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Item Open Access Computational study of the molecules of selected acylated phloroglucinols in vacuo and in solution(2012-12-19) Kabanda, Mwombeki Mwadham; Mammino, Liliana; Ghio, CaterinaItem Open Access Computational study of antimalarial pyrazole alkaloids from newbouldia laevis in vacuo and in solution(2014-11-03) Bilonda, Kabuyi Mireille; Mammino, Liliana.; Ghaio, Caterina.Item Open Access Study of frontier orbitals and close-to-homo orbitals of acylphloroglucinols(2015-01-13) Tshiwawa, Tendamudzimu; Mammino, Liliana; Ghio, CaterinaItem Open Access Synthesis and properties of some electrolyte additives for lithium-ion batteries(2015-02-19) Bebeda, Avhapfani Wendy; van Rhee, T.As an alternative energy source, lithium ion batteries have become increasingly important with a wide range of applications in industry, and many international companies are investing in this big project. This study was aimed at the development of safer lithium-ion power sources by using new organic additives to overcome the possible safety problems. In this study, the conformations and energies of several synthesized boronates were investigated through computational study using density functional theory (DFT) with the Becke’s three-parameter hybrid method utilizing the Lee-Young-Parr correlation functional (B3LYP). After initial energy optimization using Møller-Plesset Perturbation theory (MP2), the conformational preferences and energetics in vacuo were investigated using DFT calculations and the 6-31G(d,p) basis set. Subsequently, cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the compounds in terms of their usefulness as electrolyte additives. At least two of these show excellent promise for use in lithium-ion batteries.Item Open Access A study of the chemical components of extracts from kirkia wilmsii and an investigation into their properties(2015-02-24) Chigayo, K.; Mojapelo, p. l. m.; Chimuka, p. b.Item Open Access Synthetic and spectroscopic studies of 6-substituted chromone derivatives(2015-05) Ramonetha, Thata Golden; Ramaite, I. D. I.; Van Rhee, T.See the attached abstract belowItem Open Access Design and synthesis of potential malaria cysteinyl protease inhibitors(2015-05) Nethavhani, Sedzani A.; van Ree, T.; Ramaite, I. D. I.See the attached abstract belowItem Open Access Synthesis characterization and in vitro studies of some transition metal complexes of artesunate and chloroquine diphosphate antimalarial drugs(2015-05) Adeyemi, Oluwasegun Jerry; Legodi, M. A.; Traore, A. N.See the attached abstract belowItem Open Access The search for novel compunds targeting PfCDPK4 for therapeutic treatment of Malaria(2016-02-12) Makungo, Thomas; Van Ree T.; Tsekoa Tsepo; Mancama DaluDue to the increasing incidence of Plasmodium strains that are resistant to current frontline antimalarial drugs, malaria remains a global public health challenge. In recent years, the emergence of resistance to frontline antimalarial drugs including the more recently discovered artemisinin class drugs has become one of the greatest challenges of controlling malaria incidence and mortality. There is, therefore, an urgent need to develop novel targets and antimalarial drugs that are effective against drug-resistant malarial parasites. Recent studies have demonstrated that calcium dependent protein kinases (CDPKs) regulate a variety of biological processes in the malaria parasite Plasmodium falciparum and that CDPK4 is important for parasite development. The gene disruption of CDPK4 in Plasmodium berghei, which results in major defects in sexual differentiation of the parasite has highlighted the importance of CDPK4 in Plasmodium biology and suggests that it may be used as a target for therapeutic drugs. PfCDPK4 is expressed in the gamete/gametocyte stage, and this could make PfCDPK4 an essential target for malaria drug discovery. The structure of PfCDPK4 was used as a template in the discovery of malaria drug leads and in designing chemical compounds or inhibitors that will show anti-parasitic activity against the target molecule. The model structure of PfCDPK4 was generated through homology modelling, and model structure validation confirmed that the model structure of PfCDPK4 is of stereochemical quality. The molecular modelling approach of in silico screening was utilized in this research, wherein a large library of chemical compounds, some natural chemical compounds, and clinically approved