Graphene quantum dots and their metallophthalocyanines nanoconjugates as novel photoluminescent nanosensors
- Authors: Achadu, Ojodomo John
- Date: 2018
- Subjects: Quantum dots , Graphene , Phthalocyanines , Nanoconjugates , Novel photoluminescent nanosensors , Metallophthalocyanines
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/60719 , vital:27821
- Description: The fabrication and application of graphene quantum dots (GQDs)-based photoluminescent probes for the detection of analytes is presented. GQDs were functionalized with complexes such as metallophthalocyanines (MPcs), metal nanoparticles (Au@Ag NPs), 2,2,6,6-tetramethyl(piperidin-1-yl)oxyl (TEMPO), maleimide and thymine for the sensing of target analytes such as ascorbic acid (AA), biothiols (cysteine, homocysteine and glutathione) and mercury ion (Hg²+). The design strategy and approach was based on the quenching of the fluorescence of the GQDs upon functionalization with the above-mentioned complexes, which could be restored in the presence of the target analytes (due to their specific interaction affinity with the complexes). For the detection of AA, GQDs were covalently and/or non-covalently conjugated to TEMPO-bearing complexes to form GQDs-4A-TEMPO and GQDs-TEMPO-MPc systems with nanomolar limits of detection. For the detection of biothiols, Au@Ag NPs and maleimide-bearing complexes (MPc), which have specific affinity to interact with biothiols, were deployed. Hg²+ detection involved the use of GQDs and/or MPcs with thiol and thymine groups, respectively. In addition, a smart sensing platform was designed for the dual detection of biothiols and Hg²+ using supramolecular hybrid of polyethyleneimine functionalized-GQDs and MPc-Au@Ag conjugate. The probe could detect, in a sequential manner, Hg²+ and biothiols with high sensitivity. Results obtained from the LODs of the probes showed that GQDs sensing performances could be enhanced in the presence of MPcs. The probes designed in this work were successfully deployed in the assays of the target analytes in real samples and the recoveries obtained confirmed the analytical applicability of the probes.
- Full Text:
- Date Issued: 2018
- Authors: Achadu, Ojodomo John
- Date: 2018
- Subjects: Quantum dots , Graphene , Phthalocyanines , Nanoconjugates , Novel photoluminescent nanosensors , Metallophthalocyanines
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/60719 , vital:27821
- Description: The fabrication and application of graphene quantum dots (GQDs)-based photoluminescent probes for the detection of analytes is presented. GQDs were functionalized with complexes such as metallophthalocyanines (MPcs), metal nanoparticles (Au@Ag NPs), 2,2,6,6-tetramethyl(piperidin-1-yl)oxyl (TEMPO), maleimide and thymine for the sensing of target analytes such as ascorbic acid (AA), biothiols (cysteine, homocysteine and glutathione) and mercury ion (Hg²+). The design strategy and approach was based on the quenching of the fluorescence of the GQDs upon functionalization with the above-mentioned complexes, which could be restored in the presence of the target analytes (due to their specific interaction affinity with the complexes). For the detection of AA, GQDs were covalently and/or non-covalently conjugated to TEMPO-bearing complexes to form GQDs-4A-TEMPO and GQDs-TEMPO-MPc systems with nanomolar limits of detection. For the detection of biothiols, Au@Ag NPs and maleimide-bearing complexes (MPc), which have specific affinity to interact with biothiols, were deployed. Hg²+ detection involved the use of GQDs and/or MPcs with thiol and thymine groups, respectively. In addition, a smart sensing platform was designed for the dual detection of biothiols and Hg²+ using supramolecular hybrid of polyethyleneimine functionalized-GQDs and MPc-Au@Ag conjugate. The probe could detect, in a sequential manner, Hg²+ and biothiols with high sensitivity. Results obtained from the LODs of the probes showed that GQDs sensing performances could be enhanced in the presence of MPcs. The probes designed in this work were successfully deployed in the assays of the target analytes in real samples and the recoveries obtained confirmed the analytical applicability of the probes.
- Full Text:
- Date Issued: 2018
The design of quantum dots and their conjugates as luminescent probes for analyte sensing
- Authors: Adegoke, Oluwasesan
- Date: 2014
- Subjects: Quantum dots Anolytes Luminescent probes Luminescence spectroscopy Phthalocyanines Nanoparticles
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4457 , http://hdl.handle.net/10962/d1010866
- Description: The design and applications of quantum dots (QDs) as fluorescent probes for analyte sensing is presented. Cadmium based thiol-capped QDs were employed as probe for the detection of analytes. Comparative studies between core CdTe and core-shell CdTe@ZnS QDs showed that the overall sensitivity and selectivity of the sensor was dependent on the nature of the capping agent and the QDs employed, hence making CdTe@ZnS QDs a more superior sensor than the core. To explore the luminescent sensing of QDs based on the fluorescence “turn ON” mode, L-glutathione-capped CdTe QDs was conjugated to 4-amino-2,2,6,6-tetramethylpiperidine-N-oxide (4AT) to form a QDs-4AT conjugate system. The QDs-4AT nanoprobe was highly selective and sensitive to the detection of bromide ion with a very low limit of detection. Subsequently, metallo-phthalocyanines (MPcs) were employed as host molecules on the surface of QDs based on the covalent linking of the QDs to the MPc. Elucidation of the reaction mechanism showed that the fluorescence “turn ON” effect of the QDs-MPc probe in the presence of the analyte was due to axial ligation of the analytes to the Pc ring. Studies showed that the type of substituent attached to the MPc ring influenced the overall sensitivity of the probe. Additionally, a comparative investigation using newly synthesized phthalocyanine and triaza-benzcorrole complexes was conducted when these complexes were conjugated to CdSe@ZnS QDs for analyte sensing. Results showed that the triaza-benzcorrole complex can be employed as a host-molecule sensor but displayed a lower sensitivity for analyte sensing in comparison to the phthalocyanine complex.
- Full Text:
- Date Issued: 2014
- Authors: Adegoke, Oluwasesan
- Date: 2014
- Subjects: Quantum dots Anolytes Luminescent probes Luminescence spectroscopy Phthalocyanines Nanoparticles
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4457 , http://hdl.handle.net/10962/d1010866
- Description: The design and applications of quantum dots (QDs) as fluorescent probes for analyte sensing is presented. Cadmium based thiol-capped QDs were employed as probe for the detection of analytes. Comparative studies between core CdTe and core-shell CdTe@ZnS QDs showed that the overall sensitivity and selectivity of the sensor was dependent on the nature of the capping agent and the QDs employed, hence making CdTe@ZnS QDs a more superior sensor than the core. To explore the luminescent sensing of QDs based on the fluorescence “turn ON” mode, L-glutathione-capped CdTe QDs was conjugated to 4-amino-2,2,6,6-tetramethylpiperidine-N-oxide (4AT) to form a QDs-4AT conjugate system. The QDs-4AT nanoprobe was highly selective and sensitive to the detection of bromide ion with a very low limit of detection. Subsequently, metallo-phthalocyanines (MPcs) were employed as host molecules on the surface of QDs based on the covalent linking of the QDs to the MPc. Elucidation of the reaction mechanism showed that the fluorescence “turn ON” effect of the QDs-MPc probe in the presence of the analyte was due to axial ligation of the analytes to the Pc ring. Studies showed that the type of substituent attached to the MPc ring influenced the overall sensitivity of the probe. Additionally, a comparative investigation using newly synthesized phthalocyanine and triaza-benzcorrole complexes was conducted when these complexes were conjugated to CdSe@ZnS QDs for analyte sensing. Results showed that the triaza-benzcorrole complex can be employed as a host-molecule sensor but displayed a lower sensitivity for analyte sensing in comparison to the phthalocyanine complex.
- Full Text:
- Date Issued: 2014
Catalytic activities of metallophthalocyanines towards detection and transformation of pollutants
- Authors: Agboola, Bolade Oyeyinka
- Date: 2007
- Subjects: Phthalocyanines Electrochemistry Pollutants -- Biodegradation Pollutants -- Measurement
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4427 , http://hdl.handle.net/10962/d1006922
- Description: Syntheses, spectral, electrochemical and spectroelectrochemical studies of new thiol-derivatised MPc complexes were satisfactorily carried out. For the first time, spectroelectrochemistry gave evidence for the formation of Ni²⁺/Ni⁺ process in a NiPc complex. Significant insights as to the nature of Fe⁺Pc and Ni⁺Pc spectra were obtained. Transformations of chlorophenols using chemical and photochemical methods are presented. For cobalt tetrasulphophthalocyanine catalysed oxidation of chlorophenols using hydrogen peroxide as the oxidant, types of oxidation products formed depended on the solvent conditions. Photolysis of aqueous solutions of chlorophenols in the presence of immobilised non-transition metal phthalocyanine photosensitisers onto Amerlite® was carried out. For the first time, MPcS[subscript mix] complexes were immobilised on Amberlite® for use in heterogeneous photocatalysis. Photolysis of the chlorophenols resulted mainly in the formation of chlorobenzoquinone derivatives. The generation of singlet oxygen (¹O₂) by these immobilised MPc photosensitisers was found to play a major role in their photoactivities. Modifications of gold electrodes with the newly synthesised thiol-derivatised MPc complexes via electropolymerisation and SAM techniques are presented. Cyclic voltammetry, impedance spectroscopy (NiPcs only) and spectroelectrochemical techniques (NiPcs only) confirmed that the complexes formed films on gold electrodes. Stable and well packed SAM films as evidenced by the voltammetric characterisation were obtained. For the first time, optimisation of the time for SAM formation based on CV technique was studied. First example of a formation of MnPc-SAM was achieved. Catalytic activities of the NiPc towards chlorophenol depended on the nature of the NiPc in the polymer films and also anti-fouling ability of the films depended on polymer film thickness. The FeTBMPc polymer modified gold electrode showed the best catalytic activity in terms of peak potential, E[subscript p] when compared to reported work in literature for nitrate electrooxidation. Cyclic voltammetry and spectroscopy studies showed that the CoPcs, FePcs and NiPcs catalysed nitrite oxidation involve 2 electrons in total while that of McPcs involve 1 electron. Better catalytic performance towards sulphite electrooxidation were obtained for the CoPcs, FePcs and MnPcs which have metal based redox processes within the range of the sulphite electrooxidation peak while the NiPcs which did not show metal based oxidation reaction performed less.
- Full Text:
- Date Issued: 2007
- Authors: Agboola, Bolade Oyeyinka
- Date: 2007
- Subjects: Phthalocyanines Electrochemistry Pollutants -- Biodegradation Pollutants -- Measurement
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4427 , http://hdl.handle.net/10962/d1006922
- Description: Syntheses, spectral, electrochemical and spectroelectrochemical studies of new thiol-derivatised MPc complexes were satisfactorily carried out. For the first time, spectroelectrochemistry gave evidence for the formation of Ni²⁺/Ni⁺ process in a NiPc complex. Significant insights as to the nature of Fe⁺Pc and Ni⁺Pc spectra were obtained. Transformations of chlorophenols using chemical and photochemical methods are presented. For cobalt tetrasulphophthalocyanine catalysed oxidation of chlorophenols using hydrogen peroxide as the oxidant, types of oxidation products formed depended on the solvent conditions. Photolysis of aqueous solutions of chlorophenols in the presence of immobilised non-transition metal phthalocyanine photosensitisers onto Amerlite® was carried out. For the first time, MPcS[subscript mix] complexes were immobilised on Amberlite® for use in heterogeneous photocatalysis. Photolysis of the chlorophenols resulted mainly in the formation of chlorobenzoquinone derivatives. The generation of singlet oxygen (¹O₂) by these immobilised MPc photosensitisers was found to play a major role in their photoactivities. Modifications of gold electrodes with the newly synthesised thiol-derivatised MPc complexes via electropolymerisation and SAM techniques are presented. Cyclic voltammetry, impedance spectroscopy (NiPcs only) and spectroelectrochemical techniques (NiPcs only) confirmed that the complexes formed films on gold electrodes. Stable and well packed SAM films as evidenced by the voltammetric characterisation were obtained. For the first time, optimisation of the time for SAM formation based on CV technique was studied. First example of a formation of MnPc-SAM was achieved. Catalytic activities of the NiPc towards chlorophenol depended on the nature of the NiPc in the polymer films and also anti-fouling ability of the films depended on polymer film thickness. The FeTBMPc polymer modified gold electrode showed the best catalytic activity in terms of peak potential, E[subscript p] when compared to reported work in literature for nitrate electrooxidation. Cyclic voltammetry and spectroscopy studies showed that the CoPcs, FePcs and NiPcs catalysed nitrite oxidation involve 2 electrons in total while that of McPcs involve 1 electron. Better catalytic performance towards sulphite electrooxidation were obtained for the CoPcs, FePcs and MnPcs which have metal based redox processes within the range of the sulphite electrooxidation peak while the NiPcs which did not show metal based oxidation reaction performed less.
