Studies towards the development of novel multidentate ligands
- Authors: Magqi, Nceba
- Date: 2007
- Subjects: Density functionals , Ligands , Ligands -- Design , Ligands -- Analysis , Camphor
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4358 , http://hdl.handle.net/10962/d1005023 , Density functionals , Ligands , Ligands -- Design , Ligands -- Analysis , Camphor
- Description: In this study, attention has been given to the design and synthesis of novel multidentate ligands for use in the construction of ruthenium-based metathesis catalysts, and their chelating potential has been explored by computer modelling at the Density Functional Theory (DFT) level. Both Kemp’s triacid (1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic acid) and D-(+)-camphor have been investigated as molecular scaffolds for the development of such ligands. However selective elaboration of the functional groups in Kemp’s triacid proved difficult to achieve, and the research has focused on the development of camphor derivatives. The synthesis of the camphor-based ligands has involved C-8 functionalisation and ring-opening of the bicyclic system to afford tridentate products. The formation of 9-iodocamphorquinone bis(ethylene ketal) together with the desired product, the 8-iodo isomer, has been confirmed by single crystal X-ray analysis of both compounds. Formation of the 9-iodo analogue has provided new insights into the intramolecular rearrangement of camphor skeleton, and the mechanistic implications have been assessed by coset analysis. Attempts to effect nucleophilic displacement of the 8-halogeno groups by nucleophilic donor moieties proved unexpectedly difficult and, coupled with the susceptibility of the carbonyl groups to nucleophilic attack, has led to the formation of novel tricyclic products, viz., 1,6-dimethyl-3-(2-pyridylamino)-4-oxatricyclo[4.3.0.0[superscript 3,7]]-2-nonanone and 6,7-dimethyl-3-(2-pyridylamino)-4-oxatricyclo -[4.3.0.0[superscript 3,7]]-2-nonanone. However the diphenylphosphine group was successfully introduced at C-8 and oxidative ring-opening of the camphor skeleton has afforded the tridentate ligands, 2-(diphenylphosphinoylmethyl)-1,2-dimethyl-1,3-cyclopentanedicarboxylic acid and 2-(diphenylphosphinoylmethyl)-1,3-bis(hydroxymethyl)1,2-dimethylcyclopentane. One- and two-dimensional NMR and, where appropriate, high-resolution MS methods have been used to characterise the products. Three [superscript 13]C NMR chemical shift prediction programmes, viz., ChemWindow and the MODGRAPH neural network and HOSE (Hierachially Ordered Spherical description of Environment), have been applied to representative compounds to assess their efficacy. While the predicted shifts correlated reasonably well with the experimental data, they proved to be insufficiently accurate to differentiate the isomeric systems examined.
- Full Text:
- Date Issued: 2007
- Authors: Magqi, Nceba
- Date: 2007
- Subjects: Density functionals , Ligands , Ligands -- Design , Ligands -- Analysis , Camphor
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4358 , http://hdl.handle.net/10962/d1005023 , Density functionals , Ligands , Ligands -- Design , Ligands -- Analysis , Camphor
- Description: In this study, attention has been given to the design and synthesis of novel multidentate ligands for use in the construction of ruthenium-based metathesis catalysts, and their chelating potential has been explored by computer modelling at the Density Functional Theory (DFT) level. Both Kemp’s triacid (1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic acid) and D-(+)-camphor have been investigated as molecular scaffolds for the development of such ligands. However selective elaboration of the functional groups in Kemp’s triacid proved difficult to achieve, and the research has focused on the development of camphor derivatives. The synthesis of the camphor-based ligands has involved C-8 functionalisation and ring-opening of the bicyclic system to afford tridentate products. The formation of 9-iodocamphorquinone bis(ethylene ketal) together with the desired product, the 8-iodo isomer, has been confirmed by single crystal X-ray analysis of both compounds. Formation of the 9-iodo analogue has provided new insights into the intramolecular rearrangement of camphor skeleton, and the mechanistic implications have been assessed by coset analysis. Attempts to effect nucleophilic displacement of the 8-halogeno groups by nucleophilic donor moieties proved unexpectedly difficult and, coupled with the susceptibility of the carbonyl groups to nucleophilic attack, has led to the formation of novel tricyclic products, viz., 1,6-dimethyl-3-(2-pyridylamino)-4-oxatricyclo[4.3.0.0[superscript 3,7]]-2-nonanone and 6,7-dimethyl-3-(2-pyridylamino)-4-oxatricyclo -[4.3.0.0[superscript 3,7]]-2-nonanone. However the diphenylphosphine group was successfully introduced at C-8 and oxidative ring-opening of the camphor skeleton has afforded the tridentate ligands, 2-(diphenylphosphinoylmethyl)-1,2-dimethyl-1,3-cyclopentanedicarboxylic acid and 2-(diphenylphosphinoylmethyl)-1,3-bis(hydroxymethyl)1,2-dimethylcyclopentane. One- and two-dimensional NMR and, where appropriate, high-resolution MS methods have been used to characterise the products. Three [superscript 13]C NMR chemical shift prediction programmes, viz., ChemWindow and the MODGRAPH neural network and HOSE (Hierachially Ordered Spherical description of Environment), have been applied to representative compounds to assess their efficacy. While the predicted shifts correlated reasonably well with the experimental data, they proved to be insufficiently accurate to differentiate the isomeric systems examined.
- Full Text:
- Date Issued: 2007
Study of metallophthalocyanines attached onto pre-modified gold surfaces
- Authors: Mashazi, Philani Nkosinathi
- Date: 2007
- Subjects: Phthalocyanines , Electrochemistry , Electrodes, Enzyme , Glucose -- Measurement
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4361 , http://hdl.handle.net/10962/d1005026 , Phthalocyanines , Electrochemistry , Electrodes, Enzyme , Glucose -- Measurement
- Description: Tetra-carboxy acid chloride phthalocyanine complexes of cobalt, iron and manganese were synthesized and characterized using spectroscopic and electrochemical techniques. These complexes were fabricated as thin films on gold electrode following a covalent immobilization and self-assembling methods. Surface electrochemical and spectroscopic characterization showed that these complexes are surface-confined species. The characterization using spectroscopic and electrochemical methods confirmed the formation of thiol and MPc SAMs on gold electrode. The electrocatalytic behaviour of the SAM modified gold electrodes was studied for the detection of L-cysteine and hydrogen peroxide. The limits of detection (LoD) for Lcysteine were of the orders of 10[superscript -7] mol.L[superscript -1] for all the MPc complexes studied and the LoD for hydrogen peroxide at cobalt phthalocyanine modified gold electrode was of the orders of 10[superscript -7]mol.L[superscript -1] for both electrocatalytic oxidation and reduction. The modification process for gold electrodes was reproducible and showed good stability, if stored in pH 4 phosphate buffer solutions and can be used over a long period of time. The cobalt phthalocyanine modified gold electrode was also investigated for the fabrication of glucose oxidase (GOx)-based biosensor and as an electron mediator between the enzyme and gold electrode. The behaviour of the enzyme modified gold electrode towards the detection of glucose was studied and the results gave a limit of detection of the orders of 10[superscript -6] mol.L[superscript -1] with low binding constant (4.8 mM) of enzyme (GOx) to substrate (glucose) referred to as Michaelis-Menten constant. The practical applications, i.e. the real sample analysis and interference studies, for the enzyme modified gold electrodes were investigated. These studies showed that the enzyme electrode is valuable and can be used for glucose detection.
- Full Text:
- Date Issued: 2007
- Authors: Mashazi, Philani Nkosinathi
- Date: 2007
- Subjects: Phthalocyanines , Electrochemistry , Electrodes, Enzyme , Glucose -- Measurement
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4361 , http://hdl.handle.net/10962/d1005026 , Phthalocyanines , Electrochemistry , Electrodes, Enzyme , Glucose -- Measurement
- Description: Tetra-carboxy acid chloride phthalocyanine complexes of cobalt, iron and manganese were synthesized and characterized using spectroscopic and electrochemical techniques. These complexes were fabricated as thin films on gold electrode following a covalent immobilization and self-assembling methods. Surface electrochemical and spectroscopic characterization showed that these complexes are surface-confined species. The characterization using spectroscopic and electrochemical methods confirmed the formation of thiol and MPc SAMs on gold electrode. The electrocatalytic behaviour of the SAM modified gold electrodes was studied for the detection of L-cysteine and hydrogen peroxide. The limits of detection (LoD) for Lcysteine were of the orders of 10[superscript -7] mol.L[superscript -1] for all the MPc complexes studied and the LoD for hydrogen peroxide at cobalt phthalocyanine modified gold electrode was of the orders of 10[superscript -7]mol.L[superscript -1] for both electrocatalytic oxidation and reduction. The modification process for gold electrodes was reproducible and showed good stability, if stored in pH 4 phosphate buffer solutions and can be used over a long period of time. The cobalt phthalocyanine modified gold electrode was also investigated for the fabrication of glucose oxidase (GOx)-based biosensor and as an electron mediator between the enzyme and gold electrode. The behaviour of the enzyme modified gold electrode towards the detection of glucose was studied and the results gave a limit of detection of the orders of 10[superscript -6] mol.L[superscript -1] with low binding constant (4.8 mM) of enzyme (GOx) to substrate (glucose) referred to as Michaelis-Menten constant. The practical applications, i.e. the real sample analysis and interference studies, for the enzyme modified gold electrodes were investigated. These studies showed that the enzyme electrode is valuable and can be used for glucose detection.
