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Human fungal superficial infections are mainly caused by dermatophytes. These infections are distributed worldwide, common for people of all ages, in both sexes. The current treatments include taking oral antifungal drugs and topical therapy. However, treatments of superficial infections can be challenging in children and elderly mainly due to compliance issues and associated potential health risks and side-effects. Photo dynamic therapy (PDT) is a novel approach to treat fungal superficial infections. In this approach, light is used to excite a photosensitizer to turn readily available oxygen into reactive oxygen species (ROS) to kill the pathogen. In this research, we have used the pathogenic dermatophyte Trichophyton rubrum as a model to screen for photosensitizers and identify the best combinations of photosensitizer X carrier X light exposure time against T. rubrum. I obtained the In vitro photosensitizers’ Minimum Inhibitory Concentration (MIC), Minimum Fungicidal Concentration (MFC), carrier inhibitory and fungicidal combinations experimental results. In addition, ex vivo experimental results for photosensitizer and carrier systematic treatments are presented with both nail pieces and nail well apparatus. The in vitro results confirm the fungicidal ability of photosensitizer Methylene Blue and natural extracts Inula, Propolis and St. John’s Wort to T. rubrum. For ex vivo experiments, among the three natural extracts, only Inula showed promising fungicidal effect on nail pieces. Methylene Blue and carrier, Methylene Blue plus Inula and carrier combinations at certain concentrations all showed strong nail penetration ability and fungicidal effect against T. rubrum infection. These results suggest promising avenues for further clinical research and application of PDT. / Thesis / Master of Applied Science (MASc)

This thesis explores the synthesis, characterization, and electrochemical behavior of nanocomposites composed of cobalt (Co) and molybdenum (Mo) deposited onto graphene oxide (GO), COOH-functionalized multi-walled carbon nanotubes (CNT-COOH), and blends of these two graphitic nanomaterials. The study aims to investigate the structural, morphological, and electrocatalytic properties of these nanocomposites synthesized via a hydrothermal method. Using a combination of analytical techniques including Raman Spectroscopy, Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS), Cyclic Voltammetry (CV), Chronoamperometry, and UV-vis Spectroscopy, the nanocomposite structures were comprehensively characterized. SEM imaging demonstrated differential deposition of CoMo particles, demonstrating higher affinity and deposition on CNT-COOH compared to GO. EDX and XPS findings confirmed successful deposition of Co and Mo sulfides and oxides on both supports. According to XPS data, cobalt sulfides, molybdenum dioxide, and molybdenum disulfide were the dominant species synthesized in CoMo-CNT-COOH and CoMo-GO, whereas the prevalent species in CoMo-CNT-COOH-GO were cobalt and molybdenum sulfides. Electrochemical analyses, particularly CV tests, unveiled unique electro-oxidative activity of CoMo-CNT-COOH for Methyl Orange (MO) analyte at -0.4 V. CoMo-CNT-COOH exhibited approximately 68% optimum electrooxidation of MO after 5 hours for 100 mL solution initially made of 30 ppm MO and 0.5 molar sulfuric acid, indicating potential for environmental remediation applications. / Thesis / Master of Chemical Engineering (MChE)

Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch,2005. / This study comprises the preparation and full characterisation of new carbene complexes of group 10 metals (Ni, Pd or Pt), the group 9 metal, rhodium, as well as group 6 metals (Cr and/or W). N-heterocyclic carbene (NHC) complexes of nickel and palladium were prepared via oxidative addition of the corresponding carbene precursors imidazolium-, imidazolinium-, pyridinium- and quinolinium chloride salts, to M(PPh3)4 (M = Ni or Pd). Three types of carbene complexes, namely the standard five-membered two-N carbene complexes, new six-membered NHC complexes and novel six-membered rNHC complexes received attention. In the rNHC complexes the heteroatom (N) is removed from the carbene carbon. These new square planar carbene complexes of the general formula trans-[(PPh3)2MCl(L)]X (M = Ni or