kinase inhibitors were screened against the target molecule PfCDPK4. In silico screening of the Bio-Focus library against PfCDPK4 resulted in twenty-six compounds being identified; in vitro single screening at a concentration of 5 μM confirmed that three compounds exhibit moderate antimalarial activity against the NF54 strain of Plasmodium falciparum, with the percentage inhibition ranging between 42% and 47%.Item Open Access Phytochemical, biological and toxicity studies of terminalia sericea burch. (Combretaceae)(2018-05-18) Anokwuru, Chinedu Prosper; Ramaite, I. D. I.; Bessong, P. O.; Combrick, S.Terminalia sericea Burch. ex. DC (Combretaceae) is one of the 50 most popular medicinal plants in Africa. The fruit, leaves, stems and roots are commonly used for the treatment of cough, skin infections, diabetes, diarrhoea, venereal diseases and tuberculosis. However, the roots are most commonly used in the preparation of traditional medicines. Pharmacological studies have revealed that the crude root extracts display antibacterial activity against several Gram-positive and Gram-negative bacteria. Anolignan b, termilignan b and arjunic acid are reported to be the major antibacterial constituents present in the roots. Other compounds isolated from the roots include resveratrol-3-rutinoside, sericic acid, sericoside and arjunglucoside I. Authorities worldwide, including the Medicines Control Council of South Africa, have begun to regulate herbal drugs sold in the form of commercial formulations. Quality control of herbal drugs is challenging, since the chemical profiles of the raw materials may vary, depending on the origin of the plant material and the way that it was handled and processed. The chemistry, in turn, impacts on the safety and efficacy of the plant material. To date, there are no available data on parameters that can be used to standardise the quality of T. sericea raw materials. The aim of this study was therefore to provide information on the variation of the chemical constituents that contribute to the biological effects of the roots of T. sericea and also establish its safety. Since the compounds previously isolated from the roots were not commercially available, isolation of the major constituents of the roots was undertaken to obtain analytical standards. A crude dichloromethane:methanol (1:1) extract was initially fractionated using silica gel column chromatography, where after, some of the fractions were further purified using silica gel and Sephadex LH-20 column chromatography. Final purification of the enriched fractions was achieved using preparative high performance liquid chromatography coupled with mass spectrometry (prep-HPLC-MS). The structures of these compounds were subsequently elucidated using one- and two- dimensional nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry and identified as sericic acid (340 g), sericoside (500 g), resveratrol-3-rutinoside (240 mg) and arjunglucoside I (74 mg). The chemical variation within the crude root extracts of samples (n = 42) from ten populations in the Limpopo Province of South Africa, was determined using ultra performance liquid chromatography-mass spectrometry (UPLC-MS). A method was developed for the simultaneous determination of sericic acid, resveratrol-3-rutinoside, sericoside and arjungluicoside I in the extracts using UPLC with photodiode array detection (PDA). The method was validated according to the guidelines of the International Council for Harmonisation (ICH). A regression coefficient (R2) of 0.998 was obtained for sericic acid, resveratrol-3- rutinoside and arjunglucoside I, while the R2 value for sericoside was 0.999, indicating a linear relationship between the concentration and the detector response. Satisfactory limits of detection for sericic acid (25.2 ng/mL), sericoside (11.6 ng/mL), resveratrol-3-rutinoside (23.3 ng/mL) and arjunglucoside I (8.81 ng/mL) were determined. Recoveries of 98 % and 80% were obtained for samples spiked with 12.5 μg/mL and 25 μg/mL of resveratrol-3-rutinoside, respectively, indicating that the method is accurate. The intra- and inter-day variation in resveratrol-3-rutinoside concentration, measured over three days, indicated excellent analytical precision, since all the relative standard deviations were below 0.70 %. The quantitative data revealed that sericic acid (1.59 to 8.45 mg/g), sericoside (2.07 to 20.17 mg/g), resveratrol-3-rutinoside (0.65 to 29.82 mg/g) and arjunglucoside I (0.86 