Catalytic behaviour of metallophthalocyanines towards the detection of nitric oxide
- Authors: Vilakazi, Lea Sibulelo
- Date: 2002
- Subjects: Electrochemistry Nitric oxide
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4418 , http://hdl.handle.net/10962/d1006852
- Description: Electrocatalytic reduction and oxidation of nitric oxide (NO) using cobalt phthalocyanine complexes have been studied and compared to vitamin B₁₂ and other metallophthalocyanine (MPc) complexes. Modifying a glassy carbon electrode with these complexes resulted in improved sensitivity of the electrode allowing detection of NO to 10⁻⁹ mol dm⁻³. The mechanisms of catalysis were studied. Electrocatalysis of NO involves coordination of NO to the MPc complex. Hence catalytic activity is affected by the nature of the metal center. However coordination of NO to the MPc complex has to be reversible to eliminate poisoning of the electrode. Though FePc gave the best sensitivity and lowered the reduction potential more than CoPc, the strong Fe-NO bond resulted in the poisoning of the electrode hence, rendering the electrode unstable. Rate constants for NO coordination to the MPc complexes were studied. These rates were smaller than the studied NO porphyrin coordination rates. Electrocatalytic reduction of NO using MPc complexes involves a transfer of an electron from the metal center to the NO ligand. Hence, substitution of electron-donating grohps on the cobalt pthalocyanine complex resulted in improved sensitivity and catalytic activity. A CoPc modified microelectrode (11μm) was used to monitor NO in human blood components and to detect NO in a rat brain. Detections of NO were also done in aqueous solutions in the presence of interfering species such as dopamine and serotonin. An interaction between NO and serotonin was observed.
- Full Text:
- Date Issued: 2002
- Authors: Vilakazi, Lea Sibulelo
- Date: 2002
- Subjects: Electrochemistry Nitric oxide
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4418 , http://hdl.handle.net/10962/d1006852
- Description: Electrocatalytic reduction and oxidation of nitric oxide (NO) using cobalt phthalocyanine complexes have been studied and compared to vitamin B₁₂ and other metallophthalocyanine (MPc) complexes. Modifying a glassy carbon electrode with these complexes resulted in improved sensitivity of the electrode allowing detection of NO to 10⁻⁹ mol dm⁻³. The mechanisms of catalysis were studied. Electrocatalysis of NO involves coordination of NO to the MPc complex. Hence catalytic activity is affected by the nature of the metal center. However coordination of NO to the MPc complex has to be reversible to eliminate poisoning of the electrode. Though FePc gave the best sensitivity and lowered the reduction potential more than CoPc, the strong Fe-NO bond resulted in the poisoning of the electrode hence, rendering the electrode unstable. Rate constants for NO coordination to the MPc complexes were studied. These rates were smaller than the studied NO porphyrin coordination rates. Electrocatalytic reduction of NO using MPc complexes involves a transfer of an electron from the metal center to the NO ligand. Hence, substitution of electron-donating grohps on the cobalt pthalocyanine complex resulted in improved sensitivity and catalytic activity. A CoPc modified microelectrode (11μm) was used to monitor NO in human blood components and to detect NO in a rat brain. Detections of NO were also done in aqueous solutions in the presence of interfering species such as dopamine and serotonin. An interaction between NO and serotonin was observed.
- Full Text:
- Date Issued: 2002
Detection of neurotransmitters using metallophthalocyanines as electrocatalysts
- Authors: Oni, Joshua Idowu
- Date: 2002
- Subjects: Neurotransmitters Electrochemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4435 , http://hdl.handle.net/10962/d1007470
- Description: Some metallophthalocyanine complexes were synthesized and their catalytic activities towards the detection and quantification of the neurotransmitters dopamine, serotonin and histamine were investigated. The study of the possible interaction between these transmitter substances and the metallophthalocyanine complexes was undertaken. Dopamine, serotonin and histamine formed complexes with Iron (II) tetrasulfophthalocyanine. The rate and equilibrium constants obtained for the coordination are in the range of values reported in the literature for ligand coordination to iron phthalocyanine complexes. Carbon paste electrodes of millimetric diameters modified with Iron (II) tetrasulfophthalocyanine exhibited good electro catalytic activity towards the detection and analysis of dopamine and serotonin while at the same time eliminated the problem of interference posed by ascorbic acid in the electrochemical analysis of neurotransmitters. A detection limit of the order of 10-6 mol dm-3 was obtained for both dopamine and serotonin at the modified electrodes. Carbon paste ultra micro electrodes modified with iron (II) tetrasulfophthalocyanine were also used for the detection of dopamine and serotonin as well as the simultaneous determination of dopamine and ascorbic acid in a mixture. The detection limit obtained for dopamine at the ultra microelectrode was 4.2xlO-7 mol dm-3 The electrode kinetics of vitamin BI as well as the stability of the electrode towards its determination was improved upon by modifying carbon paste electrodes with manganese phthalocyanine. The modified electrodes were used for the analysis of vitamin BI in tablets.
- Full Text:
- Date Issued: 2002
- Authors: Oni, Joshua Idowu
- Date: 2002
- Subjects: Neurotransmitters Electrochemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4435 , http://hdl.handle.net/10962/d1007470
- Description: Some metallophthalocyanine complexes were synthesized and their catalytic activities towards the detection and quantification of the neurotransmitters dopamine, serotonin and histamine were investigated. The study of the possible interaction between these transmitter substances and the metallophthalocyanine complexes was undertaken. Dopamine, serotonin and histamine formed complexes with Iron (II) tetrasulfophthalocyanine. The rate and equilibrium constants obtained for the coordination are in the range of values reported in the literature for ligand coordination to iron phthalocyanine complexes. Carbon paste electrodes of millimetric diameters modified with Iron (II) tetrasulfophthalocyanine exhibited good electro catalytic activity towards the detection and analysis of dopamine and serotonin while at the same time eliminated the problem of interference posed by ascorbic acid in the electrochemical analysis of neurotransmitters. A detection limit of the order of 10-6 mol dm-3 was obtained for both dopamine and serotonin at the modified electrodes. Carbon paste ultra micro electrodes modified with iron (II) tetrasulfophthalocyanine were also used for the detection of dopamine and serotonin as well as the simultaneous determination of dopamine and ascorbic acid in a mixture. The detection limit obtained for dopamine at the ultra microelectrode was 4.2xlO-7 mol dm-3 The electrode kinetics of vitamin BI as well as the stability of the electrode towards its determination was improved upon by modifying carbon paste electrodes with manganese phthalocyanine. The modified electrodes were used for the analysis of vitamin BI in tablets.
