Liquid junction potentials at mixed electrolyte salt bridges
- Authors: Finkelstein, Noel Phillip
- Date: 1957
- Subjects: Hydrogen-ion concentration -- Measurement , Hydrogen-ion concentration , Electrochemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4473 , http://hdl.handle.net/10962/d1011835 , Hydrogen-ion concentration -- Measurement , Hydrogen-ion concentration , Electrochemistry
- Description: The potentiometric method is one of the most exact techniques of electrochemistry. Its use is widespread in both routine measurements, such as pH determination, and in applications which demand the highest accuracy. Perhaps its severest limitation is the error due to liquid junction potentials. Although this has been the subject of much study, and although various means of combating it have been proposed, it has defied all attempts at a satisfactory solution. Indeed, so serious is the position that it has become the accepted practice in the more accurate fields to abandon altogether the use of potentiometric techniques in favour of others, usually less convenient and otherwise less accurate, when the presence of liquid junctions cannot be avoided. Intro. p. 1.
- Full Text:
- Date Issued: 1957
Low symmetry metallophthalocyanines and their nanoparticle conjugates for photodynamic antimicrobial chemotherapy
- Authors: Masilela, Nkosiphile
- Date: 2013
- Subjects: Nanoparticles Anti-infective agents Chemotherapy Photochemotherapy Quantum dots Gold Silver , Phthalocyanines
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4278 , http://hdl.handle.net/10962/d1001906
- Description: This thesis reports on the syntheses of novel low symmetrically substituted Zn, Sn, Ge and Ti MPc complexes containing a single carboxylic or cysteinyl group available for attachments to MNPs. The complexes were extensively characterized by various techniques to ensure their purity. Various metallic nanoparticles consisting of silver (AgNPs), gold (AuNPs) as well as quantum dots (QDs) were successfully prepared and conjugated to the low symmetry phthalocyanine complexes. The conjugates were successfully characterized using many techniques. The Q-band maxima of the MPcs were observed at completely different wavelength regions depending on the nature of the substituents and the central metal used. Blue shifting of the Q band in the absorption spectra was observed for the complexes in the presence of AuNPs, while aggregation was observed in the presence of quantum dots. The complexes were successfully electrospun into polymer fibers for the antimicrobial inhibition of bacteria. The photophysical and photochemical properties of these complexes were extensively investigated. Higher triplet and singlet oxygen quantum yields were achieved for the Ge Pc complexes, with all the complexes giving reasonable singlet oxygen quantum yields. An enhancement in triplet and singlet oxygen quantum yields was observed for all the complexes in the presence of metal nanoparticles. However, the singlet oxygen quantum yields decreased for all the complexes when incorporated into electrospun fibers. The antimicrobial behaviour of the complexes was investigated against Bacillus Subtilis and Staphylococcus Aureus in solution and in the fiber matrix. High antimicrobial inhibitions were observed for the Ge complexes followed by the ZnPc derivatives. All the low symmetry ZnPc derivatives were conjugated to AgNPs and their antimicrobial behaviour was compared to their symmetrical counterparts. The best antimicrobial inhibition behaviour was observed for the low symmetry Pcs when compared to their symmetrical counterparts. In the absence and in the presence of AgNPs, axially ligated SiPc also showed better antimicrobial activity when it was compared to the unsubstituted ZnPc complex.
- Full Text:
- Date Issued: 2013
Mannich base metal complexes and their thiocyanate analogues as catalysts in the oxidation of Catechol
- Authors: Ayeni, Ayowole Olaolu
- Date: 2018
- Subjects: Mannich bases , Catechol , Catechol -- Oxidation , Thiocyanates , Catalysts
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62339 , vital:28156
- Description: The study focused on the design of new Cu(II) and Fe(III) complexes, with or without thiocyanate (NCS-), as possible candidates of catechol oxidation using 3,5-di-tert-butyl catechol (3,5-DTBC) as substrate. Two classes of Mannich bases were studied depending on the active methylene group from which they were formed, being either p-cresol or acetaminophen. The ligands were characterised by 1H and 13C NMR spectroscopy. Crystal structures of three of the ligands are newly reported, along with detailed discussion of polymorphism observed in one of the ligands, and the nature of the hydrogen within the ligands in the solid state as well as in solution. The Mannich bases behaved as bidentate (NO), tridentate (NNO) and tetradentate (NNOO) ligands on coordination to Cu(II) and Fe(III) ions in which the hydroxyl group may be protonated or deprotonated. Coordination was determined by IR spectroscopy, investigating shifts in vOH, vC-O and in vCNC of the Mannich bases. The vCNC stretching frequencies v1 and v2 of asymmetrical piperazine Mannich bases were observed to shift upward in few cases upon complexation and this is attributed to (chair-boat) conformational change. The mode of coordination of the thiocyanate was determined by IR spectroscopy. Of the forty metal complexes investigated, six groups of metal complexes were identified as follows: (i) Ma(Ln)aClb-cH2O; (ii) Ma(HLn)a(NCS)aClb; (iii) Ma(Ln)a(NCS)aClb; (iv) Ma(HLn)aClb-cH2O; (v) Ma(Ln)a(NCS)a-cH2O; (vi) Ma(HLn)a(NCS)a-cH2O where a = 1 - 2 ; b = 1 - 4, c = 1 - 8. Molar conductivity values of 4.38 - 161.77 Q-1.cm2.mol-1 for the Cu(II) and Fe(III) complexes in DMSO showed that they range from non-electrolytes to 1:1 and 1:2 electrolytes. Electronic spectra for the ligands and the complexes were conducted in DMF and DMSO. The ligands are characterised by and n→n* and n→n* transitions. Intraligand charge transfer transitions peculiar to the nitro group were observed at about 430 nm for the nitro containing ligands. On coordination, these bands overshadowed the d-d transitions particularly for the nitro-Mannich bases. On complexation, ligand to metal charge transfer transitions associated with the hydroxyl were observed between 320 - 420 nm. Charge transfer transitions associated with the thiocyanates were also observed and discussed. The d-d transitions for high spin Fe(III) complexes are spin forbidden and generally uninformative. Those of Cu(II) are spin allowed and allow tentative structural proposals. Square planar and octahedral geometry are generally prevalent in the Cu(II) complexes with trigonal bipyramidal observed in few instances. The Fe(III) complexes are generally octahedral. Thirty-nine of the forty synthesised Cu(II) and Fe(III) complexes were catalytically active on the substrate (3,5-DTBC) in DMF with turnover rates (kcat) reported in the range of 1.86 ± 0.09 to 112.32 ± 3.72 h-1. From this pool of complexes, sixteen isostructural pairs were identified in terms of geometry, molecular formula and the source of the Mannich base and the following conclusions were made: The presence of thiocyanate in the metal complexes reduce catecholase activity; the Cu(II) complexes generally have better activity but the Fe(III) complexes become more relatively active with highly electron donating groups while the Cu(II) complexes become less; dinuclear complexes have greater activity than the mononuclear.
