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Item Open Access AB INITIO and DFT computational study of Myristinin A and A structurally- related molecule(2019-09-20) Tshilande, Neani; Mammino, Liliana; Ghio, CaterinaThe computational study of biologically active molecules is particularly important for drug development because it provides crucial information about the properties of a molecule, which determine its biological activities. The current work considers the results of a computational study of myristinin A and a structurally-related molecule (2-(4-hydroxyphenyl)-4-[2,4,6-trihydroxy-3-(9tetradecenoyl)phenyl]-3,4-dihydro-2H-benzopyran-7-ol, here denoted as DBPO). The two compounds pertain to the class of acylphloroglucinols. They were firstly isolated from Horsfieldia amygdaline, and they exhibit a variety of biological activities, including potent anti-inflammatory activity, potent DNA-damaging activity and DNA-polymerase ß inhibition. Their molecular structures differ only by the acyl chain. Both molecules have a bulky substituent meta to the acyl group consisting of a ring system (2-(4-hydroxyphenyl)-3,4-dihydro-2H-chromen-7-ol). The DBPO molecule can exist as cis and trans isomers in relation to the double bond present in the R chain, and both isomers are here investigated individually. The OHs ortho to the acyl group can form an intramolecular hydrogen bond (referred to as the first IHB) with the sp2 O atom of the acyl group. The phenol OHs neighbouring the substituent ring system can form O–Hπ interaction with the aromatic rings of the substituent, if suitable oriented. This study focuses on the identification of the stable conformers of these molecules (considering all the possible geometries obtainable by rotations about relevant single bonds), and of the factors stabilising the conformers. Full-optimisation calculations were performed in vacuo and also in three conveniently selected solvents. The results show that the dominant stabilising factors are the first IHB and the O–Hπ interactions. Other factors which have significant influence on conformational preferences are the orientation of the ring systems of the substituent, the orientation of the OHs on substituent, the mutual orientation of the OHs of the phloroglucinol moiety and also the orientation of the acyl chain. The results in solution are consistent with the findings of other acylphloroglucinols, for instance, the narrowing of the energy gaps and the increase of the dipole moment with the increase of solvent polarity.Item Open Access Analysis of antibiotics and PFAS as potential emerging pollutants in the water bodies and their accumulation in food samples(2021-04) Mpela, Ntshani Gershom; Tavengwa, N. T.Antibiotics and perfluoroalkyl substances (PFAS) are groups of anthropogenic substances that are found in industries and consumer products, i.e., antibiotics are used in healthcare facilities, pharmaceutical companies, and agriculture, whereas PFAS are used in industries and households. These compounds find their way into the environment through emission, landfill disposal, agricultural run-offs, irrigations, leaching and wastewater spillage. Their residues are widely detected in almost every environmental compartment. Their detection in drinking water and food is one of the global concerns. Their effect in living organisms have been widely documented ranging from allergic reaction to carcinogenic effect, and in serious situations they can lead to death. In this project, the background review on the behaviour of antibiotics and PFAS in different environments are discussed in chapter two. This has been done by looking into their physico-chemical properties, distribution pathways, accumulation and toxicity in various environmental compartments through available literature. After understanding their behaviour in the environment two review papers, namely Paper I and Paper II, were written. Paper I was a book chapter which focused on the application of miniaturised liquid phase extraction techniques used for extraction of antibiotics in environmental water samples. In this book chapter, the use of liquid-liquid extraction techniques was discussed and the evolution of liquid-liquid extraction technique into miniaturised extraction technique was reviewed. Paper II was a critical review which focuses on the application of dispersive liquid-liquid micro-extraction of PFAS in different environmental samples. In this paper, the principles of dispersive liquid-liquid micro-extraction was explained. Later, its application for pre-concentration of PFAS was reviewed and the future trends were discussed. In chapter four, three lab-based papers, namely Paper III, Paper IV and Paper V, were written. In Paper III, for the first time a dispersive liquid-liquid microextraction technique was developed and applied for extraction of multi-class antibiotics in macadamia nuts prior to UHPLC-qToF-MS analysis. In paper IV, a novel deep eutectic solvent was synthesised and characterised using FTIR spectroscopy. For the first time the synthesised deep eutectic solvent was applied for extraction of multiclass antibiotics in green beans prior to UHPLC-qToF-MS analysis. In Paper V, for the first