- Full Text:
- Date Issued: 2002
Effects of Axial Ligands on the Photosensitising Properties of Silicon Octaphenoxyphthalocyanines
- Authors: Maree, Machiel David
- Date: 2002
- Subjects: Ligands , Photochemotherapy , Phthalocyanines
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4553 , http://hdl.handle.net/10962/d1018246
- Description: Various axially substituted Silicon octaphenoxyphthalocyanines were synthesised as potential photosensitisers in the photodynamic therapy of cancer. Conventional reflux reactions were used for synthesis as well as new microwave irradiation reactions, wherein the reaction times were decreased tenfold with a marginal increase in reaction yield and product purity. An interesting series of oligomeric (dimer to a nonamer) silicon octaphenoxyphthalocyanines were also successfully synthesised in a reaction similar to polymerisation reactions. These compounds were found to undergo an axial ligand transformation upon irradiation with red light (> 600 nm) in dimethylsulphoxide solution. All the ligands were transformed into the dihydroxy silicon octaphenoxyphthalocyanine with varying degrees of phototransformation quantum yields ranging in order from 10⁻³ to 10⁻⁵ depending on the axial ligand involved. During and after axial ligand transformations a photodegredation of the dihydroxy silicon octaphenoxy phthalocyanine was observed upon continued irradiation. The oligomers were found to undergo the same axial ligand transformation process with a phototransformation quantum yield of 10⁻⁵ The singlet oxygen quantum yields of the unaggregated monomeric silicon octaphenoxy phthalocyanines were all found to be approximately 0.2 with the exception of a compound with two (trihexyl)siloxy axial substituents that had a singlet oxygen quantum yield of approximately 0.4 in dimethylsulphoxide solutions. The oligomers showed a surprising trend of an increase in singlet oxygen quantum yield with an increase in phthalocyanine ring number up to the pentamer and then a dramatic decrease to the nonamer. The triplet quantum yield and triplet lifetime were determined by laser flash photolysis for selected compounds and no correlation was observed with any of these properties and the singlet oxygen quantum yields. These selected compounds all fluoresce and a very good correlation was found between the fluorescence lifetimes determined experimentally by laser photolysis and the Strickler-Berg equation for the non-aggregated compounds. Electrochemical measurements also indicate the importance of the axial ligands upon the behaviour of the phthalocyanines as cyclic voltammetric behaviour was determined by the nature of the axial ligand.
- Full Text:
- Date Issued: 2002
- Authors: Maree, Machiel David
- Date: 2002
- Subjects: Ligands , Photochemotherapy , Phthalocyanines
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4553 , http://hdl.handle.net/10962/d1018246
- Description: Various axially substituted Silicon octaphenoxyphthalocyanines were synthesised as potential photosensitisers in the photodynamic therapy of cancer. Conventional reflux reactions were used for synthesis as well as new microwave irradiation reactions, wherein the reaction times were decreased tenfold with a marginal increase in reaction yield and product purity. An interesting series of oligomeric (dimer to a nonamer) silicon octaphenoxyphthalocyanines were also successfully synthesised in a reaction similar to polymerisation reactions. These compounds were found to undergo an axial ligand transformation upon irradiation with red light (> 600 nm) in dimethylsulphoxide solution. All the ligands were transformed into the dihydroxy silicon octaphenoxyphthalocyanine with varying degrees of phototransformation quantum yields ranging in order from 10⁻³ to 10⁻⁵ depending on the axial ligand involved. During and after axial ligand transformations a photodegredation of the dihydroxy silicon octaphenoxy phthalocyanine was observed upon continued irradiation. The oligomers were found to undergo the same axial ligand transformation process with a phototransformation quantum yield of 10⁻⁵ The singlet oxygen quantum yields of the unaggregated monomeric silicon octaphenoxy phthalocyanines were all found to be approximately 0.2 with the exception of a compound with two (trihexyl)siloxy axial substituents that had a singlet oxygen quantum yield of approximately 0.4 in dimethylsulphoxide solutions. The oligomers showed a surprising trend of an increase in singlet oxygen quantum yield with an increase in phthalocyanine ring number up to the pentamer and then a dramatic decrease to the nonamer. The triplet quantum yield and triplet lifetime were determined by laser flash photolysis for selected compounds and no correlation was observed with any of these properties and the singlet oxygen quantum yields. These selected compounds all fluoresce and a very good correlation was found between the fluorescence lifetimes determined experimentally by laser photolysis and the Strickler-Berg equation for the non-aggregated compounds. Electrochemical measurements also indicate the importance of the axial ligands upon the behaviour of the phthalocyanines as cyclic voltammetric behaviour was determined by the nature of the axial ligand.
- Full Text:
- Date Issued: 2002
Effects of substituents on the photosensitizing and electrocatalytic properties of phthalocyanines
- Authors: Maree, Suzanne Elizabeth
- Date: 2002
- Subjects: Phthalocyanines
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4554 , http://hdl.handle.net/10962/d1018247
- Description: In this work a selection of octasubstituted phthalocyaninato Zinc, Ge(IV) and Sn(IV) complexes were synthesized for possible use in photodynamic therapy and their photochemistry, photophysics and electrochemistry studied. Third-generation complexes containing steroids, e.g. cholesterol and estrone, were synthesized to improve tumour selectivity. The zinc phthalocyanine complexes (ZnPc) showed that complexes containing electron-donating groups have higher photostability. Germanium phthalocyanine complexes (GePc) undergo phototransformation rather than direct photobleaching and the tin phthalocyanine complexes (SnPc) undergo photobleaching mediated by photoreduction of the phthalocyanine ring. Singlet oxygen production showed increased in the following order: GePc>SnPc>ZnPc. Triplet lifetimes of the GePc (168-340μs) are very similar to that of the ZnPc (197 - 366μs), but the triplet lifetimes of the SnPc are ten fold shorter (10 - 32μs ). Triplet quantum yields are higher for the GePc (0.20 - 0.50) and SnPc (0.08 - 0.45) than for the ZnPc (0.02 - 0.25). Fluorescence lifetimes of GePc ( 4.0 - 5.1 ns) are significantly longer than that of ZnPc (1.9 - 3.0 ns) and SnPc (0.2 - 0.4 ns). Fluorescence quantum yields decrease in the following order: GePc(0.21-0.31)>ZnPc(0.02-0.21)>SnPc(0.02- 0.06). Ring-substituted cobalt phthalocyanine complexes of the form CoPc(R)4 (R= NH2, N02, C(CH3)3, S03H and COOH) are compared for their catalytic activities towards the oxidation of cysteine. The potential for the electrocatalytic oxidation of cysteine is closely related to the Com/Co11 couple of the CoPc(R)4 complexes in acidic media and to the Con/Co1 couple in basic media. The catalytic current and the oxidation potential for cysteine are dependent on the pH of the solution, the potential becoming less positive and the currents increasing with increase in pH.
