Addition Of Ln Research Articles

Surface potential effects on metal ion binding to phosphatidylcholine membranes. 31P NMR study of lanthanide and calcium ion binding to egg-yolk lecithin vesicles

31P NMR of phosphatidylcholine (lecithin) from egg-yolk in sonicated vesicles has been measured in the presence of various ions. Addition of Ln 3+ ‡ ‡ Ln 3+ refers to ions of the lanthanide series (At. Nos. 57–70). or Ca 2+ shifted the 31P resonance of the phosphate groups of the outer surface of the vesicles. These shifts were measured at varied lanthanide or Ca 2+ concentration at different ionic strengths obtained by addition of NaCl. The shifts induced by Tb 3+ and Ca 2+ have been analyzed using the theory of the diffuse double layer. Corrections were introduced for the effect of the ionic strength on the activities of the ions. The binding efficiency is shown to be controlled by the electrostatic potential produced by the bound cations at the membrane surface. This potential is slightly modified due to weak chloride binding. Binding constants have been derived.