Oxidative desulfurization of fuel oils-catalytic oxidation and adsorptive removal of organosulfur compounds
- Authors: Ogunlaja, Adeniyi Sunday
- Date: 2014
- Subjects: Organosulfur compounds , Organosulfur compounds -- Oxidation , Organosulfur compounds -- Absorption and adsorption , Petroleum as fuel , Catalysis , Imprinted polymers , Molecular imprinting , Nanofibers , Electrospinning
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4498 , http://hdl.handle.net/10962/d1013152
- Description: The syntheses and evaluation of oxidovanadium(IV) complexes as catalysts for the oxidation of refractory organosulfur compounds in fuels is presented. The sulfones produced from the oxidation reaction were removed from fuel oils by employing molecularly imprinted polymers (MIPs). The oxidovanadium(IV) homogeneous catalyst, [V ͥ ͮ O(sal-HBPD)], as well as its heterogeneous polymer supported derivatives, poly[V ͥ ͮ O(sal-AHBPD)] and poly[V ͥ ͮ O(allylSB-co-EGDMA)], were synthesized and fully characterized by elemental analysis, FTIR, UV-Vis, XPS, AFM, SEM, BET and single crystal XRD for [V ͥ ͮ O(sal-HBPD)]. The MIPs were also characterized by elemental analysis, FTIR, SEM, EDX and BET. The catalyzed oxidation of fuel oil model sulfur compounds, thiophene (TH), benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), was conducted under batch and continuous flow processes at 40°C by using tert-butylhydroperoxide (t-BuOOH) as oxidant. The continuous flow oxidation process presented the highest overall conversions and very high selectivity for sulfones. Maximum oxidation conversions of 71%, 89%, 99% and 88% was achieved for TH, BT, DBT and 4,6-DMDBT respectively when poly[V ͥ ͮ O(allylSB-co-EGDMA)] was employed at a flow-rate of 1 mL/h with over 90% sulfone selectivity. The process was further applied to the oxidation of hydro-treated diesel containing 385 ± 4.6 ppm of sulfur (mainly dibenzothiophene and dibenzothiophene derivatives), and this resulted to a high sulfur oxidation yield (> 99%), thus producing polar sulfones which are extractible by polar solid phase extractants. Adsorption of the polar sulfone compounds was carried-out by employing MIPs which were fabricated through the formation of recognition sites complementary to oxidized sulfur-containing compounds (sulfones) on electrospun polybenzimidazole (PBI) nanofibers, cross-linked chitosan microspheres and electrospun chitosan nanofibers. Adsorption of benzothiophene sulfone (BTO₂), dibenzothiophene sulfone (DBTO₂) and 4,6-dimethyldibenzothiophene sulfone (4,6-DMDBTO₂) on the various molecularly imprinted adsorbents presented a Freundlich (multi-layered) adsorption isotherm which indicated interaction of adsorbed organosulfur compounds. Maximum adsorption observed for BTO₂, DBTO₂ and 4,6-DMDBTO₂ respectively was 8.5 ± 0.6 mg/g, 7.0 ± 0.5 mg/g and 6.6 ± 0.7 mg/g when imprinted chitosan nanofibers were employed, 4.9 ± 0.5 mg/g, 4.2 ± 0.7 mg/g and 3.9 ± 0.6 mg/g on molecularly imprinted chitosan microspheres, and 28.5 ± 0.4 mg/g, 29.8 ± 2.2 mg/g and 20.1 ± 1.4 mg/g on molecularly imprinted PBI nanofibers. Application of electrospun chitosan nanofibers on oxidized hydro-treated diesel presented a sulfur removal capacity of 84%, leaving 62 ± 3.2 ppm S in the fuel, while imprinted PBI electrospun nanofibers displayed excellent sulfur removal, keeping sulfur in the fuel after the oxidation/adsorption below the determined limit of detection (LOD), which is 2.4 ppm S. The high level of sulfur removal displayed by imprinted PBI nanofibers was ascribed to hydrogen bonding effects, and π-π stacking between aromatic sulfone compounds and the benzimidazole ring which were confirmed by chemical modelling with density functional theory (DFT) as well as the imprinting effect. The home-made pressurized hot water extraction (PHWE) system was applied for extraction/desorption of sulfone compounds adsorbed on the PBI nanofibers at a flow rate of 1 mL/min and at 150°C with an applied pressure of 30 bars. Application of molecularly imprinted PBI nanofibers for the desulfurization of oxidized hydro-treated fuel showed potential for use in refining industries to reach ultra-low sulfur fuel level, which falls below the 10 ppm sulfur limit which is mandated by the environmental protection agency (EPA) from 2015.
- Full Text:
- Date Issued: 2014
- Authors: Ogunlaja, Adeniyi Sunday
- Date: 2014
- Subjects: Organosulfur compounds , Organosulfur compounds -- Oxidation , Organosulfur compounds -- Absorption and adsorption , Petroleum as fuel , Catalysis , Imprinted polymers , Molecular imprinting , Nanofibers , Electrospinning
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4498 , http://hdl.handle.net/10962/d1013152
- Description: The syntheses and evaluation of oxidovanadium(IV) complexes as catalysts for the oxidation of refractory organosulfur compounds in fuels is presented. The sulfones produced from the oxidation reaction were removed from fuel oils by employing molecularly imprinted polymers (MIPs). The oxidovanadium(IV) homogeneous catalyst, [V ͥ ͮ O(sal-HBPD)], as well as its heterogeneous polymer supported derivatives, poly[V ͥ ͮ O(sal-AHBPD)] and poly[V ͥ ͮ O(allylSB-co-EGDMA)], were synthesized and fully characterized by elemental analysis, FTIR, UV-Vis, XPS, AFM, SEM, BET and single crystal XRD for [V ͥ ͮ O(sal-HBPD)]. The MIPs were also characterized by elemental analysis, FTIR, SEM, EDX and BET. The catalyzed oxidation of fuel oil model sulfur compounds, thiophene (TH), benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), was conducted under batch and continuous flow processes at 40°C by using tert-butylhydroperoxide (t-BuOOH) as oxidant. The continuous flow oxidation process presented the highest overall conversions and very high selectivity for sulfones. Maximum oxidation conversions of 71%, 89%, 99% and 88% was achieved for TH, BT, DBT and 4,6-DMDBT respectively when poly[V ͥ ͮ O(allylSB-co-EGDMA)] was employed at a flow-rate of 1 mL/h with over 90% sulfone selectivity. The process was further applied to the oxidation of hydro-treated diesel containing 385 ± 4.6 ppm of sulfur (mainly dibenzothiophene and dibenzothiophene derivatives), and this resulted to a high sulfur oxidation yield (> 99%), thus producing polar sulfones which are extractible by polar solid phase extractants. Adsorption of the polar sulfone compounds was carried-out by employing MIPs which were fabricated through the formation of recognition sites complementary to oxidized sulfur-containing compounds (sulfones) on electrospun polybenzimidazole (PBI) nanofibers, cross-linked chitosan microspheres and electrospun chitosan nanofibers. Adsorption of benzothiophene sulfone (BTO₂), dibenzothiophene sulfone (DBTO₂) and 4,6-dimethyldibenzothiophene sulfone (4,6-DMDBTO₂) on the various molecularly imprinted adsorbents presented a Freundlich (multi-layered) adsorption isotherm which indicated interaction of adsorbed organosulfur compounds. Maximum adsorption observed for BTO₂, DBTO₂ and 4,6-DMDBTO₂ respectively was 8.5 ± 0.6 mg/g, 7.0 ± 0.5 mg/g and 6.6 ± 0.7 mg/g when imprinted chitosan nanofibers were employed, 4.9 ± 0.5 mg/g, 4.2 ± 0.7 mg/g and 3.9 ± 0.6 mg/g on molecularly imprinted chitosan microspheres, and 28.5 ± 0.4 mg/g, 29.8 ± 2.2 mg/g and 20.1 ± 1.4 mg/g on molecularly imprinted PBI nanofibers. Application of electrospun chitosan nanofibers on oxidized hydro-treated diesel presented a sulfur removal capacity of 84%, leaving 62 ± 3.2 ppm S in the fuel, while imprinted PBI electrospun nanofibers displayed excellent sulfur removal, keeping sulfur in the fuel after the oxidation/adsorption below the determined limit of detection (LOD), which is 2.4 ppm S. The high level of sulfur removal displayed by imprinted PBI nanofibers was ascribed to hydrogen bonding effects, and π-π stacking between aromatic sulfone compounds and the benzimidazole ring which were confirmed by chemical modelling with density functional theory (DFT) as well as the imprinting effect. The home-made pressurized hot water extraction (PHWE) system was applied for extraction/desorption of sulfone compounds adsorbed on the PBI nanofibers at a flow rate of 1 mL/min and at 150°C with an applied pressure of 30 bars. Application of molecularly imprinted PBI nanofibers for the desulfurization of oxidized hydro-treated fuel showed potential for use in refining industries to reach ultra-low sulfur fuel level, which falls below the 10 ppm sulfur limit which is mandated by the environmental protection agency (EPA) from 2015.
- Full Text:
- Date Issued: 2014
Synthesis and characterization of NaYGdF4 upconversion nanoparticles and an investigation of their effects on the spectroscopic properties of two phthalocyanine dyes
- Authors: Taylor, Jessica Mary
- Date: 2014
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/54621 , vital:26594
- Description: Sphere and star shaped NaYGdF4:Yb/Er(Tm) upconversion nanoparticles were successfully synthesized utilizing a methanol assisted thermal decomposition approach and their chemical, spectroscopic and fluorescence properties were fully characterized. In addition, their influence on the spectroscopic and fluorescence properties of two phthalocyanines (Pcs) (unsubstituted tetrathiophenoxy phthalocyanine (H2Pc) and aluminium octacarboxy phthalocyanine (Cl)AlOCPc) was investigated. Upconversion nanoparticles were found to produce characteristic upconversion fluorescence emissions in the blue, green, red and NIR regions and were also shown to possess paramagnetic properties. Simple mixing with an H2Pc in toluene was found to exert no change on the spectroscopic or fluorescence properties of the Pc while covalent conjugation to a (Cl)AlOCPc resulted in a large Q band blue shift accompanied by a decrease in fluorescence lifetimes in DMSO. The red light excitation mediated singlet oxygen generation of the H2Pc mixed with upconversion nanoparticles was investigated and singlet oxygen fluorescence lifetimes were found to decrease in the presence of the nanoparticles. Upconversion mediated singlet oxygen generation, by way of resonance energy transfer to the Pc, was also attempted using 972 nm excitation; however, no singlet oxygen was detected utilizing singlet oxygen NIR emission detection. Pending further work using alternative singlet oxygen detection methods, this suggests that while upconversion nanoparticles possess excellent fluorescent imaging capabilities, they are relatively inefficient in inducing singlet oxygen production simply when mixed with phthalocyanines. Despite this, by combining phthalocyanines and upconversion nanoparticles, we present a system capable of: multimodal imaging, using both upconversion and phthalocyanines emissions, singlet oxygen generation, via direct excitation of the phthalocyanine with red laser light, and, possibly, magnetic resonance imaging, as a result of doping the upconversion nanoparticles with Gd3+ ions.
- Full Text:
- Date Issued: 2014
- Authors: Taylor, Jessica Mary
- Date: 2014
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/54621 , vital:26594
- Description: Sphere and star shaped NaYGdF4:Yb/Er(Tm) upconversion nanoparticles were successfully synthesized utilizing a methanol assisted thermal decomposition approach and their chemical, spectroscopic and fluorescence properties were fully characterized. In addition, their influence on the spectroscopic and fluorescence properties of two phthalocyanines (Pcs) (unsubstituted tetrathiophenoxy phthalocyanine (H2Pc) and aluminium octacarboxy phthalocyanine (Cl)AlOCPc) was investigated. Upconversion nanoparticles were found to produce characteristic upconversion fluorescence emissions in the blue, green, red and NIR regions and were also shown to possess paramagnetic properties. Simple mixing with an H2Pc in toluene was found to exert no change on the spectroscopic or fluorescence properties of the Pc while covalent conjugation to a (Cl)AlOCPc resulted in a large Q band blue shift accompanied by a decrease in fluorescence lifetimes in DMSO. The red light excitation mediated singlet oxygen generation of the H2Pc mixed with upconversion nanoparticles was investigated and singlet oxygen fluorescence lifetimes were found to decrease in the presence of the nanoparticles. Upconversion mediated singlet oxygen generation, by way of resonance energy transfer to the Pc, was also attempted using 972 nm excitation; however, no singlet oxygen was detected utilizing singlet oxygen NIR emission detection. Pending further work using alternative singlet oxygen detection methods, this suggests that while upconversion nanoparticles possess excellent fluorescent imaging capabilities, they are relatively inefficient in inducing singlet oxygen production simply when mixed with phthalocyanines. Despite this, by combining phthalocyanines and upconversion nanoparticles, we present a system capable of: multimodal imaging, using both upconversion and phthalocyanines emissions, singlet oxygen generation, via direct excitation of the phthalocyanine with red laser light, and, possibly, magnetic resonance imaging, as a result of doping the upconversion nanoparticles with Gd3+ ions.
