Synthesis, characterisation and spectroscopic studies of diazine-N-oxide complexes of iron(II) towards the development of sensors
- Authors: Mpiti, Unako Bongani
- Date: 2019
- Subjects: Diazines , Ligands , Iron
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/94753 , vital:31075
- Description: The characteristic magnetic and spectroscopic features associated with the red monomeric or dimeric, and polymeric pyrazine-N-oxide (PyzNO) iron(II) perchlorate complexes; Fen(μ1,1-pyzNO)2n-2(pyzNO)3n+2(ClO4)2n (n = {1, 2}*, and the novel compound {Fe(μ-pyzNO-κN,κO)n-1(pyzNO-κN)2(pyzNO-κO)2}n(ClO4)2n†, respectively, were investigated. These properties are altered substantially when the complexes are hydrated; for instance, by atmospheric exposure. The resulting species; Fe(pyzNO)5(H2O)3(ClO4)2* and [Fe(pyzNO-κN)4(H2O)2](ClO4)2.2H2O†, which have different hues of a bright yellow colour, were found to exhibit strong paramagnetism, in contrast to their anhydrous precursors, which are ‘EPR silent’. A low spin → high spin crossover (LS→HS, SCO) transition was therefore proposed to occur as the complexes become hydrated by atmospheric moisture. The red→yellow colour change is reversible, and dehydration of the yellow species by heating regenerates the red variant, a feature which lends itself to the potential applicability of the system as a sensor. Further emphasis on this potential derives from the fact that the hydration/dehydration process, and its accompanying physical changes, appears reversible even after many such treatments. It became of interest, then, to determine if these changes were limited to water-exposed samples, or if they occurred under more diverse solvent atmospheres. The reversibility of such exposure on the structure of the novel polynuclear complex was therefore investigated. In general, it was found that there occurred a strong solvent-complex association for the more polar solvents. Red→yellow, LS→HS events were seen when the complex was exposed to the vapours of p-dioxane, acetaldehyde and formaldehyde, and to a lesser extent, to that of methanol. In each case, significant structural changes were seen, as evidenced be comparative XRPD and thermo-analytical studies. Some of these changes have however been ascribed to the effects of partial dissolution upon extended exposure of the complex to the associated media. Exposure to less polar solvent atmospheres, such as those of cyclohexane, toluene, diethyl ether, etc., showed some signs of mild solvent surface adhesion, but were unaccompanied by discernible magnetic and colour changes. Another novel complex was produced during attempts to synthesize the PyzNO complexes from a mixture of a 2,2’-dimethoxypropane (DMP) and ethanol (1:1, v/v), rather than the methanol/DMP mixture which had been alternately used. The formula of the resulting complex is Fe(pyzNO)6(ClO4)2.3EtOH*. This EPR inactive product was orange in colour, and transformed into a bright yellow, strongly paramagnetic species upon atmospheric exposure. Further solvent studies showed that this species interacted significantly with all solvents tested, but generally more strongly with increasing solvent polarity. Orange→yellow colour changes occurred in environments saturated with p-dioxane, acetaldehyde and formaldehyde vapours. The DMSO-exposed sample transformed to dark red, due to suspected PyzNO substitution by the solvent. The red→yellow and orange→yellow colour changes were ascribed to the formal substitution of O-coordinated PyzNO (μ-PyzNO in the polymeric complex) by the incoming solvent. The resulting structural and geometric changes stimulated a redistribution of d electrons among the new constituent molecular orbitals of altered energy and symmetry. Therefore, although the colour changes were not conventionally solvatochromic - in that the original structure was lost on exposure – data suggested that it was the coordination of species of higher donor strength that produced the observed bathochromic shifts. A novel 4,4’-bipyridine-N-oxide Fe(II) perchlorate complex, Fe2(bipyNO)5(ClO4)4.6MeOH†, was also produced, primarily for physicochemical comparison with the PyzNO complexes. No colour or magnetic changes were seen on atmospheric exposure. The original complex was observed to be inherently paramagnetic, and no SCO events occurred upon solvent exposure. Despite this, thermal analyses showed that the complex did exhibit the strong uptake of polar solvents in general, but particularly with acetaldehyde. Significant structural changes upon exposure were limited to surface phenomena, with the exception of the acetaldehyde-exposed sample.
- Full Text:
- Date Issued: 2019
- Authors: Mpiti, Unako Bongani
- Date: 2019
- Subjects: Diazines , Ligands , Iron
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/94753 , vital:31075
- Description: The characteristic magnetic and spectroscopic features associated with the red monomeric or dimeric, and polymeric pyrazine-N-oxide (PyzNO) iron(II) perchlorate complexes; Fen(μ1,1-pyzNO)2n-2(pyzNO)3n+2(ClO4)2n (n = {1, 2}*, and the novel compound {Fe(μ-pyzNO-κN,κO)n-1(pyzNO-κN)2(pyzNO-κO)2}n(ClO4)2n†, respectively, were investigated. These properties are altered substantially when the complexes are hydrated; for instance, by atmospheric exposure. The resulting species; Fe(pyzNO)5(H2O)3(ClO4)2* and [Fe(pyzNO-κN)4(H2O)2](ClO4)2.2H2O†, which have different hues of a bright yellow colour, were found to exhibit strong paramagnetism, in contrast to their anhydrous precursors, which are ‘EPR silent’. A low spin → high spin crossover (LS→HS, SCO) transition was therefore proposed to occur as the complexes become hydrated by atmospheric moisture. The red→yellow colour change is reversible, and dehydration of the yellow species by heating regenerates the red variant, a feature which lends itself to the potential applicability of the system as a sensor. Further emphasis on this potential derives from the fact that the hydration/dehydration process, and its accompanying physical changes, appears reversible even after many such treatments. It became of interest, then, to determine if these changes were limited to water-exposed samples, or if they occurred under more diverse solvent atmospheres. The reversibility of such exposure on the structure of the novel polynuclear complex was therefore investigated. In general, it was found that there occurred a strong solvent-complex association for the more polar solvents. Red→yellow, LS→HS events were seen when the complex was exposed to the vapours of p-dioxane, acetaldehyde and formaldehyde, and to a lesser extent, to that of methanol. In each case, significant structural changes were seen, as evidenced be comparative XRPD and thermo-analytical studies. Some of these changes have however been ascribed to the effects of partial dissolution upon extended exposure of the complex to the associated media. Exposure to less polar solvent atmospheres, such as those of cyclohexane, toluene, diethyl ether, etc., showed some signs of mild solvent surface adhesion, but were unaccompanied by discernible magnetic and colour changes. Another novel complex was produced during attempts to synthesize the PyzNO complexes from a mixture of a 2,2’-dimethoxypropane (DMP) and ethanol (1:1, v/v), rather than the methanol/DMP mixture which had been alternately used. The formula of the resulting complex is Fe(pyzNO)6(ClO4)2.3EtOH*. This EPR inactive product was orange in colour, and transformed into a bright yellow, strongly paramagnetic species upon atmospheric exposure. Further solvent studies showed that this species interacted significantly with all solvents tested, but generally more strongly with increasing solvent polarity. Orange→yellow colour changes occurred in environments saturated with p-dioxane, acetaldehyde and formaldehyde vapours. The DMSO-exposed sample transformed to dark red, due to suspected PyzNO substitution by the solvent. The red→yellow and orange→yellow colour changes were ascribed to the formal substitution of O-coordinated PyzNO (μ-PyzNO in the polymeric complex) by the incoming solvent. The resulting structural and geometric changes stimulated a redistribution of d electrons among the new constituent molecular orbitals of altered energy and symmetry. Therefore, although the colour changes were not conventionally solvatochromic - in that the original structure was lost on exposure – data suggested that it was the coordination of species of higher donor strength that produced the observed bathochromic shifts. A novel 4,4’-bipyridine-N-oxide Fe(II) perchlorate complex, Fe2(bipyNO)5(ClO4)4.6MeOH†, was also produced, primarily for physicochemical comparison with the PyzNO complexes. No colour or magnetic changes were seen on atmospheric exposure. The original complex was observed to be inherently paramagnetic, and no SCO events occurred upon solvent exposure. Despite this, thermal analyses showed that the complex did exhibit the strong uptake of polar solvents in general, but particularly with acetaldehyde. Significant structural changes upon exposure were limited to surface phenomena, with the exception of the acetaldehyde-exposed sample.