- Full Text:
- Date Issued: 2007
Study of titanium, tantalum and chromium catalysts for use in industrial transformations
- Authors: Tau, Prudence Lerato
- Date: 2007
- Subjects: Titanium Tantalum Phthalocyanines Electrochemistry Photochemotherapy Chromium Spectrum analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4363 , http://hdl.handle.net/10962/d1005028
- Description: PART A The syntheses, spectroscopic and electrochemical characterisation of a series of titanium and tantalum phthalocyanine complexes are reported. The complexes are unsubstituted and substituted at either the peripheral or non-peripheral positions with sulphonates, aryloxy, arylthio or amino groups. The complexes mostly exhibit Qbands in the near-infrared region as well as interesting properties in different solvents. The interaction of differently sulphonated titanium and tantalum phthalocyanine complexes with methyl viologen (MV[superscript 2+]), and hence the stoichiometry and association constants are evaluated. Detailed photophysicochemical properties of the complexes were investigated and are for the first time presented with fluorescence lifetimes easily obtained from fluorescence quenching studies. The transformation of 1-hexene photocatalysed by aryloxy- and arylthio-appended complexes is also presented for the first time. The electrochemical properties of the complexes are unknown and are thus presented. Cyclic (CV) and square wave (SWV) voltammetries, chronocoulometry and spectroelectrochemistry are employed in the study of the complexes. Two oneelectron reductions and a simultaneous 4-electron reduction are observed for the unsubstituted Cl[subscript 3]TaPc. Reduction occurs first at the metal followed by ring-based processes. The tetra- and octa-substituted derivatives however exhibit peculiar electrochemical behaviour where a multi-electron transfer process occurs for complexes bearing certain substituents. For all complexes, the first two reductions are metal-based followed by ring-based processes. A comparative study of the electrocatalytic activities of the complexes towards the oxidation of nitrite is also investigated. The complexes are immobilised onto a glassy carbon electrode either by drop-dry or electropolymerisation methods. All the modified electrodes exhibit improved electrocatalytic oxidation of nitrite than the unmodified electrodes by a twoelectron mechanism producing nitrate ions. Catalytic currents are enhanced and nitrite overpotential reduced to ~ 0.60 V. Kinetic parameters are determined for all complexes and a mechanism is proposed. PART B: The syntheses and electrochemical characterisation of chromium and titanium complexes for the selective trimerisation of ethylene to 1-hexene are presented. The synthesis of the chromium complex requires simple steps while tedious steps are used for the air-sensitive titanium complex. The spectroscopic interaction of the chromium complex with the co-catalyst methylaluminoxane is investigated. The complexes are characterised by electrochemical methods such as cyclic voltammetry and spectroelectrochemistry.
- Full Text:
- Date Issued: 2007
- Authors: Tau, Prudence Lerato
- Date: 2007
- Subjects: Titanium Tantalum Phthalocyanines Electrochemistry Photochemotherapy Chromium Spectrum analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4363 , http://hdl.handle.net/10962/d1005028
- Description: PART A The syntheses, spectroscopic and electrochemical characterisation of a series of titanium and tantalum phthalocyanine complexes are reported. The complexes are unsubstituted and substituted at either the peripheral or non-peripheral positions with sulphonates, aryloxy, arylthio or amino groups. The complexes mostly exhibit Qbands in the near-infrared region as well as interesting properties in different solvents. The interaction of differently sulphonated titanium and tantalum phthalocyanine complexes with methyl viologen (MV[superscript 2+]), and hence the stoichiometry and association constants are evaluated. Detailed photophysicochemical properties of the complexes were investigated and are for the first time presented with fluorescence lifetimes easily obtained from fluorescence quenching studies. The transformation of 1-hexene photocatalysed by aryloxy- and arylthio-appended complexes is also presented for the first time. The electrochemical properties of the complexes are unknown and are thus presented. Cyclic (CV) and square wave (SWV) voltammetries, chronocoulometry and spectroelectrochemistry are employed in the study of the complexes. Two oneelectron reductions and a simultaneous 4-electron reduction are observed for the unsubstituted Cl[subscript 3]TaPc. Reduction occurs first at the metal followed by ring-based processes. The tetra- and octa-substituted derivatives however exhibit peculiar electrochemical behaviour where a multi-electron transfer process occurs for complexes bearing certain substituents. For all complexes, the first two reductions are metal-based followed by ring-based processes. A comparative study of the electrocatalytic activities of the complexes towards the oxidation of nitrite is also investigated. The complexes are immobilised onto a glassy carbon electrode either by drop-dry or electropolymerisation methods. All the modified electrodes exhibit improved electrocatalytic oxidation of nitrite than the unmodified electrodes by a twoelectron mechanism producing nitrate ions. Catalytic currents are enhanced and nitrite overpotential reduced to ~ 0.60 V. Kinetic parameters are determined for all complexes and a mechanism is proposed. PART B: The syntheses and electrochemical characterisation of chromium and titanium complexes for the selective trimerisation of ethylene to 1-hexene are presented. The synthesis of the chromium complex requires simple steps while tedious steps are used for the air-sensitive titanium complex. The spectroscopic interaction of the chromium complex with the co-catalyst methylaluminoxane is investigated. The complexes are characterised by electrochemical methods such as cyclic voltammetry and spectroelectrochemistry.
- Full Text:
- Date Issued: 2007
Study South Africa
- International Education Association of South Africa (IEASA), Higher Education South Africa (Organization), Kishun, Roshen
- Authors: International Education Association of South Africa (IEASA) , Higher Education South Africa (Organization) , Kishun, Roshen
- Date: 2007
- Subjects: Education, Higher -- South Africa , Universities and colleges -- South Africa , Technical Institutes -- South Africa , Vocational guidance -- South Africa
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/65090 , vital:28685 , ISBN 9780620391634
- Description: [Extract from message from Minister of Higher Education, Hon. Naledi Pandor]: It gives me great pleasure to endorse the 7th edition of Study South Africa. The International Education Association of South Africa (IEASA) has once again produced a publication that provides valuable insights and information about South African public universities and their place in the global higher education arena I welcome this publication and congratulate IEASA for its hard work in promoting our higher education institutions internationally. Study South Africa gives a comprehensive picture of higher education in our country. At a glance, the enquirer is able to see all that South African higher education has to offer diversity in terms of institutions, the wide range of affordable courses on offer, the international acceptability of South African qualifications as well as the rich multi-cultural experiences of our campuses. In short, the Guide provides a summary of everything that will assist the potential student to actualise his or her full potential. South African higher education is founded on broad social values such as respect for human life and dignity, commitment to equality and human rights, respect for diversity and nonsexism. Our education system seeks to construct citizens who are conscious of these values and therefore aware of their responsibilities in life and in the lives of others. These values are reflected in the diverse offerings by institutions covered in the Guide. In addition, we have specific mechanisms in place to facilitate internationalisation, and our immigration policies have been relaxed to make it easier for international students, academics and other higher education staff to enter the country and stay for the duration of their planned activity. We also subsidise students from the continent in terms of our policy on the state subsidisation of foreign students at higher education institutions. South Africa shares the global concern about the digital and information divide. We are of the view that access to information is empowering and would therefore like to see as many citizens of our country and the continent connected with the rest of the world, both digitally and in terms of knowledge. By staying in touch with the rest of the world through information sharing and exchange programmes, we minimise this information gap. It is for this reason, therefore, that the work of IEASA in the form of this publication is applauded, because it seeks to promote such exchanges and information sharing. There is no question that through internationalisation we can impact on our political, economic, cultural and social transformation. We can also address our skills shortage, build research capacity, enrich curricula and enhance the student experience. Collectively higher education institutions in South Africa offer an impressive array of information and communication technologies, well stocked and interconnected libraries and some scholars who are among the best in the world, making the country a destination of choice for both Africans and students from abroad. We aspire to make all our international partners, students and staff feel at home and content with what our institutions offer them, pleasant living and study or work environments. We want them to be proud of their association with South African higher education and be ambassadors for the system once they leave South Africa. , 7th Edition
- Full Text:
- Date Issued: 2007
- Authors: International Education Association of South Africa (IEASA) , Higher Education South Africa (Organization) , Kishun, Roshen
- Date: 2007
