Catalytic reactions of platinum group metal phthalocyanines
- Authors: Sekota, Mantoa Makoena C
- Date: 1999
- Subjects: Phthalocyanines Platinum group
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4396 , http://hdl.handle.net/10962/d1006151
- Description: The voltammetric behaviour of I-cysteine and other organic compounds such as hydrazine, hydroxylamine and methionine has been studied on GCE modified with phthalocyanine complexes of osmium, rhodium and ruthenium. For cysteine oxidation, the catalytic activity of the electrode was dependent the nature of the axial ligand. When cyanide and dimethylsulphoxide (DMSO) were used as axial ligands, giving (DMSO)(Cl)Rh(III)Pc, [(CN)₂Rh(III)Pc], (DMSO)₂0S(II)Pc and [(DMSO)₂Ru(II)Pc].2DMSO complexes, the peak current increased with repetitive scanning, indicating the increase in catalytic activity of the electrode after each scan. This behaviour was not observed when pyridine was used as axial ligand. The improvement of the catalytic activity of the GCE after the first scan has been attributed to the formation of the dimeric π-cation radical species at the electrode surface. Water soluble phthalocyanine complex ([(CN)₂Os(II)Pc]²⁻) and the tetramethyltetra-pyridinoporphyrazine complexes of Pd(II) and Pt(II), ([Pd(II)2,3Tmtppa(-2)]⁴⁺, [Pd(II)3,4Tmtppa(-2)]⁴⁺, [Pt(II)2,3Tmtppa(-2)]⁴⁺ and [Pt(II)3,4Tmtppa(-2)⁴⁺) have been prepared. [(CN)₂Os(II)Pc]²⁻ is soluble in water at pH greater 4 without the formation of dimers. The [M(II)Tmtppa(-2)]⁴⁺ (M = Pd or Pt) show high solubility in water and are stable only in acidic pHs. The cyclic voltammetry of the MPc and [M(II)Tmtppa(-2)]⁴⁺ complexes prepared, is also reported. The interactions of amino acids I-histidine and I-cysteine with the [M(II)Tmtppa(-2)]⁴⁺ complexes of Pd(II) and Pt(ll) were studied. All the [M(Il)Tmtppa(-2)]⁴⁺ are readily reduced to the monoanion species [M(Il)Tmtppa(-3)]³⁻ in the presence of histidine and cysteine. The rate constants for the interaction of [M(Il)Tmtppa(-2)]⁴⁺ complexes ofPt(II) and Pd(II), with histidine and cysteine range from approximately 2 x 10⁻³ to 0.26 dm³ mol⁻¹ s⁻¹. Kinetics of the interaction of [Co(Il)TSPc]⁴⁻ with amino acids, histidine and cysteine in pH 7.2 buffer were studied. The rate constants were found to be first order in both [Co(II)TSPc]⁴⁻ and the amino acid. The formation of [Co(III)TSPc]³⁻ in the presence of histidine occurred with the rate constant of 0.16 dm³ mol⁻¹ s⁻¹, whereas the formation of the [Co(I)TSPc]⁵⁻ species in the presence of cysteine gave the rate constant of 2.2 dm³ mo⁻¹ s¹. The relative quantum yield (QΔ) for singlet oxygen production by [(CN)₂Os(Il)Pc]²⁻, and [(CN)⁴Ru(II)Pc]²⁻ in DMF using diphenylisobenzofuran (DPBF) and a chemical quencher were determined. The quantum yield values were obtained as 0.39 ± 0.05 , and 0.76 ± 0.02 for [(CN₂Os(II)Pc]²⁻ and [(CN)₂Ru(II)Pc]²⁻ respectively. The differences in quantum yield values have been explained in terms of donor abilities of both the central metal and the axial ligands.