Pd; X = BF4 or PF6) L = 1,3-dimethyl-2,3-dihydro-1Himidazol- 2-ylidene, 1,3-dimethyl-2,3,4,5-tetrahydro-1H-imidazol-2-ylidene, 1-methyl-1,2-dihydropyridin- 2-ylidene, 1-methyl-1,2-dihydro-quinolin-2-ylidene, 1,4-dimethyl-1,2-dihydro-quinolin-2- ylidene, 2-methoxy-1-methyl-1,4-dihydro-quinolin-4-ylidene, 1-methyl-1,4-dihydro-pyridin-4- ylidene) have been isolated and characterised. The preparation of the corresponding carbene complexes of platinum was complicated by the formation of [PtCl(PPh3)3]BF4 and the desired carbene complexes could not be isolated in pure form. The investigation of rNHC complexes was extended to include the synthesis of (CO)5M{CSC(CNCMe2CH2O)CHCH} (M = Cr and W). The molecular and crystal structures of thirteen of the new carbene complexes including the structures of both cis- (only formed below –20°C) and trans-chloro(1-methyl-1,2-dihydro-quinolin- 2-ylidene)bis(triphenylphosphine)palladium(II) tetrafluoroborate were determined. The metalcarbene bond distances in both the palladium and nickel carbene families do not differ significantly. The carbene ligands can be arranged in a series of increasing trans-influence, using the metalchloride bond distance as a guideline, as follows: 1,3-dimethyl-2,3-dihydro-1H-imidazol-2-ylidene and 1,3-dimethyl-2,3,4,5-tetrahydro-1H-imidazol-2-ylidene < 1-methyl-1,2-dihydro-pyridin-2- ylidene < 2-methoxy-1-methyl-1,4-dihydro-quinolin-4-ylidene, 1-methyl-1,4-dihydro-pyridin-4- ylidene. The crystal and molecular structures of two platinum compounds, cis-chloro(2-methoxy-1- methyl-1,4-dihydro-quinolin-4-ylidene)bis(triphenylphosphine)platinum(II) tetrafluoroborate and the byproduct [PtCl(PPh3)3]BF4 were also determined. Trans-chloro(2-methoxy-1-methyl-1,4-dihydro-quinolin-4-ylidene)bis(triphenylphosphine) palladium(II) tetrafluoroborate was found to be a very active catalyst, compared to simpler palladium carbene and phosphine complexes, in the Mizoroki-Heck and Suzuki-Miyaura coupling reactions. Quantum mechanical calculations indicated that the rNHC ligand in this complex is bound stronger to the palladium than a standard imidazole-derived NHC ligand. Further calculations suggested that the remote heteroatom carbene (rNHC) complexes of nickel(II) are significantly more stable when compared to the normal carbene (NHC) complexes. Energy decomposition analysis suggested that the rNHC ligands are strong s-donors and weak -acceptors. Unsymmetrical imidazolium-derived bis(carbene) complexes, [Rh(NHC)2COD]Br, bromomono( carbene) complexes, Rh(Br)COD(NHC), and chloro-mono(carbene) complexes, Rh(Cl)COD(NHC) where NHC = 1-R-3-methyl-2,3-dihydro-1H-imidazol-2-ylidene (R = ethyl, propyl or butyl), were formed in each reaction of the corresponding free carbene ligand with [Rh(Cl)COD]2. [Rh(Br)COD(NHC)] formed as a result of substitution of a chloride ligand by a Br-- anion. The carbonyl complexes, cis-[Rh(CO)2X(NHC)] (X = Br or Cl; NHC = 1-ethyl-3-methyl- 2,3-dihydro-1H-imidazol-2-ylidene) were isolated after the substitution of the COD ligand in Rh(X)COD(NHC) (X = Br or Cl) with CO. Isomerisation of these cis-carbonyl complexes to the trans isomers was observed. Cis-[(h4-1,5-cyclooctadiene)bis(1-butyl-3-methyl-2,3-dihydro-1H-imidazol-2-ylidene)rhodium(I)] bromide, bromo(h4-1,5-cyclooctadiene)(1-methyl-3-propyl-2,3-dihydro-1H-imidazol-2-ylidene) rhodium(I) and cis-[(h4-1,5-cyclooctadiene)bis(1-butyl-3-methyl-2,3-dihydro-1H-imidazol-2- ylidene)rhodium(I)]bromide were also characterised by single crystal X-ray diffraction. The synthesis and structural characterisation of a series of acyclic and heterometallacyclic Fischertype carbene complexes in which a soft donor atom (P) attached to the carbene side chain is either uncoordinated, (CO)5M=C(NMe2)CH2PPh2 (M = Cr or W), bonded to the original central metals (Cr or W) in four-membered chelates, (CO)4M=C(NMe2)CH2PPh2, or coordinated to a second M(CO)5 unit (only isolated for chromium) (CO)5Cr=C(NMe2)CH2P(Ph2)Cr(CO)5, were carried out. These compounds were produced by the reaction of the anionic Fischer-type aminocarbene complexes, [(CO)5Cr=C(NMe2)CH2]Li (M = Cr or W), with ClPPh2. The formation of the four-membered chelates, via cyclisation, occurs much faster for Cr than for W. The aminocarbene-phosphine chelates represent the first examples of structurally characterised, four-membered C,P-chelate carbene complexes.

