Theses and Dissertations

Browse

Recent Submissions

Now showing 1 - 20 of 64
  • ItemEmbargo
    Innovative Extraction and Identification of Rutin Flavonoid from Moringa oleifera Leaves Using UHPLC-qTOF-MS and Computational Metabolomics Tools
    (2024-09-06) Ndou, Dakalo Lorraine; Madala, N. E.; Tavengwa, N. T.; Ndlala, A. R.
    Moringa oleifera is a tree that has been studied extensively and it has been found to host a variety of medicinal and nutritional properties. Owing to these properties, it has often been referred to as a ‘miracle tree’. M. oleifera contains a variety of metabolites such as flavonoids, glucosinolates, phenolic acids, tannins, and carotenoids that are responsible for the pharmacological properties of this plant. In this study, the metabolite of interest in M. oleifera was the rutin flavonoid. Rutin has various pharmacological properties and its presence in M. oleifera makes the plant more bioavailable. In this study, the presence of rutin was evaluated in M. oleifera plants in households from different villages within the Vhembe District. The Molecular Networking (MN) approach was utilized to revisit the chemical space of flavonoids in M. oleifera. The aim was to establish the biochemical modifications responsible for the chemical diversity of these compounds, which have been reported to be associated with the purported pharmacological properties of this plant. Modern extraction methods such as ultrasonic-assisted aqueous two-phase extraction (UA-ATPE) and pipette tip micro-solid phase extraction (PT-μSPE) were explored in the extraction of the most bio-available and most sought-after flavonoid, rutin, in M. oleifera leaf extracts. This work has been divided into four experimental chapters. In Experimental Chapter 4, the presence of rutin was evaluated in the leaves of 135 M. oleifera plants from households in different villages within the Vhembe District of Limpopo Province of South Africa. The metabolite extraction was carried out using the conventional liquid extraction method using 80% MeOH and the resulting extracts were analyzed using UHPLC-qTOF-MS. The results from the UHPLC-qTOF-MS showed that only 15 plants produced rutin. This was confirmed using tandem mass spectrometry (MS2) and an authentic standard, which further validated the detected ion as a true representation of rutin. It was concluded that different cultivars of this plant are being grown in various households within the Vhembe District. These differences are expected to result in a negative perception towards Moringa plants, and as such, knowledge of the cultivar-chemical relationship should be made public with the intention to encourage the cultivation of proper plant species. The extraction of rutin from M. oleifera leaves using UA-ATPE was reviewed in Experimental Chapter 5. An ethanol/salt ATPE was formed for the extraction of rutin. Ultrasonication was used to assist in the extraction of rutin from the leaves. Central composite design (CCD) was used to design experiments and two factors which were optimized are ultrasonic time and ultrasonic temperature. The ammonium sulphate ((NH4)2SO4), sodium chloride (NaCl), and magnesium sulphate (MgSO4) salts were used to form the ethanol/salt ATPE two phase system. The resulting Response Surface Model (RSM) was observed to be a linear fit for the ethanol/(NH4)2SO4 and the ethanol/MgSO4 ATPE systems, with R2 values of 0.7339 and 0.5782, respectively, as obtained from the analysis of variance (ANOVA). The ethanol/NaCl ATPE system yielded a quadratic fit with R2 = 0.7865 and was observed to be the best performing in the extraction of rutin from the M. oleifera leaves with optimum extraction at a temperature of 25 ºC and time of 22.5 minutes. Based on multiple reaction monitoring (MRM) through the UHPLC-qTOF-MS technique, the concentration of rutin extracted by the ethanol/NaCl ATPE system was 240 μg L-1. According to ANOVA, temperature (the B-term) was found to be the significant term with a p < 0.0500 that the extraction of rutin through UA-ATPE is temperature-dependent. Therefore, it was concluded that the extraction of rutin from M. oleifera leaves favors low temperatures. The results of the current study further demonstrate the usefulness of simple extraction techniques, such as heated water with additives like salts, as a feasible method to enrich pharmacologically relevant metabolites from plants. This reaffirms traditional protocols that are currently used by communities which include boiling plants in water to extract useful chemical compounds for the treatment of common ailments such as colds and headaches. In Experimental Chapter 6, PT-μSPE was applied in the extraction of rutin from M. oleifera leaves using activated hollow carbon nanospheres (HCNSs) as the sorbent. The activated HCNSs were characterized using FTIR, which confirmed the presence of the functional groups of interest such as OH stretch, -COO- vibration, and C=O stretch. TGA thermogram showed a difference in the thermal stability of the raw and activated HCNSs, proving that the raw HCNSs are more stable than the activated HCNSs, and SEM displayed the difference in the morphology of the raw and activated HCNSs by observing the difference in the coalescence of the material. Parameters such as loading cycles, elution solvent, concentration of rutin, pH, loading volume, and mass of sorbent were optimized. The analysis of the extracts was conducted with a UV-Vis spectrophotometer to ascertain the recovery of rutin. The optimal conditions for rutin recovery using PT-μSPE were determined to be 15 loading cycles, i-PrOH as the elution solvent, a 2 ppm as standard concentration of rutin, a pH of 2, 500 μL as loading volume, and 1.5 mg of sorbent. The LOD, LOQ, and RSD values were found to be 0.604 mg L-1, 1.830 mg L-1, and 3.26%; respectively. It was thus confirmed that the PT-μSPE method is effective in the extraction of rutin even at trace levels based on the low LOD value obtained and the RSD value obtained proved that this method is a reliable pre-concentration technique and is thus repeatable for the analysis of complex samples. Therefore, in cases where some plants produce these compounds in minute concentrations, methods such as this one presented herein can be used to estimate and concentrate the pharmacologically relevant compounds. Molecular networking (MN) was used to study the global metabolic profile of M. oleifera and is outlined in Experimental Chapter 7. Herein, Global Natural Products Social (GNPS) platform was used to generate the MN from the LC-MS data obtained from the methanolic leaf extracts of M. oleifera. The MN was viewed and analyzed using Cytoscape. Through MN, it was observed that M. oleifera contains a variety of metabolites. Other GNPS tools such as network annotation propagation (NAP), DEREPLICATOR, MS2LDA, and MolNetEhancer were further used to compliment the classical MN model. To this end, MS2LDA was used to annotate the flavonoids found within M. oleifera. Kaempferol, quercetin, and isorhamnetin flavonoids were successfully annotated by MS2LDA. Additionally, Chrysin-6,8-C-diglucoside was also annotated and reported for the first time in M. oleifera leaves. The results of this study further suggest MN models as useful tools for chemical exploration, enabling the discovery of new metabolites by leveraging existing knowledge as "chemical charms" to unearth hidden metabolites.
  • ItemEmbargo
    Synthesis and application of ion imprinted polymers for selective extraction of metal ions from different matrices
    (2024-09-06) Masindi, Muphulusi Lizzy; Mudzielwana, R.; Tavengwa, N.
