Planococcus C.C.M. 316, a gram-positive facultative marine halophile, was studied with respect to growth and membrane composition of cells grown in media containing 0.5%, 3% and 10% sea salt. Membranes were prepared from cells grown in the three sea salt concentrations and analysed to determine any changes which may have been caused by the increasing concentrations of salt in the growth media. The three membrane preparations were found to have similar compositions to those reported for other gram-positive cocci. Cells grown in the 3% sea salt concentration contained membranes with a higher protein:lipid ratio and RNA content than the membranes from cells grown in the 0.5% and 10% concentrations. Amino acid analysis of the membrane proteins showed that the composition remained virtually unchanged in the three membrane preparations. The ratio of acidic: basic amino acid residues was nearer to the figures reported for non-halophiles than for those of the extreme halophiles. Examination of the lipids showed that phospholipids predominated to the extent of about 70% of the total lipids. Cardiolipin and lysocardiolipin were the major phospholipids, with phosphatidyl ethanolamine, phosphatidyl glycerol and phosphatidyl serine present as minor components. Glyco-lipids were found to decrease with increasing sea salt concentration in the medium, and in all three membrane preparations constituted only a very small proportion of the total lipids. Neutral lipids contained long chain alcohols, mono-, di- and tri-glycerides, as well as relatively large amounts of the isoprenoid compound squalene. The major fatty acid associated with the lipids was a branched saturated C15 acid which constituted 50 - 7% of the total fatty acids in most fractions. Although increasing salt in the medium produced changes within the proteins and lipids in the membranes, these changes were not such that they could be interpreted as an increase in the halophilic nature of the membrane. The carotenoids were shown to be derived from beta carotene and to consist mainly of 3'hydroxy 4' oxo compounds, although the extent of polar substitutions was dependent on both culture age and the concentration of salt in the medium.

The transporting properties of MDCK cells have been investigated upon epithelial monolayers grown upon permeable filter supports and mounted in Ussing chambers. When mounted without edge damage epithelial monolayers of MDCK cells (strain I) exhibited a transepithelial electrical resistance of 7.9 kO.cm2 and supported a small open-circuit potential (5.9 mV, basal-lateral surface positive) and a small short circuit current in agreement with the small magnitude of the net Na+, K+ and Cl- fluxes. Addition of adrenaline to the basal-lateral, but not the apical bathing solution stimulated a net basal-lateral to apical Cl- secretion, the magnitude of which accounted for the adrenaline stimulated short circuit current response. The Cl- secretion in MDCK cells exhibited many of the features of Cl- secretion in natural epithelia including sensitivity to the loop diuretics: furosemide, bumetamide and piretanide. In a number of secretory epithelia Cl- is accumulated across the basal-lateral cell border by a diuretic sensitive Na+K+Cl cotransport system. A comparison of the actions of the loop diuretics upon adrenaline stimulated Cl secretion and upon the cotransport system in MDCK cells provided strong but indirect evidence for a central role of the cotransport system in Cl secretion across MDCK cell monolayers. Measurement of influx and efflux across the apical and basal-lateral cell border demonstrated that the apical cell border was relatively impermeable to K. Influx across the basal-lateral border consisted of three major compenents; a ouabain sensitive , pump mediated, component; a diuretic sensitive component and a ouabain and diuretic insensitive flux component. K efflux across the basal-lateral cell border also consisted of these three components. Addition of adrenaline, ATP or A23187 to MDGK cells resulted in a transient stimulation of K+ efflux across both cell borders, although flux across the basal-lateral cell border was of greatest quantitative importance. Stimulation of K efflux was dependent upon the presence of Ca2+ in the external media and exhibited a similar pharmacology; sensitive to quinine and TEA, but insensitive to inhibition by apamin, as Ca2+-dependent K permeability?s in other, natural epithelia. Identification of an adrenaline stimulated Cl- secretory mechanism, a coupled Na + K + Cl cotransport system and a Ca2+-dependent K permeability in high resistance MDCK cells supports their use a model epithelium for the study of epithelial cell function.

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Philosophiae Doctor - PhD / A fuel cell is an energy device that converts chemical energy to electrical energy. Low temperature fuel cells, namely the hydrogen fuel cell and the direct methanol fuel cell are preferred amongst other fuel cell types for stationary and vehicular applications, due to their small size and their low operating temperature. The direct methanol fuel cell has several advantages over the hydrogen fuel cell including ease of transport and storage since methanol is a liquid. Since methanol is used directly in the cell there is no need for a reforming process, which results in a less complicated system. However, direct methanol fuel cell are in their infancy and many problems need to be overcome before reaching commercialization. The direct methanol fuel cell has several disadvantages, namely, the sluggish methanol oxidation reaction, the high cost of state-of-the-art proton exchange membranes, the high methanol permeability from anode to cathode and the dependence on the conductivity on membrane water content, which limits their use to temperatures below the boiling point of water, while the need is to work at high temperatures. Attempts to overcome the disadvantages of the state-of-the-art membrane were made in this study, including the development on novel proton exchange membranes and also the modification of existing state-of-the-art membranes. / South Africa

Magister Scientiae - MSc / For a direct methanol fuel cell (DMFC), the proton exchange membrane must conduct protons and be a good methanol barrier. In addition to the high methanol permeability achieved by these membranes, they are very expensive and contribute greatly to theoverall cost of fuel cell set up. The high cost of the DMFC components is one of the main issues preventing its commercialization. The main objective of this study was thus to produce highly proton conductive membranes that are cheap to manufacture and have low methanol permeability. / South Africa

This work is the subject of an EPSRC-Tioxide Industrial CASE Award, the principal area of study being factors affecting the achievable steady state permeate flux during the crossflow microfiltration of concentrated titania dispersions. The performance of this continuous thickening process is of particular interest to Tioxide as a potential alternative to current batch filtration processes, which delay the manufacturing process.

The living organisms are varied when viewed from a macroscopic perspective, but on the molecular level they function based on the same fundamental principles. All living organisms are compartmented into cells via cellular walls made of lipid membranes. Through the wall the cell needs to transport nutrients, waste, genetic information and signaling molecules. The cell achieves this task via passive and active transport. In this thesis we focus on passive transport processes. In Chapter 1 of this thesis I introduce the topic of passive transport and its importance for biological systems. In Chapter 2 I use fluorescence methods to determine the passive transport of molecules with self intrinsic fluorescence through lipid membranes. We have built a unique fluorescence microscope which is capable of visualizing the fluorescence of molecules excited with deep UV light. With this new tool we monitored passive transport through the lipid membrane for several biologically significant molecules like for example the bacterial signal indole. Indole is an organic compound linked to important cellular processes like bacterial growth rates and cellular morphology. It is believed that indole is actively transported through the membrane of Escherichia coli via influx and efflux pumps. Here we give an unambiguous proof that indole can freely diffuse through intact bacterial lipid membranes. We extend this study to other molecules with self intrinsic fluorescence , like for example the antibiotic norfloxacin and the fluorescent dye fluorescein. We show that both these molecules can undergo passive transport through the lipid membrane.