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

A 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 ³⁵Cl and ²³Na NMR, respectively.