- Full Text:
- Date Issued: 2002
- Authors: Maree, Suzanne Elizabeth
- Date: 2002
- Subjects: Phthalocyanines
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4554 , http://hdl.handle.net/10962/d1018247
- Description: In this work a selection of octasubstituted phthalocyaninato Zinc, Ge(IV) and Sn(IV) complexes were synthesized for possible use in photodynamic therapy and their photochemistry, photophysics and electrochemistry studied. Third-generation complexes containing steroids, e.g. cholesterol and estrone, were synthesized to improve tumour selectivity. The zinc phthalocyanine complexes (ZnPc) showed that complexes containing electron-donating groups have higher photostability. Germanium phthalocyanine complexes (GePc) undergo phototransformation rather than direct photobleaching and the tin phthalocyanine complexes (SnPc) undergo photobleaching mediated by photoreduction of the phthalocyanine ring. Singlet oxygen production showed increased in the following order: GePc>SnPc>ZnPc. Triplet lifetimes of the GePc (168-340μs) are very similar to that of the ZnPc (197 - 366μs), but the triplet lifetimes of the SnPc are ten fold shorter (10 - 32μs ). Triplet quantum yields are higher for the GePc (0.20 - 0.50) and SnPc (0.08 - 0.45) than for the ZnPc (0.02 - 0.25). Fluorescence lifetimes of GePc ( 4.0 - 5.1 ns) are significantly longer than that of ZnPc (1.9 - 3.0 ns) and SnPc (0.2 - 0.4 ns). Fluorescence quantum yields decrease in the following order: GePc(0.21-0.31)>ZnPc(0.02-0.21)>SnPc(0.02- 0.06). Ring-substituted cobalt phthalocyanine complexes of the form CoPc(R)4 (R= NH2, N02, C(CH3)3, S03H and COOH) are compared for their catalytic activities towards the oxidation of cysteine. The potential for the electrocatalytic oxidation of cysteine is closely related to the Com/Co11 couple of the CoPc(R)4 complexes in acidic media and to the Con/Co1 couple in basic media. The catalytic current and the oxidation potential for cysteine are dependent on the pH of the solution, the potential becoming less positive and the currents increasing with increase in pH.
- Full Text:
- Date Issued: 2002
Photosensitizing properties of non-transition metal porphyrazines towards the generation of singlet oxygen
- Seotsanyana-Mokhosi, Itumeleng
- Authors: Seotsanyana-Mokhosi, Itumeleng
- Date: 2001 , 2013-05-02
- Subjects: Phthalocyanines , Photosensitization, Biological , Active oxygen -- Physiological effect , Photosensitizing compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4395 , http://hdl.handle.net/10962/d1006086 , Phthalocyanines , Photosensitization, Biological , Active oxygen -- Physiological effect , Photosensitizing compounds
- Description: Metallophthalocyanine complexes containing non-transition metals are very useful as sensitizers for photodynamic therapy, a cure for cancer that is based on visible light activation of tumour localized photo sensitizers. Excited sensitizers generate singlet oxygen as the main hyperactive species that destroy the tumour. Water soluble sensitizers are sought after for the convenience of delivery into the body. Thus, phthalocyanine (pc), tetrapyridinoporphyrazines (tppa) and tetramethyltetrapyridinoporphyrazines (tmtppa) with non-transition central metal atoms of Ge, Si, Sn and Zn were studied. First was the synthesis of these complexes, followed by their characterisation. The characterisation involved the use of ultraviolet and visible absorption spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy, electrochemical properties and elemental analysis. Photochemical properties of the complexes were then investigated. Photolysis of these macrocycles showed two processes; -reduction of the dye and photobleaching, which leads to the disintegration of the conjugated chromophore structure of the dye. Photobleaching is the reductive quenching of the excited state of the sensitizers. The intensity of the quenching decreased progressively from tmtppa, tppa to pc metal complexes with photobleaching quantum yields, 6.6 x 10.5⁻¹, 1.8 x 10.5⁻¹ and 5.4 x 10⁻⁶ for Zntmtppa, Zntppa and Znpc, respectively. Efficiency of singlet oxygen sensitization is solvent dependent with very different values obtained for the same compound in different solvents, for example, 0.25 and 0.38 were observed as singlet oxygen quantum yields for Gepc complex in DMSO and DMF respectively. In DMSO the efficiency of ¹O₂ generation decrease considerably from pc to tppa and finally tmtppa. In water Getmtppa exhibits much higher singlet oxygen quantum yield, hence promising to be effective as a sensitizer for photodynamic therapy.
- Full Text:
- Date Issued: 2001
- Authors: Seotsanyana-Mokhosi, Itumeleng
- Date: 2001 , 2013-05-02
- Subjects: Phthalocyanines , Photosensitization, Biological , Active oxygen -- Physiological effect , Photosensitizing compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4395 , http://hdl.handle.net/10962/d1006086 , Phthalocyanines , Photosensitization, Biological , Active oxygen -- Physiological effect , Photosensitizing compounds
- Description: Metallophthalocyanine complexes containing non-transition metals are very useful as sensitizers for photodynamic therapy, a cure for cancer that is based on visible light activation of tumour localized photo sensitizers. Excited sensitizers generate singlet oxygen as the main hyperactive species that destroy the tumour. Water soluble sensitizers are sought after for the convenience of delivery into the body. Thus, phthalocyanine (pc), tetrapyridinoporphyrazines (tppa) and tetramethyltetrapyridinoporphyrazines (tmtppa) with non-transition central metal atoms of Ge, Si, Sn and Zn were studied. First was the synthesis of these complexes, followed by their characterisation. The characterisation involved the use of ultraviolet and visible absorption spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy, electrochemical properties and elemental analysis. Photochemical properties of the complexes were then investigated. Photolysis of these macrocycles showed two processes; -reduction of the dye and photobleaching, which leads to the disintegration of the conjugated chromophore structure of the dye. Photobleaching is the reductive quenching of the excited state of the sensitizers. The intensity of the quenching decreased progressively from tmtppa, tppa to pc metal complexes with photobleaching quantum yields, 6.6 x 10.5⁻¹, 1.8 x 10.5⁻¹ and 5.4 x 10⁻⁶ for Zntmtppa, Zntppa and Znpc, respectively. Efficiency of singlet oxygen sensitization is solvent dependent with very different values obtained for the same compound in different solvents, for example, 0.25 and 0.38 were observed as singlet oxygen quantum yields for Gepc complex in DMSO and DMF respectively. In DMSO the efficiency of ¹O₂ generation decrease considerably from pc to tppa and finally tmtppa. In water Getmtppa exhibits much higher singlet oxygen quantum yield, hence promising to be effective as a sensitizer for photodynamic therapy.