- Full Text:
- Date Issued: 2018
Mapping the pyrroloiminoquinone diversity produced by latrunculid sponges using tandem mass spectrometry-driven molecular networking
- Authors: Kalinski, Jarmo-Charles
- Date: 2021-04
- Subjects: To be added
- Language: English
- Type: thesis , text , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/178468 , vital:42942
- Description: Access restricted until April 2023. , Thesis (PhD) -- Faculty of Science, Chemistry, 2021
- Full Text:
- Date Issued: 2021-04
Marine anti-malarial isonitriles : a synthetic and computational study
- Authors: Adendorff, Matthew Ralph
- Date: 2011 , 2010-05-17
- Subjects: Isocyanides , Isocyanates , Marine pharmacology , Antimalarials , Antimalarials -- Development , Drug development
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4398 , http://hdl.handle.net/10962/d1006674 , Isocyanides , Isocyanates , Marine pharmacology , Antimalarials , Antimalarials -- Development , Drug development
- Description: The development of Plasmodium falciparum malarial resistance to the current armoury of anti-malarial drugs requires the development of new treatments to help combat this disease. The marine environment is a well established source of potential pharmaceuticals. Of interest to us are isonitrile, isocyanate and isothiocyanate compounds isolated from marine sponges and molluscs which have exhibited nano-molar anti-plasmodial activities. Through quantitative structure-activity relation studies (QSAR), a literature precedent exists for a pseudoreceptor model from which a pharmacophore for the design of novel anti-malarial agents was proposed. The current theory suggests that these marine compounds exert their inhibitory action through interfering with the heme detoxification pathway in P. falciparum. We propose that the computational methods used to draw detailed conclusions about the mode of action of these marine compounds were inadequate. This thesis addresses this problem using contemporary computational methodologies and seeks to propose a more robust method for the rational design of new anti-malarial drug compounds that inhibit heme polymerization to hemozoin. In order to investigate the interactions of the marine compounds with their heme targets, a series of modern computational procedures were formulated, validated and then applied to theoretical systems. The validations of these algorithms, before their application to the marine compound-heme systems, were achieved through two case studies. The first was used to investigate the applicability of the statistical docking algorithm AutoDock to be used for the exploration of conformational space around the heme target. A theoretical P. falciparum 1-deoxy-D-xylulose-5-phosphate reductoisomerase (PfDXR) enzyme model, constructed by the Biochemistry Department at Rhodes University, provided the ideal model to validate the AutoDock program. The protein model was accordingly subjected to rigorous docking simulations with over 30 different ligand molecules using the AutoDock algorithm which allowed for the docking algorithm’s limitations to be ascertained and improved upon. This investigation facilitated the successful validation of the protein model, which can now be used for the rational design of new PfDXR-inhibiting anti-plasmodial compounds, as well as enabling us to propose an improvement of the docking algorithm for application to the heme systems. The second case study was used to investigate the applicability of an ab initio molecular dynamics algorithm for simulation of bond breaking/forming events between the marine compounds and their heme target. This validation involved the exploration of intermolecular interactions in a naturally occurring nonoligomeric zipper using the Car-Parrinello Molecular Dynamics (CPMD) method. This study allowed us to propose a model for the intermolecular forces responsible for zipper self-assembly and showcased the CPMD method’s abilities to simulate and predict bond forming/breaking events. Data from the computational analyses suggested that the interactions between marine isonitriles, isocyanates and isothiocyanates occur through bond-less electrostatic attractions rather than through formal intermolecular bonds as had been previously suggested. Accordingly, a simple bicyclic tertiary isonitrile (5.14) was synthesized using Kitano et al’s relatively underutilized isonitrile synthetic method for the conversion of tertiary alcohols to their corresponding isonitriles. This compound’s potential for heme detoxification inhibition was then explored in vitro via the pyridine-hemochrome assay. The assay data suggested that the synthesized isonitrile was capable of inhibiting heme polymerization in a similar fashion to the known inhibitor chloroquine. Attempts to synthesize tricyclic analogues of 5.14 were unsuccessful and highlighted the limitation of Kitano et al’s isonitrile synthetic methodology.