    Exposure to toxic metal ions such as Zn2+ and Pb2+ can lead to several diseases including cancer on human being. This study aims to synthesize Zn2+and Pb2+ ion imprinted polymers (IIPs) for removal of Zn2+ and Pb2+ from various sample matrixes. Polymerization was achieved by mixing the methacrylic acid (MAA) as a functional monomer, ethylene glycol di-methacrylate (EGDMA) as a cross-linker, azobis (isobutyronitrile) (AIBN) as initiator and methanol as a progen. The temperature was increased to 80 oC while stirring for 7 h. The identical procedure was used to make non- imprinted polymer (NIP), but no template was used. Imprinted polymers were extracted with 2 M HCl for the removal of templates. The point of zero, or pHPZC, was determined and infrared spectroscopy was used to characterize the final products. The results of the Fourier-transform infrared (FTIR) analysis demonstrated the removal of ion templates by broad O-H peak at a wavelength of 3500 cm-1 and pHPZC results revealed that, at acidic solution, the imprinted polymers carried positive charges, and at basic solution pH, the imprinted polymers carried negative charges the PHPZC was found 6.98 and pH level was 7.0. The maximum percentage of Zn2+ removal using the Zn-IIP was found to be 80% when the solution pH of 7.0, adsorbent dose was 5 mg, contact time at 15 min at shaking speed of 100 rpm and initial metal ion concentration of 25 mg/L were used. The adsorption kinetic data corresponded to pseudo-second order reaction kinetics with R2 = 0.99, indicating that the process occurred by chemisorption. The Langmuir isotherm showed an excellent fit with an adsorption capacity of up to 9.03 mg g-1 and R2 = 0.99, implying that adsorption was on a monolayer surface. This study shows that zinc ion imprinted polymer has higher efficiency towards Zn2+ in the solution. The finding indicates that zinc ion imprinted polymer has high adsorption efficiency of 94.00 (mg/g) in removing zinc ion from the honey sample. The removal of Pb (II) from wastewater using Pb (II) IIP was found to be 90%. Further the re-usability study was evaluated 7 times and the adsorption efficiency was high at 90%, for this study the waste material can be beneficial for reused. The functional groups of both the imprinted polymer and the non-imprinted polymer were characterized by FTIR, and the point of zero charge was determined using the optimum conditions of 50 mg adsorbent dose, initial solution pH 9, and 15 min contact time. The adsorptive nature of the IIP and NIP was evaluated by means of Langmuir and Freundlich isotherms. The Langmuir adsorption isotherm modelled the data better, as shown by the Langmuir and Freundlich correlation coefficients of 0.999 and 0.975, respectively. An inventive answer has evolved in the form of ion-imprinted polymer, which was produced using the molecular imprinting approach as a basis. Higher selectivity coefficients have been demonstrated by IIPs compared to non-imprinted polymers.
  • ItemEmbargo
    Synthesis of novel 2-thiohydantoin derivatives as potential anti-diabetic drugs
    (2024-09-06) Tshishonga, Unarine; Mnyakeni-Moleele, S. S.; Bvumbi, M. V.
    Thiohydantoin is a hydantoin with one carbonyl group replaced with a thiocarbonyl group. In this study five series (glycinates, alaninates, butanoates, vallinates and norvalinates) of thiohydantoin derivatives (21a-v) were successfully synthesized and characterized using known analytical characterization techniques. The synthesis of these compounds followed four reaction steps using conventional methods from step one with nucleophilic substitution to Knoevenagel condensation reaction as the final step. All twenty two compounds were obtained in good to excellent yields and were subjected to in vitro screening for their inhibitory activity against α-glucosidase. Among the five series of thiohydantoin derivatives, the alaninate derivative 21f exhibited the highest inhibition at both concentrations of 65 μM and 130 μM, with values of 71.13±0.61 and 64.20±0.54, respectively. The glycinate derivative 21j exhibited the highest inhibition of 60.95±1.07 at 130 μM, while butanoate derivatives showed a consistant moderate inhibition. Only compound 21z exhibited concentration-dependent trends of moderate inhibition on the norvallinates derivatives and the vallinates exhibited negligible inhibition.
  • ItemEmbargo
    Synthesis, photoisomerization and antimalarial activities of cinnamoyl chloroquinoline hybrids
    (2024-09-06) Nemudzivhadi, Anza Imanuel; Bvumbi, M. V.; Mnyakeni-Moleele, S. S.
    The primary aim of this project was to synthesize a series of cinnamoyl chloroquinoline hybrids employing a technique of molecular hybridization. Cinnamoyl chloroquinoline hybrids are compounds with the heteroaromatic core of amino-7-chloroquinoline, linked to differently substituted cinnamic acid groups by flexible primary diamines. In this study, three series (n=2, 3 and 6) of nineteen cinnamoyl chloroquinoline hybrids 18-36 were successfully synthesized by modifying known conventional methods with yields ranging from 24-74%. The structures of synthesized compounds were characterized by a combination of 1H NMR, 13C NMR, HRMS and IR analysis. Hybrids 18-36 were found to isomerize when exposed to light to form mixture of cis and trans isomers. Through chromatographic mass spectrometry (LC-MS), these isomers were studied and LC-Q-TOF-MS/MS analyses of the photo-products revealed the emergence of cis isomer which eluted before its synthesized trans counterpart, suggesting a reduced polarity. The polarity of the compounds was significantly influenced by the nature of the substituents attached to the phenyl ring. Electron-withdrawing groups such as Cl, NO2, and F increased polarity in contrast to electron donating group OCH3 which reduced polarity. The concept of photoisomerization of cinnamoyl chloroquinoline hybridswere validated by the measurement of the transformation of trans to cis isomers using 1H NMR. Compounds 18-36 were tested against wild-type drug-sensitive strain (NF54) and multidrug-resistant isolate (K1) of the human malaria parasite Plasmodium falciparum. Compounds with longer alkyl carbon chain linkers demonstrated greater antiplasmodial activity compared to those with shorter chain linkers. The in vitro studies revealed that compound 32 showed the most potent activity (in vitro 50% inhibitory concentration, 0,012 μM for strain NF54 and 0,009 μM for strain K1 and resistance index of 0.717 as a potential antimalarial agent. Other compounds (compounds 34 and 35) also showed moderate activity against a CQ-sensitive strain (NF54) and superior activity against a CQ-resistant strain (K1) of Plasmodium falciparum.
  • ItemEmbargo
    Risk assessment of the possible contamination of trace metals in fish samples from Lake Kariba, Zambia
    (2024-09-06) Poopedi, Phaphadi Maxwell; Tavengwa, Nikita T.; Chimuka, Luke
    Exposure to inorganic endocrine disrupting chemicals (EDCs) has been linked to cause carcinogenic and mutagenic effects on human health and aquatic species. Trace metals in food are widely acknowledged as a public health concern yet largely ignored in many African nations where legislation is not yet fully implemented. Thus, the study aimed to extract and determine the toxic levels of inorganic EDCs of interest at certain doses and possible health risk associated with metal ions in fish sold in the open markets from Siavonga, Lake Kariba (Zambia). Sampling was done for two consecutive years, 2021 and 2022. Two fish species, which constitute Lake Kariba, were sampled; the bream (Oreochromis mortimeri) and Kapenta (Limnothrissa miodon): Firstly, twenty-eight fresh Kariba bream (Oreochromis mortimeri), five sun-dried Kariba bream (Oreochromis mortimeri) and five batches of sun-dried Kapenta (Limnothrissa miodon) were sampled from Lake Kariba open market. Secondly, six fresh Kariba bream (Oreochromis mortimeri), five sun-dried Kariba bream (Oreochromis mortimeri) and five batches of sun-dried Kapenta (Limnothrissa miodon), were purchased in an open market in Siavonga. Fish muscle tissues were excised to analyze trace metal ions before being digested using a microwave digestion system and analyzed using ICP-OES and MS. Eleven trace elements: Aluminum (Al), Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper (Cu), Iron (Fe), Lead (Pb), Manganese (Mn), Mercury (Hg), Selenium (Se) and Zinc (Zn) were analyzed in fish muscle tissues (epaxial and hypaxial myomers). The results showed that the mean metal concentration for the first sampling was not significantly higher ( > 0.05) than the mean concentration for the second fish sampling, except for sun-dried Kapenta. The first sampling collected in November (2021) revealed that the fish collected on a Zambian open market contained higher levels of Cr, Mn and Fe ranging from 6.50±3.30 to 101.40±22.69 mg kg-1 in sun-dried bream. At the same time, sun-dried Kapenta contained high levels of Cr, Mn, Fe, As and Al ranging from 0.49±0.05 to 160.72±132.60 mg kg-1. In contrast, fresh bream contained high levels of Cr, As and Mn ranging from 13.99±7.96 and 22.30±12.20 mg kg-1. Compared to the second sampling around August (2022) they revealed high levels of Cr, Mn, As, Se and Fe ranging from 0.15±0.07 to 110.6±63.82 mg kg-1 in Sun-dried bream. In contrast, sun-dried Kapenta contained high levels of Cr, Mn, As, Se, Fe and Zn levels ranging from 0.78±0.03 to 187.8±58.59 mg kg-1. In comparison, fresh bream contained high Cr, Mn, As, Se and Fe ranging from 0.26±0.16 to 163.00±68.41 mg kg-1. The obtained results showed that the concentrations of metals exceeded the recommended maximum permissible limits proposed by the Joint Food and Agricultural Organization and World Health Organization (FAO/WHO) Expert Committee on food for fish consumption. However, fish were safe from adverse health effects due to Hg not being detected in fish sampled. The pollution index was assessed to determine the extent of pollution. The estimated daily intake (EDI) for all metals were higher than the provisional tolerable daily intakes (PTDI) recommended by FDA for both adults and children. Target hazard quotients (THQ) and hazard indices (HI) was higher than 1, indicating health risks from a non-carcinogenic lifetime of fish consumption. The lifetime average daily dose (LADD) was used to estimate the incremental lifetime cancer risk (ILCR). All metals were lower than 1×10 4 except for fresh bream 2021 for both children and adults, indicating a carcinogenic risk of 1 in 10,000 from consumption of Kapenta and Kariba bream from Lake Kariba in a lifetime. This raises concern over an adverse health effect on the consumption of fish consisting of excess trace metals. Long-term exposure to trace metals through fish consumption poses potential non-carcinogenic and carcinogenic health risks to the residents and suggests possible adverse health effects.