- Full Text:
- Date Issued: 2007
Surface properties and electrocatalytic applications of metallophthalocyanines confined on electrode surfaces
- Authors: Akinbulu, Isaac Adebayo
- Date: 2011
- Subjects: Phthalocyanines Electrochemistry Electrocatalysis Pesticides
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4365 , http://hdl.handle.net/10962/d1005030
- Description: New cobalt (13, 16 19 and 22), manganese (14, 17, 20 and 23) and iron (15, 18, 21 and 24)phthalocyanine complexes were synthesized and characterized. The UV-Vis spectral properties of the complexes were typical of the nature of central metal and position of substituent on the Pc ligand. Their electrochemical behaviors were signatures of the central metals, with varying influences of the nature and position of substituents. Nanocomposite of complex 18 and single walled carbon nanotubes (SWCNTs) (SWCNT-18)was fabricated. Formation of this nano-composite was confirmed by infrared (IR)spectroscopy, X-ray diffraction (XRD) spectroscopy and transmission electron microscopy (TEM). Self-assembled monolayers (SAMs) of SWCNT-18, complexes 13-15, and 20 were electropolymerized on glassy carbon electrodes (GCE). Complex 14 was also electrodeposited on GCE. Surface properties of the SAMs were consistent with the molecular feature of the substituent and the nature of central metal in the adsorbed species, while those of the MnPc modified GCEs were dependent on point of substitution and number of substituent. The SAM-modified gold electrodes were used for the electrocatalytic oxidation of the carbamate insecticide, carbofuran. Amplification of the current signal of the insecticide, at more energetically feasible oxidation potentials, on the SAM-modified gold electrodes, relative to bare gold electrode,justified electrocatalysis. There was enhanced sensitivity (attributed to the presence of SWCNT) of the SWCNT-18-SAM-modified gold electrode towards carbofuran, relative to the signals observed on the other SAMs. Current response of the insecticide,bendiocarb, was also intensified, at more favorable oxidation potentials, on the MnPc (14 and 17) modified GCEs, relative to the response on bare GCE, substantiating electrocatalysis. Also, catalysis of the oxidation of the herbicide, bentazon, was observed on polymeric film of complex 20. The current response of the herbicide on this film was better than that observed on bare GCE. Electrocatalysis of the analytes, on the respective modified electrodes, occurred via closely related mechanisms.
- Full Text:
- Date Issued: 2011
- Authors: Akinbulu, Isaac Adebayo
- Date: 2011
- Subjects: Phthalocyanines Electrochemistry Electrocatalysis Pesticides
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4365 , http://hdl.handle.net/10962/d1005030
- Description: New cobalt (13, 16 19 and 22), manganese (14, 17, 20 and 23) and iron (15, 18, 21 and 24)phthalocyanine complexes were synthesized and characterized. The UV-Vis spectral properties of the complexes were typical of the nature of central metal and position of substituent on the Pc ligand. Their electrochemical behaviors were signatures of the central metals, with varying influences of the nature and position of substituents. Nanocomposite of complex 18 and single walled carbon nanotubes (SWCNTs) (SWCNT-18)was fabricated. Formation of this nano-composite was confirmed by infrared (IR)spectroscopy, X-ray diffraction (XRD) spectroscopy and transmission electron microscopy (TEM). Self-assembled monolayers (SAMs) of SWCNT-18, complexes 13-15, and 20 were electropolymerized on glassy carbon electrodes (GCE). Complex 14 was also electrodeposited on GCE. Surface properties of the SAMs were consistent with the molecular feature of the substituent and the nature of central metal in the adsorbed species, while those of the MnPc modified GCEs were dependent on point of substitution and number of substituent. The SAM-modified gold electrodes were used for the electrocatalytic oxidation of the carbamate insecticide, carbofuran. Amplification of the current signal of the insecticide, at more energetically feasible oxidation potentials, on the SAM-modified gold electrodes, relative to bare gold electrode,justified electrocatalysis. There was enhanced sensitivity (attributed to the presence of SWCNT) of the SWCNT-18-SAM-modified gold electrode towards carbofuran, relative to the signals observed on the other SAMs. Current response of the insecticide,bendiocarb, was also intensified, at more favorable oxidation potentials, on the MnPc (14 and 17) modified GCEs, relative to the response on bare GCE, substantiating electrocatalysis. Also, catalysis of the oxidation of the herbicide, bentazon, was observed on polymeric film of complex 20. The current response of the herbicide on this film was better than that observed on bare GCE. Electrocatalysis of the analytes, on the respective modified electrodes, occurred via closely related mechanisms.
- Full Text:
- Date Issued: 2011
A structural investigation of the sulphated polysaccharide from Aeodes ulvoidea Schmitz
- Allsobrook, Anthony John Robert
- Authors: Allsobrook, Anthony John Robert
- Date: 1973
- Subjects: Red algae -- Composition Polysaccharides
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4437 , http://hdl.handle.net/10962/d1007482
- Description: Aeodes ulvoidea, a red seaweed of the Grateloupiaceae, yielded a highly sulphated polysaccharide which was shown to contain D- and L-galactose, 4-0-methy-L-galactose, 2-0-methyl - D- and L-galactose and 6-0-methyl-D-galactose, together with chromatographic traces of xylose and mannose. The sulphate was not labile to alkali, but it was largely removed with methanolic hydrogen chloride. Periodate oxidation of the polysaccharide, methylation of the de sulphated polysaccharide, and investigation of fifteen oligosaccharides from partial hydrolysis and acetolysis studies of the polysaccharide, indicate that (a) the polysaccharide is composed of a backbone of D-galactose residues which are 1,3- and 1,4-linked (b) at least some regions of alternating structure do occur (c) the 2-0-methylgalactose is linked through the 4-position (d) the 4-0-methyl-L-galactose is present as single unit side chains glycosidically linked to the galactose backbone at position 6, and (e) most of the 6-0-methyl-D-galactose is linked to the 4-position of 2-0-methyl-D-galactose.
- Full Text:
- Date Issued: 1973
- Authors: Allsobrook, Anthony John Robert
- Date: 1973
- Subjects: Red algae -- Composition Polysaccharides
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4437 , http://hdl.handle.net/10962/d1007482
- Description: Aeodes ulvoidea, a red seaweed of the Grateloupiaceae, yielded a highly sulphated polysaccharide which was shown to contain D- and L-galactose, 4-0-methy-L-galactose, 2-0-methyl - D- and L-galactose and 6-0-methyl-D-galactose, together with chromatographic traces of xylose and mannose. The sulphate was not labile to alkali, but it was largely removed with methanolic hydrogen chloride. Periodate oxidation of the polysaccharide, methylation of the de sulphated polysaccharide, and investigation of fifteen oligosaccharides from partial hydrolysis and acetolysis studies of the polysaccharide, indicate that (a) the polysaccharide is composed of a backbone of D-galactose residues which are 1,3- and 1,4-linked (b) at least some regions of alternating structure do occur (c) the 2-0-methylgalactose is linked through the 4-position (d) the 4-0-methyl-L-galactose is present as single unit side chains glycosidically linked to the galactose backbone at position 6, and (e) most of the 6-0-methyl-D-galactose is linked to the 4-position of 2-0-methyl-D-galactose.
- Full Text:
- Date Issued: 1973
Pyrroloiminoquinone metabolites from South African Latrunculid sponges
- Authors: Antunes, Edith Martins
- Date: 2003
- Subjects: Sponges -- South Africa PQQ (Biochemistry) Marine metabolites -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4340 , http://hdl.handle.net/10962/d1005001
- Description: An in depth chemical investigation of the major and minor pyrroloiminoquinone metabolites produced by four species of endemic South African Latrunculid sponges, collected from Algoa Bay and the Tsitsikamma Marine Reserve off the south eastern coast of South Africa, yielded eleven new and twelve known pyrroloiminoquinone metabolites. The structures of the new metabolites were determined using standard spectroscopic techniques. Tsitsikamma pedunculata was shown to contain 7,8-dehydro-3-dihydro-discorhabdin C (2.1), 14-bromo-7,8-dehydro-3-dihydro-discorhabdin C (2.2), discorhabdin S (2.3), 14-bromo-1-hydroxy-discorhabdin S (2.4), 1-bromo-2-hydroxy-4-debromo-discorhabdin S (2.5), and 2,4-debromo-3-dihydro-discorhabdin C (2.6), together with the known compounds 14-bromo-discorhabdin C (1.51), 14-bromo-3-dihydro-discorhabdin C (1.52) and 3-dihydro-discorhabdin C. The metabolites from T. pedunculata were characterised by the presence of a reduced C-3 carbonyl and bromination at C-14. Compounds isolated from a second Latrunculid sponge, Latrunculia lorii, ranged from a substituted bicyclic pyrrolecarboxylic acid, makaluvic acid A (1.47), to the simple tricyclic known pyrroloiminoquinones makaluvamine C (1.33) and damirone B (1.20) and the more complex discorhabdin D type metabolites, discorhabdin M (3.2), 1-amino discorhabdin D (3.3), 1-methoxy discorhabdin D (3.4) and 1-alanyl discorhabdin D (3.5). Discorhabdin G* (3.1) was also isolated and characterised. This is the first reported occurrence of the known compounds 1.20, 1.33 and 1.47 in a Latrunculia sponge. Discorhabdin and bis-pyrroloiminoquinone type compounds predominated in Tsitsikamma favus. Three known, tsitsikammamines A (1.71) and B (1.72), 1.52, and five new pyrroloiminoquinones, tsitsikammamine N-oxime (4.1), tsitsikammamine B N-oxime (4.2), 2.1, 2.4 and 2.6, were isolated from this sponge. A fourth Latrunculid sponge (Strongylodesma sp.) yielded three known compounds, discorhabdins A (1.57), D (1.61) and 1.53, and one new pyrroloiminoquinone 3.3. The dual role of these metabolites as cytotoxic agents and pigments resulted in an attempt to relate the photochemical properties of these metabolites to their cytotoxicity. The pyrroloiminoquinone metabolites studied exhibited moderate singlet oxygen quantum yields, while three compounds (1.57, 4.1 and 4.2) were shown to be capable of producing radicals at a wavelength of 532 nm. The possibility of a correlation between the electrochemical properties and anti-cancer (HCT-116) activity of selected pyrroloiminoquinones was explored. A study of the oesophageal and ovarian cytotoxicities of two pyrroloiminoquinones (1.57 and 1.72), together with an investigation into the intercalation and topoisomerase I inhibitory activity of the bis-pyrroloiminoquinones (1.71, 1.72, 4.1 and 4.2), are presented.
- Full Text:
- Date Issued: 2003
- Authors: Antunes, Edith Martins
- Date: 2003
- Subjects: Sponges -- South Africa PQQ (Biochemistry) Marine metabolites -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4340 , http://hdl.handle.net/10962/d1005001
- Description: An in depth chemical investigation of the major and minor pyrroloiminoquinone metabolites produced by four species of endemic South African Latrunculid sponges, collected from Algoa Bay and the Tsitsikamma Marine Reserve off the south eastern coast of South Africa, yielded eleven new and twelve known pyrroloiminoquinone metabolites. The structures of the new metabolites were determined using standard spectroscopic techniques. Tsitsikamma pedunculata was shown to contain 7,8-dehydro-3-dihydro-discorhabdin C (2.1), 14-bromo-7,8-dehydro-3-dihydro-discorhabdin C (2.2), discorhabdin S (2.3), 14-bromo-1-hydroxy-discorhabdin S (2.4), 1-bromo-2-hydroxy-4-debromo-discorhabdin S (2.5), and 2,4-debromo-3-dihydro-discorhabdin C (2.6), together with the known compounds 14-bromo-discorhabdin C (1.51), 14-bromo-3-dihydro-discorhabdin C (1.52) and 3-dihydro-discorhabdin C. The metabolites from T. pedunculata were characterised by the presence of a reduced C-3 carbonyl and bromination at C-14. Compounds isolated from a second Latrunculid sponge, Latrunculia lorii, ranged from a substituted bicyclic pyrrolecarboxylic acid, makaluvic acid A (1.47), to the simple tricyclic known pyrroloiminoquinones makaluvamine C (1.33) and damirone B (1.20) and the more complex discorhabdin D type metabolites, discorhabdin M (3.2), 1-amino discorhabdin D (3.3), 1-methoxy discorhabdin D (3.4) and 1-alanyl discorhabdin D (3.5). Discorhabdin G* (3.1) was also isolated and characterised. This is the first reported occurrence of the known compounds 1.20, 1.33 and 1.47 in a Latrunculia sponge. Discorhabdin and bis-pyrroloiminoquinone type compounds predominated in Tsitsikamma favus. Three known, tsitsikammamines A (1.71) and B (1.72), 1.52, and five new pyrroloiminoquinones, tsitsikammamine N-oxime (4.1), tsitsikammamine B N-oxime (4.2), 2.1, 2.4 and 2.6, were isolated from this sponge. A fourth Latrunculid sponge (Strongylodesma sp.) yielded three known compounds, discorhabdins A (1.57), D (1.61) and 1.53, and one new pyrroloiminoquinone 3.3. The dual role of these metabolites as cytotoxic agents and pigments resulted in an attempt to relate the photochemical properties of these metabolites to their cytotoxicity. The pyrroloiminoquinone metabolites studied exhibited moderate singlet oxygen quantum yields, while three compounds (1.57, 4.1 and 4.2) were shown to be capable of producing radicals at a wavelength of 532 nm. The possibility of a correlation between the electrochemical properties and anti-cancer (HCT-116) activity of selected pyrroloiminoquinones was explored. A study of the oesophageal and ovarian cytotoxicities of two pyrroloiminoquinones (1.57 and 1.72), together with an investigation into the intercalation and topoisomerase I inhibitory activity of the bis-pyrroloiminoquinones (1.71, 1.72, 4.1 and 4.2), are presented.