- Full Text:
- Date Issued: 2019
The development of amine-based extractants for separation of base metals in a sulfate medium
- Authors: Magwa, Nomampondo Penelope
- Date: 2015
- Subjects: Extraction (Chemistry) , Sulfates , Ligands , Benzimidazoles , Infrared spectroscopy , Nuclear magnetic resonance spectroscopy , Metal ions , Metals
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4559 , http://hdl.handle.net/10962/d1020010
- Description: Tridentate benzimidazole-based ligands, bis((1H-benzimidazol-2-yl)methyl)sulfide (BNSN) and bis((1H-benzimidazol-2-yl)methyl)amine (BNNN), along with dinonylnaphthalene sulfonic acid (DNNSA) as a synergist, were investigated as potential selective extractants for Ni2+ from base metals in a solvent extraction system using 2-octanol/Shellsol 2325 (8:2) as diluent and modifier. However, extraction studies show a lack of pH-metric separation of the later 3d metal ions with bis((1-octylbenzimidazol-2-yl)methyl)sulfide (BONSN) and bis((1- decylbenzimidazol-2-yl)methyl)amine (BDNNN) as extractants, but extractions occurred in the low pH range with an opportunity for back extraction. This investigation suggested that tridentate ligands (at least those of the nature investigated here) are not feasible extractants for separation of base metal ions due to their lack of stereochemical “tailor-making.”
- Full Text:
- Date Issued: 2015
- Authors: Magwa, Nomampondo Penelope
- Date: 2015
- Subjects: Extraction (Chemistry) , Sulfates , Ligands , Benzimidazoles , Infrared spectroscopy , Nuclear magnetic resonance spectroscopy , Metal ions , Metals
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4559 , http://hdl.handle.net/10962/d1020010
- Description: Tridentate benzimidazole-based ligands, bis((1H-benzimidazol-2-yl)methyl)sulfide (BNSN) and bis((1H-benzimidazol-2-yl)methyl)amine (BNNN), along with dinonylnaphthalene sulfonic acid (DNNSA) as a synergist, were investigated as potential selective extractants for Ni2+ from base metals in a solvent extraction system using 2-octanol/Shellsol 2325 (8:2) as diluent and modifier. However, extraction studies show a lack of pH-metric separation of the later 3d metal ions with bis((1-octylbenzimidazol-2-yl)methyl)sulfide (BONSN) and bis((1- decylbenzimidazol-2-yl)methyl)amine (BDNNN) as extractants, but extractions occurred in the low pH range with an opportunity for back extraction. This investigation suggested that tridentate ligands (at least those of the nature investigated here) are not feasible extractants for separation of base metal ions due to their lack of stereochemical “tailor-making.”
- Full Text:
- Date Issued: 2015
Synthesis and evaluation of PGM-selective ligands
- Gxoyiya, Babalwa Siliziwe Blossom
- Authors: Gxoyiya, Babalwa Siliziwe Blossom
- Date: 2013-05-28
- Subjects: Platinum group , Ligands , Ligands -- Evaluation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4450 , http://hdl.handle.net/10962/d1007849 , Platinum group , Ligands , Ligands -- Evaluation
- Description: A series of polydentate POM-selective, sulfur-containing amide ligands have been synthesized from ro-dibromoalkanes and mercaptoacetanilide, The resulting 3,6- dithiaoctanediamides and 3,7-dithianonanediamides, some of which contain a polymerisable group, were all characterized by high-resolution MS, IR, I Hand I3C NMR spectroscopic methods. Various approaches to the polymerisable ligands were explored, the most efficient proving to be the incorporation of an allyl ether moiety in the mercaptoacetanilide. The corresponding Pd(U) and Pt(II) complexes were also prepared from the metal chloride salts and characterized by elemental analysis and spectroscopic methods. The NMR data indicates that both the cis- and transcomplexes were formed, while the IR data indicates cis- coordination of the chlorine . ligands. Molecularly imprinted polymers (MIP's), prepared using platinum(II) mercaptoacetanilide and 3,6-dithiadiamide complexes, showed high selectivity for , , palladium(II) [in the presence of Pt(II), CoCII), Cu(II) and Ni(II)] as determined by . ICP-MS analysis. The more kinetically inert Pt(II) ions however, slowly displaced Pd(II), confirming the Pt(II) selectivity of the MIP's. Solvent extraction studies were conducted to explore the selectivity of the 3,6- dithiaoctanediamides and 3,7-dithianonanediamides for Pd(U) over CoCII), Cu(U) and Ni(II). The ICP-MS data indicate that, in general, equilibration was achieved within ten minutes and that the longer-chain amides were less selective than the shorter-chain analogues. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Authors: Gxoyiya, Babalwa Siliziwe Blossom
- Date: 2013-05-28
- Subjects: Platinum group , Ligands , Ligands -- Evaluation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4450 , http://hdl.handle.net/10962/d1007849 , Platinum group , Ligands , Ligands -- Evaluation