  • ItemEmbargo
    Synthesis of sulfonylthioureas containing two carbon linker as potential antidiabetic drugs
    (2024-09-06) Mbhokazi, Tiyisela Nyeleti; Mnyakeni-Moleele, S. S.; Bvumbi, M. V.
    Target compounds (18a-s) from the series (morpholine, piperidine, N-methylaniline, 2,6-dimethylaniline and diethylamine) of novel sulfonylthioureas were designed and synthesized over three reaction steps using different appropriate synthetic methods. Nucleophilic substitutions were employed in order to incorporate amines, three different carbon linkers between amines and sulfonylthioureas moiety. Furthermore, nucleophilic substitution reaction was used to incorporate appropriate substituted isothiocynates as the final main step. Compounds (18a-s) were obtained in good to excellent yields and were characterized using a combination of 1H NMR, 13C NMR, IR and HRMS analysis. Compounds (18a-s) were evaluated for their antidiabetic activity against α-glucosidase and α-amylase. The in vitro screening results showed that most compounds had little to moderate activity against α-amylase at the concentrations of 60μM, 120μM and 240μM. When compounds were tested against α-glucosidase, they showed little to moderate antidiabetic activity at the concentrations of 60μM and 120μM but exhibited significant anti-diabetic activities at 240μM. Compounds that have a phenyl group substituent (18j, 18m, 18q, 18r and 18s with inhibition 70.21±5.97, 78±3.03, 76.33±2.03, 69.55±4.11 and 84.67±3.34 respectively at 240 μM) and a methyl group substituent (18q-s) exhibited stronger inhibition activity.
  • ItemEmbargo
    Novel thiazolidinedione derivatives as corrosion inhibitors for mild steel and zinc in 1 M HCI
    (2024-09-06) Dube-Johnstone, Nhlalo M.; Murulana, L. C.; Mnyakeni-Moreele, S. S.
    Corrosion inhibition studies on mild steel (MS) and zinc in 1 M HCl were carried out at four temperatures (303.15 K, 313.15 K, 323.15 K, and 333.15 K) using eight novel thiazolidinedione derivatives (TZDs) codenamed: A1, A2, A3 (alaninates), B1, B2 (butanoates), G1, G2, and G3 (glycinates). After synthesis, the TZDs were characterized using nuclear magnetic resonance (NMR) spectroscopy. Specifically, two NMR techniques were employed: proton NMR (1H NMR) at 400MHz and carbon 13 NMR (13C NMR) at 100MHz. After characterization, five experimental techniques were employed to investigate the corrosion inhibition potential of the TZDs: weight loss (WL) analysis, potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and Fourier transform infrared spectroscopy (FTIR). The adsorption of the TZDs onto both metals was found to be best modelled by the Langmuir adsorption isotherm. Thermodynamic data showed that all TZDs adsorbed spontaneously onto both metal surfaces, transitioning from mixed type adsorption to chemisorption with an increase in temperature. However, WL analysis percentage inhibition (%IEWL) and activation energy (Ea) data showed that all TZDs adsorbed onto zinc via chemisorption. Data obtained from PDP analysis showed that the TZDs inhibit corrosion on MS at both anodic and cathodic sites, with a prevalence of cathodic action. However, on zinc, all TZDs inhibit corrosion exclusively at anodic sites. Data from EIS analysis showed that the adsorption of the TZDs onto both metals is a charge transfer driven process. The significantly depressed semi-circles obtained from zinc EIS data shows that capacitance plays much less of a role relative to MS, explaining the much lower phase shift (n) values obtained. Spectra obtained from FTIR analysis show that carbonyl, amine, nitro, aliphatic and aromatic functional groups all take part in the formation of an adsorption film on both metal surfaces.
  • ItemOpen Access
    Evaluating the potential of the membrane technology for copper recovery from effluents and wastewater generated at copper mines and processing facilities in South Africa
    (2023-10-05) Ramabulana, Mpho; Ramaite, I. D. I.; Bazhko, O.
    Membrane separation is a well-known and widely used method in water treatment. It finds applications in mining and metallurgical processes and offers many potential benefits to the mining industry, such as significant water recovery from mine wastewater, excellent metal upgrades, and reagent recycling from process streams. This study evaluated membrane technology for the recovery of copper and recycling clean water from an aqueous effluent stream generated from copper mines. The copper content in the test work was 639 mg/L copper (Cu) in a synthetic solution and 427 mg/L copper in a real solution. Seven commercial flat sheets (FS) membranes were tested at a laboratory scale, and at the pilot scale, one spiral-wound membrane was tested. The performance of membranes was assessed, as well as the effect of various process parameters. It was demonstrated that nanofiltration (NF) technology could be effectively used to treat wastewater generated by copper mines. Five of seven evaluated membranes (AMS A3011, A3012, A3014, B4021, and DOW N90) were found to reject >90% of copper into the concentrate at operating pressure of 20, 30, and 40 bar at ambient temperatures. In all the evaluated membranes the following was observed; o An increase in the operational pressure increased operational flux; o However, as pressure and temperature increased, the rejection of copper and other metals decreased. During the optimisation of DOW N90 operational parameters, the following trends were identified: o Operational pressure is required as it improved operational flux, increased the rejection of copper, and minimized flux depreciation with time. o The temperature had a negative impact on flux; however, the optimum operating temperature has to be found because copper rejection can be compromised at higher temperatures. The DOW NF90, which was tested on a pilot rig, was also found to be suitable for treatments of the diluted copper solution, with a high copper rejection achieved. And a permeate recovery of 53.64% was achieved, but this value can be improved by increasing copper in the concentrate for further recovery.
  • ItemOpen Access
    Synthesis of Novel 6, 8-Distributed-Chromone-3-Carboxamides and their evaluation as potential anti-tuberculosis agents
    (2023-10-05) Malusela, Thisundiwi; Ramaite, I. D. I.; Puka, L. R.