- Full Text:
- Date Issued: 2014
Synthesis and evaluation of novel heterocycles as potential HIV-1 enzyme inhibitors
- Ngnie Tuemgnie, Gaëlle Tatiana
- Authors: Ngnie Tuemgnie, Gaëlle Tatiana
- Date: 2014
- Subjects: Heterocyclic compounds , Enzyme inhibitors , Organic compounds , Green chemistry , Coumarins , HIV (Viruses) Enzymes
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/194293 , vital:45440 , DOI https://doi.org/10.21504/10962/194293
- Description: This project has focussed on the synthesis and the evaluation of organic compounds as potential HIV-1 enzyme inhibitors, by making use of green chemistry (microwave assisted synthesis and click chemistry), palladium catalyzed reactions (Heck and Sonogashira coupling), Baylis Hillman methodology and aldol condensation. These compounds were synthesized in good yields and fully characterised by spectroscopic techniques. Biological assay data revealed that some of the compounds possess high inhibitory activity and their effective inhibitory concentration was as good as those of drugs in clinical use. These potential drug molecules were identified by preliminary investigations carried out by molecular modelling where a trend of their inhibitory activity against different enzymes was anticipated. Benzotriazole-AZT conjugates generated by 1,3-dipolar cycloaddition of anthranilic acid derivatives with AZT showed good inhibitory activity in silico against both HIV-1 protease (PR) and HIV-1 reverse transcriptase (RT) enzymes. Still in line with our dual action strategy, cinnamate ester-AZT conjugates were synthesized in three steps starting from benzaldehyde derivatives with a click reaction at the final step. These compounds also showed some inhibitory activity against HIV-1 RT enzyme (88%). In addition, the cinnamoyl fragment attached to AZT appeared to improve the activity of AZT against HIV-1 RT. Peptide chemistry involving carbonyl diimidazole as a coupling reagent between cinnamic acid derivatives and protected amino acids was used to prepare substituted amino acid derivatives which appeared to be very active against the integrase (IN) enzyme (88%). Commercially available coumarin was iodinated and derivatized through palladium catalyzed Heck and Sonogashira reactions with activated alkenes and a terminal alkyne respectively to afford novel coumarin derivatives in good yields. Optimization studies on the Heck reaction with regards to the phosphine ligand, the palladium catalyst and the solvent were carried out to afford novel formyl substituted cinnamate esters with nonaflyl salicylaldehyde derivatives. , Thesis (PhD) -- Faculty of Science, Chemistry, 2014
- Full Text:
- Date Issued: 2014
- Authors: Ngnie Tuemgnie, Gaëlle Tatiana
- Date: 2014
- Subjects: Heterocyclic compounds , Enzyme inhibitors , Organic compounds , Green chemistry , Coumarins , HIV (Viruses) Enzymes
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/194293 , vital:45440 , DOI https://doi.org/10.21504/10962/194293
- Description: This project has focussed on the synthesis and the evaluation of organic compounds as potential HIV-1 enzyme inhibitors, by making use of green chemistry (microwave assisted synthesis and click chemistry), palladium catalyzed reactions (Heck and Sonogashira coupling), Baylis Hillman methodology and aldol condensation. These compounds were synthesized in good yields and fully characterised by spectroscopic techniques. Biological assay data revealed that some of the compounds possess high inhibitory activity and their effective inhibitory concentration was as good as those of drugs in clinical use. These potential drug molecules were identified by preliminary investigations carried out by molecular modelling where a trend of their inhibitory activity against different enzymes was anticipated. Benzotriazole-AZT conjugates generated by 1,3-dipolar cycloaddition of anthranilic acid derivatives with AZT showed good inhibitory activity in silico against both HIV-1 protease (PR) and HIV-1 reverse transcriptase (RT) enzymes. Still in line with our dual action strategy, cinnamate ester-AZT conjugates were synthesized in three steps starting from benzaldehyde derivatives with a click reaction at the final step. These compounds also showed some inhibitory activity against HIV-1 RT enzyme (88%). In addition, the cinnamoyl fragment attached to AZT appeared to improve the activity of AZT against HIV-1 RT. Peptide chemistry involving carbonyl diimidazole as a coupling reagent between cinnamic acid derivatives and protected amino acids was used to prepare substituted amino acid derivatives which appeared to be very active against the integrase (IN) enzyme (88%). Commercially available coumarin was iodinated and derivatized through palladium catalyzed Heck and Sonogashira reactions with activated alkenes and a terminal alkyne respectively to afford novel coumarin derivatives in good yields. Optimization studies on the Heck reaction with regards to the phosphine ligand, the palladium catalyst and the solvent were carried out to afford novel formyl substituted cinnamate esters with nonaflyl salicylaldehyde derivatives. , Thesis (PhD) -- Faculty of Science, Chemistry, 2014
- Full Text:
- Date Issued: 2014
Synthesis of chromium carbene scaffolds for use in medicinal chemistry
- Rafael, Christopher Carlos Ferreira
- Authors: Rafael, Christopher Carlos Ferreira
- Date: 2014
- Subjects: Carbenes (Methylene compounds) , Pharmaceutical chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4456 , http://hdl.handle.net/10962/d1010863 , Carbenes (Methylene compounds) , Pharmaceutical chemistry
- Description: This study involves using methyllithium to synthesize Fischer carbene complexes as precursors for metal templated α,β-unsaturated complexes with potential as acceptors in the Baylis Hillman reaction as well as in Dötz benzannulation. Fischer carbene complexes contain low oxidation state metal centers, are electrophilic in nature and are stabilized by π-donating substituents such as alkoxy and amino groups. The increased electron withdrawing nature of the metal carbonyl moiety was expected to improve the rates of reaction compared to organic carbonyls. Four Fischer carbenes were synthesized via nucleophilic addition of MeLi to chromium and tungsten hexacarbonyl at low temperatures followed by alkylation using either a Meerwein salt (Me₃OBF₄) to give the desired Fischer metal methyl methoxy carbenes or Et₄NBr/alkylhalide to make the corresponding ethoxy and allyloxy carbenes. Characterization was by means of ¹³C NMR, ¹H NMR, and IR. In silico studies were carried out looking at the effect of substituents on the carbene bond. Synthesis of α,β-unsaturated complexes was effected via the aldol condensation route and found to be unfavorable using enolizable aldehydes, although the use of two aryl aldehydes resulted in successful preparation of two α,β-unsaturated complexes. Difficulty in the purification of these complexes hindered their full characterization. Computational studies looked at the effect of substituents on the system as well as variation of the metal from Cr to Mo and W. Synthesis of Baylis Hillman adducts using α,β-unsaturated complexes as acceptors was unsuccessful due to the ease of product oxidization. One potential product was obtained in its crude form although purification was not possible due to oxidation. Computational studies suggested that the oxygen on the ligand negatively impacts the stability of these Fischer carbene derived Baylis Hillman adducts promoting intramolecular oxidation of the metal. The α,β-unsaturated complexes and Baylis Hillman adducts were considered to be candidates to undergo Dötz benzannulation methodology. The use of the α,β-unsaturated complexes in this reaction was generally unsuccessful, both in the microwave and in conventional reflux conditions. Computational studies of these compounds were carried out to facilitate understanding of their stability and configuration.
- Full Text:
- Date Issued: 2014
- Authors: Rafael, Christopher Carlos Ferreira
- Date: 2014
- Subjects: Carbenes (Methylene compounds) , Pharmaceutical chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4456 , http://hdl.handle.net/10962/d1010863 , Carbenes (Methylene compounds) , Pharmaceutical chemistry
- Description: This study involves using methyllithium to synthesize Fischer carbene complexes as precursors for metal templated α,β-unsaturated complexes with potential as acceptors in the Baylis Hillman reaction as well as in Dötz benzannulation. Fischer carbene complexes contain low oxidation state metal centers, are electrophilic in nature and are stabilized by π-donating substituents such as alkoxy and amino groups. The increased electron withdrawing nature of the metal carbonyl moiety was expected to improve the rates of reaction compared to organic carbonyls. Four Fischer carbenes were synthesized via nucleophilic addition of MeLi to chromium and tungsten hexacarbonyl at low temperatures followed by alkylation using either a Meerwein salt (Me₃OBF₄) to give the desired Fischer metal methyl methoxy carbenes or Et₄NBr/alkylhalide to make the corresponding ethoxy and allyloxy carbenes. Characterization was by means of ¹³C NMR, ¹H NMR, and IR. In silico studies were carried out looking at the effect of substituents on the carbene bond. Synthesis of α,β-unsaturated complexes was effected via the aldol condensation route and found to be unfavorable using enolizable aldehydes, although the use of two aryl aldehydes resulted in successful preparation of two α,β-unsaturated complexes. Difficulty in the purification of these complexes hindered their full characterization. Computational studies looked at the effect of substituents on the system as well as variation of the metal from Cr to Mo and W. Synthesis of Baylis Hillman adducts using α,β-unsaturated complexes as acceptors was unsuccessful due to the ease of product oxidization. One potential product was obtained in its crude form although purification was not possible due to oxidation. Computational studies suggested that the oxygen on the ligand negatively impacts the stability of these Fischer carbene derived Baylis Hillman adducts promoting intramolecular oxidation of the metal. The α,β-unsaturated complexes and Baylis Hillman adducts were considered to be candidates to undergo Dötz benzannulation methodology. The use of the α,β-unsaturated complexes in this reaction was generally unsuccessful, both in the microwave and in conventional reflux conditions. Computational studies of these compounds were carried out to facilitate understanding of their stability and configuration.
- Full Text:
- Date Issued: 2014
Synthetic analogues of marine bisindole alkaloids as potent selective inhibitors of MRSA pyruvate kinase
- Veale, Clinton Gareth Lancaster
- Authors: Veale, Clinton Gareth Lancaster
- Date: 2014 , 2014-04-02
- Subjects: Alkaloids , Pyruvate kinase , Staphylococcus aureus , Antibiotics , Sponges -- South Africa , Imidazoles , Biological assay , Antibacterial agents
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4563 , http://hdl.handle.net/10962/d1020893
- Description: Globally, methicillin resistant Staphylococcus aureus (MRSA) has become increasingly difficult to manage in the clinic and new antibiotics are required. The structure activity relationship (SAR) study presented in this thesis forms part of an international collaborative effort to identify potent and selective inhibitors of an MRSA pyruvate kinase (PK) enzyme target. In earlier work the known marine natural product bromodeoxytopsentin (1.6), isolated from a South African marine sponge Topsentia pachastrelloides, exhibited selective and significant inhibition of MRSA PK (IC₅₀ 60 nM). Accordingly bromodeoxytopsentin provided the initial chemical scaffold around which our SAR study was developed. Following a comprehensive introduction, providing the necessary background to the research described in subsequent Chapters, this thesis has been divided into three major parts. Part one (Chapter 2) documents the synthesis of two natural imidazole containing topsentin analogues 1.40, 1.46, five new synthetic analogues 1.58—1.61, 2.104. In the process we developed a new method for the synthesis of topsentin derivatives via selenium dioxide mediated oxidation of N-Boc protected 3-acetylindoles to yield glyoxal intermediates which were subsequently cyclized and deprotected to yield the desired products. Interestingly we were able to demonstrate a delicate relationship between the relative equivalents of selenium dioxide and water used during the oxidation step, careful manipulation of which was required to prevent the uncontrolled formation of side products. Synthetic compounds 1.40, 1.46, 1.58—1.61 were found to be potent inhibitors of MRSA PK (IC₅₀ 238, 2.1, 23, 1.4, 6.3 and 3.2 nM respectively) with 1000-10000 fold selectivity for MRSA PK over four human orthologs. In the second part of this thesis (Chapter 3) we report the successful synthesis of a cohort of previously unknown thiazole containing bisindole topsentin analogues 1.62—1.68 via a Hantzsch thiazole synthesis. Bioassay results revealed that these compounds were only moderate inhibitors of MRSA PK (IC₅₀ 5.1—20 μM) which suggested that inhibitory activity was significantly reduced upon substitution of the central imidazole ring of topsentin type analogues with a thiazole type ring. In addition in Chapter 3 we describe unsuccessful attempts to regiospecifically synthesize oxazole and imidazole topsentin analogues through a similar Hantzsch method. As a consequence of our efforts in this regard we investigated three key reactions in depth, namely the synthesis of 2.2, 3.38, 3.40, 3.41 via α-bromination of 3-acetylindole and the synthesis of indolyl-3-carbonylnitriles 2.13, 3.45—3.47 and α-oxo-1H-indole-3-thioacetamides 3.48—3.51. The investigation of the latter led to the isolation and elucidation of two anomalous N,N-dimethyl-1H-indole-3-carboxamides 3.52 and 3.53. Finally the third part of this thesis (Chapter 4) deals with in silico assessment of the binding of both the imidazole and thiazole containing bisindole alkaloids to the MRSA PK protein which initially guided our SAR studies. In this chapter we reveal that there appears to be no correlation between in silico binding predictions and in vitro MRSA PK inhibitory bioassay data. Superficially it seems that binding energy as determined by the docking program used for these studies correlated with the size of the indole substituents and did not reflect IC₅₀ MRSA PK inhibitory data. Although this led us to computationally explore possible alternative binding sites no clear alternative has been identified.
- Full Text:
- Date Issued: 2014
- Authors: Veale, Clinton Gareth Lancaster
- Date: 2014 , 2014-04-02
- Subjects: Alkaloids , Pyruvate kinase , Staphylococcus aureus , Antibiotics , Sponges -- South Africa , Imidazoles , Biological assay , Antibacterial agents
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4563 , http://hdl.handle.net/10962/d1020893
- Description: Globally, methicillin resistant Staphylococcus aureus (MRSA) has become increasingly difficult to manage in the clinic and new antibiotics are required. The structure activity relationship (SAR) study presented in this thesis forms part of an international collaborative effort to identify potent and selective inhibitors of an MRSA pyruvate kinase (PK) enzyme target. In earlier work the known marine natural product bromodeoxytopsentin (1.6), isolated from a South African marine sponge Topsentia pachastrelloides, exhibited selective and significant inhibition of MRSA PK (IC₅₀ 60 nM). Accordingly bromodeoxytopsentin provided the initial chemical scaffold around which our SAR study was developed. Following a comprehensive introduction, providing the necessary background to the research described in subsequent Chapters, this thesis has been divided into three major parts. Part one (Chapter 2) documents the synthesis of two natural imidazole containing topsentin analogues 1.40, 1.46, five new synthetic analogues 1.58—1.61, 2.104. In the process we developed a new method for the synthesis of topsentin derivatives via selenium dioxide mediated oxidation of N-Boc protected 3-acetylindoles to yield glyoxal intermediates which were subsequently cyclized and deprotected to yield the desired products. Interestingly we were able to demonstrate a delicate relationship between the relative equivalents of selenium dioxide and water used during the oxidation step, careful manipulation of which was required to prevent the uncontrolled formation of side products. Synthetic compounds 1.40, 1.46, 1.58—1.61 were found to be potent inhibitors of MRSA PK (IC₅₀ 238, 2.1, 23, 1.4, 6.3 and 3.2 nM respectively) with 1000-10000 fold selectivity for MRSA PK over four human orthologs. In the second part of this thesis (Chapter 3) we report the successful synthesis of a cohort of previously unknown thiazole containing bisindole topsentin analogues 1.62—1.68 via a Hantzsch thiazole synthesis. Bioassay results revealed that these compounds were only moderate inhibitors of MRSA PK (IC₅₀ 5.1—20 μM) which suggested that inhibitory activity was significantly reduced upon substitution of the central imidazole ring of topsentin type analogues with a thiazole type ring. In addition in Chapter 3 we describe unsuccessful attempts to regiospecifically synthesize oxazole and imidazole topsentin analogues through a similar Hantzsch method. As a consequence of our efforts in this regard we investigated three key reactions in depth, namely the synthesis of 2.2, 3.38, 3.40, 3.41 via α-bromination of 3-acetylindole and the synthesis of indolyl-3-carbonylnitriles 2.13, 3.45—3.47 and α-oxo-1H-indole-3-thioacetamides 3.48—3.51. The investigation of the latter led to the isolation and elucidation of two anomalous N,N-dimethyl-1H-indole-3-carboxamides 3.52 and 3.53. Finally the third part of this thesis (Chapter 4) deals with in silico assessment of the binding of both the imidazole and thiazole containing bisindole alkaloids to the MRSA PK protein which initially guided our SAR studies. In this chapter we reveal that there appears to be no correlation between in silico binding predictions and in vitro MRSA PK inhibitory bioassay data. Superficially it seems that binding energy as determined by the docking program used for these studies correlated with the size of the indole substituents and did not reflect IC₅₀ MRSA PK inhibitory data. Although this led us to computationally explore possible alternative binding sites no clear alternative has been identified.