- Full Text:
- Date Issued: 2001
Photocatalytic reactions of metal diphthalocyanine complexes
- Authors: Nensala, Ngudiankama
- Date: 2000
- Subjects: Metal complexes Electrochemistry Photochemistry Pentachlorophenol
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4328 , http://hdl.handle.net/10962/d1004989
- Description: Photocatalytic reactions of tin diphthalocyanine, Sn ^IVPc₂ and anionic form of Nd^III, Dy^III, Eu^III, Tm^III and Lu^III diphthalocyanine complexes ( [Pc(-2)Nd^IIIpc(-2)]⁻ , [Pc(-2)Dy^IIIPc(-2)]⁻ , [Pc(-2)Eu^IIIPc(-2)⁻, [Pc(-2)Tm^IIlPc(-2)r and [Pc(-2)LuIIIpc(-2)]⁻ respectively) in the presence of CH₂CI₂, S0₂, pentachlorophenol (PCP), 4-chlorophenol (4-Cp) and thionyl chloride have been studied. Photoreactions involving lanthanide diphthalocyanines, filtered and unfiltered radiations were employed, whereas for photoreactions involving tin diphthalocyanine, only unfiltered radiation was employed. For lanthanide diphthalocyanine complexes, LnPce-, the photosensitization power increases with the decrease of the lanthanide ionic radii, implying that the photocatalytic activity of LnPc₂⁻ complexes is associated with the π-π interaction between both phthalocyanine rings. Thus, LuPc₂⁻ is a better photocatalyst than other lanthanide diphthalocyanine complexes. Photolysis ofSnPc₂ in an acetonitrile/dichloromethane solvent mixture, using unfiltered radiation from a tungsten lamp, results in the one-electron oxidation of this species to [Pc( -2 )Sn(IV)Pc(-1)]⁻. The relative quantum yields for the disappearance of SnPc₂ are in the order of 10⁻¹. The photoreaction of SnPc₂ is preceded by excitation to nπ* excited states, before been ,quenched by CH₂CI₂. The one-electron oxidation species, [Pc(-2)Sn(lV)pc(-1)]⁻ was also formed during the photolysis of SnPc₂ in dichloromethane containing S0₂, and with quantum yields of order of 10⁻³. Visible photolysis of [Pc( -2)Nd^IIIpc(-2)]⁻, [Pc(-2)Dy^IIIPc(-2)]⁻ and [Pc(-2)Lu^IIIpc(-2)]⁻ in N,N. dimethylformamide (DMF)/dichloromethane solvent mixture containing SO₂, results in the formation of the one-electron oxidation species, Pc(-2 )Nd^IIIpc(-1), Pc( -2) Dyi^IIIPc(-1) and Pc(-2)Lu^IIIpc(-1), respectively. The relative quantum yields are in the order of 10². The photoreactions are preceded by population of the excited triplet state,³π-π* [ LnPc₂]⁻ complex, before exchanging an electron with S0₂. The one-electron oxidation species of Dy^III and Lu^III diphthalocyanine complexes have also been formed from visible photolysis of [Pc(-2 )Dy^IIIPc(-2)]⁻and [Pc(-2)Lu^IIIpc(-2)]⁻in acetonitrile containing PCP. The PCP is reductively dechlorinated to tetra- and trichlorophenols. The quantum yields for the photosensitization reactions are in the order of 1 0⁻. Photolysis, using visible radiation from 220 W Quartzline lamp, of an aqueous solution of 4-Cp, saturated with oxygen and containing a suspension of solid [Pc(-2)Nd^IIIpc(-2)]⁻, results in the formation of benzoquinone, hydro quinone and 4-chlorocatechol. The quantum yields for the degradation of 4-Cp are in the order of 10⁻. Langmuir-Hinshelwood kinetic model shows the adsorption of 4-chlorophenol onto solid [Pc(-2)Nd^IIIpc(-2)]⁻. Lanthanide diphthalocyanine complexes ([Pc-2)Nd^IIIpc(-2)]⁻. [Pc(-2)Eu^IIIpc(-2)]⁻, (Pc(-2)Tm^IIIpc( -2)]⁻ and (Pc(-2)Lu^IIIpc(-2)]⁻) undergo one or two-electron oxidation in the presence of thionyl chloride. At low concentrations of SOCI₂(<10⁻⁴ mol dm⁻³) the visible yhotolysis of [Pc(-2 )LnPc(-2)]⁻ complexes result in the one-electron oxidation, giving neutral lanthanide diphthalocyanine species, Pc(-2)Ln^IIIpc(-1). The Pc(-2 )LnPc(-I) species undergoes one-electron photooxidation to [Pc(-I )LnPc( -I)]⁻ in dichloromethane and in the presence of SOC₁₂. At large concentrations of SOC₁₂ (>10⁻² mol dm⁻³), direct two-electron oxidation of the (Pc(-2 )LnPc - 2)]⁻ species to (Pc(-1)LnPc(-1)]⁻ occurs. Spectroelectrochemical behaviours of Sn^IVPc₂ have been also studied. The cyclic voltammetry ofSnPc₂ in CH₂CI₂/TBAP show two reduction couples at -0.56 V and -0.89 V versus saturated calomel electrode (SCE) and one oxidation couple at 0.35 V versus SCE. In DMFITEAP system, the reduction couples are observed at -0.44 V and -0.81 V versus SCE whereas the oxidation couple occurred at 0.43 V versus SCE. The oxidation couple corresponds to [Pc(-2 )Sn^IVPc(-2 )]/[Pc(-2)Sn^IVPc( -I)] . and the reduction couples to [Pc(-2)Sn^IVPc( -2 )]/[Pc(-2 )Sn^IVPc( -3 )]⁻ and [Pc(-2)Snl^IVPc( -3)] ⁻/[Pc(-3 )Sn^IVPc(-3)]²⁻, respectively. The electronic absorption spectra of these reduced and oxidized species are reported.
