Activity of diverse chalcones against several targets: statistical analysis of a high-throughput virtual screen of a custom chalcone library
- Authors: Sarron, Arthur F D
- Date: 2020
- Subjects: Acetophenone , Benzaldehyde , Ketones , Pyruvate kinase , Drug development , Aromatic compounds , Heat shock proteins
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/116028 , vital:34291
- Description: Chalcone family molecules are well known to have therapeutic proprieties (anti-inflammatory, anti-microbial or anti-cancer, etc). However the mechanism of action in some cases is not well known. A virtual library of this family of compounds was constructed using custom scripts, based on the aldol condensation, and this library was modified further to analogues by expansion of the α,β-unsaturated ketone linker. Acetophenone and benzaldehyde derivatives which are available and purchasable were used as a base to design the chalcone virtual library. 8063 chalcones were constructed and geometrically optimized with Gaussian 09. Their physicochemical characteristics linked to the Lipinski rules were analyzed with Knime and CDK. The entire library was after docked against several targets including HIV-1 integrase, MRSA pyruvate kinase, HSP90, COX-1, COX-2, ALR2, MAOA, MAOB, acetylcholinesterase, butyrylcholinesterase and PLA2. With the exception of MAOA, which does not have a crystal structure ligand, all dockings were validated by redocking the original ligand provided by the literature. These targets are known in the literature to be inhibited by chalcone-derivatives. However, specificity of the particular known chalcone inhibitors to the particular targets is not known. To this end the performance of the generated chalcone library against the list of targets was of interest. The binding energy of ligand-protein complexes was generally good across the library. Statistical analysis including principal component analysis and hierarchical clustering analysis were made in order to investigate for any physical/chemical characteristics which might explain what chalcone features affect the binding energy of the ligand-protein complexes. The spherical polar coordinates defining the orientation of the binding poses were also calculated and used in the statistical analysis. The statistical analysis has allowed us to hypothesize the importance of these radial distances and the polar angles of key atoms in the chalcones in binding to the pyruvate kinase crystal structure. This was validated by the docking of another small library of compound models in which the α,β-unsaturated ketone chain of the chalcone was replaced by incrementally longer conjugated chains. Further studies on the chalcones themselves reveal rotameric systems in both cis and trans-configurations (which may impact binding), and also studied was the effect of Topliss-based modification and its impact of binding to HSP90. Molecular dynamics confirmed good binding of identified chalcone hits.
- Full Text:
- Date Issued: 2020
- Authors: Sarron, Arthur F D
- Date: 2020
- Subjects: Acetophenone , Benzaldehyde , Ketones , Pyruvate kinase , Drug development , Aromatic compounds , Heat shock proteins
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/116028 , vital:34291
- Description: Chalcone family molecules are well known to have therapeutic proprieties (anti-inflammatory, anti-microbial or anti-cancer, etc). However the mechanism of action in some cases is not well known. A virtual library of this family of compounds was constructed using custom scripts, based on the aldol condensation, and this library was modified further to analogues by expansion of the α,β-unsaturated ketone linker. Acetophenone and benzaldehyde derivatives which are available and purchasable were used as a base to design the chalcone virtual library. 8063 chalcones were constructed and geometrically optimized with Gaussian 09. Their physicochemical characteristics linked to the Lipinski rules were analyzed with Knime and CDK. The entire library was after docked against several targets including HIV-1 integrase, MRSA pyruvate kinase, HSP90, COX-1, COX-2, ALR2, MAOA, MAOB, acetylcholinesterase, butyrylcholinesterase and PLA2. With the exception of MAOA, which does not have a crystal structure ligand, all dockings were validated by redocking the original ligand provided by the literature. These targets are known in the literature to be inhibited by chalcone-derivatives. However, specificity of the particular known chalcone inhibitors to the particular targets is not known. To this end the performance of the generated chalcone library against the list of targets was of interest. The binding energy of ligand-protein complexes was generally good across the library. Statistical analysis including principal component analysis and hierarchical clustering analysis were made in order to investigate for any physical/chemical characteristics which might explain what chalcone features affect the binding energy of the ligand-protein complexes. The spherical polar coordinates defining the orientation of the binding poses were also calculated and used in the statistical analysis. The statistical analysis has allowed us to hypothesize the importance of these radial distances and the polar angles of key atoms in the chalcones in binding to the pyruvate kinase crystal structure. This was validated by the docking of another small library of compound models in which the α,β-unsaturated ketone chain of the chalcone was replaced by incrementally longer conjugated chains. Further studies on the chalcones themselves reveal rotameric systems in both cis and trans-configurations (which may impact binding), and also studied was the effect of Topliss-based modification and its impact of binding to HSP90. Molecular dynamics confirmed good binding of identified chalcone hits.
- Full Text:
- Date Issued: 2020
Alkane oxidation using metallophthalocyanine as homogeneous catalysts
- Authors: Grootboom, Natasha Denise
- Date: 2002
- Subjects: Oxidation , Alkanes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4449 , http://hdl.handle.net/10962/d1007794
- Description: Iron polychlorophthalocyanine (FePc(Cl)₁₆) and tetrasulfophthalocyanine ([M¹¹TSPc]⁴) complexes of iron, cobalt and manganese are employed as catalysts for the oxidation of cyclohexane using tert-butyl hydroperoxide (TBHP), chloroperoxybenzoic acid (CPBA) and hydrogen peroxide as oxidants. Catalysis using the FePc(Cl)₁₆ was performed in a dimethylformamide:dichloromethane (3 :7) solvent mixture. For the [Fe¹¹TSPc]⁴⁻, [Co¹¹TSPc]⁻ and [Mn¹¹TSPc]⁴⁻catalysts, a water:methanol (1:9) mixture was employed. The products of the catalysis are cyclohexanone, cyclohexanol and cyclohexanediol. The relative percentage yields, percentage selectivity and overall percentage conversion of the products depended on types of oxidant, or catalyst, concentrations of substrate or catalysts and temperature. TBHP was found to be the best oxidant since minimal destruction of the catalyst and higher selectivity in the products were observed when this oxidant was employed. Of the four catalysts investigated [Fe¹¹TSPc]⁴⁻ yielded the highest overall percentage conversion of 20%.The mechanism of the oxidation of cyclohexane in the presence of the FePc(Cl)₁₆ and [M¹¹TSPc]⁴⁻ involves the oxidation of these catalysts, forming an Fe(IlI) phthalocyanine species as an intermediate. Electrocatalysis using [Co¹¹TSPc]⁴⁻ as catalyst, employed an aqueous pH 7 buffer medium for electro-oxidation of 4-pentenoic acid. An enone is suggested as the only oxidation product of 4-pentenoic acid. No degradation of [Co¹¹TSPc]⁴⁻ was observed during the electrocatalytic process. In this process water was used as a source of oxygen therefore eliminating the production of by products from oxidant as in the case of TBHP and CPBA. This system was studied In an attempt to set up conditions for alkane electrocatalytic oxidation.
- Full Text:
- Date Issued: 2002
- Authors: Grootboom, Natasha Denise
- Date: 2002
- Subjects: Oxidation , Alkanes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4449 , http://hdl.handle.net/10962/d1007794
- Description: Iron polychlorophthalocyanine (FePc(Cl)₁₆) and tetrasulfophthalocyanine ([M¹¹TSPc]⁴) complexes of iron, cobalt and manganese are employed as catalysts for the oxidation of cyclohexane using tert-butyl hydroperoxide (TBHP), chloroperoxybenzoic acid (CPBA) and hydrogen peroxide as oxidants. Catalysis using the FePc(Cl)₁₆ was performed in a dimethylformamide:dichloromethane (3 :7) solvent mixture. For the [Fe¹¹TSPc]⁴⁻, [Co¹¹TSPc]⁻ and [Mn¹¹TSPc]⁴⁻catalysts, a water:methanol (1:9) mixture was employed. The products of the catalysis are cyclohexanone, cyclohexanol and cyclohexanediol. The relative percentage yields, percentage selectivity and overall percentage conversion of the products depended on types of oxidant, or catalyst, concentrations of substrate or catalysts and temperature. TBHP was found to be the best oxidant since minimal destruction of the catalyst and higher selectivity in the products were observed when this oxidant was employed. Of the four catalysts investigated [Fe¹¹TSPc]⁴⁻ yielded the highest overall percentage conversion of 20%.The mechanism of the oxidation of cyclohexane in the presence of the FePc(Cl)₁₆ and [M¹¹TSPc]⁴⁻ involves the oxidation of these catalysts, forming an Fe(IlI) phthalocyanine species as an intermediate. Electrocatalysis using [Co¹¹TSPc]⁴⁻ as catalyst, employed an aqueous pH 7 buffer medium for electro-oxidation of 4-pentenoic acid. An enone is suggested as the only oxidation product of 4-pentenoic acid. No degradation of [Co¹¹TSPc]⁴⁻ was observed during the electrocatalytic process. In this process water was used as a source of oxygen therefore eliminating the production of by products from oxidant as in the case of TBHP and CPBA. This system was studied In an attempt to set up conditions for alkane electrocatalytic oxidation.