- Subjects: Education, Higher -- South Africa , Universities and colleges -- South Africa , Technical Institutes -- South Africa , Vocational guidance -- South Africa
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/65090 , vital:28685 , ISBN 9780620391634
- Description: [Extract from message from Minister of Higher Education, Hon. Naledi Pandor]: It gives me great pleasure to endorse the 7th edition of Study South Africa. The International Education Association of South Africa (IEASA) has once again produced a publication that provides valuable insights and information about South African public universities and their place in the global higher education arena I welcome this publication and congratulate IEASA for its hard work in promoting our higher education institutions internationally. Study South Africa gives a comprehensive picture of higher education in our country. At a glance, the enquirer is able to see all that South African higher education has to offer diversity in terms of institutions, the wide range of affordable courses on offer, the international acceptability of South African qualifications as well as the rich multi-cultural experiences of our campuses. In short, the Guide provides a summary of everything that will assist the potential student to actualise his or her full potential. South African higher education is founded on broad social values such as respect for human life and dignity, commitment to equality and human rights, respect for diversity and nonsexism. Our education system seeks to construct citizens who are conscious of these values and therefore aware of their responsibilities in life and in the lives of others. These values are reflected in the diverse offerings by institutions covered in the Guide. In addition, we have specific mechanisms in place to facilitate internationalisation, and our immigration policies have been relaxed to make it easier for international students, academics and other higher education staff to enter the country and stay for the duration of their planned activity. We also subsidise students from the continent in terms of our policy on the state subsidisation of foreign students at higher education institutions. South Africa shares the global concern about the digital and information divide. We are of the view that access to information is empowering and would therefore like to see as many citizens of our country and the continent connected with the rest of the world, both digitally and in terms of knowledge. By staying in touch with the rest of the world through information sharing and exchange programmes, we minimise this information gap. It is for this reason, therefore, that the work of IEASA in the form of this publication is applauded, because it seeks to promote such exchanges and information sharing. There is no question that through internationalisation we can impact on our political, economic, cultural and social transformation. We can also address our skills shortage, build research capacity, enrich curricula and enhance the student experience. Collectively higher education institutions in South Africa offer an impressive array of information and communication technologies, well stocked and interconnected libraries and some scholars who are among the best in the world, making the country a destination of choice for both Africans and students from abroad. We aspire to make all our international partners, students and staff feel at home and content with what our institutions offer them, pleasant living and study or work environments. We want them to be proud of their association with South African higher education and be ambassadors for the system once they leave South Africa. , 7th Edition
- Full Text:
- Date Issued: 2007
Submerged membrane bioreactor and secondary digestion for the treatment of wine distillery wastewater: Part I: Raw wine distillery wastewater digestion
- Melamane, Xolisa L, Tandlich, Roman, Burgess, Jo E
- Authors: Melamane, Xolisa L , Tandlich, Roman , Burgess, Jo E
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/76139 , vital:30511 , https://www.prt-parlar.de/download_feb_2007/
- Description: A combination of a submerged membrane bioreactor (SMBR) and a secondary digester was tested for the treatment of wine distillery wastewater (WDW). The experimental system, consisting of four individual reactors, was tested during a 30-days study. Buffering of pH was achieved by mixing the feed stream of the system with 1000 mg/l of CaCO3 and K2HPO4 for the initial 10 days of the bioreactor system operation, and with 8000 mg/l of CaCO3 and 4000 mg/l of K2HPO4 for the remainder of the study. Buffering proved to be significant for optimum performance of the system in removal of soluble chemical oxygen demand (CODS), and volatile fatty acids (VFAs). Different batches of WDW used for feeding the reactor had variable compositions with respect to concentrations of nitrates, ammonium and the total concentration of phenolic compounds. Am-monium accumulated in the secondary digester after 14 days of treatment system operation, indicating the time required for the establishment of anaerobic conditions in the system. An additional step would be required for removal of phosphates from the effluent of the bioreactor, e.g., reverse osmosis, if the effluent is to be reused in production or other applications.
- Full Text:
- Date Issued: 2007
- Authors: Melamane, Xolisa L , Tandlich, Roman , Burgess, Jo E
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/76139 , vital:30511 , https://www.prt-parlar.de/download_feb_2007/
- Description: A combination of a submerged membrane bioreactor (SMBR) and a secondary digester was tested for the treatment of wine distillery wastewater (WDW). The experimental system, consisting of four individual reactors, was tested during a 30-days study. Buffering of pH was achieved by mixing the feed stream of the system with 1000 mg/l of CaCO3 and K2HPO4 for the initial 10 days of the bioreactor system operation, and with 8000 mg/l of CaCO3 and 4000 mg/l of K2HPO4 for the remainder of the study. Buffering proved to be significant for optimum performance of the system in removal of soluble chemical oxygen demand (CODS), and volatile fatty acids (VFAs). Different batches of WDW used for feeding the reactor had variable compositions with respect to concentrations of nitrates, ammonium and the total concentration of phenolic compounds. Am-monium accumulated in the secondary digester after 14 days of treatment system operation, indicating the time required for the establishment of anaerobic conditions in the system. An additional step would be required for removal of phosphates from the effluent of the bioreactor, e.g., reverse osmosis, if the effluent is to be reused in production or other applications.
- Full Text:
- Date Issued: 2007
Submerged membrane bioreactor and secondary digestion in the treatment of wine distillery waste: Part II: the effect of fungal pre-treatment on wine distillery wastewater digestion
- Melamane, Xolisa L, Strong, Peter James, Tandlich, Roman, Burgess, Jo E
- Authors: Melamane, Xolisa L , Strong, Peter James , Tandlich, Roman , Burgess, Jo E
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/76150 , vital:30514 , https://www.prt-parlar.de/download_feb_2007/
- Description: The effect of fungal pre-treatment using Trametes pubescens on the anaerobic digestion ultrafiltration treatment of wine distillery wastewater (WDW) was studied. The downstream biological treatment system, consisting of four individual reactors, was operated for 30 days. pH buffering was achieved by mixing the pre-treated system feed with CaCO3 and K2HPO4; this proved significant for optimum performance of the system in removal of soluble chemical oxygen demand (CODS). The experimental system was shown to eliminate an average of 86 (± 4) % of CODS present in the pre-treated WDW. Treatment in a submerged membrane bioreactor (SMBR) and subsequent secondary digester, together with pH buffering using CaCO3 and K2HPO4, led to the stabilisation of CODS removal. The residual CODS levels in the final effluent were approximately 400 mg/l, significantly lower than the concentrations observed when treating raw WDW, indicating that fungal pre-treatment might have provided additional nutrients for removal of recalcitrant components of the wastewater. The resulting effluent of the system is rich in nitrates and phosphates. Together with the residual organic content it might be used as a fertiliser. Alternatively, if water management of the wine distillery is an issue, a membrane process, such as reverse osmosis or nanofiltration could be applied to bring the parameters of the water to meet the technological needs.
- Full Text:
- Date Issued: 2007
- Authors: Melamane, Xolisa L , Strong, Peter James , Tandlich, Roman , Burgess, Jo E
- Date: 2007
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/76150 , vital:30514 , https://www.prt-parlar.de/download_feb_2007/
- Description: The effect of fungal pre-treatment using Trametes pubescens on the anaerobic digestion ultrafiltration treatment of wine distillery wastewater (WDW) was studied. The downstream biological treatment system, consisting of four individual reactors, was operated for 30 days. pH buffering was achieved by mixing the pre-treated system feed with CaCO3 and K2HPO4; this proved significant for optimum performance of the system in removal of soluble chemical oxygen demand (CODS). The experimental system was shown to eliminate an average of 86 (± 4) % of CODS present in the pre-treated WDW. Treatment in a submerged membrane bioreactor (SMBR) and subsequent secondary digester, together with pH buffering using CaCO3 and K2HPO4, led to the stabilisation of CODS removal. The residual CODS levels in the final effluent were approximately 400 mg/l, significantly lower than the concentrations observed when treating raw WDW, indicating that fungal pre-treatment might have provided additional nutrients for removal of recalcitrant components of the wastewater. The resulting effluent of the system is rich in nitrates and phosphates. Together with the residual organic content it might be used as a fertiliser. Alternatively, if water management of the wine distillery is an issue, a membrane process, such as reverse osmosis or nanofiltration could be applied to bring the parameters of the water to meet the technological needs.