to 8.44 mg/g dry weight) were the major constituents of the root samples, but their concentrations were highly variable. Chemometric analysis of the aligned UPLC-MS data was used to investigate similarities and differences in the chemical profiles of the samples using an untargeted approach. A principal component analysis (PCA) model was constructed and subsequently hierarchical cluster analysis (HCA) indicated the presence of two main groups, which were found to be independent of the populations to which the samples belong. Classes, based on the HCA class identifiers, were subsequently assigned to the samples, and an orthogonal projection to latent structures-discriminant analysis (OPLS-DA) model was then constructed, (R2 cum = 0.996 and Q2 cum = 0.967). The corresponding loadings plot allowed sericic acid, sericoside and resveratrol-3-rutinoside to be identified as biomarkers associated with the first group. Quantitative, rather than qualitative differences were responsible for the observed clustering pattern. Techniques that could be applied in quality control protocols for T. sericea root were investigated. High performance thin layer chromatography (HPTLC) analysis of the root extracts was optimised by testing different developing solvents and visualization reagents. The presence of the sericic acid (Rf = 0.80), sericoside (Rf = 0.49) and resveratrol-3-rutinoside (Rf = 0.36) were clearly visible on the plates. There were visible variations in the concentrations of resveratrol-3-rutinoside in representative samples from the 10 populations, corresponding to the UPLC results. The powdered samples were then analysed by mid-(MIR) infrared spectroscopy. Chemometric analysis of the data revealed no definitive clustering pattern. Partial least squares-discriminant analysis (PLS-DA) calibration models were established from the MIR spectral data combined with the accurate UPLC-values, for the prediction of the sericoside (R2Y = 0.848, Q2 = 0.757, RMSEP = 2.70 mg/g) and resveratrol-3-rutinoside (R2Y = 0.794, Q2 = 0.695, RMSEP = 4.37 mg/g) concentrations in powdered root samples. The antibacterial activities of the root extracts, column fractions and isolated compounds were determined using three Gram-positive and five Gram-negative bacteria, all selected due to their ability to cause intestinal and skin disorders. Extracts and fractions containing high concentrations of sericic acid exhibited the highest activities against Klebsiella pneumoniae (ATCC 13883), Pseudomonas aeruginosa (ATCC 27858), Salmonella typhimurium (ATCC 14028), Staphylococcus aureus (ATCC 25923), Staphylococcus epidermidis (ATCC 12223) and Shigella sonnei (ATCC 9292). The pure compound (sericic acid) was highly active against S. sonnei (MIC 0.078 μg/mL), a Gram- negative bacterium. There were no variations in the activity of the crude extracts against B. cereus and P. aeruginosa, while the MIC values obtained against S. typhi were variable and ranged from 0.25 to 1.0 mg/mL. Sericoside and resveratrol-3-rutinoside did not display any activity. The anti-oxidant activities were evaluated using DPPH (2,2-diphenyl-1-picrylhydrazyl) and reducing power assays. The anti-oxidant assays revealed that resveratrol-3- rutinoside exhibited lower activity (DPPH = 186 μg/mL; RP = 184 μg/mL) compared to the crude extract (DPPH = 22.3 μg/mL; RP = 24.4 μg/mL) and ascorbic acid (DPPH = 11.3 μg/mL, RP = 145 μg/mL). Sericic acid and sericoside did not display any anti- oxidant activities. The variation in the anti-oxidant activities (4.58 to 26.0 μg/mL) of the samples from different populations was an indication of chemical variability. A toxicity study of the raw powdered plant material was conducted using vervet monkeys (Chlorocebus pygerythrus). Biochemical analysis (liver function tests, kidney function tests and hematology), physical and physiological examinations were conducted. The subjects were fed a normal diet supplemented with T. sericea root powder (2.14 g/kg per day) for 120 days, where after the diet was returned to normal (washout) for another 30 days. The treatment groups presented with elevated serum enzymes at Week 4, followed by the reduction of the elevated serum enzymes levels at Week 12. These results indicate short-term hepatotoxic effects, followed by hepatoprotective activity. Reduction of the serum glucose at Week 4 suggests hypoglycemic potential. However, elevated serum creatinine levels indicated possible nephrotoxicity. In conclusion, this