120 research outputs found
Correction to: A kinetic investigation of mononuclear trans-platinum(II) complexes with mixed amine ligands
No full textThe article “A kinetic investigation of mononuclear trans-platinum(II) complexes with mixed amine ligands”, written by “Moses Ariyo Olusegun, Desigan Reddy and Deogratius Jaganyi”, was originally published electronically on the publisher’s internet portal https://link.springer.com/article/10.1007/s11243-020-00381-0 on 12 March 2020 with open access. With the author(s)’ decision to step back from Open Choice, the copyright of the article changed on 20 April 2020 to ©Springer Nature Switzerland AG 2020 and the article is forthwith distributed under the terms of copyright
The cis-effect of the n-donor moiety on the rate of chloride substitution in (N^N^N) and (N^C^N) platinum (II) complexes by nitrogen bio-relevant nucleophiles.
No full textM.Sc. University of KwaZulu-Natal, Pietermaritzburg 2013.Abstract available in PDF file
Tuning the reactivity of mononuclear tridentate platinum (II) complexes : a detailed kinetic and mechanistic approach using Azole Nucleophiles.
No full textThesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2014.The kinetic substitution reactions of two different sets of mononuclear Platinum(II) complexes with heterocyclic bio-relevant azole nucleophiles, viz. Imidazole (Im), 1-methylimidazole (MIm), 1,2-Dimethylimidazole (DIm), 1,2,4-triazole (Trz) and pyrazole (Pyz). All substitution reactions were studied under pseudo-first order conditions as a function of the incoming nucleophiles concentration and temperature using stopped-flow techniques and UV/Visible spectroscopy.
The first set of complexes included the tridentate polypyridine complexes, Pt(II)(2,2:6,2″-terpyridine)Cl]Cl.2H2O, (PtL1) Pt(II)(1,3-di(2-pyridyl)benzene)Cl, (PtL2) Pt(II)(2,6-di-(2’-quinolinyl)pyridine)Cl](Cl), (PtL3) and Pt(II)(1,3-di-(2’-quinolinyl)benzene)Cl (PtL4). The substitution of these complexes with the previously mentioned azoles showed that tuning electronic communication of the Pt(II) centre towards substitution through quinoline moieties has an opposed effect to that obtained through pyridine moieties, and verified that the trans-effect of a phenyl ring is much greater than that of a pyridine ring. The reactivity trend among the complexes was PtL2 > PtL4 > PtL1 > PtL3. Once the nucleophiles were categorised into two groups based on their structural similarities, reactivity trend observed amongst the nucleophiles was generally Im > Pyz > Trz, based on the basicity (electronic effects) and MIm > Im > DIm based on steric effects.
The second series of complexes were tridentate [Pt(bis(2-pyridylmethyl)amine)OH2](ClO4)2, Ptdpa and [Pt(bis(2-pyridylmethyl)sulfide)OH2](ClO4)2, Ptdps of which the kinetics were studies in an aqua medium and at constant ionic strength (0.1 M). Ptdps was found to be more reactive (three magnitude higher) than Ptdpa. The rate of substitution of the aqua ligand is dependent on the strength of the σ-donor character and the π-acceptability of the atom situated trans to the leaving group. The observed reactivity for the azoles followed the trend, MIm > Im > DIm > Trz > Pyz. This reactivity trend is in accordance with the basicity, and reflects steric and electrophilic effects of the nucleophiles. This was supported by DFT calculations and the X-ray crystal structure of Ptdps_Cl.
For all substitution reactions, the temperature dependent studies showed an associative activation. It is envisaged that the findings of this project will provide useful information for designing new drugs as part of a protracted search of effective anticancer drugs with a wider spectrum
Controlling the reactivity of mononuclear palladiun (II) complexes. Substitution kinetics and mechanisms.
No full textDoctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Abstract available in PDF
An investigation into the influence of bridging diamine linkers on the substitution reactions of dinuclear platinum II complexes.
No full textThesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.Abstract available in printed copy
Determination of inorganic and polynuclear aromatic hydrocarbon contents in South African sewage sludges.
