Department of Chemistry

In vitro, ex vivo, and in silico studies of phytochemicals from the stem bark of Bischofia javanica

2025-09-10T13:49:05Z

In vitro, ex vivo, and in silico studies of phytochemicals from the stem bark of Bischofia javanica Awas, Erick Okoth; Midiwo, O.Jacob; Omosa, Leonidah Kerubo.et.al The stem bark extract of Bischofia javanica, used in traditional Kenyan medicine afforded nine compounds named, santin (1), ermanin (2), rhamnocitrin (3), kumatakenin (4), abyssinone V-4′-methyl ether (5), β-sitosterol (6), betulinic acid (7), friedelin (8) and 1-methyl-1,10-phenanthrolin-1-ium (9). Structural elucidation was performed based on spectroscopic and spectrometric analyses, and the data were compared with those reported in the literature. The natural origin of 1-methyl-1,10-phenanthrolin-1-ium (9) in the plant kingdom is reported here for the first time. Ermanin (2) showed selective in vitro antiplasmodial activity with IC50 = 0.05 μM, while 1-methyl-1,10-phenanthrolinium (9) exhibited potent antiplasmodial activity with IC50 values of 1.56 μM (in vitro), and 1.20 μM (ex vivo). Furthermore, molecular docking studies revealed that 1-methyl-1,10-phenanthrolinium (9) could be considered a potential lead compound for future antimalarial drugs.

Diazinon residues levels in farm-gate Brassica oleracea var. acephala of Kimira-Oluch smallholder farm improvement project, Kenya

2025-09-10T07:26:17Z

Diazinon residues levels in farm-gate Brassica oleracea var. acephala of Kimira-Oluch smallholder farm improvement project, Kenya Oromo, George Odoyo; Owuor, Philip Okinda; Kwach, Bowa; Otieno, Peter Diazinon insecticide, though associated with human health impacts, is popularly used in the production of Brassica oleracea var. acephala (kale) at the Kimira-Oluch Smallholder Farmers Improvement Project (KOSFIP), Kenya. Diazinon controls insect pests that lower quality and profitability of produce. The preharvest interval of diazinon in kale is 12 days which may not be observed by farmers with inadequate appreciation of Good Agricultural Practices (GAP). Since the extent of GAPs adoption at KOSFIP has not been evaluated, it remains unclear whether diazinon residues levels in kale of KOSFIP could be a health risk to the consumers. Diazinon residues levels and corresponding health risks in farm-gate kale at KOSFIP were determined. Cross-sectional survey based on snowball sampling identified 40 farms applying diazinon on the vegetable. Triplicate samples were collected from each farm for residue analysis, using the QuEChERS method, and LC-ESI-MS/MS analysis. Standard normal distribution function f(z) revealed 78% of farm-gate samples had detectable residual diazinon levels and 70% were above the Codex MRL of 0.05 mg/kg. Continued application of diazinon on kale at KOSFIP is exposing consumers to short-term health risks. Efforts must be intensified to ensure GAP are adopted. The estimated farm-gate samples with health risk indices for children and adults (HRIc and HRIA) >1.0 were 64% and 26%, respectively. The residual levels are therefore potential health risks to both children and adults. Farm-gate residual levels and resultant partial HRI were comparatively higher than findings of most previous studies. Inappropriate label PHI and malpractices against GAP may be responsible for high residual levels. There should be regular surveillance and trainings of farmers on GAP for sustainable production of kale in the Lake Victoria region. Use of diazinon on kale should be discouraged and intensive routine pesticide residue screening be enhanced for conventional vegetable produce. https://doi.org/10.1371/journal.pone.0310586

Effect of the extended π-surface and N-butyl substituents of imidazoles on their reactivity, electrochemical behaviours and biological interactions of corresponding Pt(II)-CNC carbene complexes: exploring DFT and docking interactions†