- Full Text:
- Date Issued: 2002
An electrospun nanofiber colorimetric probe for detection of Alkaline Phosphatase for diagnosis of liver toxicity
- Authors: Mohale, Mamello
- Date: 2014
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/54532 , vital:26581
- Description: A novel electrospun nanofiber colorimetric probe for the detection of Alkaline Phosphatase (ALP) for diagnosis of liver toxicity was developed through electrospinning of a para nitrophenyl phosphate (pNPP) functionalised nylon polymer. The chemical stability of the enzyme substrate (pNPP) and its two products (para nitrophenol (pNP) and para nitrophenolate (pNPL)) was evaluated in biological (pH 7.4), acidic (pH 2) and alkaline (pH 9) pH, respectively. Enzyme kinetics models of Michaelis Menten (MM) and Lineweaver Burk (LB) were used to characterise free ALP. Solution and nanofiber assaying of free ALP and 10x diluted serum (spiked with ALP) was also carried out. The results demonstrated that pNPP and pNP were colourless while pNPL was yellow which indicated that all reagents were chemically stable. In addition, the chromophore of pNPL exhibited a strong molar extinction coefficient (ε) of 18,458 M-1 cm-1. LB plot being the most accurate compared to MM showed Vmax, Km and excess substrate concentration of 5.5 × 10-3 μmol/min-1, 0.025 mM and 0.25 mM respectively. Solution and nanofiber assaying of free ALP and serum confirmed a direct proportional correlation between the pNPL yellow colour intensity and enzyme activity up to 858 IU/L and 820 IU/L respectively. The dipping of the nanofiber layer into solution showed that the leaching rate of pNPP was extremely high at 1.37 × 10-3 A/min-1 as was observed after only the first 0.25 min interval. However, this was not of great concern since it was also observed that administration of the sample (20 μL) by a dropwise method minimised leaching compared to dipping. The preliminary findings on the effect of temperature on the chemical stability of pNPP indicated that it was stable below temperatures of 40°C while it hydrolysed at 80°C. Therefore a sensitive, rapid and simple colorimetric probe for the detection of ALP was developed. The probe exhibited characteristics that make it suitable to be incorporated into point of care colorimetric liver toxicity diagnostic devices for applications in resource poor settings and telemedicine.
- Full Text:
- Date Issued: 2014
- Authors: Mohale, Mamello
- Date: 2014
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/54532 , vital:26581
- Description: A novel electrospun nanofiber colorimetric probe for the detection of Alkaline Phosphatase (ALP) for diagnosis of liver toxicity was developed through electrospinning of a para nitrophenyl phosphate (pNPP) functionalised nylon polymer. The chemical stability of the enzyme substrate (pNPP) and its two products (para nitrophenol (pNP) and para nitrophenolate (pNPL)) was evaluated in biological (pH 7.4), acidic (pH 2) and alkaline (pH 9) pH, respectively. Enzyme kinetics models of Michaelis Menten (MM) and Lineweaver Burk (LB) were used to characterise free ALP. Solution and nanofiber assaying of free ALP and 10x diluted serum (spiked with ALP) was also carried out. The results demonstrated that pNPP and pNP were colourless while pNPL was yellow which indicated that all reagents were chemically stable. In addition, the chromophore of pNPL exhibited a strong molar extinction coefficient (ε) of 18,458 M-1 cm-1. LB plot being the most accurate compared to MM showed Vmax, Km and excess substrate concentration of 5.5 × 10-3 μmol/min-1, 0.025 mM and 0.25 mM respectively. Solution and nanofiber assaying of free ALP and serum confirmed a direct proportional correlation between the pNPL yellow colour intensity and enzyme activity up to 858 IU/L and 820 IU/L respectively. The dipping of the nanofiber layer into solution showed that the leaching rate of pNPP was extremely high at 1.37 × 10-3 A/min-1 as was observed after only the first 0.25 min interval. However, this was not of great concern since it was also observed that administration of the sample (20 μL) by a dropwise method minimised leaching compared to dipping. The preliminary findings on the effect of temperature on the chemical stability of pNPP indicated that it was stable below temperatures of 40°C while it hydrolysed at 80°C. Therefore a sensitive, rapid and simple colorimetric probe for the detection of ALP was developed. The probe exhibited characteristics that make it suitable to be incorporated into point of care colorimetric liver toxicity diagnostic devices for applications in resource poor settings and telemedicine.
- Full Text:
- Date Issued: 2014
An examination of the extractives of Leonotis species
- Authors: Kaplan, Errol R
- Date: 1966
- Subjects: Leonotis -- Analysis Botanical chemistry Chemistry, Analytic Chemistry, Organic
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4481 , http://hdl.handle.net/10962/d1012628
- Description: Marrubiin and the other two diterpenoids, compounds X and Y, which had previously been isolated from Leonotus leonurus have been reinvestigated. Although the structure for marrubiin is well known its stereochemistry has been the subject of protracted discussion and is by no means secure except at C₅ and C₁₀ . N.M.R. spectral evidence showed that the lactone ring was cis-fused and β-orientated. Dehydration experiments carried out by previous workers were repeated, in order to resolve the residual uncertainty regarding the stereochemistry at C₉, an attempt was made to prepare iodoacetyl marrubic acid for X-ray crystallographic studies. Compound Y, C₂₀H₂₈0₃, a triply-unsaturated compound was shown by spectral studies to contain a furan ring and an α,β- unsaturated keto-group. It possesses a hydroxyl group incapable of acetylation, but readily removed by alkali and dehydrating agents to yield a tetraunsaturated compound, anhydro~Y; the hydroxyl is thus tertiary, Isolation of 1:2:5-trimethylnaphthalene on dehydrogenation indicated a relationship with the labdane diterpene group and supported the C₂₀ formula, The position of the α,β-unsaturated keto-group was resolved by interpretation of the ultraviolet spectra of degradation products and also by isolation of 1:2:3:5- trimethylnaphthalene on dehydrogenation of a suitable grignard product, The presence of a β-substituted furan was further indicated by colour reactions and confirmed by mass and n.m.r. spectra. The skeleton of compound Y is correlated with marrubiin via "iso-ambreinolide " and its stereochemistry is discussed. Further stereochemical assignments are postulated from the study of the n.m.r. spectra. Compound X, C₂₀H₂₈0₅, was shown by spectral and chemical evidence to be a diterpenoid dilactone containing an ether bridge between C₉ and C₁₃ Isolation of 1:2:5 trimethylnaphthal ene on dehydrogenation showed it to be closely related to marrubiin, This was supported by n.m.r. spectral results. A structure for compound X is proposed and the stereochemistry discussed. The aerial portions of Leonotis leonitis were also extracted and shown to contain a new compound, compound R. Preliminary investigation showed that it was a dilactone containing a furan ring, The n.m.r. spectrum of the compound is discussed.
- Full Text:
- Date Issued: 1966
- Authors: Kaplan, Errol R
- Date: 1966
- Subjects: Leonotis -- Analysis Botanical chemistry Chemistry, Analytic Chemistry, Organic
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4481 , http://hdl.handle.net/10962/d1012628
- Description: Marrubiin and the other two diterpenoids, compounds X and Y, which had previously been isolated from Leonotus leonurus have been reinvestigated. Although the structure for marrubiin is well known its stereochemistry has been the subject of protracted discussion and is by no means secure except at C₅ and C₁₀ . N.M.R. spectral evidence showed that the lactone ring was cis-fused and β-orientated. Dehydration experiments carried out by previous workers were repeated, in order to resolve the residual uncertainty regarding the stereochemistry at C₉, an attempt was made to prepare iodoacetyl marrubic acid for X-ray crystallographic studies. Compound Y, C₂₀H₂₈0₃, a triply-unsaturated compound was shown by spectral studies to contain a furan ring and an α,β- unsaturated keto-group. It possesses a hydroxyl group incapable of acetylation, but readily removed by alkali and dehydrating agents to yield a tetraunsaturated compound, anhydro~Y; the hydroxyl is thus tertiary, Isolation of 1:2:5-trimethylnaphthalene on dehydrogenation indicated a relationship with the labdane diterpene group and supported the C₂₀ formula, The position of the α,β-unsaturated keto-group was resolved by interpretation of the ultraviolet spectra of degradation products and also by isolation of 1:2:3:5- trimethylnaphthalene on dehydrogenation of a suitable grignard product, The presence of a β-substituted furan was further indicated by colour reactions and confirmed by mass and n.m.r. spectra. The skeleton of compound Y is correlated with marrubiin via "iso-ambreinolide " and its stereochemistry is discussed. Further stereochemical assignments are postulated from the study of the n.m.r. spectra. Compound X, C₂₀H₂₈0₅, was shown by spectral and chemical evidence to be a diterpenoid dilactone containing an ether bridge between C₉ and C₁₃ Isolation of 1:2:5 trimethylnaphthal ene on dehydrogenation showed it to be closely related to marrubiin, This was supported by n.m.r. spectral results. A structure for compound X is proposed and the stereochemistry discussed. The aerial portions of Leonotis leonitis were also extracted and shown to contain a new compound, compound R. Preliminary investigation showed that it was a dilactone containing a furan ring, The n.m.r. spectrum of the compound is discussed.