- Full Text:
- Date Issued: 2007
Subtle racism amongst undergraduate learners after a decade of democracy
- Authors: Van der Westhuizen, Amanda
- Date: 2007
- Subjects: Racism in higher education -- South Africa -- Nelson Mandela Bay , Intergroup relations , Social interaction
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:9954 , http://hdl.handle.net/10948/d1018820
- Description: The concept of “race” has been the organising feature of South African society for more than three centuries. More recent social changes in the United States of America, Europe, Australia, and South Africa have lead to more subtle expressions of racism. The present study aimed to explore and describe subtle racism amongst undergraduate psychology learners at a tertiary institution in Nelson Mandela Metropolitan Municipality in 2004. The Subtle Racism Scale was used to measure anti-Black sentiment among a sample of 286 undergraduate psychology learners, obtained through non–probability, convenience sampling. Multiple regression analysis revealed the independent variables of race, age, and the race-age interaction were significantly associated with subtle racism of the participants. Research results demonstrated that participants’ level of estimated subtle racism varied according to the age and race of the participants, supporting the notion that racism in South Africa did not influence different age and race groups in a uniform manner.
- Full Text:
- Date Issued: 2007
- Authors: Van der Westhuizen, Amanda
- Date: 2007
- Subjects: Racism in higher education -- South Africa -- Nelson Mandela Bay , Intergroup relations , Social interaction
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:9954 , http://hdl.handle.net/10948/d1018820
- Description: The concept of “race” has been the organising feature of South African society for more than three centuries. More recent social changes in the United States of America, Europe, Australia, and South Africa have lead to more subtle expressions of racism. The present study aimed to explore and describe subtle racism amongst undergraduate psychology learners at a tertiary institution in Nelson Mandela Metropolitan Municipality in 2004. The Subtle Racism Scale was used to measure anti-Black sentiment among a sample of 286 undergraduate psychology learners, obtained through non–probability, convenience sampling. Multiple regression analysis revealed the independent variables of race, age, and the race-age interaction were significantly associated with subtle racism of the participants. Research results demonstrated that participants’ level of estimated subtle racism varied according to the age and race of the participants, supporting the notion that racism in South Africa did not influence different age and race groups in a uniform manner.
- Full Text:
- Date Issued: 2007
Surface chemistry and electrocatalytic behaviour of tetra-carboxy substituted iron, cobalt and manganese phthalocyanine monolayers on gold electrode
- Mashazi, Philani N, Westbroek, Philippe, Ozoemena, Kenneth I, Nyokong, Tebello
- Authors: Mashazi, Philani N , Westbroek, Philippe , Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268806 , vital:54233 , xlink:href="https://doi.org/10.1016/j.electacta.2007.08.044"
- Description: Surface chemistry and electrocatalytic properties of self-assembled monolayers of metal tetra-carboxylic acid phthalocyanine complexes with cobalt (Co), iron (Fe) and manganese (Mn) as central metal ions have been studied. These phthalocyanine molecules are immobilized on gold electrode via the coupling reaction between the ring substituents and pre-formed mercaptoethanol self-assembled monolayer (Au-ME SAM). X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy confirmed chemisorption of mercaptoethanol via sulfur group on gold electrode and also coupling reaction between phthalocyanines and Au-ME SAM. Electrochemical parameters of the immobilized molecules show that these molecules are densely packed with a perpendicular orientation. The potential applications of the gold modified electrodes were investigated towards L-cysteine detection and the analysis at phthalocyanine SAMs. Cobalt and iron tetra-carboxylic acid phthalocyanine monolayers showed good oxidation peak for L-cysteine at potentials where metal oxidation (MIII/MII) takes place and this metal oxidation mediates the catalytic oxidation of L-cysteine. Manganese tetra-carboxylic acid phthalocyanine monolayer also exhibited a good catalytic oxidation peak towards L-cysteine at potentials where MnIV/MnIII redox peak occurs and this redox peak mediates L-cysteine oxidation. The analysis of cysteine at phthalocyanine monolayers displayed good analytical parameters with good detection limits of the orders of 10−7 mol L−1 and good linearity for a studied concentration range up to 60 μmol L−1.
- Full Text:
- Date Issued: 2007
- Authors: Mashazi, Philani N , Westbroek, Philippe , Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268806 , vital:54233 , xlink:href="https://doi.org/10.1016/j.electacta.2007.08.044"
- Description: Surface chemistry and electrocatalytic properties of self-assembled monolayers of metal tetra-carboxylic acid phthalocyanine complexes with cobalt (Co), iron (Fe) and manganese (Mn) as central metal ions have been studied. These phthalocyanine molecules are immobilized on gold electrode via the coupling reaction between the ring substituents and pre-formed mercaptoethanol self-assembled monolayer (Au-ME SAM). X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy confirmed chemisorption of mercaptoethanol via sulfur group on gold electrode and also coupling reaction between phthalocyanines and Au-ME SAM. Electrochemical parameters of the immobilized molecules show that these molecules are densely packed with a perpendicular orientation. The potential applications of the gold modified electrodes were investigated towards L-cysteine detection and the analysis at phthalocyanine SAMs. Cobalt and iron tetra-carboxylic acid phthalocyanine monolayers showed good oxidation peak for L-cysteine at potentials where metal oxidation (MIII/MII) takes place and this metal oxidation mediates the catalytic oxidation of L-cysteine. Manganese tetra-carboxylic acid phthalocyanine monolayer also exhibited a good catalytic oxidation peak towards L-cysteine at potentials where MnIV/MnIII redox peak occurs and this redox peak mediates L-cysteine oxidation. The analysis of cysteine at phthalocyanine monolayers displayed good analytical parameters with good detection limits of the orders of 10−7 mol L−1 and good linearity for a studied concentration range up to 60 μmol L−1.
- Full Text:
- Date Issued: 2007
Syntheses and photophysics of new phthalocyanine derivatives of zinc, cadmium and mercury
- Chidawanyika, Wadzanai J U, Ogunsipe, Abimbola, Nyokong, Tebello
- Authors: Chidawanyika, Wadzanai J U , Ogunsipe, Abimbola , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/283940 , vital:56005 , xlink:href="https://doi.org/10.1039/B615663K"
- Description: The syntheses of novel tetra{2,(3)-pyridyloxyphthalocyaninato} complexes of zinc, cadmium and mercury (TPyZnPc, TPyCdPc and TPyHgPc) are presented. Their spectral and photophysical properties (as well as those of their unsubstituted counterparts: ZnPc, CdPc and HgPc) are investigated. TPyZnPc and TPyCdPc are aggregated in non-coordinating solvents such as chloroform, while TPyHgPc is demetallated, as evident from their respective absorption spectra. The trends in fluorescence (ΦF), triplet (ΦT) and singlet oxygen (ΦΔ) quantum yields are explained in terms of relative strengths of spin–orbit coupling induced by the respective central metal ions in the complexes. The effect of the pyridyloxy substituents is a decrease in ΦF and an increase in ΦT values. The complexes are less fluorescent in DMSO but possess higher ΦT, triplet lifetimes (τT) and ΦΔ therein.
- Full Text:
- Date Issued: 2007
- Authors: Chidawanyika, Wadzanai J U , Ogunsipe, Abimbola , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/283940 , vital:56005 , xlink:href="https://doi.org/10.1039/B615663K"
- Description: The syntheses of novel tetra{2,(3)-pyridyloxyphthalocyaninato} complexes of zinc, cadmium and mercury (TPyZnPc, TPyCdPc and TPyHgPc) are presented. Their spectral and photophysical properties (as well as those of their unsubstituted counterparts: ZnPc, CdPc and HgPc) are investigated. TPyZnPc and TPyCdPc are aggregated in non-coordinating solvents such as chloroform, while TPyHgPc is demetallated, as evident from their respective absorption spectra. The trends in fluorescence (ΦF), triplet (ΦT) and singlet oxygen (ΦΔ) quantum yields are explained in terms of relative strengths of spin–orbit coupling induced by the respective central metal ions in the complexes. The effect of the pyridyloxy substituents is a decrease in ΦF and an increase in ΦT values. The complexes are less fluorescent in DMSO but possess higher ΦT, triplet lifetimes (τT) and ΦΔ therein.