2024-11-12T15:48:09Z

Effect of the extended π-surface and N-butyl substituents of imidazoles on their reactivity, electrochemical behaviours and biological interactions of corresponding Pt(II)-CNC carbene complexes: exploring DFT and docking interactions† Onunga, O.Daniel; Jaganyi, Deogratius; Robinson, Ross; Mambanda, Allen In this study, we synthesised and characterised three C^N^C pincer (N-heterocyclic carbene)-type tridentate ligands, namely, 2,6-bis[(3-methylimidazolium-1-yl)methyl]pyridine dibromide (L1), 2,6-bis[(3-methylbenzimidazolium-1-yl)methyl]pyridine dibromide (L2) and 2,6-bis[(3-butylimidazolium-1-yl)methyl]pyridine dibromide (L3), and their corresponding six-membered chelates with Pt(II) to form PtL1–PtL3 complexes, namely, 2,6-bis[(3-methylimidazolium-1-yl)methyl]pyridinechloroplatinum(II) tetrafluoroborate (PtL1), 2,6-bis[(3-methylbenzimidazol-1-yl)methyl]pyridinechloroplatinum(II) tetrafluoroborate (PtL2) and 2,6-bis[(3-butylimidazol-1-yl)methyl]pyridinechloroplatinum(II) tetrafluoroborate (PtL3). Substitution kinetics using thiourea nucleophiles (tu, dmtu and tmtu), structural properties through theoretical DFT, biological interactions with DNA/BSA, electrochemical behaviors using cyclic voltammetry and docking simulations for Pt(II) C^N^C pincer complexes were investigated. The extended π surface of benzimidazole (PtL2) caused σ-donation in cis-Pt–C bonds, while N-butyl arms (PtL3) on the bis(3-methylimidazolium-1-yl)pyridine C^N^C pincer ligand had a steric influence on the labile ligand, leading to an increasing order of chloride substitution as follows: PtL3 < PtL2 < PtL1. The nucleophile's reactivity order is in accordance with its bulkiness, and the order is tu > dmtu > tmtu. Reactivity trends were justified by the trends in theoretical DFT data. Strong cis σ-donor ligands prevent the co-coordination of the spectator ligand. Large negative entropy of activation (ΔS#) and positive enthalpy of activation (ΔH#) support a limiting associative substitution mechanism. Biological interactions of PtL1–PtL3 with CT-DNA and BSA complexes were confirmed using spectroscopic and cyclic voltammetry (CV) titrations, and the data obtained established moderate-to-strong binding affinities. Complexes bind to CT-DNA mainly via the groove mode and to a lesser extent via intercalation, whereas they insert into the upper protein cleft of BSA. Electrochemistry results also established the groove binding mode of interaction, and −ΔG values affirmed the binding process as spontaneous. Molecular docking simulations of PtL1–PtL3 with CT-DNA and BSA corroborated with groove binding being the main binding mode.

Slowing the reactivity of dicyclometalated Pd (II) complexes through the 2, 6-bis (N-heterocyclic carbene) pyridine (C^ N^ C) non-leaving ligands: kinetic and computational study

2024-11-12T15:42:20Z

Slowing the reactivity of dicyclometalated Pd (II) complexes through the 2, 6-bis (N-heterocyclic carbene) pyridine (C^ N^ C) non-leaving ligands: kinetic and computational study Onunga, O.Daniel; Jaganyi, Deogratius; Mambanda, Allen In this study, the kinetic and mechanistic studies of the substitution of chloride ligand of [(chloro)(2,6-bis(N-heterocyclic carbene)pyridine)Pd(II)]BF4 complexes, namely Pd1, Pd2, Pd3 and Pd4, by thiourea nucleophiles viz Tu, Dmtu and Tmtu were investigated. The rate of chloride substitution of dicyclometalated complexes was monitored in aqueous media containing 20 mM LiCl using stopped-flow spectrophotometry as a function of concentration and temperature under pseudo-first-order conditions. The kinetic data fitted to the pseudo-first-order rate law, kobs = k2[Nu]. The rate of chloride substitution decreased in the order Pd1 ˃ Pd2 ˃ Pd4 ˃ > Pd3. The reactivity of Pd1 was lower by two orders of magnitude compared to [Pd(terpy)Cl]+ (terpy = terpyridine). Both complexes have strong π-acceptor non-leaving ligands that promote efficient back bonding of charge into the aromatic bis(NHC) chelates of its non-leaving ligand. Contrastingly, the lutidine-bridged complexes, (Pd2-4) form 6-membered and non-aromatic bis(NHC) chelates which cause steric influence on either side of the square plane. Their substituents also impart additional steric effects and σ-inductive effects in the rings. The combined effect significantly lowers rates of substitution. Consequently, Pd3 was the least reactive. The substitution mechanism is associative since no evidence of a mechanistic change over to the dissociative substitution was observed, despite the complexes coordinated with tridentates with two cis-σ-bound carbon donors. The article can be accessed in full via:https://link.springer.com/journal/11243/aims-and-scope

Synthesis of pumice and medical waste incinerator fly ash based phosphate geopolymers for methylene blue dye adsorption: co-valorization, parameters and mechanism