- Description: A series of polydentate POM-selective, sulfur-containing amide ligands have been synthesized from ro-dibromoalkanes and mercaptoacetanilide, The resulting 3,6- dithiaoctanediamides and 3,7-dithianonanediamides, some of which contain a polymerisable group, were all characterized by high-resolution MS, IR, I Hand I3C NMR spectroscopic methods. Various approaches to the polymerisable ligands were explored, the most efficient proving to be the incorporation of an allyl ether moiety in the mercaptoacetanilide. The corresponding Pd(U) and Pt(II) complexes were also prepared from the metal chloride salts and characterized by elemental analysis and spectroscopic methods. The NMR data indicates that both the cis- and transcomplexes were formed, while the IR data indicates cis- coordination of the chlorine . ligands. Molecularly imprinted polymers (MIP's), prepared using platinum(II) mercaptoacetanilide and 3,6-dithiadiamide complexes, showed high selectivity for , , palladium(II) [in the presence of Pt(II), CoCII), Cu(II) and Ni(II)] as determined by . ICP-MS analysis. The more kinetically inert Pt(II) ions however, slowly displaced Pd(II), confirming the Pt(II) selectivity of the MIP's. Solvent extraction studies were conducted to explore the selectivity of the 3,6- dithiaoctanediamides and 3,7-dithianonanediamides for Pd(U) over CoCII), Cu(U) and Ni(II). The ICP-MS data indicate that, in general, equilibration was achieved within ten minutes and that the longer-chain amides were less selective than the shorter-chain analogues. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
Synthesis, characterisation and biological activity of 2-(methylthiomethyl)anilines, 2-(methylthio)anilines, their Schiff-base derivatives and metal(II) (Co, Ni, Cu) complexes
- Olalekan, Temitope Elizabeth
- Authors: Olalekan, Temitope Elizabeth
- Date: 2013
- Subjects: Aniline , Schiff bases , Ligands , Nuclear magnetic resonance spectroscopy , Chelates , X-ray crystallography , Antimalarials
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4562 , http://hdl.handle.net/10962/d1020868
- Description: A series of 31 sulfur-nitrogen donor ligands and 64 metal(II) complexes have been investigated. The thiomethylated aniline ligands 2–(methylthiomethyl)aniline 2MT and 2–(methylthio)aniline 2MA were synthesized with their substituted derivatives (-Me, -MeO, -Cl, -Br, -NO2) to serve as chelating agents. These ligands behave as bidentate ligands with SN donor group with Co(II), Ni(II) and Cu(II). The Co(II) and Ni(II) complexes have the ML2Cl2 molecular formula while the Cu(II) complexes formed with MLCl2 stoichiometry where L is the bidentate ligand. The ligands and their metal(II) complexes have been characterized by elemental analysis and with spectroscopic techniques. The trend observed in the NMR spectra and IR frequencies of the thiomethylated compounds shows there is a significant difference between the 2MT and 2MA series as a result of sulfur lone pairs extending the conjugation of the aromatic ring in the case of the latter. The effect of the position and electronic nature of ring substituent on the NMR shifts of the amine protons is discussed. The 6- and 5-membered chelate complexes formed by the 2MT and 2MA ligands respectively do not show significant diversity in their spectroscopic properties. From the elemental analysis for the Co(II) and Ni(II) complexes, their compositions reveal 1:2 M:L stoichiometry with 2 chlorine atoms from the respective metal salts. In addition, the spectroscopic data are largely indicative of tetragonally distorted structures for these solid complexes. The X-ray crystallography data reveal the Cu(II) complexes exist as square pyramidal dimers and with long Cu–Cl equitorial bonds fit into the tetragonally distorted octahedral structure. The electrolytic nature of Co(II) and Cu(II) complexes in DMF were found to be similar, they behave as non electrolytes in contrast to Ni(II) complexes which are 1:1 electrolytes. The electronic spectra of these metal(II) complexes were found to be different for both their solid forms and in solutions of DMF and DMSO and this has been discussed. The thiomethylated aniline ligands possess the amine and thioether groups which are present in many known biologically active compounds, hence the biological activity of the ligands and their metal complexes were tested against three strains of bacteria and one fungus. The methoxy-substituted derivatives were found to possess better inhibitory activity and this was similarly reflected in the metal(II) complexes. The activity of the complexes can be said to be in the order, Cu(II) > Co(II) > Ni(II). The Schiff-base derivatives were prepared from the ligands and para-methoxysalicylaldehyde and their Cu(II) complexes were synthesized in order to determine their biological activity. The Schiff-base ligands were found to be less active than their parent ligands. The Cu(II) complexes are not soluble in water, DMSO or DMF, as a result and could not be evaluated for their biological activity. Based on the good results from the antimicrobial evaluation, the antiplasmodial activity of some of the Co(II), Ni(II) and Cu(II) complexes of the thiomethylated ligands against Plasmodium falciparum (FCR-3) was determined. At 50 μM concentration level, the Cu(II) complexes show activity equal or better than the prophylactic chloroquine. The Cu(II) complexes with the methoxy-substituted demonstrated exceptional activity but their Co(II) and Ni(II) analogues did not show any activity. The cytotoxicity of the active Cu(II) complexes at 50 μM concentration was determined against the breast cancer cell line (MDA-MB-231). The compounds destroyed the cancer cell in the range of 28–40%, thus showing their preferred activity against the parasitic cell instead of the cancer cell. The selectivity demonstrated by these compounds have shown them to be potential antimalarial agents and this could be further investigated.