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Please refer to fulltext for abstract. / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISCH ABSTRACT: Please refer to fulltext for abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

Στην παρούσα ερευνητική εργασία μελετάται η φωτοηλεκτροχημική διάσπαση δύο οργανικών ενώσεων: της χρωστικής Methylene Blue (MB), και της γλυκόζης. Η φωτοκαταλυτική διεργασία πραγματοποιήθηκε με φωτοβόληση υπεριώδους ακτινοβολίας UV (λάμπα Hg, 125 W). Για το σκοπό αυτό χρησιμοποιήθηκαν δύο φωτοκαταλύτες: η νανοκρυσταλλική τιτάνια (TiO2) και το οξείδιο του βολφραμίου (WO3). Η φωτοδιάσπαση των οργανικών ρύπων πραγματοποιήθηκε σε μία φωτοηλεκτροχημική κυψελίδα, η οποία αποτελείται από τα εξής μέρη: 1)Το ηλεκτρόδιο της ανόδου το οποίο φέρει το φωτοκαταλύτη. Στη φωτοάνοδο παράγονται τα ηλεκτρόνια και πραγματοποιόυνται οι αντιδράσεις οξείδωσης. 2)Το ηλεκτρόδιο της καθόδου, το οποίο φέρει τον ηλεκτροκαταλύτη, ο οποίος διευκολύνει τη μεταφορά των ηλεκτρονίων από το ηλεκτρόδιο στο διάλυμα. Στη φωτοκάθοδο πραγματοποιούνται αντιδράσεις αναγωγής. Ως ηλεκτροκαταλύτης χρησιμοποιήθηκε ο λευκόχρυσος ο οποίος είναι ευγενές μέταλλο. 3)Τον ηλεκτρολύτη, ο οποίος ρυθμίζει το pH του διαλύματος και αυξάνει την ιοντική αγωγιμότητα. Ο ηλεκτρολύτης που χρησιμοποιήθηκε είναι το καυστικό νάτριο (NaOH). Όταν ο φωτοκαταλύτης διεγείρεται με ακτινοβολία ενέργειας ίσης ή μεγαλύτερης του ενεργειακού του χάσματος, δημιουργούνται ζεύγη οπών-ηλεκτρονίων. Ένα μέρος των δημιουργούμενων ζευγών φορτίου επανασυνδέονται χάνοντας τη φωτεινή ενέργεια σε θερμότητα. Οι οπές οξειδώνουν το ρύπο απελευθερώνοντας ιόντα υδρογόνου. Τα ηλεκτρόνια ρέουν μέσω του εξωτερικού κυκλώματος στην κάθοδο, όπου αντιδρούν με τα ιόντα υδρογόνου, σχηματίζοντας είτε μοριακό υδρογόνο (υπό αναερόβιες συνθήκες), είτε νερό (υπό αερόβιες συνθήκες). Το πρώτο και σημαντικότερο στάδιο της φωτοκαταλυτικής διεργασίας είναι η προσρόφηση του ρύπου στην επιφάνεια του φωτοκαταλύτη. Ο μηχανισμός προσρόφησης γίνεται σύμφωνα με το κινητικό μοντέλο Langmuir-Hinshelwood. To TiO2 αποτελεί έναν από τους πιο διαδεδομένους και αποδοτικούς φωτοκαταλύτες. Τα υμένια TiO2 εναποτέθηκαν σε υπόστρωμα γυαλιού με τη μέδοδο Doctor Blade. Το WO3 είναι ένας εξίσου αποδοτικός φωτοκαταλύτης με το TiO2, αλλά λιγότερο δημοφιλής. Η εναπόθεση των υμενίων WO3 σε γυάλινα υποστρώματα έγινε με τη μέθοδο του ψεκασμού. Η παρασκευή του αντιηλεκτροδίου, δηλαδή του ηλεκτροδίου της καθόδου, έγινε με τη μέθοδο της ηλεκτροαπόθεσης. Το υψηλό pH του ηλεκτρολύτη (NaOH) είναι απαραίτητο για τη φωτοδιάσπαση οργανικών ενώσεων. Εκτός από την ιοντική αγωγιμότητα που προσφέρει στο φωτοηλεκτροχημικό κελί, επηρεάζει και την επιφανειακή φόρτιση του φωτοκαταλύτη. Η αύξηση της συγκέντρωσης του NaOH, δηλαδή η αύξηση των ιόντων ΟΗ-, είχε σαν αποτέλεσμα την αύξηση της σταθεράς ταχύτητας της φωτοκαταλυτικής αντίδρασης kapp και επομένως ταχύτερη φωτοδιάσπαση του ρύπου. Στα διαλύματα με τις μεγαλύτερες συγκεντρώσεις ηλεκτρολύτη ο χρόνος ημιζωής του ρύπου είναι πολύ μικρότερος συγκριτικά με τα διαλύματα χαμηλής συγκέντρωσης NaOH. Η μέτρηση της συγκέντρωσης των οργανικών ενώσεων στα υδατικά διαλύματα έγινε με φασματοφωτομετρία απορρόφησης ορατού-υπεριώδους (UV/vis). Οι φωτοαποικοδομούμενες