    This project focusses on the synthesis of novel 6,8-disubstituted-chromone-3-carboxamides and their evaluation as potential anti-tuberculosis agents. In this study, four 3-iodo-5-substituted-2-hydroxyacetophenones (58A-D) and three 3-bromo- 5-substituted-2-hydroxyacetophenones (63A-C) were successfully synthesized from 5- substituted-2-hydroxyacetophenones (57A-D). The Vilsmeier-Haack reaction was used to synthesize the 8-iodo-6-substituted-chromone-3-carbaldehydes and 8-bromo-6-substitutedchromone- 3-carbaldehydes from the 3-iodo/bromo-5-substituted-2-hydroxyacetophenones. These compounds were treated with sodium chlorite and sulfamic acid to afford corresponding chromone-3-carboxylic acids. Recrystallization with either ethanol or methanol was used to purify the synthesized compounds. All compounds were synthesized in good to excellent yields. The yields of the 3- iodo-5-substituted-2-hydroxyacetophenones (58A-D) ranged from 55 - 75 %, the 3-bromo-5- substituted-2-hydroxyacetophenones (63A-C) were synthesized with yields from 66 - 87 %, the percentage yields are significantly different probably because different methods were used. The yields of the 8-iodo-6-substituted-chromone-3-carbadehydes (59A-D) ranged from 78 – 90 %, the 8-bromo-6-substituted-chromone-3-carbaldehydes (64A-C) with yields from 85 - 87 %, 8-bromo-6-substuted-chromone-3-carboxylic acids from 47 – 52 %, and chromone-3- carboxylic acid afforded a yield of 57 %. 1H NMR, 13C NMR and FTIR spectroscopic techniques were used to characterize synthesized compounds and also confirmed by melting points for compounds reported in literature.
  • ItemOpen Access
    Synthesis of novel-6.8-disubstituted-chromone-2-carboxylic acid derivatives and their biological evaluation as potential antimalarial agents
    (2023-10-05) Mabasa, Nyiko Samuel; Ramaite, I. D. I.; Tavengwa, N. T.
    Malaria is a mosquito vector-borne disease caused by a female anopheles mosquito belonging to a plasmodium genus, affecting more than 500 million people per annum. There are five plasmodium genus responsible for causing malaria, but four of them are responsible for causing human malaria. The most common one to cause malaria in Africa is P.Falciparum. The most commonly used drugs for malaria are quinine derivatives and artemisinin derivatives which are both derived from traditional plants. Malaria parasites have become resistance to almost all the currently used drugs. In this project different synthetic approaches were used to prepare novel chromone derivatives. This study was focused on the synthesis of various 6.8-substituted-chromone-2-carboxylic acids (41) derivatives from the corresponding 5-substituted-2-hydroxyacetophenones (38). The first step included the introduction of iodine on the 5-subsituted-2-hydroxyacetophenones (38) to give 5-substituted-3-iodo-2-hydroxyacetophenones (39A-D). The same step was repeated but with bromine to give 5-substituted-3-bromo-2-hydroxyacetophenones (39E-H). The 3.5-disubstituted-2-hydroxyacetophenones (39A-H) underwent condensation with diethyl oxalate and sodium ethoxide to form ethyl-6.8-disubstituted-chromone-2-carboxylates (40A-H), which was converted to the corresponding 6.8-disubstituted-carboxylic acids (41A-H). Attempted conversion of the acids to the corresponding carboxamides 43 via the carbonyl chloride intermediates (42A-D) was unsuccessful. The percentage yield of synthesized 3.5-disubstituted-hydroxyacetophenones (39A-H) ranged between 46-82 %, whilst those of ethyl-6.8-disubstituted-chromone-2-carboxylates (40A-H) intermediates ranged between 44-95 %. The yields of synthesized 6.8-disubstituted-chromone-2-carboxylic acids (41A-H) ranged between 48-98 % while the corresponding acids chlorides (42A-D) ranged between 44-60 %. Our attempted synthesis of 6.8-disubstituted-chromone-2-carboxamides (43) was unsuccessful. Compounds (39-43) were purified by recrystallization and characterized using NMR and FTIR spectroscopic techniques.
  • ItemOpen Access
    Phytochemistry and biological studies of constituents from Breonadia Salicina (VAHL) Hepper and J. R. I. Wood
    (2023-10-05) Tlhapi, Bafedile Dorcas; Ramaite, I. D. I.; Van Rhee, T.; Anokwuru, C. P.
    Breonadia salicina (Vahl) Hepper and J.R.I. Wood is a tree used widely to treat numerous infectious diseases in South Africa and other African countries, and ethnopharmacological studies have shown a number of biological activities of the crude extracts. Furthermore, phytochemical studies have indicated that the stem bark is rich in tannins, and alkaloids have been isolated from the twigs and leaves. However, few studies have correlated the phytochemistry to the physiological activties. This study aimed to explore the phytochemistry of B. salicina using a metabolomic approach and correlating the phytochemistry to the biological activities for possible drug development. Samples of B. salicina were collected at Fondwe, Limpopo Province, South Africa. Phytochemical studies followed a metabolomics approach, with repeated column chromatography and preparative thin-layer chromatography yielding a number of pure compounds. Antimalarial and antitrypanosomal activities of the crude extracts, pure compounds, fractions, and seasonal samples were evaluated using the parasite lactate dehydrogenase (pLDH) and Trypanosoma brucei assays, respectively. Furthermore, the antioxidant activities of the crude extracts, fractions and pure compounds were evaluated using DPPH (2,2-diphenyl-1-picrylhydrazyl) and reducing power assays. The antimycobacterial activities of the crude extracts and fractions were determined against Mycobacterium tuberculosis (H37RvMA strain), and anti-diabetic activities of the crude extracts were determined using α-amylase and α-glucosidase inhibition assays. The anti-inflammatory activities of the crude extracts were assessed using the Griess assay, while the in vitro toxicology of the crude extracts was evaluated using cell toxicity, NucRed nuclei dye, MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and Hoechst 33342/Propidium iodide (PI) dual staining assays. Eight compounds (bodinioside Q, 5-O-caffeoylquinic acid, D-galactopyranose, hexadecane, kaempferol 3-O-(2’’-O-galloyl)-glucuronide, lupeol, palmitic acid, and sucrose) were isolated for the first time from the root, stem bark, and leaf extracts of B. salicina, while 51 compounds were tentatively identified from the crude extracts, fractions and seasonal samples by UPLC-QTOF-MS and 1H-NMR spectroscopy. The aligned UPLC-QTOF-MS data were analysed chemometrically to determine the chemical variability of the crude extracts of the roots, stem bark, and leaves collected during four different consecutive seasons. The principal component analysis (PCA) model, hierarchical cluster analysis (HCA) and partial least square discriminant analysis (PLS-DA) were constructed. These indicated the presence of two main clusters related to the different parts of the plant (root, stem bark, and leaf). In the antiplasmodial activity, three fractions collected in the first year affected the viability of Plasmodium falciparum, with viabilities of 16.16 ± 8.63 %, 27.01 ± 4.47 % and 31.07 ± 6.71 %; and IC50 values of 2.19 ± 0.09 μg/mL, 1.91 ± 0.05 μg/mL and 3.02 ± 0.08 μg/mL, respectively, at a concentration of 10 μg/mL. However, all the tested crude extracts and fractions collected in the first year contained potent antiplasmodial activities at a concentration of 50 μg/mL. Furthermore, the dichloromethane leaf extract collected in the second year in autumn, winter, spring and summer displayed high activities, with viabilities of 18.57 ± 1.99 %, 32.07 ± 4.91 %, 38.11 ± 5.07 % and 20.21 ± 5.19 % at a concentration of of 50 μg/mL with IC50 values of 7.90 ± 0.06 μg/mL, 18.15 ± 0.07 μg/mL, 19.40 ± 0.06 μg/mL and 15.26 ± 0.05 μg/mL at a concentration of 300 μg/mL, respectively. The pure compounds, including kaempferol 3-O-(2"-O-galloyl)-glucuronide (1) and palmitic acid (8), caused a significant decrease in parasite viability