- Full Text:
- Date Issued: 2013
- Authors: Olalekan, Temitope Elizabeth
- Date: 2013
- Subjects: Aniline , Schiff bases , Ligands , Nuclear magnetic resonance spectroscopy , Chelates , X-ray crystallography , Antimalarials
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4562 , http://hdl.handle.net/10962/d1020868
- Description: A series of 31 sulfur-nitrogen donor ligands and 64 metal(II) complexes have been investigated. The thiomethylated aniline ligands 2–(methylthiomethyl)aniline 2MT and 2–(methylthio)aniline 2MA were synthesized with their substituted derivatives (-Me, -MeO, -Cl, -Br, -NO2) to serve as chelating agents. These ligands behave as bidentate ligands with SN donor group with Co(II), Ni(II) and Cu(II). The Co(II) and Ni(II) complexes have the ML2Cl2 molecular formula while the Cu(II) complexes formed with MLCl2 stoichiometry where L is the bidentate ligand. The ligands and their metal(II) complexes have been characterized by elemental analysis and with spectroscopic techniques. The trend observed in the NMR spectra and IR frequencies of the thiomethylated compounds shows there is a significant difference between the 2MT and 2MA series as a result of sulfur lone pairs extending the conjugation of the aromatic ring in the case of the latter. The effect of the position and electronic nature of ring substituent on the NMR shifts of the amine protons is discussed. The 6- and 5-membered chelate complexes formed by the 2MT and 2MA ligands respectively do not show significant diversity in their spectroscopic properties. From the elemental analysis for the Co(II) and Ni(II) complexes, their compositions reveal 1:2 M:L stoichiometry with 2 chlorine atoms from the respective metal salts. In addition, the spectroscopic data are largely indicative of tetragonally distorted structures for these solid complexes. The X-ray crystallography data reveal the Cu(II) complexes exist as square pyramidal dimers and with long Cu–Cl equitorial bonds fit into the tetragonally distorted octahedral structure. The electrolytic nature of Co(II) and Cu(II) complexes in DMF were found to be similar, they behave as non electrolytes in contrast to Ni(II) complexes which are 1:1 electrolytes. The electronic spectra of these metal(II) complexes were found to be different for both their solid forms and in solutions of DMF and DMSO and this has been discussed. The thiomethylated aniline ligands possess the amine and thioether groups which are present in many known biologically active compounds, hence the biological activity of the ligands and their metal complexes were tested against three strains of bacteria and one fungus. The methoxy-substituted derivatives were found to possess better inhibitory activity and this was similarly reflected in the metal(II) complexes. The activity of the complexes can be said to be in the order, Cu(II) > Co(II) > Ni(II). The Schiff-base derivatives were prepared from the ligands and para-methoxysalicylaldehyde and their Cu(II) complexes were synthesized in order to determine their biological activity. The Schiff-base ligands were found to be less active than their parent ligands. The Cu(II) complexes are not soluble in water, DMSO or DMF, as a result and could not be evaluated for their biological activity. Based on the good results from the antimicrobial evaluation, the antiplasmodial activity of some of the Co(II), Ni(II) and Cu(II) complexes of the thiomethylated ligands against Plasmodium falciparum (FCR-3) was determined. At 50 μM concentration level, the Cu(II) complexes show activity equal or better than the prophylactic chloroquine. The Cu(II) complexes with the methoxy-substituted demonstrated exceptional activity but their Co(II) and Ni(II) analogues did not show any activity. The cytotoxicity of the active Cu(II) complexes at 50 μM concentration was determined against the breast cancer cell line (MDA-MB-231). The compounds destroyed the cancer cell in the range of 28–40%, thus showing their preferred activity against the parasitic cell instead of the cancer cell. The selectivity demonstrated by these compounds have shown them to be potential antimalarial agents and this could be further investigated.
- Full Text:
- Date Issued: 2013
Synthesis, characterization and antimicrobial activity of copper (II) complexes of some hydroxybenzaldimines and their derivatives
- Authors: Sobola, Abdullahi Owolabi
- Date: 2012
- Subjects: Copper , Schiff bases , Ligands
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4534 , http://hdl.handle.net/10962/d1016258
- Description: This study focuses on the antimicrobial activity of Cu(II) complexes of some orthohydroxybenzaldimines and its derivatives. Four different categories of Schiff base ligands were prepared by condensing salicylaldehyde, o-vanillin, p-vanillin and vanillin with p- and osubstituted anilines; 1-aminonaphthalene; 2- and 3-aminopyridine; 2- and 3- aminomethylpyridine as well as 2-aminobenzimidazole. The last category was prepared from ophenylenediamine and o-vanillin. The Schiff base ligands have been characterized by a combination of elemental analysis and spectral (¹H- and ¹³C-NMR, UV/Visible, infrared and Raman) data. The existence of strong intramolecular hydrogen bonding in the orthohydoxybenzaldimines was evident from the chemical shift values of the hydroxyl proton in the ¹H-NMR spectra of the Schiff base ligands. The hydroxyl proton resonates at high frequency and thus absorbed far downfield at 13.46-11.83 ppm, reflecting the presence of hydrogen bonding between the hydroxyl proton and the imine nitrogen. In the p-substituted aniline analogues of the Schiff base, a plot of the chemical shift values of the hydroxyl proton against the Hammett's substituent parameters gave a linear correlation between the electronegativities of the substituents and the chemical shift values. The nitro group with the highest electronegativity caused the least deshielding of the hydroxyl proton and thus absorbed upfield compared to the less electronegative substituents such as the CH3 and OCH3 analogues. Likewise, in the solid state infrared spectra of the ligands, the hydroxyl stretching band of the ortho-hydroxyl Schiff base ligands was observed as a very broad band and at much lower frequency, 3100-2100 cm⁻¹, indicating the existence of strong intramolecular hydrogen bonding. In the same vein, ¹H- and ¹³C-NMR spectral data for the Schiff base ligands indicated that the prepared compounds exist in the enol form in aprotic solvent, chloroform. The methine proton appeared as singlet and there was no carbonyl signal in the ¹³C-NMR spectra of the Schiff base ligands. This was supported by the infrared data having no vibrational band attributable to the carbonyl stretching of the keto-form of the Schiff base ligands in solid state. However, the UV/Visible study of the Schiff base ligands in protic solvent, methanol, suggested the existence of some of the Schiff base ligands in keto-enol form. A band at greater than 400 nm was observed in the UV/Visible spectra of the ligands and this has been attributed to the presence of the keto form of orthohydroxyl Schiff base ligands in solution. A plot of the molar absorptivity (ε) of the band at greater than 400 nm against Hammett substituent parameters revealed that the intensity of the bands increased with the electronegativity of the substituents. The Cu(II) complexes of salicylaldehyde, o-vanillin and a few p-vanillin based Schiff base ligands are reported in this work. It was observed that introduction of Cu(II) ions into the ligand system resulted in the hydrolysis of the imine band in few cases. All the isolated complexes have been characterized by elemental analysis, conductivity measurement, infrared and UV/Visible spectral data. The structures of three of the Cu(II) complexes were further confirmed by X-ray single crystal diffraction. The Schiff base ligands either coordinated as neutral base through the imine nitrogen or via the imine nitrogen and the phenolic oxygen atoms. In addition, the benzimidazole-based and ovan-2-pico analogues equally coordinated through the imidazole N-3 nitrogen and the azine nitrogen respectively; thus acted as tridentate. In general, the synthesized Cu(II) complexes fell into seven categories viz: [Cu(LH)Cl(H₂O)]Cl; [Cu(LH)₂Cl₂].xH₂O; [CuL₂]; [Cu₂L₂]; [Cu(LH)Cl(H₂O)]Cl; and [MLCl]. The Cu(II) complexes of the form, M(LH)₂Cl₂.xH₂O were either 1:1 or non-electrolyte in methanol and DMF. The third category, CuL₂, was however, non-electrolyte existing as neutral four coordinate Cu(II) complexes. X-ray single crystal structure of Cu(II) complexes derived from the ammonia-based Schiff bases revealed a square planar geometry for the complexes and this agreed with the planar geometry that has been reported for Cu(II) complexes of N-arylsalicylaldimines of the type studied in this work. The complexes, [Cu₂L₂], resulted from the ortho-hydroxyaniline analogues and were polymeric with the Schiff base ligands coordinating to the Cu(II) ions as tridentate dibasic via the imine nitrogen, phenolic oxygen and the aminophenolic oxygen atoms. Cu(II) complexes prepared from ovan-2-ampy and ovan-2-pico Schiff bases were of the forms [Cu(LH)Cl(H₂O)]Cl and [CuLCl] respectively. The X-ray crystal structure of [Cu(ovan-2- pico)Cl] revealed a four-coordinate square planar geometry for the complex. In the same vein, the o-phenylenediamine complexes were of the form [Cu(L)(H₂O)], with the X-ray crystal structure of [Cu(bis-ovanphen)(H₂O)] revealing a square pyramidal geometry. The Schiff base ligands and the isolated Cu(II) complexes have been evaluated for their antimicrobial activity against three bacterial strains (Escherichia coli ATCC® 8739™*, Staphylococcus aureus subsp. aureus ATCC® 6538™* and Bacillus subtilis subsp. spizizeni ATCC® 6633™*) and one fungal strain, Candida albicans ATCC® 2091™*, using agar disc diffusion and broth dilution techniques. It was observed that the presence of the methoxyl group at the ortho-position of the aldehyde moiety of the Schiff base ligands enhanced the activity of the ligand tremendously and thus the o-vanillin analogues showed the highest potency against the tested organisms. In addition, the hydroxyaniline analogues were equally the most promising of all the substituted aniline based Schiff bases. The o-vanillin analogues of the aminopyridines and aminomethylpyridines also exhibited significant activity against the tested organisms. All the 2-aminobenzimidazole series were active against the tested organisms. It should be noted that E. coli was the least susceptible of all the microorganisms while the highest potency was exhibited against the fungus of choice, Candida albicans. Lastly, chelation of the Schiff base ligands with Cu(II) ions did not have significant influence on the activity of the free ligands.
