Thesis (Ph.D.)(Geography)--University of Pretoria, 2004. / Title from opening screen (viewed 13 December 2005). Includes summary. Includes bibliographical references.

Thesis (Ph.D.)--Montana State University--Bozeman, 2004. / Typescript. Chairperson, Graduate Committee: Edwin H. Abbott. Includes bibliographical references (leaves 264-268).

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 200-218).

It is generally accepted that platinum antitumour drugs bind, preferentially, to Guanine N7 in DNA. Thus the kinetics of formation and the energetics of dissociation of platinum-nitrogen bonding have been investigated, using simple model bases, namely pyridine. pyrimidine. purine and some derivatives. Six complexes of the type cis-PtCl2L2, where L is a N-heterocycle, have been successfully prepared and characterized. The kinetics of the reaction between K2PtCl4 and the N-heterocyclic bases in aqueous solution have beeD studied. This was best achieved by pre-aquating the PtCl4(2-) and measuring the decrease in concentration of platinum or ligand by AA or UV spectroscopy respectively. It was found that the rate of reaction is second order, the rate being dependent on the concentration of both platinum complex and the ligand. The substitution of ligand takes place by direct replacement, involving an associative S.2 mechanism. It was found that the activation entropy and the activation energy for the reactions of platinum complexes in solution are strongly correlated. The energetics of platinum-nitrogen bond dissociation were followed using thermogravimetric analysis. Quantitative data, which enabled calculation of the activation energy for the decomposition process involving the loss of one molecule of ligand was obtained from isothermal studies. No correlation was found between the solid state studies, involving bond breaking, and the syntheses of the complexes, probably because in solution the reaction is complicated by solvent effects. Theoretical studies, which involved Molecular Orbital calculations on the N-heterocyclic bases themselves, were also carried out in an attempt to correlate the kinetic and energetic parameters with the electronic structure of the ligand. Several correlations were attempted but only one was found. This was the relationship between the solid state decomposition energy and the LUMO energy of the quarternized base.

Despite their ubiquitous use, Pt(II) anti-cancer drugs still suffer from many issues such as off-drug target effects, renal and nephrotoxicity as well as acquired and intrinsic drug resistance. To obtain a better understanding of how to mitigate these deleterious effects can be mitigated we first must know all the targets of these drugs. Highlighted in this dissertation is previous work performed by groups exploring the localization of Pt in cells using fluorescence microscopy. While Pt drugs such as cisplatin contain no native fluorescence, a great deal of work has been done to covalently modify complexes with fluorescent tags. From studies using this technique, it been reported that Pt can target a number of compartments within the cell ranging from the nucleus to the cytoplasm. With each different derivative being observed in varied cell lines it becomes difficult to deconvolute a universal pattern to where Pt localizes, furthermore, the connected fluorophore could also bias Pt localization. To add general functionality and eliminate the bias of a pre-tethered fluorophore our lab has developed a number of different azide and alkyne-modified complexes that append a “reactive handle” to Pt compounds. This modification allows for use of the bioorthogonal azide-alkyne click reaction we are able to observe Pt localization after treatment. The focus of this work includes method development to conjugate a fluorophore to our Pt complexes in vitro and in cell cultures. We examined a number of different cell lines and observed frequent localization in the nucleolus of the cell. Also in this work is the development of methods to append multiple fluorophores to each Pt site to increase our ability to visualize these complexes in cells. Finally, we have also constructed a new Pt-azide that exhibits slower exchange kinetics due to a chelating exchangeable group. The use of this new complex will enable studies to determine whether changing the leaving group results in differential localization of Pt drugs in cells.

Methods to map small-molecule interactions with cellular RNAs are important for understanding endogenous activation, such as in riboswitches, as well as the potential for exogenous compounds to target RNA. Cisplatin is one of the most widely used of the platinum anticancer drugs that are prescribed in approximately 40-50% of all chemotherapy treatments (Dyson and Sava, 2006; Harper et al., 2010). Despite nearly 40 years of experience with this class of drugs, we still lack a comprehensive understanding of the targets of Pt compounds and their effects on cells. Pt(II) compounds are well-known DNA and RNA crosslinking agents, but the latter area is under-studied. In order to better understand the impacts of cisplatin and other platinum(II)-derived small molecules on cellular RNA, we have developed a technique we call “Platinum-seq,” which couples reverse transcription mapping of platinated RNAs to high-throughput sequencing. Chapter 1 is a study of cisplatin and a novel click-functionalized platinum compound (2-ADAP Pt) binding to the HDV ribozyme, a small catalytic RNA. Chapter 2 moves our platinum mapping approaches from low-throughput, sequencing gel based methods into next-generation sequencing for high-throughput analysis of all platinum sites in cellular RNA, a method we have named “Platinum-seq.” Chapter 3 is a study of differential gene expression of Saccharomyces cerevisiae treated with cisplatin and a second novel platinum(II) compound (azaplatin), using data acquired from the work in Chapter 2. Chapter 4 describes recent efforts to implement pre-enrichment of sequencing targets using click chemistry followed by DNA hybridization, in order to enrich for platinated fragments before sequencing library construction. Together, this work represents a significant step forward in advancing analysis of Pt(II) binding to cellular RNA, a potentially important target for this widely used class of anticancer compounds. Methods developed here are broadly applicable to genome-wide identification of platinum accumulation on DNA as well, which has not been pursued despite the extensive use of these compounds.

