Photoresponsive Liquid Membrane Transport of Alkali Metal Ions Using Crowned Spirobenzopyrans

Abstract

Several azacrown ether derivatives, which are monoaza-12-crown-4, -15-crown-5, and -18-crown-6 and diaza-12-crown-4 and -18-crown-6, bearing one or two spirobenzopyran(s), which we call crowned spirobenzopyran or crowned bis(spirobenzopyran), were synthesized and were used as carriers for liquid membrane transport of alkali metal ions. The passive alkali metal transports through liquid membranes containing crowned spirobenzopyrans were carried out under dark, and UV- and visible-light irradiation conditions. The metal ion transport was accelerated and retarded by UV- and visible-light irradiation, respectively. On the other hand, the photoresponse of the metal ion selectivity in membrane transport by crowned spirobenzopyrans was different, depending on the kind of crown ether units. Especially, diaza-12-crown-4-bis(spirobenzopyran) exhibited an excellently selective and effective transporting ability for Li(+). The uphill transports of Li(+) through a liquid membrane containing monoaza-12-crown-4-spirobenzopyran or diaza-12-crown-4-bis(spirobenzopyran) were realized under the conditions where the same aqueous solution was used as the source and receiving phases with UV and visible lights being irradiated onto the boundary phases between the source and membrane phases and between the receiving and membrane phases, respectively. The uphill transport of Li(+) from the source to receiving phases through a liquid membrane containing a crowned spirobenzopyran was also attained by the proton-concentration gradient between the source and receiving phases under dark conditions, and the transporting ability was remarkably increased by photoirradiation.