Synthesis of indium and lead phthalocyanine as photocatalysts for photodynamic antimicrobial chemotherapy and photo-oxidation of pollutants
- Authors: Osifeko, Olawale L
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/5221 , vital:20790
- Description: This thesis explores the synthesis of metallophthalocyanines as potential photosensitizers for application in photodynamic antimicrobial chemotherapy and phototransformation of environmental pollutants. The metallophthalocyanines containing amino substituent were conjugated with magnetic nanoparticle and semiconductor quantum dots via an amide bond and by chemisorption onto gold nanoparticles surface. Techniques such as time-resolved fluorescence measurements, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis, fourier transform infrared (FTIR), nuclear magnetic resonance (¹H, ¹³C, and cozy of symmetrical phthalocyanine), electronic spectroscopy, as well as mass spectroscopy were employed to characterize all metallophthalocyanines. Quarternized pyridyloxy substituted phthalocyanine and asymmetric (AB3) metallophthalocyanines were embedded in electrospun polystyrene fiber. General trends are described for quantum yields of fluorescence, triplet, singlet oxygen and photodegradation as well as lifetimes of fluorescence and triplet state of the compounds. There is an increase in triplet quantum yield for Pcs in the presence of gold nanoparticles (AuNPs) and semiconductor quantum dots (QDs), but not in the presence of magnetic nanoparticles (MNPs). Photodynamic inactivation of Escherichia coli with the quarternized photosensitizers at low concentrations totally inactivate the bacteria compared to non-charged photosensitiser. Also, a similar trend was observed for the magnetic nanoparticles conjugates. Photooxidations of bisphenol A and 4-chlorophenol were carried out in this study using two asymmetric Indium(III) phthalocyanines photosensitizers. The photooxidation reactions were compared with those of a symmetrical indium(III) phthalocyanines containing four quaternized 4-pyridyloxy substituents. The complexes were embedded in electrospun polystyrene fiber for heterogeneous photocatalysis. The immobilized photosensitizers possess good singlet oxygen generation potentials in aqueous media. The asymmetrical phthalocyanine containing 4-pyridylsulfanyl and one aminophenoxy showed the best photocatalytic behavior.
- Full Text:
- Authors: Osifeko, Olawale L
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/5221 , vital:20790
- Description: This thesis explores the synthesis of metallophthalocyanines as potential photosensitizers for application in photodynamic antimicrobial chemotherapy and phototransformation of environmental pollutants. The metallophthalocyanines containing amino substituent were conjugated with magnetic nanoparticle and semiconductor quantum dots via an amide bond and by chemisorption onto gold nanoparticles surface. Techniques such as time-resolved fluorescence measurements, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis, fourier transform infrared (FTIR), nuclear magnetic resonance (¹H, ¹³C, and cozy of symmetrical phthalocyanine), electronic spectroscopy, as well as mass spectroscopy were employed to characterize all metallophthalocyanines. Quarternized pyridyloxy substituted phthalocyanine and asymmetric (AB3) metallophthalocyanines were embedded in electrospun polystyrene fiber. General trends are described for quantum yields of fluorescence, triplet, singlet oxygen and photodegradation as well as lifetimes of fluorescence and triplet state of the compounds. There is an increase in triplet quantum yield for Pcs in the presence of gold nanoparticles (AuNPs) and semiconductor quantum dots (QDs), but not in the presence of magnetic nanoparticles (MNPs). Photodynamic inactivation of Escherichia coli with the quarternized photosensitizers at low concentrations totally inactivate the bacteria compared to non-charged photosensitiser. Also, a similar trend was observed for the magnetic nanoparticles conjugates. Photooxidations of bisphenol A and 4-chlorophenol were carried out in this study using two asymmetric Indium(III) phthalocyanines photosensitizers. The photooxidation reactions were compared with those of a symmetrical indium(III) phthalocyanines containing four quaternized 4-pyridyloxy substituents. The complexes were embedded in electrospun polystyrene fiber for heterogeneous photocatalysis. The immobilized photosensitizers possess good singlet oxygen generation potentials in aqueous media. The asymmetrical phthalocyanine containing 4-pyridylsulfanyl and one aminophenoxy showed the best photocatalytic behavior.
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Synthesis, characterisation and evaluation of benzoxaborole-based hybrids as antiplasmodial agents
- Authors: Gumbo, Maureen
- Date: 2017
- Subjects: Malaria Chemotherapy , Antimalarials , Boron compounds , Drug resistance , Plasmodium falciparum , Drug development
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/59193 , vital:27456
- Description: Malaria is a mosquito-borne disease, which continues to pose a threat to the entire humanity. About 40% of the world population is estimated to be at risk of infections by malaria. Despite efforts undertaken by scientific community, government entities and international organizations, malaria is still rampant. The major problem is drug resistance, where the Plasmodium spp have over the past decades developed drug resistance against available drugs. In order to counter this problem, novel antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Benzoxaborole derivatives have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported on the compounds such as 6-(2- (alkoxycarbonyl)pyrazinyl-5-oxy)-1,3-dihydro-1-hydroxy-2,1-benzoxaboroles, which showed good antimalarial activity against both W7 and 3D7 strains without significant toxicity. On the other hand, chloroquine (CQ) and cinnamic acids have a wide variety of biological activity including antimalarial activity. Herein, a hybridisation strategy was employed to synthesise new CQ-benzoxaborole and cinnamoyl-benzoxaborole hybrids. CQ-Benzoxaborole 2.12a-c and cinnamoylbenzoxaborole 2.11a-g hydrid molecules were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (1H and 13C NMR, and mass spectrometry). CQ-benzoxaborole compounds, however, showed instability, and only 2.12b was used for in vitro biological assay and showed activity comparable to CQ. Furthermore, in vitro biological assay revealed that compounds 2.11a-g poorly inhibited the growth of P. falciparum parasites. Interestingly, these compounds, however, exhibited satisfactory activity against Trypanosoma brucei with IC50 = 0.052 μM for compound 2.11g. The cell cytotoxicity assay of all final compounds confirmed that all CQ-benzoxaborole 2.12b and cinnamoyl-benzoxaborole 2.11a-g hybrids were non-toxic against HeLa cell lines. However, efforts to further expand the structure-activity relationship (SAR) of CQbenzoxaborole by increasing the length of the linker with one extra carbon (Scheme 2.10) were not possible as an important precursor 6-formylbenzoxaborole 2.29 could not be synthesized in sufficient yields. , Thesis (MSc) -- Faculty of Faculty of Science, Chemistry, 2017
- Full Text:
- Authors: Gumbo, Maureen
- Date: 2017
- Subjects: Malaria Chemotherapy , Antimalarials , Boron compounds , Drug resistance , Plasmodium falciparum , Drug development
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/59193 , vital:27456
- Description: Malaria is a mosquito-borne disease, which continues to pose a threat to the entire humanity. About 40% of the world population is estimated to be at risk of infections by malaria. Despite efforts undertaken by scientific community, government entities and international organizations, malaria is still rampant. The major problem is drug resistance, where the Plasmodium spp have over the past decades developed drug resistance against available drugs. In order to counter this problem, novel antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Benzoxaborole derivatives have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported on the compounds such as 6-(2- (alkoxycarbonyl)pyrazinyl-5-oxy)-1,3-dihydro-1-hydroxy-2,1-benzoxaboroles, which showed good antimalarial activity against both W7 and 3D7 strains without significant toxicity. On the other hand, chloroquine (CQ) and cinnamic acids have a wide variety of biological activity including antimalarial activity. Herein, a hybridisation strategy was employed to synthesise new CQ-benzoxaborole and cinnamoyl-benzoxaborole hybrids. CQ-Benzoxaborole 2.12a-c and cinnamoylbenzoxaborole 2.11a-g hydrid molecules were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (1H and 13C NMR, and mass spectrometry). CQ-benzoxaborole compounds, however, showed instability, and only 2.12b was used for in vitro biological assay and showed activity comparable to CQ. Furthermore, in vitro biological assay revealed that compounds 2.11a-g poorly inhibited the growth of P. falciparum parasites. Interestingly, these compounds, however, exhibited satisfactory activity against Trypanosoma brucei with IC50 = 0.052 μM for compound 2.11g. The cell cytotoxicity assay of all final compounds confirmed that all CQ-benzoxaborole 2.12b and cinnamoyl-benzoxaborole 2.11a-g hybrids were non-toxic against HeLa cell lines. However, efforts to further expand the structure-activity relationship (SAR) of CQbenzoxaborole by increasing the length of the linker with one extra carbon (Scheme 2.10) were not possible as an important precursor 6-formylbenzoxaborole 2.29 could not be synthesized in sufficient yields. , Thesis (MSc) -- Faculty of Faculty of Science, Chemistry, 2017
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Synthesis, characterisation and evaluation of ferrocene-containing Novobiocin analogues for anticancer and antiplasmodial activity through inhibition of Hsp90
- Authors: Mbaba, Mziyanda
- Date: 2017
- Subjects: Antibiotics Synthesis , Ferrocene , Heat shock proteins , Antimalarials , Cancer Chemotherapy
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/65111 , vital:28690
- Description: Novobiocin (Nb) is a coumarin type antibiotic isolated from the bacterium species of Streptomyces and possesses modest anticancer and antimalarial activities. Nb and analogues have been extensively explored as potential anticancer agents through inhibition of the C- terminal domain of heat shock protein 90 (Hsp90), which plays a pivotal role in the proteinfolding machinery of cells. There has been little effort in the exploration of Nb and derivatives for antimalarial activity. Incorporation of organometallic units, such as ferrocene (Fc), into bioactive chemical scaffolds remains an attractive approach for developing new therapeutic agents for treatment of several ailments. The current study sought to investigate the anticancer and antiplasmodial effects of incorporating ferrocene (Fc) into Nb scaffold presumably through inhibition of Hsp90. The ferrocenyl Nb analogues containing simplified structural motifs such as phenyl, benzyl, and piperidine were synthesized in six to nine steps employing conventional synthetic organic protocols adapted from literature, and the compounds were accessed in reasonable yields. For comparison purposes, a selection of organic Nb analogues were also included in the study. The target compounds were characterized by spectroscopic techniques including 1-dimensional nuclear magnetic resonance (1D NMR) and high-resolution mass spectroscopy. The synthesized compounds were evaluated in vitro for potential anticancer and antiplasmodial activities using the breast cancer cell line (HCC38) and chloroquine-sensitive strain (3D7) of the malaria parasite, Plasmodium falciparum. The presence of the Fc unit was found to enhance both anticancer and antiplasmodial activities of the resultant ferrocenyl Nb compounds with IC50 values in the low to mid micromolar range. Hsp90 inhibitory studies of the ferrocenyl Nb analogues possessing superior activities (2.13a and 2.20c) were also conducted using different yeast strains expressing both human and malarial Hsp90 isoforms: hHsp90a/p and PfHsp90, respectively. The results of Hsp90 inhibitory studies suggested no direct correlation between the observed activities of the analogues and Hsp90 inhibition. However, since the conditions of the assay were not optimised due to time constrains of the project, these observed data remained to be confirmed. , Thesis (MSc) -- Faculty of Science, Chemistry, 2017