- Full Text:
- Date Issued: 2007
Synthesis and characterization of symmetrical and unsymmetrical ferrocenyl ligands for use in the preparation of Redox Active Ruthenium Alkylidene Complexes
- Authors: Saku, Duduetsang
- Date: 2007
- Subjects: Ferrocene , Ligands , Asymmetric synthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10403 , http://hdl.handle.net/10948/701 , Ferrocene , Ligands , Asymmetric synthesis
- Description: Oxidation of a ferrocenyl group in conjugation to another metal centre can alter the electron density at that metal centre and lead to a change in overall reactivity of a complex. Herein, the synthesis and characterization of redox active symmetrical and unsymmetrical ferrocenylalkene derivatives is described. A change in the standard redox potential of ferrocene (465 mV), to more positive potentials in vinylferrocene 1 (478 mV) and 4-phenylvinylferrocene 3 (499 mV), showed how manipulation of a redox potential can be effected on the ferrocenyl moiety by just using conjugation effects. A shift by +13 mV is observed in 1 and this potential more than doubled in 3 (+34 mV). Ferrocenylderived ruthenium alkylidene complexes were also prepared in a cross metathesis of 1 and 3 with Grubbs’ 1 (676.5 mV) to give complexes Ferrocenylidenebis( tricyclohexylphosphine)dichlororuthenium 14, 4-ferrocenylphenylidene-bis (tricyclohexylphosphine)dichlororuthenium 15 respectively. The extent of the electronic communication between the ferrocenyl group and the ruthenium centre was then estimated by looking at the positive or negative redox potential shifts of 14 and 15 as a result of 1 and 3. A large positive potential shift by 180 mV in 14 indicated that there was a strong electronic communication between the two metal centres, while the smaller, yet significant positive potential shift by 89.5 mV in 15 showed 3 to have a lesser effect on the ruthenium centre. Compounds 14 and 15 were tested in a Ring Closing Metathesis (RCM) of diethyldiallylmalonate showed enhanced reactivity.
- Full Text:
- Date Issued: 2007
- Authors: Saku, Duduetsang
- Date: 2007
- Subjects: Ferrocene , Ligands , Asymmetric synthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10403 , http://hdl.handle.net/10948/701 , Ferrocene , Ligands , Asymmetric synthesis
- Description: Oxidation of a ferrocenyl group in conjugation to another metal centre can alter the electron density at that metal centre and lead to a change in overall reactivity of a complex. Herein, the synthesis and characterization of redox active symmetrical and unsymmetrical ferrocenylalkene derivatives is described. A change in the standard redox potential of ferrocene (465 mV), to more positive potentials in vinylferrocene 1 (478 mV) and 4-phenylvinylferrocene 3 (499 mV), showed how manipulation of a redox potential can be effected on the ferrocenyl moiety by just using conjugation effects. A shift by +13 mV is observed in 1 and this potential more than doubled in 3 (+34 mV). Ferrocenylderived ruthenium alkylidene complexes were also prepared in a cross metathesis of 1 and 3 with Grubbs’ 1 (676.5 mV) to give complexes Ferrocenylidenebis( tricyclohexylphosphine)dichlororuthenium 14, 4-ferrocenylphenylidene-bis (tricyclohexylphosphine)dichlororuthenium 15 respectively. The extent of the electronic communication between the ferrocenyl group and the ruthenium centre was then estimated by looking at the positive or negative redox potential shifts of 14 and 15 as a result of 1 and 3. A large positive potential shift by 180 mV in 14 indicated that there was a strong electronic communication between the two metal centres, while the smaller, yet significant positive potential shift by 89.5 mV in 15 showed 3 to have a lesser effect on the ruthenium centre. Compounds 14 and 15 were tested in a Ring Closing Metathesis (RCM) of diethyldiallylmalonate showed enhanced reactivity.
- Full Text:
- Date Issued: 2007
Synthesis and electrochemical properties of benzyl-mercapto and dodecyl-mercapto tetrasubstituted manganese phthalocyanine complexes
- Agboola, Bolade, Ozoemena, Kenneth I, Westbroek, Philippe, Nyokong, Tebello
- Authors: Agboola, Bolade , Ozoemena, Kenneth I , Westbroek, Philippe , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281321 , vital:55713 , xlink:href="https://doi.org/10.1016/j.electacta.2006.09.002"
- Description: Manganese tetrakis (benzyl-mercapto) phthalocyanine (MnTBMPc) and manganese tetrakis (dodecyl-mercapto) phthalocyanine (MnTDMPc) complexes were synthesized and their spectral and electrochemical properties are reported. Cyclic voltammetric data showed three reversible to quasi-reversible and two irreversible redox processes for both complexes. Ring substituents influenced the positions of both oxidation and reduction redox couples. Spectroelectrochemistry confirmed the first two reductions to be due to MnIIIPc2−/MnIIPc2− and MnIIPc3−/MnIIPc2− processes. The first example of a formation of self-assembled monolayers (SAMs) using thiol substituted MnPc complexes is presented, the SAMs were found to show blocking characteristics towards some faradaic reactions.
- Full Text:
- Date Issued: 2007
- Authors: Agboola, Bolade , Ozoemena, Kenneth I , Westbroek, Philippe , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281321 , vital:55713 , xlink:href="https://doi.org/10.1016/j.electacta.2006.09.002"
- Description: Manganese tetrakis (benzyl-mercapto) phthalocyanine (MnTBMPc) and manganese tetrakis (dodecyl-mercapto) phthalocyanine (MnTDMPc) complexes were synthesized and their spectral and electrochemical properties are reported. Cyclic voltammetric data showed three reversible to quasi-reversible and two irreversible redox processes for both complexes. Ring substituents influenced the positions of both oxidation and reduction redox couples. Spectroelectrochemistry confirmed the first two reductions to be due to MnIIIPc2−/MnIIPc2− and MnIIPc3−/MnIIPc2− processes. The first example of a formation of self-assembled monolayers (SAMs) using thiol substituted MnPc complexes is presented, the SAMs were found to show blocking characteristics towards some faradaic reactions.
- Full Text:
- Date Issued: 2007
Synthesis and electrochemical properties of purple manganese (III) and red titanium (IV) phthalocyanine complexes octa-substituted at non-peripheral positions with pentylthio groups
- Mbambisa, Gcineka, Tau, Prudence, Antunes, Edith M, Nyokong, Tebello
- Authors: Mbambisa, Gcineka , Tau, Prudence , Antunes, Edith M , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/271252 , vital:54525 , xlink:href="https://doi.org/10.1016/j.poly.2007.08.007"
- Description: The synthesis and electrochemical characterisation of octapentylthiophthalocyaninato manganese (III) acetate (4) and octapentylthiophthalocyaninato titanium (IV) oxide (5) complexes are reported. The complexes have an unusual purple (4) and red (5) colouration since the Q-band is shifted to the near infrared region with Q-band maxima at 893 nm and 808 nm in dichloromethane for 4 and 5, respectively. The structures of the complexes were confirmed by elemental analysis and interpretation of their spectroscopic data, including 2D NMR. The cyclic voltammetry (CV) of the Mn complex (4) showed four quasi reversible couples. The reduction processes are attributed to MnIIIPc−2/MnIIPc−2 and MnIIPc−2/MnIIPc−3 and the oxidation processes to MnIVPc−2/MnIIIPc−2 and MnIVPc−1/MnIVPc−2. The processes were confirmed by spectroelectrochemistry. A well-defined spectrum of the rare MnIVPc−2 species is reported. The CV of the Ti complex (5) showed two well-resolved reduction processes due to TiIVPc−2/TiIIIPc−2 and TiIIIPc−2/TiIIPc−2. However, oxidation processes of the complex revealed adsorption behaviour and resulted in decomposition on electrolysis using spectroelectrochemistry.
- Full Text:
- Date Issued: 2007
- Authors: Mbambisa, Gcineka , Tau, Prudence , Antunes, Edith M , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/271252 , vital:54525 , xlink:href="https://doi.org/10.1016/j.poly.2007.08.007"
- Description: The synthesis and electrochemical characterisation of octapentylthiophthalocyaninato manganese (III) acetate (4) and octapentylthiophthalocyaninato titanium (IV) oxide (5) complexes are reported. The complexes have an unusual purple (4) and red (5) colouration since the Q-band is shifted to the near infrared region with Q-band maxima at 893 nm and 808 nm in dichloromethane for 4 and 5, respectively. The structures of the complexes were confirmed by elemental analysis and interpretation of their spectroscopic data, including 2D NMR. The cyclic voltammetry (CV) of the Mn complex (4) showed four quasi reversible couples. The reduction processes are attributed to MnIIIPc−2/MnIIPc−2 and MnIIPc−2/MnIIPc−3 and the oxidation processes to MnIVPc−2/MnIIIPc−2 and MnIVPc−1/MnIVPc−2. The processes were confirmed by spectroelectrochemistry. A well-defined spectrum of the rare MnIVPc−2 species is reported. The CV of the Ti complex (5) showed two well-resolved reduction processes due to TiIVPc−2/TiIIIPc−2 and TiIIIPc−2/TiIIPc−2. However, oxidation processes of the complex revealed adsorption behaviour and resulted in decomposition on electrolysis using spectroelectrochemistry.
