Synthesis, transport activity, membrane localization, and dynamics of oligoester ion channels containing diphenylacetylene units

Four new linear oligoesters containing a diphenylacetylene unit were prepared by fragment coupling sequences and the ion channel forming ability of the compounds was investigated. Activity in vesicles was very strongly controlled by overall length; the longest compound was effectively inactive. Planar bilayer studies established that all compounds are able to form channels, but that regular step changes in conductance depend on the location of the diphenylacetylene unit within the oligoester and on the electrolyte. The intrinsic fluorescence of the diphenylacetylene unit was used to probe aggregation and membrane localization. Both monomer (320 nm) and excimer (380 nm) emissions are quenched by copper ions; quenching of the excimer emission from an aqueous aggregate is very efficient. Time-dependent changes in the intensities of monomer and excimer emission show slow transfer of diphenylacetylene units from an aqueous aggregate to a membrane-bound monomer with subsequent growth of emission from a membrane-bound excimer. The latter species is not quenched by aqueous copper ions. The implications of these species and processes for the mechanism of ion channel formation by simple oligoesters are discussed.