No description available.

Magister Scientiae - MSc / The particles of the Pt metal were well dispersed on carbon nanotubes when EG was used and in isopropanol poor dispersion was observed and no further investigation was done on them. The platinum wt% on the supports observed from EDS was 21.8, 19.10 and 16.74wt% for Pt/EMWCNT, Pt/LPGCNT and Pt/ commercial CNT respectively. Pt/LPGMWCNT showed high electro-catalytic activity of 2.48 mA and active surface area of 76 m2/g, toward oxygen reduction, observed from cyclic voltammogram in iv sulfuric acid. Pt/LPGMWCNT also showed better tolerance toward methanol, however it was not highly active towards methanol, and hence the methanol oxidation peak current observed between 0.75 and 08 potential was the smallest. In this study a wide range of instruments was used to characterize the properties and behavior of Platinum nanoparticles on multi-wall carbon nanotubes. To add to the already mentioned, Scanning electrochemical microscopy (SEM), proton induced x-ray emission (PIXE), scanning electrochemical microscopy (SECM) and Brunauer-Emmett Tellar (BET) were also used. / South Africa

Efforts to discover an efficient yet environmentally friendly mode of metal nanoparticle (NP) synthesis are increasing rapidly. A ‘green’ route that avoids the high costs, toxic wastes and complicated protocols associated with chemical synthesis methods is therefore highly sought after. A biologically based protocol will provide the possibility of gaining control over the mechanism merely by manipulating the experimental conditions of the system. Given that the properties of nanoparticles are highly dependant on the morphology of the particles themselves, this mechanistic control will provide significant industrial advantages with regards to tailoring specific properties of the nanoparticles produced. The key objectives of this study were to: a) determine whether a consortium of sulfate-reducing bacteria was capable of platinum nanoparticle synthesis, b) elucidate the bioreductive, enzymatic mechanism responsible, and c) attempt to control the morphologies of the particles produced. A consortium of sulfate-reducing bacteria (SRB), isolated from sewage sludge, was used in these investigations due to the advantages a consortium provides in comparison to pure cultures. The syntrophic relationships established within the constituent species not only prevent the growth of contaminant microbes, but increases the oxygen-tolerance of the system as a whole. The sulfate-reducing consortium was shown to possess an aerobic mechanism for Pt(IV) reduction which, though different from the anaerobic bioreductive mechanism previously identified in literature, did not require an exogenous electron donor. It was demonstrated that the Pt(IV) ion becomes reduced to Pt(0) via a two-cycle mechanism involving Pt(II) as the intermediate. Further investigation elucidated the reduction of Pt(IV) to Pt(II) to be dependant on a novel Pt(IV) reductase which becomes upregulated in the presence of Cu(II), while the reduction of Pt(II) to Pt(0) occurred by means of a periplasmic hydrogenase. To our knowledge, this is the first time a coupled mechanism for Pt(IV) reduction by micro-organisms has been proposed. A cell-free, crude protein solution from the consortium produced both geometric and irregular platinum nanoparticles. The wavelength of 334 nm was chosen as a nonquantitative indicator of Pt(0) nanoparticle formation over time. The optimum conditions for nanoparticle synthesis were pH 9.0, 65 ˚C and 0.75 mM Pt(IV) as H2PtCl6 salt. In the absence of a buffer a Pt(IV) concentration > 1 mM resulted in the precipitation of protein-nanoparticle bioconjugates, due to unfavourable acidic conditions. This demonstrated that the nanoparticles were binding to and becoming stabilised by general protein in the cell-free solution. Upon addition of a sodium-bicarbonate buffer, a general increase in Pt(IV) reduction to Pt(II) was observed. The addition of the buffer also resulted in an unexplained change in particle morphology and for this reason was not used in subsequent investigations. Polyvinylpyrrolidone (PVP) was shown to compromise the reduction rate of the Pt(IV) ion by SRB cells. The presence of extracellular NP’s was suggested by the colour of the supernatant turning brown and the A334 increasing over time. Attempts to visualise the particles by transmission electron microscopy (TEM) resulted in an unexpected phenomenon where nanoparticles could be observed to form dynamically upon irradiation by the electron beam. Extended irradiation by the electron beam also resulted in structural changes of the particles occurring during observation. An increase in temperature was shown to increase the reduction rate which in turn resulted in particles decreasing in size. The starting pH was shown to have a significant effect on the reduction rate and particle morphology although specific trends could not be identified. In conclusion, the cell-soluble extract from the sulfate-reducing consortium investigated, is capable of Pt(0) nanoparticle synthesis. Precise control over the particle morphology was not attained although the mechanism was further clarified and optimal conditions for nanoparticle synthesis were determined.

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