a dispersive liquid-liquid micro-extraction technique was developed and applied for extraction of PFAS in food contact materials prior to UHPLC-qToF-MS analysis. Owing to their ease of operation, efficiency and sensitivity, these techniques can also be applied for preconcentration of antibiotics and PFAS in different food, environmental and biological samples.Item Open Access Application of modern analytical techniques for quantification of selected radioactive metals in environmental samples(2023-05-19) Nkhumeleni, Murendeni Royell; Tavengwa, N. T.; PukaIn 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.Item Open 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 MugeraThe 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.Item Open 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.Item Open Access Computational studies sulfonylureas molecules(2021-04) Vukeya, Thembani Silas; Mammino, Liliana; Ghio, CaterinaComputational studies are very important for biologically active molecules and for the development of new drugs, because the biological activities depend on their molecular structures and properties. This work presents the results of a conformational study of selected sulfonylureas molecules in vacuo. Sulfonylureas are a class of synthetic organic compounds containing a thiourea group (sulfonyl and urea groups bonded together) attached to a benzene ring, a substituent (R) on the thiourea, and another substituent (R) linked to the benzene ring by a two– or three– carbon atom chain attached to an oxygen atom which is directly attached to the benzene ring in para position with respect to the thiourea group. The interest in this class of compounds is that some compounds are used in the treatment of type 2 diabetes. Molecules with different R and R substituents have been considered. Full-optimization calculations were performed in vacuo using Density Functional Theory (DFT) and Hartree Fock (HF) methods. Attention was given to the identification of stable conformers of each of the molecules considered (obtainable by rotation of relevant bonds) and of the conformers’ stabilizing factors. The molecular properties considered include the relative energies of the conformers, the parameters of the intramolecular hydrogen bonds (IHBs), the dipole moments, the HOMO–LUMO energy gaps, and the vibrational frequencies of relevant bonds (in particular, the N–H bonds, because the N–H groups may be IHB donors). The results indicate that the number and type of IHBs are the major stabilizing factors. A maximum of three simultaneous IHBs are possible in the thiourea group. This includes the presence of bifurcated IHBs (bifurcation on the hydrogen atom of the donor), which are present in most of the stable conformers. The vibrational frequencies of the N–H bonds show changes occurring when these bonds form IHBs. The changes showed a rare phenomenon, that is, a blue shift (frequency increase) for certain IHBs, and also a much more common phenomenon (red shift. i.e., frequency decrease) for other IHBs. The geometry of the thiourea moiety, the nature of R and R, the orientation and the length of the chain between the benzene ring and R also show some influence on the calculated molecular properties.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 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 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 Corrosion inhibition exploration of synthesized carboxylic acid and amino esters on selected metals in acid medium(2020) Nesane, Tshimangadzo; Murulana, L. C.; Mnyakeni-Moleele, S. S.In this study, carboxylic acid and two ionic liquids-based amino esters were used as corrosion inhibitors for aluminium and mild steel. These compounds were selected because they are said to be non-toxic and environmentally friendly. The non-toxicity of these compounds is essential due to the increasing implementation of strict environmental regulations. The investigated compounds as corrosion inhibitors in this study include a carboxylic acid, namely, N-benzoyl2-aminobutyric acid (2-NBABA), and two amino esters which are 1-(benzyloxy)-1-oxopropan2-aminium 4-methylbenzenesulfonate (1-BOPAMS) and 4-(benzyloxy)-4-oxobutan-1aminium 4-methylbenzenesulfonate (4-BOBAMS) for aluminium and mild steel corrosion in 1.0 M hydrochloric solution (HCl) at 303-333 K. The three compounds were synthesized and characterized by spectroscopic methods (FT-IR, 13C-NMR and 1H-NMR). Their anti-corrosive properties, inhibition mechanism, inhibitor-metal adsorption behaviour and corrosion inhibition efficiency were investigated by employing several techniques such as the gravimetric, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). Fourier transform infrared spectroscopy (FT-IR) was used to investigate the functional group responsible for the adsorption/desorption process of the inhibitor molecules and those that disappeared or formed on the surfaces of mild steel and aluminium. Gravimetric analysis exhibited an increase in the inhibition efficiency as the concentrations of the inhibitors were increased for all the three inhibitors studied. Amongst the several isotherms plotted, Langmuir adsorption isotherm was found to be the best-fit