- Full Text:
- Date Issued: 2007
Synthesis and photodynamic potential of tetra-and octa-triethyleneoxysulfonyl substituted zinc phthalocyanines
- Atilla, Devrim, Savdan, Nil, Durmus, Mahmut, Gürek, Ayşe Gül, Khan, Tania, Rück, Angelika, Walt, Heinrich, Nyokong, Tebello, Ahsen, Vefa
- Authors: Atilla, Devrim , Savdan, Nil , Durmus, Mahmut , Gürek, Ayşe Gül , Khan, Tania , Rück, Angelika , Walt, Heinrich , Nyokong, Tebello , Ahsen, Vefa
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281342 , vital:55715 , xlink:href="https://doi.org/10.1016/j.jphotochem.2006.08.022"
- Description: Synthesis of the water soluble zinc phthalocyanines (3, 4) obtained from the phthalonitriles substituted with oligo(ethyleneoxy)thia groups are described. The new compounds have been characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy, including HSQC, HMBC and COSY bidimensional correlation techniques, electronic spectroscopy and mass spectra. The aggregation behaviour of the phthalocyanine compounds (3, 4) was investigated using UV–vis spectroscopy in dimethylsulphoxide. Photochemical and photophysical measurements were conducted on oligo(ethyleneoxy)thia appended zinc phthalocyanines. General trends are described for quantum yields of photodegredation, fluorescence yields, triplet lifetimes and triplet quantum yields as well as singlet oxygen quantum yields of these compounds. The phototoxicity against cancer cells of the new compounds was investigated during several in vitro experiments. The dye-sensitized photooxidation of 1,3-diphenylisobenzofurane via 1O2 was studied in dimethylsulphoxide.
- Full Text:
- Date Issued: 2007
- Authors: Atilla, Devrim , Savdan, Nil , Durmus, Mahmut , Gürek, Ayşe Gül , Khan, Tania , Rück, Angelika , Walt, Heinrich , Nyokong, Tebello , Ahsen, Vefa
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281342 , vital:55715 , xlink:href="https://doi.org/10.1016/j.jphotochem.2006.08.022"
- Description: Synthesis of the water soluble zinc phthalocyanines (3, 4) obtained from the phthalonitriles substituted with oligo(ethyleneoxy)thia groups are described. The new compounds have been characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy, including HSQC, HMBC and COSY bidimensional correlation techniques, electronic spectroscopy and mass spectra. The aggregation behaviour of the phthalocyanine compounds (3, 4) was investigated using UV–vis spectroscopy in dimethylsulphoxide. Photochemical and photophysical measurements were conducted on oligo(ethyleneoxy)thia appended zinc phthalocyanines. General trends are described for quantum yields of photodegredation, fluorescence yields, triplet lifetimes and triplet quantum yields as well as singlet oxygen quantum yields of these compounds. The phototoxicity against cancer cells of the new compounds was investigated during several in vitro experiments. The dye-sensitized photooxidation of 1,3-diphenylisobenzofurane via 1O2 was studied in dimethylsulphoxide.
- Full Text:
- Date Issued: 2007
Synthesis and solvent effects on the electronic absorption and fluorescence spectral properties of substituted zinc phthalocyanines
- Durmus, Mahmut, Nyokong, Tebello
- Authors: Durmus, Mahmut , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/293279 , vital:57071 , xlink:href="https://doi.org/10.1016/j.poly.2007.01.018"
- Description: The synthesis and spectroscopic properties of the following tetra- and octa-substituted aryloxy zinc(II) phthalocyanines are reported for the first time: 1,(4)-(tetrabenzyloxyphenoxyphthalocyaninato) zinc(II) (7); 2,(3)-(tetrabenzyloxyphenoxyphthalocyaninato) zinc(II) (8); 2,3-(octabenzyloxyphenoxyphthalocyaninato) zinc(II) (9). The new compounds have been characterized by elemental analysis, IR, 1H NMR spectroscopy and electronic spectroscopy. Spectroscopic properties of these compounds were investigated in different solvents. Protonation of non-peripherally substituted complex 7 resulted in the splitting and red-shifting of the Q-band. The peripherally substituted derivatives 8 and 9, did not show the split in the Q-band. Fluorescence spectra of the derivatives show Stokes shifts typical of MPc complexes.
- Full Text:
- Date Issued: 2007
- Authors: Durmus, Mahmut , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/293279 , vital:57071 , xlink:href="https://doi.org/10.1016/j.poly.2007.01.018"
- Description: The synthesis and spectroscopic properties of the following tetra- and octa-substituted aryloxy zinc(II) phthalocyanines are reported for the first time: 1,(4)-(tetrabenzyloxyphenoxyphthalocyaninato) zinc(II) (7); 2,(3)-(tetrabenzyloxyphenoxyphthalocyaninato) zinc(II) (8); 2,3-(octabenzyloxyphenoxyphthalocyaninato) zinc(II) (9). The new compounds have been characterized by elemental analysis, IR, 1H NMR spectroscopy and electronic spectroscopy. Spectroscopic properties of these compounds were investigated in different solvents. Protonation of non-peripherally substituted complex 7 resulted in the splitting and red-shifting of the Q-band. The peripherally substituted derivatives 8 and 9, did not show the split in the Q-band. Fluorescence spectra of the derivatives show Stokes shifts typical of MPc complexes.
- Full Text:
- Date Issued: 2007
Synthesis and solvent effects on the electronic absorption and fluorescence spectral properties of substituted zinc phthalocyanines
- Durmus, Mahmut, Nyokong, Tebello
- Authors: Durmus, Mahmut , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/283140 , vital:55914 , xlink:href="https://doi.org/10.1016/j.poly.2007.01.018"
- Description: The synthesis and spectroscopic properties of the following tetra- and octa-substituted aryloxy zinc(II) phthalocyanines are reported for the first time: 1,(4)-(tetrabenzyloxyphenoxyphthalocyaninato) zinc(II) (7); 2,(3)-(tetrabenzyloxyphenoxyphthalocyaninato) zinc(II) (8); 2,3-(octabenzyloxyphenoxyphthalocyaninato) zinc(II) (9). The new compounds have been characterized by elemental analysis, IR, 1H NMR spectroscopy and electronic spectroscopy. Spectroscopic properties of these compounds were investigated in different solvents. Protonation of non-peripherally substituted complex 7 resulted in the splitting and red-shifting of the Q-band. The peripherally substituted derivatives 8 and 9, did not show the split in the Q-band. Fluorescence spectra of the derivatives show Stokes shifts typical of MPc complexes.
- Full Text:
- Date Issued: 2007
- Authors: Durmus, Mahmut , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/283140 , vital:55914 , xlink:href="https://doi.org/10.1016/j.poly.2007.01.018"
- Description: The synthesis and spectroscopic properties of the following tetra- and octa-substituted aryloxy zinc(II) phthalocyanines are reported for the first time: 1,(4)-(tetrabenzyloxyphenoxyphthalocyaninato) zinc(II) (7); 2,(3)-(tetrabenzyloxyphenoxyphthalocyaninato) zinc(II) (8); 2,3-(octabenzyloxyphenoxyphthalocyaninato) zinc(II) (9). The new compounds have been characterized by elemental analysis, IR, 1H NMR spectroscopy and electronic spectroscopy. Spectroscopic properties of these compounds were investigated in different solvents. Protonation of non-peripherally substituted complex 7 resulted in the splitting and red-shifting of the Q-band. The peripherally substituted derivatives 8 and 9, did not show the split in the Q-band. Fluorescence spectra of the derivatives show Stokes shifts typical of MPc complexes.
- Full Text:
- Date Issued: 2007
Synthesis and structure determination of 8-and 9-iodocamphorquinone bis (ethylene ketal)
- Magqi, Nceba, Lobb, Kevin A, Kaye, Perry T, Caira, Mino R
- Authors: Magqi, Nceba , Lobb, Kevin A , Kaye, Perry T , Caira, Mino R
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/449399 , vital:74817 , xlink:href="https://doi.org/10.3184/030823407X209"
- Description: The structures of 8- and 9-iodocamphorquinone bis(ethylene ketal) have been confirmed by spectroscopic and single crystal X-ray analysis. The unexpected formation of the latter isomer is attributed to intramolecular rearrangement of the camphor skeleton, the mechanistic details of which have been explored using coset analysis.
- Full Text:
- Date Issued: 2007
- Authors: Magqi, Nceba , Lobb, Kevin A , Kaye, Perry T , Caira, Mino R
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/449399 , vital:74817 , xlink:href="https://doi.org/10.3184/030823407X209"
- Description: The structures of 8- and 9-iodocamphorquinone bis(ethylene ketal) have been confirmed by spectroscopic and single crystal X-ray analysis. The unexpected formation of the latter isomer is attributed to intramolecular rearrangement of the camphor skeleton, the mechanistic details of which have been explored using coset analysis.