- Full Text:
- Date Issued: 1966
An experimental and theoretical investigation of unstable Fischer chromium carbene complexes
- Authors: Makanjee, Che Azad
- Date: 2013 , 2013-03-27
- Subjects: Chromium , Organolithium compounds , Carbenes (Methylene compounds) , Organometallic chemistry , Organometallic compounds , Organochromium compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4284 , http://hdl.handle.net/10962/d1002953 , Chromium , Organolithium compounds , Carbenes (Methylene compounds) , Organometallic chemistry , Organometallic compounds , Organochromium compounds
- Description: This organometallic study involves the use organostannanes and organolithiums as precursors to chromium Fischer carbene complexes. Fischer carbenes are typically electrophilic and are stabilized by a single π-donor substituent, and contain low oxidation state metals (often but not always from Group 6). They are highly reactive and can give access to a range of biologically active compounds through cyclopropanations, insertions, coupling and photochemical reactions. Synthesis and characterization of three MOM-protected α-alkoxy organostannanes was successfully carried out via a nucleophilic addition of tributylstannyllithium to suitable aldehydes, and immediate protection of the alcohol with MOM. Two N-BOC protected α-amino organostannanes were successfully synthesized and characterized via α-lithiation and tin-lithium exchange in the presence of TMEDA. Tin-lithium transmetallation of the organostannanes allowed access to the organolithiums required for the synthesis of novel Fischer carbenes. Addition of chromium hexacarbonyl to the organolithiums formed the acylpentacarbonyl chromate salt which was alkylated with Meerwein salt, resulting in the Fischer carbene and a by-product, tetrabutyltin, which proved difficult to remove. Several Fischer carbenes were synthesized and characterized, some simple and known and some novel. In silico work explored the reaction coordinate of the [2+2] cycloaddition towards the formation of β-lactams, and the photoactivation cycle that precedes this process. Computational work also showed the effect of the ligand on the stability and reactivity of the carbene. It was found that in some cases the oxygen on the ligand could negatively influence the stability of the carbene (when compared to a simple methyl carbene). A link between bond orders and back donation in Fischer carbenes was explored in an attempt to theoretically predict the stability of a range of carbenes. , Microsoft� Office Word 2007
- Full Text:
- Date Issued: 2013
- Authors: Makanjee, Che Azad
- Date: 2013 , 2013-03-27
- Subjects: Chromium , Organolithium compounds , Carbenes (Methylene compounds) , Organometallic chemistry , Organometallic compounds , Organochromium compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4284 , http://hdl.handle.net/10962/d1002953 , Chromium , Organolithium compounds , Carbenes (Methylene compounds) , Organometallic chemistry , Organometallic compounds , Organochromium compounds
- Description: This organometallic study involves the use organostannanes and organolithiums as precursors to chromium Fischer carbene complexes. Fischer carbenes are typically electrophilic and are stabilized by a single π-donor substituent, and contain low oxidation state metals (often but not always from Group 6). They are highly reactive and can give access to a range of biologically active compounds through cyclopropanations, insertions, coupling and photochemical reactions. Synthesis and characterization of three MOM-protected α-alkoxy organostannanes was successfully carried out via a nucleophilic addition of tributylstannyllithium to suitable aldehydes, and immediate protection of the alcohol with MOM. Two N-BOC protected α-amino organostannanes were successfully synthesized and characterized via α-lithiation and tin-lithium exchange in the presence of TMEDA. Tin-lithium transmetallation of the organostannanes allowed access to the organolithiums required for the synthesis of novel Fischer carbenes. Addition of chromium hexacarbonyl to the organolithiums formed the acylpentacarbonyl chromate salt which was alkylated with Meerwein salt, resulting in the Fischer carbene and a by-product, tetrabutyltin, which proved difficult to remove. Several Fischer carbenes were synthesized and characterized, some simple and known and some novel. In silico work explored the reaction coordinate of the [2+2] cycloaddition towards the formation of β-lactams, and the photoactivation cycle that precedes this process. Computational work also showed the effect of the ligand on the stability and reactivity of the carbene. It was found that in some cases the oxygen on the ligand could negatively influence the stability of the carbene (when compared to a simple methyl carbene). A link between bond orders and back donation in Fischer carbenes was explored in an attempt to theoretically predict the stability of a range of carbenes. , Microsoft� Office Word 2007
- Full Text:
- Date Issued: 2013
An investigation into the antidiabetic and catalytic properties of oxovanadium(IV) complexes
- Authors: Walmsley, Ryan Steven
- Date: 2012
- Subjects: Hypoglycemic agents Ligands (Biochemistry) Complex compounds Potentiometry Proton transfer reactions Stability Imidazoles Vanadium catalysts
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4320 , http://hdl.handle.net/10962/d1004978
- Description: In part 1 of this thesis, the antidiabetic activity of a series of novel oxovanadium(IV) complexes was investigated. A range of bidentate N,O-donor ligands, which partially mimic naturally occurring bioligands, were prepared and reacted with the vanadyl ion to form the corresponding bis-coordinated complexes. Initially, 2-(2ˊ-hydroxyphenyl)-1R-imidazoline (where R = H, ethyl and ethanol) ligands were prepared. The aqueous pH-metric chemical speciation was investigated using glass electrode potentiometry which allowed for the determination of protonation and stability constants of the ligands and complexes, respectively. The species distribution diagrams generated from this information gave an indication of how the complexes might behave across the broad pH range experienced in the digestive and circulatory systems. This information was used to create an improved 2nd generation of ligands that were constructed by combining the imidazole and carboxylic acid functionalities. These corresponding bis[(imidazolyl)carboxylato]-oxovanadium(IV) complexes displayed a broader pH-metric stability. Both sets of complexes improved glucose uptake and reduced coagulation in vitro. In part 2 of this thesis, a range of homogeneous and heterogeneous oxovanadium(IV) catalysts were prepared. Firstly, Merrifield beads were functionalized with ligands from Part 1 and then reacted with vanadyl sulfate to afford the corresponding heterogeneous catalysts. These displayed promising catalytic activity for the peroxide facilitated oxidation of thioanisole, styrene and ethylbenzene as well as the oxidative bromination of phenol red. Smaller imidazole-containing beads with higher surface areas than the Merrifield beads were prepared by suspension polymerization. These beads similarly demonstrated excellent catalytic activity for the oxidation of thioanisole and were highly recyclable. In attempt to increase the exposed catalytic surface area, while retaining the ease of separation achieved in the before mentioned systems, micron to nano sized electrospun fibers containing coordinating ligands were fabricated. The corresponding oxovanadium(IV) functionalized fibers were applied to the oxidation of thioanisole using a continuous flow system. The flexible and porous nature of the fiber mats was well suited to this approach. After optimization of the reactant flow rate and catalyst amount, near quantitative (> 99%) oxidation was achieved for an extended period. In addition, leaching of vanadium was mitigated by modification of the attached ligand or polymer material.
- Full Text:
- Date Issued: 2012
- Authors: Walmsley, Ryan Steven
- Date: 2012
- Subjects: Hypoglycemic agents Ligands (Biochemistry) Complex compounds Potentiometry Proton transfer reactions Stability Imidazoles Vanadium catalysts
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4320 , http://hdl.handle.net/10962/d1004978
- Description: In part 1 of this thesis, the antidiabetic activity of a series of novel oxovanadium(IV) complexes was investigated. A range of bidentate N,O-donor ligands, which partially mimic naturally occurring bioligands, were prepared and reacted with the vanadyl ion to form the corresponding bis-coordinated complexes. Initially, 2-(2ˊ-hydroxyphenyl)-1R-imidazoline (where R = H, ethyl and ethanol) ligands were prepared. The aqueous pH-metric chemical speciation was investigated using glass electrode potentiometry which allowed for the determination of protonation and stability constants of the ligands and complexes, respectively. The species distribution diagrams generated from this information gave an indication of how the complexes might behave across the broad pH range experienced in the digestive and circulatory systems. This information was used to create an improved 2nd generation of ligands that were constructed by combining the imidazole and carboxylic acid functionalities. These corresponding bis[(imidazolyl)carboxylato]-oxovanadium(IV) complexes displayed a broader pH-metric stability. Both sets of complexes improved glucose uptake and reduced coagulation in vitro. In part 2 of this thesis, a range of homogeneous and heterogeneous oxovanadium(IV) catalysts were prepared. Firstly, Merrifield beads were functionalized with ligands from Part 1 and then reacted with vanadyl sulfate to afford the corresponding heterogeneous catalysts. These displayed promising catalytic activity for the peroxide facilitated oxidation of thioanisole, styrene and ethylbenzene as well as the oxidative bromination of phenol red. Smaller imidazole-containing beads with higher surface areas than the Merrifield beads were prepared by suspension polymerization. These beads similarly demonstrated excellent catalytic activity for the oxidation of thioanisole and were highly recyclable. In attempt to increase the exposed catalytic surface area, while retaining the ease of separation achieved in the before mentioned systems, micron to nano sized electrospun fibers containing coordinating ligands were fabricated. The corresponding oxovanadium(IV) functionalized fibers were applied to the oxidation of thioanisole using a continuous flow system. The flexible and porous nature of the fiber mats was well suited to this approach. After optimization of the reactant flow rate and catalyst amount, near quantitative (> 99%) oxidation was achieved for an extended period. In addition, leaching of vanadium was mitigated by modification of the attached ligand or polymer material.
- Full Text:
- Date Issued: 2012
An investigation into the properties of cotton fibres as used in nonwoven fabrics
- Authors: Lutseke, Nothando Sazikazi
- Date: 1989
- Subjects: Cotton -- Analysis , Fibers -- Analysis , Nonwoven fabrics -- Analysis , Textile chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4552 , http://hdl.handle.net/10962/d1018241
- Description: The purpose of this investigation was to determine the properties that characterise cotton fibres in the various stages in the CPNF process as well as to determine which fibre characteristics a r e required to entangle the fibres to produce a successful CPNF . The criteria adopted in this work for a successful CPNF include: 1. the tensile strength of the fabrics 2. a well-defined pattern 3. absorbency and wicking The properties selected for investigation were 1. the cotton fibre surface (using SEM and DSC analyses) 2. the degree of degradation of the cotton fibre as a result of the CPNF process (using cellulose fluidity measurements) 3. the non-cellulosic content of the fibre (using IR, DSC, and Chemical analyses) 4. fibre friction 5. absorbency and wicking 6. tensile properties Analysis of the results indicates clearly what the fundamental properties of the cotton fibre must be for a successful cotton CPNF to be manufactured. The conclusions also indicate the necessary properties a man-made fibre must have to produce a successful CPNF.