- Full Text:
- Authors: Mbaba, Mziyanda
- Date: 2017
- Subjects: Antibiotics Synthesis , Ferrocene , Heat shock proteins , Antimalarials , Cancer Chemotherapy
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/65111 , vital:28690
- Description: Novobiocin (Nb) is a coumarin type antibiotic isolated from the bacterium species of Streptomyces and possesses modest anticancer and antimalarial activities. Nb and analogues have been extensively explored as potential anticancer agents through inhibition of the C- terminal domain of heat shock protein 90 (Hsp90), which plays a pivotal role in the proteinfolding machinery of cells. There has been little effort in the exploration of Nb and derivatives for antimalarial activity. Incorporation of organometallic units, such as ferrocene (Fc), into bioactive chemical scaffolds remains an attractive approach for developing new therapeutic agents for treatment of several ailments. The current study sought to investigate the anticancer and antiplasmodial effects of incorporating ferrocene (Fc) into Nb scaffold presumably through inhibition of Hsp90. The ferrocenyl Nb analogues containing simplified structural motifs such as phenyl, benzyl, and piperidine were synthesized in six to nine steps employing conventional synthetic organic protocols adapted from literature, and the compounds were accessed in reasonable yields. For comparison purposes, a selection of organic Nb analogues were also included in the study. The target compounds were characterized by spectroscopic techniques including 1-dimensional nuclear magnetic resonance (1D NMR) and high-resolution mass spectroscopy. The synthesized compounds were evaluated in vitro for potential anticancer and antiplasmodial activities using the breast cancer cell line (HCC38) and chloroquine-sensitive strain (3D7) of the malaria parasite, Plasmodium falciparum. The presence of the Fc unit was found to enhance both anticancer and antiplasmodial activities of the resultant ferrocenyl Nb compounds with IC50 values in the low to mid micromolar range. Hsp90 inhibitory studies of the ferrocenyl Nb analogues possessing superior activities (2.13a and 2.20c) were also conducted using different yeast strains expressing both human and malarial Hsp90 isoforms: hHsp90a/p and PfHsp90, respectively. The results of Hsp90 inhibitory studies suggested no direct correlation between the observed activities of the analogues and Hsp90 inhibition. However, since the conditions of the assay were not optimised due to time constrains of the project, these observed data remained to be confirmed. , Thesis (MSc) -- Faculty of Science, Chemistry, 2017
- Full Text:
Synthesis, characterisation and evaluation of novel ferrocene-thiazole derivatives as antiplasmodial agents
- Authors: Hakizimana, Emmanuel Victor
- Date: 2017
- Subjects: Plasmodium , Malaria -- Chemotherapy , Plasmodium falciparum , Plasmodium -- Inhibitors , Drug resistance in microorganisms , Thiaszoles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/5304 , vital:20807
- Description: Malaria is mosquito-transmitted disease which continues to pose threat to humanity, despite the efforts undertaken by the scientific community, government entities and international organizations. The major problem is that Plasmodium species have developed resistance against available drugs. In order to counter this problem, antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Thiazole derivatives, in particular aminomethylthiazole analogues, have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported the hit compound MMV010539, which showed good antimalarial activity against both K1 (CQ and multidrug resistant strains) and NF54 (CQ sensitive strain). In this study, MMV010539 was deemed to be as an attractive compound to generate novel analogues by addition of ferrocenyl organometallic unit. The ferrocene based compounds have shown biological activity; and with ferroquine currently in clinical trials there has been increasing research into identifying new ferrocenyl-containing molecules as potential antimalarial agents. Herein, thiazole ferrocene based molecules 3.22a-e were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (¹H and ¹³C NMR, FT-IR spectroscopy and mass spectrometry). The cell cytotoxicity assay of all final compounds confirmed that all ferrocene-thiazole blends 3.22a-e were non-toxic against HeLa cell lines. However, the in vitro biological assay revealed that despite the absence of cell cytotoxicity these compounds poorly inhibited the growth of Plasmodium falciparum parasite. As the aim was to expand further the structure-activity relationship (SAR) of MMV010539, this study confirmed the previous findings that there is a limited structural modification that could be accommodated as indicated in Figure 3.3 (Panel C). Moreover, the combination of ferrocenyl moiety and various alkylamines resulted in compounds with poor antiplasmodial potency, further suggesting that the free amine (Panel A, Figure 3.3) is important for activity.
- Full Text:
- Authors: Hakizimana, Emmanuel Victor
- Date: 2017
- Subjects: Plasmodium , Malaria -- Chemotherapy , Plasmodium falciparum , Plasmodium -- Inhibitors , Drug resistance in microorganisms , Thiaszoles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/5304 , vital:20807
- Description: Malaria is mosquito-transmitted disease which continues to pose threat to humanity, despite the efforts undertaken by the scientific community, government entities and international organizations. The major problem is that Plasmodium species have developed resistance against available drugs. In order to counter this problem, antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Thiazole derivatives, in particular aminomethylthiazole analogues, have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported the hit compound MMV010539, which showed good antimalarial activity against both K1 (CQ and multidrug resistant strains) and NF54 (CQ sensitive strain). In this study, MMV010539 was deemed to be as an attractive compound to generate novel analogues by addition of ferrocenyl organometallic unit. The ferrocene based compounds have shown biological activity; and with ferroquine currently in clinical trials there has been increasing research into identifying new ferrocenyl-containing molecules as potential antimalarial agents. Herein, thiazole ferrocene based molecules 3.22a-e were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (¹H and ¹³C NMR, FT-IR spectroscopy and mass spectrometry). The cell cytotoxicity assay of all final compounds confirmed that all ferrocene-thiazole blends 3.22a-e were non-toxic against HeLa cell lines. However, the in vitro biological assay revealed that despite the absence of cell cytotoxicity these compounds poorly inhibited the growth of Plasmodium falciparum parasite. As the aim was to expand further the structure-activity relationship (SAR) of MMV010539, this study confirmed the previous findings that there is a limited structural modification that could be accommodated as indicated in Figure 3.3 (Panel C). Moreover, the combination of ferrocenyl moiety and various alkylamines resulted in compounds with poor antiplasmodial potency, further suggesting that the free amine (Panel A, Figure 3.3) is important for activity.
- Full Text:
Synthesis, characterisation and evaluation of novel ferrocene-thiazole derivatives as antiplasmodial agents
- Authors: Hakizimana, Emmanuel Victor
- Date: 2017
- Subjects: Plasmodium , Malaria -- Chemotherapy , Plasmodium falciparum , Plasmodium -- Inhibitors , Drug resistance in microorganisms , Thiaszoles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/96068 , vital:31232
- Description: Malaria is mosquito-transmitted disease which continues to pose threat to humanity, despite the efforts undertaken by the scientific community, government entities and international organizations. The major problem is that Plasmodium species have developed resistance against available drugs. In order to counter this problem, antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Thiazole derivatives, in particular aminomethylthiazole analogues, have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported the hit compound MMV010539, which showed good antimalarial activity against both K1 (CQ and multidrug resistant strains) and NF54 (CQ sensitive strain). In this study, MMV010539 was deemed to be as an attractive compound to generate novel analogues by addition of ferrocenyl organometallic unit. The ferrocene based compounds have shown biological activity; and with ferroquine currently in clinical trials there has been increasing research into identifying new ferrocenyl-containing molecules as potential antimalarial agents. Herein, thiazole ferrocene based molecules 3.22a-e were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (¹H and ¹³C NMR, FT-IR spectroscopy and mass spectrometry). The cell cytotoxicity assay of all final compounds confirmed that all ferrocene-thiazole blends 3.22a-e were non-toxic against HeLa cell lines. However, the in vitro biological assay revealed that despite the absence of cell cytotoxicity these compounds poorly inhibited the growth of Plasmodium falciparum parasite. As the aim was to expand further the structure-activity relationship (SAR) of MMV010539, this study confirmed the previous findings that there is a limited structural modification that could be accommodated as indicated in Figure 3.3 (Panel C). Moreover, the combination of ferrocenyl moiety and various alkylamines resulted in compounds with poor antiplasmodial potency, further suggesting that the free amine (Panel A, Figure 3.3) is important for activity.
- Full Text:
- Authors: Hakizimana, Emmanuel Victor
- Date: 2017
- Subjects: Plasmodium , Malaria -- Chemotherapy , Plasmodium falciparum , Plasmodium -- Inhibitors , Drug resistance in microorganisms , Thiaszoles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/96068 , vital:31232
- Description: Malaria is mosquito-transmitted disease which continues to pose threat to humanity, despite the efforts undertaken by the scientific community, government entities and international organizations. The major problem is that Plasmodium species have developed resistance against available drugs. In order to counter this problem, antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Thiazole derivatives, in particular aminomethylthiazole analogues, have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported the hit compound MMV010539, which showed good antimalarial activity against both K1 (CQ and multidrug resistant strains) and NF54 (CQ sensitive strain). In this study, MMV010539 was deemed to be as an attractive compound to generate novel analogues by addition of ferrocenyl organometallic unit. The ferrocene based compounds have shown biological activity; and with ferroquine currently in clinical trials there has been increasing research into identifying new ferrocenyl-containing molecules as potential antimalarial agents. Herein, thiazole ferrocene based molecules 3.22a-e were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (¹H and ¹³C NMR, FT-IR spectroscopy and mass spectrometry). The cell cytotoxicity assay of all final compounds confirmed that all ferrocene-thiazole blends 3.22a-e were non-toxic against HeLa cell lines. However, the in vitro biological assay revealed that despite the absence of cell cytotoxicity these compounds poorly inhibited the growth of Plasmodium falciparum parasite. As the aim was to expand further the structure-activity relationship (SAR) of MMV010539, this study confirmed the previous findings that there is a limited structural modification that could be accommodated as indicated in Figure 3.3 (Panel C). Moreover, the combination of ferrocenyl moiety and various alkylamines resulted in compounds with poor antiplasmodial potency, further suggesting that the free amine (Panel A, Figure 3.3) is important for activity.