- Full Text:
- Date Issued: 1999
- Authors: Sekota, Mantoa Makoena C
- Date: 1999
- Subjects: Phthalocyanines Platinum group
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4396 , http://hdl.handle.net/10962/d1006151
- Description: The voltammetric behaviour of I-cysteine and other organic compounds such as hydrazine, hydroxylamine and methionine has been studied on GCE modified with phthalocyanine complexes of osmium, rhodium and ruthenium. For cysteine oxidation, the catalytic activity of the electrode was dependent the nature of the axial ligand. When cyanide and dimethylsulphoxide (DMSO) were used as axial ligands, giving (DMSO)(Cl)Rh(III)Pc, [(CN)₂Rh(III)Pc], (DMSO)₂0S(II)Pc and [(DMSO)₂Ru(II)Pc].2DMSO complexes, the peak current increased with repetitive scanning, indicating the increase in catalytic activity of the electrode after each scan. This behaviour was not observed when pyridine was used as axial ligand. The improvement of the catalytic activity of the GCE after the first scan has been attributed to the formation of the dimeric π-cation radical species at the electrode surface. Water soluble phthalocyanine complex ([(CN)₂Os(II)Pc]²⁻) and the tetramethyltetra-pyridinoporphyrazine complexes of Pd(II) and Pt(II), ([Pd(II)2,3Tmtppa(-2)]⁴⁺, [Pd(II)3,4Tmtppa(-2)]⁴⁺, [Pt(II)2,3Tmtppa(-2)]⁴⁺ and [Pt(II)3,4Tmtppa(-2)⁴⁺) have been prepared. [(CN)₂Os(II)Pc]²⁻ is soluble in water at pH greater 4 without the formation of dimers. The [M(II)Tmtppa(-2)]⁴⁺ (M = Pd or Pt) show high solubility in water and are stable only in acidic pHs. The cyclic voltammetry of the MPc and [M(II)Tmtppa(-2)]⁴⁺ complexes prepared, is also reported. The interactions of amino acids I-histidine and I-cysteine with the [M(II)Tmtppa(-2)]⁴⁺ complexes of Pd(II) and Pt(ll) were studied. All the [M(Il)Tmtppa(-2)]⁴⁺ are readily reduced to the monoanion species [M(Il)Tmtppa(-3)]³⁻ in the presence of histidine and cysteine. The rate constants for the interaction of [M(Il)Tmtppa(-2)]⁴⁺ complexes ofPt(II) and Pd(II), with histidine and cysteine range from approximately 2 x 10⁻³ to 0.26 dm³ mol⁻¹ s⁻¹. Kinetics of the interaction of [Co(Il)TSPc]⁴⁻ with amino acids, histidine and cysteine in pH 7.2 buffer were studied. The rate constants were found to be first order in both [Co(II)TSPc]⁴⁻ and the amino acid. The formation of [Co(III)TSPc]³⁻ in the presence of histidine occurred with the rate constant of 0.16 dm³ mol⁻¹ s⁻¹, whereas the formation of the [Co(I)TSPc]⁵⁻ species in the presence of cysteine gave the rate constant of 2.2 dm³ mo⁻¹ s¹. The relative quantum yield (QΔ) for singlet oxygen production by [(CN)₂Os(Il)Pc]²⁻, and [(CN)⁴Ru(II)Pc]²⁻ in DMF using diphenylisobenzofuran (DPBF) and a chemical quencher were determined. The quantum yield values were obtained as 0.39 ± 0.05 , and 0.76 ± 0.02 for [(CN₂Os(II)Pc]²⁻ and [(CN)₂Ru(II)Pc]²⁻ respectively. The differences in quantum yield values have been explained in terms of donor abilities of both the central metal and the axial ligands.
- Full Text:
- Date Issued: 1999
Electrochemical studies of gold bioaccumulation by yeast cell wall components
- Authors: Lack, Barbara Anne
- Date: 1999
- Subjects: Hydrometallurgy , Electrochemical analysis , Gold ores , Gold
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4311 , http://hdl.handle.net/10962/d1004969 , Hydrometallurgy , Electrochemical analysis , Gold ores , Gold
- Description: Gold, amongst other group 11 metals, was almost certainly one of the first three metals known to man. In addition to the economic importance of the metal, gold has a wide variety of applications in the medical, electrocatalytical and micro-electronics fields. However, the determination of gold ions in solution, with accuracy, precision, sensitivity and selectivity is still an interesting and much debated topic in analytical chemistry. A system whereby gold ions have been successfully detected employing an electrochemical technique, known as stripping voltammetry, has been developed. The electrochemical method was chosen over other available techniques for the sensitivity, particularly at low concentrations, and selectivity properties; notably in the presence of other metal ions. Under acidic conditions, the electrochemical technique was applied and the presence of gold(III), at a concentration of 2.53 x 10⁻⁵ mol dm⁻³ in a mine waste water sample, was detected. Biomass, in particular yeast and algal types, have been successfully employed in extracting low concentrations of gold ions from industrial effluents. The manipulation of the biological facility for mineral interaction, biohydrometallurgy, may yield numerous potential new technologies. South Africa in particular would benefit from this area of research, since the country is a major ore and metal refining country and if the output and the efficiency of the mines could be improved, even by a small percentage, the financial rewards would be vast. In this study, the application of adsorptive cathodic stripping voltammetry (AdCSV) of gold(III) in the presence of various Saccharomyces cerevisiae cell wall components, was investigated to determine which, if any, were involved specifically in the chemical binding of the gold ions. The chitin and mannan extracts showed the most promise with detection limits of 1.10 x 10⁻⁶ mol dm⁻³ and 9 x 10⁻⁹ mol dm⁻³, respectively; employing the AdCSV technique. A modification of the stripping voltammetry technique, Osteryoung square wave stripping voltammetry (OSWSV), provided the lowest detection limit, for gold(IIl) in the presence of mannan, of 1.70 x 10⁻¹¹ mol dm⁻³ ; utilising a modified carbon paste electrode. The detection of gold(III) has been shown to be dependent on the type of electrode employed, the electrolyte solution and the presence of interfering agents. The effect of copper(II) and silver(I) on the detection of the gold(III) in solution was investigated; whilst the silver(I) has shown no detrimental effects on gold (III) detection systems, copper(II) has indicated the possibility of forming an inter-metallic compound with the gold(III). However, mannan has shown to selectively and preferentially bind the gold(III) in the presence of a ten-fold excess of copper(II). Nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy, as well as computer modelling techniques were employed to further investIgate the mannan-gold(III) interaction and proposed complex formed. The NMR, IR and computer modelling data are in agreement with the electrochemical data on proposing a mannan-gold(III) complex. The co-ordination site was established to be in the vicinity of the H-I and H-2 protons and the gold(III) adopts a square-planar geometry upon co-ordination. The benefits of the research are useful from a biological perspective (i. e. as more is known about the binding sites, microbiologists/biochemists may work on the optimisation of parameters for these sites or work could be furthered into the enhanced expression of the sites) and an industrial one. In addition to the' two major benefits, an improved understanding of gold and its chemistry would be achieved, which is advantageous for other fields of research as well.