- Full Text:
- Date Issued: 1989
- Authors: Lutseke, Nothando Sazikazi
- Date: 1989
- Subjects: Cotton -- Analysis , Fibers -- Analysis , Nonwoven fabrics -- Analysis , Textile chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4552 , http://hdl.handle.net/10962/d1018241
- Description: The purpose of this investigation was to determine the properties that characterise cotton fibres in the various stages in the CPNF process as well as to determine which fibre characteristics a r e required to entangle the fibres to produce a successful CPNF . The criteria adopted in this work for a successful CPNF include: 1. the tensile strength of the fabrics 2. a well-defined pattern 3. absorbency and wicking The properties selected for investigation were 1. the cotton fibre surface (using SEM and DSC analyses) 2. the degree of degradation of the cotton fibre as a result of the CPNF process (using cellulose fluidity measurements) 3. the non-cellulosic content of the fibre (using IR, DSC, and Chemical analyses) 4. fibre friction 5. absorbency and wicking 6. tensile properties Analysis of the results indicates clearly what the fundamental properties of the cotton fibre must be for a successful cotton CPNF to be manufactured. The conclusions also indicate the necessary properties a man-made fibre must have to produce a successful CPNF.
- Full Text:
- Date Issued: 1989
An investigation of certain complex ions of trivalent chromium by spectrophotometric and other physical methods
- Authors: Burley, Ralph Walter
- Date: 1950
- Subjects: Chromium
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4521 , http://hdl.handle.net/10962/d1014675
- Description: Although chromium coordination compounds are of considerable technological importance, they have been subjected to few thorough investigations since Werner's original experlments, in spite of the fact that we now possess a number of accurate physical methods, not available in Werner's time for the study of coordination complexes, The object of the work described in this thesis was to obtain further information on the chemistry of complex chromium(III) ions with special reference to the dioxalato-diaquochromiate system, [Cr(C₂0₄)₂(H₂0)₂]. For this purpose; spectrophotometric and potentlometrlc measurements were combined to yield information on a number of topics, The spectrophotometric investigations consisted in measuring the absorption spectra of the potassium salts of the complexes under consideration and in observing the changes in light absorption which occur during their formatlon and decomposition. The instrument used was a Beckmann Quartz Spectrophotometer model du. More than than twelve new absorption spectra were measured in this work and in conjunction with the spectra of other chromium and cobalt complexes reported by earlier workers, these are used to review the position of spectrophotometry as a method of investigating chromium complexes. The reasons for the shapes of the absorption spectra are discussed and it is concluded that spectrophotometry is useful for observing the progress of reactions involving complex ions and for analysing solutions, but that more fundamental data cannot be expected from the absorption curves.
- Full Text:
- Date Issued: 1950
- Authors: Burley, Ralph Walter
- Date: 1950
- Subjects: Chromium
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4521 , http://hdl.handle.net/10962/d1014675
- Description: Although chromium coordination compounds are of considerable technological importance, they have been subjected to few thorough investigations since Werner's original experlments, in spite of the fact that we now possess a number of accurate physical methods, not available in Werner's time for the study of coordination complexes, The object of the work described in this thesis was to obtain further information on the chemistry of complex chromium(III) ions with special reference to the dioxalato-diaquochromiate system, [Cr(C₂0₄)₂(H₂0)₂]. For this purpose; spectrophotometric and potentlometrlc measurements were combined to yield information on a number of topics, The spectrophotometric investigations consisted in measuring the absorption spectra of the potassium salts of the complexes under consideration and in observing the changes in light absorption which occur during their formatlon and decomposition. The instrument used was a Beckmann Quartz Spectrophotometer model du. More than than twelve new absorption spectra were measured in this work and in conjunction with the spectra of other chromium and cobalt complexes reported by earlier workers, these are used to review the position of spectrophotometry as a method of investigating chromium complexes. The reasons for the shapes of the absorption spectra are discussed and it is concluded that spectrophotometry is useful for observing the progress of reactions involving complex ions and for analysing solutions, but that more fundamental data cannot be expected from the absorption curves.
- Full Text:
- Date Issued: 1950
An investigation of reactions directed towards the synthesis of 2-methyl-2-(methylthio)propanal oxime
- Authors: Whittaker, Ruth Eleanor
- Date: 1995
- Subjects: Pesticides -- Synthesis , Insecticides , Aldicarb -- Synthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4322 , http://hdl.handle.net/10962/d1004980 , Pesticides -- Synthesis , Insecticides , Aldicarb -- Synthesis
- Description: The processes leading to the formation of 2-methyl-2-(methylthio)propanal oxime, known industrially as aldicarb oxime, have been studied. The three stages of the synthesis, viz., chlorination, thiomethylation and oximation have been thoroughly investigated, with the aim of optimising the yield and purity of aldicarb oxime. Attention has been focused on the chlorination step, and the effects of altering various conditions have been determined; the reaction has been carried out in the absence and presence of heat, solvent and buffer, and the extent of chlorine addition has also been varied. These studies have led to some improvement in the yield for this step. Several simple and inexpensive methods for purifying contaminated batches of aldicarb oxime have also been examined. Possible aldicarb oxime contaminants, identified by GLC and GC-MS analysis, have been synthesised for use as chromatographic and spectroscopic standards, and confirmation of the presence of a number of these contaminants has been achieved. Aldehyde trimers have been found to be the primary contaminants present in aldicarb oxime and the thermal stability of these trimers, their corresponding monomers and aldicarb oxime itself has been studied using variable temperature ¹H NMR spectroscopy. Novel pyridine derivatives, with potential as aldicarb analogues, have been synthesised and characterised using spectroscopic methods.
- Full Text:
- Date Issued: 1995
- Authors: Whittaker, Ruth Eleanor
- Date: 1995
- Subjects: Pesticides -- Synthesis , Insecticides , Aldicarb -- Synthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4322 , http://hdl.handle.net/10962/d1004980 , Pesticides -- Synthesis , Insecticides , Aldicarb -- Synthesis
- Description: The processes leading to the formation of 2-methyl-2-(methylthio)propanal oxime, known industrially as aldicarb oxime, have been studied. The three stages of the synthesis, viz., chlorination, thiomethylation and oximation have been thoroughly investigated, with the aim of optimising the yield and purity of aldicarb oxime. Attention has been focused on the chlorination step, and the effects of altering various conditions have been determined; the reaction has been carried out in the absence and presence of heat, solvent and buffer, and the extent of chlorine addition has also been varied. These studies have led to some improvement in the yield for this step. Several simple and inexpensive methods for purifying contaminated batches of aldicarb oxime have also been examined. Possible aldicarb oxime contaminants, identified by GLC and GC-MS analysis, have been synthesised for use as chromatographic and spectroscopic standards, and confirmation of the presence of a number of these contaminants has been achieved. Aldehyde trimers have been found to be the primary contaminants present in aldicarb oxime and the thermal stability of these trimers, their corresponding monomers and aldicarb oxime itself has been studied using variable temperature ¹H NMR spectroscopy. Novel pyridine derivatives, with potential as aldicarb analogues, have been synthesised and characterised using spectroscopic methods.
- Full Text:
- Date Issued: 1995
An investigation of the equivalent circuit of a conductivity cell
- Authors: Allison, Francis Sutton
- Date: 1954
- Subjects: Electrolytic cells
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4508 , http://hdl.handle.net/10962/d1013376
- Description: ( i) A linear circuit is shown not to explain the behaviour of a conductivity cell towards a long rectangular pulse of amplitude less than the decomposition potential of the solution in the cell. (ii) It is shown that the flow of current through the cell is governed by diffusion to the electrode. The diffusion current expression is the familiar one used in the case of diffusion up to a plane micro-electrode, except that in this case the concentration in the layer next to the electrode is not zero, but only somewhat less than the bulk concentration. (iii) Except during a short initial period (less than 10 seconds), the resistance of the electrolytic cell varies directly with the square root of the time for which an e.m.f. (less than the decomposition potential) is applied to the cell, and inversely with the concentration difference between the electrode surface and the bulk of the solution.
- Full Text:
- Date Issued: 1954
- Authors: Allison, Francis Sutton
- Date: 1954
- Subjects: Electrolytic cells
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4508 , http://hdl.handle.net/10962/d1013376
- Description: ( i) A linear circuit is shown not to explain the behaviour of a conductivity cell towards a long rectangular pulse of amplitude less than the decomposition potential of the solution in the cell. (ii) It is shown that the flow of current through the cell is governed by diffusion to the electrode. The diffusion current expression is the familiar one used in the case of diffusion up to a plane micro-electrode, except that in this case the concentration in the layer next to the electrode is not zero, but only somewhat less than the bulk concentration. (iii) Except during a short initial period (less than 10 seconds), the resistance of the electrolytic cell varies directly with the square root of the time for which an e.m.f. (less than the decomposition potential) is applied to the cell, and inversely with the concentration difference between the electrode surface and the bulk of the solution.