No full textThesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.A total of 34 sewage sludge samples were collected from South African provinces: KwaZulu- Natal, Gauteng, North West and Western Cape province. The samples were analysed for mineral ions and polynuclear aromatic hydrocarbons (PAH). The methods used for sample preparation were US-EPA 3050B and 3540C for mineral ions and PAHs respectively. The moisture content was also analysed. A minimum of 4.5 % and maximum of 99.5 % moisture were detected in the samples. The sludge that had stayed longer in their sampling points had low moisture contents than those that were sampled immediately after production. A total of 22-minaral ions were detected in the samples. When these were quantified an abundance trend that was found to be most common was: P>Ca>Fe>Al>Mg>K>Zn>Na>Mn>Cu>Ba>Cr>Pb>Si>Se>Sr>B>Ni>Mo>Co>Cd>Be. Phosphorous was the most abundant mineral ion in most of the samples apart from calcium, which was found to be abundant in a few cases. Comparing these results to the South African guideline limits, it emerges that most of the sewage works are compliant with the guidelines. The mineral ion that was found to be above the set limit in most occasions was selenium. The current South African guidelines were found to compare favourably to those of other countries. In the study 16 PAHs were also analysed, based on frequency of occurrence these were found to be: benzo(b)fluorathene ~ benzo(k fIuoranthene> phenanthrene> acenaphthylene> fluorine> naphthalene> benzo(a)anthracene> chrysene> acenaphthene> benzo(a)pyrene> fluoranthene> anthracene ~ pyrene> benzo(g,h,i)perylene> indeno(l ,2,3-cd)pyrene> dibenzo(a,h)anthracene Dibenzo(a,h)pyrene was below the detection limit in all the samples analysed while benzo(b)fluoranthene and benzo(k)fluoranthene were the most abundant compounds. All the samples analysed had concentration of benzo(a)pyrene below the South African limit of 2.53 mg kg"1. Comparing these guidelines with other international countries, South Africa specifies a single compound for monitoring while in other countries more than one compound is monitored. Thus South African guidelines need to be put in line with those of major EU countries such as Germany and Denmark with respect to PAH limits
A survey of organic pollutants in the South African sewage sludges.
No full textThesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.A comprehensive literature survey looking at different aspects of organic contaminants in sewage sludge is incorporated in the thesis. It is clear from the data available that plants do not take up most of the organic pollutants. However, a risk of contamination of the food chain exists when sludge is spread directly onto crops that are to be consumed raw or semi-cooked. The major source of human exposure to sludge-borne organic pollutants is through the consumption of animal products such as meat and milk through the bioaccumulation of compounds such as polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs), polychlorinated biphenyls (PCBs) or polynuclear aromatic hydrocarbons (PAHs). This is due to the ingestion of soil and sludge by livestock due to the spreading of sludge on the land used for grazing. Currently little is known about the plant uptake of phthalates and nonylphenols, which are present in relatively high levels in sludge. Included in the literature survey is a list of the most common methods normally used for extraction of organic compounds and the possible methods of analysis. What is noted is that there is no universally accepted and validated analytical method for analysing most of the organic compounds. In addition, data concerning levels of organic pollutants is scarce worldwide. The methods selected for this project were EPA Methods 35IOC (Liquid-liquid extraction) and 3540C (Soxhlet extraction) for the aqueous and solid sewage sludge respectively. These two methods were chosen because they are simple, inexpensive and effective. The chosen purification method was the sulfur clean-up process (EPA Method 3660B). This is because sulfur precipitates were observed in most of the concentrated extracts, especially from the solid samples. A total of 109 samples from 78 sewage works were extracted, using Soxhlet extraction for solids and liquid-liquid extraction for liquid samples. All the extracts were analysed using GC-MS. The identification of the organic compounds was made possible by the use of GC-MS Wiley library. A total of 712 organic compounds were identified in the South African sewage sludge. These included Phenols, Pesticides, PAHs, Phthalates, PCBs, Furans, Amines, Aldehydes, Esters, Acids, Chlorinated Hydrocarbons, Alcohols, Hydrocarbons and Others (all sorts of organic compounds that did not belong to the named categories). The extraction efficiency and reproducibility using a "clean" sludge matrix was carried out. The results showed that the method chosen for extraction i.e. Soxhlet method had an efficiency of over 80% and the results were reproducible. A total of 14 samples were selected for the quantification of p-cresol, nonylphenol and pesticides listed in the current legislation. The results showed negative results for pesticides, confirming that the pesticides listed in the legislation are not the compounds that need to be regulated as far as organic pollutants are concerned. The reasons for this are most likely due to the fact that most of the pesticides listed are banned or their use is severely restricted. The results for the quantification of p-cresol and nonylphenol, when comparing the liquid and the solid extracts of the liquid sludge, show that 99% of p-cresol is concentrated in the liquid phase. The opposite is true when looking at nonylphenol where 90% of it is trapped in the solid matrix leaving 10% in the liquid phase. It is also noted that liquid sludge contains high concentrations of both p-cresol and nonylphenol when compared to the solid sludge
Turning reactivity of platinum(II) complexes : a kinetic and mechanistic investigation into substitution behaviour of mono-and Dinuclear platinum(II) complexes.