- Full Text:
- Date Issued: 2003
Development of styrene based imprinted sorbents for selective clean-up of metalloporphyrins in organic media
- Authors: Awokoya, Kehinde Nurudeen
- Date: 2014
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/54521 , vital:26580
- Description: Most crude oils contain traces of vanadium and nickel complex with porphyrins (VTPP and NTPP) within their asphaltene fraction. Although these metals are only present in trace quantities, they have a significant and detrimental impact on the refining process by degrading the quality of intermediate and end products. Therefore, their selective removal is highly desirable. This thesis presents the development of nickel porphyrin, nickel vanadyl porphyrin imprinted nanofibers and vanadyl porphyrin imprinted polymer (MIP) particles for application as selective sorbents. Computational model based on the combination of molecular dynamics simulations and quantum mechanics was successfully applied to the styrene functional monomer selection. The particle was prepared by bulk polymerization and the nanofibers by a novel approach combining molecular imprinting and electrospinning technology. The morphologies, thermal stabilities and porosities of the imprinted sorbents were studied using SEM, TGA, and BET nitrogen gas adsorption. Chloroform was found to swell the polymer particles to a higher degree than methanol and acetonitrile. The adsorption characteristics of the imprinted sorbents best fitted with Freundlich isotherm model. The imprinted sorbents recorded high extraction efficiencies (EEs) of > 99 % in selectively extracting the metalloporphyrins. The impact of the template on the affinity of recognition for NTPP was evaluated. The results showed that the NTPP adsorption capacity increased as the molar ratio of NTPP to styrene was increased from 1:1 to 3:1. The optimal ratio of template to functional monomer which yielded the best specific affinity and highest recovery (99.9 %) was 3:1. The effects of trifluoroacetic acid (TFA), dichloromethane (DCM), dimethyl sulphoxide (DMSO), pentane (PEN) on electro-spinnability of the polymer solutions and the morphological appearance of the nanofibers were investigated. The imprinted nanofibers exhibited the same selectivity specialism for both NTPP and VTPP. A remarkable stability in relation to reusability was observed when imprinted nanofibers were used, as they could be reused nine times without incurring any significant loss in removal efficiency. The results were validated by analysing a certified reference material. The imprinted sorbents were therefore found to be selective sorbents that are well suited for handling trace metals in organic media.
- Full Text:
- Date Issued: 2014
- Authors: Awokoya, Kehinde Nurudeen
- Date: 2014
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/54521 , vital:26580
- Description: Most crude oils contain traces of vanadium and nickel complex with porphyrins (VTPP and NTPP) within their asphaltene fraction. Although these metals are only present in trace quantities, they have a significant and detrimental impact on the refining process by degrading the quality of intermediate and end products. Therefore, their selective removal is highly desirable. This thesis presents the development of nickel porphyrin, nickel vanadyl porphyrin imprinted nanofibers and vanadyl porphyrin imprinted polymer (MIP) particles for application as selective sorbents. Computational model based on the combination of molecular dynamics simulations and quantum mechanics was successfully applied to the styrene functional monomer selection. The particle was prepared by bulk polymerization and the nanofibers by a novel approach combining molecular imprinting and electrospinning technology. The morphologies, thermal stabilities and porosities of the imprinted sorbents were studied using SEM, TGA, and BET nitrogen gas adsorption. Chloroform was found to swell the polymer particles to a higher degree than methanol and acetonitrile. The adsorption characteristics of the imprinted sorbents best fitted with Freundlich isotherm model. The imprinted sorbents recorded high extraction efficiencies (EEs) of > 99 % in selectively extracting the metalloporphyrins. The impact of the template on the affinity of recognition for NTPP was evaluated. The results showed that the NTPP adsorption capacity increased as the molar ratio of NTPP to styrene was increased from 1:1 to 3:1. The optimal ratio of template to functional monomer which yielded the best specific affinity and highest recovery (99.9 %) was 3:1. The effects of trifluoroacetic acid (TFA), dichloromethane (DCM), dimethyl sulphoxide (DMSO), pentane (PEN) on electro-spinnability of the polymer solutions and the morphological appearance of the nanofibers were investigated. The imprinted nanofibers exhibited the same selectivity specialism for both NTPP and VTPP. A remarkable stability in relation to reusability was observed when imprinted nanofibers were used, as they could be reused nine times without incurring any significant loss in removal efficiency. The results were validated by analysing a certified reference material. The imprinted sorbents were therefore found to be selective sorbents that are well suited for handling trace metals in organic media.
- Full Text:
- Date Issued: 2014
Mannich base metal complexes and their thiocyanate analogues as catalysts in the oxidation of Catechol
- Authors: Ayeni, Ayowole Olaolu
- Date: 2018
- Subjects: Mannich bases , Catechol , Catechol -- Oxidation , Thiocyanates , Catalysts
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62339 , vital:28156
- Description: The study focused on the design of new Cu(II) and Fe(III) complexes, with or without thiocyanate (NCS-), as possible candidates of catechol oxidation using 3,5-di-tert-butyl catechol (3,5-DTBC) as substrate. Two classes of Mannich bases were studied depending on the active methylene group from which they were formed, being either p-cresol or acetaminophen. The ligands were characterised by 1H and 13C NMR spectroscopy. Crystal structures of three of the ligands are newly reported, along with detailed discussion of polymorphism observed in one of the ligands, and the nature of the hydrogen within the ligands in the solid state as well as in solution. The Mannich bases behaved as bidentate (NO), tridentate (NNO) and tetradentate (NNOO) ligands on coordination to Cu(II) and Fe(III) ions in which the hydroxyl group may be protonated or deprotonated. Coordination was determined by IR spectroscopy, investigating shifts in vOH, vC-O and in vCNC of the Mannich bases. The vCNC stretching frequencies v1 and v2 of asymmetrical piperazine Mannich bases were observed to shift upward in few cases upon complexation and this is attributed to (chair-boat) conformational change. The mode of coordination of the thiocyanate was determined by IR spectroscopy. Of the forty metal complexes investigated, six groups of metal complexes were identified as follows: (i) Ma(Ln)aClb-cH2O; (ii) Ma(HLn)a(NCS)aClb; (iii) Ma(Ln)a(NCS)aClb; (iv) Ma(HLn)aClb-cH2O; (v) Ma(Ln)a(NCS)a-cH2O; (vi) Ma(HLn)a(NCS)a-cH2O where a = 1 - 2 ; b = 1 - 4, c = 1 - 8. Molar conductivity values of 4.38 - 161.77 Q-1.cm2.mol-1 for the Cu(II) and Fe(III) complexes in DMSO showed that they range from non-electrolytes to 1:1 and 1:2 electrolytes. Electronic spectra for the ligands and the complexes were conducted in DMF and DMSO. The ligands are characterised by and n→n* and n→n* transitions. Intraligand charge transfer transitions peculiar to the nitro group were observed at about 430 nm for the nitro containing ligands. On coordination, these bands overshadowed the d-d transitions particularly for the nitro-Mannich bases. On complexation, ligand to metal charge transfer transitions associated with the hydroxyl were observed between 320 - 420 nm. Charge transfer transitions associated with the thiocyanates were also observed and discussed. The d-d transitions for high spin Fe(III) complexes are spin forbidden and generally uninformative. Those of Cu(II) are spin allowed and allow tentative structural proposals. Square planar and octahedral geometry are generally prevalent in the Cu(II) complexes with trigonal bipyramidal observed in few instances. The Fe(III) complexes are generally octahedral. Thirty-nine of the forty synthesised Cu(II) and Fe(III) complexes were catalytically active on the substrate (3,5-DTBC) in DMF with turnover rates (kcat) reported in the range of 1.86 ± 0.09 to 112.32 ± 3.72 h-1. From this pool of complexes, sixteen isostructural pairs were identified in terms of geometry, molecular formula and the source of the Mannich base and the following conclusions were made: The presence of thiocyanate in the metal complexes reduce catecholase activity; the Cu(II) complexes generally have better activity but the Fe(III) complexes become more relatively active with highly electron donating groups while the Cu(II) complexes become less; dinuclear complexes have greater activity than the mononuclear.
- Full Text:
- Date Issued: 2018
- Authors: Ayeni, Ayowole Olaolu
- Date: 2018
- Subjects: Mannich bases , Catechol , Catechol -- Oxidation , Thiocyanates , Catalysts
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62339 , vital:28156
- Description: The study focused on the design of new Cu(II) and Fe(III) complexes, with or without thiocyanate (NCS-), as possible candidates of catechol oxidation using 3,5-di-tert-butyl catechol (3,5-DTBC) as substrate. Two classes of Mannich bases were studied depending on the active methylene group from which they were formed, being either p-cresol or acetaminophen. The ligands were characterised by 1H and 13C NMR spectroscopy. Crystal structures of three of the ligands are newly reported, along with detailed discussion of polymorphism observed in one of the ligands, and the nature of the hydrogen within the ligands in the solid state as well as in solution. The Mannich bases behaved as bidentate (NO), tridentate (NNO) and tetradentate (NNOO) ligands on coordination to Cu(II) and Fe(III) ions in which the hydroxyl group may be protonated or deprotonated. Coordination was determined by IR spectroscopy, investigating shifts in vOH, vC-O and in vCNC of the Mannich bases. The vCNC stretching frequencies v1 and v2 of asymmetrical piperazine Mannich bases were observed to shift upward in few cases upon complexation and this is attributed to (chair-boat) conformational change. The mode of coordination of the thiocyanate was determined by IR spectroscopy. Of the forty metal complexes investigated, six groups of metal complexes were identified as follows: (i) Ma(Ln)aClb-cH2O; (ii) Ma(HLn)a(NCS)aClb; (iii) Ma(Ln)a(NCS)aClb; (iv) Ma(HLn)aClb-cH2O; (v) Ma(Ln)a(NCS)a-cH2O; (vi) Ma(HLn)a(NCS)a-cH2O where a = 1 - 2 ; b = 1 - 4, c = 1 - 8. Molar conductivity values of 4.38 - 161.77 Q-1.cm2.mol-1 for the Cu(II) and Fe(III) complexes in DMSO showed that they range from non-electrolytes to 1:1 and 1:2 electrolytes. Electronic spectra for the ligands and the complexes were conducted in DMF and DMSO. The ligands are characterised by and n→n* and n→n* transitions. Intraligand charge transfer transitions peculiar to the nitro group were observed at about 430 nm for the nitro containing ligands. On coordination, these bands overshadowed the d-d transitions particularly for the nitro-Mannich bases. On complexation, ligand to metal charge transfer transitions associated with the hydroxyl were observed between 320 - 420 nm. Charge transfer transitions associated with the thiocyanates were also observed and discussed. The d-d transitions for high spin Fe(III) complexes are spin forbidden and generally uninformative. Those of Cu(II) are spin allowed and allow tentative structural proposals. Square planar and octahedral geometry are generally prevalent in the Cu(II) complexes with trigonal bipyramidal observed in few instances. The Fe(III) complexes are generally octahedral. Thirty-nine of the forty synthesised Cu(II) and Fe(III) complexes were catalytically active on the substrate (3,5-DTBC) in DMF with turnover rates (kcat) reported in the range of 1.86 ± 0.09 to 112.32 ± 3.72 h-1. From this pool of complexes, sixteen isostructural pairs were identified in terms of geometry, molecular formula and the source of the Mannich base and the following conclusions were made: The presence of thiocyanate in the metal complexes reduce catecholase activity; the Cu(II) complexes generally have better activity but the Fe(III) complexes become more relatively active with highly electron donating groups while the Cu(II) complexes become less; dinuclear complexes have greater activity than the mononuclear.
