Effects of Lithium and Other Monovalent Ions on Palmitoyl Oleoyl Phosphatidylcholine Bilayer.

Interactions of monovalent salts with lipid membranes are explored with molecular dynamics (MD) simulations. The simulations included the monovalent ions Na+ and K+, for their importance in physiology, Li+ for its small size and importance in several medical conditions including bipolar disorder, and Rb+ for its large size. All simulations included Cl- as counterions. One bilayer was simulated without salt as a control. Palmitoyl oleoyl phosphatidylcholine (POPC) bilayers experienced reductions in area per lipid with the addition of salt; the smaller the ion the smaller the area, with the exception of Li+. Li+ exhibited unique binding affinities between phosphates and sn-2 carbonyls that lowered the order of the top part of sn-2 chain, which increased the area per lipid, compared to other ionic simulations. Further, we observe that monovalent salts alter bilayer properties through structural changes and not so much through the changes in surface potential.