- Full Text:
- Date Issued: 1954
An investigation of the orientation of certain long-chain fatty acids at the air-water interface
- Authors: Saayman, Henry Martin
- Date: 1962
- Subjects: Fatty acids , Surface chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4496 , http://hdl.handle.net/10962/d1013117
- Description: The results obtained for the cross-sectional areas of the series of long-chain fatty acids may best be summarized with the aid of Graph 9. This graphical representation of the molecular areas, in Ų , against the chain length (n), of the fatty acid molecules, illustrates variation of the areas with chain length for the series in recrystallized form, and also for selected samples in the zone purified and vacuum distilled forms. On the graph, the limits of variation of the molecular areas have been represented as lines of a length corresponding to twice the standard deviation (2S). This is to give representation that the standard deviation may be positive or negative in relation to the mean. For molecules with n odd and lying between 15 and 19, the molecular area decreases. This may be due to the effect of 3 factorsg (1) A general decrease in lateral translation because of the increasing molecular mass (translational kinetic energy per molecule = ½ mc ⁻²), resulting in closer spacing of molecules. (2) A general, but steady decrease in the angle of tilt of the molecules which thus tend to be held more erect in the condensed film. (3) A general decrease in the precessional motion of the hydrophobic chain groups. For molecules with n odd and between 19 and 23, the molecular areas increase probably due to the steady increase in molecular mass causing the long chains to commence to buckle, tilt or topple in their upper regions. This tilting becomes greater because of the increasing gravitational effect on the heavier molecules which tends to make them assume a flatter posture in relation to the surface. The lower values observed for margaric and nonadecanoic acids, may be due to increasing symmetry in the chain, with corresponding economy in packing in condensed monolayers. This effect may be connected with increasing cylindrical symmetry of the hydrocarbon chain for even values of n. The results of this investigution, incomplete as it is, - serve to indicate what might reasonably be expected to happen in the orientation of these fatty acids in monolayers. Further work, especially on a greater range of acids with even n, is clearly necessary in order to establish the tentative ideas which have been suggested. However, in the present research, work was limited to those acids in the series which were obtainable without undue difficulty or delay, those which would spread readily under the conditions of experiments carried out at 20°C, and those which could be purified relatively easily. The acids below n = 15 in the series were found to be too soluble in aqueous substrates, at operating temperatures of 20°C, to yield reliable evidence with the Langmuir trough technique. The acids above n = 23 were unobtainable commercially and the synthesis of those acids from the lower members in the series presented problems of isolating the required specimens and difficulty in purifying these, which were considered b be beyond the scope of the present research. Summary and conclusion, p. 122.
- Full Text:
- Date Issued: 1962
- Authors: Saayman, Henry Martin
- Date: 1962
- Subjects: Fatty acids , Surface chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4496 , http://hdl.handle.net/10962/d1013117
- Description: The results obtained for the cross-sectional areas of the series of long-chain fatty acids may best be summarized with the aid of Graph 9. This graphical representation of the molecular areas, in Ų , against the chain length (n), of the fatty acid molecules, illustrates variation of the areas with chain length for the series in recrystallized form, and also for selected samples in the zone purified and vacuum distilled forms. On the graph, the limits of variation of the molecular areas have been represented as lines of a length corresponding to twice the standard deviation (2S). This is to give representation that the standard deviation may be positive or negative in relation to the mean. For molecules with n odd and lying between 15 and 19, the molecular area decreases. This may be due to the effect of 3 factorsg (1) A general decrease in lateral translation because of the increasing molecular mass (translational kinetic energy per molecule = ½ mc ⁻²), resulting in closer spacing of molecules. (2) A general, but steady decrease in the angle of tilt of the molecules which thus tend to be held more erect in the condensed film. (3) A general decrease in the precessional motion of the hydrophobic chain groups. For molecules with n odd and between 19 and 23, the molecular areas increase probably due to the steady increase in molecular mass causing the long chains to commence to buckle, tilt or topple in their upper regions. This tilting becomes greater because of the increasing gravitational effect on the heavier molecules which tends to make them assume a flatter posture in relation to the surface. The lower values observed for margaric and nonadecanoic acids, may be due to increasing symmetry in the chain, with corresponding economy in packing in condensed monolayers. This effect may be connected with increasing cylindrical symmetry of the hydrocarbon chain for even values of n. The results of this investigution, incomplete as it is, - serve to indicate what might reasonably be expected to happen in the orientation of these fatty acids in monolayers. Further work, especially on a greater range of acids with even n, is clearly necessary in order to establish the tentative ideas which have been suggested. However, in the present research, work was limited to those acids in the series which were obtainable without undue difficulty or delay, those which would spread readily under the conditions of experiments carried out at 20°C, and those which could be purified relatively easily. The acids below n = 15 in the series were found to be too soluble in aqueous substrates, at operating temperatures of 20°C, to yield reliable evidence with the Langmuir trough technique. The acids above n = 23 were unobtainable commercially and the synthesis of those acids from the lower members in the series presented problems of isolating the required specimens and difficulty in purifying these, which were considered b be beyond the scope of the present research. Summary and conclusion, p. 122.
- Full Text:
- Date Issued: 1962
An investigation of the structural problems in relation to some synthetic waxes
- Authors: Stokhuyzen, Rolf
- Date: 1970
- Subjects: Chemistry, Analytic , Waxes , Synthetic products
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4443 , http://hdl.handle.net/10962/d1007695 , Chemistry, Analytic , Waxes , Synthetic products
- Description: From Introduction: Wax and wax-like substances have been defined in many ways. One reasonably extensive definition, by Hatt and Lamberton (1956) is given below: "The term "wax" seems best used to denote a group of substances which qualitatively have certain physical properties in common. These properties are familiar ones, for in almost all countries some natural wax - beeswax, Japan wax, Chinese insect wax, the carnauba and candelilla waxes of the Americas - has been an important material in art and industry from prehistoric times. Waxes are understood to be opaque or translucent solids, which melt without decomposition to form mobile liquids at temperatures in the region of 100⁰C. They differ in hardness, but are all essentially soft substances with poor mechanical strength. Most waxes can be easily shaped or kneaded at a little above ambient temperatures. In fact, the term could easily have been made to cover the whole class now named thermoplastics." Pure n-paraffins would be too crystalline and brittle for use as waxes, whereas mixtures of n-paraffins have some valuable properties. The molecules bear such close resemblance to one another that they form mixed crystals of lowered crystallinity and the melting point is a function of the mean molecular weight. This is a desirable feature for it permits crystallinity and brittleness to be reduced without a marked loss in the melting point or hardness. It also allows a mixture to simulate a pure compound very closely. Waxes, in general, have been put to a large number of uses. They are used, for example, in candles, polishes, paper-coating, plastics, printing, matches, rust protectants and insulation. Each application requires its own appropriate range of wax properties.
- Full Text:
- Date Issued: 1970
- Authors: Stokhuyzen, Rolf
- Date: 1970
- Subjects: Chemistry, Analytic , Waxes , Synthetic products
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4443 , http://hdl.handle.net/10962/d1007695 , Chemistry, Analytic , Waxes , Synthetic products
- Description: From Introduction: Wax and wax-like substances have been defined in many ways. One reasonably extensive definition, by Hatt and Lamberton (1956) is given below: "The term "wax" seems best used to denote a group of substances which qualitatively have certain physical properties in common. These properties are familiar ones, for in almost all countries some natural wax - beeswax, Japan wax, Chinese insect wax, the carnauba and candelilla waxes of the Americas - has been an important material in art and industry from prehistoric times. Waxes are understood to be opaque or translucent solids, which melt without decomposition to form mobile liquids at temperatures in the region of 100⁰C. They differ in hardness, but are all essentially soft substances with poor mechanical strength. Most waxes can be easily shaped or kneaded at a little above ambient temperatures. In fact, the term could easily have been made to cover the whole class now named thermoplastics." Pure n-paraffins would be too crystalline and brittle for use as waxes, whereas mixtures of n-paraffins have some valuable properties. The molecules bear such close resemblance to one another that they form mixed crystals of lowered crystallinity and the melting point is a function of the mean molecular weight. This is a desirable feature for it permits crystallinity and brittleness to be reduced without a marked loss in the melting point or hardness. It also allows a mixture to simulate a pure compound very closely. Waxes, in general, have been put to a large number of uses. They are used, for example, in candles, polishes, paper-coating, plastics, printing, matches, rust protectants and insulation. Each application requires its own appropriate range of wax properties.