- Full Text:
- Date Issued: 2018
Development of molecularly imprinted polymer based solid phase extraction sorbents for the selective cleanup of food and pharmaceutical residue samples
- Authors: Batlokwa, Bareki Shima
- Date: 2012
- Subjects: Sorbents -- Research Nanofibers -- Research Aflatoxins -- Research Electrospinning -- Research Extraction (Chemistry) -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4309 , http://hdl.handle.net/10962/d1004967
- Description: This thesis presents the development of chlorophyll, cholic acid, aflatoxin B1 molecularly imprinted polymer (MIP) particles and cholic acid MIP nanofibers for application as selective solid phase extraction (SPE) sorbents. The particles were prepared by bulk polymerization and the nanofibers by a novel approach combining molecular imprinting and electrospinning technology. The AFB1 MIP particles were compared with an aflatoxin specific immunoextraction sorbent in cleaning-up and pre-concentrating aflatoxins from nut extracts. They both recorded high extraction efficiencies (EEs) of > 97 % in selectively extracting the aflatoxins (AFB1, AFB2, AFG1 and AFG2). High reproducibility marked by the low %RSDs of < 1% and low LODs of ≤ 0.02 ng/g were calculated in all cases. The LODs were within the monitoring requirements of the European Commission. The results were validated with a peanut butter certified reference material. The chlorophyll MIP on the other hand selectively removed chlorophyll that would otherwise interfere during pesticide residue analysis (PRA) from > 0.6 to <0.09 Au in green plants extracts. The extracted chlorophyll was removed to far below the level of ≥ 0.399 Au that is usually associated with interference during PRA. Furthermore, the MIP demonstrated better selectivity by removing only chlorophyll (> 99%) in the presence of planar pesticides than the currently employed graphitized carbon black (GCB) that removed both the chlorophyll (> 88%) and planar pesticides (> 89%). For the interfering cholic acid during drug residue analysis, cholic acid MIP electrospun nanofibers demonstrated to be more sensitive and possessing higher loading capacity than the MIP particles. 100% cholic acid was removed by the nanofibers from standard solutions relative to 80% by the particles. This showed that the nanofibers have better performance than the micro particles and as such have potential to replace the particle based SPE sorbents that are currently in use. All the templates were optimally removed from the prepared MIPs by employing a novel pressurized hot water extraction template removal method that was used for the first time in this thesis. The method employed only water, an environmentally friendly solvent to remove templates to ≥ 99.6% with template residual bleeding of ≤ 0.02%.
- Full Text:
- Date Issued: 2012
- Authors: Batlokwa, Bareki Shima
- Date: 2012
- Subjects: Sorbents -- Research Nanofibers -- Research Aflatoxins -- Research Electrospinning -- Research Extraction (Chemistry) -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4309 , http://hdl.handle.net/10962/d1004967
- Description: This thesis presents the development of chlorophyll, cholic acid, aflatoxin B1 molecularly imprinted polymer (MIP) particles and cholic acid MIP nanofibers for application as selective solid phase extraction (SPE) sorbents. The particles were prepared by bulk polymerization and the nanofibers by a novel approach combining molecular imprinting and electrospinning technology. The AFB1 MIP particles were compared with an aflatoxin specific immunoextraction sorbent in cleaning-up and pre-concentrating aflatoxins from nut extracts. They both recorded high extraction efficiencies (EEs) of > 97 % in selectively extracting the aflatoxins (AFB1, AFB2, AFG1 and AFG2). High reproducibility marked by the low %RSDs of < 1% and low LODs of ≤ 0.02 ng/g were calculated in all cases. The LODs were within the monitoring requirements of the European Commission. The results were validated with a peanut butter certified reference material. The chlorophyll MIP on the other hand selectively removed chlorophyll that would otherwise interfere during pesticide residue analysis (PRA) from > 0.6 to <0.09 Au in green plants extracts. The extracted chlorophyll was removed to far below the level of ≥ 0.399 Au that is usually associated with interference during PRA. Furthermore, the MIP demonstrated better selectivity by removing only chlorophyll (> 99%) in the presence of planar pesticides than the currently employed graphitized carbon black (GCB) that removed both the chlorophyll (> 88%) and planar pesticides (> 89%). For the interfering cholic acid during drug residue analysis, cholic acid MIP electrospun nanofibers demonstrated to be more sensitive and possessing higher loading capacity than the MIP particles. 100% cholic acid was removed by the nanofibers from standard solutions relative to 80% by the particles. This showed that the nanofibers have better performance than the micro particles and as such have potential to replace the particle based SPE sorbents that are currently in use. All the templates were optimally removed from the prepared MIPs by employing a novel pressurized hot water extraction template removal method that was used for the first time in this thesis. The method employed only water, an environmentally friendly solvent to remove templates to ≥ 99.6% with template residual bleeding of ≤ 0.02%.
- Full Text:
- Date Issued: 2012
The thermodynamics of binary liquid mixtures of compounds containing multiple bonds.
- Authors: Baxter, Rodney Charles
- Date: 1989
- Subjects: Solution (Chemistry)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4531 , http://hdl.handle.net/10962/d1016079
- Description: Excess thermodynamic properties have been determined for several binary liquid mixtures with the aim of testing various thermodynamic theories and postulates. Excess molar enthalpies, HEm, have been determined using an LKB flow microcalorimeter and excess molar volumes, VEm, have been determined using an Anton Paar vibrating tube densitometer. The activity coefficients at infinite dilution ƴ∞₁₃, have been determined using an atmospheric pressure gas-liquid chromatograph. The excess molar enthalpies and the excess molar volumes have been measured at 298.15 K for systems involving the bicyclic compounds decahydronaphthalene (decalin), 1,2,3,4-tetrahydronaphthalene (tetralin), bicyclohexyl, or cyclohexylbenzene mixed with 1- hexene, 1-hexyne, 1-heptene, 1-heptyne, cyclohexene, 1,3-cyclohexadiene, 1,4- cyclohexadiene, or benzene. These excess properties have also been measured for systems where the bicyclic compound has been replaced with benzene, cyclohexane or n-hexane. The results show defmite trends related to the size, shape, and the degree of unsaturation of the component molecules. The Flory theory has been used to predict excess molar enthalpies and excess molar volumes for {(a bicyclic compound or benzene or cyclohexane or n-hexane) +(an n-alkane or a 1-alkene or a 1-alkyne or a cycloalkane or cyclohexene or a cycloalkadiene or benzene)}. The one parameter equations offer reasonably good correlations between the predicted and the experimental results. More insight into the origins of the contnbutions to the excess thermodynamic properties for these systems has been gained by considering the approximate equations of Patterson and co-workers, which separate the interactional and the free volume contributions to the excess molar enthalpy and the excess molar volume. The one parameter equations have adequately rationalized a good deal of the observed behaviour for HEm and VEm. The theory of Liebermann and co-workers, which does not employ any adjustable parameters, has not been as successful at predicting the excess thermodynamic properties for the above systems. The activity coefficients at infinite dilution have been measured at 278.15 K, 288.15 K and 298.15 K for n-bexane, 1-bexene, 1-hexyne, n-heptane, 1-heptene, 1-heptyne, cyclohexane, cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, and benzene, in decalin, tetralin, bicyclohexyl, and cyclohexylbenzene. Solvent losses from the column have been accounted for by an extrapolation procedure. The activity coefficient results together with the HEm and VEm values have been used to calculate the partial molar excess thermodynamic properties of mixing at infinite dilution. The partial molar excess properties at infinite dilution for decalin mixtures are similar to those for bicyclohexyl mixtures. There is also a similarity between the properties of the tetralin mixtures and the cyclohexylbenzene mixtures. The cycloalkadienes, benzene and the 1-alkynes exhibit a strong dissociation effect on being mixed with the saturated solvents, decalin and bicyclohexyl, but associate strongly with tetralin and with cyclohexylbenzene. The Flory theory bas been used to predict activity coefficients at infinite dilution from the experimentally determined HEm results for { (n-bexane or 1-hexene or 1-hexyne or naheptane or 1-heptene or 1-beptyne) + (a bicyclic compound)}. The theory is much better at predicting values for mixtures where both components are either saturated molecules or are unsaturated molecules than for {saturated + unsaturated} mixtures.
- Full Text:
- Date Issued: 1989
- Authors: Baxter, Rodney Charles
- Date: 1989
- Subjects: Solution (Chemistry)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4531 , http://hdl.handle.net/10962/d1016079
- Description: Excess thermodynamic properties have been determined for several binary liquid mixtures with the aim of testing various thermodynamic theories and postulates. Excess molar enthalpies, HEm, have been determined using an LKB flow microcalorimeter and excess molar volumes, VEm, have been determined using an Anton Paar vibrating tube densitometer. The activity coefficients at infinite dilution ƴ∞₁₃, have been determined using an atmospheric pressure gas-liquid chromatograph. The excess molar enthalpies and the excess molar volumes have been measured at 298.15 K for systems involving the bicyclic compounds decahydronaphthalene (decalin), 1,2,3,4-tetrahydronaphthalene (tetralin), bicyclohexyl, or cyclohexylbenzene mixed with 1- hexene, 1-hexyne, 1-heptene, 1-heptyne, cyclohexene, 1,3-cyclohexadiene, 1,4- cyclohexadiene, or benzene. These excess properties have also been measured for systems where the bicyclic compound has been replaced with benzene, cyclohexane or n-hexane. The results show defmite trends related to the size, shape, and the degree of unsaturation of the component molecules. The Flory theory has been used to predict excess molar enthalpies and excess molar volumes for {(a bicyclic compound or benzene or cyclohexane or n-hexane) +(an n-alkane or a 1-alkene or a 1-alkyne or a cycloalkane or cyclohexene or a cycloalkadiene or benzene)}. The one parameter equations offer reasonably good correlations between the predicted and the experimental results. More insight into the origins of the contnbutions to the excess thermodynamic properties for these systems has been gained by considering the approximate equations of Patterson and co-workers, which separate the interactional and the free volume contributions to the excess molar enthalpy and the excess molar volume. The one parameter equations have adequately rationalized a good deal of the observed behaviour for HEm and VEm. The theory of Liebermann and co-workers, which does not employ any adjustable parameters, has not been as successful at predicting the excess thermodynamic properties for the above systems. The activity coefficients at infinite dilution have been measured at 278.15 K, 288.15 K and 298.15 K for n-bexane, 1-bexene, 1-hexyne, n-heptane, 1-heptene, 1-heptyne, cyclohexane, cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene, and benzene, in decalin, tetralin, bicyclohexyl, and cyclohexylbenzene. Solvent losses from the column have been accounted for by an extrapolation procedure. The activity coefficient results together with the HEm and VEm values have been used to calculate the partial molar excess thermodynamic properties of mixing at infinite dilution. The partial molar excess properties at infinite dilution for decalin mixtures are similar to those for bicyclohexyl mixtures. There is also a similarity between the properties of the tetralin mixtures and the cyclohexylbenzene mixtures. The cycloalkadienes, benzene and the 1-alkynes exhibit a strong dissociation effect on being mixed with the saturated solvents, decalin and bicyclohexyl, but associate strongly with tetralin and with cyclohexylbenzene. The Flory theory bas been used to predict activity coefficients at infinite dilution from the experimentally determined HEm results for { (n-bexane or 1-hexene or 1-hexyne or naheptane or 1-heptene or 1-beptyne) + (a bicyclic compound)}. The theory is much better at predicting values for mixtures where both components are either saturated molecules or are unsaturated molecules than for {saturated + unsaturated} mixtures.
- Full Text:
- Date Issued: 1989
Structural and synthetic investigations of South African marine natural products
- Authors: Beukes, Denzil Ronwynne
- Date: 2000
- Subjects: Natural products -- South Africa Marine invertebrates -- South Africa Marine metabolites -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4350 , http://hdl.handle.net/10962/d1005015
- Description: A chemical investigation of six different marine invertebrates, collected along the South African coastline, resulted in the isolation and structural elucidation of fifteen previously undescribed secondary metabolites along with seven known compounds. The structures of the new metabolites were determined by a combination of spectroscopic and chemical methods. The endemic false limpet Siphonaria capensis was shown to contain two unusual polypropionate metabolites capensinone (162) and capensifuranone (163) as well as 2,4,6,8-tetramethyl-2-undecenoic acid (164) and the known polypropionates (E)- and (Z)siphonarienfuranone (149 and 161). Capensinone is the first example of a marine polypropionate containing a cyc1opentenone moiety. An investigation of the endemic South African soft coral Pieterfaurea unilobata yielded six new, highly oxygenated, pregnadiene sterols (180-185) and the known metabolite (169). Compounds 180-185 are the first pregnadienes obtained from the marine environment containing a C-7 substituent. An alternative procedure for the quick assignment of the absolute configuration at C-3 in this series of compounds was proposed. A companson of the pyrroloiminoquinone alkaloids of three undescribed l'}trunculid sponges resulted in the isolation of 3-dih¥drodiscorhabdin C (243), 3-dihydrodiscorhabdin B (244), discorhabdin H (197) and the previously reported alkaloids discorhabdin A (189) and discorhabdin D (192). While all three sponges were found to be morphologically different they all contained discorhabdin A as the major metabolite and discorhabdin H as one of their minor metabolites. It was found that a feature common to most of the South African latrunculid sponges is the reduction of the C-3 carbonyl gr,o up in some of the minor metabolites. The indole alkaloids, dilemmaones A-C (261-263), containing an unusual cyc1opentanone-indole skeleton, were isolated in trace amounts by bioassay guided fractionation of an extract obtained from a mixed collection of sponges collected near Cape Town. In an attempt to acquire more of these novel compounds for further investigation of their biological activity, several synthetic strategies towards their total synthesis were explored. A key feature of these approaches was the exploitation of the regioselective Gassman's artha-alkylation procedure for the introduction of an aromatic methyl substituent.