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Tetra 4-(propargyloxy)phenoxy phthalocyanines: synthesis, spectroscopic, nonlinear optical and electrocatalytic properties
- Authors: Mwanza, Daniel
- Date: 2017
- Subjects: Phthalocyanines , Nonlinear optics , Electrocatalysis , Spectrum analysis , Thermogravimetry , Phthalocyanines Spectra
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/65144 , vital:28695
- Description: This study presents the synthesis, spectroscopic, photophysical and theoretical characterisation of metal-free (H2TPrOPhOPc), cobalt (CoTPrOPhOPc) and manganese (MnTPrOPhOPc) tetra 4-(4-propargyloxy) phenoxy phthalocyanines. Thermal analysis using thermogravimetric analysis (TGA) confirmed the excellent thermal stability of synthesized tetra 4-(4- propargyloxy) phenoxy phthalocyanines. The metal complexes, CoTPrOPhOPc and MnTPrOPhOPc, exhibited better thermal stability when compared to H2TPrOPhOPc. The residual percentage weight remaining was approximately 70% for CoTPrOPhOPc and MnTPrOPhOPc and 45% for H2TPrOPhOPc after 600°C, clearly confirming the stability of the metal complexes. The MTPrOPhOPcs (where M = H2, Co and Mn) complexes exhibited excellent nonlinear optical properties with strong reverse saturable absorption (RSA), especially when 560 nm excitation laser was used. Their nonlinear optical properties followed this trend: H2TPrOPhOPc > CoTPrOPhOPc > MnTPrOPhOPc. According to the trend observed, the H2TPrOPhOPc was an excellent nonlinear optical limiter when compared to the CoTPrOPhOPc and MnTPrOPhOPc. All the investigated complexes exhibited optical limiting properties comparable to the phthalocyanine complexes reported in the literature. The MTPrOPhOPc complexes were further studied for their electrocatalytic and electroanalytical properties towards the detection of hydrogen peroxide. For the electrocatalytic studies, the synthesized complexes were immobilized onto gold electrode surfaces pre-functionalized with phenylazide (Au-PAz) monolayer. Copper (I) catalyzed alkynyl-azide cycloaddition reaction was used to covalently immobilize the MTPrOPhOPcs onto the gold electrode surfaces to form Au-PAz-MTPrOPhOPc. The MTPrOPhOPcs modified gold surfaces (Au-PAz-MTPrOPhOPc) exhibited good reproducibility and stability in various electrolyte conditions. Electrochemical and surface characterisation of the functionalised gold electrode surfaces confirmed the presence of the MTPrOPhOPcs and their electroanalysis was excellent towards electrocatalytic reduction of H2O2, with the limit of detection (LoD) and limit of quantification (LoQ) in the ^M range. The electrocatalytic reduction peaks for H2O2 were observed at -0.37 V for Au-PAz-MnTPrOPhOPc and -0.31 V for Au-PAz-CoTPrOPhOPc when Ag|AgCl pseudo-reference electrode was used. The Au-PAz-MnTPrOPhOPc and Au- PAz-CoTPrOPhOPc gold electrode surfaces showed good sensitivity and reproducibility towards the electrocatalytic reduction of hydrogen peroxide in pH 7.4 phosphate buffer solution. , Thesis (MSc) -- Faculty of Science, Chemistry, 2017
- Full Text:
- Authors: Mwanza, Daniel
- Date: 2017
- Subjects: Phthalocyanines , Nonlinear optics , Electrocatalysis , Spectrum analysis , Thermogravimetry , Phthalocyanines Spectra
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/65144 , vital:28695
- Description: This study presents the synthesis, spectroscopic, photophysical and theoretical characterisation of metal-free (H2TPrOPhOPc), cobalt (CoTPrOPhOPc) and manganese (MnTPrOPhOPc) tetra 4-(4-propargyloxy) phenoxy phthalocyanines. Thermal analysis using thermogravimetric analysis (TGA) confirmed the excellent thermal stability of synthesized tetra 4-(4- propargyloxy) phenoxy phthalocyanines. The metal complexes, CoTPrOPhOPc and MnTPrOPhOPc, exhibited better thermal stability when compared to H2TPrOPhOPc. The residual percentage weight remaining was approximately 70% for CoTPrOPhOPc and MnTPrOPhOPc and 45% for H2TPrOPhOPc after 600°C, clearly confirming the stability of the metal complexes. The MTPrOPhOPcs (where M = H2, Co and Mn) complexes exhibited excellent nonlinear optical properties with strong reverse saturable absorption (RSA), especially when 560 nm excitation laser was used. Their nonlinear optical properties followed this trend: H2TPrOPhOPc > CoTPrOPhOPc > MnTPrOPhOPc. According to the trend observed, the H2TPrOPhOPc was an excellent nonlinear optical limiter when compared to the CoTPrOPhOPc and MnTPrOPhOPc. All the investigated complexes exhibited optical limiting properties comparable to the phthalocyanine complexes reported in the literature. The MTPrOPhOPc complexes were further studied for their electrocatalytic and electroanalytical properties towards the detection of hydrogen peroxide. For the electrocatalytic studies, the synthesized complexes were immobilized onto gold electrode surfaces pre-functionalized with phenylazide (Au-PAz) monolayer. Copper (I) catalyzed alkynyl-azide cycloaddition reaction was used to covalently immobilize the MTPrOPhOPcs onto the gold electrode surfaces to form Au-PAz-MTPrOPhOPc. The MTPrOPhOPcs modified gold surfaces (Au-PAz-MTPrOPhOPc) exhibited good reproducibility and stability in various electrolyte conditions. Electrochemical and surface characterisation of the functionalised gold electrode surfaces confirmed the presence of the MTPrOPhOPcs and their electroanalysis was excellent towards electrocatalytic reduction of H2O2, with the limit of detection (LoD) and limit of quantification (LoQ) in the ^M range. The electrocatalytic reduction peaks for H2O2 were observed at -0.37 V for Au-PAz-MnTPrOPhOPc and -0.31 V for Au-PAz-CoTPrOPhOPc when Ag|AgCl pseudo-reference electrode was used. The Au-PAz-MnTPrOPhOPc and Au- PAz-CoTPrOPhOPc gold electrode surfaces showed good sensitivity and reproducibility towards the electrocatalytic reduction of hydrogen peroxide in pH 7.4 phosphate buffer solution. , Thesis (MSc) -- Faculty of Science, Chemistry, 2017
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The effects of graphene and other nanomaterials on the electrocatalytic behaviour of phthalocyanines
- Authors: Shumba, Munyaradzi
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/37952 , vital:24712
- Description: Carbon based nanomaterials, gold nanorods and metallophthalocyanine nanoconjugates have been developed for electrocatalysis. Carbon based nanomaterials used are multiwalled carbon nanotubes, pristine graphene oxide nanosheets, nitrogen, boron, sulphur, phosphorus doped graphene oxide nanosheets. Cobalt phthalocyanine (CoPc), cobalt tetra aminophenoxy phthalocyanine (CoTAPc), cobalt tetra aminophenoxy phthalocyanine (CoTAPhPc), cobalt mono carboxyphenoxy phthalocyanine (CoMCPhPc) and cobalt tetra carboxyphenoxy phthalocyanine (CoTCPhPc) are the phthalocyanines employed in this work. Metallophthalocyanines were employed either in their bulk form or in their nanosized form. Electrode modification by these nanomaterials was either done sequentially, premixed or linked nanoconjugates. In all sequential modification, phthalocyanines were employed on top of other nanomaterials. Sequentially modified electrodes gave higher detection currents than both premixed and covalently bonded nanoconjugates. The nanomaterials reported here were characterised by transmission electron microscopy, Raman spectroscopy, time of flight secondary ion mass spectrometry, and X-ray diffraction among other techniques. The modified electrodes were further characterised by scanning electron microscopy, scanning electrochemical microscopy, X-ray photoelectron spectroscopy and cyclic voltammetry, while square wave, linear scan and cyclic voltammetry, rotating disc electrode and chronoamperometry have been used to evaluate the electrocatalytic behaviour of the previously mentioned towards either oxidation or reduction of L-cysteine and/or hydrogen peroxide respectively. Generally, the nanoconjugates resulted in superior catalytic performance compared to the performance of individual nanomaterials. Zinc octacarboxy phthalocyanine (ZnOCPc) conjugated to either GONS or rGONS were employed to compare electrocatalytic detection of hydrogen peroxide to its luminescence sensing.
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The effects of graphene and other nanomaterials on the electrocatalytic behaviour of phthalocyanines
- Authors: Shumba, Munyaradzi
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/37952 , vital:24712
- Description: Carbon based nanomaterials, gold nanorods and metallophthalocyanine nanoconjugates have been developed for electrocatalysis. Carbon based nanomaterials used are multiwalled carbon nanotubes, pristine graphene oxide nanosheets, nitrogen, boron, sulphur, phosphorus doped graphene oxide nanosheets. Cobalt phthalocyanine (CoPc), cobalt tetra aminophenoxy phthalocyanine (CoTAPc), cobalt tetra aminophenoxy phthalocyanine (CoTAPhPc), cobalt mono carboxyphenoxy phthalocyanine (CoMCPhPc) and cobalt tetra carboxyphenoxy phthalocyanine (CoTCPhPc) are the phthalocyanines employed in this work. Metallophthalocyanines were employed either in their bulk form or in their nanosized form. Electrode modification by these nanomaterials was either done sequentially, premixed or linked nanoconjugates. In all sequential modification, phthalocyanines were employed on top of other nanomaterials. Sequentially modified electrodes gave higher detection currents than both premixed and covalently bonded nanoconjugates. The nanomaterials reported here were characterised by transmission electron microscopy, Raman spectroscopy, time of flight secondary ion mass spectrometry, and X-ray diffraction among other techniques. The modified electrodes were further characterised by scanning electron microscopy, scanning electrochemical microscopy, X-ray photoelectron spectroscopy and cyclic voltammetry, while square wave, linear scan and cyclic voltammetry, rotating disc electrode and chronoamperometry have been used to evaluate the electrocatalytic behaviour of the previously mentioned towards either oxidation or reduction of L-cysteine and/or hydrogen peroxide respectively. Generally, the nanoconjugates resulted in superior catalytic performance compared to the performance of individual nanomaterials. Zinc octacarboxy phthalocyanine (ZnOCPc) conjugated to either GONS or rGONS were employed to compare electrocatalytic detection of hydrogen peroxide to its luminescence sensing.
- Full Text:
Electrode surface modification using iron(II) phthalocyanine immobilized via electrografting and click chemistry and clicked onto azide-functionalized quantum dots: applications in electrocatalysis
- Authors: Nxele, Siphesihle Robin
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3464 , vital:20501
- Description: Tetrakis(5-hexynoxy)Fe(II) phthalocyanine was used alone and in combination with quantum dots (QDs) in order to test the electrocatalytic ability with hydrazine and paraquat as the analytes of interest. This novel phthalocaynine was successfully synthesised and characterized using various characterisation techniques. The QDs used were the well-known core-shell CdSe/ZnS nanostructures. The fabrication of glassy carbon electrodes involved covalent attachment by electrochemical grafting and click chemistry for the first part of the work and the second part involved the conjugation of the synthesised QDs and the phthalocyanine by click chemistry. This approach of conjugating these nanostructures introduced another aspect of novelty to the work reported in this thesis. The immobilisation of this conjugate on a glassy carbon electrode (GCE) was achieved by adsorption. Characterisation techniques such as infrared spectroscopy, x-ray diffractometry, UV/vis spectroscopy, transmission electron microscopy and x-ray photoelectron spectroscopy were used to characterise the molecules and conjugates of interest. With respect to the electrocatalytic part of the work, electrode surface characterisation involved scanning electrochemical microscopy and cyclic voltammetry to determine changes in the nature of the surface as well as reactivity of the surface at different modification steps. Detection limits and the sensitivity determined for the electrocatalysts fabricated here proved to be an improvement compared to other reported work involving phthalocyanines and the test analytes chosen for application. With respect to the conjugate, the electrocatalytic ability was improved when the QDs and phthalocyanine were combined using click chemistry compared to using the phthalocyanine alone.
