Magister Scientiae - MSc (Chemistry)

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Polyphenolic, tannin and chemical compositional changes in leaves of sub-tropical grasses and fynbos shrubs at elevated atmospheric CO2 concentrations
(University of the Western Cape, 2002) Hattas, Dawood; Mabusela, Wilfred T; Stock, William D; Green, Ivan R
The effects of elevated atmospheric CO2 concentrations on plant polyphenolic concentration, tannin concentration and chemical composition were investigated in leaves of sub-tropical grass species and fynbos shrubs. The working hypothesis was based on predictions that carbon based secondary compounds (polyphenolics and tannins) would increase when carbon in excess of growth requirements accumulate in plant leaves under nutrient imbalanced conditions. This imbalance would arise due to an increase in atmospheric CO2 level. Furthermore, empirical evidence suggests that nutrient paucity would enhance carbon-based secondary compound production. This hypothesis was tested in two different systems involving plants with differential photosynthetic mechanisms and growth strategies. Polyphenolics, tannins and chemical composition (N, P, C and TNC) were quantified in grass species from a natural, C4 dominated, sub-tropical grassland in KwaZulu/Natal. Three plots were subjected to different freeair CO2 enrichment treatments, i.e. elevated (550-800 ppm), intermediate no more than 400 ppm) and ambient CO2 (currently at 365 ppm). One of the seven grass species, Alloteropsis semialata, had C3 photosynthetic mechanism. Polyphenolics, tannins and chemical composition (N, P, C and TNC) were quantified in three fynbos species grown in open-top chambers under controlled greenhouse conditions. The plants were grown under ambient (360 ppm) and ambient+ 350 ppm CO2 in typical low nutrient acid sands of the fynbos biome. This study shows that despite some of the grasses having the capacity to produce tannin-like substances, polyphenolics and tannins do not increase in the grass species studied. Polyphenolic and tannin concentrations were increased only in Leucadendron laureolum amongst the fynbos species. Its sister species Leucadendron xanthoconus did not show any change in phenolic or tannin concentrations. Chemical composition in grasses were largely unaffected by elevated CO2, however, some species-specific responses were observed. The C3 A. semialata showed a decrease in P concentration and a consequent increase in C:P ratio at elevated CO2. Only L. laureolum showed a response in chemical composition at elevated CO2, whereas its sister species did not show any response except a decrease in N concentration. In conclusion, fast growing grass species invest extra carbon into growth rather than polyphenolics and tannins and show small species-specific chemical changes at elevated atmospheric CO2 concentrations. Increased investment into phenolics and tannins as well as changes in chemical composition in fynbos species were species-specific even within plants from the same genus. Thus generalizations about plant responses to elevated CO2 based on theoretical principles cannot be directly applied. This is especially true in complex natural environments where ecophysiological processes may dictate phytochemical responses.
Electrochemical evaluation of chemically Modified microelectrodes
(2001) Moeletsi, JM; Crouch, AM
Aniline and N-alkylated substituted anilines have been polymerized by chemical and electrochemical methods. The chemically synthesized polymers indicated that N-alkylation improves solubility remarkably in common organic solvents. The compounds were characterized by FTIR, 1H NMR, TGA and also studied by cyclic voltammetry on glassy carbon macroelectrodes for comparison with electrochemical synthesized polymers.
Green synthesis of silver nanoparticles using honey from the meliponinae stingless bee species and antibacterial studies.
(University of the Western Cape, 2023) Leteba, Semphete; Mabusela, W T
Green synthesis of silver nanoparticles (AgNPs) is an environmentally friendly approach for preparing nanoparticles using biological sources as the reducing agent. Apart from using plant extracts, honey, that is used in this study affords to act as a reducing and capping agent. Silver nanoparticles have been reported to show good antibacterial and anti-inflammatory properties and can be potentially applied as antibacterial agents. Additionally, to their attractive characteristics, they are biocompatible which makes them safe for therapeutic applications. Similarly, stingless bees honey has been reported to have anti-inflammatory properties and have been historically used to heal wounds.