- Full Text:
- Date Issued: 2012
- Authors: Sobola, Abdullahi Owolabi
- Date: 2012
- Subjects: Copper , Schiff bases , Ligands
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4534 , http://hdl.handle.net/10962/d1016258
- Description: This study focuses on the antimicrobial activity of Cu(II) complexes of some orthohydroxybenzaldimines and its derivatives. Four different categories of Schiff base ligands were prepared by condensing salicylaldehyde, o-vanillin, p-vanillin and vanillin with p- and osubstituted anilines; 1-aminonaphthalene; 2- and 3-aminopyridine; 2- and 3- aminomethylpyridine as well as 2-aminobenzimidazole. The last category was prepared from ophenylenediamine and o-vanillin. The Schiff base ligands have been characterized by a combination of elemental analysis and spectral (¹H- and ¹³C-NMR, UV/Visible, infrared and Raman) data. The existence of strong intramolecular hydrogen bonding in the orthohydoxybenzaldimines was evident from the chemical shift values of the hydroxyl proton in the ¹H-NMR spectra of the Schiff base ligands. The hydroxyl proton resonates at high frequency and thus absorbed far downfield at 13.46-11.83 ppm, reflecting the presence of hydrogen bonding between the hydroxyl proton and the imine nitrogen. In the p-substituted aniline analogues of the Schiff base, a plot of the chemical shift values of the hydroxyl proton against the Hammett's substituent parameters gave a linear correlation between the electronegativities of the substituents and the chemical shift values. The nitro group with the highest electronegativity caused the least deshielding of the hydroxyl proton and thus absorbed upfield compared to the less electronegative substituents such as the CH3 and OCH3 analogues. Likewise, in the solid state infrared spectra of the ligands, the hydroxyl stretching band of the ortho-hydroxyl Schiff base ligands was observed as a very broad band and at much lower frequency, 3100-2100 cm⁻¹, indicating the existence of strong intramolecular hydrogen bonding. In the same vein, ¹H- and ¹³C-NMR spectral data for the Schiff base ligands indicated that the prepared compounds exist in the enol form in aprotic solvent, chloroform. The methine proton appeared as singlet and there was no carbonyl signal in the ¹³C-NMR spectra of the Schiff base ligands. This was supported by the infrared data having no vibrational band attributable to the carbonyl stretching of the keto-form of the Schiff base ligands in solid state. However, the UV/Visible study of the Schiff base ligands in protic solvent, methanol, suggested the existence of some of the Schiff base ligands in keto-enol form. A band at greater than 400 nm was observed in the UV/Visible spectra of the ligands and this has been attributed to the presence of the keto form of orthohydroxyl Schiff base ligands in solution. A plot of the molar absorptivity (ε) of the band at greater than 400 nm against Hammett substituent parameters revealed that the intensity of the bands increased with the electronegativity of the substituents. The Cu(II) complexes of salicylaldehyde, o-vanillin and a few p-vanillin based Schiff base ligands are reported in this work. It was observed that introduction of Cu(II) ions into the ligand system resulted in the hydrolysis of the imine band in few cases. All the isolated complexes have been characterized by elemental analysis, conductivity measurement, infrared and UV/Visible spectral data. The structures of three of the Cu(II) complexes were further confirmed by X-ray single crystal diffraction. The Schiff base ligands either coordinated as neutral base through the imine nitrogen or via the imine nitrogen and the phenolic oxygen atoms. In addition, the benzimidazole-based and ovan-2-pico analogues equally coordinated through the imidazole N-3 nitrogen and the azine nitrogen respectively; thus acted as tridentate. In general, the synthesized Cu(II) complexes fell into seven categories viz: [Cu(LH)Cl(H₂O)]Cl; [Cu(LH)₂Cl₂].xH₂O; [CuL₂]; [Cu₂L₂]; [Cu(LH)Cl(H₂O)]Cl; and [MLCl]. The Cu(II) complexes of the form, M(LH)₂Cl₂.xH₂O were either 1:1 or non-electrolyte in methanol and DMF. The third category, CuL₂, was however, non-electrolyte existing as neutral four coordinate Cu(II) complexes. X-ray single crystal structure of Cu(II) complexes derived from the ammonia-based Schiff bases revealed a square planar geometry for the complexes and this agreed with the planar geometry that has been reported for Cu(II) complexes of N-arylsalicylaldimines of the type studied in this work. The complexes, [Cu₂L₂], resulted from the ortho-hydroxyaniline analogues and were polymeric with the Schiff base ligands coordinating to the Cu(II) ions as tridentate dibasic via the imine nitrogen, phenolic oxygen and the aminophenolic oxygen atoms. Cu(II) complexes prepared from ovan-2-ampy and ovan-2-pico Schiff bases were of the forms [Cu(LH)Cl(H₂O)]Cl and [CuLCl] respectively. The X-ray crystal structure of [Cu(ovan-2- pico)Cl] revealed a four-coordinate square planar geometry for the complex. In the same vein, the o-phenylenediamine complexes were of the form [Cu(L)(H₂O)], with the X-ray crystal structure of [Cu(bis-ovanphen)(H₂O)] revealing a square pyramidal geometry. The Schiff base ligands and the isolated Cu(II) complexes have been evaluated for their antimicrobial activity against three bacterial strains (Escherichia coli ATCC® 8739™*, Staphylococcus aureus subsp. aureus ATCC® 6538™* and Bacillus subtilis subsp. spizizeni ATCC® 6633™*) and one fungal strain, Candida albicans ATCC® 2091™*, using agar disc diffusion and broth dilution techniques. It was observed that the presence of the methoxyl group at the ortho-position of the aldehyde moiety of the Schiff base ligands enhanced the activity of the ligand tremendously and thus the o-vanillin analogues showed the highest potency against the tested organisms. In addition, the hydroxyaniline analogues were equally the most promising of all the substituted aniline based Schiff bases. The o-vanillin analogues of the aminopyridines and aminomethylpyridines also exhibited significant activity against the tested organisms. All the 2-aminobenzimidazole series were active against the tested organisms. It should be noted that E. coli was the least susceptible of all the microorganisms while the highest potency was exhibited against the fungus of choice, Candida albicans. Lastly, chelation of the Schiff base ligands with Cu(II) ions did not have significant influence on the activity of the free ligands.