isotherm for the three compounds on the metal surfaces. The isotherm provided a clear indication on the mechanism of adsorption which was mixed-type adsorption for both aluminium and mild steel. The impendence result showed an increase in the Rct values as the concentration of the inhibitors was raised, resulting in an increase in the surface coverage by the inhibitor molecules. The adsorption of the inhibitor molecules on the aluminium and mild steel surface led to the decrease in the double-layer capacitance (Cdl) as the molecules of the inhibitors replaced the water molecules at the metal/solution interface reducing the local dielectric constant while increasing the double layer thickness. The data gathered showed that the adsorption of the three inhibitors prevented the dissolution of the mild steel and aluminium in 1.0 M HCl without altering the corrosion mechanism of the metals. The PDP results obtained indicated that the three inhibitors affected both the anodic and cathodic half-reactions to a similar extent. The anodic and cathodic Tafel curves were both affected by the introduction of the inhibitors which revealed that the investigated inhibitors act as mixed-type corrosion inhibitors. Fourier transform infrared spectroscopy studies showed that the corrosion process was reduced due to the interaction of the three inhibitors with mild steel and aluminium resulting in the formation of a Fe-inhibitor and Al-inhibitor complexes.Item Open 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.Item 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 Design, synthesis and biological evaluation of novel tetra-substituted quinoline-3-carboxamides derivatives(2020-03-24) Hlungwani, Isaac; Ramaite, I. D. I.; Mnyakeni-Moleele, S. S.Quinolines are well known naturally occurring heterocyclic compounds with nitrogen as a heteroatom. Quinolines are also one of the major classes of naturally occurring compounds and the interest in their chemistry is due to the wide range of their biological activities. The objective of the project was the synthesis of novel tetra-substituted quinoline-3carboxamides and subsequent transformation to other novel derivatives and evaluation of their biological activities against malaria and cytotoxicity. In achieving the objective, 2-chloroquinoline-3-carbaldehyde analogues 54A-G were synthesised from the reaction of acetanilides 53A-G and acetic acid. Knoevenagal reaction of 2chloroquinoline-3-carbaldehydes 54A-G with thiazolidinedi-2,4-one 62 provided 2chloroquinoline-3-methylene thiazolidinedi-2,4-one 55A-G which then underwent nucleophilic substitution reaction with sodium azide and afforded (Z)-5-((tetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56A-F. (Z)-ethyl-2-(2-5-((7bromotetrazolo [1,5a] quinolin-4-yl) methylene-2,4-dioxothiazolidin-3-yl) acetamido) acetate 57 was synthesised from the reaction of (Z)-5-((7-bromotetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56D and ethyl-2-(2-chloroacetamido) acetate 65. The structures of the compounds were characterised by 1D NMR (1H, 13C, and DEPT 135), IR spectroscopy, elemental analysis and high-resolution mass spectroscopy. Novel selected synthesised quinoline compounds were evaluated of in vitro for two biological assays; namely anti-malarial activity and cytotoxicity. The anti-malaria activities of the novel quinoline compounds against 3D7 strain of the malaria parasite Plasmodium falciparum displayed that 2,6-dichloroquinoline-3-methylene thiazolidinedi-2,4-one 55C, (Z)-5-((7-fluorotetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56B and (Z)-5((7-ethoxytetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56F are potential malaria drugs since they reduced the percentage parasite viability to 25.80, 12.40 and 20.40 respectively. These results were further substantiated by their IC50 values 0.40, 0.04 and 0.50 µg/mL. Compound 56B displayed the highest cytotoxicity activity against human cervix adenocarcinoma cells displaying percentage viability of 14.22 %. Compounds 56F and 56C displayed moderate cytotoxicity activity at 56.60 and 59.81 % viability.Item Open Access Design, synthesis and biological evaluation of novel tetrasubstituted quinoline-3-carboxamides derivatives(2020-03-24) Hlungwani, Isaac; Ramaite, I D. I.; Mnyakeni-Moleele, S. S.Quinolines are well known naturally occurring heterocyclic compounds with nitrogen as a heteroatom. Quinolines are also one of the major classes of naturally occurring compounds and the interest in their chemistry is due to the wide range of their biological activities. The objective of the project was the synthesis of novel tetra-substituted quinoline-3carboxamides and subsequent transformation to other novel derivatives and evaluation of their biological activities against malaria and cytotoxicity. In achieving the objective, 2-chloroquinoline-3-carbaldehyde analogues 54A-G were synthesised from the reaction of acetanilides 53A-G and acetic acid. Knoevenagal reaction of 2chloroquinoline-3-carbaldehydes 54A-G with thiazolidinedi-2,4-one 62 provided 2chloroquinoline-3-methylene thiazolidinedi-2,4-one 55A-G which then underwent nucleophilic substitution reaction with sodium azide and afforded (Z)-5-((tetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56A-F. (Z)-ethyl-2-(2-5-((7bromotetrazolo [1,5a] quinolin-4-yl) methylene-2,4-dioxothiazolidin-3-yl) acetamido) acetate 57 was synthesised from the reaction of (Z)-5-((7-bromotetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56D and ethyl-2-(2-chloroacetamido) acetate 65. The structures of the compounds were characterised by 1D NMR (1H, 13C, and DEPT 135), IR spectroscopy, elemental analysis and high-resolution mass spectroscopy. Novel selected synthesised quinoline compounds were evaluated of in vitro for two biological assays; namely anti-malarial activity and cytotoxicity. The anti-malaria activities of the novel quinoline compounds against 3D7 strain of the malaria parasite Plasmodium falciparum displayed that 2,6-dichloroquinoline-3-methylene thiazolidinedi-2,4-one 55C, (Z)-5-((7-fluorotetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56B and (Z)-5((7-ethoxytetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56F are potential malaria drugs since they reduced the percentage parasite viability to 25.80, 12.40 and 20.40 respectively. These results were further substantiated by their IC50 values 0.40, 0.04 and 0.50 µg/mL. Compound 56B displayed the highest cytotoxicity activity against human cervix adenocarcinoma cells displaying percentage viability of 14.22 %. Compounds 56F and 56C displayed moderate cytotoxicity activity at 56.60 and 59.81 % viability.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 Determination of carbamates from samples by molecularly imprinted polymers(2021-04) Mabaso, Nyeleti Bridget; Tavengwa, N. T.; Pakade, V. F.In this work, new clean sorbent that has greater selectivity was used in the determination of pesticides residues in complex matrices at the desired limits of quantification. This work is divided into 3 papers focusing on molecularly imprinted polymers. Paper I is a review on challenges in elution of the template from molecularly imprinted polymers (MIPs). MIPs are materials that exhibit selective recognition towards the desired template. It possesses advantages of high selectivity, low-cost and low limit of detection. It is a promising alternative for natural antibodies that suffer from poor stability and high cost. However, the MIP has challenges of expensive templates, and the template might not get removed even after extensive washing or the MIP may get damaged during the removal process and this step often requires lengthy optimization which can alter the accuracy of the results. The review summarises the effective ways of washing off the template molecules, paying attention to the effect of washing techniques, pairing agents, and the number of elution cycles applied to achieve satisfactory template removal. It also reviews the use of dummy template and computational chemistry to select appropriate solvent and functional monomer. Finally, challenges and prospects in template bleeding are discussed. In Paper II, carbaryl was used to synthesize dummy template molecularly imprinted polymers (DMIPs) for the determination of carbofuran in grapes. The sorbent was used to selectively extract carbofuran from other closely related compounds. Carbofuran is one of the most toxic carbamate pesticides, and it is banned in most countries. Carbofuran was determined by carbaryl dummy templated molecularly imprinted polymer from grapes. FTIR characterization showed the C=O stretching absorbance in the region of 1714-1730 cm-1 between unwashed MIP, NIP, and washed MIP with different intensities. Various parameters affecting the extraction efficiency of the imprinted polymers were evaluated to optimize the selective pre-concentration of carbamates in grape samples. Under optimal condition, the enrichment factors of up to 215 were obtained. This method was successfully applied to quantitively detect carbamates residue in grape sample. The results during application showed that all the grape samples were found to contain no carbamates. In Paper III, pirimicarb is a carbamate pesticide used for controlling pests on vegetables and is used in gardens and household. Pirimicarb was determined using molecularly imprinted polymer from oranges. The MIP material was characterised with FTIR where all the peaks were similar except their intensities. The MIP and NIP were optimised using different parameters and enrichment factor of 19 was obtained. The linear range was 0.25-2.5 mg L-1 and percentage recoveries of three carbamates ranges were 69.43 -84.67%. The limit of detection and limit of quantification 0.41-0.61 and 1.24-1.86 mgL-1. The method indicated repeatability as the RSD ranged from 1.37-9.23. The potential of the developed MIP-SPE method for the selective sample clean-up were investigated in the analysis of oranges. It was found that none of the analytes were detected in the orange samples.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 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.Item Open 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.Item Embargo Hydrothermal synthesis of nano-scaled pure, Sn-doped, and Zn-doped Co3O4 structures and their gas sensing applications(2024-09-06) Letsoalo, Modjadji Rebecca; Shingange, Katekani; Maluta, Eric