Organometallic improvement of some tuberculosis drugs
(University of the Western Cape, 2023) Cwasi, Phelisa; Onani, Martin
Metal-based drugs are preferred motifs that serve as major pharmacophores in bioactive compounds for a variety of diseases, including as tuberculosis (TB). Heterocyclic, Schiff bases, aliphatic amines and other ligands are among the many potential scaffolds in drug design. To contribute to the development of these drugs, we discovered the metal-based organometallic complexes that could potentially be effective against tuberculosis, which is a common bacterial infectious disease that is caused by the bacillus mycobacterium tuberculosis (Mtb). As the demand for new compounds with desired antibacterial properties has grown over the past few decades, interest in Schiff bases has also significantly increased. Thus, in this study, five Schiff base ligands namely {HL1 = (Z)-4-chloro-2-((phenylimino)methyl)phenol, HL2 = (Z)-4-chloro-2-((o-tolylimino)methyl)phenol, HL3 = (Z)-4-chloro-2-((ptolylimino) methyl)phenol, HL4 = (Z)-4-chloro-2-(((2,4- dimethylphenyl)limino)methyl)phenol and HL5 = (Z)-4-chloro-2-(((2,6- dimethylphenyl)limino)methyl)phenol} were synthesized and fully characterized and complexed with CuCl2 for the synthesis of copper (II) salicylaldimine compounds.
ISOLATION AND CHARACTERIZATION OF ANTIMICROBIAL COMPOUNDS FROM GALENIA AFRICANA
(University of the Western Cape, 2001) Vries, Felicity; Green, I.R; Klaasen, J.A
Galenia africona, commonly known as "kraalbos" or "geelbos" belonging to the family Aizoaceae, is a dominant plant throughout the Namaqualand area. It is an active invader and is especially abundant in disturbed areas around kraals, along roads, and water points which shows that it grows well on trampled soil. "Kraalbos" is not very palatable to livestock, but is grazed under pressure. The plant can cause liver damage and severe ascites, a condition referred to as "waterpens" in sheep and occasionally in goats. The Hottentots chew the plant to relieve toothache and it is said to blister the mucous membrane of the mouth if used too much. The plant was also used in the treatment of veneral diseases. Dried samples of G. africana collected in Steinkopf and Concordia were sequentially extracted with various solvents starting with hexane, chloroform, ethanol and sterile distilled water. Each concentrated extract were tested for its inhibitory activity against fungi and bacteria by using the agar well diffusion method. The mycelial growth of Fusqrium graminearum and Fusarium verticillioides cultured on PDA was inhibited by the CHCI3 and EtOH extracts. The minimum inhibitory concentration (MIC) of these two extracts was calculated for both fungal and bacterial species. Overall results showed that the EtOH extract from G. africana has strong inhibitory activity in vitro against fungi and bacteria. The above findings advocate further investigation of the EtOH extract. It will be necessary to identiff the active components and to evaluate their potential for use as antimicrobials. The ethanol extract was purified using silica gel column chromatography and thin - layer chromatography. Four fractions showed significant antifungal activity as evidenced by a clear zone of inhibition. One fraction was tested against a range of fungi and a few bacterial isolates. This fraction inhibited the growth of most of the fungal isolates with Alternaria sp., Fusarium equiseti, F. gramineorum, F. verticillioides and Phaeomoniella clamydospora being the most sensitive ones. Both Bacillus sp. and Staphylococcus atffeus were inhibited in the presence of the fraction. The MIC's for fungi showed values ranging from 10 to 2.5% and bacteria from 2.5 to 1.25 %. The active fraction inoculated onto individual filter paper disks displayed potent antifungal activity on agar plates seeded with conidia of the various fungal isolates being tested. The filter paper disk method showed more sensitivity than the agar well diffusion method in the detection of the antifungal activity of the active fraction.
