Ion selectivity control in ester- and amide-armed diaza-crown ethers: sidearm effects in co-operative binding and specific transport

A variety of double-armed diaza-18-crown-6 derivatives were prepared, in which ester-, amide-, and ether-functionalized arms were attached as secondary donor sites. Their cation-binding behaviour was largely dependent on the nature of the donor groups on the flexible arms. Typically, an amide-armed diaza-18-crown-6 derivative enveloped Zn2+ ion in a cryptand-like cavity, while an ester-armed one formed an encapsulated complex with Na+ ion. This type of armed crown ether exhibited characteristic guest-selectivity and high binding dynamics, and provided efficient cation-transport phenomena.