- Full Text:
- Date Issued: 2007
Synthesis of novel coumarin derivatives as potential inhibitors of HIV-1 protease
- Authors: Rose, Nathan Rolf
- Date: 2007 , 2013-07-01
- Subjects: Coumarins , Protease Inhibitors , Heterocyclic compounds -- Derivatives , HIV infections -- Treatment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4430 , http://hdl.handle.net/10962/d1007220 , Coumarins , Protease Inhibitors , Heterocyclic compounds -- Derivatives , HIV infections -- Treatment
- Description: This research has focused on the development of novel coumann derivatives containing peptide-like side chains as potential HIV-1 protease inhibitors. The reaction of various salicylaldehyde derivatives with tert-butyl acrylate In the presence of 1,4- diazabicyclo[2.2.2]octane (DABCO) has afforded a series of Baylis-Hillman adducts in moderate yield. Cyclisation of the adducts in the presence of HCI afforded the corresponding 3-(chloromethyl)coumarin derivatives, which have been reacted with various amine hydrochlorides in the presence of Proton Sponge® to afford a series of novel 3- (aminomethyl)coumarin derivatives, which were fully characterised by NMR and HRMS methods. Various approaches to the introduction of hydroxyl or amino groups at the C-4 position of coumarin and the 3-(chloromethyl)coumarin derivatives have been explored; these have included dihydroxylation of the coumarin double bond, and the synthesis of 4- benzylaminocoumarin derivatives as potential intermediates. The Vilsmeier-Haack and Mannich reactions have also been investigated as possible methods of introducing the desired peptide-like functionality. Computer modelling of selected structures has indicated that some of the novel 3- (aminomethyl)coumarin derivatives may exhibit activity as inhibitors of HIV-1 protease. The planned enzyme inhibition assays were unfortunately precluded by the aqueous insolubility of the selected compounds. Three ¹³C NMR chemical shift algorithms, viz., Modgraph Neural Network, Modgraph HOSE and Chern Window, have been applied to selected compounds prepared in this study. The Modgraph Neural Network algorithm was found, in all cases, to provide the most accurate correlations with the experimentally-determined chemical shifts. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2007
- Authors: Rose, Nathan Rolf
- Date: 2007 , 2013-07-01
- Subjects: Coumarins , Protease Inhibitors , Heterocyclic compounds -- Derivatives , HIV infections -- Treatment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4430 , http://hdl.handle.net/10962/d1007220 , Coumarins , Protease Inhibitors , Heterocyclic compounds -- Derivatives , HIV infections -- Treatment
- Description: This research has focused on the development of novel coumann derivatives containing peptide-like side chains as potential HIV-1 protease inhibitors. The reaction of various salicylaldehyde derivatives with tert-butyl acrylate In the presence of 1,4- diazabicyclo[2.2.2]octane (DABCO) has afforded a series of Baylis-Hillman adducts in moderate yield. Cyclisation of the adducts in the presence of HCI afforded the corresponding 3-(chloromethyl)coumarin derivatives, which have been reacted with various amine hydrochlorides in the presence of Proton Sponge® to afford a series of novel 3- (aminomethyl)coumarin derivatives, which were fully characterised by NMR and HRMS methods. Various approaches to the introduction of hydroxyl or amino groups at the C-4 position of coumarin and the 3-(chloromethyl)coumarin derivatives have been explored; these have included dihydroxylation of the coumarin double bond, and the synthesis of 4- benzylaminocoumarin derivatives as potential intermediates. The Vilsmeier-Haack and Mannich reactions have also been investigated as possible methods of introducing the desired peptide-like functionality. Computer modelling of selected structures has indicated that some of the novel 3- (aminomethyl)coumarin derivatives may exhibit activity as inhibitors of HIV-1 protease. The planned enzyme inhibition assays were unfortunately precluded by the aqueous insolubility of the selected compounds. Three ¹³C NMR chemical shift algorithms, viz., Modgraph Neural Network, Modgraph HOSE and Chern Window, have been applied to selected compounds prepared in this study. The Modgraph Neural Network algorithm was found, in all cases, to provide the most accurate correlations with the experimentally-determined chemical shifts. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2007
Synthesis of P-Methane-3,8-Diol
- Authors: Mpuhlu, Batsho
- Date: 2007
- Subjects: Insect baits and repellents
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10411 , http://hdl.handle.net/10948/570 , http://hdl.handle.net/10948/d1011717 , Insect baits and repellents
- Description: The synthesis of para-menthane-3,8-diol in a batch reactor was investigated in some detail with the view to evaluate the potential of producing said p-menthane- 3,8-diol in a continuous-flow reactor from the results obtained from the batch process. The methodology used as base for this investigation was a published procedure by Takasago of Japan. The Takasago-method produced 92.3 percent Yield for the product para-menthane-3,8-diol, and 2.7 percent Yield of the by-product, acetal. The objective for this investigation was to produce a minimum p-menthane-3,8- diol content of 97.0 percent and a maximum content of 3.0 percent for the by-product acetal. The batch production process was evaluated in detail using statistical experimental design methodologies. Three process variables, namely catalyst loading, organic/aqueous phase ratio and reaction temperature were selected for the study. The experimental method was based on the Takasago procedure, however the substrate was added as a single slug as opposed to gradual addition method and the reaction period was reduced to 30 minutes. Apart from statistical analysis, mechanistic aspects were also used to interpret the following results. Using a central composite design, three response models (one for the conversion of citronellal, p-menthane-3,8-diol and acetal formation) were determined. An analysis of the response surfaces indicated that, to increase the citronellal conversion all three variables should be increased. To increase the amount of pmenthane- 3,8-diol, the reaction temperature and acid concentration should be increased, but the Aq/org ratio should be decreased as the acid catalyst concentration is increased. To minimize the amount of acetals formed during the reaction, the Aq/org ratio should be decreased; temperature and acid concentration can be decreased or increased. The reaction mechanism suggested that p-menthane-3,8-diol may be formed along two pathways: One pathway directly forms p-menthane-3,8-diol, whilst the second pathway forms the isopulegol first, then proceeds to form product by hydrolysis. The acetal is formed as result of the reaction between unreacted citronellal and p-menthane-3,8-diol. From the design experiments it was suggested that reaction time can be reduced to 8 minutes at reaction temperatures between, 80-85 0C The product and acetal were isolated by simple vacuum evaporation of the low boiling citronellal and isopulegol. Results from recycling the catalyst phase were similar to those of the initial process. The results of this investigation has clearly shown that with a proper understanding of the effect of process variables on the performance of the batch synthesis route, the conversion of this traditionally batch (actually semi-batch) process into a continuous process is quite feasible provided that suitable equipment is available. The most important features required for such equipment would be: Intense mixing throughout the reaction zone so as to maximise the surface area between the two immiscible phases, hence the rate of mass transfer between the two phases; and the ability to run reactions above the boiling point of water. Plans for the further study of the process are already well underway and sections of static mixing tubes have been acquired to build a continuous lab scale tubular reactor that would be capable of providing the level of mixing required.
- Full Text:
- Date Issued: 2007
- Authors: Mpuhlu, Batsho
- Date: 2007
- Subjects: Insect baits and repellents
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10411 , http://hdl.handle.net/10948/570 , http://hdl.handle.net/10948/d1011717 , Insect baits and repellents
- Description: The synthesis of para-menthane-3,8-diol in a batch reactor was investigated in some detail with the view to evaluate the potential of producing said p-menthane- 3,8-diol in a continuous-flow reactor from the results obtained from the batch process. The methodology used as base for this investigation was a published procedure by Takasago of Japan. The Takasago-method produced 92.3 percent Yield for the product para-menthane-3,8-diol, and 2.7 percent Yield of the by-product, acetal. The objective for this investigation was to produce a minimum p-menthane-3,8- diol content of 97.0 percent and a maximum content of 3.0 percent for the by-product acetal. The batch production process was evaluated in detail using statistical experimental design methodologies. Three process variables, namely catalyst loading, organic/aqueous phase ratio and reaction temperature were selected for the study. The experimental method was based on the Takasago procedure, however the substrate was added as a single slug as opposed to gradual addition method and the reaction period was reduced to 30 minutes. Apart from statistical analysis, mechanistic aspects were also used to interpret the following results. Using a central composite design, three response models (one for the conversion of citronellal, p-menthane-3,8-diol and acetal formation) were determined. An analysis of the response surfaces indicated that, to increase the citronellal conversion all three variables should be increased. To increase the amount of pmenthane- 3,8-diol, the reaction temperature and acid concentration should be increased, but the Aq/org ratio should be decreased as the acid catalyst concentration is increased. To minimize the amount of acetals formed during the reaction, the Aq/org ratio should be decreased; temperature and acid concentration can be decreased or increased. The reaction mechanism suggested that p-menthane-3,8-diol may be formed along two pathways: One pathway directly forms p-menthane-3,8-diol, whilst the second pathway forms the isopulegol first, then proceeds to form product by hydrolysis. The acetal is formed as result of the reaction between unreacted citronellal and p-menthane-3,8-diol. From the design experiments it was suggested that reaction time can be reduced to 8 minutes at reaction temperatures between, 80-85 0C The product and acetal were isolated by simple vacuum evaporation of the low boiling citronellal and isopulegol. Results from recycling the catalyst phase were similar to those of the initial process. The results of this investigation has clearly shown that with a proper understanding of the effect of process variables on the performance of the batch synthesis route, the conversion of this traditionally batch (actually semi-batch) process into a continuous process is quite feasible provided that suitable equipment is available. The most important features required for such equipment would be: Intense mixing throughout the reaction zone so as to maximise the surface area between the two immiscible phases, hence the rate of mass transfer between the two phases; and the ability to run reactions above the boiling point of water. Plans for the further study of the process are already well underway and sections of static mixing tubes have been acquired to build a continuous lab scale tubular reactor that would be capable of providing the level of mixing required.