- Full Text:
- Date Issued: 2012
The design and synthesis of multidentate N-heterocyclic carbenes as metathesis catalyst ligands
- Authors: Truscott, Byron John
- Date: 2011
- Subjects: Carbenes (Methylene compounds) , Heterocyclic compounds , Ligands , Ligands -- Design , Metathesis (Chemistry) , Catalysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4304 , http://hdl.handle.net/10962/d1004962 , Carbenes (Methylene compounds) , Heterocyclic compounds , Ligands , Ligands -- Design , Metathesis (Chemistry) , Catalysis
- Description: This study has focused on the design and preparation of bi– and tridentate N–Heterocyclic Carbene (NHC) ligands in order to investigate the effect of a multidentate approach to the formation, stability and catalytic activity of coordination complexes. Chapters 1 – 3 provide background information of relevant catalysis, carbene and coordination chemistry, followed by previous work performed within our research group. In Chapter 4 attention is given to the synthetic aspects of the research conducted, comprising two distinct approaches to the preparation of unsymmetrical saturated and unsaturated NHCs. Firstly, an investigation of the saturated NHC ligands yielded three novel, unsymmetrical pro–ligands, viz., two halopropyl imidazolinium salts and a bidentate hydroxypropyl imidazolinium salt. Secondly, eight imidazolium salts have been generated, including a hydroxypropyl analogue and novel decyl and tridentate malonyl derivatives. These compounds were prepared using microwave–assisted methodology for the alkylation of N– mesitylimidazole – an approach that drastically reduced reaction times (from 8 hours – 7 days to ca. 0.5 – 2 hours) and facilitated isolation of the imidazolium salts. Many of the compounds prepared in this study are novel and were fully characterized using HRMS and 1– and 2–D NMR analysis. Coordination studies using a selection of the prepared pro–ligands afforded an alkoxy–NHC silver derivative and four novel Ru–complexes, viz., Grubbs II–type Ru–complexes containing:– chloropropyl imidazolinylidene; propenyl imidazolylidene; and bidentate alkoxypropyl imidazolylidene ligands. Furthermore, a well–defined benzyl mesitylimidazolylidene Ru–complex has been isolated, which exhibited good stability in air. DFT–level geometry–optimization studies, using the Accelrys DMol3 package have given valuable insights into the likely geometries of the prepared and putative catalysts.
- Full Text:
- Date Issued: 2011
- Authors: Truscott, Byron John
- Date: 2011
- Subjects: Carbenes (Methylene compounds) , Heterocyclic compounds , Ligands , Ligands -- Design , Metathesis (Chemistry) , Catalysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4304 , http://hdl.handle.net/10962/d1004962 , Carbenes (Methylene compounds) , Heterocyclic compounds , Ligands , Ligands -- Design , Metathesis (Chemistry) , Catalysis
- Description: This study has focused on the design and preparation of bi– and tridentate N–Heterocyclic Carbene (NHC) ligands in order to investigate the effect of a multidentate approach to the formation, stability and catalytic activity of coordination complexes. Chapters 1 – 3 provide background information of relevant catalysis, carbene and coordination chemistry, followed by previous work performed within our research group. In Chapter 4 attention is given to the synthetic aspects of the research conducted, comprising two distinct approaches to the preparation of unsymmetrical saturated and unsaturated NHCs. Firstly, an investigation of the saturated NHC ligands yielded three novel, unsymmetrical pro–ligands, viz., two halopropyl imidazolinium salts and a bidentate hydroxypropyl imidazolinium salt. Secondly, eight imidazolium salts have been generated, including a hydroxypropyl analogue and novel decyl and tridentate malonyl derivatives. These compounds were prepared using microwave–assisted methodology for the alkylation of N– mesitylimidazole – an approach that drastically reduced reaction times (from 8 hours – 7 days to ca. 0.5 – 2 hours) and facilitated isolation of the imidazolium salts. Many of the compounds prepared in this study are novel and were fully characterized using HRMS and 1– and 2–D NMR analysis. Coordination studies using a selection of the prepared pro–ligands afforded an alkoxy–NHC silver derivative and four novel Ru–complexes, viz., Grubbs II–type Ru–complexes containing:– chloropropyl imidazolinylidene; propenyl imidazolylidene; and bidentate alkoxypropyl imidazolylidene ligands. Furthermore, a well–defined benzyl mesitylimidazolylidene Ru–complex has been isolated, which exhibited good stability in air. DFT–level geometry–optimization studies, using the Accelrys DMol3 package have given valuable insights into the likely geometries of the prepared and putative catalysts.
- Full Text:
- Date Issued: 2011
Studies towards the synthesis of novel tridentate ligands for use in ruthenium metathesis catalysts
- Authors: Millward, Tanya
- Date: 2009
- Subjects: Ligands , Catalysis , Metathesis (Chemistry) , Ruthenium , Complex compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4360 , http://hdl.handle.net/10962/d1005025 , Ligands , Catalysis , Metathesis (Chemistry) , Ruthenium , Complex compounds
- Description: This work has focussed on the preparation of a variety of tridentate ligands, designed to form ruthenium complexes as potential metathesis catalysts. Various approaches to the tridentate, malonate-tethered imidazolidine system have been investigated, and a promising route to accessing ligands of this type is discussed. A tridentate malonate-tethered pyridine ligand has been successfully prepared and its dithallium salt has been accessed by hydrolysis with thallium carbonate; approaches to a longer-chain analogue have also been investigated. A thallium pyridine-2,6- dicarboxylate ligand has been has been successfully prepared, as have a range of pyridine diamine ligands, with various alkyl and aromatic substituents on the amine donor atoms. Preliminary investigations into the potential of these compounds as ligands for alkylidene ruthenium complexes are reported using molecular modelling techniques. The geometries and steric energies of the ligands and their corresponding complexes have been analysed, and results obtained from two different software packages are compared. Finally, some preliminary complexation studies have been undertaken.