study has indicated the variability in the chemical constituents of the roots of T. sericea, which affects the antibacterial and anti-oxidant activities. Sericic acid, resveratrol-3-rutinoside, and sericoside were, for the first time, identified as biomarkers that can be used for the quality control of raw root material to be used in herbal products. Sericic acid was also found to be the main antibacterial constituent of the roots. The hepatoprotective, nephrotoxic and hematotoxic effects observed in monkeys to which the root powder had been administered is cause for concern.Item Open Access Investigation of anticorrosive properties of some ionic liquids on selected metals(2018-05-18) Nkuna, Anitah; Legodi, M. A.; Murulana, L. C.; Kirui, J. K.The corrosion potential of three ionic liquids (ILs) namely, 5-(Trifluoromethyl)dibenzothiophenium tetrafluoroborate (TDTB), 5-(Trifluoromethyl)dibenzothiophenium trifluoromethanesulfonate (TDTM) and 1-Ethyl-3-methylimidazolium ethyl sulfate [EMIM][ESO4] was studied for mild steel and zinc corrosion in 1.0 M hydrochloric acid using electrochemical, spectroscopic and gravimetric techniques. The studied ILs showed appreciable inhibition efficiencies at the considered concentration range. The highest inhibition efficiencies were observed at 30°C when inhibitor concentration was 8.0 × 10-2 M. The gravimetric data revealed that inhibition efficiencies decreased with an increase in temperature, the lowest inhibition efficiencies for mild steel and zinc were observed at 50°C. The potentiodynamic polarization results indicated that all three inhibitors are mixed-type inhibitors, with TDTM being a predominantly anodic inhibitor. The orders of inhibition efficiency at 8.0 × 10-2 M were TDTM > TDTB > [EMIM][ESO4] and TDTB > TDTM > [EMIM]ESO4] for mild steel and zinc, respectively. All inhibitors showed superior performance in mild steel than in zinc. The adsorption of the studied ILs on mild steel and zinc obeyed the Langmuir adsorption isotherm. The Gibbs free energy of adsorption (ΔG°ads) indicated that the adsorption process was spontaneous, and that corrosion inhibition occurred by a physical adsorption process. Surface morphology analysis through scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) revealed a great improvement in the surface morphologies of mild steel and zinc specimens in the inhibited systems. The Fourier transform infrared spectroscopy studies confirmed the chemical interactions between the metal surface and the ILs. This is observed by means of the disappearance of characteristic absorption bands in the adsorption film FTIR spectra.Item Open Access Synthetic studies and biological evaluation of chromone - 3 - carbaldehydes(2018-08-21) Gordon, Allen Tauya; Ramaite, I D. I.; Muyakeni - Moleele, S. S.Chromones are well known naturally occurring heterocyclic compounds with oxygen as a heteroatom. Chromones are also one of the major classes of naturally occurring compounds, and the interest in their chemistry is due to their wide range of their biological activity. In this study, three classes of target compounds were synthesized through three different pathways. The first pathway, chromone-3-carbaldehyde analogues were afforded in good to excellent yield followed by the oxidation thereof to 4-oxo-4H-chromene-3-carboxylic acids. A series of chromone-3-carboxamides was obtained from corresponding 4-oxo-4H-chromene-3-carboxylic acid via the in situ generation of the corresponding acid chloride in good yield. The second class of compounds were achieved by reacting corresponding chromone-3-carbaldehyde analogues with thiazolidine-2,4-dione to afford 5-((4-oxo-4H-chromen-3-yl)methylene)thiazolidine-2,4-dione analogues. The third class of compounds followed the same reaction pathway as the second class of compounds from corresponding 8-allyl-chromone-3-carbaldehyde analogues to afford 5-((8-allyl-4-oxo-4H-chromen-3-yl)methylene)thiazolidine-2,4-dione analogues in good yield. Compounds were characterized by 1D NMR (1H, 13C and DEPT), 2D NMR (COSY, HSQC and HMBC), IR and elemental analysis (CHN analysis). Selected synthesized chromone derivatives were evaluated in vitro for two biological assays; namely trypanocidal activity and cytotoxicity. Among all tested compounds, 41A, 55B and 63D displayed promising trypanocidal activity by reducing the percentage parasite viability to 0.61, 0.15 and 0.21 respectively. These results were further substantiated by their IC50 