experiments were used to determine the influence of diazinon application rates and PHI conditions on residual levels. Main treatments were 0.0000, 0.6125, 1.2500, 1.8625 and 2.5000 litres ha-1, respectively, split for 0, 5, 10, 13, 16, 18, 20 and 21 days post application harvesting. Samples were prepared using QuEChERS method, and subjected to LC-ESI-MS/MS analysis. Farm-gate samples had residual diazinon levels (92.5%) of which 67.57% were above the Codex Maximum Residue Limits. Of the samples, 40% had Health Risk Index >1.0, higher than most previous studies. Malpractices against Good Agricultural Practices (GAPs) may be responsible for higher residual levels with consequent increased health risks to consumers. The results demonstrate the need for surveillance and increased farmer education to reduce diazinon residue levels in the farm-gate vegetables. Residual diazinon levels increased (P≤0.05) with increasing rates of application and were inversely proportional to increasing PHI in agreement with previous studies. Application rates ≥ 1.25 litres/ha required longer PHI than the labeled, suggesting that the recommended PHI is inappropriate for the vegetable in the study area. A review of PHI from 12 to 14 is recommended for rate of 1.25 litres/ha. The use of diazinon on Brassica oleracea var. acephala at KOSFIP should be discouraged and alternative pesticides be used according to GAPs.