Interaction of cucurbit [n=6, 7, 8] with aniline and its derivates

Interaction of cucurbit[n=6, 7, 8]urils(Q[6], Q[7], Q[8]) with aniline and its derivates and influence of pH on the interaction were studied by using UV spectroscopy, fluorescence spectrophotometry and H-1 NMR technique in details. The experimental results revealed that the interaction, such as interaction models and ratio of the interacted Q[n] with the guest, is closely related with pH of a host-guest system. Generally, there are five interaction stages: there is no obvious interaction between Q[n] and the title guest(s) at the "highest" and the "lowest" pH; the Q[n] includes the guest with a 1:1 ratio between the "highest" and a "higher" pH or the "lowest" and a "lower" pH; between the higher and the lower pH, the Q[n], even some Q[6]-guest systems, includes the guest with a 1:2 ratio. However, the values of the "highest", "higher" "lowest" "lower" pH are different for different Q[n]-guest systems, and in this work, a relevant simple method was used to determine these different pH values. Based on the experimental results, the structure of the Q[n] and the guests, the reasons of different interaction models and ratio at different pH were discussed.