Typescript. / Digitized by Kansas Correctional Industries

Biological cells and subcellular organelles are surrounded by membranes to form compartments performing specialized functions. Adsorption or partitioning of biologically active compounds into the membrane is the first step in the process of modification of cell function. This work is concerned with the problem of distribution of charged molecules between water and electrically charged membrane surface and between water and octanol. Part I of this thesis is focused on the electrostatic interactions taking place between charges on the membrane and ions present in the aqueous region of the membrane/water interface. The objective was to explore theoretically the origin of anomalous behavior of Ruthenium Red (RuR), a positively charged hexavalent ion. It was discovered in studies of RuR adsorption to negatively charged membranes that within the framework of the Gouy-Chapman theory of the membrane/water interface, RuR behaves as an ion with effective charge less than its physical charge. Moreover, the effective charge was found to be dependent on the density of electric charge at the membrane surface. Two theoretical models of the interfacial region were examined: the Rod Model and the Maximum Density Model. The Rod Model takes into account steric constraints imposed on RuR at the vicinity of the membrane surface. The Maximum Density Model attempts to account for non-ideal behavior by including repulsive interactions. These theoretical studies illustrate the consequences of finite size and ion-ion interactions of adsorption of large molecular ions to electrically charged membrane surfaces. Part II is an experimental study whose objective was to determine the partition coefficient of the negatively charged 2,3,4,5-tetrachlorophenol (TeCP) between water and octanol. The study was based on spectrophotometric measurements of the equilibrium concentrations of TeCP in water and octanol as a function of pH. The octanol/water partition coefficient for both the non-ionized and ionized species of TeCP were determined. It was found that the partition coefficient of ionized TeCP to lipid membrane is about 400 times greater than that for octanol. This result supports the hypothesis that the octanol/water partition coefficient of ionized chlorophenols cannot be used for predicting their distribution between water and lipid-bilayercontaining elements of the environment.