Artificial lipid membranes have been used in biophysical studies as well defined models of biological membranes. In the present work we studied adsorption of ions to artificial lipid membranes, composed of phosphatidylcholine (PC) and phosphatidylserine (PS), and to biological membrane from sarcoplasmic reticulum (SR). The studies of ion adsorption and electrokinetic characterization of membranes were done by means of microelectrophoresis of PC/PS liposomes and SR vesicles. The ions of interest were positively charged potassium (K), calcium (Ca), tetraphenylarsonium (TPAs), tetraphenylphosphonium (TPP) and negatively charged pentachlorophenol (PCP). Electrophoretic mobility of PC/PS liposomes and SR vesicles has been measured as a function of pH, ionic strength and the concentration of adsorbing ions. From the data we have determined the isoelectric point and the density of electric charge of the SR membrane. We have shown that the mobility of PC/PS liposomes and SR vesicles can be understood in terms of electrostatic screening of membrane surface charge by the diffuse double layer of counterions and by ion adsorption. The experimental results, with the exception of Ca and SR membranes, have been found consistent with the adsorption model based on Langmuir adsorption isotherm and Grahame's equation relating the membrane electric potential and the membrane surface charge. The adsorption of ions to membranes have been characterized by the ion association constant and the membrane surface area of adsorption site. These quantities have been obtained from the fit of the adsorption model to the electrophoretic mobility data and the results are reported in the thesis. The following two findings are most interesting and important. First, the adsorption of K and lipophilic ions TPAs, TPP, and PCP to both the SR membrane and the artificial PC/PS membrane can be well characterized by the the adsorption model. The theoretical predictions of the adsorption model agree with the experimental results for a single (although different for PC/PS and SR membranes) set of ion adsorption constant and adsorption site area. This indicates a similarity between the biomembrane and the artificial lipid membrane. In contrast, such similarity was not found for calcium. Adsorption properties of SR membrane and artificial lipid membrane for Ca were found to be very different. Whereas the adsorption of Ca on PC/PS membranes could be described by one set of adsorption sites, the results for the SR vesicles indicate the presence of more than two types of Ca adsorption sites in the SR membrane. This finding is of physiological significance since the SR membrane regulates calcium transport in the muscle cell. Second, the adsorption affinity of SR membrane to all ions has been found to be significantly smaller compared to that of the lipid bilayer. This indicates that membrane proteins in the SR membrane reduce ion adsorption. This effect cannot be due to electrostatic interactions because the artificial lipid membranes had similar surface charge density as the biological membrane and the reduced adsorption was observed for both the positively charged TPAs and TPP as well as for the negatively charged PCP.

Abstract not available

No description available.

One of the primary concerns with space travel is the protection of astronauts from potentially lethal radiation. A major source of potentially lethal radiation is our own sun. During Solar Cycle 23 there were 97 detected Solar Particle Events (SPEs). In order to develop radiation protection guidelines and establish methods to protect astronauts the spectrum of particles emitted during a SPE must be understood. Data for oxygen and iron particle fluence was taken from the Solar Isotope Spectrometer. The fluence was sorted and formatted for each solar particle event. After determining the contribution to skin dose for oxygen, the time evolution of each event was analyzed. After analyzing the raw count data, a threshold was set that could be applied to each event. Using this threshold count rate as the starting point, each event was plotted and fitted with a smoothing polynomial function. The slope calculated from this function was then plotted against the previously calculated skin dose and a Weibull function was fitted to the data. The resulting plot provides a method to predict the cumulative dose due to the oxygen fluence over the first 24 hours of an event and thereby provide a warning of future high dose rate in time to achieve significant dose sparing for most events. For the ten events that delivered the highest oxygen dose, the dose sparing that could be achieved by taking shelter when the high dose rate was predicted was greater than 70 percent for all but one event. The one outlier achieved a dose paring of only 57 percent.

Thèse de doctorat : Science et ingénierie des matériaux : Vandoeuvre-les-Nancy, INPL : 2005. / Titre provenant de l'écran-titre. Bibliogr.

Reproduction de : Thèse de doctorat : Chimie-Physique : Metz : 1993. / Titre provenant de l'écran-titre. Notes bibliographiques. Index.

Reproduction de : Thèse de doctorat : Physique des matériaux : Lyon 1 : 2005. Reproduction de : Thèse de doctorat : Physique des matériaux : Université de Turin : 2005. / Thèse soutenue en co-tutelle. Thèse en anglais. Titre provenant de l'écran titre. 129 réf. bibliogr.

Thesis (M.S. in E.A.S.)--School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 2004. Directed by Michael H. Bergin. / Includes bibliographical references (leaves 53-56).

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: Brian J. Bahnson, Dept. of Chemistry & Biochemistry. Includes bibliographical references.

Thesis (Ph. D.)--University of Oregon, 2003. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 235-246). Also available for download via the World Wide Web; free to University of Oregon users.