values 4.3, 1.3 and 1.9 μg/mL respectively. Compounds 41B and 59A also showed significant trypanocidal activity, however it was below the positive control. Compounds 41A and 55B displayed cytotoxicity against the HeLa cells whilst compound 63D displayed no toxicity against the HeLa cells.Item Open Access Isolation and structure elucidation of bioctive compounds from Rauvolfia Caffra Sond(2018-09-21) Tlhapi, Bafedile Dorcas; Ramaite, I.D.I.; van Ree, T.Rauvolfia caffra Sond, a species of evergreen trees and shrubs in the dogbane family, (Apocynaceae), is used as a medicinal plant among traditional communities in many countries for the treatment of malaria, diabetes, coughs, gastrointestinal disturbances, skin infections, impotence, insomnia, diarrhoea, dysentery, scabies, worm infections, and both parasitic and microbial infections. Phytochemical studies have revealed that indole alkaloids are the major constituents of the stem bark. However, there are limited studies linking the compounds with the ethnomedicinal uses. The aim of this study is to isolate and characterize bioactive compounds from Rauvolfia caffra Sond. The highest phenolic content found in a fraction was 16.06±0.125 mg GAE/g, while the highest flavonoid content measured was 9.453±0.081 mg QE/g. In the DPPH free radical scavenging activity and reducing power tests, a lowest IC50 value of 0.022±0.003 μg/mL and IC0.5 value 0.518±0.044 μg/mL, respectively, was found. Six compounds were isolated from the stem bark, including lupeol, a pentacyclic tri-terpenoid isolated for the first time from the genus Rauvolfia; raucaffricine, a rare glycoalkaloid of the monoterpenoid indole class; N-methylsarpagine, an indole alkaloid isolated for the time from R. caffra and spegatrine, an indole alkaloid isolated for the first time from R. caffra, respectively. Concerning antimicrobial activity, the highest activity of a fraction was against B. cereus with MIC values as low as 12.5 mg/mL. One fraction at the tested concentration (250 μg/mL) decreased the viability of Plasmodium falciparum (4.149±6.979 %) with an IC50 value of 6.533 μg/mL. The crude extract and some fractions affected the viability of the Trypanosomes at the tested concentration (250 μg/mL), giving -0.133 ± 0.206 %, 11.334 ± 2.692 %, 1.026 ± 0.143 % and 20.769 ± 9.054 % with IC50 values of 18.50 μg/mL, 14.15 μg/mL, 15.58 μg/mL and 34.71 μg/mL, respectively. Furthermore, the fractions did not show significant cytotoxic effects at a concentration of 50 μg/mL.Item Open Access Synthesis of Glitazone Analogues as Anti-Diabetic Drugs(2018-09-21) Tshiluka, Ndivhuwo Raymond; Mnyakeni - Moleele, S. S.; Ramaite, I D. I.In this study, three series of novel glitazones (acetates, glycinates and alaninates) were designed and prepared by using appropriate synthetic methods to incorporate aromatic ring, alicyclic amines and alanine moiety instead of glycine moiety as a linker via two carbons. This was done over five reaction steps. Compounds were synthesized using conventional methods from step one with nucleophilic substitution to Knoevenagel condensation reaction as the final step and were characterized by using a combination of 1H NMR, 13C NMR, IR spectroscopies as well as HRMS analysis. Fourteen final compounds were successfully obtained in good to excellent yields. Furthermore, the same compounds were subjected to in vitro screening for their inhibitory activities against α-glucosidase and α-amylase. Among all the synthesized compounds, 36f exhibited excellent antidiabetic activities against α-glucosidase. Compounds 36a, 36b, 36i and 36j also displayed good activities and have potential to be further investigated whereas compounds 36c, 36e, 36g and 36h exhibited moderated activities against α-glucosidase. Only compounds 36a, 36b, 36f, 36i and 36j displayed weak activities against α-amylase and the rest of the compounds were not active at all against α-amylase.Item Open Access Synthesis of Novel -1, 3, 5 - Triazine - Based - Anti-Tuberculosis Drugs.