Solute partitioning into model biological membranes studied with time-resolved emission spectroscopy and calorimetry

Abstract

Bioaccumulation and bioconcentration are terms used to quantify the concentration of the solute in an organism with respect to the source of exposure. Empirical values are commonly used to predict a solutes tendency for bioconcentration. While they are useful zeroth order indicators, empirical values lack the chemical specificity required to fully understand the exact solute-solute and solute-lipid chemical interactions that occur when a solute is introduced to a biological membrane. The work described here uses fluorescence spectroscopy and thermoanalytical techniques to quantify solute partitioning into model biological membranes. The model membranes used in this study are lipid bilayer vesicles that are analyzed as a function of temperature from the rigid gel-phase through the transition temperature and into the fluid liquid-crystalline phase. Studies described in this work seek to create a quantitative, mechanistic description of solute behavior in heterogeneous chemical environments. Each body of work either altered the solute used for partitioning or altered the membrane to add chemical complexity. The first body of work describes a proof-of-concept study analyzing the change in partitioning behavior from small structural changes in the solute. This study found that small changes to the solute affects membrane permeability in a way that is not accounted for in empirical models. The subsequent study sought to understand how the addition of amino acids to the membrane changes partitioning tendencies. Further analysis was done to study the partitioning behavior of amino acid L-Phenylalanine. Studies showed L-Phenylalanine integrates into the membrane and experiences a conformationally restricted environment. Additional studies were done on a pharmaceutical candidate and found membrane permeability does not correlate with drug activity. The drug was predicted to interact with the target-protein directly. Furthermore, analysis on the herbicide Dicamba has shown some indication of membrane interaction; however, more studies are required to fully understand the partitioning behavior.