2024-11-11T15:04:46Z

Synthesis of pumice and medical waste incinerator fly ash based phosphate geopolymers for methylene blue dye adsorption: co-valorization, parameters and mechanism Collins Onyango, Wilfrida Nyairo, Bowa Kwach, Victor Shikuku, Tome Sylvain, Hermann Dzoujo Tamaguelon, Claus Rüscher In this study, four geopolymer composites, GP-0, GP-10, GP-20 and GP-30, were synthesized from pumice, an abundant and inexpensive volcanic rock precursor, substituted with fractions of 0, 10, 20 and 30% by weight of medical waste incinerator fly ash (MWI-FA), respectively. The materials were characterized by standard methods (FTIR, XRF, BET surface area measurement, XRD, SEM-EDX and TGA). The materials were morphologically distinct and the specific surface areas (SSA) decreased with an increase in MWI-FA fraction. The adsorption performances of the geocomposites were evaluated in batch mode for the removal of methylene blue (MB), a toxic dye, from water. The study determined that the dye was optimally removed at circumneutral pH, 303 K temperature, 0.6 g/40 mL adsorbent dosage and 30 min contact time. The equilibrium data were best described using the Sips isotherm model. The geopolymers had ∼30 times higher adsorption capacities than pristine pumice. The maximum adsorption capacities of the geopolymers, ∼31 mg g−1, were indistinguishable despite an increase in MWI-FA indicating that MWI-FA provided new energetically favorable adsorption sites compensating diminished SSA. The adsorption kinetics was best described using the pseudo-second order kinetic model wherein the rate constant (K2) increased with the MWI-FA fraction suggesting porosity structures with reduced tortuosity. Thermodynamically, the adsorption process was exothermic (ΔH < 0), physical (ΔH and Ea < 40 kJ mol−1) spontaneous (ΔG < 0) and enthalpy-driven. Adsorption diminished in a saline environment. The exhausted adsorbent was recoverable and recycled twice using hot water before significant loss of adsorption potential. The composite geopolymers present a plausible strategy for stabilization of up to 30% MWI-FA without compromising the adsorptive properties for dye removal from water.

Simple and robust algorithms to estimate liveweight in African smallholder cattle

2024-11-07T09:14:19Z

Simple and robust algorithms to estimate liveweight in African smallholder cattle Goopy, J.P; Pelster, D.E; Onyango, Alice; Marshall, K; Lukuyu, M Measurement of liveweight of stock is one of the most important production tools available to farmers – playing a role in nutrition, fertility management, health and marketing. Yet most farmers in sub-Saharan Africa do not have access to scales on which to weigh cattle. Heart girth measurements (and accompanying algorithms) have been used as a convenient and cost-effective alternative to scales, however despite a plethora of studies in the extant literature, the accuracy and sensitivity of such measures are not well described. Using three datasets from phenotypically and geographically diverse cattle populations, we developed and validated new algorithms with similar R2 to extant studies but lower errors of prediction over a full range of observed weights, than simple linear regression, that was valid for measurements in an unassociated animal population in sub-Saharan Africa. Our results further show that heart girth measurements are not sufficiently sensitive to accurately assess seasonal liveweight fluctuations in cattle and thus should not be relied on in situations where high precision is a critical consideration.

IPCC Tier 1 methodology overestimates the carbon footprint of smallholder cattle production systems in Kenya

2024-11-07T09:07:15Z

IPCC Tier 1 methodology overestimates the carbon footprint of smallholder cattle production systems in Kenya Korir, Daniel; Ndung’u, W Phyllis; Onyango, Alice; Arndt, Claudia; Goopy, John; Marquardt, Svenja; Eckard, Richard Highlights• Use of Tier 2 resulted in 19-25% lower total GHG emissions compared to Tier 1.• Using locally measured methane yield instead of the defaults resulted in 19-25% lower GHG emission estimates.• Energy allocation method results in lower milk EI compared to using protein output. https://doi.org/10.21203/rs.3.rs-3148140/v1

The Nexus between Electoral Management System and Post-Election Violence in Kenya Since 1963

2024-11-04T09:33:56Z

The Nexus between Electoral Management System and Post-Election Violence in Kenya Since 1963 Ochieng, Charles Otieno P; Matanga, Frank Khachina; Iteyo, Crispinous The study investigates the relationship between Kenya's electoral management system and post-election violence, which has per sisted despite numerous reforms since the country's independence in 1963. The primary aim was to identify structural issues with in the electoral administration that contribute to violence following elections. The research analyzed key components of the elec toral management system and the causes of post-election violence. Utilizing consociationalism theory, voting theory, and rational choice theory, the study employed a historical design with both qualitative and quantitative methods. The research was conducted from July to December 2022. The target population included eligible voters (260), politicians (50), IEBC officials (40), political analysts (60), humanitarian-aid organizations representatives (10), local election observers (5), international election observers (5), security personnel (10), and county administrative staff (10). A stratified random sampling method was employed to collect data using both questionnaires and interviews. The targeted population established the strata of 641,396, and a random sample was taken from each stratum, arriving at a sample size of 450 respondents. The findings revealed that Kenya's electoral system is primarily based on the First Past the Post (FPTP) model, which is a plurality/majority system. The study identified several key factors contributing to post-election violence, including the "winner-takes-all" nature of elections, disputes over election results due to perceived bias in the electoral management body, and voter incitement by politicians. A statistically significant correlation was established between the electoral management system and post-election violence (β=.685, t = 16.225, Sig. =.000). The find ings indicated that the self-interest and impunity of political leaders, along with ethnic divisions and mistrust, hinder the IEBC's ability to conduct fair and credible elections. A significant association was also found between the causes and consequences of post-election violence (β=.757, t = 19.088, Sig. =.000). The study recommends exploring alternative electoral systems, such as proportional representation and mixed-member models, to promote inclusivity and fair representation. By establishing a connec tion between the electoral management system and post-election violence, this research contributes to peace and conflict studies, addressing a relatively understudied area in Kenya and the broader region.