(2018-09-21) Rapudi, Munaka; Moleele, S. Mnyakeni; Ramaite, I. D. I.Identification of unique leads represents a significant challenge in drug discovery. This challenge is widely visible in neglected diseases such as tuberculosis, which is an infectious disease caused by bacillus Mycobacterium tuberculosis. The urgent need in search of new biological entities to fight back TB and drug resistant TB is a drive behind this project. Several specific synthetic protocols have been developed using 1,3,5-triazines due to the important biological properties which they display. The chemistry and an extensive spectrum of biological activities of s-triazines have been examined since several decades and this heterocyclic core has received emerging consensus. Hence, the aim of this project was to synthesize novel anti-TB drugs total with the usage of 1,3,5-triazine as a linker between known anti-TB drugs together with different types of amines. A total of 20 compounds were synthesized, 3 compounds were mono-substituted with an average yield of 75 %, 6 compounds were di-substituted with an average yield of 63 % and 11 compounds were tri-substituted with an average yield of 93 %. Out of 10 compounds which were analysed for biological activity 8 of which showed biological activity against M.smegmatis. Furthermore compound 26 which was hybridized with an amine and a known anti-TB drug inhibited better biological activity. In conclusion the influence of cyanuric chloride in combination with pyrrolidine and anti-TB drugs deserves further study. The newly synthesized compounds were characterized by IR, melting point, GC-MS, biological testing, 1H and 13C NMR.Item Open Access Determination of anions and cations in natural water(2018-09-21) Netshifhefhe, Humbelani Kelly; Ramaite, I. D. I.; Puka, R.Surface water is used for domestic and agricultural activities in Musina region and other surrounding areas. This is because of the shortage of potable water. As a result, the people living in the region and its surrounding areas are potentially exposed to hazardous contaminants that may be present in the surface water. It is therefore important to ascertain the quality of the surface water in the region. Surface water samples were collected from Mutale, Nwanedi, Tshipise and Nzhelele rivers. The samples were analysed for anions such as fluoride (F-), chloride (Cl-), nitrate (NO3-), phosphate (PO43-), sulphate (SO42-); cations such as aluminium (Al), calcium (Ca), iron (Fe), potassium (K), magnesium (Mg), sodium (Na) and trace metals such as lithium (Li), vanadium (V), chromium (Cr), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), molybdenum (Mo), cadmium (Cd), thallium (Tl) and lead (Pb) by using analytical techniques such as IC, ICP-OES and ICP-MS. The same samples were also investigated for other parameters such as pH, temperature, EC, TH, TDS, Na % and SAR. The WHO (2008), SANS 241 (2006) and Canadian guideline (2017) were used as a water quality guideline for drinking purposes. Higher concentrations of Li, V, Cr, Ni, Cu, Zn, Al, Ca, Mg, K and Na in river water were detected in rainy season, whereas higher concentrations of As, Mo, K and Fe were recorded in dry season. The concentration of F-, Cd, Tl and Pb showed low contamination level in river samples. The results demonstrated that Tshipise river water was contaminated with high concentration of parameters: TDS (1864.0.8-3372.8 mg L-1), EC (2960.3-5270 mS cm-1), F- (6.403-8.419 mg L-1), SO42- (289.657-326.598 mg L-1), Na (836.690-922.810 mg L-1) and As (10.017-11.267 μg L-1) and relative to the (WHO) water guidelines. Nwanedi river also showed higher values of EC (298.0-699.0) mS cm-1 and TDS (190.3-447.5) mg L-1. In this study, the results indicated that water from Tshipise and Nwanedi river is not suitable for human consumption based on the guidelines of drinking water. The results also indicated that the soil sample had abundance of Ca, Al, Mn and Fe with concentration ranging from 0.13-10595, 0.0084-4.16, 0.0455-1116.5, 2.4-287404 mg Kg-1 respectively.Item Open Access Synthesis of 1, 3, 5 - Triazine Based Antimalarial Drugs(2018-09-21) Mugwena, Dakalo Sandra; Mnyakeni-Moleele, S. S.; Ramaite, I. D. I.This dissertation focuses on the application of 1, 3, 5-triazine in a pharmaceutical point of view since it has wide range of uses as described in chapter 1. Malaria is one of the most prevalent and deadly infectious diseases worldwide though there are already many synthesized anti-malarial drugs which are in use presently, drug resistance seems to be one of the major problem and combination therapy seems to be the only solution for now. Hence in this study we used hybridization as a tool (Figure 9) to synthesize new antimalarial drugs using 1, 3, 5-triazine as an intermediate linker, linking known anti-malarial drug, different amine and chloroquine-like amines together using nucleophilic substitution reaction. As explained in chapter