- Full Text:
- Authors: Nxele, Siphesihle Robin
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3464 , vital:20501
- Description: Tetrakis(5-hexynoxy)Fe(II) phthalocyanine was used alone and in combination with quantum dots (QDs) in order to test the electrocatalytic ability with hydrazine and paraquat as the analytes of interest. This novel phthalocaynine was successfully synthesised and characterized using various characterisation techniques. The QDs used were the well-known core-shell CdSe/ZnS nanostructures. The fabrication of glassy carbon electrodes involved covalent attachment by electrochemical grafting and click chemistry for the first part of the work and the second part involved the conjugation of the synthesised QDs and the phthalocyanine by click chemistry. This approach of conjugating these nanostructures introduced another aspect of novelty to the work reported in this thesis. The immobilisation of this conjugate on a glassy carbon electrode (GCE) was achieved by adsorption. Characterisation techniques such as infrared spectroscopy, x-ray diffractometry, UV/vis spectroscopy, transmission electron microscopy and x-ray photoelectron spectroscopy were used to characterise the molecules and conjugates of interest. With respect to the electrocatalytic part of the work, electrode surface characterisation involved scanning electrochemical microscopy and cyclic voltammetry to determine changes in the nature of the surface as well as reactivity of the surface at different modification steps. Detection limits and the sensitivity determined for the electrocatalysts fabricated here proved to be an improvement compared to other reported work involving phthalocyanines and the test analytes chosen for application. With respect to the conjugate, the electrocatalytic ability was improved when the QDs and phthalocyanine were combined using click chemistry compared to using the phthalocyanine alone.
- Full Text:
Gold nanoparticle–based colorimetric probes for dopamine detection
- Authors: Ngomane, Nokuthula
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4565 , http://hdl.handle.net/10962/d1021261
- Description: Colorimetric probes have become important tools in analysis and biomedical technology. This thesis reports on the development of such probes for the detection of dopamine (DA). Liquid and different solid state probes were developed utilizing un–functionalized gold nanoparticles (UF–AuNPs). The liquid state probe is based on the growth and aggregation of the UF–AuNPs in the presence of DA. Upon addition of the UF–AuNPs to various concentrations of DA, the shape, size and colour change results in spectral shifts from lower to higher wavelengths. The analyte can be easily monitored by the naked eye from 5.0 nM DA with a calculated limit of detection of 2.5 nM (3σ) under optimal pH. Ascorbic acid (AA) has a potential to interfere with DA detection in solution since it is often present in biological fluids, but in this case the interference was limited to solutions where its concentration was beyond 200 times greater than that of DA. Since most of the previously reported colorimetric probes, especially those for DA are solution based, the main focus of the thesis was in the development of a solid state based colorimetric probe in the form of nanofibre mats. To overcome the interference challenges experienced in the solution studies (the interference by high concentrations of AA), the suitability of molecularly imprinted polymers (MIPs) for the selective detection of DA was investigated. The results showed that the MIPs produced did not play a significant role in enhancing the selectivity towards DA. A probe composed of just the UF–AuNPs and Nylon–6 (UF–AuNPs + N6) was also developed. The UF–AuNPs were synthesized following an in situ reduction method. The probe was only selective to DA and insensitive to other catecholamines at physiological pH. Thus, the probe did not require any addition functionalities to achieve selectivity and sensitive to DA. The liquid state probe and the composite UF–AuNPs + N6 nanofibre probe were successfully applied to a whole blood sample and showed good selectivity towards DA. The simple, sensitive and selective probe could be an excellent alternative for on–site and immediate detection of DA without the use of instrumentation. For quantification of DA using the solid state probe, open–source software imageJ was used to assist in the analysis of the nanofibre colours. It was observed that the intensity of the colour increased with the increase in concentration of DA in a linear fashion. The use of imageJ can also be a great alternative where the colour changes are not so clear or for visually impaired people. The solid state probe developed can detect DA qualitatively and quantitatively. The work also forms a good foundation for development of such probes for other analyte.
- Full Text:
- Authors: Ngomane, Nokuthula
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4565 , http://hdl.handle.net/10962/d1021261
- Description: Colorimetric probes have become important tools in analysis and biomedical technology. This thesis reports on the development of such probes for the detection of dopamine (DA). Liquid and different solid state probes were developed utilizing un–functionalized gold nanoparticles (UF–AuNPs). The liquid state probe is based on the growth and aggregation of the UF–AuNPs in the presence of DA. Upon addition of the UF–AuNPs to various concentrations of DA, the shape, size and colour change results in spectral shifts from lower to higher wavelengths. The analyte can be easily monitored by the naked eye from 5.0 nM DA with a calculated limit of detection of 2.5 nM (3σ) under optimal pH. Ascorbic acid (AA) has a potential to interfere with DA detection in solution since it is often present in biological fluids, but in this case the interference was limited to solutions where its concentration was beyond 200 times greater than that of DA. Since most of the previously reported colorimetric probes, especially those for DA are solution based, the main focus of the thesis was in the development of a solid state based colorimetric probe in the form of nanofibre mats. To overcome the interference challenges experienced in the solution studies (the interference by high concentrations of AA), the suitability of molecularly imprinted polymers (MIPs) for the selective detection of DA was investigated. The results showed that the MIPs produced did not play a significant role in enhancing the selectivity towards DA. A probe composed of just the UF–AuNPs and Nylon–6 (UF–AuNPs + N6) was also developed. The UF–AuNPs were synthesized following an in situ reduction method. The probe was only selective to DA and insensitive to other catecholamines at physiological pH. Thus, the probe did not require any addition functionalities to achieve selectivity and sensitive to DA. The liquid state probe and the composite UF–AuNPs + N6 nanofibre probe were successfully applied to a whole blood sample and showed good selectivity towards DA. The simple, sensitive and selective probe could be an excellent alternative for on–site and immediate detection of DA without the use of instrumentation. For quantification of DA using the solid state probe, open–source software imageJ was used to assist in the analysis of the nanofibre colours. It was observed that the intensity of the colour increased with the increase in concentration of DA in a linear fashion. The use of imageJ can also be a great alternative where the colour changes are not so clear or for visually impaired people. The solid state probe developed can detect DA qualitatively and quantitatively. The work also forms a good foundation for development of such probes for other analyte.
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Improved singlet oxygen generation by a novel bodipy dye and a study of upconverison nanoparticles mixed with a functionalized bodipy compound
- Wildervanck, Martijn Johannes
- Authors: Wildervanck, Martijn Johannes
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3718 , vital:20538
- Description: This research explores the use of the versatile 4,4-difluoro-4-boro-3a,4a-diaza-s-indacene (BODIPY) dyes and the modification of their spectroscopic properties. The synthesis of a tetramethyl-BODIPY bearing a sterically hindered meso-phenyl ring with an ethynyl functional group at the para-position was compared to that of its freely rotating counterpart with no methyl substituents on the BODIPY core, with the fluorescence properties in particular proving to be markedly different. These phenyl-ethynyl-substituted BODIPYs were used as the starting materials for the synthesis of novel BODIPY dyes for sensor applications via Sonogashira coupling reactions at the ethynyl position, but this resulted instead in the serendipitous synthesis of a novel BODIPY dimer in which the para-positions of the meso-phenyl rings are linked by a diethynyl bridge. Following iodination at the 2, 6-positions, the dimer was found to have a singlet oxygen quantum yield of 0.88, compared to the value of 0.86 that was obtained for the analogous monomer. Since the εmax values for the main spectral bands of the dimers are significantly higher, the compounds may be of interest for singlet oxygen generation applications. A second study was carried out on the interaction between methyl ester functionalized BODIPY dyes and upconversion nanoparticles (UCNPs) to explore the possible use of BODIPY-UCNP conjugates in biomedical applications. The singlet oxygen generation properties of the BODIPY were tested following iodination at the 2, 6-positions, a singlet oxygen quantum yield value of 0.86 was obtained. Three sets of oleate capped UCNPs were synthesized with different diameters and were rendered water dispersible with the addition of a silica shell. The necessary scaffolding for conjugation to the BODIPY was provided by amine groups following functionalization of this shell. All of the sets of oleate capped and silica coated UCNPs were characterized by transmission electron microscopy (TEM) and X-ray diffractometry (XRD) and their emission properties were studied upon excitation at 978 nm with a diode laser with a Picoquant Fluotime 300 spectrophotometer that enables the measurement of anti-Stokes emission. The potential utility of UCNP-BODIPY conjugates for singlet oxygen applications, such as PDT, was then assessed.
- Full Text:
- Authors: Wildervanck, Martijn Johannes
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3718 , vital:20538
- Description: This research explores the use of the versatile 4,4-difluoro-4-boro-3a,4a-diaza-s-indacene (BODIPY) dyes and the modification of their spectroscopic properties. The synthesis of a tetramethyl-BODIPY bearing a sterically hindered meso-phenyl ring with an ethynyl functional group at the para-position was compared to that of its freely rotating counterpart with no methyl substituents on the BODIPY core, with the fluorescence properties in particular proving to be markedly different. These phenyl-ethynyl-substituted BODIPYs were used as the starting materials for the synthesis of novel BODIPY dyes for sensor applications via Sonogashira coupling reactions at the ethynyl position, but this resulted instead in the serendipitous synthesis of a novel BODIPY dimer in which the para-positions of the meso-phenyl rings are linked by a diethynyl bridge. Following iodination at the 2, 6-positions, the dimer was found to have a singlet oxygen quantum yield of 0.88, compared to the value of 0.86 that was obtained for the analogous monomer. Since the εmax values for the main spectral bands of the dimers are significantly higher, the compounds may be of interest for singlet oxygen generation applications. A second study was carried out on the interaction between methyl ester functionalized BODIPY dyes and upconversion nanoparticles (UCNPs) to explore the possible use of BODIPY-UCNP conjugates in biomedical applications. The singlet oxygen generation properties of the BODIPY were tested following iodination at the 2, 6-positions, a singlet oxygen quantum yield value of 0.86 was obtained. Three sets of oleate capped UCNPs were synthesized with different diameters and were rendered water dispersible with the addition of a silica shell. The necessary scaffolding for conjugation to the BODIPY was provided by amine groups following functionalization of this shell. All of the sets of oleate capped and silica coated UCNPs were characterized by transmission electron microscopy (TEM) and X-ray diffractometry (XRD) and their emission properties were studied upon excitation at 978 nm with a diode laser with a Picoquant Fluotime 300 spectrophotometer that enables the measurement of anti-Stokes emission. The potential utility of UCNP-BODIPY conjugates for singlet oxygen applications, such as PDT, was then assessed.
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Nanocomposites of carbon nanomaterials and metallophthalocyanines : applications towards electrocatalysis
- Authors: Nyoni, Stephen
- Date: 2016
- Subjects: Nanocomposites (Materials) , Nanostructured materials , Electrocatalysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4561 , http://hdl.handle.net/10962/d1020846
- Description: Nanohybrid materials have been prepared and examined for their electrocatalytic activity. The nanocomposites have been prepared from carbon nanomaterials (multiwalled carbon nanotubes (MWCNTs) and graphene nanosheets), cadmium selenide quantum dots and metallophthalocyanines (MPcs). The MPcs used in this work are cobalt tetraamino-phthalocyanine (CoTAPc) and tetra (4-(4,6-diaminopyrimidin-2-ylthio) phthalocyaninatocobalt (II)) (CoPyPc). Their activity has also been explored in different forms; polymeric MPcs, iodine doped MPcs and covalently linked MPcs. The premixed drop-dry, sequential drop-dry and electropolymerisation electrode modification techniques were used to prepare nanocomposite catalysts on the glassy carbon electrode (GCE) surface. The sequential drop dry technique for MPc and MWCNTs gave better catalytic responses in terms of limit of detection, catalytic and electron transfer rate constants relative to the premixed. MWCNTs and CdSe-QDs have been used as intercalating agents to reduce restacking of graphene nanosheets during nanocomposite preparation. Voltammetry, chronoamperometry, scanning electrochemical microscopy and electrochemical impedance spectroscopy methods are used for electrochemical characterization modified GCE. X-ray photoelectron spectroscopy, X-ray diffractometry, transmission electron microscopy, scanning electron microscopy, infra-red spectroscopy, Raman spectroscopy were used to explore surface functionalities, morphology and topography of the nanocomposites. Electrocatalytic activity and possible applications of the modified electrodes were tested using oxygen reduction reaction, l-cysteine oxidation and paraquat reduction. Activity of nanocomposites was found superior over individual nanomaterials in these applications.
