Modulation of transmembrane anion transport of porphyrin boxes by dynamic window size engineering

The development of synthetic transmembrane anion transport systems is of considerable interest, not only for mimicking the functions of natural transmembrane proteins but also for practical applications. We have recently reported a porous organic cage, porphyrin box (PB(8)) having multiple windows surrounded by octyl chains as an iodide selective anion channel. Herein, we report the modulation of transmembrane transport of halides ([Formula: see text], [Formula: see text], and [Formula: see text] by dynamic window size engineering of the cage with different alkyl chain lengths (hexyl PB(6), octyl PB(8) and decyl PB(10)). ‘Apparent’ transport rates were measured by the HPTS fluorescence assay, which shows a gradual decrease in the transport rate upon increasing the length of alkyl chains of PB. We calculate the transport rate per PB in order to make a fair comparison as the ‘apparent’ transport rate is proportional to the number of PBs embedded in the lipid membrane. The transport rate per PB reveals that increasing the length of the alkyl chains of PBs results in a substantial fall in the iodide transport rate while only marginally decreasing the transport rates of bromide and chloride, thereby decreasing the selectivity of iodide transport.