four of this dissertation, triazine is used to synthesize mono-, di- and tri-amino-1, 3, 5-triazine substituted products. Using THF as a solvent and K2CO3 as a base changing in temperatures, from 0 oC 25 oC or reflux. Some products were synthesized using microwave irradiation. The application of triazine as an intermediate linker in the above mentioned condition yielded five mono-amino substituted dichloro-1, 3, 5-triazine (21-25) in an average yield of 82%, three amino substitution chloro-1, 3, 5-triazine (26-28) in an average yield of 87%, two amino substituted-1, 3, 5-triazine (29, 30) in an average of 90%, nine chloroquine-like synthesized compounds (33-41) in 84 % average yields respectively.Item Open Access Computational study of antimalarial alkaloids of plant origin(2019-05-15) Bilonda, Kabuyi Mireille; Mammino Liliana; Ghio, CaterinaThis thesis is concerned with the computational study of naphthylisoquinoline alkaloids having antimalarial properties. The study was considered interesting because of the importance of gathering information on antimalarial molecules and because these molecules had not yet been studied computationally. The alkaloids considered in this study had been isolated from tropical lianas belonging to the Dioncophyllaceae and Ancistrodaceae families. They comprise alkaloids with both monomeric and dimeric structures. The monomeric structures consist of one unit and the dimeric ones of two units, with each unit containing a naphthalene moiety and an isoquinoline moiety. 33 monomeric molecules were studied, which represent a large portion of all the monomeric naphthylisoquinoline alkaloids isolated so far. Two dimeric molecules with antimalarial activity were investigated, namely, jozimine A2 and mbandakamine A. A third dimeric molecule, with a structure close to that of jozimine A2 but different activity (michellamine A, anti-HIV) was also calculated for comparison purposes. This work utilised electronic structures methods and involved the conformational study of all the molecules selected to identify the stabilising factors in vacuo and in solution. Two levels of theory (HF/ 6-31G (d,p) and DFT/B3LYP/ 6-31+G(d,p)) were utilised to compare their performance for compounds of this type, also in view of a future study extending to other compounds of the same class. The molecules were firstly studied in vacuo and secondly in three different solvents – chloroform, acetonitrile and water – characterized by different polarities and different H-bonding abilities. Quantum chemical calculations in solution were carried out using the Polarisable Continuum Model (PCM). The main stabilizing factors are the presence and types of intramolecular hydrogen bonds (IHBs), which are the dominant factors, and also the mutual orientation of the moieties. The possible IHBs comprise OH⋯O (or OH⋯N and NH⋯O for mbandakamine A) and other H-bond types interactions such as OH⋯ and CH⋯O (or CH⋯O and CH⋯N for mbandakamine A). The moieties prefer to be perpendicular one to another, which is a common tendency of aromatic vii systems. In monomeric structures, there may be only one OH⋯O and possibly also one of each of the other two types of IHBs interactions. In dimeric structures, there may be up to four (five in mbandakamine A) OH⋯O IHBs simultaneously and also other H-bond type interactions. The results provide a comprehensive picture of the molecular properties of these compounds, such as conformational preferences, dipole moments, HOMO-LUMO energy gaps, harmonic vibrational frequencies, solvent effect and influence of the solvent on molecular properties which respond to polarisation by the solvent. Altogether, these results may contribute to a better understanding of their biological activity and to the design of molecular structures with enhanced biological activity. This is the reason of focusing the efforts on the investigation of chemical and physical properties of these alkaloids molecules.Item Open Access Determination of the mineral composition of water and soil samples from Tshipise thermal spring, Mphephu thermal spring and Siloam borehole using inductively coupled plasma mass spectrometry and x-ray fluorescence spectrometry(2019-05-17) Dube - Johnstone, Nhlalo Michael; Mnyakeni-Moleele, S. S.; Puke, L. R.In this study, three sampling sites (Tshipise thermal spring, Mphephu thermal spring and Siloam borehole) in Limpopo Province South Africa were considered for an investigation into the mineral composition