- Full Text:
- Date Issued: 2011
Measurements of the solubilities of some silver halides in water by electrical methods
- Authors: Malan, George McPherson
- Date: 1955
- Subjects: Silver halides -- Solubility , Silver halides -- Analysis , Conductometric analysis , Potentiometry , Silver halides
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4515 , http://hdl.handle.net/10962/d1013502
- Description: [Introduction, p. 3] The solubilities of the silver halides cannot be determined by the conventional methods of analytical chemistry because they are too sparingly soluble (of the order 1 x 10⁻⁵ to 1 x 10⁻⁶ g . equiv./1. at 25°C.) However, electrical, and to a lesser extent optical methods, are admirably suited because of their greater sensitivity. The conductometric and potentiometric methods are the two most important electrical techniques for the measurement of the solubilities of sparingly soluble salts, and are the ones employed in this research. There are large discrepancies between the published values for the solubility of silver chloride. Results obtained by the conductometric and potentiometric methods disagree. In addition, figures quoted by independent authors using the same method differ by as much as 15%.
- Full Text:
- Date Issued: 1955
Mechanistic studies of unusual Miruta-Baylis-Hillman reactions
- Authors: Nyoni, Dubekile
- Date: 2012
- Subjects: Chemical reactions Benzaldehyde Acrylonitrile Methyl acrylate Coumarins
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4400 , http://hdl.handle.net/10962/d1006692
- Description: This study has focussed on the application of synthetic, kinetic and exploratory theoretical methods in elucidating the reaction mechanisms of four Morita-Baylis-Hillman (MBH) type reactions, viz, i) the reactions of the disulfide 2,2'-dithiodibenzaldehyde with various activated alkenes in the presence of DBU and Ph₃P, ii) the reactions of chromone-3-carbaldehydes with MVK, iii) the reactions of chromone-2-carbaldehydes with acrylonitrile and iv) with methyl acrylate. Attention has also been given to the origin of the observed regioselectivity in Michaelis-Arbuzov reactions of 3-(halomethyl)coumarins. Cleavage of the sulfur-sulfur bond of aryl and heteroaryl disulfides by the nitrogen nucleophile DBU has been demonstrated, and a dramatic increase in the rate of tandem MBH and disulfide cleavage reactions of 2,2'-dithiodibenzaldehyde with the activated alkenes, MVK, EVK, acrylonitrile, methyl acrylate and tert-butyl acrylate has been achieved through the use of the dual organo-catalyst system, DBU-Ph₃P – an improvement accompanied by an increase in the yields of the isolated products. Detailed NMR-based kinetic studies have been conducted on the DBU-catalysed reactions of 2,2'-dithiodibenzaldehyde with MVK and methyl acrylate, and a theoretical kinetic model has been developed and complementary computational studies using Gaussian 03, at the DFT-B3LYP/6-31G(d) level of theory have provided valuable insights into the mechanism of these complex transformations. Reactions of chromone-3-carbaldehydes with MVK to afford chromone dimers and tricyclic products have been repeated, and a novel, intermediate MBH adduct has been isolated. The mechanisms of the competing pathways have been elucidated by DFT calculations and the development of a detailed theoretical kinetic model has ensued. Unusual transformations in MBH-type reactions of chromone-2-carbaldehydes with acrylonitrile and methyl acrylate have been explored and the structures of the unexpected products have been established using 1- and 2-D NMR, HRMS and X-ray crystallographic techniques. Attention has also been given to the synthesis of 3-(halomethyl)coumarins via the MBH reaction, and their subsequent Michaelis-Arbuzov reactions with triethyl phosphite. An exploratory study of the kinetics of the phosphonation reaction has been undertaken and the regio-selectivity of nucleophilic attack at the 4- and 1'-positions in the 3-chloro- and 3-(iodomethyl)coumarins has been investigated by calculating Mulliken charges, LUMO surfaces and Fukui condensed local softness functions.
- Full Text:
- Date Issued: 2012
Metal complexes of black wattle tannins and related model polyphenols
- Authors: Slabbert, Neville Patrick
- Date: 1973
- Subjects: Metal complexes Tannins
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4432 , http://hdl.handle.net/10962/d1007407
- Description: Apart from their general usage as tanning agents for hides and skins, the natural tannins have been used since earliest times for various other purposes. The blue-black iron tannate complex was used by ancient Egyptians as a hairdye and for many conturies this complex was the main source of writing inks. Wattle tannin is known to form complexes with many metal ions. The chief use of tannin complexes has been in gravimetric analyses, since aqueous solutions of tannins readily precipitate metal ions under certain experimentel conditions. At the present time the nature of the precipitated complexes has not been investigated however, because in the gravimetric method the complexes are ignited and the metal determined as its oxide; hence no knowledge of the complexes themselves was required.