at a concentration of 50 μg/mL, with viabilities of 29.37 ± 1.29 % and 24.97 ± 5.21 %; and IC50 values of 9.06 ± 0.036 μg/mL and 6.792 ± 0.046 μg/mL at a concentration of 200 μg/mL. In the antitrypanosomal test, the crude methanol leaf extract, dichloromethane leaf extract, and two fractions attained in the first year strongly affected the viability of trypanosomes at the tested concentration of (50 μg/mL), with a viability of 6.74 ± 0.06 %, 6.38 ± 2.15 %, 7.78 ± 0.08 % and 5.05 ± 0.35 %; and IC50 values of 11.4 ± 0.42 μg/mL, 10.6 ± 0.07 μg/mL, 2.0 ± 0.09 μg/mL and 7.1 ± 0.14 μg/mL at a concentration of 300 μg/mL, respectively. Furthermore, the crude methanol leaf extract collected in the second year in autumn, spring and summer displayed higher activities, with viabilities of 5.84 ± 0.38 %, 26.66 ± 3.91 % and 9.05 ± 0.80 % at a concentration of 50 μg/mL; and IC50 values of 12.0 ± 0.36 μg/mL, 5.2 ± 0.74 μg/mL and 10.6 ± 0.07 μg/mL at a concentration of 300 μg/mL, respectively. However, the crude dichloromethane leaf extract collected in the second year in autumn, winter, spring and summer displayed higher activities, with viabilities of 3.50 ± 0.59 %, 4.13 ± 0.06 %, 29.47 ± 1.25 % and 3.85 ± 0.10 % at a concentration of 50 μg/mL; and IC50 values of 4.6 ± 1.82 μg/mL, 5.1 ± 0.30 μg/mL, 5.1 ± 0.72 μg/mL and 4.0 ± 0.08 μg/mL at a concentration of 300 μg/mL, respectively. The isolated compounds, including bodinioside Q (4), kaempferol 3-O-(2"-O-galloyl)-glucuronide (1), lupeol (2), and palmitic acid (8), exhibited antitrypanosomal activity with viabilities of 12.99 ± 0.53 %, 20.38 ± 2.35 %, 5.46 ± 0.04 %, and 5.83 ± 0.28 % at a concentration of 20 μg/mL; and IC50 values of 4.0 ± 0.09 μg/mL, 1.1 ± 0.22 μg/mL, 4.2 ± 0.27 μg/mL and 5.7 ± 0.09 μg/mL, respectively; On the other hand, the reference drug pentamidine showed an IC50 of 10.2 ± 0.07 μg/mL. The anti-oxidant assays revealed that the crude stem bark extract had the highest DPPH free radical scavenging activity, with an IC50 of 41.7263 ± 7.6401 μg/mL. Furthermore, the crude root extract had the highest reducing power with an IC0.5 of 0.1481 ± 0.1441 μg/mL. In the antimycobacterial activity test, none of the tested plant samples produced significant antimycobacterial activity at a concentration of 90 μg/mL. All the samples produced a MIC value of >62.5 μg/mL against 7H9_ADC_GLU_TW, 7H9_ADC_GLU_N_TW and 7H9_ADC_GLY_TW media. Furthermore, the crude stem bark and root extracts showed very strong antidiabetic activity at the lowest tested concentration of 62.5 μg/mL, with an inhibition of 74.53 ± 0.737 % and 79.1 ± 1.494 % against α-amylase enzyme. However, for the α-glucosidase inhibition assay, the crude stem bark and root extracts showed complete inhibition at the lowest tested concentration of 31.3 μg/mL at 98.20 ± 0.15 % and 97.98 ± 0.22 %. The crude dichloromethane leaf extract showed a decrease in nitrite concentration at the highest concentration of 200 μg/mL, with a cell viability of 79.06 ± 1.88 %, indicating anti-inflammatory activity. The crude stem bark, root and methanol leaf extracts were not cytotoxic against Vero cells at the concentrations of 15.125 μg/mL, 31.25 μg/mL, 125 μg/mL and 250 μg/mL. Furthermore, none of the extracts were cytotoxic at the following concentrations: 50 μg/mL, 100 μg/mL and 200 μg/mL, against RAW 264.7 macrophages. However, the crude stem bark and root extracts showed cytotoxic effects against Vero cells at 250 μg/mL.
  • ItemOpen Access
    Experimental and theoretical studies of the inhibition potential of Lippia javanica plant extracts for the corrosion of aluminium, mild steel, and zinc metals in acidic medium
    (2023-10-05) Nesane, Tshimangadzo; Murulana, L. C.; Kabanda, M. M.; Madala, N. E.
    Corrosion is a natural phenomenon considered a chemical and an electrochemical process of metals interacting with the surrounding corrosive environment. Inhibition is a preventive measure used by corrosion engineers to reduce the effects of corrosion on metals, the environment, society, and the economy. The current study investigates the use of the Lippia javanica plant as an ecofriendly green inhibitor for mild steel (MS), aluminium (Al), and zinc (Zn) corrosion in a 1 M HCl environment. The leaf extracts were prepared by the Soxhlet extraction method using methanol, ethanol, and acetone as solvents. The leaf extracts of L. javanica were characterized using Fouriertransform infrared spectroscopy (FT-IR) and Liquid chromatography-mass spectrometry (LC/MS) analysis. The inhibitory potential of L. javanica extracts was established by performing weight loss measurements, electrochemical methods such as potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) techniques. The weight loss assessment was carried out at different temperatures (303 to 333 K) and varying concentrations of the extracts from 200 to 800 ppm. The technique was also used to determine the stability of the extract with varying immersion times. Weight loss measurements showed that the inhibition efficiency increased with increasing concentration of the extracts up to 800 ppm for all three metals. Increasing the temperature of the corrosive environment resulted in a decrease in the inhibition efficiency of Al and MS corrosion, with that of Zn increasing with temperature. The variation of inhibition efficiency with time showed a similar trend, with the protective efficiency of Al and MS decreasing with time and Zn increasing with immersion time. Increasing Zn’s inhibition efficiency with temperature and immersion time implies a chemical protection mode. The reduction in the inhibition efficiency with temperature and immersion time for Al and MS suggests a physical protection mode. According to EIS measurements, the extracts adsorb onto Al, Zn, and MS surfaces to create a protective coating with pseudo-capacitive properties. The only component of the Zn and MS Nyquist plots in the high frequency was a capacitive loop, but the Al plots also showed an inductive loop at a lower frequency. The higher frequency loop represents the resistance for the charge transfer during the corrosion process. In contrast, the lower frequency loop represents the relaxing of hydrogen ions and the adsorption of corrosive chloride ions onto the oxide film. The PDP results revealed that for Al and MS, the three extracts had a similar impact on both the anodic and cathodic half-reactions. In contrast, both half-reactions were affected for Zn, but the cathodic area was more significantly impacted. Undulation Tafel curves for MS and Zn were observed with and without the extracts; however, a longer passive region was detected for Al, particularly in the presence of the plant extracts. The investigational extracts function as mixed-type corrosion inhibitors for Al, Zn, and MS, as indicated by the control of both the anodic and cathodic areas with the introduction of the extracts. Among the many plotted isotherms for the three extracts on the metal surfaces, the Langmuir adsorption isotherm was determined to be the best-fit isotherm. The isotherm confirmed the mechanism of adsorption, which was a mixed-type adsorption for Al, Zn, and MS. Spectroscopy studies revealed that the interaction of the three extracts with Al, Zn, and MS resulted in the formation of metal-inhibitor complexes, which slowed the corrosion process. Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) studies demonstrated that L. javanica leaf extracts form a protective film on Al, Zn, and MS surfaces, protecting them from the corrosive environment. Theoretical simulations showed that the primary extract constituent (verbascoside) had binding energy greater than 13 kcal/mol on the surfaces of Zn(110), Al(111), and Fe(110). The high binding energy indicates a mixed-type binding process that includes chemisorption and physisorption. All corrosion experiments revealed that the three extracts exhibited superior inhibition performance for all the three metals studied with comparable results in 1 M HCl corrosive solution.