of their water and soil samples. Tshipise and Mphephu thermal springs are well developed and located within tourist resorts. On the other hand, Siloam is a borehole on the grounds of a private household. The water is used for various domestic purposes such as laundry, general cleaning of the household and bathing. Water and soil samples from the three sites were collected once per week every week in February 2018. The sampling bottles were spiked with 1M HNO3 before sampling to keep any metal ions present in the water samples in solution. The soil and water samples were analysed for their chemical composition using X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) respectively. XRF analysis of the soil samples found many major oxides of which SiO2 made up 63.67%, 85.37% and 46.28% by mass of Tshipise, Mphephu and Siloam soil samples respectively. XRF analysis also showed the presence of dangerous levels of heavy metals such as As, Tl, Pb and V. The analysis of the water samples by ICP-MS found that Tshipise, Mphephu and Siloam mineral water were soft, soft-moderately hard and soft-hard respectively with regards to the water hardness scale according to the United States Geological Survey (USGS) and the Water Quality Association (WQA). Analysis of water samples also found the presence of As, Cd, Cr and V. Arsenic was found to occur at concentrations above the Maximum Allowable Concentration (MAC) set by the World Health Organisation (WHO) (10 μg L-1) for Tshipise, Mphephu and Siloam mineral water (13.63 μg L-1, 15.83 μg L-1 and 20.97 μg L-1 respectively). Water temperatures for the three sites ranged from 38°C (Siloam borehole) to 64°C (Tshipise thermal spring). The pH values were 7.25 (Siloam borehole), 7.40 (Mphephu thermal spring) and 8.67 (Tshipise thermal spring). Due to the presence of As, Tl, Pb, V, Cd and Cr, the mineral water from all three thermal springs is unsafe to consume as it would lead to serious negative health effects some of which are outlined in this study.Item Open Access Isolation and characterization of antidiabetic constituents of Bridelia Micrantha(2019-08-20) Maluleke, Khanyisa Amanda; Mnyakeni-Moleele, S. S.; Tselanyane, M.Bridelia micrantha (Hochst) Baill (B. micrantha) is a South African medicinal plant used by traditional healers in the treatment of different human ailments including diabetes, gastrointestinal ailments, joint aches, cough, conjunctivitis, skin problems and malaria. Previous studies have demonstrated the antidiabetic activities of B. micrantha crude extracts in in vivo studies. However, there are no studies on the compounds responsible for the antidiabetic activity of the plant. The purpose of this study was to isolate and characterize the antidiabetic constituents from B. micrantha. Materials and methods Crude methanolic extracts of root, stem and leaf were investigated using in vitro antidiabetic enzyme assays. Antioxidant activities were evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing power assays. The isolation of the antidiabetic constituents was carried out using column chromatography on silica gel. Purification of the active fraction was carried out using preparative thin layer chromatography (pTLC). Structure elucidation of the compound was carried out using Nuclear Magnetic Resonance (NMR) spectroscopy and by comparison with literature. Results The results obtained in this study indicated that root, stem and leaf extracts exhibited high inhibition activity against α-glucosidase (98.52, 98.62 and 81.62% respectively). A moderate inhibition against α-amylase enzyme was observed for root (65.62%) and stem (61.86%) extracts. Leaf fraction LFR5 exhibited a high inhibition activity of 96.19% against α-glucosidase. Moreover, the isolated compound showed 96.74% inhibition against α-glucosidase. DPPH results revealed that antioxidant activity of crude extracts was not significantly different and they were concentration-dependent. Reducing power results revealed that stem (119.31 μg/mL) extract had higher activities compared to root (125.17 μg/mL) and leaf (291.88 μg/mL) extracts. Conclusion Quercetin-3-O-β-D-glucopyranosyl-(1→4)-α-L-rhamnoside was successfully isolated from B. micrantha leaves. Furthermore, quercetin-3-O-β-D-glucopyranosyl-(1→4)-α-L-rhamnoside demonstrated the ability to inhibit significantly the carbohydrate hydrolysing enzyme α-glucosidase and therefore validate the ethnomedicinal use of B. micrantha in the management of diabetes