- Full Text:
- Date Issued: 1973
Metal interactions with neural substrates and their role in neurodegeneration
- Authors: Lack, Barbara Anne
- Date: 2003
- Subjects: Nervous system -- Degeneration Neurotoxicology Chemical reactions Metals -- Physiological effect Melatonin -- Physiological effect
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4391 , http://hdl.handle.net/10962/d1005709
- Description: "Life" may be characterized as a controlled stationary flow equilibrium, maintained by energy consuming chemical reactions. The physiological functioning of these life systems include at least 28 of the elements isolated on the periodic table thus far, most of which are metals. However, as with Paracelsus Principle: "The dose makes the poison", there exists a definite link between metal levels, essential and toxic, and the onset of neurodegenerative diseases. The economic costs of brain dysfunction are enormous, but this pales in comparison to the staggering emotional toll on the victims themselves and their families. In an attempt to improve the understanding of the causes of neurodegeneration, this study focuses on one potential aspect: the possible link between metals and neurotransmitter homeostasis utilising a variety of electronanalytical techniques. Adsorptive cathodic stripping voltammetry was employed to investigate the binding affinities and complex formation of melatonin and its precursor serotonin with calcium, potassium, sodium, lithium and aluminium. The results showed that all the metals studied formed complexes with both pineal indoleamines. However, the stability and affmity of the ligands toward the various metals varied greatly. The study suggests a further role for melatonin, that of metalloregulator and possible metal detoxifier in the brain, the in vivo studies which followed will further substantiate this notion. This research additionally focused on the cholinergic system, in particular acetylcholine complex formation studies with mercury, lead, cadmium, copper and zinc using the adsorptive cathodic stripping voltammetry method. The formation and characterisation of a solid mercury-acetylcholine complex lent further strength to the in situ electrochemical complex formation observed. The results showed the preference of acetylcholine for environmentally toxic heavy metals (such as Cd²⁺) over those divalent cations that occur naturally in the body. The possible metalloregulatory role melatonin played in the three brain regIOns: cerebellum, cortex and corpus striatum of male Wistar rats was studied as an in vivo extension of the earlier in vitro studies. Anodic stripping voltammetry was employed to detect metal levels present. The results showed that daily injections of melatonin was responsible for significantly decreasing copper(I), cadmium(II) and lead(II) levels in various regions of the rat brain of those animals that had undergone a pinealectomy in comparison to the saline injected group having undergone the same treatment. Histological and electrochemical stripping techniques were applied to investigate the implications of high A1³⁺ levels in the brain regions, particularly the hippocampus. Melatonin showed signs of promise in indirect symptom alleviation and by significantly decreasing A1³⁺ levels in rats that had been dosed with melatonin prior to A1³⁺ treatments in comparison with the control groups. Finally a preliminary study outlining a method for the production of a calcium selective microelectrode was undertaken. Further work is still needed to optimise the microelectrode production as well as its possible applications. However, whilst the overall conclusions of this entire multidisciplinary study may indeed only be in effect one piece of a very large puzzle on neurodegenerative diseases, this piece will no doubt serve as a building block for further ideas and work in this field.
- Full Text:
- Date Issued: 2003
Metallophthalocyanine derivatives as catalysts for the detection of sulphur dioxide, cyanide, nitrite and amino acids
- Authors: Thamae, Mamothibe Amelia
- Date: 2003
- Subjects: Cyanides Nitric oxide Electrochemistry Nitrites Suplhur dioxide Amino acids
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4295 , http://hdl.handle.net/10962/d1004542
- Description: Electrocatalytic reduction and oxidation of nitrite using cobalt phthalocyanine derivatives was studied. The detection limit of 1 x 10⁻¹° mol dm⁻³ was achieved when these molecules were employed as catalysts for nitrite detection. The mechanisms for nitrite catalysis were proposed. The position of the peripheral substituents on cobalt porphyrazines (related to cobalt phthalocyanines) affected the catalytic activity of these complexes. The highest activity for nitrite reduction was observed on the cobalt(II) 2,3-tetramethyltetrapyridinoporphyrazine ([CoTm-2,3-tppa]⁴⁺), with cobalt phthalocyanine showing the lowest activity, and the cobalt(II) 3,4- tetramethyltetrapyridinoporphyrazine ([CoTm-3,4-tppa]⁴⁺), showing intermediate behaviour. A mixture of a negatively charged cobalt(II) tetrasulfophthalocyanine ([Co¹¹TSPc]⁴⁻) and a positively charged [CoTm-3,4-tppa]⁴⁺ showed better activity for nitrite reduction than did the individual components. Cobalt porphyrazines lowered the potentials for nitrite reduction in that peaking was observed, as opposed to cobalt phthalocyanine, where only the increase in currents was observed without peaking. Using the cobalt phthalocyanine derivatives, nitrite can be reduced to ammonia with high current efficiency. A glassy carbon electrode modified with [Co¹¹TSPc]⁴⁻ was employed for the determination of nitrite. Nitrate had an insignificant effect on nitrite oxidation on these modified electrodes. Electrocatalytic determination of S0₂ was studied as a function of pH at a glassy carbon electrode modified with iron(II) tetrasulfophthalocaynine. It was found that depending on pH, S0₂.xH₂0, HS0₃⁻ and/or SO₃²⁻ are the main compounds in solution and that these compounds behave differently at the electrode surface. Detection limits ranging from 4.0 ± 0.1 x 10⁻⁵ to 7.5 ± 0.1 x 10⁻⁵ mol dm⁻³ depending on pH were observed. Similar results were obtained when cobalt(II) tetrasulfophthalocaynine was employed for S0₂ catalysis under the same experimental conditions. Cysteine and histidine determination using oxidation currents was performed on glassy carbon electrodes modified with [CoTm-3,4-tppa]⁴⁺ (represented as [CoTm-3,4-tppa]⁴⁺-GCE) in pH 7 Tris buffer. The detection limit of 1.0 x 10⁻⁵ mol dm⁻³ for cysteine and 2.24 x 10⁻⁷ mol dm⁻³ for histidine were obtained. Cyanide can be detected down to 1 x 10⁻¹¹ mol dm⁻³ using [CoTm-3,4-tppa]⁴⁺-GCE in pH 10.8 buffer. Cyanide and S0₂ coordinate to the [CoTSPc]⁴⁻ species. The coordination is accompanied by oxidation of the central Co(II) metal, forming a [Co¹¹¹CoTSPc]³⁻ species. The rate constants for cyanide coordination to the [Co¹¹TSPc]⁴⁻ complex are larger than those reported for the coordination of cyanide to FePc and RuPc complexes in non-aqueous media. Autoreduction of [Co¹¹Tmtppa]⁴⁺ occurred in the presence of either histidine or cysteine, with the formation of metal reduced species, [Co¹Tmtppa(-2)]³⁺. Nitric oxide and nitrite coordinate to the [Co¹¹Tmtppa]⁴⁺ species, without auto-reduction of this species, which was observed for cysteine or histidine. The use of [Co¹¹TSPc]⁴ resulted in improved rate of interaction with nitrite when compared to the [Co¹¹Tmtppa]⁴⁺ species.