- Full Text:
- Date Issued: 2000
- Authors: Beukes, Denzil Ronwynne
- Date: 2000
- Subjects: Natural products -- South Africa Marine invertebrates -- South Africa Marine metabolites -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4350 , http://hdl.handle.net/10962/d1005015
- Description: A chemical investigation of six different marine invertebrates, collected along the South African coastline, resulted in the isolation and structural elucidation of fifteen previously undescribed secondary metabolites along with seven known compounds. The structures of the new metabolites were determined by a combination of spectroscopic and chemical methods. The endemic false limpet Siphonaria capensis was shown to contain two unusual polypropionate metabolites capensinone (162) and capensifuranone (163) as well as 2,4,6,8-tetramethyl-2-undecenoic acid (164) and the known polypropionates (E)- and (Z)siphonarienfuranone (149 and 161). Capensinone is the first example of a marine polypropionate containing a cyc1opentenone moiety. An investigation of the endemic South African soft coral Pieterfaurea unilobata yielded six new, highly oxygenated, pregnadiene sterols (180-185) and the known metabolite (169). Compounds 180-185 are the first pregnadienes obtained from the marine environment containing a C-7 substituent. An alternative procedure for the quick assignment of the absolute configuration at C-3 in this series of compounds was proposed. A companson of the pyrroloiminoquinone alkaloids of three undescribed l'}trunculid sponges resulted in the isolation of 3-dih¥drodiscorhabdin C (243), 3-dihydrodiscorhabdin B (244), discorhabdin H (197) and the previously reported alkaloids discorhabdin A (189) and discorhabdin D (192). While all three sponges were found to be morphologically different they all contained discorhabdin A as the major metabolite and discorhabdin H as one of their minor metabolites. It was found that a feature common to most of the South African latrunculid sponges is the reduction of the C-3 carbonyl gr,o up in some of the minor metabolites. The indole alkaloids, dilemmaones A-C (261-263), containing an unusual cyc1opentanone-indole skeleton, were isolated in trace amounts by bioassay guided fractionation of an extract obtained from a mixed collection of sponges collected near Cape Town. In an attempt to acquire more of these novel compounds for further investigation of their biological activity, several synthetic strategies towards their total synthesis were explored. A key feature of these approaches was the exploitation of the regioselective Gassman's artha-alkylation procedure for the introduction of an aromatic methyl substituent.
- Full Text:
- Date Issued: 2000
Synthetic and spectroscopic studies of indolizine derivatives
- Authors: Bode, Moira Leanne
- Date: 1994
- Subjects: Indole alkaloids -- Derivatives Spectrum analysis Chemistry, Organic DNA -- Synthesis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4385 , http://hdl.handle.net/10962/d1005050
- Description: The crystalline compound resulting from thermal cyclization of the Baylis-Hillman product, methyl 3-hydroxy-2-methylene-3-(2-pyridyl)propanoate, has been identified as the indolizine derivative, methyl indolizine-2-carboxylate, and this approach involving the reaction of pyridine-2-carboxaldehydes and acrylate analogues has been established as a general route to 2-substituted indolizines. The ease of cyclization the Baylis-Hillman products to indolizines has been shown to increase by converting the hydroxy group to an acetoxy group, and a range of acetylated Baylis-Hillman products were prepared and cyc1ized to the corresponding 2-substituted indolizines, generally in good overall yield. In the reaction of pyridine-2-carboxaldehyde and methyl vinyl ketone, the intermediate cyclized readily and directly to the corresponding indolizine. One- and two-dimensional ¹H and ¹³C NMR analysis of the 2-substituted indolizine products has permitted complete assignment of all ¹H and ¹³C NMR signals, as well as the measurement of all coupling constants for these compounds. A kinetic and mechanistic study has been conducted on the Baylis-Hillman reaction using ¹H NMR spectroscopy. A range of substrates has been examined and the reaction has been found to be third-order overall. A mechanism involving an addition - elimination sequence is proposed, which fits the kinetic data and accounts for observed substituent effects. Reaction of N,N-dimethylacrylamide with pyridine-2-carboxaldehyde in the presence of the tertiary amine catalyst, DABCO, in chloroform, yielded an unexpected product which has been identified by single crystal X-ray diffraction analysis as 1-(2,2,2-trichloro-1-hydroxyethyl)pyridine. Attempted extension of the general indolizine route to the preparation of chromene systems by reacting salicylaldehyde with methyl acrylate in the presence of DABCO, also led to an unexpected, crystalline material, identified by single crystal X-ray diffraction analysis as the coumarin derivative, 3-[(2-formylphenoxy)methyl]coumarin.A series of chloroquine analogues have been prepared from indolizine-2-carboxylic acid, pyrrolo[I,2-a]quinoline-2-carboxylic acid and imidazo[I,2-a]pyridine-2-carboxylic acid by reaction with suitable amines in the presence of the coupling reagent 1, I' -carbonyldiimidazole. This route has been shown to be a vast improvement on earlier procedures and has provided access to both secondary and tertiary indolizine-2-carboxamides. A range of N,N-dialkylindolizine-2-carboxamides have been prepared by this route, and the influence of substituents on their N-CO rotational energy barriers has been determined using variable temperature ¹H and ¹³C NMR techniques. Intercalation with natural DNA by both chloroquine and the synthesized chloroquine analogues has been examined using UV spectrophotometry, and ¹H and ³¹P NMR spectroscopy. The pyrrolo[I,2-a]quinolines have been shown to be DNA intercalators with binding affinities similar to that of the known antimalarial intercalator, chloroquine. In a preliminary study the synthesis of a short oligonucleotide has been undertaken and changes have been observed in the ¹H and ³¹P NMR spectra of the oligonucleotide on addition of the intercalator, chloroquine.
- Full Text:
- Date Issued: 1994
- Authors: Bode, Moira Leanne
- Date: 1994
- Subjects: Indole alkaloids -- Derivatives Spectrum analysis Chemistry, Organic DNA -- Synthesis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4385 , http://hdl.handle.net/10962/d1005050
- Description: The crystalline compound resulting from thermal cyclization of the Baylis-Hillman product, methyl 3-hydroxy-2-methylene-3-(2-pyridyl)propanoate, has been identified as the indolizine derivative, methyl indolizine-2-carboxylate, and this approach involving the reaction of pyridine-2-carboxaldehydes and acrylate analogues has been established as a general route to 2-substituted indolizines. The ease of cyclization the Baylis-Hillman products to indolizines has been shown to increase by converting the hydroxy group to an acetoxy group, and a range of acetylated Baylis-Hillman products were prepared and cyc1ized to the corresponding 2-substituted indolizines, generally in good overall yield. In the reaction of pyridine-2-carboxaldehyde and methyl vinyl ketone, the intermediate cyclized readily and directly to the corresponding indolizine. One- and two-dimensional ¹H and ¹³C NMR analysis of the 2-substituted indolizine products has permitted complete assignment of all ¹H and ¹³C NMR signals, as well as the measurement of all coupling constants for these compounds. A kinetic and mechanistic study has been conducted on the Baylis-Hillman reaction using ¹H NMR spectroscopy. A range of substrates has been examined and the reaction has been found to be third-order overall. A mechanism involving an addition - elimination sequence is proposed, which fits the kinetic data and accounts for observed substituent effects. Reaction of N,N-dimethylacrylamide with pyridine-2-carboxaldehyde in the presence of the tertiary amine catalyst, DABCO, in chloroform, yielded an unexpected product which has been identified by single crystal X-ray diffraction analysis as 1-(2,2,2-trichloro-1-hydroxyethyl)pyridine. Attempted extension of the general indolizine route to the preparation of chromene systems by reacting salicylaldehyde with methyl acrylate in the presence of DABCO, also led to an unexpected, crystalline material, identified by single crystal X-ray diffraction analysis as the coumarin derivative, 3-[(2-formylphenoxy)methyl]coumarin.A series of chloroquine analogues have been prepared from indolizine-2-carboxylic acid, pyrrolo[I,2-a]quinoline-2-carboxylic acid and imidazo[I,2-a]pyridine-2-carboxylic acid by reaction with suitable amines in the presence of the coupling reagent 1, I' -carbonyldiimidazole. This route has been shown to be a vast improvement on earlier procedures and has provided access to both secondary and tertiary indolizine-2-carboxamides. A range of N,N-dialkylindolizine-2-carboxamides have been prepared by this route, and the influence of substituents on their N-CO rotational energy barriers has been determined using variable temperature ¹H and ¹³C NMR techniques. Intercalation with natural DNA by both chloroquine and the synthesized chloroquine analogues has been examined using UV spectrophotometry, and ¹H and ³¹P NMR spectroscopy. The pyrrolo[I,2-a]quinolines have been shown to be DNA intercalators with binding affinities similar to that of the known antimalarial intercalator, chloroquine. In a preliminary study the synthesis of a short oligonucleotide has been undertaken and changes have been observed in the ¹H and ³¹P NMR spectra of the oligonucleotide on addition of the intercalator, chloroquine.
- Full Text:
- Date Issued: 1994
Nonlinear optical studies of metallophtalocyanines and hemiporphyrazines in solution
- Authors: Britton, Jonathan
- Date: 2014
- Subjects: Phthalocyanines Photochemistry Nanoparticles Nanostructured materials Polymers Quantum dots
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4464 , http://hdl.handle.net/10962/d1011608
- Description: This thesis presents the study of the effects of CdTe-TGA quantum dots (QDs) on optical limiting ability of different phthalocyanine (Pc) complexes (5-12) containing Zn, Ga, In central metals and substituted with benzyloxyphenoxy, phenoxy, tertbutylphenoxy and amino groups in solution and in poly (methyl methacrylate) (PMMA) films. The optical limiting parameters of Pcs were higher for tertbutylphenoxy when compared to benzyloxyphenoxy and phenoxy substituents, in DMSO. Non-peripheral substitution decreased the optical limiting parameters. Third-order susceptibility (Im[χ⁽³⁾]/α) values of Pcs in the absence and presence of CdTe QDs were in the 10⁻¹² to 10⁻¹° esu cm range. Hyperpolarizabilities (γ) ranged from 10⁻³¹ to 10⁻²⁹ esu L for Pc alone or in mixture with QDs. The effect on the optical limiting abilities of twelve embedded phthalocyanines containing In, Ga, Zn and Al as central metals in polymer thin films was also examined. The effect of forming a covalent link zinc tetraamino phthalocyanine (12) with poly (methyl acrylic acid) (PMAA) and Zn (13) and OHAl (14) octacarboxy phthalocyanines to polyethylenimine (PEI) was also studied. The hyperpolarizability of the twelve phthalocyanines in polymer was found to be in the range of 10⁻²⁶ to 10⁻²⁴ esu.L. This is significantly higher than the hyperpolarizabilities of these phthalocyanines in solution. Non-linear optical (NLO) parameters were determined for phthalocyanine complexes containing In, Ga and Zn as central metals when embedded in PMMA polymer in the presence of quantum dots (QDs). The QDs mainly employed were CdTe-TGA (TGA = thioglylcolic acid). Triplet lifetimes increased as k (excited state (σex) to ground state (σg) absorption cross section ratio) values decreased with the addition of the CdTe-TGA to the phthalocyanines. The saturation energy density (Fsat) values were smaller in the films when compared to the solutions. Complex 7 tetrasubstituted with tert-butylphenoxy groups at non-peripheral positions was also studied in the presence of CdS-TGA, CdSe-TGA, fullerenes and single walled carbon nanotubes. There is a general improvement in optical limiting ability of Pc complexes in the presence of nanomaterials (NMs). Degradation studies seem to indicate that placing a phthalocyanine within a polymer thin film may protect it slightly from photo- and thermal degradation. 3(4), 15(16)-Bis-(4 -tert-butyl-phenoxy)-10, 22-diaminohemiporphyrazinato chloroindium hemiporphyrazine was synthesized from 1, 3, 5-triaminobenzene and 4-tert-butyl-phenoxyisoindoline. The structure of the complex was confirmed using mass, nuclear magnetic resonance and infrared spectroscopies. The nonlinear parameters of the compound was also analyzed in dimethylformamide and found to be significantly greater than previously analyzed phthalocyanines.