The oxidation of the lower primary alcohols ln a catalytic membrane reactor
(University of the Western Cape, 2000) Masters, Gerard Jerome; Linkov, Vladimir M
Methanol and ethanol are important chemical feedstock used in industrial chemistry, since they are the starting materials for the synthesis of various products, including hydrocarbons and mild oxidation products. For instance, methanol can be oxidised to methyl format, which can be transformed into industrially important products such as N, N-dimethyl formamide or acetic acid. Both methanol and ethanol have also been used as probe reactions, in which they are used to characterise catalysts according to the type of active sites presents, namely redox, acidic or basic. The lower primary alcohols are also currently being used in fuel cell research, since the oxidation of alcohols has been proposed as an anode reaction for fuel cells. ln the latter case, the important reaction is the complete oxidation of the alcohol to carbon dioxide and water. lt is apparent from industrial examples that methanol oxidation can lead to various products by varying the nature of the catalyst and the reaction conditions.
Titanium compounds and plant growth
(University of the Western Cape, 2001) Khoza, G; Raitt, L
The effect of titanium compounds on the growth of tomato plants, Lycopersicum esculentum (cultivar Floridade), was studied under greenhouse conditions. Aqueous suspensions (TiO2) and solutions (complexes of titanium (IV) with L(+)-ascorbic acid and oxalic acid) were applied as foliar sprays and soil treatments. A new compound of titanium (IV) with L(+)-ascorbic acid was prepared and characterised. Some titanium compounds appeared to enhance some growth parameters in some instances, but titanium did not consistently result in improved growth or increased nitrogen concentration within the plants. Titanium uptake was also monitored and established by means of PIXE measurements on plant tissue.
Pyrazolyl palladium complexes with heterocyclic carbonyl linkers as catalyst precursors for ethylene and phenylacetylene polymerization.
(University of the Western Cape, 2003) Mohlala, Matshwenyego. Sarah; Darkwa, James; Mapolie, Selwyn. F
The pyrazolyl ligands 2,6-bis(3,5-r2p*azolylcarbonyl)pyridine {r : 'bu (l1), me (l2)),2,6-bis(3-methylpyrazolylcarbonyl)pyridine(l3)'2'6- bis(pyrazolylcarbonyl)pyridine (l4) and 2,5-bis(3,5-rzpyrazolylcarbonyl)thiophene { r :,bu (l5), me (l6) were prepared by the reaction of 2,6-pyridinedicarbonyl dichloride and 2,5-thiophenedicarbonyl dichloride with the appropriate pymzoles and were characterizedby,h,',c1'h}nmr,irspectroscopyandelementalanalysis.reactions of the ligands l1-l3, l4 and l5 and pdclzuecn)z in a ratio of 1:1 yielded mononuclear and binuclear complexes [2,6-bis(3,5-rzpyrazolyl-1. carbonyl)pyridinelpalladiumod dichloride tr : 'bu (1), me (2))' [2'6-bis(3- methylpyrazolyl-1-carbonyl)pyridinelpalladium@) dichloride (3) and di-p-chlorodichlorobis[ 2,5-bis(rzpyrazolyl 1+arbonyl)thiophene]dipalladium(tr) {r : tbu (4)' r : me (5)). complex i was characterized by th' "c1th) nmr' ir spectroscopy and elemental analysis while complexes 2-5, which were insoluble in most common organic solvents, were charac teizedby elemental analysis and ir spectroscopy' the structures of the ligands l3,l6and complex 1, deduced ft'om spectroscopic studies' were confirmed by single crystal x-ray diftaction analysis'
The synthesis of methoxy-2-hydroxy-1,4- naphthoquinones and their reaction with aliphatic aldehydes under basic conditions.