  • ItemOpen Access
    Application of modern analytical techniques for quantification of selected radioactive metals in environmental samples
    (2023-05-19) Nkhumeleni, Murendeni Royell; Tavengwa, N. T.; Puka
    In this study, the recent micro-extraction and pre-concentration techniques, namely vortex-assisted liquid-liquid micro-extraction (VA-LLME), dispersive liquid-liquid micro-extraction (DLLME) and membrane assisted solvent extraction (MASE) were used for the extraction of radioactive metals from the environmental samples. The VA-LLME and MASE were used for the extraction of cobalt, while DLLME was used for the extraction of palladium. The work is divided into five papers. The first paper of this work reviewed the modern developments for efficient applications of DLLME technique during analysis of radioactive metals in environmental samples (paper I). This study discussed various modifications of the DLLME technique used for improving the technique during the analysis of radioactive metals, as well as the challenges it present. The major advantage, among others, of DLLME is miniaturisation in which the volumes of the extraction and dispenser solvent are reduced tremendously. This was in attempt to solve challenging factors during the analysis of radioactive metals such as their existance in trace level that is normally lower than the limits of detection of most analytical instruments. Recent developments for efficient analytical separation techniques during analysis of radionuclides in environmental samples were reviewed (paper II). This part outlined the efficient analytical extraction and separation techniques during analysis of radionuclides with focus on the review of non-consecutive extraction of analytes, non-toxic solvents, less-hazardous waste generation, and high selective and green analytical separation methods. Furthermore, possible simultaneous selective extraction of metals of interest in a complex matrix such as water, soil and minerals were dicussed. This offers tremendous advantages for extraction and separation techniques of radionuclides. Cobalt concentration in environmental water samples was pre-concentrated using VA-LLME and detected using flame atomic absorption spectrometry (FAAS) (paper III). Based on the results, 2 min vortex time, 3 mL sample volume, 6.0 sample pH level, 600 mL volume of complexing angent give, and 300 μL extraction solvent give the highest enrichment factors. Trace amount of cobalt in real samples, were 102.5 ± 1.0 μg L-1 (n = 3, RSD) which is below the maximum acceptable limit for cobalt, according to Water Quality Guidelines for cobalt by British Columbia Report. The pre-concentration of palladium in the environmental samples by DLLME was studied (paper IV). The important parameters that have an impact on the effectiveness of DLLME technique were also optimized using the univariate approach. The methanol and chloroform was used as dispenser solvent and extraction solvent, respectively. The volumes of 500 μL for dispenser solvent and, 400 μL for extraction solvent showed the maximum enrichment factors. Dithozone was used as a chelating agent in this study, and acetone was used as a diluent to dissolve the sedimented phase in the DLLME method. The volume of 600 μL was an adequate amount of acetone used to ensure that sufficent palladium species in the samples are converted to form a complex. Cobalt extraction by MASE was also investigated (paper V). The key parameters that have an impact on the effectiveness of MASE technique were also optimized using the univariate approach. The maximum enrichment factors were obtained at the pH of 3.5; 60 min extaction time and 2.0 rpm stirring rate. Under the optimized conditions, the developed method was used for the analysis of real samples. The samples obtained from the area suspected to the exposure of cobalt were pre-concentrated using MASE prior to analysis with graphite furnace atomic absorption spectrometry (GFAAS). Hexane and dithizone were used as extraction solvent and chelating agent, respectively. The pH of the samples was adjusted using nitric acid or sodium hydroxide solution. The ammonium chloride buffer solution was used to precisely maintain constant sample pH at nearly optimal value during the MASE technique.
  • ItemOpen Access
    Synthesis and biological evaluation of novel potential anti-diabetic drugs
    (2022-11-10) Tshiluka, Ndivhuwo Raymond; Mnyakeni-Moleele, S. S.; Bvumbi, M. V.
    Glitazones are derivatives of thiazolidine with two carbonyls at 2- and 4-positions. Replacing the thio group with amino group gives rise to hydantoins while replacing carbonyl group at positions 2 with the thio group produces rhodanines. In this study, three class: glitazones, hydantoins and rhodanines were successfully synthesized using known conventional methods and evaluated for their anti-diabetic activity. The structures of synthesized compounds 103a-o, 104a-v and 105a-j were elucidated by a combination of 1H NMR, 13C NMR, HRMS and IR spectroscopic analysis. The project began by utilizing a four-step synthesis of 5-(4-arylidine)-2,4-thiazolidinedione butanoates, valinates and norvalinates 103a-o. The initial synthetic step involved conversion of 1,3-thiazolidine-2,4-dione into its potassium salt, which was then treated with ethyl (2-chloroacetamido) butanoates, valinates and norvalinates, respectively, to obtain the penultimate products. These products were then subjected to a Knoevenagel condensation reaction with different aldehydes to obtain the desired products in low to excellent yields (6-65%). Cytotoxicity results of the synthesized esters 103a-o revealed that only compound 103d and 103h were toxic exhibiting cells lives of 1374.556±168.976 and 1782.722±157.3676 μM respectively. The results of the α-glucosidase inhibitory of the newly synthesized compounds 103a-o indicated that they had no activities at 10, 50 and 100 μM. Only the butanoate 103a (33.38±5.65%), 103d (37.69±0.39%) together with valinate 103f (32.66±4.31%), 103h (29.67±3.09%) and norvalinate 103m (31.83±2.85%) and 103o (51.49 ±5.65%) were found to be moderately active against α-glucosidase at 200 μM. The second part of this study describes the synthesis of 5-(4-benzylidine)-2,4-hydantoin esters 104a-v, which were successfully synthesized over four reaction steps using conventional methods. Their synthesis began by subjecting hydantoin to Knoevenagel condensation reaction conditions with different aldehydes to obtain penultimate products which were further reacted with ethyl or methyl ethyl 2-(2-bromoacetamido) esters in order to obtain the desired products as esters in low to moderate yields (24-63%). In vitro cytotoxicity results of the synthesized intermediates showed that compounds 110c exhibiting 464±78 μM and compound 110d with live cell of 1997±80 μM were found to be toxic. Among the newly synthesized ethyl or methyl esters 104a-v, no α-glucosidase activities was observed at 10, 50 and 100 μM. At the highest concertation of 200 μM, alaninate 104a (51.65±2.92%), valinate (45.23±3.60%) norvalinate (42±76.3.60%) butanoate 104f (52.05±2.83 %), 104g (48.47±2.33%), 104o (57.77±2.79%) and 104p (57.41±6.38%) showed moderate α-glucosidase inhibition. The last part of this study was an attempt to design and synthesize a new series of novel 5-arylidene-2,4-rhodhanine conjugates with improved anti-diabetic biological properties. To this end some fused 5-(4-benzylidine)-2,4-rhodanine esters 105a-j was prepared by known conventional methods from readily available starting materials. The synthesis began by subjecting rhodhanine in Knoevenagel condensation with various aldehydes to obtain 5-(4-arylidne)-2,4-rhodhanines as intermediates. Finally, nucleophilic substitution of 5-(4-arylidne)-2,4-rhodhanines with ethyl 2-(bromoacetamido) esters gave the desired compounds 105a-j in good to excellent yields (52-94%). In vitro cytotoxicity results showed that unsubstituted phenyl 111a, piperonyl 111e, 3-hydro-4-methoxyphenyl 111f and furanyl 111g with live cells of 2716±289, 2372±172, 2464±132 and 2868±132 μM respectively were nontoxic among the synthesized intermediates 111a-g. In vitro toxicity results of the target compounds 105a-j showed that only the para fluorophenyl alaninate 105b exhibiting live cell of 2982±112, para nitrophenyl butanoate 105f with live cell of 2551±158 and para fluoro butanoate 105g exhibiting 2551±186 μM were found to be nontoxic. An in vitro antidiabetic screening results showed that all the synthesized compounds 111a-g and 105a-j were not activity against the α-glucosidase at 10, 50 and 100 μM. Only the unsubstituted phenyl derivative 111a among the synthesized intermediate 111a-g was the most active exhibiting moderate α-glucosidase activity of 50.44±1.31% at 200 μM. With the final synthesized compound 105a-j, para nitrophenyl butanoate 105f was the most active followed by, para fluorophenyl alaninate 105b and para nitrophenyl alaninate 105c, exhibiting α-glucoside inhibition of 51.32±3.62%, 42.88±4.33% and 40.20±1.65% respectively.