- Full Text:
- Date Issued: 1970
An ion imprinted polymer for the determination of Ni (II) ions from mine tailing samples
- Authors: Rammika, Modise
- Date: 2011
- Subjects: Imprinted polymers , Metal ions , Polymerization , Mineral industries -- Waste disposal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4323 , http://hdl.handle.net/10962/d1004981 , Imprinted polymers , Metal ions , Polymerization , Mineral industries -- Waste disposal
- Description: A Ni(II)-dimethylglyoxime ion imprinted polymer {Ni(II)-DMG IIP} was synthesized by the trapping method using the bulk polymerisation format. The structures of the imprinted and non-imprinted polymer were evaluated by infrared spectroscopy and the morphology was observed by scanning electron microscopy. The Ni(II)-DMG IIP was optimised for pH, mass, time and by the uniform design experimental method for the molar ratios of monomer to crosslinker to porogen and template to ligands as well as keeping these parameters constant and varying the quantities of initiator, 2,2'-azobisisobutyronitrile (AIBN). The optimum pH was 8.5, optimum mass was 50 mg, optimum time was 1 min and the optimum molar ratios of crosslinker to monomer, monomer to template and nickel(II) sulfate hexahydrate (NiSO₄.6H₂O) to 4-vinylpyridine to dimethylglyoxime were found to be 3.3:1.0, 0.6:1.0 and 1.0:0.6:3.6 respectively with 30 mg and 8 mL as the optimum amounts of initiator and porogen respectively. Through this optimisation, recovery of Ni(II) was increased from 98 to 100%. Selectivity of the ion imprinted polymer was evaluated by analysing, using an inductively coupled plasma-optical emission spectrometer, for Ni(II) ions that were spiked with varying concentrations of Co(II), Cu(II), Zn(II), Pd(II), Fe(II), Ca(II), Mg(II), Na(I) and K(I) in aqueous samples. Selectivity studies also confirmed that the ion imprinted polymer had very good selectivity characterised by % RSD of less than 5 %. Co(II) was the only ion found to slightly interfere with the determination of Ni(II). The limits of detection and quantification were found to be 3x10⁻⁴ μg/mL and 9x10⁻⁴ μg/mL respectively. The method was evaluated by a custom solution of ground water certified reference material (SEP-3) and sandy soil reference material (BCR-142R) and the concentrations of Ni(II) obtained were not significantly different to the certified ones. The Ni(II)-DMG IIP was then evaluated in aqueous and soil samples where recoveries of 93 to 100% and 98 to 99% respectively were obtained with enrichment factors ranging from 2 to 18 in aqueous and 27 to 40 in soil samples. Finally, the Ni(II)-DMG IIP was used to analyse mine tailings samples and Ni(II) recovery of 99% was obtained with an enrichment factor of 2.
- Full Text:
- Date Issued: 2011
- Authors: Rammika, Modise
- Date: 2011
- Subjects: Imprinted polymers , Metal ions , Polymerization , Mineral industries -- Waste disposal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4323 , http://hdl.handle.net/10962/d1004981 , Imprinted polymers , Metal ions , Polymerization , Mineral industries -- Waste disposal
- Description: A Ni(II)-dimethylglyoxime ion imprinted polymer {Ni(II)-DMG IIP} was synthesized by the trapping method using the bulk polymerisation format. The structures of the imprinted and non-imprinted polymer were evaluated by infrared spectroscopy and the morphology was observed by scanning electron microscopy. The Ni(II)-DMG IIP was optimised for pH, mass, time and by the uniform design experimental method for the molar ratios of monomer to crosslinker to porogen and template to ligands as well as keeping these parameters constant and varying the quantities of initiator, 2,2'-azobisisobutyronitrile (AIBN). The optimum pH was 8.5, optimum mass was 50 mg, optimum time was 1 min and the optimum molar ratios of crosslinker to monomer, monomer to template and nickel(II) sulfate hexahydrate (NiSO₄.6H₂O) to 4-vinylpyridine to dimethylglyoxime were found to be 3.3:1.0, 0.6:1.0 and 1.0:0.6:3.6 respectively with 30 mg and 8 mL as the optimum amounts of initiator and porogen respectively. Through this optimisation, recovery of Ni(II) was increased from 98 to 100%. Selectivity of the ion imprinted polymer was evaluated by analysing, using an inductively coupled plasma-optical emission spectrometer, for Ni(II) ions that were spiked with varying concentrations of Co(II), Cu(II), Zn(II), Pd(II), Fe(II), Ca(II), Mg(II), Na(I) and K(I) in aqueous samples. Selectivity studies also confirmed that the ion imprinted polymer had very good selectivity characterised by % RSD of less than 5 %. Co(II) was the only ion found to slightly interfere with the determination of Ni(II). The limits of detection and quantification were found to be 3x10⁻⁴ μg/mL and 9x10⁻⁴ μg/mL respectively. The method was evaluated by a custom solution of ground water certified reference material (SEP-3) and sandy soil reference material (BCR-142R) and the concentrations of Ni(II) obtained were not significantly different to the certified ones. The Ni(II)-DMG IIP was then evaluated in aqueous and soil samples where recoveries of 93 to 100% and 98 to 99% respectively were obtained with enrichment factors ranging from 2 to 18 in aqueous and 27 to 40 in soil samples. Finally, the Ni(II)-DMG IIP was used to analyse mine tailings samples and Ni(II) recovery of 99% was obtained with an enrichment factor of 2.
- Full Text:
- Date Issued: 2011
An ion imprinted polymer for the selective extraction of mercury (II) ions in aqueous media
- Authors: Batlokwa, Bareki Shima
- Date: 2010 , 2013-07-18
- Subjects: Mercury , Metal ions , Imprinted polymers , Polymerization
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4294 , http://hdl.handle.net/10962/d1004541 , Mercury , Metal ions , Imprinted polymers , Polymerization
- Description: This thesis presents the application of an imprinted mercury(lI) polymer that we synthesized by copolymerizing the functional and cross-linking monomers, N'-[3-(Trimethoxysilyl)propyl] diethylenetriamine (TPET) and tetraethylorthosilicate (TEOS) in the presence of mercury (II) ions as template. A bulk polymerization method following a double-imprinting procedure and employing hexadecyltrimethylammonium bromide (CTAB), as a second template to improve the efficiency of the polymer was employed in the synthesis. The imprinted polymer particles were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and their average size determined by screen analysis using standard test sieves. The relative selective coefficients (k') of the imprinted polymer evaluated from selective binding studies between Hg ²⁺and Cu²⁺ or Hg²⁺ and Cd²⁺, were 10588 and 3147, respectively. These values indicated highly favored Hg²⁺ extractions over the two competing ions. Application of the polymer to various real water samples (tap, sea, river, pulverized coal solution, treated and untreated sewerage from the vicinity of Grahamstown in South Africa) showed high extraction efficiencies (EEs) of Hg²⁺ ions; (over 84% in all cases) as evaluated from the detected unextracted Hg²⁺ ions by inductively coupled plasma optical emission spectroscopy (ICP-OES). The limit of detection (LOD, 3ơ) of the method was evaluated to be 0.036 ng ml⁻¹ and generally the data (n=10) had percentage relative standard deviation (%RSD) of less than 4%. These findings indicate that the double-imprinted polymer has potential to be used as an efficient extraction material for the selective pre-concentration of mercury(lI) ions in aqueous environments. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2010
- Authors: Batlokwa, Bareki Shima
- Date: 2010 , 2013-07-18
- Subjects: Mercury , Metal ions , Imprinted polymers , Polymerization
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4294 , http://hdl.handle.net/10962/d1004541 , Mercury , Metal ions , Imprinted polymers , Polymerization
- Description: This thesis presents the application of an imprinted mercury(lI) polymer that we synthesized by copolymerizing the functional and cross-linking monomers, N'-[3-(Trimethoxysilyl)propyl] diethylenetriamine (TPET) and tetraethylorthosilicate (TEOS) in the presence of mercury (II) ions as template. A bulk polymerization method following a double-imprinting procedure and employing hexadecyltrimethylammonium bromide (CTAB), as a second template to improve the efficiency of the polymer was employed in the synthesis. The imprinted polymer particles were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and their average size determined by screen analysis using standard test sieves. The relative selective coefficients (k') of the imprinted polymer evaluated from selective binding studies between Hg ²⁺and Cu²⁺ or Hg²⁺ and Cd²⁺, were 10588 and 3147, respectively. These values indicated highly favored Hg²⁺ extractions over the two competing ions. Application of the polymer to various real water samples (tap, sea, river, pulverized coal solution, treated and untreated sewerage from the vicinity of Grahamstown in South Africa) showed high extraction efficiencies (EEs) of Hg²⁺ ions; (over 84% in all cases) as evaluated from the detected unextracted Hg²⁺ ions by inductively coupled plasma optical emission spectroscopy (ICP-OES). The limit of detection (LOD, 3ơ) of the method was evaluated to be 0.036 ng ml⁻¹ and generally the data (n=10) had percentage relative standard deviation (%RSD) of less than 4%. These findings indicate that the double-imprinted polymer has potential to be used as an efficient extraction material for the selective pre-concentration of mercury(lI) ions in aqueous environments. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2010
An x-ray investigation of the thermal decomposition of unirradiated and irradiated silver permanganate.
- Authors: Woods, Geoffrey Steward
- Date: 1963
- Subjects: Decomposition (Chemistry) , Materials -- Thermal properties , Solids -- Thermal properties , Permanganates , Silver compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4511 , http://hdl.handle.net/10962/d1013450
- Description: [From Introduction] The first step in the study of the thermal decompositions of solids is an examination of the kinetics, since this casts much light on the mechanism of the reaction. It must be borne in mind, however, that a theoretical expression, derived on the basis of a particular mechanism, even if it fits the observed experimental results, is not conclusive proof of the validity of the mechanism when applied to the decomposition under examination.
- Full Text:
- Date Issued: 1963
- Authors: Woods, Geoffrey Steward
- Date: 1963
- Subjects: Decomposition (Chemistry) , Materials -- Thermal properties , Solids -- Thermal properties , Permanganates , Silver compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4511 , http://hdl.handle.net/10962/d1013450
- Description: [From Introduction] The first step in the study of the thermal decompositions of solids is an examination of the kinetics, since this casts much light on the mechanism of the reaction. It must be borne in mind, however, that a theoretical expression, derived on the basis of a particular mechanism, even if it fits the observed experimental results, is not conclusive proof of the validity of the mechanism when applied to the decomposition under examination.