Potential of biochar amendment as phosphorus source in tropical paddy soil

2024-11-04T07:36:10Z

Potential of biochar amendment as phosphorus source in tropical paddy soil Ong’injo, Rogers Omondi; Kengara, Fredrick Orori; Shikanga, Emmanuel Phosphorus (P) is an essential element for crop production but its non-renewable natural sources are on the verge of depletion. The few remaining P sources may be depleted in the next 30–50 years. This calls for P recycling strategies with biochar application being an appealing approach. However, very limited information is available on the use of biochar as a P source and how it affects the various P fractions in tropical paddy soils. Therefore, the aim of this study was to establish whether biochar could potentially be used as a P source. A sample tropical paddy soil was treated with 1% biochar (derived from maize straw) and/or potassium dihydrogen phosphate, waterlogged and then incubated in airtight amber glass containers at 25 ℃, to mimic tropical paddy soil conditions. Soil aliquots were sampled periodically, followed by extraction and analysis of P fractions. The generated data was subjected to correlation analysis to explore the relationships among the P fractions. The study established that under anaerobic conditions, biochar amendment and P fertilization had no effect on aluminium bound P, calcium bound P, occluded P, moderately labile P and non-labile P. Additional P increased loosely sorbed P but biochar reduced it, even when combined with supplementary P fertilization. It was established that biochar increased iron bound P and to a greater extent with P fertilization. Additional P increased labile P while it was not affected by biochar. Apart from the effect on loosely sorbed P, biochar performed as well as the P fertilizer—or better in case of Fe-bound P. There is therefore promising potential for utilization of biochar as an alternative renewable P source.

Phytoremediation Potential of Cyperus Rotundus L. in Soils Contaminated with Potentially Toxic Elements, the Case of Abandoned Artisanal Small-Scale Gold Mines in Kenya

2024-11-04T07:29:28Z

Phytoremediation Potential of Cyperus Rotundus L. in Soils Contaminated with Potentially Toxic Elements, the Case of Abandoned Artisanal Small-Scale Gold Mines in Kenya Shikanga, Emmanuel Amukohe Phytoremediation involves the use of plants for removal of pollutants from soil before its conversion for agricultural use. Cyperus rotundus L. is a reed that naturally grows in marshy and swampy areas including abandoned artisanal small-scale gold mines. This study was aimed at determining the potential of C. rotundus reeds for removal of Cu, Pb and Cd from soil polluted by artisanal small-scale gold mining (ASGM) activities in in western Kenya. C. rotundus plant and soil samples were collected in triplicate from five randomly selected localities where ASGM is practiced in western Kenya. The control samples were sourced from a locality where ASGM operations have never been conducted. After washing and separating the plants samples into leaves and roots, both soil and plant samples were air dried, oven dried and milled to fine powder. The replicate samples from each locality were combined to form a composite sample which was then digested and the levels of Cu, Pb and Cd, determined using an atomic absorption spectrophotometer in triplicate. Data analysis was done using Microsoft Excel version 2013. The levels of Pb, Cu and Cd, in the samples from the abandoned mines were higher than those of control samples. The levels of metals in the soil samples collected from the mines were in the order Cu>Pb>Cd. Quantities of the metals in the soil, root and leaf samples were in the order root>soil>leaf for Pb and Cd, while for Cu, it was roots>leaves>soil. The BCF values for C. rotundus roots and leaves of the different metals were in the order Cu>Pb>Cd and Cu>Cd>Pb respectively. The TF values for Cu (0.85Â±0.01 â€“ 0.99Â±0.03) were highest followed Cd (0.42Â±0.03 â€“ 0.86Â±0.03) and lowest for Pb (0.31Â±0.03 â€“ 0.80Â±0.01). The MAI values were in the range 66.6-101. Uptake of Cu by the plant results in increased uptake of Pb but decreased uptake of Cd from the soil, while the uptake of Pb is not affected by availability of Cd in the soil and root tissues. Phytoremediation of Cu, Pb and Cd from soil polluted ASGM activities using C. rotundus is an environmentally friendly and cost-effective method of reduction of heavy metal toxicity in the soil.