Efficient sodium cation transport across liposome membranes using synthetic carriers

A series of 12 synthetic ionophores containing an amide subtituent connected via a methylene bridge to an aza-crown ring were evaluated for their ability to transport Na + across large unilamellar vesicles (LUVs) using dynamic 23 Na NMR spectroscopy. The structures contain lipophilic groups connected to the amide nitrogen, ranging in size from C 5 H 11 to C 18 H 37 , and are either tertiary or secondary amides. The crown ether ring size was also varied from 12-C-4 to 15-C-5 to 18-C-6. Surprisingly, the Na + transport efficiencies were very high, with one synthetic system exhibiting an overall transport rate constant similar to that for a naturally-occurring ionophore, monensin