Cucurbit[7]uril host-guest complexation of nereistoxin investigated by competitive binding of palmatine fluorescent probe

The inclusion complex formation of nereistoxin (NTX) with cucurbit[7] uril (CB[7]) in aqueous solution was investigated by competitive binding of palmatine (PAL) fluorescent probe. The CB[7]-PAL complex exhibited high fluorescence in aqueous solution, which was quenched in the presence of NTX. This is due to the extrusion of PAL from the CB[7] cavity into the aqueous phase by NTX. The association constants (K) for the inclusion complexation of the host and guest were determined. The encapsulation of NTX and PAL as they compete for occupancy of the CB[7] cavity was studied using absorption, spectrofluorimetry, H-1 NMR, and molecular modelling calculations.