- Full Text:
- Date Issued: 2009
- Authors: Millward, Tanya
- Date: 2009
- Subjects: Ligands , Catalysis , Metathesis (Chemistry) , Ruthenium , Complex compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4360 , http://hdl.handle.net/10962/d1005025 , Ligands , Catalysis , Metathesis (Chemistry) , Ruthenium , Complex compounds
- Description: This work has focussed on the preparation of a variety of tridentate ligands, designed to form ruthenium complexes as potential metathesis catalysts. Various approaches to the tridentate, malonate-tethered imidazolidine system have been investigated, and a promising route to accessing ligands of this type is discussed. A tridentate malonate-tethered pyridine ligand has been successfully prepared and its dithallium salt has been accessed by hydrolysis with thallium carbonate; approaches to a longer-chain analogue have also been investigated. A thallium pyridine-2,6- dicarboxylate ligand has been has been successfully prepared, as have a range of pyridine diamine ligands, with various alkyl and aromatic substituents on the amine donor atoms. Preliminary investigations into the potential of these compounds as ligands for alkylidene ruthenium complexes are reported using molecular modelling techniques. The geometries and steric energies of the ligands and their corresponding complexes have been analysed, and results obtained from two different software packages are compared. Finally, some preliminary complexation studies have been undertaken.
- Full Text:
- Date Issued: 2009
Studies towards the development of novel multidentate ligands
- Authors: Magqi, Nceba
- Date: 2007
- Subjects: Density functionals , Ligands , Ligands -- Design , Ligands -- Analysis , Camphor
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4358 , http://hdl.handle.net/10962/d1005023 , Density functionals , Ligands , Ligands -- Design , Ligands -- Analysis , Camphor
- Description: In this study, attention has been given to the design and synthesis of novel multidentate ligands for use in the construction of ruthenium-based metathesis catalysts, and their chelating potential has been explored by computer modelling at the Density Functional Theory (DFT) level. Both Kemp’s triacid (1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic acid) and D-(+)-camphor have been investigated as molecular scaffolds for the development of such ligands. However selective elaboration of the functional groups in Kemp’s triacid proved difficult to achieve, and the research has focused on the development of camphor derivatives. The synthesis of the camphor-based ligands has involved C-8 functionalisation and ring-opening of the bicyclic system to afford tridentate products. The formation of 9-iodocamphorquinone bis(ethylene ketal) together with the desired product, the 8-iodo isomer, has been confirmed by single crystal X-ray analysis of both compounds. Formation of the 9-iodo analogue has provided new insights into the intramolecular rearrangement of camphor skeleton, and the mechanistic implications have been assessed by coset analysis. Attempts to effect nucleophilic displacement of the 8-halogeno groups by nucleophilic donor moieties proved unexpectedly difficult and, coupled with the susceptibility of the carbonyl groups to nucleophilic attack, has led to the formation of novel tricyclic products, viz., 1,6-dimethyl-3-(2-pyridylamino)-4-oxatricyclo[4.3.0.0[superscript 3,7]]-2-nonanone and 6,7-dimethyl-3-(2-pyridylamino)-4-oxatricyclo -[4.3.0.0[superscript 3,7]]-2-nonanone. However the diphenylphosphine group was successfully introduced at C-8 and oxidative ring-opening of the camphor skeleton has afforded the tridentate ligands, 2-(diphenylphosphinoylmethyl)-1,2-dimethyl-1,3-cyclopentanedicarboxylic acid and 2-(diphenylphosphinoylmethyl)-1,3-bis(hydroxymethyl)1,2-dimethylcyclopentane. One- and two-dimensional NMR and, where appropriate, high-resolution MS methods have been used to characterise the products. Three [superscript 13]C NMR chemical shift prediction programmes, viz., ChemWindow and the MODGRAPH neural network and HOSE (Hierachially Ordered Spherical description of Environment), have been applied to representative compounds to assess their efficacy. While the predicted shifts correlated reasonably well with the experimental data, they proved to be insufficiently accurate to differentiate the isomeric systems examined.
- Full Text:
- Date Issued: 2007
- Authors: Magqi, Nceba
- Date: 2007
- Subjects: Density functionals , Ligands , Ligands -- Design , Ligands -- Analysis , Camphor
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4358 , http://hdl.handle.net/10962/d1005023 , Density functionals , Ligands , Ligands -- Design , Ligands -- Analysis , Camphor
- Description: In this study, attention has been given to the design and synthesis of novel multidentate ligands for use in the construction of ruthenium-based metathesis catalysts, and their chelating potential has been explored by computer modelling at the Density Functional Theory (DFT) level. Both Kemp’s triacid (1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic acid) and D-(+)-camphor have been investigated as molecular scaffolds for the development of such ligands. However selective elaboration of the functional groups in Kemp’s triacid proved difficult to achieve, and the research has focused on the development of camphor derivatives. The synthesis of the camphor-based ligands has involved C-8 functionalisation and ring-opening of the bicyclic system to afford tridentate products. The formation of 9-iodocamphorquinone bis(ethylene ketal) together with the desired product, the 8-iodo isomer, has been confirmed by single crystal X-ray analysis of both compounds. Formation of the 9-iodo analogue has provided new insights into the intramolecular rearrangement of camphor skeleton, and the mechanistic implications have been assessed by coset analysis. Attempts to effect nucleophilic displacement of the 8-halogeno groups by nucleophilic donor moieties proved unexpectedly difficult and, coupled with the susceptibility of the carbonyl groups to nucleophilic attack, has led to the formation of novel tricyclic products, viz., 1,6-dimethyl-3-(2-pyridylamino)-4-oxatricyclo[4.3.0.0[superscript 3,7]]-2-nonanone and 6,7-dimethyl-3-(2-pyridylamino)-4-oxatricyclo -[4.3.0.0[superscript 3,7]]-2-nonanone. However the diphenylphosphine group was successfully introduced at C-8 and oxidative ring-opening of the camphor skeleton has afforded the tridentate ligands, 2-(diphenylphosphinoylmethyl)-1,2-dimethyl-1,3-cyclopentanedicarboxylic acid and 2-(diphenylphosphinoylmethyl)-1,3-bis(hydroxymethyl)1,2-dimethylcyclopentane. One- and two-dimensional NMR and, where appropriate, high-resolution MS methods have been used to characterise the products. Three [superscript 13]C NMR chemical shift prediction programmes, viz., ChemWindow and the MODGRAPH neural network and HOSE (Hierachially Ordered Spherical description of Environment), have been applied to representative compounds to assess their efficacy. While the predicted shifts correlated reasonably well with the experimental data, they proved to be insufficiently accurate to differentiate the isomeric systems examined.