- Full Text:
- Date Issued: 2000
- Authors: Nensala, Ngudiankama
- Date: 2000
- Subjects: Metal complexes Electrochemistry Photochemistry Pentachlorophenol
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4328 , http://hdl.handle.net/10962/d1004989
- Description: Photocatalytic reactions of tin diphthalocyanine, Sn ^IVPc₂ and anionic form of Nd^III, Dy^III, Eu^III, Tm^III and Lu^III diphthalocyanine complexes ( [Pc(-2)Nd^IIIpc(-2)]⁻ , [Pc(-2)Dy^IIIPc(-2)]⁻ , [Pc(-2)Eu^IIIPc(-2)⁻, [Pc(-2)Tm^IIlPc(-2)r and [Pc(-2)LuIIIpc(-2)]⁻ respectively) in the presence of CH₂CI₂, S0₂, pentachlorophenol (PCP), 4-chlorophenol (4-Cp) and thionyl chloride have been studied. Photoreactions involving lanthanide diphthalocyanines, filtered and unfiltered radiations were employed, whereas for photoreactions involving tin diphthalocyanine, only unfiltered radiation was employed. For lanthanide diphthalocyanine complexes, LnPce-, the photosensitization power increases with the decrease of the lanthanide ionic radii, implying that the photocatalytic activity of LnPc₂⁻ complexes is associated with the π-π interaction between both phthalocyanine rings. Thus, LuPc₂⁻ is a better photocatalyst than other lanthanide diphthalocyanine complexes. Photolysis ofSnPc₂ in an acetonitrile/dichloromethane solvent mixture, using unfiltered radiation from a tungsten lamp, results in the one-electron oxidation of this species to [Pc( -2 )Sn(IV)Pc(-1)]⁻. The relative quantum yields for the disappearance of SnPc₂ are in the order of 10⁻¹. The photoreaction of SnPc₂ is preceded by excitation to nπ* excited states, before been ,quenched by CH₂CI₂. The one-electron oxidation species, [Pc(-2)Sn(lV)pc(-1)]⁻ was also formed during the photolysis of SnPc₂ in dichloromethane containing S0₂, and with quantum yields of order of 10⁻³. Visible photolysis of [Pc( -2)Nd^IIIpc(-2)]⁻, [Pc(-2)Dy^IIIPc(-2)]⁻ and [Pc(-2)Lu^IIIpc(-2)]⁻ in N,N. dimethylformamide (DMF)/dichloromethane solvent mixture containing SO₂, results in the formation of the one-electron oxidation species, Pc(-2 )Nd^IIIpc(-1), Pc( -2) Dyi^IIIPc(-1) and Pc(-2)Lu^IIIpc(-1), respectively. The relative quantum yields are in the order of 10². The photoreactions are preceded by population of the excited triplet state,³π-π* [ LnPc₂]⁻ complex, before exchanging an electron with S0₂. The one-electron oxidation species of Dy^III and Lu^III diphthalocyanine complexes have also been formed from visible photolysis of [Pc(-2 )Dy^IIIPc(-2)]⁻and [Pc(-2)Lu^IIIpc(-2)]⁻in acetonitrile containing PCP. The PCP is reductively dechlorinated to tetra- and trichlorophenols. The quantum yields for the photosensitization reactions are in the order of 1 0⁻. Photolysis, using visible radiation from 220 W Quartzline lamp, of an aqueous solution of 4-Cp, saturated with oxygen and containing a suspension of solid [Pc(-2)Nd^IIIpc(-2)]⁻, results in the formation of benzoquinone, hydro quinone and 4-chlorocatechol. The quantum yields for the degradation of 4-Cp are in the order of 10⁻. Langmuir-Hinshelwood kinetic model shows the adsorption of 4-chlorophenol onto solid [Pc(-2)Nd^IIIpc(-2)]⁻. Lanthanide diphthalocyanine complexes ([Pc-2)Nd^IIIpc(-2)]⁻. [Pc(-2)Eu^IIIpc(-2)]⁻, (Pc(-2)Tm^IIIpc( -2)]⁻ and (Pc(-2)Lu^IIIpc(-2)]⁻) undergo one or two-electron oxidation in the presence of thionyl chloride. At low concentrations of SOCI₂(<10⁻⁴ mol dm⁻³) the visible yhotolysis of [Pc(-2 )LnPc(-2)]⁻ complexes result in the one-electron oxidation, giving neutral lanthanide diphthalocyanine species, Pc(-2)Ln^IIIpc(-1). The Pc(-2 )LnPc(-I) species undergoes one-electron photooxidation to [Pc(-I )LnPc( -I)]⁻ in dichloromethane and in the presence of SOC₁₂. At large concentrations of SOC₁₂ (>10⁻² mol dm⁻³), direct two-electron oxidation of the (Pc(-2 )LnPc - 2)]⁻ species to (Pc(-1)LnPc(-1)]⁻ occurs. Spectroelectrochemical behaviours of Sn^IVPc₂ have been also studied. The cyclic voltammetry ofSnPc₂ in CH₂CI₂/TBAP show two reduction couples at -0.56 V and -0.89 V versus saturated calomel electrode (SCE) and one oxidation couple at 0.35 V versus SCE. In DMFITEAP system, the reduction couples are observed at -0.44 V and -0.81 V versus SCE whereas the oxidation couple occurred at 0.43 V versus SCE. The oxidation couple corresponds to [Pc(-2 )Sn^IVPc(-2 )]/[Pc(-2)Sn^IVPc( -I)] . and the reduction couples to [Pc(-2)Sn^IVPc( -2 )]/[Pc(-2 )Sn^IVPc( -3 )]⁻ and [Pc(-2)Snl^IVPc( -3)] ⁻/[Pc(-3 )Sn^IVPc(-3)]²⁻, respectively. The electronic absorption spectra of these reduced and oxidized species are reported.