- Full Text:
- Authors: Nyoni, Stephen
- Date: 2016
- Subjects: Nanocomposites (Materials) , Nanostructured materials , Electrocatalysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4561 , http://hdl.handle.net/10962/d1020846
- Description: Nanohybrid materials have been prepared and examined for their electrocatalytic activity. The nanocomposites have been prepared from carbon nanomaterials (multiwalled carbon nanotubes (MWCNTs) and graphene nanosheets), cadmium selenide quantum dots and metallophthalocyanines (MPcs). The MPcs used in this work are cobalt tetraamino-phthalocyanine (CoTAPc) and tetra (4-(4,6-diaminopyrimidin-2-ylthio) phthalocyaninatocobalt (II)) (CoPyPc). Their activity has also been explored in different forms; polymeric MPcs, iodine doped MPcs and covalently linked MPcs. The premixed drop-dry, sequential drop-dry and electropolymerisation electrode modification techniques were used to prepare nanocomposite catalysts on the glassy carbon electrode (GCE) surface. The sequential drop dry technique for MPc and MWCNTs gave better catalytic responses in terms of limit of detection, catalytic and electron transfer rate constants relative to the premixed. MWCNTs and CdSe-QDs have been used as intercalating agents to reduce restacking of graphene nanosheets during nanocomposite preparation. Voltammetry, chronoamperometry, scanning electrochemical microscopy and electrochemical impedance spectroscopy methods are used for electrochemical characterization modified GCE. X-ray photoelectron spectroscopy, X-ray diffractometry, transmission electron microscopy, scanning electron microscopy, infra-red spectroscopy, Raman spectroscopy were used to explore surface functionalities, morphology and topography of the nanocomposites. Electrocatalytic activity and possible applications of the modified electrodes were tested using oxygen reduction reaction, l-cysteine oxidation and paraquat reduction. Activity of nanocomposites was found superior over individual nanomaterials in these applications.
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Study into the synthesis, characterisation and applications of Vanadium-based metal organic frameworks, using 1, 2, 4, 5-benzenetetracarboxylic acid
- Authors: Feldmann, Wesley
- Date: 2016
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/55245 , vital:26680
- Description: This study focussed on the synthesis, characterisation and catalytic application of synthesised vanadium-based Metal-Organic Frameworks using 1,2,4,5-benzenetetracarboxylic acid as a ligand. A number of synthetic methods were tested in multiple attempts to synthesise a V-MOF, these included; ambient, gel, reflux and solvothermal methods of synthesis. Two products of interest were identified, an ambient synthesis produced a vanadium-based complex with the empirical formula: V2O2(Na2H2B4C).6H2O (RU-V2) and a solvothermal synthesis produced a MOF with the empirical formula: V2O2(H2O)2(B4C) (RU-V1). Both products were characterised using elemental analysis, infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry and X-ray powder diffraction. The catalytic activity of these products was tested, alongside the activity of the solid decavanadate ion, for the conversion of cyclohexene to cyclohexene oxide. The decavanadate ion was included to determine if the ion was catalytically active in the solid state, to potentially be used in the construction of a future MOF or V-complex. The reaction for the conversion of cyclohexene to cyclohexene oxide was chosen, as it has been previously conducted using a V-MOF and was found to be successful. The product of the reaction, the epoxide: cyclohexene oxide, is a very useful precursor for a number of reactions involved in the pharmaceutical industry, so developing catalysts which are able to convert cyclohexene to the epoxide with high yields and selectivities are well sought after in industry. The results of the catalytic reactions were varied, as the materials exhibited high yields and selectivities to the epoxide, but these results were only obtained when water was present in the reaction mixture. Water was able to bring about the cleavage of the bonds between the metal and ligand in a highly coordinated framework, at a faster rate than other solvents, such as decane. This ultimately leads to the structural decomposition of the entire complex or framework, depending upon the reaction time. The use of water was a double edged sword in that it was required to initiate the catalytic reaction, but was also the reason that the catalytic materials were noted to decompose over time. The solid decavanadate ion was only noted to exhibit homogeneous activity by dissolving into the small volume of water present in the reaction mixture. The study proved that using a multidentate ligand such as 1,2,4,5-benzenetetracarboxylic acid yielded products which were highly coordinated in nature and would therefore not have large open spaces associated with them, which is commonly observed with other MOFs. Instead the closed nature of the synthesised complexes and frameworks offered a different environment for catalytic reactions, where the small pores/channels had a controlling and inhibiting effect on the reaction. The conversion of cyclohexene to the epoxide is accompanied with a number of undesired side products, so when using the synthesised closed-natured MOF, it was found that there was a greater selectivity for the epoxide over other potential products. This indicates that close natured MOFs may find application in catalytic reactions which require high selectivities for a particular product.
- Full Text:
- Authors: Feldmann, Wesley
- Date: 2016
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/55245 , vital:26680
- Description: This study focussed on the synthesis, characterisation and catalytic application of synthesised vanadium-based Metal-Organic Frameworks using 1,2,4,5-benzenetetracarboxylic acid as a ligand. A number of synthetic methods were tested in multiple attempts to synthesise a V-MOF, these included; ambient, gel, reflux and solvothermal methods of synthesis. Two products of interest were identified, an ambient synthesis produced a vanadium-based complex with the empirical formula: V2O2(Na2H2B4C).6H2O (RU-V2) and a solvothermal synthesis produced a MOF with the empirical formula: V2O2(H2O)2(B4C) (RU-V1). Both products were characterised using elemental analysis, infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry and X-ray powder diffraction. The catalytic activity of these products was tested, alongside the activity of the solid decavanadate ion, for the conversion of cyclohexene to cyclohexene oxide. The decavanadate ion was included to determine if the ion was catalytically active in the solid state, to potentially be used in the construction of a future MOF or V-complex. The reaction for the conversion of cyclohexene to cyclohexene oxide was chosen, as it has been previously conducted using a V-MOF and was found to be successful. The product of the reaction, the epoxide: cyclohexene oxide, is a very useful precursor for a number of reactions involved in the pharmaceutical industry, so developing catalysts which are able to convert cyclohexene to the epoxide with high yields and selectivities are well sought after in industry. The results of the catalytic reactions were varied, as the materials exhibited high yields and selectivities to the epoxide, but these results were only obtained when water was present in the reaction mixture. Water was able to bring about the cleavage of the bonds between the metal and ligand in a highly coordinated framework, at a faster rate than other solvents, such as decane. This ultimately leads to the structural decomposition of the entire complex or framework, depending upon the reaction time. The use of water was a double edged sword in that it was required to initiate the catalytic reaction, but was also the reason that the catalytic materials were noted to decompose over time. The solid decavanadate ion was only noted to exhibit homogeneous activity by dissolving into the small volume of water present in the reaction mixture. The study proved that using a multidentate ligand such as 1,2,4,5-benzenetetracarboxylic acid yielded products which were highly coordinated in nature and would therefore not have large open spaces associated with them, which is commonly observed with other MOFs. Instead the closed nature of the synthesised complexes and frameworks offered a different environment for catalytic reactions, where the small pores/channels had a controlling and inhibiting effect on the reaction. The conversion of cyclohexene to the epoxide is accompanied with a number of undesired side products, so when using the synthesised closed-natured MOF, it was found that there was a greater selectivity for the epoxide over other potential products. This indicates that close natured MOFs may find application in catalytic reactions which require high selectivities for a particular product.
- Full Text:
Synthesis of chiral ketopinic acid-derived catalysts and their evaluation in asymmetric transformations
- Authors: Hassan, Yusuf
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/550 , vital:19969
- Description: Four new (+)-ketopinic acid-derived Mn(III) complexes, three of which possess pseudo C2- symmetry, were synthesised as chiral catalyst candidates. The ligands were prepared by refluxing (+)-ketopinic acid with ethane-1,2-diamine, the resolved (R,R)- and (S,S)-1,2-diaminocyclohexanes, and 1,2-diaminobenzene in chloroform. Treatment of the ligands with manganese(II) acetate tetrahydrate in refluxing ethanol afforded the respective complexes as brown amorphous powders. Characterisation of the ligands and the corresponding complexes was achieved using 1-D and 2-D NMR, IR spectroscopy, and elemental analysis. Various homogeneous asymmetric transformations, were investigated using these four complexes, viz., aldol, and Baylis-Hillman reactions, aza-Michael addition of piperidine to the Baylis-Hillman adducts, epoxidation, and ketone and imine reduction. Asymmetric aldol reactions of benzaldehyde with the aryl ketones, acetophenone, propiophenone, -tetralone, 4-nitroacetophenone, and 4-methoxyacetophenone, conducted in the presence of 10 mole % of the chiral catalysts, afforded enantioselectivities of up to 99% e.e. Asymmetric Baylis-Hillman reactions of methyl- and tert-butyl acrylates with pyridine-2- carbaldehyde, 6-methylpyridine-2-carbaldehyde, 5-chlorosalicylaldehyde, benzaldehyde, 4-chlorobenzaldehyde, and 2-nitrobenzaldehyde were conducted in the presence of catalyst 139 (10 mole %) to afford enantioselectivities of up to 44% e.e. Aza-Michael addition of piperidine to racemic Baylis- Hillman adducts in the presence of the catalyst 139 (10 mole %) was found to proceed with diastereoselectivities of up to 91% d.e. Asymmetric epoxidation of trans-methyl styrene, styrene, trans-stilbene, cis-stilbene, and indene, using a 5 mole % chiral catalyst loading and m-CPBA as the oxygen source, gave enantioselectivities of up to 32 % e.e. Asymmetric reductions of acetophenone, 3-chloropropiophenone, 4-hydroxyacetophenone, -tetralone, and 2-hydroxy-1-acetonapthone were investigated using NaBH4 as the reducing agent and a 10 mole % loading of the chiral catalysts. A stereoselectivity of 68% e.e. was obtained in the reduction of acetophenone, but attempts to reduce the selected imines to the corresponding chiral amines proved to be unsuccessful — even in the absence of the catalysts. It thus became apparent that the catalytic version of the reaction was not feasible.
