Sodium ion internalized within phospholipid membranes

[super 23]Na NMR evidence is provided showing that sodium ions can locate itself inside the actual phospholipid bilayer. A vesicular membrane composed of a conventional phospholipid (1-palmitoyl-2-oleoyl phosphatidylcholine or POPC) admixed with a lesser amount of a 'designer' phospholipid that possesses ester groups along its normally all-hydrocarbon chains is used to show that the ester groups create membrane 'pockets' in which sodium ions reside.