Thesis (M.Sc. (Biochemistry)) --University of Limpopo,1998 / Refer to document

Thesis (M.Sc. (Chemistry)) --University of Limpopo, 2007 / The biochemical mechanism of apoptosis induced by lithium remains unclear, although there is evidence suggesting the involvement of Bax and Bcl-2. Bcl-2 family of proteins play a critical role in the regulation of apoptosis in various tumour cell lines. This pathway may be altered in cancer cells. We have used calyculin-A (CL-A), an inhibitor of protein phosphatase 2A (PP2A), to investigate the mechanism by which lithium induces apoptosis in HL-60 cells. Previous studies in our laboratory established that lithium induces apoptosis of HL-60 cells at 10 mM and above; while CL-A induces apoptosis at 1 nM and above. The observed apoptotic effects were additive. These observations led to the hypothesis that lithium and CL-A exert their biological effects by acting on a similar target. It was, therefore, the aim of this study to establish whether lithium would also exert similar inhibitory effects on the apoptotic and cell cycle regulatory genes. We further aimed at delineating the effects of both lithium and CL-A on the expression profiles of apoptotic and cell cycle regulatory genes. In this study, HL-60 cells were treated with lithium, CL-A and the combination of both. This was followed by the assessment of cell proliferation and viability at specific time points, using Coulter Counter and trypan blue dye exclusion assay, respectively. Concentrations of lithium at 10 mM and 20 mM were found to inhibit cell proliferation and exerted modest effects on cell viability in a time- and dose-dependent manner. Likewise, CL-A inhibited cell proliferation and viability in a time- and dose-dependent fashion. The combination of lithium and CL-A showed additive inhibitory effects on the growth of HL-60 cells. Further, semi-quantitative RT-PCR analyses of apoptotic (bax and bcl-2) and cell cycle regulatory genes (cdc2 and cyclin-B1) were determined. Our data revealed an under-expression of bcl-2 mRNA and an up-regulation of bax mRNA in HL-60 cells treated with lithium, CL-A and the combination of both. In addition, the expression levels of cdc2 mRNA remained constant, while cyclin-B1 mRNA expression levels were up-regulated after 24 h in HL-60 cells that were treated with cytotoxic concentrations of lithium and CL-A alone. Furthermore, the combination of lithium and CL-A showed an up-regulation of cyclin-B1 mRNA while cdc2 mRNA levels remained constant in both treated and untreated HL-60 cells. To corroborate the RT-PCR data, we present evidence by Western blot analysis that Bcl-2 family of proteins and cell cycle regulatory genes indeed play a critical role in the regulation of apoptosis in HL-60 cells. Western blot analysis revealed a down-regulation of Bcl-2 under all treatment conditions. However, lithium and CL-A alone failed to show any detectable expression levels of both Bax and cyclin-B1 proteins. In contrast, the combination of both lithium and CL-A showed an up-regulation of Bax and Cdc2 proteins in HL-60 cells. These findings suggest that the molecular mechanism elicited by lithium, CL-A and the combination of both on the growth inhibition of HL-60 cells involves an aberrant expression of apoptotic and cell cycle regulatory genes. In addition, these observations may allude to a notion that both lithium and CL-A may be used and administered successfully as positive alternative anticancer drugs. / the National Research Foundation,and the University of Limpopo Research and Administration

Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xi, 125 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 121-125).

Thesis (M.S.)--University of Michigan, 1985.

Thesis (M.S.)--University of Michigan, 1985.