- Full Text:
- Date Issued: 1963
Analytical procedures for the determination of wattle polyphenols in wastewaters
- Authors: Hendry, Antony John
- Date: 1984
- Subjects: Liquid chromatography , Spectrophotometry , High performance liquid chromatography , Water -- Purification
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4431 , http://hdl.handle.net/10962/d1007221 , Liquid chromatography , Spectrophotometry , High performance liquid chromatography , Water -- Purification
- Full Text:
- Date Issued: 1984
- Authors: Hendry, Antony John
- Date: 1984
- Subjects: Liquid chromatography , Spectrophotometry , High performance liquid chromatography , Water -- Purification
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4431 , http://hdl.handle.net/10962/d1007221 , Liquid chromatography , Spectrophotometry , High performance liquid chromatography , Water -- Purification
- Full Text:
- Date Issued: 1984
Anisotropic copper oxide nanorods decorated with gold and palladium nanoparticles and their enzymatic properties
- Authors: Sicwetsha, Simbongile
- Date: 2021-04
- Subjects: To be added
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/178547 , vital:42949
- Description: Access restricted until April 2023. , Thesis (MSc) -- Faculty of Science, Chemistry, 2021
- Full Text:
- Date Issued: 2021-04
- Authors: Sicwetsha, Simbongile
- Date: 2021-04
- Subjects: To be added
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/178547 , vital:42949
- Description: Access restricted until April 2023. , Thesis (MSc) -- Faculty of Science, Chemistry, 2021
- Full Text:
- Date Issued: 2021-04
Antimalarial activity of quinoline thiosemicarbazones: synthesis and antiplasmodial evaluation
- Nqeno, Lukhanyiso Khanyisile
- Authors: Nqeno, Lukhanyiso Khanyisile
- Date: 2022-04-06
- Subjects: Antimalarials , Quinoline , Thiosemicarbazones , Malaria Chemotherapy , Plasmodium falciparum , Malaria Africa, Sub-Saharan , Iron chelates Therapeutic use
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/291292 , vital:56841
- Description: Africa is one of the regions that is most affected by malaria, as 90% of all malaria deaths occur in sub-saharan Africa. Malaria is a life threatening disease responsible for an estimated 800000 deaths each year, the majority of these deaths occurred in children under the age of five. The disease is a mosquito-borne, and it is transmitted to humans by the female Anopheles mosquito. The parasite responsible for this disease belong to the Plasmodium genus with Plasmodium falciparum causing the most severe cases of the disease in humans. The most widely available anti-malarials were designed to specifically target the pathogenic blood stage in humans, however, in order to completely eradicate malaria there is a need for the development of medicines that not only target the pathogenic blood stage of the parasite but also block parasite transmission and eliminate asymptomatic and cryptic hepatic forms of the parasite. Iron chelators have recently gained importance as potent antimalarials, to cause infection nearly all protozoa obtain growth essential iron from their hosts. Iron is required for the development of the parasite. Deprivation of utilizable iron by chelation is a proficient approach to arrest parasite growth and associated infection. Thiosemicarbazones are known iron chelating agents by bonding through the sulfur and azomethine nitrogen atoms. This study is aimed at the identification of thiosemicarbazone based derivatives as possible antimalarial agents. Due to their iron chelation abilities there has been increasing interest in the investigation of thiosemicarbazones as possible antimalarials. During the course of this project, several thiosemicarbazone derivatives were synthesized and their structure confirmed using routine analytical techniques (NMR, FTIR, and HRMS). The synthesized compounds were evaluated in vitro against the chloroquine sensitive strain (3D7) of P. falciparum for antimarial activity. The compounds were also evaluated agsinst Hela cells for overt cytotoxicity. The compounds generally showed poor antimalarial activity. One compound (LKN11) was identified to possess intrinsic and moderate antimalarial activity of 6.6 μM. The compounds were generally not cytotoxic against Hela cell at concentrations of up to 20 μM, with only compound LKN10 showing modest cytotoxic activity of 9.5 μM. This research went on to identify two thiosemicarbazone based derivatives which had a significant effect on HeLa and pLDH cells. , Thesis (MSc) -- Faculty of Science, Chemistry, 2022
- Full Text:
- Date Issued: 2022-04-06
- Authors: Nqeno, Lukhanyiso Khanyisile
- Date: 2022-04-06
- Subjects: Antimalarials , Quinoline , Thiosemicarbazones , Malaria Chemotherapy , Plasmodium falciparum , Malaria Africa, Sub-Saharan , Iron chelates Therapeutic use
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/291292 , vital:56841
- Description: Africa is one of the regions that is most affected by malaria, as 90% of all malaria deaths occur in sub-saharan Africa. Malaria is a life threatening disease responsible for an estimated 800000 deaths each year, the majority of these deaths occurred in children under the age of five. The disease is a mosquito-borne, and it is transmitted to humans by the female Anopheles mosquito. The parasite responsible for this disease belong to the Plasmodium genus with Plasmodium falciparum causing the most severe cases of the disease in humans. The most widely available anti-malarials were designed to specifically target the pathogenic blood stage in humans, however, in order to completely eradicate malaria there is a need for the development of medicines that not only target the pathogenic blood stage of the parasite but also block parasite transmission and eliminate asymptomatic and cryptic hepatic forms of the parasite. Iron chelators have recently gained importance as potent antimalarials, to cause infection nearly all protozoa obtain growth essential iron from their hosts. Iron is required for the development of the parasite. Deprivation of utilizable iron by chelation is a proficient approach to arrest parasite growth and associated infection. Thiosemicarbazones are known iron chelating agents by bonding through the sulfur and azomethine nitrogen atoms. This study is aimed at the identification of thiosemicarbazone based derivatives as possible antimalarial agents. Due to their iron chelation abilities there has been increasing interest in the investigation of thiosemicarbazones as possible antimalarials. During the course of this project, several thiosemicarbazone derivatives were synthesized and their structure confirmed using routine analytical techniques (NMR, FTIR, and HRMS). The synthesized compounds were evaluated in vitro against the chloroquine sensitive strain (3D7) of P. falciparum for antimarial activity. The compounds were also evaluated agsinst Hela cells for overt cytotoxicity. The compounds generally showed poor antimalarial activity. One compound (LKN11) was identified to possess intrinsic and moderate antimalarial activity of 6.6 μM. The compounds were generally not cytotoxic against Hela cell at concentrations of up to 20 μM, with only compound LKN10 showing modest cytotoxic activity of 9.5 μM. This research went on to identify two thiosemicarbazone based derivatives which had a significant effect on HeLa and pLDH cells. , Thesis (MSc) -- Faculty of Science, Chemistry, 2022
- Full Text:
- Date Issued: 2022-04-06
Antimalarial secondary metabolites from Morinda lucida
- Authors: Chithambo, Bertha
- Date: 2017
- Subjects: Botanical chemistry , Anthraquinones , Antimalarials , Rubiaceae -- Therapeutic use , Malaria -- Treatment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/45730 , vital:25535
- Description: Antimalarial activities of secondary metabolites from Morinda lucida (Rubiaceae), were investigated. Even though M. lucida is traditionally used to treat malaria, diabetes, jaundice, hypertension, dysentery and many other diseases, the compounds in this plant have not yet been fully investigated and characterised. Most of the studies that have been done on this plant focused on the medicinal properties of the crude extracts but have not gone further to isolate and characterise the compounds. In this study, the methanol - dichloromethane crude extract from the bark of M. lucida was fractionated into fractions 1-8. Fractions 2-5 were purified in order to isolate active secondary metabolites. The isolated pure compounds were characterised and identified. An in vitro antimalarial assay was carried out on the crude extract, fractions, pure compounds and solutions made from different combinations of pure compounds using the parasite lactate dehydrogenase (pLDH) assay. An IC50 done on the methanolic crude extract gave a value of 25 µg/mL. The % cell viability for the crude extract in cell toxicity assay remained at 100%. Each of the pure compounds tested had very little activity. Their activities were increased when samples from the different compounds were mixed. One of these mixtures reduced malaria viability to about 22 % at 20 µM and gave an IC50 value of 17 µM. Antibacterial assays were also carried out on the crude extract and fractions. Fractions 2 and 3 were relatively active (MIC values ranging between 125-1000 µg/mL) against M. cattarhalis and E. faecalis. Fraction 2 was also the most active on S. typhimurium and S. aureus (MIC value of 1000 µg/mL) compared with the other fractions. This same fraction also showed some activity against M. tuberculosis with MIC90 and MIC99 values of 40.9 and 46.3 µg/mL respectively in an anti-tuberculosis assay.The following compounds, comprising of iridoids (asperuloside and asperulosidic acid), terpenoids (stigmasterol, P-sitosterol, campesterol, lanosterol and cycloartenol) and anthraquinones [5,15-O-dimethylmorindol, 1,7-dihydroxy-2-methoxy-5-(methoxymethyl) anthraquinone and 1,6-dihydroxy-2-methoxy-5-(methoxymethyl)anthraquinone], were isolated. All these compounds have been isolated from different plants before with the exception of 1,7-dihydroxy-2-methoxy-5-(methoxymethyl)anthraquinone and 1,6-dihydroxy-2-methoxy-5-(methoxymethyl)anthraquinone which were tentatively assigned the structures due to insufficient data. To the best of our knowledge, this is the first report on the identification of all of the mentioned compounds, with the exception of ß-sitosterol and stigmasterol, from M. lucida. Molecular docking was performed on one of the isolated anthraquinones (5,15-O- dimethylmorindol) to check if it can bind to cytochrome bci, a known target for atovaquone. This compound interacted with the same amino acids that atovaquone, a well known antimalarial agent, interacted with on cytochrome bc1 indicating a possible similar mode of action.