- Full Text:
- Date Issued: 2014
The design of quantum dots and their conjugates as luminescent probes for analyte sensing
- Authors: Adegoke, Oluwasesan
- Date: 2014
- Subjects: Quantum dots Anolytes Luminescent probes Luminescence spectroscopy Phthalocyanines Nanoparticles
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4457 , http://hdl.handle.net/10962/d1010866
- Description: The design and applications of quantum dots (QDs) as fluorescent probes for analyte sensing is presented. Cadmium based thiol-capped QDs were employed as probe for the detection of analytes. Comparative studies between core CdTe and core-shell CdTe@ZnS QDs showed that the overall sensitivity and selectivity of the sensor was dependent on the nature of the capping agent and the QDs employed, hence making CdTe@ZnS QDs a more superior sensor than the core. To explore the luminescent sensing of QDs based on the fluorescence “turn ON” mode, L-glutathione-capped CdTe QDs was conjugated to 4-amino-2,2,6,6-tetramethylpiperidine-N-oxide (4AT) to form a QDs-4AT conjugate system. The QDs-4AT nanoprobe was highly selective and sensitive to the detection of bromide ion with a very low limit of detection. Subsequently, metallo-phthalocyanines (MPcs) were employed as host molecules on the surface of QDs based on the covalent linking of the QDs to the MPc. Elucidation of the reaction mechanism showed that the fluorescence “turn ON” effect of the QDs-MPc probe in the presence of the analyte was due to axial ligation of the analytes to the Pc ring. Studies showed that the type of substituent attached to the MPc ring influenced the overall sensitivity of the probe. Additionally, a comparative investigation using newly synthesized phthalocyanine and triaza-benzcorrole complexes was conducted when these complexes were conjugated to CdSe@ZnS QDs for analyte sensing. Results showed that the triaza-benzcorrole complex can be employed as a host-molecule sensor but displayed a lower sensitivity for analyte sensing in comparison to the phthalocyanine complex.
- Full Text:
- Date Issued: 2014
- Authors: Adegoke, Oluwasesan
- Date: 2014
- Subjects: Quantum dots Anolytes Luminescent probes Luminescence spectroscopy Phthalocyanines Nanoparticles
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4457 , http://hdl.handle.net/10962/d1010866
- Description: The design and applications of quantum dots (QDs) as fluorescent probes for analyte sensing is presented. Cadmium based thiol-capped QDs were employed as probe for the detection of analytes. Comparative studies between core CdTe and core-shell CdTe@ZnS QDs showed that the overall sensitivity and selectivity of the sensor was dependent on the nature of the capping agent and the QDs employed, hence making CdTe@ZnS QDs a more superior sensor than the core. To explore the luminescent sensing of QDs based on the fluorescence “turn ON” mode, L-glutathione-capped CdTe QDs was conjugated to 4-amino-2,2,6,6-tetramethylpiperidine-N-oxide (4AT) to form a QDs-4AT conjugate system. The QDs-4AT nanoprobe was highly selective and sensitive to the detection of bromide ion with a very low limit of detection. Subsequently, metallo-phthalocyanines (MPcs) were employed as host molecules on the surface of QDs based on the covalent linking of the QDs to the MPc. Elucidation of the reaction mechanism showed that the fluorescence “turn ON” effect of the QDs-MPc probe in the presence of the analyte was due to axial ligation of the analytes to the Pc ring. Studies showed that the type of substituent attached to the MPc ring influenced the overall sensitivity of the probe. Additionally, a comparative investigation using newly synthesized phthalocyanine and triaza-benzcorrole complexes was conducted when these complexes were conjugated to CdSe@ZnS QDs for analyte sensing. Results showed that the triaza-benzcorrole complex can be employed as a host-molecule sensor but displayed a lower sensitivity for analyte sensing in comparison to the phthalocyanine complex.
- Full Text:
- Date Issued: 2014
The development of functionalized electrospun nanofibers for the control of pathogenic microorganisms in water.
- Authors: Kleyi, Phumelele Eldridge
- Date: 2014
- Subjects: Electrospinning , Nanofibers , Pathogenic microorganisms , Pathogenic microorganisms -- Detection , Drinking water -- Microbiology , Water quality -- Measurement , Imidazoles , Spectrum analysis , Anti-infective agents , Polymerization
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4497 , http://hdl.handle.net/10962/d1013134
- Description: The thesis presents the development of functionalized electrospun nylon 6 nanofibers for the eradication of pathogenic microorganisms in drinking water. Imidazole derivatives were synthesized as the antimicrobial agents and were characterized by means of NMR spectroscopy, IR spectroscopy, elemental analysis and X-ray crystallography. The first set of compounds (2-substituted N-alkylimidazoles) consisted of imidazole derivatives substituted with different alkyl groups (methyl, ethyl, propyl, butyl, heptyl, octyl, decyl and benzyl) at the 1-position and various functional groups [carboxaldehyde (CHO), alcohol (CH2OH) and carboxylic acid (COOH)] at the 2-position. It was observed that the antimicrobial activity of the compounds increased with increasing alkyl chain length and decreasing pKa of the 2-substituent. It was also observed that the antimicrobial activity was predominantly against a Gram-positive bacterial strains [Staphylococcus aureus (MIC = 5-160 μg/mL) and Bacillus subtilis subsp. spizizenii (MIC = 5-20 μg/mL)], with the latter being the more susceptible. However, the compounds displayed poor antimicrobial activity against Gram-negative bacterial strain, E. coli (MIC = 150- >2500 μg/mL) and did not show any activity against the yeast, C. albicans. The second set of compounds consisted of the silver(I) complexes containing 2-hydroxymethyl-N-alkylimidazoles. The complexes displayed a broad spectrum antimicrobial activity towards the microorganisms that were tested and their activity [E. coli (MIC = 5-40 μg/mL), S. aureus (MIC = 20-80 μg/mL), Bacillus subtilis subsp. spizizenii (MIC = 5-40 μg/mL) and C. albicans (MIC = 40-80 μg/mL)] increased with the alkyl chain length of the 2-hydroxymethyl-N-alkylimidazole. The third set of compounds consisted of the vinylimidazoles containing the vinyl group either at the 1-position or at the 4- or 5- position. The imidazoles with the vinyl group at the 4- or 5-position contained the alkyl group (decyl) at the 1-position. For the fabrication of the antimicrobial nanofibers, the first two sets of imidazole derivatives (2-substituted N-alkylimidazoles and silver(I) complexes) were incorporated into electrospun nylon 6 nanofibers while the third set (2-substituted vinylimidazoles) was immobilized onto electrospun nylon 6 nanofibers employing the graft polymerization method. The antimicrobial nylon nanofibers were characterized by IR spectroscopy and SEM-EDAX (EDS). The electrospun nylon 6 nanofibers incorporated with 2-substituted N-alkylimidazoles displayed moderate to excellent levels of growth reduction against S. aureus (73.2-99.8 percent). For the electrospun nylon 6 nanofibers incorporated with silver(I) complexes, the levels of growth reduction were >99.99 percent, after the antimicrobial activity evaluation using the shake flask method. Furthermore, the grafted electrospun nylon 6 nanofibers showed excellent levels of growth reduction for E. coli (99.94-99.99 percent) and S. aureus (99.93-99.99 percent). The reusability results indicated that the grafted electrospun nylon 6 nanofibers maintained the antibacterial activity until the third cycle of useage. The cytotoxicity studies showed that grafted electrospun nylon 6 nanofibers possess lower cytotoxic effects on Chang liver cells with IC50 values in the range 23.48-26.81 μg/mL. The thesis demonstrated that the development of antimicrobial electrospun nanofibers, with potential for the eradication of pathogenic microoganisms in water, could be accomplished by incorporation as well as immobilization strategies.
- Full Text:
- Date Issued: 2014
- Authors: Kleyi, Phumelele Eldridge
- Date: 2014
- Subjects: Electrospinning , Nanofibers , Pathogenic microorganisms , Pathogenic microorganisms -- Detection , Drinking water -- Microbiology , Water quality -- Measurement , Imidazoles , Spectrum analysis , Anti-infective agents , Polymerization
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4497 , http://hdl.handle.net/10962/d1013134
- Description: The thesis presents the development of functionalized electrospun nylon 6 nanofibers for the eradication of pathogenic microorganisms in drinking water. Imidazole derivatives were synthesized as the antimicrobial agents and were characterized by means of NMR spectroscopy, IR spectroscopy, elemental analysis and X-ray crystallography. The first set of compounds (2-substituted N-alkylimidazoles) consisted of imidazole derivatives substituted with different alkyl groups (methyl, ethyl, propyl, butyl, heptyl, octyl, decyl and benzyl) at the 1-position and various functional groups [carboxaldehyde (CHO), alcohol (CH2OH) and carboxylic acid (COOH)] at the 2-position. It was observed that the antimicrobial activity of the compounds increased with increasing alkyl chain length and decreasing pKa of the 2-substituent. It was also observed that the antimicrobial activity was predominantly against a Gram-positive bacterial strains [Staphylococcus aureus (MIC = 5-160 μg/mL) and Bacillus subtilis subsp. spizizenii (MIC = 5-20 μg/mL)], with the latter being the more susceptible. However, the compounds displayed poor antimicrobial activity against Gram-negative bacterial strain, E. coli (MIC = 150- >2500 μg/mL) and did not show any activity against the yeast, C. albicans. The second set of compounds consisted of the silver(I) complexes containing 2-hydroxymethyl-N-alkylimidazoles. The complexes displayed a broad spectrum antimicrobial activity towards the microorganisms that were tested and their activity [E. coli (MIC = 5-40 μg/mL), S. aureus (MIC = 20-80 μg/mL), Bacillus subtilis subsp. spizizenii (MIC = 5-40 μg/mL) and C. albicans (MIC = 40-80 μg/mL)] increased with the alkyl chain length of the 2-hydroxymethyl-N-alkylimidazole. The third set of compounds consisted of the vinylimidazoles containing the vinyl group either at the 1-position or at the 4- or 5- position. The imidazoles with the vinyl group at the 4- or 5-position contained the alkyl group (decyl) at the 1-position. For the fabrication of the antimicrobial nanofibers, the first two sets of imidazole derivatives (2-substituted N-alkylimidazoles and silver(I) complexes) were incorporated into electrospun nylon 6 nanofibers while the third set (2-substituted vinylimidazoles) was immobilized onto electrospun nylon 6 nanofibers employing the graft polymerization method. The antimicrobial nylon nanofibers were characterized by IR spectroscopy and SEM-EDAX (EDS). The electrospun nylon 6 nanofibers incorporated with 2-substituted N-alkylimidazoles displayed moderate to excellent levels of growth reduction against S. aureus (73.2-99.8 percent). For the electrospun nylon 6 nanofibers incorporated with silver(I) complexes, the levels of growth reduction were >99.99 percent, after the antimicrobial activity evaluation using the shake flask method. Furthermore, the grafted electrospun nylon 6 nanofibers showed excellent levels of growth reduction for E. coli (99.94-99.99 percent) and S. aureus (99.93-99.99 percent). The reusability results indicated that the grafted electrospun nylon 6 nanofibers maintained the antibacterial activity until the third cycle of useage. The cytotoxicity studies showed that grafted electrospun nylon 6 nanofibers possess lower cytotoxic effects on Chang liver cells with IC50 values in the range 23.48-26.81 μg/mL. The thesis demonstrated that the development of antimicrobial electrospun nanofibers, with potential for the eradication of pathogenic microoganisms in water, could be accomplished by incorporation as well as immobilization strategies.