- Full Text:
- Date Issued: 2000
Synthetic and analytical studies of biomimetic metal complexes
- Authors: Wellington, Kevin Wayne
- Date: 2000
- Subjects: Biomimetics Metal complexes Metalloenzymes Metal ions Ligands
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4377 , http://hdl.handle.net/10962/d1005042
- Description: Several series of novel diamido, diamino and diimino ligands containing different spacers and heterocyclic donors have been synthesised. The spacers include the flexible biphenyl, the rigid 1,1 O-phenanthroline and various acyclic moieties, while the heterocyclic donors comprise pyridine, imidazole or benzimidazole groups. These ligands have been designed to complex copper and act as biomimetic models of the active site of the enzyme, tyrosinase, and their complexes with copper, cobalt, nickel and platinum have been analysed using microanalytical, IR, UV-Visible and cyclic voltammetric techniques. Attempted reduction of the biphenyl-based diimino ligands resulted in an unexpected intramolecular cyclisation affording azepine derivatives, the structures of which were elucidated with the aid of single crystal X-ray analysis of cobalt and nickel complexes. Computer modelling methods have been used to explore the conformational options of the copper complexes, and to assess the accessibility of the dinuclear copper site to substrate molecules. Computer modelling has also been used, in conjunction with the available analytical data, to visualise the possible structures of selected ligands and complexes. The copper complexes, although predominantly polymeric, were evaluated as biomimetic catalysts using 3,5-di-t-butylphenol and 3,5-di-t-butylcatechol as substrates. Some of the complexes clearly displayed biomimetic potential, exhibiting both phenolase and catecholase activity.
- Full Text:
- Date Issued: 2000
- Authors: Wellington, Kevin Wayne
- Date: 2000
- Subjects: Biomimetics Metal complexes Metalloenzymes Metal ions Ligands
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4377 , http://hdl.handle.net/10962/d1005042
- Description: Several series of novel diamido, diamino and diimino ligands containing different spacers and heterocyclic donors have been synthesised. The spacers include the flexible biphenyl, the rigid 1,1 O-phenanthroline and various acyclic moieties, while the heterocyclic donors comprise pyridine, imidazole or benzimidazole groups. These ligands have been designed to complex copper and act as biomimetic models of the active site of the enzyme, tyrosinase, and their complexes with copper, cobalt, nickel and platinum have been analysed using microanalytical, IR, UV-Visible and cyclic voltammetric techniques. Attempted reduction of the biphenyl-based diimino ligands resulted in an unexpected intramolecular cyclisation affording azepine derivatives, the structures of which were elucidated with the aid of single crystal X-ray analysis of cobalt and nickel complexes. Computer modelling methods have been used to explore the conformational options of the copper complexes, and to assess the accessibility of the dinuclear copper site to substrate molecules. Computer modelling has also been used, in conjunction with the available analytical data, to visualise the possible structures of selected ligands and complexes. The copper complexes, although predominantly polymeric, were evaluated as biomimetic catalysts using 3,5-di-t-butylphenol and 3,5-di-t-butylcatechol as substrates. Some of the complexes clearly displayed biomimetic potential, exhibiting both phenolase and catecholase activity.
- Full Text:
- Date Issued: 2000
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
Electrochemical studies of metal-ligand interactions and of metal binding proteins
- Authors: Limson, Janice Leigh
- Date: 1999
- Subjects: Electrochemical analysis , Metals -- Analysis , Proteins -- Analysis , Electrochemistry -- Technique
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4551 , http://hdl.handle.net/10962/d1018239
- Description: Electrochemical methods were researched for the analysis of metals, proteins and the identification of metal binding proteins. Adsorptive cathodic stripping voltamrnetry for metal analysis combines the inherent sensitivity of electrochemical techniques with the specificity of ligands for the nonfaradaic preconcentration of analytes at the electrode. The utility of catechol, resorcinol, 4-methylcatechol and 4-t-butylcatechol as ligands was explored for the sensitive analysis of copper, bismuth, cadmium and lead on a mercury film glassy carbon electrode. Metal complexes of lead, copper and bismuth with resorcinol showed the largest increase in current with increase in metal concentration, whereas complexes of these metals with 4-t-butylcatechol showed the lowest current response. Cadmium showed the highest current responses with 4-methylcatechol. The four metals could be determined simultaneously in the presence of resorcinol, although considerable interference was observed between bismuth and copper. The electroanalysis of cysteine and cysteine containing proteins at carbon electrodes are impaired by slow electron transfer rates at carbon electrodes, exhibiting high overpotentials, greater than 1 V vs Ag! Agel. Metallophthalocyanines have been shown to promote the electrocatalysis of cysteine at lowered potentials. Chemical modification of electrodes with appropriate modifiers is a means of incorporating specificity into electroanalysis, with applications in electrocatalysis. A glassy carbon electrode was modified by electrodeposition of cobalt (II) tetrasulphophthalocyanine [Co(II)TSPct to produce a chemically modified glassy carbon electrode (CMGCE). The CoTSPc-CMGCE catalysed the oxidation of cysteine in the pH range 1 to 10. The significance of this electrode is an application for analysis of proteins at biological pH's. A biscyanoruthenium(II) phthalocyanine CMGCE catalysed the oxidation of cysteine at 0.43 V vs Ag/AgCl a significant lowering in the overpotential for the oxidation of cysteine. Metallothionein, a metal binding protein, is believed to be involved in metal homeostasis and detoxification in the peripheral organs of living systems. A method for the quantitative determination of this protein utilising its high cysteine content was presented. At pH 8.4 Tris-HCl buffer, and using a CoTSPc-CMGCE modified by electrodeposition of the modifier, the anodic peaks for the oxidation of metallothionein was observed at 0. 90 V vs Ag/ AgCI. Ferredoxin is a simple iron-sulphur protein. One tenth of its residues are cysteine. Ferredoxin is involved in simple electron transfer processes during photosynthesis and respiration. Electrochemical studies of spinach ferredoxin were conducted at a CoTSPc-CMGCE. Anodic currents for the oxidation of the cysteine fragment of ferredoxin was observed at 0.85 V vs Ag/AgCl in HEPES buffer at pH 7.4, representing a new method for analysis of this protein. Voltammetric studies of its ferric/ferrous transition have shown quasi-reversible waves atE~ -0.62 V vs Ag/AgCl only in the presence of promoters. At a CoTSPc-CMGCE, a cathodic wave attributed to the reduction of Fe(III)/Fe(II) was observed at Epc -0.34 V vs Ag/AgCl. This represents an alternative method for voltammetric studies of the ferric/ferrous transition at significantly lowered potentials. Melatonin, a pineal gland hormone functions m setting and entraining circadian rhythms and in neuroprotection as a free radical scavenger and general antioxidant. Using adsorptive cathodic stripping voltammetry, the binding affinities of melatonin, serotonin and tryptophan for metals, were measured. The results showed that the following metal complexes were formed: aluminium with melatonin, serotonin and tryptophan; cadmium with melatonin and tryptophan; copper with melatonin and serotonin; iron (III) with melatonin and serotonin; lead with melatonin, tryptophan and serotonin, zinc with melatonin and tryptophan and iron (II) with tryptophan. The studies suggest a further role for melatonin in the reduction of free radical generation and in metal detoxification and may explain the accumulation of aluminium in Alzheimer's disease.
