Electrostatic Interactions at Membrane-water Interfaces and Distribution of 2, 4, 6-Trichlorophenol in a Membrane Model System

• Main Author: Sieder, Isolde
• Format: Others
• Published: PDXScholar 1995
• Subjects: Ionization > Computer simulation; Membranes (Biology); Phenols; Physics
• Online Access: https://pdxscholar.library.pdx.edu/open_access_etds/5087; https://pdxscholar.library.pdx.edu/cgi/viewcontent.cgi?article=6159&context=open_access_etds

It is generally accepted that biological membranes consist of a lipid bilayer matrix with proteins incorporated into the lipid bilayer. Typically, these membranes are negatively charged due to the presence of negatively charged lipids in the bilayer as well as negatively charged molecular groups on proteins. Biologically active molecules, such as environmental pollutants, enter the membrane from the aqueous phase by adsorption or partitioning into the lipid bilayer. The thesis consists of two parts. Part I is a computational study of spatial distribution of electric potential in the aqueous portion of the membrane-water interface using two models of charge distribution: (i) the discrete charge model, in which charges are located on a square lattice either on the surface or embedded in the membrane: (ii) the continuous charge density (smeared charge), Gouy-Chapman, model in which the charge is assumed to be evenly spread on the membrane surface. The computed distributions of electric potential are used to predict spatial distributions of positively charged hexavalent cation of Ruthenium Red (RuR) at the membranewater interface. It was found that anomalous behavior of RuR cannot be explained by this version of the discrete charge theory. Part II is concerned with the distribution of ionized and un-ionized species of 2,4,6-Trichlorophenol (2,4,6-TrCP) in octanol-water system, which is often used as an experimental model for predicting the distribution of toxic chemicals in the environment. In this experimental study we obtained the pH dependence of the total distribution coefficient of 2,4,6-TrCP from which the octanol water partition coefficients of the un-ionized and ionized species were determined. We compared the octanol-water partition coefficient of several chlorophenols with experimental data on adsorption of ionized chlorophenols to lipid membranes. It was found that the membrane-water partition coefficient of ionized 2,4,6-TrCP is about 240 greater than that predicted from the octanol-water system. This finding supports the hypothesis that octanol-water partition coefficients cannot be used for predicting concentrations of ionized species of chlorophenols in lipid membranes.