- Full Text:
- Date Issued: 2014
Synthesis and evaluation of novel inhibitors of 1-Deoxy-D-xylolose-5-phosphate reductoisomerase as potential antimalarials
- Authors: Conibear, Anne Claire
- Date: 2013-07-19
- Subjects: Antimalarials -- Development , Malaria -- Chemotherapy , Drug development , Enzyme kinetics , Phosphate esters
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4451 , http://hdl.handle.net/10962/d1008282 , Antimalarials -- Development , Malaria -- Chemotherapy , Drug development , Enzyme kinetics , Phosphate esters
- Description: Malaria continues to be an enormous health-threat in the developing world and the emergence of drug resistance has further compounded the problem. The parasite-specific enzyme, 1-deoxY-D-xylulose-S-phosphate reductoisomerase (DXR), has recently been validated as a promising antimalarial drug target. The present study comprises a combination of synthetic, physical organic, computer modelling and bioassay techniques directed towards the development of novel DXR inhibitors. A range of 2-heteroarylamino-2-oxoethyl- and 2- heteroarylamino-2-oxopropyl phosphonate esters and their corresponding phosphonic acid salts have been synthesised as analogues of the highly active DXR inhibitor, fosmidomycin. Treatment of the heteroarylamino precursors with chloroacetyl chloride or chloropropionyl chloride afforded chloroamide intermediates, Arbuzov reactions of which led to the corresponding diethyl phosphonate esters. Hydrolysis of the esters has been effected using bromotrimethylsilane. Twenty-four new compounds have been prepared and fully characterised using elemental (HRMS or combustion) and spectroscopic (1- and 2-D NMR and IR) analysis. A 31p NMR kinetic study has been carried out on the two-step silylation reaction involved in the hydrolysis of the phosphonate esters and has provided activation parameters for the reaction. The kinetic analysis was refined using a computational method to give an improved fit with the experimental data. Saturation transfer difference (STD) NMR analysis, computer-simulated docking and enzyme inhibition assays have been used to evaluate the enzyme-binding and -inhibition potential of the synthesised ligands. Minimal to moderate inhibitory activity has been observed and several structure-activity relationships have been identified. In silica exploration of the DXR active site has revealed an additional binding pocket and information on the topology of the active site has led to the de novo design of a new series of potential ligands. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Authors: Conibear, Anne Claire
- Date: 2013-07-19
- Subjects: Antimalarials -- Development , Malaria -- Chemotherapy , Drug development , Enzyme kinetics , Phosphate esters
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4451 , http://hdl.handle.net/10962/d1008282 , Antimalarials -- Development , Malaria -- Chemotherapy , Drug development , Enzyme kinetics , Phosphate esters
- Description: Malaria continues to be an enormous health-threat in the developing world and the emergence of drug resistance has further compounded the problem. The parasite-specific enzyme, 1-deoxY-D-xylulose-S-phosphate reductoisomerase (DXR), has recently been validated as a promising antimalarial drug target. The present study comprises a combination of synthetic, physical organic, computer modelling and bioassay techniques directed towards the development of novel DXR inhibitors. A range of 2-heteroarylamino-2-oxoethyl- and 2- heteroarylamino-2-oxopropyl phosphonate esters and their corresponding phosphonic acid salts have been synthesised as analogues of the highly active DXR inhibitor, fosmidomycin. Treatment of the heteroarylamino precursors with chloroacetyl chloride or chloropropionyl chloride afforded chloroamide intermediates, Arbuzov reactions of which led to the corresponding diethyl phosphonate esters. Hydrolysis of the esters has been effected using bromotrimethylsilane. Twenty-four new compounds have been prepared and fully characterised using elemental (HRMS or combustion) and spectroscopic (1- and 2-D NMR and IR) analysis. A 31p NMR kinetic study has been carried out on the two-step silylation reaction involved in the hydrolysis of the phosphonate esters and has provided activation parameters for the reaction. The kinetic analysis was refined using a computational method to give an improved fit with the experimental data. Saturation transfer difference (STD) NMR analysis, computer-simulated docking and enzyme inhibition assays have been used to evaluate the enzyme-binding and -inhibition potential of the synthesised ligands. Minimal to moderate inhibitory activity has been observed and several structure-activity relationships have been identified. In silica exploration of the DXR active site has revealed an additional binding pocket and information on the topology of the active site has led to the de novo design of a new series of potential ligands. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
Synthesis and evaluation of PGM-selective ligands
- Gxoyiya, Babalwa Siliziwe Blossom
- Authors: Gxoyiya, Babalwa Siliziwe Blossom
- Date: 2013-05-28
- Subjects: Platinum group , Ligands , Ligands -- Evaluation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4450 , http://hdl.handle.net/10962/d1007849 , Platinum group , Ligands , Ligands -- Evaluation
- Description: A series of polydentate POM-selective, sulfur-containing amide ligands have been synthesized from ro-dibromoalkanes and mercaptoacetanilide, The resulting 3,6- dithiaoctanediamides and 3,7-dithianonanediamides, some of which contain a polymerisable group, were all characterized by high-resolution MS, IR, I Hand I3C NMR spectroscopic methods. Various approaches to the polymerisable ligands were explored, the most efficient proving to be the incorporation of an allyl ether moiety in the mercaptoacetanilide. The corresponding Pd(U) and Pt(II) complexes were also prepared from the metal chloride salts and characterized by elemental analysis and spectroscopic methods. The NMR data indicates that both the cis- and transcomplexes were formed, while the IR data indicates cis- coordination of the chlorine . ligands. Molecularly imprinted polymers (MIP's), prepared using platinum(II) mercaptoacetanilide and 3,6-dithiadiamide complexes, showed high selectivity for , , palladium(II) [in the presence of Pt(II), CoCII), Cu(II) and Ni(II)] as determined by . ICP-MS analysis. The more kinetically inert Pt(II) ions however, slowly displaced Pd(II), confirming the Pt(II) selectivity of the MIP's. Solvent extraction studies were conducted to explore the selectivity of the 3,6- dithiaoctanediamides and 3,7-dithianonanediamides for Pd(U) over CoCII), Cu(U) and Ni(II). The ICP-MS data indicate that, in general, equilibration was achieved within ten minutes and that the longer-chain amides were less selective than the shorter-chain analogues. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Authors: Gxoyiya, Babalwa Siliziwe Blossom
- Date: 2013-05-28
- Subjects: Platinum group , Ligands , Ligands -- Evaluation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4450 , http://hdl.handle.net/10962/d1007849 , Platinum group , Ligands , Ligands -- Evaluation
- Description: A series of polydentate POM-selective, sulfur-containing amide ligands have been synthesized from ro-dibromoalkanes and mercaptoacetanilide, The resulting 3,6- dithiaoctanediamides and 3,7-dithianonanediamides, some of which contain a polymerisable group, were all characterized by high-resolution MS, IR, I Hand I3C NMR spectroscopic methods. Various approaches to the polymerisable ligands were explored, the most efficient proving to be the incorporation of an allyl ether moiety in the mercaptoacetanilide. The corresponding Pd(U) and Pt(II) complexes were also prepared from the metal chloride salts and characterized by elemental analysis and spectroscopic methods. The NMR data indicates that both the cis- and transcomplexes were formed, while the IR data indicates cis- coordination of the chlorine . ligands. Molecularly imprinted polymers (MIP's), prepared using platinum(II) mercaptoacetanilide and 3,6-dithiadiamide complexes, showed high selectivity for , , palladium(II) [in the presence of Pt(II), CoCII), Cu(II) and Ni(II)] as determined by . ICP-MS analysis. The more kinetically inert Pt(II) ions however, slowly displaced Pd(II), confirming the Pt(II) selectivity of the MIP's. Solvent extraction studies were conducted to explore the selectivity of the 3,6- dithiaoctanediamides and 3,7-dithianonanediamides for Pd(U) over CoCII), Cu(U) and Ni(II). The ICP-MS data indicate that, in general, equilibration was achieved within ten minutes and that the longer-chain amides were less selective than the shorter-chain analogues. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
A Comparative study of two copper(II) based metal-organic frameworks : Cu2¼(OH)½B4C•8H2O and Cu2Na(OH)B4C•7H2O
- Authors: Coombes, Matthew
- Date: 2013
- Subjects: Copper , Organometallic compounds , Supramolecular organometallic chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4533 , http://hdl.handle.net/10962/d1016245
- Description: This study focussed on two copper(II)-containing metal-organic frameworks (MOFs): Cu2Na(OH)B4C•7H2O and Cu2¼(OH)½B4C•8H2O (B4C = 1,2,4,5- benzenetetracarboxylate). They are both covalent, three-dimensional metalorganic framework polymers containing voids filled with water molecules. Both were characterised by elemental analysis, infrared spectroscopy, X-ray powder diffractometry (both in situ and regular), thermogravimetric analysis, differential scanning calorimetry and X-ray photoelectron spectroscopy. These two MOFs are essentially identical, with the only difference being the substitution of sodium by copper at every 4th site (disordered throughout the crystal). The guest inclusion properties of both MOFs were studied and compared. Although both structures collapse on dehydration, it was observed that Cu2Na(OH)B4C•7H2O is able to take up signifcant amounts of water, methanol and ethanol. All these processes are fully reversible. Car-Parrinello molecular dynamics studies suggest that it is a strong interaction between the oxygen atoms on these molecules with the sodium cation of the MOF that is responsible for this signifcant uptake. In contrast, Cu2¼ (OH)½ B4C•8H2O, the MOF without a sodium cation, did not demonstrate any methanol or ethanol uptake, but was able to take up some water. The uptake of water, however, is not a fully reversible process. The absence of sodium likely results in insuffcient energy to draw methanol and ethanol into the framework, while a subtle rotation of a carboxylate group on dehydration decreases the ability of the framework to form hydrogen bonds, thus reducing the ability to take up water. A series of hydrothermal syntheses were performed in order to develop a method of synthesis superior to the current gel-based synthesis that requires several months and has poor yields. The hydrothermal products were characterized by elemental analysis, infrared spectroscopy, X-ray powder diffractometry, thermogravimetric analysis and differential scanning calorimetry. It was shown that the MOF Cu2Na(OH)B4C•7H2O may be synthesised in almost 100% yield by using a temperature of 120°C over a period of 72 hours. It was not possible to synthesise Cu2¼ (OH)½ B4C•8H2O in a 100% yield - it was only obtained as a minor product.
- Full Text:
- Date Issued: 2013
- Authors: Coombes, Matthew
- Date: 2013
- Subjects: Copper , Organometallic compounds , Supramolecular organometallic chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4533 , http://hdl.handle.net/10962/d1016245
- Description: This study focussed on two copper(II)-containing metal-organic frameworks (MOFs): Cu2Na(OH)B4C•7H2O and Cu2¼(OH)½B4C•8H2O (B4C = 1,2,4,5- benzenetetracarboxylate). They are both covalent, three-dimensional metalorganic framework polymers containing voids filled with water molecules. Both were characterised by elemental analysis, infrared spectroscopy, X-ray powder diffractometry (both in situ and regular), thermogravimetric analysis, differential scanning calorimetry and X-ray photoelectron spectroscopy. These two MOFs are essentially identical, with the only difference being the substitution of sodium by copper at every 4th site (disordered throughout the crystal). The guest inclusion properties of both MOFs were studied and compared. Although both structures collapse on dehydration, it was observed that Cu2Na(OH)B4C•7H2O is able to take up signifcant amounts of water, methanol and ethanol. All these processes are fully reversible. Car-Parrinello molecular dynamics studies suggest that it is a strong interaction between the oxygen atoms on these molecules with the sodium cation of the MOF that is responsible for this signifcant uptake. In contrast, Cu2¼ (OH)½ B4C•8H2O, the MOF without a sodium cation, did not demonstrate any methanol or ethanol uptake, but was able to take up some water. The uptake of water, however, is not a fully reversible process. The absence of sodium likely results in insuffcient energy to draw methanol and ethanol into the framework, while a subtle rotation of a carboxylate group on dehydration decreases the ability of the framework to form hydrogen bonds, thus reducing the ability to take up water. A series of hydrothermal syntheses were performed in order to develop a method of synthesis superior to the current gel-based synthesis that requires several months and has poor yields. The hydrothermal products were characterized by elemental analysis, infrared spectroscopy, X-ray powder diffractometry, thermogravimetric analysis and differential scanning calorimetry. It was shown that the MOF Cu2Na(OH)B4C•7H2O may be synthesised in almost 100% yield by using a temperature of 120°C over a period of 72 hours. It was not possible to synthesise Cu2¼ (OH)½ B4C•8H2O in a 100% yield - it was only obtained as a minor product.