(University of the Western Cape, 2003) Pearce, R.S; Ameer, F; Green, I.R
Although literature reports on the synthesis of variously substituted 2-hydroxy-1 ,4- naphthoquinones appeared to be reasonable; in our hands difficulty was experienced in duplicating much of the work. In order to address this problem, two protocols were used with the one involving conversion of substituted a-tetralones into hydroxyquinones using a solution of the tetralones in an oxygenated solution of tertiary butyl alcohol containing potassium tertiary butoxide, and the other involving Diels-Alder Condensation, oxidation, pyrolysis and basic hydrolysis of a 2-methoxy-1,4-naphthoquinone 79 into the corresponding 2-hydroxy analogue 80. Condensation reaction between 2-hydroxyy-8-methoxy-1,4-naphthoquinone 80 and caproaldehyde 111, produced the 3-alkenyl analogue 115 which was cyclised to the corresponding naphtho[2,3-b ]pyrenquinone 116 and eventually reduced to 8- methoxynaphtho[2,3-b ]pyran-5, 10-dione 1) 7. Condensation between 2-hydroxynaphthoquinone 80 and 4-dioxolanopentanal under basic conditions afforded the desired adduct which was cyclised with dichlorodicyanobenzoquinone, reduced and then hydrolysed with acid to produce 2- acetyl-3,4-dihydronaphtho[2,3-b ]pyran-5, 10-dione 125. By the employment of an alternative sequence of events, the corresponding 4-hydroxy analogue of the above 2- acetylnaphthopyrandione 125 was also prepared for evaluations. Finally condensation between 2-hydroxy-8-methoxy-1,4-naphthoquinone 80 and 5- dioxolanohexanal 128 under basic conditions afforded the 3-hexenyldioxolano 129 derivative, which was cyclised to the naphthopyrene 130 but the yields were disappointing in this instance.
Hydrothermal synthesis and optimisation of zeolite Na-Pl from South African coal fly ash
(University of Western Cape, 2009) Musyoka, Nicholas Mulei; Petrik, Leslie F
Millions of tonnes of fly ash are generated worldwide every year to satisfy the large demand for energy. Management of this fly ash has been a concern and various approaches for its beneficial use have been investigated. Over the last two decades, there has been intensive research internationally that has focused on the use of different sources of fly ash for zeolite synthesis. However, most of the studies have concentrated on class C fly ash and very few have reported the use of South African class F fly ash as feedstock for zeolite synthesis. Class F fly ash from South Africa has been confirmed to be a good substrate for zeolite synthesis due to its compositional dominance of aluminosilicate and silicate phases. However, because differences in quartz-mullite/glass proportions of fly ash from different sources produces impure phases or different zeolite mineral phases under the same activation conditions, the present study focused on optimization of synthesis conditions to obtain pure phase zeolite Na-P I from class F South African coal fly ash. Synthesis variables evaluated in this study were; hydrothermal treatment time (12 - 48 hours), temperature (100 - 160 oC) and addition of varying molar quantities of water during the hydrothermal treatment step (HzO:SiOz molar ratio ranged between 0 - 0.49).Once the most suitable conditions for the synthesis of pure phase zeolite Na-Pl from fly ash were identified, a statistical approach was adopted to refine the experiments, that was designed to evaluate the interactive effects of some of the most important synthesis variables. In this case, the four synthesis variables; NaOH concentration (NaOH: SiOz molar ratio ranged between 0.35 - 0.71), ageing temperature (35 'C - 55 'C), hydrothermal treatment time (36 - 60 hours) and temperature (130 "C - 150 oC) were studied. The response was determined by evaluating the improvement in the cation exchange capacity of the product zeolite. The starting materials (fly ashes from Arnot, Hendrina and Duvha power stations) and the synthesized zeolite product were characteized