ABSTRACT
To comprehend ion binding to phospholipid molecules or to phospholipid membranes, the behavior of ions in bulk solution and in the vicinity of a membrane-solution interface should be understood. These ions play a fundamental role in the ionization of phosphatidylcholine molecules, for example, as in this case the supplementary electron comes from the trimethylammonium nitrogen. Protonation or deprotonation of the phospholipid headgroups changes the chemical nature and net charge of the lipid bilayers. It also may affect crucially the molecular conformation and hydrogen bonding capabilities of the individual lipid molecules and may modify the colloidal properties of the lipid aggregates, phospholipid phase transitions, lipid bilayer interactions with protein molecules. Binding of inorganic anions to phospholipid membranes is less well explored than the association between lipids and cations. In spite of this, there is convincing evidence that the binding of anions to lipid bilayers is as strongly affected by electrostatic forces as lipid-cation association.