- Full Text:
- Date Issued: 2017
- Authors: Chithambo, Bertha
- Date: 2017
- Subjects: Botanical chemistry , Anthraquinones , Antimalarials , Rubiaceae -- Therapeutic use , Malaria -- Treatment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/45730 , vital:25535
- Description: Antimalarial activities of secondary metabolites from Morinda lucida (Rubiaceae), were investigated. Even though M. lucida is traditionally used to treat malaria, diabetes, jaundice, hypertension, dysentery and many other diseases, the compounds in this plant have not yet been fully investigated and characterised. Most of the studies that have been done on this plant focused on the medicinal properties of the crude extracts but have not gone further to isolate and characterise the compounds. In this study, the methanol - dichloromethane crude extract from the bark of M. lucida was fractionated into fractions 1-8. Fractions 2-5 were purified in order to isolate active secondary metabolites. The isolated pure compounds were characterised and identified. An in vitro antimalarial assay was carried out on the crude extract, fractions, pure compounds and solutions made from different combinations of pure compounds using the parasite lactate dehydrogenase (pLDH) assay. An IC50 done on the methanolic crude extract gave a value of 25 µg/mL. The % cell viability for the crude extract in cell toxicity assay remained at 100%. Each of the pure compounds tested had very little activity. Their activities were increased when samples from the different compounds were mixed. One of these mixtures reduced malaria viability to about 22 % at 20 µM and gave an IC50 value of 17 µM. Antibacterial assays were also carried out on the crude extract and fractions. Fractions 2 and 3 were relatively active (MIC values ranging between 125-1000 µg/mL) against M. cattarhalis and E. faecalis. Fraction 2 was also the most active on S. typhimurium and S. aureus (MIC value of 1000 µg/mL) compared with the other fractions. This same fraction also showed some activity against M. tuberculosis with MIC90 and MIC99 values of 40.9 and 46.3 µg/mL respectively in an anti-tuberculosis assay.The following compounds, comprising of iridoids (asperuloside and asperulosidic acid), terpenoids (stigmasterol, P-sitosterol, campesterol, lanosterol and cycloartenol) and anthraquinones [5,15-O-dimethylmorindol, 1,7-dihydroxy-2-methoxy-5-(methoxymethyl) anthraquinone and 1,6-dihydroxy-2-methoxy-5-(methoxymethyl)anthraquinone], were isolated. All these compounds have been isolated from different plants before with the exception of 1,7-dihydroxy-2-methoxy-5-(methoxymethyl)anthraquinone and 1,6-dihydroxy-2-methoxy-5-(methoxymethyl)anthraquinone which were tentatively assigned the structures due to insufficient data. To the best of our knowledge, this is the first report on the identification of all of the mentioned compounds, with the exception of ß-sitosterol and stigmasterol, from M. lucida. Molecular docking was performed on one of the isolated anthraquinones (5,15-O- dimethylmorindol) to check if it can bind to cytochrome bci, a known target for atovaquone. This compound interacted with the same amino acids that atovaquone, a well known antimalarial agent, interacted with on cytochrome bc1 indicating a possible similar mode of action.
- Full Text:
- Date Issued: 2017
Application of Baylis-Hillman methodology in the construction of complex heterocyclic targets
- Ganto, Mlungiseleli MacDonald
- Authors: Ganto, Mlungiseleli MacDonald
- Date: 2009
- Subjects: Heterocyclic compounds -- Derivatives Heterocyclic chemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4401 , http://hdl.handle.net/10962/d1006703
- Description: Baylis-Hillman reactions using various aromatic aldehydes, activated alkenes and catalysts have been used to: - access an extensive range of poly-heterocyclic products;explore chemoselectivity; and optimise reaction efficiency. Chromone-3-carbaldehydes and chromone-2-carbaldehydes, prepared via Vielsmeier-Haack and Kostanecki-Robinson methodology, respectively, have been used as Baylis-Hillman substrates with four different catalysts, viz., 1,4-diazabicyclo[2.2.2]octane (DABCO), 3-hydroxyquinuclidine (3-HQ), imidazole and N’,N’,N’,N’- tetramethylpropanediamine (TMPDA), and with methyl vinyl ketone (MVK), methyl acrylate, cyclic enones (2-cyclohexen-1-one, 2-cyclopenten-1-one and chromones) as activated alkenes. Reactions of the chromone- -carbaldehydes with MVK afforded dimeric Baylis-Hillman adducts when catalyzed by DABCO but when the same reactions were repeated using 3-HQ as catalyst, the dimeric products were accompanied by tricyclic Baylis-Hillman adducts. Use of excess MVK, however, led to mixtures of the normal Baylis-Hillman adducts and the tricyclic adducts – interestingly, with the apparent absence of the dimeric products. While reactions of chromone-3-carbaldehydes with methyl acrylate afforded the normal Baylis-Hillman adducts, the chromone-2- carbaldehydes produced, instead, rearrangement products, consistent with an earlier, single observation. Reactions of 2-nitrobenzaldehydes with cyclic enones using imidazole as catalyst afforded the normal Baylis-Hillman adducts, reductive cyclisation of the 2-cyclohexen-1- one and 2-cyclopenten-1-one adducts, using acetic acid and iron powder, afforded the corresponding quinoline erivatives. Treatment of cyclic enones with pyridine-2-carbaldehydes and quinoline-2-carbaldehydes using TMPDA as catalyst generally gave the expected Baylis-Hillman adducts. However, indolizine derivatives were isolated directly from Baylis-Hillman reactions involving pyridine-2-carbaldehydes and 2-cyclohexen-1-one. The remaining Baylis-Hillman adducts were cyclized to the corresponding indolizines by treatment with acetic anhydride both under reflux and under microwave-assisted conditions, the latter approach providing remarkably rapid and efficient access to the polycyclic products. Computer modelling studies have been conducted on selected polycyclic products at the Molecular Mechanics (MM), Quantum Mechanical (QM) and Density Functional (DFT) levels. The theoretical results have been used to calculate UV, IR and NMR absorption data, which have been compared, in turn, with the experimental spectroscopic data. Use has also been made of the estreNova NMR prediction programme and, generally, good agreement has been observed between the predicted and experimental spectroscopic data.
- Full Text:
- Date Issued: 2009
- Authors: Ganto, Mlungiseleli MacDonald
- Date: 2009
- Subjects: Heterocyclic compounds -- Derivatives Heterocyclic chemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4401 , http://hdl.handle.net/10962/d1006703
- Description: Baylis-Hillman reactions using various aromatic aldehydes, activated alkenes and catalysts have been used to: - access an extensive range of poly-heterocyclic products;explore chemoselectivity; and optimise reaction efficiency. Chromone-3-carbaldehydes and chromone-2-carbaldehydes, prepared via Vielsmeier-Haack and Kostanecki-Robinson methodology, respectively, have been used as Baylis-Hillman substrates with four different catalysts, viz., 1,4-diazabicyclo[2.2.2]octane (DABCO), 3-hydroxyquinuclidine (3-HQ), imidazole and N’,N’,N’,N’- tetramethylpropanediamine (TMPDA), and with methyl vinyl ketone (MVK), methyl acrylate, cyclic enones (2-cyclohexen-1-one, 2-cyclopenten-1-one and chromones) as activated alkenes. Reactions of the chromone- -carbaldehydes with MVK afforded dimeric Baylis-Hillman adducts when catalyzed by DABCO but when the same reactions were repeated using 3-HQ as catalyst, the dimeric products were accompanied by tricyclic Baylis-Hillman adducts. Use of excess MVK, however, led to mixtures of the normal Baylis-Hillman adducts and the tricyclic adducts – interestingly, with the apparent absence of the dimeric products. While reactions of chromone-3-carbaldehydes with methyl acrylate afforded the normal Baylis-Hillman adducts, the chromone-2- carbaldehydes produced, instead, rearrangement products, consistent with an earlier, single observation. Reactions of 2-nitrobenzaldehydes with cyclic enones using imidazole as catalyst afforded the normal Baylis-Hillman adducts, reductive cyclisation of the 2-cyclohexen-1- one and 2-cyclopenten-1-one adducts, using acetic acid and iron powder, afforded the corresponding quinoline erivatives. Treatment of cyclic enones with pyridine-2-carbaldehydes and quinoline-2-carbaldehydes using TMPDA as catalyst generally gave the expected Baylis-Hillman adducts. However, indolizine derivatives were isolated directly from Baylis-Hillman reactions involving pyridine-2-carbaldehydes and 2-cyclohexen-1-one. The remaining Baylis-Hillman adducts were cyclized to the corresponding indolizines by treatment with acetic anhydride both under reflux and under microwave-assisted conditions, the latter approach providing remarkably rapid and efficient access to the polycyclic products. Computer modelling studies have been conducted on selected polycyclic products at the Molecular Mechanics (MM), Quantum Mechanical (QM) and Density Functional (DFT) levels. The theoretical results have been used to calculate UV, IR and NMR absorption data, which have been compared, in turn, with the experimental spectroscopic data. Use has also been made of the estreNova NMR prediction programme and, generally, good agreement has been observed between the predicted and experimental spectroscopic data.
- Full Text:
- Date Issued: 2009