- Full Text:
- Date Issued: 2013
A marine chemical ecology study of the sea hare, Bursatella leachii in South Africa
- Authors: D'Souza, Nicole
- Date: 2013 , 2013-03-22
- Subjects: Sea hares (Mollusks) -- South Africa -- Kenton-on-Sea , Sea hares (Mollusks) -- Ecology -- South Africa -- Kenton-on-Sea , Sea hares (Mollusks) -- Behavior -- South Africa -- Kenton-on-Sea , Sea hares (Mollusks) -- Defenses -- Behavior -- South Africa -- Kenton-on-Sea
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4283 , http://hdl.handle.net/10962/d1002952 , Sea hares (Mollusks) -- South Africa -- Kenton-on-Sea , Sea hares (Mollusks) -- Ecology -- South Africa -- Kenton-on-Sea , Sea hares (Mollusks) -- Behavior -- South Africa -- Kenton-on-Sea , Sea hares (Mollusks) -- Defenses -- Behavior -- South Africa -- Kenton-on-Sea
- Description: The large cosmopolitan sea hare Bursatella leachii is a common resident in Eastern Cape river mouths during summer and late autumn where they congregate in beds of Zostera capensis to breed. In this thesis, the previously known toxic formamide marine secondary metabolite (-)-bursatellin (2.2), which may deter predators of South African specimens of the globally distributed sea hare Bursatella leachii, was isolated and identified (Chapter 2). There have been no previous chemical ecology studies of B. leachii and the latter half of this thesis is devoted to chemical ecology studies of this organism. Interestingly, the isolation of the (-)-diastereomer of 2.2 from specimens of B. leachii collected from the Kariega River mouth (near Kenton-on-Sea) suggests that the South African specimens of this species are similar to specimens collected from Puerto Rico and from the Mediterranean Sea. Two different chromatographic techniques for isolating 2.2 were compared in order to maximize the amount of 2.2 isolated from the Kariega River mouth sea hares. The doubling of selected resonances observed in both the ¹H and ¹³C NMR spectra of the bursatellin isolated in this study suggest one of three possibilities; either firstly, the presence of closely related compound(s), secondly, the presence of diastereomers or thirdly the presence of rotamers. Through NMR kinetic studies, we were able to establish that the presence of rotamers was very unlikely due to no change in the relative ratio (3:1) of the ¹H NMR signals with an increase in temperature. Although the attempted synthesis of the acetate derivative (2.28), as a means of separating a diastereomeric mixture was successful, the chromatographic separation of the proposed acetylated diastereomers was not successful. Preparation of the camphanate ester derivatives (e.g. 2.30) proved to be unsuccessful. Five B. leachii specimens were dissected, their organs separated and individually extracted with methanol. The methanol extracts were individually chromatographed on HP-20 media, and the distribution of bursatellin determined by isolation and NMR. It was evident from this investigation that the distribution of 2.2 within individual B. leachii specimens was found to be highest within the B. leachii ink gland. The lower amounts of 2.2 contained in the digestive system, relative to other organs, was hypothesized to occur because 2.2 is sequestered from the diet of the sea hare and efficiently moved from the gut to various organs around the body where it is stored. The absence of 2.2 from the skin was surprising and may be a result of a smaller mass of skin relative to other organs coupled with the limitations of the chromatographic separation techniques employed. Surprisingly, no bursatellin was found within juvenile sea hares. Chapter three discusses the isolation of ilimaquinone (3.1) and pelorol (3.19) from the sponge Hippospongia metachroma and the structure elucidation of each compound using computer modeling to illustrate the conformation. It was deemed necessary to isolate these well known and abundant bioactive marine natural products from a sponge as standard compounds in the bioassays given the paucity of 2.2 available for this study. Chapter four describes the assays used to test the biological activity of the bursatellin 2.2 compared to the generally bioactive ilimaquinone and the structurally related and commercially available broad spectrum antibiotic chloramphenicol. B. leachii, a shell-less marine mollusc inhabits a variety of intertidal habitats and, therefore, is exposed to several different predators, yet does not appear to have any specific predators. Potential predators of this sea hare in the Kariega Estuary could be fish and amphipods which are found in close proximity to these sea hares. Results of the assays showed that at roughly natural concentrations, (calculated from the isolated chromatographic yield) feeding was deterred by the fish and amphipods, which implied that 2.2 may confer a defensive role within the organism. The relatively high concentration present within the ink gland of B. leachii may support this hypothesis. Surprisingly, given its structural similarity to chloramphenicol, 2.3 did not show any antimicrobial action against five of the six bacterial strains against which it was screened [chloramphenicol inhibited the growth of all the bacterial strains at very low concentrations (0.25 mg/mL)]. Bursatellin was found to be only active against Staphylococus aureus at high concentrations ca. 2 mg/mL when compared to chloramphenicol. Neither bursatellin nor chloramphenicol showed anti-fungal activity. Although this study suggests that the sea hares may use chemical defences in addition to opaline ink to defend themselves, they also live within the seagrass Z. capensis, which possibly provides the sea hare with a cryptic form of physical defence against several predators that are unable to swim freely within the weed beds in the littoral zone of the estuary. , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 2013
- Authors: D'Souza, Nicole
- Date: 2013 , 2013-03-22
- Subjects: Sea hares (Mollusks) -- South Africa -- Kenton-on-Sea , Sea hares (Mollusks) -- Ecology -- South Africa -- Kenton-on-Sea , Sea hares (Mollusks) -- Behavior -- South Africa -- Kenton-on-Sea , Sea hares (Mollusks) -- Defenses -- Behavior -- South Africa -- Kenton-on-Sea
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4283 , http://hdl.handle.net/10962/d1002952 , Sea hares (Mollusks) -- South Africa -- Kenton-on-Sea , Sea hares (Mollusks) -- Ecology -- South Africa -- Kenton-on-Sea , Sea hares (Mollusks) -- Behavior -- South Africa -- Kenton-on-Sea , Sea hares (Mollusks) -- Defenses -- Behavior -- South Africa -- Kenton-on-Sea
- Description: The large cosmopolitan sea hare Bursatella leachii is a common resident in Eastern Cape river mouths during summer and late autumn where they congregate in beds of Zostera capensis to breed. In this thesis, the previously known toxic formamide marine secondary metabolite (-)-bursatellin (2.2), which may deter predators of South African specimens of the globally distributed sea hare Bursatella leachii, was isolated and identified (Chapter 2). There have been no previous chemical ecology studies of B. leachii and the latter half of this thesis is devoted to chemical ecology studies of this organism. Interestingly, the isolation of the (-)-diastereomer of 2.2 from specimens of B. leachii collected from the Kariega River mouth (near Kenton-on-Sea) suggests that the South African specimens of this species are similar to specimens collected from Puerto Rico and from the Mediterranean Sea. Two different chromatographic techniques for isolating 2.2 were compared in order to maximize the amount of 2.2 isolated from the Kariega River mouth sea hares. The doubling of selected resonances observed in both the ¹H and ¹³C NMR spectra of the bursatellin isolated in this study suggest one of three possibilities; either firstly, the presence of closely related compound(s), secondly, the presence of diastereomers or thirdly the presence of rotamers. Through NMR kinetic studies, we were able to establish that the presence of rotamers was very unlikely due to no change in the relative ratio (3:1) of the ¹H NMR signals with an increase in temperature. Although the attempted synthesis of the acetate derivative (2.28), as a means of separating a diastereomeric mixture was successful, the chromatographic separation of the proposed acetylated diastereomers was not successful. Preparation of the camphanate ester derivatives (e.g. 2.30) proved to be unsuccessful. Five B. leachii specimens were dissected, their organs separated and individually extracted with methanol. The methanol extracts were individually chromatographed on HP-20 media, and the distribution of bursatellin determined by isolation and NMR. It was evident from this investigation that the distribution of 2.2 within individual B. leachii specimens was found to be highest within the B. leachii ink gland. The lower amounts of 2.2 contained in the digestive system, relative to other organs, was hypothesized to occur because 2.2 is sequestered from the diet of the sea hare and efficiently moved from the gut to various organs around the body where it is stored. The absence of 2.2 from the skin was surprising and may be a result of a smaller mass of skin relative to other organs coupled with the limitations of the chromatographic separation techniques employed. Surprisingly, no bursatellin was found within juvenile sea hares. Chapter three discusses the isolation of ilimaquinone (3.1) and pelorol (3.19) from the sponge Hippospongia metachroma and the structure elucidation of each compound using computer modeling to illustrate the conformation. It was deemed necessary to isolate these well known and abundant bioactive marine natural products from a sponge as standard compounds in the bioassays given the paucity of 2.2 available for this study. Chapter four describes the assays used to test the biological activity of the bursatellin 2.2 compared to the generally bioactive ilimaquinone and the structurally related and commercially available broad spectrum antibiotic chloramphenicol. B. leachii, a shell-less marine mollusc inhabits a variety of intertidal habitats and, therefore, is exposed to several different predators, yet does not appear to have any specific predators. Potential predators of this sea hare in the Kariega Estuary could be fish and amphipods which are found in close proximity to these sea hares. Results of the assays showed that at roughly natural concentrations, (calculated from the isolated chromatographic yield) feeding was deterred by the fish and amphipods, which implied that 2.2 may confer a defensive role within the organism. The relatively high concentration present within the ink gland of B. leachii may support this hypothesis. Surprisingly, given its structural similarity to chloramphenicol, 2.3 did not show any antimicrobial action against five of the six bacterial strains against which it was screened [chloramphenicol inhibited the growth of all the bacterial strains at very low concentrations (0.25 mg/mL)]. Bursatellin was found to be only active against Staphylococus aureus at high concentrations ca. 2 mg/mL when compared to chloramphenicol. Neither bursatellin nor chloramphenicol showed anti-fungal activity. Although this study suggests that the sea hares may use chemical defences in addition to opaline ink to defend themselves, they also live within the seagrass Z. capensis, which possibly provides the sea hare with a cryptic form of physical defence against several predators that are unable to swim freely within the weed beds in the littoral zone of the estuary. , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 2013
A study of electrospun nanofibers and diatomaceous earth materials for the extraction of alkaloids, flavonoids and aromatic amines in various matrices
- Mothibedi, Kediemetse (Kedimetse)
- Authors: Mothibedi, Kediemetse (Kedimetse)
- Date: 2013 , 2013-04-07
- Subjects: Nanofibers , Electrospinning , Sorbents , Extraction (Chemistry) , Alkaloids , Flavonoids , Amines , Matrices , Goldenseal , Ginkgo , Dyes and dyeing -- Chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4288 , http://hdl.handle.net/10962/d1003052 , Nanofibers , Electrospinning , Sorbents , Extraction (Chemistry) , Alkaloids , Flavonoids , Amines , Matrices , Goldenseal , Ginkgo , Dyes and dyeing -- Chemistry
- Description: The thesis explored the use of different sorbent materials in solid phase extraction method development. The methods included the use of the polymeric Agilent Bond Elut Plexa solid phase extraction and electrospun polymer-silica composite sorbents for clean-up and preconcentration. Sample clean-up for alkaloids (hydrastine and berberine) in goldenseal, Hydrastis canadensis and flavonoids (quercetin, kaempferol and isorhamnetin) in Ginkgo biloba was achieved using Bond Elut Plexa SPE sorbent. Clean-up of flavonoids in Ginkgo biloba was also achieved using electrospun polymer-silica composite (polystyrene-silica, polyacrylonitrile-silica and nylon 6-silica) sorbents. All analysis of flavonoids and alkaloids was carried out using an Agilent 1200 Series HPLC coupled with a diode array detector. Good peak separation was achieved in less than 6 min employing an Agilent ZORBAX Eclipse Plus C18 column (4.6 x 75 mm, 3.5 μm) at 35⁰C. The mobile phases employed were 0.1% phosphoric acid/methanol gradient and 0.5% phosphoric acid/methanol (40:60) for alkaloids and flavonoids respectively. The calibration curves exhibited linearity up to 120 μg mL⁻¹ with correlation coefficients of more than 0.9980. The recoveries ranged from 73-109% with relative standard deviation of less than 5% for all analytes. Agilent Chem Elut supported liquid extraction was employed for the development of a sample preparation method for the determination of 24 banned aromatic amines from azo dyes in textile following the EU standard method EN 14362-1:2003 (E) and the Chinese standard method GB/T 17592-2006. The supported liquid extraction was effective in the extraction of the aromatic amines from textile (cotton, wool and polyester/cotton [80%:20%]). Most of the recoveries obtained were conforming to the minimum requirements set in the EN 14362-1:2003 (E) standard method and the relative standard deviations were less than 15%. Good peak separation was obtained within 70 min run time using the Agilent Zorbax SB-Phenyl column (4.6 mm x 250 mm, 5-micron) or the Agilent DB-35 MS (J & W) (30 m x 0.25 mm, 0.25 μm film thickness. It was demonstrated that the polymeric Agilent Bond Elut Plexa, electrospun nanofibers and diatomaceous earth were effective in extraction of alkaloids, flavonoids and aromatic amines in different matrices. The developed methods were simple, rapid and reproducible.
- Full Text:
- Date Issued: 2013
- Authors: Mothibedi, Kediemetse (Kedimetse)
- Date: 2013 , 2013-04-07
- Subjects: Nanofibers , Electrospinning , Sorbents , Extraction (Chemistry) , Alkaloids , Flavonoids , Amines , Matrices , Goldenseal , Ginkgo , Dyes and dyeing -- Chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4288 , http://hdl.handle.net/10962/d1003052 , Nanofibers , Electrospinning , Sorbents , Extraction (Chemistry) , Alkaloids , Flavonoids , Amines , Matrices , Goldenseal , Ginkgo , Dyes and dyeing -- Chemistry
- Description: The thesis explored the use of different sorbent materials in solid phase extraction method development. The methods included the use of the polymeric Agilent Bond Elut Plexa solid phase extraction and electrospun polymer-silica composite sorbents for clean-up and preconcentration. Sample clean-up for alkaloids (hydrastine and berberine) in goldenseal, Hydrastis canadensis and flavonoids (quercetin, kaempferol and isorhamnetin) in Ginkgo biloba was achieved using Bond Elut Plexa SPE sorbent. Clean-up of flavonoids in Ginkgo biloba was also achieved using electrospun polymer-silica composite (polystyrene-silica, polyacrylonitrile-silica and nylon 6-silica) sorbents. All analysis of flavonoids and alkaloids was carried out using an Agilent 1200 Series HPLC coupled with a diode array detector. Good peak separation was achieved in less than 6 min employing an Agilent ZORBAX Eclipse Plus C18 column (4.6 x 75 mm, 3.5 μm) at 35⁰C. The mobile phases employed were 0.1% phosphoric acid/methanol gradient and 0.5% phosphoric acid/methanol (40:60) for alkaloids and flavonoids respectively. The calibration curves exhibited linearity up to 120 μg mL⁻¹ with correlation coefficients of more than 0.9980. The recoveries ranged from 73-109% with relative standard deviation of less than 5% for all analytes. Agilent Chem Elut supported liquid extraction was employed for the development of a sample preparation method for the determination of 24 banned aromatic amines from azo dyes in textile following the EU standard method EN 14362-1:2003 (E) and the Chinese standard method GB/T 17592-2006. The supported liquid extraction was effective in the extraction of the aromatic amines from textile (cotton, wool and polyester/cotton [80%:20%]). Most of the recoveries obtained were conforming to the minimum requirements set in the EN 14362-1:2003 (E) standard method and the relative standard deviations were less than 15%. Good peak separation was obtained within 70 min run time using the Agilent Zorbax SB-Phenyl column (4.6 mm x 250 mm, 5-micron) or the Agilent DB-35 MS (J & W) (30 m x 0.25 mm, 0.25 μm film thickness. It was demonstrated that the polymeric Agilent Bond Elut Plexa, electrospun nanofibers and diatomaceous earth were effective in extraction of alkaloids, flavonoids and aromatic amines in different matrices. The developed methods were simple, rapid and reproducible.