ουσίες, λειτουργούν ως «θυσιαστήριες ενώσεις», αφού μειώνουν το ρυθμό επανασύνδεσης ηλεκτρονίων-οπών και επομένως συμβάλλουν στην αύξηση της απόδοσης του συστήματος, ενώ παράλληλα η διάσπασή τους προσφέρει τεράστιο περιβαλλοντικό όφελος. Από τις δύο οργανικές ενωσεις που μελετήθηκαν, μόνο η χρωστική Methylene Blue λειτούργησε αποτελεσματικά ως θυσιαστήρια ένωση. Αντιθέτως η γλυκόζη, που είναι πολύπλοκο μόριο, δεν κατάφερε να διασπαστεί. Τέλος έγινε σύγκριση της δραστικότητας των δύο φωτοκαταλυτών, κατά τη φωτοαποικοδόμηση των οργανικών ρύπων που μελετήθηκαν. Παρατηρήθηκε ότι και το TiO2 και το WO3 είναι εξίσου αποδοτικοί φωτοκαταλύτες. Σε αντίθεση με το TiO2, το WO3 δεν είναι ανθεκτικό στη φωτοδιάβρωση, καθιστώντας αδύνατη την επαναχρησιμοποίησή του σε περισσότερες από δύο φωτοκαταλυτικές διεργασίες. / The present study deals with the photo electrochemical degradation of two organic compounds, namely Methylene Blue and glucose. The photocatalytic process was carried out using UV radiation (Hg lamp, 125 W). The employed photo catalysts were titanium dioxide (TiO2) and tungsten oxide (WO3) deposited in the form of thin films on SnO2:F-coated glass. The photodecomposition of organic wastes was carried out in a photo electrochemical (PEC) cell with the following components: 1) The anode electrode which carries the photo catalyst. The photo anode produces electrodes and oxidation reactions take place there. 2) The cathode electrode, which carries the electro catalyst and facilitates the transfer of electrons from the cathode to the liquid phase. Reduction reactions take place at the cathode. In this study, a noble metal, Pt was used as electro catalyst. Thin films of Pt were obtained by electrodeposition on SnO2:F-coated glass slides. 3) The electrolyte which is added to adjust the Ph in order to increase the ionic conductivity. In this study, an aqueous solution of NaOH has been used as electrolyte. The operation of such a PEC cell is as follows: The absorption of photons by the photocatalyst leads to the creation of electron-hole pairs. The photodegradable substance is oxidized by the holes, liberating hydrogen ions in the aqueous solution. Electrons are transferred through the external circuit towards the cathode, where they reduce hydrogen ions producing hydrogen molecules (in the absence of oxygen). The initial step of the photoelectrocatalytic decomposition is the adsorption of the organic waste on the surface of the photocatalyst according to the Langmuir-Hinshelwood mechanism. TiO2 is among the most successful photo catalysts for heterogeneous photo catalytic degradation of organic wastes. Thin films of nano crystalline titania were deposited on glass substrates using the Doctor Blade method. Another wide band gap semiconductor with that can be used in heterogeneous photo catalysis is WO3. It was also tested and compared with TiO2. The pH value of the electrolyte (NaOH) was found to affect strongly the process. High pH values were required to obtain high OH- concentration because efficient hole scavenging and production of hydrogen radicals is ensured, especially when an organic sacrificial agent is added. As a consequence, the apparent rate constant kapp was increased with increasing NaOH concentrations. The photodegradable substances act like “sacrificial agents” preventing the recombination of electron-hole pairs, which is the main cause for low efficiencies. Of the two organic wastes that have been studied, only MB could be successfully degraded. Finally, the photo catalytic activity of TiO2 and WO3 was compared. Although both catalysts were equally efficient, WO3 is characterized by low stability. .