chemically, mineralogically and morphologically by X-Ray fluorescence spectrometry, X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. Other ch.aracterization technique used in the study wereFourier transform infrared spectroscopy to provide structural information and also monitor evolution of crystallinity during slmthesis, as well as cation exchange capacity to determine the amount of exchangeable positively charged ions. Nitrogen adsorption was used to determine the surface area and porosity, and inductively coupled mass spectrometry for multi-elemental analysis of the post-synthesis supernatants
Substituted nick el pyrazole and palladiumpyruzolyl complexes as catalyst precursors for ethylene polymeization
(University of the Western Cape, 2003) Nelana, S; Darkwa, J
This study concerns the synthesis of pyrazole and substituted pyrazole nickel complexes of the type [(3,5-R,R',pz)2NiB rz ( Pz : pyrazole; R = R' = cHr (1), tBu (a)l and of the type [(3,5-R,R'pz)aNiBrz R: H, R' : CHr (2)] R: R' :H (3)l' These complexes were synthesized by reacting (DME)NiBrz and the appropriate pyrazole or substituted pyrazole in dichloromethane. The products were obtained in moderate to good yields. All the complexes isolated were charac teizedby a combination of IR spectroscopy, tH NNm. spectroscopy and elemental analysis' Complexes I and 2 were further characteri zedby single crystal X-ray crystallography. Complex 1 was found to have a tetrahedral geometry and complex 2 has an octahedral geometry' In addition to the pyrazole nickel complexes, new pyr.volyl ligands with alkane-o'oldione linkers tRpzC(OXCHz),C(O)pzR); R: CHr' n: 0 (A1)' n:2 (A2)'n:3 (A3) and R: tBu, n = 3 (A4)] were synthesized. These new ligands were charactenzed by IR spectroscopy, ,H NNfi, "C NNffi. spectoscopy and elemental analysis' They were further reacted with (cHrCN)2PdCl2 in attempts to obtain a'obis(3'5- Rzpyrazolyl)alkane-cr,rodione palladium chloride complexes' These ligands tend to undergo hydrolysis when they are reacted wittr (CHTCN)zPdClz as confirmed by tH NMR spectral analysis. one complex, 1,5.bis(3,5.Mezpz)pentane-1,5-dione palladium chloride was successfully prepared under very dry solvent conditions' The 1,5-bis(3,5-Mezpz)pentane-1,Sdione palladium chloride complex was characteized by 'HNMR spectroscoPY.
The synthesis of prodrugs and novel analogues of Beta-sympathomimetic bronchodilators
(University of the Western Cape, 1998) Adams, Mortimer Hilary; Ameer, Farouk; Green, Ivan R.
Prodrugs are reversible derivatives of active drugs destined to undergo chemical or enzymatic transformation to the active drug after administration in order that the active drug may subsequently elicit the desired pharmacological response . In synthesizing a prodrug, the physico chemical properties of a drug are altered by suitable functionalisation of an appropriate appendage of the drug molecule such that some barrier or problem may be circumvented or obviated in totality. Prodrugs of bronchodilators have been prod used with the aim of reducing enzymatic degradation, improving their bio-availability and, displaying a marked separation between their desirable bronchodilator and undesirable cardiovascular activities. Chlorphentermine (II), a lung accurnulating arnine, was used as a carrier molecule in novel prodrugs which potentially possess these attributes. Model prodrugs viz. CPE (20) and CPETA (t4), consisting of chlorpltentennine (ll) connected through a propionic ester link to ethanol and etafedrine (13), respectively, were synthesized by reacting the alcohols with acryloyl chloride and the resultant acrylates subsequently reacted with chlorphentennine (II). CPA (21), the prodmg hydrolysis product of CPE (20), was also synthesized. Closely related analoEres of CPETA (t4) narnely PETA (15) and CPAP' (16) were then synthesized. PETA (15) was synthesized by the condensation of methylamino- I -phenylpropane (phentenrtine) and etaf-edrine ( I 3).