- Full Text:
- Date Issued: 2003
Metallophthalocyanine-gold nanoparticle conjugates for photodynamic antimicrobial chemotherapy
- Authors: Mthethwa, Thandekile Phakamisiwe
- Date: 2015
- Subjects: Nanochemistry , Phthalocyanines , Photochemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4543 , http://hdl.handle.net/10962/d1017923
- Description: This thesis presents the synthesis of neutral and cationic metallophthalocyanines and their gold nanoparticles conjugates. The spectroscopic characterization of these compounds is presented herein. The studies presented in this work shows that the conjugation of gold nanoparticles influenced both photophysical and photochemical properties. Gold nanoparticles were found to enhance the singlet oxygen quantum yield while lowering the fluorescence quantum yields. This work also looks at the effect of anisotropic gold nanoparticles such as nanorods and bipyramids on the photophysical behaviour of the metallophthalocyanines. The effect of the size of the gold nanorods was investigated herein. The results show that photophysical and photochemical properties can be influenced by both size and shape of the nanoparticles. Physical characterization about the loading of nanoparticles was also looked into. Parameters such as the surface area, the number of surface atoms, the number of atoms as well as the number of nanoparticles loaded on the surface of the phthalocyanines were studied. The self-assembled monolayers formed by phthalocyanines on gold surfaces were studied using the X-ray photoelectron spectroscopy (XPS). The gold nanoparticles synthesized herein include both organic and water soluble, different capping agents (citrate, tetraammonium bromide (TAOBr) and cetrimethylammonium bromide (CTAB). The concentration of the gold nanoparticles was measured on the inductively coupled plasma (ICP) and their size and shape were obtained from the transmission electron microscopy (TEM) images. A cationic aluminium phthalocyanine and its conjugates were used for photoinactivation of bacteria and fungi. The results show significant reduction and higher activity in the presence of gold nanoparticles, especially nanorods. A small chapter in this work presents an attempted work on the binding of metallothionein protein with protophorphyrin (IX). The pH and concentration dependent binding studies were investigated
- Full Text:
- Date Issued: 2015
Metallophthalocyanines as electrocatalysts and superoxide dismutase mimics
- Authors: Matemadombo, Fungisai
- Date: 2010
- Subjects: Mimicry (Chemistry) Electrocatalysis Superoxide dismutase Electrochemistry Phthalocyanines
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4325 , http://hdl.handle.net/10962/d1004985
- Description: Syntheses, spectral, electrochemical, and spectroelectrochemical studies of iron, cobalt, and manganese phthalocyanines are reported. The novel coordination of cobalt tetracarboxy metallophthalocyanine to an electrode premodified with aryl radicals and its use in the detection of thiocyanate are reported. This work describes the catalytic activity of cobalt phthalocyanine (CoPc) derivatives adsorbed onto glassy carbon electrodes for the electrocatalytical detection of nitrite, Lcysteine, and melatonin. The modified electrodes efficiently detected nitrite. The CoPc derivative modified electrodes proficiently detected L-cysteine whereas an un-modified electrode could not. This work presents the innovative electrochemical detection of melatonin using electrodes adsorbed with CoPc derivatives. These electrodes detected melatonin at more favorable electrochemical parameters relative to an un-modified gold electrode. The limits of melatonin detection of the modified electrodes lay in the 10⁻⁷ to 10⁻⁶ M region. The modified electrodes accurately detected capsule melatonin concentrations as specified by the supplier and could differentiate between a mixture of melatonin, tryptophan, and ascorbic acid. They reliably detected nitrite, L-cysteine, and melatonin in the 10⁻⁴ to 10⁻² M region. Metallophthalocyanine complexes substituted with thio groups were employed as self assembled monolayers (SAMs). Voltammetry, impedance, atomic force microscopy, and scanning electrochemical microscopy proved that the SAMs all act as selective and efficient barriers to ion permeability. All the SAMs in this work can be used as effective electrochemical sensors of nitrite and L-cysteine in the 10⁻⁴ to 10⁻² M region with competitive limits of detection whereas an un-modified electrode cannot detect Lcysteine. The manganese phthalocyanine SAM modified electrodes are arguably better nitrite and L-cysteine electrocatalysts relative to their iron and cobalt counterparts. Manganese phthalocyanines were used as superoxide dismutase (SOD) mimics. All manganese phthalocyanine complexes in this work acted as SOD mimics in an enzymatic system of superoxide production. From cellular studies, complexes 6d, 6e, 8d, 8e act as intracellular SOD mimics and are without significantly high cellular toxicity.
- Full Text:
- Date Issued: 2010
Metallophthalocyanines linked to metal nanoparticles and folic acid for use in photodynamic therapy of cancer and photoinactivation of bacterial microorganisms.