- Full Text:
- Date Issued: 1999
- Authors: Lack, Barbara Anne
- Date: 1999
- Subjects: Hydrometallurgy , Electrochemical analysis , Gold ores , Gold
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4311 , http://hdl.handle.net/10962/d1004969 , Hydrometallurgy , Electrochemical analysis , Gold ores , Gold
- Description: Gold, amongst other group 11 metals, was almost certainly one of the first three metals known to man. In addition to the economic importance of the metal, gold has a wide variety of applications in the medical, electrocatalytical and micro-electronics fields. However, the determination of gold ions in solution, with accuracy, precision, sensitivity and selectivity is still an interesting and much debated topic in analytical chemistry. A system whereby gold ions have been successfully detected employing an electrochemical technique, known as stripping voltammetry, has been developed. The electrochemical method was chosen over other available techniques for the sensitivity, particularly at low concentrations, and selectivity properties; notably in the presence of other metal ions. Under acidic conditions, the electrochemical technique was applied and the presence of gold(III), at a concentration of 2.53 x 10⁻⁵ mol dm⁻³ in a mine waste water sample, was detected. Biomass, in particular yeast and algal types, have been successfully employed in extracting low concentrations of gold ions from industrial effluents. The manipulation of the biological facility for mineral interaction, biohydrometallurgy, may yield numerous potential new technologies. South Africa in particular would benefit from this area of research, since the country is a major ore and metal refining country and if the output and the efficiency of the mines could be improved, even by a small percentage, the financial rewards would be vast. In this study, the application of adsorptive cathodic stripping voltammetry (AdCSV) of gold(III) in the presence of various Saccharomyces cerevisiae cell wall components, was investigated to determine which, if any, were involved specifically in the chemical binding of the gold ions. The chitin and mannan extracts showed the most promise with detection limits of 1.10 x 10⁻⁶ mol dm⁻³ and 9 x 10⁻⁹ mol dm⁻³, respectively; employing the AdCSV technique. A modification of the stripping voltammetry technique, Osteryoung square wave stripping voltammetry (OSWSV), provided the lowest detection limit, for gold(IIl) in the presence of mannan, of 1.70 x 10⁻¹¹ mol dm⁻³ ; utilising a modified carbon paste electrode. The detection of gold(III) has been shown to be dependent on the type of electrode employed, the electrolyte solution and the presence of interfering agents. The effect of copper(II) and silver(I) on the detection of the gold(III) in solution was investigated; whilst the silver(I) has shown no detrimental effects on gold (III) detection systems, copper(II) has indicated the possibility of forming an inter-metallic compound with the gold(III). However, mannan has shown to selectively and preferentially bind the gold(III) in the presence of a ten-fold excess of copper(II). Nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy, as well as computer modelling techniques were employed to further investIgate the mannan-gold(III) interaction and proposed complex formed. The NMR, IR and computer modelling data are in agreement with the electrochemical data on proposing a mannan-gold(III) complex. The co-ordination site was established to be in the vicinity of the H-I and H-2 protons and the gold(III) adopts a square-planar geometry upon co-ordination. The benefits of the research are useful from a biological perspective (i. e. as more is known about the binding sites, microbiologists/biochemists may work on the optimisation of parameters for these sites or work could be furthered into the enhanced expression of the sites) and an industrial one. In addition to the' two major benefits, an improved understanding of gold and its chemistry would be achieved, which is advantageous for other fields of research as well.
- Full Text:
- Date Issued: 1999
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