- Full Text:
- Authors: Hassan, Yusuf
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/550 , vital:19969
- Description: Four new (+)-ketopinic acid-derived Mn(III) complexes, three of which possess pseudo C2- symmetry, were synthesised as chiral catalyst candidates. The ligands were prepared by refluxing (+)-ketopinic acid with ethane-1,2-diamine, the resolved (R,R)- and (S,S)-1,2-diaminocyclohexanes, and 1,2-diaminobenzene in chloroform. Treatment of the ligands with manganese(II) acetate tetrahydrate in refluxing ethanol afforded the respective complexes as brown amorphous powders. Characterisation of the ligands and the corresponding complexes was achieved using 1-D and 2-D NMR, IR spectroscopy, and elemental analysis. Various homogeneous asymmetric transformations, were investigated using these four complexes, viz., aldol, and Baylis-Hillman reactions, aza-Michael addition of piperidine to the Baylis-Hillman adducts, epoxidation, and ketone and imine reduction. Asymmetric aldol reactions of benzaldehyde with the aryl ketones, acetophenone, propiophenone, -tetralone, 4-nitroacetophenone, and 4-methoxyacetophenone, conducted in the presence of 10 mole % of the chiral catalysts, afforded enantioselectivities of up to 99% e.e. Asymmetric Baylis-Hillman reactions of methyl- and tert-butyl acrylates with pyridine-2- carbaldehyde, 6-methylpyridine-2-carbaldehyde, 5-chlorosalicylaldehyde, benzaldehyde, 4-chlorobenzaldehyde, and 2-nitrobenzaldehyde were conducted in the presence of catalyst 139 (10 mole %) to afford enantioselectivities of up to 44% e.e. Aza-Michael addition of piperidine to racemic Baylis- Hillman adducts in the presence of the catalyst 139 (10 mole %) was found to proceed with diastereoselectivities of up to 91% d.e. Asymmetric epoxidation of trans-methyl styrene, styrene, trans-stilbene, cis-stilbene, and indene, using a 5 mole % chiral catalyst loading and m-CPBA as the oxygen source, gave enantioselectivities of up to 32 % e.e. Asymmetric reductions of acetophenone, 3-chloropropiophenone, 4-hydroxyacetophenone, -tetralone, and 2-hydroxy-1-acetonapthone were investigated using NaBH4 as the reducing agent and a 10 mole % loading of the chiral catalysts. A stereoselectivity of 68% e.e. was obtained in the reduction of acetophenone, but attempts to reduce the selected imines to the corresponding chiral amines proved to be unsuccessful — even in the absence of the catalysts. It thus became apparent that the catalytic version of the reaction was not feasible.
- Full Text:
Synthesis, spectroscopic and nonlinear optical properties of metal-free and nickel β substituted binuclear phthalocyanines
- Authors: Kabwe, Kapambwe Peter
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3013 , vital:20352
- Description: In this project, nickel and metal-free 4β-(4-tert-butylphenoxy) phthalocyanine, biphenyl bridged binuclear 4-tert-butylphenoxy phthalocyanine and naphthalene bridged binuclear 4-tert-butylphenoxy phthalocyanine have been synthesised. The Z-scan technique has been employed to comparatively study their second order nonlinear optical (NLO) properties. This work, shows that the presence of H-aggregation in binuclear Pcs of metal-free and nickel 4β-(4-tertbutylphenoxy) phthalocyanines do not have an effect on the magnitude of second order nonlinear absorption coefficient (β) as compared to monomeric Pcs. Density functional (DFT) calculations of dipolar/octupolar contributions were performed, in order to explain experimentally determined β values. Spectroscopic and photophysical properties of the synthesised compounds have been determined using a range of different spectroscopic techniques, including magnetic circular dichroism (MCD), time correlated single photon counting spectroscopy (TCSPC), UV-visible absorption spectroscopy, mass spectroscopy and IR Spectroscopy.
- Full Text:
- Authors: Kabwe, Kapambwe Peter
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3013 , vital:20352
- Description: In this project, nickel and metal-free 4β-(4-tert-butylphenoxy) phthalocyanine, biphenyl bridged binuclear 4-tert-butylphenoxy phthalocyanine and naphthalene bridged binuclear 4-tert-butylphenoxy phthalocyanine have been synthesised. The Z-scan technique has been employed to comparatively study their second order nonlinear optical (NLO) properties. This work, shows that the presence of H-aggregation in binuclear Pcs of metal-free and nickel 4β-(4-tertbutylphenoxy) phthalocyanines do not have an effect on the magnitude of second order nonlinear absorption coefficient (β) as compared to monomeric Pcs. Density functional (DFT) calculations of dipolar/octupolar contributions were performed, in order to explain experimentally determined β values. Spectroscopic and photophysical properties of the synthesised compounds have been determined using a range of different spectroscopic techniques, including magnetic circular dichroism (MCD), time correlated single photon counting spectroscopy (TCSPC), UV-visible absorption spectroscopy, mass spectroscopy and IR Spectroscopy.
- Full Text:
The chemistry of Algoa Bay ascidians
- Authors: Bromley, Candice Leigh
- Date: 2016
- Subjects: Sea squirts -- South Africa -- Algoa Bay , Marine metabolites , Chemistry, Analytic , Liquid chromatography , Inductively coupled plasma mass spectrometry , Metal ions , Nucleosides , Vanadium
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4560 , http://hdl.handle.net/10962/d1020606
- Description: This thesis investigates the chemistry of 25 ascidian species collected from Algoa Bay, South Africa with a concerted focus on metal accumulation by these ascidians and the possible interaction of these metals with ascidian metabolites. Chapter 2 details the screening techniques employed to establish the presence of nitrogenous metabolites (1H- 15N HMBC), hyper-accumulated metal ions (ICP-MS) and potential metal ion/ ascidian metabolite complexes (LC-ICP-MS/ESI-MS). Unfortunately, exhaustive attempts to detect intact metal ion/ascidian metabolite complexes through the use of liquid chromatography with parallel inductively coupled plasma mass spectrometry/electrospray mass spectrometry (LC-ICPMS/ ESI-MS) were unsuccessful. However, the LC-ICP-MS/ESI-MS data obtained for the crude organic extracts of six of the Algoa Bay ascidian species, Distaplia skoogi, Aplidium monile, Aplidium sp., Didemnum sp., Leptoclindines sp. and Polycitor sp. enabled identification of a number of ten halogenated metabolites, namely the indoles 2.28-2.30, and the tyramine and tyrosine derivatives (2.31-2.33, 2.41, 2.43, 2.44 and 2.46), within the ascidian extracts. This study confirmed that LC-ICP-MS/ESI-MS is a powerful tool for the dereplication of halogenated metabolites in complex mixtures especially where these compounds are present in very small amounts. This study is also the first report of these compounds (eight of which are known) in African ascidians. Compounds 2.32 and 2.46 have not been reported before from a marine source. Compounds 2.28-2.30 and 2.33 were present in sufficient amounts in the respective ascidian extracts to allow their isolation and structure elucidation using standard spectroscopic techniques Chapter 3 explores the ability of ascidians to accumulate a wide range of metal ions at concentrations which are often orders of magnitude higher than those of the surrounding sea water. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the total ion concentrations of 24 metals in 25 Algoa Bay ascidian species. To the best of our knowledge this is the largest and most extensive investigation of metal concentrations in a group of different ascidians occurring in the same area. Hypotheisizing that the metal ion concentrations for each ascidian specimen screened may represent a unique fingerprint for each specimen principal component analysis (PCA) was used in an attempt to establish whether there were spatial, temporal or phylogenetic relationships associated with the metal concentration fingerprints of the ascidians that formed part of this study. The PCA results showed that there were no statistically significant relationships between ascidian metal ion concentrations and either the collection year or the collection site of the ascidians. However, species from the family Didemnidae provided the clearest statistical evidence supporting a phylogenetic relationship between these ascidians and their hyperaccumulated metal ion profiles. Furthermore, these results suggested that ascidian species are indeed actively concentrating metal ions from the surrounding sea water and are not simply sinks for passively accumulated metal ions. Interestingly, the concentration of vanadium in the set of ascidians studied did not appear to correlate with any of the other metals accumulated by these ascidians suggesting that there is possibly a unique method employed for the accumulation of vanadium by ascidians. Chapter 4 investigated this possibility further after the nucleosides 4.10, 4.11, 4.13, 4.15, 4.17 and 4.40 were isolated from the vanadium accumulating ascidian Aplidium monile. Studies into the interactions between nucleosides and vanadyl are unfortunately rare and usually qualitative in nature with limited information provided about the stability or structures of the complexes formed. The vanadyl accumulating aplousobranch ascidians e.g. Aplidium monile dominated our study of Algoa Bay ascidians therefore providing us with the rationale to investigate the relatively little studied binding ability and stability of vandyl-nucleoside complexes. Potentiometric studies were conducted to determine the stability constants of complexes formed between the oxovanadium ion vanadyl (VO2+) and the commercially available nucleosides 4.10-4.14. The data afforded by this analysis clearly confirmed the complexity of the vanadyl/nucleoside complexation and suggested that guanosine (4.12) formed the most stable complex with oxovanadium ions. We were also able to establish a third protonation constant for the hydroxyl moiety in 4.12 with a logK 8.87 which has not been previously reported. Finally, Chapter 5 revisited the cytoxicity two Algoa Bay ascidians, Clavelina sp. and Atriolum marinense the extracts from which produced promising bioactivity results in previous studies against oesophageal cancer cells. The HP-20 fractionated extracts of Clavelina sp. and Atriolum marinense proved to be similalrly cytotoxic to breast cancer cells. With the exception for the 100% acetone(aq)fractions the NMR data for both species suggested that most active non polar fractions were dominated by what appeared to be structurally unremarkable fatty acid glycerides and as such were not pursued further. Purification of the 100% acetone(aq)fraction of A. marinense resulted in the isolation of a styrene trimer, 5.1, common to both ascidian extracts. The NMR simulation software WIN-DAISY was employed to confirm the structure of 5.1. Attempts to establish if 5.1 was an isolation artefact or a product of marine pollution were inconclusive
- Full Text:
- Authors: Bromley, Candice Leigh
- Date: 2016
- Subjects: Sea squirts -- South Africa -- Algoa Bay , Marine metabolites , Chemistry, Analytic , Liquid chromatography , Inductively coupled plasma mass spectrometry , Metal ions , Nucleosides , Vanadium
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4560 , http://hdl.handle.net/10962/d1020606