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

The reactions of five trihalomethyl group substituted electron-deficient olefins with electron-rich olefins were studied in order to determine the effect of steric bulk upon the subsequent reactions of the tetramethylene intermediates initially formed. Reactions of β-trihalomethyl group substituted olefins yielded cyclobutane adducts, resulting from a gem dimethyl effect which accelerates the collapse of the tetramethylene intermediate. Reactions of α-trihalomethyl group substituted olefins gave both small molecule and polymeric products. Polymers were produced in reactions where steric interactions between the termini of the tetramethylene intermediates prevented ring formation. Ester substituted electron-deficient olefins reacted with electron-rich olefins to give both cyclobutane and 6-alkoxy-3,4-dihydro-2H-pyran derivatives. A transition from concerted to stepwise reaction was observed, resulting from steric hindrance in the transition state leading to [4+2] cycloaddition. Exploratory studies of ion-radical propagation and chain transfer in polymerization processes were also conducted. The acid catalyzed free radical polymerization of imines was attempted, along with chain transfer studies of zwitterion-radical intermediates.

N-Heterocyclic carbenes (NHCs) are an important class of compounds responsible for a wide variety of chemical transformations. NHCs may be used as organocatalysts that permit non-traditional carbon carbon bond formations due to their renowned ability to invert the electrophilic character of aldehyde carbonyl groups, a concept otherwise known as polarity reversal or umpolung reactivity. Despite their ubiquity with respect to accessing the umpolung of aldehydes, fundamental studies of these reactive species are still rather limited and narrow in scope. As a result, clarifying and solving problems relevant to umpolung-themed asymmetric catalysis becomes quite challenging. In this regard, our work has been focused on a three-pronged approach towards providing a more unified understanding of these complex catalytic systems. First, we describe the synthesis of unprecedented carboxylate-tethered triazolium NHCs and use them in the intramolecular Stetter reaction to understand their function. Second, we describe the acidities of a broad range of both chiral and achiral NHCs that have never had their acidities assessed before and use them to construct the first linear free-energy relationships of their kind. Finally, we develop a simple and noninvasive experimental protocol in which we can quickly benchmark the performance of a series of chiral catalysts by way of single competition experiments. We anticipate that these studies will have direct implications on the development of novel NHC-catalyzed reactions.