  • ItemOpen Access
    The design and synthesis of mixed ligand metal organic frameworks for xylene inclusion
    (2022-11-10) Dlamini, Nonhlahla Fortunate; Batisai, E.; Barbour, L. J.
    Host-guest chemistry, also known as inclusion chemistry, is an important subfield of supramolecular chemistry where there is great current interest owing to its great promise in the areas of separation of small molecules, sensors, and chiral separation. The term ‘inclusion compounds’ refers to the association between large compounds (host) that is able to enclose a smaller molecule (guest). This association utilizes non-covalent interactions, and the supramolecular entity is known as a “host-guest complex” or supermolecule. The aim of the study is to design and synthesize mixed ligands metal organic frameworks (MOFs) for xylene inclusion. The first part of the study involves the synthesis and characterisation of five pyridine N-donor and O-donor ligands, namely: 2,7-di(pyridin-4-yl)benzo[lmn][3,8]phenthroline-1,3,6,8(2H,7H)tetraone(Lig1), 2,7-bis(pyridin-3-ylmethyl)benzo[lmn][3,8]phenthroline-1,3,6,8(2H,7H)tetraone(Lig2), 2-(pyridin-4-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (Lig3), 2-(pyridin-4-ylmethyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (Lig4) and N,N'-bis(glycinyl)pyromellitic diimide (Lig5). The second part involves the synthesis and characterization of MOFs. The MOFs will be synthesized by reacting the pyridine N-donor ligands, carboxylate O-donor co-ligands (fumaric acid; 2.2-bipyridine; 2.2-bipyridine-4.4’-dicarboxylic acid, 4.4’-oxybis(benzoic acid) and 2.6-naphthalenedicarboxylic acid) and transition metal salts in DMF under solvothermal conditions. The synthesized MOFs were characterized using thermogravimetric analysis (TGA), single crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD). Xylene inclusion experiments were performed on the MOFs and the resulting inclusion compounds were characterized using TGA, SCXRD and PXRD.
  • ItemOpen Access
    Preparation and Characterisation of Na2Fe2(MoO4)3 Solid Solution as Potential Cathode Material in Sodium-Ion Batteries
    (2022-11-10) Moyana, Constatia; Legodi, M. A.; van Ree, Teuns; Sikhwivhilu, L. M.
    Na2Fe2(MoO4)3 is a good cathode material for sodium storage due to its low cost, non-toxicity of iron and three open dimensional crystal framework. Na2Fe2(MoO4)3 was synthesised using the one pot sol-gel method. Na2Fe2(MoO4)3 was then doped using chromium, zinc, copper, calcium and potassium to improve electrochemical performance. A sol-gel method was used to synthesise Na2MyMxFe2-x-y(MoO4)3 (where 0 ≤ x ≤ 0.5,0 ≤ y ≤ 0.5). A weakness of the synthesis method used was that it was not viscous. The presence of lead and sulphur which should not be part of the product is due to the use of iron sulphate as a source of iron. The presence of lead seems to be due to the contamination of the cathode material. The synthesized materials were calcined at 600 °C for 3 hours to produce the desired material as shown by the elemental distribution. The synthesised material was characterised by XRD, XRF, SEM-EDS, FTIR and Raman spectroscopy. The synthesis of Na2Fe2(MoO4)3 was successful because the FTIR spectra shows the observed bands of 1674.13 cm-1 for metal oxide (Na-O),1429.75 cm-1 due to (C-O),567 cm-1 due to (Fe-O) and 814.77 cm-1 due to (Mo-O), XRF shows relative the composition of the sample is Fe= 9.543 and Mo= 44.003.The SEM micrographs reveal that the morphology consists of a smooth surface with irregular shapes and particle size is approximately 1 μm. The XRD parent and doped samples present nine characteristic peaks at 13.87, 22.05, 25.60, 29.15,34.64 and 55.62° corresponding to the crystal planes 200, 311, 212, 124,420 and 0.108. Using stoichiometric amounts of reactant, Na2Fe2(MoO4)3 was doped at the Fe site and the Na site was successfully synthesised using a one pot sol-gel synthesises method followed by calcination in the presence of air for 3 hours at 600 °C
  • ItemOpen Access
    Application of modern extraction methods for determining toxic phytochemical compounds contained in Solanum plants
    (2022-07-15) Mokgehle, Tebogo Mphatlalala; Tavengwa, N. T.; Madala, Ntakadzeni; Gitari, Wilson Mugera
    The Solanum genus is among the most diverse and valuable in terms of agricultural utility and vegetable crops. This study was directed at the characterization of toxic metabolites contained in Solanum retroflexum and Solanum mauritianum following extraction by aqueous two phase extraction (ATPE), microwave assisted extraction (MAE) and pressurized hot water extraction (PHWE) with the aid of UHPLC-qTOF-MS. The application of qTOF-MS offered unprecedented sensitivity for thorough identification of similar metabolites such as solanelagnin, solanine, solamargine, solasonine and solasodine following ATPE. Furthermore, the application of ATPE in the presence of precipitating agents in a form of kosmotropes and chaotropes enabled simultaneous extraction of multiple glycoalkaloids in a single step. The ATPE technique was also observed to be a versatile technique which saw it being compatible with PHWE and MAE. In particular, the application of microwave assisted aqueous two-phase extraction (MA-ATPE) was quantitatively shown to be a better extractant of solasonine and solamargine compared to MAE and MAE+ATPE. Additionally, the synergy of microwaves and salting-out in the ‘one-pot’ MA-ATPE technique was a contributing factor for enhanced extraction of glycoalkaloids at shorter extraction periods. Multivariate chemometric studies were designed using Design Expert 11 for optimizing the extraction of solasodine (m/z 414 → 396) and solanine (m/z 868 → 722) based on MRM quantification in MA-ATPE, ATPE and PHWE-ATPE. Comparison of ATPE and PHWE-ATPE for the extraction of solasodine from Solanum mauritianum indicated that ATPE was a better extractor of solasodine by a factor of approximately 1.5. The effect of temperature in PHWE-ATPE was shown to be insignificant (p > 0.05) and could account for the lower extraction of solasodine compared to ATPE. Furthermore, the effect of mass of plant powder during ATPE was a statistically significant (P < 0.05) parameter behind the enhanced extraction of solasodine. Quantification studies based on MRM transition showed that the kosmotrope-Na2CO3 was a better extractant than the chaotrope-NaCl for solanine in MA-ATPE and solasodine in ATPE and PHWE-ATPE. This observation, herein, was due to the greater negative charge density of the divalent carbonate ion from Na2CO3, which was pivotal in salting-out of the analyte (solanine or solasodine) through the formation of strong hydrogen bonds among water molecules surrounding the solute. As a prototype, ATPE and MA-ATPE could be quick, green purification and enrichment methods for phytochemicals with strong pharmaceutical relevance, which could meet the insatiable appetite for affordable medicines in the market.