- Description: This thesis investigates the chemistry of 25 ascidian species collected from Algoa Bay, South Africa with a concerted focus on metal accumulation by these ascidians and the possible interaction of these metals with ascidian metabolites. Chapter 2 details the screening techniques employed to establish the presence of nitrogenous metabolites (1H- 15N HMBC), hyper-accumulated metal ions (ICP-MS) and potential metal ion/ ascidian metabolite complexes (LC-ICP-MS/ESI-MS). Unfortunately, exhaustive attempts to detect intact metal ion/ascidian metabolite complexes through the use of liquid chromatography with parallel inductively coupled plasma mass spectrometry/electrospray mass spectrometry (LC-ICPMS/ ESI-MS) were unsuccessful. However, the LC-ICP-MS/ESI-MS data obtained for the crude organic extracts of six of the Algoa Bay ascidian species, Distaplia skoogi, Aplidium monile, Aplidium sp., Didemnum sp., Leptoclindines sp. and Polycitor sp. enabled identification of a number of ten halogenated metabolites, namely the indoles 2.28-2.30, and the tyramine and tyrosine derivatives (2.31-2.33, 2.41, 2.43, 2.44 and 2.46), within the ascidian extracts. This study confirmed that LC-ICP-MS/ESI-MS is a powerful tool for the dereplication of halogenated metabolites in complex mixtures especially where these compounds are present in very small amounts. This study is also the first report of these compounds (eight of which are known) in African ascidians. Compounds 2.32 and 2.46 have not been reported before from a marine source. Compounds 2.28-2.30 and 2.33 were present in sufficient amounts in the respective ascidian extracts to allow their isolation and structure elucidation using standard spectroscopic techniques Chapter 3 explores the ability of ascidians to accumulate a wide range of metal ions at concentrations which are often orders of magnitude higher than those of the surrounding sea water. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the total ion concentrations of 24 metals in 25 Algoa Bay ascidian species. To the best of our knowledge this is the largest and most extensive investigation of metal concentrations in a group of different ascidians occurring in the same area. Hypotheisizing that the metal ion concentrations for each ascidian specimen screened may represent a unique fingerprint for each specimen principal component analysis (PCA) was used in an attempt to establish whether there were spatial, temporal or phylogenetic relationships associated with the metal concentration fingerprints of the ascidians that formed part of this study. The PCA results showed that there were no statistically significant relationships between ascidian metal ion concentrations and either the collection year or the collection site of the ascidians. However, species from the family Didemnidae provided the clearest statistical evidence supporting a phylogenetic relationship between these ascidians and their hyperaccumulated metal ion profiles. Furthermore, these results suggested that ascidian species are indeed actively concentrating metal ions from the surrounding sea water and are not simply sinks for passively accumulated metal ions. Interestingly, the concentration of vanadium in the set of ascidians studied did not appear to correlate with any of the other metals accumulated by these ascidians suggesting that there is possibly a unique method employed for the accumulation of vanadium by ascidians. Chapter 4 investigated this possibility further after the nucleosides 4.10, 4.11, 4.13, 4.15, 4.17 and 4.40 were isolated from the vanadium accumulating ascidian Aplidium monile. Studies into the interactions between nucleosides and vanadyl are unfortunately rare and usually qualitative in nature with limited information provided about the stability or structures of the complexes formed. The vanadyl accumulating aplousobranch ascidians e.g. Aplidium monile dominated our study of Algoa Bay ascidians therefore providing us with the rationale to investigate the relatively little studied binding ability and stability of vandyl-nucleoside complexes. Potentiometric studies were conducted to determine the stability constants of complexes formed between the oxovanadium ion vanadyl (VO2+) and the commercially available nucleosides 4.10-4.14. The data afforded by this analysis clearly confirmed the complexity of the vanadyl/nucleoside complexation and suggested that guanosine (4.12) formed the most stable complex with oxovanadium ions. We were also able to establish a third protonation constant for the hydroxyl moiety in 4.12 with a logK 8.87 which has not been previously reported. Finally, Chapter 5 revisited the cytoxicity two Algoa Bay ascidians, Clavelina sp. and Atriolum marinense the extracts from which produced promising bioactivity results in previous studies against oesophageal cancer cells. The HP-20 fractionated extracts of Clavelina sp. and Atriolum marinense proved to be similalrly cytotoxic to breast cancer cells. With the exception for the 100% acetone(aq)fractions the NMR data for both species suggested that most active non polar fractions were dominated by what appeared to be structurally unremarkable fatty acid glycerides and as such were not pursued further. Purification of the 100% acetone(aq)fraction of A. marinense resulted in the isolation of a styrene trimer, 5.1, common to both ascidian extracts. The NMR simulation software WIN-DAISY was employed to confirm the structure of 5.1. Attempts to establish if 5.1 was an isolation artefact or a product of marine pollution were inconclusive
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The effect of shaped nanoparticles on the photophysicochemical behaviour of metallophthalocyanines
- Authors: D'Souza, Sarah
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/529 , vital:19967
- Description: The synthesis, spectroscopic characterization and photophysicochemical analysis of novel and known metallophthalocyanines are reported in this thesis. The novel lowsymmetry compounds were extensively studied. Selected phthalocyanines were conjugated to a variety of nanoparticles consisting of silver (AgNPs), gold (AuNPs) and zinc oxide (ZnO NPs) in order to improve their photophysical and photochemical behaviour. As with the phthalocyanines, the nanoparticles and phthalocyaninenanoparticle conjugates were thoroughly investigated. Research on the effect of the solvent used, as well as the influence of nanoparticle composition and shape on the properties of the phthalocyanines, were performed. The findings showed that there was a general increase in triplet quantum yields of the phthalocyanines in the presence of the nanoparticles. It was also noted that the use of different solvents directly affected the photophysicochemical properties. In the case of the nanoparticle conjugates, photophysical and photochemical changes were observed. Of significance were the gold nanostars, which decreased the degree of phthalocyanine aggregation in water, resulting in increased fluorescence lifetimes. The studies also revealed that the effect of the nanoparticle shape on the phthalocyanine properties was highly dependent on the nanoparticle material. The photodynamic antimicrobial activity of selected phthalocyanine-zinc oxide nanoparticle conjugates was investigated against Staphylococcus aureus (S. aureus) in solution. The phthalocyanines alone exhibited remarkable growth inhibition, however the presence of the nanoparticles in the conjugates increased the photoinactivation of S. aureus.
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- Authors: D'Souza, Sarah
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/529 , vital:19967
- Description: The synthesis, spectroscopic characterization and photophysicochemical analysis of novel and known metallophthalocyanines are reported in this thesis. The novel lowsymmetry compounds were extensively studied. Selected phthalocyanines were conjugated to a variety of nanoparticles consisting of silver (AgNPs), gold (AuNPs) and zinc oxide (ZnO NPs) in order to improve their photophysical and photochemical behaviour. As with the phthalocyanines, the nanoparticles and phthalocyaninenanoparticle conjugates were thoroughly investigated. Research on the effect of the solvent used, as well as the influence of nanoparticle composition and shape on the properties of the phthalocyanines, were performed. The findings showed that there was a general increase in triplet quantum yields of the phthalocyanines in the presence of the nanoparticles. It was also noted that the use of different solvents directly affected the photophysicochemical properties. In the case of the nanoparticle conjugates, photophysical and photochemical changes were observed. Of significance were the gold nanostars, which decreased the degree of phthalocyanine aggregation in water, resulting in increased fluorescence lifetimes. The studies also revealed that the effect of the nanoparticle shape on the phthalocyanine properties was highly dependent on the nanoparticle material. The photodynamic antimicrobial activity of selected phthalocyanine-zinc oxide nanoparticle conjugates was investigated against Staphylococcus aureus (S. aureus) in solution. The phthalocyanines alone exhibited remarkable growth inhibition, however the presence of the nanoparticles in the conjugates increased the photoinactivation of S. aureus.
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The removal of toxic anions from wastewater using electrospun nanofibers
- Authors: Moronkola, Bridget Adekemi
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4564 , http://hdl.handle.net/10962/d1020991
- Description: The presence of arsenic and phosphate in waters, especially wastewater, has become a worldwide problem even till the present time. The current regulation of drinking standard water has become more stringent and requires arsenic content to be reduced to a few parts per billion. Nevertheless, phosphorous pollution, known as the eutrophication, is regarded as one of the main causes of water quality deterioration. Hence, the decontamination of phosphorous from aqueous solutions is of importance for eutrophication control and phosphorous recovery. Efforts are being made to remove these contaminants, arsenic (v) and phosphate from wastewater using low cost adsorbents. In the present study, removal of arsenic(v) and phosphate from wastewater using two novel fabricated sorbent materials; polyvinylmethylketone functionalized 2-amino4,6-dihydroxylpyrimidine (APPMKNFs) prepared via a Schiff base condensation reaction and aminated polyvinylbenzylchloride (PVBC) prepared through a substitution reaction and then quaternized using three alkyl groups (R’ = CH₃, C₂H₅ and C₃H₇) were investigated. The experiments were carried out in batch and solid phase extraction mode. Preliminary experiments were done with series of four sorbent materials (APPMKNFs, R’ = CH₃, C₂H₅ and C₃H₇) in order to find out a suitable and low cost adsorbents for the effective removal of arsenic (v) and phosphate. The best sorbent materials were obtained after the optimization and preparation experiments. The APPMKNFs and R’ = CH₃ were effective for arsenic (v) and phosphate removal from wastewater. The effect of pH, initial sorbate concentration, amount of sorbent, effect of co-exisiting anions and the reusability in batch and solid phase extraction mode were also investigated. From the experiment conducted, the pH shows a decisive factor on arsenic and phosphate removal. Analysis of adsorbent dosage, Kinetic studies and co-existing anions were carried out in order to evaluate sorption parameters. The adsorption isotherms were well fitted by Langmuir than Freundlch isotherm for (APPMKNFs). And more...
- Full Text:
- Authors: Moronkola, Bridget Adekemi
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4564 , http://hdl.handle.net/10962/d1020991
- Description: The presence of arsenic and phosphate in waters, especially wastewater, has become a worldwide problem even till the present time. The current regulation of drinking standard water has become more stringent and requires arsenic content to be reduced to a few parts per billion. Nevertheless, phosphorous pollution, known as the eutrophication, is regarded as one of the main causes of water quality deterioration. Hence, the decontamination of phosphorous from aqueous solutions is of importance for eutrophication control and phosphorous recovery. Efforts are being made to remove these contaminants, arsenic (v) and phosphate from wastewater using low cost adsorbents. In the present study, removal of arsenic(v) and phosphate from wastewater using two novel fabricated sorbent materials; polyvinylmethylketone functionalized 2-amino4,6-dihydroxylpyrimidine (APPMKNFs) prepared via a Schiff base condensation reaction and aminated polyvinylbenzylchloride (PVBC) prepared through a substitution reaction and then quaternized using three alkyl groups (R’ = CH₃, C₂H₅ and C₃H₇) were investigated. The experiments were carried out in batch and solid phase extraction mode. Preliminary experiments were done with series of four sorbent materials (APPMKNFs, R’ = CH₃, C₂H₅ and C₃H₇) in order to find out a suitable and low cost adsorbents for the effective removal of arsenic (v) and phosphate. The best sorbent materials were obtained after the optimization and preparation experiments. The APPMKNFs and R’ = CH₃ were effective for arsenic (v) and phosphate removal from wastewater. The effect of pH, initial sorbate concentration, amount of sorbent, effect of co-exisiting anions and the reusability in batch and solid phase extraction mode were also investigated. From the experiment conducted, the pH shows a decisive factor on arsenic and phosphate removal. Analysis of adsorbent dosage, Kinetic studies and co-existing anions were carried out in order to evaluate sorption parameters. The adsorption isotherms were well fitted by Langmuir than Freundlch isotherm for (APPMKNFs). And more...
