Mechanism of Ion Transport by Fluorescent Oligoester Channels

The synthesis and membrane activity of a suite of linear oligoesters containing a common diphenylacetylene unit core and differing in the hydroxyl terminus are reported. Active compounds formed high-conductance channels efficiently in both vesicle and planar bilayers, with one compound showing a very unusual slow loss of transport activity over a 20-30 min period. Steady-state and time-resolved fluorescence studies establish the rapid partition of active compounds to the bilayer and identify at least three types of membrane-associated species by their differing fluorescence lifetimes. The change in the distribution of species is correlated with the slow loss of activity. The results are interpreted in terms of an aggregate within a single bilayer leaflet that is nonetheless competent to transport ionic species through the bilayer. The properties of such structures, revealed by these compounds, appear to be consistent with commonly observed behaviors of other synthetic ion channels.