- Full Text:
- Date Issued: 1999
- Authors: Limson, Janice Leigh
- Date: 1999
- Subjects: Electrochemical analysis , Metals -- Analysis , Proteins -- Analysis , Electrochemistry -- Technique
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4551 , http://hdl.handle.net/10962/d1018239
- Description: Electrochemical methods were researched for the analysis of metals, proteins and the identification of metal binding proteins. Adsorptive cathodic stripping voltamrnetry for metal analysis combines the inherent sensitivity of electrochemical techniques with the specificity of ligands for the nonfaradaic preconcentration of analytes at the electrode. The utility of catechol, resorcinol, 4-methylcatechol and 4-t-butylcatechol as ligands was explored for the sensitive analysis of copper, bismuth, cadmium and lead on a mercury film glassy carbon electrode. Metal complexes of lead, copper and bismuth with resorcinol showed the largest increase in current with increase in metal concentration, whereas complexes of these metals with 4-t-butylcatechol showed the lowest current response. Cadmium showed the highest current responses with 4-methylcatechol. The four metals could be determined simultaneously in the presence of resorcinol, although considerable interference was observed between bismuth and copper. The electroanalysis of cysteine and cysteine containing proteins at carbon electrodes are impaired by slow electron transfer rates at carbon electrodes, exhibiting high overpotentials, greater than 1 V vs Ag! Agel. Metallophthalocyanines have been shown to promote the electrocatalysis of cysteine at lowered potentials. Chemical modification of electrodes with appropriate modifiers is a means of incorporating specificity into electroanalysis, with applications in electrocatalysis. A glassy carbon electrode was modified by electrodeposition of cobalt (II) tetrasulphophthalocyanine [Co(II)TSPct to produce a chemically modified glassy carbon electrode (CMGCE). The CoTSPc-CMGCE catalysed the oxidation of cysteine in the pH range 1 to 10. The significance of this electrode is an application for analysis of proteins at biological pH's. A biscyanoruthenium(II) phthalocyanine CMGCE catalysed the oxidation of cysteine at 0.43 V vs Ag/AgCl a significant lowering in the overpotential for the oxidation of cysteine. Metallothionein, a metal binding protein, is believed to be involved in metal homeostasis and detoxification in the peripheral organs of living systems. A method for the quantitative determination of this protein utilising its high cysteine content was presented. At pH 8.4 Tris-HCl buffer, and using a CoTSPc-CMGCE modified by electrodeposition of the modifier, the anodic peaks for the oxidation of metallothionein was observed at 0. 90 V vs Ag/ AgCI. Ferredoxin is a simple iron-sulphur protein. One tenth of its residues are cysteine. Ferredoxin is involved in simple electron transfer processes during photosynthesis and respiration. Electrochemical studies of spinach ferredoxin were conducted at a CoTSPc-CMGCE. Anodic currents for the oxidation of the cysteine fragment of ferredoxin was observed at 0.85 V vs Ag/AgCl in HEPES buffer at pH 7.4, representing a new method for analysis of this protein. Voltammetric studies of its ferric/ferrous transition have shown quasi-reversible waves atE~ -0.62 V vs Ag/AgCl only in the presence of promoters. At a CoTSPc-CMGCE, a cathodic wave attributed to the reduction of Fe(III)/Fe(II) was observed at Epc -0.34 V vs Ag/AgCl. This represents an alternative method for voltammetric studies of the ferric/ferrous transition at significantly lowered potentials. Melatonin, a pineal gland hormone functions m setting and entraining circadian rhythms and in neuroprotection as a free radical scavenger and general antioxidant. Using adsorptive cathodic stripping voltammetry, the binding affinities of melatonin, serotonin and tryptophan for metals, were measured. The results showed that the following metal complexes were formed: aluminium with melatonin, serotonin and tryptophan; cadmium with melatonin and tryptophan; copper with melatonin and serotonin; iron (III) with melatonin and serotonin; lead with melatonin, tryptophan and serotonin, zinc with melatonin and tryptophan and iron (II) with tryptophan. The studies suggest a further role for melatonin in the reduction of free radical generation and in metal detoxification and may explain the accumulation of aluminium in Alzheimer's disease.
