Cucurbit[8]uril-improved recognition using a fluorescent sensor for different metal cations

Metal cations in aqueous solutions at different pHs (1.5, 4.5 and7.2) can be detected using the known inclusion complex H33258@Q8 as a fluorescent probe. Indeed, the fluorescence intensity of H33258 increases rapidly upon increasing the amount of Q[8] up to a Q[8]:H33258 ratio of 2:1, even at pH 1.5. The experimental results reveal that the probe not only exhibited selective recognition of metal cations at different pH but also showed different recognition for metal cations at different pHs. At pH 7.2, the probe responded to quite a variety metal cations, including one of the third main group elements, Al³⁺, four transition metal cations, Hg²⁺, Fe³⁺, Fe²⁺, and Cr³⁺ and three lanthanide cations Eu³⁺, Tm³⁺ and Yb³⁺; At pH 4.5, the probe responded to only two transition metal cations, Hg²⁺ and Fe³⁺. Unexpectedly, the probe lost its recognition properties at pH 1.5.