Molecular recognition of aminoacid by cucurbiturils

Molecular recognition properties of cucurbit(n)urils (n=7, 8) [Q(7), Q(8)] toward aminoacid hydrochlorides were studied by ¹H NMR and UV-Vis methods. The experimental results reveals that such hosts can exhibit a special recognition property toward an aromatic moiety of the aromatic aminoacids such as L-Tyr, L-Try and L-Phe, and a weak binding toward other aminoacids without the aromatic moiety, such as L-Ala. Q(7) with these guests always formed a host-guest complex with a 1:1 ratio, and based on this model, the stability constants of the host-guest complexes were obtained. Q(8) with L-Tyr or L-Try formed a host-guest complex with a 1:1 ratio. However, Q(8) with a 1:2 ratio with L-Phe formed a host-guest complex. Studies on fluorescence properties of the aminoacids show that Q(7) or Q(8) could be an agent of fluorescence enhancement or fluorescence quenching, which was related to the structure of a certain aminoacid.