- Full Text:
- Date Issued: 1999
Homogenous and heterogenous catalytic activity of metallophthalocyanines towards electrochemical detection of organic compounds
- Authors: Mafatle, Tsukutlane J P
- Date: 1998
- Subjects: Electrochemistry , Organic compounds , Phenols
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4316 , http://hdl.handle.net/10962/d1004974 , Electrochemistry , Organic compounds , Phenols
- Description: Cysteine plays an important role in many biological and pharmaceutical systems. Therefore, in view of its importance, it is essential to find means of detecting it at the lowest possible levels. In this regard, electrochemical techniques have been found to be capable of detecting analytes even at micro levels. However, electrochemical determination of cysteine occurs at a very high potentials. These overpotentials makes quantitative analysis or detection of cysteine difficult at most conventional carbon electrodes. On platinum electrode, the oxidation of cysteine has been reported to occur in the potential range 0.7 to 1.45 V (vs NHE). Therefore, the object of this investigative study has been to find an active complex that could replace platinum and other expensive metals as electrodes. Such a complex should also be capable of reducing the potential at which the oxidation of cysteine occurs on carbon electrodes. As a result, this manuscript gives a full report on the investigative study of electrocatalytic activity of molybdenum phthalocyanine complexes towards detection of cysteine. Molybdenum phthalocyanine, OMo(OH)Pc, and its tetrasulfonated derivative, [OMo(OH)TSPc]⁴⁻ were successfully used to reduce the potential needed to initiate the oxidation of cysteine on carbon paste electrodes (CPE). The oxidation of cysteine on CPE modified with [OMo(OH)Pc]⁴⁻ was found to occur at 0.29 V (vs Ag/AgCl), and in the presence of [OMo(OH)TSPc]⁴⁻ species in solution the oxidation occurred at 0.33 V (vs Ag/AgCl). Molybdenum, in the oxidation states of Mo(IV), Mo(V) and Mo(VI), is found in biological systems as an essential trace element, participating in a number of enzymatic reactions, where it is believed to be coordinated to sulphur-containing ligands in many molybdenum enzymes. This therefore explains why molybdenum phthalocyanines were employed in electroanalytical detection of sulphur containing amino acid, cysteine. Electrochemical methods have also been successfully used in detection of environmental pollutants such as phenolic compounds. Phenolic compounds are oxidised at readily accessible potentials. However, like cysteine, there are problems associated with the electrochemical detection of these important environmental pollutants. Their electrooxidation is known to form dimeric and/or polymeric oxidation products which adsorb onto the electrode surface, thus -videactivating it. Therefore, to address this problem, cobalt phthalocyanine (CoPc) and its tetrasulfonated derivative, [CoTSPc]⁴⁻ were employed in electrocatalytic detection of phenolic compounds. These complexes were found to increase the anodic peak currents for the oxidation of o-cresol, m-cresol, p-cresol, phenol, 2-chlorophenol and 4-chlorophenol. In addition, CoPc deposited onto the glassy carbon electrode improved the stability of the electrode, by reducing electrode poisoning caused by the electrooxidation products of the mentioned phenolic compounds. The potential at which the oxidation occurred and the current response of individual phenolic compounds depended on the degree of substitution and the type of substituent on the phenol molecule. In general, the current response was found to be lower for chlorinated phenols compared with the cresols and phenol. To establish the role of the central metal in the catalytic process, comparison of the electrocatalytic activity of some of the first row transition metal phthalocyanines, for the detection of mono-substituted phenolic compounds, showed the following trend: Co⁽¹¹⁾ > Mn⁽¹¹⁾ > Fe⁽¹¹⁾Pc > Ni⁽¹¹⁾Pc > Cu⁽¹¹⁾Pc > H₂Pc > Zn⁽¹¹⁾Pc > Bare GCE. A report is also given on electrocatalysis using [CoTSPc]⁴⁻ electrochemically deposited on the glassy carbon electrode. This was also found to enhance the anodic peak currents for the oxidation of all phenolic compounds. A report on the effects of scan rate, operating potential, analyte concentration and other variables is also given.
- Full Text:
- Date Issued: 1998
- Authors: Mafatle, Tsukutlane J P
- Date: 1998
- Subjects: Electrochemistry , Organic compounds , Phenols
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4316 , http://hdl.handle.net/10962/d1004974 , Electrochemistry , Organic compounds , Phenols
- Description: Cysteine plays an important role in many biological and pharmaceutical systems. Therefore, in view of its importance, it is essential to find means of detecting it at the lowest possible levels. In this regard, electrochemical techniques have been found to be capable of detecting analytes even at micro levels. However, electrochemical determination of cysteine occurs at a very high potentials. These overpotentials makes quantitative analysis or detection of cysteine difficult at most conventional carbon electrodes. On platinum electrode, the oxidation of cysteine has been reported to occur in the potential range 0.7 to 1.45 V (vs NHE). Therefore, the object of this investigative study has been to find an active complex that could replace platinum and other expensive metals as electrodes. Such a complex should also be capable of reducing the potential at which the oxidation of cysteine occurs on carbon electrodes. As a result, this manuscript gives a full report on the investigative study of electrocatalytic activity of molybdenum phthalocyanine complexes towards detection of cysteine. Molybdenum phthalocyanine, OMo(OH)Pc, and its tetrasulfonated derivative, [OMo(OH)TSPc]⁴⁻ were successfully used to reduce the potential needed to initiate the oxidation of cysteine on carbon paste electrodes (CPE). The oxidation of cysteine on CPE modified with [OMo(OH)Pc]⁴⁻ was found to occur at 0.29 V (vs Ag/AgCl), and in the presence of [OMo(OH)TSPc]⁴⁻ species in solution the oxidation occurred at 0.33 V (vs Ag/AgCl). Molybdenum, in the oxidation states of Mo(IV), Mo(V) and Mo(VI), is found in biological systems as an essential trace element, participating in a number of enzymatic reactions, where it is believed to be coordinated to sulphur-containing ligands in many molybdenum enzymes. This therefore explains why molybdenum phthalocyanines were employed in electroanalytical detection of sulphur containing amino acid, cysteine. Electrochemical methods have also been successfully used in detection of environmental pollutants such as phenolic compounds. Phenolic compounds are oxidised at readily accessible potentials. However, like cysteine, there are problems associated with the electrochemical detection of these important environmental pollutants. Their electrooxidation is known to form dimeric and/or polymeric oxidation products which adsorb onto the electrode surface, thus -videactivating it. Therefore, to address this problem, cobalt phthalocyanine (CoPc) and its tetrasulfonated derivative, [CoTSPc]⁴⁻ were employed in electrocatalytic detection of phenolic compounds. These complexes were found to increase the anodic peak currents for the oxidation of o-cresol, m-cresol, p-cresol, phenol, 2-chlorophenol and 4-chlorophenol. In addition, CoPc deposited onto the glassy carbon electrode improved the stability of the electrode, by reducing electrode poisoning caused by the electrooxidation products of the mentioned phenolic compounds. The potential at which the oxidation occurred and the current response of individual phenolic compounds depended on the degree of substitution and the type of substituent on the phenol molecule. In general, the current response was found to be lower for chlorinated phenols compared with the cresols and phenol. To establish the role of the central metal in the catalytic process, comparison of the electrocatalytic activity of some of the first row transition metal phthalocyanines, for the detection of mono-substituted phenolic compounds, showed the following trend: Co⁽¹¹⁾ > Mn⁽¹¹⁾ > Fe⁽¹¹⁾Pc > Ni⁽¹¹⁾Pc > Cu⁽¹¹⁾Pc > H₂Pc > Zn⁽¹¹⁾Pc > Bare GCE. A report is also given on electrocatalysis using [CoTSPc]⁴⁻ electrochemically deposited on the glassy carbon electrode. This was also found to enhance the anodic peak currents for the oxidation of all phenolic compounds. A report on the effects of scan rate, operating potential, analyte concentration and other variables is also given.
- Full Text:
- Date Issued: 1998