- Full Text:
- Date Issued: 2013
An experimental and theoretical investigation of unstable Fischer chromium carbene complexes
- Authors: Makanjee, Che Azad
- Date: 2013 , 2013-03-27
- Subjects: Chromium , Organolithium compounds , Carbenes (Methylene compounds) , Organometallic chemistry , Organometallic compounds , Organochromium compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4284 , http://hdl.handle.net/10962/d1002953 , Chromium , Organolithium compounds , Carbenes (Methylene compounds) , Organometallic chemistry , Organometallic compounds , Organochromium compounds
- Description: This organometallic study involves the use organostannanes and organolithiums as precursors to chromium Fischer carbene complexes. Fischer carbenes are typically electrophilic and are stabilized by a single π-donor substituent, and contain low oxidation state metals (often but not always from Group 6). They are highly reactive and can give access to a range of biologically active compounds through cyclopropanations, insertions, coupling and photochemical reactions. Synthesis and characterization of three MOM-protected α-alkoxy organostannanes was successfully carried out via a nucleophilic addition of tributylstannyllithium to suitable aldehydes, and immediate protection of the alcohol with MOM. Two N-BOC protected α-amino organostannanes were successfully synthesized and characterized via α-lithiation and tin-lithium exchange in the presence of TMEDA. Tin-lithium transmetallation of the organostannanes allowed access to the organolithiums required for the synthesis of novel Fischer carbenes. Addition of chromium hexacarbonyl to the organolithiums formed the acylpentacarbonyl chromate salt which was alkylated with Meerwein salt, resulting in the Fischer carbene and a by-product, tetrabutyltin, which proved difficult to remove. Several Fischer carbenes were synthesized and characterized, some simple and known and some novel. In silico work explored the reaction coordinate of the [2+2] cycloaddition towards the formation of β-lactams, and the photoactivation cycle that precedes this process. Computational work also showed the effect of the ligand on the stability and reactivity of the carbene. It was found that in some cases the oxygen on the ligand could negatively influence the stability of the carbene (when compared to a simple methyl carbene). A link between bond orders and back donation in Fischer carbenes was explored in an attempt to theoretically predict the stability of a range of carbenes. , Microsoft� Office Word 2007
- Full Text:
- Date Issued: 2013
- Authors: Makanjee, Che Azad
- Date: 2013 , 2013-03-27
- Subjects: Chromium , Organolithium compounds , Carbenes (Methylene compounds) , Organometallic chemistry , Organometallic compounds , Organochromium compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4284 , http://hdl.handle.net/10962/d1002953 , Chromium , Organolithium compounds , Carbenes (Methylene compounds) , Organometallic chemistry , Organometallic compounds , Organochromium compounds
- Description: This organometallic study involves the use organostannanes and organolithiums as precursors to chromium Fischer carbene complexes. Fischer carbenes are typically electrophilic and are stabilized by a single π-donor substituent, and contain low oxidation state metals (often but not always from Group 6). They are highly reactive and can give access to a range of biologically active compounds through cyclopropanations, insertions, coupling and photochemical reactions. Synthesis and characterization of three MOM-protected α-alkoxy organostannanes was successfully carried out via a nucleophilic addition of tributylstannyllithium to suitable aldehydes, and immediate protection of the alcohol with MOM. Two N-BOC protected α-amino organostannanes were successfully synthesized and characterized via α-lithiation and tin-lithium exchange in the presence of TMEDA. Tin-lithium transmetallation of the organostannanes allowed access to the organolithiums required for the synthesis of novel Fischer carbenes. Addition of chromium hexacarbonyl to the organolithiums formed the acylpentacarbonyl chromate salt which was alkylated with Meerwein salt, resulting in the Fischer carbene and a by-product, tetrabutyltin, which proved difficult to remove. Several Fischer carbenes were synthesized and characterized, some simple and known and some novel. In silico work explored the reaction coordinate of the [2+2] cycloaddition towards the formation of β-lactams, and the photoactivation cycle that precedes this process. Computational work also showed the effect of the ligand on the stability and reactivity of the carbene. It was found that in some cases the oxygen on the ligand could negatively influence the stability of the carbene (when compared to a simple methyl carbene). A link between bond orders and back donation in Fischer carbenes was explored in an attempt to theoretically predict the stability of a range of carbenes. , Microsoft� Office Word 2007
- Full Text:
- Date Issued: 2013
Application of bidentate N,N'-donor extractants in the hydrometallurgical separation of base metals from an acidic sulfate medium
- Authors: Okewole, Adeleye Ishola
- Date: 2013
- Subjects: Hydrometallurgy Sulfates Nanofibers Electrospinning Sorbents Extraction (Chemistry) Solvent extraction Stereochemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4281 , http://hdl.handle.net/10962/d1002610
- Description: Bidentate imidazole-based extractants, 1-octylimidazole-2-aldoxime (OIMOX) and 1-octyl-2-(2′-pyridyl)imidazole (OPIM), along with dinonylnaphthalene sulfonic acid (DNNSA) as a synergist, were investigated as potential selective extractants for Cu²⁺and Ni²⁺ respectively from base metals in a solvent extraction system. The study was extended to evaluate the sorption and separation of Ni²⁺ from other base metals in a solid-solution system using microspherical Merrifield resins and nanofibers functionalized with 2,2′-pyridylimidazole. Copper was effectively separated with OIMOX and DNNSA as extractants from nickel with ΔpH½ ≈1.05 and the extraction order of Cu²⁺ > Ni²⁺ > Zn²⁺ > Cd²⁺> Co²⁺ was achieved as a function of pH. At pH 1.65 the extracted copper, from a synthetic mixture of the base metals reached 90.13(±0.90)%, and through a two-step extraction process 98.22(±0.29)% copper was recovered with negligible nickel and cobalt impurities. Stripping of the copper from the loaded organic phase using TraceSelect sulphuric acid at pH 0.35 yielded 96.60(±0.44)% of the loaded quantity after the second stage of stripping. The separation of Ni²⁺ from the borderline and hard acids; Co²⁺, Cu²⁺, Zn²⁺, Fe2²⁺, Fe²⁺, Mn²⁺, Mg2²⁺ and Ca²⁺ at a pH range of 0.5-3.5 with OPIM and DNNSA was acvieved to the tune of a ΔpH½≈ 1.6 with respect to cobalt from a sulfate and sulfate/chloride media. A three-stage counter-current extraction of Ni²⁺, at the optimized pH of 1.89, from a synthetic mixture of Ni²⁺, Co²⁺ and Cu²⁺, yielded 99.01(±1.79)%. The total co-extracted Cu²⁺ was 48.72(±0.24)% of the original quantity in the mixture, and it was 19.85(±0.28%) for Co²⁺. The co-extracted Cu²⁺ was scrubbed off from the loaded organic phase at pH≈8.5 by using an ammonium buffer, while co-extracted Co²⁺ was selectively and quantitatively stripped with H₂SO₄ at pH 1.64. The total recovery of Ni²⁺ by stripping at pH 0.32 was 94.05(±1.70)%. In the solid-liquid system, Ni²⁺ was separated from Co²⁺, Cu²⁺, and Fe²⁺ with the microspherical resins funtionalised with 2,2′-pyridylimidazole by a separation factor (β) in the range 22-45. Electrospun nanofibers as sorbents yielded high sorption capacity in the range of 0.97 - 1.45 mmol.g⁻¹ for the same metals ions. Thus, 1-octylimidazole-2-aldoxime (OIMOX), and1-octyl-2-(2′-pyridyl)imidazole (OPIM) can be effectively utilized alongside DNNSA as a co-extractant in the separation of Cu²⁺ and Ni²⁺ respectively from base metals in acidic sulfate medium in a solvent extraction process, and the latter as a selective ligand in the solid-liquid separation of Ni²⁺ from Co²⁺, Cu²⁺, and Fe²⁺.
- Full Text:
- Date Issued: 2013
- Authors: Okewole, Adeleye Ishola
- Date: 2013
- Subjects: Hydrometallurgy Sulfates Nanofibers Electrospinning Sorbents Extraction (Chemistry) Solvent extraction Stereochemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4281 , http://hdl.handle.net/10962/d1002610
- Description: Bidentate imidazole-based extractants, 1-octylimidazole-2-aldoxime (OIMOX) and 1-octyl-2-(2′-pyridyl)imidazole (OPIM), along with dinonylnaphthalene sulfonic acid (DNNSA) as a synergist, were investigated as potential selective extractants for Cu²⁺and Ni²⁺ respectively from base metals in a solvent extraction system. The study was extended to evaluate the sorption and separation of Ni²⁺ from other base metals in a solid-solution system using microspherical Merrifield resins and nanofibers functionalized with 2,2′-pyridylimidazole. Copper was effectively separated with OIMOX and DNNSA as extractants from nickel with ΔpH½ ≈1.05 and the extraction order of Cu²⁺ > Ni²⁺ > Zn²⁺ > Cd²⁺> Co²⁺ was achieved as a function of pH. At pH 1.65 the extracted copper, from a synthetic mixture of the base metals reached 90.13(±0.90)%, and through a two-step extraction process 98.22(±0.29)% copper was recovered with negligible nickel and cobalt impurities. Stripping of the copper from the loaded organic phase using TraceSelect sulphuric acid at pH 0.35 yielded 96.60(±0.44)% of the loaded quantity after the second stage of stripping. The separation of Ni²⁺ from the borderline and hard acids; Co²⁺, Cu²⁺, Zn²⁺, Fe2²⁺, Fe²⁺, Mn²⁺, Mg2²⁺ and Ca²⁺ at a pH range of 0.5-3.5 with OPIM and DNNSA was acvieved to the tune of a ΔpH½≈ 1.6 with respect to cobalt from a sulfate and sulfate/chloride media. A three-stage counter-current extraction of Ni²⁺, at the optimized pH of 1.89, from a synthetic mixture of Ni²⁺, Co²⁺ and Cu²⁺, yielded 99.01(±1.79)%. The total co-extracted Cu²⁺ was 48.72(±0.24)% of the original quantity in the mixture, and it was 19.85(±0.28%) for Co²⁺. The co-extracted Cu²⁺ was scrubbed off from the loaded organic phase at pH≈8.5 by using an ammonium buffer, while co-extracted Co²⁺ was selectively and quantitatively stripped with H₂SO₄ at pH 1.64. The total recovery of Ni²⁺ by stripping at pH 0.32 was 94.05(±1.70)%. In the solid-liquid system, Ni²⁺ was separated from Co²⁺, Cu²⁺, and Fe²⁺ with the microspherical resins funtionalised with 2,2′-pyridylimidazole by a separation factor (β) in the range 22-45. Electrospun nanofibers as sorbents yielded high sorption capacity in the range of 0.97 - 1.45 mmol.g⁻¹ for the same metals ions. Thus, 1-octylimidazole-2-aldoxime (OIMOX), and1-octyl-2-(2′-pyridyl)imidazole (OPIM) can be effectively utilized alongside DNNSA as a co-extractant in the separation of Cu²⁺ and Ni²⁺ respectively from base metals in acidic sulfate medium in a solvent extraction process, and the latter as a selective ligand in the solid-liquid separation of Ni²⁺ from Co²⁺, Cu²⁺, and Fe²⁺.
- Full Text:
- Date Issued: 2013
Characterisation of surfaces modified through self-assembled monolayers and click chemistry
- Authors: Coates, Megan Patricia
- Date: 2013
- Subjects: Monomolecular films Gold Adsorption Nanotubes Self-assembly (Chemistry) Self-assembly (Chemistry) Scanning electrochemical microscopy X-ray photoelectron spectroscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4277 , http://hdl.handle.net/10962/d1001684
- Description: Different approaches to surface modification were investigated in this work on gold, glassy carbon, multi-walled carbon nanotube paper and on single-walled carbon nanotubes adsorbed on glassy carbon. These approaches include electrochemical grafting, electropolymerisation, click chemistry, axial ligation, adsorption and self-assembled monolayers. The modified surfaces were characterised using a variety of techniques; predominantly electrochemistry, scanning electrochemical microscopy and X-ray photoelectron spectroscopy. For the formation of self-assembled monolayers on gold, four new manganese(III) phthalocyanines (1a-d), octa-substituted at the peripheral position with pentylthio, decylthio, benzylthio, and phenylthio groups were synthesized and characterised. X-ray photoelectron spectroscopy was used to show the formation of a sulphur-gold bond. A number of approaches using 4-azidoaniline (2a) combined with azide-alkyne click chemistry and electrochemistry were also used to anchor ferrocene and pyridine moieties on to the carbon surfaces, including direct in situ diazotation and grafting, electropolymerisation, and the synthesis of the diazonium salt followed by grafting. Iron phthalocyanine was linked to the pyridine-clicked surfaces through axial ligation, where the strong axial bond formed by the interaction between the central metal and the lone pair of the nitrogen in the pyridine group resulted in stable modified electrodes. The potential of these surfaces for the detection of analytes such as thiocyanate, hydrazine and sulphite are briefly shown as well. This work also describes for the first time the possibility of performing local micro-electrochemical grafting of a gold substrate by 4-azidobenzenediazonium (2b) using scanning electrochemical microscopy in a single and simple one step approach, without complications from adsorption.
- Full Text:
- Date Issued: 2013
- Authors: Coates, Megan Patricia
- Date: 2013
- Subjects: Monomolecular films Gold Adsorption Nanotubes Self-assembly (Chemistry) Self-assembly (Chemistry) Scanning electrochemical microscopy X-ray photoelectron spectroscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4277 , http://hdl.handle.net/10962/d1001684
- Description: Different approaches to surface modification were investigated in this work on gold, glassy carbon, multi-walled carbon nanotube paper and on single-walled carbon nanotubes adsorbed on glassy carbon. These approaches include electrochemical grafting, electropolymerisation, click chemistry, axial ligation, adsorption and self-assembled monolayers. The modified surfaces were characterised using a variety of techniques; predominantly electrochemistry, scanning electrochemical microscopy and X-ray photoelectron spectroscopy. For the formation of self-assembled monolayers on gold, four new manganese(III) phthalocyanines (1a-d), octa-substituted at the peripheral position with pentylthio, decylthio, benzylthio, and phenylthio groups were synthesized and characterised. X-ray photoelectron spectroscopy was used to show the formation of a sulphur-gold bond. A number of approaches using 4-azidoaniline (2a) combined with azide-alkyne click chemistry and electrochemistry were also used to anchor ferrocene and pyridine moieties on to the carbon surfaces, including direct in situ diazotation and grafting, electropolymerisation, and the synthesis of the diazonium salt followed by grafting. Iron phthalocyanine was linked to the pyridine-clicked surfaces through axial ligation, where the strong axial bond formed by the interaction between the central metal and the lone pair of the nitrogen in the pyridine group resulted in stable modified electrodes. The potential of these surfaces for the detection of analytes such as thiocyanate, hydrazine and sulphite are briefly shown as well. This work also describes for the first time the possibility of performing local micro-electrochemical grafting of a gold substrate by 4-azidobenzenediazonium (2b) using scanning electrochemical microscopy in a single and simple one step approach, without complications from adsorption.
