2.B.135.   The Photo-activated Tolane-based Anion Antiporter (PTAA) Family

Chattopadhayay et al. 2025 described 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, compound 1 b emerged as the most active transporter. Its bis(o-nitrobenzyl) derivative, i.e., protransporter 1 b', was inefficient in transporting cations. 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 Å and a permeability ratio of $P_{{Cl}^{-}}/P_{K^{+}}=7.3\pm 1.5$ . 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 (Chattopadhayay et al. 2025).

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