- Full Text:
- Date Issued: 2014
- Authors: Britton, Jonathan
- Date: 2014
- Subjects: Phthalocyanines Photochemistry Nanoparticles Nanostructured materials Polymers Quantum dots
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4464 , http://hdl.handle.net/10962/d1011608
- Description: This thesis presents the study of the effects of CdTe-TGA quantum dots (QDs) on optical limiting ability of different phthalocyanine (Pc) complexes (5-12) containing Zn, Ga, In central metals and substituted with benzyloxyphenoxy, phenoxy, tertbutylphenoxy and amino groups in solution and in poly (methyl methacrylate) (PMMA) films. The optical limiting parameters of Pcs were higher for tertbutylphenoxy when compared to benzyloxyphenoxy and phenoxy substituents, in DMSO. Non-peripheral substitution decreased the optical limiting parameters. Third-order susceptibility (Im[χ⁽³⁾]/α) values of Pcs in the absence and presence of CdTe QDs were in the 10⁻¹² to 10⁻¹° esu cm range. Hyperpolarizabilities (γ) ranged from 10⁻³¹ to 10⁻²⁹ esu L for Pc alone or in mixture with QDs. The effect on the optical limiting abilities of twelve embedded phthalocyanines containing In, Ga, Zn and Al as central metals in polymer thin films was also examined. The effect of forming a covalent link zinc tetraamino phthalocyanine (12) with poly (methyl acrylic acid) (PMAA) and Zn (13) and OHAl (14) octacarboxy phthalocyanines to polyethylenimine (PEI) was also studied. The hyperpolarizability of the twelve phthalocyanines in polymer was found to be in the range of 10⁻²⁶ to 10⁻²⁴ esu.L. This is significantly higher than the hyperpolarizabilities of these phthalocyanines in solution. Non-linear optical (NLO) parameters were determined for phthalocyanine complexes containing In, Ga and Zn as central metals when embedded in PMMA polymer in the presence of quantum dots (QDs). The QDs mainly employed were CdTe-TGA (TGA = thioglylcolic acid). Triplet lifetimes increased as k (excited state (σex) to ground state (σg) absorption cross section ratio) values decreased with the addition of the CdTe-TGA to the phthalocyanines. The saturation energy density (Fsat) values were smaller in the films when compared to the solutions. Complex 7 tetrasubstituted with tert-butylphenoxy groups at non-peripheral positions was also studied in the presence of CdS-TGA, CdSe-TGA, fullerenes and single walled carbon nanotubes. There is a general improvement in optical limiting ability of Pc complexes in the presence of nanomaterials (NMs). Degradation studies seem to indicate that placing a phthalocyanine within a polymer thin film may protect it slightly from photo- and thermal degradation. 3(4), 15(16)-Bis-(4 -tert-butyl-phenoxy)-10, 22-diaminohemiporphyrazinato chloroindium hemiporphyrazine was synthesized from 1, 3, 5-triaminobenzene and 4-tert-butyl-phenoxyisoindoline. The structure of the complex was confirmed using mass, nuclear magnetic resonance and infrared spectroscopies. The nonlinear parameters of the compound was also analyzed in dimethylformamide and found to be significantly greater than previously analyzed phthalocyanines.
- Full Text:
- Date Issued: 2014
The chemistry of Algoa Bay ascidians
- Authors: Bromley, Candice Leigh
- Date: 2016
- Subjects: Sea squirts -- South Africa -- Algoa Bay , Marine metabolites , Chemistry, Analytic , Liquid chromatography , Inductively coupled plasma mass spectrometry , Metal ions , Nucleosides , Vanadium
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4560 , http://hdl.handle.net/10962/d1020606
- Description: This thesis investigates the chemistry of 25 ascidian species collected from Algoa Bay, South Africa with a concerted focus on metal accumulation by these ascidians and the possible interaction of these metals with ascidian metabolites. Chapter 2 details the screening techniques employed to establish the presence of nitrogenous metabolites (1H- 15N HMBC), hyper-accumulated metal ions (ICP-MS) and potential metal ion/ ascidian metabolite complexes (LC-ICP-MS/ESI-MS). Unfortunately, exhaustive attempts to detect intact metal ion/ascidian metabolite complexes through the use of liquid chromatography with parallel inductively coupled plasma mass spectrometry/electrospray mass spectrometry (LC-ICPMS/ ESI-MS) were unsuccessful. However, the LC-ICP-MS/ESI-MS data obtained for the crude organic extracts of six of the Algoa Bay ascidian species, Distaplia skoogi, Aplidium monile, Aplidium sp., Didemnum sp., Leptoclindines sp. and Polycitor sp. enabled identification of a number of ten halogenated metabolites, namely the indoles 2.28-2.30, and the tyramine and tyrosine derivatives (2.31-2.33, 2.41, 2.43, 2.44 and 2.46), within the ascidian extracts. This study confirmed that LC-ICP-MS/ESI-MS is a powerful tool for the dereplication of halogenated metabolites in complex mixtures especially where these compounds are present in very small amounts. This study is also the first report of these compounds (eight of which are known) in African ascidians. Compounds 2.32 and 2.46 have not been reported before from a marine source. Compounds 2.28-2.30 and 2.33 were present in sufficient amounts in the respective ascidian extracts to allow their isolation and structure elucidation using standard spectroscopic techniques Chapter 3 explores the ability of ascidians to accumulate a wide range of metal ions at concentrations which are often orders of magnitude higher than those of the surrounding sea water. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the total ion concentrations of 24 metals in 25 Algoa Bay ascidian species. To the best of our knowledge this is the largest and most extensive investigation of metal concentrations in a group of different ascidians occurring in the same area. Hypotheisizing that the metal ion concentrations for each ascidian specimen screened may represent a unique fingerprint for each specimen principal component analysis (PCA) was used in an attempt to establish whether there were spatial, temporal or phylogenetic relationships associated with the metal concentration fingerprints of the ascidians that formed part of this study. The PCA results showed that there were no statistically significant relationships between ascidian metal ion concentrations and either the collection year or the collection site of the ascidians. However, species from the family Didemnidae provided the clearest statistical evidence supporting a phylogenetic relationship between these ascidians and their hyperaccumulated metal ion profiles. Furthermore, these results suggested that ascidian species are indeed actively concentrating metal ions from the surrounding sea water and are not simply sinks for passively accumulated metal ions. Interestingly, the concentration of vanadium in the set of ascidians studied did not appear to correlate with any of the other metals accumulated by these ascidians suggesting that there is possibly a unique method employed for the accumulation of vanadium by ascidians. Chapter 4 investigated this possibility further after the nucleosides 4.10, 4.11, 4.13, 4.15, 4.17 and 4.40 were isolated from the vanadium accumulating ascidian Aplidium monile. Studies into the interactions between nucleosides and vanadyl are unfortunately rare and usually qualitative in nature with limited information provided about the stability or structures of the complexes formed. The vanadyl accumulating aplousobranch ascidians e.g. Aplidium monile dominated our study of Algoa Bay ascidians therefore providing us with the rationale to investigate the relatively little studied binding ability and stability of vandyl-nucleoside complexes. Potentiometric studies were conducted to determine the stability constants of complexes formed between the oxovanadium ion vanadyl (VO2+) and the commercially available nucleosides 4.10-4.14. The data afforded by this analysis clearly confirmed the complexity of the vanadyl/nucleoside complexation and suggested that guanosine (4.12) formed the most stable complex with oxovanadium ions. We were also able to establish a third protonation constant for the hydroxyl moiety in 4.12 with a logK 8.87 which has not been previously reported. Finally, Chapter 5 revisited the cytoxicity two Algoa Bay ascidians, Clavelina sp. and Atriolum marinense the extracts from which produced promising bioactivity results in previous studies against oesophageal cancer cells. The HP-20 fractionated extracts of Clavelina sp. and Atriolum marinense proved to be similalrly cytotoxic to breast cancer cells. With the exception for the 100% acetone(aq)fractions the NMR data for both species suggested that most active non polar fractions were dominated by what appeared to be structurally unremarkable fatty acid glycerides and as such were not pursued further. Purification of the 100% acetone(aq)fraction of A. marinense resulted in the isolation of a styrene trimer, 5.1, common to both ascidian extracts. The NMR simulation software WIN-DAISY was employed to confirm the structure of 5.1. Attempts to establish if 5.1 was an isolation artefact or a product of marine pollution were inconclusive
- Full Text:
- Date Issued: 2016
- Authors: Bromley, Candice Leigh
- Date: 2016
- Subjects: Sea squirts -- South Africa -- Algoa Bay , Marine metabolites , Chemistry, Analytic , Liquid chromatography , Inductively coupled plasma mass spectrometry , Metal ions , Nucleosides , Vanadium
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4560 , http://hdl.handle.net/10962/d1020606
- Description: This thesis investigates the chemistry of 25 ascidian species collected from Algoa Bay, South Africa with a concerted focus on metal accumulation by these ascidians and the possible interaction of these metals with ascidian metabolites. Chapter 2 details the screening techniques employed to establish the presence of nitrogenous metabolites (1H- 15N HMBC), hyper-accumulated metal ions (ICP-MS) and potential metal ion/ ascidian metabolite complexes (LC-ICP-MS/ESI-MS). Unfortunately, exhaustive attempts to detect intact metal ion/ascidian metabolite complexes through the use of liquid chromatography with parallel inductively coupled plasma mass spectrometry/electrospray mass spectrometry (LC-ICPMS/ ESI-MS) were unsuccessful. However, the LC-ICP-MS/ESI-MS data obtained for the crude organic extracts of six of the Algoa Bay ascidian species, Distaplia skoogi, Aplidium monile, Aplidium sp., Didemnum sp., Leptoclindines sp. and Polycitor sp. enabled identification of a number of ten halogenated metabolites, namely the indoles 2.28-2.30, and the tyramine and tyrosine derivatives (2.31-2.33, 2.41, 2.43, 2.44 and 2.46), within the ascidian extracts. This study confirmed that LC-ICP-MS/ESI-MS is a powerful tool for the dereplication of halogenated metabolites in complex mixtures especially where these compounds are present in very small amounts. This study is also the first report of these compounds (eight of which are known) in African ascidians. Compounds 2.32 and 2.46 have not been reported before from a marine source. Compounds 2.28-2.30 and 2.33 were present in sufficient amounts in the respective ascidian extracts to allow their isolation and structure elucidation using standard spectroscopic techniques Chapter 3 explores the ability of ascidians to accumulate a wide range of metal ions at concentrations which are often orders of magnitude higher than those of the surrounding sea water. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the total ion concentrations of 24 metals in 25 Algoa Bay ascidian species. To the best of our knowledge this is the largest and most extensive investigation of metal concentrations in a group of different ascidians occurring in the same area. Hypotheisizing that the metal ion concentrations for each ascidian specimen screened may represent a unique fingerprint for each specimen principal component analysis (PCA) was used in an attempt to establish whether there were spatial, temporal or phylogenetic relationships associated with the metal concentration fingerprints of the ascidians that formed part of this study. The PCA results showed that there were no statistically significant relationships between ascidian metal ion concentrations and either the collection year or the collection site of the ascidians. However, species from the family Didemnidae provided the clearest statistical evidence supporting a phylogenetic relationship between these ascidians and their hyperaccumulated metal ion profiles. Furthermore, these results suggested that ascidian species are indeed actively concentrating metal ions from the surrounding sea water and are not simply sinks for passively accumulated metal ions. Interestingly, the concentration of vanadium in the set of ascidians studied did not appear to correlate with any of the other metals accumulated by these ascidians suggesting that there is possibly a unique method employed for the accumulation of vanadium by ascidians. Chapter 4 investigated this possibility further after the nucleosides 4.10, 4.11, 4.13, 4.15, 4.17 and 4.40 were isolated from the vanadium accumulating ascidian Aplidium monile. Studies into the interactions between nucleosides and vanadyl are unfortunately rare and usually qualitative in nature with limited information provided about the stability or structures of the complexes formed. The vanadyl accumulating aplousobranch ascidians e.g. Aplidium monile dominated our study of Algoa Bay ascidians therefore providing us with the rationale to investigate the relatively little studied binding ability and stability of vandyl-nucleoside complexes. Potentiometric studies were conducted to determine the stability constants of complexes formed between the oxovanadium ion vanadyl (VO2+) and the commercially available nucleosides 4.10-4.14. The data afforded by this analysis clearly confirmed the complexity of the vanadyl/nucleoside complexation and suggested that guanosine (4.12) formed the most stable complex with oxovanadium ions. We were also able to establish a third protonation constant for the hydroxyl moiety in 4.12 with a logK 8.87 which has not been previously reported. Finally, Chapter 5 revisited the cytoxicity two Algoa Bay ascidians, Clavelina sp. and Atriolum marinense the extracts from which produced promising bioactivity results in previous studies against oesophageal cancer cells. The HP-20 fractionated extracts of Clavelina sp. and Atriolum marinense proved to be similalrly cytotoxic to breast cancer cells. With the exception for the 100% acetone(aq)fractions the NMR data for both species suggested that most active non polar fractions were dominated by what appeared to be structurally unremarkable fatty acid glycerides and as such were not pursued further. Purification of the 100% acetone(aq)fraction of A. marinense resulted in the isolation of a styrene trimer, 5.1, common to both ascidian extracts. The NMR simulation software WIN-DAISY was employed to confirm the structure of 5.1. Attempts to establish if 5.1 was an isolation artefact or a product of marine pollution were inconclusive
- Full Text:
- Date Issued: 2016
A study of irradiation effects in solids
- Authors: Brown, Michael Ewart
- Date: 1966
- Subjects: Decomposition (Chemistry) , Crystals -- Thermal properties , Oxalates -- Thermal properties , Solids -- Effect of radiation on
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4509 , http://hdl.handle.net/10962/d1013387
- Description: One of the primary objects of this research was to determine, if possible, the nature of the radiation damage prior to thermal decomposition. The X-ray study has not wholly achieved this although more information has been derived from it than from similar work on AgMnO₄ However, the diffuse reflections obtained do indicate, quite strongly, the creation of point defects during irradiation. This is of value since such assumptions have been made in the explanation of the kinetics of decomposition of a number of irradiated solids (BaN₆,CaN₆). In addition the X-ray work has suggested future research which should produce useful information; namely, a precise study of the diffuse reflections. Another object of the research was to attempt to determine what characteristics, if any, of the kinetics of the decomposition of an unirradiated solid would predetermine a marked irradiation effect. It is obvious that the type of nuclear growth which occurs e.g. branching chain, or power law, does not characterise a substance with regard to a possible irradiation effect . The photosensitivity, or otherwise, also does not determine whether there will be an irradiation effect. However, the one property that the substances which have been studied, have in common, is a polyatomic anion, but here again ammonium dichromate does not show an acceleration of the decomposition after irradiation. Consequently it is considered that it is not possible to say, a priori, whether a solid will undergo an accelerated decomposition after irradiation. Each new solid, unless it belongs to a particular class e.g. the alkaline earth azides , must be considered afresh. Nevertheless it does appear that the irradiation effect can take two forms: - (i) the production of an unstable compound e.g. nickel oxalate, the decomposition of which affects the normal pyrolysis; and (ii) the production of point defects which determine the nature of the subsequent thermal decomposition e.g . CaN₆ . It is possible that the effect requires an interaction of the created point defects with the existing line defects.