- Authors: Matlou, Gauta Gold
- Date: 2020
- Subjects: Cancer -- Photochemotherapy , Nanoparticles , Phthalocyanines , Anti-infective agents -- Therapeutic use , Photochemotherapy , Photochemistry
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/166540 , vital:41377
- Description: This thesis presents on the synthesis and characterization of novel asymmetric and symmetrical metallophthalocyanines (MPcs) substituted with carboxylic acid functional groups and centrally metallated with zinc and indium. The MPcs are further covalently linked to cysteine capped silver nanoparticles (cys-AgNPs), amino functionalized magnetic nanoparticles (AMNPs) and folic acid (FA) through an amide bond between the carboxylic group of MPcs and the amino group of FA, cys-AgNPs or AMNPs. The covalent linkage of MPcs to FA improved the water solubility of MPcs and allowed for singlet oxygen quantum yield determination in water. Asymmetric MPcs and their conjugates were found to have improved photochemical and photophysical properties compared to symmetrical MPcs and their conjugates. The heavy atom effect of AMNPs and AgNPs improved the triplet and singlet oxygen quantum yields of MPcs. MPcs and their conjugates (MPc-FA, MPc-AMNPs, MPc-AgNPs) were found to have lower in vitro dark cytotoxicity and higher photodynamic therapy (PDT) activity on MCF-7 breast cancer cells. The water soluble MPc-FA had better PDT activity when compared to MPc-AMNPs due to the active targeting of folic acid-folate binding on cancer cell surface. MPcs and MPc-AgNPs conjugates also showed excellent in vitro cytotoxicity on S. aureus under light irradiation compared to dark cytotoxicity. The photosensitizing properties of MPcs and their conjugates are demonstrated for the first time in this thesis, both on breast cancer cells (MCF-7) through photodynamic therapy and on microorganisms (S. aureus) through photodynamic antimicrobial chemotherapy.
- Full Text:
- Date Issued: 2020
Metathesis catalysts : an integrated computational, mechanistic and synthetic study
- Authors: Sabbagh, Ingrid Theresa
- Date: 2006
- Subjects: Metathesis (Chemistry) Catalysis Metal catalysts Chemical kinetics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4397 , http://hdl.handle.net/10962/d1006208
- Description: An integrated approach to the design of potential rutheniun-based metathesis catalysts is described, in which closely defined synthetic forays provide the focus and rationale for detailed computational and mechanistic studies. The ground-state geometry of a 1st-generation Grubbs catalyst has been explored at the molecular mechanics, semi-empirical and DFT levels, and the resulting structures have been shown to compare favourably with literature data and with the structure of a known crystalline analogue. The DMol³ DFT code has also been shown to represent accurately both the geometry of the corresponding co-ordinatively unsaturated monophosphine derivative, and the ligand dissociation energy associated with its formation. A DFT free-energy profile of the degenerate metathesis of ethylene has been generated, using a truncated model of the 1st-generation Grubbs catalyst, permitting location, for the first time, of the three expected transition states and providing new information regarding the rate-determining step. DFT methods have been used to facilitate the design of a tridentate camphor-derived ligand for use in the construction of a novel Grubbs-type catalyst. The phosphine ligand dissociation energy of the putative catalyst and the ethylene metathesis energy profile of a truncated model have also been studies at the DFT level. The attempted synthesis of the proposed ligand proceeded via a novel 8-bromocamphoric anhydride intermediate and afforded several unexpected and novel products, including a cisfused γ-Iactone, and a bromo camphoric acid derivative. Single crystal X-ray analysis of the latter reveals a chiral, polymeric H-bonded packing arrangement, rendering it suitable for chiral inclusion studies. Computational methods, including the GAUSSIAN-based GIAO NMR prediction technique, were used to support the structural characterisation of the novel camphor derivatives. DFT-Ievel computational analysis of the C-8- and C-9 bromination of camphor has afforded theoretical insights which permit the reconciliation of two earlier empirical explanations regarding the regioselectivity of these transformations; moreover, the theoretical results suggest that a third, previously disregarded factor, plays a significant role. A coset analysis, in conjunction with DFT-Ievel energy profiling, has also been used to resolve conflicting opinions regarding the origin of the major byproduct. Computed electronic parameters (CEP's) have been calculated for the anionic ligands involved in a series of 2nd-generation Grubbs-Hoveyda-type catalysts, and used to explain some apparently anomalous trends in catalyst activity. A linear relationship between ligand CEP's and selected ¹H NMR chemical shifts has also been demonstrated and used to identify a transient ruthenium complex in solution. The ability of the malonate di-anion to bind to ruthenium in a bidentate manner has been explored and demonstrated, under suitable conditions. DFT methods have been used to design and assess the ruthenium-chelating potential of a novel tridentate malonate derivative. A synthetic pathway to this ligand has been designed and several novel heterocyclic intermediates have been isolated and characterised. An NMR-based kinetic study of the Grubbs-catalysed self-metathesis of l-octene has been completed, and the effects of temperature, concentration and solvent variations on the kinetic parameters have been studied. Application of the Guggenheim method and a simplified mechanistic model has permitted the accurate calculation of pseudorate constants for the initiation and, for the first time, the propagation phase of the reaction. Theoretical studies of this reaction at the DFT and molecular mechanics levels have been shown to support previous assumptions regarding the selectivity and temperature-dependence of metallacycle formation.
