Long-lived and highly conducting ion channels formed by lipophilic ethylenediamine palladium(II) complexes

The synthesis of a lipophilic ethylenediamine palladium(II) complex and its activity in planar bilayer membranes are reported. In acetonitrile solution containing one equivalent of 4,4-bipyridine the complex forms the expected metallosupramolecular tetrameric square. The same mixture provokes transmembrane conductance of three types: an initial period of erratic behavior, occasional short channel-like openings, and frequent very long-lived and highly conducting channel openings. The apparent pore radii of both short and long openings vary continuously over the range of 0.1 - 1.5 nm, and long-lived pores will form in the absence of 4,4'-bipyridine. The long-lived channels are presumed to involve an extended aggregate of the palladium complex and lipids surrounding a toroidal pore in the membrane.