- Full Text:
- Date Issued: 2013
Characterization and application of phthalocyanine-gold nanoparticle conjugates
- Authors: Tombe, Sekai Lana
- Date: 2013
- Subjects: Phthalocyanines , Gold , Zinc , Nanoparticles , Bioconjugates , Photochemistry , Photocatalysis , Electrospinning , Polymers , Pollutants , Phenols , Azo dyes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4293 , http://hdl.handle.net/10962/d1004517 , Phthalocyanines , Gold , Zinc , Nanoparticles , Bioconjugates , Photochemistry , Photocatalysis , Electrospinning , Polymers , Pollutants , Phenols , Azo dyes
- Description: This work presents the syntheses, photophysical and photochemical characterization of arylthio zinc phthalocyanines and their gold nanoparticle conjugates. Spectroscopic and microscopic studies confirmed the formation of the phthalocyanine-gold nanoparticle conjugates which exhibited enhanced photophysicochemical properties in comparison to the phthalocyanines. The studies showed that the presence of gold nanoparticles significantly lowered fluorescence quantum yields and lifetimes. However, this interaction did not restrict the formation of excited singlet and triplet states and hence the formation of singlet oxygen required for photocatalysis. The conjugates showed significantly higher singlet oxygen quantum yields and therefore enhanced photocatalytic activity compared to the phthalocyanines. The zinc phthalocyanines and their gold nanoparticle conjugates were successfully incorporated into electrospun polymer fibers. Spectral characteristics of the functionalized electrospun fibers indicated that the phthalocyanines and phthalocyanine-gold nanoparticle conjugates were bound and their integrity was maintained within the polymeric fiber matrices. The photophysical and photochemical properties of the complexes were equally maintained within the electrospun fibers. The functionalized fibers were applied for the photoconversion of 4-chlorophenol and Orange G as model organic pollutants. , Microsoft� Word 2010 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 2013
- Authors: Tombe, Sekai Lana
- Date: 2013
- Subjects: Phthalocyanines , Gold , Zinc , Nanoparticles , Bioconjugates , Photochemistry , Photocatalysis , Electrospinning , Polymers , Pollutants , Phenols , Azo dyes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4293 , http://hdl.handle.net/10962/d1004517 , Phthalocyanines , Gold , Zinc , Nanoparticles , Bioconjugates , Photochemistry , Photocatalysis , Electrospinning , Polymers , Pollutants , Phenols , Azo dyes
- Description: This work presents the syntheses, photophysical and photochemical characterization of arylthio zinc phthalocyanines and their gold nanoparticle conjugates. Spectroscopic and microscopic studies confirmed the formation of the phthalocyanine-gold nanoparticle conjugates which exhibited enhanced photophysicochemical properties in comparison to the phthalocyanines. The studies showed that the presence of gold nanoparticles significantly lowered fluorescence quantum yields and lifetimes. However, this interaction did not restrict the formation of excited singlet and triplet states and hence the formation of singlet oxygen required for photocatalysis. The conjugates showed significantly higher singlet oxygen quantum yields and therefore enhanced photocatalytic activity compared to the phthalocyanines. The zinc phthalocyanines and their gold nanoparticle conjugates were successfully incorporated into electrospun polymer fibers. Spectral characteristics of the functionalized electrospun fibers indicated that the phthalocyanines and phthalocyanine-gold nanoparticle conjugates were bound and their integrity was maintained within the polymeric fiber matrices. The photophysical and photochemical properties of the complexes were equally maintained within the electrospun fibers. The functionalized fibers were applied for the photoconversion of 4-chlorophenol and Orange G as model organic pollutants. , Microsoft� Word 2010 , Adobe Acrobat 9.53 Paper Capture Plug-in
- Full Text:
- Date Issued: 2013
Critical studies in carbon electrode materials with applications in the electroanalysis of the mycotoxin citrinin
- Authors: Niland, Michael John
- Date: 2013
- Subjects: Electrodes, Carbon , Mycotoxins
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4555 , http://hdl.handle.net/10962/d1018256
- Description: Guided by increasing legislation, the analysis of food borne toxins, including mycotoxins, seeks to address market related demands for the development of analytical systems to monitor this threat to food security and human health. This Thesis is directed at the assessment of the application of electrochemistry for direct electroanalysis and characterisation of the mycotoxin citrinin (CIT) in aqueous media as well as fundamental investigations of the surface of polished and oxidised glassy carbon electrodes (GCE). This study provides the first known account of CIT detection through electrochemical methods. Although electrochemically active, CIT current responses (Ip) were highly irreproducible at polished GCE with a coefficient of variation (C.V.) of 20.16 %. As stability of Ip across multiple electrode preparations is a key requirement in electroanalysis, investigations were directed at attaining stability in CIT Ip. Achieving stability in CIT Ip was investigated via two approaches, including: accounting for Ip variability between electrode preparations as a result of variable GCE surface conditions as a post-data-acquisition analysis and secondly, removing Ip variability through modification of GCE. Accounting for variability in Ip was investigated through the application of double layer capacitance as an indicator of the activity of an electrode, and in so doing serving as a relative mediator of Ip responses between electrodes. Application of this procedure dropped CIT C.V. to a third of starting value across polished GCE (C.V. = 7.18 %), chemically oxidised GCE (Pi-GCE, C.V = 8.47 %) and functionalised multi-walled carbon nanotube modified GCE (fMWCNT, C.V. = 25.79 %) and was effective with analysis of structurally distinct molecules, 2,4-dimethylaniline (2,4-DMA) and 1,2,4-trihydroxybenzene (Triol). Furthermore, it afforded the ability to determine discreet solution overlapping data sets of Ip. Stabilising Ip through GCE surface modification was achieved by anodic electro-oxidation of GCE and allowed for direct electroanalysis of CIT and subsequent characterisation and analysis of CIT in complex media as it reduced C.V. of CIT Ip to 0.73 %. Fundamental investigations of the electrode surface condition are described such that the source of variability could be identified and the interactions of CIT with the electrode understood. Two surface oxidation techniques were applied in modification of GCE; anodic electro-oxidation (EOx GCE) and chemical oxidation using piranha solution (Pi-GCE), analysis of which has previously not been reported. Fundamental analyses to determine surface morphology and chemistry of Pi-GCE, EOx-GCE and polished GCE were conducted using high resolution scanning electron microscopy (HRSEM), scanning electrochemical microscopy (SECM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR) and via electroanalytical methods. These studies showed that both oxidation procedures introduced a variety of oxide species at GCE surface, and further that the extent of those species was similar with total % O being 27.67 % and 33.47 % at Pi-GCE and EOx-GCE respectively. Although chemically similar, each surface was morphologically distinct. Electrochemical analyses at the surfaces revealed Pi-GCE to behave more similarly to polished GCE than EOx-GCE. As CIT responses were found to be stable at EOx-GCE (C.V. = 0.73 %) as opposed to Pi-GCE (C.V. = 22.87 %), stability of CIT Ip was likely to be as a result of a physical interaction with electrode morphology rather than interaction on a chemical basis. Morphological analyses revealed polished GCE and Pi-GCE to be highly morphologically irregular at the micro-scale. Although comparatively smooth, the surface morphology of EOx-GCE does not account for the stability of Ip. This study thus proposed a theory to describe the mechanism by which the limited conductivity and porosity of EOx-GCE allow for it to provide a relatively stable surface area within the oxide layer, adjacent to the electrode surface, and thus provided a stable platform for electroanalysis. Voltammetric characterization of CIT at EOx-GCE revealed that anodic oxidation in aqueous media involved an uneven number of electrons to protons via an ECE mechanism. This was illustrated to be nt = 2e- accompanied by the transfer of 1H⁺ per molecule oxidised. A proposed reaction scheme for the initial stages of CIT oxidation was suggested to involve both hydroxyl and carboxyl moieties of the CIT molecule. CIT oxidation was shown to arise as a result of a relatively complex mass transport regime which included both adsorptive and diffusive derived Ip₁. The LOD in buffered aqueous media was found to be 16 nM, a highly competitive result in relation to chromatographic techniques. Further application of EOx-GCE in complex media illustrated that CIT associates non-specifically with the components of food samples, primarily proteins. As a result of this, extraction of CIT from such media is mandatory. Liquid-liquid extraction illustrated a recovery in CIT Ip₁ and in so doing provided a means of accurately and sensitively detecting CIT from food samples with an LOD of 20 nM. These responses were corroborated by HPLC analyses on the same extractions and illustrate the applicability of electroanalysis as an analytical technique.
- Full Text:
- Date Issued: 2013
- Authors: Niland, Michael John
- Date: 2013
- Subjects: Electrodes, Carbon , Mycotoxins
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4555 , http://hdl.handle.net/10962/d1018256
- Description: Guided by increasing legislation, the analysis of food borne toxins, including mycotoxins, seeks to address market related demands for the development of analytical systems to monitor this threat to food security and human health. This Thesis is directed at the assessment of the application of electrochemistry for direct electroanalysis and characterisation of the mycotoxin citrinin (CIT) in aqueous media as well as fundamental investigations of the surface of polished and oxidised glassy carbon electrodes (GCE). This study provides the first known account of CIT detection through electrochemical methods. Although electrochemically active, CIT current responses (Ip) were highly irreproducible at polished GCE with a coefficient of variation (C.V.) of 20.16 %. As stability of Ip across multiple electrode preparations is a key requirement in electroanalysis, investigations were directed at attaining stability in CIT Ip. Achieving stability in CIT Ip was investigated via two approaches, including: accounting for Ip variability between electrode preparations as a result of variable GCE surface conditions as a post-data-acquisition analysis and secondly, removing Ip variability through modification of GCE. Accounting for variability in Ip was investigated through the application of double layer capacitance as an indicator of the activity of an electrode, and in so doing serving as a relative mediator of Ip responses between electrodes. Application of this procedure dropped CIT C.V. to a third of starting value across polished GCE (C.V. = 7.18 %), chemically oxidised GCE (Pi-GCE, C.V = 8.47 %) and functionalised multi-walled carbon nanotube modified GCE (fMWCNT, C.V. = 25.79 %) and was effective with analysis of structurally distinct molecules, 2,4-dimethylaniline (2,4-DMA) and 1,2,4-trihydroxybenzene (Triol). Furthermore, it afforded the ability to determine discreet solution overlapping data sets of Ip. Stabilising Ip through GCE surface modification was achieved by anodic electro-oxidation of GCE and allowed for direct electroanalysis of CIT and subsequent characterisation and analysis of CIT in complex media as it reduced C.V. of CIT Ip to 0.73 %. Fundamental investigations of the electrode surface condition are described such that the source of variability could be identified and the interactions of CIT with the electrode understood. Two surface oxidation techniques were applied in modification of GCE; anodic electro-oxidation (EOx GCE) and chemical oxidation using piranha solution (Pi-GCE), analysis of which has previously not been reported. Fundamental analyses to determine surface morphology and chemistry of Pi-GCE, EOx-GCE and polished GCE were conducted using high resolution scanning electron microscopy (HRSEM), scanning electrochemical microscopy (SECM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR) and via electroanalytical methods. These studies showed that both oxidation procedures introduced a variety of oxide species at GCE surface, and further that the extent of those species was similar with total % O being 27.67 % and 33.47 % at Pi-GCE and EOx-GCE respectively. Although chemically similar, each surface was morphologically distinct. Electrochemical analyses at the surfaces revealed Pi-GCE to behave more similarly to polished GCE than EOx-GCE. As CIT responses were found to be stable at EOx-GCE (C.V. = 0.73 %) as opposed to Pi-GCE (C.V. = 22.87 %), stability of CIT Ip was likely to be as a result of a physical interaction with electrode morphology rather than interaction on a chemical basis. Morphological analyses revealed polished GCE and Pi-GCE to be highly morphologically irregular at the micro-scale. Although comparatively smooth, the surface morphology of EOx-GCE does not account for the stability of Ip. This study thus proposed a theory to describe the mechanism by which the limited conductivity and porosity of EOx-GCE allow for it to provide a relatively stable surface area within the oxide layer, adjacent to the electrode surface, and thus provided a stable platform for electroanalysis. Voltammetric characterization of CIT at EOx-GCE revealed that anodic oxidation in aqueous media involved an uneven number of electrons to protons via an ECE mechanism. This was illustrated to be nt = 2e- accompanied by the transfer of 1H⁺ per molecule oxidised. A proposed reaction scheme for the initial stages of CIT oxidation was suggested to involve both hydroxyl and carboxyl moieties of the CIT molecule. CIT oxidation was shown to arise as a result of a relatively complex mass transport regime which included both adsorptive and diffusive derived Ip₁. The LOD in buffered aqueous media was found to be 16 nM, a highly competitive result in relation to chromatographic techniques. Further application of EOx-GCE in complex media illustrated that CIT associates non-specifically with the components of food samples, primarily proteins. As a result of this, extraction of CIT from such media is mandatory. Liquid-liquid extraction illustrated a recovery in CIT Ip₁ and in so doing provided a means of accurately and sensitively detecting CIT from food samples with an LOD of 20 nM. These responses were corroborated by HPLC analyses on the same extractions and illustrate the applicability of electroanalysis as an analytical technique.