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Application of Baylis-Hillman methodology in the synthesis of HIV-1 enzyme inhibitors
- Authors: Manyeruke, Meloddy Hlatini
- Date: 2015
- Subjects: HIV infections , Enzyme inhibitors , AZT (Drug) , Bioconjugates
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4540 , http://hdl.handle.net/10962/d1017920
- Description: The application of Baylis-Hillman methodology has afforded access to a range of β-hydroxypropionate ester-AZT conjugates as potential dual-action HIV-1 IN/RT inhibitors. Two families comprising a total of nine β-hydroxypropionate ester-AZT conjugates were synthesised. The first family was accessed using O-benzylated salicylaldehydes and methyl acrylate and the second from unprotected salicylaldehydes using tert-butyl acrylate as the activated alkene. Spectroscopic methods were employed to fully characterize the compounds. Propargylation of the respective Baylis-Hillman adducts was achieved via conjugate addition of propargylamine. The resulting products were then employed in Cu(I)-catalysed “click” reactions with azidothymidine (AZT) to yield the desired β-hydroxypropionate ester-AZT conjugates. Exploratory studies were also conducted to access 4-hydroxycoumarins from Baylis-Hillman derived adducts and to construct customized chiral Baylis-Hillman reaction sites. Many 4- hydroxycoumarins are known to exhibit a wide range of biological activities, and extending Baylis-Hillman methodology to access these systems is an important challenge. Two approaches were investigated. The first involved the formation of a 4-phthalimidocoumarin, aromatisation and hydrolysis of which was expected to lead to the 4-hydroxycoumarin target. The second, a variation of the first, involved the use of 4-(chrolomethyl)coumarin intermediates. Unfortunately, while various intermediates were prepared and characterised, neither approach led ultimately to the desired targets. N-substituted borneol-10-sulfonamides were constructed from camphor-10- sulfonyl chloride as chiral Baylis-Hillman reaction sites. In a preliminary study, however, none of the N-substituted borneol-10-sulfonamides exhibited Baylis-Hillman catalytic activity.
- Full Text:
- Authors: Manyeruke, Meloddy Hlatini
- Date: 2015
- Subjects: HIV infections , Enzyme inhibitors , AZT (Drug) , Bioconjugates
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4540 , http://hdl.handle.net/10962/d1017920
- Description: The application of Baylis-Hillman methodology has afforded access to a range of β-hydroxypropionate ester-AZT conjugates as potential dual-action HIV-1 IN/RT inhibitors. Two families comprising a total of nine β-hydroxypropionate ester-AZT conjugates were synthesised. The first family was accessed using O-benzylated salicylaldehydes and methyl acrylate and the second from unprotected salicylaldehydes using tert-butyl acrylate as the activated alkene. Spectroscopic methods were employed to fully characterize the compounds. Propargylation of the respective Baylis-Hillman adducts was achieved via conjugate addition of propargylamine. The resulting products were then employed in Cu(I)-catalysed “click” reactions with azidothymidine (AZT) to yield the desired β-hydroxypropionate ester-AZT conjugates. Exploratory studies were also conducted to access 4-hydroxycoumarins from Baylis-Hillman derived adducts and to construct customized chiral Baylis-Hillman reaction sites. Many 4- hydroxycoumarins are known to exhibit a wide range of biological activities, and extending Baylis-Hillman methodology to access these systems is an important challenge. Two approaches were investigated. The first involved the formation of a 4-phthalimidocoumarin, aromatisation and hydrolysis of which was expected to lead to the 4-hydroxycoumarin target. The second, a variation of the first, involved the use of 4-(chrolomethyl)coumarin intermediates. Unfortunately, while various intermediates were prepared and characterised, neither approach led ultimately to the desired targets. N-substituted borneol-10-sulfonamides were constructed from camphor-10- sulfonyl chloride as chiral Baylis-Hillman reaction sites. In a preliminary study, however, none of the N-substituted borneol-10-sulfonamides exhibited Baylis-Hillman catalytic activity.
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Design, development and evaluation of novel lead compounds as HIV-1 enzyme inhibitors
- Authors: Sekgota, Khethobole Cassius
- Date: 2015
- Subjects: Enzyme inhibitors , Viruses -- Reproduction , HIV (Viruses)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4546 , http://hdl.handle.net/10962/d1017926
- Description: This project has been concerned with the application of the Baylis-Hillman methodology to the synthesis of medicinally important diketo acid analogues (cinnamate ester-AZT conjugates and 3-hydroxy ester-AZT conjugates) as dual-action HIV-1 IN/RT inhibitors; and on exploratory studies in the preparation of 3-(amidomethyl)-(1H)-2-quinolones as PR inhibitors; and (1H)-2- quinolone-AZT conjugates as dual action IN/RT inhibitors. A series of Baylis-Hillman adducts has been prepared, typically in moderate to excellent yield, by reacting 2-nitrobenzaldehyde with methyl acrylate, ethyl acrylate and methyl vinyl ketone in the presence of 1,4- diazabicyclo[2.2.2]octane (DABCO). Subsequently, various transformations that include conjugate addition of primary and secondary amines to the α,ß-unsaturated moiety to obtain 2- (aminomethyl)-3-hydroxy-3-(2-nitrophenyl)propanoate derivatives, effective SN2´ substitution of the BH ß-hydroxy by a Vilsmeier-Haack in situ-generated chloride to afford Baylis-Hillman allyl chlorides, iron in acetic acid-catalyzed cyclisation to 3-acetoxymethyl-(1H)-2-quinolone derivatives were achieved. Thus, using the Baylis-Hillman methodology, two nuanced classes of diketo acid analogues were constructed. These involved conjugating appropriate propargylamine derivatives with AZT using the „click‟ reaction. In an exploratory study, the quinolone derivative, precisely 3-acetoxymethyl- (1H)-quinol-2-one, was transformed into 3-hydroxymethyl-(1H)-quinol-2-one using potassium carbonate in a mixture of methanol and water (1:1). Following successful hydrolysis, the resulting alcohol was transformed to the corresponding chloride, 3-chloromethyl-(1H)-quinol-2- one, using thionyl chloride. Subsequent nucleophilic substitution afforded 3-(aminomethyl)- (1H)-2-quinolone derivatives which were subsequently transformed to 3-(amidomethyl)-(1H)-2- quinolones; and 3-[(propargylamino)-methyl]-(1H)-quinol-2-one as precursors to quinolone- AZT derivatives. All compounds were characterized by NMR, IR, and where appropriate, high resolution MS
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- Authors: Sekgota, Khethobole Cassius
- Date: 2015
- Subjects: Enzyme inhibitors , Viruses -- Reproduction , HIV (Viruses)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4546 , http://hdl.handle.net/10962/d1017926
- Description: This project has been concerned with the application of the Baylis-Hillman methodology to the synthesis of medicinally important diketo acid analogues (cinnamate ester-AZT conjugates and 3-hydroxy ester-AZT conjugates) as dual-action HIV-1 IN/RT inhibitors; and on exploratory studies in the preparation of 3-(amidomethyl)-(1H)-2-quinolones as PR inhibitors; and (1H)-2- quinolone-AZT conjugates as dual action IN/RT inhibitors. A series of Baylis-Hillman adducts has been prepared, typically in moderate to excellent yield, by reacting 2-nitrobenzaldehyde with methyl acrylate, ethyl acrylate and methyl vinyl ketone in the presence of 1,4- diazabicyclo[2.2.2]octane (DABCO). Subsequently, various transformations that include conjugate addition of primary and secondary amines to the α,ß-unsaturated moiety to obtain 2- (aminomethyl)-3-hydroxy-3-(2-nitrophenyl)propanoate derivatives, effective SN2´ substitution of the BH ß-hydroxy by a Vilsmeier-Haack in situ-generated chloride to afford Baylis-Hillman allyl chlorides, iron in acetic acid-catalyzed cyclisation to 3-acetoxymethyl-(1H)-2-quinolone derivatives were achieved. Thus, using the Baylis-Hillman methodology, two nuanced classes of diketo acid analogues were constructed. These involved conjugating appropriate propargylamine derivatives with AZT using the „click‟ reaction. In an exploratory study, the quinolone derivative, precisely 3-acetoxymethyl- (1H)-quinol-2-one, was transformed into 3-hydroxymethyl-(1H)-quinol-2-one using potassium carbonate in a mixture of methanol and water (1:1). Following successful hydrolysis, the resulting alcohol was transformed to the corresponding chloride, 3-chloromethyl-(1H)-quinol-2- one, using thionyl chloride. Subsequent nucleophilic substitution afforded 3-(aminomethyl)- (1H)-2-quinolone derivatives which were subsequently transformed to 3-(amidomethyl)-(1H)-2- quinolones; and 3-[(propargylamino)-methyl]-(1H)-quinol-2-one as precursors to quinolone- AZT derivatives. All compounds were characterized by NMR, IR, and where appropriate, high resolution MS
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Electrode surface modification using metallophthalocyanines and metal nanoparticles : electrocatalytic activity
- Authors: Maringa, Audacity
- Date: 2015
- Subjects: Phthalocyanines , Nanoparticles , Electrocatalysis , Scanning electron microscopy , X-ray photoelectron spectroscopy , Electrochemistry , Scanning electrochemical microscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4541 , http://hdl.handle.net/10962/d1017921
- Description: Metallophthalocyanines and metal nanoparticles were successfully synthesized and applied for the electrooxidation of amitrole, nitrite and hydrazine individually or when employed together. The synthesized materials were characterized using the following techniques: predominantly scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemistry and scanning electrochemical microscopy (SECM). Different electrode modification methods were used to modify the glassy carbon substrates. The methods include adsorption, electrodeposition, electropolymerization and click chemistry. Modifying the glassy carbon substrate with MPc (electropolymerization) followed by metal nanoparticles (electrodeposition) or vice versa, made a hybrid modified surface that had efficient electron transfer. This was confirmed by electrochemical impedance studies with voltammetry measurements having lower detection potentials for the analytes. This work also describes for the first time the micropatterning of the glassy carbon substrate using the SECM tip. The substrate was electrografted with 4-azidobenzenediazonium salt and then the click reaction was performed using ethynylferrocene facilitated by Cu⁺ produced at the SECM tip. The SECM imaging was then used to show the clicked spot.
- Full Text:
- Authors: Maringa, Audacity
- Date: 2015
- Subjects: Phthalocyanines , Nanoparticles , Electrocatalysis , Scanning electron microscopy , X-ray photoelectron spectroscopy , Electrochemistry , Scanning electrochemical microscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4541 , http://hdl.handle.net/10962/d1017921
- Description: Metallophthalocyanines and metal nanoparticles were successfully synthesized and applied for the electrooxidation of amitrole, nitrite and hydrazine individually or when employed together. The synthesized materials were characterized using the following techniques: predominantly scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemistry and scanning electrochemical microscopy (SECM). Different electrode modification methods were used to modify the glassy carbon substrates. The methods include adsorption, electrodeposition, electropolymerization and click chemistry. Modifying the glassy carbon substrate with MPc (electropolymerization) followed by metal nanoparticles (electrodeposition) or vice versa, made a hybrid modified surface that had efficient electron transfer. This was confirmed by electrochemical impedance studies with voltammetry measurements having lower detection potentials for the analytes. This work also describes for the first time the micropatterning of the glassy carbon substrate using the SECM tip. The substrate was electrografted with 4-azidobenzenediazonium salt and then the click reaction was performed using ethynylferrocene facilitated by Cu⁺ produced at the SECM tip. The SECM imaging was then used to show the clicked spot.
- Full Text: