Cucurbit[7]uril complexations of bis(isoquinolinium)alkane dications in aqueous solution

The 1:1 and 2:1 host–guest complexation of a series of 1,n-bis(isoquinolinium)alkane dications (Iq(CH₂)_nIq²⁺, n = 2, 4, 5, 6, 8, 9, 10 and 12, and Iq(p-xylene)Iq²⁺) by cucurbit7]uril (CB7]) in aqueous solution has been investigated by ¹H NMR spectroscopy and ESI mass spectrometry. The site of binding of the first CB7] is dependent on the nature of the central linker group, with encapsulation of the p-xylene group or the polymethylene chain when n = 6–10.With shorter (n = 2–5) or longer (n = 12) chains, the first CB7] binds over an isoquinolinium group. With a second CB7], the binding of the central group is abandoned in favour of the CB7] hosts encapsulating the two cationic isoquinolinium termini. The 1:1 and 2:1 host–guest stability constants are related to modes of binding and the nature of the central linkers, and are compared with dicationic guests bearing different terminal groups.