The synthesis of analogues of the Anti-TB (agent: Diospyrin)
(University of the Western Cape, 2005) Sitoza, Mluleki; Green, Ivan R.
Diospyrin, a bisnaphthyl quinone molecule with proven anti-TB activity can be retrosynthetically formulated into two halves. In this work, the analogue chosen to be synthesized was similarly retrosynthesized into two halves. The one half, 2-bromo-5- methoxy-1 ,4-naphthoquinone was synthesized successfully starting from 1,5- diacetoxynaphthalene which was oxidized and brominated with N-bromosuccimide to the corresponding 5-acetoxy-2-bromo-1,4-naphthoquin one. Hydrolysis of the acetoxy group was effected with methanolic potassium hydroxide followed by methylation of the phenolic group by methyl iodide and silver (II) oxide. The second half of the analogue, 7-bromo-1,4,6-trimethoxynaphthalene was attempted to be synthesized in the following way. Condensation between benzoquinone and Danishefsky's diene afforded an adduct which after much investigation was converted into 1,4,6-triacetoxynaphthalene. Through the process of transformations viz., oxidation, hydrolysis and phenol protection, the triacetoxynaphthalene was converted into 6- hydroxy-1,4-dimethoxynaphthalene. Attempts to brominate both this latter phenol as well as the original Diels-Alder adduct at C-7 proved to be problematic but gave some interesting results. Finally, by converting the 6-hydroxy-1,4-dimethoxyna phthalene into the corresponding carbamate, it could be transformed into the C-7 boronic acid albeit in low yield. Intwo reference Suzuki coupling experiments, the boronic acid derived from the carbamate of phenol was condensed with 2-bromo-1,4-dimethoxybenzen e and 6- methoxynaphthyl-2-boronic acid was coupled with 2-bromo-5-methoxy- 1,4- naphthoquinone. Finally, Suzuki coupling between 2-bromo-5-methoxy-1,4-naphthoquino ne and C-7 boronic acid of 6-(N,N-diethylcarbamyloxy) -1,4-dimethoxynaphthalene proved to be problematic with a very low yield of biaryl product being detected.
The development of l-phenylalanine biosensor using boron-doped diamond (bdd) electrode modified with poly aniline-polyvinyl sulphonate composite film
(University of the Western Cape, 2010) Mangombo, Zelo; Baker, Priscilla G.L.
The aim of this project was to develop a biosensor on a modified boron-doped diamond (BDD) platform in order to determine L-phenylalanine (L-Phe) levels in the aqueous media and real samples. A BDD electrode modified with polyaniline (PANI) film doped with polyvinyl sulphonate (PVS), containing in-situ deposited tyrosinase (Tyr) enzyme was studied with special emphasis on the detection of L-phenylalanine (L-Phe). The PANI-PVS film was electrochemically coated on the BDD surface by cyclic voltammetry (CV) at 50 mV s-1 (versus Ag/AgCI). An increase in current density with increasing number of cycles was an indication of the polymer growth. The morphologies of the composite films were characterized by scanning electron microscopy (SEM).
The synthesis, characterization and reactivity of some mononuclear hydrocarbyl compounds of iron
(University of the Western Cape, 1997) Joorst, Genevieve; Mapolie, S.F.
Mononuclear hydrocarbyl compounds of the type LnM(CH2)nCH:CH2 (L"M : Cp*Fe(CO)2 and CpFe(CO)2, n: 2-4,6), Cp(CO)zFe(CH2)nOH (n : 4-6,8) and Cp*(CO)2Fe(CH2)+OH have been synthesized. All these compounds have been l3 fully characterized using analytical techniques such as[R, H and C NMR spectroscopy, microanalysis and mass spectrometry The results of some activity studies on the above hydrocarbyl compounds are reported in this thesis. For example, the reactivity of the r'1l-alkenyl compounds Cp (CO)2Fe(CH2).CH=CHZ (n: 2 and 3) to hydrozirconation was studied. Although the expected binuclear hydrocarbyl compounds Cp(CO)2Fe(CH2)na2Zr(Cl)Cpz (n: 2 and 3) were not isolated, their presence in solution were detected by carrying out insitu reactions. The n1-alkenyl compounds were also subjected to a p-hydride abstraction reaction. This afforded a series of cationic n2-diene compounds with general formula {Cp(CO)zFe(CnH2n-2) } PF6. Some of the reactions of the w-hydroxyalkyls were also investigated. The bromination of these hydroxy species leads to the formation of w-bromoalkyls of the type Cp(CO)2Fe(CH2)'Br (n 4 and 8). The w-hydroxyalkyls cp(co)2Fe(CH2)nOH (n : 4-6,8) were reacted with trifluoroacetic acid which results in iron-carbon cleavage. Finally the reaction of some w-hydroxyalkyls with triflic anhydride gives different results depending on the type of solvent employed. In THF a metal containing polyether is isolated as the major product, while in diethyl ether the major species isolated is a o-chloroalkyl of the type Cp(Co)2Fe(CH2)nCl (n : 4 and 5)' In the case of the reaction in THF, a small amount of the binuclear hydrocarbyl compound [CpFe(Co)z]{p-(CHz)a}can be isolated if [CpFe(Co)z] is added to the reaction mixture
Pyramlyl palladium(Il) complexes as phenylacetylene oligomerization and polymerization catalysts'
(University of the Western Cape, 2004) SegaPelo, T; Darkwa, J
PyrazoM compounds have been extensively used to prepare metal complexes, but it is only recently that they have been investigated as catalysts for the polymerization of unsaturated hydrocarbons. In catalyzn11g the polymerization of ethylene, the electrophilicity of the metal centre plays an important role since the key step in the polymerization is coordination of the ethylene. A similar facile coordination would be expected for acetylene and one would therefore expect pyrazolyl palladium complexes to be good catalysts for the transformation of acetylenes. This thesis is an investigation of pyrazolyl palladium complexes as catalysts for the polymerization and oligomeruation of substituted acetylenes.
Synthesis, characterisation and reactions of ferrocene anchored bis(phosphino) palladium (II) and platinum (II) aryldichalcogenide complexes
(University of the Western Cape, 2000) Maisela, Letladi lawrence; Darkwa, James; Crouch, Andrew M
Reactions of M(dppf)Cl2 (M : Pd, Pt) and Pd(dippf)Cl2 with equimolar amounts of the aryldichalcogen reagents, 1,2-benzenedithiol (1,2-(HS)C6H4(SH) (a)), 3,4-toluenedithiol ((HS)C6H3Me(SH)) (b), 3,6-dichloro 1,2-benzenedithiol ((HS)C6H2C12(SH)) (c), 2- mercaptophenol ((HS)C6H4(OH)) (d), thiosalicylic acid ((HS)C6H4(CO2H) (e) and thionicotinic acid (HS)C5H3N(CO2H)) (f) in the presence of triethylamine afforded complexes of the type M(dppf(SC6H4E-o) (where dppf : 1,1'- bis(diphenylphosphino)ferrocene and dippf : 1,1'-bis(diisopropylphosphino)ferrrocene). In addition to the above series, M(dpp0(SC6H5)2 (M : Pd, Pt) and Pd(dippf)(SC6H5)2 were prepared in an attempt to synthesise complexes of the general formula M(dppf)(SC6H4E-o) (M: Pd, Pt; E : Se, Te) via in situ generation of LiSC6H4ELi-o. All complexes isolated were characterised by a combination of IR, 1H, 31P {1H} NMR, mass spectrometry and elemental analysis. Further characterisation of Pd(dppf)(SC6H4S-o), Pd(dippf)(SC6H4S-o), Pd(dippf(SC6H3MeS-o), Pd(dippf)(SC6H5)2, Pt(dppf)(SC6H4S-o) and Pt(dppf)(SC6H4O -o) by single crystal X-ray diffraction studies confirmed the structures deduced from the spectroscopic data. Mass spectrometry data suggests that the Pt(II) complexes are more stable than the analogous Pd(II) complexes. Electrochemical data also show that the dippf complexes were easier to oxidise compared to the dppf, as were the Pd complexes compared to the Pt analogues. In complexes containing homoleptic sulfur ligands (1a-c, 2a-c and 3a-c) the ease of oxidation of the ligand was b > a > c which conforms to either the electron releasing group (b) or an electron withdrawing group (c) on the ligand. Aryldithiolato Pd(dppf) and Pd(dippf) complexes reacted with dimethylacetylene dicarboxylate (DMAD) to form hexamethylbenzene hexacarboxylate (HMBC) and tetramethylcyclobuta-1,3-diene tetracarboxylate (TMCTC) as the dominant products. The same series of aryldithiolato complexes that reacted with DMAD reacted reversibly with sulfur dioxide, a process that was monitored by UV-vis and 1H NMR spectroscopy.