- Full Text:
- Date Issued: 1966
- Authors: Brown, Michael Ewart
- Date: 1966
- Subjects: Decomposition (Chemistry) , Crystals -- Thermal properties , Oxalates -- Thermal properties , Solids -- Effect of radiation on
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4509 , http://hdl.handle.net/10962/d1013387
- Description: One of the primary objects of this research was to determine, if possible, the nature of the radiation damage prior to thermal decomposition. The X-ray study has not wholly achieved this although more information has been derived from it than from similar work on AgMnO₄ However, the diffuse reflections obtained do indicate, quite strongly, the creation of point defects during irradiation. This is of value since such assumptions have been made in the explanation of the kinetics of decomposition of a number of irradiated solids (BaN₆,CaN₆). In addition the X-ray work has suggested future research which should produce useful information; namely, a precise study of the diffuse reflections. Another object of the research was to attempt to determine what characteristics, if any, of the kinetics of the decomposition of an unirradiated solid would predetermine a marked irradiation effect. It is obvious that the type of nuclear growth which occurs e.g. branching chain, or power law, does not characterise a substance with regard to a possible irradiation effect . The photosensitivity, or otherwise, also does not determine whether there will be an irradiation effect. However, the one property that the substances which have been studied, have in common, is a polyatomic anion, but here again ammonium dichromate does not show an acceleration of the decomposition after irradiation. Consequently it is considered that it is not possible to say, a priori, whether a solid will undergo an accelerated decomposition after irradiation. Each new solid, unless it belongs to a particular class e.g. the alkaline earth azides , must be considered afresh. Nevertheless it does appear that the irradiation effect can take two forms: - (i) the production of an unstable compound e.g. nickel oxalate, the decomposition of which affects the normal pyrolysis; and (ii) the production of point defects which determine the nature of the subsequent thermal decomposition e.g . CaN₆ . It is possible that the effect requires an interaction of the created point defects with the existing line defects.
- Full Text:
- Date Issued: 1966
The adsorption of chelating reagents on oxide minerals
- Bryson, Michael Andrew Walker
- Authors: Bryson, Michael Andrew Walker
- Date: 1986
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:20969 , http://hdl.handle.net/10962/5729
- Description: This work constitutes a fundamental study of the interaction between chelating reagents and oxide minerals . The adsorption mechanisms have been elucidated for most of the systems generated by the oxides of copper(II) or iron(III) and chelating reagents octyl hydroxamate, N-phenylbenzohydroxamate, salicylaldoxime, 5-nitrosalicylaldoxime or 8-hydroxyquinoline. The results of the preliminary work on one of the systems, viz. the oxide-hydroxamate system, indicated that the classical type adsorption process, in which the reagent forms a uniform layer of chelate over the oxide surface was not applicable. Rather, the adsorption occurred via the formation of a discrete metal-chelate precipitate at the oxide surface. In order to better understand the associated with copper (II) oxide, adsorption process the oxide was recrystallized to produce a coarser material with a more uniform surface. This allowed the oxide surface to be viewed under the scanning electron microscope and also enabled the relative concentration of "surface" and "bulk" chelate to be assessed. A detailed investigation of the effect of the system variables; pH, conditioning period, concentration, temperature, surface area and dispersing reagent on the rate of precipitation of the copper chelate species of general form, Cu(chel)2' was made. In addition the chemical nature of the adsorbed species and the structural form of the precipitates were determined with the aid of infra-red spectroscopy and the scanning electron microscope. On the basis of these results a model has been formulated for the adsorption processes. In this model the adsorption dissolution, is considered to occur in stages: 1. Oxide dissolution, 2. metal complex formation, 3. Metal chelate precipitation at the oxide surface and 4. “bulk” chelate formation by post-precipitation processes. The precipitation process was examined in more detail by the study of the adsorption of chelate on copper metal. The results of this study showed that it was possible to relate the structural type of precipitate formed, ie. fibrous or platelike, to the degree of supersaturation of the metal complex in solution. Furthermore, it was found that the precipitate structure determined whether it remained attached to the surface or detached. Contact angle measurements of air bubbles on copper metal conditioned with chelate were related to the adsorption results in an attempt to isolate the optimum conditions for flotation of oxide minerals.
- Full Text:
- Date Issued: 1986
- Authors: Bryson, Michael Andrew Walker
- Date: 1986
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:20969 , http://hdl.handle.net/10962/5729
- Description: This work constitutes a fundamental study of the interaction between chelating reagents and oxide minerals . The adsorption mechanisms have been elucidated for most of the systems generated by the oxides of copper(II) or iron(III) and chelating reagents octyl hydroxamate, N-phenylbenzohydroxamate, salicylaldoxime, 5-nitrosalicylaldoxime or 8-hydroxyquinoline. The results of the preliminary work on one of the systems, viz. the oxide-hydroxamate system, indicated that the classical type adsorption process, in which the reagent forms a uniform layer of chelate over the oxide surface was not applicable. Rather, the adsorption occurred via the formation of a discrete metal-chelate precipitate at the oxide surface. In order to better understand the associated with copper (II) oxide, adsorption process the oxide was recrystallized to produce a coarser material with a more uniform surface. This allowed the oxide surface to be viewed under the scanning electron microscope and also enabled the relative concentration of "surface" and "bulk" chelate to be assessed. A detailed investigation of the effect of the system variables; pH, conditioning period, concentration, temperature, surface area and dispersing reagent on the rate of precipitation of the copper chelate species of general form, Cu(chel)2' was made. In addition the chemical nature of the adsorbed species and the structural form of the precipitates were determined with the aid of infra-red spectroscopy and the scanning electron microscope. On the basis of these results a model has been formulated for the adsorption processes. In this model the adsorption dissolution, is considered to occur in stages: 1. Oxide dissolution, 2. metal complex formation, 3. Metal chelate precipitation at the oxide surface and 4. “bulk” chelate formation by post-precipitation processes. The precipitation process was examined in more detail by the study of the adsorption of chelate on copper metal. The results of this study showed that it was possible to relate the structural type of precipitate formed, ie. fibrous or platelike, to the degree of supersaturation of the metal complex in solution. Furthermore, it was found that the precipitate structure determined whether it remained attached to the surface or detached. Contact angle measurements of air bubbles on copper metal conditioned with chelate were related to the adsorption results in an attempt to isolate the optimum conditions for flotation of oxide minerals.
- Full Text:
- Date Issued: 1986
A dielectric and spectroscopic study of molecular association in solutions of alcohols
- Authors: Campbell, Colin
- Date: 1975
- Subjects: Alcohols , Dielectrics , Spectrum analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4454 , http://hdl.handle.net/10962/d1010424
- Description: This study is concerned with the association characteristics of solutions of alcohols in some non-polar solvents. The permittivities at 2 MHz and 25°C for solutions of the straight chain octanols in cyclohexane, carbon tetrachloride and benzene have been examined over the entire solute concentration range, with particular attention -1 being paid to the range below 0.1 molℓ⁻¹ By applying the Kirkwood- Fröhlich equation to these data, the apparent dipole moments of the alcohols as a function of concentration have been evaluated. These concentration dependencies have been correlated with infrared absorption results on the same systems to provide information on the sizes and configurations of the proposed hydrogen bonded multimers. It is concluded that, at very low solute concentrations, the alcohol molecules exist as monomers; but with increasing concentration, two types of hydrogen bonded multimers are formed, the first (at low concentrations) being of high dipole moment and the second (at higher concentrations) being of low dipole moment. At high concentrations, the molecules associate to form a three-dimensional network. Attempts have been made to determine equilibrium parameters for molecular models which are consistent with the qualitative understanding of the association behaviour. These parameters were obtained by applying least-squares, curve-fitting techniques to the low concentration permittivity data. A similar investigation has been conducted on solutions of 2,3,4-trimethyl-3-pentanol in the same solvents. The steric hindrance around the hydroxyl group of this alcohol modifies the association behaviour so that a three-dimensional network does not form at high solute concentrations. Proton magnetic resonance chemical shifts for the hydroxyl proton of this alcohol in carbon tetrachloride solutions have been measured. Attempts have also been made to determine equilibrium parameters which describe formation of the hydrogen bonded multimers. To extend this study to include solutes other than octanols, similar experiments have been conducted on solutions of t-butanol in hexadecane, a system which has recently been investigated by other workers using different experimental techniques. The association behaviour of this system is qualitatively similar to that of the straight-chain octanols. The combination of permittivity and infrared measurements, although proving extremely powerful in interpreting the association characteristics of dilute alcohol solutions, is less adequate at high solute concentrations. Attention was therefore directed towards dielectric relaxation and viscosity studies to investigate concentrated solutions. The relaxation times at 20°C of the low frequency dispersion have been measured for solutions of 1-propanol, 1-butanol, 1-hexanol, 1-octanol and 1-decanol in cyclohexane using time domain reflectometry techniques. Similar measurements have also been made on solutions of 1-butanol and 1-octanol in carbon tetrachloride and in benzene. The concentration dependence of the viscosities of certain of these systems has also been examined in an independent study. The ratio of the dielectric relaxation time to the viscosity, the "reduced relaxation time", is qualitatively similar for each system studied. This similarity leads to an explanation of the molecular process responsible for the low frequency dispersion in terms of the proximity of the hydroxyl groups in concentrated alcohol solutions and the fraction of the groups which are not involved in hydrogen bonding.
- Full Text:
- Date Issued: 1975
- Authors: Campbell, Colin
- Date: 1975
- Subjects: Alcohols , Dielectrics , Spectrum analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4454 , http://hdl.handle.net/10962/d1010424
- Description: This study is concerned with the association characteristics of solutions of alcohols in some non-polar solvents. The permittivities at 2 MHz and 25°C for solutions of the straight chain octanols in cyclohexane, carbon tetrachloride and benzene have been examined over the entire solute concentration range, with particular attention -1 being paid to the range below 0.1 molℓ⁻¹ By applying the Kirkwood- Fröhlich equation to these data, the apparent dipole moments of the alcohols as a function of concentration have been evaluated. These concentration dependencies have been correlated with infrared absorption results on the same systems to provide information on the sizes and configurations of the proposed hydrogen bonded multimers. It is concluded that, at very low solute concentrations, the alcohol molecules exist as monomers; but with increasing concentration, two types of hydrogen bonded multimers are formed, the first (at low concentrations) being of high dipole moment and the second (at higher concentrations) being of low dipole moment. At high concentrations, the molecules associate to form a three-dimensional network. Attempts have been made to determine equilibrium parameters for molecular models which are consistent with the qualitative understanding of the association behaviour. These parameters were obtained by applying least-squares, curve-fitting techniques to the low concentration permittivity data. A similar investigation has been conducted on solutions of 2,3,4-trimethyl-3-pentanol in the same solvents. The steric hindrance around the hydroxyl group of this alcohol modifies the association behaviour so that a three-dimensional network does not form at high solute concentrations. Proton magnetic resonance chemical shifts for the hydroxyl proton of this alcohol in carbon tetrachloride solutions have been measured. Attempts have also been made to determine equilibrium parameters which describe formation of the hydrogen bonded multimers. To extend this study to include solutes other than octanols, similar experiments have been conducted on solutions of t-butanol in hexadecane, a system which has recently been investigated by other workers using different experimental techniques. The association behaviour of this system is qualitatively similar to that of the straight-chain octanols. The combination of permittivity and infrared measurements, although proving extremely powerful in interpreting the association characteristics of dilute alcohol solutions, is less adequate at high solute concentrations. Attention was therefore directed towards dielectric relaxation and viscosity studies to investigate concentrated solutions. The relaxation times at 20°C of the low frequency dispersion have been measured for solutions of 1-propanol, 1-butanol, 1-hexanol, 1-octanol and 1-decanol in cyclohexane using time domain reflectometry techniques. Similar measurements have also been made on solutions of 1-butanol and 1-octanol in carbon tetrachloride and in benzene. The concentration dependence of the viscosities of certain of these systems has also been examined in an independent study. The ratio of the dielectric relaxation time to the viscosity, the "reduced relaxation time", is qualitatively similar for each system studied. This similarity leads to an explanation of the molecular process responsible for the low frequency dispersion in terms of the proximity of the hydroxyl groups in concentrated alcohol solutions and the fraction of the groups which are not involved in hydrogen bonding.