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- Date Issued: 2006
Molecular simulations of potential agents and targets of Alzheimer’s disease
- Authors: Joli, Luxolo
- Date: 2020
- Subjects: Alzheimer's disease -- Chemotherapy , Alzheimer's disease -- Treatment , Ligands (Biochemistry) , Proteins -- Chemistry , Molecular dynamics -- Simulation methods
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/146411 , vital:38523
- Description: Alzheimer's Disease (AD) is a neurodegenerative brain disorder that was first discovered in 1901 by Dr Aloïs Alzheimer and was later reported publicly in 1906. The German doctor had a 51-yearold woman patient called Auguste Deter, who was suffering from a rare brain disorder with early signs of memory loss and cognition. Alzheimer's Disease is the most common type of dementia that affects people with the age of 65 years and older. There is no single known cause of Alzheimer’s disease however, amyloid β-peptide (Aβ1–40/42) was found to be at the centre of AD pathogenesis and this connection was referred as “amyloid hypothesis”. It is suspected that an accumulation of amyloid β-peptide is a major contributor to neuronal dysfunction and degeneration. Alzheimer’s disease is complex and therefore, currently there is no medication available that treats the disease. However, there are approaches that focus on helping people maintain mental function, manage behavioral symptoms, and slow down the symptoms of disease. According to South Africa’s 2011 census, there are approximately 2.2 million people in South Africa with some form of dementia and therefore there is a need to find a treatment for the disease. This study aims to find agents and targets of Alzheimer’s Disease by using different computational techniques such as molecular modelling. The study will use compounds from the South African Compounds Database (SANCDB) and the following therapeutic targets α-, β- and γ-secretase, acetylcholinesterase, tau protein and neprilysin. A successful High-throughput Virtual Screening (HTVS) study to determine lead compounds was performed using a computational program called KNIME. Molecular docking was achieved with GLIDE as it allows for exhaustive ligand flexibility. The docking calculations were carried out using the high level of precision XP (extra precision) for enhanced docking accuracy. The binding affinities (docking scores) for the best bound ligands obtained from docking were in the order of -5 kcal/mol or less. The ligandSANC00370 was the best binding ligand against the protein 1J1C_B and had the best binding energy of -13.94 kcal/mol compared to others. The receptor-ligand complexes were analyzed using the interaction diagrams obtained from the Discovery Studio Visualizer and Maestro programs. Molecular Dynamics simulations were performed on the complexes obtained from docking to help in optimizing their interactions. The simulations were performed using the Desmond tool with the OPLS3 force field. 100 ns simulations were performed for six systems with the best docking score results epresenting each of the therapeutic targets and for the other complex systems, 50 ns simulations were performed. The Desmond simulations were analyzed using the Simulations Interaction Diagrams such as PL-RMSD, L-RMSF, P-RMSF, L-Torsions, P-SSE, LP-Contacts and L-Properties. Maestro was used to visualize the stability of the ligands in the active site during the simulation. All 13 Desmond simulations were successful however, there were 9 simulations which produced satisfactory results while the others were nsatisfactory. Based on the molecular docking and Molecular Dynamics results of this study, 9 potential targets and 6 potential agents were obtained successfully and can be studied further as therapeutics for Alzheimer’s Disease.
- Full Text:
- Date Issued: 2020
Nanocomposites of carbon nanomaterials and metallophthalocyanines : applications towards electrocatalysis
- Authors: Nyoni, Stephen
- Date: 2016
- Subjects: Nanocomposites (Materials) , Nanostructured materials , Electrocatalysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4561 , http://hdl.handle.net/10962/d1020846
- Description: Nanohybrid materials have been prepared and examined for their electrocatalytic activity. The nanocomposites have been prepared from carbon nanomaterials (multiwalled carbon nanotubes (MWCNTs) and graphene nanosheets), cadmium selenide quantum dots and metallophthalocyanines (MPcs). The MPcs used in this work are cobalt tetraamino-phthalocyanine (CoTAPc) and tetra (4-(4,6-diaminopyrimidin-2-ylthio) phthalocyaninatocobalt (II)) (CoPyPc). Their activity has also been explored in different forms; polymeric MPcs, iodine doped MPcs and covalently linked MPcs. The premixed drop-dry, sequential drop-dry and electropolymerisation electrode modification techniques were used to prepare nanocomposite catalysts on the glassy carbon electrode (GCE) surface. The sequential drop dry technique for MPc and MWCNTs gave better catalytic responses in terms of limit of detection, catalytic and electron transfer rate constants relative to the premixed. MWCNTs and CdSe-QDs have been used as intercalating agents to reduce restacking of graphene nanosheets during nanocomposite preparation. Voltammetry, chronoamperometry, scanning electrochemical microscopy and electrochemical impedance spectroscopy methods are used for electrochemical characterization modified GCE. X-ray photoelectron spectroscopy, X-ray diffractometry, transmission electron microscopy, scanning electron microscopy, infra-red spectroscopy, Raman spectroscopy were used to explore surface functionalities, morphology and topography of the nanocomposites. Electrocatalytic activity and possible applications of the modified electrodes were tested using oxygen reduction reaction, l-cysteine oxidation and paraquat reduction. Activity of nanocomposites was found superior over individual nanomaterials in these applications.
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- Date Issued: 2016
Nanocomposites of nickel phthalocyanines as electrocatalysts for the oxidation of chlorophenols an experimental and theoretical approach
- Authors: Khene, Mielie Samson
- Date: 2012
- Subjects: Nanocomposites (Materials) -- Research Phthalocyanines -- Research Chlorophenols -- Research Electrocatalysis -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4326 , http://hdl.handle.net/10962/d1004986
- Description: In this work the interaction between peripherally (b) substituted nickel tetrahydroxyphthalocyanines (b-NiPc(OH)4 and poly-b-Ni(O)Pc(OH)4) with 4-chlorophenol is theoretically rationalized by performing calculations at the B3LYP/6-31G(d) level. Density functional theory (DFT) and molecular orbital theory are used to calculate the condensed Fukui function for phthalocyanine derivatives and 4-chlorophenol, in order to determine the reactive sites involved when 4-chlorophenol is oxidized, and to compare theoretically predicted reactivity to experimentally determined electrocatalytic activity. Electrocatalytic activities of adsorbed NiPc derivatives: OPGE-α-NiPc(OH)8 (OPGE = ordinary pyrolytic graphite electrode, α = nonperipheral substitution), OPGE-a-NiPc(OH)4 and OPGE-β- NiPc(OH)4 are compared with those of the polymerized counterparts: OPGE-poly-α-Ni(O)Pc(OH)8, OPGE poly-a-NiPc(OH)4 and OPGE-poly-β-NiPc(OH)4, respectively. β-NiPc(NH2)4, β-NiPc(OH)4, α-NiPc(OH)4, α-NiPc(OH)8, α-NiPc(C10H21)8 are adsorbed on singled walled carbon nanotube (SWCNT) and β-NiPc(NH2)4-SWCNT (linked to SWCNT), are used to modify glassy carbon electrode (GCE) and employed for the electro oxidation of chlorophenols. The β-NiPc(NH2)4-SWCNT gave the best current response for the oxidation of 4-chlorophenol. α-NiPc(OH)8-SWCNT and α-NiPc(C10H21)8 gave the best resistance to electrode fouling due to oxidation by product of 4-chlorophenol. The synthesis of conjugates of cadmium telluride quantum dots (CdTe-QDs) capped with thioglycolic acid and peripherally substituted nickel tetraamino phthalocyanine (β-NiPc(NH2)4) complex were also employed for the oxidation of chlorophenols. Separation of one of the diastereomers of 1, 2-subnaphthalocyanine (SubNPc) was achieved as well as separation of the enantiomers. The absorption and magnetic circular dichroism spectra, together with theoretical calculations, reveal rather small variations in the frontier molecular orbitals of the SubNPc compared to conventional subphthalocyanine (SubPc), except for the destabilization of the highest occupied molecular orbital (HOMO), which results in a characteristic absorption in the Soret band region. The chirality of SubNPc, including the cyclic dichroism (CD) signs and intensities, are discussed in detail.
