Facilitated transport of sodium or potassium chloride across vesicle membranes using a ditopic salt-binding macrobicycle

dA synthetic receptor, with an ability to bind sodium or potassium chloride as a contact ion-pair, is shown to effectively transport either salt across vesicle membranes. Significant transport is observed even when the transporter : phospholipid ratio is as low as 1 : 2500. Chloride efflux from unilamellar vesicles is monitored using a chloride selective electrode. Mechanistic studies indicate that the facilitated efflux is due to the uncomplexed transporter diffusing into the vesicle and the transporter-salt complex diffusing out. Vesicle influx experiments are also reported, where the facilitated influx of chloride and sodium ions into vesicles is observed directly by Cl-35 and Na-23 NMR, respectively.