- Full Text:
- Date Issued: 2013
Electrocatalytic detection of pesticides with electrodes modified with nanoparticles of phthalocyanines and multiwalled carbon nanotubes
- Authors: Siswana, Msimelelo Patrick
- Date: 2013
- Subjects: Phthalocyanines Pesticides Electrocatalysis Electrochemistry Nanotubes Nanoparticles Transmission electron microscopy Scanning electron microscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4282 , http://hdl.handle.net/10962/d1002613
- Description: Three types of electrodes: carbon paste electrodes modified with nanoparticles of metallophthalocyanines (MPcNP-CPEs, M = Mn, Fe, Ni, Co), basal plane pyrolytic graphite electrodes modified with iron or nickel phthalocyanine nanoparticles and multiwalled carbon nanotube composites (FePcNP/MWCNT-BPPGE or NiPcNP/MWCNT-BPPGE),and basal plane pyrolytic graphite electrodes modified with multiwalled carbon nanotubes and electropolymerized metal tetra-aminophthalocyanines (poly-MTAPc-MWCNT-BPPGE), where M is Mn, Fe, Ni or Co, were prepared. Electrochemical characterizations showed that faster electron transfer kinetics occurred at the NiPcNP/MWCNT-BPPGE than at the FePcNP/MWCNT-BPPGE surface. SEM and electrochemical characterizations of poly-MTAPc-MWCNT-BPPGE showed that MTAPc had been deposited on the MWCNTBPPGE surface, and that the poly-CoTAPc-MWCNT-BPPGE exhibited the fastest electron transfer kinetics of all the poly-MTAPc-MWCNT-BPPGEs. Using amitrole and asulam as test analytes, electrochemical experiments showed that, amongst the CPEs, the FePcNP-CPE and NiPcNP-CPE displayed the most electrocatalytic behavior towards amitrole and asulam oxidation, respectively, and further experiments were done to obtain the electrochemical parameters associated with these electrodes and the corresponding analytes. Although, the FePcNP/MWCNT- BPPGE displayed electrocatalytic behavior towards amitrole oxidation in comparison with the bare BPPGE, it was less electrocatalytic than the FePcNP-CPE in terms of detection potential. The NiPcNP/MWCNT-BPPGE displayed the same detection potential as the NiPcNP-CPE. The poly-FeTAPc-MWCNT-BPPGE exhibited the most electrocatalytic behavior towards amitrole, of all the electrodes investigated, and the poly-CoTAPc-MWCNT-BPPGE displayed the best electrocatalytic behavior towards asulam, amongst the poly-MTAPc-MWCNT-BPPGEs.
- Full Text:
- Date Issued: 2013
- Authors: Siswana, Msimelelo Patrick
- Date: 2013
- Subjects: Phthalocyanines Pesticides Electrocatalysis Electrochemistry Nanotubes Nanoparticles Transmission electron microscopy Scanning electron microscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4282 , http://hdl.handle.net/10962/d1002613
- Description: Three types of electrodes: carbon paste electrodes modified with nanoparticles of metallophthalocyanines (MPcNP-CPEs, M = Mn, Fe, Ni, Co), basal plane pyrolytic graphite electrodes modified with iron or nickel phthalocyanine nanoparticles and multiwalled carbon nanotube composites (FePcNP/MWCNT-BPPGE or NiPcNP/MWCNT-BPPGE),and basal plane pyrolytic graphite electrodes modified with multiwalled carbon nanotubes and electropolymerized metal tetra-aminophthalocyanines (poly-MTAPc-MWCNT-BPPGE), where M is Mn, Fe, Ni or Co, were prepared. Electrochemical characterizations showed that faster electron transfer kinetics occurred at the NiPcNP/MWCNT-BPPGE than at the FePcNP/MWCNT-BPPGE surface. SEM and electrochemical characterizations of poly-MTAPc-MWCNT-BPPGE showed that MTAPc had been deposited on the MWCNTBPPGE surface, and that the poly-CoTAPc-MWCNT-BPPGE exhibited the fastest electron transfer kinetics of all the poly-MTAPc-MWCNT-BPPGEs. Using amitrole and asulam as test analytes, electrochemical experiments showed that, amongst the CPEs, the FePcNP-CPE and NiPcNP-CPE displayed the most electrocatalytic behavior towards amitrole and asulam oxidation, respectively, and further experiments were done to obtain the electrochemical parameters associated with these electrodes and the corresponding analytes. Although, the FePcNP/MWCNT- BPPGE displayed electrocatalytic behavior towards amitrole oxidation in comparison with the bare BPPGE, it was less electrocatalytic than the FePcNP-CPE in terms of detection potential. The NiPcNP/MWCNT-BPPGE displayed the same detection potential as the NiPcNP-CPE. The poly-FeTAPc-MWCNT-BPPGE exhibited the most electrocatalytic behavior towards amitrole, of all the electrodes investigated, and the poly-CoTAPc-MWCNT-BPPGE displayed the best electrocatalytic behavior towards asulam, amongst the poly-MTAPc-MWCNT-BPPGEs.
- Full Text:
- Date Issued: 2013
Low symmetry metallophthalocyanines and their nanoparticle conjugates for photodynamic antimicrobial chemotherapy
- Authors: Masilela, Nkosiphile
- Date: 2013
- Subjects: Nanoparticles Anti-infective agents Chemotherapy Photochemotherapy Quantum dots Gold Silver , Phthalocyanines
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4278 , http://hdl.handle.net/10962/d1001906
- Description: This thesis reports on the syntheses of novel low symmetrically substituted Zn, Sn, Ge and Ti MPc complexes containing a single carboxylic or cysteinyl group available for attachments to MNPs. The complexes were extensively characterized by various techniques to ensure their purity. Various metallic nanoparticles consisting of silver (AgNPs), gold (AuNPs) as well as quantum dots (QDs) were successfully prepared and conjugated to the low symmetry phthalocyanine complexes. The conjugates were successfully characterized using many techniques. The Q-band maxima of the MPcs were observed at completely different wavelength regions depending on the nature of the substituents and the central metal used. Blue shifting of the Q band in the absorption spectra was observed for the complexes in the presence of AuNPs, while aggregation was observed in the presence of quantum dots. The complexes were successfully electrospun into polymer fibers for the antimicrobial inhibition of bacteria. The photophysical and photochemical properties of these complexes were extensively investigated. Higher triplet and singlet oxygen quantum yields were achieved for the Ge Pc complexes, with all the complexes giving reasonable singlet oxygen quantum yields. An enhancement in triplet and singlet oxygen quantum yields was observed for all the complexes in the presence of metal nanoparticles. However, the singlet oxygen quantum yields decreased for all the complexes when incorporated into electrospun fibers. The antimicrobial behaviour of the complexes was investigated against Bacillus Subtilis and Staphylococcus Aureus in solution and in the fiber matrix. High antimicrobial inhibitions were observed for the Ge complexes followed by the ZnPc derivatives. All the low symmetry ZnPc derivatives were conjugated to AgNPs and their antimicrobial behaviour was compared to their symmetrical counterparts. The best antimicrobial inhibition behaviour was observed for the low symmetry Pcs when compared to their symmetrical counterparts. In the absence and in the presence of AgNPs, axially ligated SiPc also showed better antimicrobial activity when it was compared to the unsubstituted ZnPc complex.
- Full Text:
- Date Issued: 2013
- Authors: Masilela, Nkosiphile
- Date: 2013
- Subjects: Nanoparticles Anti-infective agents Chemotherapy Photochemotherapy Quantum dots Gold Silver , Phthalocyanines
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4278 , http://hdl.handle.net/10962/d1001906
- Description: This thesis reports on the syntheses of novel low symmetrically substituted Zn, Sn, Ge and Ti MPc complexes containing a single carboxylic or cysteinyl group available for attachments to MNPs. The complexes were extensively characterized by various techniques to ensure their purity. Various metallic nanoparticles consisting of silver (AgNPs), gold (AuNPs) as well as quantum dots (QDs) were successfully prepared and conjugated to the low symmetry phthalocyanine complexes. The conjugates were successfully characterized using many techniques. The Q-band maxima of the MPcs were observed at completely different wavelength regions depending on the nature of the substituents and the central metal used. Blue shifting of the Q band in the absorption spectra was observed for the complexes in the presence of AuNPs, while aggregation was observed in the presence of quantum dots. The complexes were successfully electrospun into polymer fibers for the antimicrobial inhibition of bacteria. The photophysical and photochemical properties of these complexes were extensively investigated. Higher triplet and singlet oxygen quantum yields were achieved for the Ge Pc complexes, with all the complexes giving reasonable singlet oxygen quantum yields. An enhancement in triplet and singlet oxygen quantum yields was observed for all the complexes in the presence of metal nanoparticles. However, the singlet oxygen quantum yields decreased for all the complexes when incorporated into electrospun fibers. The antimicrobial behaviour of the complexes was investigated against Bacillus Subtilis and Staphylococcus Aureus in solution and in the fiber matrix. High antimicrobial inhibitions were observed for the Ge complexes followed by the ZnPc derivatives. All the low symmetry ZnPc derivatives were conjugated to AgNPs and their antimicrobial behaviour was compared to their symmetrical counterparts. The best antimicrobial inhibition behaviour was observed for the low symmetry Pcs when compared to their symmetrical counterparts. In the absence and in the presence of AgNPs, axially ligated SiPc also showed better antimicrobial activity when it was compared to the unsubstituted ZnPc complex.
- Full Text:
- Date Issued: 2013
Novel applications of Morita-Baylis-Hillman methodology in organic synthesis
- Authors: Mciteka, Lulama Patrick
- Date: 2013 , 2013-04-22
- Subjects: Organic compounds -- Synthesis -- Research Asymmetric synthesis Asymmetry (Chemistry) Chemical reactions -- Research Camphor -- Research AZT (Drug) -- Research Chemical inhibitors -- Research Chemistry -- Methodology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4439 , http://hdl.handle.net/10962/d1007598
- Description: The overall approach in the present investigation has been to explore applications of the Morita-Baylis-Hillman (MBH) reaction in asymmetric synthesis and in the continuation of systems with medicinal potential. To this end, a series of varied camphor-derived acrylate esters was prepared to serve as chiral substrates in asymmetric Morita-Baylis- Hillman reactions. Reduction of N-substituted camphor-10-sulfonamides afforded the 3- exo-hydroxy derivatives as the major products. Acylation of the corresponding sodium alkoxides gave the desired 3-exo-acrylate esters, isolation of which was complicated by concomitant formation of hydrochlorinated and diastereomeric competition products. Bulky camphorsulfonamides containing alkyl, dialkyl, aromatic and adamantyl groups were selected as N-substituents with the view of achieving stereoselective outcome in subsequent MBH reactions. The synthesis of novel camphor-derived Morita-Baylis-Hillman adducts using various pyridine-carboxaldehydes proceeded with exceptionally high yields with diastereoselectivities ranging from 7-33 % d.e. Both 1D and 2D NMR and HRMS techniques were employed to confirm the structures and an extensive study of the electropositive fragmentation patterns of a number of camphor-derived chiral acrylate esters was conducted. Attention has also been given to the application of MBH methodology in the construction of heterocyclic ‘cinnamate-like’ AZT conjugates which were designed to serve as dualaction HIV-1 integrase-reverse transcriptase (IN-RT) inhibitors. A number of pyridine carboxaldehyde-derived MBH adducts were synthesized using methyl, ethyl and t-butyl acrylates in the presence of 3-hydroxyquinuclidine (3-HQ) as catalyst. The yields for these reactions were excellent. The resulting MBH adducts were acetylated and subjected to aza-Michael addition using propargylamine. The resulting alkylamino compounds were then used in ‘Click reactions’ to form the targeted AZT-conjugates in moderate to excellent yield. In silico docking of computer modelled AZT-conjugates into the HIV-1 integrase and reverse transcriptase enzyme-active sites and potential hydrogen-bonding interaction with active-site amino acid residues were identified. The electrospray MS fragmentations of the AZT and the novel AZT-conjugates were also investigated and common fragmentation pathways were identified.
- Full Text:
- Date Issued: 2013
- Authors: Mciteka, Lulama Patrick
- Date: 2013 , 2013-04-22
- Subjects: Organic compounds -- Synthesis -- Research Asymmetric synthesis Asymmetry (Chemistry) Chemical reactions -- Research Camphor -- Research AZT (Drug) -- Research Chemical inhibitors -- Research Chemistry -- Methodology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4439 , http://hdl.handle.net/10962/d1007598
- Description: The overall approach in the present investigation has been to explore applications of the Morita-Baylis-Hillman (MBH) reaction in asymmetric synthesis and in the continuation of systems with medicinal potential. To this end, a series of varied camphor-derived acrylate esters was prepared to serve as chiral substrates in asymmetric Morita-Baylis- Hillman reactions. Reduction of N-substituted camphor-10-sulfonamides afforded the 3- exo-hydroxy derivatives as the major products. Acylation of the corresponding sodium alkoxides gave the desired 3-exo-acrylate esters, isolation of which was complicated by concomitant formation of hydrochlorinated and diastereomeric competition products. Bulky camphorsulfonamides containing alkyl, dialkyl, aromatic and adamantyl groups were selected as N-substituents with the view of achieving stereoselective outcome in subsequent MBH reactions. The synthesis of novel camphor-derived Morita-Baylis-Hillman adducts using various pyridine-carboxaldehydes proceeded with exceptionally high yields with diastereoselectivities ranging from 7-33 % d.e. Both 1D and 2D NMR and HRMS techniques were employed to confirm the structures and an extensive study of the electropositive fragmentation patterns of a number of camphor-derived chiral acrylate esters was conducted. Attention has also been given to the application of MBH methodology in the construction of heterocyclic ‘cinnamate-like’ AZT conjugates which were designed to serve as dualaction HIV-1 integrase-reverse transcriptase (IN-RT) inhibitors. A number of pyridine carboxaldehyde-derived MBH adducts were synthesized using methyl, ethyl and t-butyl acrylates in the presence of 3-hydroxyquinuclidine (3-HQ) as catalyst. The yields for these reactions were excellent. The resulting MBH adducts were acetylated and subjected to aza-Michael addition using propargylamine. The resulting alkylamino compounds were then used in ‘Click reactions’ to form the targeted AZT-conjugates in moderate to excellent yield. In silico docking of computer modelled AZT-conjugates into the HIV-1 integrase and reverse transcriptase enzyme-active sites and potential hydrogen-bonding interaction with active-site amino acid residues were identified. The electrospray MS fragmentations of the AZT and the novel AZT-conjugates were also investigated and common fragmentation pathways were identified.
- Full Text:
- Date Issued: 2013