Phytochemical synthesis and antimicrobial application of gold nanoparticles from extract of Artemisia annua
(University of the Western Cape, 2023) Ntamo, Akhona; Mabusela, Wilfred
Metallic nanoparticles synthesized using chemical methods and physical methods are considered toxic to the environment due to the use of toxic solvents. The biological synthesis methods such as the use of plant extracts are of interest because they are biocompatible, environmentally friendly, and relatively cost-effective. Gold nanoparticles (AuNPs) have been synthesized using plant aqueous extract as a reducing agent and have shown selective antibacterial activity and good antifungal properties. This study used an aqueous extract of Artemisia annua to synthesize biogenic AuNPs and tested them for antimicrobial activity. The A.annua-AuNPs were characterized using Ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), Dynamic light scattering (DLS), and High-resolution transmission electron microscopy (HRTEM).
Synthesis and evaluation of metformin derivatives for anti-diabetes
(University of the Western Cape, 2022) Parker, Amina; Titinchi, Salam
Type 2 diabetes mellitus (T2DM) is a significant public health crisis and is placed amongst the top ten leading causes of death worldwide. Metformin is the first-line drug used to treat T2DM, which is mainly attributed to its potent insulin sensitising properties and relatively low cost and side effects compared to other anti-diabetic drugs. However, metformin is associated with side effects such as gastrointestinal intolerance and reduced activity over time, while its variable pharmacokinetics, pharmacodynamics and pharmacogenomics leads to reduced effectiveness in some patients. In recent years, organic chemistry has been used to synthesise structural analogues of existing drugs, with more potent activity and target specificity than the parent drugs.
Solid phase micro extraction: an alternative technique for the determination of volatile orgnanic compounds in groundwater
(University of the Western Cape, 2004) Beukes, James Arthur; Green, I.R
Standard methods for sample preparation use toxic organic solvents and can be replaced by utilizing a new sample preparation and concentration technique. One such technique, compatible with capillary gas chromatography was developed in this study that shows promise of increased speed, cost-efficiency and ease of automation: The solid phase micro extraction (SPME) process has two steps: partitioning of analytes between the coating of a SPME fibre and the sample matrix, followed by desorption of concentrated extracts directly into an analytical instrument. In the first step, the coated fibre is exposed to the sample or its headspace which causes the target analytes to partition from the sample matrix into the coating. The fibre bearing concentrated analytes is then transferred to an instrument for desorption, whereupon separation and quantitation of extracts can take place. SPME can be used as a sample preparation technique for liquid, gas and solid samples. Results show that SPME, when fully optimized can successfully be used for the determination of volatile organic compounds in groundwater at a fraction of the equipment cost. The technique can also be used as a screening tool before the validated purge and trap methods are employed.

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