- Full Text:
- Date Issued: 1975
Electrochemistry and photophysicochemical studies of titanium, tantalum and vanadium phthalocyanines in the presence of nanomaterials
- Authors: Chauke, Vongani Portia
- Date: 2012
- Subjects: Phthalocyanines -- Synthesis Electrochemistry Titanium Tantalum Vanadium
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4313 , http://hdl.handle.net/10962/d1004971
- Description: The syntheses of tetra- and octa-substituted phthalocyanine complexes of titanium (IV) oxide vanadium (IV) oxide and tantalum (V) hydroxide and their electrochemical characterisation are presented in this work. The structures and purity of these complexes were confirmed by NMR, infrared and mass spectroscopies and elemental analysis. They show good solubility in most common solvents especially non-viscous solvents such as dichloromethane and chloroform. The cyclic voltammograms (CV) showed reversible to quasi reversible behavior for all the reduction couples and the oxidation peaks were irreversible. Spectroelectrochemistry of the complexes confirmed metal and ring redox processes for TaPc and TiPc derivatives and ring based processes only for VPc complexes. The synthesis of gold nanoparticles and their conjugation with the new phthalocyanines was carried out. Similarly, single walled carbon nanotubes were conjugated to selected tantalum complexes and the characterization of all the nanomaterials and their conjugates using different techniques that include TEM, XRD and AFM is also presented in this work. The photophysical and photochemical properties and photocatalytic oxidation of cyclohexene properties of the newly synthesised in the presence of gold nanoparticles were investigated. The compounds were stable, well within the stability range for phthalocyanines. The singlet oxygen quantum yield values increased drastically in the presence of gold nanoparticles. The photocatalytic products obtained from the reaction were cyclohexene oxide, 2-cyclohexen-1-ol, 2-cyclohexene-1-one and 1,4-cyclohexanediol. The percentage conversion values, yields and selectivity values improved significantly in the presence of AuNPs. Singlet oxygen was determined to be the main agent involved in the photocatalytic oxidation of cyclohexene. The electrocatalytic oxidation of bisphenol A and p-nitrophenol was carried out using nickel tetraamino phthalocyanine and all the newly synthesised metallophthalocyanine in the presence of gold nanoparticles and single walled carbon nanotubes. The charge transfer behaviour of AuNPs was enhanced in the presence of TaPc, TiPc and VPc complexes. The presence of single walled carbon nanotubes further improved electron transfer and minimised electrode passivation.
- Full Text:
- Date Issued: 2012
- Authors: Chauke, Vongani Portia
- Date: 2012
- Subjects: Phthalocyanines -- Synthesis Electrochemistry Titanium Tantalum Vanadium
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4313 , http://hdl.handle.net/10962/d1004971
- Description: The syntheses of tetra- and octa-substituted phthalocyanine complexes of titanium (IV) oxide vanadium (IV) oxide and tantalum (V) hydroxide and their electrochemical characterisation are presented in this work. The structures and purity of these complexes were confirmed by NMR, infrared and mass spectroscopies and elemental analysis. They show good solubility in most common solvents especially non-viscous solvents such as dichloromethane and chloroform. The cyclic voltammograms (CV) showed reversible to quasi reversible behavior for all the reduction couples and the oxidation peaks were irreversible. Spectroelectrochemistry of the complexes confirmed metal and ring redox processes for TaPc and TiPc derivatives and ring based processes only for VPc complexes. The synthesis of gold nanoparticles and their conjugation with the new phthalocyanines was carried out. Similarly, single walled carbon nanotubes were conjugated to selected tantalum complexes and the characterization of all the nanomaterials and their conjugates using different techniques that include TEM, XRD and AFM is also presented in this work. The photophysical and photochemical properties and photocatalytic oxidation of cyclohexene properties of the newly synthesised in the presence of gold nanoparticles were investigated. The compounds were stable, well within the stability range for phthalocyanines. The singlet oxygen quantum yield values increased drastically in the presence of gold nanoparticles. The photocatalytic products obtained from the reaction were cyclohexene oxide, 2-cyclohexen-1-ol, 2-cyclohexene-1-one and 1,4-cyclohexanediol. The percentage conversion values, yields and selectivity values improved significantly in the presence of AuNPs. Singlet oxygen was determined to be the main agent involved in the photocatalytic oxidation of cyclohexene. The electrocatalytic oxidation of bisphenol A and p-nitrophenol was carried out using nickel tetraamino phthalocyanine and all the newly synthesised metallophthalocyanine in the presence of gold nanoparticles and single walled carbon nanotubes. The charge transfer behaviour of AuNPs was enhanced in the presence of TaPc, TiPc and VPc complexes. The presence of single walled carbon nanotubes further improved electron transfer and minimised electrode passivation.
- Full Text:
- Date Issued: 2012
Photophysiochemical studies of d¹⁰ metallophthalocyanines and their interaction with nanoparticles
- Chidawanyika, Wadzanai Janet Upenyu
- Authors: Chidawanyika, Wadzanai Janet Upenyu
- Date: 2010
- Subjects: Nanoparticles Phthalocyanines Photochemistry Electrochemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4335 , http://hdl.handle.net/10962/d1004996
- Description: The syntheses, extensive spectroscopic characterization, photophysical and photochemical studies have been conducted for a variation of d10 metallophthaloycanines (MPcs). Comparisons have been made taking into consideration the nfluence of the central metal ion, solvent properties, substituent type and position. Coordination to heavy central metals i.e. Hg gives enhanced triplet state properties. Low symmetry metallophthalocyanine complexes were similarly haracterized and the influence of nteractions with nanoparticles on their photophysical and photochemical properties determined. The MPcs have been linked and adsorbed or mixed with nanoparticles i.e. hemically functionalized single-walled carbon nanotubes SWCNT) and mercaptocarboxylic acid capped CdTe quantum dots (QDs) and changes in the spectra accounted for with respect to the proposed conjugate structures. Distinct differences ccur for linked and adsorbed or mixed conjugates in the bsorption, infrared (IR) and Raman spectra and for thermal ravimetric decay profiles, suggesting successful formation f covalent bonds (linked) and point to structurally ifferent materials. SWCNT quench MPc fluorescence by a photoinduced electron transfer mediated process to give low fluorescence quantum yields. The QDs were used as energy transfer donors and facilitate energy transfer, through Förster resonance energy transfer (FRET) from the QDs to the MPcs. Improved FRET efficiencies were found for linked MPc-QD conjugates relative to the mixed species. Photophysicochemical properties of MPcs were, in general, improved as a result of interactions with nanoparticles.
- Full Text:
- Date Issued: 2010
- Authors: Chidawanyika, Wadzanai Janet Upenyu
- Date: 2010
- Subjects: Nanoparticles Phthalocyanines Photochemistry Electrochemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4335 , http://hdl.handle.net/10962/d1004996
- Description: The syntheses, extensive spectroscopic characterization, photophysical and photochemical studies have been conducted for a variation of d10 metallophthaloycanines (MPcs). Comparisons have been made taking into consideration the nfluence of the central metal ion, solvent properties, substituent type and position. Coordination to heavy central metals i.e. Hg gives enhanced triplet state properties. Low symmetry metallophthalocyanine complexes were similarly haracterized and the influence of nteractions with nanoparticles on their photophysical and photochemical properties determined. The MPcs have been linked and adsorbed or mixed with nanoparticles i.e. hemically functionalized single-walled carbon nanotubes SWCNT) and mercaptocarboxylic acid capped CdTe quantum dots (QDs) and changes in the spectra accounted for with respect to the proposed conjugate structures. Distinct differences ccur for linked and adsorbed or mixed conjugates in the bsorption, infrared (IR) and Raman spectra and for thermal ravimetric decay profiles, suggesting successful formation f covalent bonds (linked) and point to structurally ifferent materials. SWCNT quench MPc fluorescence by a photoinduced electron transfer mediated process to give low fluorescence quantum yields. The QDs were used as energy transfer donors and facilitate energy transfer, through Förster resonance energy transfer (FRET) from the QDs to the MPcs. Improved FRET efficiencies were found for linked MPc-QD conjugates relative to the mixed species. Photophysicochemical properties of MPcs were, in general, improved as a result of interactions with nanoparticles.
- Full Text:
- Date Issued: 2010
Electrospun nanofibers : an alternative sorbent material for solid phase extraction
- Chigome, Samuel, Samuel Chigome
- Authors: Chigome, Samuel , Samuel Chigome
- Date: 2012 , 2012-03-26
- Subjects: Nanofibers -- Research Electrospinning -- Research Sorbents -- Research Extraction (Chemistry) -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4314 , http://hdl.handle.net/10962/d1004972
- Description: The work described in the thesis seeks to lay a foundation for a better understanding of the use of electrospun nanofibers as a sorbent material. Three miniaturised electrospun nanofiber based solid phase extraction devices were fabricated. For the first two, 10 mg of electrospun polystyrene fibers were used as a sorbent bed for a micro column SPE device (8 mm bed height in a 200 μl pipette tip) and a disk (I) SPE device (5 mm 1 mm sorbent bed in a 1000 μl SPE barrel). While for the third, 4.6 mg of electrospun nylon nanofibers were used as a sorbent bed for a disk (II) SPE device, (sorbent bed consisting of 5 5 mm 350 μm stacked disks in a 500 μl SPE barrel). Corticosteroids were employed as model analytes for performance evaluation of the fabricated SPE devices. Quantitative recoveries (45.5-124.29 percent) were achieved for all SPE devices at a loading volume of 100 μl and analyte concentration of 500 ng ml-1. Three mathematical models; the Boltzmann, Weibull five parameter and the Sigmoid three parameter were employed to describe the break through profiles of each of the sorbent beds. The micro column SPE device exhibited a breakthrough volume of 1400 μl, and theoretical plates (7.98-9.1) while disk (I) SPE device exhibited 400-500 μl and 1.39-2.82 respectively. Disk (II) SPE device exhibited a breakthrough volume of 200 μl and theoretical plates 0.38-1.15. It was proposed that the formats of future electrospun nanofiber sorbent based SPE devices will be guided by mechanical strength of the polymer. The study classified electrospun polymer fibers into two as polystyrene type (relatively low mechanical strength) and nylon type (relatively high mechanical strength).
- Full Text:
- Date Issued: 2012
- Authors: Chigome, Samuel , Samuel Chigome
- Date: 2012 , 2012-03-26
- Subjects: Nanofibers -- Research Electrospinning -- Research Sorbents -- Research Extraction (Chemistry) -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4314 , http://hdl.handle.net/10962/d1004972
- Description: The work described in the thesis seeks to lay a foundation for a better understanding of the use of electrospun nanofibers as a sorbent material. Three miniaturised electrospun nanofiber based solid phase extraction devices were fabricated. For the first two, 10 mg of electrospun polystyrene fibers were used as a sorbent bed for a micro column SPE device (8 mm bed height in a 200 μl pipette tip) and a disk (I) SPE device (5 mm 1 mm sorbent bed in a 1000 μl SPE barrel). While for the third, 4.6 mg of electrospun nylon nanofibers were used as a sorbent bed for a disk (II) SPE device, (sorbent bed consisting of 5 5 mm 350 μm stacked disks in a 500 μl SPE barrel). Corticosteroids were employed as model analytes for performance evaluation of the fabricated SPE devices. Quantitative recoveries (45.5-124.29 percent) were achieved for all SPE devices at a loading volume of 100 μl and analyte concentration of 500 ng ml-1. Three mathematical models; the Boltzmann, Weibull five parameter and the Sigmoid three parameter were employed to describe the break through profiles of each of the sorbent beds. The micro column SPE device exhibited a breakthrough volume of 1400 μl, and theoretical plates (7.98-9.1) while disk (I) SPE device exhibited 400-500 μl and 1.39-2.82 respectively. Disk (II) SPE device exhibited a breakthrough volume of 200 μl and theoretical plates 0.38-1.15. It was proposed that the formats of future electrospun nanofiber sorbent based SPE devices will be guided by mechanical strength of the polymer. The study classified electrospun polymer fibers into two as polystyrene type (relatively low mechanical strength) and nylon type (relatively high mechanical strength).
- Full Text:
- Date Issued: 2012