  • ItemOpen Access
    Synthesis of Novel 6-Amino-Substituted-1,2,4-Triazines scaffolds as Potential Antibacterial Agents
    (2022-07-15) Mutshaeni, Fhumulani Baldwin; Mnyakeni-Moleele, S. S.; Ramaite, I. D.I.
    1,2,4-Triazine and its derivatives have proven their importance in the biological world since they are used in the treatment of diseases like cancer and HIV/AIDS. Thus this project was aimed at synthesizing novel 1,2,4-triazine-containing compounds, 6-aryl-1,2,4-triazine-3-amines and 6-amino-1,2,4-triazine-3,5-(2H,4H)-diones compounds in particular. Synthesis of 6-amino-1,2,4-triazine-3,5-(2H,4H)-diones started by the bromination of 6-azauracil which was subsequently reacted with different amines like acyclic primary amines, aryl primary amines and secondary amines. Products were obtained in good to excellent yields. Two different classes of 6-aryl-1,2,4-triazine-containing compounds were synthesized. The first class contained the 6-aryl-1,2,4-triazine-3-amine moiety whereas the second class contained the 6-aryl-1,2,4-triazine-3,5-diamine moiety. Synthesis of the first class of compounds commenced by the bromination of 1,2,4-triazine-3-amine which was subsequently reacted with different aryl boronic acids under Suzuki coupling reaction conditions using tetrakis(triphenylphosphine)palladium(0) as a catalyst. Products were obtained in poor to excellent yields. The second class of these novel compounds were obtained by firstly aminating 1,2,4-triazine-3-amine using the Chichibabin reaction followed by the bromination step. The resultant 6-bromo-1,2,4-triazine-3,5-diamine was Suzuki coupled with different aryl boronic acids to obtain desired products in moderate to excellent yields.
  • ItemOpen Access
    Computational and adsorption investigation of some quinoxaline derivatives on selected metals in acidic media
    (2022-07-15) Masuku, Gift Moses; Murulana, L. C.; Kabanda, M. M.; Nxumalo, W.
    This research study reports the inhibition of mild steel (MS), zinc (Zn) in 1.0 M HCl and 1.0 M H2SO4, and the inhibition of aluminium (Al) in 0.5 M HCl by three selected quinoxaline derivatives namely, quinoxalone-6-carboxylic acid (Q6CA), 3-hydroxy-2-quinoxaline carboxylic acid (H2QCA), and Methyl quinoxaline-6-carboxylate (MQ6CA) at 303 – 333 K. The corrosion inhibition characteristics including corrosion mechanism, corrosion inhibition efficiencies, and inhibitor-metal adsorption/desorption behavior were analyzed using gravimetric analysis, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP). Fourier transform infrared spectroscopy (FTIR) was utilized to give more insight into the functional groups that formed or disappeared during the adsorption/desorption of the studied quinoxaline molecules on the metal surfaces. Atomic absorption spectroscopy (AAS) was employed to determine the amount of MS and Zn ions that remained in the solutions after gravimetric analysis. Density functional theory (DFT) was utilized to compute all theoretical studies. The gravimetric analysis for mild steel show that the inhibition efficiency increased with the increase in the concentrations of the studied quinoxalines and decreased with the increase in temperature of the corrosive environment, whereas for zinc the inhibition efficiency increased with the increase in the temperature of the corrosive environment for all the quinoxaline compounds. The compounds inhibited the mild steel and zinc corrosion by adsorption on the active sites on the surfaces without altering the mechanism of the adsorption process. The studied compounds obeyed the Langmuir isotherm, and this isotherm indicated the adsorption mechanism which was mixed-typed adsorption with chemisorption dominant for both mild and zinc. The trend of inhibition efficiency for both mild steel and zinc varied in the order: MQ6CA>Q6CA>H2QCA. PDP results indicated that the studied quinoxalines shifted the polarization curves towards the region of low current densities as compared to the uninhibited system, which suggested that the inhibitor molecules reduced the anodic dissolution of mild steel, zinc, and aluminium and also suppressed the hydrogen evolution reaction. The obtained potentiodynamic polarization parameters revealed that all three inhibitors studied acted as mixed-type inhibitors, that is, anodic and cathodic inhibitor that protected the mild steel, zinc, and aluminium surfaces through spontaneous adsorption. Moreover, the increase in the concentration of the inhibitors increased the inhibition efficiency. EIS results showed that the studied quinoxalines retarded the rate of corrosion of mild steel, zinc, and aluminium surfaces through the adsorption process. For all the investigated metals the charge transfer resistance values increased with the increase in concentration of the inhibitors. iii | P a g e The AAS analysis revealed a decrease in the concentration of iron and zinc ions in the presence of the studied inhibitors as compared to the blank solutions. The inhibition efficiency increased with an increase in the concentration of the inhibitors. The FTIR spectra confirmed the formation of the inhibitor-Fe2+ and inhibitor-Zn2+ complexes. The obtained adsorption energies from the DFT results revealed that the studied quinoxalines exhibit a mixed-type adsorption mechanism, with the domination of the chemisorption process.
  • ItemOpen Access
    Synthesis and Characterisation of Porous Mixed-Ligand Metal-Organic Frameworks for Sorption Studies
    (2022-07-15) Mbonzhe, Luccile; Batisai, Eustina; Oliver, Clive
    Metal-organic frameworks (MOFs) have been identified as promising physisorption candidates because of their unique structures. MOFs are a class of crystalline materials consisting of coordinate bonds between metal ions and organic ligands. The permanent porosity of MOFs enables them to be applied as gas storage and, carbon capture and utilization materials. The main portion of this study describes the synthesis of new porous MOFs from simple building blocks. A total of four (4) organic ligands, namely; N,N’–bis–(3-pyridylmethyl)–benzophone diimide (L1), N,N’–bis–(3-pyridylmethyl)–biphenyl diimide (L2), N,N’–bis(pyridin-4–ylmethyl) naphthalene diimide, N,N’–bis–(3-pyridylmethyl)–biphenyl diimide (L3) and N,N’–bis(gly)–biphenyl diimide (L4) were successfully synthesized and characterized. The second part of this study describes the synthesis of five (5) new MOFs, namely; {[Zn2(OBZ)2(L2)]ꞏ(DMF)3}n (LMMOF01), {[Zn(TPA)(L4)0.5]ꞏ(DMF)2}n (LMMOF02), {[Co3(TPA)3(L1)]ꞏ(DMF)4}n (LMMOF03), {[Co(BYP)(L4)]ꞏ(H2O)}n (LMMOF04) and {[Cu(L4)0.5]ꞏ(DMF)}n (LMMOF05). The MOFs were synthesized from the reactions of the pyridyl N-donor diimide ligands, carboxylate O-donor co-ligands (terephthalic acid (TPA), 4,4-oxybis benzoic acid (OBZ) and 2,2-bipyridy (BPY)) and transition metal salts. The MOFs were characterized using single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD) and variable temperature (VT-PXRD). The thermal stability of MOFs was determined using thermogravimetric analysis (TGA) and hot stage microscopy (HSM). SCXRD revealed that LMMOF01 and LMMOF03 are 3-D, LMMOF02 is 2-D while LMMOF04 and LMMOF05 are 1-D. The 2-D and 3-D MOFs possess channels that are occupied by the solvent molecules. The porosity of the MOFs was tested using carbon dioxide, nitrogen and hydrogen gases.