- Full Text:
- Date Issued: 2007
Effects of Axial Ligands on the Photosensitising Properties of Silicon Octaphenoxyphthalocyanines
- Authors: Maree, Machiel David
- Date: 2002
- Subjects: Ligands , Photochemotherapy , Phthalocyanines
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4553 , http://hdl.handle.net/10962/d1018246
- Description: Various axially substituted Silicon octaphenoxyphthalocyanines were synthesised as potential photosensitisers in the photodynamic therapy of cancer. Conventional reflux reactions were used for synthesis as well as new microwave irradiation reactions, wherein the reaction times were decreased tenfold with a marginal increase in reaction yield and product purity. An interesting series of oligomeric (dimer to a nonamer) silicon octaphenoxyphthalocyanines were also successfully synthesised in a reaction similar to polymerisation reactions. These compounds were found to undergo an axial ligand transformation upon irradiation with red light (> 600 nm) in dimethylsulphoxide solution. All the ligands were transformed into the dihydroxy silicon octaphenoxyphthalocyanine with varying degrees of phototransformation quantum yields ranging in order from 10⁻³ to 10⁻⁵ depending on the axial ligand involved. During and after axial ligand transformations a photodegredation of the dihydroxy silicon octaphenoxy phthalocyanine was observed upon continued irradiation. The oligomers were found to undergo the same axial ligand transformation process with a phototransformation quantum yield of 10⁻⁵ The singlet oxygen quantum yields of the unaggregated monomeric silicon octaphenoxy phthalocyanines were all found to be approximately 0.2 with the exception of a compound with two (trihexyl)siloxy axial substituents that had a singlet oxygen quantum yield of approximately 0.4 in dimethylsulphoxide solutions. The oligomers showed a surprising trend of an increase in singlet oxygen quantum yield with an increase in phthalocyanine ring number up to the pentamer and then a dramatic decrease to the nonamer. The triplet quantum yield and triplet lifetime were determined by laser flash photolysis for selected compounds and no correlation was observed with any of these properties and the singlet oxygen quantum yields. These selected compounds all fluoresce and a very good correlation was found between the fluorescence lifetimes determined experimentally by laser photolysis and the Strickler-Berg equation for the non-aggregated compounds. Electrochemical measurements also indicate the importance of the axial ligands upon the behaviour of the phthalocyanines as cyclic voltammetric behaviour was determined by the nature of the axial ligand.
- Full Text:
- Date Issued: 2002
- Authors: Maree, Machiel David
- Date: 2002
- Subjects: Ligands , Photochemotherapy , Phthalocyanines
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4553 , http://hdl.handle.net/10962/d1018246
- Description: Various axially substituted Silicon octaphenoxyphthalocyanines were synthesised as potential photosensitisers in the photodynamic therapy of cancer. Conventional reflux reactions were used for synthesis as well as new microwave irradiation reactions, wherein the reaction times were decreased tenfold with a marginal increase in reaction yield and product purity. An interesting series of oligomeric (dimer to a nonamer) silicon octaphenoxyphthalocyanines were also successfully synthesised in a reaction similar to polymerisation reactions. These compounds were found to undergo an axial ligand transformation upon irradiation with red light (> 600 nm) in dimethylsulphoxide solution. All the ligands were transformed into the dihydroxy silicon octaphenoxyphthalocyanine with varying degrees of phototransformation quantum yields ranging in order from 10⁻³ to 10⁻⁵ depending on the axial ligand involved. During and after axial ligand transformations a photodegredation of the dihydroxy silicon octaphenoxy phthalocyanine was observed upon continued irradiation. The oligomers were found to undergo the same axial ligand transformation process with a phototransformation quantum yield of 10⁻⁵ The singlet oxygen quantum yields of the unaggregated monomeric silicon octaphenoxy phthalocyanines were all found to be approximately 0.2 with the exception of a compound with two (trihexyl)siloxy axial substituents that had a singlet oxygen quantum yield of approximately 0.4 in dimethylsulphoxide solutions. The oligomers showed a surprising trend of an increase in singlet oxygen quantum yield with an increase in phthalocyanine ring number up to the pentamer and then a dramatic decrease to the nonamer. The triplet quantum yield and triplet lifetime were determined by laser flash photolysis for selected compounds and no correlation was observed with any of these properties and the singlet oxygen quantum yields. These selected compounds all fluoresce and a very good correlation was found between the fluorescence lifetimes determined experimentally by laser photolysis and the Strickler-Berg equation for the non-aggregated compounds. Electrochemical measurements also indicate the importance of the axial ligands upon the behaviour of the phthalocyanines as cyclic voltammetric behaviour was determined by the nature of the axial ligand.
- Full Text:
- Date Issued: 2002
Exploratory studies of novel ligand systems
- Authors: Taylor, Steven John
- Date: 1992
- Subjects: Ligands , Coordination compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4315 , http://hdl.handle.net/10962/d1004973 , Ligands , Coordination compounds
- Description: A range of novel ligand systems have been developed in three distinct phases and preliminary studies have been initiated to evaluate their complexation potential. Phase I incorporated the synthesis of single strand ligand systems, which were mainly based on amino acid residues. Techniques have been developed for the attachment of these ligand systems onto, firstly, a styrene monomer, and then later onto a pseudo-styrene linking group, viz. the p-toluoyl group. The linking reactions were based on the formation of amides or esters by the reaction of an acid chloride system with an amine or alcohol. Phase II involved the synthesis of bis-chain ligand systems and their attachment onto the p-toluoyl linking group. A further linking group was also developed at this stage, viz. the xylyl group. In the preparation of phase II ligand systems, use was made of malonic ester and iminodiacetic acid derivatives. Phase III has involved the synthesis of cyclic ligand systems, with skeletons based upon the structures used in phase I and phase II and two crown ether type systems have been prepared.
- Full Text:
- Date Issued: 1992
- Authors: Taylor, Steven John
- Date: 1992
- Subjects: Ligands , Coordination compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4315 , http://hdl.handle.net/10962/d1004973 , Ligands , Coordination compounds
- Description: A range of novel ligand systems have been developed in three distinct phases and preliminary studies have been initiated to evaluate their complexation potential. Phase I incorporated the synthesis of single strand ligand systems, which were mainly based on amino acid residues. Techniques have been developed for the attachment of these ligand systems onto, firstly, a styrene monomer, and then later onto a pseudo-styrene linking group, viz. the p-toluoyl group. The linking reactions were based on the formation of amides or esters by the reaction of an acid chloride system with an amine or alcohol. Phase II involved the synthesis of bis-chain ligand systems and their attachment onto the p-toluoyl linking group. A further linking group was also developed at this stage, viz. the xylyl group. In the preparation of phase II ligand systems, use was made of malonic ester and iminodiacetic acid derivatives. Phase III has involved the synthesis of cyclic ligand systems, with skeletons based upon the structures used in phase I and phase II and two crown ether type systems have been prepared.
- Full Text:
- Date Issued: 1992
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