The use of ions to control the charge and phase behavior of phospholipid membranes

The object of this thesis is to probe lipid-lipid interactions by examining the phase behavior of simple phosphatidic acid mixtures and “lipid raft” mixtures as a function of bulk pH and ion concentration, which are physiologically relevant control parameters. The results are organized in five chapters as follows. Chapter 1 provides an overview of biological lipids, their phase behavior and the parameters that affect it, and the electrostatics of charged surfaces. The materials and methods used in this work are presented in chapter 2. Chapters 3 and 4 explore the responses of PA/PC bilayers to simultaneous and sequential changes in KCl and CaCl2 concentrations, respectively, at different pH values. Finally, chapter 5 examines the miscibility transition of “lipid raft” mixtures as a function of bulk NaCl concentration