Photo-activation of Tolane-based Synthetic Ion Channel for Transmembrane Chloride Transport

While natural channels respond to external stimuli to regulate ion concentration across cell membranes, creating a synthetic version remains challenging. Here, we present a photo-responsive uncaging technique within an artificial ion channel system, which activates the ion transport process from a transport-inactive o-nitrobenzyl-based caged system. From the comparative ion transport screening, 1 b emerged as the most active transporter. Interestingly, its bis(o-nitrobenzyl) derivative, i.e., protransporter 1 b ' was inefficient in transporting ions. Detailed transport studies indicated that compound 1 b is an anion selective transporter with a prominent selectivity towards chloride ions by following the antiport mechanism. Compound 1 b ' did not form an ion channel, but after the o-nitrobenzyl groups were photocleaved, it released 1 b, forming a transmembrane ion channel. The channel exhibited an average diameter of 6.5 +/- 0.2 & Aring; and a permeability ratio of PCl-/PK+=7.3 +/- 1.5 ${{P}_{{Cl}<^>{-}}/{P}_{{K}<^>{+}}=7.3\pm 1.5}$ . The geometry-optimization of protransporter 1 b ' indicated significant non-planarity, corroborating its inefficient self-assembly. In contrast, the crystal structure of 1 b demonstrates strong self-assembly via the formation of an intermolecular H-bond. Geometry optimization studies revealed the plausible self-assembled channel model and the interactions between the channel and chloride ion.