- Full Text:
- Date Issued: 2007
Synthesis of triprenylated toluquinone and toluhydroquinone metabolites from a marine-derived Penicillium fungus
- Authors: Scheepers, Brent Ashley
- Date: 2007
- Subjects: Penicillium , Antineoplastic agents , Marine fungi , Quinone
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4373 , http://hdl.handle.net/10962/d1005038 , Penicillium , Antineoplastic agents , Marine fungi , Quinone
- Description: This project forms part of a collaborative effort between the marine natural products chemists at Rhodes University and the medical biochemists at the University of Cape Town’s School of Medicine. Our UCT collaborators tested the cytotoxicity of a group of toluhydroquinones and toluquinones (9-15) against the oesophageal cancer cell line WHCO1 and revealed that the triprenylated toluhydroquinone 11 and it’s oxidised analogue 12 were the most active. This thesis presents an investigation into the role of the polyprenyl side-chain in the cytotoxicity of compound 11 and it’s oxidised analogue 12 by synthesizing and testing the cytotoxicity of simplified analogues of this compound. The synthesis of the two ortho-prenylated toluhydroquinone analogues 5-methyl-2-[(2'E,6'E)-3',7' -dimethyl-2',6'-octadienyl]-1,4-benzenediol (19) and 5-methyl-2-[(2'E,6'E)-3',7',11'-trimethyl-2',6',10'-dodecatrienyl]-1,4-benzenediol (21) and their two ortho-prenylated toluquinone analogues, 5-methyl-2-[(2'E,6'E)-3',7'-dimethyl-2',6'-octadienyl]-2,5-cyclohexadiene-1,4-dione (20) and 5-methyl-2-[(2'E,6'E)-3',7',11'-trimethyl-2',6',10'-dodecatrienyl]-2,5-cyclohexadiene-1,4-dione (22) is described. Our initial attempts to couple geranyl bromide, farnesyl bromide and farnesal to the aromatic precursors m-cresol and 1,4-dimethoxy-2-methylbenzene using directed ortho-prenylation and phenoxide carbon-alkylation were unsuccessful. The four target analogues were eventually synthesized via the initial metal halogen exchange reaction between 1-bromo-2,5-dimethoxy-4-methylbenzene and geranyl bromide/farnesyl bromide using n-BuLi and TMEDA in ditheyl ether at 0 °C to yield 92 and 104 respectively in moderate yield. The demethylation of both compounds preceded smoothly using AgO giving the target analogues 20 and 22 in good yield (approx. 90 %). The reduction of quinones 20 and 22 with sodium dithionite gave 19 and 21 in quantitative yield. The synthesis reported here is the first regioselective synthesis of these compounds. The anti-oesophageal cancer activity of 19-22 and two commercially available non-prenylated analogues 17 and 18 were tested against WHCO1. The conclusion drawn from the anti-oesophageal cancer study was that the polyprenyl side-chain plays a negligable role in the cytotoxicity of compounds such as 11 and 9 against the oesophageal cancer cell line WHCO1.
- Full Text:
- Date Issued: 2007
- Authors: Scheepers, Brent Ashley
- Date: 2007
- Subjects: Penicillium , Antineoplastic agents , Marine fungi , Quinone
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4373 , http://hdl.handle.net/10962/d1005038 , Penicillium , Antineoplastic agents , Marine fungi , Quinone
- Description: This project forms part of a collaborative effort between the marine natural products chemists at Rhodes University and the medical biochemists at the University of Cape Town’s School of Medicine. Our UCT collaborators tested the cytotoxicity of a group of toluhydroquinones and toluquinones (9-15) against the oesophageal cancer cell line WHCO1 and revealed that the triprenylated toluhydroquinone 11 and it’s oxidised analogue 12 were the most active. This thesis presents an investigation into the role of the polyprenyl side-chain in the cytotoxicity of compound 11 and it’s oxidised analogue 12 by synthesizing and testing the cytotoxicity of simplified analogues of this compound. The synthesis of the two ortho-prenylated toluhydroquinone analogues 5-methyl-2-[(2'E,6'E)-3',7' -dimethyl-2',6'-octadienyl]-1,4-benzenediol (19) and 5-methyl-2-[(2'E,6'E)-3',7',11'-trimethyl-2',6',10'-dodecatrienyl]-1,4-benzenediol (21) and their two ortho-prenylated toluquinone analogues, 5-methyl-2-[(2'E,6'E)-3',7'-dimethyl-2',6'-octadienyl]-2,5-cyclohexadiene-1,4-dione (20) and 5-methyl-2-[(2'E,6'E)-3',7',11'-trimethyl-2',6',10'-dodecatrienyl]-2,5-cyclohexadiene-1,4-dione (22) is described. Our initial attempts to couple geranyl bromide, farnesyl bromide and farnesal to the aromatic precursors m-cresol and 1,4-dimethoxy-2-methylbenzene using directed ortho-prenylation and phenoxide carbon-alkylation were unsuccessful. The four target analogues were eventually synthesized via the initial metal halogen exchange reaction between 1-bromo-2,5-dimethoxy-4-methylbenzene and geranyl bromide/farnesyl bromide using n-BuLi and TMEDA in ditheyl ether at 0 °C to yield 92 and 104 respectively in moderate yield. The demethylation of both compounds preceded smoothly using AgO giving the target analogues 20 and 22 in good yield (approx. 90 %). The reduction of quinones 20 and 22 with sodium dithionite gave 19 and 21 in quantitative yield. The synthesis reported here is the first regioselective synthesis of these compounds. The anti-oesophageal cancer activity of 19-22 and two commercially available non-prenylated analogues 17 and 18 were tested against WHCO1. The conclusion drawn from the anti-oesophageal cancer study was that the polyprenyl side-chain plays a negligable role in the cytotoxicity of compounds such as 11 and 9 against the oesophageal cancer cell line WHCO1.
- Full Text:
- Date Issued: 2007
Synthesis, photophysical and photochemical properties of aryloxy tetra-substituted gallium and indium phthalocyanine derivatives
- Durmus, Mahmut, Nyokong, Tebello
- Authors: Durmus, Mahmut , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281431 , vital:55724 , xlink:href="https://doi.org/10.1016/j.tet.2006.11.089"
- Description: The synthesis, photophysical and photochemical properties of the tetra-substituted aryloxy gallium(III) and indium(III) phthalocyanines are reported for the first time. General trends are described for photodegradation, singlet oxygen, fluorescence, and triplet quantum yields and triplet lifetimes of these compounds. The introduction of phenoxy and tert-butylphenoxy substituents on the ring resulted in lowering of fluorescence quantum yields and lifetimes, and triplet quantum yields, and an increase of kIC, kISC, and kF. Photoreduction of the complexes was observed during laser flash photolysis. The singlet oxygen quantum yields (ΦΔ), which give an indication of the potential of the complexes as photosensitizers in applications where singlet oxygen is required (Type II mechanism) ranged from 0.41 to 0.91. Thus, these complexes show potential as Type II photosensitizers.
- Full Text:
- Date Issued: 2007
- Authors: Durmus, Mahmut , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281431 , vital:55724 , xlink:href="https://doi.org/10.1016/j.tet.2006.11.089"
- Description: The synthesis, photophysical and photochemical properties of the tetra-substituted aryloxy gallium(III) and indium(III) phthalocyanines are reported for the first time. General trends are described for photodegradation, singlet oxygen, fluorescence, and triplet quantum yields and triplet lifetimes of these compounds. The introduction of phenoxy and tert-butylphenoxy substituents on the ring resulted in lowering of fluorescence quantum yields and lifetimes, and triplet quantum yields, and an increase of kIC, kISC, and kF. Photoreduction of the complexes was observed during laser flash photolysis. The singlet oxygen quantum yields (ΦΔ), which give an indication of the potential of the complexes as photosensitizers in applications where singlet oxygen is required (Type II mechanism) ranged from 0.41 to 0.91. Thus, these complexes show potential as Type II photosensitizers.
- Full Text:
- Date Issued: 2007