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- Date Issued: 2012
Nonlinear optical behavior of lanthanide phthalocyanines and their conjugates with a selection of nanomaterials
- Authors: Sekhosana, Kutloano Edward
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/4580 , vital:20695
- Description: This thesis presents novel asymmetrical and symmetrical lanthanide phthalocyanines (Pcs) characterized using a number techniques including proton nuclear magnetic resonance, electron spin resonance, time correlated single photon counting, FTIR spectrometry, MALDI-TOF mass spectrometry, UV-Vis spectrometry, Raman spectroscopy and CHNS elemental analysis. The design of theses lanthanide Pcs takes the form of mononuclear, binuclear, trinuclear, bis- and tris(phthalocyanines). Nanomaterials such as zinc oxide nanoparticles (ZnO NPs), multi-walled carbon nanotubes (MWCNTs) and graphene oxide nanosheets (GONS) (oxidized and reduced) were employed for covalent linkage to mono- and binuclear phthalocyanines as conjugates. Transmission electron microscopy was used to characterize ZnO NPs, MWCNTs and GONS alone and when linked to lanthanide Pcs. Lanthanide Pcs alone and when linked to ZnO NPs, MWCNTs and GONS where embedded in polymers such as poly (methyl methacrylate) (PMMA), poly (bisphenol A carbonate) (PBC) and poly (acrylic acid) (PAA) for thin film preparation. The thickness of the thin films was determined by utilization of the knife edge attachment of the A Bruker D8 Discover X-ray diffraction (XRD). Optical limiting properties of lanthanide Pcs alone and as conjugates in solution and when incorporated into polymers were determined by employing a Z-scan technique. It emerged that low symmetry lanthanide Pcs (19, 20 and 21), the blue forms of bis(phthalocyanines) (only in solution; 24 and 28) as well as tris(phthalocyanines) (30 and 31) exhibit low limiting threshold (Ilim) values in solution and thin films (particularly PBC and PAA). The low limiting threshold values make these lanthanide Pcs reliable optical limiters.
- Full Text:
- Date Issued: 2017
Nonlinear optical properties of metal free thio alkyl and tert-butyl phenoxy phthalocyanine
- Authors: Joseph, Otto
- Date: 2021-10
- Subjects: Nonlinear optics , Phthalocyanines , Time-dependent density functional theory , Magnetic circular dichroism , Reverse saturable absorption (RSA) , Real Time Dependent Density Functional Theory (RT-TDDFT)
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/190712 , vital:45021
- Description: This work reports on the nonlinear optical properties of tetra - and octa substituted phthalocyanines (Pcs) utilising pentane thiol and 4-tertbutyl phenol as substituents. Their nonlinear absorption coefficient (𝛽) and absorption cross sections were determined using the Z-scan technique with a 10 ns pulse laser at 532 nm. The molecular second order hyperpolarizability Im[γ] was observed and the following Im[γ] trend was obtained for 𝛼-H2Pc(SC5H11)4 isomers, 5.93 ×10−31 (Cs) 2.24×10−32(D2h) > 1.21×10−32(C4h) > 1.05×10−32 (C2v) esu, respectively, in chloroform. Symmetry was seen to have an effect on the observed reverse saturable absorption (RSA) response. Based on the five level model rate equation nonlinear fit of the RSA response curves and Real Time Time Dependant Density Functional Theory (RT-TDDFT) results, the singlet excited state population dynamics was found to play a significant role in producing the observed Im[γ] trend. , Thesis (MSc) -- Faculty of Science, Chemistry, 2021
- Full Text:
- Date Issued: 2021-10
Nonlinear optical properties of Sn(IV) phthalocyanines: experimental and theoretical approach
- Authors: Louzada, Marcel Severiano
- Date: 2017
- Subjects: Phthalocyanines , Nonlinear optics
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/57852 , vital:26996
- Description: This work presents the nonlinear properties of six Sn(IV) Phthalocyanines. Three of the phthalocyanines are linked by an alkylthiol substituent and the rest are linked with a phenoxy substituent. For all six compounds non-linear optic analysis was carried out in four solvents: chloroform, toluene, dichloromethane, and tetrahydrofuran, and their differences were recorded. Calculation of the linear, singlet excited, triplet excited and two photon absorption cross-sections were also carried out and the results compared. To form a comparison the first order hyperpolarizabilities, DFT calculations were also performed and the results compared to see if the behaviour between the two properties can be predicted using DFT.
- Full Text:
- Date Issued: 2017