No full textThesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.Systematic kinetic and thermodynamic analyses of the substitution reactions of different
Pt(II) complexes with a series of bio-relevant nucleophiles have been investigated as a
function of concentration and temperature, using standard stopped-flow and UV–Vis
Spectrophotometric methods. For this purpose, five different systems involving squareplanar
Pt(II) complexes, viz. (i) mononuclear Pt(II) complexes with tridentate nitrogendonor
ligands of varying degree of π-conjugation, and (ii) polynuclear Pt(II) complexes
with azine, pyridyl units separated by S, S-S and CH2CH2 spacer groups, and α,ω-
alkanediamine bridging ligands were synthesised and characterised by various
spectroscopic methods. All substitution reactions of the Pt(II) chlorido complexes of the
type [Pt(terpy)Cl]+ were studied in the presence of 10 mM LiCl to prevent spontaneous
parallel reaction due to hydrolysis or solvolysis. The substitution reactions of the
coordinated water molecules in the dinuclear Pt(II) complexes by thiourea nucleophiles
of varying steric hindrance were studied under acidic conditions. The concentration of
the nucleophile solution was prepared in 0.1 M NaClO4, at pH 2.0 and always at least 10-
fold excess to provide pseudo first-order conditions. The pKa values of the coordinated
aqua ligands of the dinuclear Pt(II) complexes were determined by Spectrophotometric
acid-base titrations. DFT calculations were also performed in an effort to account for the
observed reactivity of homologous analogues in each series of complexes, in terms of
NBO charges and energies of frontier molecular orbitals.
Substitution reactions of the Mononuclear Pt(II) complexes with tridentate ligands
showed reactivity of the complexes is controlled by the π–acceptor characteristics of the
chelate ligands. The fused rigid pyridyl system allows electronic interaction between the
platinum centre and the pyridyl ligands, because of the extended conjugated π-system.
This effect is controlled by how the fused ring system around the terpy moiety is
structured. The isoquinoline moiety was found to reduce the effective π-backbonding
and the lability of CH3PhisoqPtCl complex compared to 1,10-phenanthroline and
terpyridine systems, indicating that isoquinoline ligand is a net σ-donor.
The results obtained for the substitution reactions of the diaqua Pt(II) complexes with
the thiourea and ionic (Br-, I- SCN-) nucleophiles demonstrate that reactivity increases
with decreasing pKa values as well as decreasing distance between the Pt(II)centres. An
increase in steric crowding at the Pt(II) centre imposed by the methyl groups on the
azine linker decelerates the lability of the aqua ligands. The 1H and 195Pt NMR
spectroscopic results confirmed degradation of the aromatic-based bridging ligand from
the metal centre. The final cleavage of the complex linkers was only achieved after
addition of excessive amounts of thiourea and other strong nucleophiles. The negative
activation entropies and second-order kinetics for all the substitution reactions support
the Associative mode of substitution mechanism
A kinetic and mechanistic study on the substitution behaviour of mononuclear and dinuclear platinum (II) complex.
No full textPh. D. Chemistry. University of KwaZulu-Natal, Pietermaritzburg 2013.Abstract available in PDF file
A kinetic and equilibrium study of rooibos tea infusions.
No full textThesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998The total mineral ion concentration of Rooibos Tea was determined using ICP-OES. Significant concentrations of Na, K, Mg, Ca, P were found, and trace levels of Al, Fe, Mo, Sr, Zn, Ba, Cu and Pb detected. Protocatechuic acid, aspalathin and rutin were identified in Rooibos tea infusions analysed with HPLC. Analysis of tea samples by Ion Chromatography showed the presence of Cr and S042- ions. Rooibos Tea liquor had a pH of 4.6 once equilibrium had been reached. Partition coefficients (1.0 - 1.4 mm sieving fraction) for Na+, K+, Mg2+, protocatechuic acid, aspalathin, rutin, S042- and Cl were determined for infusions at 80 C using a graphical and a successive extraction method. A total mineral content method was also used to determine the partition coefficients for the mineral ions. The Na+, K+, Mg2+,SO42-, H2P04- (as P) and Cl ions as well as protocatechuic acid,
aspalathin and rutin all displayed first order behavior, allowing the determination of infusion rate constants. The particle size effect was investigated at 80 C. All the mineral ions showed an increase in infusion rate constant with decreasing particle size, protocatechuic acid and aspalathin showed no trend, while the rutin infusion rate constant was independent of particle size. Calcium uptake by the leaf was observed, this was more pronounced with the smaller particle sizes. Infusion rate constants and hence diffusion coefficients were determined for the nine species for temperatures ranging from 45 to 90 C. These diffusion coefficients for the mineral ions were compared with those for the respective species in aqueous media to give hindrance factors, which were of the order of 102. Except for Cl, all hindrance factors increased with an increase in temperature. The infusion rate constants for all the species at the various temperatures were fitted to an Arrhenius equation and activation energies of infusion determined. The values were lower than those predicted theoretically
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