>Magister Scientiae - MSc / Spinel lithium manganese oxide (LiMn2O4), for its low cost, easy preparation and nontoxicity, is regarded as a promising cathode material for lithium-ion batteries. However, a key problem prohibiting it from large scale commercialization is its severe capacity fading during cycling. The improvement of electrochemical cycling stability is greatly attributed to the suppression of Jahn-Teller distortion (Robertson et al., 1997) at the surface of the spinel LiMn2O4 particles. These side reactions result in Mn2+ dissolution mainly at the surface of the cathode during cycling, therefore surface modification of the cathode is deemed an effective way to reduce side reactions. The utilization of a nanocomposite which comprises of metallic Cu and Au were of interest because their oxidation gives rise to a variety of catalytically active configurations which advances the electrochemical property of Li-ion battery. In this research study, an experimental strategy based on doping the LiMn2O4 with small amounts of Cu-Au nanocomposite cations for substituting the Mn3+ ions, responsible for disproportionation, was employed in order to increase conductivity, improve structural stability and cycle life during successive charge and discharge cycles. The spinel cathode material was synthesized by coprecipitation method from a reaction of lithium hydroxide and manganese acetate using 1:2 ratio. The Cu-Au nanocomposite was synthesized via a chemical reduction method using copper acetate and gold acetate in a 1:3 ratio. Powder samples of LiMxMn2O4 (M = Cu-Au nanocomposite) was prepared from a mixture of stoichiometric amounts of Cu-Au nanocomposite and LiMn2O4 precursor. The novel LiMxMn2O4 material has a larger surface area which increases the Li+ diffusion coefficient and reduces the volumetric changes and lattice stresses caused by repeated Li+ insertion and expulsion. Structural and morphological sample analysis revealed that the modified cathode material have good crystallinity and well dispersed particles. These results corroborated the electrochemical behaviour of LiMxMn2O4 examined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The diffusion coefficients for LiMn2O4 and LiMxMn2-xO4 obtained are 1.90 x10-3 cm2 / s and 6.09 x10-3 cm2 / s respectively which proved that the Cu-Au nanocomposite with energy band gap of 2.28 eV, effectively improved the electrochemical property. The charge / discharge value obtained from integrating the area under the curve of the oxidation peak and reduction peak for LiMxMn2-xO4 was 263.16 and 153.61 mAh / g compared to 239.16 mAh / g and 120 mAh / g for LiMn2O4. It is demonstrated that the presence of Cu-Au nanocomposite reduced side reactions and effectively improved the electrochemical performance of LiMn2O4.

<p>The widespread commercialization of electric vehicles is currently hindered by their inability to compete with conventional gasoline-powered vehicles in terms of refueling time. The main barrier to achieving fast charge of lithium-ion batteries is the plating of metallic lithium on the surface of the graphite negative electrode, which is known to occur most prevalently at high C-rates, low temperatures, and high states of charge (SOC). While it is accepted that the lithium plating process is largely reversible, the factors affecting the reversibility of lithium plating have not been thoroughly investigated. This work seeks to determine the most influential factors affecting the reversibility of lithium plating in order to devise strategies to mitigate long-term damage to the cell if lithium plating has been detected. It was determined that the temperature during the rest phase following plating has the most significant influence on plating reversibility, with cells undergoing rest at 30 ℃ exhibiting nearly twice the Coulombic inefficiency of cells undergoing rest at 0 ℃. Additionally, a novel technique was developed to observe the relaxation processes directly in a graphite electrode just after lithium plating has occurred. The occurrence of electrochemical stripping and the dissolution of overshooting phases in graphite were verified through direct <i>in-situ</i> observation. A two-part model is presented to describe the progression of the relaxation processes in graphite after lithium plating occurs under high rate operation.</p>

Lithium batteries have revolutionized emerging electronic applications and will play more important roles in the future. Unfortunately, the energy density of commercial lithium-ion batteries (100-265 Wh kg-1) cannot satisfy the fast-growing demand for energy storage technologies. Lithium-sulfur (Li-S) batteries stand out for high energy density (2567 Wh kg-1), low-cost, and environmentally benign attributes. However, the development of Li-S full-batteries is still hindered by the dissolution of polysulfides into the organic electrolytes and poor ions transfer at the interfaces of electrolytes and lithium-intercalated electrodes (e.g., lithiated graphite). Improving the electrolytes is a crucial aspect for the development of battery technologies, but the knowledge concerning the electrolyte microstructures remains elusive. This dissertation unravels the microstructures of organic electrolytes and paves the way to the development of Li-S batteries. Firstly, we demonstrate the key role of electrolyte chemistry in the battery performances by showing a synergetic effect of electrolytes coupled with designed sulfur cathodes. Secondly, we investigate the microstructure of electrolytes and discover previously unexplored solvent-solvent and solvent-anion interactions. We show that the interactions are useful to elucidate important battery operations, such as ions transfer at electrolyte-electrode interfaces, and reveal a potential probe for developing battery electrolytes. Thirdly, we optimize the electrolyte composition to obtain a highly reversible Li+ intercalation/deintercalation at the graphite anode, giving high performances of Li-S full-batteries in a dilute electrolyte concentration. Finally, we unravel the key role of additives in suppressing Li+ solvation in the electrolytes. Nitrate (NO3-) anions are observed to incorporate into the solvation shells, change the local environment of Li+ cations, and then lead to an effective Li+ desolvation followed by improved battery performances. Key significances of this dissertation are (i) observation of detailed electrolyte microstructures showing a potential probe for developing battery electrolytes; (ii) evidences of the electrolyte chemistry plays a predominant role in the electrolyte-electrode interfacial reactions, which prevails over the role of commonly believed solid electrolyte interphase (SEI); and (iii) new mechanistic insights into the key role of additives in the electrolyte microstructures. Furthermore, the presented methodology paves the way for developing electrolytes for broad electrochemical applications.

No description available.

No description available.